TREM2/PLCγ2 signalling in immune cells: function, structural insight, and potential therapeutic modulation

May combine two claims.

PLCγ2 p.P522R is associated with reduction of cholesterol ester accumulation and increased phagocytosis.

“reduction of cholesterol ester accumulation,Increased phagocytosis [36]”

• cites [36] Maguire E, Menzies GE, Phillips T, Sasner M, Williams HM, Czubala MA, et al. The Alzheimer’s disease protective P522R variant of PLCG2, consistently enhances stimulus-dependent PLCγ2 activation, depleting substrate and altering cell function. bioRxiv. 2020; Available from: http://biorxiv.org/content/early/2020/04/28/2020.04.27.059600.abstract. sourceDisputed

  The Results section, “Expression of the AD protective PLCγ2 R522 variant impaired phagocytic and enhanced endocytic clearance” (page unavailable), reports significantly reduced—not increased—phagocytosis in R522-expressing cells compared with P522 controls. The paper reports reduced PI(4,5)P2 levels, but the passages found do not establish reduced cholesterol ester accumulation. (LLM, conf=0.90)

  Checked by a reasoning model — may be wrong.

  Experimental — accuracy not yet measured

May combine two claims.

The PLCγ2 p.P522R variant causes an increase in microglial phagocytosis and survival, whereas TREM2 LOAD variants typically induce a reduction in these phenotypes.

“Whilst TREM2 LOAD variants typically induce a reduction in microglial phagocytosis and survival, the PLCγ2 p.P522R variant causes an increase in these beneficial microglial phenotypes [35, 36]”

• cites [35] Takalo M, Wittrahm R, Wefers B, Parhizkar S, Jokivarsi K, Kuulasmaa T, et al. The Alzheimer’s disease-associated protective Plcγ2-P522R variant promotes immune functions. Mol Neurodegener. 2020;15:52. sourcePartly supported

  The Findings report increased phagocytosis in P522R-expressing microglia-like BV2 cells and enhanced survival in P522R knock-in bone marrow-derived macrophages, not directly in microglia. They also describe impaired microglial survival with TREM2 deficiency and propose opposite effects for TREM2 risk and PLCγ2 protective variants, but do not establish that TREM2 LOAD variants typically reduce both phenotypes. (LLM, conf=0.87)

  Experimental — accuracy not yet measured
• cites [36] Maguire E, Menzies GE, Phillips T, Sasner M, Williams HM, Czubala MA, et al. The Alzheimer’s disease protective P522R variant of PLCG2, consistently enhances stimulus-dependent PLCγ2 activation, depleting substrate and altering cell function. bioRxiv. 2020; Available from: http://biorxiv.org/content/early/2020/04/28/2020.04.27.059600.abstract. sourceDisputed

  The Results section reports that microglia expressing PLCγ2 R522 had significantly reduced, not increased, phagocytosis of E. coli and zymosan particles compared with P522 controls. The paper reports enhanced endocytic clearance of Aβ oligomers, but that is a different phenotype; the cited passages do not establish increased microglial survival or the claimed effects of TREM2 LOAD variants. (LLM, conf=0.90)

  Checked by a reasoning model — may be wrong.

  Experimental — accuracy not yet measured

• AssumptionRests on an assumption: TREM2 LOAD variants are predominantly loss-of-function and increase the risk of AD.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Variants of TREM2 and PLCG2 are known to cause diseases such as Nasu-Hakola disease (TREM2) and PLCγ2-associated antibody deficiency (PLAID) or autoinflammation and PLAID (APLAID).

“with variants of these genes known to cause diseases such as Nasu-Hakola disease (TREM2) [22], and PLCγ2-associated antibody deficiency (PLAID), or autoinflammation and PLAID (APLAID) [3].”

• cites [22] Li JT, Zhang Y. TREM2 regulates innate immunity in Alzheimer’s disease. J Neuroinflam. 2018;15:1–7. sourceSupported
• cites [3] Koss H, Bunney TD, Behjati S, Katan M. Dysfunction of phospholipase Cγ in immune disorders and cancer. Trends Biochem Sci. 2014;39:603–11. sourceSupported

May combine two claims.

The PLCG2 p.Pro522Arg polymorphism is associated with slowed disease progression, which correlated with a reduction of pTau181 and tTau in cerebrospinal fluid (CSF).

“slowed disease progression, which correlated with a reduction of pTau181 and tTau in cerebrospinal fluid (CSF) [8]”

• cites [8] Kleineidam L, Chouraki V, Próchnicki T, van der Lee SJ, Madrid-Márquez L, Wagner-Thelen H, et al. PLCG2 protective variant p.P522R modulates tau pathology and disease progression in patients with mild cognitive impairment. Acta Neuropathol. 2020;139:1025–44. sourceSupported

May combine two claims.

PLCγ2 is a main effector downstream of TREM2 and is an intracellular lipase recruited to the membrane upon activation.

“A main effector downstream of TREM2, PLCγ2 is an intracellular lipase recruited to the membrane upon activation [3, 4].”

• cites [3] Koss H, Bunney TD, Behjati S, Katan M. Dysfunction of phospholipase Cγ in immune disorders and cancer. Trends Biochem Sci. 2014;39:603–11. sourcePartly supported

  The introduction (p. 2) describes PLCγ2 as a signaling enzyme activated by immune-cell receptors, and Box 1 (p. 18) describes its recruitment to a signaling scaffold and activation as a phospholipase. The cited passages do not identify TREM2 as an upstream receptor or establish PLCγ2 as a main effector downstream of it. Box 1 says Btk—not PLCγ2—is recruited to the membrane environment, so the specific membrane-recruitment claim is not established here. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [4] Xing J, Titus AR, Humphrey MB. The TREM2-DAP12 signaling pathway in Nasu–Hakola disease: a molecular genetics perspective. Res Rep Biochem. 2015;5:89–100 Available from: https://pubmed.ncbi.nlm.nih.gov/26478868.Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

This could be representative of changes in TREM2 expression or shedding, both of which are altered during ageing and disease, thereby reducing TREM2-mediated signalling and subsequent conversion of microglia to DAM.

“This could be representative of changes in TREM2 expression or shedding, both of which are altered during ageing and disease [55], thereby reducing TREM2-mediated signalling and subsequent conversion of microglia to DAM [56].”

• cites [55] Heslegrave A, Heywood W, Paterson R, Magdalinou N, Svensson J, Johansson P, et al. Increased cerebrospinal fluid soluble TREM2 concentration in Alzheimer’s disease. Mol Neurodegener. 2016;11:3. sourcePartly supported

  The Results (page unavailable) show higher CSF soluble TREM2 in Alzheimer’s disease, and the Discussion (page unavailable) cites increased Trem2 expression in mouse models of the disease. The paper does not establish that ageing independently alters TREM2 expression or shedding, or that its measured soluble-TREM2 change reflects altered shedding. The later claim about signalling and conversion to DAM is attached to [56], not this source. (LLM, conf=0.83)

  Experimental — accuracy not yet measured
• cites [56] Ulland TK, Colonna M. TREM2 — a key player in microglial biology and Alzheimer disease. Nat Rev Neurol. 2018;14:667–75. sourceNot checked — no full text of the source

May combine two claims.

Phagocytic deficits in LDAM were observed, in line with defective conversion of microglia to the protective DAM phenotype.

“However, phagocytic deficits in LDAM were observed, in line with defective conversion of microglia to the protective DAM phenotype [20]”

• cites [20] Marschallinger J, Iram T, Zardeneta M, Lee SE, Lehallier B, Haney MS, et al. Lipid-droplet-accumulating microglia represent a dysfunctional and proinflammatory state in the aging brain. Nat Neurosci. 2020;23:194–208. sourcePartly supported

  The Results section ('LDAM have phagocytosis deficits') reports markedly reduced uptake of Zymosan and myelin debris by LDAM. The Discussion ('LDAM in neurodegeneration') contrasts poorly phagocytic LDAM with actively phagocytic DAM, but says that possible conversion between microglial states remains to be investigated. It does not establish defective conversion to DAM. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Lipid-associated macrophages have recently been identified in mouse and human adipose tissue, where TREM2 expression was found to regulate lipid homeostasis.

“lipid-associated macrophages have recently been identified in mouse and human adipose tissue, where TREM2 expression was found to regulate lipid homeostasis [57].”

• cites [57] Jaitin DA, Adlung L, Thaiss CA, Weiner A, Li B, Descamps H, et al. Lipid-associated macrophages control metabolic homeostasis in a Trem2-dependent manner. Cell. 2019;178(3):686–698.e14. sourceSupported

May combine two claims.

In the CNS, TREM2 interacts with a variety of ligands, but it is most notably a receptor for lipid substrates.

“In the CNS, TREM2 interacts with a variety of ligands, but it is most notably a receptor for lipid substrates [17, 19, 48].”

• cites [17] Yeh FL, Wang Y, Tom I, Gonzalez LC, Sheng M. TREM2 binds to Apolipoproteins, including APOE and CLU/APOJ, and thereby facilitates uptake of amyloid-Beta by microglia. Neuron. 2016;91:328–40. sourceNot checked — no full text of the source
• cites [19] Nugent AA, Lin K, van Lengerich B, Lianoglou S, Przybyla L, Davis SS, et al. TREM2 regulates microglial cholesterol metabolism upon chronic phagocytic challenge. Neuron. 2020;105:837–54. sourceNot checked — no full text of the source
• cites [48] Shirotani K, Hori Y, Yoshizaki R, Higuchi E, Colonna M, Saito T, et al. Aminophospholipids are signal-transducing TREM2 ligands on apoptotic cells. Sci Rep. 2019;9:1–9. sourcePartly supported

  The Introduction lists several lipid ligands alongside nonlipid TREM2-binding substances, supporting the claim that TREM2 interacts with varied ligands, including lipids. But the Results and Discussion identify the signal-transducing ligands in mouse cerebral cortex only as membrane-associated and different from aminophospholipids; they do not establish that TREM2 is primarily a receptor for lipids in the CNS. Page numbers are unavailable in our copy. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

May combine two claims.

TREM2 binds lipids exposed on the surface of apoptotic cells, as well as ApoE and lipidated Amyloid beta (Aβ).

“TREM2 binds lipids exposed on the surface of apoptotic cells [49, 50], as well as ApoE [51] and lipidated Amyloid beta (Aβ) [52].”

• cites [49] Hardy J. Membrane damage is at the core of Alzheimer’s disease. Lancet Neurol. 2017;16:342. sourceNot checked — no full text of the source
• cites [50] Wang Y, Cella M, Mallinson K, Ulrich JD, Young KL, Robinette ML, et al. TREM2 lipid sensing sustains the microglial response in an Alzheimer’s disease model. Cell. 2015;160:1061–71. sourceSupported
• cites [51] Atagi Y, Liu CC, Painter MM, Chen XF, Verbeeck C, Zheng H, et al. Apolipoprotein E is a ligand for triggering receptor expressed on myeloid cells 2 (TREM2). J Biol Chem. 2015;290:26043–50. sourceSupported
• cites [52] Kober DL, Brett TJ, Mol J, Author B. TREM2-ligand interactions in health and disease. J Mol Biol. 2017;429:1607–29. sourcePartly supported

  In §3, “TREM2 binds anionic ligands on mammalian cells” (page unavailable), the review reports TREM2 binding to phospholipids in laboratory assays. It also reports increased binding to some apoptotic cells, but says it is unclear which ligand accounts for that binding; apoptotic Jurkat cells exposing phosphatidylserine did not bind Fc-TREM2. Thus, the cited source does not establish that the lipids exposed on apoptotic-cell surfaces are what TREM2 binds. The ApoE and Aβ clauses carry separate citations. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

PLCγ2 activation leads to an increase in cytoplasmic calcium, that supports the assembly of the NLRP3 inflammasome, and pro-inflammatory cytokine release in human blood monocytes, bone-marrow-derived macrophages and dendritic cells.

“PLCγ2 activation leads to an increase in cytoplasmic calcium, that supports the assembly of the pyrin (PYD)-domain-containing protein 3 (NLRP3) inflammasome, and pro-inflammatory cytokine release in human blood monocytes [31], bone-marrow-derived macrophages (BMDM) and dendritic cells [32].”

• cites [31] Chae JJ, Park YH, Park C, Hwang IY, Hoffmann P, Kehrl JH, et al. Brief report: connecting two pathways through Ca2+ signaling: NLRP3 inflammasome activation induced by a hypermorphic PLCG2 mutation. Arthritis Rheum. 2015;67:563–7. sourcePartly supported

  The Results (page unavailable) link PLC-mediated calcium signaling to NLRP3 activation and IL-1β secretion in human peripheral blood mononuclear cells (PBMCs). The Methods (page unavailable) confirm that PBMCs, not isolated blood monocytes, were studied, so the claim is more cell-specific than this source supports. The macrophage and dendritic-cell portion is attached to a different citation [32] and is not assessed here. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [32] Aki D, Minoda Y, Yoshida H, Watanabe S, Yoshida R, Takaesu G, et al. Peptidoglycan and lipopolysaccharide activate PLCγ2, leading to enhanced cytokine production in macrophages and dendritic cells. Genes Cells. 2008;13:199–208. sourcePartly supported

  The Discussion and results report that PLCγ2 contributes to intracellular calcium mobilization in bone-marrow-derived macrophages and dendritic cells, and that it is required for full pro-inflammatory cytokine production. The paper does not link this calcium response to NLRP3 inflammasome assembly. Human blood monocytes are attached to a different citation in the citing sentence, so they are not assessed here. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

In T-cell signalling, several adaptor proteins are associated with activated PLCγ1, including LAT, SLP76 and GADS.

“In the context of T-cell signalling, it is documented that several adaptor proteins are associated with activated PLCγ1, including LAT, SH2-domain-containing leukocyte protein of 76 kDa (SLP76) and GRB2-related adaptor downstream of Shc (GADS) [72].”

• cites [72] Manna A, Zhao H, Wada J, Balagopalan L, Tagad HD, Appella E, et al. Cooperative assembly of a four-molecule signaling complex formed upon T cell antigen receptor activation. Proc Natl Acad Sci U S A. 2018;115:E11914–23. sourcePartly supported

  The Discussion describes PLC-γ1 binding in a complex with LAT, Gads and SLP-76 after T-cell receptor engagement. The Abstract says this complex recruits PLC-γ1 to the membrane, where it is subsequently activated; it does not establish that the three adaptors are associated with PLC-γ1 after activation. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The partner protein could be a RTK or a phosphotyrosine motif associated with an adaptor protein, such as LAT in T-cells, or BLNK in B-cells.

“The partner protein could be a RTK [84, 88] or a phosphotyrosine motif associated with an adaptor protein, such as LAT in T-cells [72], or BLNK in B-cells [89].”

• cites [84] Liu Y, Bunney TD, Khosa S, Macé K, Beckenbauer K, Askwith T, et al. Structural insights and activating mutations in diverse pathologies define mechanisms of deregulation for phospholipase C gamma enzymes. EBioMedicine. 2020;51:1–12. sourceSupported
• cites [88] Bae JH, Lew ED, Yuzawa S, Tomé F, Lax I, Schlessinger J. The selectivity of receptor tyrosine kinase signaling is controlled by a secondary SH2 domain binding site. Cell. 2009;138:514–24. sourceSupported
• cites [72] Manna A, Zhao H, Wada J, Balagopalan L, Tagad HD, Appella E, et al. Cooperative assembly of a four-molecule signaling complex formed upon T cell antigen receptor activation. Proc Natl Acad Sci U S A. 2018;115:E11914–23. sourceSupported
• cites [89] Ishiai M, Sugawara H, Kurosaki M, Kurosaki T. Cutting edge: association of phospholipase C-γ2 Src homology 2 domains with BLNK is critical for B cell antigen receptor signaling. J Immunol. 1999;163:1746–9. sourceSupported

May combine two claims.

Once recruited to the DAP12 ITAM motif, Syk is phosphorylated by Src on its activation loop and this then initiates an autophosphorylation of other Syk molecules.

“Once recruited to the DAP12 ITAM motif, Syk is phosphorylated by Src on its activation loop and this then initiates an autophosphorylation of other Syk molecules [69]”

• cites [69] El-Hillal O, Kurosaki T, Yamamura H, Kinet J-P, Scharenberg AM. Syk kinase activation by a src kinase-initiated activation loop phosphorylation chain reaction. Proc Natl Acad Sci. 1997;94:1919 LP–1924. sourcePartly supported

  The Discussion describes a Src-family kinase initiating Syk activation-loop phosphorylation, followed by activated Syk phosphorylating other Syk molecules. The study examines Fc receptor-induced activation, however, and does not establish the claimed recruitment to a DAP12 ITAM motif. (LLM, conf=0.87)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

CD45 is expressed in microglia, albeit not to the extent of its expression in T-cells, where it is one of the most abundant proteins in the plasma membrane.

“It is known to be expressed in microglia [67], albeit not to the extent of its expression in T-cells, where it is one of the most abundant proteins in the plasma membrane (PM) [68].”

• cites [67] Cosenza-Nashat MA, Kim MO, Zhao ML, Suh HS, Lee SC. CD45 isoform expression in microglia and inflammatory cells in HIV-1 encephalitis. Brain Pathol. 2006;16:256–65. sourceSupported
• cites [68] Courtney AH, Shvets AA, Lu W, Griffante G, Mollenauer M, Horkova V, et al. CD45 functions as a signaling gatekeeper in T cells. Sci Signal. 2019;12:eaaw8151. sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The N-terminal SH2 (nSH2) domain is positioned at a distance from the core catalytic domains, and is essentially the principal interaction domain for binding to the phosphotyrosine residues in partner proteins.

“The N-terminal SH2 (nSH2) domain is positioned at a distance from the core catalytic domains, and is essentially the principal interaction domain for binding to the phosphotyrosine residues in partner proteins [87].”

• cites [87] Bunney TD, Esposito D, Mas-Droux C, Lamber E, Baxendale RW, Martins M, et al. Structural and functional integration of the PLCγ interaction domains critical for regulatory mechanisms and signaling deregulation. Structure. 2012;20:2062–75. sourceSupported

May combine two claims.

There are currently no structures for the full-length PLCγ2 molecule, but useful information can be inferred from the recently-published crystal and cryo-electron microscopy (cryoEM) structures of the closely related PLCγ1 molecule.

“Conversely, there are currently no structures for the full-length PLCγ2 molecule, but we can infer some useful information from the recently-published crystal and cryo-electron microscopy (cryoEM) structures of the closely related PLCγ1 molecule [83, 84].”

• cites [83] Hajicek N, Keith NC, Siraliev-Perez E, Temple BRS, Huang W, Zhang Q, et al. Structural basis for the activation of plc-γ isozymes by phosphorylation and cancer-associated mutations. Elife. 2019;8:1–25. sourceSupported
• cites [84] Liu Y, Bunney TD, Khosa S, Macé K, Beckenbauer K, Askwith T, et al. Structural insights and activating mutations in diverse pathologies define mechanisms of deregulation for phospholipase C gamma enzymes. EBioMedicine. 2020;51:1–12. sourceSupported

May combine two claims.

DAG leads to activation of protein kinase C (PKC) isozymes, the NLRP3 inflammasome, as well as other proteins.

“and DAG leading to activation of protein kinase C (PKC) isozymes, the NLRP3 inflammasome [31, 34], as well as other proteins [77].”

• cites [31] Chae JJ, Park YH, Park C, Hwang IY, Hoffmann P, Kehrl JH, et al. Brief report: connecting two pathways through Ca2+ signaling: NLRP3 inflammasome activation induced by a hypermorphic PLCG2 mutation. Arthritis Rheum. 2015;67:563–7. sourcePartly supported

  The Introduction says PLCγ2 produces DAG and InsP3, and the Discussion says PLCγ2 can trigger protein kinase C signaling. The Results link NLRP3 inflammasome activation to the PLC–InsP3–Ca2+ pathway, not to DAG; the paper therefore does not support the claimed DAG-to-NLRP3 link. Page numbers are unavailable in our copy. (LLM, conf=0.87)

  Experimental — accuracy not yet measured
• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source
• cites [77] Griner EM, Kazanietz MG. Protein kinase C and other diacylglycerol effectors in cancer. Nat Rev Cancer. 2007;7:281–94. sourceNot checked — no full text of the source

May combine two claims.

Phosphorylated BLNK binds to PLCγ2, and recruited PLCγ2 is phosphorylated and activated by BTK.

“Phosphorylated BLNK binds to PLCγ2, and recruited PLCγ2 is phosphorylated and activated by BTK [70].”

• cites [70] Rodriguez R, Matsuda M, Storey A, Katan M. Requirements for distinct steps of phospholipase Cγ2 regulation, membrane-raft-dependent targeting and subsequent enzyme activation in B-cell signalling. Biochem J. 2003;374:269–80. sourcePartly supported

  The Discussion (page unavailable) identifies BLNK as a suggested binding partner of PLCγ2 and reports that Btk is required for activation of raft-targeted PLCγ2 after B-cell receptor stimulation. It describes direct phosphorylation of PLCγ2 by Btk only as a suggested role, not an established step, and shows that raft-targeted PLCγ2 can be activated without BLNK. The sentence therefore overstates the proposed sequence as a demonstrated mechanism. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

PIP2 plays a crucial role in regulating actin polymerisation, endocytosis, exocytosis, ion channels and G-protein-coupled receptors.

“PIP2 plays a crucial role in regulating a number of cellular processes or molecules, including actin polymerisation, endocytosis, exocytosis, ion channels and G-protein-coupled receptors [78, 79].”

• cites [78] Hammond GRV, Burke JE. Novel roles of phosphoinositides in signaling, lipid transport, and disease. Curr Opin Cell Biol. 2020;63:57–67. sourcePartly supported

  The Introduction section on integral membrane protein signaling identifies PI(4,5)P2 as a key regulator of ion-channel opening and describes its effects on GPCR signaling. It also says GPCR endocytosis is proposed to require phosphoinositide binding, but does not specifically establish a PIP2 role there. Searches of our copy for actin and exocytosis found no support for those parts of the list; page numbers were not available in the indexed passages. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [79] Katan M, Cockcroft S. Phosphatidylinositol (4,5) bisphosphate: diverse functions at the plasma membrane. Essays Biochem. 2020;64:513–31. sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing).

A crystal structure is available for TREM2.

“A crystal structure is available for TREM2 [82].”

• cites [82] Gratuze M, Leyns CEG, Holtzman DM. New insights into the role of TREM2 in Alzheimer’s disease. Mol Neurodegener. 2018;13:66. sourceSupported

May combine two claims.

PLCγ2 p.P522R is associated with improved survival and increased inflammatory responses.

“Improved survival, increased inflammatory responses [35]”

• cites [35] Takalo M, Wittrahm R, Wefers B, Parhizkar S, Jokivarsi K, Kuulasmaa T, et al. The Alzheimer’s disease-associated protective Plcγ2-P522R variant promotes immune functions. Mol Neurodegener. 2020;15:52. sourceSupported

May combine two claims.

p.R47H and p.R62H reduce ligand binding.

“such as reduced ligand binding (p.R47H [96], p.R62H [97])”

• cites [96] Xiang X, Piers TM, Wefers B, Zhu K, Mallach A, Brunner B, et al. The Trem2 R47H Alzheimer’s risk variant impairs splicing and reduces Trem2 mRNA and protein in mice but not in humans. Mol Neurodegener. 2018;13:1–14. sourceSupported
• cites [97] Song W, Hooli B, Mullin K, Jin SC, Cella M, Ulland TK, et al. Alzheimer’s disease-associated TREM2 variants exhibit either decreased or increased ligand-dependent activation. Alzheimers Dement. 2017;13:381–7. sourceSupported

May combine two claims.

TREM2 p.R47H is associated with reduced cell adhesion and altered surface levels observed in iPSC-derived macrophages.

“reduced cell adhesion and altered surface levels observed in iPSC-derived macrophages [39]”

• cites [39] Hall-Roberts H, Agarwal D, Obst J, Smith TB, Monzón-Sandoval J, Di Daniel E, et al. TREM2 Alzheimer’s variant R47H causes similar transcriptional dysregulation to knockout, yet only subtle functional phenotypes in human iPSC-derived macrophages. Alzheimers Res Ther. 2020;12:151. sourceSupported

May combine two claims.

The most characterised variant of TREM2 (p.R47H) shows defects in ligand binding, which impacts the ability of TREM2 to recognise damage, and induce microglial changes, resulting in a dampened response to pathological insults such as Aβ deposition.

“The most characterised variant of TREM2 (p.R47H) shows defects in ligand binding [6, 37, 38, 97], which impacts the ability of TREM2 to recognise damage, and induce microglial changes, resulting in a dampened response to pathological insults such as Aβ deposition.”

• cites [6] Guerreiro R, Wojtas A, Bras J, Carrasquillo M, Rogaeva E, Majounie E, et al. TREM2 variants in Alzheimer’s disease. N Engl J Med. 2013;368:117–27. sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  Experimental — accuracy not yet measured
• cites [37] Cheng-Hathaway PJ, Reed-Geaghan EG, Jay TR, Casali BT, Bemiller SM, Puntambekar SS, et al. The Trem2 R47H variant confers loss-of-function-like phenotypes in Alzheimer’s disease. Mol Neurodegener. 2018;13:29 Available from. https://doi.org/10.1186/s13024-018-0262-8. sourcePartly supported

  Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  Experimental — accuracy not yet measured
• cites [38] Sayed FA, Kodama L, Udeochu JC, Fan L, Carling GK, Le D, et al. AD-linked R47H-TREM2 mutation induces disease-enhancing proinflammatory microglial states in mice and humans. bioRxiv. 2020;2020.07.24.218719 Available from: http://biorxiv.org/content/early/2020/07/25/2020.07.24.218719.abstract. sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  Experimental — accuracy not yet measured
• cites [97] Song W, Hooli B, Mullin K, Jin SC, Cella M, Ulland TK, et al. Alzheimer’s disease-associated TREM2 variants exhibit either decreased or increased ligand-dependent activation. Alzheimers Dement. 2017;13:381–7. sourcePartly supported

  Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

  Experimental — accuracy not yet measured

May combine two claims.

TREM2 p.H157Y increases shedding from microglia, leading to phagocytosis deficits.

“Increased shedding from microglia [45], leading to phagocytosis deficits [46]”

• cites [45] Thornton P, Sevalle J, Deery MJ, Fraser G, Zhou Y, Ståhl S, et al. TREM 2 shedding by cleavage at the H157-S158 bond is accelerated for the Alzheimer’s disease-associated H157Y variant. EMBO Mol Med. 2017;9:1366–78. sourcePartly supported

  The Results section reports that H157Y increases TREM2 shedding, but that comparison was performed in HEK293 cells, not microglia. The paper separately reports TREM2 shedding from murine microglia. The phagocytosis-deficit clause is attached to a different citation, so it is not judged here. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [46] Schlepckow K, Monroe KM, Kleinberger G, Cantuti-Castelvetri L, Parhizkar S, Xia D, et al. Enhancing protective microglial activities with a dual function TREM 2 antibody to the stalk region. EMBO Mol Med. 2020;12:1–22. sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing).

Homozygous Q33X, Y38C and T66M variants have been identified in patients with Nasu-Hakola disease.

“Homozygous Q33X, Y38C and T66M variants have been identified in patients with Nasu-Hakola disease [44, 47, 95].”

• cites [44] Borroni B, Ferrari F, Galimberti D, Nacmias B, Barone C, Bagnoli S, et al. Heterozygous TREM2 mutations in frontotemporal dementia. Neurobiol Aging. 2014;35:934.e7–934.e10. sourcePartly supported

  The Discussion states that homozygous Q33X and T66M mutations have previously been demonstrated to cause Nasu-Hakola disease. The Results also links both variants to the disease in homozygosity, but our copy does not identify Y38C in patients with Nasu-Hakola disease (searched: Y38C Nasu-Hakola homozygous). No page numbers were available in the indexed passages. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [47] Jiang T, Hou J-K, Gao Q, Yu J-T, Zhou J-S, Zhang H-DZ, et al. TREM2 p.H157Y Variant and the Risk of Alzheimer’s Disease: A Meta-Analysis Involving 14,510 Subjects. Curr Neurovasc Res. 2016;13(4):318–20. sourceNot checked — no full text of the source
• cites [95] Paloneva J, Manninen T, Christman G, Hovanes K, Mandelin J, Adolfsson R, et al. Mutations in two genes encoding different subunits of a receptor signaling complex result in an identical disease phenotype. Am J Hum Genet. 2002;71:656–62. sourceNot checked — no full text of the source

May combine two claims.

Many of these genes act together in distinct signalling pathways and TREM2 and PLCγ2 interact in the same cascade to modulate microglial migration, phagocytosis, and survival.

“Many of these genes act together in distinct signalling pathways and, of note, TREM2 and PLCγ2 interact in the same cascade (Fig. 1) to modulate microglial migration, phagocytosis, and survival [34, 94].”

• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source
• cites [94] Zheng H, Cheng B, Li Y, Li X, Chen X, Zhang Y. TREM2 in Alzheimer’s disease: microglial survival and energy metabolism. Front Aging Neurosci. 2018;10:395. sourcePartly supported

  The Genetics of AD section names PLCG2 and TREM2 among genes associated with AD, and the TREM2 and Microglial Survival section links TREM2 to microglial migration, phagocytosis, and survival. Neither section establishes that TREM2 and PLCγ2 interact in the same signalling cascade to modulate those functions. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

May combine two claims.

TREM2 p.R47H is associated with impaired myeloid cell response to plaque in vivo and reduced proliferation.

“Impaired myeloid cell response to plaque in vivo and reduced proliferation [37]”

• cites [37] Cheng-Hathaway PJ, Reed-Geaghan EG, Jay TR, Casali BT, Bemiller SM, Puntambekar SS, et al. The Trem2 R47H variant confers loss-of-function-like phenotypes in Alzheimer’s disease. Mol Neurodegener. 2018;13:29 Available from. https://doi.org/10.1186/s13024-018-0262-8. sourceSupported

May combine two claims.

Several LOAD-associated variants in genes expressed within microglia have been identified, which have direct effects on microglial phenotype, and can alter the course of the disease.

“Several LOAD-associated variants in genes expressed within microglia have been identified [92], which have direct effects on microglial phenotype [93], and can alter the course of the disease.”

• cites [92] Efthymiou AG, Goate AM. Late onset Alzheimer’s disease genetics implicates microglial pathways in disease risk. Mol Neurodegener. 2017;12:43. sourceSupported
• cites [93] McQuade A, Blurton-Jones M. Microglia in Alzheimer’s disease: exploring how genetics and phenotype influence risk. J Mol Biol. 2019;431:1805–17. sourceSupported

May combine two claims.

TREM2 deficiency results in higher deposition of amyloid in the hippocampus of 5XFAD mice and reduces recruitment of microglia to plaques.

“TREM2 deficiency has been reported to result in a higher deposition of amyloid in the hippocampus of 5XFAD mice, and was found to reduce the recruitment of microglia to plaques [16, 50]”

• cites [16] Yuan P, Condello C, Keene CD, Wang Y, Bird TD, Paul SM, et al. TREM2 Haplodeficiency in mice and humans impairs the microglia barrier function leading to decreased amyloid compaction and severe axonal dystrophy. Neuron. 2016;90:724–39. sourcePartly supported

  The Results section ('Trem2 haplodeficiency abolishes the microglia barrier') reports about 20% fewer plaque-associated microglia with Trem2 deficiency, supporting reduced recruitment to plaques. But the Results section on plaque compaction finds no significant difference in total plaque number, and the cited passages do not establish higher amyloid deposition specifically in the hippocampus of 5XFAD mice. Page numbers are unavailable in our copy. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [50] Wang Y, Cella M, Mallinson K, Ulrich JD, Young KL, Robinette ML, et al. TREM2 lipid sensing sustains the microglial response in an Alzheimer’s disease model. Cell. 2015;160:1061–71. sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The variant p.R47H seems to attenuate neurodegeneration in the PS19 model of tauopathy, and positive modulation of Trem2 function might lead to increased microgliosis and damage in advanced stages of tauopathy.

“A recent report, however, highlights that the variant p.R47H seems to attenuate neurodegeneration in the PS19 model of tauopathy, and a positive modulation of the Trem2 function might lead to increase microgliosis and damage in advanced stages of tauopathy [13]”

• cites [13] Gratuze M, Leyns CEG, Sauerbeck AD, St-Pierre MK, Xiong M, Kim N, et al. Impact of TREM2R47H variant on tau pathology-induced gliosis and neurodegeneration. J Clin Invest. 2020;130:4954–68. sourceSupported

May combine two claims.

Microglia from individuals carrying the TREM2 R47H mutation failed to surround Aβ plaques, which correlated with an increase in filamentous amyloid deposits and phospho-tau-positive neurites in the brain.

“microglia from individuals carrying the TREM2 R47H mutation failed to surround Aβ plaques, which correlated with an increase in filamentous amyloid deposits and phospho-tau-positive neurites in the brain [16, 103]”

• cites [16] Yuan P, Condello C, Keene CD, Wang Y, Bird TD, Paul SM, et al. TREM2 Haplodeficiency in mice and humans impairs the microglia barrier function leading to decreased amyloid compaction and severe axonal dystrophy. Neuron. 2016;90:724–39. sourceSupported
• cites [103] Nizami S, Hall-Roberts H, Warrier S, Cowley SA, Di Daniel E. Microglial inflammation and phagocytosis in Alzheimer’s disease: potential therapeutic targets. Br J Pharmacol. 2019;176:3515–32. sourcePartly supported

  The TREM2 section reports that, in human AD brains carrying R47H or R62H, fewer microglia associate with amyloid plaques than in noncarriers; it does not say they fail to surround plaques, or isolate the finding to R47H. It discusses more diffuse, filamentous plaques and neurite damage in related comparisons, but does not report that these carriers had increased filamentous deposits and phospho-tau-positive neurites. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

May combine two claims.

TREM2 deficiency leads to adverse phenotypes involving mostly the brain and the bones, manifesting more severely in humans than mice.

“TREM2 deficiency leads to adverse phenotypes involving mostly the brain and the bones, and manifesting more severely in humans than mice [42, 105]”

• cites [42] Jonsson T, Stefansson H, Steinberg S, Jonsdottir I, Jonsson PV, Snaedal J, et al. Variant of TREM2 associated with the risk of Alzheimer’s disease. N Engl J Med. 2012;368:107–16. sourcePartly supported

  The Discussion (page unavailable in our copy) links TREM2 loss-of-function mutations to a human disease affecting the brain and bones. It does not compare the severity of TREM2 deficiency in humans and mice, so that part of the claim is unsupported. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [105] Deczkowska A, Keren-Shaul H, Weiner A, Colonna M, Schwartz M, Amit I. Disease-associated microglia: a universal immune sensor of Neurodegeneration. Cell. 2018;173:1073–81. sourceNot checked — no full text of the source

May combine two claims.

In human cell lines overexpressing PLCγ2, p.P522R activity measured by P3/1 accumulation and intracellular calcium flux was elevated compared to WT PLCγ2 upon EGF receptor stimulation, but not at basal levels.

“the activity of the AD-protective variant (measured by P3/1 accumulation and intracellular calcium flux) was elevated in comparison to the WT PLCγ2 upon EGF receptor stimulation, but not at basal levels”

• cites [26] Magno L, Lessard CB, Martins M, Lang V, Cruz P, Asi Y, et al. Alzheimer’s disease phospholipase C-gamma-2 (PLCG2) protective variant is a functional hypermorph. Alzheimers Res Ther. 2019;11(1):16. sourcePartly supported

  The Results section (Fig. 4a–d; page unavailable) reports higher inositol-phosphate production and a small increase in intracellular calcium release for p.P522R versus WT after EGF stimulation. The Fig. 4 caption says activity was measured under basal conditions, but the passages do not state that p.P522R and WT had equal basal activity. They also distinguish intracellular calcium release from extracellular calcium entry, for which no significant difference was found. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

May combine two claims.

In mouse microglia, basal levels of PIP2 may be decreased in cells harbouring p.P522R, suggesting that in mouse brain the P522R mutation might elicit an increase in basal PLCγ2 function.

“Recent studies in mouse microglia have indicated that basal levels of PIP2 may be decreased in cells harbouring the p.P522R variant, suggesting that in the mouse brain the P522R mutation might elicit an increase in basal PLCγ2 function [36]”

• cites [36] Maguire E, Menzies GE, Phillips T, Sasner M, Williams HM, Czubala MA, et al. The Alzheimer’s disease protective P522R variant of PLCG2, consistently enhances stimulus-dependent PLCγ2 activation, depleting substrate and altering cell function. bioRxiv. 2020; Available from: http://biorxiv.org/content/early/2020/04/28/2020.04.27.059600.abstract. sourceSupported

May combine two claims.

Genomic deletions within the PLCG2 coding region cause PLAID disorders, which manifest with cold-induced urticaria and variable immunologic defects, including antibody deficiency and autoimmune disease.

“genomic deletions within the PLCG2 coding region cause PLAID disorders, which manifest with cold-induced urticaria and variable immunologic defects, including antibody deficiency and autoimmune disease [113]”

• cites [113] Ombrello MJ, Remmers EF, Sun G, Freeman AF, Datta S, Torabi-Parizi P, et al. Cold Urticaria, immunodeficiency, and autoimmunity related to PLCG2 deletions. N Engl J Med. 2012;366:330–8. sourceSupported

May combine two claims.

Newly characterised APLAID mutations (A708P, L848P, L845P-L848Del, M1141) have been associated with the most severe outcome described so far, including complete B-cell depletion and agamma-globulinemia, leading to severe multisystemic autoinflammation, cutaneous manifestations, and recurrent bacterial infections.

“Newly characterised APLAID mutations (A708P, L848P, L845P-L848Del, M1141) have been associated with the most severe outcome described so far, including complete B-cell depletion and agamma-globulinemia, leading to severe multisystemic autoinflammation, cutaneous manifestations [100, 111], and recurrent bacterial infections [100]”

• cites [100] Martín-Nalda A, Fortuny C, Rey L, Bunney TD, Alsina L, Esteve-Solé A, et al. Severe autoinflammatory manifestations and antibody deficiency due to novel Hypermorphic PLCG2 mutations. J Clin Immunol. 2020;40:987–1000. sourcePartly supported

  The Discussion (page unavailable) identifies the p.Leu845_Leu848 deletion patient as the severest APLAID case described to date, with absent B cells and immunoglobulins, cutaneous inflammation, and severe recurrent bacterial infections. It describes the p.Ala708Pro patient's B-cell and antibody deficits as mild-to-moderate, so complete depletion cannot be attributed to all the listed mutations. The paper discusses p.Leu848Pro as an earlier reported variant but does not substantiate the claim about M1141. (LLM, conf=0.90)

  Experimental — accuracy not yet measured
• cites [111] Morán-Villaseñor E, Saez-de-Ocariz M, Torrelo A, Arostegui JI, Yamazaki-Nakashimada MA, Alcántara-Ortigoza MA, et al. Expanding the clinical features of autoinflammation and phospholipase Cγ2-associated antibody deficiency and immune dysregulation by description of a novel patient. J Eur Acad Dermatology Venereol. 2019;33:2334–9. sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

There are no reported cases of humans with PLCγ2 deficiency.

“Although there are no reported cases of humans with PLCγ2 deficiency [101]”

• cites [101] Novice T, Kariminia A, Del Bel KL, Lu H, Sharma M, Lim CJ, et al. A Germline mutation in the C2 domain of PLCγ2 associated with gain-of-function expands the phenotype for PLCG2-related diseases. J Clin Immunol. 2020;40:267–76. sourceSupported

May combine two claims.

The majority of hypermorphic variants (S707Y, Y495C, D993G) have been identified in the context of APLAID disorders, and in some mouse models with autoinflammatory phenotypes.

“the majority of hypermorphic variants (S707Y, Y495C, D993G) have been identified in the context of APLAID disorders, and in some mouse models with autoinflammatory phenotypes [3, 109, 110]”

• cites [3] Koss H, Bunney TD, Behjati S, Katan M. Dysfunction of phospholipase Cγ in immune disorders and cancer. Trends Biochem Sci. 2014;39:603–11. sourcePartly supported

  The immune-diseases section (pp. 3–4) identifies S707Y in APLAID and describes gain-of-function PLCγ2 mutations in autoinflammatory mouse strains. The structural section (pp. 8–9) places Y495C in ALI14 mice; the table (p. 20) lists D993G in ALI5 mice, although the main text calls that substitution D993L. The copy does not establish that a majority of hypermorphic variants occur in these contexts, and it does not place Y495C or D993G in APLAID patients. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [109] Abe K, Fuchs H, Boersma A, Hans W, Yu P, Kalaydjiev S, et al. A novel N-ethyl-N-nitrosourea-induced mutation in phospholipase Cγ2 causes inflammatory arthritis, metabolic defects, and male infertility in vitro in a murine model. Arthritis Rheum. 2011;63:1301–11. sourceNot checked — no full text of the source
• cites [110] Everett KI, Bunney TD, Yoon Y, Rodrigues-Lima F, Harris R, Driscoll PC, et al. Characterization of phospholipase Cγ enzymes with gain-of-function mutations. J Biol Chem. 2009;284:23083–93. sourceNot checked — no full text of the source

May combine two claims.

Communication between the CNS and the peripheral immune systems is crucial, and monocyte infiltration in the brain could influence microglia responses.

“communication between the CNS and the peripheral immune systems is crucial, and monocyte infiltration in the brain could influence microglia responses [117]”

• cites [117] Dionisio-Santos DA, Olschowka JA, O’Banion MK. Exploiting microglial and peripheral immune cell crosstalk to treat Alzheimer’s disease. J Neuroinflam. 2019;16:1–13. sourcePartly supported

  In the Introduction sections on microglia and peripheral immune cells (page unavailable), the review says peripheral immune cells can modulate microglial responses and that monocytes may enter the CNS in Alzheimer’s disease. It does not specifically establish that infiltrating monocytes alter microglial responses; that link is more specific than the passages support. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

TREM2 is upregulated in microglia in AD human brains and in several models of neurodegenerative disorders.

“TREM2 is upregulated in microglia in AD human brains and in several models of neurodegenerative disorders [14]”

• cites [14] Keren-Shaul H, Spinrad A, Weiner A, Matcovitch-Natan O, Dvir-Szternfeld R, Ulland TK, et al. A Unique Microglia Type Associated with Restricting Development of Alzheimer’s Disease. Cell. 2017;169:1276–1290.e17 Elsevier. sourcePartly supported

  The Results report strong Trem2 induction in disease-associated microglia in the 5XFAD Alzheimer’s mouse model and Trem2 upregulation in an ALS mouse model. The Introduction and Discussion identify DAM markers in human AD brains, but the passages do not establish that TREM2 itself is upregulated in human AD microglia; they also do not establish this across several neurodegenerative-disorder models. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

PLCG2 GOF polymorphisms have been recently associated with other disorders, such as inflammatory bowel disease and resistance of chronic lymphocytic leukaemia cells to the BTK inhibitor ibrutinib.

“PLCG2 GOF polymorphisms have also been recently associated with other disorders, such as inflammatory bowel disease [114] and resistance of chronic lymphocytic leukaemia cells to the BTK inhibitor ibrutinib [99, 115]”

• cites [114] de Lange KM, Moutsianas L, Lee JC, Lamb CA, Luo Y, Kennedy NA, et al. Genome-wide association study implicates immune activation of multiple integrin genes in inflammatory bowel disease. Nat Genet. 2017;49:256–61. sourcePartly supported

  The paper reports two likely functional PLCG2 missense variants associated with inflammatory bowel disease (section labelled Abstract; page unavailable). It does not establish that those IBD-associated variants are gain-of-function. The ibrutinib-resistance clause has separate citations and is not attributed to this paper. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [99] Liu T-M, Woyach JA, Zhong Y, Lozanski A, Lozanski G, Dong S, et al. Hypermorphic mutation of phospholipase C, gamma 2 acquired in ibrutinib resistant CLL confers BTK independency upon BCR activation. Blood. 2015;126:61–8. sourceSupported
• cites [115] Walliser C, Wist M, Hermkes E, Zhou Y, Schade A, Haas J, et al. Functional characterization of phospholipase C-γ2 mutant protein causing both somatic ibrutinib resistance and a germline monogenic autoinflammatory disorder. Oncotarget. 2018;9:34357–78. sourceSupported

May combine two claims.

A recent study on a centenarian cohort suggested this variant could exert a beneficial effect on the entire immune system and promote healthy ageing, thus indicating that protection might also be mediated via the peripheral immune system, and could span the entire organism.

“As a recent study on a centenarian cohort suggested, this variant could exert a beneficial effect on the entire immune system and promote healthy ageing [9], thus indicating that protection might also be mediated via the peripheral immune system, and could span the entire organism”

• cites [9] van der Lee SJ, Conway OJ, Jansen I, Carrasquillo MM, Kleineidam L, van den Akker E, et al. A nonsynonymous mutation in PLCG2 reduces the risk of Alzheimer’s disease, dementia with Lewy bodies and frontotemporal dementia, and increases the likelihood of longevity. Acta Neuropathol. 2019;138:237–50. sourcePartly supported

  The Results (Association with longevity; page unavailable) report enrichment of rs72824905-G among cognitively healthy centenarians, and the Introduction (page unavailable) says PLCG2 functions in immune cells in both the brain and periphery. These passages support a possible link to healthy ageing, but the paper does not show that this variant benefits the entire immune system; its Discussion says the variant’s functional effects still need study. The statement about organism-wide protection follows the citation and is the citing authors’ inference. (LLM, conf=0.83)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

A potential link between PLCG2 and macular degeneration has also been described.

“A potential link between PLCG2 and macular degeneration has also been described [116]”

• cites [116] Waksmunski AR, Grunin M, Kinzy TG, Igo RP, Haines JL, Bailey JNC. Pathway analysis integrating genome-wide and functional data identifies PLCG2 as a candidate gene for age-related macular degeneration. Investig Ophthalmol Vis Sci. 2019;60:4041–51. sourceSupported

May combine two claims.

Recent in vivo and in vitro models seem to support the idea that activation of Trem2 leads to reduced amyloidogenesis by a more efficient clearance, and promotes cell phagocytosis and survival, at least in mouse models.

“recent in vivo and in vitro models seem to support the idea that activation of Trem2 leads to reduced amyloidogenesis by a more efficient clearance, and promotes cell phagocytosis and survival, at least in mouse models ([46], see more below)”

• cites [46] Schlepckow K, Monroe KM, Kleinberger G, Cantuti-Castelvetri L, Parhizkar S, Xia D, et al. Enhancing protective microglial activities with a dual function TREM 2 antibody to the stalk region. EMBO Mol Med. 2020;12:1–22. sourcePartly supported

  The Results (page unavailable in our copy) report that the TREM2-stimulating antibody 4D9 reduced cortical plaque burden and soluble Aβ in mice, increased Aβ uptake by cultured mouse microglia, and improved survival of cultured mouse macrophages. The Discussion says the fate of engulfed Aβ is unknown, so the proposed explanation that more efficient clearance caused the reduction in amyloidogenesis is not established by this paper. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

May combine two claims.

Agonistic monoclonal antibodies directed at the receptor, now in clinical trial phase 2, seem to reduce neurotoxic plaques and neurite dystrophy in a mouse model of AD.

“Agonistic monoclonal antibodies directed at the receptor, now in clinical trial phase 2, seem to reduce neurotoxic plaques and neurite dystrophy in a mouse model of AD [125]”

• cites [125] Wang S, Mustafa M, Yuede CM, Salazar SV, Kong P, Long H, et al. Anti-human TREM2 induces microglia proliferation and reduces pathology in an Alzheimer’s disease model. J Exp Med. 2020;217. Available from. https://doi.org/10.1084/jem.20200785. sourcePartly supported

  The Introduction and Discussion report that agonistic anti-TREM2 antibody AL002c reduced filamentous neurotoxic plaques and neurite dystrophy in AD-model mice. The Introduction identifies the related clinical antibody AL002 as having been studied in a phase I trial; our copy does not support the claim that it was in phase II. Page numbers are not provided in the supplied passages. (LLM, conf=0.90)

  Experimental — accuracy not yet measured

Classified as probably not a substantial claim. May combine two claims.

Akt is a central effector downstream of several signal transduction pathways, and is involved in numerous cellular responses, such as protein synthesis, cell proliferation, cell motility, metabolism, survival, apoptosis, cell growth and cytokine production.

“Akt is a central effector downstream of several signal transduction pathways, and it is involved in numerous cellular responses, such as protein synthesis, cell proliferation, cell motility, metabolism, survival, apoptosis, cell growth and cytokine production”

• cites [126] Cianciulli A, Porro C, Calvello R, Trotta T, Lofrumento DD, Panaro MA. Microglia mediated neuroinflammation: focus on PI3K modulation. Biomolecules. 2020;10:1–19. sourceSupported

May combine two claims.

Other similar strategies, based on monoclonal antibodies (4D9), act via a dual mechanism: as direct agonists of TREM2 signalling, and by stabilizing TREM2 on the cell surface and reducing its shedding.

“Other similar strategies, based on monoclonal antibodies (4D9), act via a dual mechanism: as direct agonists of the TREM2 signalling, and by stabilizing TREM2 on the cell surface and reducing its shedding [46]”

• cites [46] Schlepckow K, Monroe KM, Kleinberger G, Cantuti-Castelvetri L, Parhizkar S, Xia D, et al. Enhancing protective microglial activities with a dual function TREM 2 antibody to the stalk region. EMBO Mol Med. 2020;12:1–22. sourceSupported

Classified as probably not a substantial claim.

It has been suggested that p.R47H leads to hyperactivation of Akt downstream of Trem2.

“it has been suggested that p.R47H leads to hyperactivation of Akt downstream of Trem2 [38]”

• cites [38] Sayed FA, Kodama L, Udeochu JC, Fan L, Carling GK, Le D, et al. AD-linked R47H-TREM2 mutation induces disease-enhancing proinflammatory microglial states in mice and humans. bioRxiv. 2020;2020.07.24.218719 Available from: http://biorxiv.org/content/early/2020/07/25/2020.07.24.218719.abstract. sourceSupported

May combine two claims.

This strategy demonstrated increased microglial uptake of myelin debris and amyloid β-peptide in vitro, and reduced amyloid plaque burden in the cortex of APPNLGF mice.

“This strategy demonstrated increased microglial uptake of myelin debris and amyloid β-peptide in vitro, and reduced amyloid plaque burden in the cortex of APPNLGF mice [46]”

• cites [46] Schlepckow K, Monroe KM, Kleinberger G, Cantuti-Castelvetri L, Parhizkar S, Xia D, et al. Enhancing protective microglial activities with a dual function TREM 2 antibody to the stalk region. EMBO Mol Med. 2020;12:1–22. sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

These cascades have been mostly studied in vitro and/or in surrogate cell lines (such as BV2), and they still need to be thoroughly mapped in microglia cells and in specific disease-contexts.

“So far, these cascades have been mostly studied in vitro and/or in surrogate cell lines (such as BV2), and they still need to be thoroughly mapped in microglia cells and in specific disease-contexts”

May combine two claims.

Although genetic evidence suggests that mild potentiation of PLCγ2 signalling downstream of TREM2 is protective, no specific PLCγ2-targeted therapeutics have been developed to date.

“Although genetic evidence suggests that mild potentiation of PLCγ2 signalling downstream of TREM2 is protective (see above), no specific PLCγ2-targeted therapeutics have been developed to date”

Probably not a substantial claim: may not pass S3 (load-bearing).

PLCγ2 is expressed in cells of the hematopoietic lineage.

“PLCγ2 is expressed in cells of the hematopoietic lineage [5].”

• cites [5] Wang D, Feng J, Wen R, Marine J-C, Sangster MY, Parganas E, et al. Phospholipase Cγ2 is essential in the functions of B cell and several fc receptors. Immunity. 2000;13:25–35. sourceNot checked — no full text of the source

May combine two claims.

PLCγ2 is implicated as a key signalling node that links TREM2 activation with microglial lipid metabolism, and altered phenotype in KO cells.

“PLCγ2 is implicated as a key signalling node that links TREM2 activation with microglial lipid metabolism, and altered phenotype in KO cells [34].”

• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source

May combine two claims.

The protective PLCγ2 variant p.P522R may act to modulate lipid metabolism and restore microglial functionality.

“suggesting that it may act to modulate lipid metabolism and restore microglial functionality.”

May combine two claims.

Together these studies highlight the pathogenic effect of lipid accumulation, and the importance of lipid metabolism in microglia.

“Whilst contradictory, together these studies highlight the pathogenic effect of lipid accumulation, and the importance of lipid metabolism in microglia.”

May combine two claims.

PLCγ2 and PLCγ1 share the same domain structure and have significant amino acid identity, so it is possible to derive a homology model of PLCγ2 that includes domain linkers.

“Both proteins share the same domain structure (Fig. 2a), and have significant amino acid identity: consequently it is possible to derive a homology model of PLCγ2 that includes domain linkers (Fig. 2b).”

May combine two claims.

PLCγ2 activation downstream of Rac is phosphorylation-independent and involves the lipid-modified, GTP-bound form of Rac.

“PLCγ2 activation downstream of Rac is phosphorylation-independent and involves the lipid-modified, GTP-bound form of Rac [73].”

• cites [73] Bunney TD, Opaleye O, Roe SM, Vatter P, Baxendale RW, Walliser C, et al. Structural insights into formation of an active signaling complex between Rac and phospholipase C gamma 2. Mol Cell. 2009;34:223–33. sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Another consequence of PIP2 hydrolysis is the production of protons, which can lead to localised decreases in the juxtamembrane pH.

“Another consequence of PIP2 hydrolysis is the production of protons, which can lead to localised decreases in the juxtamembrane pH [80, 81].”

• cites [80] Huang J, Liu CH, Hughes SA, Postma M, Schwiening CJ, Hardie RC. Activation of TRP channels by protons and Phosphoinositide depletion in Drosophila photoreceptors. Curr Biol. 2010;20:189–97. sourceNot checked — no full text of the source
• cites [81] Molinari G. Is hydrogen ion (H+) the real second messenger in calcium signalling? Cell Signal. 2015;27:1392–7. sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

The catalytic capabilities of PLCγ isoforms reside in the core region of the enzyme, which consists of an N-terminal PH domain, EF-hands, TIM-like barrel and a C2 domain.

“The catalytic capabilities of PLCγ isoforms reside in the core region of the enzyme, which consists of an N-terminal PH domain, EF-hands, TIM-like barrel and a C2 domain.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

PLCγ isozymes are unique in that their regulatory domains are inserted within linkers in the TIM-like barrel, and consist of a spPH, two SH2 and an SH3 domain.

“PLCγ isozymes are unique in that their regulatory domains are inserted within linkers in the TIM-like barrel, and consist of a spPH, two SH2 and an SH3 domain.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The substrate recognition site and residues involved in inositol-lipid hydrolysis are within the catalytic, TIM-like barrel domain.

“The substrate recognition site and residues involved in inositol-lipid hydrolysis are within the catalytic, TIM-like barrel domain.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Src kinase is a non-receptor tyrosine kinase that is constitutively membrane-localised due to myristoylation at its N-terminus.

“Src kinase is a non-receptor tyrosine kinase that is constitutively membrane-localised due to myristoylation at its N-terminus [65].”

• cites [65] Boggon TJ, Eck MJ. Structure and regulation of Src family kinases. Oncogene. 2004;23:7918–27. sourceNot checked — no full text of the source

May combine two claims.

It is likely that the signalling pathways linking TREM2/DAP12 activation to downstream targets are analogous to those described in Fc receptor signalling, in as much as Src phosphorylation on the tyrosine residues of DAP12 creates a binding site for Syk.

“it is likely that the signalling pathways are analogous to those described in Fc receptor signalling, in as much as Src phosphorylation on the tyrosine residues of DAP12 creates a binding site for the non-receptor spleen tyrosine kinase (Syk).”

May combine two claims.

PI3K converts PIP2 into PIP3, which seems to be important for the recruitment of the scaffolding proteins.

“PI3K then converts phosphatidylinositol (4,5)-bisphosphate (PIP2) into PIP3, which seems to be important for the recruitment of the scaffolding proteins [4].”

• cites [4] Xing J, Titus AR, Humphrey MB. The TREM2-DAP12 signaling pathway in Nasu–Hakola disease: a molecular genetics perspective. Res Rep Biochem. 2015;5:89–100 Available from: https://pubmed.ncbi.nlm.nih.gov/26478868.Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

IP3 production leads to Ca2+ release from intracellular stores.

“with IP3 production leading to Ca2+ release from intracellular stores”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

PLCγ is localised to the cytoplasm in resting cells, and therefore its activation is a two-step process involving recruitment to the membrane compartment, and then removal of autoinhibition.

“An important consideration with regards to PLCγ signalling is that the molecule is localised to the cytoplasm in “resting” cells, and therefore its activation is a two-step process involving recruitment to the membrane compartment, and then removal of autoinhibition (Fig. 1d).”

May combine two claims.

Both TREM2 KO and PLCG2 KO iPSC-derived microglia were equivalently deficient in clearing axonal debris, which correlated with an increase in lipid accumulation in these cells.

“Both TREM2 KO and PLCG2 KO iPSC-derived microglia were equivalently deficient in clearing axonal debris, which correlated with an increase in lipid accumulation in these cells.”

• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source

May combine two claims.

BTK has been shown to recruit PLCγ2 to the PM, and the activation can occur through Rac in the absence of phosphorylation.

“BTK has been shown to recruit PLCγ2 to the PM, and the activation can occur through Rac in the absence of phosphorylation [74].”

• cites [74] Wist M, Meier L, Gutman O, Haas J, Endres S, Zhou Y, et al. Noncatalytic Bruton’s tyrosine kinase activates PLCγ2 variants mediating ibrutinib resistance in human chronic lymphocytic leukemia cells. J Biol Chem. 2020;295:5717–36. sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Within microglia it has been suggested that LAT, LAB or LAT2, rather than BLNK, could be phosphorylated by Syk, or that Syk may directly phosphorylate and activate PLCγ2, thus bypassing BTK.

“Within microglia it has been suggested that Linkers for Activation of T- and B-cells (LAT, LAB or LAT2), rather than BLNK, could be phosphorylated by Syk, or that Syk may directly phosphorylate and activate PLCγ2, thus bypassing BTK in these cells [4, 62].”

• cites [4] Xing J, Titus AR, Humphrey MB. The TREM2-DAP12 signaling pathway in Nasu–Hakola disease: a molecular genetics perspective. Res Rep Biochem. 2015;5:89–100 Available from: https://pubmed.ncbi.nlm.nih.gov/26478868.Not checked yet

  Not checked in the free run.

• cites [62] Whittaker GC, Orr SJ, Quigley L, Hughes L, Francischetti IMB, Zhang W, et al. The linker for activation of B cells (LAB)/non-T cell activation linker (NTAL) regulates triggering receptor expressed on myeloid cells (TREM)-2 signaling and macrophage inflammatory responses independently of the linker for activation of T cells. J Biol Chem. 2010;285:2976–85. sourceNot checked — no full text of the source

May combine two claims.

These inhibitory interactions are released after phosphorylation; selective activation by Rac may occur via a different mechanism.

“These inhibitory interactions are released after phosphorylation; selective activation by Rac may occur via a different mechanism.”

May combine two claims.

rs12446759 is located in a region upstream of the PLCG2 coding sequence, with unknown effect on expression, or protein function.

“This is located in a region upstream of the PLCG2 coding sequence, with unknown effect on expression, or protein function.”

May combine two claims.

Mutations at either of these interfaces can be sufficient to disrupt the autoinhibition, and lead to an activated PLCγ.

“Mutations at either of these interfaces can be sufficient to disrupt the autoinhibition, and lead to an activated PLCγ.”

May combine two claims.

There are two regions of auto-inhibitory interface: contact between the TIM-like barrel and spPH domains, and contacts between the C2 and cSH2 domains.

“Specifically, there are two regions of auto-inhibitory interface. Firstly, contact between the TIM-like barrel and spPH domains and, secondly, contacts between the C2 and cSH2 domains.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The SH3 domain binds to poly-proline motifs in adaptors and other proteins.

“The SH3 domain binds to poly-proline motifs in adaptors and other proteins [90].”

• cites [90] Bae YS, Lee HY, Jung YS, Lee M, Suh PG. Phospholipase Cγ in toll-like receptor-mediated inflammation and innate immunity. Adv Biol Regul. 2017;63:92–7. sourceNot checked — no full text of the source

May combine two claims.

The SH3 domain is not visible in the cryoEM structure: this suggests that this domain and its associated linkers are highly flexible in the WT protein.

“The SH3 domain is not visible in the cryoEM structure: this suggests that this domain and its associated linkers are highly flexible in the WT protein.”

May combine two claims.

The same study identified a mutation in BLNK negatively associated with AD (OR = 0.89), with considerable eQTL colocalization in dorso-lateral prefrontal cortex and in microglia.

“The same study also identified a mutation in BLNK negatively associated with AD (OR = 0.89), with considerable expression-quantitative-trait-loci (eQTL) colocalization in dorso-lateral prefrontal cortex and in microglia [11].”

• cites [11] Bellenguez C, Kucukali F, Jansen I, Andrade V, Morenau-Grau S, Amin N, et al. Large meta-analysis of genome-wide association studies expands knowledge of the genetic etiology of Alzheimer disease and highlights potential translational opportunities. medRxiv. 2020; Available from: http://medrxiv.org/content/early/2020/10/03/2020.10.01.20200659.abstract.Not checked yet

  Not checked in the free run.

May combine two claims.

As TREM2 elicits its functional effect via activation of PLCγ2, KO of PLCγ2 produces similar phenotypes; PLCG2 KO iPSC microglia and macrophages exhibit reduced signalling, phagocytic deficits, and reduction in lipid metabolism, which are also observed in TREM2 KO iPSC lines.

“As TREM2 elicits its functional effect via activation of PLCγ2, it is not surprising that KO of PLCγ2 produces similar phenotypes and, indeed, PLCG2 KO iPSC microglia and macrophages exhibit reduced signalling, phagocytic deficits, and reduction in lipid metabolism, which are also observed in TREM2 KO iPSC lines [34].”

• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

Several mutations in TREM2 (at least 27) have now been associated with disease.

“Several mutations in TREM2 (at least 27) have now been associated with disease.”

May combine two claims.

Although the functional effects of these mutations vary, and the impacts on TREM2 signalling require further investigation, these variants seem to predominately result in a degree of TREM2 LOF.

“Although the functional effects of these mutations vary, and the impacts on TREM2 signalling require further investigation, these variants seem to predominately result in a degree of TREM2 LOF.”

May combine two claims.

PLCγ2 mutations can be classified into two principal groups: those that cause disease and mainly affect the autoinhibitory interface (mostly strongly activating), and those that very mildly activate, with P522R the only known example to date.

“We can therefore classify mutations in PLCγ2 into two principal groups. The first group includes mutations that cause disease and mainly affect the autoinhibitory interface. These are mostly strongly activating (Fig. 2c). In contrast are the mutations that very mildly activate, the only known example to date is P522R.”

May combine two claims.

p.P522R increases lipid metabolism in human iPSC macrophages, with cells harbouring this mutation exhibiting reduced accumulation of cholesterol esters compared with WT cells.

“The p.P522R variant has also been shown to increase lipid metabolism in human iPSC macrophages, with cells harbouring this mutation exhibiting a reduced accumulation of cholesterol esters when compared with WT cells [34]”

• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source

May combine two claims.

P522R position is distinct from the autoinhibitory interface and is linked to a quantitatively lower hypermorphic effect on PLCγ2 activity compared to pathogenic mutations.

“This position is clearly distinct from the autoinhibitory interface, and it is linked to a quantitatively lower hypermorphic effect on the activity of PLCγ2 compared to the pathogenic mutations”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

TREM2 and PLCγ2 variants can cause a broad range of effects and disturbances depending on the type of mutation, cell type and organ/system affected.

“TREM2 and PLCγ2 variants can cause a broad range of effects and disturbances depending on the type of mutation, cell type and organ/system affected”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

A common theme is the involvement of the immune system and various forms of inflammation.

“A common theme, however, is the involvement of the immune system and various forms of inflammation”

May combine two claims.

PLCγ2-deficient mice are viable, but exhibit haemorrhaging in various organs in addition to severe immunodeficiency.

“PLCγ2-deficient mice are viable, but exhibit haemorrhaging in various organs in addition to severe immunodeficiency [5]”

• cites [5] Wang D, Feng J, Wen R, Marine J-C, Sangster MY, Parganas E, et al. Phospholipase Cγ2 is essential in the functions of B cell and several fc receptors. Immunity. 2000;13:25–35. sourceNot checked — no full text of the source

May combine two claims.

Loss of PLCγ2 severely impacts mostly immune cells, and hampers key responses to insult.

“Therefore, loss of PLCγ2 severely impacts mostly immune cells, and hampers key responses to insult”

May combine two claims.

Human iPSC PLCγ2 KO differentiated into microglia-like cells are unable to properly phagocytose, and produce an insufficient response to lipid challenge.

“human iPSC PLCγ2 KO differentiated into microglia-like cells are unable to properly phagocytose, and produce an insufficient response to lipid challenge (see section above, [34])”

• cites [34] Andreone BJ, Przybyla L, Llapashtica C, Rana A, Davis SS, van Lengerich B, et al. Alzheimer’s-associated PLCγ2 is a signaling node required for both TREM2 function and the inflammatory response in human microglia. Nat Neurosci. 2020;23:927–38. sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The effect of PLCγ2 activation on NLRP3-mediated inflammation may be receptor dependent and, in the presence and context of TREM2 signalling, there may not be an exacerbation of this specific inflammatory response.

“The effect of PLCγ2 activation on NLRP3-mediated inflammation may be receptor dependent and, in the presence and context of TREM2 signalling, there may not be an exacerbation of this specific inflammatory response”

May combine two claims.

This protective action has been demonstrated with respect to neurological symptoms, and therefore it is most likely to be mediated by brain immune cells: microglia.

“This protective action has been demonstrated with respect to neurological symptoms, and therefore it is most likely to be mediated by the brain immune cells: microglia”

May combine two claims.