TREM2 activation on microglia promotes myelin debris clearance and remyelination in a model of multiple sclerosis

In the paper

“TREM2 is a phospholipid sensing receptor known to sustain microglial cell activation and expansion in response to demyelination or amyloid plaques in Alzheimer’s disease (AD) [8, 42, 50].”

What the sources say

• Partly supported

  The Abstract and the Results section on microglial proliferation report that TREM2 supports microglial activation and proliferation during cuprizone-induced demyelination. The Discussion also reports fewer plaque-associated microglia in an AD mouse model with one copy of TREM2, but does not establish that TREM2 sustains both activation and expansion at amyloid plaques. The Introduction says TREM2 ligands are poorly characterized; it does not identify TREM2 as a phospholipid-sensing receptor. Page numbers were not available in our copy. (LLM, conf=0.88)

  cites [8] Cantoni C, Bollman B, Licastro D, Xie M, Mikesell R, Schmidt R et al (2015) TREM2 regulates microglial cell activation in response to demyelination in vivo. Acta Neuropathol 129:429–447. https://doi.org/10.1007/s00401-015-1388-1 sourceExperimental — accuracy not yet measured
• Partly supported

  The Introduction and Results report that TREM2 detects phospholipids and supports microglial activation in response to demyelination; the Abstract reports microglial expansion during aging. The Discussion only proposes that TREM2 may support a microglial response to β-amyloid plaques in Alzheimer’s disease, rather than establishing activation or expansion in response to those plaques. (LLM, conf=0.88)

  cites [42] Poliani PL, Wang Y, Fontana E, Robinette ML, Yamanishi Y, Gilfillan S et al (2015) TREM2 sustains microglial expansion during aging and response to demyelination. J Clin Investig 125:2161–2170. https://doi.org/10.1172/JCI77983 sourceExperimental — accuracy not yet measured
• Partly supported

  The Discussion states that TREM2 supports microglial expansion and activation around Aβ plaques in the 5XFAD Alzheimer’s disease model, and the Results identify it as a sensor for several lipids. The Discussion only suggests that TREM2 may trigger a microglial response to damaged myelin; it does not establish that TREM2 sustains microglial activation and expansion during demyelination. (LLM, conf=0.86)

  cites [50] Wang Y, Cella M, Mallinson K, Ulrich JD, Young KL, Robinette ML et al (2015) TREM2 lipid sensing sustains the microglial response in an Alzheimer’s disease model. Cell 160:1061–1071. https://doi.org/10.1016/j.cell.2015.01.049 sourceExperimental — accuracy not yet measured

In the paper

“Current MS immunomodulatory treatments target CNS inflammation, while therapies capable of regenerating myelin and halting disease progression are lacking [28].”

What the sources say

• Partly supported

  The Introduction says current anti-inflammatory and immunomodulatory treatments are partly effective early in MS but offer limited benefit in the progressive phase. Its remyelination discussion calls therapies that promote myelin repair an attractive option, but does not explicitly establish that such therapies are lacking; nor does it say that no therapy can halt disease progression. (LLM, conf=0.84)

  cites [28] Lassmann H, Bruck W, Lucchinetti CF (2007) The immunopathology of multiple sclerosis: an overview. Brain Pathol 17:210–218. https://doi.org/10.1111/j.1750-3639.2007.00064.x sourceExperimental — accuracy not yet measured

In the paper

“Here, we explored the effect of antibody-mediated TREM2 activation on microglia in a well-established toxin-induced model of demyelination in the CNS resulting from exposure to the copper chelator cuprizone (CPZ) in the diet [31].”

What the sources say

• Supported

  The paper describes dietary exposure to cuprizone, a copper chelator, as an experimental model that reproducibly induces extensive demyelination in mouse brain. It also reviews work on the model from several laboratories over three decades, supporting the description 'well-established.' The indexed passage has no section or page label. (LLM, conf=0.94)

  cites [31] Matsushima GK, Morell P (2001) The neurotoxicant, cuprizone, as a model to study demyelination and remyelination in the central nervous system. Brain Pathol 11:107–116 source

In the paper

“These events lead to OPC recruitment, differentiation into mature OLs, and then remyelination which is almost complete within few weeks from toxin withdrawal [31].”

What the sources say

• Supported

  The paper’s opening summary describes oligodendrocyte progenitor cells proliferating and invading demyelinated areas in cuprizone-treated mice, followed by almost complete remyelination within weeks of stopping cuprizone. Its reference list also identifies progenitor differentiation as part of demyelination and remyelination, supporting the sequence in the claim. (LLM, conf=0.88)

  cites [31] Matsushima GK, Morell P (2001) The neurotoxicant, cuprizone, as a model to study demyelination and remyelination in the central nervous system. Brain Pathol 11:107–116 source

In the paper

“Microglia activation and myelin debris clearance are critical steps for successful remyelination [29].”

What the sources say

• ?Could not verify

  The available copy identifies the review as concerning the pro-remyelination properties of microglia, but the retrieved passages are bibliographic information rather than discussion of the proposed steps. Searches for microglial activation and myelin debris clearance found no passage establishing that either is critical for successful remyelination. (LLM, conf=0.72)

  cites [29] Lloyd AF, Miron VE (2019) The pro-remyelination properties of microglia in the central nervous system. Nat Rev Neurol 15:447–458. https://doi.org/10.1038/s41582-019-0184-2 sourceExperimental — accuracy not yet measured

In the paper

“TREM2 clustering promotes calcium flux stimulating NFAT-activity that induces luciferase expression [50].”

What the sources say

• Partly supported

  The Results section (‘TREM2 is a sensor for anionic and zwitterionic lipids’) says that TREM2 engagement leads to calcium mobilization and NFAT-controlled reporter expression. But it identifies the reporter as GFP, not luciferase, and describes lipid engagement rather than TREM2 clustering. The Experimental Procedures (‘Reporter assay’) also measure GFP-positive cells. (LLM, conf=0.88)

  cites [50] Wang Y, Cella M, Mallinson K, Ulrich JD, Young KL, Robinette ML et al (2015) TREM2 lipid sensing sustains the microglial response in an Alzheimer’s disease model. Cell 160:1061–1071. https://doi.org/10.1016/j.cell.2015.01.049 sourceExperimental — accuracy not yet measured

In the paper

“We previously showed that Trem2−/− mice have a striking defect in microglia activation and myelin debris clearance in the CPZ model [8].”

What the sources say

• Supported

  The Discussion explicitly reports defective microglial activation and clearance of myelin debris in TREM2-deficient mice in the CPZ model. The Results section on myelin-debris clearance also reports greater accumulation of degraded myelin in TREM2−/− mice than in wild-type mice. No page numbers are supplied in the passages. (LLM, conf=0.94)

  cites [8] Cantoni C, Bollman B, Licastro D, Xie M, Mikesell R, Schmidt R et al (2015) TREM2 regulates microglial cell activation in response to demyelination in vivo. Acta Neuropathol 129:429–447. https://doi.org/10.1007/s00401-015-1388-1 source

In the paper

“A role of TREM2 in phagocytic pathways in the human brain was previously suggested [13].”

What the sources say

• Supported

  The Results section, “Insights into TREM2-related signaling pathways,” identifies enrichment of an Fc gamma R-mediated phagocytosis pathway among TREM2-related genes in human brain. It proposes that TREM2 on microglia might initiate phagocytosis, matching the citing sentence’s qualified wording, “was previously suggested.” (LLM, conf=0.94)

  cites [13] Forabosco P, Ramasamy A, Trabzuni D, Walker R, Smith C, Bras J et al (2013) Insights into TREM2 biology by network analysis of human brain gene expression data. Neurobiol Aging 34:2699–2714. https://doi.org/10.1016/j.neurobiolaging.2013.05.001 source

In the paper

“TREM2 has often been referred to as a phagocytic receptor as it was demonstrated to be involved in microglia phagocytosis of apoptotic neurons [46], myelin [8] and β-amyloid [24].”

What the sources say

• Supported

  The citation to this paper is attached specifically to apoptotic neurons; myelin and β-amyloid have separate citations. In the Results section, TREM2 knockdown reduced microglial phagocytosis of apoptotic neuronal material, while overexpression increased it. Page numbers are not provided in our copy. (LLM, conf=0.94)

  cites [46] Takahashi K, Rochford CD, Neumann H (2005) Clearance of apoptotic neurons without inflammation by microglial triggering receptor expressed on myeloid cells-2. J Exp Med 201:647–657 source
• Supported

  The citation to Cantoni et al. [8] is attached to myelin, not to apoptotic neurons or β-amyloid. The paper reports defective myelin-debris clearance and impaired myelin degradation in TREM2-deficient microglia during cuprizone-induced demyelination (Abstract; page not provided). (LLM, conf=0.94)

  cites [8] Cantoni C, Bollman B, Licastro D, Xie M, Mikesell R, Schmidt R et al (2015) TREM2 regulates microglial cell activation in response to demyelination in vivo. Acta Neuropathol 129:429–447. https://doi.org/10.1007/s00401-015-1388-1 source
• ?Not checked — no full text of the sourcecites [24] Kleinberger G, Yamanishi Y, Suarez-Calvet M, Czirr E, Lohmann E, Cuyvers E et al (2014) TREM2 mutations implicated in neurodegeneration impair cell surface transport and phagocytosis. Sci Transl Med 6:243ra286. https://doi.org/10.1126/scitranslmed.3009093 source

In the paper

“However, our current and previous findings indicate a more complex TREM2 function not only in myelin uptake, but also in promoting myelin debris degradation through the phagolysosomal pathway [8].”

What the sources say

• Partly supported

  The Results section ('Defective myelin degradation by microglia in TREM2−/− mice'; page unavailable) finds impaired myelin breakdown and persistent myelin-filled phagosomes in TREM2-deficient mice, supporting a role for TREM2 in degradation. But it reports no difference in myelin uptake and says the findings do not support an uptake defect. It implicates phagosome processing without establishing the specific phagolysosomal pathway claimed. (LLM, conf=0.88)

  cites [8] Cantoni C, Bollman B, Licastro D, Xie M, Mikesell R, Schmidt R et al (2015) TREM2 regulates microglial cell activation in response to demyelination in vivo. Acta Neuropathol 129:429–447. https://doi.org/10.1007/s00401-015-1388-1 sourceExperimental — accuracy not yet measured

In the paper

“Here we show that TREM2 was highly expressed within active MS lesions by lipid-laden microglia/macrophages known to display an alternatively activated M2 profile and to promote the resolution of inflammation and clearance of myelin debris [5].”

What the sources say

• Partly supported

  The Introduction describes foamy macrophages in MS lesions as myelin-scavenging cells derived from microglia or monocytes, and the results say they resemble anti-inflammatory M2 macrophages. The Discussion says they are *likely* to contribute to resolution of inflammation; it does not establish that they promote resolution as a demonstrated function. The TREM2-expression finding is introduced as the citing authors’ own result, not one attributed to this source. (LLM, conf=0.87)

  cites [5] Boven LA, Van Meurs M, Van Zwam M, Wierenga-Wolf A, Hintzen RQ, Boot RG et al (2006) Myelin-laden macrophages are anti-inflammatory, consistent with foam cells in multiple sclerosis. Brain 129:517–526 sourceExperimental — accuracy not yet measured

In the paper

“In our previous work, we provided initial evidence to support this hypothesis by showing that TREM2 is not a limiting factor in myelin engulfment, but it was clearly essential for microglia capacity to degrade myelin during chronic demyelination [8].”

What the sources say

• Supported

  In Results (‘Defective myelin degradation by microglia in TREM2−/− mice’), the authors report no difference in measured myelin uptake and say their in vivo findings do not support an uptake defect. The same section reports persistent myelin-containing phagosomes after 12 weeks of cuprizone treatment and suggests a defect in myelin breakdown; the Discussion likewise identifies impaired capacity to degrade myelin. (LLM, conf=0.93)

  cites [8] Cantoni C, Bollman B, Licastro D, Xie M, Mikesell R, Schmidt R et al (2015) TREM2 regulates microglial cell activation in response to demyelination in vivo. Acta Neuropathol 129:429–447. https://doi.org/10.1007/s00401-015-1388-1 source

In the paper

“The antibody’s specificity was verified by binding to wild-type (Trem2+/+), but not Trem2−/− thioglycollate-induced macrophages (THG-Mac) (Supplementary Fig. 1a).”

In the paper

“By confocal analysis we showed TREM2 specific expression in ionized calcium-binding adapter molecule 1(Iba1)+ cells in active MS lesion, which were identified as oil-red O+ lipid laden macrophages-microglia by histology (Fig. 1a, b).”

In the paper

“Principal component analysis showed the ability of gene expression data to discriminate NHD from control subjects (Supplementary Fig. 4e).”

In the paper

“Significantly more MA were counted in the CC after AL002a treatment compared to control at WK 4 + 3D (MA: 32% ± 0.0192 in AL002a-treated group vs. MA: 23% ± 0.0122 in control group) and this was even more pronounced at WK 4 + 7D (MA: 53% ± 0.0124 in AL002a-treated group vs. MA:42% ± 0.0179 in control group) (Fig. 7j).”

In the paper

“A GO cellular component analysis confirmed that genes from the phagocytic pathway are both significantly co-expressed with TREM2 and altered in NHD patients (Supplementary Table 5).”

In the paper

“This was accompanied by increased microglia activation and by a higher expression of proteins involved in phagocytic and degradative pathways.”

In the paper

“Mice treated with AL002a showed significantly lower Nf-L levels in the plasma at WK 4 + 3D compared to the control, with a trend of reduced levels also observed at WK 4 + 7D (Fig. 8a).”

In the paper

“Analysis of MBP internalization by immunofluorescence revealed a significant increase in MBP amount detected inside Iba1+ cells treated with AL002a after 1 h (Fig. 5d, e), while no differences between the two groups were detected at 30’ and 3 h.”

In the paper

“We then demonstrated that treatment with AL002a in vivo promotes efficient clearance of myelin debris, with increased myelin phagocytosis and intracellular degradation after CPZ-induce demyelination.”

In the paper

“AL002a treatment increased OPC density and differentiation into mature OL”

In the paper

“AL002a was able to reach the brain and it was detected in the CC and in the cortex (Ctx) (Supplementary Fig. 1d).”

In the paper

“Gene ontology (GO) analysis revealed that genes involved in the phagosome pathway are among the top-pathways significantly altered in NHD subjects compared to controls along with changes in immune response pathways (Fig. 9b, and Supplementary Table 2 and 3).”

In the paper

“Our data demonstrate that AL002a is a potent TREM2 agonist antibody capable of activating TREM2 in vitro and in vivo and to potentiate myelin-induced activation of TREM2 signaling.”

In the paper

“This was accompanied by increased microglia expression of markers of activation (Iba1 and CD80) and phagolysosomal activity (CD68 and LAMP1).”

In the paper

“Interestingly, in the current study at this time point no differences in the number of microglia were detected between Trem2+/− and Trem2+/+ mice, despite more myelin debris were accumulating in the CC of Trem2+/−.”

In the paper

“First, we tested AL002a in Trem2+/+ mice, without detecting any difference in damaged myelin accumulation, number of microglia or OPC in the CC compared to the control group at 4 weeks on CPZ (data not shown).”

In the paper

“TREM2 engagement leads to DAP12 phosphorylation, followed by recruitment and activation of the spleen-associated tyrosine kinase (SYK), resulting in downstream signaling events leading to proliferation, survival, phagocytosis, and secretion of cytokines and chemokines [47].”

What the sources say

• ?Not checked — no full text of the sourcecites [47] Ulland TK, Colonna M (2018) TREM2—a key player in microglial biology and Alzheimer disease. Nat Rev Neurol 14:667–675. https://doi.org/10.1038/s41582-018-0072-1 source

In the paper

“Microglial cells and infiltrating monocytes/macrophages can have a dual role in MS lesions. They could contribute to myelin damage and lesion expansion, or they may have a protective role by clearing myelin debris, reducing inflammation and secreting regenerative factors promoting remyelination [48].”

What the sources say

• ?Not checked — no full text of the sourcecites [48] Voet S, Prinz M, van Loo G (2019) Microglia in central nervous system inflammation and multiple sclerosis pathology. Trends Mol Med 25:112–123. https://doi.org/10.1016/j.molmed.2018.11.005 source

In the paper

“These results are relevant as they propose TREM2 on microglia as a potential new target to promote remyelination.”

• Also stated in: § Introduction · hedged

  “This provides the proof of concept that antibody-mediated TREM2 activation could promote remyelination, suggesting this as a potential novel therapeutic avenue in MS and other demyelinating disorders.”

In the paper

“In MS, impaired generation of OLs from OPCs leads to persistent demyelination, myelin debris accumulation, and axonal damage which clinically manifests as neurological disability [11].”

What the sources say

• ?Not checked — no full text of the sourcecites [11] Dulamea AO (2017) Role of oligodendrocyte dysfunction in demyelination, remyelination and neurodegeneration in multiple sclerosis. Adv Exp Med Biol 958:91–127. https://doi.org/10.1007/978-3-319-47861-6_7 source

In the paper

“A critical modulator of microglia functions is the triggering receptor expressed on myeloid cells-2 (TREM2), an innate immune receptor expressed by several myeloid cells including brain microglia [23, 45].”

What the sources say

• ?Not checked — no full text of the sourcecites [23] Kiialainen A, Hovanes K, Paloneva J, Kopra O, Peltonen L (2005) Dap12 and Trem2, molecules involved in innate immunity and neurodegeneration, are co-expressed in the CNS. Neurobiol Dis 18:314–322 source
• ?Not checked — no full text of the sourcecites [45] Schmid CD, Sautkulis LN, Danielson PE, Cooper J, Hasel KW, Hilbush BS et al (2002) Heterogeneous expression of the triggering receptor expressed on myeloid cells-2 on adult murine microglia. J Neurochem 83:1309–1320 source

In the paper

“Homozygous loss-of-function mutations in TREM2 or DAP12 genes cause Nasu–Hakola disease (NHD), a rare genetic disorder characterized by fatal presenile dementia and bone cysts [38, 39].”

What the sources say

• ?Not checked — no full text of the sourcecites [38] Paloneva J, Kestila M, Wu J, Salminen A, Bohling T, Ruotsalainen V et al (2000) Loss-of-function mutations in TYROBP (DAP12) result in a presenile dementia with bone cysts. Nat Genet 25:357–361. https://doi.org/10.1038/77153 source
• ?Not checked — no full text of the sourcecites [39] Paloneva J, Manninen T, Christman G, Hovanes K, Mandelin J, Adolfsson R et al (2002) Mutations in two genes encoding different subunits of a receptor signaling complex result in an identical disease phenotype. Am J Hum Genet 71:656–662 source

In the paper

“TREM2 binds on the membrane to the DNAX-activation protein 12 (DAP12) which is an adaptor protein required for TREM2 surface expression and intracellular signaling [47].”

What the sources say

• ?Not checked — no full text of the sourcecites [47] Ulland TK, Colonna M (2018) TREM2—a key player in microglial biology and Alzheimer disease. Nat Rev Neurol 14:667–675. https://doi.org/10.1038/s41582-018-0072-1 source

In the paper

“AL002a was screened for TREM2 specificity by selecting for binding to wild-type (Trem2+/+), but not Trem2−/− BMDM.”

In the paper

“Neuropathological findings in NHD include loss of myelin and axons in the brain, with reactive astrocytosis and microglial activation [25].”

What the sources say

• ?Not checked — no full text of the sourcecites [25] Klunemann HH, Ridha BH, Magy L, Wherrett JR, Hemelsoet DM, Keen RW et al (2005) The genetic causes of basal ganglia calcification, dementia, and bone cysts: DAP12 and TREM2. Neurology 64:1502–1507 source

In the paper

“In conclusion, AL002a treatment preserved axonal health during CPZ treatment, thus preventing neurodegeneration.”

• Also stated in: § Discussion · hedged

  “Importantly, our study has also shown that AL002a treatment after CPZ is associated with reduced Nf-L plasma levels (a markers of axonal/neuronal damage), suggesting that increased remyelination also results in preserved axonal integrity, further proven by increased SMI31 staining in the CC of AL002a-treated mice.”

In the paper

“These results demonstrate that AL002a is a potent inducer of TREM2 intracellular signaling in vitro (by both cross-linking and soluble stimulation) and in vivo (by soluble stimulation).”

In the paper

“Overall, these data from NHD individuals, confirmed that TREM2 receptor plays a critical role in phagocytic pathways in human myeloid cells and that during NHD pathology genes involved in phagocytosis are specifically dysregulated.”

In the paper

“Trem2 haploinsufficiency leads to inefficient myelin debris clearance, reduced OPC recruitment, even if it does not impact on the number of microglia accumulating in the CC.”

In the paper

“Therefore, AL002a leads to a significant increase in myelin phagocytosis by Trem2+/− BMDM after 1 h, and also it accelerates their degradative capacity at later time points.”

In the paper

“In conclusion, our data demonstrate that AL002a acts as a potent TREM2 agonist both in vitro and in vivo, and its agonistic activity is boosted by the presence of myelin.”

In the paper

“These findings suggest that AL002a antibody treatment enhanced myelin debris internalization by microglia at WK 4, as demonstrated by a higher dMBP amount detected inside CD68+ structures in microglia (Fig. 5a, c), accompanied by decreased dMBP total volume per field (Fig. 4b, c) at WK 4 + 3D.”

In the paper

“These results demonstrate that AL002a is a strong inducer of DAP12 phosphorylation (after cross-linking and as soluble), and it acts as an agonist of TREM2 signaling.”

In the paper

“These results suggest that the presence of a fully functional TREM2 receptor on microglia is critical for efficient myelin debris removal and quick OPC recruitment observed in Trem2+/+ mice.”

In the paper

“Altogether our study indicates that strategies aimed at targeting TREM2 on microglia in the CNS are feasible and might be a promising intervention in MS to promote microglia functions in clearing myelin debris, favoring the recruitment of OPCs, and their subsequent differentiation into mature myelin-generating oligodendrocytes, eventually leading to remyelination and axonal protection.”

In the paper

“NHD is characterized by loss of myelin and microglia activation in the CNS [25].”

What the sources say

• ?Not checked — no full text of the sourcecites [25] Klunemann HH, Ridha BH, Magy L, Wherrett JR, Hemelsoet DM, Keen RW et al (2005) The genetic causes of basal ganglia calcification, dementia, and bone cysts: DAP12 and TREM2. Neurology 64:1502–1507 source

In the paper

“Remyelination is known to protect axons from ongoing degeneration [18].”

What the sources say

• ?Not checked — no full text of the sourcecites [18] Irvine KA, Blakemore WF (2008) Remyelination protects axons from demyelination-associated axon degeneration. Brain 131:1464–1477. https://doi.org/10.1093/brain/awn080 source

In the paper

“This could suggest that one copy of TREM2 is sufficient to sustain microglia expansion after CPZ-induced damage, but cannot support a fully functional response by microglia to clear the conspicuous amount of myelin debris derived from massive oligodendrocyte death.”