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Cited by 214Neuroinflammation and Neurodegeneration MechanismsPhagocytosis and Immune RegulationAlzheimer's disease research and treatments

Trem2 promotes anti-inflammatory responses in microglia and is suppressed under pro-inflammatory conditions

Open access
Liu, Wenfei, Taso, Orjona, Wang, Rui, Bayram, Sevinc, Graham, Andrew C, Garcia-Reitboeck, Pablo, Mallach, Anna, Andrews, William D +7 more·2020·Human Molecular Genetics
DOI 10.1093/hmg/ddaa209PMC PMC7689298

Published version of a preprint

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Abstract

Genome-wide association studies have reported that, amongst other microglial genes, variants in TREM2 can profoundly increase the incidence of developing Alzheimer’s disease (AD). We have investigated the role of TREM2 in primary microglial cultures from wild type mice by using siRNA to decrease Trem2 expression, and in parallel from knock-in mice heterozygous or homozygous for the Trem2 R47H AD risk variant. The prevailing phenotype of Trem2 R47H knock-in mice was decreased expression levels of Trem2 in microglia, which resulted in decreased density of microglia in the hippocampus. Overall, primary microglia with reduced Trem2 expression, either by siRNA or from the R47H knock-in mice, displayed a similar phenotype. Comparison of the effects of decreased Trem2 expression under conditions of lipopolysaccharide (LPS) pro-inflammatory or IL-4 anti-inflammatory stimulation revealed the importance of Trem2 in driving a number of the genes up-regulated in the anti-inflammatory phenotype. RNA-seq analysis showed that IL-4 induced the expression of a program of genes including Arg1 and Ap1b1 in microglia, which showed an attenuated response to IL-4 when Trem2 expression was decreased. Genes showing a similar expression profile to Arg1 were enriched for STAT6 transcription factor recognition elements in their promoter, and Trem2 knockdown decreased levels of STAT6. LPS-induced pro-inflammatory stimulation suppressed Trem2 expression, thus preventing TREM2’s anti-inflammatory drive. Given that anti-inflammatory signaling is associated with tissue repair, understanding the signaling mechanisms downstream of Trem2 in coordinating the pro- and anti-inflammatory balance of microglia, particularly mediating effects of the IL-4-regulated anti-inflammatory pathway, has important implications for fighting neurodegenerative disease.

AI snapshot

Written from the paper’s full text.

TL;DR

Trem2 loss, via siRNA knockdown or the Trem2 R47H knock-in mouse, reduces microglial density/CD68 and impairs IL-4-driven anti-inflammatory gene expression, partly by lowering STAT6. Pro-inflammatory LPS strongly suppresses Trem2 expression, which may limit TREM2’s anti-inflammatory support.

Key findings

  • In 4-month-old homozygous Trem2 R47H KI mice, hippocampal CA1 microglial density was decreased (two-way ANOVA main effect of genotype P < 0.01), CD68-positive microglia were decreased (P < 0.0001), and the proportion of CD68-positive microglia was lower (P < 0.001).
  • Acute Trem2 siRNA (sequence 2, ~80% knockdown; sequence 3, 50–60%) reduced phagocytosis of E. coli by 48.1 ± 9.1%, and Trem2 R47H KI microglia showed more apoptosis (14.6% Annexin V-positive/PI-negative) than WT (7.3%).
  • LPS suppressed Trem2 expression by more than 85% by 24 h; Trem2 knockdown had little additional effect on LPS-induced Tnf or Il1b.
  • IL-4 induced anti-inflammatory genes including Arg1; this response was attenuated with reduced Trem2 (Arg1 one-way ANOVA P = 0.002; WT vs homozygous P = 0.01). Trem2 knockdown decreased total STAT6 protein (two-way ANOVA main effect P < 0.0001) and AKT phosphorylation at Thr308 (P < 0.01) and Ser473 (P < 0.05). RNA-seq found 311 genes decreased and 408 increased in Trem2 R47H KI microglia (DESeq2 FDR < 0.05), and 184 increased/83 decreased with IL-4 (FDR < 0.05).

Methods

  • Primary microglial cultures from WT and Trem2 R47H KI mice were used with siRNA-mediated Trem2 knockdown, LPS (1 μg/ml) or IL-4 (20 ng/ml) treatment, plus hippocampal histology from 4-month-old mice.
  • Main assays included RT-qPCR, RNA-seq, ELISA, western blot, phagocytosis, Annexin V/PI flow cytometry, and immunohistochemistry.
  • RNA-seq analysis used DESeq2 (FDR < 0.05), WGCNA co-expression networks, and i-cisTarget promoter motif enrichment; statistics used ANOVA with Sidak’s post hoc tests, t-tests, and Fisher’s exact test where appropriate.

Limitations

  • The paper states that the Trem2 R47H KI mouse’s reduced Trem2 expression is due to a mouse-specific splicing effect not seen in humans, so the study can conclude little about the R47H mutation itself and mainly models Trem2 loss of function.
  • The paper states that in vitro LPS/IL-4 polarization may not reflect in vivo microglial activation, which involves mixed cues and single-cell heterogeneity; young Trem2 R47H mice also showed no differences in the studied genes in hippocampal homogenates.
  • Evident from the text: findings rely heavily on primary mouse microglial cultures, hippocampal tissue gene expression is diluted by non-microglial cells, and some cell death occurred in culture.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1093/hmg/ddaa209

Cites

121 of 121 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 159 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    Homozygous Trem2 R47H knock-in mice display a significant decrease of CD68-positive microglia in the hippocampus.

    “Interestingly, we also observed a significant decrease of CD68 positive microglia in the homozygous Trem2 R47H mice (two-way ANOVA: main effect of genotype P < 0.0001).”
    Quote in the paperNot a substantial claim
  • Findingown data

    Acute Trem2 knockdown produces a significant change in the gene expression profile of microglia under non-stimulated conditions.

    “Overall, acute Trem2 knockdown produced a significant change in the gene expression profile of microglia under non-stimulated conditions, which might result in a shift of the microglial functional phenotype.”
    Quote in the paperSubstantial claim
  • Findingreasoning

    Trem2 knockdown by siRNA has little effect on LPS-induced up-regulation of Tnf or Il1b at the transcriptional level compared with control cultures.

    “As expected, considering so little Trem2 remained under these conditions, knockdown of Trem2 by siRNA had little effect on LPS-induced gene expression with up-regulation of Tnf or Il1b being unchanged at the transcriptional level with Trem2 knockdown compared with control cultures (Supplementary Material, Fig. S6).”
    Quote in the paperSubstantial claim
  • Findingown data

    Microglia with Trem2 knockdown show a significant reduction (48.1 ± 9.1%) of phagocytosis of Escherichia coli conjugated to pHrodo compared with non-targeting siRNA-treated microglia.

    “We found that microglia with Trem2 knockdown showed a significant reduction (48.1 ± 9.1%) of phagocytosis of Escherichia coli, conjugated to pHrodo (a pH-sensitive fluorescent dye), compared with the non-targeting siRNA treated microglia (Supplementary Material, Fig. S4), confirming previous reports and further validating this cell system.”
    Quote in the paperSubstantial claim
  • Findingown data

    Genes increased in response to IL-4, such as Igf1, Cd68 and C1qa, also show decreased expression in homozygous Trem2 R47H microglia regardless of IL-4 treatment.

    “Similarly to the Trem2 knockdown experiments, genes for which expression was increased in response to IL-4, such as Igf1, Cd68 and C1qa, also showed decreased expression in the homozygous Trem2 R47H microglia, regardless of IL-4-treatment (Fig. 5C; two-way ANOVA: main effect of IL-4-treatment, and main effect of Trem2 genotype, but no interaction for Igf1, Cd68 and C1qa).”
    Quote in the paperSubstantial claim
  • May combine two claims. 62
  • Classified as probably not a substantial claim. 29

  • May combine two claims.

    Findingown data

    Soluble TREM2 protein level in conditioned medium is decreased in response to LPS for wild-type microglia and for homozygous Trem2 R47H knock-in microglia.

    “In addition, the soluble TREM2 protein level in the conditioned medium in response to LPS was decreased for the microglia from the WT littermates (Fig. 3D), and the level of TREM2 protein in the medium conditioned by cells from the homozygous Trem2 R47H KI mice was also decreased, supporting the transcriptional findings.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In microglia from homozygous Trem2 R47H knock-in mice, LPS causes no substantial change to Tnf expression but a decrease in Il1b expression.

    “Similar results were seen in microglia from the homozygous Trem2 R47H KI mice with no substantial change to Tnf expression but a decrease in Il1b expression (Supplementary Material, Fig. S7).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Tgfb1 is significantly decreased in homozygous Trem2 R47H microglia independent of IL-4 treatment, and the fold-change in Tgfb1 up-regulation in response to IL-4 is similar for wild-type and homozygous Trem2 R47H cells.

    “The other anti-inflammatory marker Tgfb1 was significantly decreased in homozygous Trem2 R47H microglia independent of IL-4-treatment, and the fold-change in Tgfb1 up-regulation in response to treatment was similar for WT and homozygous Trem2 R47H cells (Fig. 5B).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Arg1 expression is undetectable in non-stimulated microglia, reaches levels well above detection threshold at 24 h after IL-4 treatment, and by 48 h expression levels have further doubled.

    “Arg1 expression was undetectable in our non-stimulated microglia, but reached levels well above detection threshold at 24 h after IL-4 treatment, and by 48 h expression levels had further doubled.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    LPS strongly up-regulates TNF-alpha protein release from microglial cells, but Trem2 knockdown causes no significant change.

    “Consistent with the transcriptional results, the protein level of TNF-alpha released from the microglial cells showed that LPS strongly up-regulated TNF-alpha, but there was no significant change caused by Trem2 knockdown (Supplementary Material, Fig. S6).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Tgfb1 expression increases with IL-4 stimulation, but in contrast to Arg1 the effect of Trem2 knockdown and IL-4 shows no interaction for Tgfb1.

    “The Tgfb1 expression also showed an increase with IL-4 stimulation, however, in contrast to Arg1 the effect of Trem2 knockdown and IL-4 showed no interaction.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Expression of C1qa, Cd68, Igf1, Csf1r, Spi1, Aif1 and Plcg2 is significantly lower in cells with acute Trem2 knockdown, and this is not dependent on IL-4 stimulation.

    “Interestingly, the expression of all of these genes was significantly lower in cells with acute Trem2 knockdown, and was not dependent on IL-4 stimulation (no significant interaction of knockdown versus IL-4).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    IL-4-induced up-regulation of Arg1 is considerably decreased in the Trem2 knockdown group, with a significant difference between Trem2 knockdown and control at 48 h post IL-4 treatment.

    “Upon IL-4 treatment, Arg1 expression showed a time-dependent up-regulation, however, this up-regulation was considerably decreased in the Trem2 knockdown group (two-way ANOVA: interaction between main effects of Trem2 knockdown and IL-4 treatment time, P = 0.05; Sidak’s multiple comparisons: significant difference between the Trem2 knockdown group and the control at 48 h post IL-4 treatment, P < 0”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In microglia from Trem2 R47H knock-in mice, IL-4 strongly induces Arg1, and reduced Trem2 expression prevents this induction in a gene dose-dependent manner.

    “Our findings were similar in the microglia from the Trem2 R47H KI mice, with Arg1 showing a strong induction by IL-4 treatment and the down-regulation of Trem2 in the microglia from Trem2 R47H KI mice significantly preventing this change in a gene dose-dependent manner (Fig. 5B, one-way ANOVA: P = 0.002, Sidak’s multiple comparisons: P = 0.08 for WT versus heterozygous, and P = 0.01 for WT versus”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The proportion of CD68-positive microglia is significantly lower in homozygous Trem2 R47H knock-in mice, indicating that the decrease in CD68-positive microglia is not primarily due to the total microglia number change.

    “This change was not primarily due to the total microglia number change because the proportion of CD68 positive microglia also showed a substantial decrease (two-way ANOVA: main effect of genotype P < 0.001; Fig. 1B and C).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    RNA-seq analysis showed that IL-4 induced the expression of a program of genes including Arg1 and Ap1b1 in microglia, which showed an attenuated response to IL-4 when Trem2 expression was decreased.

    “RNA-seq analysis showed that IL-4 induced the expression of a program of genes including Arg1 and Ap1b1 in microglia, which showed an attenuated response to IL-4 when Trem2 expression was decreased.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    IL-4 caused robust phosphorylation of STAT6, with phosphorylated STAT6 not detectable in the absence of IL-4 but clearly measurable 48 h after IL-4 treatment.

    “IL-4 caused robust phosphorylation of STAT6, with phosphorylated STAT6 not detectable in the absence of IL-4 but clearly measurable 48 h after IL-4 treatment.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    There was overlap of genotype and IL-4 affecting common genes (such as Arg1), but Trem2 and IL-4 had independent effects, and no module was significant for both genotype and IL-4 treatment.

    “While there was an overlap of genotype and IL-4 affecting common genes (such as Arg1), we also saw that Trem2 and IL-4 had independent effects. Thus, the strong drive of Trem2 R47H KI genotype and IL-4 meant there was no module that was significant for both genotype and IL-4 treatment.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Both decreased Trem2 expression and IL-4 treatment displayed strong effects on gene expression.

    “both manipulations displayed strong effects on gene expression.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    RNA-seq showed 408 genes with increased expression in Trem2 R47H KI microglia versus WT (DESeq2 FDR < 0.05), including App, Hspa1b, and Ccnd2.

    “Genes showing increased expression in the Trem2 R47H KI microglia included App (amyloid precursor protein), Hspa1b (heat-shock 70 kDa protein 1B) and Ccnd2 (cyclin D2) (408 genes with increased expression, DESeq2 FDR < 0.05; Fig. 6A; Supplementary Material, Table S2).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Igf1 expression was decreased when Trem2 expression was knocked down or if the Trem2 R47H variant was carried by primary microglial cultures.

    “Igf1 expression was also decreased when Trem2 expression was knocked-down or if the Trem2 R47H variant was carried by the primary microglial cultures.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Total AKT protein level was not significantly affected by Trem2 knockdown, although there was a slight increase in AKT levels in response to IL-4 treatment.

    “the total AKT protein level was not significantly affected by Trem2 knockdown, although there was a slight increase in AKT levels in response to IL-4 treatment.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    There was a decrease in microglial density in the hippocampus of Trem2 R47H mice, and the remaining microglia had dramatically reduced CD68 protein levels.

    “we saw a decrease in the density of microglia in vivo in the hippocampus, and that the remaining microglia had dramatically reduced CD68 protein levels.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    Igf1 expression is inhibited by pro-inflammatory stimuli and enhanced in anti-inflammatory environments.

    “Our findings, in line with previous studies (59,68–71), show that Igf1 expression is inhibited by pro-inflammatory stimuli and enhanced in anti-inflammatory environments.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [59] Butovsky, 2018, Microglial signatures and their role in health and disease, Nat. Rev. Neurosci. source

      Not checked in the free run.

    • cites [68] Arkins, 1995, Interferon-gamma inhibits macrophage insulin-like growth factor-I synthesis at the transcriptional level, Mol. Endocrinol.

      Not checked in the free run.

    • cites [69] Suh, 2013, Insulin-like growth factor 1 and 2 (IGF1, IGF2) expression in human microglia: differential regulation by inflammatory mediators, J. Neuroinflammation source

      Not checked in the free run.

    • cites [70] Wynes, 2003, Induction of macrophage insulin-like growth factor-I expression by the Th2 cytokines IL-4 and IL-13, J. Immunol. source

      Not checked in the free run.

    • cites [71] Barrett, 2015, Involvement of IGF-1 and Akt in M1/M2 activation state in bone marrow-derived macrophages, Exp. Cell Res. source

      Not checked in the free run.

  • May combine two claims.

    Findingown data

    In hippocampal homogenates from young adult Trem2 R47H mice, no differences in expression of Stat6 and Igf1 were seen, despite a slight but significant reduction in the number of microglia.

    “In hippocampal homogenates from young adult Trem2 R47H mice, we did not see differences in expression of the genes we studied, including Stat6 and Igf1, despite a slight but significant reduction in the number of microglia.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In the presence of LPS, decrease in expression of Trem2 began as early as 3 h after LPS application and reached more than an 85% decrease by 24 h.

    “In the presence of LPS, decrease in expression of Trem2 began as early as 3 h after LPS application and reached more than an 85% decrease by 24 h.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    IL-4 stimulation had little effect on Trem2 expression, whereas LPS largely suppressed Trem2.

    “In contrast to IL-4 stimulation, which had little effect on Trem2 expression, LPS largely suppressed Trem2.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Separate mechanisms regulate basal levels of some genes like Tgfb1, which may be Trem2-dependent at least in part, compared with mechanisms that regulate levels following induction, which can be Trem2-independent.

    “These findings suggest that separate mechanisms regulate basal levels of some genes like Tgfb1 (which may be Trem2-dependent at least in part), compared with mechanisms that regulate levels following induction (which can be Trem2-independent).”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    In hippocampal tissue, microglial gene expression is greatly diluted by the much greater contribution of other cell types, so small changes in gene expression are harder to detect than in enriched microglia.

    “It is important to note that in the hippocampal tissue, the gene expression in microglia is greatly diluted by the much greater contribution of other cell types and so small changes in gene expression will be much more difficult to detect than in enriched microglia.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Pro-inflammatory conditions inhibit microglial Trem2 expression, which might result in a state of temporary or chronic TREM2-deficiency in microglia.

    “This suggests that pro-inflammatory conditions inhibit microglial Trem2 expression, which might result in a state of temporary or chronic ‘TREM2-deficiency’ in microglia.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    TREM2 promotes an anti-inflammatory response via an IL-4-independent mechanism supporting expression of common genes such as Igf1, Cd68 and C1qa, which are induced by IL-4 in control cells and suppressed by Trem2 reduction.

    “TREM2 promotes an anti-inflammatory response via two mechanisms: (i) an IL-4 independent mechanism supporting the expression of common genes, such as Igf1, Cd68 and C1qa, which are induced by IL-4 in control cells and suppressed by Trem2 reduction, but there is lack of interaction between the effects of Trem2 and IL-4 on these genes, and so here TREM2 and IL-4 likely act via independent parallel”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    TREM2 promotes an anti-inflammatory response via an IL-4-dependent mechanism where the gene expression response to IL-4 depends on TREM2, such as for Arg1, with a significant interaction between the effects of Trem2 and IL-4.

    “(ii) an IL-4-dependent mechanism where the gene expression response to IL-4 depends on TREM2, genes such as Arg1, where there is a significant interaction between the effects of Trem2 and IL-4.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    TREM2 is widely expressed in various cell types derived from the myeloid lineage, such as bone osteoclasts, and lung and peritoneal macrophages.

    “It has been reported to be widely expressed in various cell types derived from the myeloid lineage, such as bone osteoclasts (12,13), and lung and peritoneal macrophages (14).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [12] Humphrey, 2006, TREM2, a DAP12-associated receptor, regulates osteoclast differentiation and function, J. Bone Miner. Res. source

      Not checked in the free run.

    • cites [13] Paloneva, 2003, DAP12/TREM2 deficiency results in impaired osteoclast differentiation and osteoporotic features, J. Exp. Med. source

      Not checked in the free run.

    • cites [14] Turnbull, 2006, Cutting edge: TREM-2 attenuates macrophage activation, J. Immunol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Trem2 knockdown via a lentiviral strategy increased pro-inflammatory gene expression and decreased phagocytosis of labeled apoptotic neuronal membranes in primary microglia stressed with co-culture of apoptosis-induced primary neurons.

    “The same study also showed that Trem2 knockdown via a lentiviral strategy increased pro-inflammatory gene expression and decreased phagocytosis of labeled apoptotic neuronal membranes in primary microglia stressed with co-culture of apoptosis-induced primary neurons.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [17] Takahashi, 2005, Clearance of apoptotic neurons without inflammation by microglial triggering receptor expressed on myeloid cells-2, J. Exp. Med. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    LPS-induced pro-inflammatory stimulation suppresses Trem2 expression, thus preventing TREM2's anti-inflammatory drive.

    “LPS-induced pro-inflammatory stimulation suppressed Trem2 expression, thus preventing TREM2’s anti-inflammatory drive.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    TREM2 suppresses LPS-induced pro-inflammatory markers up-regulated in primary alveolar macrophages in vitro and in the BV-2 microglial cell line.

    “TREM2 was also found to suppress LPS-induced pro-inflammatory markers up-regulated in primary alveolar macrophages in vitro (28), and the BV-2 microglial cell line (29).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [28] Gao, 2013, Silencing of triggering receptor expressed on myeloid cells-2 enhances the inflammatory responses of alveolar macrophages to lipopolysaccharide, Mol. Med. Rep. source

      Not checked in the free run.

    • cites [29] Zhong, 2015, DAP12 stabilizes the C-terminal fragment of the triggering receptor expressed on myeloid cells-2 (TREM2) and protects against LPS-induced pro-inflammatory response, J. Biol. Chem. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    The effects of IL-4 stimulation on gene expression mimic changes seen in association with plaque development in transgenic mice, where Trem2 levels are also strongly increased, whereas the pro-inflammatory effects of LPS have the opposite effect.

    “Interestingly, the effects of IL-4 stimulation on gene expression mimic the changes seen in association with plaque development in transgenic mice (44), where Trem2 levels are also strongly increased, whereas the pro-inflammatory effects of LPS have the opposite effect.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [44] Salih, 2019, Genetic variability in response to amyloid beta deposition influences Alzheimer's disease risk, Brain Commun. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Evidence from in vitro studies supports the role of TREM2 in restricting inflammation and promoting phagocytosis.

    “Evidence from in vitro studies has accumulated to support the role of TREM2 in restricting inflammation and promoting phagocytosis.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    TREM2 expression was first observed in macrophages and dendritic cells, but not granulocytes or monocytes.

    “TREM2 expression was first observed in macrophages and dendritic cells, but not granulocytes or monocytes (9–11).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [9] Bouchon, 2000, Cutting edge: inflammatory responses can be triggered by TREM-1, a novel receptor expressed on neutrophils and monocytes, J. Immunol. source

      Not checked in the free run.

    • cites [10] Bouchon, 2001, A DAP12-mediated pathway regulates expression of CC chemokine receptor 7 and maturation of human dendritic cells, J. Exp. Med. source

      Not checked in the free run.

    • cites [11] Daws, 2001, Cloning and characterization of a novel mouse myeloid DAP12-associated receptor family, Eur. J. Immunol. source

      Not checked in the free run.

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

    Premisecitation

    Further TREM2 variants such as R62H, H157Y, Q33X, T66M and Y38C are risk factors of Alzheimer's disease or other CNS diseases.

    “In addition to the R47H variant, further TREM2 variants have been revealed to be risk factors of AD or other CNS diseases, such as R62H (8,20), H157Y (25), Q33X, T66M and Y38C (26,27).”
    Quote in the paperNot a substantial claim0 of 5 sources checked
    • cites [8] Sims, 2017, Rare coding variants in PLCG2, ABI3, and TREM2 implicate microglial-mediated innate immunity in Alzheimer's disease, Nat. Genet. source

      Not checked in the free run.

    • cites [20] Jin, 2014, Coding variants in TREM2 increase risk for Alzheimer's disease, Hum. Mol. Genet. source

      Not checked in the free run.

    • cites [25] Jiang, 2016, A rare coding variant in TREM2 increases risk for Alzheimer's disease in Han Chinese, Neurobiol. Aging source

      Not checked in the free run.

    • cites [26] Guerreiro, 2013, Novel compound heterozygous mutation in TREM2 found in a Turkish frontotemporal dementia-like family, Neurobiol. Aging source

      Not checked in the free run.

    • cites [27] Guerreiro, 2013, Using exome sequencing to reveal mutations in TREM2 presenting as a frontotemporal dementia-like syndrome without bone involvement, JAMA Neurol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    TREM2 stimulated microglial chemotaxis and phagocytosis of fluorescent beads in primary microglia transduced with flag epitope tagged TREM2.

    “It was first reported in a study using primary microglia transduced with flag epitope tagged TREM2 that TREM2 stimulated microglial chemotaxis, and phagocytosis of fluorescent beads (17).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [17] Takahashi, 2005, Clearance of apoptotic neurons without inflammation by microglial triggering receptor expressed on myeloid cells-2, J. Exp. Med. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Premisenone given

    Other cellular functions of TREM2, particularly anti-inflammatory or alternative activation, and the molecular mechanisms mediating the actions of TREM2, are not well understood.

    “However, other cellular functions of TREM2, particularly anti-inflammatory or alternative activation, and the molecular mechanisms mediating the actions of TREM2, are not well understood.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    Stat6 gene expression was decreased with reduced Trem2 expression, confirming decreased levels of the translated protein.

    “The expression level of the Stat6 gene was also decreased with reduced Trem2 expression (Fig. 9C), and so confirms the decreased levels of the translated protein.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Down-regulated genes in Trem2 R47H KI microglia were associated with microglial activation, suggesting that down-regulation of genes with reduced Trem2 expression may dampen some states of microglial activation.

    “the genes down-regulated in cells carrying the Trem2 R47H KI alleles were associated with microglial activation, suggesting down-regulation of genes with reduced Trem2 expression may dampen some states of microglial activation (Supplementary Material, Fig. S12).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Apolipoproteins, lipids and Aβ itself act as ligands of TREM2 to facilitate microglial phagocytosis and clearance of Aβ and apoptotic neurons.

    “Recently, it was further shown that apolipoproteins, lipids and Aβ itself acted as ligands of TREM2 to facilitate microglial phagocytosis and clearance of Aβ and apoptotic neurons (32–35).”
    Quote in the paperNot a substantial claim0 of 4 sources checked
    • cites [32] Atagi, 2015, Apolipoprotein E is a ligand for triggering receptor expressed on myeloid cells 2 (TREM2), J. Biol. Chem. source

      Not checked in the free run.

    • cites [33] Yeh, 2016, TREM2 binds to apolipoproteins, including APOE and CLU/APOJ, and thereby facilitates uptake of amyloid-Beta by microglia, Neuron source

      Not checked in the free run.

    • cites [34] Zhao, 2018, TREM2 is a receptor for beta-amyloid that mediates microglial function, Neuron source

      Not checked in the free run.

    • cites [35] Nugent, 2020, TREM2 regulates microglial cholesterol metabolism upon chronic phagocytic challenge, Neuron source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    TREM2 deficiency leads to a smaller STAT6 pool in microglia, resulting in decreased amount of phosphorylated STAT6 upon IL-4 stimulation.

    “These results suggest that TREM2 deficiency leads to a smaller STAT6 pool in microglia, resulting in decreased amount of phosphorylated STAT6 upon IL-4 stimulation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Trem2 deficiency exacerbates microglial pro-inflammatory activation in response to various stimuli and accompanies impaired phagocytosis.

    “In general, these studies suggest that Trem2 deficiency exacerbates microglial pro-inflammatory activation in response to various stimuli, and accompanies impaired phagocytosis.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Phosphorylation of STAT6 is a key step downstream in the IL-4 cascade that leads to Arg1 expression.

    “previous studies have shown that phosphorylation of STAT6 is a key step downstream in the IL-4 cascade that leads to Arg1 expression (49–51).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [49] Luzina, 2012, Regulation of inflammation by interleukin-4: a review of "alternatives", J. Leukoc. Biol. source

      Not checked in the free run.

    • cites [50] Nelms, 1999, The IL-4 receptor: signaling mechanisms and biologic functions, Annu. Rev. Immunol. source

      Not checked in the free run.

    • cites [51] Gordon, 2010, Alternative activation of macrophages: mechanism and functions, Immunity source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Trem2 knockdown decreased total levels of phosphorylated STAT6, but this could be explained by a decrease in overall STAT6 levels rather than an effect on phosphorylation per se.

    “Trem2 knockdown also decreased the total levels of phosphorylated STAT6 but this could be explained by a decrease in the overall levels of STAT6 rather than an effect on phosphorylation per se.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Pharmacological blockade of CSF1 receptors impairs microglial survival and can completely remove microglia from the mouse brain.

    “Pharmacological blockade of CSF1 receptors has been shown to impair microglial survival and can completely remove microglia from the mouse brain (53–55).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [53] Elmore, 2014, Colony-stimulating factor 1 receptor signaling is necessary for microglia viability, unmasking a microglia progenitor cell in the adult brain, Neuron source

      Not checked in the free run.

    • cites [54] Dagher, 2015, Colony-stimulating factor 1 receptor inhibition prevents microglial plaque association and improves cognition in 3xTg-AD mice, J. Neuroinflammation source

      Not checked in the free run.

    • cites [55] Olmos-Alonso, 2016, Pharmacological targeting of CSF1R inhibits microglial proliferation and prevents the progression of Alzheimer's-like pathology, Brain source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    The decrease in Igf1 may not affect microglial survival because the IGF1 receptor is found largely on neurons, but it could contribute to neurodegeneration.

    “While this may not affect microglial survival as the IGF1 receptor is found largely on neurons, it could contribute to neurodegeneration, being an important factor in neuronal survival and lifespan across many species (67).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [67] Broughton, 2009, Insulin/IGF-like signalling, the central nervous system and aging, Biochem. J. source

      Not checked in the free run.

    • Rests on an assumption: The IGF1 receptor is found largely on neurons.

  • May combine two claims.

    Interpretationreasoning

    No difference in Csf1r expression was seen in remaining microglia in brain tissue from young adult Trem2 R47H KI mice, possibly suggesting different populations of microglia with loss of those more vulnerable to Trem2 knockdown.

    “Interestingly no difference in Csf1r expression was seen in the remaining microglia in the brain tissue from the young adult Trem2 R47H KI mice, possibly suggesting different populations of microglia, with loss of those more vulnerable to the effects of Trem2 knockdown than others, at least in whole tissue.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    The Igf1 expression decrease caused by Trem2 deficiency may suggest a microglial phenotype shift towards pro-inflammatory activation and away from non-inflammatory, and a decrease of the pro-survival role of IGF1 on neurons.

    “Thus, the Igf1 expression decrease caused by Trem2 deficiency may suggest a microglial phenotype shift towards pro-inflammatory activation and away from non-inflammatory, and a decrease of the pro-survival role of IGF1 on neurons.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Trem2 R47H KI mice can largely be considered a model of Trem2 down-regulation, validated by siRNA data in primary microglia.

    “Hence, we can largely consider these mice as a model of Trem2 down-regulation, validated by our siRNA data in primary microglia.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The Trem2 decrease in R47H KI mice does not occur in human tissue with this mutation but is a mouse-specific effect related to altered splicing.

  • Classified as probably not a substantial claim.

    Premisecitation

    PI3K-AKT signaling is downstream of TREM2.

    “considering that PI3K-AKT signaling is downstream of TREM2”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [40] Zheng, 2017, TREM2 promotes microglial survival by activating Wnt/beta-catenin pathway, J. Neurosci. source

      Not checked in the free run.

    • cites [52] Paradowska-Gorycka, 2013, Structure, expression pattern and biological activity of molecular complex TREM-2/DAP12, Hum. Immunol. source

      Not checked in the free run.

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

    Premisecitation

    Igf1 is abundantly expressed by microglia during postnatal development, aging, or following brain injuries and plays a vital role in promoting neuronal survival.

    “Igf1 is abundantly expressed by microglia during postnatal development, aging or following brain injuries and plays a vital role in promoting neuronal survival (59,63–66).”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [59] Butovsky, 2018, Microglial signatures and their role in health and disease, Nat. Rev. Neurosci. source

      Not checked in the free run.

    • cites [63] Ueno, 2013, Layer V cortical neurons require microglial support for survival during postnatal development, Nat. Neurosci. source

      Not checked in the free run.

    • cites [64] Fernandez, 2012, The many faces of insulin-like peptide signalling in the brain, Nat. Rev. Neurosci. source

      Not checked in the free run.

    • cites [65] Kohman, 2012, Wheel running attenuates microglia proliferation and increases expression of a proneurogenic phenotype in the hippocampus of aged mice, Brain Behav. Immun. source

      Not checked in the free run.

    • cites [66] Thored, 2009, Long-term accumulation of microglia with proneurogenic phenotype concomitant with persistent neurogenesis in adult subventricular zone after stroke, Glia source

      Not checked in the free run.

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

    Premisecitation

    Some microglial populations are selectively dependent on Trem2, as shown by single-cell RNA-seq.

    “Differences in gene expression profiles of different microglial populations have been recently described using single cell RNA-seq showing some microglial populations are selectively dependent on Trem2 (58–62).”
    Quote in the paperNot a substantial claim0 of 5 sources checked
    • cites [58] Keren-Shaul, 2017, A unique microglia type associated with restricting development of Alzheimer's disease, Cell source

      Not checked in the free run.

    • cites [59] Butovsky, 2018, Microglial signatures and their role in health and disease, Nat. Rev. Neurosci. source

      Not checked in the free run.

    • cites [60] Sala Frigerio, 2019, The major risk factors for Alzheimer's disease: age, sex, and genes modulate the microglia response to Abeta plaques, Cell Rep. source

      Not checked in the free run.

    • cites [61] Zhou, 2020, Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and TREM2-independent cellular responses in Alzheimer's disease, Nat. Med. source

      Not checked in the free run.

    • cites [62] Hammond, 2019, Single-cell RNA sequencing of microglia throughout the mouse lifespan and in the injured brain reveals complex cell-state changes, Immunity source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    IL-33 ameliorated AD-associated phenotypes by promoting anti-inflammatory functions, which included induction of Arg1.

    “IL-33 ameliorated AD-associated phenotypes by promoting anti-inflammatory functions, which included induction of Arg1 (80).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [80] Fu, 2016, IL-33 ameliorates Alzheimer's disease-like pathology and cognitive decline, Proc. Natl. Acad. Sci. USA source

      Not checked in the free run.

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

    Premisecitation

    ARG1 in myeloid cells mainly functions as an enzyme to hydrolyze arginine to produce ornithine as part of the urea cycle, which promotes tissue repair through generation of polyamines and collagens, and reduces nitric oxide production from inducible nitric oxide synthase through decreasing intracellular arginine availability.

    “ARG1 in myeloid cells mainly functions as an enzyme to hydrolyze arginine to produce ornithine as part of the urea cycle, which both promotes tissue repair through generation of polyamines and collagens, and also reduces nitric oxide production from inducible nitric oxide synthase through decreasing intracellular arginine availability (76–78).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [76] Yang, 2014, Functions of arginase isoforms in macrophage inflammatory responses: impact on cardiovascular diseases and metabolic disorders, Front. Immunol. source

      Not checked in the free run.

    • cites [77] Mills, 2000, M-1/M-2 macrophages and the Th1/Th2 paradigm, J. Immunol. source

      Not checked in the free run.

    • cites [78] Modolell, 1995, Reciprocal regulation of the nitric oxide synthase/arginase balance in mouse bone marrow-derived macrophages by TH1 and TH2 cytokines, Eur. J. Immunol. source

      Not checked in the free run.

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

    Premisecitation

    Dusp4 null mice show impaired T cell activation.

    “Dusp4 null mice show impaired T cell activation (83).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [83] Barbour, 2016, MAP kinase phosphatase 2 deficient mice develop attenuated experimental autoimmune encephalomyelitis through regulating dendritic cells and T cells, Sci. Rep. source

      Not checked in the free run.

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

    Premisecitation

    Aβ binding to scavenger receptors induces oxidative stress, which may impair AP1B1-dependent internalization of Aβ.

    “work with a microglial cell line suggests that Aβ binding to scavenger receptors induces oxidative stress, which then may impair AP1B1-dependent internalization of the Aβ (82).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [82] Manzano-Leon, 2006, Beta-adaptin: key molecule for microglial scavenger receptor function under oxidative stress, Biochem. Bioph. Res. Co. source

      Not checked in the free run.

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

    Premisecitation

    ARG1-positive microglia modify Aβ accumulation.

    “ARG1-positive microglia have been shown to modify Aβ accumulation (79)”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [79] Cherry, 2015, Arginase 1+ microglia reduce Abeta plaque deposition during IL-1beta-dependent neuroinflammation, J. Neuroinflammation source

      Not checked in the free run.

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

    Interpretationreasoning

    The lack of gene expression changes in vivo may be due to a supportive environment from healthy neurons and astrocytes, providing regulating input to the microglia in young mice.

    “Lack of gene expression changes in vivo may be due to a supportive environment from healthy neurons and astrocytes, providing regulating input to the microglia in young mice.”
    Quote in the paperNot a substantial claim

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

    Premisecitation

    Anti-inflammatory processes mediated by IL-4 provide benefits in models representing early stages of neurodegenerative conditions such as AD and amyotrophic lateral sclerosis.

    “Anti-inflammatory processes are associated with tissue repair, such as those mediated by IL-4, working through microglia and macrophages, and have been shown to provide benefits in models representing the early stages of neurodegenerative conditions, such as AD and amyotrophic lateral sclerosis, and other disorders related to cell death (45,72,73).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [45] Rossi, 2018, Interleukin 4 modulates microglia homeostasis and attenuates the early slowly progressive phase of amyotrophic lateral sclerosis, Cell Death Dis. source

      Not checked in the free run.

    • cites [72] Bosurgi, 2017, Macrophage function in tissue repair and remodeling requires IL-4 or IL-13 with apoptotic cells, Science source

      Not checked in the free run.

    • cites [73] Kiyota, 2010, CNS expression of anti-inflammatory cytokine interleukin-4 attenuates Alzheimer's disease-like pathogenesis in APP+PS1 bigenic mice, FASEB J. source

      Not checked in the free run.

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

    Premisecitation

    ITGAX-positive microglia are a source of Igf1 expression.

    “ITGAX-positive microglia are a source of Igf1 expression (59).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [59] Butovsky, 2018, Microglial signatures and their role in health and disease, Nat. Rev. Neurosci. source

      Not checked in the free run.

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

    Premisecitation

    AP1B1 is part of the clathrin-associated adaptor protein complex AP-1 and is involved in endocytosis and intracellular trafficking.

    “AP1B1 is part of the clathrin-associated adaptor protein complex AP-1 and is involved in endocytosis and intracellular trafficking (81).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [81] Li, 2019, Developmental heterogeneity of microglia and brain myeloid cells revealed by deep single-cell RNA sequencing, Neuron source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Reduced Trem2 expression in cultured primary microglia suggests an attenuated anti-inflammatory phenotype, impacting cellular processes involving vesicle function, indicating that genes dependent on both Trem2 and IL-4 affect cytokine release or the response to extracellular cytokines.

    “Our findings in cultured primary microglia suggest an attenuated anti-inflammatory phenotype with reduced expression of Trem2 (Fig. 10), impacting cellular processes involving vesicle function, indicating that genes dependent on both Trem2 and IL-4 affect cytokine release or the response to extracellular cytokines.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    Itgax/CD11C is an integrin or cell surface antigen, and is up-regulated in a number of recent RNA-seq studies in response to amyloid plaques.

    “Itgax/CD11C is an integrin or cell surface antigen, and is up-regulated in a number of recent RNA-seq studies in response to amyloid plaques (58,59,61,84).”
    Quote in the paperNot a substantial claim0 of 4 sources checked
    • cites [58] Keren-Shaul, 2017, A unique microglia type associated with restricting development of Alzheimer's disease, Cell source

      Not checked in the free run.

    • cites [59] Butovsky, 2018, Microglial signatures and their role in health and disease, Nat. Rev. Neurosci. source

      Not checked in the free run.

    • cites [61] Zhou, 2020, Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and TREM2-independent cellular responses in Alzheimer's disease, Nat. Med. source

      Not checked in the free run.

    • cites [84] Krasemann, 2017, The TREM2-APOE pathway drives the transcriptional phenotype of dysfunctional microglia in neurodegenerative diseases, Immunity source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    IL-4-induced up-regulation of a number of genes including Arg1 is critically dependent on phosphorylation of STAT6.

    “As the IL-4-induced up-regulation of a number of genes including Arg1 is critically dependent on phosphorylation of STAT6 (75)”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [75] Gray, 2005, Induction of arginase I transcription by IL-4 requires a composite DNA response element for STAT6 and C/EBPbeta, Gene source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    LPS/IFNγ stimulation down-regulated Trem2 expression via TLR4 receptors in cell lines and primary cultures of microglia/macrophages and also in mouse brains.

    “This finding is consistent with previous studies showing that LPS/IFNγ stimulation down-regulated Trem2 expression via TLR4 receptors in cell lines and primary cultures of microglia/macrophages and also in mouse brains (14,16,42,88,89).”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [14] Turnbull, 2006, Cutting edge: TREM-2 attenuates macrophage activation, J. Immunol. source

      Not checked in the free run.

    • cites [16] Schmid, 2002, Heterogeneous expression of the triggering receptor expressed on myeloid cells-2 on adult murine microglia, J. Neurochem. source

      Not checked in the free run.

    • cites [42] Owens, 2017, Divergent Neuroinflammatory regulation of microglial TREM expression and involvement of NF-kappaB, Front. Cell. Neurosci.

      Not checked in the free run.

    • cites [88] Zheng, 2016, Opposing roles of the triggering receptor expressed on myeloid cells 2 and triggering receptor expressed on myeloid cells-like transcript 2 in microglia activation, Neurobiol. Aging source

      Not checked in the free run.

    • cites [89] Zhou, 2019, Imbalance of microglial TLR4/TREM2 in LPS-treated APP/PS1 transgenic mice: a potential Link between Alzheimer's disease and systemic inflammation, Neurochem. Res. source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    The effects seen in primary cultured microglia probably reflect a different mean activation state from microglia in the brain environment, although there remains a significant overlap with microglia expression profiles in vivo that are dependent on Trem2 levels and IL-4 simulation.

    “The effects seen in the primary cultured microglia probably reflect a different mean activation state from microglia in the brain environment, although there remains a significant overlap with microglia expression profiles in vivo that are dependent on Trem2 levels and IL-4 simulation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    In microglia originating from Trem2 R47H KI mice with a similar level of Trem2 down-regulation, there was about a 39% decrease in the activation of Il1b compared with WT mice, possibly suggesting that the Trem2 R47H mutation underlies this effect.

    “in microglia originating from Trem2 R47H KI mice with a similar level of Trem2 down-regulation, there was about a 39% decrease in the activation of Il1b compared with WT mice possibly suggesting that the Trem2 R47H mutation underlies this effect.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The down-regulation of Trem2 in Trem2 R47H KI mice is present throughout life.

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

    Interpretationreasoning

    Other possible explanations for the difference include that the down-regulation of Trem2 in these mice is present throughout life and so these microglia may have a different state when isolated than those in which Trem2 is knocked down acutely.

    “There are, however, other possible explanations for this difference, as the down-regulation of Trem2 in these mice is present throughout life and so these microglia may have a different state when isolated than those in which Trem2 is knocked down acutely.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The down-regulation of Trem2 in Trem2 R47H KI mice is present throughout life.

  • May combine two claims.

    Interpretationreasoning

    This might be one of the major mechanisms underlying various neurodegenerative diseases with advanced age by suppression of WT TREM2 in many sporadic cases, considering that TREM2 variants associated with loss-of-function are extremely rare in frequency in humans.

    “This might be one of the major mechanisms underlying various neurodegenerative diseases with advanced age by suppression of WT TREM2 in many sporadic cases, considering that TREM2 variants associated with loss-of-function are extremely rare in frequency in humans (2).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [2] Guerreiro, 2013, TREM2 variants in Alzheimer's disease, N. Engl. J. Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Impaired or absent Trem2 function attenuates the microglial response to amyloid pathology by regulating microglial number around plaques, regulating microglial activity, and restricting neuritic damage.

    “Recent important studies have also shown that impaired/absent Trem2 function attenuates the microglial response to amyloid pathology by regulating microglial number around plaques, regulating microglial activity, and restricting neuritic damage (37,61,84–87,95–99).”
    Quote in the paperNot a substantial claim0 of 10 sources checked
    • cites [37] Cheng-Hathaway, 2018, The Trem2 R47H variant confers loss-of-function-like phenotypes in Alzheimer's disease, Mol. Neurodegener. source

      Not checked in the free run.

    • cites [61] Zhou, 2020, Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and TREM2-independent cellular responses in Alzheimer's disease, Nat. Med. source

      Not checked in the free run.

    • cites [84] Krasemann, 2017, The TREM2-APOE pathway drives the transcriptional phenotype of dysfunctional microglia in neurodegenerative diseases, Immunity source

      Not checked in the free run.

    • cites [85] Song, 2018, Humanized TREM2 mice reveal microglia-intrinsic and -extrinsic effects of R47H polymorphism, J. Exp. Med. source

      Not checked in the free run.

    • cites [86] Griciuc, 2019, TREM2 acts downstream of CD33 in modulating microglial pathology in Alzheimer's disease, Neuron source

      Not checked in the free run.

    • cites [87] Linnartz-Gerlach, 2019, TREM2 triggers microglial density and age-related neuronal loss, Glia source

      Not checked in the free run.

    • cites [95] Leyns, 2019, TREM2 function impedes tau seeding in neuritic plaques, Nat. Neurosci. source

      Not checked in the free run.

    • cites [96] Prokop, 2019, Impact of TREM2 risk variants on brain region-specific immune activation and plaque microenvironment in Alzheimer's disease patient brain samples, Acta Neuropathol. source

      Not checked in the free run.

    • cites [97] Sayed, 2018, Differential effects of partial and complete loss of TREM2 on microglial injury response and tauopathy, Proc. Natl. Acad. Sci. USA source

      Not checked in the free run.

    • cites [98] Meilandt, 2020, Trem2 deletion reduces late-stage amyloid plaque accumulation, elevates the Abeta42:Abeta40 ratio, and exacerbates axonal dystrophy and dendritic spine loss in the PS2APP Alzheimer's mouse model, J. Neurosci. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationreasoning

    This might reflect a mechanism for microglia to perform specific functional requirements under pro-inflammatory conditions.

    “This might reflect a mechanism for microglia to perform specific functional requirements under pro-inflammatory conditions.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    Accumulated pro-inflammation and oxidative stress in the brain, often observed in aged brains and aged microglia, could cause sustained suppression of Trem2 expression and thus an impairment of TREM2-dependent microglial functions.

    “accumulated pro-inflammation and oxidative stress in the brain, which is often observed in aged brains and aged microglia (90–94), could cause sustained suppression of Trem2 expression and thus an impairment of TREM2-dependent microglial functions.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [90] Prolla, 2002, DNA microarray analysis of the aging brain, Chem. Senses source

      Not checked in the free run.

    • cites [91] Godbout, 2005, Exaggerated neuroinflammation and sickness behavior in aged mice following activation of the peripheral innate immune system, FASEB J. source

      Not checked in the free run.

    • cites [92] Lee, 2000, Gene-expression profile of the ageing brain in mice, Nat. Genet. source

      Not checked in the free run.

    • cites [93] Verbitsky, 2004, Altered hippocampal transcript profile accompanies an age-related spatial memory deficit in mice, Learn. Mem. source

      Not checked in the free run.

    • cites [94] Sierra, 2007, Microglia derived from aging mice exhibit an altered inflammatory profile, Glia source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Pro-inflammatory mediators, either locally produced or infiltrating into the CNS from the periphery following blood-brain barrier breakdown, could induce down-regulation of microglial Trem2 expression and subsequently induce a microglial state with low TREM2-signaling.

    “Taken together, pro-inflammatory mediators, either locally produced, or infiltrating into the CNS from the periphery following blood–brain barrier breakdown, could induce down-regulation of microglial Trem2 expression and subsequently induce a microglial state with low TREM2-signaling (Fig. 10).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Microglia in vivo probably never receive simple purified LPS or IL-4 stimuli to govern their activation state, or at least not across the whole population.

    “In contrast to populations of microglia polarized with purified LPS or IL-4 stimuli in vitro, microglia in vivo probably never receive such simple stimuli to govern their activation state or at least not across the whole population.”
    Quote in the paperSubstantial claim

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

    Study design and conductnone given

    Cells pre-incubated with 10 μm cytochalasin-D for 30 min prior to the phagocytosis assay were used as a negative control.

    “Cells pre-incubated with 10 μm cytochalasin-D for 30 min prior to the phagocytosis assay were used as a negative control.”
    Quote in the paperNot a substantial claim

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

    Study design and conductnone given

    All RT-qPCR reactions were checked for a single peak with the melt-curve analysis reflecting a single PCR product.

    “All RT-qPCR reactions were checked for a single peak with the melt-curve analysis reflecting a single PCR product.”
    Quote in the paperNot a substantial claim

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

    Study design and conductnone given

    Unstained cells and cells treated with 50 nM staurosporine for 24 h were used as negative and positive controls respectively to allow correct gating.

    “Unstained cells, and cells treated with 50 nM staurosporine for 24 h were used as negative and positive controls respectively to allow correct gating.”
    Quote in the paperNot a substantial claim

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

    Study design and conductown data

    Expression levels of the housekeeping genes Arf1, H3f3b and Rps28 were stable between the different experimental samples when higher molecular weight RNA was measured.

    “Expression levels of the housekeeping genes Arf1, H3f3b and Rps28 were shown to be stable between the different experimental samples when higher molecular weight RNA was measured (Supplementary Material, Figs S9 and S10).”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    To account for differences in cell number between wells, cell lysates were collected in parallel with supernatants and tested for beta-actin by western blot, which was used for normalization of TNF-alpha levels.

    “To account for the differences in the cell number between different wells of microglia, cell lysates were collected in parallel with the supernatants from the same wells and then tested for levels of a housekeeping protein beta-actin (Ab8227, Abcam, RRID: AB_2305186) by western blot, which was used for normalization of TNF-alpha levels.”
    Quote in the paperSubstantial claim

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

    Study design and conductown data

    Primers were designed to span at least two exons and tested for specificity against the entire mouse transcriptome.

    “Primers were designed to span at least two exons and tested for specificity against the entire mouse transcriptome using Primer-BLAST (NCBI) and supplied by Eurofins MWG Operon.”
    Quote in the paperNot a substantial claim

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

    Study design and conductnone given

    The experimenter was blind to the genotype of the samples during quantification and analysis.

    “Experimenter was blind to the genotype of the samples during quantification and analysis.”
    Quote in the paperNot a substantial claim

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

    Study design and conductown data

    Typical RNA integrity values around 9.0 from 10.0 were obtained regardless of siRNA, genotype of mice or treatment type.

    “Typical RNA Integrity values (RIN) around 9.0 from 10.0 were obtained regardless of siRNA, genotype of mice or treatment type.”
    Quote in the paperNot a substantial claim
82 of 82

  • The paper relies on this without support.

    The Trem2 R47H knock-in mouse phenotype is effectively a model of down-regulation of TREM2 activity, with changes in microglial number and activation due to a combination of partial Trem2 knockdown and any effect of the R47H mutation.

    “The changes in microglial number and activation in this mouse will thus be a combination of the partial knockdown of Trem2 and any effect of the R47H mutation. Hence this is effectively an in vivo model of down regulation of TREM2 activity, through the combination of these two factors.”

  • The paper relies on this without support.

    Anti-inflammatory signaling is associated with tissue repair.

    “Given that anti-inflammatory signaling is associated with tissue repair, understanding the signaling mechanisms downstream of Trem2 in coordinating the pro- and anti-inflammatory balance of microglia, particularly mediating effects of the IL-4-regulated anti-inflammatory pathway, has important implications for fighting neurodegenerative disease.”

  • The paper relies on this without support.

    The Trem2 decrease in R47H KI mice does not occur in human tissue with this mutation but is a mouse-specific effect related to altered splicing.

    “This does not occur in human tissue with this mutation but appears to be a mouse specific effect related to altered splicing.”

  • The paper relies on this without support.

    ARG1 is an important anti-inflammatory marker induced upon IL-4 stimulation.

    “ARG1 is an important anti-inflammatory marker induced upon IL-4 stimulation.”

  • The paper relies on this without support.

    DUSP4 is a phosphatase for a number of MAPK family members, also known as MKP-2.

    “DUSP4 is a phosphatase for a number of mitogen-activated protein kinase (MAPK) family members, also known as MAPK phosphatase 2 (MKP-2).”

  • The paper relies on this without support.

    Hub genes drive the response of the entire network.

    “Hub genes are those with the highest connectivity within a co-expression network, and are postulated to drive the response of the entire network.”

  • The paper relies on this without support.

    TREM2 variants have high odds ratios for AD risk and R47H is the most common.

    “Of the many genes that have been revealed in GWAS to increase the risk of AD, variants of TREM2 have high odds ratios. The most common of these is the R47H mutation.”

  • The paper relies on this without support.

    The down-regulation of Trem2 in Trem2 R47H KI mice is present throughout life.

    “the down-regulation of Trem2 in these mice is present throughout life”

  • The paper relies on this without support.

    The IGF1 receptor is found largely on neurons.

    “the IGF1 receptor is found largely on neurons”

  • The paper relies on this without support.

    Anti-inflammatory signaling was not studied.

    “However anti-inflammatory signaling was not studied.”

  • The paper relies on this without support.

    The down-regulation of Trem2 expression in Trem2 R47H KI mice is not reflected in humans with the R47H mutation.

    “the down-regulation of Trem2 expression in the Trem2 R47H KI mice which is not reflected in humans with this mutation”
11 of 11

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • In microglia, signalling through TREM2 typically dampens the pro-inflammatory response.

    “in microglia, signalling through TREM2 typically dampens this pro-inflammatory response [33, 34]”

    From TREM2/PLCγ2 signalling in immune cells: function, structural insight, and potential therapeutic modulation (2021) · cites this paper as [33]

    The Results section on IL-4 responses says TREM2 pushes microglia toward an anti-inflammatory phenotype. But the Results section on LPS stimulation reports that reducing Trem2 did not significantly change the measured pro-inflammatory response; LPS instead suppressed Trem2 expression. The paper therefore supports an anti-inflammatory role for TREM2, but not the broader claim that its signalling typically dampens a pro-inflammatory response. (LLM, conf=0.87)

    Experimental — accuracy not yet measured

  • Investigations in microglia suggested that the TREM2 pathway promotes anti-inflammatory responses.

    “investigations in microglia suggested that the TREM2 pathway promotes anti-inflammatory responses [33]”

    From TREM2/PLCγ2 signalling in immune cells: function, structural insight, and potential therapeutic modulation (2021) · cites this paper as [33]

  • Down-regulation of microglial TREM2 expression and signaling might be one of the major pathogenetic mechanisms in sporadic cases of Alzheimer's disease, in which advanced age, oxidative stress, and neuroinflammation contribute to suppression of wild-type TREM2.

    “Regarding the relation of TREM2 with OS, it has been supposed that a down-regulation of microglial TREM2 expression and signaling might be one of the major pathogenetic mechanisms in sporadic cases of AD in which advanced age, OS, neuroinflammation contribute to the suppression of wild-type TREM2, considering that TREM2 mutation is rare in humans [123].”

    From Role of Oxidative Damage in Alzheimer’s Disease and Neurodegeneration: From Pathogenic Mechanisms to Biomarker Discovery (2021) · cites this paper as [123]

Cites

Flagged first, then by citations

3 of the 124 references couldn’t be matched to a known paper.

Research works printed but not linked: 1

  1. Benitez, 2013, TREM2 and neurodegenerative disease, N. Engl. J. Med., 369, 1567

Cited by

Sorted by citations

Related

Authors
Liu, W., Taso, O., Wang, R., Bayram, S., Graham, A. C., Garcia-Reitboeck, P., Mallach, A., Andrews, W. D., Piers, T. M., Botia, J. A., Pocock, J. M., Cummings, D. M., Hardy, J., Edwards, F. A., & Salih, D. A.
Affiliations
  • University College London (GB)
  • UK Dementia Research Institute (GB)
  • Hitachi Rail Europe Ltd, London EC1N 2PB, UK
  • UCL Queen Square Institute of Neurology (GB)
  • Department of Information and Communications Engineering, Universidad de Murcia, Murcia E-30100, Spain
Corresponding author
Salih, Dervis A
ORCID
Venue
Human Molecular Genetics
Publisher
Oxford University Press (OUP)
Published
2020-09-22
Volume
29
Issue
19
Pages
3224-3248
ISSN
  • 0964-6906 (ISSN-L)
  • 1460-2083
DOI
10.1093/hmg/ddaa209
PMC
PMC7689298
OpenAlex
W3087562324
Semantic Scholar
5497aa312aaaa12d27ea668158ff648a6d0d0ead
Cited by
214
References
124
Citations by year
2026: 35 · 2025: 61 · 2024: 31 · 2023: 33 · 2022: 32 · 2021: 19 · 2020: 2 · 2019: 1
FWCI
8.41
Type
journal article
Language
en
Open access
Licence
Locations
  • Human Molecular Genetics (publishedVersion, cc-by)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • UCL Discovery (University College London) (submittedVersion)
Funders
  • Alzheimer's Research Foundation (ARUK-SRF2013-7, ARUK-PG2019B-018)
  • Biotechnology and Biological Sciences Research Council (BB/M009513/1)
Topics
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Immunology and Microbiology › Immunology › Phagocytosis and Immune Regulation
  • Health Sciences › Medicine › Physiology › Alzheimer's disease research and treatments
Keywords
TREM2, microglia, anti-inflammatory response, pro-inflammatory response, IL-4 signaling, lipopolysaccharide, STAT6, Arg1, microglial density, hippocampus, neuroinflammation, neurodegeneration
MeSH terms
RNA-Seq, Animals, Animals, Newborn, Gene Expression Regulation, Inflammation, Membrane Glycoproteins, Mice, Inbred C57BL, Mutation, Receptors, Immunologic, Microglia, Mice, Knockout, Inflammation Mediators, STAT6 Transcription Factor, Mice, Transcriptome

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-10.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-10.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

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