TREM2 deficiency eliminates TREM2+ inflammatory macrophages and ameliorates pathology in Alzheimer's disease mouse models - PubMed (original) (raw)

. 2015 Mar 9;212(3):287-95.

doi: 10.1084/jem.20142322. Epub 2015 Mar 2.

Crystal M Miller 2, Paul J Cheng 1, Leah C Graham 3, Shane Bemiller 4, Margaret L Broihier 5, Guixiang Xu 2, Daniel Margevicius 2, J Colleen Karlo 5, Gregory L Sousa 3, Anne C Cotleur 2, Oleg Butovsky 6, Lynn Bekris 2, Susan M Staugaitis 2, James B Leverenz 2, Sanjay W Pimplikar 1, Gary E Landreth 5, Gareth R Howell 3, Richard M Ransohoff 2, Bruce T Lamb 7

Affiliations

TREM2 deficiency eliminates TREM2+ inflammatory macrophages and ameliorates pathology in Alzheimer's disease mouse models

Taylor R Jay et al. J Exp Med. 2015.

Abstract

Variants in triggering receptor expressed on myeloid cells 2 (TREM2) confer high risk for Alzheimer's disease (AD) and other neurodegenerative diseases. However, the cell types and mechanisms underlying TREM2's involvement in neurodegeneration remain to be established. Here, we report that TREM2 is up-regulated on myeloid cells surrounding amyloid deposits in AD mouse models and human AD tissue. TREM2 was detected on CD45(hi)Ly6C(+) myeloid cells, but not on P2RY12(+) parenchymal microglia. In AD mice deficient for TREM2, the CD45(hi)Ly6C(+) macrophages are virtually eliminated, resulting in reduced inflammation and ameliorated amyloid and tau pathologies. These data suggest a functionally important role for TREM2(+) macrophages in AD pathogenesis and an unexpected, detrimental role of TREM2 in AD pathology. These findings have direct implications for future development of TREM2-targeted therapeutics.

© 2015 Jay et al.

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Figures

Figure 1.

Figure 1.

TREM2 expression is increased around Aβ plaques. (a) A novel Trem2 knockout with a LacZ reporter under the control of the Trem2 promoter was generated. (b–m) TREM2 IHC was performed in WT mice at 2 (b), 4 (c), 6 (d), and 12 mo (e) of age, in APPPS1 mice at 2 (f), 4 (g), 6 (h), and 12 mo (i) of age, and in 5XFAD mice at 2 (j), 4 (k), 6 (l), and 8 mo (m) of age (n = 4–5). Insets show Congo red costaining with arrows indicating plaques. (n–q) TREM2 was also observed around plaques (n, p, and q) but not in regions lacking Aβ deposition (o) in human AD cases (n = 2). Arrows point to Congo red–positive plaques. (r) TREM2 immunoreactivity was not observed in APPPS1;Trem2−/− mice (n = 7). Insets show Congo red costaining with arrows indicating plaques. (s and t) TREM2 expression was also assessed by qRT-PCR (s; two-way ANOVA, age P = 0.083, genotype P = 0.0036, interaction P = 0.185; Bonferroni-corrected Student’s t tests shown; n = 6–8 per group) and Western blot (t; n = 2–3). Arrowhead indicates position of TREM2-specific band. Error bars indicate SEM. *, P < 0.05. At least three independent experiments were performed for all analyses. Bars, 100 µm (bars in b and n apply to b–p and r).

Figure 2.

Figure 2.

TREM2 is expressed in plaque-associated myeloid cells. (a) In situ hybridization with TREM2 probes colocalized with Iba1 (n = 2). (b) X-gal staining of brain tissue from 4-mo-old APPPS1;Trem2LacZ/+ mice colocalized with fluorescent IHC for Iba1 and 6E10 (n = 3). (c–f) Confocal microscopy was used to assess TREM2 colocalization with 6E10+ plaque-associated myeloid cells (c; Iba1), astrocytes (d; GFAP), neurons (e; MAP2), or oligodendrocytes (f; MBP; n = 8). At least two independent experiments were performed for all analyses. Bars: (a) 20 µm; (b–f) 50 µm.

Figure 3.

Figure 3.

TREM2 is specifically expressed on CD11b+CD45hiF4/80+ macrophages in AD mice. (a and b) Isolated brain myeloid cells were gated on CD11b (a) and divided into CD45lo and CD45hi populations (b). (c and f) TREM2+ cells were exclusively CD45hi (c) and F4/80+ (f; n = 41). (d and e) TREM2 expression was quantified on CD45lo and CD45hi populations in APPPS1 mice (d; two-way ANOVA, age P < 0.0001; genotype/cell type P < 0.0001, interaction P < 0.0001; Bonferroni-corrected Student’s t tests shown; n = 2–8), 5XFAD mice (e; two-way ANOVA, age P = 0.025, genotype/cell type P < 0.0001, interaction P = 0.0003; Bonferroni-corrected Student’s t tests shown; n = 5–9), and WT controls (d and e; n = 4–14). Error bars indicate SEM. **, P < 0.01; ***, P < 0.001. (g and h) Flow cytometry on APPPS1;Trem2−/− mice (g) revealed a lack of TREM2+ cells compared with APPPS1;Trem2+/+ mice (h; n = 7). At least two independent experiments were performed for all analyses.

Figure 4.

Figure 4.

Plaque-associated myeloid cells are reduced in TREM2-deficient mice. (a–c) Confocal microscopy was used to examine Iba1 and 6E10 expression in 4-mo-old APPPS1;Trem2−/− mice (b) and APPPS1;Trem2+/+ controls (a; quantified in c). (d and e) IHC and Congo red costaining (arrows) was performed for Ly6C in APPPS1;Trem2+/+ mice (d) and APPPS1;Trem2−/− animals (e). (a, b, d, and e) Insets show higher-magnification images. (f–h) CD45 and Congo red staining (arrows) was performed in human AD tissue (f; n = 2), APPPS1;Trem2+/+ mice (g), and APPPS1;Trem2−/− mice (h). (i–k) P2RY12 and Congo red staining (arrows) was performed in human AD tissue (i; n = 2), APPPS1;Trem2+/+ mice (j), and APPPS1;Trem2−/− animals (k). (l) TREM2 colocalized with CD45 but not P2RY12. (m–o) qRT-PCR was performed on whole brain lysates to examine transcript levels of myeloid cell markers (m), proinflammatory cytokines (n), and antiinflammatory markers (o). All experiments used n = 7–8 mice per group unless otherwise noted, and at least two independent experiments were performed for all analyses. Error bars indicate SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001. Bars: (a and b) 50 µm; (d–l) 20 µm.

Figure 5.

Figure 5.

TREM2 deficiency reduces Aβ accumulation. (a) IHC with 6E10 was performed on brain slices from 4-mo-old APPPS1;Trem2+/+ and APPPS1;Trem2−/− mice (quantified in c; n = 7–8). (b) Analysis of ThioS plaque number revealed similar results (quantified in d; n = 7–8). (a and b) Insets show a higher magnification of the hippocampus. Bar, 1 mm. (e) APP and Aβ levels were assessed by Western blot using 6E10. (f and g) Quantified relative to GAPDH, there was no significant change in APP protein levels (f) but a significant reduction in Aβ (g) in APPPS1;Trem2−/− mice (n = 3–4). (h and i) ELISAs on brain lysates also showed a significant reduction in insoluble Aβ42 and a trend toward a reduction in soluble Aβ42 (h) and a trend toward a reduction in soluble and insoluble Aβ40 (i; n = 3–4). #, P < 0.10; *, P < 0.05; ***, P < 0.001. At least two independent experiments were performed for all analyses.

Figure 6.

Figure 6.

TREM2 deficiency reduces astrocytosis and MAPT phosphorylation. (a and b) Astrocytosis was assessed in 4-mo-old APPPS1;Trem2+/+ (a) and APPPS1;Trem2−/− mice (b) using IHC for GFAP and 6E10 (n = 7–8). (c and f) The number of GFAP+ cells surrounding plaques was quantified (c; n = 3–4), and results were confirmed by qRT-PCR (f; n = 7–8). (d, e, g, and h) Hyperphosphorylated MAPT was detected in APPPS1;Trem2−/− (e and h) and APPPS1;Trem2+/+ mice (d and g) with AT8 (d and e) and AT180 antibodies (g and h; n = 7–8). Arrows indicate Congo red–positive plaques. (i) Quantification of the area of AT180 immunoreactivity revealed significant decreases in APPPS1;Trem2−/− mice (n = 3–4). At least two independent experiments were performed for all analyses. Error bars indicate SEM. *, P < 0.05; **, P < 0.01. Bar, 50 µm.

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