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TREM2 deficiency attenuates neuroinflammation and protects against neurodegeneration in a mouse model of tauopathy

  1. David M. Holtzmana,b,c,2
  1. aDepartment of Neurology, Washington University School of Medicine, St. Louis, MO 63110;
  2. bHope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, MO 63110;
  3. cKnight Alzheimer’s Disease Research Center, Washington University School of Medicine, St. Louis, MO 63110;
  4. dDepartment of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110
  1. Edited by Don W. Cleveland, University of California, San Diego, La Jolla, CA, and approved September 15, 2017 (received for review June 7, 2017)

  1. Fig. S1.

    Full scans of immunoblot data. Unedited film from PSD-95 (~83-kDa) and ERK1/2 (~44- and 42-kDa) immunoblots.

  2. Fig. 2.

    No differences were observed in tau phosphorylation or solubility in 9-mo-old T2+/+PS and T2?/?PS mice. Quantification of the percent area covered by biotinylated AT8 staining in the (A) piriform cortex (P = 0.9499; T2+/+PS, n = 13; T2?/?PS, n = 21) and (B) hippocampus (P = 0.0652; T2+/+PS, n = 13; T2?/?PS, n = 20). Representative images of biotinylated AT8 p-tau staining in the (C) piriform cortex and (D) hippocampus from T2+/+PS and T2?/?PS mice. (Scale bars, 1 mm.) (E) Tau solubility in the hippocampus was quantified using a human-tau (htau) specific sandwich ELISA to measure (Left) RAB-soluble htau (P = 0.8562; T2+/+PS, n = 14; T2?/?PS, n = 17), (Center) RIPA-soluble htau (P = 0.1233; T2+/+PS, n = 14; T2?/?PS, n = 17), and (Right) FA-soluble htau levels (P = 0.9584; T2+/+PS, n = 14; T2?/?PS, n = 17). Data are presented as mean ± SEM. Significance was determined using an unpaired, two-tailed Student’s t test.

  3. Fig. 3.

    TREM2 deficiency reduces microgliosis in PS19 mice. Quantification of the percent area covered by Iba1 staining in the (A) piriform cortex (P = 0.0242; T2+/+PS, n = 14; T2?/?PS, n = 21) and (B) hippocampus (P = 0.0266; T2+/+PS, n = 14; T2?/?PS, n = 21). Representative images of Iba1 staining in the (C) piriform cortex and (D) hippocampus from T2+/+PS and T2?/?PS mice. (Scale bars, 1 mm.) (E) Quantification of immunofluorescence staining for Iba1-positive cell bodies in the piriform cortex (P = 0.0478; T2+/+PS, n = 12; T2?/?PS, n = 20). (F) Representative images of Iba1 immunofluorescence staining in the piriform cortex. Microglia in T2+/+PS mice display a more ramified phenotype as opposed to in T2?/?PS mice where microglia appear quiescent. Images represent maximum-intensity projections of z stacks. (Scale bars, 50 μm.) Data are mean ± SEM. Significance was determined using an unpaired, two-tailed Student’s t test with *P < 0.05.

  4. Fig. S2.

    No effect of TREM2 deficiency on KI-67–positive microglia in the piriform cortex. (A) Quantification of KI-67–positive microglia in the piriform cortex (P = 0.6844; T2+/+PS: 0.9725 ± 0.2171, n = 13; T2?/?PS: 0.8738 ± 0.2406, n = 22). (B) Representative image of KI-67–positive microglia. Images represent maximum-intensity projections of z stacks. (Scale bars: 50 μm.) Data are mean ± SEM. Significance was determined using an unpaired, two-tailed Student’s t test with *P < 0.05.

  5. Fig. S3.

    Correlations between tau pathology, microgliosis, and degeneration in the hippocampus of T2+/+PS and T2?/?PS mice. Significant correlations were observed between Iba1 microglial staining and (A) AT8 p-tau staining (T2+/+PS: n = 12, **P < 0.01, R2 = 0.6743; T2?/?PS: n = 21, **P < 0.01, R2 = 0.3392) and (B) FA-soluble htau levels (T2+/+PS: n = 12, **P < 0.01, R2 = 0.5560; T2?/?PS: n = 16, *P < 0.05, R2 = 0.2475) in both groups, but were stronger in T2+/+PS mice. Additionally, significant correlations for ventricular size and (C) AT8 p-tau staining (T2+/+PS: n = 13, *P < 0.05, R2 = 0.4312; T2?/?PS: n = 19, not significant P > 0.05, R2 = 0.0064) and (D) FA-soluble htau levels (T2+/+PS: n = 13, *P < 0.05, R2 = 0.3185; T2?/?PS: n = 14, not significant P > 0.05, R2 = 0.0114) were observed for T2+/+PS but not T2?/?PS mice. Solid, colored lines represent the best-fit line with a linear regression, and black, dashed lines represent 95% confidence intervals.

  6. Fig. 4.

    Decreased microglial activation and inflammatory gene expression in T2?/?PS mice. (A) Expression of microglial homeostatic (Tmem119: P = 0.1755; and P2ry12: P = 0.6323) and activated markers in the cortex of T2+/+PS and T2?/?PS mice (Cst7: P = 0.0274; Spp1: P = 0.2256; ApoE: P = 0.0088). (B) Representative images of ApoE-positive puncta in Iba1-positive cell bodies from coimmunofluorescence staining in the piriform cortex of T2+/+PS and T2?/?PS mice. Images represent maximum-intensity projections of z stacks. (Scale bars, 50 μm.) (C) Quantification of the percentage of Iba1-positive microglial cell bodies with ApoE accumulation in the piriform cortex (P = 0.0003; T2+/+PS, n = 12; T2?/?PS, n = 20). (D) Expression of inflammatory genes in the cortex of T2+/+PS and T2?/?PS mice (IL-1α, P = 0.0021; IL-1β, P = 0.0009; TNF-α, P = 0.0133; and C1q, P = 0.0136; IL-6, P = 0.5512). n = 9–10 for all qRT-PCR analyses. All graphs represent the mean ± SEM. Significance was determined using an unpaired, two-tailed Student’s t test with “ns” denoting not significant, *P < 0.05, **P < 0.01, and ***P < 0.001.

  7. Fig. 5.

    Reduced astrogliosis in T2?/?PS mice. (A) Expression of cortical GFAP (P = 0.0019). Quantification of the percent area covered by GFAP staining in the (B) piriform cortex (P = 0.0282; T2+/+PS, n = 14; T2?/?PS, n = 20) and (C) hippocampus (P = 0.0067; T2+/+PS, n = 14; T2?/?PS, n = 19). Representative images of GFAP immunohistochemistry in the (D) piriform cortex and (E) hippocampus of T2+/+PS and T2?/?PS mice. (Scale bars, 1 mm.) Data are mean ± SEM. Significance was determined using an unpaired, two-tailed Student’s t test with *P < 0.05 and **P < 0.01.

  8. Fig. S4.

    Correlations between astrogliosis, tau pathology, and microgliosis in the hippocampus of T2+/+PS and T2?/?PS mice. Strong, significant correlations were observed between GFAP staining and (A) AT8 p-tau staining (T2+/+PS: n = 12, **P < 0.01, R2 = 0.5130; T2?/?PS: n = 19, ***P < 0.001, R2 = 0.6311) for both T2+/+PS and T2?/?PS mice. (B) Correlations between GFAP and Iba1 were reduced in T2?/?PS compared with T2+/+PS mice (T2+/+PS: n = 13, **P < 0.01, R2 = 0.5610; T2?/?PS: n = 19, *P < 0.05, R2 = 0.2430). Solid, colored lines represent the best-fit line with a linear regression, and black, dashed lines represent 95% confidence intervals.

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