T lymphocytes potentiate endogenous neuroprotective inflammation in a mouse model of ALS

Abstract

Amyotrophic Lateral Sclerosis (ALS) is an adult-onset, progressive, motor neuron degenerative disease, in which the role of inflammation is not well established. Innate and adaptive immunity were investigated in the CNS of the Superoxide Dismutase 1 (SOD1)(G93A) transgenic mouse model of ALS. CD4+ and CD8+ T cells infiltrated SOD1(G93A) spinal cords during disease progression. Cell-specific flow cytometry and gene expression profiling showed significant phenotypic changes in microglia, including dendritic cell receptor acquisition, and expression of genes linked to neuroprotection, cholesterol metabolism and tissue remodeling. Microglia dramatically up-regulated IGF-1 and down-regulated IL-6 expression. When mutant SOD1 mice were bred onto a TCRbeta deficient background, disease progression was significantly accelerated at the symptomatic stage. In addition, microglia reactivity and IGF-1 levels were reduced in spinal cords of SOD1(G93A) (TCRbeta-/-) mice. These results indicate that T cells play an endogenous neuroprotective role in ALS by modulating a beneficial inflammatory response to neuronal injury.

Fig. 1.

Microglia and lymphocyte dynamics in spinal cords of ALS Tg mice. (A) Spinal cords analyzed for resident microglia, infiltrating lymphocytes, monocytes at day 65, day 100, and day 135; representative populations are labeled (A), (B), and (C). (B–C) Cumulative analyses of lymphocytes. Resident microglia show specific increases in SOD1^G93A spinal cord over time (p-values by t test). (D) Representative lymphocyte analysis for CD4⁺, CD8+ T cells, CD19+ B cells, and NK1.1+ natural killer cells. (E) Proportional increases in specific lymphocyte subsets relative to total immune cells in spinal cord, brain of SOD1^G93A mice. (Error bars show SEM.)

Fig. 2.

Microglia acquire dendritic cell markers in ventral horns of SOD1^G93A Tg mice. (A) Spinal cord microglia were analyzed for CD11c surface levels by FACS. SOD1^G93A(G93A), but not non-Tg(NT) or SOD1^WT(WT) microglia show increases in CD11c MFI (One-way ANOVA, *, P < 0.05; ***, P < 0.001) (B) CD11b+ microglia expressing CD11c accumulate in ventral horns, but not dorsal horns, of SOD1^G93A spinal cord. Lumbar section at day 135 with corresponding high magnification images are shown. (Scale bar, 50 μm.)

Fig. 3.

Expression profile of directly purified microglia in mutant SOD1 mice. Microglia were purified by density gradient, magnetic bead selection from spinal cords of SOD1^G93A, SOD1^WT and non-Tg mice. Expression levels of (A) IGF-1 (B) Osteopontin (C) IL-1R antagonist and (D) IL-6 were determined by quantitative PCR. Statistical analysis between SOD1^G93A and non-Tg microglia are by t test.

Fig. 4.

The Th2 Cytokine IL-4, a factor in modulation of microglia response. (A) N9 microglia cells, uninfected (U) or transduced with human SOD1^G93A (G93A), SOD1^WT (WT), empty vector (EV) lentivirus, were treated with IL-4, and assayed for human SOD1, IGF-1, IL-6 expression. Experiments performed in triplicate, *, P < 0.05; **, P < 0.01; and ***, P < 0.001, by t test. (B) Primary adult microglia cultured from SOD1^G93A or non-Tg mice were treated with IL-4 or IFN-γ. IL-4 induced IGF-1 and CD11c expression by quantitative PCR. Microglia display morphological changes by light microscopy. By FACS, IL-4 induces CD11c while IFN-γ induces MHC Class II surface expression; CD40 levels were unaffected (tinted histograms, untreated microglia) (C) IL-4 ELISPOT performed on CNS isolated leukocytes at day 135, stimulated with Con A (Con. A) or untreated (UT) for 48 h; numbers of IL-4 secreting cell colonies were determined (P value by t test).

Fig. 5.

Decreased microglia reactivity and IGF-1 expression in absence of T cells. (A) Spinal cord lumbar sections from non-Tg, SOD1^G93A and SOD1^G93A TCR−/− end-stage mice were stained for CD68 (microglia, red), GFAP (astrocytes, green) and imaged by confocal microscopy. In the absence of T cells, CD68 fluorescence decreases while GFAP is unchanged. (Scale bar, 20 μm.) Cumulative analysis of CD68, and GFAP pixels in serial sections (n.s., not significant) (B) Lumbar sections were stained for IGF-1 (red) and CD11b (green). The CD11b antibody used (M1/70) only recognized activated microglia in fixed tissue sections. In SOD1^G93A spinal cord, microglia co-localized with expression of IGF-1 (60x magnification), and in SOD1^G93A TCR−/− mice, CD11b and IGF-1 staining decreased (Ventral horn gray matter is delineated by dotted white lines). Scale bar = 50 μm. Image analysis of IGF-1 integrated intensity/CD11b (C), IGF-1 (I), and co-localized (Col) pixels show the dependence of IGF-1 levels on T cells (one way ANOVA, ***, P < 0.001.)

Fig. 6.

Accelerated disease progression in mutant SOD1 mice deficient in T cells. (A–B) Kaplan Meier curves for survival and symptomatic onset in SOD1^G93A (males, n = 22; females, n = 20), SOD1^G93ATCR± (m, n = 16; f, n = 13), SOD1^G93ATCR−/− (m, n = 13; f, n = 11) and TCR−/− (m, n = 7; f, n = 10) animals. (C) Weight loss plotted for SOD1^G93ATCR± and TCR−/− littermates. (D) Decline in motor symptoms scored over time between genotypes. For C and D, statistically significant time-points are indicated; *, P < 0.05 by t test. (E) Duration of early and late symptomatic phases of disease for SOD1^G93ATCR+/+, TCR±, and TCR−/− mice. Statistical analysis by one-way ANOVA.