SN79, a sigma receptor antagonist, attenuates methamphetamine-induced astrogliosis through a blockade of OSMR/gp130 signaling and STAT3 phosphorylation

Abstract

Methamphetamine (METH) exposure results in dopaminergic neurotoxicity in striatal regions of the brain, an effect that has been linked to an increased risk of Parkinson's disease. Various aspects of neuroinflammation, including astrogliosis, are believed to be contributory factors in METH neurotoxicity. METH interacts with sigma receptors at physiologically relevant concentrations and treatment with sigma receptor antagonists has been shown to mitigate METH-induced neurotoxicity in rodent models. Whether these compounds alter the responses of glial cells within the central nervous system to METH however has yet to be determined. Therefore, the purpose of the current study was to determine whether the sigma receptor antagonist, SN79, mitigates METH-induced striatal reactive astrogliosis. Male, Swiss Webster mice treated with a neurotoxic regimen of METH exhibited time-dependent increases in striatal gfap mRNA and concomitant increases in GFAP protein, indicative of astrogliosis. This is the first report that similar to other neurotoxicants that induce astrogliosis through the activation of JAK2/STAT3 signaling by stimulating gp-130-linked cytokine signaling resulting from neuroinflammation, METH treatment also increases astrocytic oncostatin m receptor (OSMR) expression and the phosphorylation of STAT3 (Tyr-705) in vivo. Pretreatment with SN79 blocked METH-induced increases in OSMR, STAT3 phosphorylation and astrocyte activation within the striatum. Additionally, METH treatment resulted in striatal cellular degeneration as measured by Fluoro-Jade B, an effect that was mitigated by SN79. The current study provides evidence that sigma receptor antagonists attenuate METH-induced astrocyte activation through a pathway believed to be shared by various neurotoxicants.

Keywords: Astrocyte; Glia; Methamphetamine neurotoxicity; Neuroinflammation; Sigma receptor.

Figure 1

METH (5 mg/kg x 4) treatment resulted in time-dependent increases in striatal gfap mRNA expression. METH was found to significantly increase gfap expression at both 12 and 24 h post-treatment. Two-way ANOVA, followed by post hoc Bonferroni's multiple comparison tests. n=5/group. **p < 0.01, ***p < 0.001, Sal/METH vs. Sal/Sal

Figure 2

Treatment with SN79 was found to attenuate METH-induced increases in striatal gfap mRNA expression at both 12 (A) and 24 h (B), indicating a blockade of astrocyte activation. One-way ANOVA, followed by post hoc Tukey's multiple comparison tests. n=10/group. ***p < 0.001, Sal/METH vs. Sal/Sal; ###p < 0.001, SN79/METH vs. Sal/METH

Figure 3

SN79 mitigates METH-induced increases in striatal GFAP immunoreactivity. METH (5 mg/kg x 4) resulted in significant increases in GFAP immunofluorescence. This effect was blocked by SN79 (3 mg/kg × 4) treatment. (A) Qualitative images of GFAP immunoreactivity in response to METH and blockade by SN79 treatment. Clockwise from top left: Sal/Sal, Sal/METH, SN79/METH, SN79/Sal. Large images = 20×; Inset images = 63×. (B) Quantification of the attenuation of METH-induced increases in GFAP immunoreactivity by SN79 treatment. One-way ANOVA, followed by post hoc Tukey's multiple comparison tests. n=5/group, 3 slices/brain averaged for each data point. **p < 0.01, Sal/METH vs. Sal/Sal; ##p < 0.01, SN79/METH vs. Sal/METH

Figure 4

SN79 (3 mg/kg × 4) treatment blocks METH-induced (5 mg/kg × 4) increases in striatal osmr mRNA expression at 12 (A) and 24 h (B). One-way ANOVA, followed by post hoc Tukey's multiple comparison tests. n=10/group. ***p < 0.001, Sal/METH vs. Sal/Sal; ###p < 0.001, SN79/METH vs. Sal/METH

Figure 5

(A) METH treatment increased OSMR immunoreactivity in the striatum, an effect mitigated by SN79 treatment. One-way ANOVA, followed by post hoc Tukey's multiple comparison tests. n=5/group, 3 slices/brain averaged for each data point. **p < 0.01, ***p< 0.001, Sal/METH vs. Sal/Sal; ##p < 0.01, SN79/METH vs. Sal/METH (B) Representative images showing increases in GFAP immunoreactivity, increases in astrocytic OSMR immunoreactivity and their colocalization in the striatum by treatment group. Top to bottom: Sal/Sal, Sal/METH, SN79/Sal, SN79/METH Left to right: DAPI nuclear staining, GFAP, OSMR, overlay image. Large images = 20×; Inset images = 63×. (C) Pearson's correlation of increases in OSMR immunoreactivity and increases in GFAP immunoreactivity, indicating an increase in OSMR that is specific to striatal astrocytes.

Figure 6

SN79 mitigates METH-induced increases in the phosphorylation of STAT3 (Tyr-705). (A) METH treatment (5 mg/kg × 4) increases the phosphorylation of STAT3 (Tyr-705) at 12 h, an effect that is mitigated by treatment with SN79 (3 mg/kg × 4). One-way ANOVA followed by post hoc Tukey's multiple comparison tests. **p < 0.01, Sal/METH vs. Sal/Sal; #p < 0.05, SN79/METH vs. Sal/METH (B) No differences were detected between any of the treatment groups in total STAT3 expression.

Figure 7

SN79 (3 mg/kg × 4) treatment attenuates METH-induced (5 mg/kg × 4) neuronal degeneration in the striatum as measured by Fluoro-Jade B staining. (A) Representative images of Fluoro-Jade B labeled degenerating neurons in the striatum for each respective treatment group. Clockwise from top left: Sal/Sal, Sal/METH, SN79/METH, SN79/Sal. (B) Quantification of striatal neuronal degeneration by treatment group. One-way ANOVA, followed by post hoc Tukey's multiple comparison tests. n=5/group, 3 slices/brain averaged for each data point. ***p < 0.001, Sal/METH vs. Sal/Sal; ##p < 0.01, SN79/METH vs. Sal/METH