Oncostatin M promotes excitotoxicity by inhibiting glutamate uptake in astrocytes: implications in HIV-associated neurotoxicity

Abstract

BackgroundElevated levels of oncostatin M (OSM), an interleukin-6 cytokine family member, have been observed in HIV-1-associated neurocognitive disorders (HAND) and Alzheimer’s disease. However, the function of OSM in these disease conditions is unclear. Since deficient glutamate uptake by astrocytes is instrumental in HAND-associated neurotoxicity, we hypothesized that OSM impairs glutamate uptake in astrocytes and thereby promotes neuronal excitotoxicity.MethodsPrimary cultures of mouse cortical astrocytes, neurons, microglia, and BV2 cell line were used. The expression of glutamate transporters (GLAST/EAAT1 and GLT-1/EAAT2) was investigated using real-time PCR and Western blot, and their activity was assessed by measuring 3H-d-aspartate uptake. Neuronal toxicity was measured using the colorimetric MTT (3-(4,5-dimethylthiazol-2-yl-) 2,5-diphenyltetrazolium bromide) assay and immunocytochemistry. A chimeric HIV-1 that infects murine cells (EcoHIV/NL4-3-GFP virus (EcoHIV)) was used to investigate whether the virus induces OSM, OSM receptor (OSMR)-β, glycoprotein 130 (gp130), GLT-1, GLAST (mRNA and protein), and OSM release (ELISA) in cultured BV2 cells, primary microglia, or astrocytes. Statistical analyses of the data were performed using one-way ANOVA (to allow multiple comparisons) and two-tailed Student’s t test.ResultsOSM treatment (10 ng/mL) time-dependently reduced GLAST and GLT-1 expression and inhibited 3H-d-aspartate uptake in cultured astrocytes in a concentration-dependent manner, an effect prevented by the Janus kinase (JAK)/signal transducers and activators of transcription (STAT)3 inhibitor AG490. Down-regulation of astrocytic glutamate transport by OSM resulted in NMDA receptor-dependent excitotoxicity in cortical neurons. Infection with EcoHIV induced OSM gene expression and protein release in BV2 cells and microglia, but not in astrocytes. Conversely, EcoHIV caused a fivefold increase in OSMR-β mRNA (but not gp130) and protein in astrocytes, but not in microglia, which did not express OSMR-β protein. Finally, astrocytic expression of GLAST gene was unaffected by EcoHIV, whereas GLT-1 mRNA was increased by twofold.ConclusionsWe provide first evidence that activation of JAK/STAT3 signaling by OSM inhibits glutamate uptake in astrocytes, which results in neuronal excitotoxicity. Our findings with EcoHIV suggest that targeting OSMR-β signaling in astrocytes might alleviate HIV-1-associated excitotoxicity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0613-8) contains supplementary material, which is available to authorized users.

Neurochemical regulation of the expression and function of glial fibrillary acidic protein in astrocytes

“…Pro‐survival JAK2/STAT3 cascade is localized primarily within astrocytic nuclei (Oliva, Kang, Sanchez‐Molano, Furones, & Atkins, ). This cascade is responsible for the activation of GFAP gene by many factors, such as cholera toxin and interleukin (IL)‐6 in C6 malignant glioma cells (Shu et al, ), oncostatin M (OSM) in cortical neurons (Moidunny et al, ), epidermal growth factor in human glioblastoma (He et al, ), and IL‐33 in spinal glia (Du et al, ). In contrast, the inhibition of astrocyte proliferation and GFAP expression is due to suppression of JAK2/STAT3 pathway by some other factors, such as sevoflurane in the hippocampus of neonatal rats (Wang, Lu, Feng, & Zhang, ), oleanolic acid in neural stem cells (Zhang et al, ), and SN79 in striatum in mice (Robson et al, ).…”

“…Pro-survival JAK2/STAT3 cascade is localized primarily within astrocytic nuclei (Oliva, Kang, Sanchez-Molano, Furones, & Atkins, 2012). This cascade is responsible for the activation of GFAP gene by many factors, such as cholera toxin and interleukin (IL)-6 in C6 malignant glioma cells (Shu et al, 2011), oncostatin M (OSM) in cortical neurons (Moidunny et al, 2016), epidermal growth factor in human glioblastoma (He et al, 2013), and IL-33 in spinal glia (Du et al, 2019).…”

Differential activation of neuronal and glial STAT3 in the spinal cord of the SOD1G93A mouse model of amyotrophic lateral sclerosis

“…Although the FCs of the pSTAT3 + /S100b + astrocytes were increased even more in 15-and 21-week-old SOD1 G93A mice, our findings suggested that astrocytic STAT3 was activated in the SOD1 G93A mice in the presymptomatic stage by a mechanism that was developed independently of axonal impairment and neuroinflammation. In this regard, an interesting study has shown that the activation of astrocytic STAT3 impairs the ability of astrocytes to remove glutamate from the extracellular space, which contributes to excitotoxic neuronal damage (Moidunny et al, 2016). Although future studies are needed, these findings suggest that the activation of astrocytic STAT3 may increase the glutamate toxicity that occurs in the early stages of ALS (van Zundert et al, 2012).…”

Selective peroxisome proliferator‐activated receptor‐gamma modulator, INT131 exhibits anti‐inflammatory effects in an EcoHIV mouse model

“…This concentration of EcoHIV was based on previous studies using a comparable concentration in a similar in vitro system to induce an inflammatory response. 43 Exposure of the cells to EcoHIV significantly increased the inflammatory markers TNFα, IL-1β, IL-6, CCL2, CCL3, CXCL10, and C3; at 24-h post-EcoHIV exposure (Figure 1). Previous studies from our laboratory have shown that exposure to full PPARγ agonists (rosiglitazone or pioglitazone) reversed HIV-1 envelope gp120 or EcoHIV induced mRNA expression of pro-inflammatory cytokines and oxidative stress markers in primary cultures of mixed rodent astrocytes and microglia.…”

“…EcoHIV is a robust rodent model to investigate HIV-related brain pathologies, we and others have demonstrated that infection of mice leads to neuroinflammation and neurocognitive impairments. 34,42,43 We assessed the effect of INT131 treatment on the expression of inflammatory markers in vitro, utilizing primary cultures of mouse mixed glial cells exposed to EcoHIV, and in vivo, in mice intracranially injected with EcoHIV. Additionally, we conducted a pharmacokinetic (PK) study to characterize INT131 brain tissue penetration.…”