Astrocytes Survive Chronic Infection and Cytopathic Effects of thets1 Mutant of the Retrovirus Moloney Murine Leukemia Virus by Upregulation of Antioxidant Defenses

Abstract

The ts1 mutant of Moloney murine leukemia virus (MoMuLV) induces a neurodegenerative disease in mice, in which glial cells are infected by the retrovirus but neurons are not. ts1 infection of primary astrocytes, or of the immortalized astrocytic cell line C1, results in accumulation of the ts1 gPr80 env envelope protein in the endoplasmic reticulum (ER), with ER and oxidative stress. Notably, only about half of the infected astrocytes die in these cultures, while the other half survive, continue to proliferate, and continue to produce virus. To determine how these astrocytes survive ts1 infection in culture, we established a chronically infected subline of the living cells remaining after the death of all acutely infected cells in an infected C1 cell culture (C1-ts1-S). We report here that C1-ts1-S cells proliferate more slowly, produce less virus, show reduced H 2 O 2 levels, increase their uptake of cystine, and maintain higher levels of intracellular GSH and cysteine compared to acutely infected or uninfected C1 cells. C1-ts1-S cells also upregulate their thiol antioxidant defenses by activation of the transcription factor NF-E2-related factor 2 (Nrf2) and its target genes. Interestingly, despite maintenance of higher levels of intracellular reduced thiols, C1-ts1-S cells are more sensitive to cystine deprivation than uninfected C1 cells. We conclude that some ts1-infected astrocytes survive and adapt to virus-induced oxidative stress by successfully mobilizing their thiol redox defenses.

Retrovirus-Induced Oxidative Stress with Neuroimmunodegeneration Is Suppressed by Antioxidant Treatment with a Refined Monosodium α-Luminol (Galavit)

“…Western blotting analysis of cell and tissue proteins was performed as described previously (45,46). The antibodies used in Western blotting analysis included anti-Nrf2 (Santa Cruz Biotechnology, Santa Cruz, CA), anti-glutathione peroxidase (GPx) (Chemicon International, Temecula, CA), and anti-xCT.…”

“…We have reported that the Nrf2 antioxidative response pathway is activated in astrocyte cultures infected with ts1 (45) and that some cells in such cultures survive infection as a consequence of these defenses (46).…”

“…However, only about 40% of astrocytes infected with ts1 in culture die, while the remaining astrocytes survive and continue to proliferate (28,46,50). In infected mice, likewise, some ts1-infected astrocytes die while others are activated and accumulate in astrogliotic foci in the spongiform lesions (56,71).…”

The Human Endogenous Retrovirus Envelope Glycoprotein, Syncytin-1, Regulates Neuroinflammation and Its Receptor Expression in Multiple Sclerosis: A Role for Endoplasmic Reticulum Chaperones in Astrocytes

“…For example, infection by murine leukemia virus (MuLV) down-modulates expression of its cell surface receptor, mCAT-1 (21). Several lines of evidence implicate glia in retrovirus-induced ER stress and neuropathogenesis (22). Infection of astrocytes with Moloney MuLV (MoMuLV)-ts1, leads to an ER stress response defined by neuroinflammation and neurodegeneration.…”

“…Infection of astrocytes with Moloney MuLV (MoMuLV)-ts1, leads to an ER stress response defined by neuroinflammation and neurodegeneration. In fact, envelope proteins from both the retroviruses, MoMuLV-ts1 and FrCas E , mediate ER stress in the brain (22)(23)(24)(25) and directly affect oligodendrocyte viability by inducing the proapoptotic ER stress gene, GADD153/CHOP (26).…”