Mitochondrial oxidative stress and dysfunction are strongly implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). Glutathione (GSH) is an endogenous antioxidant that exists as distinct cytosolic and mitochondrial pools. The status of the mitochondrial GSH pool is reliant on transport from the cytosol through the 2-oxoglutarate carrier (OGC), an inner membrane anion carrier. We have previously reported that the outer mitochondrial membrane protein, Bcl-2, directly binds GSH and is a key regulator of OGC-dependent mitochondrial GSH transport. Here, we show that G93A mutant SOD1 (Cu, Zn-superoxide dismutase) reduces the binding of GSH to Bcl-2 and disrupts mitochondrial GSH uptake in vitro. In the G93A mutant hSOD1 mouse model of ALS, mitochondrial GSH is significantly depleted in spinal cord of end-stage mice. Finally, we show that OGC is heavily S-nitrosylated in the spinal cord of end-stage mice and consequently, the GSH uptake capacity of spinal cord mitochondria isolated from these mutant mice is significantly diminished. Collectively, these findings suggest that spinal cord GSH depletion, particularly at the level of the mitochondria, plays a significant role in ALS pathogenesis induced by mutant SOD1. Furthermore, the depletion of mitochondrial GSH in the G93A mutant hSOD1 mouse model may be caused by the S-nitrosylation of OGC and the capacity of mutant SOD1 to disrupt the Bcl-2/GSH interaction, resulting in a disruption of mitochondrial GSH transport.
Keywords: 2-oxoglutarate carrier; Bcl-2; S-nitrosylation; SOD1; glutathione; mitochondria.