Mitochondrial dysfunction in S0D1G93A-bearing astrocytes promotes motor neuron degeneration:: Prevention by mitochondrial-targeted antioxidants

Mitochondrial dysfunction and oxidative stress contribute to motor neuron degeneration in amyotrophic lateral sclerosis (ALS). Recent reports indicate that astrocytes expressing the mutations of superoxide dismutase- 1 (SOD1) may contribute to motor neuron injury in ALS. Here, we provide evidence that mitochondrial dysfunction in S0D1(G93A) rat astrocytes causes astrocytes to induce apoptosis of motor neurons. Mitochondria from S0D1(G93A) rat astrocytes displayed a defective respiratory function, including decreased oxygen consumption, lack of ADP-dependent respiratory control, and decreased membrane potential. Protein 3-nitrotyrosine was detected immunochemically in mitochondrial proteins from S0D1(G93A) astrocytes, suggesting that mitochondrial defects were associated with nitroxidative damage. Furthermore, superoxide radical formation in mitochondria was increased in S0D1(G93A) astrocytes. Similar defects were found in mitochondria isolated from the spinal cord of S0D1(G93A) rats, and pretreatment of animals with the spin trap 5,5-dimethyl-1-pyrroline N-oxide restored mitochondrial function, forming adducts with mitochondrial proteins in vivo. As shown previously, S0D1(G93A) astrocytes induced death of motor neurons in cocultures, compared with nontransgenic ones. This behavior was recapitulated when nontransgenic astrocytes were treated with mitochondrial inhibitors. Remarkably, motor neuron loss was prevented by preincubation of S0D1(G93A) astrocytes with antioxidants and nitric oxide synthase inhibitors. In particular, low concentrations (similar to 10 nM) of two mitochondrial-targeted antioxidants, ubiquinone and carboxy-proxyl nitroxide, each covalently coupled to a triphenylphosphonium cation (Mito-Q and Mito-CP, respectively), prevented mitochondrial dysfunction, reduced superoxide production in S0D1(G93A) astrocytes, and restored motor neuron survival. Together, our results indicate that mitochondrial dysfunction in astrocytes critically influences motor neuron survival and support the potential pharmacological utility of mitochondrial-targeted antioxidants in ALS treatment.