Neural mitochondrial Ca2+ capacity impairment precedes the onset of motor symptoms in G93A Cu/Zn‐superoxide dismutase mutant mice

Abstract

Mitochondrial respiratory chain dysfunction, impaired intracellular Ca 2+ homeostasis and activation of the mitochondrial apoptotic pathway are pathological hallmarks in animal and cellular models of familial amyotrophic lateral sclerosis associated with Cu/Zn‐superoxide dismutase mutations. Although intracellular Ca 2+ homeostasis is thought to be intimately associated with mitochondrial functions, the temporal and causal correlation between mitochondrial Ca 2+ uptake dysfunction and motor neuron death in familial amyotrophic lateral sclerosis remains to be established. We investigated mitochondrial Ca 2+ handling in isolated brain, spinal cord and liver of mutant Cu/Zn‐superoxide dismutase transgenic mice at different disease stages. In G93A mutant transgenic mice, we found a significant decrease in mitochondrial Ca 2+ loading capacity in brain and spinal cord, as compared with age‐matched controls, very early on in the course of the disease, long before the onset of motor weakness and massive neuronal death. Ca 2+ loading capacity was not significantly changed in liver G93A mitochondria. We also confirmed Ca 2+ capacity impairment in spinal cord mitochondria from a different line of mice expressing G85R mutant Cu/Zn‐superoxide dismutase. In excitable cells, such as motor neurons, mitochondria play an important role in handling rapid cytosolic Ca 2+ transients. Thus, mitochondrial dysfunction and Ca 2+‐mediated excitotoxicity are likely to be interconnected mechanisms that contribute to neuronal degeneration in familial amyotrophic lateral sclerosis.