Cu/Zn superoxide dismutase typical for familial amyotrophic lateral sclerosis increases the vulnerability of mitochondria and perturbs Ca2+ homeostasis in SOD1G93A mice.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the selective loss of defined motoneuron populations in the brainstem and spinal cord. Although low cytosolic calcium (Ca(2+)) buffering and a strong interaction between metabolic mechanisms and Ca(2+) have been associated with selective motoneuron vulnerability, the underlying cellular mechanisms are barely understood. To elucidate the underlying molecular events, we used rapid charge-cooled device imaging to evaluate Ca(2+) signaling and metabolic signatures in the brainstem slices of SOD1(G93A) mice, the mouse model of human ALS, at 8 to 9 and 14 to 15 weeks of age, corresponding to the presymptomatic and symptomatic stages of motor dysfunction, respectively, and compared the results with corresponding age-matched wild-type littermates. We also monitored the mitochondrial membrane potential (Delta(Psim)) of brainstem motoneurons, a valuable tool for characterizing the metabolic signature of intrinsic energy profiles and considered to be a good experimental measure for monitoring energy metabolism in cells. We found that different pharmacological interventions substantially disrupt Delta(Psim) in SOD1(G93A) motoneurons during the symptomatic stage. Furthermore, we investigated the impact of impaired mitochondrial mechanisms on Ca(2+) regulation by using the membrane-permeable indicator fura-acetoxy methyl ester. Taken together, the results indicate that mitochondrial disruptions are critical elements of SOD1(G93A)-mediated motoneuron degeneration in which selective motoneuron vulnerability results from a synergistic accumulation of risk factors, including the disruption of electrochemical potential, low Ca(2+) buffering, and strong mitochondrial control of Ca(2+). The stabilization of mitochondria-related signal cascades may represent a useful strategy for clinical neuroprotection in ALS.