Calcium-influx increases SOD1 aggregates via nitric oxide in cultured motor neurons

Abstract

Familial amyotrophic lateral sclerosis (fALS) is caused by mutations in Cu/Zn-superoxide dismutase (SOD1), and SOD1 aggregation and calcium toxicity are involved in neuronal death. However, the effect of altered calcium homeostasis on the SOD1 aggregation is unknown. To investigate whether calcium triggers mutant SOD1 aggregation in vitro, human mutant SOD1 (G93A) was transfected into motor neuronal cell line (VSC 4.1 cells). These cells were then treated with calcium ionophore A23187 or agents that induce intracellular calcium release like cyclic ADP ribose, ryanodine or thapsigargin. A23187 was found to increase mutant SOD1 aggregation and neuronal nitric oxide synthase (nNOS) expression. Moreover, the NOS inhibitor (L-NAME) and a NO-dependent cyclic GMP cascade inhibitor (ODQ) reduced SOD1 aggregation, whereas an exogenous NO donor (GSNO) increased mutant SOD1 aggregation, which was also prevented by NOS or cGMP cascade inhibitor. Our data demonstrate that calcium-influx increases SOD1 aggregation by upregulating NO in cultured motor neuronal cells.

Calcium-dependent protein folding in amyotrophic lateral sclerosis

“…In the SOD1 G93A model, treating with Ca 2+ ionophore or knocking down the GluR2 expression in Ca 2+ -permeable AMPA receptors enhances insolubility and toxicity of mutated SOD1 [33][34][35]. Decreasing the intracellular Ca 2+ level by blocking the AMPA receptors or enhancing the Ca 2+ buffer capacity had a protective effect in fALS cell culture and transgenic mouse models [36][37][38].…”

Mitochondrial dysfunction and intracellular calcium dysregulation in ALS

“…In addition, mitochondrial calcium handling defects have been shown in organotypic brainstem slices (Jaiswal and Keller, 2009) and cultured neuronal cells (Jaiswal et al, 2009). Mitochondrial calcium handling impairment could contribute to abnormally high intracellular calcium levels (Carri et al, 1997; Kruman et al, 1999) and makes ALS MNs vulnerable to degeneration (Kim et al, 2007; Kim et al, 2002). Consistent with the involvement of muscle mitochondria in fALS, in skeletal muscle of mutant SOD1 mice, depolarized mitochondria were localized to neuromuscular junctions, and were accompanied by hyperactive calcium release from the sarcoplasmic reticulum (Zhou et al, 2009).…”

The Potential Role of Nitric Oxide Synthase in Survival and Regeneration of Magnocellular Neurons of Hypothalamo-Neurohypophyseal System

“…These results suggest that NO is related with neuronal death. Moreover, the findings in that NOS inhibitors rescue variable proportions of neurons [10][11][12][13][14] serve to further prove that NO may be neurotoxic. For example, inhibition of neuronal nitric oxide synthase prevents iron-induced cerebellar Purkinje cell loss in the rat [15].…”