Importance of calcium in Parkinson’s diseasepathophysiology

Parkinson Disease (PD) is the most common progressive neurodegenerative movement disorder characterized by preferential loss of ventral midbrain dopaminergic neurons of substantia nigra pars compacta. It has been recently suggested that high Ca2+ levels due to Cav1.3 channeldependent pacemaking activity may contribute to SNpc susceptibility in PD. Based on this, in the present study, we hypothesized that perturbed neuronal calcium homeostasis is one of the major factors in the genesis of PD, and examined the mechanism of dopaminergic neuronal protection provided by nimodipine, an L-type calcium channel blocker in cellular and animal models of the disease. We used the pakinsonian neurotoxin, MPP+ in SH-SY5Y, MPTP in mice to induce PD pathology and/or behavioral phenotypes and employed parkinsonian cybrids to study the PD phenotype. Cell viability via MTT assay, calcium imaging employing Fura-2AM, mitochondrila morphology by Mitotracker Green and mitochondrial membrane potential using TMRM were investigated in SH-SY5Y cells. Animal behaviors were monitored, striatal dopamine levels were measured employing HPLC-electrochemical detection procedure and nigral neuronal loss was determined using tyrosine hydroxylase immunohistochemistry. Mitochondrial integrity and their functions were examined using DCFDA fluorescence and oxygen consumption analysis. In SHSY5Y cells, pretreatment with nimodipine attenuated MPP+-mediated increase in intracellular calcium, reduction in cell viability, decrease mitochondrial membrane potential and corrected the aberrations in mitochondrial morphology. In mice, MPTP-induced behavioral dysfunctions (reduced swimming ability, akinesia and catalepsy), striatal dopamine depletion, increases in mitochondrial reactive oxygen species generation and loss in mitochondrial respiration were corrected by nimodipine administration. The level of intracellular calcium was elevated in PD cybrids. Further, the expression of calcium binding protein calbindin as measured by real time PCR and Immunoblot, was found to be decreased while that of calcium activated phosphatase calcineurin B and protease calpain protein levels were found to be increased after the neurotoxin treatment, while this trend was significantly attenuated following nimodipine treatment (both in vitro and in vivo). These results suggest that the L-type calcium channel blocker, nimodipine protects against the parkinsonian neurotoxin-induced cell death by correcting the defects in mitochondrial integrity and functions, caused by increased intracellular calcium in dopaminergic neurons.