Cell-Permeable Calpain Inhibitor SJA6017 Provides Functional Protection to Spinal Motoneurons Exposed to MPP.

Extra-nigral central nervous system sites have been found to be affected in Parkinson's disease (PD). In addition to substantia nigra, degeneration of spinal cord motor neurons may play a role in the motor symptoms of PD. To this end, hybrid rodent VSC 4.1 cells differentiated into motoneurons were used as a cell culture model following exposure to Parkinsonian neurotoxicant MPP. SJA6017, a cell-permeable calpain inhibitor, was tested for its neuroprotective efficacy against the neurotoxicant. SJA6017 attenuated MPP-induced rise in intracellular free Ca and concomitant increases in the active form of calpain. It also significantly prevented increased levels of proteases and their activities, as shown by reduced levels of 145 kDa calpain-specific and 120 kDa caspase-3-specific spectrin breakdown products. Exposure to MPP elevated the levels of reactive oxygen species in VSC 4.1 motoneurons; this was significantly diminished with SJA6017. The motor proteins in spinal motoneurons, i.e., dynein and kinesin, were also impaired following exposure to MPP through calpain-mediated mechanisms; this process was partially ameliorated by SJA6017 pretreatment. Cytoprotection provided by SJA6017 against MPP-induced damage to VSC 4.1 motoneurons was confirmed by restoration of membrane potential via whole-cell patch-clamp assay. This study demonstrates that calpain inhibition is a prospective route for neuroprotection in experimental PD; moreover, calpain inhibitor SJA6017 appears to be an effective neuroprotective agent against MPP-induced damage in spinal motoneurons.