Spatial and Temporal Regulation of Cytoplasmic Free Ca

Disruption of neuronal Ca homeostasis plays a well-established role in cell death in a number of neurodegenerative disorders. Recent evidence suggests that proteolysis of the type 1 inositol 1,4,5-trisphosphate receptor (InsP3R1), a Ca 2+ release channel on the endoplasmic reticulum, generates a dysregulated channel, which may contribute to aberrant Ca signaling and neurodegeneration in disease states. However, the specific effects of InsP3R1 proteolysis on neuronal Ca 2+ homeostasis are unknown, as are the functional contributions of this pathway to neuronal death. This study evaluates the consequences of calpain-mediated InsP3R1 proteolysis on neuronal Ca signaling and survival using adeno-associated viruses to express a recombinant cleaved form of the channel (capn-InsP3R1) in rat primary cortical neurons. Here, we demonstrate that expression of capn-InsP3R1 in cortical cultures reduced cellular viability. This effect was associated with increased resting cytoplasmic Ca concentration ([Ca]i), increased [Ca]i response to glutamate, and enhanced sensitivity to excitotoxic stimuli. Together, our results demonstrate that InsP3R1 proteolysis disrupts neuronal Ca 2+ homeostasis, and potentially acts as a feed-forward pathway to initiate or execute neuronal death.