Calpain-cleaved type 1 inositol 1,4,5-trisphosphate receptor impairs ER Ca2+buffering and causes neurodegeneration in primary cortical neurons

Disruption of neuronal Ca2+ 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 Ca2+ release channel on the endoplasmic reticulum, generates a dysregulated channel, which may contribute to aberrant Ca2+ signaling and neurodegeneration in disease states. However, the specific effects of InsP3R1 proteolysis on neuronal Ca2+ 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 Ca2+ 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 Ca2+ concentration ([Ca2+]i), increased [Ca2+]i response to glutamate, and enhanced sensitivity to excitotoxic stimuli. Together, our results demonstrate that InsP3R1 proteolysis disrupts neuronal Ca2+ homeostasis, and potentially acts as a feed-forward pathway to initiate or execute neuronal death.