IP3R1-mediated Ca²⁺ overload promotes SAH-induced neuron apoptosis through MAMs

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating acute hemorrhagic stroke. The communication between the endoplasmic reticulum (ER) and mitochondria, mediated by mitochondria-associated membranes (MAMs), is critical for neuronal homeostasis. This study investigates whether disrupted ER-mitochondrial coupling at MAMs, characterized by altered contact distance and area, contributes to early brain injury (EBI) after SAH by facilitating pathological Ca²⁺ transfer via the IP3R1/GRP75/VDAC1 complex. We further explore the therapeutic potential of targeting this complex.

Primary cortical neurons exposed to oxyhemoglobin (OxyHb) and a mouse model of SAH were employed. The dynamic changes in MAM structure (ER-mitochondria distance, contact length), ER stress, and Ca²⁺ handling were assessed. Using shRNA-mediated knockdown and lentiviral overexpression of IP3R1, we evaluated its role in modulating MAM integrity, ER stress markers (p-eIF2α, ATF4, CHOP), Ca²⁺ dynamics, and neuronal apoptosis.

SAH induction led to a significant decrease in ER-mitochondria distance and an increase in MAM contact area, concurrent with upregulation of the IP3R1/GRP75/VDAC1 complex. These changes were associated with elevated ER stress and increased cytosolic and mitochondrial Ca²⁺ levels. Knockdown of IP3R1 rescued the SAH-induced ultrastructural changes at MAMs, attenuated ER stress, and reduced Ca²⁺ overload, thereby decreasing neuronal apoptosis and alleviating neurological deficits. Conversely, IP3R1 overexpression exacerbated these pathological outcomes.

Pathological enhancement of ER-mitochondria coupling via the IP3R1/GRP75/VDAC1 complex is a key driver of Ca²⁺-mediated neuronal apoptosis in EBI after SAH. Targeted downregulation of IP3R1 represents a promising therapeutic strategy to restore MAM homeostasis and mitigate brain injury.