Pannexin 2 restrains ER stress-induced Ca2+ dysregulation and inflammatory cardiomyocyte death

Abstract

BackgroundEndoplasmic reticulum (ER) stress and ER-mitochondria Ca2+ dysregulation contribute to cardiomyocyte injury, yet endogenous regulators at ER-mitochondria interfaces that restrain this cascade remain poorly defined. Pannexin 2 (Panx2), the most structurally divergent pannexin isoform, has been implicated in stress response, but its cardiac localization and function are unclear. MethodsPanx2 localization and function were assessed in human AC16 cardiomyocytes using high-resolution confocal imaging and complementary loss- and gain-of-function approaches during thapsigargin-induced ER stress, with validation in adult mouse ventricular cardiomyocytes. ResultsPanx2 localizes predominantly to the ER and mitochondria-associated membranes, rather than the plasma membrane. Panx2 knockdown reduced ER Ca2+ stores and increased basal cytosolic and mitochondrial Ca2+. During ER stress, Panx2 deficiency markedly amplified Ca2+ dysregulation, mitochondrial dysfunction, unfolded protein response activation, and cytotoxicity, with PERK-dominant signaling and increased IRE1a activation. Notably, PERK inhibition preferentially rescued the Panx2-deficient phenotype, providing the greatest improvement in viability and reduction in cytotoxicity. Panx2 deficiency also enhanced inflammasome/ pyroptotic signaling via the NLRP3-caspase-1-gasdermin D axis. Conversely, Panx2 overexpression suppressed PERK activation and attenuated ER stress-induced injury. Panx2 ablation similarly sensitizes adult ventricular cardiomyocytes to ER stress. ConclusionsPanx2 functions as an organelle-associated checkpoint at ER-mitochondria interfaces that stabilizes Ca2+ homeostasis and limits PERK-dominant ER stress signaling and inflammatory cell death programs in cardiomyocytes, providing a mechanistic framework for cardiomyocyte loss in cardiac disease. Research PerspectiveO_ST_ABS1. What New Question Does This Study Raise?C_ST_ABSDoes Panx2 serve as an endogenous "stress threshold" determinant in cardiomyocytes in vivo, governing when ER stress transitions from adaptive signaling to PERK-driven mitochondrial failure and inflammasome-associated inflammatory cell death during cardiac injury (e.g., ischemia-reperfusion, pressure overload, or cardiometabolic stress)? 2. What Question Should Be Addressed Next?In clinically relevant models of heart disease (ischemia-reperfusion), test whether cardiomyocyte-specific Panx2 loss or augmentation alters infarct size, arrhythmia burden, ventricular remodeling, and functional recovery, and determine whether targeting the Panx2-PERK axis (e.g., selective PERK modulation in the acute reperfusion window or Panx2-directed strategies) reduces cardiomyocyte loss without impairing adaptive stress signaling needed for repair.