Ca²⁺entry via Trpm2 is essential for cardiac myocyte bioenergetics maintenance

Abstract

Five days post-injection, gKO-GFP heart slices had higher reactive oxygen species (ROS) levels but lower oxygen consumption rate (OCR) than WT-GFP heart slices. Trpm2 but not E960D decreased ROS and restored OCR in gKO hearts back to normal levels. In gKO myocytes expressing Trpm2 or its mutants, Trpm2 but not E960D reduced the elevated mitochondrial superoxide (O 2 .Ϫ ) levels in gKO myocytes. After hypoxia-reoxygenation (H/R), Trpm2 but not E906D or P1018L (inactivates Trpm2 current) lowered O 2 .Ϫ levels in gKO myocytes and only in the presence of extracellular Ca 2ϩ , indicating sustained Ca 2ϩ entry is necessary for Trpm2-mediated preservation of mitochondrial function. After ischemic-reperfusion (I/R), cardiac-specific Trpm2 KO hearts exhibited lower maximal first time derivative of LV pressure rise (ϩdP/dt) than WT hearts in vivo. After doxorubicin treatment, Trpm2 KO mice had worse survival and lower ϩdP/dt. We conclude 1) cardiac Trpm2-mediated Ca 2ϩ influx is necessary to maintain mitochondrial function and protect against H/R injury; 2) Ca 2ϩ influx via cardiac Trpm2 confers protection against H/R and I/R injury by reducing mitochondrial oxidants; and 3) Trpm2 confers protection in doxorubicin cardiomyopathy. ischemic cardiomyopathy; doxorubicin cardiomyopathy; voltage-independent Ca 2ϩ channels; cardiac Trpm2 currents; mitochondrial superoxide; hypoxia-reoxygenation IN MAMMALIAN CELLS, THE TRANSIENT receptor potential (Trp) protein superfamily is a diverse group of voltage-independent, cation-permeable channels organized into six subfamilies based on amino acid sequence homology (9, 30). Monomeric Trp proteins have six putative transmembrane (TM) domains and intracellular NH 2 and COOH termini. To form a functional channel, Trp proteins assemble into either homo-or heterotetramers, with the putative pore formed by loops between the fifth and sixth TM domains (21, 23). The Trp-melastatin (Trpm) subfamily consists of eight mammalian members (Trpm1-Trpm8)(30), of which Trpm2 (27), -m4, -m5, and -m6 (49) are expressed in the heart. Although Trpm4 is associated with conduction abnormalities and cardiac arrhythmias (1, 36), there is little information on the physiological and pathophysiological function of Trpm2 in the heart.

Mitochondrial calcium overload is a key determinant in heart failure

“…S3 L and M), consistent with previous observations in failing human hearts (6). Further studies are needed to investigate in detail other systems, including neurohormonal and (epi)genetic mechanisms, endoplasmic reticulum (ER) stress, necrosis/apoptosis, and autophagy, that might participate in the regulation of bioenergetic homeostasis in HF (5,6,19,25,29).…”

“…Albeit Ca 2+ is required for activation of key enzymes (i.e., pyruvate dehydrogenase phosphatase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase) in the tricarboxylic acid (also known as Krebs) cycle (18,19), excessive mitochondrial Ca 2+ uptake has been associated with cellular dysfunction (14,20). Furthermore, the exact source of mitochondrial Ca 2+ has not been clearly established.…”

Depletion of the Human Ion Channel TRPM2 in Neuroblastoma Demonstrates Its Key Role in Cell Survival through Modulation of Mitochondrial Reactive Oxygen Species and Bioenergetics

“…The E960D construct was previously generated by our laboratory and the loss of function has been authenticated (38,45). Expression of wild type TRPM2 but not E960D in the KO reconstituted cell viability at or close to the level observed in the scrambled control (Fig.…”

Trpm2 enhances physiological bioenergetics and protects against pathological oxidative cardiac injury: Role of Pyk2 phosphorylation

“…Total Pyk2/CLSQ in cKO was significantly higher ( # p = 0.0020) than WT myocytes. BAPTA: 1,2-bis (2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid; KO: knockout; LV: left ventricular; Pyk2: proline-rich tyrosine kinase 2; WT: wild type cardiac dysfunction and prolonged survival of animals treated with doxorubicin (Hoffman et al, 2015). Finally, the recent observation that S. J.…”

“…3.5 | Loss of Trpm2 results in less pPyk2 and its downstream prosurvival signaling targets after ischemia/reperfusion injury In the heart, both ROS (Hoffman et al, 2015;Miller et al, 2013;Miller et al, 2014;Tsutsui, Kinugawa, & Matsushima, 2011) and cyclic ADPR (cADPR; Xie et al, 2003) production are increased after I/R. Since both ROS and cADPR can activate Trpm2, we measure pPyk2 and Pyk2 in WT and cKO hearts subjected to sham operation or I/R injury.…”