Activation and Inhibition Mechanisms of Calcium-Activated Nonselective Cation Channels

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Project Summary Ca2+-activated nonselective cation (CAN) channels are among a few ion channels that convert intracellular Ca2+ signaling into changes in membrane potential, in contrast to most ion channels that directly or indirectly use membrane potential to regulate intracellular Ca2+ signaling. This unique property allows CAN channels to play critical roles in many tissues and organs. While the existence of CAN channels has been known for decades, recent evidence has established that monovalent cation-permeable TRPM4 and TRPM5 are the long sought for CAN channels. Indeed, numerous TRPM4 mutations are linked to severe human diseases, e.g., cardiac conduction block, Bragada syndrome, PSEK (a skin disease). Despite their functional significance, little is known about the molecular mechanisms governing TRPM4&5 channels activity. Ca2+ is the only known physiological activator for them, though membrane potential also regulates channel activity but only in the presence of Ca2+. However, while the Ca2+-binding sites have been identified by cryo-EM studies, how Ca2+ and voltage activate TRPM4&5 channels remains unknown. Furthermore, while most known disease-causing TRPM4 mutations lead to a gain-of-function phenotype, no effective inhibitor for TRPM4&5 is currently available. Based on our preliminary functional data on TRPM4 Ca2+ and voltage activation, our discovery of novel TRPM4 mutations causing human skin disease, a new disease-causing mutant channel CRISPR mouse model exhibiting skin phenotypes, and our recent discovery of a novel TRPM4 inhibition process, we plan to use a multidisciplinary approach aiming at revealing the fundamental mechanisms of TRPM4&5 activation and inhibition.