Abstract P1086: Lrrc10 Is A Multifaceted Modulator Of Cardiac Calcium And Sodium Channels

Abstract

L-type calcium channels (LTCC) are vital for heart physiology as they allow entry of calcium to the cardiomyocyte, ultimately leading to contraction. These channels are exquisitely modulated by auxiliary subunits and a vast array of regulatory proteins. Heart-specific leucine-rich repeat-containing protein 10 (Lrrc10) plays a key role as a regulator of LTCC. Previous work has shown that Lrrc10 knockdown in zebrafish disrupts development of the cardiac tube, while ablation of Lrrc10 in mice results in heart dysfunction and maladaptation to increased cardiac afterload. Moreover, human mutations in Lrrc10 gene have been linked to dilated cardiomyopathy, and sudden unexplained nocturnal death syndrome (SUNDS). Still, the molecular mechanisms underlying Lrrc10 regulation of LTCC is not fully established. Beyond this, it is unknown whether Lrrc10 modulates other cardiac ion channels. Here, we hypothesized that Lrrc10 serves as a versatile regulator of four-domain voltage-gated ion channels, while mutations in Lrrc10 differentially disrupt channel regulation. Using whole-cell and single-channel electrophysiology, we found that Lrrc10: 1) upregulates LTCC currents by increasing peak open probability; 2) accelerates calcium-dependent inactivation; and 3) evokes a hyperpolarizing-shift in voltage-dependence of activation. Flow cytometric FRET 2-hybrid assay showed that Lrrc10 interacts with LTCC cytoplasmic subunits, specifically the N- and C-termini. We further used FRET 2-hybrid analysis to evaluate the interaction of Lrrc10 with related cardiac ion channels. We observed robust Lrrc10 interaction with Na V 1.5 channels. Multi-channel electrophysiology recordings revealed increased late sodium currents, suggesting that Lrrc10 also modulates Na V 1.5 activity. Additionally, electrophysiological studies showed that Lrrc10 variants linked to dilated cardiomyopathy and SUNDS disparately alter modulation of calcium and sodium channels. In conclusion, Lrrc10 is a multifaceted regulator of four-domain, voltage-gated cardiac ion channels, a finding that will lend critical insights into heart function and disease.