Genetic and Molecular Mechanisms of Heart Disease

PROJECT SUMMARY / ABSTRACT Heart disease is a leading cause of morbidity and mortality, and the incidence of heart failure (HF) is growing, while costing our public healthcare system over $30B per year. HF coincides with significant perturbations in cardiac gene regulation, mitochondrial function, and ion channel expression and activity, and my research program embodies three independent projects related to these pathological processes. For Project #1, our goal is to define microRNA (miR) targeting events and their biological-relevance in heart and to understand the clinical significance of SNPs that alter cardiovascular miR functions. MiRs play key roles in cardiac biology and disease; however, identifying their targets is critical to understanding how. There remains a lack of empirical miR targeting data from primary tissues, and this has slowed the translational impacts of miR research. We address this by employing high-throughput methods to generate global miR-target interactomes in heart tissues. Our hypothesis is that heart disease is influenced by rewired miR-target interactions and SNPs perturbing these interactions. We are filling knowledge gaps regarding the mechanistic targets of cardiac miRs by defining and comparing miR binding sites in nonfailing and diseased human hearts. Our data point to clinically-relevant SNPs that may modulate cardiomyopathy- and arrhythmia-related miR- target interactions, and we functionally test these interactions and determine if SNPs are linked to clinical outcomes in patients. For Project #2, our goals are to better define the function of mitoregulin and establish its role in cardiac ischemia-reperfusion (IR) injury. Upon IR, mitochondrial Ca2+ overload and ROS trigger mitochondrial permeability transition (mPT) pore opening to induce cell death. We previously discovered that a heart/muscle-enriched long “non- coding” RNA encodes a mitochondrial microprotein that increases mitochondrial respiration and Ca2+ retention capacity, while reducing ROS; we named this protein mitoregulin (Mtln). The precise molecular function of Mtln remains unclear, and Mtln’s influence on cardiac stress has not been adequately studied. We are working to address our central hypothesis that 1) Mtln protects against cardiac IR injury by delaying Ca2+- and ROS-triggered mPT and/or by maintaining mitochondrial membrane integrity, and 2) Mtln overexpression (OE) will blunt cardiac IR injury and HF, providing a new therapeutic avenue. For Project #3, our goals are to define regulatory paths controlling SCN5A (encodes the primary cardiac Na+ channel, NaV1.5) and to characterize non-canonical actions of NaV1.5 beyond its known role in conduction. We discovered a SNP that bolsters miR-mediated silencing of SCN5A and associates with lower cardiac NaV1.5 levels, conduction slowing, and increased non-arrhythmic death in HF patients. Our central hypothesis is that lower SCN5A/NaV1.5 expression elevates one’s susceptibility to subclinical cardiac pathologies that transform into significant risk in the setting of HF. We are defining two novel modes of SCN5A/NaV1.5 regulation and examining underappreciated roles for NaV1.5 in cardiomyocyte metabolism and oxidative stress to better understand how lower NaV1.5 could worsen HF. Overall, these projects will advance our mechanistic understanding of heart disease at both the molecular and genetic level, with significant potential to someday improve clinical care.