The Role of End-Binding Protein 2 and Microtubule Network in Inherited Cardiac Arrhythmias

/ ABSTRACT Inherited cardiac arrhythmias are a significant and devastating cause of sudden cardiac death (SCD) both in the US and globally. One prominent example is Brugada syndrome (BrS), which is a significant cause of SCD in young patients, typically with structurally normal hearts. The first BrS-associated gene, SCN5A, which encodes the cardiac sodium channel NaV1.5, was reported in 1998 and since then several other ion channel genes and their interactors have been implicated. Despite these advances, only ~30% of BrS cases have a known variant in one of these genes, leaving the remaining ~70% genetically undiagnosed. Recently, our collaboration conducted the largest BrS genome-wide association study (GWAS) to date, which identified 9 novel genetic loci. At one locus, MAPRE2, which encodes the microtubule plus end-binding protein 2 (EB2), emerged as one of the top candidates based on bioinformatic analyses. My preliminary data using both a mapre2 null (KO) and N- terminus truncated mutant (ΔN-EB2) support the role of MAPRE2 as a novel gene contributing to BrS. Specifically, mapre2 loss-of-function leads to decreased NaV function both in the embryonic and adult ventricular myocytes, a hallmark of BrS, as well as general sarcomeric disarray and microtubule network disorganization. Furthermore, MAPRE2 may interact genetically with HEY2, a well-known cardiovascular developmental gene which has been strongly implicated in BrS. Finally, RNA-sequencing implicates the Wnt pathway in mapre2 loss- of-function and treatment with SB216763, a GSK3β inhibitor and activator of Wnt, rescues ECG abnormalities in adult mapre2 mutant fish. These and other evidence led me to hypothesize that MAPRE2 loss-of-function leads to trafficking and subcellular localization defects of NaV1.5 and associated proteins, and more generally disrupts the microtubule network and cytoskeleton, contributing to cardiac arrhythmogenesis. During the K99 phase, I will explore MAPRE2 as a novel gene contributing to BrS and define its pathogenesis, paying special attention to its unique 43 aa N-terminus which is absent in the other family members (EB1 and EB3). During the R00 phase, I will study HEY2’s gene-gene interaction with MAPRE2 and SCN5A in the context of BrS and NaV1.5 dysfunction. I will also define more broadly the role of EB2 and microtubule network in cardiac Wnt signaling and arrhythmogenesis including carrying out a phenotypic chemical screen using zebrafish embryos based on in vivo Wnt/β-catenin activity, explore GSK3β inhibition as a novel therapeutic avenue for BrS and related arrhythmias, and study genetic interaction between MAPRE2 with an established arrhythmogenic cardiomyopathy mutant. Together, this proposal will allow me to fulfill my short-term goal of gaining skills and expertise in cardiac genetics and zebrafish research, as well as build novel tools and genetic models during the K99 phase. This will enable me to pursue my long-term objective during the R00 phase and beyond: to define a paradigm shift in our understanding of inherited cardiac arrhythmias and discover novel therapeutics useful in treating BrS and related NaV arrhythmias. Project Number: 4R00HL161472-03 | Fiscal Year: 2025 | NIH Institute/Center: National Heart Lung and Blood Institute (NHLBI) | Principal Investigator: David Chiang | Institution: BRIGHAM AND WOMEN'S HOSPITAL, BOSTON, MA | Award Amount: $248,363 | Activity Code: R00 | Study Section: NSS View on NIH RePORTER: https://reporter.nih.gov/project-details/4R00HL16147203