In the past fifty years, great advancements in the diagnosis, treatment and prevention of cardiovascular disease have been made, yet cardiovascular disease remains the leading cause of death in the U.S. Notably, over half of these deaths are associated with arrhythmias. Unfortunately, we still lack a fundamental understanding of the molecular mechanisms underlying complex human arrhythmias. We assert that the study of congenital arrhythmias offers significant and novel insight into pathways underlying familial and acquired forms of cardiovascular disease. Further, combining this clinical and genetic data with targeted animal models, electrophysiology, and molecular approaches provides exciting opportunities to identify fundamental new information linking human disease with specific molecular mechanisms. Our preliminary data support a new molecular mechanism for human arrhythmia based on dysfunction in the cardiac ?II spectrin-based pathway. Specifically, our preliminary findings identify putative loss-of- function variants in the ?II spectrin pathway in patients with Brugada syndrome arrhythmias. Brugada syndrome is a cardiac arrhythmia syndrome which causes potentially fatal ventricular arrhythmias in young adults. It affects 1 in 2,000 adults and often presents with sudden death or syncope. The pathophysiology of Brugada syndrome is thought to be due to the reduced action potential duration, often due to reduced sodium outflow through the cardiac voltage gated sodium channel, Nav1.5. Spectrins are adapter molecules critical for membrane biogenesis, organization, and signaling in neurons and erythrocytes. Recently, we identified two unrelated families with Brugada syndrome, each harboring a missense point mutation in SPTAN1, which encodes ?II spectrin. Notably, both variants have negligible minor allele frequencies and are localized within three residues of each other within the C-terminal EF hand motif, an area essential for ?/? spectrin ternary complex integration with actin. However, the role of ?II spectrin for cardiac excitability is unknown and essentially unstudied, particularly for arrhythmia. Our preliminary findings in arrhythmia patients as well as in a new animal model of cardiac ?II spectrin-deficiency support new and unexpected roles for this molecule in heart. Based on our data, we hypothesize that ?II spectrin is an unanticipated, submembrane ?node? critical for ion channel and cytoskeletal regulation at the intercalated disc. Specifically, we hypothesize that ?II spectrin, through interactions with ?IV spectrin, actin, and ankyrin-G, facilitates the proper organization and function of the intercalated disc and the localization of the sodium channel Nav1.5. Further, we predict that dysfunction in the ?II spectrin pathway results in severe electrical and structural phenotypes. We anticipate that these findings will uncover novel fundamental pathways governing excitable cell biology.

Public Health Relevance

Heart disease is the number one killer of Americans. The proposed research will define a role of ?II spectrin in the heart and will determine the mechanism by which variants in ?II spectrin can cause deadly heart disease. Findings from the proposed work will further our understanding of basic cardiac function and of potentially fatal arrhythmogenesis, providing avenues for future therapeutic targets.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Individual Predoctoral NRSA for M.D./Ph.D. Fellowships (ADAMHA) (F30)
Project #
5F30HL137331-04
Application #
9967088
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Meadows, Tawanna
Project Start
2017-07-01
Project End
2022-06-30
Budget Start
2020-07-01
Budget End
2021-06-30
Support Year
4
Fiscal Year
2020
Total Cost
Indirect Cost
Name
Ohio State University
Department
Physiology
Type
Schools of Medicine
DUNS #
832127323
City
Columbus
State
OH
Country
United States
Zip Code
43210
Makara, Michael A; Curran, Jerry; Lubbers, Ellen R et al. (2018) Novel Mechanistic Roles for Ankyrin-G in Cardiac Remodeling and Heart Failure. JACC Basic Transl Sci 3:675-689
Murphy, Nathaniel P; Lubbers, Ellen R; Mohler, Peter J (2017) Advancements in the use of gene therapy for cardiac arrhythmia. Heart Rhythm 14:1061-1062