Ankyrin Dependent Mitochondrial Function And Bioenergetics In The Heart

Author

Janani SubramaniamFollow
Janani SubramaniamFollow

Author ORCID Identifier

0000-0002-0533-7687

Date of Graduation

12-2022

Document Type

Dissertation (PhD)

Program Affiliation

Cell and Regulatory Biology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Dr. Shane Cunha

Committee Member

Dr. Carmen Dessauer

Committee Member

Dr. Kartik Venkatachalam

Committee Member

Dr. Rebecca Berdeaux

Committee Member

Dr. Kristin Eckel-Mahan

Committee Member

Dr. Pierre McCrea

Abstract

ANK2 mutations in patients are associated with numerous arrhythmias, cardiomyopathies, and other heart defects. In the heart, AnkB, the protein encoded by ANK2, clusters relevant ion channels and cell adhesion molecules in several important domains; however, its role at Mitochondria Associated ER/SR Membranes (MAMs) has yet to be investigated. MAMs are crucial to mitochondrial function and metabolism and are signaling hubs implicated in various cardiac pathologies. Among several functions, these sites mediate the direct transfer of calcium from the ER/SR to the mitochondria to modulate ATP synthesis. Given that mitochondrial function and energy production are paramount to cardiovascular heath, the work in this thesis explores the role of AnkB in recruiting and tethering wolframin (Wfs-1), a novel ankyrin binding protein along with Inositol Triphosphate Receptor (IP₃R), Sigma1-R (Sig1R), and Voltage Dependent Anion Channel (VDAC) at MAMs to constitute a Ca²⁺ signaling domain.

Through a series of cellular fractionation, co-immunoprecipitation, functional assays, and fluorometry, we evaluated AnkB dependent protein complex formation at MAMs and the energetic implications of decreased AnkB in the heart. We found that 3-month-old AnkB^+/- mice display lowered cardiac performance along with trends toward cardiac remodeling. Further, we are first to report AnkB expression at MAMs, where it colocalizes with and co-immunoprecipitates Ca²⁺ regulating proteins including IP₃R, Sig1R, Wfs-1, and VDAC. Reduction in AnkB leads to elevated cardiac mitochondrial Ca²⁺ levels with a host of metabolic implications including increased oxygen consumption through the electron transport chain (ETC), overproduction of reactive oxygen species (ROS), decreased mitochondrial membrane potential (MMP), and inefficient oxidative phosphorylation (OXPHOS)/ATP production. Altogether, these results further elucidate the role of AnkB in the heart and provide novel insights into the mitochondrial aspect of AnkB related cardiac dysfunction.

Keywords

ankyrin, calcium, mitochondria, metabolism, heart disease