Date of Graduation
5-2012
Document Type
Dissertation (PhD)
Program Affiliation
Cell and Regulatory Biology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Heinrich Taegtmeyer, M.D., D.Phil.
Committee Member
Joseph L. Alcorn, Ph.D.
Committee Member
Yi-Ping Li, Ph.D.
Committee Member
Gary D. Lopaschuk, Ph.D.
Committee Member
Ali J. Marian, M.D.
Committee Member
William E. Mitch, M.D.
Abstract
The degradation of proteins by the ubiquitin proteasome system is essential for cellular homeostasis in the heart. An important regulator of metabolic homeostasis is AMP-activated protein kinase (AMPK). During nutrient deprivation, AMPK is activated and intracellular proteolysis is enhanced through the ubiquitin proteasome system (UPS). Whether AMPK plays a role in protein degradation through the UPS in the heart is not known. Here I present data in support of the hypothesis that AMPK transcriptionally regulates key players in the UPS, which, under extreme conditions can be detrimental to the heart. The ubiquitin ligases MAFbx /Atrogin-1 and MuRF1, key regulators of protein degradation, and AMPK activity are increased during nutrient deprivation. Pharmacologic and genetic activation of AMPK is sufficient for the induction of MAFbx/Atrogin-1 and MuRF1 in cardiomyocytes and in the heart in vivo. Comprehensive experiments demonstrate that the molecular mechanism by which AMPK regulates MuRF1 expression is through the transcription factor myocyte enhancer factor 2 (MEF2), which is involved in stress response and cardiomyocyte remodeling. MuRF1 is required for AMPK-mediated protein degradation through the UPS in cardiomyocytes. Consequently, the absence of MuRF1 during chronic fasting preserves cardiac function, possibly by limiting degradation of critical metabolic enzymes. Furthermore, during cardiac hypertrophy, chronic activation of AMPK also leads to cardiac dysfunction, possibly through enhanced protein degradation and metabolic dysregulation. Collectively, my findings demonstrate that AMPK regulates expression of ubiquitin ligases which are required for UPS-mediated protein degradation in the heart. Based on these results, I propose that specific metabolic signals may serve as modulators of intracellular protein degradation in the heart.
Keywords
AMP-Activated Protein Kinase, Protein Degradation, Ubiquitin Proteasome System, Ubiquitin ligases, MAFbx/Atrogin-1, MuRF1, Cardiac Hypertrophy, Heart failure, Nutrient Stress, Cardiac metabolism
Included in
Biochemical Phenomena, Metabolism, and Nutrition Commons, Cardiology Commons, Cardiovascular Diseases Commons, Cardiovascular System Commons, Cell Biology Commons, Endocrinology, Diabetes, and Metabolism Commons, Molecular Biology Commons