Clair Crewe - OUHSC Graduate College

THE GRADUATE COLLEGE OF THE
UNIVERSITY OF OKLAHOMA HEALTH SCIENCES CENTER
ANNOUNCES THE FINAL EXAMINATION OF
Clair Crewe
FOR THE DEFENSE OF THE DOCTOR OF PHILOSOPHY DEGREE
GRADUATE COLLEGE
DEPARTMENT OF BIOCHEMISTRY AND MOLECULAR BIOLOGY
Tuesday, June 16, 2015
10:00 am Biomedical Research Center, Room 109
Novel Regulatory Mechanisms For Cardiac Pyruvate Dehydrogenase Kinase
4 (PDK4) Expression: Implications For Physiology and Pathophysiology
COMMITTEE IN CHARGE: Luke Szweda, Ph.D., Chair; Christopher West, Ph.D.; Ann
Louise Olson, Ph.D.; Karla Rodgers, Ph.D.; Lorin Olson, Ph.D.
ABSTRACT:
Normal cardiac function depends on the ability to switch between fatty acid and glucose oxidation
for energy production in response to changes in substrate availability and energetic demand. In
obese and diabetic individuals, increased reliance on fatty acid oxidation and reduced metabolic
flexibility are thought to contribute to the development of cardiovascular disease. Mechanisms that
promote metabolic inflexibility were investigated. Within 1 d of supplying mice with a high fat diet,
isolated cardiac mitochondria displayed a diminished ability to utilize the glycolytically derived
substrate pyruvate. The inhibition of pyruvate dehydrogenase (PDH) was found to be responsible.
PDH suppression was the result of a rapid and selective increase in pyruvate dehydrogenase kinase
4 (PDK4) expression. We have shown that diet-induced PDK4 upregulation is responsible for the
observed metabolic inflexibility, drives cardiac insulin resistance and impedes the ability of heart to
respond to an energetic stress. For these reasons, mouse models and a contracting cardiomyocyte
cell line (HL-1) were used to identify the mechanisms that regulate PDK4 expression. We have
discovered that PDK4 protein level is intricately regulated at all levels: transcription, translation and
degradation in response to substrate availability. Of particular interest is the mechanism regulating
its degradation, as it would be a good candidate for drug discovery to selectively manipulate the
cellular content of PDK4 for a therapeutic advantage. We present evidence that PDK4 is remarkably
short-lived, compared to most mitochondrial proteins, with a half-life of ~ 1hr. We have identified
PDK4 as one of few known natively folded substrates of the mitochondrial Lon protease. Moreover,
the metabolic state of the mitochondria regulates the interaction of PDK4 with the PDH complex.
Changes in the PDK4-PDH interaction results in altered accessibility of PDK4 to Lon-mediated
proteolysis, which ultimately regulates the rate of PDK4 degradation. Finally we demonstrate that
this information can be harnessed to pharmacologically promote PDK4 degradation in vitro and in
vivo. Therefore, these novel regulatory mechanisms can be exploited to meet the therapeutic need in
disease conditions where strict reliance on fatty acid oxidation for ATP production has been
implicated in pathology such as obesity-related cardiac dysfunction.