Abstract 3212: A Cardioprotective Role for the E3 Ubiquitin Ligase CHIP During Cardiac Hypertrophy Through a Novel Mechanism of AMPK Regulation
Mechanisms facilitating protein folding, degradation, and post-translational modifications play an integral role in maintaining protein quality control and function. CHIP contributes to all of these processes through its ability to directly ubiquitinate proteins and its interaction with cellular chaperones. Pathologic cardiac hypertrophy is a dynamic process involving cellular remodeling and metabolic changes in response to stimuli such as pressure overload. Using mice lacking expression of CHIP, we tested the role of this gene in the adaptive response to pressure overload using trans aortic banding (TAB). One week of TAB resulted in pronounced hypertrophy (2-fold increase in heart: body weight) and a 30±3% decrease in fractional shortening determined by echocardiography in CHIP−/− mice compared to sham operated CHIP −/− and wild-type (WT) animals. Histological analysis of banded CHIP−/− heart sections demonstrated increased fibrosis and accumulation of intracellular neutral lipids, suggesting an altered metabolic response to TAB. Consistent with this hypothesis, banded CHIP−/− mice had a 48±4% and 39±5% decrease in mRNA and protein levels, respectively, of the metabolic transcriptional co-activator PGC-1alpha compared to banded WT mice. PGC-1alpha expression is sufficient to promote cardiac mitochondrial biogenesis; likewise, compared to banded WT mice, banded CHIP−/− mice had both a 43±10% decrease in mitochondrial biogenesis and a 49±2% and 61±7% decrease in steady-state ATP levels and ex vivo rates of ATP generation, respectively. Upstream of PGC-1alpha regulation is the energy-sensing kinase AMPK, activated in conditions where energy is needed triggered by a decrease in ATP and increase in AMP. Despite the deficit in ATP generation, there was an 40±4% decrease in the active form of AMPK, a 47±6% decrease in AMPK activity, and decreased phosphorylation of AMPK substrates ACC and eNOS in banded CHIP−/− hearts compared to WT animals. In cell culture models, CHIP is necessary and sufficient for AMPK activation and mono-ubiquitinates the AMPKalpha subunit in vitro. These data demonstrate for the first time the mono-ubiquitination of AMPK and the vital role of CHIP in cardiac hypertrophy and energy homeostasis.
This research has received full or partial funding support from the American Heart Association, Mid-Atlantic Affiliate (Maryland, North Carolina, South Carolina, Virginia & Washington, DC).