ABL Presented at EB2011
Acute rapamycin administration controls ubiquitination and enhanced Akt activation in pressure-induced cardiac hypertrophy in rats
Rebecca K. Harston1,3, Phillip C. Moschella1, Sundaravadivel Balasubramanian1, Catalin F. Baicu1, Michael R. Zile1,2 and Dhandapani Kuppuswamy1,2
From the 1Cardiology Division of the Department of Medicine, Gazes Cardiac Research Institute, Medical University of South Carolina, and the 2Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC 29425, 3Advanced BioScience Laboratories, Inc., Rockville, Maryland 20850
Ubiquitin-mediated proteasomal degradation is necessary for increased ventricular mass induced by pressure overload hypertrophy and activates survival signaling required for compensated hypertrophic growth. Another molecular keystone regulating both growth and survival pathways is the mammalian target of rapamycin (mTOR). mTOR forms two complexes: mTORC1 activates S6K1 to enhance protein synthesis and mTORC2 activates Akt to promote survival. Inhibition of mTORC1 genetically or pharmacologically via rapamycin inhibits growth and increases lifespan in invertebrates. Recently, rapamycin administration in both young and old mice was shown to increase lifespan by an unknown mechanism. Here we tested whether the ubiquitin-mediated regulation of growth and survival in hypertrophic myocardium is linked to the mTOR pathway. For in vivo studies, right ventricle pressure overload (RVPO) in rats was conducted by pulmonary artery banding, so the normally loaded LV served as an internal control. Rapamycin (0.75 mg/kg/day i.p.) or vehicle alone was administered for 3 days, and the level of ubiquitinated proteins was shown to increase via immunoblot and immunofluorescence imaging following 48 h PO. Rapamycin pretreatment significantly increased the PO-induced mTORC2 induction of S473 phosphorylation of Akt, and this molecular mechanism was confirmed by immunoprecipitation experiments in cardiomyocyte culture. Analysis of prosurvival signaling showed rapamycin increased PO-induced degradation of phosphorylated inhibitor of kB (IkB), enhanced expression of cellular inhibitor of apoptosis (cIAP1) and elimination of active caspase-3. This is the first study to show rapamycin may enhance survival signaling downstream of mTORC2 in mammals during PO cardiac hypertrophy.
