Abstract 264: Beta3 Integrin Promotes Protein Ubiquitination and Prosurvival Signaling in Cardiomyocytes

Abstract

Cardiac hypertrophy occurs in response to stress, such as increased hemodynamic load. Upon hypertrophic stimulus, β3-integrin, a cell surface receptor that mediates nonreceptor tyrosine kinases (NTKs) and mammalian target of rapamycin (mTOR) signaling, undergoes activation. Using β3-integrin global knockout mice, our recent work shows that β3-integrin is required for mTORC2/ubiquitin-mediated prosurvival signaling during early pressure overload (PO). Also, attenuation of β3-integrin signaling during PO causes cardiomyocyte (CM) apoptosis and thus compromised ventricular function. Therefore, we hypothesized that β3-integrin is essential to ubiquitin-mediated prosurvival signaling in CM, with the involvement of key downstream players, such as NTKs, mTOR, E3 ligases, and apoptotic proteins. To generate CM-specific β3-integrin KO mice, cardiac troponin-T2 promoter (cTnT)-driven, reverse tetracycline-dependent transactivator (rtTA)-inducible Cre mice were crossed with β3-integrin-floxed mice. The resulting cTnT-rtTA-Cre/β3-integrin-floxed mice, were administered doxycycline (Dox) at 1 mg/ml for a period of 7 days before transverse aortic constriction (TAC) or Sham surgery. After 72 h PO, protein was isolated from left ventricle tissue and subjected to immunoblotting. Offspring from the above mating have been bred, genotyped and appropriate colonies have been established. PO-induced β3-integrin expression was lost in CM, but not in cardiac fibroblasts of transgenic mice. Furthermore, a robust reduction in protein Ub was also seen in these mice following Dox treatment and PO. Loss of downstream mediators of cardioprotective signaling is being explored in these transgenic mice. In conclusion, we have developed a mouse with CM-specific deletion of β3 integrin. Initial analysis also demonstrates a lack of protein Ub in isolated CM taken from these animals. Further PO studies will identify downstream mediators of β3-integrin essential to survival in cardiomyocytes. The information gained will identify targets and develop novel therapeutic methods to enhance and/or sustain cardioprotection and thereby prevent/delay maladaptive changes in hypertrophying myocardium.