Abstract 16959: Cardiac Grb2-associated Binder 1 Deficiency Causes Dilated Cardiomyopathy and Heart Failure Due to Severe Mitochondrial Damage and Cardiomyocyte Apoptosis

Abstract

Background: Receptor tyrosine kinase (RTK) inhibitors as novel anticancer therapy are associated with clinical heart failure. Better understanding molecular mechanisms underlying such a side effect may provide new strategies to prevent RTK inhibitors-induced heart failure. Grb2-associated binder 1 (Gab1), a member of the docking protein family, is a central mediator for RTK signaling. We hypothesized that the deletion of Gab1 causes dilated cardiomyopathy and heart failure. Methods and Results: Using alpha-MHC-Cre mice and Gab1 loxp mice, we generated cardiac-specific Gab1 knockout (Gab1-cKO) mice. Gab1-cKO mice were viable and born at the expected Mendelian ratio. With echocardiography, hemodynamic measurements and histological analysis, we found that cardiac Gab1 deficiency in mice caused progressive dilated cardiomyopathy and heart failure. At age 3-6 months, ejection fraction and dp/dt max in Gab1-cKO mice were considerably lower than those in Gab1 wild-type littermates. Moreover, under mechanical stress via transverse aortic constriction at young age (around 6 weeks) before onset of heart failure, Gab1-cKO mice suffered more severe dilated cardiomyopathy and induced lethality. The deletion of Gab1 in heart during adulthood by crossing Gab1-loxp mice with tamaxifen-inducible alpha-MHC-Cre mice also resulted in cardiac dysfunction and heart failure. Mechanistically, we observed loss of mitochondrial membrane potential and increase of cardiomyocyte apoptosis in Gab1-cKO heart. Transmission electronic microscopy studies showed frequent damaged mitochondria with cristae lysis and apparent abnormal internal membrane whorls in Gab1-cKO heart. Signaling studies revealed that proapoptotic genes including p38 and caspase 3 were overly activated in Gab1-cKO heart. Gene array and quantitative PCR analysis showed that antiapoptotic genes such as Bcl2 were downregulated, whereas proapopotic genes such Bnip3 were upregulated in Gab1-cKO heart. Conclusion: Gab1 is a crucial regulator of cardiac function through maintaining mitochondrial integrity and cell survival, suggesting that the preservation of Gab1 signaling could be one of therapeutic strategies to prevent heart failure induced by anticancer RTK inhibitors.