Modulation of Sarcomere Function via Seven-Transmembrane Receptor Signaling to Ameliorate Cardiomyopathy

Work presented in this thesis describes efforts to investigate mechanisms of improving cardiac function via cellular signaling downstream of seven-transmembrane receptors (7TMRs), also known as G-protein coupled receptors. In the cardiomyocyte, agonism of 7TMRs can have a profound functional effect. This can be mediated through multiple mechanisms, such as altering the post-translational modification status or expression of proteins involved in calcium homeostasis or sarcomere and sarcomere-associated proteins. Because alterations in myofilament-Ca-responsiveness are commonly seen in cardiomyopathy, we hypothesized that normalizing the myofilament-Ca-response via 7TMRs might ameliorate disease. A dilated cardiomyopathy–linked mouse model expressing a mutant tropomyosin (Tm-E54K) was studied using an angiotensin II type 1 receptor (AT1R) antagonist, losartan, and a novel compound, TRV120067, able to selectively engage beta-arrestin 2 signaling pathways downstream of the AT1R. TRV120067-treated Tm-E54K mice showed improved cardiac structure and function, whereas losartan-treated mice had no improvement. Myofilaments of TRV120067-treated Tm-E54K mice had significantly improved myofilament-Ca-responsiveness, which was depressed in untreated Tm-E54K mice. We attributed these functional changes observed in Tm-E54K mice treated with TRV120067 to increased myosin light chain phosphorylation. In a second line of experiments we employed a hypertrophic cardiomyopathy–linked mouse model expressing a mutant tropomyosin (Tm-E180G) and investigated the impact of sphingosine-1-phosphate receptor (S1PR) signaling on cardiac function and structure. We found that S1PR modulation with the immunomodulatory drug, FTY720, has profound effects on cardiac hypertrophy and improved diastolic function in the Tm-E180G mice. We attributed the functional effects to modification of the cross-bridge kinetic due to reversal of oxidative modification of cardiac myosin-binding protein C. These data suggest that modulating novel signaling pathways via 7TMRs to target sarcomere function may be promising therapeutic approach for the treatment of cardiomyopathy and heart failure.