The Sphingosine-1-Phosphate Receptor Modulator, FTY720, Reverses Diastolic Dysfunction and Hypertrophy in Hypertrophic Cardiomyopathy

Abstract

Background: Hypertrophic cardiomyopathy (HCM) patients present with progressively worsening hypertrophy, diastolic dysfunction and fibrosis, ending in heart failure with preserved ejection fraction. At the molecular level, a common pathology found is an increase in myofilament-calcium (Ca) sensitivity. Previously, we have shown that oxidative modification of myofilament proteins, as a result of increased oxidative stress in HCM, may be a direct mediator of this increase. FTY720 is an immunomodulating drug, clinically used in the treatment of multiple sclerosis, which we have previously identified to have anti-fibrotic and anti-hypertrophic effects in a model of pressure-overload-induced hypertrophy. We sought to understand whether agonism of the sphingosine-1-phosphate receptor by FTY720 would be of therapeutic benefit in HCM, and its effects on oxidative modification. Methods: We treated an HCM mouse model linked to a mutation in tropomyosin (Tm-E180G) and non-transgenic (NTG) littermates with FTY720 or vehicle for six weeks. We assessed cardiac function and morphology using echocardiography and pressure-volume (PV) relations and the myofilament-Ca-response using detergent-treated (skinned) fibers. We also investigated if signaling pathways were altered. Results: We found that FTY720-treated Tm-E180G mice had a significant reduction in left atrial size, E/A and E/Em ratios compared to significantly increased baseline measurements as assessed by echocardiography. PV relations revealed significant improvements in the end- diastolic pressure volume relationship, preload recruitable stroke work, and relaxation constant (Tau). FTY720-treated NTG mice displayed a significant decrease in ejection fraction and rate of maximum pressure development in early systole compared to vehicle-treated NTG mice assessed by PV relations. Skinned fiber bundlesrevealed a significant decrease in myofilament- Ca-responsiveness in FTY720-treated Tm-E180G mice. We attributed these functional improvements to a down-regulation of S-glutathionylation of cardiac myosin binding protein-C in FTY720-treated Tm-E180G mice. The increases in oxidative modification in vehicle treated Tm- E180G mice were due to an up-regulation of NADPH oxidase 2 enzyme expression (NOX2). We attributed the and fibrosis and hypertrophy to increased periostin, TGF-beta expression, and GATA4 phosphorylation respectively. These maladaptive changes were reversed by FTY720 treatment. Conclusions: In Tm-E180G mice, FTY720 improves diastolic function and morphology by reversing oxidative modification of myofilament proteins, resulting in a decrease in myofilament- Ca-responsiveness, via down-regulation of NOX2 and other maladaptive remodeling signals.