The Effects of Growth Differentiation Factor 11 on Pathological Cardiac Hypertrophy

Abstract

Pathological cardiac hypertrophy (PCH) occurs in response to pathological stimuli affecting the heart such as coronary artery disease, myocardial infarction, or hypertension. PCH is also be independent risk factor for cardiac events and/or sudden death. Despite therapeutic advancements in the treatment of cardiovascular diseases (CVD) and heart failure, deaths due to CVD remain the leading cause of mortality worldwide. Furthermore, treatment of these cardiovascular diseases slows their progression, but individuals eventually progress to heart failure, which has a 5-year survival rate of approximately 50 percent. There is a clear need for development of new therapies that can reverse PCH and the associated damage to the heart. As healthcare improves, populations are living longer, and illness due to age increases. One issue that occurs with aging is loss of normal cardiac function leading to heart failure. This functional decline is accompanied by morphological changes in the heart, including hypertrophy. Although it is well documented that myocardial remodeling occurs with aging, the mechanisms underlying these changes are poorly understood. Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor β (TGF-β) superfamily of proteins, which regulate a number of cellular processes. Shared circulation of a young mouse with an old mouse or a single daily intraperitoneal (IP) injection of GDF11 for 30 days was shown to reverse aging-induced pathological cardiac hypertrophy. This molecule is highly homologous with another TGF-β family member, myostatin, which is a known negative growth regulator of skeletal muscle. We began by attempting to validate published data claiming that a single daily intraperitoneal (IP) injection of 0.1 mg/kg/day of GDF11 could reverse aging induced cardiac hypertrophy. We performed a blinded study during which treated 24-month-old C57BL/6 male mice with a single IP injection of 0.1 mg/kg/day of GDF11for 28 days and monitored changes in cardiac function and structure using echocardiography (ECHO). We also looked for differences in fibrosis, myocyte size, markers of pathological hypertrophy and heart weight. We were unable to find any differences between vehicle treated age mice and GDF11 treated aged mice in any of the measured parameters. While we did find an increase in heart weight between 8-week-old mice and the 24-month-old mice, there was no difference in the heart weight to body weight ratios of these groups of animals. From these data we concluded that our aged- mice did not have pathological hypertrophy and the dose of GDF11 used in this study did not have any effect on cardiac structure or function. Hypertensive heart disease results in changes in cardiac structure and function including left ventricular hypertrophy, systolic and/or diastolic dysfunction. It is also a leading cause of heart failure. Members of the TGF-β superfamily of proteins have been shown to be involved in many of the processes that occur in the heart in response to hypertension, such as the fibrotic response. Although it was previously shown that treatment with 0.1 mg/kg of GDF11 did not prevent pressure overload induced cardiac hypertrophy, we found this dose was too low to alter cardiac structure in our aging study. In addition, a single GDF11 dose is insufficient to fully address this issue. We therefore performed a blinded dose-ranging study to investigate the effects of GDF11 on pressure overload induced cardiac hypertrophy using transverse aortic constriction (TAC) which mimics the effects of chronic hypertension on the heart. In this study, animals received TAC surgery and were assigned to treatment groups so that there were no differences in wall thickness, cardiac function, or pressure gradients across the aortic constriction at the start of the treatments 1 week after TAC. Mice were given 0.5 mg/kg/day of GDF11, 1.0 mg/kg/day GDF11, 5.0 mg/kg/day of GDF11, or vehicle via a single daily IP injection for 14 days. Using these higher doses, we found that GDF11 had dose dependent effects on both cardiac structure and function following TAC. Myocyte cross sectional area was dose-dependently decreased compared to vehicle treated mice in both sham and TAC conditions. Cardiac function was preserved in the 1.0 and 5.0 mg/kg groups treatment groups after TAC. Left ventricular internal chamber dimensions were preserved with the 1.0 mg/kg treatment group. Treatment with GDF11 caused a dose dependent decrease on both body weight and heart weight in both normal and TAC mice, but with an effect on heart weight in the TAC mice that was independent of body weight. However, the 5.0 mg/kg dose caused large reductions in body weight (cachexia) and death. Our results show that GDF11 can reduce pathological hypertrophy and cardiac remodeling after pressure overload, but there is a narrow therapeutic range.