ROCK1 plays an essential role in the transition from cardiac hypertrophy to failure in mice

Abstract

Pathological cardiac hypertrophy caused by diverse etiologies eventually leads to cardiac dilation and functional decompensation. We have recently reported that genetic deletion of Rho-associated coiled-coil containing protein kinase 1 (ROCK1) inhibited several pathological events including cardiomyocyte apoptosis in compensated hypertrophic hearts. The present study investigated whether ROCK1 deficiency can prevent the transition from hypertrophy to heart failure. Transgenic mice with cardiac-restricted overexpression of Gαq develop compensated cardiac hypertrophy at young ages, but progress into lethal cardiomyopathy accompanied by increased apoptosis after pregnancy or at old ages. The studies were first carried out using age- and pregnancy-matched wild-type, Gαq, ROCK1^−/−, and Gαq/ROCK1^−/− mice. The potent beneficial effect of ROCK1 deletion is demonstrated by abolishment of peripartum mortality, and significant attenuation of left ventricular (LV) dilation, wall thinning, and contractile dysfunction in the peripartum Gαq transgenic mice. Increase in cardiomyocyte apoptosis was suppressed by ROCK1 deletion, associated with increased extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) activation and inhibition of mitochondrial translocation of Bax. In addition, ROCK1 deficiency also improved survival, inhibited cardiomyocyte apoptosis, and preserved LV dimension and function in old Gαq mice at 12 months. Furthermore, transgenic overexpression of ROCK1 increased cardiomyocyte apoptosis and accelerated hypertrophic decompensation in Gαq hearts in the absence of pregnancy stress. The present study provides for the first time in vivo evidence for the long-term beneficial effects of ROCK1 deficiency in hypertrophic decompensation and suggests that ROCK1 may be an attractive therapeutic target to limit heart failure progression.

Introduction

Heart failure is a leading cause for human morbidity and mortality, and the incidence of heart failure has been constantly increasing during the past decades. Cardiac hypertrophy is initially a compensatory response to diverse etiologies, but it eventually leads to heart failure or sudden death due to decompensation [1], [2], [3]. Identifying the signaling mechanisms underlying the development of cardiac hypertrophy and the transition to heart failure will be helpful for the design of effective therapeutics. Rho-associated coiled-coil containing protein kinase (ROCK) is a downstream mediator of RhoA, and plays a critical role in mediating the effects of RhoA on stress fiber formation, smooth muscle contraction, cell adhesion, membrane ruffling, cell motility and apoptosis [4], [5], [6]. Studies using pharmacological inhibitors, Y27632 and fasudil, suggest an in vivo role for ROCK in the pathogenesis of cardiac hypertrophy and remodeling [7], [8], [9]. However, these inhibitors do not distinguish between ROCK1 and ROCK2, the two isoforms of ROCK family, and could also have non-selective effects [10]. Recent genetic studies by our laboratory and others support the concept that ROCK1 and ROCK2 have distinct non-redundant functions in cardiac hypertrophy and remodeling [11], [12], [13], [14].

We showed that ROCK1 deletion did not impair compensatory hypertrophic response, but significantly reduced cardiomyocyte apoptosis and fibrosis in response to pressure overload induced by transverse aortic constriction [11], [12]. In addition, ROCK1 deletion did not affect the development of cardiac hypertrophy in Gαq transgenic mice, but prevented chamber dilation and contractile dysfunction at young ages (12 weeks) [13]. The Gq class of heterotrimeric G proteins is an important transducer of humoral (i.e., α1-adrenergic agonists, angiotensin II, endothelin and prostaglandin F2α) and mechanical stimuli that are important in cardiac hypertrophy. Transgenic expression of Gαq in the myocardium elicits cardiac hypertrophy and contractile dysfunction, but without significant increase in cardiomyocyte apoptosis at young ages [15], [16]. These results indicate that ROCK1 does not play a significant role in compensatory hypertrophic responses, and raise the possibility that ROCK1 plays a critical role in the maladaptive response which contributes to the transition from compensatory cardiac hypertrophy to heart failure.

To explore this concept and determine long-term impact of ROCK1 deficiency in the setting of cardiomyopathy, the present study examined the effects of ROCK1 deletion on decompensation of the hypertrophic Gαq hearts under two different stress conditions: multiple pregnancy and at 12-month-old age. Previous reports have validated this decompensation model as hypertrophic Gαq hearts progress into heart failure after additional stresses such as pregnancy, aging or pressure overload [15], [17], [18], [19]. Our results show that ROCK1 deletion strikingly improved animal survival and prevented the development of heart failure under both conditions by preserving chamber dimension and contractile function, suppressing increase in cardiomyocyte apoptosis and cardiac fibrosis. In addition, transgenic overexpression of ROCK1 alone did not cause significant changes in heart structure/function, but increased cardiomyocyte apoptosis and accelerated hypertrophic decompensation in Gαq hearts in the absence of pregnancy stress. These results provide the first in vivo evidence for an essential role for ROCK1 in cardiac decompensation.