Rad GTPase Deficiency Leads to Cardiac Hypertrophy

Abstract

Background-Rad (Ras associated with diabetes) GTPase is the prototypic member of a subfamily of Ras-related small G proteins. The aim of the present study was to define whether Rad plays an important role in mediating cardiac hypertrophy. Methods and Results-We document for the first time that levels of Rad mRNA and protein were decreased significantly in human failing hearts (nϭ10) compared with normal hearts (nϭ3; PϽ0.01). Similarly, Rad expression was decreased significantly in cardiac hypertrophy induced by pressure overload and in cultured cardiomyocytes with hypertrophy induced by 10 mol/L phenylephrine. Gain and loss of Rad function in cardiomyocytes significantly inhibited and increased phenylephrine-induced hypertrophy, respectively. In addition, activation of calcium-calmodulin-dependent kinase II (CaMKII), a strong inducer of cardiac hypertrophy, was significantly inhibited by Rad overexpression. Conversely, downregulation of CaMKII␦ by RNA interference technology attenuated the phenylephrine-induced hypertrophic response in cardiomyocytes in which Rad was also knocked down. To further elucidate the potential role of Rad in vivo, we generated Rad-deficient mice and demonstrated that they were more susceptible to cardiac hypertrophy associated with increased CaMKII phosphorylation than wild-type littermate controls. Conclusions-The present data document for the first time that Rad is a novel mediator that inhibits cardiac hypertrophy through the CaMKII pathway. The present study will have significant implications for understanding the mechanisms of cardiac hypertrophy and setting the basis for the development of new strategies for treatment of cardiac hypertrophy.

Role of protein phosphorylation in excitation-contraction coupling in taurine deficient hearts

“…Calcium calmodulin-dependent protein kinase II (CaMKII) was assayed according to the method of Chang et al (5). Protein phosphatase 1 and 2A subfamilies were assayed using 32 Pphosphorylase-a as substrate as described by Ahmed et al (1).…”

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

“…Similarly, Rad has been shown to be decreased in the model of PhE-induced cardiomyocyte hypertrophy (73). Silencing of Rad expression by siRNA in rat neonatal cardiomyocytes strongly increased protein synthesis and ANF expression, whereas overexpression of Rad significantly reduced PhE-induced protein synthesis and ANF expression, and decreased CaM kinase II activity (73). In vivo, Rad-deficient mice were more susceptible than normal mice to cardiac hypertrophy, with increased CaM kinase II activity (73) and more severe cardiac fibrosis related to an increase in CTGF expression (579).…”

“…In addition to its inhibitory role on Ca 2ϩ channels, Rad has been shown to play a protecting role in cardiac hypertrophy. Rad is abundantly expressed in human heart, and its expression is strongly decreased in left ventricular myocardium samples from patients with heart failure that displayed severe hypertrophic morphology (73). Similarly, Rad has been shown to be decreased in the model of PhE-induced cardiomyocyte hypertrophy (73).…”

“…Rad is abundantly expressed in human heart, and its expression is strongly decreased in left ventricular myocardium samples from patients with heart failure that displayed severe hypertrophic morphology (73). Similarly, Rad has been shown to be decreased in the model of PhE-induced cardiomyocyte hypertrophy (73). Silencing of Rad expression by siRNA in rat neonatal cardiomyocytes strongly increased protein synthesis and ANF expression, whereas overexpression of Rad significantly reduced PhE-induced protein synthesis and ANF expression, and decreased CaM kinase II activity (73).…”

Aliskiren affects fatty-acid uptake and lipid-related genes in rodent and human cardiomyocytes

“…We also added two more genes to our confirmation analyses, namely Rrad, whose expression was diminished by aliskiren (p<0.001) with the greatest FC after 3h aliskiren treatment (-2.46 FC) and which is involved in cardiomyocyte contractility, viability and glucose metabolism [44][45][46], and Arid 5a, whose expression was also diminished by aliskiren treatment (-2.16 FC) with the lowest p value in the whole array (p=7.38X10 -5 ).…”