Effects Of Atorvastatin And Irbesartan On Pressure Overload-Induced Cardiac Hypertrophy In Rats: Role Of The Pyk2 Signalling Pathway

【Objective】Cardiac hypertrophy is one of the major adaptive responses to various extracellular stimuli, including hemodynamic overload (mechanical stress) and neurohumoral factors. On the other hand, cardiac hypertrophy is also known as a strong predictor for mortality and morbidity, and the most important single risk factor for heart failure. Despite numerous studies have been performed, the molecular mechanisms underlying cardiomyocyte hypertrophy, however, remain unclear. On the other hand, a lot of intracellular signaling pathways have been found to play important roles in hypertrophic processes of cardiomyocytes. The proline-rich tyrosine kinase 2 (Pyk2), is tyrosine phosphorylated and activated in response to elevation of [Ca2+]i or various stress signals. The signaling pathways downstream of the Pyk2 activation include MAPK cascades and phosphoinositide-3 kinase (PI3K)/Akt. This study is designed to investigated whether pressure overload augmented the expression and phosphorylation of Pyk2 in left ventricular myocardium developing hypertrophy in rats, we also investigated the effects of Atorvastatin and Irbesartan on Pyk2/Rac1 signalling pathway in pressure overload-induced cardiac hypertrophy.【Methods】Suprarenal abdominal aortic coarctation was performed to create pressure overload induced left ventricular hypertrophy model in rats. Rats were randomly assigned into 5 groups: 1) Sham group; 2) Atorvastatin (5 mg·kg-1·d-1) given orally by gastric gavage for 4 weeks; 3) Irbesartan (20 mg·kg-1·d-1) given orally by gastric gavage for 4 weeks; 4) Combining treatment group with Atorvastatin (5 mg·kg-1·d-1) and Irbesartan (20 mg·kg-1·d-1) given orally by gastric gavage for 4 weeks; and 5)Vehicle group. Before the animals were euthanized 4 weeks after surgery, hemodynamics parameters were recorded by carotid artery catheterization. Stained pathological section was observed under light microscope to measure cardiomyocyte diameter transversa and collagen volume fraction. Intracellular reactive oxygen species (ROS) levels were measured using 2′,7′-dichlorofluorescein (DCF) diacetate probes. Rac1 mRNA and Pyk2 mRNA expression were detected by RT-PCR, and their proteins as well as Pyk2 Tyr402 protein expression were assayed by Western blot.【Results】①All banded groups had higher LVMI, cardiomyocyte diameter transversa and collagen volume fraction than that in sham group, all banded groups also had higher intracellular ROS levels(P<0.05-0.01), and LVMI had a linear correlation with the level of ROS in vehicle group(P<0.05). Atorvastatin and Irbesartan had effective impact on attenuation of the increasing of these parameters(P<0.05-0.01).②Rac-1 and Pyk2 mRNA expression, as well as Rac-1, Pyk2 and Pyk2 Tyr402 protein expression were statistically increased in all banded groups than that in sham group(P<0.05-0.01). There is a linear correlation between LVMI and Pyk2 mRNA expression both in sham group and vehicle group(P<0.05-0.01).③Atorvastatin and Irbesartan groups had lower Rac-1 and Pyk2 mRNA expression, as well as Rac-1, Pyk2 and Pyk2 Tyr402 protein expression than that in vehicle group(P<0.05-0.01).④Compared with either drug alone, combined Atorvastatin and Irbesartan treatment had greater decreasing of LVMI, intracellular ROS levels, Rac-1 and Pyk2 mRNA expression, as well as Pyk2 Tyr402 protein expression(P<0.05-0.01).【Conclusion】①Oxidative stress plays important role in pressure overload induced left ventricular hypertrophy.②Pyk2/Rac-1 signalling pathway exert an important role in left ventricular hypertrophy progression, this may provide a potential therapeutic target for cardiac hypertrophy.③Both Atorvastatin and Irbesartan have effective impact on attenuation of pressure overload induced left ventricular hypertrophy. Part of this anti-hypertrophy effect may be attributed to their anti-oxidative properties, which was mediated by down-regulation of Pyk2/Rac-1 expression and phosphorylation. Dual therapy with Atorvastatin and Irbesartan produces an additive reduction in pressure overload induced left ventricular hypertrophy.