The Effect Of Polymorphisms Of The Renin-Angiotensin System Genes And ALK7 On The Arterial Stiffness

BackgroundThe overall prevalence of arterial stiffness is increasing resulting from the ageing of the population and the development of medical technology. Arterial stiffness, which is associated with cardiovascular morbidity and mortality, is one of the independent cardiovascular risk factors. Pulse wave velocity (PWV) is considered as an efficient index of arterial stiffness in evaluating vascular risk.Increased activity of renin-angiotensin system (RAS) plays an important role in the progression of arterial stiffness. Drugs that interfere with RAS, namely angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), can decrease the proliferation of vascular smooth muscle, improve vascular compliance and elasticity. Recent studies revealed that, genetic variation in components of RAS, such as I/D polymorphism of angiotensin I-converting enzyme gene (ACE), A1166C polymorphism of angiotensin II type 1 receptor gene (AGTR1) and M235T polymorphism of angiotensinogen geen (AGT), may affect arterial stiffness through modulating vascular structure and function. Those findings provided new proofs for the early prediction of arterial stiffness risk and individualized treatment. Given the limited sample sizes and inconsistent results, further investigation is needed to testify the clinical application value of RAS polymorphism test.ObjectivesWe performed a meta-analysis of studies evaluating the impact of polymorphisms of the rennin-angiotensin system genes on arterial stiffness as estimated by PWV.MethodsElectronic databases were systematically searched before October 2014. Articles were selected according to inclusion and exclusion criteria. Two reviewers independently extracted data sets including the basic characteristics of the study population, the distribution of genotype, and PWV. Meat-analysis was performed using Revman 5.2 software and STATA 11.0 software.ResultsA total of 10 studies met our inclusion criteria. Five studies (n=4687) on ACE I/D polymorphism, seven studies (n=1687) on AGTR1 A1166C polymorphism,and three studies (n=3507) on AGT M235T polymorphism. Overall, the meta-analysis showed no significant association between ACE I/D polymorphism and PWV in every model. Further subgroup analysis by ethnicity revealed that, no significant association between ACE I/D polymorphism and PWV in Caucasians. In Asians, significant association was found each model. Meta-analysis showed significant association between AGTR1 A1166C polymorphism and PWV was only found in Asians. However, no significant association with PWV was found in AGT M235T polymorphism.ConclusionThe present meta-analysis suggested that ACE I/D and AGTR1 A1166C polymorphisms might be implicated in the pathogenesis of arterial stiffness in Asians. While AGT M235T polymorphisms may not be a good predictor of PWV.BackgroundMacrovascular complications are the leading causes of increased morbidity and mortality in diabetic patients. Arterial stiffness is an important feature of diabetic macrovascular complications. Several studies show that the alteration of extracellular matrix (ECM), especially the proportions of elastin and collagen fibrosis can primarily lead to the arterial stiffness. However, the mechanism underlying the associations between diabetes and macrovascular stiffness has not been fully elucidated.Activin receptor-like kinase 7 (ALK7), a new member of type I TGF-β receptors, has been demonstrated to be associated with cell proliferation, differentiation and apoptosis. Smad2 and Smad3 are crucial downstream mediators of ALK7 signaling pathway. Previous findings showed that Smad2/3 were critical for the collagen accumulation induced by pro-fibrotic factors, such as angiotensin II and advanced glycation end products.We hypothesized that upregulated ALK7 induced by type 2 diabetes participates in aortic stiffness through Smad2/3 signaling pathway. However, no similar study has been reported before.ObjectivesWe established the type 2 diabetes rat model and used ALK7 gene silencing in vivo to investigate the role of ALK7 in the progression of diabetes-induced aortic stiffness as well as to explore the mechanisms. We try to put forward a new potential target for the treatment of human diabetic macrovascular stiffness.Methods1. The diabetic rats were redivided into control group (Control), diabetes group (DM), diabetes treated with empty virus (vehicle) control group (DM+Vehicle) and diabetes treated with ALK7-shRNA group (DM+ALK7-shRNA).2. In order to build the type 2 diabetic model, rats of diabetes group were provided with a high-fat diet and received a single dose of streptozotocin (STZ) (27.5 mg/kg) through intraperitoneal injection. Rats in the DM+Vehicle group and DM+ALK7-shRNA group were respectively injected with a control empty virus or an adenovirus harboring ALK7 gene.3. Serum total cholesterol (TC), triglyceride (TG) levels, fast blood glucose (FBG) and FINS was tested using enzyme-linked immunosorbent assay.4. Heart rate (HR), systolic blood pressure(SBP), diastolic blood pressure(DBP), and mean arterial pressure(MAP) were measured by use of a noninvasive tail-cuff system.5. The sections were stained with verhoeff staining, hematoxylin and eosin (H&E), masson’s trichrome staining and sirius red staining for shape and arrangement of media, elastin and collagen content, respectively.6. Using immunohistochemical staining to test the content ofcollagen Ⅰ and collagen Ⅲ.7. Using western blot analysis to evaluate the content of ALK7, phosphor-Smad2, phosphor-Smad3, Smad2/3.Results1. The diabetic rats got increased serum levels of TC, TG and FBG. The ISI in DM rat was significantly decreased. With ALK7 silencing, the metabolism abnormalities and insulin resistance were significantly ameliorated.2. Verhoeff, HE, masson’s trichrome and sirius red staining demonstrated the irregularities in the arrangement of elastin fibers in DM group and an increase in the ratio of collagen-elastin ratio (C/E). With ALK7-shRNA treatment, improvement was seen in the arrangement of aortic media and aortic stiffness was obviously alleviated.3. Immunohistochemical detection of collagen Ⅰ and Ⅲ revealed content of collagen Ⅰ and Ⅲ increased in the diabetic group and that the collagen Ⅰ-to-Ⅲ ratio significantly elevated. With ALK7-shRNA treatment, the deposition of collagen Ⅰ and collagen III were notably alleviated.4. Western blot analysis manifested the aortic protein expression of ALK7 and the phosphorylation level of smad2 and smad3 were strongly increased in diabetic rat. AfterALK7-shRNA treatment, the protein expression of ALK7 decreased by 42.10%. Simultaneously, the expression level of P-smad2 and P-smad3 went down by 25.09% and 30.84%, respectively.Conclusion ALK7 played an important role in diabetes-induced aortic stiffness. ALK7 genesilencing alleviated insulin resistance and hyperlipidemia, as well as improved aorticstiffness, which could be an attractive potential target of medical intervention.