Mechanism Of TRPV1Activation Improves Vasorelaxation Dysfunction Mediated By High-fat Diet In Mice

Backgrounds and objectives:Hypertension is an important chronic disease that influences health, and it is also themajor reason that leads to CAD、stroke and heart or renal failure. The pathogenesis ofhypertension is related with both genetic and environment factors. Epidemiology studiesindicate that diet factors, such as high-fat diet, sodium and potassium in food, could affectblood pressure.Transient Receptor Potential Vanilloid1(TRPV1), which is also called capsaicinreceptor, attracted great attention for its protection effects in cardiovascular disease. We foundthat diet capsaicin could activate TRPV1in vascular endothelium, promote eNOS/NOpathway, and, consequently, reduce blood pressure of SHR rat; TRPV1activation also easesoxidative stress induced by high-salt diet, reduces superoxide anion production, increases NObioavailability, and finally improves endothelium-dependent vasorelaxation dysfunction andincrease of blood pressure induced by high-salt diet. It’s well known that vasorelaxation andvasoconstriction are related not only with endothelium, but also with smooth muscle in themedia of artery. So it is interesting to explore whether mechanism of non-endothelium,especially the interaction between TRPV1and vascular smooth mucle, is involved in TRPV1activation that attenuate vascular dysfunction. It is in favour of searching for new target thatcapsaicin modifies blood pressure.Rho is also named small GTP-binding protein. There is a lot of evidence that activationof RhoA and Rho kinase results in constriction of smooth muscle, increase of vascular tension,and thus contributes to hypertension; Studies also indicated that antagonist of RhoA and Rhokinase lowers blood pressure. It is still not clear that whether TRPV1activation could affectRhoA and Rho kinse pathway.Expreesion and activation of potassium channel are closely related to the occurrence anddevelopment of hypertension, atherosclerosis and diabetes mellitus. There are four types of potassium channel in vascular smooth muscle cell (VSMC). One of them is voltage-gatedpotassium channel (Kv) that loads outward potassium current. Kv distributes wildly in VSMC,and plays an important role in cell constriction and maintance of vascular basic tension. Renet.al reported that IGF-I benefits diabetic hearts via Rho inhibition and antagonism ofdiabetes-induced decrease in pAkt, eNOS uncoupling, and Kv channel expression.Therelationship between TRPV1activation and Kv channel is still unclear.To investigate the role of TRPV1activation in RhoA/Rho kinase signal pathway and Kv,we establish high-fat diet-induced hypertension model and primary culture VSMC, explorethe mechanisms involved in the process that activation of TRPV1by capsaicin improvesvascular dysfunction, and elucidate the role of RhoA and Rho kinase and Kv during theprocess.Materials and methods:The research includes in-vitro and in-vivo experiment. Part one, in-vitro experiment wasperformed on primary cultured VSMC from aorta of C57BL/6J mice. Part two, in in-vivoexperiment, male,10weeks of age C57BL/6J mice, were randomly divided into four groupsthat received normal diet (ND), normal diet plus capsaicin (NC), high-fat diet (HD) orhigh-fat diet high-fat diet (HC), respectively, for24weeks. Then, the following measurementswere performed.1. Identification of VSMC and expression of TRPV1in primarily cultured aorta VSMCwith immunohistochemical method.2. Expression of TRPV1in VSMC with RT-PCR and Western Blot.3. Change of [Ca2+]i in mesenteric artery with sitmulation of TRPV1agonist orantagonist.4. Mean arterial BP of mice breathing spontaneously was detected with a pressuretransducer.5. Vasoconstriction and vasorelaxtion of aorta after intervention with high-fat andcapsaicin diet recorded by a four-chamber wire myograph.6. Protein expression of RhoA, Rho kinase and Kv in aorta tissue from mice and VSMCintervened with TRPV1agonist/antagonist and RhoA and Rho kinase agonist/antagonist byWestern Blot.Results: 1. Immunohistochemical method, RT-PCR and Western Blot all indicated expression ofTRPV1in VSMC; TRPV1has biological function.2. Tail-cuff blood pressure was greatly increased in mice on high-fat diet, bothendothelium dependent and non-endothelium dependent vasorelaxation were reduced inmice on high-fat diet group. Dietary capsaicin intervention could improve high-fat dietmediated-endothelium dependent and non-endothelium dependent vasorelaxationdysfunction.3. High-fat diet could upregulated the protein expression of RhoA and Rho kinase inaorta. Dietary capsaicin intervention reduced the protein expression of RhoA and Rho kinase,but upregulated the expression of Kv1.4in Aorta. Activation of TRPV1by capsaicinsuppressed the expression of RhoA and Rho kinase, upregulated the expression of Kv1.4inVSMC.Conclusion:High-fat diet increased blood pressure and mediated vasorelaxation dysfunction in micewhich related to upregulated the protein expression of RhoA and Rho kinase. The mechanismof capsaicin improve high-fat diet mediated-vasorelaxation dysfunction associated withsuppression of RhoA and Rho kinase expression and upregulation of Kv1.4expression.