RGS5/16-dependent phenotype regulation of arterial vascular smooth muscle cells

动脉的一个关键特征是它们能够使血管壁的结构适应微环境的变化。例如，血流量的慢性增加促进动脉扩张，而血压升高(高血压)会导致动脉壁增厚和僵硬。后者实际上是包括心肌梗死或中风在内的心血管疾病的主要危险因素。这种依赖于微环境的结构性动脉重塑是由生物力学或神经体液刺激触发的内侧血管平滑肌细胞(VSMCs)的激活引起的。在这种背景下，G蛋白的活性和信号转导是这两种刺激协调动脉VSMCs表型变化的信号转导的限制因素。G蛋白的活性本身是由一个内源性蛋白家族控制的，该家族被称为“G蛋白信号调节因子”(RGS)。我们先前已经证明，生物力学刺激VSMC足以增加RGS5的胞浆丰度，RGS5是RhoA激活所需的，RhoA是生物力学诱导的动脉重塑过程中VSMC表型的关键决定因素。同样，体内RGS5的缺失可以阻止血流诱导(动脉形成)和高血压诱导的小鼠动脉重塑以及RhoA的激活。RGS5是G-αQ/11和G-αI/O信号通路的内源性抑制因子，对RhoA的激活起着至关重要的作用。此外，最近的结果表明，RGS5的缺失释放了依赖于GαQ/11的蛋白激酶C活性，从而抑制了RhoA的激活。此外，高血压还诱导了RGS16的表达--RGS5的功能同源物--在缺乏RGS5的情况下，RGS16的表达进一步增加。有趣的是，RGS5和RGS16都有抑制GαQ/11和GαI/O亚基的能力，但亲和力不同。总而言之，根据我们的发现，我们假设RGS5对于平衡G蛋白介导的信号是必不可少的。这似乎是减弱GαQ/11-PKC信号轴的先决条件，G PKC信号轴促进生物力学应激下的动脉VSMC依赖于RhoA的激活。因此，本研究旨在(1)研究RGS5在VSMC特异性过表达对动脉功能和动脉重塑过程的影响，并阐明RhoA激活的机制；(2)探讨RGS16在G蛋白和高血压诱导的VSMC反应和动脉重塑中的调节和功能作用。

A pivotal feature of arteries is their capacity to adapt the architecture of the vascular wall to alterations in the microenvironment. For instance, a chronic increase in blood flow promotes arterial dilation while elevated blood pressure (hypertension) results in thickening and stiffening of the arterial wall. The latter is in fact a main risk factor for cardiovascular diseases including myocardial infarction or stroke. This microenvironment-dependent structural arterial remodeling is caused by activation of medial vascular smooth muscle cells (VSMCs) triggered by biomechanical or neurohumoral stimuli. In this context, G protein activity and signaling is a limiting factor for signal transduction of both kinds of stimuli to orchestrate phenotype changes of arterial VSMCs. G-protein activity itself is controlled by an endogenous protein family known as “regulators of G-protein signaling” (RGS). We have previously shown that biomechanical stimulation of VSMCs was sufficient to increase cytoplasmic abundance of RGS5 which was required for RhoA activation – a critical determinant of the VSMC phenotype during biomechanically-induced arterial remodeling processes. Likewise, loss of RGS5 in vivo prevented both flow-induced (arteriogenesis) as well as hypertension-induced arterial remodeling in mice as well as RhoA activation. RGS5 is an endogenous inhibitor of Gαq/11 and Gαi/o signaling and hence appears to be crucial for activation of RhoA. Moreover, recent results suggested that loss of RGS5 unleashes Gαq/11-dependent PKC activity which subsequently inhibited RhoA activation. Furthermore, hypertension also induced RGS16 expression – a functional homologue to RGS5 – which was further increased in the absence of RGS5. Interestingly, RGS5 and RGS16 both have the ability to inhibit Gαq/11 and Gαi/o subunits but differ in their affinity. Collectively, based on our findings we hypothesize that RGS5 is essential to balance G-protein-mediated signals. This seems to be a prerequisite to attenuate the Gαq/11-PKC- signaling axis which promotes RhoA-dependent activation of arterial VSMCs exposed to biomechanical stress. Consequently, this project aims at (1) characterizing the impact of VSMC-specific overexpression of RGS5 on arterial function and arterial remodeling processes as well as delineating the mechanism of RhoA activation in this context and (2) exploring the regulation and functional contribution of RGS16 to G-protein- and hypertension-induced VSMC responses and arterial remodeling.