The Role Gai2 Signaling in Hypertension

描述(申请人提供)：高血压是一种常见的疾病，其特征是血管舒张性张力增加，平滑肌重塑和血管炎症。血管平滑肌(VSM)生物学的这些方面受到G蛋白偶联信号转导的广泛调控，这在高血压状态下可能是异常的。在这方面，G1i2引起了人们的兴趣，因为(A)G1i2在高血压动物和人类的VSM和其他细胞中的表达和活性增加，(B)百日咳毒素抑制G1i2在患有遗传性和非遗传性高血压的啮齿动物中具有降压作用，以及(C)GI异源三聚体G23亚基的多态性与G1i2活性增加和高血压相关。然而，尽管这些发现表明依赖于G1i2的信号可以影响血压控制，但尚不清楚VSM中G1i2表达/活性的增加是否有助于高血压状态的发生或维持。在这个方案中，我们将利用最近产生的转基因小鼠来询问VSM中G1i2信号改变的病理生理学意义，这些转基因小鼠选择性地在平滑肌中过表达G1i2或G1i2抑制的‘minigene’。初步实验表明，G1i2过度表达小鼠的动脉环比非转基因小鼠的动脉环产生的收缩力要大得多。这是一个有意义的观察，因为它提供了第一个证据，直接将VSM中G1i2的表达水平与血管舒缩反应联系起来。此外，仅G1i2表达增加就足以增强VSM的血管收缩反应，这一发现为整个假说提供了支持：VSM中G1i2表达/活性的诱导是高血压发病和/或维持的中心事件。为了验证这一假设，目标1将在活体模型中调查G1i2诱导VSM的意义。在VSM中增加表达G1i2的转基因小鼠的血压和心功能将在急性血管升压剂/血管扩张剂挑战后和实验诱导的高血压期间进行评估。目的2确定G1i2调节血管紧张素转换酶反应性的机制(S)。由于初步数据显示，G1i2过表达小鼠和非转基因小鼠培养的VSM细胞中激动剂诱导的细胞内钙通量的大小没有差异，因此本目标将重点放在钙敏化作为G1i2增强血管收缩的主要机制上。目的3将利用在VSM中表达G1i2抑制基因的转基因小鼠来确定抑制VSM中的G1i2信号是否可以预防或减轻血管运动高反应性和高血压的发展。这些目标的成功完成将直接证实或驳斥G1i2信号改变在高血压中的作用，从而可能导致针对G1i2而不是单个G蛋白偶联受体的新型降压治疗。公共卫生相关性：高血压是一种高度流行的疾病，是心脏病和中风的主要风险因素。高血压时G蛋白受体信号的异常可能通过增强动脉的收缩和损害动脉的松弛而导致血压升高。这些研究的成功完成可能会提高我们对这些异常的理解，从而最终可能导致治疗高血压的新策略。

DESCRIPTION (provided by applicant): Hypertension is a common disease characterized by increased vasomotor tone, smooth muscle remodeling and vessel inflammation. These aspects of vascular smooth muscle (VSM) biology are extensively regulated by G-protein-coupled signal transduction, which can be abnormal in the hypertensive state. In this regard, G1i2 has generated interest because (a) G1i2 expression and activity are increased in VSM and other cells from hypertensive animals and humans, (b) inhibition of G1i2 with pertussis toxin has an antihypertensive effect in rodents with genetic and non-genetic forms of hypertension, and (c) polymorphisms in the G23 subunit of the Gi heterotrimer are associated with increased G1i2 activity and hypertension. However, while these findings indicate that G1i2-dependent signaling can influence blood pressure control, it is unclear whether an increase in G1i2 expression/activity in VSM contributes to the pathogenesis or maintenance of the hypertensive state. In this proposal, we will interrogate the pathophysiological significance of altered G1i2 signaling in VSM by taking advantage of recently generated transgenic mice that selectively overexpress either G1i2 or a G1i2 inhibitory 'minigene' in smooth muscle. Preliminary experiments show that arterial rings from the G1i2 overexpressing mice generate significantly greater contractile forces than arterial rings from their nontransgenic littermates. This is a significant observation because it provides the first evidence that directly links the level of G1i2 expression in VSM to vasomotor responsiveness. Moreover, the finding that increased G1i2 expression alone is sufficient to increase the vasoconstrictor response of VSM provides supporting rationale for the overall hypothesis: the induction of G1i2 expression/activity in VSM is a central event in the pathogenesis and/or maintenance of hypertension. To examine this hypothesis, Aim 1 will investigate the significance of G1i2 induction in VSM in an in vivo model. Blood pressure and cardiac function in transgenic mice with augmented expression of G1i2 in VSM will be assessed following acute vasopressor/vasodilator challenges, and during experimentally induced hypertension. Aim 2 will determine the mechanism(s) by which G1i2 regulates VSM responsiveness. Because preliminary data show that the magnitude of agonist-induced intracellular calcium fluxes in cultured VSM cells from G1i2 overexpressors and nontransgenic mice do not differ, this aim will focus on calcium sensitization as the primary mechanism by which G1i2 enhances vasoconstriction. Aim 3 will use transgenic mice that express a G1i2 inhibitory 'minigene' in VSM to determine whether inhibition of G1i2 signaling in VSM can prevent or attenuate the development of vasomotor hyperresponsiveness and hypertension. The successful completion of these aims will directly substantiate or refute a role for altered G1i2 signaling in hypertension, and thereby could lead to novel antihypertensive therapies that target G1i2 rather than individual G-protein-coupled receptors. PUBLIC HEALTH RELEVANCE: Hypertension is a highly prevalent disease that is a major risk factor for cardiac disease and stroke. G-protein receptor signaling abnormalities in hypertension may contribute to elevated blood pressure by enhancing contraction and impairing relaxation of arteries. Successful completion of these studies may improve our understanding of these abnormalities, and thereby could ultimately lead to novel strategies to treat hypertension.