Molecular mechanism of hypertension-induced renal injury: the role of HIF-1alpha

缺氧诱导因子（HIF）-1α是一种转录因子，在几乎所有的肿瘤细胞中表达上调。 慢性肾脏病（CKD）的类型。HIF-1α通过激活纤维化因子促进胶原的积累， 因素有证据表明HIF-1α的长期激活在CKD中是有害的，尽管 HIF-1α的上调在急性肾损伤中具有保护作用。合并高血压占优势 在CKD进展中的作用。尽管研究发现，受损的肾脏自动调节传递升高的 肾脏灌注压（RPP）进入肾脏微血管，导致RPP诱导的CKD肾损伤， 关于介导RPP诱导的损伤的分子机制是已知的。我们的初步数据显示， 在大鼠5/6肾消融/梗死中沉默HIF-1α减轻肾损伤而不影响高血压 维持正常RPP可阻断肾组织中HIF-1α的表达，抑制肾组织中HIF-1α的表达。 提示HIF-1α可能介导RPP诱导的肾损伤。HIF脯氨酰 羟化酶（含脯氨酰羟化酶结构域的蛋白质，PHD）是促进蛋白质水解的主要酶。 HIF-1α的降解，并存在于肾脏中以调节肾脏HIF-1α。我们最近发现， 在TGF-β和ANG II诱导的HIF-1α活化和随后的肾细胞损伤中起关键作用。我们 初步数据表明，肾PHD活性被升高的RPP抑制， 减轻5/6 A/I大鼠的肾损伤。因此，PHD介导的HIF-1α调节可能是一个重要的机制。 介导RPP诱导的损伤的机制。此外，PHD活性被TRPC 6的激活所抑制，TRPC 6是一种 瞬时受体电位通道的成员。已知TRPC 6的激活可产生肾性炎症。 损伤此外，TRPC 6参与各种细胞类型中的机械/压力感觉，包括 足细胞因此，TRPC 6可能是将RPP应力传递到下游的上游介质 分子途径导致RPP诱导的损伤。我们的初步数据显示，肾脏TRPC 6水平 伺服控制阻断5/6 A/I大鼠RPP的增加，可抑制RPP的增加。在 此外，TRPC 6 shRNA可阻断5/6 A/I大鼠肾脏中HIF-1α的表达。上述信息 导致一种假设，即升高的RPP激活TRPC 6，TRPC 6抑制PHD活性以诱导HIF-1α- 介导的促纤维化基因，从而导致CKD中的肾损伤。提出了三个具体目标。 目的1：验证HIF-1α过度活化介导CPP诱导的慢性肾病肾损伤的假说。 目的2：验证RPP升高抑制PHD活性以上调HIF-1α，从而产生HIF-1α的假说。 CKD中的慢性肾损伤。目的3：检验TRPC 6是上游调节器感知的假设 压力应激调节PHD/HIF-1α通路在RPP诱导的CKD肾损伤中的作用结果从这些 这些研究将明确TRPC 6/PHD/HIF-1α通路的重要分子机制 在RPP诱导的CKD损伤中，这将最终为CKD提供新的治疗靶点。

Hypoxia inducible factor (HIF)-1α is a transcription factor that has been shown to be up-regulated in almost all types of chronic kidney diseases (CKD). HIF-1α stimulates the collagen accumulation by activating fibrogenic factors. There is evidence suggesting that the long-term activation of HIF-1α is injurious in CKD, although upregulation of HIF-1α is protective in acute kidney injury. The coexistent hypertension plays a predominant role in the progression of CKD. Despite the findings that impaired renal autoregulation transmits the elevated renal perfusion pressure (RPP) into the renal microvasculature, causing RPP-induced renal injury in CKD, little is known regarding the molecular mechanism mediating RPP-induced injury. Our preliminary data showed that silencing of HIF-1α attenuated renal injury without effect on hypertension in a rat 5/6 renal ablation/infarction model (5/6 A/I); maintaining a normal RPP blocked the increase of renal HIF-1α and suppressed the renal injury in this CKD model, indicating that HIF-1α may mediate RPP-induced renal injury. HIF prolyl- hydroxylases (prolyl hydroxylase domain-containing proteins, PHDs) are the major enzymes to promote the degradation of HIF-1α and present in the kidneys to regulate renal HIF-1α. We recently showed that PHDs play a critical role in TGF-- and ANG II-induced activation of HIF-1α and consequent injuries in renal cells. Our preliminary data showed that renal PHD activity was inhibited by elevated RPP and that activating PHD activity attenuated renal injury in 5/6 A/I rats. Thus, PHD-mediated regulation of HIF-1α could be an important mechanism mediating RPP-induced injury. Further, the PHD activity is inhibited by the activation of TRPC6, a member of the Transient Receptor Potential Channels. The activation of TRPC6 is known to produce renal injury. Moreover, TRPC6 participates in the mechanical/pressure sensation in various cell types, including podocytes. Therefore, TRPC6 may be the upstream mediator that transmits the RPP stress into downstream molecular pathways to cause RPP-induced injury. Our preliminary data showed that the levels of renal TRPC6 was increased, which was inhibited by servo-control to block the increase of RPP in rats with 5/6 A/I. In addition, TRPC6 shRNA blocked the increase of HIF-1α in the kidneys of 5/6 A/I rats. The above information leads to a hypothesis that the elevated RPP activates TRPC6, which inhibits PHD activity to induce HIF-1α- mediated profibrogenic genes, consequently causing renal injuries in CKD. Three specific aims are proposed. Aim 1: To test the hypothesis that over-activation of HIF-1α mediates RPP-induced chronic renal injury in CKD. Aim 2: To test the hypothesis that elevated RPP inhibits PHD activity to up-regulate HIF-1α, thereby producing chronic renal injury in CKD. Aim 3: To test the hypothesis that TRPC6 is the upstream regulator sensing pressure stress to regulate PHD/HIF-1α pathway in RPP-induced renal injury in CKD. The results from these proposed studies will define an important molecular mechanism associated with TRPC6/PHD/HIF-1α pathway in RPP-induced injury in CKD, which will ultimately suggest new therapeutic targets for CKD.