Molecular Mechanisms of Distal Sodium Transport in Insulin Resistance

描述（由申请人提供）：胰岛素抵抗影响了50%以上的高血压患者，并加重了他们患心血管疾病的风险。这种综合征的特点是由于肾远端肾单位钠重吸收增加而引起的盐敏感性高血压。目前还没有针对这类患者的靶向治疗方法。利尿剂可以抵消胰岛素抵抗的钠离子效应，但这些药物会对碳水化合物和脂质代谢产生不利影响，这可能会降低它们对高血压的益处。识别引起高血压的分子机制将为该综合征的治疗提供新的靶点。这种血压升高的几个原因包括代偿性高胰岛素血症，尽管外周胰岛素抵抗，但可能增加钠转运，胰岛素样生长因子-1 (IGF-1)，也被证明可以增加体内钠的重吸收，或者可能改变独立于胰岛素或IGF-1的细胞内信号中间体。最近的证据表明，位于集管中的上皮钠通道（ENaC）可能负责胰岛素抵抗中远端钠转运的增强。小额赠款奖（NIH R03）将为首席研究员（PI）提供必要的资源，以直接测试胰岛素抵抗相关高血压是由于ENaC活性增加引起的假设：(1)高胰岛素血症，(2)IGF-1，或(3)远端肾元内胰岛素后或IGF-1后受体信号的改变。PI将从胰岛素抵抗小鼠和对照小鼠中分离收集管（CD）细胞，并研究胰岛素、IGF-1或载体对受体激活的剂量和时间依赖性影响。此外，PI将应用标准的生物化学和RNA干扰技术来阐明调节胰岛素、IGF-1或载体处理的原代培养细胞中钠转运的分子途径。使用胰岛素抵抗的两种饮食和一种遗传模型，将允许对数据得出更广泛、更临床适用的结论。PI之前花了三年时间研究K08对ENaC运输的调节，在该奖项的最后两年将研究病理生理学中钠运输的相关问题。拟议的实验是可行的，并将为产生一个独立的r01资助的研究项目奠定基础，与主要导师不同。

DESCRIPTION (provided by applicant): Insulin resistance affects more than 50% of all hypertensive subjects and worsens their risk for cardiovascular disease. This syndrome is characterized by salt-sensitive hypertension due to increased sodium reabsorption in the distal nephron of the kidney. Currently there is no targeted therapy for this group of patients. Diuretics would counteract the natriferric effects of insulin resistance, but these agents adversely affect carbohydrate and lipid metabolism which may mitigate their benefit for hypertension. Discerning the molecular mechanisms which cause hypertension would highlight novel therapeutic targets for this syndrome. Several causes of this elevated blood pressure include compensatory hyperinsulinemia which may increase sodium transport despite peripheral insulin resistance, insulin-like growth factor-1 (IGF-1), which has also been demonstrated to increase sodium reabsorption in vivo, or perhaps altered intracellular signaling intermediates independent of insulin or IGF-1. Recent evidence suggests that the epithelial sodium channel (ENaC) which resides in the collecting duct may be responsible for enhanced distal sodium transport in insulin resistance. The Small Grant Award (NIH R03) will provide to the principal investigator (PI) the necessary resources to directly test the hypotheses that insulin resistance-associated hypertension is due to increased ENaC activity due to: (1) hyperinsulinemia, (2) IGF-1, or (3) altered post-insulin or post-IGF-1 receptor signaling within the distal nephron. The PI will isolate collecting duct (CD) cells from insulin-resistant vs. control mice and investigate the dose and time-dependent effects of insulin, IGF-1, or vehicle on receptor activation. Additionally, the PI will apply standard biochemistry and RNA interference techniques to elucidate the molecular pathways which regulate sodium transport in insulin, IGF-1, or vehicle-treated primary culture cells. Using two dietary and one genetic model of insulin resistance, will allow for broader, more clinically applicable conclusions to the data. The PI previously spent three years on the K08 studying the regulation of ENaC trafficking and for the final two years of the award will pursue related questions on sodium transport in pathophysiology. The proposed experiments are feasible and will lay the groundwork for generation of an independent R01-funded research program distinct from the primary mentor. PROJECT NARRATIVE As the incidence of insulin resistance increases in the general population, so will the incidence of hypertension and cardiovascular disease. By comparing sodium transport in kidney cells from mice with and without insulin resistance, we can learn more about how insulin resistance causes salt-sensitive hypertension and how to design specific therapies for this subset of individuals.