Mechanisms of Diabetic Renal Damage: Role of the Kinin Receptors

描述(申请人提供)：缓激肽受体(B1，B2)是与糖尿病肾病的增殖和纤维化反应有关的GPCRs。缓激肽受体在糖尿病肾小球中的表达增加，它们的激活启动了促纤维化基因：CTGF和TGF2R1的转录。免疫共沉淀和荧光共定位研究表明，B2受体与质膜上的血管紧张素2型受体(AT1R)形成异二聚体。AT1-B2异源二聚体的形成增强了钙信号转导，从而可能加重纤维化反应。我们假设AT1R的高表达增加了AT1-B2异源二聚体的数量，并通过SII[Sar1，Ile4，Ile8]-血管紧张素(AT1R的一种肽拮抗剂，导致2-arrestin依赖的内化而不与G蛋白偶联)而不是氯沙坦(一种非肽中性拮抗剂)促进缓激素非依赖性的B2受体的内化。在AT1R四环素诱导的HEK细胞模型中，SII预处理是缓激肽诱导的钙信号的非竞争性拮抗剂，而氯沙坦则没有作用。在原代培养的大鼠VSMCs上也得到了类似的结果。我们假设，诱导受体内化的AT1R拮抗剂可以在有利于异源二聚体形成的条件下作为缓激肽信号的变构拮抗剂发挥作用，这表明它们在预防糖尿病肾病进展方面是有用的。

DESCRIPTION (provided by applicant): Bradykinin receptors (B1, B2) are GPCRs that have been implicated in the proliferative and fibrotic response that characterizes diabetic nephropathy. Bradykinin receptor expression is increased in the diabetic glomerulus, and their activation initiates transcription of the pro-fibrotic genes: CTGF and TGF2R1. Co-immunoprecipitation and fluorescent colocalization studies have shown that the B2 receptor forms heterodimers with the angiotensin 2 type 1 (AT1R) receptor on the plasma membrane. AT1-B2 heterodimer formation potentiates calcium signaling which may aggravate the fibrotic response. We hypothesize that elevated expression of the AT1R increases the population of AT1-B2 heterodimers, and promotes bradykinin- independent internalization of B2 receptors by SII[Sar1, Ile4, Ile8]-angiotensin (a peptide antagonist of the AT1R that causes 2-arrestin dependent internalization without coupling to G proteins) but not by losartan (a non-peptide neutral antagonist). In an AT1R tetracycline-inducible HEK cell model, SII pretreatment was a non- competitive antagonist of bradykinin-induced calcium signaling whereas losartan had no effect. Similar results were obtained in primary rat VSMCs. We hypothesize that AT1R antagonists that induce receptor internalization can function as allosteric antagonists of bradykinin signaling in conditions that favor the formation of heterodimers, suggesting their utility in the prevention of diabetic nephropathy progression.