Department of Physiology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.
Nephrol Dial Transplant. 2010 Jan;25(1):48-54. doi: 10.1093/ndt/gfp409. Epub 2009 Aug 8.
Arginine vasopressin (AVP) binding to the V2 receptor (V2R) in renal collecting duct principal cells induces a cAMP signalling cascade resulting in the activation of protein kinase A (PKA), translocation of aquaporin-2 (AQP2) to the apical membrane and an increase in AQP2 expression. Consequently, concentration of urine is initiated. X-linked nephrogenic diabetes insipidus (NDI), characterized by the inability to concentrate urine in response to AVP, is caused by mutations in the V2R gene. Initiation of AQP2 translocation, while circumventing the V2R-cAMP-PKA pathway has been suggested as a putative therapy for these patients. In this respect, the activation of a cAMP-independent and cGMP-dependent pathway for AQP2 membrane insertion by different cyclic guanosine monophosphate (cGMP) pathway activators, such as atrial natriuretic peptide (ANP), l-arginine and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), has been put forward. However, it is unclear whether they can increase AQP2 expression.
Mouse cortical collecting duct (mpkCCD) cells were incubated with ANP, l-arginine and 8-Br-cGMP for 2 h and subjected to immunocytochemistry and cell surface biotinylation assays to examine their effect on AQP2 translocation. To test the effect of cGMP pathway activators on AQP2 expression, the mpkCCD cells were treated with dDAVP, ANP and l-arginine for 4 days, or with 8-Br-cGMP for the last day. AQP2 protein levels were determined by immunoblotting.
ANP, l-arginine and 8-Br-cGMP induced the translocation of AQP2 in the mpkCCD cells. However, in contrast to dDAVP, ANP, l-arginine and 8-Br-cGMP did not increase the expression of AQP2.
Our results suggest that while activators of the cGMP pathway are likely beneficial in the treatment of X-linked NDI, their ability to relieve NDI in the patients may be improved when combined with agents stimulating AQP2 expression.
精氨酸加压素（AVP）与肾集合管主细胞上的 V2 受体（V2R）结合，诱导 cAMP 信号级联反应，导致蛋白激酶 A（PKA）激活、水通道蛋白-2（AQP2）向顶端膜易位以及 AQP2 表达增加。因此，尿液浓缩开始。X 连锁肾性尿崩症（NDI）的特征是不能对 AVP 作出反应而浓缩尿液，是由 V2R 基因的突变引起的。绕过 V2R-cAMP-PKA 途径启动 AQP2 易位已被提议作为这些患者的潜在治疗方法。在这方面，不同的环鸟苷酸单磷酸（cGMP）途径激活剂，如心房利钠肽（ANP）、l-精氨酸和 8-溴鸟苷 3'，5'-环单磷酸（8-Br-cGMP），已被提出通过激活 cAMP 非依赖性和 cGMP 依赖性途径来促进 AQP2 膜插入。然而，目前尚不清楚它们是否能增加 AQP2 的表达。
将小鼠皮质集合管（mpkCCD）细胞与 ANP、l-精氨酸和 8-Br-cGMP 孵育 2 小时，然后进行免疫细胞化学和细胞表面生物素化测定，以检查它们对 AQP2 易位的影响。为了测试 cGMP 途径激活剂对 AQP2 表达的影响，将 mpkCCD 细胞用 dDAVP、ANP 和 l-精氨酸处理 4 天，或用 8-Br-cGMP 处理最后一天。通过免疫印迹法测定 AQP2 蛋白水平。
ANP、l-精氨酸和 8-Br-cGMP 诱导了 mpkCCD 细胞中 AQP2 的易位。然而，与 dDAVP 不同，ANP、l-精氨酸和 8-Br-cGMP 并没有增加 AQP2 的表达。
我们的结果表明，虽然 cGMP 途径的激活剂在治疗 X 连锁 NDI 中可能是有益的，但当与刺激 AQP2 表达的药物联合使用时，它们缓解 NDI 患者病情的能力可能会得到改善。
