Altered renal distal tubule structure and renal Na+ and Ca2+ handling in a mouse model for Gitelman's syndrome
Altered renal distal tubule structure and renal Na+ and Ca2+ handling in a mouse model for Gitelman's syndrome
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DOI：
10.1097/01.asn.0000138234.18569.63
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发表时间：
2004-09-01
影响因子：
13.6
通讯作者：
Kaissling, B
中科院分区：
文献类型：
--
作者：
Loffing, J;Vallon, V;Kaissling, B
Gitelman综合征是一种由远曲小管（DCT）噻嗪敏感性NaCl协同转运蛋白（NCC）功能缺失突变引起的常染色体隐性肾小管病，其特征为轻度肾Na+消耗、低钙尿、低镁血症和低钾血症。为了进一步了解Gitelman综合征的病理生理学，在基因靶向小鼠模型中研究了NCC消融对远端小管形态、离子转运蛋白沿着其长度的分布和丰度以及肾小管Na+和Ca 2+处理的影响。NCC缺陷小鼠血浆醛固酮水平显著升高，并表现出低钙尿、低镁血症和代偿性高血压。远端小管标记蛋白的免疫荧光检测和超微结构分析显示，早期DCT，生理上缺乏上皮Na+（ENaC）和Ca 2+（TRPV 5）通道，几乎不存在于NCC缺陷小鼠。相反，晚期DCT似乎完整，保留了顶端ENaC和TRPV 5以及基底外侧Na+-Ca 2+交换器的表达。连接小管上皮细胞肥大，并伴有ENaC顶端丰度增加。Ca 2+重吸收在远端回旋中似乎没有改变（即，DCT和连接小管），如通过实时逆转录-PCR、蛋白质印迹和TRPV 5和Na+-Ca 2+交换体的免疫组织化学以及显微穿刺实验所示。最后的实验进一步表明，减少肾小球滤过和增强的Na+和Ca ~（2+）上游和Na+下游的DCT的重吸收分数提供了一些补偿的Na+运输缺陷的DCT和有助于低钙尿症。因此，NCC的丧失导致肾远端小管的主要结构重塑，这沿着肾小球和肾小管功能的显著变化，这可以解释Gitelman综合征的一些临床特征。
Gitelman's syndrome, an autosomal recessive renal tubulopathy caused by loss-of-function mutations in the thiazide-sensitive NaCl co-transporter (NCC) of the distal convoluted tubule (DCT), is characterized by mild renal Na+ wasting, hypocalciuria, hypomagnesemia, and hypokalemic alkalosis. For gaining further insights into the pathophysiology of Gitelman's syndrome, the impact of NCC ablation on the morphology of the distal tubule, on the distribution and abundance of ion transport proteins along its length, and on renal tubular Na+ and Ca2+ handling in a gene-targeted mouse model was studied. NCC-deficient mice had significantly elevated plasma aldosterone levels and exhibited hypocalciuria, hypomagnesemia, and compensated alkalosis. Immunofluorescent detection of distal tubule marker proteins and ultrastructural analysis revealed that the early DCT, which physiologically lacks epithelial Na+ (ENaC) and Ca2+ (TRPV5) channels, was virtually absent in NCC-deficient mice. In contrast, the late DCT seemed intact and retained expression of the apical ENaC and TRPV5 as well as basolateral Na+-Ca2+ exchanger. The connecting tubule exhibited a marked epithelial hypertrophy accompanied by an increased apical abundance of ENaC. Ca2+ reabsorption seemed unaltered in the distal convolution (i.e., the DCT and connecting tubule) as indicated by real-time reverse transcription-PCR, Western blotting, and immunohistochemistry for TRPV5 and Na+-Ca2+ exchanger and micropuncture experiments. The last experiments further indicated that reduced glomerular filtration and enhanced fractional reabsorption of Na+ and Ca2+ upstream and of Na+ downstream of the DCT provide some compensation for the Na+ transport defect in the DCT and contribute to the hypocalciuria. Thus, loss of NCC leads to major structural remodeling of the renal distal tubule that goes along with marked changes in glomerular and tubular function, which may explain some of the clinical features of Gitelman's syndrome.