NHE4在肾脏氨代谢中无作用。

Lack of a role of NHE4 in renal ammonia metabolism.

作者信息

Lee Hyun-Wook, Harris Autumn N, Hyndman Kelly A, Weiner I David

机构信息

Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida, United States.

Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, United States.

出版信息

Am J Physiol Renal Physiol. 2025 Jun 1;328(6):F752-F765. doi: 10.1152/ajprenal.00044.2025. Epub 2025 Apr 16.

Abstract

The cation exchanger, Na/H exchanger isoform 4 (NHE4), has been thought to have a central role in renal ammonia metabolism and handling by acting in a Na for NH exchange mode at the basolateral plasma membrane in the thick ascending limb (TAL) of the loop of Henle. These studies aimed to determine the effect of NHE4 deletion on ammonia metabolism under basal conditions and in response to metabolic acidosis. Constitutive NHE4 deletion resulted in increased urine ammonia excretion associated with significantly lower urine pH; this increase did not lead to metabolic alkalosis. In response to exogenous acid-loading, NHE4 deletion did not impair the changes in ammonia excretion. Immunoblot analysis and immunohistochemistry showed mild increases in proximal tubule ammoniagenic enzyme expression with NHE4 deletion. Both immunoblot analysis and immunohistochemistry showed no detectable NHE4 protein expression in the mouse kidney. Single-nucleus RNAseq of mouse kidneys showed no NHE4 mRNA expression in renal epithelial cells. Analysis of five publicly available mouse and human cell-specific RNAseq datasets also showed a lack of NHE4 mRNA expression in the TAL. We conclude that NHE4 is unnecessary for ammonia metabolism either under basal conditions or in response to acid-loading because it is not expressed in the TAL. NHE4 has previously been suggested to mediate a critical role in renal ammonia metabolism through its role in thick ascending limb (TAL) ammonia transport. This manuscript shows that its deletion does not alter renal ammonia handling and that neither the mouse nor human kidney expresses NHE4 in the TAL.

摘要

阳离子交换体钠/氢交换体亚型4(NHE4)被认为在肾脏氨代谢和处理过程中发挥核心作用,它通过在髓袢升支粗段(TAL)的基底外侧质膜上以钠换氨的模式发挥作用。这些研究旨在确定NHE4缺失在基础条件下以及对代谢性酸中毒反应时对氨代谢的影响。组成性NHE4缺失导致尿氨排泄增加,同时尿pH显著降低;这种增加并未导致代谢性碱中毒。对外源性酸负荷的反应中,NHE4缺失并未损害氨排泄的变化。免疫印迹分析和免疫组织化学显示,NHE4缺失时近端小管产氨酶表达略有增加。免疫印迹分析和免疫组织化学均显示在小鼠肾脏中未检测到NHE4蛋白表达。小鼠肾脏的单核RNA测序显示肾上皮细胞中无NHE4 mRNA表达。对五个公开可用的小鼠和人类细胞特异性RNA测序数据集的分析也显示在TAL中缺乏NHE4 mRNA表达。我们得出结论,NHE4在基础条件下或对酸负荷的反应中对氨代谢并非必需,因为它在TAL中不表达。此前有人提出NHE4通过其在髓袢升支粗段(TAL)氨转运中的作用在肾脏氨代谢中发挥关键作用。本手稿表明其缺失不会改变肾脏对氨的处理,并且小鼠和人类肾脏在TAL中均不表达NHE4。

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