Gleason Catherine E, Frindt Gustavo, Cheng Chih-Jen, Ng Michael, Kidwai Atif, Rashmi Priyanka, Lang Florian, Baum Michel, Palmer Lawrence G, Pearce David
J Clin Invest. 2015 Jan;125(1):117-28. doi: 10.1172/JCI73935. Epub 2014 Nov 21.
The epithelial Na+ channel (ENaC) is essential for Na+ homeostasis, and dysregulation of this channel underlies many forms of hypertension. Recent studies suggest that mTOR regulates phosphorylation and activation of serum/glucocorticoid regulated kinase 1 (SGK1), which is known to inhibit ENaC internalization and degradation; however, it is not clear whether mTOR contributes to the regulation of renal tubule ion transport. Here, we evaluated the effect of selective mTOR inhibitors on kidney tubule Na+ and K+ transport in WT and Sgk1-/- mice, as well as in isolated collecting tubules. We found that 2 structurally distinct competitive inhibitors (PP242 and AZD8055), both of which prevent all mTOR-dependent phosphorylation, including that of SGK1, caused substantial natriuresis, but not kaliuresis, in WT mice, which indicates that mTOR preferentially influences ENaC function. PP242 also substantially inhibited Na+ currents in isolated perfused cortical collecting tubules. Accordingly, patch clamp studies on cortical tubule apical membranes revealed that mTOR inhibition markedly reduces ENaC activity, but does not alter activity of K+ inwardly rectifying channels (ROMK channels). Together, these results demonstrate that mTOR regulates kidney tubule ion handling and suggest that mTOR regulates Na+ homeostasis through SGK1-dependent modulation of ENaC activity.
上皮钠通道（ENaC）对于钠稳态至关重要，该通道的失调是多种高血压的基础。最近的研究表明，mTOR调节血清/糖皮质激素调节激酶1（SGK1）的磷酸化和激活，已知SGK1可抑制ENaC的内化和降解；然而，尚不清楚mTOR是否参与肾小管离子转运的调节。在此，我们评估了选择性mTOR抑制剂对野生型（WT）和Sgk1基因敲除小鼠以及分离的集合管中肾小管钠和钾转运的影响。我们发现，两种结构不同的竞争性抑制剂（PP242和AZD8055）均可阻止包括SGK1在内的所有mTOR依赖性磷酸化，它们在WT小鼠中引起大量利尿，但不引起尿钾增多，这表明mTOR优先影响ENaC功能。PP242还显著抑制了分离的灌注皮质集合管中的钠电流。相应地，对皮质肾小管顶端膜进行的膜片钳研究表明，抑制mTOR可显著降低ENaC活性，但不会改变钾内向整流通道（ROMK通道）的活性。总之，这些结果表明mTOR调节肾小管离子处理，并提示mTOR通过对ENaC活性的SGK1依赖性调节来调节钠稳态。
