Active sodium reabsorption is the major factor influencing renal oxygen consumption and production of reactive oxygen species (ROS). Increased sodium reabsorption uses more oxygen, which may worsen medullary hypoxia and produce more ROS via enhanced mitochondrial ATP synthesis. Both mechanisms may activate the hypoxia-inducible factor (HIF) pathway. Because the collecting duct is exposed to low oxygen pressure and variations of active sodium transport, we assessed whether the HIF pathway controls epithelial sodium channel (ENaC)–dependent sodium transport.

We investigated HIF’s effect on ENaC expression in mpkCCD_cl4 cells (a model of collecting duct principal cells) using real-time PCR and western blot and ENaC activity by measuring amiloride-sensitive current. We also assessed the effect of hypoxia and sodium intake on abundance of kidney sodium transporters in wild-type and inducible kidney tubule–specific Hif1α knockout mice.

In cultured cells, activation of the HIF pathway by dimethyloxalylglycine or hypoxia inhibited sodium transport and decreased expression of βENaC and ENaC, as well as of Na,K-ATPase. HIF1α silencing increased βENaC and ENaC expression and stimulated sodium transport. A constitutively active mutant of HIF1α produced the opposite effect. Aldosterone and inhibition of the mitochondrial respiratory chain slowly activated the HIF pathway, suggesting that ROS may also activate HIF. Decreased ENaC abundance induced by hypoxia in normal mice was abolished in Hif1α knockout mice. Similarly, Hif1α knockout led to increased ENaC abundance under high sodium intake.

This study reveals that ENaC expression and activity are physiologically controlled by the HIF pathway, which may represent a negative feedback mechanism to preserve oxygenation and/or prevent excessive ROS generation under increased sodium transport.

主动钠重吸收是影响肾脏耗氧量和活性氧 (ROS) 产生的主要因素。钠重吸收增加会消耗更多氧气，这可能会加剧髓质缺氧并通过增强线粒体 ATP 合成产生更多 ROS 。这两种机制都可能激活缺氧诱导因子 (HIF) 通路。由于集合管暴露于低氧压和主动钠转运的变化，我们评估了 HIF 通路是否控制上皮钠通道 (ENaC) 依赖性钠转运。

我们使用实时 PCR 和蛋白质印迹研究了 HIF 对 mpkCCD _{cl4细胞（集合管主细胞模型）中 ENaC 表达的影响，并通过测量阿米洛利敏感电流来研究 ENaC 活性。}我们还评估了缺氧和钠摄入对野生型和诱导型肾小管特异性Hif1α基因敲除小鼠肾钠转运蛋白丰度的影响。

在培养细胞中，二甲基草酰甘氨酸或缺氧激活 HIF 通路会抑制钠转运并降低β ENaC 和ENaC，以及 Na,K-ATPase。HIF1 α沉默增加了β ENaC 和ENaC 表达并刺激钠转运。HIF1 α的组成型活性突变体产生了相反的效果。醛固酮和线粒体呼吸链的抑制会缓慢激活 HIF 通路，表明 ROS 也可能激活 HIF。减少正常小鼠缺氧诱导的 ENaC 丰度在Hif1α基因敲除小鼠中消失。同样，Hif1α敲除导致增加高钠摄入量下的 ENaC 丰度。

这项研究表明ENaC 的表达和活性受 HIF 通路的生理控制，这可能代表一种负反馈机制，可以在钠转运增加的情况下保持氧合作用和/或防止过度产生 ROS。