Deletion of the Gamma Subunit of ENaC in Endothelial Cells Does Not Protect against Renal Ischemia Reperfusion Injury

Abstract

Acute kidney injury due to renal ischemia-reperfusion injury (IRI) may lead to chronic or end stage kidney disease. A greater understanding of the cellular mechanisms underlying IRI are required to develop therapeutic options aimed at limiting or reversing damage from IRI. Prior work has shown that deletion of the α subunit of the epithelial Na+ channel (ENaC) in endothelial cells protects from IRI by increasing the availability of nitric oxide. While canonical ENaCs consist of an α, β, and γ subunit, there is evidence of non-canonical ENaC expression in endothelial cells involving the α subunit. We therefore tested whether the deletion of the γ subunit of ENaC also protects mice from IRI to differentiate between these channel configurations. Mice with endothelial-specific deletion of the γ subunit and control littermates were subjected to unilateral renal artery occlusion followed by 48 h of reperfusion. No significant difference was noted in injury between the two groups as assessed by serum creatinine and blood urea nitrogen, levels of specific kidney injury markers, and histological examination. While deletion of the γ subunit did not alter infiltration of immune cells or cytokine message, it was associated with an increase in levels of total and phosphorylated endothelial nitric oxide synthase (eNOS) in the injured kidneys. Our studies demonstrate that even though deletion of the γ subunit of ENaC may allow for greater activation of eNOS, this is not sufficient to prevent IRI, suggesting the protective effects of α subunit deletion may be due, in part, to other mechanisms.

Effects of amiloride on acetylcholine‐dependent arterial vasodilation evolve over time in mice on a high salt diet

“…The existence of non‐canonical channels consisting of an α subunit coupled with the acid sensing ion channel 1a (ASIC1a) has been proposed in pulmonary ECs (Czikora et al, 2017 ). Additionally, mice lacking the α‐subunit of ENaC in ECs have a different response to renal ischemia‐reperfusion compared to mice that lack the γ subunit in ECs, supporting the idea that ENaC with different subunit compositions have different functional effects in endothelia (Mutchler et al, 2021 ; Tarjus et al, 2019 ). Given the low ENaC mRNA levels in ECs, further analyses are needed to ascertain ENaC subunit composition in specific endothelial beds, and additional work is needed to understand what other proteins ENaC subunits may be multimerizing with.…”

The epithelial sodium channel in inflammation and blood pressure modulation

“…Recent work suggests that δ subunit variants are associated with vascular function and blood pressure ( 22 , 40 , 47 – 49 ). ENaC in endothelial cells influences vascular tone by increasing intracellular Na + , stabilizing f-actin, and inhibiting endothelial nitric oxide synthase (eNOS), leading to endothelial stiffening, and reduced nitric oxide production ( 12 , 50 – 52 ). This work has largely been performed in cultured cells.…”

“…This work has largely been performed in cultured cells. This regulatory pathway may be relevant in vivo , as mice with an endothelial γ subunit knockout have increased eNOS levels and eNOS activation ( 52 ). In addition, elevation of intracellular Na + concentration hindered the transportation of l-arginine, resulting in impaired generation of nitric oxide ( 53 , 54 ).…”

Lessons learned about epithelial sodium channels from transgenic mouse models

“…The absence of the endothelial αENaC subunit reduced renal ischemia reperfusion injury through improving eNOS activation and kidney perfusion [62]. Deletion of γENaC subunit in endothelial cells did not protect against renal ischemia reperfusion injury [33]. However, whether ENaC inhibits nitric oxide production thereby mediating vascular tone and myogenic response or rather helps preserving a homeostatic response still needs to be evaluated [63].…”

“…A variety of extracellular and intracellular factors regulate ENaC in kidney, and hormones, ions, phospholipids, proteases, kinases as well as posttranslational modifications and mechanical forces can differentially activate the channel (see also recent reviews [3,33]. The implication of a classical ENaC regulator, namely the mineralocorticoid receptor (MR) was recently evaluated using kidney-specific MR knockout mice.…”