Tet1 deficiency exacerbates oxidative stress in acute kidney injury by regulating superoxide dismutase.

Rationale: Increased methylation of key genes has been observed in kidney diseases, suggesting that the ten-eleven translocation (Tet) methyl-cytosine dioxygenase family as well as 5mC oxidation may play important roles. As a member of the Tet family, the role of Tet1 in acute kidney injury (AKI) remains unclear. Methods: Tet1 knockout mice, with or without tempol treatment, a scavenger of reactive oxygen species (ROS), were challenged with ischemia and reperfusion (I/R) injury or unilateral ureteral obstruction (UUO) injury. RNA-sequencing, Western blotting, qRT-PCR, bisulfite sequencing, chromatin immunoprecipitation, immunohistochemical staining, and dot blot assays were performed. Results: Tet1 expression was rapidly upregulated following I/R or UUO injury. Moreover, Tet1 knockout mice showed increased renal injury and renal cell death, increased ROS accumulation, G2/M cell cycle arrest, inflammation, and fibrosis. Severe renal damage in injured Tet1 knockout mice was alleviated by tempol treatment. Mechanistically, Tet1 reduced the 5mC levels in an enzymatic activity-dependent manner on the promoters of Sod1 and Sod2 to promote their expression, thus lowering injury-induced excessive ROS and reducing I/R or UUO injury. Conclusions: Tet1 plays an important role in the development of AKI by promoting SOD expression through a DNA demethylase-dependent mechanism.

Tubular Elabela-APJ axis attenuates ischemia-reperfusion induced acute kidney injury and the following AKI-CKD transition by protecting renal microcirculation.

Rationale: Ischemia-reperfusion injury (I/R) is a common cause of acute kidney injury (AKI). Post-ischemic recovery of renal blood supply plays an important role in attenuating injury. Exogenous application of elabela (ELA) peptides has been demonstrated by us and others to alleviate AKI, partly through its receptor APJ. However, the endogenous role of ELA in renal I/R remains unclear. Methods: Renal tubule specific ELA knockout (ApelaKsp KO) mice challenged with bilateral or unilateral I/R were used to investigate the role of endogenous ELA in renal I/R. RNA-sequencing analysis was performed to unbiasedly investigate altered genes in kidneys of ApelaKsp KO mice. Injured mice were treated with ELA32 peptide, Nω-hydroxy-nor-L-arginine (nor-NOHA), prostaglandin E2 (PGE2), Paricalcitol, ML221 or respective vehicles, individually or in combination. Results: ELA is mostly expressed in renal tubules. Aggravated pathological injury and further reduction of renal microvascular blood flow were observed in ApelaKsp KO mice during AKI and the following transition to chronic kidney disease (AKI-CKD). RNA-seq analysis suggested that two blood flow regulators, arginine metabolizing enzyme arginase 2 (ARG2) and PGE2 metabolizing enzyme carbonyl reductases 1 and 3 (CBR1/3), were altered in injured ApelaKsp KO mice. Notably, combination application of an ARG2 inhibitor nor-NOHA, and Paricalcitol, a clinically used activator for PGE2 synthesis, alleviated injury-induced AKI/AKI-CKD stages and eliminated the worst outcomes observed in ApelaKsp KO mice. Moreover, while the APJ inhibitor ML221 blocked the beneficial effects of ELA32 peptide on AKI, it showed no effect on combination treatment of nor-NOHA and Paricalcitol. Conclusions: An endogenous tubular ELA-APJ axis regulates renal microvascular blood flow that plays a pivotal role in I/R-induced AKI. Furthermore, improving renal blood flow by inhibiting ARG2 and activating PGE2 is an effective treatment for AKI and prevents the subsequent AKI-CKD transition.