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

by Selleckchem | Dec 07 2023

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.

Comments:

**Rationale:**
Ischemia-reperfusion injury (I/R) is a leading cause of acute kidney injury (AKI). Restoring renal blood supply post-ischemia is crucial for minimizing injury. Studies have shown that exogenous application of elabela (ELA) peptides, acting partially through its receptor APJ, can alleviate AKI. However, the natural role of ELA in renal I/R is unclear. This research aims to explore the intrinsic role of ELA in I/R and its impact on renal microvascular blood flow.

**Methods:**
To investigate the endogenous role of ELA in renal I/R, renal tubule-specific ELA knockout (ApelaKsp KO) mice were subjected to bilateral or unilateral I/R. RNA-sequencing analysis was employed to identify gene alterations in ApelaKsp KO mouse kidneys. Injured mice were treated with ELA32 peptide, Nω-hydroxy-nor-L-arginine (nor-NOHA), prostaglandin E2 (PGE2), Paricalcitol, ML221, or their respective vehicles, both individually and in combinations.

**Results:**
ELA expression was predominantly found in renal tubules. ApelaKsp KO mice exhibited worsened pathological injury and reduced renal microvascular blood flow during AKI and the subsequent transition to chronic kidney disease (AKI-CKD). RNA-seq analysis revealed altered expression of two blood flow regulators: arginine metabolizing enzyme arginase 2 (ARG2) and PGE2 metabolizing enzymes carbonyl reductases 1 and 3 (CBR1/3) in injured ApelaKsp KO mice. Combined treatment with an ARG2 inhibitor (nor-NOHA) and Paricalcitol, a clinically used PGE2 synthesis activator, effectively alleviated AKI and prevented the progression to AKI-CKD, significantly improving outcomes in ApelaKsp KO mice. The APJ inhibitor ML221 blocked the beneficial effects of ELA32 peptide on AKI but had no impact on the combination treatment of nor-NOHA and Paricalcitol.

**Conclusions:**
The study establishes the presence of an endogenous tubular ELA-APJ axis that regulates renal microvascular blood flow, playing a pivotal role in I/R-induced AKI. Furthermore, enhancing renal blood flow through ARG2 inhibition and PGE2 activation proves to be an effective therapeutic approach for AKI, preventing its transition to AKI-CKD. This research sheds light on a novel treatment strategy for I/R-induced kidney injuries.