Intermedin protects peritubular capillaries by inhibiting eNOS uncoupling through AMPK/GTPCH-I/BH4 pathway and alleviate CKD following AKI.

BACKGROUND

Even after recovery of kidney function following AKI, progression to CKD may still occur, characterized by a reduction in peritubular capillaries (PTC) and subsequent kidney fibrosis. Reactive oxygen species (ROS) from uncoupled eNOS are suspected to damage endothelial cells and cause PTC rarefaction observed in AKI-CKD. Intermedin (IMD) inhibits eNOS uncoupling by activating AMPK, but its impact on AKI-CKD transition remains unclear.

METHODS

We utilized IMD-deficient (IMD-/-) mice to explore its effects on AKI-CKD transition, PTC density, endothelial damage, and kidney ROS in a kidney ischemia/reperfusion injury (IRI) model. To elucidate its protective mechanism for PTCs, we subsequently investigated the effects of IMD on endothelial cells and ROS using a hypoxia/reoxygenation (HR) model with human umbilical vein endothelial cells (HUVECs). Finally, we investigated the influence of IMD on AMPK/GTPCH-I/BH4/eNOS to explore its mechanism in alleviating oxidative stress.

RESULTS

Compared with IMD+/+ littermate sham controls, PTC density was significantly reduced in IMD-/- sham mice, with significantly increased oxidative stress. Post-AKI, both IMD+/+ and IMD-/- mice demonstrated substantial declines in kidney function and histology, along with significant fibrosis, PTC reduction, and heightened oxidative stress. Moreover, the severity of kidney damage in IMD-/- mice following AKI was considerably more pronounced than in IMD+/+ mice. HR significantly induced eNOS uncoupling and oxidative stress in HUVECs. Treatment with IMD effectively inhibited eNOS uncoupling and ROS production, achieving levels comparable to the antioxidant N-acetylcysteine. The inhibitory effect of IMD on eNOS uncoupling was abrogated when L-NAME was introduced after HR. HR significantly impaired AMPK activation, which could be reversed by IMD. Additional experiments with inhibitors of GTPCH-I and AMPK, and exogenous BH4, confirmed that IMD protects endothelial cells by activating AMPK/GTPCH-I/BH4, thereby inhibiting eNOS uncoupling and ROS production.

CONCLUSION

We concluded that IMD inhibits AKI-CKD transition by protecting endothelial cells of PTC via AMPK/GTPCH-I/BH4/eNOS pathway.