Inhibition of Endothelial PHD2 Suppresses Post-Ischemic Kidney Inflammation through Hypoxia-Inducible Factor-1
Ganeshkumar Rajendran, Michael Schonfeld, Ratnakar Tiwari, Shengping Huang, Rafael Torosyan, Timothy A. Fields, Jihwan Park, Katalin Suszták, Pinelopi P. Kapitsinou
Abstract
Significance Statement The hypoxia-inducible factors (HIFs) HIF-1 and HIF-2 promote cellular adaptation to oxygen deprivation and their activity is controlled by prolyl-4-hydroxylase domain-containing proteins 1 to 3 (PHD1 to PHD3), PHD2 thought to be the main oxygen sensor. Here the authors examined the effects of endothelial-specific ablation of PHD2 on renal injury in mice, demonstrating that endothelial Phd2 ablation offered protection by suppressing expression of proinflammatory genes and recruitment of inflammatory cells in a manner that was dependent on HIF-1—but not on HIF-2. Phd2 inhibition was insufficient to induce detectable HIF activity in the kidney endothelium, but in vitro experiments implicated a humoral factor in the anti-inflammatory effects of endothelial PHD2/HIF-1 signaling. Targeting the endothelial PHD2/HIF-1 axis might offer a novel therapeutic strategy to improve outcomes in AKI. Background Prolyl-4-hydroxylase domain-containing proteins 1–3 (PHD1 to PHD3) regulate the activity of the hypoxia-inducible factors (HIFs) HIF-1 and HIF-2, transcription factors that are key regulators of hypoxic vascular responses. We previously reported that deficiency of endothelial HIF-2 exacerbated renal ischemia-reperfusion injury, whereas inactivation of endothelial PHD2, the main oxygen sensor, provided renoprotection. Nevertheless, the molecular mechanisms by which endothelial PHD2 dictates AKI outcomes remain undefined. Methods To investigate the function of the endothelial PHD2/HIF axis in ischemic AKI, we examined the effects of endothelial-specific ablation of PHD2 in a mouse model of renal ischemia-reperfusion injury. We also interrogated the contribution of each HIF isoform by concurrent endothelial deletion of both PHD2 and HIF-1 or both PHD2 and HIF-2. Results Endothelial deletion of Phd2 preserved kidney function and limited transition to CKD. Mechanistically, we found that endothelial Phd2 ablation protected against renal ischemia-reperfusion injury by suppressing the expression of proinflammatory genes and recruitment of inflammatory cells in a manner that was dependent on HIF-1 but not HIF-2. Persistence of renoprotective responses after acute inducible endothelial-specific loss of Phd2 in adult mice ruled out a requirement for PHD2 signaling in hematopoietic cells. Although Phd2 inhibition was not sufficient to induce detectable HIF activity in the kidney endothelium, in vitro experiments implicated a humoral factor in the anti-inflammatory effects generated by endothelial PHD2/HIF-1 signaling. Conclusions Our findings suggest that activation of endothelial HIF-1 signaling through PHD2 inhibition may offer a novel therapeutic approach against ischemic AKI.