Abstract
Background and Aims
Acute kidney injury (AKI) is increasingly recognized as a major risk factor for progression to CKD. However, the mechanisms governing AKI to CKD progression are poorly understood. Hypoxia is a key player in the pathophysiology of the AKI to CKD transition. Thus, we aimed to investigate the exact mechanisms of AKI to CKD progression mediated by hypoxia.
Method
Mild ischemic injury and severe ischemic injury (AKI-to-CKD transition) were established by clamping renal pedicle for 30 and 40 minutes, respectively. Meanwhile, the mice model of AKI-to-CKD transition was treated with HIF-1α inhibitor, PX-478. In vitro, PHD inhibition and combined PHD with FIH inhibition mimic the HIF-1α activation caused by mild or severe hypoxia, respectively. Besides the human proximal tubular epithelial cell line HK-2, tubular cells were isolated from mice for primary culture. KLF5 knockdown, FIH and HIF-1α C-terminal transcriptional activation domain (C-TAD) overexpression in tubular cells were achieved by Lentiviral transfection. Immunocoprecipitation was used to explore the relationship between the HIF-1α and FIH-1. Luciferase reporter assay was used to investigate whether KLF5 was regulated transcriptionally by HIF-1α C-TAD. To explore the roles of FIH-1 and HIF-1α C-TAD in vivo, FIH-1 and HIF-1α C-TAD overexpression (Lentivirus-mediated) was given after severe ischemic injury or mild ischemic injury via tail vein injection, respectively.
Results
AKI to CKD progression was highly associated with the time-course expression of tubular HIF-1α in severe ischemia/reperfusion injury. Interestingly, ameliorated AKI-to-CKD transition was observed by treating PX-478, which destabilized HIF-1α. In vitro, fibrogenesis could be induced by combined PHD with FIH inhibitor treatment in TEC. More interestingly, alleviated fibrogenesis could be achieved by knockdown of KLF5 and overexpression of FIH, respectively, while HIF-1α C-TAD overexpression promoted fibrogenesis in tubular cells. Immunocoprecipitation results indicated that HIF-1α and FIH-1 are interactive. Furthermore, we demonstrated that KLF5 could be regulated transcriptionally by HIF-1α C-TAD by luciferase reporter assay. In vivo, AKI to CKD progression was ameliorated significantly when mice model of AKI-to-CKD transition intervened with FIH-1 overexpression (Lentivirus-mediated). However, treatment of HIF-1α C-TAD (Lentivirus-mediated) in mild ischemic injury model could promote progression of CKD significantly.
Conclusion
FIH-1 mediated HIF-1α C-TAD activation was the key mechanism of AKI to CKD transition by transcriptionally regulating the KLF5 pathway in tubules. Blockade of FIH-1 mediated HIF-1α C-TAD in tubules may serve as a novel therapeutic approach to ameliorate AKI to CKD progression.
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