The Role Of HIF1-?/BNIP3-mediated Mitophagy In Acute Renal Injury

Acute kidney injury is a group of clinical syndromes characterized by a decline in renal function.Acute kidney injury can easily progress to chronic kidney disease,and the long-term survival rate of patients is reduced and the mortality rate is increased.At present,the clinical treatment of acute kidney injury is limited,which causes a huge economic burden for patients and society.Acute kidney injury induced by ischemiareperfusion is caused by decreased blood perfusion,insufficient blood supply to the kidneys,loss of oxygen and nutrients,disorder of cellular metabolism,mitochondrial dysfunction,and increased oxidative stress in cells,leading to cell death.Therefore,early intervention to reduce cell damage,protect mitochondrial function,reduce cellular oxidative stress,and reduce apoptosis is a target for the treatment of acute kidney injury.One of the significant changes in ischemia-reperfusion injury is an increase in the expression of hypoxia-induced factor 1a(HIF1a).The study found that HIF1 a has protective effects on ischemia-reperfusion injury,but the mechanism is still unclear,especially the protective mechanism of HIF1 a in ischemia-reperfusion-induced acute kidney injury still needs to be explored.Ischemia-reperfusion induces autophagy in cells,which degrades the organelles and macromolecules damaged by intracellular lysosomes,and maintains the normal metabolism of cells.When the degraded organelle is mitochondria,it is called mitochondrial autophagy.Many studies suggest that mitochondrial autophagy has protective effects on ischemia-reperfusion injury,but other studies suggest that mitophagy increases ischemia-reperfusion brain damage.Therefore,the role of mitochondrial autophagy in ischemia-reperfusion injury,especially in acute renal injury induced by ischemia-reperfusion and its mechanism remains to be studied.Therefore,this study mainly studies the effects and mechanisms of HIF1 a and mitochondrial autophagy on acute kidney injury induced by ischemiareperfusion in vivo and in vitro.In the first part of the study,a hypoxia-reoxygenation model was established in a human renal tubular epithelial cell line HK2 cell model which was HIF1 a knocked out.The effect of HIF1 a on hypoxia-reoxygenation HK2 cell model was examined by detecting HIF1 a expression,mitochondrial autophagy-related protein LC3 B,TOMM20expression,TUNEL staining and ROS production.The results showed that the expression of HIF1 a was increased in hypoxia-reoxygenation,and the expression ofThe role of HIF1-?/ bnip3-mediated mitophagy in acute renal autophagy protein LC3 B was increased,and the expression of mitochondrial protein TOMM20 was decreased,indicating that hypoxia induced HIF1 a expression and induced mitochondrial autophagy.Hypoxia and reoxygenation induced apoptosis and ROS production.When HIF1 a was knocked out,the expression of LC3 B decreased and the expression of TOMM20 increased,indicating that the level of mitochondrial autophagy was inhibited,and the number of cells positive for TUNEL staining increased,and ROS production increased.It indicated that knockdown of HIF1 a inhibited intracellular mitochondrial autophagy and increased the level of apoptosis and ROS production.At the same time,we found that hypoxia induced the increase of HIF1 a expression and also induced the increase of BNIP3 expression in the downstream of HIF1 a,while knocking out HIF1 a inhibited mitochondrial autophagy and inhibited the expression of BNIP3.To demonstrate whether HIF1 a regulates mitochondrial autophagy by regulating the expression of its downstream gene BNIP3,we overexpressed BNIP3 to HIF1a-knocked out HK2 cells,and then established an anoxic reoxygenation model.Compared with non-overexpressioned-BNIP3 HIF1 aknockedout HK2 cells,the levels of mitochondrial autophagy increased,apoptosis decreased,and ROS production decreased when BNIP3 overexpressed in HIF1 aknockedout HK2 cells,which proved that HIF1 a can regulate mitochondrial autophagy by regulating its downstream gene BNIP3,thereby reducing apoptosis.In the second part of the study,we used HIF1a-floxp mice and cadherin-16-CRE mice to construct renal tubular-specific HIF1 a knockout mice,and established a model of acute renal injury with ischemia-reperfusion to verify HIF1 a and mitochondrial' role in vivo.By detecting serum creatinine,renal histopathological staining,mitochondriaassociated protein in renal tissue,electron microscopy of autophagosomes and mitochondrial autophagy,we found that ischemia-reperfusion significantly induced mitochondrial autophagy and HIF1 a expression in renal cortex.Knockout of HIF1 a significantly reduced the level of mitophagy and increased the level of apoptosis in renal cortex,and aggravated renal damage induced by ischemia-reperfusion.In summary,we demonstrated that HIF1 a can promote the mitochondrial autophagy by regulating the expression of BNIP3 in vitro and in vivo,thus protecting the acute kidney injury induced by ischemia-reperfusion.