Protective Role of Hypoxia-Inducible Factor-2α against Ischemic Damage and Oxidative Stress in the Kidney

Abstract

Central to cellular responses to hypoxic environment is the hypoxia-inducible factor (HIF) transcriptional control system. A role for HIF-2␣ was investigated in a model of renal ischemia-reperfusion injury (IRI) associated with oxidative stress using HIF-2␣ knockdown mice. In these mice, HIF-2␣ expression was approximately one half that of wild-type mice, whereas HIF-1␣ expression was equivalent. HIF-2␣ knockdown mice were more susceptible to renal IRI, as indicated by elevated blood urea nitrogen levels and semiquantitative histologic analysis. Immunostaining with markers of oxidative stress showed enhanced oxidative stress in the kidney of HIF-2␣ knockdown mice, which was associated with peritubular capillary loss. C ellular responses to oxygen play an important role in many aspects of physiologic homeostasis. Central to these responses is the hypoxia-inducible factor (HIF) transcriptional control system (1-3). HIF is a heterodimeric transcription factor that is composed of ␣ and ␤ subunits. Whereas HIF-1␣ is known as a key regulator in a wide range of cellular adaptation responses to hypoxia, relatively little is known about biologic significance of its isoform, HIF-2␣.Although ischemic renal injury plays a major role in acute renal failure, tubulointerstitial hypoxia has also been implicated in the pathogenesis and progression of chronic renal disease regardless of the underlying disease (4 -7). In the kidney, HIF-1␣ is induced mainly in tubular and glomerular epithelial cells in response to hypoxia, whereas HIF-2␣ is localized in glomerular cells, peritubular endothelial cells, and fibroblasts (8 -10). Because mice with complete deficiency of HIF-2␣ are embryonic or perinatal lethal (11-13), analysis of a biologic function of HIF-2␣ after birth has been hampered. To study a postnatal biologic role of HIF-2␣, we previously established HIF-2␣ knockdown (kd) mice. These mice show normal development, whereas expression of HIF-2␣ mRNA in the kidney was reduced to 50% without any changes of HIF-1␣ mRNA expression (14). In this study, we induced the well-established ischemia-reperfusion injury (IRI) model of the kidney in HIF-2␣ kd mice to clarify a pathophysiologic role of HIF-2␣ in adult mice. Materials and Methods AnimalsHIF-2␣ kd mice were generated as described previously. This mice were viable and fertile, and also our screening did not reveal any pathologic abnormalities as we previously described (14). These mice were back-crossed with C57BL/6J mice for nine generations. Male C57BL/6J wild-type (WT) and homozygous HIF-2␣ kd mice at the age of 6 to 8 wk were used. To rescue HIF-2␣ specifically in the endothelium, we used for intercrossing Tie1-Cre transgenic (Tie1-Cre) mice (15) whose genetic background was C57BL/6J. Mice were housed in a specific pathogen-free facility and were confirmed to be negative for common murine viral pathogens by routine sera analyses. All experiments were conducted in accordance with the Guide for Animal Experimentation at the University of Tokyo.

Hypoxia-Inducible Transcription Factors Stabilization in the Thick Ascending Limb Protects against Ischemic Acute Kidney Injury

“…The observation that an endothelial HIF-2␣ knockout mouse was more susceptible to renal injury 55 has raised the possibility that enhancing HIF-2␣ activity in the endothelium could underlie the reported protective effects of HIF activators. Our experiments imply, however, that endothelial HIF induction is not required for protection via HIF activation.…”

Cytoglobin, a Novel Member of the Globin Family, Protects Kidney Fibroblasts against Oxidative Stress under Ischemic Conditions

“…4 On this basis, up-regulation of Cygb in the hypoxic kidney may be an adaptive response to increase the efficiency of mitochondrial respiration under oxygen deprivation states. In addition, oxidative stress likely mediates many of the deleterious effects of I/R injury, 36,37 with the tubulointerstitium as the main target. 38,39 Recent studies suggest that Cygb may sense oxygen concentration and act as a regulatory protein that protects cells from ROS.…”

Hypoxia Inducible Factor-2α Stabilization and Maxi-K + Channel β 1 -Subunit Gene Repression by Hypoxia in Cardiac Myocytes

“…This observation is appealing because although Hif-1␣ is known to participate in hypoxic/ischemic cardioprotection, 8,25,34 the involvement in this process of exclusive Hif-2␣-dependent genes was not suspected. However, Hif-2␣ has been suggested to contribute to the protective adaptive responses of kidney tissue 10 and neurons 11 to ischemia, and there are data indicating that Hif-2␣ is necessary for the regulation of antioxidant genes. 43,44 It has been shown that Hif proteins are increased in the periinfarct zone after myocardial infarction, with Hif-2␣ expression occurring in remote areas from the infarct.…”

“…8 Whether there are genes selectively regulated by Hif-2␣ is under debate, and the role of Hif-2␣ in adaptation of cardiomyocytes to hypoxia is unknown. 9 Hif-2␣ has, however, been suggested to participate in the protective adaptive responses of kidney tissue 10 and neurons 11 to ischemia.…”