Hypoxia-inducible factors and tubular cell survival in isolated perfused kidneys

Abstract

Adaptation to hypoxic environment is conferred through hypoxia-inducible transcription factors (HIFs). We have previously shown that the HIF system is transiently activated in vivo in radiocontrast-induced acute renal failure, associated with profound hypoxia in the renal medulla. Medullary thick ascending limbs (mTALs), the most affected nephron segments in this model, were virtually unable to mount an adaptive HIF response. Here, we study correlations between oxygenation, HIF activation, and cell viability in a related ex vivo model, the isolated perfused rat kidney (IPK). In IPKs perfused with cell-free oxygenated medium, severe medullary hypoxic damage developed, affecting 42+/-9% of mTALs in the mid-inner stripe. HIF-1alpha tubular immunostaining was noted with a zonal and tubular pattern largely similar to our findings in vivo: in 34+/-3% of collecting ducts (CDs) within the mid-inner stripe and extensively in the papillary tip, whereas mTALs were all HIF-negative. In IPKs supplemented with RBCs (improved oxygen supply), mTAL damage was totally prevented and CDs' HIF expression was attenuated (22+/-4%). By contrast, although measures designed to reduce medullary hypoxia by decreasing tubular reabsorptive activity (furosemide, ouabain, or high-albumin-non-filtering system) reduced mTAL damage, all paradoxically resulted in increased HIF expression in CDs (51+/-4%), and 17+/-3% of mTALs became immunostained as well. Our data confirm that CDs and mTALs have markedly different HIF responses, which correlate with their viability under hypoxic stress. mTALs transcriptional adaptation occurs within a narrow hypoxic range, and it appears that workload reduction can shift mTALs into this window of opportunity for HIF activation and survival.

Hypoxia and the HIF system in kidney disease

“…The isolated perfused rat kidneys serve as a well-recognized model of hypoxic renal cell injury when perfused with cell-free oxygenated medium. The pattern of both HIF activation and pimonidazole accumulation in the isolated kidneys perfused with cell-free medium was remarkably consistent and in concordance with the findings in the multi-insult rat model of ARF [26].…”

Renal Hypoxia and Dysoxia After Reperfusion of the Ischemic Kidney

“…Differences in HIF expression among tubular cell types have been proposed to underlie their wide disparity in vulnerability to hypoxic injury. Rosenberger et al (180) showed that cells from the collecting duct and medullary thick ascending limbs (mTALs) have markedly different HIF responses, which were correlated with their viability during hypoxic stress and inversely correlated with tissue damage. The authors showed that HIF expression does not increase continuously with increasing severity of cellular hypoxia, and they proposed that above a certain hypoxia threshold, responses to HIF expression fail and injury may become irreversible.…”

“…Over the last decade, the role of hypoxiainducible factors (HIFs) in O 2 supply and adaptation to hypoxic conditions has found increasing support. HIFs are O 2 -sensitive transcription factors involved in O 2 -dependent gene regulation that mediate cellular adaptation to O 2 deprivation and tissue protection under hypoxic conditions in the kidney (180,181).…”

Sulfatide-Reactive Natural Killer T Cells Abrogate Ischemia-Reperfusion Injury

“…HIF-1 and HIF target genes such as EPO, VEGF, and GLUT-1 are upregulated as an adaptive response to hypoxia. [32][33][34] Previous studies have demonstrated that chemical preactivation of HIF protected renal IRI and induced upregulation of HIF-target genes. 35,36 Although HIF-1␣ expression was marginally enhanced by IRI or hypoxia only in our study, NKT activation by sulfatide increased HIF-1␣ expression significantly.…”