ABSTRACT
Hypoxia-inducible factors (HIFs) are key mediators of cellular adaptation to hypoxia, but also respond to non-hypoxic stimuli. To clarify involvement in metabolic disturbances, HIFs were characterised in rats subjected to insulin-induced hypoglycaemia or cellular glucoprivation provoked by 2-deoxy-D-glucose (2-DG). Using real-time qPCR, organ-specific expression of HIF-1alpha, -2alpha, -3alpha, -1beta, and of the target gene GLUT-1 was determined. Distribution of HIF-3alpha proteins was examined by immunohistochemistry. Both, insulin and 2-DG resulted in a widespread increase in HIF-3alpha mRNA. HIF-2alpha mRNA increased in lung and heart after 2-DG only, whereas other HIFs remained unaffected. A pronounced increase of protein levels in cerebral cortex was observed for HIF-3alpha. Functional significance of HIF induction was reflected in enhancement of GLUT-1 mRNA. Transcriptional up-regulation of HIF-3alpha represents a typical response to in vivo hypoglycaemia and glucoprivation. These data suggest an involvement of the HIF system in metabolic derangements as for instance caused by diabetes.
Subject(s)
Deoxyglucose/administration & dosage , Hippocampus/metabolism , Insulin/administration & dosage , Transcription Factors/metabolism , Animals , Apoptosis Regulatory Proteins , Cells, Cultured , Dose-Response Relationship, Drug , Gene Expression Regulation/drug effects , Gene Expression Regulation/physiology , Hippocampus/drug effects , Hypoxia/metabolism , Male , Mice , Organ Specificity , Rats , Rats, Wistar , Repressor Proteins , Tissue DistributionABSTRACT
The role of the hypoxia-inducible factor (HIF) subunits 1alpha and 1beta in cellular response to hypoxia is well established, whereas little is known about HIF-2alpha and HIF-3alpha with respect to organ distribution and transcriptional regulation by hypoxia. We investigated mRNA levels of all HIF subunits and of their target genes erythropoietin (EPO) and glucose-transporter 1 (GLUT1) in rats undergoing systemic hypoxia for 30 or 120 min by quantitative real-time RT-PCR. In normoxia, persistently high mRNA levels of all HIF subunits were detected in cerebral cortex, hippocampus, and lung; the heart contained the lowest amounts. Hypoxia did not affect mRNA levels of HIF-1alpha, -1beta, and -2alpha. HIF-3alpha mRNA levels increased in all organs examined after 2 h of hypoxia. A significant rise of EPO and GLUT1 mRNA levels occurred in cortex, heart, liver, and kidney after 2 h of hypoxia, indicating activation of the HIF system. Protein levels of all HIF subunits, determined in brain and lung by immunoblotting, showed a marked increase corresponding to the duration of hypoxia. Our results suggest that induction at the transcriptional level is a unique feature of HIF-3alpha, which therefore may represent a rapidly reacting component of the HIF system in protection against hypoxic damage.