Hypoxia-inducible factor-1α regulates the expression of genes in hypoxic hepatic stellate cells important for collagen deposition and angiogenesis.
OBJECTIVE
Several studies have shown that regions of hypoxia develop in the liver during chronic injury. Furthermore, it has been demonstrated that hypoxia stimulates the release of mediators from hepatic stellate cells (HSCs) that may affect the progression of fibrosis. The mechanism by which hypoxia modulates gene expression in HSCs is not known. Recent studies demonstrated that the hypoxia-activated transcription factor, hypoxia-inducible factor (HIF)-1α, is critical for the development of fibrosis. Accordingly, the hypothesis was tested that HIF-1α is activated in HSCs and regulates the expression of genes important for HSC activation and liver fibrosis.


METHODS
Hepatic stellate cells were isolated from mice and exposed to hypoxia. HIF-1α and HIF-2α activation were measured, and gene expression was analysed by gene array analysis. To identify the genes regulated by HIF-1α, HSCs were isolated from control and HIF-1α-deficient mice.


RESULTS
Exposure of primary mouse HSCs to 0.5% oxygen activated HIF-1α and HIF-2α. mRNA levels of numerous genes were increased in HSCs exposed to 0.5% oxygen, many of which are important for HSC function, angiogenesis and collagen synthesis. Of the mRNAs increased, chemokine receptor (Ccr) 1, Ccr5, macrophage migration inhibitory factor, interleukin-13 receptor α1 and prolyl-4-hydroxylase α2 (P4h α2) were completely HIF-1α dependent. Upregulation of the vascular endothelial growth factor and the placental growth factor was partially HIF-1α dependent and upregulation of angiopoietin-like 4 and P4h α1 was HIF-1α independent.


CONCLUSIONS
Results from these studies demonstrate that hypoxia, through activation of HIF-1α, regulates the expression of genes that may alter the sensitivity of HSCs to certain activators and chemotaxins, and regulates the expression of genes important for angiogenesis and collagen synthesis.
Copple
Bryan L
BL
Department of Pharmacology, Toxicology, and Experimental Therapeutics, University of Kansas Medical Center, Kansas City, KS 66160, USA. bcopple@kumc.edu
Bai
Shan
S
Burgoon
Lyle D
LD
Moon
Jeon-Ok
JO
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D015153:Blotting, Western; D015687:Cell Hypoxia / Q000502:physiology*; D017931:DNA Primers / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D055166:Hepatic Stellate Cells / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D053661:Interleukin-13 Receptor alpha1 Subunit / Q000378:metabolism; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D008103:Liver Cirrhosis / Q000378:metabolism / Q000503:physiopathology*; D008263:Macrophage Migration-Inhibitory Factors / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D046228:Microarray Analysis; D054389:Receptors, CCR1 / Q000378:metabolism; D019713:Receptors, CCR5 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D017931:DNA Primers; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D053661:Interleukin-13 Receptor alpha1 Subunit; D019746:Intramolecular Oxidoreductases; D008263:Macrophage Migration-Inhibitory Factors; D054389:Receptors, CCR1; D019713:Receptors, CCR5; D000099162:Endothelial PAS Domain-Containing Protein 1; C515301:Ccr1 protein, mouse; C076231:Mif protein, mouse