Hypoxia-inducible factor-1α regulates the expression of genes in hypoxic hepatic stellate cells important for collagen deposition and angiogenesis

Background/Aims 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)-1 alpha, is critical for the development of fibrosis. Accordingly, the hypothesis was tested that HIF-1 alpha 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-1 alpha and HIF-2 alpha activation were measured, and gene expression was analysed by gene array analysis. To identify the genes regulated by HIF-1 alpha, HSCs were isolated from control and HIF-1 alpha-deficient mice. Results Exposure of primary mouse HSCs to 0.5% oxygen activated HIF-1 alpha and HIF-2 alpha. 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 alpha 1 and prolyl-4-hydroxylase alpha 2 (P4h alpha 2) were completely HIF-1 alpha dependent. Upregulation of the vascular endothelial growth factor and the placental growth factor was partially HIF-1 alpha dependent and upregulation of angiopoietin-like 4 and P4h alpha 1 was HIF-1 alpha independent. Conclusions Results from these studies demonstrate that hypoxia, through activation of HIF-1 alpha, 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.