Hypoxia-inducible factor-dependent production of profibrotic mediators by hypoxic hepatocytes.
OBJECTIVE
During the development of liver fibrosis, mediators are produced that stimulate cells in the liver to differentiate into myofibroblasts and to produce collagen. Recent studies demonstrated that the transcription factor, hypoxia-inducible factor-1alpha (HIF-1alpha), is critical for upregulation of profibrotic mediators, such as platelet-derived growth factor-A (PDGF-A), PDGF-B and plasminogen activator inhibitor-1 (PAI-1) in the liver, during the development of fibrosis. What remains unknown is the cell type-specific regulation of these genes by HIF-1alpha in liver cell types. Accordingly, the hypothesis was tested that HIF-1alpha is activated in hypoxic hepatocytes and regulates the production of profibrotic mediators by these cells.


METHODS
In this study, hepatocytes were isolated from the livers of control and HIF-1alpha- or HIF-1beta-deficient mice and exposed to hypoxia.


RESULTS
Exposure of primary mouse hepatocytes to 1% oxygen stimulated nuclear accumulation of HIF-1alpha and upregulated PAI-1, vascular endothelial cell growth factor and the vasoactive peptides adrenomedullin-1 (ADM-1) and ADM-2. In contrast, the levels of PDGF-A and PDGF-B mRNAs were unaffected in these cells by hypoxia. Exposure of HIF-1alpha-deficient hepatocytes to 1% oxygen only partially prevented upregulation of these genes, suggesting that other hypoxia-regulated transcription factors, such as HIF-2alpha, may also regulate these genes. In support of this, HIF-2alpha was activated in hypoxic hepatocytes, and exposure of HIF-1beta-deficient hepatocytes to 1% oxygen completely prevented upregulation of PAI-1, vascular endothelial cell growth factor and ADM-1, suggesting that HIF-2alpha may also contribute to upregulation of these genes in hypoxic hepatocytes.


CONCLUSIONS
Collectively, our results suggest that HIFs may be important regulators of profibrotic and vasoactive mediators by hypoxic hepatocytes.
Copple
Bryan L
BL
Department of Pharmacology, Toxicology, and Experimental Therapeutics, University of Kansas Medical Center, Kansas City, KS 66160, USA. bcopple@kumc.edu
Bustamante
Juan J
JJ
Welch
Timothy P
TP
Kim
Nam Deuk
ND
Moon
Jeon-Ok
JO
D053607:Adrenomedullin / Q000235:genetics / Q000378:metabolism; D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D015687:Cell Hypoxia; D002470:Cell Survival; D002478:Cells, Cultured; D022781:Hepatocytes / Q000378:metabolism* / Q000473:pathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008103:Liver Cirrhosis / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000235:genetics / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1
D053607:Adrenomedullin; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009479:Neuropeptides; D017395:Plasminogen Activator Inhibitor 1; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D000099162:Endothelial PAS Domain-Containing Protein 1; C497397:Arnt protein, mouse; C497443:Hif1a protein, mouse; C514552:intermedin protein, mouse; C075278:platelet-derived growth factor A; C467480:vascular endothelial growth factor A, mouse