Hypoxia promotes fibrogenesis in human renal fibroblasts.
BACKGROUND
The mechanisms underlying progressive renal fibrosis are unknown, but the common association of fibrosis and microvascular loss suggests that hypoxia per se may be a fibrogenic stimulus.


METHODS
To determine whether human renal fibroblasts (HRFs), the primary matrix-producing cells in the tubulointerstitium, possess oxygen-sensitive responses relevant to fibrogenesis, cells were exposed to 1% O2 in vitro.


RESULTS
Hypoxia simultaneously stimulated extracellular matrix synthesis and suppressed turnover with increased production of collagen alpha1(I) (Coll-I), decreased expression of collagenase, and increased tissue inhibitor of metalloproteinase (TIMP)-1. These effects are time dependent, require new RNA and protein synthesis, and are specific to hypoxia. The changes in Coll-I and TIMP-1 gene expression involve a heme-protein O2 sensor and protein kinase- and tyrosine kinase-mediated signaling. Although hypoxia induced transforming growth factor-beta1 (TGF-beta1), neutralizing anti-TGF-beta1-antibody did not block hypoxia-induced Coll-I and TIMP-1 mRNA expression. Furthermore, hypoxic-cell conditioned-medium had no effect on the expression of these mRNAs in naive fibroblasts, suggesting direct effects on gene transcription. Transient transfections identified a hypoxia response element (HRE) in the TIMP-1 promoter and demonstrated HIF-1-dependent promoter activation by decreased ambient pO2.


CONCLUSIONS
These data suggest that hypoxia co-ordinately up-regulates matrix production and decreases turnover in renal fibroblasts. The results support a role for hypoxia in the pathogenesis of fibrosis and provide evidence for novel, direct hypoxic effects on the expression of genes involved in fibrogenesis.
Norman
J T
JT
Department of Medicine, Royal Free and University College Medical School, London, United Kingdom. rmhajtn@ucl.ac.uk
Clark
I M
IM
Garcia
P L
PL
D000199:Actins / Q000235:genetics; D016587:Antimutagenic Agents / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D003094:Collagen / Q000235:genetics / Q000378:metabolism; D017364:Collagenases / Q000235:genetics / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D003676:Deferoxamine / Q000494:pharmacology; D005109:Extracellular Matrix / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D000860:Hypoxia / Q000378:metabolism* / Q000473:pathology*; D007672:Kidney Cortex / Q000473:pathology*; D007676:Kidney Failure, Chronic / Q000378:metabolism / Q000473:pathology; D010100:Oxygen / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000032:analysis; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1
D000199:Actins; D016587:Antimutagenic Agents; D002614:Chelating Agents; D017077:Culture Media, Conditioned; D012333:RNA, Messenger; C508960:TGFB1 protein, human; D019715:Tissue Inhibitor of Metalloproteinase-1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D003035:Cobalt; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D017364:Collagenases; C018021:cobaltous chloride; D003676:Deferoxamine; D010100:Oxygen