Hypoxia-dependent HIF-1 activation impacts on tissue remodeling in graves' ophthalmopathy-implications for smoking

Abstract

Context: In Graves' ophthalmopathy (GO), inflammation with tissue expansion in a closed compartment like the bony orbit and smoking may cause tissue hypoxia. Objectives: In this study,weinvestigated whether hypoxia-inducible factor-1 (HIF-1) action impacts on tissue remodeling in GO with the aim to identify possible new therapeutic targets. Design/Setting/Participants: Orbital fibroblasts (OFs) were derived from GO patients and control (Ctrl) persons.Weanalyzed HIF-1α levels in response to hypoxiaandcigarettesmokeextract, as well as HIF-1-dependent vascular endothelial growth factor (VEGF) release and adipogenic differentiation, by using HIF-1α small interfering RNA, or HIF-1 inhibitor BAY 87-2243. Main Outcome Measures: Western blot, real-time PCR, ELISA, and immunohistochemistry were used to analyze HIF-1α, VEGF, CD31, and adiponectin. Adipogenic differentiation was measured with Nile red assay. Results: Higher HIF-1α levels in OFs were correlated with the clinical activity score of GO patients. Cigarette smoke extract elevated HIF-1α levels. HIF-1-dependent VEGF secretion was enhanced in GO-OF compared to Ctrl-OF, and as an in vivo consequence, we found a higher vessel density inGO tissue than in Ctrl tissue. Hypoxia strongly stimulated HIF-1-dependent adipogenesis and adiponectin release of GO-OF and enhanced TSH receptor-mediated adipogenesis. Conclusions: Hypoxia impacts on tissue remodeling in GO by stimulating angiogenesis and adipogenesis through activation of HIF-1-dependent pathways in OFs. Our results offer a molecular mechanism for the detrimental influence of smoking on GO and an explanation as to why decompression can improve the outcome of patients. Drug-targeted inhibition of HIF-1/VEGF may provide a therapeutic option to control tissue expansion in GO.