title: Hypoxia-inducible factor regulates osteoclast-mediated bone resorption: role of angiopoietin-like 4.
abstract: Hypoxia and the hypoxia-inducible factor (HIF) transcription factor regulate angiogenic-osteogenic coupling and osteoclast-mediated bone resorption. To determine how HIF might coordinate osteoclast and osteoblast function, we studied angiopoietin-like 4 (ANGPTL4), the top HIF target gene in an Illumina HumanWG-6 v3.0 48k array of normoxic vs. hypoxic osteoclasts differentiated from human CD14(+) monocytes (14.3-fold induction, P<0.0004). ANGPTL4 mRNA and protein were induced by 24 h at 2% O(2) in human primary osteoclasts, monocytes, and osteoblasts. ANGPTL4 protein was observed by immunofluorescence in osteoclasts and osteoblasts in vivo. Normoxic inducers of HIF (CoCl(2), desferrioxamine, and l-mimosine) and 100 ng/ml ANGPTL4 stimulated osteoclastic resorption 2- to 3-fold in assays of lacunar dentine resorption, without affecting osteoclast viability. Isoform-specific HIF-1α small interfering RNA ablated hypoxic induction of ANGPTL4 and of resorption, which was rescued by addition of exogenous ANGPTL4 (P<0.001). In the osteoblastic Saos2 cell line, ANGPTL4 caused a dose-dependent increase in proliferation (P<0.01, 100 ng/ml) and, at lower doses (1-25 ng/ml), mineralization. These results demonstrate that HIF is sufficient to enhance osteoclast-mediated bone resorption and that ANGPTL4 can compensate for HIF-1α deficiency with respect to stimulation of osteoclast activity and also augments osteoblast proliferation and differentiation.
authors.affiliation: Botnar Research Centre, University of Oxford, Nuffield Orthopaedic Centre, Headington, Oxford, OX3 7LD, UK. helen.knowles@ndorms.ox.ac.uk
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Knowles
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Cleton-Jansen
authors.forename: Eberhard
authors.initials: E
authors.lastname: Korsching
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Athanasou
mesh_terms: D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D015153:Blotting, Western; D001862:Bone Resorption / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D034741:RNA, Small Interfering
chemical_list: C474772:ANGPTL4 protein, human; D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering