title: Expression of angiopoietin-like protein 4 at the fracture site: Regulation by hypoxia and osteoblastic differentiation.
abstract: Vascular disruption that occurs as a consequence of bone fracture, leads to hypoxia at the site of damage. Hypoxia regulates the expression of a number of genes that can modulate energy conservation, cell survival, tissue regeneration and angiogenesis. In this study we investigated the expression of Angiopoietin-like 4, an adipocytokine that has additional roles in angiogenesis, at the fracture site. We demonstrate that Angptl4 mRNA expression increased early during fracture healing (day 3) returning close to baseline at day14. In the callus, Angptl4 mRNA was visualized in areas of condensing mesenchymal cells, callus cartilage and was especially high in mineralizing osteoblasts located in areas of new bone formation. In vitro, Angptl4 mRNA expression in osteoblasts increased under hypoxic conditions and in cells treated with the hypoxia mimetic desferrioxamine. Angptl4 levels were strongly induced at day 14 in differentiating MC3T3-E1 osteoblastic cells. Exogenous ANGPTL4 increased expression of Runx2, Spp1, vegfa, and Alp mRNA in differentiating osteoblasts. We suggest that the distribution of Angptl4 in the callus may be driven by hypoxia and that Angptl4 may play a role in osteoblastic differentiation, and possibly angiogenesis via regulation of VEGF. Further studies could reveal a dual role for Angptl4 in angiogenesis and osteogenesis.
authors: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, 1285 Veterinary Medicine Drive, Davis, California, 95616.
authors: Sabrina S
authors: SS
authors: Wilson
authors: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, 1285 Veterinary Medicine Drive, Davis, California, 95616.
authors: Alice
authors: A
authors: Wong
authors: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, 1285 Veterinary Medicine Drive, Davis, California, 95616.
authors: Chrisoula A
authors: CA
authors: Toupadakis
authors: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, 1285 Veterinary Medicine Drive, Davis, California, 95616.
authors: Clare E
authors: CE
authors: Yellowley
mesh_terms: D016475:3T3 Cells; D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins / Q000378:metabolism*; D000818:Animals; D001842:Bone and Bones / Q000473:pathology; D002454:Cell Differentiation; D017102:Fracture Healing; D050723:Fractures, Bone / Q000473:pathology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D000860:Hypoxia / Q000473:pathology*; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018919:Neovascularization, Physiologic; D010006:Osteoblasts / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins; C407088:Angptl4 protein, mouse; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse
keywords: angiopoietin-like 4; fracture; hypoxia; osteoblast; osteogenesis