title: Hsp90 and angiogenesis in bone disorders--lessons from the avian growth plate.
abstract: Thiram-induced tibial dyschondroplasia (TD) and vitamin-D deficiency rickets are avian bone disorders of different etiologies characterized by abnormal chondrocyte differentiation, enlarged and unvascularized growth plates, and lameness. Heat-shock protein 90 (Hsp90) is a proangiogenic factor in mammalian tissues and in tumors; therefore, Hsp90 inhibitors were developed as antiangiogenic factors. In this study, we evaluated the association between Hsp90, hypoxia, and angiogenesis in the chick growth plate. Administration of the Hsp90 inhibitor to TD- and rickets-afflicted chicks at the time of induction resulted in reduction in growth-plate size and, contrary to its antiangiogenic effect in tumors, a major invasion of blood vessels occurred in the growth plates. This was the result of upregulation of the VEGF receptor Flk-1, the major rate-limiting factor of vascularization in TD and rickets. In addition, the abnormal chondrocyte differentiation, as characterized by collagen type II expression and alkaline phosphatase activity, and the changes in hypoxia-inducible factor-1α (HIF-1α) in both disorders were restored. All these changes resulted in prevention of lameness. Inhibition of Hsp90 activity reduced growth-plate size, increased vascularization, and mitigated lameness also in TD chicks with established lesions. In summary, this is the first reported demonstration of involvement of Hsp90 in chondrocyte differentiation and growth-plate vascularization. In contrast to the antiangiogenic effect of Hsp90 inhibitors observed in mammals, inhibition of Hsp90 activity in the unvascularized TD- and rickets-afflicted chicks resulted in activation of the angiogenic switch and reinstated normal growth-plate morphology.
authors.affiliation: Institute of Animal Sciences, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel.
authors.forename: Ayelet
authors.initials: A
authors.lastname: Herzog
authors.forename: Olga
authors.initials: O
authors.lastname: Genin
authors.forename: Ahron
authors.initials: A
authors.lastname: Hasdai
authors.forename: Dima
authors.initials: D
authors.lastname: Shinder
authors.forename: Mark
authors.initials: M
authors.lastname: Pines
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D016227:Benzoquinones / Q000494:pharmacology; D002454:Cell Differentiation / Q000502:physiology; D002645:Chickens; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology; D024043:Collagen Type II / Q000378:metabolism; D004195:Disease Models, Animal; D006132:Growth Plate / Q000098:blood supply* / Q000473:pathology / Q000503:physiopathology*; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D008297:Male; D018919:Neovascularization, Physiologic / Q000502:physiology*; D010009:Osteochondrodysplasias / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D012279:Rickets / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D024043:Collagen Type II; D018841:HSP90 Heat-Shock Proteins; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047029:Lactams, Macrocyclic; D042461:Vascular Endothelial Growth Factor A; C448659:17-(dimethylaminoethylamino)-17-demethoxygeldanamycin; D040301:Vascular Endothelial Growth Factor Receptor-2; D000469:Alkaline Phosphatase