title: Induction of osteoblast aggregation, detachment, and altered integrin expression by bear serum.
abstract: Animal models have long been used to elucidate the mechanisms responsible for osteoporosis in humans. The American black bear, an animal that does not experience extensive bone loss normally associated with long-term immobilization (when hibernating), may provide an insight into the nature of the pathogenesis of the disease. Circulating growth and differentiation factors present in the serum may facilitate continued proliferation of bone-forming cells. The aim of our study was to determine the effects of bear serum on human osteoblasts when cultured for extended periods of time. Unexpectedly, exposure to the bear serum in vitro led to the detachment of osteoblasts from the surface of the culture plate after 3 d of incubation. The osteoblasts pulled off the polystyrene surface in sheets and aggregated into floating conglomerations of viable cells. In contrast, osteoblasts cultured in fetal calf serum maintained adherence to the surface of the culture plate. Detachment of osteoblasts propagated in bear serum was time dependent and was associated with an increased expression of integrins compared with osteoblasts propagated in fetal calf serum, as indicated by reverse transcriptase-polymerase chain reaction and immunostaining.
authors.affiliation: Department of Orthopaedic Surgery, Division of Arthritis Surgery, The Johns Hopkins University, The Good Samaritan Hospital, Professional Office Building, Suite G-1, 5601 Loch Raven Boulevard, Baltimore, Maryland 21239, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Overstreet
authors.forename: Timothy
authors.initials: T
authors.lastname: Floyd
authors.forename: Anna
authors.initials: A
authors.lastname: Polotsky
authors.forename: David S
authors.initials: DS
authors.lastname: Hungerford
authors.forename: Carmelita G
authors.initials: CG
authors.lastname: Frondoza
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002449:Cell Aggregation / Q000502:physiology*; D048430:Cell Shape; D002478:Cells, Cultured; D006801:Humans; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D044967:Serum / Q000378:metabolism*; D001503:Ursidae / Q000097:blood*
chemical_list: D016023:Integrins; D021122:Protein Subunits