title: A comparison of type I collagen, fibronectin, and vitronectin in supporting adhesion of mechanically strained osteoblasts.
abstract: We used an adhesion assay for cells cultured under high dynamic strain to measure human osteoblast-like HOS cell adherence to immobilized type I collagen, fibronectin, and vitronectin. These conditions were designed to model the increased forces present at unstable fractures or loose joint prostheses. At a constant, low protein-coating density (1000 molecules/microm2) and 20% cyclic strain for 24 h, type I collagen, fibronectin, and vitronectin supported 24.6 +/- 2%, 16.7 +/- 3%, and 1.1 +/- 1% adherence, respectively, which paralleled the relative number of integrin-binding sites in each protein. Thus, when the number of available binding sites was limited, strain resistance was proportional to the number of integrin-ligand interactions. In contrast, at high protein-coating densities (> or = 2,500 molecules/microm2), vitronectin supported greater adherence (45.7 +/- 2%) when compared with type I collagen (37 +/- 2%) or fibronectin (34.8 +/- 2%) and directed constitutive expression of osteopontin (OPN), which suggested that there exist discrete signals on vitronectin receptor occupancy that promoted cell adherence and survival under strain. Integrin-mediated binding was necessary for resistance to strain, as evidenced by the low levels of strain resistance observed when cells were adherent in a nonintegrin-dependent manner. These findings support the utilization of at least two distinct mechanisms (i.e., tensegrity and integrin-mediated signal transduction) by HOS cells to remain adherent and viable on exposure to mechanical forces.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: Mario E
authors.initials: ME
authors.lastname: Lacouture
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Schaffer
authors.forename: Lloyd B
authors.initials: LB
authors.lastname: Klickstein
mesh_terms: D001696:Biomechanical Phenomena; D002448:Cell Adhesion / Q000502:physiology; D002470:Cell Survival; D002478:Cells, Cultured; D024042:Collagen Type I / Q000502:physiology*; D005353:Fibronectins / Q000502:physiology*; D022001:Focal Adhesions / Q000502:physiology; D015870:Gene Expression; D006801:Humans; D016023:Integrins / Q000502:physiology; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology* / Q000502:physiology*; D053495:Osteopontin; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012795:Sialoglycoproteins / Q000235:genetics; D015398:Signal Transduction; D013499:Surface Properties; D019096:Vitronectin / Q000502:physiology*
chemical_list: D024042:Collagen Type I; D005353:Fibronectins; D016023:Integrins; D012333:RNA, Messenger; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; D019096:Vitronectin; D053495:Osteopontin