title: Skeletal unloading inhibits the in vitro proliferation and differentiation of rat osteoprogenitor cells.
abstract: Loss of weight bearing in the growing rat decreases bone formation, osteoblast numbers, and bone maturation in unloaded bones. These responses suggest an impairment of osteoblast proliferation and differentiation. To test this assumption, we assessed the effects of skeletal unloading using an in vitro model of osteoprogenitor cell differentiation. Rats were hindlimb elevated for 0 (control), 2, or 5 days, after which their tibial bone marrow stromal cells (BMSCs) were harvested and cultured. Five days of hindlimb elevation led to significant decreases in proliferation, alkaline phosphatase (AP) enzyme activity, and mineralization of BMSC cultures. Differentiation of BMSCs was analyzed by quantitative competitive polymerase chain reaction of cDNA after 10, 15, 20, and 28 days of culture. cDNA pools were analyzed for the expression of c-fos (an index of proliferation), AP (an index of early osteoblast differentiation), and osteocalcin (a marker of late differentiation). BMSCs from 5-day unloaded rats expressed 50% less c-fos, 61% more AP, and 35% less osteocalcin mRNA compared with controls. These data demonstrate that cultured osteoprogenitor cells retain a memory of their in vivo loading history and indicate that skeletal unloading inhibits proliferation and differentiation of osteoprogenitor cells in vitro.
authors.affiliation: Veterans Administration Medical Center, Department of Medicine, University of California, San Francisco 94121, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Kostenuik
authors.forename: B P
authors.initials: BP
authors.lastname: Halloran
authors.forename: E R
authors.initials: ER
authors.lastname: Morey-Holton
authors.forename: D D
authors.initials: DD
authors.lastname: Bikle
mesh_terms: D000469:Alkaline Phosphatase / Q000096:biosynthesis; D000818:Animals; D001835:Body Weight; D001846:Bone Development; D001854:Bone Marrow Cells / Q000502:physiology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D019417:Hindlimb Suspension; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology* / Q000502:physiology; D015675:Osteocalcin / Q000096:biosynthesis; D016133:Polymerase Chain Reaction; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017154:Stromal Cells / Q000166:cytology / Q000502:physiology*; D013977:Tibia; D014158:Transcription, Genetic; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D015675:Osteocalcin; D000469:Alkaline Phosphatase