title: Modeled microgravity inhibits osteogenic differentiation of human mesenchymal stem cells and increases adipogenesis.
abstract: Space flight-induced bone loss has been attributed to a decrease in osteoblast function, without a significant change in bone resorption. To determine the effect of microgravity (MG) on bone, we used the Rotary Cell Culture System [developed by the National Aeronautics and Space Administration (NASA)] to model MG. Cultured mouse calvariae demonstrated a 3-fold decrease in alkaline phosphatase (ALP) activity and failed to mineralize after 7 d of MG. ALP and osteocalcin gene expression were also decreased. To determine the effects of MG on osteoblastogenesis, we cultured human mesenchymal stem cells (hMSC) on plastic microcarriers, and osteogenic differentiation was induced immediately before the initiation of modeled MG. A marked suppression of hMSC differentiation into osteoblasts was observed because the cells failed to express ALP, collagen 1, and osteonectin. The expression of runt-related transcription factor 2 was also inhibited. Interestingly, we found that peroxisome proliferator-activated receptor gamma (PPARgamma2), which is known to be important for adipocyte differentiation, adipsin, leptin, and glucose transporter-4 are highly expressed in response to MG. These changes were not corrected after 35 d of readaptation to normal gravity. In addition, MG decreased ERK- and increased p38-phosphorylation. These pathways are known to regulate the activity of runt-related transcription factor 2 and PPARgamma2, respectively. Taken together, our findings indicate that modeled MG inhibits the osteoblastic differentiation of hMSC and induces the development of an adipocytic lineage phenotype. This work will increase understanding and aid in the prevention of bone loss, not only in MG but also potentially in age-and disuse-related osteoporosis.
authors.affiliation: The University of Alabama at Birmingham, 220 West Pavilion, 619 South 19th Street, Birmingham, Alabama 35233-7331, USA.
authors.forename: Majd
authors.initials: M
authors.lastname: Zayzafoon
authors.forename: William E
authors.initials: WE
authors.lastname: Gathings
authors.forename: Jay M
authors.initials: JM
authors.lastname: McDonald
mesh_terms: D017667:Adipocytes / Q000166:cytology*; D000469:Alkaline Phosphatase / Q000032:analysis / Q000235:genetics; D000818:Animals; D002113:Calcification, Physiologic; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D024042:Collagen Type I / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D008648:Mesoderm / Q000166:cytology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009363:Neoplasm Proteins / Q000235:genetics; D010006:Osteoblasts / Q000166:cytology; D015675:Osteocalcin / Q000235:genetics; D010012:Osteogenesis / Q000502:physiology*; D015676:Osteonectin / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D013234:Stem Cells / Q000166:cytology*; D014157:Transcription Factors / Q000235:genetics; D014481:United States; D018557:United States National Aeronautics and Space Administration; D014893:Weightlessness / Q000009:adverse effects*
chemical_list: D024042:Collagen Type I; D009363:Neoplasm Proteins; D015676:Osteonectin; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D015675:Osteocalcin; D000469:Alkaline Phosphatase