title: Nascent osteoblast matrix inhibits osteogenesis of human mesenchymal stem cells in vitro.
abstract: BACKGROUND
  Adult mesenchymal stem cells (MSCs) are considered promising candidates for cell-based therapies. Their potential utility derives primarily from their immunomodulatory activity, multi-lineage differentiation potential, and likely progenitor cell function in wound healing and repair of connective tissues. However, in vitro, MSCs often senesce and spontaneously differentiate into osteoblasts after prolonged expansion, likely because of lack of regulatory microenvironmental signals. In vivo, osteoblasts that line the endosteal bone marrow surface are in close proximity to MSCs in the marrow stroma and thus may help to regulate MSC fate.
  
  
  METHODS
  We examined here how osteogenic differentiation of MSCs in vitro is affected by exposure to osteoblastic cells (OBCs). Human bone marrow MSCs were exposed to OBCs, derived by induced osteogenic differentiation of MSCs, either directly in contact co-cultures, or indirectly to OBC-conditioned medium or decellularized OBC extracellular matrix (ECM).
  
  
  RESULTS
  Our results showed that OBCs can act as negative regulators of MSC osteogenesis. mRNA expression profiling revealed that OBCs did not affect MSC osteogenesis in direct contact cultures or via secreted factors. However, seeding MSCs on decellularized OBC ECM significantly decreased expression of several osteogenic genes and maintained their fibroblastic morphologies. Proteomic analysis identified some of the candidate protein regulators of MSC osteogenesis.
  
  
  CONCLUSIONS
  These findings provide the basis for future studies to elucidate the signaling mechanisms responsible for osteoblast matrix-mediated regulation of MSC osteogenesis and to better manipulate MSC fate in vitro to minimize their spontaneous differentiation.
authors.affiliation: Department of Health and Human Services, Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, USA. ckolf@jhmi.edu.|Department of Biology, Johns Hopkins University, Baltimore, MD, USA. ckolf@jhmi.edu.|Johns Hopkins Medicine, Media Relations and Public Affairs, 901 S. Bond St., Suite 550, Baltimore, MD, 21231, USA. ckolf@jhmi.edu.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Kolf
authors.affiliation: Department of Health and Human Services, Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, USA. Lin.song@stryker.com.|Stryker Orthopedics, 325 Corporate Drive, Mahwah, NJ, 07430, USA. Lin.song@stryker.com.
authors.forename: Lin
authors.initials: L
authors.lastname: Song
authors.affiliation: Department of Health and Human Services, Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, USA. helmjm@mail.nih.gov.|Translational Genomics Research Branch, National Institute for Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, 20892, USA. helmjm@mail.nih.gov.
authors.forename: Jeannine
authors.initials: J
authors.lastname: Helm
authors.affiliation: Department of Health and Human Services, Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, USA. rst13@pitt.edu.|Department of Orthopaedic Surgery, Center for Cellular and Molecular Engineering, University of Pittsburgh School of Medicine, 450 Technology Drive, Room 221, Pittsburgh, PA, 15219, USA. rst13@pitt.edu.
authors.forename: Rocky S
authors.initials: RS
authors.lastname: Tuan
mesh_terms: D053687:Adult Stem Cells / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D005109:Extracellular Matrix / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism*; D010012:Osteogenesis / Q000235:genetics / Q000502:physiology*; D060066:Protein Interaction Maps; D015398:Signal Transduction
chemical_list: D017077:Culture Media, Conditioned