title: Single cell sorting identifies progenitor cell population from full thickness bovine articular cartilage.
abstract: OBJECTIVE
  To date, no approved clinical intervention successfully prevents the progressive degradation of injured articular cartilage that leads to osteoarthritis (OA). Stem/progenitor cell populations within tissues of diarthrodial joint have shown their therapeutic potential in treating OA. However, this potential has not been fully realized due in part to the heterogeneity of these subpopulations. Characterization of clonal populations derived from a single cell may help identify more homogenous stem/progenitor populations within articular cartilage. Moreover, chondrogenic potential of clonal populations from different zones could be further examined to elucidate their differential roles in maintaining articular cartilage homeostasis.
  
  
  METHODS
  We combined Fluorescence-activated cell sorting (FACS) and clonogenicity screening to identify stem/progenitor cells cloned from single cells. High-efficiency colony-forming cells (HCCs) were isolated, and evaluated for stem/progenitor cell characteristics. HCCs were also isolated from different zones of articular cartilage. Their function was compared by lineage-specific gene expression, and differentiation potential.
  
  
  RESULTS
  A difference in colony-forming efficiency was observed in terms of colony sizes. HCCs were highly clonogenic and multipotent, and overexpressed stem/progenitor cell markers. Also, proliferation and migration associated genes were over-expressed in HCCs. HCCs showed zonal differences with deep HCCs more chondrogenic and osteogenic than superficial HCCs.
  
  
  CONCLUSIONS
  Our approach is a simple yet practical way to identify homogeneous stem/progenitor cell populations with clonal origin. The discovery of progenitor cells demonstrates the intrinsic self-repairing potential of articular cartilage. Differences in differentiation potential may represent the distinct roles of superficial and deep zone stem/progenitor cells in the maintenance of articular cartilage homeostasis.
authors.affiliation: Department of Orthopaedics and Rehabilitation, The University of Iowa, Iowa City, IA, USA; Department of Biomedical Engineering, The University of Iowa, Iowa City, IA, USA. Electronic address: yin-yu@uiowa.edu.
authors.forename: Y
authors.initials: Y
authors.lastname: Yu
authors.affiliation: Department of Orthopaedics and Rehabilitation, The University of Iowa, Iowa City, IA, USA. Electronic address: Hongjun-zheng@uiowa.edu.
authors.forename: H
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Department of Orthopaedics and Rehabilitation, The University of Iowa, Iowa City, IA, USA; Veterans Affairs Medical Center, Iowa City, IA, USA. Electronic address: joseph-buckwalter@uiowa.edu.
authors.forename: J A
authors.initials: JA
authors.lastname: Buckwalter
authors.affiliation: Department of Orthopaedics and Rehabilitation, The University of Iowa, Iowa City, IA, USA; Department of Biomedical Engineering, The University of Iowa, Iowa City, IA, USA. Electronic address: james-martin@uiowa.edu.
authors.forename: J A
authors.initials: JA
authors.lastname: Martin
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology* / Q000378:metabolism; D002417:Cattle; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation / Q000235:genetics; D002469:Cell Separation / Q000379:methods; D002478:Cells, Cultured; D002633:Chemotaxis / Q000235:genetics / Q000502:physiology; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D020219:Chondrogenesis / Q000235:genetics / Q000502:physiology; D003114:Colony-Forming Units Assay; D005434:Flow Cytometry / Q000379:methods; D015870:Gene Expression; D039902:Multipotent Stem Cells / Q000166:cytology; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism
keywords: Articular cartilage; Single cell; Stem/progenitor cell