title: Microenvironment regulation of PRG4 phenotype of chondrocytes.
abstract: Articular cartilage is a heterogeneous tissue with superficial (S), middle (M), and deep (D) zones. Chondrocytes in the S zone secrete the lubricating PRG4 protein, while chondrocytes from the M and D zones are more specialized in producing large amounts of the glycosaminoglycan (GAG) component of the extracellular matrix. Soluble and insoluble chemicals and mechanical stimuli regulate cartilage development, growth, and homeostasis; however, the mechanisms of regulation responsible for the distinct PRG4-positive and negative phenotypes of chondrocytes are unknown. The objective of this study was to determine if interaction between S and M chondrocytes regulates chondrocyte phenotype, as determined by coculture in monolayer at different ratios of S:M (100:0, 75:25, 50:50, 25:75, 0:100) and at different densities (240,000, 120,000, 60,000, and 30,000 cells/cm(2)), and by measurement of PRG4 secretion and expression, and GAG accumulation. Coculture of S and M cells resulted in significant up-regulation in PRG4 secretion and the percentage of cells expressing PRG4, with simultaneous down-regulation of GAG accumulation. Tracking M cells with PKH67 dye in coculture revealed that they maintained a PRG4-negative phenotype, and proliferated less than S cells. Taken together, these results indicate that the up-regulated PRG4 expression in coculture is a result of preferential proliferation of PRG4-expressing S cells. This finding may have practical implications for generating a large number of phenotypically normal S cells, which can be limited in source, for tissue engineering applications.
authors.affiliation: Department of Bioengineering, University of California-San Diego, La Jolla, California 92093-0412, USA.
authors.forename: Megan E
authors.initials: ME
authors.lastname: Blewis
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Schumacher
authors.forename: Travis J
authors.initials: TJ
authors.lastname: Klein
authors.forename: Tannin A
authors.initials: TA
authors.lastname: Schmidt
authors.forename: Michael S
authors.initials: MS
authors.lastname: Voegtline
authors.forename: Robert L
authors.initials: RL
authors.lastname: Sah
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology* / Q000378:metabolism; D002417:Cattle; D002452:Cell Count; D018929:Cell Culture Techniques / Q000379:methods*; D002455:Cell Division; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism; D018920:Coculture Techniques; D003470:Culture Media / Q000378:metabolism; D006025:Glycosaminoglycans / Q000378:metabolism; D010641:Phenotype; D011509:Proteoglycans / Q000378:metabolism*; D015398:Signal Transduction; D012995:Solubility; D023822:Tissue Engineering / Q000379:methods; D000099158:Proteoglycan 4
chemical_list: D003470:Culture Media; D006025:Glycosaminoglycans; D011509:Proteoglycans; C498836:PRG4 protein, Bos taurus; D000099158:Proteoglycan 4