title: Periostin expression distinguishes between light and dark hypertrophic chondrocytes.
abstract: Hypertrophic chondrocytes exist in two forms detectable by electron microscopy, light and dark chondrocytes; the functional implications of the heterogeneous morphology are unknown. The aims of the study were to establish a method for separating light from dark hypertrophic chondrocytes and to identify genes differentially expressed between the two populations. Three-dimensional pellet cultures of chondrocytes from cartilage of neonatal rats were induced to undergo hypertrophy by treatment with triiodothyronine. Cultures were dissociated and subjected to density gradient centrifugation. The cell fraction with the lowest density comprised predominantly light hypertrophic chondrocytes, and the fraction with the highest density comprised predominantly dark hypertrophic chondrocytes. An Affymetrix GeneChip rat expression array was used to compare expression between dark cell-containing pellets and the light cell-enriched fraction. Genes identified on the array as putative dark cell-selective genes included genes encoding extracellular matrix proteins and enzymic modulators thereof. Expression of a subset of genes (Col1a1, periostin, osteoglycin, tPA/Plat, and Chst11) was confirmed as dark cell-selective using quantitative reverse transcriptase polymerase chain reaction. The most highly differentially expressed dark cell-selective gene was periostin. In immunocytochemical studies of light and dark cell-enriched fractions, periostin staining was detectable in dark, but not light hypertrophic chondrocytes. The results provide insight into molecular differences between light and dark hypertrophic chondrocytes.
authors.affiliation: School of Veterinary Science, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Kuan-Sheng
authors.initials: KS
authors.lastname: Chen
authors.forename: Liliana
authors.initials: L
authors.lastname: Tatarczuch
authors.forename: Michiko
authors.initials: M
authors.lastname: Mirams
authors.forename: Yasser A
authors.initials: YA
authors.lastname: Ahmed
authors.forename: Charles N
authors.initials: CN
authors.lastname: Pagel
authors.forename: Eleanor J
authors.initials: EJ
authors.lastname: Mackie
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002356:Cartilage / Q000473:pathology*; D015815:Cell Adhesion Molecules / Q000096:biosynthesis* / Q000235:genetics; D018929:Cell Culture Techniques / Q000379:methods*; D002469:Cell Separation / Q000379:methods*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D020869:Gene Expression Profiling; D006984:Hypertrophy / Q000139:chemically induced; D008854:Microscopy, Electron; D010012:Osteogenesis; D051381:Rats; D011919:Rats, Inbred Strains; D014284:Triiodothyronine / Q000378:metabolism
chemical_list: D015815:Cell Adhesion Molecules; C512835:POSTN protein, human; D014284:Triiodothyronine