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Transcriptional profiling of growth plate chondrocyte differentiation yields insight into endochondral ossification

ABSTRACT: A variety of cell cultures models and in vivo approaches have been used to study gene expression during chondrocyte differentiation. The extent to which the in vitro models reflect bona fide gene regulation in the growth plate has not been quantified. In addition, studies that evaluate global gene expression changes among different growth plate zones are limited. To address these issues, we completed a microarray screen of three growth plate zones derived from manually segmented embryonic mouse tibiae. Classification of genes differentially expressed between each respective growth plate zone, functional categorization as well as characterization of gene expression patterns, cytogenetic loci, signaling pathways and functional motifs confirmed documented data and pointed to novel aspects of chondrocyte differentiation. Parallel comparisons of the microdissected tibiae data set to our previously completed micromass culture screen further corroborated the suitability of micromass cultures for modeling gene expression in chondrocyte development. The micromass culture system demonstrated striking similarities to the in vivo microdissected tibiae screen; however, the micromass system was unable to accurately distinguish gene expression differences in the hypertrophic and mineralized zones of the growth plate. These studies will allow us to better understand zone-specific gene expression patterns in the growth plate. Ultimately, this work will help define both the genomic context in which genes are expressed in the long bones and the extent to which the micromass culture system is able to recapitulate chondrocyte development in endochondral ossification. Keywords: Growth plate microdissection

ORGANISM(S): Mus musculus

PROVIDER: GSE7685 | GEO | 2007/09/01

SECONDARY ACCESSION(S): PRJNA99437

REPOSITORIES: GEO

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Project description:A variety of cell cultures models and in vivo approaches have been used to study gene expression during chondrocyte differentiation. The extent to which the in vitro models reflect bona fide gene regulation in the growth plate has not been quantified. In addition, studies that evaluate global gene expression changes among different growth plate zones are limited. To address these issues, we completed a microarray screen of three growth plate zones derived from manually segmented embryonic mouse tibiae. Classification of genes differentially expressed between each respective growth plate zone, functional categorization as well as characterization of gene expression patterns, cytogenetic loci, signaling pathways and functional motifs confirmed documented data and pointed to novel aspects of chondrocyte differentiation. Parallel comparisons of the microdissected tibiae data set to our previously completed micromass culture screen further corroborated the suitability of micromass cultures for modeling gene expression in chondrocyte development. The micromass culture system demonstrated striking similarities to the in vivo microdissected tibiae screen; however, the micromass system was unable to accurately distinguish gene expression differences in the hypertrophic and mineralized zones of the growth plate. These studies will allow us to better understand zone-specific gene expression patterns in the growth plate. Ultimately, this work will help define both the genomic context in which genes are expressed in the long bones and the extent to which the micromass culture system is able to recapitulate chondrocyte development in endochondral ossification. Experiment Overall Design: Tibiae from 15.5 day old mouse embryos were isolated and partitioned into three distinct zones. Total RNA was isolated from each segment and the individual segments pooled within a litter. Experiment Overall Design: Samples were hybridized to Affymetrix MOE 430 2.0 mouse chips for analysis. Four independent trials were executed for each zone. Experiment Overall Design: Number of time points: 1 Experiment Overall Design: Number of treatments: 0 Experiment Overall Design: Number of Samples: 4 replicates per zone Experiment Overall Design: Affymetrix chip: MOE 430 2.0 Experiment Overall Design: Tissue or origin: Tibiae Experiment Overall Design: Species E15.5 mice Experiment Overall Design: Samples: Total RNA

Project description:Background: Glucocorticoids (GCs) are widely used anti-inflammatory drugs. While useful in clinical practice, patients taking GCs often suffer from skeletal side effects including growth retardation and decreased bone quality in adults. On a physiological level, GCs have been implicated in the regulation of chondrogenesis and osteoblast differentiation, as well as maintaining homeostasis in cartilage and bone. We identified the glucocorticoid receptor (GR) as a potential regulator of chondrocyte hypertrophy in a microarray screen of primary limb bud mesenchyme micromass cultures. Some targets of GC regulation in chondrogenesis are known, but the global effects of pharmacological GC doses on chondrocyte gene expression have not been comprehensively evaluated. Results: This study systematically identifies a spectrum of GC target genes in embryonic growth plate chondrocytes treated with synthetic GR agonist, dexamethasone (DEX), at 6 and 24 hrs. Conventional analysis of this data set and gene set enrichment analysis (GSEA) was performed. Transcripts associated with metabolism were enriched in the DEX condition along with extracellular matrix genes. In contrast, a subset of growth factors and cytokines were negatively correlated with DEX treatment. Comparing DEX-induced gene expression data to developmental changes in gene expression in micromass cultures revealed an additional layer of complexity in which DEX maintains the expression of certain chondrocyte marker genes while inhibiting factors that promote vascularization and ultimately ossification of the cartilaginous template. Conclusions: Together, these results provide insight into the mechanisms and major molecular classes functioning downstream of DEX in primary chondrocytes monolayers. In addition, comparison of our data with microarray studies of DEX treatment in other cell types demonstrated that the majority of DEX effects are tissue-specific. This study provides novel insights into the effects of pharmacological GC on chondrocyte gene transcription and establishes the basis for subsequent functional studies. Experiment Overall Design: Primary chondrocytes isolated from the tibiae, humeri and femurs of 15.5 day old mice are treated with 10EXP-7M DEX or an equal volume of the DMSO vehicle for 24 hrs. Total RNA is isolated after 6 hrs and 24 hrs of treatment. Samples from three independent experiments independent time courses were hybridized to Affymetrix MOE 430 2.0 mouse chips. Experiment Overall Design: Number of time points: 2 (6hr and 24 hr) Experiment Overall Design: Number of treatments: 2 (DEX and the vehicle control) Experiment Overall Design: Number of Samples: 3 replicates per time point per treatment Experiment Overall Design: Affymetrix chip: MOE 430 2.0 Experiment Overall Design: Cell type: Primary chondrocyte Experiment Overall Design: Tissue or origin: Tibiae, humerus, femur Experiment Overall Design: Species E15.5 mice Experiment Overall Design: Samples: Total RNA

Project description:Background: Glucocorticoids (GCs) are widely used anti-inflammatory drugs. While useful in clinical practice, patients taking GCs often suffer from skeletal side effects including growth retardation and decreased bone quality in adults. On a physiological level, GCs have been implicated in the regulation of chondrogenesis and osteoblast differentiation, as well as maintaining homeostasis in cartilage and bone. We identified the glucocorticoid receptor (GR) as a potential regulator of chondrocyte hypertrophy in a microarray screen of primary limb bud mesenchyme micromass cultures. Some targets of GC regulation in chondrogenesis are known, but the global effects of pharmacological GC doses on chondrocyte gene expression have not been comprehensively evaluated. Results: This study systematically identifies a spectrum of GC target genes in embryonic growth plate chondrocytes treated with synthetic GR agonist, dexamethasone (DEX), at 6 and 24 hrs. Conventional analysis of this data set and gene set enrichment analysis (GSEA) was performed. Transcripts associated with metabolism were enriched in the DEX condition along with extracellular matrix genes. In contrast, a subset of growth factors and cytokines were negatively correlated with DEX treatment. Comparing DEX-induced gene expression data to developmental changes in gene expression in micromass cultures revealed an additional layer of complexity in which DEX maintains the expression of certain chondrocyte marker genes while inhibiting factors that promote vascularization and ultimately ossification of the cartilaginous template. Conclusions: Together, these results provide insight into the mechanisms and major molecular classes functioning downstream of DEX in primary chondrocytes monolayers. In addition, comparison of our data with microarray studies of DEX treatment in other cell types demonstrated that the majority of DEX effects are tissue-specific. This study provides novel insights into the effects of pharmacological GC on chondrocyte gene transcription and establishes the basis for subsequent functional studies. Keywords: Time course and pharmacological treatment

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Transcriptional profiling of growth plate chondrocyte differentiation yields insight into endochondral ossification

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