title: Inhibition of p38 MAPK signaling in chondrocyte cultures results in enhanced osteogenic differentiation of perichondral cells.
abstract: Chondrocytes and osteoblasts originate from the same progenitor cell; however, both are characterized by distinct gene expression profiles once they are differentiated. Signals from differentiating chondrocytes, such as Indian hedgehog (Ihh), regulate the differentiation of osteoblast precursor cells. The MAPK pathways play important roles in controlling the differentiation of both chondrocytes and osteoblasts, with the p38 pathway being particularly relevant in skeletal cells. In the present study, we investigated the effects of p38 inhibition on osteoblastic marker gene expression in chondrocyte cultures. Using high-density micromass cultures of mesenchymal cells as well as chondrocytes that had differentiated in vivo and were maintained in short-term monolayer culture, we demonstrate elevated Runx2, Osterix and Osteocalcin transcript levels in chondrocyte cultures upon inhibition of p38 activity with the pharmacological inhibitor PD169316. Osteocalcin immunolocalization was restricted to perichondral/periosteal cells in micromass cultures, suggesting that inhibition of p38 results in increased periosteal osteogenesis. Coinciding with increased expression of these genes, we observed elevated levels of transcripts for Ihh and its target gene, Ptch, in response to p38 inhibition. Addition of recombinant hedgehog protein mimicked some effects of p38 inhibitors. We therefore suggest that p38 signaling regulates chondrocyte-perichondral cell communication during skeletal development, partially through increased Ihh signaling.
authors.affiliation: CIHR Group in Skeletal Development and Remodeling, Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1.
authors.forename: Lee-Anne
authors.initials: LA
authors.lastname: Stanton
authors.forename: Frank
authors.initials: F
authors.lastname: Beier
mesh_terms: D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D053823:Hedgehog Proteins / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D015675:Osteocalcin / Q000235:genetics; D010012:Osteogenesis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D012313:RNA / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D017931:DNA Primers; D004791:Enzyme Inhibitors; D053823:Hedgehog Proteins; D007093:Imidazoles; D047908:Intracellular Signaling Peptides and Proteins; D011994:Recombinant Proteins; C493716:Runx2 protein, mouse; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; C514061:ihh protein, mouse; D015675:Osteocalcin; D012313:RNA; D048051:p38 Mitogen-Activated Protein Kinases; C408604:2-(4-nitrophenyl)-4-(4-fluorophenyl)-5-(4-pyridinyl)-1H-imidazole