title: Alterations in the sensing and transport of phosphate and calcium by differentiating chondrocytes.
abstract: During endochondral bone formation and fracture healing, cells committed to chondrogenesis undergo a temporally restricted program of differentiation that is characterized by sequential changes in their phenotype and gene expression. This results in the manufacture, remodeling, and mineralization of a cartilage template on which bone is laid down. Articular chondrocytes undergo a similar but restricted differentiation program that does not proceed to mineralization, except in pathologic conditions such as osteoarthritis. The pathogenesis of disorders of cartilage development and metabolism, including osteochondrodysplasia, fracture non-union, and osteoarthritis remain poorly defined. We used the CFK2 model to examine the potential roles of phosphate and calcium ions in the regulatory pathways that mediate chondrogenesis and cartilage maturation. Differentiation was monitored over a 4-week period using a combination of morphological, biochemical, and molecular markers that have been characterized in vivo and in vitro. CFK2 cells expressed the type III sodium-dependent phosphate transporters Glvr-1 and Ram-1, as well as a calcium-sensing mechanism. Regulated expression and activity of Glvr-1 by extracellular phosphate and parathyroid hormone-related protein was restricted to an early stage of CFK2 differentiation, as evidenced by expression of type II collagen, proteoglycan, and Ihh. On the other hand, regulated expression and activity of a calcium-sensing receptor by extracellular calcium was most evident after 2 weeks of differentiation, concomitant with an increase in type X collagen expression, alkaline phosphatase activity and parathyroid hormone/parathyroid hormone-related protein receptor expression. On the basis of these temporally restricted changes in the sensing and transport of phosphate and calcium, we predict that extracellular phosphate plays a role in the commitment of chondrogenic cells to differentiation, whereas extracellular calcium plays a role at a later stage in their differentiation program.
authors.affiliation: Department of Medicine, McGill University, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital Montréal, Québec, Canada H3T 1E2.
authors.forename: D
authors.initials: D
authors.lastname: Wang
authors.forename: L
authors.initials: L
authors.lastname: Canaff
authors.forename: D
authors.initials: D
authors.lastname: Davidson
authors.forename: A
authors.initials: A
authors.lastname: Corluka
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.forename: G N
authors.initials: GN
authors.lastname: Hendy
authors.forename: J E
authors.initials: JE
authors.lastname: Henderson
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015139:Blotting, Southern; D001846:Bone Development; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D019902:Chondrocytes / Q000166:cytology*; D003094:Collagen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007668:Kidney / Q000378:metabolism; D010280:Parathyroid Glands / Q000378:metabolism; D044162:Parathyroid Hormone-Related Protein; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism*; D021381:Protein Transport; D011506:Proteins / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012260:Ribonucleases / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors
chemical_list: D044162:Parathyroid Hormone-Related Protein; D010710:Phosphates; D011506:Proteins; D011509:Proteoglycans; D003094:Collagen; D012964:Sodium; D012260:Ribonucleases; D000469:Alkaline Phosphatase; D002118:Calcium