title: Development of the terminally differentiated state sensitizes epiphyseal chondrocytes to apoptosis through caspase-3 activation.
abstract: The maturation of epiphyseal chondrocytes is accompanied by dramatic changes in energy metabolism and shifts in proteins concerned with the induction of apoptosis. We evaluated the role of mitochondria in this process by evaluating the membrane potential (Delta psi m) of chondrocytes of embryonic tibia and the epiphyseal growth plate. We observed that there was a maturation-dependent change in fluorescence, indicating a fall in the Delta psi m. The level of mitochondrial Bcl-2 was decreased during maturation, while in the same time period there was an obvious increase in Bax levels in the mitochondrial fraction of the terminally differentiated chondrocytes. Bcl(xL), another anti-apoptotic protein, was also robustly expressed in the mitochondrial fraction, but its expression was not dependent on the maturation status of the chondrocytes. We found that caspase-3 was present throughout the growth plate and in hypertrophic cells in culture. We blocked caspase-3 activity and found that alkaline phosphatase staining and mineral formation was decreased, and the cells had lost their characteristic shape. Moreover, we noted that the undifferentiated cells were insensitive to elevated concentrations of inorganic phosphate (Pi). It is concluded that during hypertrophy, the change in membrane potential, the increased binding of a pro-apoptotic protein to mitochondria, and the activation of caspase-3 serve to prime cells for apoptosis. Only when the terminally differentiated chondrocytes are challenged with low levels of apoptogens there is activation of apoptosis.
authors.affiliation: Department of Cellular and Molecular Pathology, IRCCS San Raffaele Pisana, Rome, Italy. bruna.pucci@sanraffaele.it
authors.forename: Bruna
authors.initials: B
authors.lastname: Pucci
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Adams
authors.forename: Jolanta
authors.initials: J
authors.lastname: Fertala
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Snyder
authors.forename: Kyle D
authors.initials: KD
authors.lastname: Mansfield
authors.forename: Marco
authors.initials: M
authors.lastname: Tafani
authors.forename: Theresa
authors.initials: T
authors.lastname: Freeman
authors.forename: Irving M
authors.initials: IM
authors.lastname: Shapiro
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D019902:Chondrocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006132:Growth Plate / Q000166:cytology* / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D010755:Organophosphates / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism
chemical_list: D010755:Organophosphates; D019253:Proto-Oncogene Proteins c-bcl-2; D053148:Caspase 3