Journal
CALCIFIED TISSUE INTERNATIONAL
Volume 88, Issue 2, Pages 96-108Publisher
SPRINGER
DOI: 10.1007/s00223-010-9433-5
Keywords
Phosphate; Nitric oxide; Apoptosis; Growth plate chondrocyte; Endochondral ossification; JNK MAP kinase
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Funding
- Children's Healthcare of Atlanta
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Chondrocytes in the hypertrophic zone of the growth plate undergo apoptosis during endochondral bone development via mechanisms that involve inorganic phosphate (Pi) and nitric oxide (NO). Recent evidence suggests that Pi-dependent NO production plays a role in apoptosis of cells in the resting zone as well. This study examined the mechanism by which Pi induces NO production and the signaling pathways by which NO mediates its effects on apoptosis in these cells. Pi decreased the number of viable cells based on MTT activity; the number of TUNEL-positive cells and the level of DNA fragmentation were increased, indicating an increase in apoptosis. Blocking NO production using the NO synthase (NOS) inhibitor l-NAME or cells from eNOS(-/-) mice blocked Pi-induced chondrocyte apoptosis, indicating that NO production is necessary. NO donors NOC-18 and SNOG both induced chondrocyte apoptosis. SNOG also upregulated p53 expression, the Bax/Bcl-2 expression ratio, and cytochrome c release from mitochondria, as well as caspase-3 activity, indicating that NO induces apoptosis via a mitochondrial pathway. Inhibition of JNK, but not of p38 or ERK1/2, MAP kinase was able to block NO-induced apoptosis, indicating that JNK is necessary in this pathway. Pi elevates NO production via eNOS in resting zone chondrocytes, which leads to a mitochondrial apoptosis pathway dependent on JNK.
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