Phosphate-induced apoptosis of hypertrophic chondrocytes is associated with a decrease in mitochondrial membrane...

Area of Science:

• Skeletal Biology
• Cellular Biology
• Endocrinology

Background:

• Growth plate abnormalities are linked to impaired chondrocyte apoptosis and disruptions in vitamin D action or phosphate reabsorption.
• Low phosphate levels inhibit hypertrophic chondrocyte apoptosis, while phosphate treatment activates this process via the mitochondrial pathway.

Purpose of the Study:

• To investigate the factors regulating hypertrophic chondrocyte apoptosis.
• To elucidate the role of phosphate in chondrocyte apoptosis and growth plate maturation.

Main Methods:

• Primary murine chondrocytes were cultured to assess mitochondrial membrane potential (JC-1 fluorescence) and apoptosis following phosphate treatment.
• Erk1/2 phosphorylation was evaluated in vitro and in vivo.
• Murine embryonic metatarsals were cultured under phosphate-restricted conditions to analyze parathyroid hormone-related protein (PTHrP) mRNA and phospho-Erk levels.

Main Results:

• Phosphate treatment increased the percentage of cells with low mitochondrial membrane potential in hypertrophic chondrocytes.
• Phosphate-induced apoptosis was dependent on Erk1/2 phosphorylation, confirmed by in vivo inhibition studies.
• Phosphate restriction in cultured metatarsals led to increased PTHrP mRNA and decreased phospho-Erk in hypertrophic chondrocytes.

Conclusions:

• Phosphate plays a key role in regulating mitochondrial membrane potential in hypertrophic chondrocytes, promoting apoptosis.
• The Erk1/2 signaling pathway is essential for phosphate-mediated chondrocyte apoptosis and growth plate maturation.
• The parathyroid hormone-related protein (PTHrP) signaling pathway is involved in phosphate's regulation of chondrocyte apoptosis and growth plate development.