Background: Cell-mediated initiation of enchondral ossification is essential for growth plate maturation. The matrix mineralization inhibitors matrix Gla protein (MGP) and osteocalcin (OC) represent key regulators of matrix mineralization and are highly expressed in growth plate chondrocytes. Pharmacological or nutritional phylloquinone (K1) depletion is known to affect skeletal mineralization by reduced gamma-carboxilisation of MGP and OC. Constituents of mineral matrix such as calcium and magnesium (Mg) additionally regulate expression of mineralization inhibitors on gene expression level.
Objective and hypotheses: The effects of clinically relevant modifiers of mineralization inhibitor activity on growth plate chondrocytes is unclear. This study aims to investigate the effects of K and Mg on growth plate chondrocyte differentiation and proliferation.
Method: Chondrogenic ATDC5 alginate bead cultured are treated with 1, 10 or 100 uM K1 with or without presence of 2.5 mM Mg for 14 d. Chondrocyte differentiation marker and matrix inhibitor expression is investigated by RT-PCR. BrdU and EZ4U assays are used for cell proliferation and metabolic activity determination.
Results: K1 reduces expression of collagen type I, II and X in a dose dependent manner. Presence of 2.5 mM Mg partly rescued collagen expression resulting in significantly increased collagen type II and X expression during differentiation.
Conclusion: We found K1 and Mg as modifiers of MGP and OC activity, to affect chondrocyte differentiation inversely. While K1 downregulates collagen expression in ATDC5 prechondrocytes, Mg reverses these effects. Our data point to a possible counter regulation of matrix mineralization and growth plate maturation by Mg and K1.
10 - 12 Sep 2016
European Society for Paediatric Endocrinology