Low Magnesium Concentration Enforces Bone Calcium Deposition Irrespective of 1,25-Dihydroxyvitamin D(3) Concentration

Efficient coordination between Mg(2+) and vitamin D maintains adequate Ca(2+) levels during lactation. This study explored the possible interaction between Mg(2+) (0.3, 0.8, and 3 mM) and 1,25-dihydroxyvitamin D(3) (1,25D; 0.05 and 5 nM) during osteogenesis using bovine mesenchymal stem cells. After 21 days, differentiated osteocytes were subjected to OsteoImage analysis, alkaline phosphatase (ALP) activity measurements, and immunocytochemistry of NT5E, ENG (endoglin), SP7 (osterix), SPP1 (osteopontin), and the BGLAP gene product osteocalcin. The mRNA expression of NT5E, THY1, ENG, SP7, BGLAP, CYP24A1, VDR, SLC41A1, SLC41A2, SLC41A3, TRPM6, TRPM7, and NIPA1 was also assessed. Reducing the Mg(2+) concentration in the medium increased the accumulation of mineral hydroxyapatite and ALP activity. There was no change in the immunocytochemical localization of stem cell markers. Expression of CYP24A1 was higher in all groups receiving 5 nM 1,25D. There were tendencies for higher mRNA abundance of THY1, BGLAP, and NIPA1 in cells receiving 0.3 mM Mg(2+) and 5 nM 1,25D. In conclusion, low levels of Mg(2+) greatly enhanced the deposition of bone hydroxyapatite matrix. The effect of Mg(2+) was not modulated by 1,25D, although the expression of certain genes (including BGLAP) tended to be increased by the combination of low Mg(2+) and high 1,25D concentrations.