1α,25-Dihydroxyvitamin D3 modulation in lipid metabolism in established bone marrow-derived stromal cells, MC3T3-G2/PA6

MC3T3-G2/PA6 (PA6) cells established from newborn mouse calvaria are preadipocytic stromal cells, which differentiate into adipocytes in response to glucocorticoids. We examined the effects of 1α,25-dihydroxyvitamin D3[1α,25(OH)2D3] on adipogenesis in PA6 cells were cultured with 10−8 M dexamethasone, adipocytes containing oil red O-positive droplets first appeared on day 7 (3 days after confluence was attained) and the maximal synthesis of neutral lipids occurred on day 12. Simultaneous addition of 1α,25(OH)2D3 at 10−9 M completely blocked this dexamethasone-induced neutral lipid synthesis throughout the 14-day culture period. Dose-response studies of vitamin D3 derivatives showed that 1α,25(OH)2D3 was the most potent in inhibiting neutral lipid synthesis in PA6 cells, followed by 1α-hydroxyvitamin D3, 25-hydroxyvitamin D3 and 24R,25-dihydroxyvitamin D3, in that order. Dexamethasone greatly enhanced incorporation of [14C]-acetic acid into triacylglycerol in PA6 cells. The incorporation was markedly inhibited by the addition of 10−9 M 1α,25(OH)2D3 Instead, 1α,25(QH)2D3 greatly increased incorporation of [14C]-acetic acid into phospholipids, such as phosphatidylcholine and phosphatidylethanolamine, irrespective of the presence or absence of dexamethasone. These results suggest that 1α,25(OH)2D3 modulation of lipid metabolism in bone marrow stromal cells is receptor mediated.