High extracellular Ca2+ enhances the adipocyte accumulation of bone marrow stromal cells through a decrease in cAMP

Abstract Bone marrow stromal cells (BMSCs) are common progenitors of both adipocytesand osteoblasts. We recently suggested that increased [Ca 2+ ] o caused by bone resorptionmight accelerate adipocyteaccumulation in response to treatment with both insulin and dexamethasone. In this study, we investigated the mechanism by which high [Ca 2+ ] o enhances adipocyteaccumulation. We used primary mouse BMSCs and evaluated the levels of adipocyteaccumulation by measuring Oil Red Ostaining. CaSR agonists (both Ca 2+ and Sr 2+ ) enhanced the accumulation of adipocytesamong BMSCs in response to treatment with both insulin and dexamethasone. We showed that high [Ca 2+ ] o decreases the concentration of cAMP using ELISA. Real-time RT-PCR revealed that increasing the intracellular concentration of cAMP (both chemical inducer (1 μM forskolinand 200 nM IBMX) and a cAMP analog (10 μM pCPT-cAMP)) suppressed the expression of PPARγ and C/EBPα. In addition, forskolin, IBMX, and pCPT-cAMP inhibited the enhancement in adipocyteaccumulation under high [Ca 2+ ] o in BMSCs. However, this inhibited effect was not observed in BMSCs that were cultured in a basal concentration of [Ca 2+ ] o . We next observed that the accumulation of adipocytesin the of bone marrow of middle-aged mice (25–40 weeks old) is higher than that of young mice (6 weeks old) based on micro CT. ELISA results revealed that the concentration of cAMP in the bone marrow mononuclear cells of middle-aged mice is lower than that of young mice. These data suggest that increased [Ca 2+ ] o caused by bone resorptionmight accelerate adipocyteaccumulation through CaSR following a decrease in cAMP.