Bisphosphonates and adipogenesis: evidence for alendronate inhibition of adipocyte differentiation in 3T3-L1 preadipocytes through a vitamin D receptor mediated effect

Background: Adipocyte and osteoblast derive from the same mesenchimal progenitor. Age- related decrease in bone mass is accompanied by an increase in marrow adipose tissue. Vita- min D3 (VD3) inhibits adipogenesis in 3T3-L1 preadipocytes. Recently it has been demon- strated that alendronate (ALN) inhibits adipo- genesis while promoting osteoblast differentia- tion of mesenchimal stem cells. Aim of the Study: To evaluate the role of ALN on adipocyte differ-entiation in vitro and the potential synergic role of VD3 co-treatment. Procedures: Murine 3T3-L1 and 3T3-F442A preadipocytes were routinely differentiated in presence of ALN and VD3 10−9 - 10−7 M for 7 days and then stained with Oil Red O. The effect of these treatments on mRNA ex- pression of the main molecular markers of adi- pocyte differentiation (PPARγ and C/EBPα) and VD Receptor (VDR) were analyzed through RT- PCR. Results: Both ALN and VD3 showed a marked anti-adipogenic effect on 3T3-L1 cells. Co-incubation of ALN 10−8 M and VD3 10−9 M dis- played no synergic effect on inhibition of adi- pogenesis. PPARγ mRNA expression was sig- nificantly reduced by ALN and VD3. mRNA ex- pression of C/EBPα was reduced only by VD3 treatment. An increase in VDR mRNA expression of 3T3-L1 cells was observed with both ALN and VD3. On the contrary, 3T3-F442A cells, which are in a more advanced adipogenic differentiation stage compared to 3T3-L1, did not express de- tectable levels of VDR. Interestingly, adipose dif- ferentiation of 3T3-F442A was not affected by ALN nor VD3. These results suggest that VDR may represent the molecular target of the anti- adipogenic effect of ALN. Conclusion: VDR plays a critical role in mediating the anti-adipogenic effect of ALN. Further studies