Reduction by strontium of the bone marrow adiposity in mice and repression of the adipogenic commitment of multipotent C3H10T1/2 cells

Multipotent mesenchymal cells (MMCs) differentiate into osteoblasts or adipocytes through RUNX2 and PPAR gamma 2, respectively. Strontium ranelate has been shown to promote osteoblastogenesis and prevent adipogenesis in long-term experiments using MMCs. The present study involved in-vitro and in-vivo investigations of whether Sr might first be an inhibitor of adipogenesis, thus explaining late osteoblastogenesis. It was established in vivo that Sr reduces adipogenesis in mice treated only for 3 weeks with a 6 mmol/kg/day dose of Sr while the trabecular bone volume is increased. In order to decipher molecular mechanisms during inhibition of adipogenesis, we used murine MMCs C3H10T1/2 cultured under adipogenic conditions (AD) and treated Sr of a concentration up to 3 mM. It was shown that early on (day 1), Sr dose-dependently reduced PPAR gamma 2 and CEBPot. mRNA without affecting the RUNX2 gene expression whereas it repressed ALP mRNA. Later (day 5), PPAR gamma 2 and CEBP alpha mRNA remained inhibited by Sr, preventing adipocyte lipid accumulation, while Runx2 and ALP mRNA were increased. Moreover, under the mentioned conditions, Sr was able to quickly induce the Cyclin D1 gene expression, proliferation and fibronectin fibrillogenesis, both involved in the inhibition of adipogenesis. The inhibition of the ERK pathway by U0126 blunted the Srinduced PPAR gamma 2 repression while restoring the lipid accumulation. These results demonstrated that Sr was capable of rapidly reducing adipogenesis by a selective PPAR gamma 2 repression that can be explained by its ability to promote MMC proliferation. This article is part of a Special Issue entitled: Interactions Between Bone, Adipose Tissue and Metabolism. (C) 2011 Elsevier Inc. All rights reserved.