The expression of lipid metabolism genes in bone are altered by mechanical stimuli

Osteoblasts and adipocytes are two differentiated cell types which are both derived from mesenchymal stem cells (MSCs) and a reciprocal relationship may exist between osteoblastogenesis and adipogenesis in the bone marrow. Our previous studies in the mouse have indicated that low-magnitude, high-frequency mechanical stimuli can stimulate bone formation. To investigate whether lipid metabolism gene expression is altered during the application of low-level mechanical stimuli, adult female BALB/cByJ mice were subject to either disuse, mechanical vibration, or control conditions. RNA was extracted from the bones upon sacrifice after 4d. By microarray we screened lipid metabolism genes and confirmed them with real-time RT-PCR. Three genes were picked up - PPAR-gamma, Alox15 and Lrp5. PPAR-gamma and Alox15 were significantly down-regulated with mechanical vibrations, while Lrp5 was significantly down-regulated with disuse as indicated by the microarray data. It is speculated that mechanical stimuli down-regulate PPARgamma and Alox15, both of which are involved in promotion of osteoblastogenesis and inhibition of adipogenesis, result in bone formation and fat loss. However, disuse modulated gene expression changes in lipid metabolism were not necessarily opposite from those suffering from mechanical stimuli.