Reduced femoral bone mass in both diet-induced and genetic hyperlipidemia mice

Growing evidence argues for a relationship between lipid and bone metabolisms with inconsistent conclusions. Sphingosine-1-phosphate (S1P) has been recognized as a suitable candidate for possible link between lipid metabolism and bone metabolism. This study was designed to investigate the effects of hyperlipidemia on bone metabolism using diet-induced and genetic-induced hyperlipidemia animal models and to explore whether S1P is involved. Wild-type mice and low-density lipoprotein receptor gene deficient (LDLR^-/-) mice at age of 8weeks were placed on either control diet or high-fat diet (HFD) for 12weeks. Bone structural parameters were determined using microCT. Cross-linked type I collagen (CTx) and S1P levels in plasma were measured by ELISA methods. Bone marrow cells from wild type and LDLR^-/- mice were induced to differentiate into osteoblasts, osteoclasts and adipocytes respectively. Gene expressions in distal femur metaphyses and cultured cells were studied by qRT-PCR. Moderate hypercholesterolemia was found in HFD-feeding mice; severe hypercholesterolemia and moderate hypertriglyceridemia were present in LDLR^-/- mice. Femoral trabecular bone mass was reduced in both diet-induced and genetic hyperlipidemia mice. Mice feeding on HFD showed higher CTx levels, and mice with hyperlipidemia had elevated S1P levels. Correlation analysis found a positive correlation between CTx and S1P levels. Lower Runx2 expression and higher TRAP expression were found in both diet-induced and genetic hyperlipidemia mice, indicating decreased osteoblastic functions and increased osteoclastic functions in these mice. Bone marrow cells from LDLR^-/- mice also showed increased adipogenesis and inhibited osteogenesis accompanied by enhanced PPARγ expression. In conclusion, our study found decreased bone mass in both diet-induced and genetic hyperlipidemia mice.