Yoshikawa Yoshihiro, Yoshizawa Tatsuya, Domae Eisuke, Hirai Yuya, Kamada Aiko, Okazaki Toshiro, Ikeo Takashi
Department of Biochemistry, Osaka Dental University.
Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University.
Biomed Res. 2019;40(5):189-196. doi: 10.2220/biomedres.40.189.
Sphingomyelin is a major lipid of the plasma membrane and is enriched in microdomains of the plasma membrane that are critical for signal transduction. However, the function of sphingomyelin in the cell membrane of osteoblasts has not been clarified. Therefore, we examined how sphingomyelin synthase 2 (SMS2) affects osteoclast differentiation by osteoblasts. We knocked down the expression of SMS2 with siRNA targeting the Sgms2 gene in mouse primary osteoblasts. The effects of SMS2 knockdown in osteoblasts were examined using polymerase chain reaction and western blotting. The knockdown of SMS2 suppressed the formation of TRAP-positive multinucleated cells by co-culture of osteoblasts and bone marrow cells compared to the control. We found that receptor activator of nuclear factor κB ligand (RANKL) mRNA expression was significantly reduced by 1,25(OH)D stimulation in SMS2 siRNA osteoblasts. The knockdown of SMS2 repressed the expression of retinoid-X-receptor-α (RXRα) regardless of 1,25(OH)D stimulation. TRAP-positive multinucleated cell formation was significantly reduced by RXRα siRNA in osteoblasts in a co-culture system. These results suggest that SMS2 regulates osteoclast differentiation by inducing RANKL expression via RXRα.
鞘磷脂是质膜的主要脂质，在质膜的微结构域中含量丰富，这些微结构域对信号转导至关重要。然而，鞘磷脂在成骨细胞膜中的功能尚未阐明。因此，我们研究了鞘磷脂合成酶2（SMS2）如何影响成骨细胞介导的破骨细胞分化。我们用靶向Sgms2基因的siRNA敲低了小鼠原代成骨细胞中SMS2的表达。使用聚合酶链反应和蛋白质印迹法检测了SMS2敲低对成骨细胞的影响。与对照组相比，SMS2的敲低抑制了成骨细胞与骨髓细胞共培养时TRAP阳性多核细胞的形成。我们发现，在SMS2 siRNA转染的成骨细胞中，1,25(OH)D刺激显著降低了核因子κB受体激活剂配体（RANKL）mRNA的表达。无论是否有1,25(OH)D刺激，SMS2的敲低均抑制了视黄酸X受体α（RXRα）的表达。在共培养系统中，RXRα siRNA显著减少了成骨细胞中TRAP阳性多核细胞的形成。这些结果表明，SMS2通过RXRα诱导RANKL表达来调节破骨细胞分化。
