Kusuyama Joji, Kamisono Ai, ChangHwan Seong, Amir Muhammad S, Bandow Kenjiro, Eiraku Nahoko, Ohnishi Tomokazu, Matsuguchi Tetsuya
Department of Oral Biochemistry, Field of Developmental Medicine, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Department of Oral and Maxillofacial Surgery, Field of Oral and Maxillofacial Rehabilitation, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
J Cell Physiol. 2018 Mar;233(3):2549-2559. doi: 10.1002/jcp.26130. Epub 2017 Sep 28.
Bone marrow stromal cells (BMSCs) are multipotent cells that can differentiate into adipocytes and osteoblasts. Inadequate BMSC differentiation is occasionally implicated in chronic bone metabolic disorders. However, specific signaling pathways directing BMSC differentiation have not been elucidated. Here, we explored the roles of spleen tyrosine kinase (Syk) in BMSC differentiation into adipocytes and osteoblasts. We found that Syk phosphorylation was increased in the early stage, whereas its protein expression was gradually decreased during the adipogenic and osteogenic differentiation of two mouse mesenchymal stromal cell lines, ST2 and 10T(1/2), and a human BMSC line, UE6E-7-16. Syk inactivation with either a pharmacological inhibitor or Syk-specific siRNA suppressed adipogenic differentiation, characterized by decreased lipid droplet appearance and the gene expression of fatty acid protein 4 (Fabp4), peroxisome proliferator-activated receptor γ2 (Pparg2), CCAAT/enhancer binding proteins α (C/EBPα), and C/EBPβ. In contrast, Syk inhibition promoted osteogenic differentiation, represented by increase in matrix mineralization and alkaline phosphatase (ALP) activity, as well as the expression levels of osteocalcin, runt-related transcription factor 2 (Runx2), and distal-less homeobox 5 (Dlx5) mRNAs. We also found that Syk-induced signals are mediated by phospholipase C γ1 (PLCγ1) in osteogenesis and PLCγ2 in adipogenesis. Notably, Syk-activated PLCγ2 signaling was partly modulated through B-cell linker protein (BLNK) in adipogenic differentiation. On the other hand, growth factor receptor-binding protein 2 (Grb2) was involved in Syk-PLCγ1 axis in osteogenic differentiation. Taken together, these results indicate that Syk-PLCγ signaling has a dual role in regulating the initial stage of adipogenic and osteogenic differentiation of BMSCs.
骨髓基质细胞（BMSCs）是多能细胞，可分化为脂肪细胞和成骨细胞。BMSC分化不足偶尔与慢性骨代谢紊乱有关。然而，指导BMSC分化的特定信号通路尚未阐明。在此，我们探讨了脾酪氨酸激酶（Syk）在BMSC向脂肪细胞和成骨细胞分化中的作用。我们发现，在两种小鼠间充质基质细胞系ST2和10T（1/2）以及人BMSC系UE6E-7-16的脂肪生成和成骨分化早期，Syk磷酸化增加，而其蛋白表达逐渐降低。用药物抑制剂或Syk特异性siRNA使Syk失活可抑制脂肪生成分化，其特征为脂滴出现减少以及脂肪酸蛋白4（Fabp4）、过氧化物酶体增殖物激活受体γ2（Pparg2）、CCAAT/增强子结合蛋白α（C/EBPα）和C/EBPβ的基因表达降低。相反，Syk抑制促进成骨分化，表现为基质矿化和碱性磷酸酶（ALP）活性增加，以及骨钙素、 runt相关转录因子2（Runx2）和远端缺失同源盒5（Dlx5）mRNA的表达水平增加。我们还发现，Syk诱导的信号在成骨过程中由磷脂酶Cγ1（PLCγ1）介导，在脂肪生成过程中由PLCγ2介导。值得注意的是，Syk激活的PLCγ2信号在脂肪生成分化中部分通过B细胞连接蛋白（BLNK）调节。另一方面，生长因子受体结合蛋白2（Grb2）参与成骨分化中的Syk-PLCγ1轴。综上所述，这些结果表明Syk-PLCγ信号在调节BMSCs脂肪生成和成骨分化的初始阶段具有双重作用。
