Kasai Takayuki, Bandow Kenjiro, Suzuki Hiraku, Chiba Norika, Kakimoto Kyoko, Ohnishi Tomokazu, Kawamoto Shin-ichiro, Nagaoka Eiichi, Matsuguchi Tetsuya
Department of Oral Biochemistry, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
J Cell Physiol. 2009 Dec;221(3):740-9. doi: 10.1002/jcp.21917.
Osteoblasts, originating from mesenchymal stem cells, play a pivotal role in bone formation and mineralization. Several transcription factors including runt-related transcription factor 2 (Runx2) have been reported to be essential for osteoblast differentiation, whereas the cytoplasmic signal transduction pathways controlling the differentiation process have not been fully elucidated. AMP-activated protein kinase (AMPK) is a serine-threonine kinase generally regarded as a key regulator of cellular energy homeostasis, polarity, and division. Recent lines of evidence have indicated that the activity of the catalytic alpha subunit of AMPK is regulated through its phosphorylation by upstream AMPK kinases (AMPKKs) including LKB1. Here, we explored the role of AMPK in osteoblast differentiation using in vitro culture models. Phosphorylation of AMPKalpha was significantly decreased during osteoblastic differentiation in both primary osteoblasts and MC3T3-E1, a mouse osteoblastic cell line. Conversely, the terminal differentiation of primary osteoblasts and MC3T3-E1 cells, represented by matrix mineralization, was significantly inhibited by glucose restriction and stimulation with metformin, both of which are known activators of AMPK. Matrix mineralization of MC3T3-E1 cells was also inhibited by the forced expression of a constitutively active form of AMPKalpha. Metformin significantly inhibited gene expression of Runx2 along with osteoblast differentiation markers including osteocalcin (Ocn), bone sialo protein (Bsp), and osteopontin (Opn). Thus, our present data indicate that differentiation of osteoblasts is functionally associated with decreased AMPK activity.
成骨细胞起源于间充质干细胞，在骨形成和矿化过程中发挥着关键作用。据报道，包括 runt 相关转录因子 2（Runx2）在内的几种转录因子对成骨细胞分化至关重要，而控制分化过程的细胞质信号转导途径尚未完全阐明。AMP 激活的蛋白激酶（AMPK）是一种丝氨酸 - 苏氨酸激酶，通常被认为是细胞能量稳态、极性和分裂的关键调节因子。最近的一系列证据表明，AMPK 催化性α亚基的活性通过其上游 AMPK 激酶（AMPKKs）包括 LKB1 的磷酸化来调节。在此，我们使用体外培养模型探讨了 AMPK 在成骨细胞分化中的作用。在原代成骨细胞和小鼠成骨细胞系 MC3T3 - E1 的成骨细胞分化过程中，AMPKα的磷酸化显著降低。相反，原代成骨细胞和 MC3T3 - E1 细胞的终末分化，以基质矿化表示，受到葡萄糖限制和二甲双胍刺激的显著抑制，这两种都是已知的 AMPK 激活剂。MC3T3 - E1 细胞的基质矿化也受到组成型活性形式的 AMPKα的强制表达的抑制。二甲双胍显著抑制 Runx2 以及包括骨钙素（Ocn）、骨唾液蛋白（Bsp）和骨桥蛋白（Opn）在内的成骨细胞分化标志物的基因表达。因此，我们目前的数据表明成骨细胞的分化在功能上与 AMPK 活性降低相关。
