Osteogenic differentiation, the process by which bone marrow mesenchymal stem/stromal (a.k.a. skeletal stem) cells and osteoprogenitors form osteoblasts, is a critical event for bone formation during development, fracture repair, and tissue maintenance. Extra cellular and intracellular signaling pathways triggering osteogenic differentiation are relatively well known; however, the ensuing change in cell energy metabolism is less clearly defined. We and others have previously reported activation of mitochondria during osteogenic differentiation. To further elucidate the involved bioenergetic mechanisms and triggers, we tested the effect of osteogenic media containing ascorbate and β-glycerol phosphate, or various osteogenic hormones and growth factors on energy metabolism in long bone (ST2)- and calvarial bone (MC3T3-E1)-derived osteoprogenitors. We show that osteogenic media and differentiation factors, Wnt3a and BMP2, stimulate mitochondrial oxidative phosphorylation (OxPhos) with little effect on glycolysis. The activation of OxPhos occurs acutely, suggesting a metabolic signaling change rather than protein expression change. To this end, we found that the observed mitochondrial activation is Akt dependent. Akt is activated by osteogenic media, Wnt3a, and BMP2, leading to increased phosphorylation of various mitochondrial Akt targets, a phenomenon known to stimulate OxPhos. In sum, our data provide comprehensive analysis of cellular bioenergetics during osteoinduction in cells of two different origins (mesenchyme vs neural crest) and identify Wnt3a and BMP2 as physiological stimulators of mitochondrial respiration through Akt activation.

中文翻译：

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成骨分化过程中的能量代谢：Akt 的作用

成骨分化是骨髓间充质干/基质（又名骨骼干）细胞和骨祖细胞形成成骨细胞的过程，是发育、骨折修复和组织维持过程中骨形成的关键事件。触发成骨分化的细胞外和细胞内信号通路相对众所周知。然而，随后的细胞能量代谢变化尚不清楚。我们和其他人以前曾报道过成骨分化过程中线粒体的激活。为了进一步阐明所涉及的生物能量机制和触发因素，我们测试了含有抗坏血酸和 β-甘油磷酸盐或各种成骨激素和生长因子的成骨培养基对长骨 (ST2) 和颅骨 (MC3T3-E1) 能量代谢的影响衍生的骨祖细胞。我们表明，成骨培养基和分化因子 Wnt3a 和 BMP2 可刺激线粒体氧化磷酸化 (OxPhos)，而对糖酵解几乎没有影响。OxPhos 的激活发生剧烈，表明代谢信号变化而不是蛋白质表达变化。为此，我们发现观察到的线粒体激活依赖于 Akt。Akt 被成骨介质、Wnt3a 和 BMP2 激活，导致各种线粒体 Akt 靶标的磷酸化增加，这是一种已知会刺激 OxPhos 的现象。总之，我们的数据提供了对两种不同来源（间充质与神经嵴）细胞骨诱导过程中细胞生物能量学的综合分析，并通过 Akt 激活将 Wnt3a 和 BMP2 鉴定为线粒体呼吸的生理刺激物。