Smith Charles Owen, Eliseev Roman A
Center for Musculoskeletal Research, University of Rochester School of Medicine & Dentistry, Rochester, New York, USA.
Stem Cells Dev. 2021 Feb;30(3):149-162. doi: 10.1089/scd.2020.0141. Epub 2021 Jan 11.
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.
成骨分化是骨髓间充质干/基质（又称骨骼干细胞）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较为人所知；然而，随之而来的细胞能量代谢变化却不太明确。我们和其他人之前曾报道过成骨分化过程中线粒体的激活。为了进一步阐明其中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-甘油磷酸的成骨培养基，或各种成骨激素和生长因子对源自长骨（ST2）和颅骨（MC3T3-E1）的骨祖细胞能量代谢的影响。我们发现成骨培养基和分化因子Wnt3a和BMP2刺激线粒体氧化磷酸化（OxPhos），而对糖酵解影响很小。OxPhos的激活迅速发生，表明是代谢信号变化而非蛋白质表达变化。为此，我们发现观察到的线粒体激活是Akt依赖性的。Akt被成骨培养基、Wnt3a和BMP2激活，导致各种线粒体Akt靶点的磷酸化增加，这是一种已知可刺激OxPhos的现象。总之，我们的数据对两种不同来源（间充质与神经嵴）细胞在骨诱导过程中的细胞生物能量学进行了全面分析，并确定Wnt3a和BMP2是通过Akt激活来刺激线粒体呼吸的生理刺激因子。
