Uncarboxylated osteocalcin (uOC) is a circulating bone matrix protein, which has previously been shown to regulate glucose uptake and systemic metabolism. However, the cellular mechanism by which uOC acts has yet to be elucidated. C2C12 mouse myotubes were treated for 72 h with uOC (1–100 ng/mL). Cellular metabolism was analyzed using oxygen consumption and extracellular acidification rate. Metabolic gene and protein expression were measured via quantitative real-time polymerase chain reaction and Western blot, respectively. Additionally, C2C12 myotubes were treated with 10 ng/mL uOC to examine glucose uptake and activation of insulin signaling with or without insulin resistance. Finally, cellular lipid content was measured via Oil Red O and Nile Red staining. uOC treatment resulted in dose-dependent alterations of oxygen consumption with little effect on regulators of mitochondrial metabolism. Basal expression of regulators of glucose uptake were unaffected by uOC treatment. However, insulin-stimulated glucose uptake was blunted by uOC treatment with no concurrent alterations in insulin signaling. While chronic insulin treatment resulted in suppressed activation of Akt, concurrent uOC treatment was unable to prevent these detrimental effects on insulin signaling. uOC treatment had no effect on markers of lipogenesis and cellular lipid content. These findings suggest that 72-h uOC treatment may alter oxygen consumption without effect on regulators of mitochondrial biogenesis. Additionally, uOC treatment suppressed insulin-stimulated glucose uptake in cultured myotubes but had little effect on insulin signaling or regulators of cellular metabolism and was unable to mitigate insulin resistance.

中文翻译：

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未羧化的骨钙素减少胰岛素刺激的葡萄糖摄取，而不影响胰岛素信号和肌管中线粒体生物发生的调节剂。

未羧化骨钙素（uOC）是一种循环的骨基质蛋白，以前已被证明可以调节葡萄糖的摄取和全身代谢。但是，尚未阐明uOC作用的细胞机制。用uOC（1–100 ng / mL）处理C2C12小鼠肌管72小时。使用氧气消耗和细胞外酸化率分析细胞代谢。通过定量实时聚合酶链反应和蛋白质印迹分别测量代谢基因和蛋白质表达。另外，用10 ng / mL uOC处理C2C12肌管，以检查葡萄糖摄取和有或没有胰岛素抵抗的胰岛素信号传导的激活。最后，通过油红O和尼罗红染色测量细胞脂质含量。uOC处理导致氧气消耗的剂量依赖性变化，而对线粒体代谢调节剂的影响很小。葡萄糖摄取调节剂的基础表达不受uOC处理的影响。然而，uOC治疗使胰岛素刺激的葡萄糖摄取减弱，而胰岛素信号传导没有同时改变。虽然慢性胰岛素治疗导致Akt的激活受到抑制，但同时进行uOC治疗无法预防这些对胰岛素信号传导的有害影响。uOC处理对脂肪生成和细胞脂质含量的标志物没有影响。这些发现表明72小时的uOC处理可能会改变耗氧量，而不会影响线粒体生物发生的调节剂。另外，