Department of Exercise Science, High Point University, High Point, NC, 27268, USA.
School of Kinesiology, Auburn University, Auburn, AL, 36849, USA.
J Physiol Biochem. 2020 Feb;76(1):169-178. doi: 10.1007/s13105-020-00732-6. Epub 2020 Feb 13.
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.
未羧化骨钙素（uOC）是一种循环骨基质蛋白，先前已被证明可调节葡萄糖摄取和全身代谢。然而，uOC 发挥作用的细胞机制尚未阐明。用 uOC（1-100ng/mL）处理 C2C12 小鼠肌管 72 小时。通过耗氧量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 Western blot 分别测量代谢基因和蛋白质表达。此外，用 10ng/mL uOC 处理 C2C12 肌管，检查葡萄糖摄取和胰岛素信号激活情况，以及是否存在胰岛素抵抗。最后，通过油红 O 和尼罗红染色测量细胞内脂质含量。uOC 处理导致耗氧量呈剂量依赖性改变，而对线粒体代谢调节剂的影响很小。uOC 处理对葡萄糖摄取调节剂的基础表达没有影响。然而，uOC 处理会削弱胰岛素刺激的葡萄糖摄取，而胰岛素信号没有同时改变。虽然慢性胰岛素处理导致 Akt 的激活受到抑制，但同时用 uOC 处理并不能防止这些对胰岛素信号的不利影响。uOC 处理对脂肪生成标志物和细胞内脂质含量没有影响。这些发现表明，72 小时 uOC 处理可能改变耗氧量，而对线粒体生物发生调节剂没有影响。此外，uOC 处理抑制了培养的肌管中胰岛素刺激的葡萄糖摄取，但对胰岛素信号或细胞代谢调节剂几乎没有影响，并且无法减轻胰岛素抵抗。
