Cell Induction and Regulation Field, Department of Clinical Application, Center for iPS Cell Research and Application, Kyoto University, Japan.
Cell Induction and Regulation Field, Department of Clinical Application, Center for iPS Cell Research and Application, Kyoto University, Japan.
Biochem Biophys Res Commun. 2019 Sep 3;516(4):1097-1102. doi: 10.1016/j.bbrc.2019.06.139. Epub 2019 Jul 5.
The maturation of chondrocytes is strictly regulated for proper endochondral bone formation. Although recent studies have revealed that intracellular metabolic processes regulate the proliferation and differentiation of cells, little is known about how changes in metabolite levels regulate chondrocyte maturation. To identify the metabolites which regulate chondrocyte maturation, we performed a metabolome analysis on chondrocytes of Sik3 knockout mice, in which chondrocyte maturation is delayed. Among the metabolites, acetyl-CoA was decreased in this model. Immunohistochemical analysis of the Sik3 knockout chondrocytes indicated that the expression levels of phospho-pyruvate dehydrogenase (phospho-Pdh), an inactivated form of Pdh, which is an enzyme that converts pyruvate to acetyl-CoA, and of Pdh kinase 4 (Pdk4), which phosphorylates Pdh, were increased. Inhibition of Pdh by treatment with CPI613 delayed chondrocyte maturation in metatarsal primordial cartilage in organ culture. These results collectively suggest that decreasing the acetyl-CoA level is a cause and not result of the delayed chondrocyte maturation. Sik3 appears to increase the acetyl-CoA level by decreasing the expression level of Pdk4. Blocking ATP synthesis in the TCA cycle by treatment with rotenone also delayed chondrocyte maturation in metatarsal primordial cartilage in organ culture, suggesting the possibility that depriving acetyl-CoA as a substrate for the TCA cycle is responsible for the delayed maturation. Our finding of acetyl-CoA as a regulator of chondrocyte maturation could contribute to understanding the regulatory mechanisms controlling endochondral bone formation by metabolites.
软骨细胞的成熟受到严格调控，以保证正常的软骨内骨形成。尽管最近的研究表明细胞内代谢过程调节细胞的增殖和分化，但对于代谢物水平如何调节软骨细胞成熟知之甚少。为了鉴定调控软骨细胞成熟的代谢物，我们对 Sik3 敲除小鼠的软骨细胞进行了代谢组学分析，该模型中软骨细胞成熟被延迟。在这些代谢物中，乙酰辅酶 A（acetyl-CoA）在该模型中减少。Sik3 敲除软骨细胞的免疫组织化学分析表明，磷酸丙酮酸脱氢酶（phospho-Pdh）的表达水平增加，磷酸化形式的 Pdh 是将丙酮酸转化为乙酰辅酶 A 的酶，而 Pdh 激酶 4（Pdk4）是磷酸化 Pdh 的酶。用 CPI613 抑制 Pdh 可延迟体外培养的跖骨干骺端软骨中软骨细胞的成熟。这些结果共同表明，降低乙酰辅酶 A 水平是软骨细胞成熟延迟的原因而不是结果。Sik3 似乎通过降低 Pdk4 的表达水平来增加乙酰辅酶 A 水平。用鱼藤酮阻断三羧酸循环中的 ATP 合成也可延迟体外培养的跖骨干骺端软骨中软骨细胞的成熟，这表明剥夺乙酰辅酶 A 作为三羧酸循环的底物可能是导致成熟延迟的原因。我们发现乙酰辅酶 A 是软骨细胞成熟的调节剂，这有助于理解代谢物调控软骨内骨形成的调控机制。
