OBJECTIVE In muscle cells, the peroxisome proliferator-activated receptor γ co-activator 1 (PGC-1) signaling network, which has been shown to be disturbed in the skeletal muscle in several chronic diseases, tightly controls mitochondrial biogenesis and oxidative substrate metabolism. Previously, we showed that inactivation of glycogen synthase kinase (GSK)-3β potently increased Pgc-1α abundance and oxidative metabolism in skeletal muscle cells. The current study aims to unravel the molecular mechanism driving the increase in Pgc-1α mediated by GSK-3β inactivation. METHODS GSK-3β was inactivated genetically or pharmacologically in C2C12 myotubes and the requirement of transcription factors known to be involved in Pgc-1α transcription for increases in Pgc-1α abundance mediated by inactivation of GSK-3β was examined. RESULTS Enhanced PGC-1α promoter activation after GSK-3β inhibition suggested a transcriptionally-controlled mechanism. While myocyte enhancer factor (MEF)2 transcriptional activity was unaltered, GSK-3β inactivation increased the abundance and activity of the transcription factors estrogen-related receptor (ERR)α and ERRγ. Pharmacological inhibition or knock-down of ERRα and ERRγ however failed to prevent increases in Pgc-1α mRNA mediated by GSK-3β inactivation. Interestingly, GSK-3β inactivation activated transcription factor EB (TFEB), evidenced by decreased phosphorylation and enhanced nuclear localization of the TFEB protein. Moreover, knock-down of TFEB completely prevented increases in Pgc-1α gene expression, PGC-1α promoter activity and PGC-1α protein abundance induced by GSK-3β inactivation. Furthermore, mutation of a specific TFEB binding site on the PGC-1α promoter blocked promoter activation upon inhibition of GSK-3β. CONCLUSIONS In skeletal muscle, GSK-3β inactivation causes dephosphorylation and nuclear translocation of TFEB resulting in TFEB-dependent induction of Pgc-1α expression.

中文翻译：

---

骨骼肌中 GSK-3β-TFEB 信号轴对 PGC-1α 表达的调节。


目的 在肌肉细胞中，过氧化物酶体增殖物激活受体 γ 共激活剂 1 (PGC-1) 信号网络严格控制线粒体生物合成和氧化底物代谢，该网络已被证明在多种慢性疾病中在骨骼肌中受到干扰。之前，我们发现糖原合成酶激酶（GSK）-3β 的失活可有效增加骨骼肌细胞中 Pgc-1α 的丰度和氧化代谢。目前的研究旨在揭示 GSK-3β 失活介导的 Pgc-1α 增加的分子机制。方法 GSK-3β 在 C2C12 肌管中通过基因或药理学失活，并检查了已知参与 Pgc-1α 转录的转录因子对 GSK-3β 失活介导的 Pgc-1α 丰度增加的需求。结果 GSK-3β 抑制后 PGC-1α 启动子激活增强，提示存在转录控制机制。虽然肌细胞增强因子 (MEF)2 转录活性未改变，但 GSK-3β 失活增加了转录因子雌激素相关受体 (ERR)α 和 ERRγ 的丰度和活性。然而，ERRα 和 ERRγ 的药理学抑制或敲低未能阻止 GSK-3β 失活介导的 Pgc-1α mRNA 增加。有趣的是，GSK-3β 失活激活了转录因子 EB (TFEB)，证据是 TFEB 蛋白的磷酸化减少和核定位增强。此外，敲低 TFEB 完全阻止了 GSK-3β 失活诱导的 Pgc-1α 基因表达、PGC-1α 启动子活性和 PGC-1α 蛋白丰度的增加。此外，PGC-1α 启动子上特定 TFEB 结合位点的突变阻止了 GSK-3β 抑制后启动子的激活。 结论 在骨骼肌中，GSK-3β 失活导致 TFEB 去磷酸化和核转位，从而导致 TFEB 依赖性诱导 Pgc-1α 表达。