FoxO轉錄因子已經被指出在細胞中有多樣的功能，包括葡萄糖的代謝、壓力反應、分化、細胞週期、細胞的死亡與生存。在FoxO家族成員中的foxo6主要表達在正在發育階段的腦部及肌肉組織，但是其在骨骼肌中主要的功能目前還不知道。PGC-1α是一個轉錄作用的協同活化子且也是一個重要的代謝調控者。而PGC-1α也會調控粒線體的生成，所以當在骨格肌大量表達PGC-1α會導致粒腺體含量增加。當我們誘導C2C12-mFoxO6肌原母細胞株去經歷終極分化，其肌管的大小及肌管的數量都遠比C2C12-control肌原母細胞株來得小及少。當我們誘導Sol8-mFoxO6肌原母細胞株分化，也可以觀察到並沒有肌管的形成。然而我們觀察到C2C12-mFoxO6細胞週期主要都在G0/G1期。我們開始去分析adheren junction的表現量，在細胞分化階段中，這些adheren junction的基因表現量在C2C12穩定表現FoxOs的細胞株中並沒有太大的不一樣，但是在Sol8-mFoxO6細胞株中它們表現量幾乎都是被調控下降的，我們進一步發現Sol8-mFoxO6及C2C12-mFoxO6的分化情形可以在處理胰島素之後有所回復且在Sol8-mFoxO6中其MyoD、myogenin及M-cadherin的表現量可以被回復增加。我們也發現在緊靠擠滿的C2C12中大量表現FoxO6可以抑制PGC-1α的表現，因此我們認為也許是FoxO6經由結合到PGC-1α啟動子上面導致其活性被抑制。經由Reporter assay證明FoxO6的確可以抑制PGC-1α啟動子的活性。在未來，我們希望可以明確知道PGC-1α與FoxO6之間調控的路徑及其對於肌肉分化調控的路徑為何。 FoxO transcription factors have been implicated in regulating diverse cellular functions including glucose metabolism, stress response, differentiation, cell cycle, cell death and cell survival. One of the members, Foxo6, is majorly expressed in the developing brain and muscle but whose functions in skeletal muscle are largely unknown. PGC-1α is a transcriptional coactivator and important metabolic regulator. It regulates mitochondrial biogenesis and overexpression of PGC-1α results in mitochondrial content increase in skeletal muscle. When C2C12-mFoxO6 myoblast were induced to undergo terminal differentiation, the number and size of myotube formed were significantly smaller than that of C2C12-control cells. No myotube formation was observed when Sol8-mFoxO6 myoblasts were induced to differentiation. However strong cell cycle exit was observed in C2C12-mFoxO6 cells. We set out to analyze the expression of adheren junction. At differentiation stage, the expression levels of these genes are not significantly different among C2C12 stable clones. But they genes were down-regulated in Sol8-mFoxO6. We further found that terminal differentiation of Sol8-mFoxO6 and C2C12-mFoxO6 can be rescued by insulin treatment and expression of myoD, myogenin and M-cadherin can be increased in Sol8-mFoxO6 cells. We also found that overexpression of Foxo6 repress expression of PGC-1α gene in confluent C2C12 myoblast. Thus, we think Foxo6 protein may inhibit PGC-1α promoter activity via direct binding to it. Reporter assays demonstrate that FoxO6 suppresses the PGC-1 promoter activity. In the future, we hope that we can define the regulation network involing PGC-1 and FoxO6 and how myogenesis is regulated by the network.
