FoxO1 protects the heart against ischemia

总结 叉头盒蛋白O（FoxO）家族转录因子是进化上保守的蛋白质， 心脏在发育和出生后生理过程中的重要作用。FoxO在以下方面发挥着双重作用： 以环境依赖方式调节细胞存活/死亡：它们介导心肌细胞（CM）细胞 在某些条件下死亡，但在其他条件下促进细胞存活。FoxOs可以促进细胞死亡 通过刺激Bim、TRAIL、FasL、Bcl-6和NOXA的转录，或通过 下调IRS。另一方面，内源性FoxO促进CM存活以响应氧化应激。 应激和介导Sirt 1在缺血/再灌注（I/R）期间CM中的促存活作用。此外，FoxO 1- 自噬基因的依赖性转录是饥饿期间CM存活所必需的。目前， 然而，FoxO如何介导它们的二分细胞功能还没有很好地理解。更好地理解 潜在的机制可能只促进FoxO 1的有益功能， 在临床环境中抑制心脏中FoxO 1的促死亡功能。我们的初步结果表明 Mst 1是一种促凋亡激酶，它可以通过顺序性地将FoxO 1从促凋亡转化为促存活， CM中FoxO 1和C/EBP-beta的磷酸化。我们的总体假设是，Mst 1转换了 转录因子FoxO 1通过FoxO 1顺序磷酸化从促凋亡到促存活 在DNA结合结构域（DBD）和在Thr 250（小鼠）的C/EBP-结合酶。我们将：目标1显示FoxO 1 在心肌缺血和I/R期间通过Mst 1诱导at磷酸化促进CM存活 目的2证明Mst 1诱导FoxO 1从原- 凋亡FoxO靶基因及其与C/EBP-β的相关性促进促存活基因的转录 目的3证明Mst 1诱导的C/EBP-γ在Thr 250的磷酸化是FoxO 1- C/EBP-β的Thr 250磷酸化促进促存活因子的转录; 目的4证明Thr 250的C/EBP-1磷酸化是有益的，并在细胞凋亡中起重要作用。 介导缺血和I/R期间Mst 1-FoxO 1通路的有益作用。我们会用心脏- 特异性FoxO 1敲除（KO）（FoxO 1cKO）和心脏特异性C/EBP-KO（C/EBP-KO）小鼠，以及 新产生的C/EBP-100（T250 E）敲入（KI）小鼠与AAV介导的基因递送结合， 蛋白质组学我们的研究将阐明FoxO转录因子调控的分子机制 相反的细胞功能，即生存和死亡，以协调的方式，并通过 与Mst 1和C/EBP-1相互作用。从这项研究中获得的知识应该有助于发展 将FoxO转录因子的功能从二分型转变为完全型的分子干预 心脏保护和促进CM在心肌损伤情况下的存活。

Summary Forkhead box protein O (FoxO) family transcription factors are evolutionarily conserved proteins that play essential roles during development and in postnatal physiology in the heart. FoxOs play a dichotomous role in the regulation of cell survival/death in a context-dependent manner: they mediate cardiomyocyte (CM) cell death under some conditions but promote cell survival under other conditions. FoxOs can promote cell death by stimulating transcription of Bim, TRAIL, FasL, Bcl-6 and NOXA or lead to insulin resistance by downregulating IRS. On the other hand, endogenous FoxOs promote CM survival in response to oxidative stress and mediate the pro-survival effects of Sirt1 in CMs during ischemia/reperfusion (I/R). Moreover, FoxO1- dependent transcription of autophagy genes is required for survival of CMs during starvation. At present, however, how FoxOs mediate their dichotomous cellular functions is not well understood. Better understanding of the underlying mechanisms may make it possible to promote only the salutary function of FoxO1 while inhibiting the pro-death function of FoxO1 in the heart in the clinical setting. Our preliminary results suggest that Mst1, a pro-apoptotic kinase, can convert FoxO1 from pro-apoptotic to pro-survival through sequential phosphorylation of FoxO1 and C/EBP- in CMs. Our overall hypothesis is that Mst1 converts the function of the transcription factor FoxO1 from pro-apoptotic to pro-survival through sequential phosphorylation of FoxO1 at the DNA binding domain (DBD) and C/EBP-at Thr250 (mouse). We will: Aim 1 Show that FoxO1 promotes CM survival during myocardial ischemia and I/R through Mst1-induced phosphorylation of at the DBD; Aim 2 Demonstrate that Mst1 induces dissociation of FoxO1 from the promoter of pro- apoptotic FoxO target genes and association with C/EBP- to promote transcription of pro-survival molecules; Aim 3 Demonstrate that Mst1-induced phosphorylation of C/EBP- at Thr250 is FoxO1- dependent, and that Thr250 phosphorylation of C/EBP- promotes transcription of pro-survival factors; Aim 4 Demonstrate that C/EBP- phosphorylation at Thr250 is salutary and plays an essential role in mediating the salutary effect of the Mst1-FoxO1 pathway during ischemia and I/R. We will use cardiac- specific FoxO1 knockout (KO) (FoxO1cKO) and cardiac-specific C/EBP- KO (C/EBP- cKO) mice, as well as newly generated C/EBP- (T250E) knock-in (KI) mice in conjunction with AAV-mediated gene delivery and proteomics. Our study will elucidate the molecular mechanism by which FoxO transcription factors regulate directionally opposite cellular functions, namely survival and death, in a coordinated manner and through interaction with Mst1 and C/EBP-. Knowledge obtained from this study should be useful for the development of molecular interventions to convert the function of FoxO transcription factors from dichotomous to fully cardioprotective and facilitate survival of CMs in the setting of myocardial injury.