Vilchinskaya Natalia, Altaeva Erzhena, Lomonosova Yulia
Myology Laboratory, Institute of Biomedical Problems, Russian Academy of Sciences, 76a, Khoroshevskoe Shosse, Moscow, 123007, Russia.
Department of Paediatrics, University of Oxford, Children's Hospital, John Radcliffe, Oxford, OX3 9DU, UK; Institute of Developmental and Regenerative Medicine, Roosevelt Dr, IMS-Tetsuya Nakamura Building, Oxford, OX3 7TY, UK; MDUK Oxford Neuromuscular Centre, University of Oxford, South Parks Road, Oxford, OX1 3QX, UK.
Adv Biol Regul. 2022 Aug;85:100903. doi: 10.1016/j.jbior.2022.100903. Epub 2022 Jul 31.
Expression of FoxO transcription factors increases during certain forms of atrophy. In a dephosphorylated state, FoxOs participate in ubiquitin-mediated proteasomal degradation through the transcriptional activation of E3-ubiquitin ligases such as MAFbx/atrogin-1 and MuRF1. There is exhaustive research demonstrating that FoxO3a is sufficient to induce MAFbx/atrogin-1 and MuRF-1 expressions. In contrast, the data are conflicting on the requirement of FoxO1 signaling in the activation of the E3-ubiquitin ligases. Moreover, no reports currently exist on the particular role of FoxO1 in the molecular mechanisms involved in the progression of physiological muscle wasting. Here, we have applied the most extensively used rodent model of microgravity/functional unloading to stimulate disuse-induced skeletal muscle atrophy such as rat hindlimb suspension (HS). We showed that inhibition of FoxO1 activity by a selective inhibitor AS1842856 completely reversed an increase in expression of MuRF-1, but not MAFbx/atrogin-1, observed upon HS. Furthermore, we demonstrated that FoxO1 induced upregulation of another E3-ubiquitin-ligase of a MuRF protein family MuRF-2 in skeletal muscle subjected to disuse. Prevention of the MuRF increase upon HS impeded upregulation of transcript expression of a negative regulator of NFATc1 pathway calsarcin-2, which was associated with a partial reversion of MyHC-IId/x and MyHC-IIb mRNA expressions. Importantly, FoxO1 inhibition induced a marked increase in p70S6k phosphorylation, an important stage in the initiation of protein translation, concomitant with the restoration of global protein synthesis in the skeletal muscle of the HS rats. Examination of eIF3f expression and the eEF2k/eEF2 pathway, other factors controlling translation initiation and elongation respectively, did not reveal any impact of FoxO1 on their activity. Lastly, we observed a decrease in transcript levels of Sesn3, but not Sesn1 and Sesn2, upon disuse, which was completely reversed by FoxO1 inhibition. These data demonstrate that FoxO1 signaling contributes to the development of disuse-induced skeletal muscle atrophy, including slow to fast MyHC isoform shift, mostly through upregulation of MuRF-1 and MuRF-2 expression. Furthermore, FoxO1 inhibition is required to recover Sesn3 mRNA expression in atrophic conditions, which likely contributes to the enhanced p70S6k activity and restoration of the protein synthesis rate.
在某些形式的萎缩过程中，FoxO转录因子的表达会增加。处于去磷酸化状态时，FoxOs通过转录激活E3泛素连接酶（如MAFbx/atrogin-1和MuRF1）参与泛素介导的蛋白酶体降解。有大量研究表明，FoxO3a足以诱导MAFbx/atrogin-1和MuRF-1的表达。相比之下，关于E3泛素连接酶激活中FoxO1信号传导的必要性，数据存在矛盾。此外，目前尚无关于FoxO1在生理性肌肉萎缩进展所涉及分子机制中的特定作用的报道。在此，我们应用了最广泛使用的微重力/功能卸载啮齿动物模型来刺激废用性诱导的骨骼肌萎缩，如大鼠后肢悬吊（HS）。我们发现，选择性抑制剂AS1842856对FoxO1活性的抑制完全逆转了HS后观察到的MuRF-1表达增加，但未逆转MAFbx/atrogin-1的表达增加。此外，我们证明FoxO1在废用性骨骼肌中诱导了MuRF蛋白家族的另一种E3泛素连接酶MuRF-2的上调。防止HS后MuRF增加可阻碍NFATc1途径负调节因子calsarcin-2转录表达的上调，这与MyHC-IId/x和MyHC-IIb mRNA表达的部分逆转相关。重要的是，FoxO1抑制诱导p70S6k磷酸化显著增加，这是蛋白质翻译起始的一个重要阶段，同时伴随着HS大鼠骨骼肌中整体蛋白质合成的恢复。对eIF3f表达以及分别控制翻译起始和延伸的其他因素eEF2k/eEF2途径的检查未发现FoxO\alpha对其活性有任何影响。最后，我们观察到废用后Sesn3的转录水平下降，但Sesn1和Sesn2未下降，FoxO1抑制可完全逆转这种下降。这些数据表明，FoxO1信号传导有助于废用性诱导的骨骼肌萎缩的发展，包括慢肌向快肌肌球蛋白亚型转变，主要是通过上调MuRF-1和MuRF-2的表达。此外，在萎缩条件下恢复Sesn3 mRNA表达需要抑制FoxO1，这可能有助于增强p70S6k活性和恢复蛋白质合成速率。
