Targeting Sirtuin-1 to enhance Foxp3+ regulatory T-cell function

描述（由申请方提供）：免疫应答需要在激活和减弱之间保持微妙的平衡。同样，自身免疫性疾病和器官移植的治疗面临的挑战是实现足够的免疫抑制，以防止器官排斥或限制自身反应性，而不损害宿主的能力，以防止感染和恶性肿瘤。调节性T细胞（Treg）是对自身耐受性至关重要的重要T细胞亚群，能够抑制或关闭抗原特异性免疫应答（1）。转录因子Forkhadbox-p3（Foxp 3）在Treg的发育和功能中起关键作用。Foxp 3受到转录调节，但也受到翻译后修饰的调节。我们已经证明Foxp 3蛋白内赖氨酸残基的乙酰化可以增强Treg功能（2）。这种乙酰化还保护Foxp 3免受蛋白酶体降解，从而有助于最佳Treg功能。Foxp 3乙酰化受几种组蛋白/蛋白乙酰转移酶（HAT）和组蛋白/蛋白脱乙酰酶（HDAC）的竞争作用调节。我们建议研究Sirtuin-1（Sirt 1）的作用，这是一种在真核生物中高度保守的III类HDAC，是细胞代谢和寿命的重要介质。我们已经开始利用具有Sirt 1靶向缺失的小鼠，这是重要的，因为具有全局Sirt 1敲除的小鼠患有代谢问题和寿命缩短。此外，我们采用Sirt 1小分子抑制剂来测试野生型小鼠中瞬时Sirt 1抑制的效果。我们的初步数据表明，Sirt 1的靶向缺失增加了Foxp 3的乙酰化和表达，并增强了Treg的免疫抑制功能。此外，TCR 4中Sirt 1的缺失或其药理学抑制可减弱同种异体移植物排斥反应和小鼠心脏同种异体移植物的存活。因此，我们的中心假设是靶向Sirt 1可能在自身免疫和移植中具有治疗价值。我们的目标是探索Sirt 1缺失或抑制如何：1）改善同种异体移植物存活和功能（在诱导糖尿病和肾衰竭的小鼠受体中）; 2）增强自身免疫（在小鼠炎症性肠病模型中）;以及，进一步了解3）Sirt 1如何影响T细胞生物学的不同分子机制，而不仅仅是促进Foxp 3乙酰化。我们的研究结果可能会被证明是重要的新的免疫调节策略的发展应用于自身免疫和移植。我们提出的研究对于增加对Sirt 1在免疫反应中的功能的理解也很重要，因为Sirt 1激活剂白藜芦醇（已经在柜台上可用）和其他更有效的小分子Sirt 1激活剂（3）越来越受到关注，用于治疗各种疾病和促进整体健康。此外，Sirt 1抑制剂正在考虑作为抗肿瘤药物（4）。因此，我们警告说，随着这种治疗方案的不断发展，更多地了解Sirt 1在免疫系统中的作用至关重要。 公共卫生相关性（由申请人提供）：我们研究了Sirtuin-1作为减弱免疫应答的新型治疗靶点，这与改善治疗选择以实现免疫抑制有关，例如用于患有自身反应性免疫疾病的患者或器官移植的接受者。此外，重要的是要了解更多关于Sirtuin-1在免疫系统中的作用，因为许多研究人员追求Sirtuin-1增强（糖尿病，代谢综合征）或Sirtuin-1抑制（某些癌症）。

DESCRIPTION (provided by applicant): The immune response requires a delicate balance between activation and attenuation. Likewise, therapies for autoimmune diseases and organ transplantation face the challenge of achieving enough immunosuppression to prevent organ rejection or limit autoreactivity without impairing the host's ability to protect against infections and malignancy. Regulatory T-cells (Treg) are an important T-cell subset crucial to self-tolerance, capable dampening or switching off antigen-specific immune responses (1). The transcription factor Forkheadbox-p3 (Foxp3) plays a key role in the development and functions of Treg. Foxp3 is regulated transcriptionally but also by post-translational modifications. We have shown that acetylation of lysine residues within the Foxp3 protein can enhance Treg function (2). Such acetylation also protects Foxp3 from proteasomal degradation and thus contributes to optimal Treg functions. Foxp3 acetylation is regulated by the competing actions of several histone/protein acetyltransferases (HAT) and histone/protein deacetylases (HDAC). We propose to study the role of Sirtuin-1 (Sirt1), a class III HDAC highly conserved across eukaryotic species and an important mediator of cellular metabolism and longevity, in Tregs. We have begun to exploit use of mice with targeted deletions of Sirt1, which is important as mice with global Sirt1 knockout suffer from metabolic problems and shortened lifespan. In addition, we have employed Sirt1 small molecule inhibitors to test the effect of transient Sirt1 inhibition in wild-type mice. Our preliminary data show that the targeted deletion of Sirt1 increases the acetylation and expression of Foxp3, and enhances the immunosuppressive functions of Treg. In addition, deletion of Sirt1 in Tregs, or its pharmacologic inhibition, attenuates allograft rejection and prolongs survival of murine cardiac allografts. Therefore, our central hypothesis is that targeting Sirt1 may have therapeutic value in autoimmunity and transplantation. Our aims are to explore how Sirt1 deletion or inhibition: 1) improves allograft survival and function (in murine recipients with induced diabetes and renal failure); 2) alleviates autoimmunity (in murine inflammatory bowel disease models); and, further, understand 3) distinct molecular mechanisms how Sirt1 influences T-cell biology beyond simply promoting Foxp3 acetylation. Our findings will likely prove important to the development of new immunomodulatory strategies for application in autoimmunity and transplantation. Our proposed studies are also important for an increased understanding of the functions of Sirt1 in immune responses, given the rising attention being given to the Sirt1 activator resveratrol (already available over the counter) and other more potent small molecule Sirt1 activators (3), for therapy of various diseases and for promotion of overall well-being. In addition, Sirt1 inhibitors are under consideration as anti-neoplastic drugs (4). Therefore, we caution that it is critical to learn more about the role of Sirt1 in the immune system as such treatment options are evolving. PUBLIC HEALTH RELEVANCE (provided by applicant): We study Sirtuin-1 as a novel therapeutic target to attenuate the immune response, which is relevant to improve treatment options to achieve immunosuppression, e.g. for patients suffering from self-reactive immune disease, or recipients of an organ transplant. Furthermore, it is important to learn more about the role of Sirtuin-1 in the immune system, as many investigators pursue Sirtuin-1 enhancement (diabetes mellitus, metabolic syndrome), or Sirtuin-1 suppression (certain cancers).