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

描述（由申请人提供）：免疫反应需要在激活和衰减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也面临着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抵御感染和恶性肿瘤的能力的挑战。调节性t细胞（Treg）是一种重要的t细胞亚群，对自身耐受至关重要，能够抑制或关闭抗原特异性免疫反应(1)。转录因子Forkheadbox-p3 （Foxp3）在Treg的发育和功能中起着关键作用。Foxp3受转录调控，但也受翻译后修饰的调控。我们已经证明Foxp3蛋白内赖氨酸残基的乙酰化可以增强Treg功能(2)。这种乙酰化还可以保护Foxp3免受蛋白酶体降解，从而有助于优化Treg功能。Foxp3的乙酰化受多种组蛋白/蛋白乙酰转移酶（HAT）和组蛋白/蛋白去乙酰化酶（HDAC）的竞争作用调控。我们建议研究Sirtuin-1 （Sirt1）在Tregs中的作用，Sirt1是一种在真核生物物种中高度保守的III类HDAC，是细胞代谢和长寿的重要介质。我们已经开始利用Sirt1靶向缺失的小鼠，这很重要，因为Sirt1全基因敲除的小鼠会出现代谢问题和寿命缩短。此外，我们还利用Sirt1小分子抑制剂在野生型小鼠中测试了Sirt1瞬时抑制的效果。我们的初步数据显示，Sirt1的靶向缺失增加了Foxp3的乙酰化和表达，增强了Treg的免疫抑制功能。此外，Tregs中Sirt1的缺失或其药理学抑制可以减轻同种异体移植排斥反应，延长小鼠心脏移植的存活时间。因此，我们的中心假设是靶向Sirt1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Sirt1缺失或抑制如何：1)改善同种异体移植物的存活和功能（在小鼠诱导糖尿病和肾功能衰竭的受体中）；2)减轻自身免疫（小鼠炎症性肠病模型）；并进一步了解Sirt1如何影响t细胞生物学的独特分子机制，而不仅仅是促进Foxp3乙酰化。我们的发现可能对开发新的免疫调节策略以应用于自身免疫和移植具有重要意义。鉴于Sirt1激活剂白藜芦醇（已经在柜台上提供）和其他更有效的小分子Sirt1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，我们提出的研究对于提高对Sirt1在免疫反应中的功能的理解也很重要。此外，Sirt1抑制剂正在考虑作为抗肿瘤药物(4)。因此，我们警告说，随着治疗方案的发展，更多地了解Sirt1在免疫系统中的作用是至关重要的。

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).