Sirtuins, Bioageing, and Cancer
The Sirtuins are a family of orthologues of yeast Sir2 found in a wide range of organisms from bacteria to man. They display a high degree of conservation between species, in both sequence and function, indicative of their key biochemical roles. Sirtuins are heavily implicated in cell cycle, cell division, transcription regulation, and metabolism, which places the various family members at critical junctures in cellular metabolism. Typically, Sirtuins have been implicated in the preservation of genomic stability and in the prolongation of lifespan though many of their target interactions remain unknown. Sirtuins play key roles in tumourigenesis, as some have tumour-suppressor functions and others influence tumours through their control of the metabolic state of the cell. Their links to ageing have also highlighted involvement in various age-related and degenerative diseases. Here, we discuss the current understanding of the role of Sirtuins in age-related diseases while taking a closer look at their roles and functions in maintaining genomic stability and their influence on telomerase and telomere function.
Sirtuins 是酵母 Sir2的一个家族，存在于从细菌到人类的各种生物体中。它们在序列和功能上都表现出高度的物种间保护性，表明它们在生物化学方面的重要作用。去乙酰化酶与细胞周期、细胞分裂、转录调控和新陈代谢密切相关，在细胞新陈代谢中处于关键时刻。通常情况下，去乙酰化酶与基因组稳定性的保持和寿命的延长有关，尽管它们之间的许多相互作用仍然是未知的。去乙酰化酶在肿瘤形成中起着关键作用，因为有些具有抑制肿瘤的功能，其他的则通过控制细胞的代谢状态来影响肿瘤。它们与老龄化的联系也突出表明，它们参与了各种与年龄有关的疾病和退化性疾病。在这里，我们讨论了目前的理解的角色 Sirtuins 在年龄相关的疾病，同时采取了进一步的角色和功能，维持基因组的稳定性及其对端粒酶和端粒功能的影响。
Sirtuins are a highly conserved family of proteins found in all organisms from yeast to mammals. All are orthologues of the yeast protein, silent information regulator 2 (Sir2)  and their primary targets are acetylated lysines of various peptides and proteins, including histones. Along with sequence homology, they also share functional similarities although the functions performed in mammals are more complex than in yeast, as reflected in the number of distinct orthologous forms. These play key roles in cellular stress and ageing, and as such, their function has been linked to diseases associated with ageing, including Alzheimer’s , Parkinson’s Disease , cancer , type II diabetes , and atherosclerosis .
去乙酰化酶是一个高度保守的蛋白质家族，在从酵母到哺乳动物的所有生物体中都有发现。所有这些都是酵母蛋白的直链结构，沉默信息调节因子2(Sir2) ，它们的主要目标是各种肽和蛋白质(包括组蛋白)的乙酰化 lysine。除了序列同源性外，它们还具有功能上的相似性，尽管哺乳动物的功能比酵母更复杂，这反映在不同的直系同源形式的数量上。这些基因在细胞应激和衰老中起着关键作用，因此，它们的功能与与衰老相关的疾病有关，包括阿尔茨海默氏症、帕金森氏症、癌症、 II 型糖尿病和动脉粥样硬化。
Every member of the family contains a highly conserved core domain consisting of a NAD+-binding site and a catalytic domain . Sirtuin function is tied to cellular energy production through nicotinamide adenine dinucleotide-(NAD+-) dependent deacetylation reactions, as well as o-ADP ribosylation, in response to changes in the cellular NAD+/NADPH ratio. Sirtuins appear to be involved in the extension of life span and health promotion in several species including yeast, nematodes and flies . Pertinent to this is the observation that Sirtuins can be activated through caloric restriction, stress, or by pharmacological agents . Sirtuins have a pivotal role in the expansion of lifespan in lower organisms via caloric restriction [10–15]. This phenomenon is also believed to occur in higher mammals, and ongoing studies in monkey models have demonstrated promising results in proving this connection . Additionally, some small-scale studies with centigenarians have demonstrated that allelic variants of some Sirtuin genes are linked to longevity in humans [17–19]. Despite this, the involvement of Sirtuins in enhanced human health and lifespan is still the subject of great debate. There is, however, increasing corroborative evidence of their links to cancer processes, genomic instability and other diseases of ageing.
该家族的每个成员都含有一个高度保守的核心结构域，包括一个 NAD + 结合位点和一个催化结构域。Sirtuin 功能与细胞能量的产生有关，通过烟酰胺腺嘌呤二核苷酸依赖的脱乙酰化反应，以及 o-ADP 核糖基化反应，以响应细胞 NAD +/NADPH 比值的变化。去乙酰化酶似乎参与延长寿命和促进健康的一些物种，包括酵母，线虫和苍蝇。与此相关的是观察到 Sirtuins 可以通过热量限制、应激或药理药物激活。去乙酰化酶通过热量限制在低等生物体的寿命延长中起着关键作用[10-15]。这种现象也被认为发生在高等哺乳动物身上，正在进行的猴子模型研究已经证明了这种联系的可喜结果。此外，一些对百分位数人群的小规模研究表明，一些 Sirtuin 基因的等位变异与人类的长寿有关[17-19]。尽管如此，去乙酰化酶参与改善人类健康和寿命仍然是一个很大的争论主题。然而，越来越多的证据表明它们与癌症、基因组不稳定性和其他老龄化疾病有关。
Central to such associations is the observation that Sirtuin activity is directly correlated with the metabolic state of the cell . Sirtuins act as substrate-specific type III protein lysine deacetylases, in contrast to the classic deacetylases, which facilitates a link between cell metabolism and control of transcription. Briefly, the deacetylation involves a unique enzymatic NAD+-dependent reaction which begins with amide cleavage from NAD+ leading to the formation of Nicotinamide (NAM) and a covalent ADP-ribose peptide-imidate intermediate (ADPR). This intermediate is transformed to O-acetyl-ADP-ribose and the deacetylated protein is released from the complex (Figure 1, ). Due to the reliance of Sirtuin deacetylation activity on NAD+, it is hardly surprising that evidence suggesting NAD+ and NAD+ generating pathways are directly involved in the regulation of Sirtuin activity is mounting rapidly. This is supported by the observation that the Nicotinamide (NAM) product site can be occupied in the presence of substrates and reaction intermediates [22, 23]. Bound NAM is able to inhibit the enzymatic activities of Sirtuins and can, in some cases, reverse the reaction, thus regenerating NAD+ and the acetylated substrate. Sirtuins, together with other NAD+ consumers (ADP-ribosyltransferases and cAMP ribose synthetase), have also been implicated in the salvage/elimination of NAM, thus playing a vital role in the homeostatic maintenance of NAD+ metabolism [7, 24].
这种关联的核心是观察到 Sirtuin 活性与细胞的代谢状态直接相关。与传统的去乙酰化酶相比，去乙酰化酶作为底物特异性的 III 型蛋白赖氨酸去乙酰化酶，促进了细胞代谢和转录调控之间的联系。简单地说，脱乙酰反应包括一个独特的酶促 NAD + 依赖性反应，从 NAD + 的酰胺裂解开始，形成尼克酰胺(NAM)和一个共价的 adp- 核糖肽-亚咪酯中间体(ADPR)。该中间体被转化为 o- 乙酰基 -adp- 核糖，脱乙酰化蛋白从复合物中释放(图1，)。由于 Sirtuin 脱乙酰化活性依赖于 NAD + ，所以提示 NAD + 和 NAD + 生成途径直接参与 Sirtuin 活性调节的证据正在迅速增加。这是支持的观察，烟酰胺(NAM)的产品网站可以占领在存在的底物和反应中间体[22,23]。结合 NAM 能抑制 Sirtuins 的酶活性，在某些情况下可逆转反应，从而再生 NAD + 和乙酰化底物。Sirtuins 和其他 NAD + 消费者(adp 核糖转移酶和 cAMP 核糖合成酶)也参与了 NAM 的抢救/消除，因此在 NAD + 代谢的稳态维持中起着重要作用[7,24]。
Figure 1 图1Protein deacetylation by Sirtuins. Sirtuins deacetylate lysine (K) residues of target proteins using cofactor—Nicotinamide-adenine-dinucleotide (NAD 蛋白质去乙酰化辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因子辅因+) and releasing Nicotinamide (NAM). 2′-O-acetyl-ADP ribose is generated as a result of transfer of the acetyl group of K onto ADP-ribose residue. Deacetylation is inhibited by NAM, which can also reverse the reaction to reproduce NAD ) ，并释放烟酰胺(NAM)。将 k 的乙酰基转移到 adp- 核糖残基上，生成2′-o- 乙酰 -adp 核糖。NAM 对去乙酰化有抑制作用，可逆转 NAD 的产生+.
在人类中，已经鉴定出7种 Sirtuins (Sirt1-7)[25,26] ，它们都具有独特的特征、功能和定位(表1)。
|Enzymatic activity 酶活性Localisation本地化Substrates/targets 基质/目标Function 功能SIRT1Deacetylase 脱乙酰基酶Nuclear/cytoplamic 核/胞质层p53, FOXO, NF P53，FOXO，NFκB, MyoD, Ku70, LXR, PPAR 70，LXR，pprγ, p300, Tat, PCAF, ER 300，Tat，PCAF，ERα, AR, SMAD7, PCAF, p73, Sox9, HES1, PGC1 7，PCAF，p73，Sox9，HES1，PGC1α, HEY2, NcoR/SMRT, E2F1, RelA/p65 ，HEY2，NcoR/SMRT，E2F1，RelA/p65Glucose metabolism, fatty-acid and cholesterol metabolism, differentiation, insulin secretion, and neuroprotection 葡萄糖代谢、脂肪酸和胆固醇代谢、分化、胰岛素分泌和神经保护SIRT2Deacetylase 脱乙酰基酶Nuclear/cytoplamic 核/胞质层α-tubulin, FOXO 微管蛋白 FOXOCell-cycle control, tubulin deacetylation 细胞周期控制，微管蛋白去乙酰化SIRT3Deacetylase 脱乙酰基酶AceCS2, GDH complex1 2，GDH complex1ATP production, regulation of mitochondrial proteins deacetylation, and fatty-acid oxidation ATP 的产生，线粒体蛋白质脱乙酰化和脂肪酸氧化的调节Mitochondrial线粒体SIRT4ADP-ribosylotransferase Adp- 核糖转移酶GDH, IDE, ANT GDH，IDE，ANTInsulin secretion 胰岛素分泌SIRT5Deacetylase 脱乙酰基酶CPS1Urea cycle 尿素循环SIRT6Deacetylase ADP-ribosylotransferase 脱乙酰酶 adp- 核糖基转移酶Nuclear核能NF 神经纤维瘤κB, Hif1 B，Hif1α, helicase, DNA polymerase 目的: 研究解旋酶、 DNA 聚合酶的生物学特性βTelomeres and telomeric functions, DNA repair 端粒和端粒功能，DNA 修复SIRT7Deacetylase 脱乙酰基酶Nuclear核能RNA polymerase type I, E1A, SMAD6 I 型 RNA 聚合酶，E1A，SMAD6RNA polymerase I transcription RNA聚合酶I 转录|
Table 1 表一The mammalian Sirtuins. 哺乳动物去乙酰化酶
Sirt1、 Sirt6和 Sirt7主要位于细胞核内，而 Sirtuins 3-5主要位于线粒体内。相反，Sirt2有一个主要的胞质局部化[28,29]。
The Sirtuins contain nuclear localisation signals (NLSs) as well as nuclear export signals (NESs) and their intracellular localisation is determined by cell/tissue type and physiological conditions. Sirt6 and Sirt7 contain a single NLS, while Sirt1 contains 2 NLS and 2 NES domains [29, 30]. The presence of an N-terminal mitochondrial targeting sequence ensures Sirt3–5 localisation within the mitochondrial matrix [31, 32], whereupon the signal sequence is cleaved, activating the enzymatic function of the proteins. Interestingly, it has been recently suggested that under specific conditions (stress), Sirt3 can translocate from mitochondria to the nucleus [33, 34].
Sirtuins 包含核定位信号(NLSs)和核输出信号(NESs) ，其细胞内定位取决于细胞/组织类型和生理条件。Sirt6和 Sirt7包含一个 NLS，而 Sirt1包含2个 NLS 和2个 NES 域[29,30]。N 端线粒体靶向序列的存在确保了 Sirt3-5在线粒体基质内的定位[31,32] ，从而切断信号序列，激活蛋白质的酶功能。有趣的是，最近有人提出，在特定条件下(压力) ，Sirt3可以从线粒体转移到细胞核。
Sirtuins are actively involved in the regulation of gene expression, principally due to their histone deacetylase activity and the consequential ability to influence the activity of a wide range of transcription factors. It has been shown that all Sirtuins, with the exception of Sirt4 and Sirt7, have histone deacetylase activity (HDAC). Sirt1 can affect core histones (H1, H2, H3, and H4), but it preferentially deacetylates H3 (K9, K14 and K56 residues), H4 (K16) and H1 (K26) [35–37]. The specific deacetylation of lysine residues at H3K9/H4K16 and H1K26 by Sirt1 has been linked to gene silencing and chromatin remodelling. Additionally, histone deacetylation can facilitate the methylation of histones, for example, di/tri-methylation of H3 on the K9 residue and H4 on the K20 residue. These modifications have been linked to global transcriptional repression and are characteristic for facultative heterochromatin . This reaction can be further enhanced by Sirtuins; for example, H3K9 methylation is enhanced by Sirt1. Sirt1 binds to the histone methyltransferase Suv39H1 (suppressor of variegation 3–9 homolog 1) and facilitates binding of this protein to chromatin. Sirt1 is then activated by deacetylation of Suv39H1 [36, 39]. There are additional regulation mechanisms involved in the chromatin silencing mediated by Sirt1-Suv39H1 complex, it has recently been shown that deleted in breast cancer 1 (DBC1), not only inhibits both Sirt1 and Suv39H1 activity, but also disrupts the interaction between these two molecules leading to the increased methylation of H3K9 . The other interesting aspect of Sirt1 involvement in the epigenetic regulation of gene expression is its association with aberrant expression of the methylated genes that can be facilitated by its interaction with Dnmt3b  or Dmnt1 . Overall, the ability of Sirt1 to remodel chromatin, together with the ability of this enzyme to deacetylate and/or interact with a broad range of transcription factors (i.e, p300, NFκB, FOXO, E2F1, and Smad7 (Table 1)) suggest that Sirt1 may be a major player in the regulation of organism homeostasis, stress responses, endocrine signalling, and cell metabolism.
去乙酰化酶积极参与基因表达的调节，主要是由于它们的组蛋白脱乙酰酶活性和影响一系列转录因子的活性的结果能力。除了 Sirt4和 Sirt7之外，所有的 Sirtuins 都具有组蛋白脱乙酰酶活性(HDAC)。Sirt1能影响核心组蛋白(H1、 H2、 H3和 H4) ，但优先脱乙酰化 H3(K9、 K14和 K56残基)、 H4(K16)和 H1(K26)[35-37]。Sirt1对 H3K9/H4K16和 H1K26赖氨酸残基的特异性去乙酰化与基因沉默和染色质重塑有关。此外，组蛋白去乙酰化可以促进组蛋白的甲基化，例如，K9残基上的 H3和 K20残基上的 H4的双/三甲基化。这些修饰与全球转录抑制有关，并且是兼性异染色质的特征。这个反应可以通过 Sirtuins 进一步增强，例如，H3K9甲基化被 Sirt1增强。Sirt1与组蛋白甲基转移酶 Suv39H1结合(多样性3-9同源抑制基因1) ，促进该蛋白与染色质的结合。然后 Sirt1被 Suv39H1脱乙酰基激活。Sirt1-Suv39H1复合物介导的染色质沉默还涉及其他调节机制，最近的研究表明，在乳腺癌1型(DBC1)中被删除的染色质沉默不仅抑制 Sirt1和 Suv39H1的活性，而且破坏这两个分子之间的相互作用，导致 H3K9的甲基化增加。Sirt1参与基因表达的表观遗传调控的另一个有趣的方面是它与甲基化基因异常表达的关联，这可以通过它与 Dnmt3b 或 Dmnt1的相互作用得到促进。总的来说，Sirt1重塑染色质的能力，连同这种酶去乙酰化和/或与一系列广泛的转录因子相互作用的能力(即，p300，NFκB，FOXO，E2F1，和 Smad7(表1))表明，Sirt1可能是调节机体内稳态，应激反应，内分泌信号和细胞代谢的主要参与者。
Acetylated lysine residues on Histone 4 (H4K16) and Histone H3 (H3K9) are targets for Sirt2 deacetylation when the nuclear envelope disassembles during the mitotic process . This makes Sirt2 a regulator of the cell cycle, involved in the promotion of chromatin condensation. Similarly, Sirt3 deacetylates H4K16 and H3K9 in vitroalthough the importance of this process under in vivo conditions remains somewhat controversial .
组蛋白4(H4K16)和组蛋白 H3(H3K9)上的乙酰化赖氨酸残基是 Sirt2脱乙酰化的靶标，当核膜在有丝分裂过程中发生拆分时。这使得 Sirt2成为细胞周期的调节因子，参与促进染色质凝聚。类似地，Sirt3在体外脱乙酰 H4K16和 H3K9，尽管这一过程在体内条件下的重要性仍然有些争议。
Finally, Sirt6 deacetylates H3K9 at telomeres, indicating that this particular molecule may be a modulator of cellular senescence and ageing induced chromosomal abnormalities .
Sirtuins are also involved in the regulation of RNA Polymerase II transcribed genes although their involvement in the formation of the transcription initiation complex has not been proven to date . Interestingly, Sirtuins affect transcription of ribosomal RNA also. Sirt1 and Sirt7 have opposing effects on rRNA transcription; Sirt1 deacetylates TATA box-binding protein associated factor (TAFI68) leading to the inhibition of Polymerase I , while Sirt7 directly binds to polymerase I and induces enzyme activity .
去乙酰化酶也参与调节 RNA聚合酶Ⅱ转录基因，尽管它们参与转录起始复合物的形成迄今为止还没有被证实。有趣的是，去乙酰化酶也影响核糖体 RNA 的转录。Sirt1和 Sirt7对 rRNA 转录有相反的作用，Sirt1去乙酰化 TATA box 结合蛋白相关因子(TAFI68)导致聚合酶 i 的抑制，而 Sirt7直接结合聚合酶 i 并诱导酶活性。
A search for Sirtuin-binding sites revealed many putative targets. However, all of these targets follow on a common theme in Sirtuin function, namely, cellular stress responses . These incorporate cell death responses, senescence, stress-related transcription regulation, cell-cycle control, cell metabolism, genomic stability and formation, and maintenance and control of telomeric function (Table 1). These activities for Sirtuins reinforce the link between key features of cellular bioage and disease, centred on telomere stability and cellular lifespan. Extrapolating Sirtuin activity to longevity, already established in lower organisms is thus intuitive for higher animals though it remains unproven. The increasing evidence for Sirtuin involvement in age related diseases is a key link to their function in the control of the cell lifespan and genomic stability [49–51]. This involvement in age-related disease further supports the link between Sirtuin function and longevity, possibly making Sirtuins the key to unlocking the causes and treatments for many age related diseases.
对 sirtuin 结合位点的研究发现了许多假定的靶点。然而，所有这些靶点都遵循 Sirtuin 功能的一个共同主题，即细胞应激反应。这些包括细胞死亡反应，衰老，应激相关的转录调节，细胞周期控制，细胞代谢，基因组稳定性和形成，以及端粒功能的维护和控制(表1)。这些去乙酰化酶的活动加强了细胞生物学特征和疾病之间的联系，主要集中在端粒稳定性和细胞寿命上。将 Sirtuin 活性外推至长寿，已经在低等生物体中确立，因此对于高等动物来说是直观的，尽管它仍未得到证实。越来越多的证据表明 Sirtuin 参与了与年龄有关的疾病，这是它们在控制细胞寿命和基因组稳定性方面的功能的一个关键环节[49-51]。这种与年龄有关的疾病的参与进一步支持 Sirtuin 功能和长寿之间的联系，可能使 Sirtuin 成为解开许多与年龄有关的疾病的原因和治疗的关键。
2. Sirtuins and Genomic Instability
The involvement of Sirtuin function in disease is typified by Sirt1, which is rapidly emerging as a tumour keystone, providing both tumour suppressor and tumour promoter functionality . Sirt1 has been shown to be overexpressed in several cancers, including prostate , acute myeloid leukaemia , colon cancer , and some nonmelanoma skin cancers . Sirt1 has also been observed to be repressed in many other cancers, including glioblastoma, bladder, ovarian, and prostate cancers . This duality of purpose indicates the pivotal role this Sirtuin exerts in the cell. Overexpression of Sirt1 can lead to deacetylation of p53 [58, 59] and reduction of many tumour suppressor genes, thus promoting genomic instability by reducing the cell’s ability to respond to DNA damage and stress. Conversely, it can also deacetylate B-catenin causing the oncogenic form of this protein to translocate to the cytoplasm, thus reducing the growth of tumours . More recently, Oberdoerffer et al. have demonstrated that redistribution of Sirt1 in a mouse model of genomic instability results in improved survival rates and transcription profiles similar to those found in the ageing process, particularly involved in repairing DNA breaks and other forms of genomic instability . Further investigation into Sirt1 involvement in genomic instability has been hampered by an inability to produce a viable null model, as Sirt1 knockout mice die during the mid-gestation stage although it was determined that these mice showed histone modifications and impaired DNA-damage repair. Additionally, Sirt1 and p53 heterozygotes showed an increase in tumour formation in multiple tissues, a phenotype that could be at least partially rescued by activation of Sirt1 using Resveratrol . It is still undetermined whether this Sirtuin acts as a tumour keystone with suppressor or promoter functions.
参与 Sirtuin 功能的疾病是典型的 Sirt1，这是迅速出现的肿瘤基石，提供肿瘤抑制和肿瘤促进剂功能。Sirt1在几种癌症中表达过度，包括前列腺癌、急性髓系白血病、结肠癌和一些非黑色素瘤皮肤癌。Sirt1也被观察到在许多其他癌症中被抑制，包括胶质母细胞瘤、膀胱癌、卵巢癌和前列腺癌。这种目的的双重性表明了 Sirtuin 在细胞中发挥的关键作用。Sirt1的过度表达会导致 p53[58,59]的去乙酰化和许多肿瘤抑制基因的减少，从而降低细胞应对 DNA 损伤和应激的能力，从而促进基因组的不稳定性。相反，它也可以脱乙酰基 b 连环蛋白导致这种蛋白的致癌形式转移到细胞质，从而减少肿瘤的生长。最近，oberdorerffer 等人证明了 Sirt1在基因组不稳定的小鼠模型中的重新分布导致了生存率和转录谱的提高，这与衰老过程中发现的类似，特别是涉及修复 DNA 断裂和其他形式的基因组不稳定。由于 Sirt1基因敲除小鼠在妊娠中期死亡，无法建立可行的缺失模型，进一步研究 Sirt1参与基因组不稳定性受到阻碍，尽管已确定这些小鼠表现出组蛋白修饰和 dna 损伤修复受损。此外，Sirt1和 p53杂合子在多种组织中显示肿瘤形成的增加，这种表型至少可以通过使用白藜芦醇激活 Sirt1而得到部分挽救。目前还不清楚这种去乙酰化酶是否作为肿瘤抑制基石或启动子功能。
Sirt2, which acts as a G2 checkpoint mitotic regulator, appears to have a similar dichotomous role in both the formation and prevention of gliomas . Increased expression of Sirt2 has been linked to a prolonged cell-cycle, with severe delays in cell cycle progression, suggesting a tumour suppressor role . Furthermore, its role as a mitotic checkpoint protein helps prevent chromosome instability and the development of hyperploidy . Downregulation of Sirt2 has been shown to interfere with cell cycle progression and in some cases can induce cell-cycle arrest , while overexpression has been shown to cause a prolongation of the mitotic phase of the cell cycle  resulting in multinucleated cells [28, 65]. The induction of multiploidy phenotypes indicates that Sirt2 plays a role in chromosomal stability by controlling the cell division associated separation of recently replicated chromosomes. Sirt2 directly deacetylates α-tubulin, providing it with a further mechanism for the control over mitosis and its ability to ensure single ploidy cells , thus ensuring genomic stability during mitosis.
Sirt2，作为 g 2检查点有丝分裂调节器，在神经胶质瘤的形成和预防中似乎有一个类似的二分法的作用。Sirt2的表达增加与细胞周期延长有关，细胞周期进展严重延迟，提示肿瘤抑制作用。此外，它作为有丝分裂检查点蛋白的作用有助于防止染色体不稳定性和超倍性的发展。Sirt2的下调已被证明干扰细胞周期进程，在某些情况下可诱导细胞周期停滞 ，而过度表达已被证明导致细胞周期有丝分裂期延长导致多核细胞[28,65]。多倍体表型的诱导表明，Sirt2通过控制新近复制的染色体的细胞分裂相关的分离，在染色体稳定性中起着重要作用。Sirt2直接去乙酰化 α- 微管蛋白，为控制有丝分裂和确保单倍体细胞的能力提供了进一步的机制，从而确保了有丝分裂过程中基因组的稳定性。
Sirt3 may play a role in mitochondrial redox regulation  though data on its role is equivocal. Two independent studies have demonstrated that Sirt3 null mice have no associated phenotype, with normal development and fertility [66, 67]. Conversely, another Sirt3 null model, using mouse embryonic fibroblasts, has demonstrated abnormal mitochondrial function, including an increase in stress-induced ROS and genomic instability . In this model, expression of a single oncogene (c-myc or ras) was sufficient for neoplastic transformation of the cells, which could be reversed by introducing superoxide dismutase to counteract the increase in ROS. It has now been shown, by the same group, that this effect is dependent upon deacetylation of mnSOD . Mice with Sirt3 knockouts also developed oestrogen receptor (ER)+ and Progesterone receptor (PR)+ mammary tumours, suggesting that Sirt3 is a mitochondrially localised tumour suppressor. However, there is still some debate over the localisation of Sirt3, with the majority of studies claiming that Sirt3 is exclusively mitochondrial [70, 71]. Notably, two distinct forms (long and short) of Sirt3 have been reported [72–74] with the short version lacking a mitochondrial localisation signal peptide, indicating it may be localised elsewhere. This may account for the equivocal reports that Sirt3 can be localised to the nucleus. There are also reports that suggest Sirt3 translocates to the nucleus upon overexpression of Sirt5 or oxidative challenge to the cell [33, 34]. These reports did not investigate whether this was accomplished by translocation of Sirt3 from mitochondria to the nucleus, de novo synthesis, or expression of the short version of Sirt3.
Sirt3可能在线粒体氧化还原调节中发挥作用，尽管关于其作用的数据是模棱两可的。两个独立的研究已经证明 Sirt3缺失小鼠没有与正常发育和生育相关的表型。相反，另一个使用小鼠胚胎成纤维细胞的 Sirt3缺失模型，已证明线粒体功能异常，包括应激诱导的活性氧增加和基因组不稳定。在这个模型中，一个原癌基因(c-myc 或 ras)的表达足以使细胞发生肿瘤性转化，这可以通过引入超氧化物歧化酶来抵消活性氧的增加而逆转。现在同一个研究小组已经证明，这种效应取决于 mnSOD 的脱乙酰化作用。配有 Sirt3基因敲除基因的小鼠也发生了雌激素受体(ER) + 和孕酮受体(PR) + 乳腺肿瘤，这表明 Sirt3是线粒体局部肿瘤抑制基因。然而，对于 Sirt3的本地化仍然存在一些争议，大多数研究声称 Sirt3是完全的线粒体。值得注意的是，Sirt3有两种不同的形式(长的和短的)[72-74] ，短的形式缺乏一个线粒体定位信号肽，这表明它可能定位在其他地方。这也许可以解释那些模棱两可的报道，即 Sirt3可以局部化到核心。也有报道表明 Sirt3在 Sirt5过度表达或对细胞的氧化挑战时转位到细胞核。这些报告并没有调查是否通过 Sirt3从线粒体移位到细胞核、从头合成或短版本 Sirt3的表达来实现这一目的。
Sirt4 shows no discernable NAD+-dependent deacetylase activity in vitro [75, 76], confirmed by a lack of mitochondrial protein acetylation variation in a null mouse model . Like Sirt3 null mice, Sirt4 null mice demonstrate an overtly normal phenotype . Sirt4 is associated with insulin secretion by pancreatic β-cells, which may link it to type II diabetes, an age-related disorder. There is no direct evidence to date, however, that Sirt4 has any direct affect on genomic stability, through either over- or underexpression. Recently it has been suggested that Sirt3 and Sirt4 activities are antiapoptotic in response to DNA damage when extremely low levels of NAD+ are present .
Sirt4在体外没有显示出明显的 NAD + 依赖的去乙酰化酶活性[75,76] ，证实了缺乏线粒体蛋白乙酰化变异的小鼠模型。和 Sirt3缺失小鼠一样，Sirt4缺失小鼠表现出明显正常的表型。Sirt4与胰岛 β 细胞分泌胰岛素有关，胰岛 β 细胞可能与 II 型糖尿病有关，II 型糖尿病是一种与年龄有关的疾病。然而，到目前为止还没有直接的证据表明 Sirt4通过过度或过度表达对基因组稳定性有任何直接的影响。最近有人提出，Sirt3和 Sirt4的活动是抗凋亡的反应，DNA 损伤时，极低水平的 NAD + 存在。
Sirt5 localises to the mitochondrial matrix, where its N-terminus is cleaved. Sirt5 appears to operate exclusively in the mitochondria and one of its major targets is carbamoyl phosphate synthase 1 (CPS1) , which is responsible for converting ammonia to urea. It also regulates the entry of ammonia into the urea cycle. Therefore, it would appear that the major function of Sirt5 in vivo is to enhance the body’s reaction to the breakdown of amino acids during calorie restriction via CPS1 and Cytochrome C [79, 80]. Very little else is known about the function of Sirt5 other than that it has been demonstrated that Sirt5 plays a role in the localisation of Sirt3 . Sirt3 is ordinarily present in the mitochondria; however, overexpression of Sirt5 causes Sirt3 to localise to the nucleus this phenomenon has also been shown as part of the cell stress response . Whether this is due to increased expression of Sirt3 Short has yet to be established. This indicates that Sirt5 may contribute, in part, to the cellular response to stress, or that it is produced as a result of the stress response. Given the dependence of Sirtuins on NAD+for their action, it is feasible that Sirt5 is part of the sensing apparatus to initiate the stress response and would then activate it’s deacetylation functions to affect other transcription factors, thus initiating the cell wide stress reaction, which may include sending Sirt3 to the nucleus. Therefore, Sirt5 may exert an influence over genomic stability via the action of Sirt3.
5定位于线粒体基质，在那里它的 n 端被切开。Sirt5似乎只在线粒体中运作，其主要靶点之一是氨甲酰磷酸合成酶1(CPS1) ，该合成酶负责将氨转化为尿素。它还规定了氨进入尿素循环。因此，Sirt5在体内的主要功能似乎是通过 CPS1和细胞色素 c [79,80]增强机体对卡路里限制期间氨基酸分解的反应。除了已经证明 Sirt5在 Sirt3的本地化过程中发挥了作用之外，对 Sirt5的功能知之甚少。Sirt3通常存在于线粒体中，然而 Sirt5的过度表达导致 Sirt3定位于细胞核，这种现象也被证明是细胞应激反应的一部分。这是否是由于 Sirt3 Short 的表达增加尚未确定。这表明，Sirt5可能在一定程度上促进了细胞对压力的反应，或者说，它是压力反应的结果。鉴于 Sirtuins 对 NAD + 的作用依赖性，Sirt5可能是启动应激反应的传感器的一部分，然后激活它的去乙酰化功能，影响其他转录因子，从而引发细胞广泛的应激反应，其中可能包括发送 Sirt3到细胞核。因此，Sirt5可能通过 Sirt3的作用影响基因组的稳定性。
The role of Sirt6 has been established as being a key component of base excision repair (BER), as part of intra-cellular DNA-damage responses. Sirt6 directly stabilises DNA-dependant protein kinase at the site of dsDNA breaks, allowing the formation of the DNA repair complex and the initiation of repairs . Sirt6 also associates directly with chromatin, demonstrated by its association with chromatin enriched cellular fractions . Sirt6 has also been shown to localise to the promoter regions of NF-κB activated proteins, whereupon it deacetylates the associated H3 histone at Lysine 9, thereby silencing the recently activated genes . Sirt6 deficiency is associated with shortened lifespan and accelerated ageing phenotypes. In fact, mice with Sirt6 knockouts have been shown to have a progeroid phenotype, with extreme hypoglycaemia and are unable to survive beyond 4 weeks. The lethal hypoglycaemia observed in Sirt6 deficient mice is a direct result of its H3K9 deacetylase function which controls the expression of glycolytic genes . Furthermore, knockout mice demonstrate a very high level of genomic instability and hypersensitivity to DNA damage [82, 84], confirming Sirt6’s key role in DNA damage repair and also demonstrating its close relationship with the original Sir protein in yeast, Sir2. It was also noted that the increased sensitivity to DNA damage did not appear to be a function of impaired cell-cycle checkpoints, nor the dsDNA break repair mechanism. Deletion of Sirt6 results in chromosomal abnormalities including breaks and fusions, as well as a breakdown in BER, a phenotype that can be rescued by introduction of a fragment of Polymerase β (Polb), which has been determined as a target for Sirt6 . The deacetylation of histones by Sirt6 is likely to have a stabilising effect on the genome, for example, H3K56  although a direct link has yet to be established.
作为细胞内 dna 损伤反应的一部分，Sirt6的作用已被确定为碱基切除修复的一个关键组成部分。Sirt6直接稳定 DNA 依赖性蛋白激酶在 dsDNA 断裂部位，允许 DNA 修复复合体的形成和修复的开始。Sirt6还与染色质直接相关，这可以通过它与染色质富集的细胞分数的相关性得到证实。Sirt6也被证明定位于 NF-κB 活化蛋白的启动子区域，因此它在赖氨酸9上去乙酰化相关的 h 3组蛋白，从而沉默最近激活的基因。Sirt6缺乏与寿命缩短和加速衰老表型有关。事实上，有 Sirt6基因敲除的小鼠已被证明具有早衰型表型，血糖极低，无法存活超过4周。在 Sirt6缺陷小鼠中观察到的致死性低血糖是其 H3K9去乙酰化酶功能控制糖酵解基因表达的直接结果。此外，基因敲除小鼠表现出非常高水平的基因组不稳定性和 DNA 损伤的过敏，证实了 Sirt6在 DNA 损伤修复中的关键作用，也证明了它与酵母中原始 Sir 蛋白 Sir2的密切关系。还有人指出，DNA 损伤敏感性的增加似乎不是受损细胞周期检查点的功能，也不是 dsDNA 断裂修复机制。Sirt6的缺失导致染色体异常，包括断裂和融合，以及 BER 的崩溃，这种表型可以通过引入一段聚合酶 β (Polb)来挽救，这段聚合酶 β 已被确定为 Sirt6的目标。Sirt6对组蛋白的去乙酰化作用可能对基因组有稳定作用，例如 H3K56 ，尽管还没有建立直接的联系。
Sirt7 directly interacts with RNA polymerase I (Pol I) and histones, giving a direct link between this Sirtuin and genomic stability . This link is demonstrated by increasing Sirt7 levels directly increasing Pol I function and inhibition of Sirt7 leading to decreased Pol I activity . Complete depletion of Sirt7 results in cell death, after a complete halt to cell proliferation; it is believed that this direct linkage allows Sirt7 to regulate Pol I function with regard to NAD+ levels, tying it to cell metabolism and energy levels in keeping with the original postulate of Shiels and Davies (2003) . They argue that cellular responses to stress and damage centre on how much damage has been accrued, how much energy the cell needs to effect any repair, and how much fuel it must burn to achieve this. If the damage is too great; the cell will effect death, however, if the damage is not critical, then cellular energy metabolism is regulated to allow repair, and ribosome biogenesis is modulated to facilitate this [48, 88].
Sirt7直接与 RNA聚合酶I (Pol i)和组蛋白相互作用，在 Sirtuin 和基因组稳定性之间建立了直接联系。这种联系表现为增加 Sirt7水平直接增加 Pol i 功能和抑制 Sirt7导致 Pol i 活性降低。Sirt7的完全缺失导致细胞死亡，在完全停止细胞增殖之后; 据认为，这种直接联系使 Sirt7能够在 NAD + 水平方面调节 Pol i 功能，将其与细胞新陈代谢和能量水平联系起来，与 Shiels 和 Davies (2003)的原始假设相一致。他们认为，细胞对压力和损伤的反应主要取决于累积了多少损伤，细胞需要多少能量来进行修复，以及需要消耗多少燃料才能达到这一目的。如果损伤太大，细胞会导致死亡，然而，如果损伤不严重，那么细胞能量代谢就会被调节以允许修复，核糖体的生物发生就会被调节以促进修复[48,88]。
All cells have an in built mitotic clock associated with telomeres , this clock is continually reset in germ line cells by telomerase, and it also appears to be modified, turned off, or reset in cancer to allow tumours to grow unabated. It has been well established that ageing is associated with the degradation of telomeres, which ultimately leads to cell senescence and apoptosis when the cell has reached the end of its useful life . The system of telomeric instability associating with age is an essential checkpoint in the control of life and disease, in particular cancer. Sirtuins are rapidly emerging as the key link between ageing, disease, metabolism and cellular stress.
3. Sirtuins and the Regulation of Cellular Stress Responses
The intricate role Sirtuins play in the control of the cell metabolism is mediated through their dependence on NAD+; this control inextricably links their function with the metabolic status of the cell. It also provides a sensing platform for the response to cellular stress.
Sirtuins 在控制细胞新陈代谢中的复杂作用是通过他们对 NAD + 的依赖而介导的; 这种控制与细胞的新陈代谢状态有着千丝万缕的联系。它还为细胞应激反应提供了一个传感平台。
p53 tumour suppressor is involved in the regulation of apoptosis and its reactivity is tightly regulated. Under physiological condition, this molecule is maintained at very low levels in the cells, but its expression is rapidly increased in response to stress in order to fulfil its regulatory functions . It has been documented that p53 activity can be modulated by SIRT1 in particular; overexpression of SIRT1 not only abrogated p53 dependent apoptosis in response to oxidative stress, DNA damage, and ionizing radiation, but also sensitised cells to apoptosis induced by these factors [58, 59]. Various studies have demonstrated that SIRT1 plays a critical role in the regulation of both p53 dependent and p53 independent apoptosis in response to oxidative stress. This regulation occurs via the deacetylation of p53 which leads to its retention in the cytoplasm and enhances passage of p53 into the mitochondria [91, 92]. The ability to modulate p53 acetylation establishes SIRT1 in the inhibition of cell senescence in response to oxidative stress. In this case, SIRT1 is recruited to the PML bodies and p53, where it blocks p53-dependent transactivation; this phenomenon has been observed in human endothelial cells, where Downregulation of SIRT1 led to increased acetylation of p53 and development of a premature senescence phenotype [93, 94]. In contrast to SIRT1, SIRT2 overexpression promotes neurodegeneration and affects the ability of cells to recover after cellular stress, mainly due to Downregulation of 14-3-3ζ [95, 96].
P53肿瘤抑制基因参与细胞凋亡的调控，其反应性受到严格控制。在生理状况下，这种分子在细胞中维持在非常低的水平，但是为了完成其调节功能，它的表达在压力下会迅速增加。已有文献证明，SIRT1特别能够调节 p53的活性，SIRT1的过度表达不仅能够降低 p53依赖性凋亡对氧化应激、 DNA 损伤和电离辐射的反应，而且能够增强细胞对这些因素诱导的凋亡的敏感性[58,59]。各种研究表明，SIRT1在 p53依赖性和 p53独立性细胞凋亡的调节中发挥着关键作用，这种调节作用可能与细胞凋亡氧化应激有关。这种调节是通过 p53的脱乙酰化作用发生的，脱乙酰化作用导致 p53滞留在细胞质中，促进 p53进入线粒体[91,92]。调节 p53乙酰化的能力建立了 SIRT1在细胞衰老中对氧化应激的反应。在这种情况下，SIRT1被招募到 PML 小体和 p53，在那里它阻止 p53依赖的转录激活; 这种现象已经在人类内皮细胞中观察到，在那里 SIRT1的下调导致 p53乙酰化增加和早衰表型的发展[93,94]。与 SIRT1相反，SIRT2的过度表达促进了神经退行性疾病，并影响细胞在细胞应激后的恢复能力，这主要是由于14-3-3ζ 的下调[95,96]。
Another mechanism by which Sirt1 can regulate the cellular response to stress is the ability of Sirt1 to regulate members of the FOXO (Forkhead box class O) transcription factor family. Sirtuin 1 deacetylates 3 members of FOXO family, Foxo1, Foxo3a, and Foxo4 [97, 98]. Sirt1 regulation of Foxo3a function in mammalian cells reduces apoptosis in response to cellular stress, but also increases the expression of genes involved in DNA repair and cell-cycle check points . SIRT1 activates Foxo1 and Foxo4 which are involved in the promotion of cell-cycle arrest by induction of p27Kip1and in enhancing cellular defences against oxidative stress through the regulation of manganese superoxide dismutase, catalase, and GADD45 (growth arrest and DNA damage inducible α) [98, 99]. It has been demonstrated that Sirt2 under oxidative stress deacetylates Foxo3a, and thus enhances the expression of Foxo-regulated genes and reduces ROS levels in cells . Similarly to Sirt1, Sirt7 depletion in mice leads to a specific phenotype, characterised by p53 hyperacetylation and lack of resistance to the oxidative or genotoxic stress .
Sirt1调节细胞对压力反应的另一个机制是 Sirt1调节 FOXO (叉头盒类 o)转录因子家族成员的能力。Sirtuin 1脱乙酰化 FOXO 家族的3个成员，Foxo1，Foxo3a 和 Foxo4[97,98]。Sirt1调控 Foxo3a 在哺乳动物细胞中的功能减少了细胞应激引起的凋亡，但也增加了与 DNA 修复和细胞周期检查点有关的基因的表达。SIRT1激活 Foxo1和 Foxo4，通过诱导 p27Kip1促进细胞周期阻滞，并通过调节锰超氧化物歧化酶、过氧化氢酶和 GADD45(生长阻滞和 DNA 损伤诱导的 α)增强细胞对抗性。已经证明，Sirt2在氧化应激下脱乙酰化 Foxo3a，从而增强 foxo 调节基因的表达，降低细胞中的活性氧水平。与 Sirt1相似，Sirt7在小鼠中的缺失导致了一种特殊的表型，其特征是 p53高乙酰化和缺乏对氧化或基因毒性应激的抵抗力。
4. Sirtuins, Telomeres, and Telomerase
TNFα has been shown to induce telomerase activity in lymphocytes , this proinflammatory cytokine is controlled by NF-κB which in turn is influenced by Sirt1. Therefore, Sirt1 has direct influence over TNFα activation of telomerase activity. Whether this activation can be achieved in cells other than lymphocytes or whether it can contribute to the immortalisation of tumour cells has yet to be elucidated. Inhibition of Sirt1 has also been associated with increased telomerase activity in human cells .
Tnfα 已被证明能诱导淋巴细胞端粒酶活性，这种促炎性细胞因子受 NF-κB 控制，而 NF-κB 又受 Sirt1的影响。因此，Sirt1对 tnfα 激活端粒酶活性有直接影响。这种激活是否可以在淋巴细胞以外的细胞中实现，或者它是否有助于肿瘤细胞的永生还有待阐明。抑制 Sirt1也与人类细胞端粒酶活性的增加有关。
Sirt2 is predominantly cytoplasmic and is unlikely to play any role in telomere biology. Sirt3–5 are mitochondrial and to date have no information linking them to telomeric sites, telomerase, or mitotic division. However, Sirt6 is absolutely essential for dsDNA repair, playing an active role in the recruitment of other factors to the site of dsDNA breaks . Sirt6 also appears to be extremely important in the maintenance of telomeres and telomeric function. Recent studies have demonstrated that reduction or removal of Sirt6 results in telomere dysfunction and end-to-end chromosomal fusions. This absence of Sirt6 is similar in symptoms to Werner’s syndrome, which is a disease characterised by premature ageing. It is an extremely rare, autosomal recessive disorder caused by a mutation in the WRN gene encoding DNA helicase . This results in genomic instability and telomeric attrition, the process by which this occurs is unknown. It is believed that Sirt6 is essential for proper telomere maintenance and function. Sirt6-deficient cells have been shown to have an increased susceptibility to genotoxic DNA damage resulting in the accumulation of chromosomal abnormalities resulting in genomic instability. Sirt6-deficient mice exhibit an accelerated ageing phenotype; however, the researchers were unable to determine any cellular lifespan change . In another study using Sirt6 null mice it was demonstrated that these mice have a progeroid like syndrome, profound hypoglycaemia, and premature death at around the 4-week stage . This appears to indicate that Sirt6 does, in fact, have a major impact on organismal lifespan control.
2主要是细胞质，不太可能在端粒生物学中发挥任何作用。Sirt3-5是线粒体，到目前为止还没有与端粒位点、端粒酶或有丝分裂相关的信息。然而，Sirt6对 dsDNA 修复绝对是必不可少的，它在 dsDNA 断裂部位的其他因素的补充中扮演着积极的角色。Sirt6似乎在维持端粒和端粒功能方面也极其重要。最近的研究表明，减少或去除 Sirt6导致端粒功能障碍和端到端的染色体融合。这种 Sirt6的缺失与沃纳氏综合征的症状相似，沃纳氏综合征是一种以过早衰老为特征的疾病。它是一种极为罕见的常染色体隐性遗传疾病，由编码 DNA 解旋酶的 WRN 基因突变引起。这导致基因组的不稳定性和端粒磨损，其发生的过程是未知的。人们认为，Sirt6是必不可少的端粒适当的维护和功能。Sirt6缺陷细胞已被证明具有增加易感性的基因毒性 DNA 损伤导致积累的染色体异常导致基因组不稳定。Sirt6基因缺陷的小鼠表现出加速老化的表型; 然而，研究人员无法确定任何细胞寿命的改变。在另一项使用 Sirt6基因缺失小鼠的研究中，证明这些小鼠具有类似早衰症候群的症状，严重的低血糖，以及4周左右的过早死亡。这似乎表明，事实上，Sirt6确实对生物寿命控制有重大影响。
Very little is known about Sirt7, and although it is localised to the nucleolus, there has been no evidence presented that suggests any involvement with telomere function, formation, or stability.
5. The Association of Sirtuins with Diseases of Ageing
5. Sirtuins 与老龄化疾病协会
Sirt1 is heavily implicated in several diseases associated with ageing, as well as with ageing itself. This Sirtuin has been shown to protect axons from damage in animal models of the Wallerian degenerative disease (Parkinson’s disease) . Furthermore, the use of resveratrol (a Sirt1 activator) in models of Huntington’s disease shows that Sirt1 is able to reduce cell death by inhibition of NF-κB signalling . Alzheimer’s disease has also been linked to Sirt1 function and calorie restriction in monkeys . A recent study has demonstrated that Sirt1 overexpression in the brain of mice directly reduces β-Amyloid production and the formation of plaques . Another study demonstrated that induction of Sirt1 function also reduced macular degeneration by protecting retinal ganglial cells . Furthermore, it has been shown that Sirt1 has a direct influence on the pancreatic β cell production of insulin. Along with Sirt3, altered expression of these Sirtuins has been implicated in the development of Type II Diabetes ; however, no links with Type I diabetes have yet been established. This activity is believed to occur through acetyl coenzyme A synthetase (AceCS) upon which both Sirt1 and 3 act to produce acetate. The production of acetate has been shown to be disrupted in diabetes as well as in ageing. Sirt4 has also been shown to be downregulated in pancreatic b cells in response to calorie restriction implicating it in diabetes although no links have yet been demonstrated.
Sirt1与老龄化以及自身老龄化相关的几种疾病有着密切的联系。这种 Sirtuin 在帕金森氏病的动物模型中已被证明可以保护轴突免受损伤。此外，在亨廷顿病模型中使用白藜芦醇(一种 Sirt1激活剂)表明 Sirt1能够通过抑制 NF-κB 信号通路来减少细胞死亡。阿尔茨海默病也与猴子的 Sirt1功能和卡路里限制有关。最近的一项研究表明，Sirt1在小鼠大脑中的过度表达直接减少了 β- 淀粉样蛋白的产生和斑块的形成。另一项研究表明 Sirt1功能的诱导也可以通过保护视网膜神经节细胞减少老年黄斑变性。此外，研究还表明，Sirt1对胰岛素的胰岛 β 细胞产生有直接影响。随着 Sirt3，改变这些 Sirtuins 的表达已被牵连到二型糖尿病的发展 ; 然而，尚未建立与 i 型糖尿病的联系。这种活动被认为是通过乙酰辅酶A 合成酶(AceCS)发生的，Sirt1和3都在其上产生乙酸盐。醋酸盐的生产已被证明在糖尿病和老化过程中受到干扰。尽管还没有证据表明 Sirt4与糖尿病之间存在联系，但已经证明，由于卡路里限制与糖尿病有关，胰腺 b 细胞的水平也会下降。
Although Sirt2 is associated mainly with the brain, there have been no links made between this Sirtuin and neurodegenerative diseases. The limited amount of information available on Sirt5 makes it very difficult to make any connections between this Sirtuin and diseases of ageing; however, its heavy involvement in the mitochondria leads to speculation that it may be related to metabolic disorders.
虽然 Sirt2主要与大脑有关，但是在这种 Sirtuin 和神经退行性疾病之间没有联系。关于 Sirt5的信息有限，因此很难将 Sirtuin 与衰老性疾病联系起来，然而，它对线粒体的大量参与使得人们推测它可能与代谢紊乱有关。
Sirt3 has been linked to overall longevity in humans, although the studies conducted were small scale. The first study linked a polymorphism in Sirt3 to increased longevity in males , and the authors also determined that the chromosomal location of Sirt3 is also home to four other proteins associated with longevity (tyrosine hydroxylase, proinsulin, IGF2, and HRAS1). A subsequent study confirmed this observation but went further to suggest that decreased levels of Sirt3 was detrimental to longevity in males . Furthermore, Lescai et al., (2009)  linked a Sirt3 SNP to longevity in centenarians from Italy, France, and Germany. Recently, Sirt3 has been directly linked to age-related hearing loss .
Sirt3一直被认为与人类的总体寿命有关，尽管这些研究规模较小。第一项研究将 Sirt3的多态性与延长男性寿命联系起来 ，作者还确定了 Sirt3的染色体位置也是其他四种与长寿相关的蛋白质(酪氨酸羟化酶、胰岛素原、 IGF2和 HRAS1)的所在地。随后的一项研究证实了这一观察结果，但进一步表明 Sirt3水平的降低对男性的寿命有害。此外，Lescai 等人(2009)将 Sirt3 SNP 与来自意大利、法国和德国的百岁老人的长寿联系起来。最近，Sirt3已被直接与年龄相关的听力损失联系起来。
Sirt6 is heavily associated with DNA damage, telomeres, and cancer. Another link to degenerative disease exists with the association between Sirt6 and WRN which is implicated in premature ageing like Werner Syndrome . Furthermore, Sirt6 actively represses genes associated with age-related cellular senescence and it is, therefore, highly likely that more associations will be discovered and that Sirt6 will become a key player and target in the research and treatment of cancer and other age-related diseases. There is also a suggestion that it may play a key role in the maintenance of organ integrity particularly associated with ageing . Another key mediator in age-related diseases is inflammation, which in this context is generally induced by age-related increases in NF-κB activity. This activity is directly opposed by both Sirt1 and Sirt6, where Sirt1 acts directly on the RelA subunit causing deacetylation and reducing its action. Sirt6 is also sequestered to NF-κB activated targets and shuts them down at the transcription level. Thus, both Sirtuins may be active in age-related inflammatory disorders. Although no direct causal links between these Sirtuins and inflammatory disorders have been made, the level of circumstantial evidence suggest that formal demonstration may be a matter of time and research.
Sirt6与 DNA 损伤、端粒和癌症密切相关。另一个与神经退行性疾病有关的因素是 Sirt6和 WRN 之间的联系，这种联系与过早衰老有关，如 Werner 综合症。此外，Sirt6主动抑制与年龄相关的细胞衰老相关的基因，因此，很可能会发现更多的相关性，Sirt6将成为癌症和其他年龄相关疾病的研究和治疗的关键角色和目标。还有人建议，它可能在维持器官完整性方面发挥关键作用，特别是与衰老有关的器官。另一个与年龄相关疾病的关键调节因子是炎症，在这种情况下，炎症通常是由与年龄相关的 NF-κB 活性增加引起的。这种活性直接受到 Sirt1和 Sirt6的反对，而 Sirt1直接作用于 RelA 亚基，导致脱乙酰化和减少其作用。Sirt6也被隔离在 NF-κB 激活的靶点上，并在转录水平关闭它们。因此，这两种去乙酰化酶都可能在年龄相关的炎症性疾病中起作用。虽然这些去乙酰化酶和炎症性疾病之间没有直接的因果关系，但是间接证据的水平表明，正式的证明可能只是时间和研究的问题。
Sirt1 and Sirt7 are associated with age-related cardiovascular disease through their interactions with p53, Fox01 and nitric oxide synthetase (NOS). Sirt1 has also been shown to improve the regeneration of vascular endothelia and smooth muscle cells .
Sirt1和 Sirt7通过与 p53、 Fox01和一氧化氮合成酶(NOS)的相互作用与年龄相关的心血管疾病相关。Sirt1也被证明能促进血管内皮细胞和平滑肌细胞的再生。
6. Sirtuins and Cancer
Cancer is now established as a disease of ageing. Consequently it was inevitable that Sirtuins would play a vital role in tumourigenesis. The roles played by Sirtuins at key points in the cell are also highly indicative of their roles in modulating the aberrant survival and replication of tumour cells. The most obvious involvement for Sirtuins in cancer comes from Sirt1 and Sirt7 mediation of p53-function, which is well established as a focal point in many cancers. Sirt1 (and Sirt7) deacetylates p53 reducing its influence over cell cycle control during stress and in response to DNA damage. Thus overexpression of Sirt1 deactivates p53 and disrupts p53 dependent pathways and this results in a large reduction in the cell’s ability to respond to stress and DNA damage [58, 59]. This has lead to many researchers describing Sirt1 as a tumour promoter, a suggestion that has now been supported by several studies. These identify increased levels of Sirt1 associated with various cancers including prostate , AML , primary colon  and several nonmalignant skin cancers . Overexpression studies resulted in lowered production and or action of several key tumour suppressors including FOXO family members , p73 , RB , and several others [116–119]. However, the story for Sirt1 is not so simple. Several studies have reported decreased levels in cancer, for example glioma, bladder, prostate, and ovarian cancers . Several studies have reinforced this connection demonstrating a reduced level of Sirt1 associated with tumourigenesis [118, 120–122]. In fact, Sirt1 acts as a tumour keystone, where its level and action maintain a fine and delicate balance between suppression and promotion of oncogenesis. Based on the available evidence, it is plausible that Sirt1 acts as a suppressor and then a promoter (or vice versa) depending on the stage and situation of tumourigenesis.
癌症现在被确定为一种衰老的疾病。因此，去乙酰化酶在肿瘤形成中扮演重要角色是不可避免的。去乙酰化酶在细胞中的关键位点所发挥的作用也高度表明了它们在调节肿瘤细胞异常存活和复制中的作用。Sirtuins 在癌症中最明显的参与来自于 Sirt1和 Sirt7对 p53功能的调节，这在许多癌症中被公认为一个焦点。Sirt1(和 Sirt7)去乙酰化 p53减少其在应激期间对细胞周期控制的影响和对 DNA 损伤的反应。因此，Sirt1的过度表达使 p53失活，破坏了 p53的依赖性通路，导致细胞应对压力和 DNA 损伤的能力大大降低[58,59]。这已经导致许多研究人员将 Sirt1描述为肿瘤促进剂，一个建议，现在已经得到了一些研究的支持。这些研究发现 Sirt1水平升高与多种癌症有关，包括前列腺癌、急性髓系白血病、原发性结肠癌和几种非恶性皮肤癌。过度表达的研究导致一些关键肿瘤抑制因子的产生和作用降低，包括 FOXO 家族成员 ，p73 ，RB  ，以及其他一些肿瘤抑制因子[116-119]。然而，Sirt1的情况并非如此简单。一些研究已经报道了癌症，例如神经胶质瘤、膀胱癌、前列腺癌和卵巢癌的水平下降。一些研究加强了这种联系，证明与肿瘤发生相关的 Sirt1水平降低[118,120-122]。事实上，Sirt1作为肿瘤的基石，其水平和作用在抑制和促进肿瘤发生之间保持微妙的平衡。基于现有的证据，它是合理的，Sirt1作为抑制，然后作为启动子(或反之亦然)取决于肿瘤发生的阶段和情况。
Control of cell-cycle progression by Sirt2 has been shown to be essential in the prevention of tumours, as it is suppressed in gliomas . Sirt3 is the only mitochondrial Sirtuin to have a demonstrated role in tumourigenesis to date and its reduction in several cancers leads to an increase in ROS which results in enhanced tumour growth . Interestingly, Sirt5 overexpression has been implicated in a study of pancreatic cancer .
Sirt2对细胞周期进展的控制已被证明在预防肿瘤中是必不可少的，因为它在神经胶质瘤中被抑制。Sirt3是迄今为止唯一被证实在肿瘤形成中发挥作用的线粒体 Sirtuin，它在几种癌症中的减少导致 ROS 的增加，从而促进肿瘤生长。有趣的是，Sirt5的过度表达已经牵涉到一项关于胰腺癌的研究中。
The role of Sirt6 in controlling NF-κB function and DNA damage repair also indicate a key role in tumourigenesis although very little information is available on specific correlations with cancer to date some studies have been conducted which demonstrate a link through interaction with GCIP in colon tumours . Our group has previously demonstrated that Sirtuins 3–7 are elevated in some forms of breast cancer  and mRNA levels of Sirt7 have been inversely correlated with the ability to undergo tumourigenesis in mouse cell lines . Sirtuin influence and types of cancer where associations have been shown are summarised in Table 2.
Sirt6在控制 NF-κB 功能和 DNA 损伤修复方面的作用也表明它在肿瘤形成中起着关键作用，尽管迄今为止关于肿瘤特定相关性的信息很少，但一些研究已经证明它与结肠肿瘤 GCIP 之间存在相互作用。我们的研究小组先前已经证明 Sirtuins 3-7在某些形式的乳腺癌中升高，Sirt7的 mRNA 水平与小鼠细胞系的肿瘤发生能力呈负相关。表2总结了 Sirtuin 的影响和癌症的类型。
|Association with cancer 与癌症的关系Sirt11Acute myeloid leukemia, colon, nonmalignant skin, bladder, prostate ovarian cancers, and glioma—mediates p53 function 急性骨髓性白血病、结肠、良性皮肤、膀胱、前列腺癌和神经胶质瘤介导 p53的功能Sirt22Glioma—control of cell cycle progression 神经胶质瘤ーー细胞周期进程的调控Sirt3Breast cancer—decrease in levels is associated with a general increase in tumour growth due to increase in ROI 乳腺癌水平的下降与肿瘤生长的增加有关，这是由于 ROI 的增加Sirt4Breast cancer—metabolic 乳腺癌ー新陈代谢Sirt55Pancreatic, breast cancers—metabolic 胰腺癌、乳腺癌ー代谢Sirt66Colon, breast cancers—mediates NF 结肠癌、乳腺癌ー介导坏死性结肠炎κB and GCIP function 和 GCIP 功能Sirt7Breast cancer—mediates p53 function 乳腺癌介导 p53功能|
Table 2 表二Cancers associated with Sirtuins and their proposed mechanism of involvement. 与 Sirtuins 相关的肿瘤及其参与机制的研究进展
An interesting link between Sirtuin levels and circadian rhythm has also been reported . This is noteworthy given the understood disruption of circadian rhythm in cancer . This opens the possibility of the use of chronotherapy using Sirtuin regulators at specific times to target tumours .
也有报道说 Sirtuin 水平和昼夜节律之间有有趣的联系。这是值得注意的，因为我们知道昼夜节律在癌症中的破坏作用。这使得在特定时间使用 Sirtuin 调节剂来治疗肿瘤成为可能。
It is obvious that the Sirtuins, in line with the function of Sir2 in yeast, play critical roles in the maintenance of the genome in all organisms. These vital roles have led to speculation that these molecules are heavily involved in two key areas, tumourigenesis and ageing. Further, evidence for these proteins in such crucial roles is accumulating at an accelerating rate. As this area of molecular science consolidates and advances, the Sirtuin family of proteins are gaining significance in human biology and disease. This group show strong potential to become valuable predictive and prognostic markers for disease and as therapeutic targets for the management of a variety of cancer types and other age-related diseases.
很明显，与酵母中 Sir2的功能一致的 Sirtuins 在所有生物的基因组维持中起着关键作用。这些重要的作用已经引起人们的猜测，这些分子在两个关键领域，肿瘤形成和衰老中起着重要作用。此外，这些蛋白质在这些关键作用的证据正在以加速的速度积累。随着这一分子科学领域的巩固和进步，Sirtuin 蛋白家族在人类生物学和疾病中获得了重要意义。这一群体显示了成为有价值的疾病预测和预后标志物以及作为各种癌症类型和其他与年龄有关的疾病的治疗目标的巨大潜力。