衰老及相关疾病细胞分子机制研究进展

人类及其他生物随时间推移逐渐发生细胞功能丧失,即细胞衰老.这个过程如突显在某个组织器官,则可引起这个组织和器官的衰老性疾病.然而,最近的研究表明,哺乳动物在出生之前胚胎发育的生理条件下,即已经出现细胞和组织的复制性衰老现象.机制研究显示多种分子从细胞(核)内外引起生理性和应激性细胞复制性衰老.而自然界中某些生物随时间推移生命力增强、并不发生衰老.这些现象的分子机制,还有如发生在脑及代谢性疾病中的非复制性细胞衰老等,都还是个谜.本文就近期衰老的机制、细胞衰老的类型以及某些衰老相关疾病的分子基础的最新研究进展做一个扼要综述.论文包含以下几个部分:a.细胞衰老的定义、分类和机制;b.生理性衰老:发育中程序化衰老;c.内环境稳态与组织器官衰老;d.一型细胞复制性衰老及相关疾病:端粒长度与预测衰老及肿瘤预后、特发性肺纤维化、高血压;e.二型非复制性细胞衰老及相关疾病:帕金森病、糖尿病;f.衰老与长寿的物种多样性.     

细胞衰老与老龄化疾病

随着人口老龄化加剧,细胞衰老的生物学基础及其相关分子机制的研究已成为一个重要的研究方向。细胞衰老是多种因素引起的细胞周期永久性阻滞,与老化疾病如糖尿病、骨质疏松、动脉粥样硬化、神经退行性疾病等有关。现介绍细胞衰老及细胞衰老与年龄相关疾病的分子生物学机制,重点介绍衰老领域的最新研究进展:清除衰老细胞能改善或延缓老龄化疾病,延长机体寿命。     

清除衰老细胞在衰老与老龄化相关疾病中的研究进展

衰老是一个新兴的重要研究领域,随着该领域相关知识的积累和技术的进步,人们逐渐意识到衰老本身可以被针对性地干预,实现延长寿命并且延缓衰老相关疾病的发生发展,具有重要的科学和现实意义.引起个体衰老的众多因素中,衰老细胞的积累被认为是导致器官衰老发生退行性变,最终引起衰老相关疾病的重要原因.近年来,多项研究表明,清除体内衰老细胞可以延缓多种衰老相关疾病的发生,直接证明了衰老细胞是导致衰老相关疾病的重要原因之一,为治疗衰老相关疾病提供了新靶点.细胞衰老是由于损伤积累诱发了细胞周期抑制通路的激活,细胞永久地退出细胞增殖周期.衰老细胞会发生细胞形态、转录谱、蛋白质稳态、表观遗传以及代谢等系列特征的改变,同时衰老细胞对凋亡发生抵抗从而在体内多器官组织积累.衰老细胞会激活炎症因子分泌通路,导致组织局部非感染性炎症微环境,进而导致器官退行性变及多种衰老相关疾病的发生发展.因此针对衰老细胞对凋亡抵抗的特性,多个研究小组通过筛选小分子化合物库,发现某些化合物能够选择性清除衰老细胞,这些小分子化合物被称为"senolytics",意为"衰老细胞杀伤性化合物".衰老细胞杀伤性化合物在多种衰老相关疾病动物模型中能够延缓疾病的发展并延长哺乳动物寿命.因此,靶向杀伤衰老细胞对多种衰老相关疾病的治疗从而提高健康寿命具有重要的临床应用前景.除靶向杀伤衰老细胞策略以外,干细胞移植、基因编辑、异体共生等策略在抗衰老研究发展中也具有重要意义,具有启发性.本文通过汇总近期衰老细胞清除领域的重要进展和多种抗衰老策略,将细胞衰老研究发展史做简要梳理,就细胞衰老与衰老相关疾病的关系作一综述,重点讨论衰老细胞在多种衰老相关疾病中作为治疗靶点的应用潜力,并就其局限性和进一步的研究方向进行探讨.     

生物衰老的主要分子机制概述

衰老是一种包括生理性衰老和病理性衰老的正常自然规律,与其他生物过程一样,受一些信号通路和分子机制的调控。研究发现调控生物衰老机制的信号通路之间存在相互作用。综述了胰岛素通路、雷帕霉素通路及Sirtuins家族这3种与自噬相关的延缓衰老的经典信号通路,总结了氧化应激、细胞衰老、免疫衰老等影响机体衰老的主要原因及方式,希望在此基础上发现新的互作通路,探索出更多新颖的分子机制和方法以预防、延缓或减轻多种与衰老相关的疾病。     

氧化应激诱导的细胞衰老过程中细胞生长相关基因的表达

应激诱导的细胞早衰与复制性细胞衰老有相似的细胞表型,但其机制不尽相同.分析二者的衰老相关基因表达特点对了解应激因素诱导细胞衰老的机制有重要意义. 本文对过氧化氢诱导的HeLa细胞早衰过程中的关键衰老相关基因及其转录后调控因子的表达做了分析.结果发现,在复制性衰老过程中明显降低的cyclin A、cyclin B1、c-fos及HuR,在温和过氧化氢诱导的细胞早衰过程中并无明显改变;在氧化应激诱导的细胞早衰过程中,p21与p16表达升高,AUF1则降低,与复制性衰老过程一致;p21 mRNA半衰期在复制性衰老过程中无明显变化,但在氧化应激诱导的细胞早衰过程中则显著延长.上述结果提示,尽管氧化应激诱导的细胞早衰与复制性衰老存在相似基因表达变化,调控机制则不尽相同.     

前景可观的senolytics延缓衰老的研究进展

细胞衰老呈现不可逆的永久性细胞周期停滞的状态,它可以促进组织在发育过程中和损伤后的重塑,但也会导致老年生物体组织再生潜力和功能的下降,以及炎症和肿瘤的发生。研究发现,清除衰老细胞可以延缓衰老相关疾病的发生。因此,探究衰老细胞的分子特征与探索清除衰老细胞的新药成为衰老研究领域的热点。近年来,人们发现一类称为senolytics的小分子化合物能特异性靶向衰老细胞并帮助清除衰老细胞,从而延长哺乳动物的寿命及健康寿命。该文对衰老细胞的分子特征、作为衰老相关疾病的治疗靶点及具有senolytics活性的化合物作用机制和潜在应用进行了综述。     

miR-223促进小鼠胚胎成纤维细胞复制性衰老

微小RNA（MicroRNAs（或miRNAs）是作为强大的基因表达调控子,广泛参与多种生命过程,在细胞衰老进程中的作用也日益受到关注。miR-223是一个典型的抑癌基因,可显著抑制细胞增殖能力。此外,miR-223与阿尔茨海默症、心血管疾病以及类风湿性关节炎等衰老相关疾病的发生发展密切相关。尽管如此,miR-223在细胞衰老进程中的作用及其分子机制尚未见报道。本研究通过连续传代建立了小鼠胚胎成纤维细胞（MEF细胞）的复制性衰老模型,并利用荧光定量qRT-PCR检测发现,miR-223在衰老MEF细胞中的表达水平显著上调。随后,通过转染miR-223模拟物Agomir-223在MEF细胞中过表达miR-223,结果显示过表达miR-223可显著促进MEF细胞的衰老表型并抑制其增殖能力,而抑制miR-223的表达可延缓MEF细胞的复制性衰老进程。进一步利用生物信息学方法预测获得多个miR-223的候选衰老相关靶基因,包括Rasa1、Ddit4和Smad1等。然而双萤光素酶报告系统结果显示,miR-223并不显著影响其萤光强度,表明它们很可能并不是miR-223的下游靶基因。综上所述,miR-223可显著促进MEF细胞复制性衰老,然而其调节细胞衰老进程的分子机制依然有待深入研究。     

miR-223促进小鼠胚胎成纤维细胞复制性衰老北大核心CSCD

微小RNA(miRNAs)作为强大的基因表达调控子,广泛参与多种生命过程,在细胞衰老进程中的作用也日益受到关注。miR-223是一个典型的抑癌基因,可显著抑制细胞增殖能力。miR-223与阿尔茨海默症、心血管疾病以及类风湿性关节炎等衰老相关疾病的发生发展密切相关。尽管如此,miR-223在细胞衰老进程中的作用及其分子机制尚未见报道。本研究通过连续传代建立了小鼠胚胎成纤维细胞(MEF细胞)的复制性衰老模型,并利用荧光定量qRT-PCR检测发现,miR-223在衰老MEF细胞中的表达水平显著上调。随后,通过转染miR-223模拟物Agomir-223在MEF细胞中过表达miR-223。结果显示,过表达miR-223可显著促进MEF细胞的衰老表型并抑制其增殖能力,而抑制miR-223的表达可延缓MEF细胞的复制性衰老进程。进一步利用生物信息学方法预测,获得多个miR-223的候选衰老相关靶基因,包括Rasa1、Ddit4和Smad1等。然而,双萤光素酶报告系统结果显示,miR-223并不显著影响其萤光强度,表明它们很可能并不是miR-223的下游靶基因。综上所述,miR-223可显著促进MEF细胞复制性衰老,然而其调节细胞衰老进程的分子机制依然有待深入研究。     

端粒生物学与胸主动脉瘤的研究进展

摘要：随着细胞生理性衰老,端粒（telomere）即染色体末端的重复性 DNA 序列会出现累积性损伤,而血管内皮细胞、平滑肌细胞衰老相关的端粒损伤和修复则被认为是退行性血管疾病发病的分子机制之一。胸主动脉瘤为老年人群中的重要致死性疾病之一,与衰老相关的退行性变在其中发挥着重要的作用。因此本文主要对端粒/端粒酶在胸主动脉瘤发病和进展中的作用做了概述,总结了血管病理学中端粒/端粒酶的调控机制。     

miRNAs与衰老相关信号通路的研究进展

miRNAs是一类负调控基因表达的内源性非编码小分子RNA,在细胞衰老过程中发挥重要作用. 细胞衰老是指可增殖细胞在各种应激下出现细胞周期阻滞,并且丧失增殖能力,进入一种不可逆的、相对稳定的状态. p53、p21、p16、SIRT1、胰岛素/IGF-1及mTOR等蛋白是衰老相关信号通路中的重要分子,参与细胞衰老过程. 研究表明,miRNAs可以通过调控这些衰老相关蛋白所在的信号通路,促进或延缓细胞衰老. 本文综述细胞衰老相关的miRNAs,以及它们对衰老相关信号通路的影响,为深化认识衰老和衰老相关疾病的分子机制奠定基础.     

Integrating cellular senescence with the concept of damage accumulation in aging: Relevance for clearance of senescent cells

Understanding the aging process and ways to manipulate it is of major importance for biology and medicine. Among the many aging theories advanced over the years, the concept most consistent with experimental evidence posits the buildup of numerous forms of molecular damage as a foundation of the aging process. Here, we discuss that this concept integrates well with recent findings on cellular senescence, offering a novel view on the role of senescence in aging and age‐related disease. Cellular senescence has a well‐established role in cellular aging, but its impact on the rate of organismal aging is less defined. One of the most prominent features of cellular senescence is its association with macromolecular damage. The relationship between cell senescence and damage concerns both damage as a molecular signal of senescence induction and accelerated accumulation of damage in senescent cells. We describe the origin, regulatory mechanisms, and relevance of various damage forms in senescent cells. This view on senescent cells as carriers and inducers of damage puts new light on senescence, considering it as a significant contributor to the rise in organismal damage. Applying these ideas, we critically examine current evidence for a role of cellular senescence in aging and age‐related diseases. We also discuss the differential impact of longevity interventions on senescence burden and other types of age‐related damage. Finally, we propose a model on the role of aging‐related damage accumulation and the rate of aging observed upon senescent cell clearance.     

Aging of the cells: Insight into cellular senescence and detection Methods

Cellular theory of aging states that human aging is the result of cellular aging, in which an increasing proportion of cells reach senescence. Senescence, from the Latin word senex, means “growing old,” is an irreversible growth arrest which occurs in response to damaging stimuli, such as DNA damage, telomere shortening, telomere dysfunction and oncogenic stress leading to suppression of potentially dysfunctional, transformed, or aged cells. Cellular senescence is characterized by irreversible cell cycle arrest, flattened and enlarged morphology, resistance to apoptosis, alteration in gene expression and chromatin structure, expression of senescence associated- β-galactosidase (SA-β-gal) and acquisition of senescence associated secretory phenotype (SASP). In this review paper, different types of cellular senescence including replicative senescence (RS) which occurs due to telomere shortening and stress induced premature senescence (SIPS) which occurs in response to different types of stress in cells, are discussed. Biomarkers of cellular senescence and senescent assays including BrdU incorporation assay, senescence associated- β-galactosidase (SA-β-gal) and senescence-associated heterochromatin foci assays to detect senescent cells are also addressed.     

From cell senescence to age-related diseases: differential mechanisms of action of senescence-associated secretory phenotypes

Cellular senescence is a process by which cells enter a state of permanent cell cycle arrest. It is commonly believed to underlie organismal aging and age-associated diseases. However, the mechanism by which cellular senescence contributes to aging and age-associated pathologies remains unclear. Recent studies showed that senescent cells exert detrimental effects on the tissue microenvironment, generating pathological facilitators or aggravators. The most significant environmental effector resulting from senescent cells is the senescence-associated secretory phenotype (SASP), which is constituted by a strikingly increased expression and secretion of diverse pro-inflammatory cytokines. Careful investigation into the components of SASPs and their mechanism of action, may improve our understanding of the pathological backgrounds of age-associated diseases. In this review, we focus on the differential expression of SASP-related genes, in addition to SASP components, during the progress of senescence. We also provide a perspective on the possible action mechanisms of SASP components, and potential contributions of SASP-expressing senescent cells, to age-associated pathologies. [BMB Reports 2015; 48(10): 549-558]     

Exploiting tumor cell senescence in anticancer therapy

Cellular senescence is a physiological process of irreversible cell-cycle arrest that contributes to various physiological and pathological processes of aging. Whereas replicative senescence is associated with telomere attrition after repeated cell division, stress-induced premature senescence occurs in response to aberrant oncogenic signaling, oxidative stress, and DNA damage which is independent of telomere dysfunction. Recent evidence indicates that cellular senescence provides a barrier to tumorigenesis and is a determinant of the outcome of cancer treatment. However, the senescence-associated secretory phenotype, which contributes to multiple facets of senescent cancer cells, may influence both cancer-inhibitory and cancer-promoting mechanisms of neighboring cells. Conventional treatments, such as chemo- and radiotherapies, preferentially induce premature senescence instead of apoptosis in the appropriate cellular context. In addition, treatment-induced premature senescence could compensate for resistance to apoptosis via alternative signaling pathways. Therefore, we believe that an intensive effort to understand cancer cell senescence could facilitate the development of novel therapeutic strategies for improving the efficacy of anticancer therapies. This review summarizes the current understanding of molecular mechanisms, functions, and clinical applications of cellular senescence for anticancer therapy. [BMB Reports 2014; 47(2): 51-59]     

Mitochondrial effectors of cellular senescence: beyond the free radical theory of aging

Cellular senescence is a process that results from a variety of stresses, leading to a state of irreversible growth arrest. Senescent cells accumulate during aging and have been implicated in promoting a variety of age‐related diseases. Mitochondrial stress is an effective inducer of cellular senescence, but the mechanisms by which mitochondria regulate permanent cell growth arrest are largely unexplored. Here, we review some of the mitochondrial signaling pathways that participate in establishing cellular senescence. We discuss the role of mitochondrial reactive oxygen species (ROS), mitochondrial dynamics (fission and fusion), the electron transport chain (ETC), bioenergetic balance, redox state, metabolic signature, and calcium homeostasis in controlling cellular growth arrest. We emphasize that multiple mitochondrial signaling pathways, besides mitochondrial ROS, can induce cellular senescence. Together, these pathways provide a broader perspective for studying the contribution of mitochondrial stress to aging, linking mitochondrial dysfunction and aging through the process of cellular senescence.     

Cellular aging beyond cellular senescence: Markers of senescence prior to cell cycle arrest in vitro and in vivo

The field of research on cellular senescence experienced a rapid expansion from being primarily focused on in vitro aspects of aging to the vast territories of animal and clinical research. Cellular senescence is defined by a set of markers, many of which are present and accumulate in a gradual manner prior to senescence induction or are found outside of the context of cellular senescence. These markers are now used to measure the impact of cellular senescence on aging and disease as well as outcomes of anti‐senescence interventions, many of which are at the stage of clinical trials. It is thus of primary importance to discuss their specificity as well as their role in the establishment of senescence. Here, the presence and role of senescence markers are described in cells prior to cell cycle arrest, especially in the context of replicative aging and in vivo conditions. Specifically, this review article seeks to describe the process of “cellular aging”: the progression of internal changes occurring in primary cells leading to the induction of cellular senescence and culminating in cell death. Phenotypic changes associated with aging prior to senescence induction will be characterized, as well as their effect on the induction of cell senescence and the final fate of cells reviewed. Using published datasets on assessments of senescence markers in vivo, it will be described how disparities between quantifications can be explained by the concept of cellular aging. Finally, throughout the article the applicational value of broadening cellular senescence paradigm will be discussed.     

Ganglioside GM1 Contributes to the State of Insulin Resistance in Senescent Human Arterial Endothelial Cells

Vascular endothelial cells (ECs) play central roles in physiologically important functions of blood vessels and contribute to the maintenance of vascular integrity. Therefore, it is considered that the impairment of EC functions leads to the development of vascular diseases. However, the molecular mechanisms of the EC dysfunctions that accompany senescence and aging have not yet been clarified. The carbohydrate antigens carried by glycoconjugates (e.g. glycoproteins, glycosphingolipids, and proteoglycans) mainly present on the cell surface serve not only as marker molecules but also as functional molecules. In this study, we have investigated the abundance and functional roles of glycosphingolipids in human ECs during senescence and aging. Among glycosphingolipids, ganglioside GM1 was highly expressed in abundance on the surface of replicatively and prematurely senescent ECs and also of ECs derived from an elderly subject. Insulin signaling, which regulates important functions of ECs, is impaired in senescent and aged ECs. Actually, by down-regulating GM1 on senescent ECs and overloading exogenous GM1 onto non-senescent ECs, we showed that an increased abundance of GM1 functionally contributes to the impairment of insulin signaling in ECs. Taken together, these findings provide the first evidence that GM1 increases in abundance on the cell surface of ECs under the conditions of cellular senescence and aging and causes insulin resistance in ECs. GM1 may be an attractive target for the detection, prevention, and therapy of insulin resistance and related vascular diseases, particularly in older people.     

HCSGD:An integrated database of human cellular senescence genes

Cellular senescence is an irreversible cell cycle arrest program in response to various exogenous and endogenous stimuli like telomere dysfunction and DNA damage.It has been widely accepted as an antitumor program and is also found closely related to embryo development,tissue repair,organismal aging and age-related degenerative diseases.In the past decades,numerous efforts have been made to uncover the gene regulatory mechanisms of cellular senescence.There is a strong demand to integrate these data from various resources into one open platform.To facilitate researchers on cellular senescence,we have developed Human Cellular Senescence Gene Database(HCSGD) by integrating multiple online published data sources into a comprehensive senescence gene annotation platform(http://bioinfo.au.tsinghua.edu.cn/member/xwwang/HCSGD).Potential Human Cellular Senescence Genes(HCSGS)were collected by combining information from published literatures,gene expression profiling data and Protein-Protein Interaction networks.Additionally,genes are annotated with gene ontology annotation and microRNA/drug/compound target information.HCSGD provides a valuable resource to visualize cellular senescence gene networks,browse annotated functional information,and retrieve senescenceassociated genes with a user-friendly web interface.     

NAD metabolism: Role in senescence regulation and aging

The geroscience hypothesis proposes that addressing the biology of aging could directly prevent the onset or mitigate the severity of multiple chronic diseases. Understanding the interplay between key aspects of the biological hallmarks of aging is essential in delivering the promises of the geroscience hypothesis. Notably, the nucleotide nicotinamide adenine dinucleotide (NAD) interfaces with several biological hallmarks of aging, including cellular senescence, and changes in NAD metabolism have been shown to be involved in the aging process. The relationship between NAD metabolism and cellular senescence appears to be complex. On the one hand, the accumulation of DNA damage and mitochondrial dysfunction induced by low NAD⁺ can promote the development of senescence. On the other hand, the low NAD⁺ state that occurs during aging may inhibit SASP development as this secretory phenotype and the development of cellular senescence are both highly metabolically demanding. However, to date, the impact of NAD⁺ metabolism on the progression of the cellular senescence phenotype has not been fully characterized. Therefore, to explore the implications of NAD metabolism and NAD replacement therapies, it is essential to consider their interactions with other hallmarks of aging, including cellular senescence. We propose that a comprehensive understanding of the interplay between NAD boosting strategies and senolytic agents is necessary to advance the field.