Regulatory role of acupuncture and moxibustion in immunosenescence and epigenetic mechanisms

doi:10.3969/j.issn.2095-4344.2015.11.026

Abstract

Abstract:

BACKGROUND: The acupuncture and moxibustion is an effective method to regulate the immunosenescence. The epigenetic modification has become a focus in the research of immunosenescence regulation.

OBJECTIVE: To summarize the relationship between epigenetic regulation and the regulatory role of acupuncture and moxibustion on immunosenescence, and to explore the relevant mechanisms.

METHODS: We searched CNKI, VIP, WANFANG DATA, SinoMed, Ebsco Medline, Springer, ScienceDirect and Embase by computer for relevant articles published from January 1999 to August 2014. The keywords were “acupuncture”, “moxibustion”, “aging”, “immunosenescence” and “epigenetic” in Chinese and English. All databases were cross-searched to minimize missing data. We excluded documents based on inclusion and exclusion criteria thereby checking the title and abstract.

RESULTS AND CONCLUSION: Finally 64 articles were included, including 8 Chinese publications and 56 English publications. The innate immune system and the adaptive immune system can vary with aging, which is the most obvious feature in immunosenescence. The acupuncture and moxibustion can improve immunosenescence overall. The epigenetic modification plays an important role in immunosenescence. The acupuncture and moxibustion can affect the epigenetic modification directly. However, the epigenetic mechanism underlying the regulatory role of acupuncture and moxibustion in immunosenescence needs further studies.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

全文链接：

Key words: Epigenomics, Methylation, Acetylation, Acupuncture

CLC Number:

R318

Shen Wen-bin, Zhou Ci-li, Wu Huan-gan, Huang Yan, Zhao Chen, Cui Yun-hua. Regulatory role of acupuncture and moxibustion in immunosenescence and epigenetic mechanisms [J]. Chinese Journal of Tissue Engineering Research, 2015, 19(11): 1782-1787.

Figures/Tables 2

2.1 针灸对免疫衰老的调节作用免疫衰老以固有免疫系统增龄性改变和适应性免疫系统增龄性改变并存为显著特征。大量研究已证实，针灸能提高免疫系统功能，对免疫器官、免疫细胞及细胞因子等均具有调节作用[6]，从整体水平上改善免疫衰老。 2.1.1 免疫衰老的特征性表现免疫衰老在固有免疫系统中的特征性表现：固有免疫反应是机体免疫的第一步，其功能会随着年龄增长而逐渐降低，并且可能会进一步影响到由细胞或体液介导的适应性免疫[7]。肿瘤坏死因子α主要由巨噬细胞分泌，是一种重要的炎性因子，研究发现老年大鼠的肿瘤坏死因子α水平较成年大鼠明显降低[8]。自然杀伤细胞是Ⅰ型固有淋巴细胞，无需提前致敏即具有杀死肿瘤细胞和病毒感染细胞的能力，对不同的病原体均能做出快速回应。有研究表明在衰老过程中自然杀伤细胞的频率、表型和分布会出现大量的改变[2，9-10]，尽管在单细胞水平上衰老对其结合目的细胞和分泌穿孔素的能力没有产生影响，但其细胞毒性作用却严重受损[11]。另外CD16的表达及其诱发抗体依赖性自然杀伤细胞毒性作用也受到衰老的影响[12]。有研究证明自然杀伤细胞的数量和细胞毒性作用的改变与老年人发生感染和死亡的风险较高有直接关系[9，13-14]。机体内关键的早期固有免疫反应不仅依靠着中性粒细胞的活性和吞噬能力，还依靠着其向感染位点的趋化和定向迁移能力，体外实验表明老年小鼠的中性粒细胞定向迁移能力低于青年小鼠[15]。同样的，在人体试验中也证实了这一点，老年人的中性粒细胞表现出了定向迁移能力受损的特点[16]。在免疫衰老过程中，固有免疫系统的中性粒细胞、巨噬细胞和自然杀伤细胞等多种细胞的数量及功能会出现一些特征性改变。免疫衰老在适应性免疫系统中的特征性表现：适应性免疫系统是机体防御系统的第三道防线，在第一、二道防线被病原体突破之后被激活，起着识别和杀灭病原体的作用。胸腺是人体重要的免疫器官，但随着年龄的增长，胸腺的大小和质量会逐步减少，中年以前每年减少3%，以后则每年减少1%[17]。胸腺中的淋巴细胞伴随年龄增长逐渐减少，脂肪组织逐渐增多，这主要是因为能够分泌胸腺激素的胸腺上皮细胞减少造成的[18]。胸腺作为T细胞发育成熟的重要场所，胸腺间质细胞为造血母细胞发育成T淋巴细胞提供了一个特殊的微环境[19-20]，但在免疫衰老的过程中胸腺间质细胞的结构和功能会受到严重损伤[21-22]，例如会出现胸腺囊肿，胸腺上皮细胞器丢失等。适应性免疫系统在免疫衰老过程中最常见的变化包括T细胞和B细胞增殖能力减弱，种类减少，记忆型细胞增多，幼稚细胞减少，1型辅助性T细胞(Helper T cell 1，Th1)和2型辅助性T细胞(Helper T cell 2，Th2)比例反转[23]。T淋巴细胞的减少会明显减弱机体的免疫监视功能，从而导致老年人更容易患感染性疾病、癌症及疫苗失效等[22，24-26]。调节性T细胞具有维持外周免疫耐受和调节自身免疫细胞的作用，当调节性T细胞的数量过多时，机体对感染性疾病、神经性病变和癌症的易感性也会随之增加[27-29]。Garg等[30]运用流式细胞术证实了老龄小鼠比幼年小鼠拥有更高水平的调节性T细胞，而在人体中，Gregg等[31]同样也证实了调节性T细胞在T细胞总量中所占的比例随着年龄逐渐升高，这在一定程度上解释了老年人容易患以上这些疾病的原因。有研究认为初始B细胞数目下降可能是发生免疫衰老的重要标志[32]。随着年龄增长，B细胞分泌抗体的能力下降[33]，并且在一些研究中发现老年小鼠产生的抗体对目标的亲和力较低，不能有效的控制感染[34]。而一些和自身免疫性疾病相关的抗体却会随着年龄逐渐增加，例如，健康年轻人的类风湿因子水平只有5%，老年人则增加到5倍的水平，70岁以上健康老年人的抗核抗体水平要比健康成年人高很多[35]。 2.1.2 针灸对免疫衰老的调节在免疫衰老的进程中，机体的多种免疫器官、组织、细胞和分子的功能及结构受其影响，且这种影响是多样化的，或升高或降低，很难用一种治疗方法解决。而针灸具有整体调节、双向良性调节和多靶点调节的作用特点，因此可以运用针灸的方法改善免疫衰老对机体免疫系统的影响。固有免疫系统中针灸对免疫衰老的调节：针灸可增加固有免疫系统中相关细胞的数量，增强细胞的功能，促进细胞分泌。朱梅等[36-37]发现针刺足三里和关元穴对老年大鼠肝内巨噬细胞的影响是多方面的，首先是使巨噬细胞的数量明显增加，其次是增大了细胞体积，再次是增强了细胞的吞噬功能，并且使细胞处于激活状态。另有研究发现艾灸也具有相似作用，艾灸可以显著促进巨噬细胞对已被吞噬的细菌的杀灭和清除作用，并且能够明显下调多种炎症细胞因子的表达，如白细胞介素1、白细胞介素10等。适应性免疫系统中针灸对免疫衰老的调节：伴随年龄的增长，免疫器官逐渐萎缩退化，组织结构逐渐发生改变，功能逐渐减退。最具有代表性的为胸腺，老年时期的胸腺已基本被脂肪组织所代替，功能也基本丧失。研究证实艾灸能明显延缓D-半乳糖造成的衰老小鼠免疫器官的萎缩退化，提高衰老小鼠的胸腺指数[38]。T淋巴细胞亚群的分布异常与多种疾病有直接关系，临床实验研究表明温和灸能明显提高老年人CD3+和CD4+T细胞的含量，恢复CD4+/CD8+的比值[39]，改善老年人的免疫功能。淋巴细胞的增殖能力会出现增龄性降低，Pavão等[40]选用12个健康年轻人(平均年龄27.6岁)和12个健康老年人(平均年龄65.6岁)研究针刺对心理压力和淋巴细胞增殖能力的影响，实验开始前测得老年人淋巴细胞增殖能力明显低于年轻人(P=0.01)，经过针刺干预后年轻人组的淋巴细胞增殖能力无任何改变(P=0.31)，而老年人组明显提高(P=0.004)，更值得注意的是，针刺干预后的老年人组淋巴细胞增殖能力水平和年轻人组基本相同，除此以外还证实了针刺对于健康老年人能够有效的缓解压力和紧张情绪。艾灸可以提高老年人T淋巴细胞总数，使由免疫衰老改变的CD4+/CD8+细胞比值恢复正常，同时能够促进白细胞介素2的分泌[41]。淋巴B细胞在受到抗原刺激后能产生多种免疫球蛋白，参与机体的免疫反应，目前所使用的大多数疫苗就是通过刺激B淋巴细胞产生抗体的，老年人对疫苗的反应性降低或许与此有关。肖凌等[42]采用百白破疫苗免疫衰老模型大鼠，“双固一通”针法进行干预，结果发现针灸能明显降低衰老大鼠的血脂水平，提高衰老大鼠对疫苗的反应性，起到改善免疫衰老的作用。 2.2 针灸调节免疫衰老的表观遗传机制探讨表观遗传存在于人类整个生命过程中，表观遗传修饰主要包括DNA甲基化，组蛋白修饰，染色质结构变异和RNA干扰等[43]。已有研究表明表观遗传调控和免疫衰老具有很大的相关性，伴随着年龄增长出现的表观遗传修饰改变很可能是免疫衰老发生的基因机制。这也为研究针灸调节免疫衰老的机制提供了一个新的方向。 2.2.1 表观遗传调控与免疫衰老的相关性表观遗传调控主要通过修饰基因和蛋白影响免疫衰老相关基因的功能和状态，从而调控免疫衰老。例如表观遗传调控对免疫反应相关基因和衰老差异表达相关基因起到了非常重要的调节作用，其中最具代表性的基因为白细胞介素2基因和γ干扰素基因[44]。老年小鼠中CD3+和CD4+细胞DNA甲基化水平只有年轻小鼠的20%和25%[30]。人类整个基因组的5-甲基胞嘧啶在衰老过程中会逐渐减少并且和人类潜在的最长寿命成反比[45-46]。运用基因敲除的方法敲除小鼠的DNA甲基转移酶1基因，与未敲除的小鼠对比后发现当这种基因敲除的小鼠生长到了老年阶段时，发现在其肝脏和唾液腺中自身抗体滴度较低，且衰老相关的淋巴细胞浸润较少；18个月大的DNA甲基转移酶1基因缺失小鼠不如正常对照小鼠的T细胞免疫老化明显，且更好的保持了T细胞免疫功能， T细胞发展成记忆T细胞的速度慢，分泌白细胞介素2的水平更高，T细胞增殖反应更好；另一方面，DNA甲基转移酶1基因缺失小鼠甲基胞嘧啶结合蛋白2表达水平增加，这在蛋白机制上解释了这些小鼠中的DNA甲基化水平出现差异的原因[47]。组蛋白H4乙酰化和H3磷酸乙酰化发生在促炎分子信号出现之后，组蛋白的乙酰化又进一步使DNA招募到的核转录因子κB增多[48]，核转录因子κB只有在活化之后才能进入细胞核参与转录调控，在多种老年组织中可观察到活化的核转录因子κB异常增多，这个现象也被认为是免疫衰老的最初原因[49](图1)。 2.2.2 针灸调节免疫衰老与表观遗传调控机制研究表观遗传调控最突出的特征是所有的修饰均是在不改变基因序列的前提下进行的，通过修饰基因、改变蛋白结构、控制DNA与其它分子的结合多途径、多层次的影响和调节遗传信息的表达，最终在机体的整体水平上起到调控作用。而从以上有关针灸对免疫衰老的调节可以看出针灸能够从器官、组织、细胞和分子多种水平上全面整体的改善免疫衰老，这和表观遗传调控的特征有很大程度的契合。因此，可以将表观遗传调控引入针灸调节免疫衰老的机制中来，这有利于更好的揭示针灸调节免疫衰老的机制。表观遗传调控就像是控制着大门的控制器，在生命的各个进程中控制着大门的开放和关闭，但这个控制器很容易被所处的环境改变[50-58]，针灸对于免疫衰老的调节可能和针灸改变了这个控制器有关。有研究已证实艾灸可以增强小鼠心肌细胞中组蛋白乙酰化酶p300的表达，激活了心肌细胞中的抗细胞凋亡蛋白Bcl-2蛋白的表达，起到了保护心肌细胞的作用[59]。另一项研究则证实针刺能明显增加缺血性心肌梗死模型大鼠组蛋白H3K9乙酰化酶与血管内皮生长因子启动子区的结合，促进血管内皮生长因子的转录表达，介导缺血心肌血管新生，起到了保护缺血心肌的作用[60](图2)。这2项研究表明了针灸确实通过调控表观遗传修饰起到调节机体功能的作用，这为今后针灸调节免疫衰老的表观遗传学机制研究提供了借鉴。多项研究证实针灸能有效改善免疫衰老，表观遗传学与免疫衰老密切相关。例如，随着年龄增加，巨噬细胞吞噬能力下降，活性降低，表观遗传学研究表明衰老小鼠巨噬细胞的组蛋白去乙酰化酶水平比年轻小鼠高[61]，而针刺能增强老年大鼠巨噬细胞功能[36-37]。初始T细胞中，由于白细胞介素2基因启动子区的高甲基化状态而处于静息态。但在激活信号传递给T细胞后20 min，白细胞介素2基因甲基化水平逐渐降低[62]，白细胞介素2基因开始转录，白细胞介素2分泌增加。研究证实艾灸能明显提高衰老大鼠血清白细胞介素2含量，至于艾灸是否是通过改变白细胞介素2基因甲基化水平增加白细胞介素2含量的，今后作者会进一步关注。 "

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