骨代谢与肠道菌群

doi:10.3969/j.issn.2095-4344.2015.42.021

摘要/Abstract

摘要：

背景：骨代谢与肠道菌群肠道内定植了数量众多、种类丰富的肠道菌群，它们和宿主间形成了互利共生的关系，对宿主的健康产生着重大影响。研究发现肠道菌群不仅调控肠道活动，并且能通过调节免疫系统状态进而干预骨代谢。
目的：综述肠道菌群对骨代谢影响研究的新进展。
方法：以“Gut microbiota，immunesystem，bonemetabolism，osteoporosis”为关键词检索PubMed 数据库，选择内容与肠道菌群、免疫及骨代谢相关文献，同一领域文献则选择近期发表或发表在权威杂志文章。最总共纳入文献46篇，从肠道菌群与免疫、骨代谢与免疫、肠道菌群与骨代谢3方面进行综述。
结果与结论：肠道菌群对骨质疏松症的影响研究将涉及到骨生理学、肠胃病学、免疫学以及微生物学等多门学科。无菌小鼠与人体内实验研究发现肠道菌群对骨代谢具有重要影响，利用抗生素、益生菌、益生元干预肠道菌群进一步证实了肠道菌群对骨量具有很好的调节作用。这些作用主要表现在迅速生长期，例如骨量需求较大的青春期，以及骨量丢失较明显的妇女更年期。
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

关键词: 组织构建, 骨组织工程, 肠道菌群, 骨代谢, 骨密度, 骨质疏松症, 免疫, 益生元, 益生菌, 无菌动物, 破骨细胞, 国家自然科学基金

Abstract:

BACKGROUND: The gut microbiota in our intestine performs numerous useful functions and has a major impact on the host’s health. Recently some studies have revealed that the gut microbiota cannot only control intestinal activity but also affect bone metabolism by regulating the immune system.

OBJECTIVE: To review the new research development in the effects of gut microbiota on bone metabolism.

METHODS: We retrieved the PubMed database using “gut microbiota, immune system, bone metabolism, osteoporosis” as keywords. A total of 46 articles were included which were related to gut microbiota, immune system and bone metabolism. For the articles in the same field, those published recently or in authorized journals were selected.

RESULTS AND CONCLUSION: Gut microbiota-osteoporosis research will bridge the gaps between bone physiology, gastroenterology, immunology, and microbiology. In vivo experiments in the germ-free mice and human body have found that the gut microbiota has important effects on bone metabolism, and the intervention of antibiotics, probiotics and prebiotics has further confirmed the effects of gut microbiota on bone mass. The gut microbiota has more obvious effects on bone mass in the adolescent and post-menopause periods.
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

Key words: Bacteria, Lower Gastrointestinal Tract, Metabolism, Bone Density, Osteoporosis, Immunity, Tissue Engineering

袁斯远，何芳，盛彤，石见佳子，王新祥. 骨代谢与肠道菌群[J]. 中国组织工程研究, 2015, 19(42): 6838-6842.

Yuan Si-yuan, He Fang, Sheng Tong, Ishimi Yoshiko, Wang Xin-xiang. Bone metabolism and gut microbiota[J]. Chinese Journal of Tissue Engineering Research, 2015, 19(42): 6838-6842.

图/表（结果） 1

2.1 肠道菌群与免疫人体肠道菌群来自母体及外环境细菌迅速定植。随着婴儿自身机体发育以及离乳后饮食结构的改变，肠道菌群结构在不断改变；3岁左右，肠道菌群的多样性基本趋于成人的菌群结构^[12-13](见图1)。在此期间由于受到肠道菌群与环境因素的影响，新生儿的免疫系统快速成熟。肠道菌群构成随着年龄不断改变，尤其是65岁以后^[14-16]。肠道菌群与宿主处于共生状态，肠道菌群帮助宿主消化食物，防止病原微生物的入侵；宿主则为肠道菌群提供有利的生存环境。然而在病理状态下，饮食的改变、抗生素的使用以及病原微生物的入侵等能够改变肠道菌群的构成，最终导致免疫及代谢紊乱所引起一系列疾病发生，包括多种肠炎、风湿性关节炎、多发性硬化病、糖尿病、食物过敏、湿疹、哮喘、肥胖以及代谢综合征等^[7-9^，^17-18]。

研究表明，无菌动物的黏膜免疫系统发育不健全，肠道相关的淋巴组织发育不完全；并且，无菌动物脾脏CD4⁺T细胞与生发中心明显减少。所以肠道菌群对免疫系统的健全起到重要作用^[19]。以同卵双胞胎为研究对象的一项实验研究表明，克罗恩病患者体内黏附侵袭性大肠杆菌数量明显增加，而具有抗炎作用的柔嫩梭菌的数量则明显减少^[20-21]。对克罗恩病患者排泄物分析表明，在克罗恩疾病活跃期共生于机体肠道的正常菌群双歧杆菌显著下降，而在缓解期则逐渐恢复到正常水平^[22]。

2.2 骨代谢与免疫骨骼的重建是通过具有骨形成功能的成骨细胞与具有骨吸收功能的破骨细胞完成的^[23]。成骨细胞起源于多能的间充质干细胞；破骨细胞则由单核细胞分化而来，单核细胞是破骨细胞、巨噬细胞和树突状细胞的共同前驱细胞^[24]。局部微环境影响着单核细胞的分化方向。在巨噬细胞集落刺激因子存在的情况下，能够增加破骨细胞的形成和存活^[24]。

骨质疏松症与免疫的关系比较明确，研究表明一些自生免疫性疾病如风湿性关节炎等发病过程中骨量的丢失是由T细胞释放的炎性因子所介导的^[25]。绝经后雌激素缺乏引起炎性因子增加能够加大破骨细胞的形成以及延长破骨细胞的存活^[26-27]。血清中超敏C-反应蛋白的升高与骨吸收、骨量丢失以及骨质疏松症相关^[28-31]。肿瘤坏死因子α和白细胞介素1阻滞治疗能够明显降低绝经后早期妇女血清骨吸收标志物^[32]。另有报道，对T细胞缺乏小鼠利用抗CD4抗体、抗CD8抗体干预能够预防卵巢切除引起的骨量丢失^[33]。所以，骨髓中T细胞形成的增加与T细胞释放的细胞因子增多能够引起骨量丢失甚至骨质疏松症^[34]。

2.3 肠道菌群与骨代谢

2.3.1 肠道菌群与骨代谢最近，有研究显示肠道菌群缺乏的无菌小鼠松质骨与皮质骨骨密度较正常动物明显增加，其中股骨远端骨量较正常动物上升39%^[35-36]。骨量的升高是由骨小梁数量的增加与骨小梁间隙增宽决定的，但是无菌动物骨小梁厚度较正常动物并没有改变，而皮质骨升高明显。通过无菌小鼠骨髓培养发现无菌小鼠骨骼中破骨细胞减少，骨髓产生的CD4⁺T细胞与破骨前驱细胞明显减少；同时，其骨形成速率较正常小鼠并没有改变，表明无菌小鼠骨量的增加主要是通过抑制破骨细胞的生成进而减少骨吸收来实现的。另一方面，无菌小鼠骨骼中白细胞介素6与肿瘤坏死因子 α mRNA的表达明显减少，所以无菌小鼠骨量上升有可能是通过免疫系统的调节来实现的^[35-36]。另有实验表明3周龄无菌小鼠肠道种植正常的肠道菌群后其皮质骨及松质骨骨量皆达到正常水平并且骨髓中CD4⁺T细胞与破骨前驱细胞也趋于正常，进一步论证骨密度的增加与骨骼中炎症因子的表达及破骨细胞生成减少密切相关^[35]。所以，影响无菌动物骨量改变主要的原因是机体免疫状态的改变影响破骨细胞的生成实现的。

2.3.2 肠道菌群与绝经后骨代谢分别对正常及无菌小鼠注射阻滞性激素产生的促性腺激素释放激素亮丙瑞林以模拟卵巢切除骨质疏松小鼠模型。结果发现，亮丙瑞林干预的正常小鼠骨密度下降较肠道菌群缺乏小鼠更明显，表明肠道菌群在性激素缺乏引起的骨质疏松过程中起到重要作用。另外，亮丙瑞林干预的正常小鼠血清中骨吸收的重要标志物羧基端端肽浓度明显升高，而肠道菌群缺乏小鼠血清中羧基端端肽浓度则变化不明显。

此外亮丙瑞林干预的正常小鼠骨髓中TNF-α⁺CD4⁺T细胞与TNF-α⁺CD8⁺T明显增加，而肠道菌群缺乏小鼠骨髓中则变化不明显。这些结果显示肠道菌群能通过调节免疫系统来应答体内雌激素缺乏^[36]。另外绝经后妇女肠道菌群构成的改变对骨量流失也有重大影响，因此绝经后妇女肠道菌群的紊乱会明显增加雌激素缺乏引起的骨量下降^[16]。

2.3.3 益生菌、益生元与骨代谢肠道菌群受到抗生素，益生菌、益生元、饮食等多因素影响。对新生小鼠进行为期3周抗生素治疗发现不会明显引起细菌数量的改变，但是能够引起肠道菌群的结构的变化以及小鼠骨密度增加^[17]。低浓度盘尼西林干预能够增加成年雌性小鼠的骨密度^[18]。四环素能够通过降低骨吸收而抑制卵巢切除小鼠的骨密度下降及提高骨生物力学指标^[37-38]。这些实验显示抗生素的干预能够引起肠道菌群构成的改变及骨密度的增加，进一步说明了肠道菌群对骨代谢起到重要影响。

益生菌是来源于宿主并对宿主健康有一定促进作用的微生物，同时也是具有保持肠道微生态系统生态平衡作用的重要微生物。益生菌能够刺激肠道免疫系统以提高机体健康状况。一些益生菌已被用于实验研究和炎症性肠病的治疗^[39]。实验研究证实给鸡中添加适当的益生菌能够明显提高鸡胫骨骨密度^[40]。副干酪乳杆菌或副干酪乳杆菌联合植物乳杆菌干预去卵巢小鼠6周都能抑制骨吸收而防治性激素缺乏引起的骨量流失^[41]。其他益生菌对卵巢切除小鼠骨量流失的预防作用也有报道。Britton等^[42]研究证实瑞特乳酸菌能够降低卵巢切除小鼠的海绵骨骨密度下降。以上干预能够增加骨髓中CD4⁺T细胞，进一步确实了肠道菌群影响骨免疫系统进一步抑制骨吸收。另有实验表明，经口服瑞特乳酸菌能够减轻正常雄性小鼠肠道炎症并能提高其海绵骨骨量^[43]。所以，益生菌的干预能够调节骨免疫系统而降低卵巢切除小鼠及正常雄性小鼠的骨量流失。

益生元低聚半乳糖在大鼠及人体内对肠道菌群及骨量的影响也已被研究。大鼠实验表明低聚半乳糖能够增加肠道菌群中双歧杆菌的比例并能提高大鼠骨量^[44]。以青少年女性为实验对象利用低聚半乳糖干预3周发现低聚半乳糖能够增加人体内钙的吸收以及人肠道菌群双歧杆菌的比例，这与以大鼠为研究对象的实验结果是一致的^[45]。而且，Abrams等^[46]发现低聚半乳糖能够增加青春期成长过程中的骨盐沉积。

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引言

原发性骨质疏松症(以下简称骨质疏松症)是与社会人口老龄化关系最为密切的疾病之一，是老年人的常见病和多发病，以骨量减少、骨组织结构退化为特征、导致骨脆性增高及骨折危险性增加的一种全身性代谢性骨病。骨质疏松症最大的危害是骨质疏松性骨折，50% 女性和20%男性在其一生中，至少并发一次骨质疏松性骨折[1]。骨质疏松症的发病是由20-30岁时所能到达的峰值骨量和年龄增长相关的骨丢失两方面决定的。人体峰值骨量50%-85%是由遗传决定，而环境因素在年龄增长相关的骨丢失中起到更加重要的作用[2]。
近年来肠道菌群与人体健康间的关系引起人们强烈地关注。肠道微生态系统是人体最大的微生态系统，栖息着大约1014数量级的细菌，其基因组的基因数约为人类基因组基因总数的150倍[3]。肠道菌群与人体相互依存，影响着人体肠道内分泌细胞、肠道神经系统、肠道通透性以及免疫系统等的功能；在促进食物消化、产生维生素等营养物质、抵御外来致病菌侵入、刺激免疫系统等方面有着重要作用。肠道微生态系统的平衡受到饮食，药物等一系列的环境因素影响[4-6]。病原体的侵入、抗生素的使用、组织破坏等都能够打破这种平衡而诱导肠道内、外一系列炎症性疾病发生，包括多种肠炎、风湿性关节炎、多发性硬化病、糖尿病、食物过敏、湿疹、哮喘、肥胖以及代谢综合征等[7-9]。
近年来研究发现，肠道菌群所引起的炎症反应，自身免疫状态改变与人体的低骨量相关，揭示了肠道菌群与骨骼间的关系[10-11]。有研究已经证实肠道菌群能够影响宿主的免疫系统，而免疫系统的改变与骨代谢密切相关。因此，肠道菌群有可能是通过调控宿主免疫系统来作用于骨代谢。文章就近年来有关肠道菌群对骨代谢影响研究作一综述。
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