胸腺增龄性萎缩的机理及其逆转

由第Ⅲ、Ⅳ对咽囊胚层发育而来的胸腺是重要的中枢免疫器官、Ｔ细胞分化成熟场所。动物在出生后胸腺的重量均与年龄增长呈负相关[1] 。成年Ｓｐｒａｇｕｅ Ｄａｗｌｅｙ大鼠胸腺结构光镜和电镜观察见坏死和纤维化的区域随年龄增长而逐渐扩大 ,皮质区域进行性缩小 ,胸腺细胞体积     

miR-194 在增龄性胸腺萎缩中的表达及靶基因研究

目的:检测增龄性胸腺萎缩过程中miR-194 与PTPN12 的表达水平变化,并分析二者相互作用,阐明其中的分子调节机制。方法:选用C57BL/6 小鼠,分为4 组:1 月龄组、6 月龄组、10 月龄组和19 月龄组,每组6 只,雌雄各半。麻醉后取出胸腺组织,用CD45 抗体与LS 柱吸附洗脱,筛选出胸腺上皮细胞。实时荧光定量PCR 与Western blot 方法检测随年龄增长,胸腺上皮细胞中miR-194 与PTPN12 基因的表达变化趋势。体外实验共转染miR-194 与PTPN12 荧光素酶报告载体到HEK293 细胞内,分别于24、48 h 后检测自发荧光值。结果:随月龄增长,miR-194 表达出现下调趋势(P<0.05),而PTPN12 基因表达出现上调趋势(P<0.05),且二者呈负相关性(P<0.05)。体外荧光素酶报告基因结果显示,miR=194 与PTPN12 基因3’UTR 区域发生直接作用,并在48 h 结合效率最高。结论:PTPN12 是miR-194 靶基因之一,参与了增龄性胸腺萎缩过程,是调节胸腺上皮细胞功能的重要因子。     

胸腺发育与衰老相关基因调控的研究进展

胸腺是人体内重要的中枢免疫器官,是T淋巴细胞成熟的场所.在骨髓中产生的淋巴造血祖细胞通过血液进入胸腺,与胸腺基质细胞相互作用,最终形成成熟的CD4+/CD8+T细胞,返回到血液中参与细胞免疫.现在已发现许多基因参与胸腺发育、衰老,如Foxn1、Hox、Wnt4等.这些基因在胸腺组织内形成一个网络,相互制约影响,调控着胸...     

增龄相关性胸腺萎缩

胸腺是Ｔ细胞发育的重要场所,随增龄而出现的老化,特别是胸腺所表现出的明显的萎缩势必影响到Ｔ细胞的发育,进而造成外周淋巴组织中Ｔ细胞的质与量的异常。本文对近年此方面的研究进展作一简要综述。     

Wnt信号通路与胸腺发育

胸腺是人体重要的中枢淋巴器官,是T淋巴细胞分化发育的场所。起源于骨髓的淋巴细胞祖细胞,在胸腺中历经阳性选择和阴性选择后发育为成熟的T细胞,然后通过血液循环参与外周细胞免疫。研究表明,Wnt信号通路广泛存在于胸腺上皮细胞和T细胞,它不但影响胸腺上皮细胞的形态、功能,而且对于维持T细胞前体细胞和后期T细胞的分化发育都很重要。最近研究发现,Wnt信号通路参与了胸腺增龄性萎缩过程的调节,Wnt信号通路的改变可引起上皮网络结构的改变,最终导致胸腺微环境的破坏。因此,研究Wnt信号通路在胸腺发育中的作用,对于探索胸腺增龄性萎缩的调控机制和改善老年人的健康状况有重要意义。     

增龄相关性胸腺萎缩

胸腺是Ｔ 细胞发育的重要场所,随增龄而出现的老化,特别是胸腺所表现出的明显的萎缩势必影响到Ｔ 细胞的发育,进而造成外周淋巴组织中Ｔ 细胞的质与量的异常。这就继发性影响机体对病原微生物的免疫应答水平。胸腺萎缩究竟是怎样触发和如何受控的呢？ 目前有一些假说理论和实验依据来解释其成因。本文对近年此方面的研究进展作一简要综述。     

小鼠增龄相关性胸腺基因的克隆

目的：用基因差异显示技术研究小鼠胸腺增龄相关基因。方法：利用差异显示反转录PCR（DDRT－PCR）技术对1月龄和10月龄小鼠胸腺mRNA差异表达进行分析,获得差异显示的表达序列标签（ESTs)。选其1个1月龄高表达的EST为探针,从小鼠胸腺cDNA文库中筛选出一个827bp的阳性克隆,并用PCR扩增延长为1406bp的cDNA片段（mt22-1406)。结果：同源性分析结果表明,mt22-1406含一编码438A的开放阅读框,与人延伸因子1γ（EF1γ）高度同源,其Genbank接收号为BE241062。结论：获得一个含完整开放阅读框与小鼠胸腺增龄相关的基因。     

T细胞定向迁移诱导实验性自身免疫性脑脊髓炎小鼠胸腺萎缩

目的 初步探讨实验性自身免疫性脑脊髓炎(EAE)小鼠胸腺萎缩的机制.方法 髓鞘少突胶质细胞糖蛋白(MOG)免疫C57BL/6小鼠诱导EAE,卵清白蛋白(OVA)免疫的小鼠作为对照;不同时间点计数胸腺、脾脏、淋巴结细胞总数,检测脾脏中胸腺来源细胞及中枢神经系统(CNS)浸润细胞.结果 MOG肽成功诱导EAE动物模型,小鼠出现典型的肢体运动功能障碍,脊髓可见大量炎性细胞浸润;MOG和OVA免疫均诱导胸腺细胞增加,第5天达到高峰,随后逐渐下降;EAE发病后胸腺细胞迅速减少,发病高峰期几乎完全消失,胸腺严重萎缩;MOG和OVA免疫后脾脏和淋巴结细胞总数持续升高,新近胸腺来源的T细胞增加尤其明显;EAE发病后脾脏T细胞总数减少,CNS浸润淋巴细胞总数增加.结论 大量T细胞在胸腺发育成熟并释放到外周,进而定向迁移至CNS诱导EAE是胸腺萎缩的主要原因.     

胸腺内免疫耐受机制的研究进展

正常机体的免疫系统能有效地区分"自身"与"异己"成份。免疫系统对自身抗原的无反应性是通过免疫耐受机制而形成;自身耐受机制的破坏常导致自身免疫性疾病的产生。胸腺在形成中枢免疫耐受以及指导T细胞发育中有着重要的作用。近年来对胸腺免疫耐受机制的研究已取得不少新的进展,本文就胸腺内自身抗原表达、胸腺APC细胞、胸腺细胞选择机制以及参与其中的细胞膜辅助分子,如CD40、CD28、Fas、CD30等在胸腺免疫耐受形成机制中的作用及意义作一综述。     

Medullary thymic epithelial stem cells: role in thymic epithelial cell maintenance and thymic involution

The thymus consists of two distinct anatomical regions, the cortex and the medulla; medullary thymic epithelial cells (mTECs) play a crucial role in establishing central T-cell tolerance for self-antigens. Although the understanding of mTEC development in thymic organogenesis as well as the regulation of their differentiation and maturation has improved, the mechanisms of postnatal maintenance remain poorly understood. This issue has a central importance in immune homeostasis and physiological thymic involution as well as autoimmune disorders in various clinicopathological settings. Recently, several reports have demonstrated the existence of TEC stem or progenitor cells in the postnatal thymus, which are either bipotent or unipotent. We identified stem cells specified for mTEC-lineage that are generated in the thymic ontogeny and may sustain mTEC regeneration and lifelong central T-cell self-tolerance. This finding suggested that the thymic medulla is maintained autonomously by its own stem cells. Although several issues, including the relationship with other putative TEC stem/progenitors, remain unclear, further examination of mTEC stem cells (mTECSCs) and their regulatory mechanisms may contribute to the understanding of postnatal immune homeostasis. Possible relationships between decline of mTECSC activity and early thymic involution as well as various autoimmune disorders are discussed.     

Genetic regulation of thymic involution

In this review, we have summarized our work using combined complex statistical genetics, bioinformatics, and functional genomics to determine the genetic basis of the age-related thymic involution in C57BL/6J X DBA/2J recombinant inbred mice and the parental B6 and D2 mice. We have shown that these mice provided a valuable genetic model that can permit resampling of thymuses from different aged but genetically identical animals and determination of the relative significance of age-associated changes in the thymus. Our results suggest that the quantitative trait loci (QTL) regulating the Con A-induced thymocyte proliferative response were mapped to mouse chromosome Chr 11 (D11Mit51 at 18 cM), a region that harbors the IL-12b gene. The importance of IL-12b in maintaining thymic integrity and function during the aging process was confirmed by a more rapid involution of the thymus in IL-12b knockout (IL-12b-/-) mice compared to wild-type (WT) mice. Functionally, IL-12 provided a strong synergistic effect to augment the IL-7 or IL-2 induced thymocyte proliferative response, especially in both aged WT and IL-12b-/- mice, but not in normal young mice. In contract to the proliferative response, the age-related decline in the total number of thymocytes was determined at different age, and mapped to loci on Chr 9, 62 cM and Chr 10, 32 cM. Using matrix-assisted laser desorption/ionisation-time of flight-mass spectrometry (MALDI-TOF-MS), increased expression of peroxiredoxin was found to be correlated with thymic involution. Our results suggest the possibility to identify the complex molecular network that can be associated with the regulation of thymic involution in aged mice using a high-dimensional functional genomics approach.     

Beta-catenin expression in thymocytes accelerates thymic involution

Age‐related thymic involution in mammals is accompanied by decreased generation of naïve T cells without significant reduction in the number of peripheral T cells. This leads to inefficient immune responses and inadequate combating of infections and other challenges to the immune system in older mammals. The molecular mechanisms that underlie this phenomenon are not known. In this report we show that expression of β‐catenin in thymocytes enhances thymic involution. The effect of β‐catenin expression is seen in all the thymic sub‐populations, suggesting that an age‐related developmental process is accelerated. We also show that, as in normal mice, thymic involution does not lead to a drastic reduction in splenic T cells in β‐catenin‐transgenic mice. This study identifies β‐catenin expression in thymocytes as a molecular target of age‐related thymic involution.     

Epithelial-cell architecture during involution of the human thymus

One hundred thymus glands were assessed histologically as to their degree of involution. Epithelial cells were demonstrated by an immunoperoxidase method using a monoclonal antibody against cytokeratin. The distribution of these cells was studied in the medulla, the cortico-medullary junction, the cortical parenchyma and the subcapsular cortex. As involution proceeds, the loss of cells from the thymus is almost totally confined to the lymphoid-cell elements. The architecture of the epithelial-cell network remains largely intact although there is extensive collapse of the structure due to the loss of the intervening lymphocytes. Even when involution is apparently complete; sheets of epithelial cells can be demonstrated in the thymic remnant.     

A study of the chick thymus microenvironment during development: Analysis by monoclonal antibodies against thymic epithelium

The process of T-lymphocyte differentiation within the thymus involves a series of molecular interactions. In this work we have carried out an analysis of the chick thymus microenvironment in order to evaluate its heterogeneity during development. We have produced 11 monoclonal antibodies whose staining patterns detected by the immunoperoxidase technique allowed us to divide them into five groups. A first group (E19-E2, P0-E5, and P15-T1) binds to thymic medullary stroma showing a reticular pattern on medullary epithelial cells and whose significance would be related to thymic stromal secretion. The second group of monoclonal antibodies (P15-T3) stains thymic corpuscles of 10- and 15-day chicks. The third group of antibodies includes P0-E1, P0-E3, P5-A6, and P15-T2 whose staining pattern is both medullary and cortical. The fourth group (P10-HB1 and P10-HB2) binds to thymic stromal and cortical thymocytes, and the fifth group (P5-A1) is characterized by the staining of medullary vessels of 5-day chicks. These five groups of monoclonal antibodies corroborate the existence of an antigenic diversity of the chick thymus microenvironment. Their possible relationships with T-cell differentiation and stromal-thymocyte interactions are discussed. © 1993 Wiley-Liss, Inc.     

CD147 deficiency in T cells prevents thymic involution by inhibiting the EMT process in TECs in the presence of TGFβ

Thymic involution during aging is a major cause of decreased T-cell production and reduced immunity. Here, we show that the loss of CD147 on T cells prevents thymic senescence, resulting in slowed shrinkage of the thymus with age and increased production of naive T cells. This phenotype is the result of slowing of the epithelial–mesenchymal transition (EMT) process in thymic epithelial cells (TECs), which eventually leads to reduced adipocyte accumulation. In an in vitro coculture system, we found that TGFβ is an important factor in the EMT process in TECs and that it can reduce the expression of E-cadherin through p-Smad2/FoxC2 signaling. Moreover, CD147 on T cells can accelerate the decline in E-cadherin expression by interacting with Annexin A2 on TECs. In the presence of TGFβ, Annexin A2 and E-cadherin colocalize on TECs. However, CD147 on T cells competitively binds to Annexin A2 on TECs, leading to the isolation of E-cadherin. Then, the isolated E-cadherin is easily phosphorylated by phosphorylated Src kinase, the phosphorylation of which was induced by TGFβ, and finally, p-E-cadherin is degraded. Thus, in the thymus, the interaction between T cells and TECs contributes to thymic involution with age. In this study, we illuminate the mechanism underlying the triggering of the EMT process in TECs and show that inhibiting TGFβ and/or CD147 may serve as a strategy to hinder age-related thymic involution.     

Premature thymic involution is independent of structural plasticity of the thymic stroma

The thymus is the organ devoted to T‐cell production. The thymus undergoes multiple rounds of atrophy and redevelopment before degenerating with age in a process known as involution. This process is poorly understood, despite the influence the phenomenon has on peripheral T‐cell numbers. Here we have investigated the FVB/N mouse strain, which displays premature thymic involution. We find multiple architectural and cellular features that precede thymic involution, including disruption of the epithelial–endothelial relationship and a progressive loss of pro‐T cells. The architectural features, reminiscent of the human thymus, are intrinsic to the nonhematopoietic compartment and are neither necessary nor sufficient for thymic involution. By contrast, the loss of pro‐T cells is intrinsic to the hematopoietic compartment, and is sufficient to drive premature involution. These results identify pro‐T‐cell loss as the main driver of premature thymic involution, and highlight the plasticity of the thymic stroma, capable of maintaining function across diverse interstrain architectures.     

Extracellular matrix components of the mouse thymic microenvironment. III. Thymic epithelial cells express the VLA6 complex that is involved in laminin-mediated interactions with thymocytes

We describe herein the expression of the VLA6 complex by murinethymic epithelial cells (TEC). The immunohistochemical distributionrevealed that VLA6 is found in both thymic medullary and subcapsullaryareas. Moreover, studies by immunoelectron microscopy revealeda membrane labeling of the VLA6 molecule, including at desmosomalsites. By means of immunoblottlng, immunoprecipitation, andaffinity chromatography of extracts from a mouse TEC line, wefurther demonstrated that VLA6 is a laminin (LN) receptor inthese cells. In keeping with this finding, we showed that TECadhesion, spreading, and proliferation were enhanced in vitroby LN. The fact that VLA6 is also expressed by the large majorityof thymocytes raised the hypothesis that it might be involvedin LN-mediated TEC—thymocyte interactions. Interestingly,in vitro experiments showed that there is an increase in theTEC—thymocyte adhesion upon glucocorticold hormone treatment,a situation in which the expression of VLA6 as well as LN isenhanced. Most importantly, this adhesion can be reversed bypre-treating TEC with an anti-6 integrin mAb. Additionally,spontaneous in vitro thymocyte release by thymic nurse cellcomplexes was enhanced by LN and partially blocked by anti-6or anti-ß1 antibodies. Our results suggest that VLA6is involved in LN-mediated TEC—thymocyte interactionsthat can be relevant for thymic microenvironmental cell physiologyand intrathymic T cell differentiation events.     

Molecular inflammation: underpinnings of aging and age-related diseases

Recent scientific studies have advanced the notion of chronic inflammation as a major risk factor underlying aging and age-related diseases. In this review, low-grade, unresolved, molecular inflammation is described as an underlying mechanism of aging and age-related diseases, which may serve as a bridge between normal aging and age-related pathological processes. Accumulated data strongly suggest that continuous (chronic) upregulation of pro-inflammatory mediators (e.g., TNF-α, IL-1β, IL-6, COX-2, iNOS) are induced during the aging process due to an age-related redox imbalance that activates many pro-inflammatory signaling pathways, including the NF-κB signaling pathway. These pro-inflammatory molecular events are discussed in relation to their role as basic mechanisms underlying aging and age-related diseases. Further, the anti-inflammatory actions of aging-retarding caloric restriction and exercise are reviewed. Thus, the purpose of this review is to describe the molecular roles of age-related physiological functional declines and the accompanying chronic diseases associated with aging. This new view on the role of molecular inflammation as a mechanism of aging and age-related pathogenesis can provide insights into potential interventions that may affect the aging process and reduce age-related diseases, thereby promoting healthy longevity.     

Thymic microenvironment and NZB mice: the abnormal thymic microenvironment of New Zealand mice correlates with immunopathology

There are distinct microenvironmental abnormalities of thymic architecture in several murine models of SLE defined using immunohistochemistry and a panel of mAb dissected at thymic epithelial markers. To address the issue of the relationship between the thymic microenvironment and autoimmunity, we studied backcross (NZB x NZW) F1 x NZW mice in which 50% of offspring develop nephritis associated with proteinuria and anti-DNA antibodies. We reasoned that if thymic abnormalities are associated with development of disease, the correlation of abnormalities with lupus-like disease in individual backcross mice will form the foundation for identification of the mechanisms involved. In parallel, we directed a genetic linkage analysis, using markers previously shown to be linked to nephritis and IgG autoantibody production, to determine if such loci were similarly associated with microenvironmental changes. Our data demonstrate that all (NZB x NZW) F1 x NZW backcross mice with disease have microenvironmental defects. Although the microenvironmental defects are not sufficient for development of autoimmune disease, the severity of thymic abnormalities correlates with titers of IgG autoantibodies to DNA and with proteinuria. Consistent with past studies of (NZB x NZW) F1 x NZW mice, genetic markers on proximal chromosome 17 (near MHC) and distal chromosome 4 showed trends for linkage with nephritis. Although the markers chosen only covered about 10-15% of the genome, the results demonstrated trends for linkage with thymic medullary abnormalities for loci on distal chromosome 4 and distal chromosome 1. We believe it will be important to define the biochemical nature of the molecules recognized by these mAbs to understand the relationships between thymic architecture and immunopathology.