Homocysteine Stimulates T Cell Activation, Apoptosis and Thymic Involution

我们在这一领域的研究主要集中在两个具体的影响同型半胱氨酸对免疫细胞及其功能，即细胞凋亡和细胞因子的表达。已显示Hcy在许多细胞系和细胞类型（包括免疫细胞）中诱导凋亡。我们已经发现用L-Hcy处理静息和活化的人和鼠T细胞导致凋亡性细胞死亡的剂量依赖性增加。 在这方面，L或D，L形式的Hcy比Hcy硫内酯更有效，而S-腺苷Hcy（SAH）被发现活性显著降低。 我们还发现，同型半胱氨酸的促凋亡作用被废除，除了血清，泛和特异性半胱天冬酶抑制剂和PARP抑制剂的文化。这些结果表明，L-Hcy，像其他凋亡应激因子，导致激活的caspase级联反应，并最终裂解的关键细胞蛋白，促进线粒体细胞色素c的释放，DNA片段化，并最终导致典型的形态学变化观察到的细胞凋亡。此外，体内输注L-Hcy而非SAH诱导胸腺细胞数量（特别是CD 4 + CD 8 + T细胞）、胸腺重量和胸腺形态的显著变化显著减少。虽然这些发现是挑衅性的，一个具体的作用，同型半胱氨酸在年龄或疾病相关的胸腺萎缩仍有待确定。 我们目前正在撰写这部作品以供出版。此外，我们已经发现，在L-Hcy或硫内酯而不是SAH的存在下，纯化的人或鼠T细胞的活化导致几种Th 1和Th 17而不是Th 2细胞因子的表达显著增加。这些效果也观察到后，在体内输注同型半胱氨酸到正常和TCR转基因小鼠。此外，我们已经发现，免疫细胞实际上在活化时产生各种形式的Hcy，并且这些各种Hcy似乎在T细胞活化和功能中发挥内源性调节作用。最近的研究已经证明，活化后，老化的T细胞比年轻的T细胞产生更多的SAH，并且这些相同的培养物产生SAH水解酶，其切割腺苷基团，导致A2 aR的活化和细胞因子表达的抑制以及IL-10产生的增加。 这些数据表明，T细胞代谢随年龄的变化可能会影响同型半胱氨酸水平，这可能会调节细胞因子的表达和T细胞表型。 另外的工作已经开始使用质谱法来鉴定和定量培养上清液和血清/血浆中的各种形式的Hcy。 我们相信，发展我们的能力，筛选这些同型半胱氨酸介质可能阐明与心血管和炎症性疾病状态相关的免疫激活的潜在机制。 我们目前也正在完成几份可能出版的手稿。 总的来说，同型半胱氨酸似乎对免疫细胞产生了许多不同的影响，这可能会改变循环和组织微环境中的免疫功能，随着年龄的增长和炎症和/或自身免疫性疾病的病理。更好地了解同型半胱氨酸及其代谢产物对免疫功能的潜在调节作用，可能会导致潜在的治疗策略的发展，以控制和优化免疫反应与年龄，艾滋病和各种年龄相关的疾病状态。

Our studies in this area have focused on two specific effects of Hcy on immune cells and their function, namely cellular apoptosis and cytokine expression. Hcy has been shown to induce apoptosis in a number of cell lines and cell type including immune cells. We have found that treatment of resting and activated human and murine T cells with L-Hcy results in a dose-dependent increase in apoptotic cell death. The L or D,L forms of Hcy was more potent than Hcy thiolactone in this respect, while S-adenosyl Hcy (SAH) was found to be significantly less active. We also found that the pro-apoptotic effects of Hcy were abrogated with the addition of serum, pan- and specific-caspase inhibitors and PARP inhibitors to the cultures. These results suggest that L-Hcy, like other apoptotic stressors, leads to the activation of the caspase cascade and eventually to the cleavage of the key cellular proteins facilitating the release of mitochondrial cytochrome c, DNA fragmentation, and eventually leading to the typical morphological changes observed in cells undergoing apoptosis. In addition, in vivo infusion of L-Hcy but not SAH induced a dramatic reduction in thymocyte numbers (in particular CD4+CD8+ T cells), thymic weights and a dramatic change in thymic morphology. While these findings are provocative, a specific role for Hcy in age- or disease-associated thymic atrophy remains to be defined. We are currently writing up this work for publication. In addition, we have found that activation of purified human or murine T cells in the presence of L-Hcy or thiolactone but not SAH results in a significant increase in the expression of several Th1 and Th17 but not Th2 cytokines. These effects were also observed upon in vivo infusion of Hcy into normal and TCR transgenic mice. In addition, we have found that immune cells actually produce the various forms of Hcy upon activation and that these various Hcy appear to play an endogenous regulatory role in T cell activation and function. More recent studies have demonstrated that aged T cells produce more SAH than younger T cells post activation and that these same cultures produce SAH hydrolyase that cleaves of an adenosine group resulting in the activation of the A2aR and a suppression of cytokine expression and an increase in IL-10 production. These data suggest that alterations in T cell metabolism with age may influence homocysteine levels which may modulate cytokine expression and T cell phenotypes. Additional work has been initiated using mass spectroscopy to identify and quantitate various forms of Hcy in culture supernatants and serum/plasma. We believe that developing our ability to screen these Hcy mediators may elucidate potential mechanisms of immune activation associated with cardiovascular and inflammatory disease states. We are also currently completing several manuscripts for possible publication. Overall, Hcy appears to exert a number of differential effects on immune cells, which may alter immune function in the circulation and tissue microenvironment with age and inflammatory and/or autoimmune disease pathology. A greater understanding of the potential modulatory effects of Hcy and its metabolites on immune function may result in the development of potential therapeutic strategies to control and optimize immune responses with age, AIDS and in various age-associated disease states.