Larbi Anis, Douziech Nadine, Khalil Abdelouahed, Dupuis Gilles, Gheraïri Saber, Guérard Karl-Philippe, Fülöp Tamàs
Research Center on Aging, Sherbrooke Geriatric University Institute, University of Sherbrooke, Sherbrooke, Que., Canada J1H 5N4.
Exp Gerontol. 2004 Apr;39(4):551-8. doi: 10.1016/j.exger.2003.10.031.
Aging is associated with a decline in immune functions. Among them, T-cell activation is altered at several points of the signaling cascade following TCR engagement. Recent findings suggest that lipid rafts act as a platform in the initiation of T-cell activation. We have previously demonstrated that cholesterol content in T-cells increased with aging, especially in lipid rafts. Cholesterol, which is a major component of lipid rafts, serves to stabilize their structure. We hypothesized that restoring T-cell cholesterol content and membrane fluidity would restore, at least in part, T-cell function via lipid rafts. We measured the lipid rafts coalescence, the p56(Lck) and linker of activated T-cell (LAT) signaling molecules recruitment and activation, the cholesterol content and fluidity in T-cell membrane after different methyl-beta-cyclodextrin (MBCD) treatments. Our results show that high concentration of MBCD (10 mM) completely disorganized the lipid rafts in T-cell membranes of young and elderly donors, however, T-cells from elderly donors were less sensitive than T-cells of young donors to low concentration of MBCD (0.5 mM). p56(Lck) and LAT recruitment and activation were affected in T-cells of both aged groups. MBCD treatment did not affect the cholesterol content and fluidity of T-cell membranes of young donors, while the cholesterol content was decreased and fluidity increased in lipid rafts of elderly donors. These results suggested that cholesterol extraction by MBCD increased the fluidity and disrupted lipid rafts organization. The increase in cholesterol content in lipid rafts with aging and its decrease by biochemical extraction were able to affect early signaling molecules activation. Restoring cholesterol content and fluidity may have beneficial effects, however, MBCD disorganized the membrane and this might not completely restore the T-cell activation via lipid rafts with aging. Altogether these results suggest that defects in cholesterol cellular homeostasis may be part of T-cell immunosenescence via lipid rafts dysfunction.
衰老与免疫功能下降有关。其中，T细胞活化在TCR参与后的信号级联反应的多个环节发生改变。最近的研究结果表明，脂筏在T细胞活化的起始过程中充当一个平台。我们之前已经证明，T细胞中的胆固醇含量会随着衰老而增加，尤其是在脂筏中。胆固醇是脂筏的主要成分，有助于稳定其结构。我们推测，恢复T细胞胆固醇含量和膜流动性至少可以部分地通过脂筏恢复T细胞功能。我们测量了不同甲基-β-环糊精（MBCD）处理后T细胞膜中脂筏的聚结、p56(Lck)和活化T细胞连接蛋白（LAT）信号分子的募集和活化、胆固醇含量和流动性。我们的结果表明，高浓度的MBCD（10 mM）完全破坏了年轻和老年供体T细胞膜中的脂筏，然而，老年供体的T细胞对低浓度的MBCD（0.5 mM）的敏感性低于年轻供体的T细胞。两个年龄组的T细胞中p56(Lck)和LAT的募集和活化均受到影响。MBCD处理对年轻供体T细胞膜的胆固醇含量和流动性没有影响，而老年供体脂筏中的胆固醇含量降低且流动性增加。这些结果表明，MBCD提取胆固醇增加了流动性并破坏了脂筏的组织。随着衰老脂筏中胆固醇含量的增加及其通过生化提取的减少能够影响早期信号分子的活化。恢复胆固醇含量和流动性可能具有有益作用，然而，MBCD破坏了膜结构，这可能无法完全通过脂筏恢复衰老T细胞的活化。总之，这些结果表明胆固醇细胞内稳态的缺陷可能是通过脂筏功能障碍导致T细胞免疫衰老的一部分。
