Regulation and function of telomerase in T cells

端粒酶是一种核糖核蛋白酶，催化端粒合成和其他非端粒延长活性。端粒酶活性在T细胞发育、分化和激活过程中受到严格调控。随着年龄的增长，外周淋巴细胞端粒变短，但淋巴细胞端粒酶活性是否也随年龄增长而降低尚不清楚。我们先前对200名BLSA受试者的T和B细胞端粒酶活性的研究表明，静息和体外激活的T细胞的端粒酶活性随着年龄的增长而下降，而静息的B细胞的端粒酶活性却不随年龄的增长而降低。为了进一步了解这种与年龄相关的淋巴细胞端粒酶活性降低的基础，我们分析了T细胞亚群中关键的端粒酶成分端粒酶逆转录酶(TERT)的mRNA水平。TERT是一种限速因子，在静息T细胞中可检测到TERT mRNA，并在T细胞激活时迅速上调。由于已经检测到多个TERT mRNA选择性剪接产物(Asp)，目前尚不清楚这些mRNAs是否为T细胞中的全长(FL)和/或功能丧失的Asp。我们分析了年轻人(36岁)和老年人(69岁)的幼稚和记忆中的CD4和CD8 T细胞的全长(FL)和三种类型的逆转录酶零的ASP(α、β和αβ)。结果表明，静息状态下，CD4N细胞hTERT全长表达水平最高，其次为CD_4中枢(CM)、CD_8中枢(CM)、CD_8中枢(CM)、CD_4效应记忆(EM)。CD8效应记忆细胞中未检测到hTERT基因。用抗CD3、抗CD28抗体激活TCR后，CD4亚群的hTERT表达高于CD8亚群。此外，NAVE细胞比记忆细胞表达更多的hTERT mRNA，CM细胞比EM细胞表达更多的hTERT基因。与年轻受试者相比，老年受试者幼稚的CD4T细胞的FL hTERT基因表达显著减少。这一发现表明，全长hTERT mRNA的减少是随着年龄的增长T细胞端粒酶活性降低的原因。目前的研究正试图了解这种与年龄相关的hTERT mRNA减少的机制，并识别可能延长hTERT mRNA的小分子。

Telomerase is a ribonucleoprotein enzyme that catalyzes telomere synthesis and other non-telomere lengthening activity. Telomerase activity is tightly regulated during T cell development, differentiation, and activation. With age, telomere shortens in peripheral lymphocytes but it is unknown whether reduction of telomerase activity in lymphocytes also occurs with age. Our previous study of telomerase activity in T and B cells over 200 BLSA participants showed that telomerase activity declined with age in resting and in vitro activated T cells, and in the resting B cells but not in vitro activated B cells. To further understand the basis of this age-related reduction of telomerase activity in lymphocytes, we analyzed mRNA level of the key telomerase component, telomerase reverse transcriptase (TERT) in T cell subsets. TERT serves as a rate-limiting factor and TERT mRNA is detectable in resting T cells and rapidly upregulated upon T cell activation. Because multiple TERT mRNA alternatively spliced products (ASPs) have been detected, it is unclear whether the mRNAs are full-length (FL) and/or loss-of-function ASPs in T cells. We analyzed the full-length (FL) and 3 types of reverse transcriptase-null ASPs (alpha, beta, and alpha+beta) in nave and memory CD4 and CD8 T cells from young (<36 year old) and old (>69 year old) humans. We found that resting nave CD4 T cells (CD4N) expressed highest level of full length hTERT mRNA, followed by CD4 central (CM), nave CD8 T cells, CD8 central (CM), CD4 effector memory (EM) cells. hTERT mRNA was undetectable in CD8 effector memory cells. Upon TCR activation with anti-CD3 + anti-CD28 antibodies, CD4 subsets showed greater hTERT expression than CD8 subsets. Furthermore, nave cells showed greater amounts of hTERT mRNA than memory cells, and CM was greater than EM. Compared to the young subjects, naive CD4 T cells from aged subjects had significantly less FL hTERT mRNA. This finding suggests that reduced full length hTERT mRNA is responsible for reduced telomerase activity in T cells with age. Current studies are trying to understand the mechanism underlying this age-related reduction of hTERT mRNA and to identify small molecules that could extend hTERT mRNA.