von Zglinicki T, Pilger R, Sitte N
Institute of Pathology, Charité, Humboldt-University Berlin, Germany.
Free Radic Biol Med. 2000 Jan 1;28(1):64-74. doi: 10.1016/s0891-5849(99)00207-5.
Telomere shortening triggers replicative senescence in human fibroblasts. The inability of DNA polymerases to replicate a linear DNA molecule completely (the end replication problem) is one cause of telomere shortening. Other possible causes are the formation of single-stranded overhangs at the end of telomeres and the preferential vulnerability of telomeres to oxidative stress. To elucidate the relative importance of these possibilities, amount and distribution of telomeric single-strand breaks, length of the G-rich overhang, and telomere shortening rate in human MRC-5 fibroblasts were measured. Treatment of nonproliferating cells with hydrogen peroxide increases the sensitivity to S1 nuclease in telomeres preferentially and accelerates their shortening by a corresponding amount as soon as the cells proliferate. A reduction of the activity of intracellular peroxides using the spin trap alpha-phenyl-t-butyl-nitrone reduces the telomere shortening rate and increases the replicative life span. The length of the telomeric single-stranded overhang is independent of DNA damaging stresses, but single-strand breaks accumulate randomly all along the telomere after alkylation. The telomere shortening rate and the rate of replicative aging can be either accelerated or decelerated by a modification of the amount of oxidative stress. Quantitatively, stress-mediated telomere damage contributes most to telomere shortening under standard conditions.
端粒缩短会引发人类成纤维细胞的复制性衰老。DNA聚合酶无法完全复制线性DNA分子（末端复制问题）是端粒缩短的一个原因。其他可能的原因包括端粒末端形成单链悬突以及端粒对氧化应激的优先易损性。为了阐明这些可能性的相对重要性，对人类MRC - 5成纤维细胞中端粒单链断裂的数量和分布、富含鸟嘌呤的悬突长度以及端粒缩短率进行了测量。用过氧化氢处理非增殖细胞会优先增加端粒对S1核酸酶的敏感性，并且一旦细胞增殖，端粒会相应加速缩短。使用自旋捕捉剂α - 苯基 - t - 丁基硝基酮降低细胞内过氧化物的活性可降低端粒缩短率并延长复制寿命。端粒单链悬突的长度与DNA损伤应激无关，但烷基化后单链断裂会沿着端粒随机积累。通过改变氧化应激的量，端粒缩短率和复制性衰老速率可以加速或减速。从数量上看，在标准条件下，应激介导的端粒损伤对端粒缩短的贡献最大。
