Age-dependence of relative telomere length profiles during spermatogenesis in man

Abstract

Telomeres, the protective structures at the outmost ends of chromosomes, shorten in all somatic cells with each cell-division and by cumulative oxidative damage. To counteract that these shortened telomeres are passed on to offspring, the telomeres are elongated by the enzyme, telomerase, during human spermatogenesis. A few groups have tried to elucidate this process by measuring telomerase activity in the various cell-types during spermatogenesis, but until now, no one has ever measured telomere length (TL) during these different stages in humans. Some groups have measured TL in spermatozoa and surprisingly found that telomeres of older men are longer, than those from younger men. To elucidate this phenomenon we investigated if the distribution of TL over the various precursor germ cells in old males differed from young males, perhaps indicating a more ubiquitous telomere elongation in testes from older men. We therefore obtained testicular biopsies from 6 older and 6 younger men undergoing vasectomy. The cells were suspended as single cells and smeared onto slides, followed by characterization of cell stages by phase contrast microscopy. Mean TL in individual cells was subsequently measured by telomere QFISH. Our data revealed no difference in the TL profile during spermatogenesis between younger and older men. All men had a similar profile which strongly resembled the telomerase expression profile found by others. This indicates that the longer telomeres in older men are not caused by a wider window of telomere elongation, stretching over more cell-types of spermatogenesis.