Peripheral lymphocyte telomere dysfunction: a valid surrogate marker for female fertility?

Abstract

Telomeres are multiple short tandem DNA repeat sequences (5′-TTAGGG-3′), that cap the ends of linear chromosomes and bind a specialized telomere protein complex called shelterin to form telomere loops. The telomeres function to protect the genome from degradation, unwanted deletion, or recombination (chromosome end fusions and genomic instability) to maintain its genetic integrity. Without telomere protection, DNA damage response pathways result in cell cycle arrest, genomic instability, apoptosis, or senescence. Cellular aging is associated with decreasing telomere length (TL), decreased telomerase, and increased oxidative stress. Telomere shortening may result from normal cell division senescence and secondary insults derived from reactive oxygen species, toxins, inflammatory and immune responses, environmental exposures, and significant perceived psychologic stress. Decreasing TL has been associated with increased susceptibility to diseases such as cancer, cardiovascular disease, and depression. In female reproduction, decreasing TL and decreased telomerase activity in the ovary have been associated with reproductive aging. Short TL contributes to meiotic dysfunction and abnormal spindle of the oocyte, which subsequently accelerates oocyte apoptosis. Because the ovarian tissue is not readily accessible, there is an increased interest in defining the value of surrogates such as peripheral lymphocyte TL in ascertaining the ovarian age. Although associations have been made between peripheral lymphocyte TL and the pathologies of infertility, peripheral lymphocyte TL calculations are nonspecific and results are mixed concerning fertility. A recent systematic review reported 21 positively associated studies where individual tissue (granulosa cells/endometrium) ± peripheral lymphocyte TL were investigated: 11 studies demonstrated a shorter TL, whereas 10 demonstrated a longer TL. Reports are also mixed concerning polycystic ovary syndrome, with some having longer peripheral lymphocyte TLs and others shorter; similar discrepancies were noted with endometriosis (1Vasilopoulos E. Fragkiadaki P. Kalliora C. Fragou D. Docea A.O. Vakonaki E. et al.The association of female and male infertility with telomere length.Int J Mol Med. 2019; 44: 375-389PubMed Google Scholar). Also, reduced peripheral lymphocyte TL has been linked to various confounding factors known to reduce TL, such as physical inactivity, diet, stress, body mass index, smoking, chronic inflammation, oxidative stress, socioenvironmental characteristics, and, surprisingly, with greater parity, hormone replacement therapy and dietary antioxidants/vitamins. Many of these studies are difficult to compare and limit our conclusions owing to low numbers of subjects, different testing modalities for TL, different tissues being sampled, and various disease states associated with infertility. Nevertheless, the above review, along with a prior publication this year in Fertility and Sterility (2Lara Molina E.E. Franasiak J.M. Marin D. Tao X. Díaz-Gimeno P. Florensa M. et al.Cumulous cells have longer telomeres than leukocytes in reproductive age women.Fertil Steril. 2020; 113: 217-223Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar), discourages oversimplifying the reproductive implications of TL screening from peripheral blood leukocytes. In contrast to peripheral lymphocytes, the TL in the oocytes and their ovarian follicular cells appear to be governed by different mechanisms than the regulation of TL in somatic cells. Dissimilarly from somatic cells, telomerase activity has been observed to decrease as the ovarian follicular telomeres lengthen through the follicular development process. Therefore, the telomere lengthening through folliculogenesis is likely governed by a mechanism different from the elements controlling TL in peripheral lymphocytes (2Lara Molina E.E. Franasiak J.M. Marin D. Tao X. Díaz-Gimeno P. Florensa M. et al.Cumulous cells have longer telomeres than leukocytes in reproductive age women.Fertil Steril. 2020; 113: 217-223Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar, 3Fattet A. Toupance S. Thornton S.N. Monnin N. Guéant J. Benetos A. Koscinski I. Telomere length in granulosa cells and leukocytes: a potential marker of female fertility? A systematic review of the literature.J Ovarian Res. 2020; 13: 96Crossref PubMed Scopus (9) Google Scholar). Infertility effects are known to be different in men and women. Women are more affected by age-related aneuploidy and the resultant decreased fertility, which is not observed in men. Telomeric differences exist, too. TLs in sperm increase with age, which may be attributed to the difference in telomerase activity, an enzyme that prevents attrition of telomeres and is expressed in spermatogonia. Reig-Viader et al. assessed the relationship between telomerase, TERRA (long noncoding RNA transcribed by telomeres), telomeres, and meiotic recombination in testicular biopsy specimens in fertile and infertile men and found that telomere structures were compromised in germ cells of infertile men (4Reig-Viader R. Capilla L. Vila-Cejudo M. Garcia F. Anguita B. Garcia-Caldes M. et al.Telomere homeostasis is compromised in spermatocytes from patients with idiopathic infertility.Fertil Steril. 2014; 102: 728-738Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar). Although sperm TL can potentially be used as a new biomarker, more research is needed to determine its utility in assisted reproduction. In addition, germ cells may have very different telomere biology than somatic cells, with the current hypothesis being that embryos need to reset the TLs during early emrbyogenesis. Thus, it may not be surprising to see these differences within male gametes or female gametes and their follicular development. In this issue, M’kacher et al. report increased peripheral lymphocyte telomere aberrations in infertility in addition to TLs, and their data add more facets to our knowledge concerning telomeres in female infertility (5M’kacher R. Colicchio B. Marquet V. Borie C. Najar W. Hempel W.M. et al.Telomere aberrations, including telomere loss, doublets, and extreme shortening, are increased in infertility patients.Fertil Steril. 2021; 115: 164-173Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar). This retrospective study tested 50 infertility patients (25 with known constitutional chromosomal abnormalities and 25 with normal chromosomes) and 150 healthy donors as control subjects. They used two methods to quantitate telomeres in peripheral lymphocytes. One used interphase cells to test for TL and the proportion of cells with severe telomere shortening with the use of an automated approach to assess 10,000 nuclei. The second captured metaphase cells where mean TLs and, more importantly, individual chromosome TLs were measured automatically in 100 metaphases. In addition, intracellular variations could also be monitored. These cytogenetic slides allowed for identification of telomere aberrations (telomere loss, deletions, and doublets) within each chromosome with automatic scoring—validated by an individual operator to remove false aberrations. Telomere aberrations have not been studied in depth previously in this infertile population. The data demonstrated significantly shorter TLs and more telomere aberrations (particularly extreme telomere loss and doublets) in patients with infertility compared with healthy donors; these findings were more profound with infertile patients with structural chromosomal abnormalities. Telomere aberrations may result in genetic instability, DNA breaks, and micronuclei. Although these data result from a retrospective study, the authors have developed rapid, automated approaches to assess these telomere aberrations that can provide results within a clinically relevant time period. Further studies are needed for validation, and prospective studies are needed to confirm these findings. The true value of this report is in shedding light on telomere biology beyond TLs to their resultant telomere aberrations in female infertility. Yet, caution remains, as the summary of the published literature highlights a lack of true understanding of the TL and telomere function complexities in reproduction. Although measuring peripheral lymphocyte TL and dysfunction is an enticing concept to use as a surrogate marker for ovarian aging or infertility, the published data are very limited and not ready for prime time. Given the inherent differences in telomere biology between germ cells and somatic cells and specifically in the ovarian follicular microenvironment and peripheral blood cells, more studies are needed to understand these biological mechanisms and hopefully develop more bench-to-bedside assessments of ovarian aging, infertility, and possibly embryo development for better selection and improved outcomes in assisted reproductive technologies. Telomere aberrations, including telomere loss, doublets, and extreme shortening, are increased in patients with infertilityFertility and SterilityVol. 115Issue 1PreviewTo test the hypothesis that telomere shortening and/or loss are risk factors for infertility. Full-Text PDF