Balance of Apoptosis and Proliferation of Germ Cells Related to Spermatogenesis in Aged Men

Abstract

To clarify whether germ cell apoptosis is related to a decrease of germ cells in the aged testis with impaired spermatogenesis, we investigated the apoptotic rate of each germ cell type. Testicular specimens were obtained by orchiectomy from 36 men with advanced prostate cancer and by testicular biopsy from 21 men with obstructive azoospermia, which served as controls. The terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) technique was used to identify apoptosis. As a marker of cell proliferation activity, the expression of Ki-67 was immunohistochemically evaluated. Expression of Bcl-xl, which regulates apoptosis of germ cells, was also immunohistochemically examined. Histologically, except for spermatogonia, the ratios of primary spermatocytes, round spermatids, and elongated spermatids to Sertoli cells were significantly decreased in aged testes. The apoptotic rate in spermatogonia was significantly lower in aged men than it was in controls (0.11% +/- 0.06% vs 0.34% +/- 0.21%). Expression of Ki-67 in spermatogonia was decreased in aged men (18.6% +/- 6.0%) compared with that of controls (24.9% +/- 3.3%), suggesting that germ cell proliferation diminished with aging. Consequently, the balance of spermatogonial proliferation and apoptosis showed no difference between the two groups. This was believed to be one of reasons why spermatogonial numbers in aged testes was similar to those of controls. The apoptotic rate of primary spermatocytes in aged men was significantly elevated compared with that of controls (0.60% +/- 0.54% vs 0.22% +/-0.12%), resulting in a decrease of the number of primary spermatocytes per Sertoli cell. The expression of Bcl-xl was inversely correlated with the apoptotic rate in primary spermatocytes, suggesting that Bcl-xl may be related to the regulation of primary spermatocyte apoptosis. Based on these findings, we conclude that accelerated apoptosis of primary spermatocytes might account for a part of the mechanism of germ cell loss in aging men.

Apoptotic sperm biomarkers and the correlation between conventional sperm parameters and clinical characteristics

“…Previous reports demonstrated the association between advancing age and the expression of early apoptotic markers as evidenced by the significant increase in plasma membrane translocation of PS, as well as with a more subtle proportion of spermatozoa carrying DNA fragmentation (Moskovtsev et al, 2010;Wyrobek et al, 2006). Moreover, it has been shown that apoptosis increases with age, producing an accelerated germ cell loss (Kimura et al, 2003), related to the falling androgen levels and/or an increase in oxidative stress in the tissue (Samanta, Sahoo, & Chainy, 1999). …”

Effects of aging on the male reproductive system

“…In spermatogonia of aged men, both expression of Ki-67, a marker of cell proliferation activity, and apoptotic rate were found to be decreased compared to young controls [92]. In contrast to spermatogonia, apoptotic rate of primary spermatocytes, as shown by TUNEL positivity, was significantly elevated compared to controls, which might, in part, explain the mechanism of germ cell loss in aged men [92]. The discrepancy might be due to an age-related deterioration of spermatogonial stem cell niche accompanied by a compensatory decrease in apoptotic spermatogonia [91].…”

“…Although apoptosis is essential for spermatogenesis under normal conditions, the balance between proliferation of spermatogonia and apoptosis of different germ cell types appears to be disturbed with aging [91]. In spermatogonia of aged men, both expression of Ki-67, a marker of cell proliferation activity, and apoptotic rate were found to be decreased compared to young controls [92]. In contrast to spermatogonia, apoptotic rate of primary spermatocytes, as shown by TUNEL positivity, was significantly elevated compared to controls, which might, in part, explain the mechanism of germ cell loss in aged men [92].…”

Testicular apoptosis after dietary zinc deficiency: Ultrastructural and TUNEL studies

“…Nodera et al [2001] also reported the appearance of TUNEL positive cells after 3 w of zinc deficiency in testes and thymus of 7 w old Sprague Dawley rats. Abnormally accelerated apoptosis of germ cells may lead to an imbalance of cell proliferation and death resulting in spermatogenic impairment [Takagi et al 2001;Kimura et al 2003]. The correct balance between the apoptotic pathways is important for the maintenance of genomic integrity while preventing unnecessary cell death [Clarke and Allan 2009].…”