Ageing in men with normal spermatogenesis alters spermatogonial dynamics and nuclear morphology in Sertoli cells

Abstract

Background: Ageing in men is believed to be associated with fertility decline and elevated risk of congenital disorders for the offspring. The previous studies also reported reduced germ and Sertoli cell numbers in older men. However, it is not clear whether ageing in men with normal spermatogenesis affects the testis and germ cell population dynamics in a way sufficient for transmitting adverse age effects to the offspring. Objectives: We examined men with normal spermatogenesis at different ages concerning effects on persisting testicular cell types, that is the germ line and Sertoli cells, as these cell populations are prone to be exposed to age effects. Material and methods: Ageing was assessed in testicular biopsies of 32 patients assigned to three age groups: (i) 28.8 AE 2.7 years; (ii) 48.1 AE 1 years; and (iii) 70.9 AE 6.2 years, n = 8 each, with normal spermatogenesis according to the Bergmann-Kliesch score, and in a group of meiotic arrest patients (29.9 AE 3.8 years, n = 8) to decipher potential links between different germ cell types. Besides morphometry of seminiferous tubules and Sertoli cell nuclei, we investigated spermatogenic output/efficiency, and dynamics of spermatogonial populations via immunohistochemistry for MAGE A4, PCNA, CREM and quantified A-pale/A-dark spermatogonia. Results: We found a constant spermatogenic output (CREM-positive round spermatids) in all age groups studied. In men beyond their mid-40s (group 2), we detected increased nuclear and nucleolar size in Sertoli cells, indirectly indicating an elevated protein turnover. From the 7th decade (group 3) of life onwards, testes showed increased proliferation of undifferentiated spermatogonia, decreased spermatogenic efficiency and elevated numbers of proliferating A-dark spermatogonia. Discussion and conclusion: Maintaining normal sperm output seems to be an intrinsic determinant of spermatogenesis. Ageing appears to affect this output and might provoke compensatory proliferation increase in A spermatogonia which, in turn, might hamper germ cell integrity.

Development and Disease-Dependent Dynamics of Spermatogonial Subpopulations in Human Testicular Tissues

“…Note that the five adult testicular tissues included in this study may not be representative for adult samples in general due to the limited number of samples and the advanced age of the men. This assumption is corroborated by the recent report that increased levels of spermatogonial proliferation throughout adult age can be observed, which might be a compensatory mechanism to maintain spermatogenesis [30].…”

“…Adult testicular tissue was obtained from patients who underwent orchiectomy as part of prostate cancer treatment [30,42]. All adult controls (n = 7; 62-79 years) had normal spermatogenesis and exhibited a Bergmann-Kliesch score between 8 and 9, meaning that 75-94% of tubules contained elongated spermatids [43].…”

“…Subpopulations of adult spermatogonia have been distinguished based on protein marker expression profiles [22,23] and, more recently, by single-cell RNA-sequencing approaches [24][25][26][27]. Consistently, most spermatogonia express germline-specific markers such as melanoma-associated antigen 4 (MAGEA4) [23,[28][29][30]. Accumulating evidence reveals that the most primitive spermatogonial state exhibits a transcriptomic profile similar to infant spermatogonia [24,27], with an expression of stem cell-specific transcripts such as the undifferentiated embryonic cell transcription factor 1 (UTF1) and a relatively low proliferative activity [22,24,25,27,31,32].…”

A germ cell‐specific ageing pattern in otherwise healthy men

“…It is likely that these early germ cells are also prone to increased DNA methylation maintenance errors, similar to other somatic tissues during ageing, leading to a germ cell-specific pattern of epigenetic drift. Moreover, our group has recently described that, in order to maintain sperm production levels, testes of older men require activation and recruitment of additional, normally quiescent, spermatogonia (Pohl et al, 2019). These changes in counselling should be provided for couples undergoing assisted reproduction when the male partner is above 49 years of age (Jennings et al, 2017;Toriello et al, 2008).…”

Healthy ageing men have normal reproductive function but display germline-specific molecular changes

“…It is therefore likely that male germ cells are also prone to increased DNA methylation maintenance errors as they age. Moreover, to maintain sperm production levels, testes of older men require require activation and recruitment of additional, otherwise quiescent, spermatogonia (36). This changed spermatogonial activity pattern could cause the observed methylation, and even DNA instability, changes.…”