Age‐related epigenetic modifications contribute to dysfunction of male germline progenitor cells

Abstract

Ageing is a complex time‐dependent biological process that takes place in every cell and organ, eventually leading to degenerative changes that affect normal biological functions. In the past decades, the number of couples to conceive children at advanced ages has increased significantly. It is widely recognized that advanced maternal age poses higher birth defect risk due to oocyte ageing. However, the effect of advanced paternal age on male germ cell quality is largely overlooked, and the impact has been implicated in a variety of disease conditions affecting the offspring. Mammalian spermatogenesis is a tissue‐specific, stem cell‐dependent process that relies on self‐renewal and differentiation of male germline stem cells to support continual production of spermatozoa. Currently, the mechanisms regulating these processes remain largely unknown, and emerging evidence has suggested that epigenetic profiles shift dramatically during aging. Epigenetic modifications on DNA methylation and demethylation pathways through formation of 5‐methylcytosine (5mC) and 5‐Hydroxymethylcytosine (5hmC) have profound influences on developmental programs, but its role remains elusive in male germ cell development. In this study, we examined the dynamics of DNA methylation and gene expression in undifferentiated and differentiating cell populations in early male germ cell development by performing RNA‐seq and whole genome 5mC/5hmC profiling at single‐‐base resolution. We defined signaling and transcriptional difference involving key self‐‐renewal pathways in undifferentiated and differentiated cell populations and found that differentially methylated genes were enriched in various age‐related cellular developmental processes. We also observed methylation changes associated with OCT4 and GDNF, which are both important for undifferentiated spermatogonia maintenance. Finally, 5hmC was enriched specifically in proximal upstream and downstream regions relative to TSS and its presence correlates positively with gene expression, we found genes enriched in undifferentiated populations display higher promoter 5hmC levels, indicating 5hmC is associated with stemness‐‐related genes and stem cell capacity.Support or Funding InformationHong Kong Research Grant Council (RGC) ‐General Research Fund project no. 469713, 468312