The Background of Varicocele-Related Infertility

Purpose: The aim of this narrative review is to evaluate the molecular and cellular effects of varicocele on male infertility from a holistic perspective. The study examines the role of varicocele on spermatogenesis and testicular homeostasis, specifically within the axis of oxidative stress, apoptotic mechanisms, hormonal changes, epigenetic regulations, and the ubiquitin–proteasome system (UPS). Materials and methods: A comprehensive literature search was conducted in PubMed, Web of Science, Scopus, and Google Scholar databases for the period between 1973 and 2025 using the keywords "varicocele," "male infertility," "oxidative stress," "apoptosis," and "ubiquitin proteasome system." Case reports and irrelevant publications were excluded, and the molecular, histopathological, and hormonal effects of varicocele were systematically reviewed. Results: The findings indicate that varicocele leads to increased oxidative stress and mitochondrial dysfunction within the testicular microenvironment. This process is associated with sperm DNA damage, loss of motility, and morphological abnormalities. While increased apoptosis triggers germ cell loss and spermatogenesis impairment, a decrease in Leydig cell function results in reduced testosterone production. Furthermore, varicocele alters the epigenetic profile through DNA and RNA methylation and histone modifications; UPS dysfunction impairs protein homeostasis, adversely affecting sperm maturation and function. Histopathological examinations reveal degeneration in the seminiferous tubules, basement membrane thickening, and significant changes in Sertoli–Leydig cell structure. Conclusions: Varicocele is not merely a vascular disorder but a multidimensional cause of infertility arising from the interaction of oxidative stress, apoptotic activation, hormonal imbalance, epigenetic disruption, and UPS dysfunction. By synthesizing the molecular and histopathological mechanisms of