Varicocoele-associated male infertility: Cellular and molecular perspectives of pathophysiology.

Abstract

Varicocoele is a common risk factor associated with reduced male fertility potential. The current understanding of varicocoele pathophysiology does not completely explain the clinical manifestation of infertility. The present treatment options such as antioxidant supplementation and varicocoelectomy only help ≈35% of men to achieve spontaneous pregnancy. This review aims to summarize the available knowledge on cellular and molecular alterations implicated to varicocoele-associated male infertility and also highlights the new knowledge generated by "omics" technologies. PubMed, MEDLINE, Cochrane and Google Scholar databases are searched using different combinations of keywords (varicocoele, infertile/fertile men with varicocoele, cellular changes, molecular mechanisms, proteome, epigenome, transcriptome and metabolome). A total of 229 relevant human and animal studies published till 2021 were included in this review. Current understanding advocates oxidative stress (OS) as a major contributory factor to varicocoele-associated male infertility. Excessive OS causes alteration in testicular microenvironment and sperm DNA fragmentation, which further contributes to infertility. Molecular and omics studies have identified several promising biomarkers such as AAMP, SPINT1, MKI67 (genetic markers), sperm quality and function related protein markers, global sperm DNA methylation level (epigenetic marker), Hspa2, Protamine, Gadd7, Dynlt1 and Beclin1 (mRNA markers), PRDX2, HSPA, APOA2, YKL40 (seminal protein markers), total choline and PHGDH (metabolic markers). Mature spermatozoa harbours a plethora of molecular information in form of proteome, epigenome and transcriptome, which could provide very important clues regarding pathophysiology of varicocoele-associated infertility. Recent molecular and omics studies in infertile men with varicocoele have identified several promising biomarkers. Upon further validation with larger and well-defined studies, some of these biomarkers could aid in varicocoele management. The present evidences suggest that inclusion of OS and sperm DNA fragmentation tests could be useful to the diagnostic workup for men with varicocoele. Furthermore, including precise molecular markers may assist in diagnostics and prognostics of varicocoele-associated male infertility.