The human epididymis: its function in sperm maturation.

Abstract

Spermatozoa acquire their fertilizing ability and forward motility properties during epididymal transit. Our knowledge of gamete physiology is based on studies conducted in laboratory and domestic species; our knowledge of these processes in humans is limited. Medical indications for assisted reproductive technologies (ART) have progressed to include male infertility. Surgical procedures allow collection of spermatozoa from all along the human excurrent ducts, and the former have been used with some success in reproductive medicine. This has raised questions over the role of the epididymis in human sperm physiology. To reanalyze what we now know about epididymal physiology in humans and to assess the relevance of laboratory animal models for understanding human physiology and the pathophysiology of the epididymis. A systematic bibliographic search of PubMed for articles published in English before May 2015 was carried out using the search terms 'epididymis' and 'sperm maturation'. Literature on the consequences of vasectomy on the epididymis was also searched. Whereas the proximal epididymis is almost exclusively occupied by efferent ducts, the sperm reservoir capacity is poorly developed in humans. At the molecular level, the human transcriptome and proteome show some segment specificity; conflicting results persist with regard to secretome variation along the tubule. The number of genes regulated along the excurrent ducts in men is lower when compared to rodent species, but remains significant. It is challenging to reconcile biochemical and physiological studies with clinical data obtained from men undergoing reanastomosis of the vas deferens at different points along the excurrent duct. We propose that vasectomy/vasovasostomy is a model to understand the consequences of obstruction on epididymis function in humans. Despite the scarcity of biological material available, the interspecies variability of the male reproductive tract urges us to use modern molecular and cellular biology tools to better understand human epididymis physiology in order to apply ART in a more responsible manner.