Aquaporins and male (in)fertility: Expression and role throughout the male reproductive tract.

Aquaporins (AQPs) are a family of transmembrane channel proteins responsible for the transport of water and small uncharged molecules. Thirteen distinct isoforms of AQPs have been identified in mammals (AQP0-12). Throughout the male reproductive tract, AQPs greatly enhance water transport across all biological barriers, providing a constant and expeditious movement of water and playing an active role in the regulation of water and ion homeostasis. This regulation of fluids is particularly important in the male reproductive tract, where proper fluid composition is directly linked with a healthy and competent spermatozoa production. For instance, in the testis, fluid regulation is essential for spermatogenesis and posterior spermatozoa transport into the epididymal ducts, while maintaining proper ionic conditions for their maturation and storage. Alterations in the expression pattern of AQPs or their dysfunction is linked with male subfertility/infertility. Thus, AQPs are important for male reproductive health. In this review, we will discuss the most recent data on the expression and function of the AQPs isoforms in the human, mouse and rat male reproductive tract. In addition, the regulation of AQPs expression and dysfunction linked with male infertility will be discussed.