The Semen pH Affects Sperm Motility and Capacitation

Factors and pathways involved in capacitation: how are they regulated?

In mammals, fertilization occurs via a comprehensive progression of events. Freshly ejaculated sperm have yet to acquire progressive motility or fertilization ability. They must first undergo a series of biochemical and physiological changes, collectively known as capacitation. Capacitation is a significant prerequisite to fertilization. During the process of capacitation, changes in membrane properties, intracellular ion concentration and the activities of enzymes, together with other protein modifications, induce multiple signaling events and pathways in defined media in vitro or in the female reproductive tract in vivo. These, in turn, stimulate the acrosome reaction and prepare spermatozoa for penetration of the egg zona pellucida prior to fertilization. In the present review, we conclude all mainstream factors and pathways regulate capacitation and highlight their crosstalk. We also summarize the relationship between capacitation and assisted reproductive technology or human disease. In the end, we sum up the open questions and future avenues in this field.

The impact of ejaculatory abstinence on semen analysis parameters: a systematic review

OBJECTIVE

The aim of this study was to evaluate recent publications and determine the impact of ejaculatory abstinence on semen analysis parameters as well as fertility outcomes.

METHODS

This was a systematic review of 28 recent publications. The focus of this study was the impact of abstinence on semen parameters and fertility outcomes in papers published since the year 2000. The specific parameters evaluated were volume, sperm count, motility, morphology, pH, DNA fragmentation rate, viability, and pregnancy or fertilization rates following assisted reproduction.

RESULTS

Twenty-eight recent publications met inclusion criteria. Analysis of publications showed that longer abstinence is associated with increases in semen volume and sperm count. Studies evaluating the effect of abstinence on motility, morphology, and DNA fragmentation rates are contradictory and inconclusive, although a trend appears to exist toward improvements in semen parameters with shorter abstinence. Semen pH was unaffected by abstinence. The majority of publications found no difference in rates of viability with varying abstinence times, although total number of viable sperm increases with increasing abstinence. Some studies evaluating the impact of ejaculatory abstinence on intrauterine insemination (IUI), intracytoplasmic sperm injection (ICSI), and in vitro fertilization (IVF) demonstrated an association between short abstinence and improved outcomes.

CONCLUSIONS

The impact of abstinence on sperm quality is complex. While certain semen parameters improve with longer abstinence, others appear to improve with shorter abstinence. No clear recommendations can be made regarding ideal abstinence due to the conflicting nature of current evidence. Going forward, more research is needed to evaluate the impact of abstinence on pregnancy and fertilization rates.

Parallel Evolution of Sperm Hyper-Activation Ca2+ Channels

Sperm hyper-activation is a dramatic change in sperm behavior where mature sperm burst into a final sprint in the race to the egg. The mechanism of sperm hyper-activation in many metazoans, including humans, consists of a jolt of Ca²⁺ into the sperm flagellum via CatSper ion channels. Surprisingly, all nine CatSper genes have been independently lost in several animal lineages. In Drosophila, sperm hyper-activation is performed through the cooption of the polycystic kidney disease 2 (pkd2) Ca²⁺ channel. The parallels between CatSpers in primates and pkd2 in Drosophila provide a unique opportunity to examine the molecular evolution of the sperm hyper-activation machinery in two independent, nonhomologous calcium channels separated by > 500 million years of divergence. Here, we use a comprehensive phylogenomic approach to investigate the selective pressures on these sperm hyper-activation channels. First, we find that the entire CatSper complex evolves rapidly under recurrent positive selection in primates. Second, we find that pkd2 has parallel patterns of adaptive evolution in Drosophila. Third, we show that this adaptive evolution of pkd2 is driven by its role in sperm hyper-activation. These patterns of selection suggest that the evolution of the sperm hyper-activation machinery is driven by sexual conflict with antagonistic ligands that modulate channel activity. Together, our results add sperm hyper-activation channels to the class of fast evolving reproductive proteins and provide insights into the mechanisms used by the sexes to manipulate sperm behavior.

Revisiting The Relationship between The Ejaculatory Abstinence Period and Semen Characteristics

Variation in the ejaculatory abstinence period suggested by different guidance bodies have resulted in a growing concern among researchers and clinicians over what the precise period of ejaculatory abstinence ought to be for an optimal semen sample. Several studies have thus been undertaken to examine the association between the length of sexual abstinence and semen characteristics. Not all studies, however, have arrived at the same conclusions. This study aims to review all existing literature published during the past few decades pertaining to the influence of ejaculatory abstinence on semen quality. For the purpose of this systematic review, all data related to sexual abstinence duration and seminal parameters were re-analysed to homogenize the current data. Thorough PubMed, MEDLINE and Google Scholar, a literature search was conducted using the keywords "sexual abstinence", "ejaculatory abstinence", "semen", "spermatozoa", "semen analysis", "sperm parameters", "motility", "reactive oxygen species (ROS)" and "DNA fragmentation". After carefully reviewing all the literature, 30 relevant papers, both written in English and published between January 1979 and December 2016, were included in this review. The weight of the evidence suggests that the decline in semen volume and sperm concentration with shorter abstinence periods is accompanied by a substantial improvement in sperm motility characteristics, especially progressive motility and velocity. Nevertheless, available data are insufficient to support definitive conclusions regarding the influence of the ejaculatory abstinence period on advanced semen parameters (ROS, DNA fragmentation and seminal plasma antioxidant capacity) and pregnancy rates. In conclusion, taking all data into account, shortening of the abstinence period may be beneficial to sperm quality. Furthermore, we recommend that the current guidelines regarding the prescribed abstinence period should be revisited.

Putative functions of tissue kallikrein-related peptidases in vaginal fluid

Cervical-vaginal fluid (CVF) is a complex biological fluid that hydrates the mucosa of the lower female reproductive system. In-depth proteomic and biochemical studies on CVF have revealed that it contains large amounts of endogenous proteases and protease inhibitors, including an abundance of several members of the tissue kallikrein-related peptidase (KLK) family. Despite their ubiquitous presence in human tissues and fluids, KLK expression levels vary considerably, with maximum expression observed in reproduction-related tissues and fluids. The roles of KLKs in the lower female reproductive system are not fully understood. The activation of KLKs in CVF is dependent on pH and various modes of KLK regulation in the vagina exist. KLKs have been postulated to have roles in physiological functions related to antimicrobial processes, vaginal and cervical epithelial desquamation, sperm transport, and the processing of fetal membranes as observed in preterm premature rupture of membranes. Increased understanding of the functional roles of KLKs in the lower female reproductive system could lead to new diagnostic and therapeutic modalities for conditions such as vaginal infections and vaginal atrophy.

Predominance of sperm motion in corners

Sperm migration through the female tract is crucial to fertilization, but the role of the complex and confined structure of the fallopian tube in sperm guidance remains unknown. Here, by confocal imaging microchannels head-on, we distinguish corner- vs. wall- vs. bulk-swimming bull sperm in confined geometries. Corner-swimming dominates with local areal concentrations as high as 200-fold that of the bulk. The relative degree of corner-swimming is strongest in small channels, decreases with increasing channel size, and plateaus for channels above 200 μm. Corner-swimming remains predominant across the physiologically-relevant range of viscosity and pH. Together, boundary-following sperm account for over 95% of the sperm distribution in small rectangular channels, which is similar to the percentage of wall swimmers in circular channels of similar size. We also demonstrate that wall-swimming sperm travel closer to walls in smaller channels (~100 μm), where the opposite wall is within the hydrodynamic interaction length-scale. The corner accumulation effect is more than the superposition of the influence of two walls, and over 5-fold stronger than that of a single wall. These findings suggest that folds and corners are dominant in sperm migration in the narrow (sub-mm) lumen of the fallopian tube and microchannel-based sperm selection devices.