Male infertility and semen evaluation : andrology in the age of precision medicine and agriculture

Abstract

Infertility has been considered a chronic disease for millennia, and remedies have been sought, both holistic/spiritual and medicinal. Infertility testing is not a modern concept either, with the first test method on record being described over 900 years ago, attributed to female physician Trota of Salerno (1050-1097). This, by today’s standard amusing testing “protocol” predated the first observation of human spermatozoon by van Leeuwenhoek and Hamm by nearly 500 years, though it was hardly a forerunner of contemporary andrology, which emerged in the late 19th and early 20th century. In those times, the sperm count and appearance/morphology were the gold standards. Ironically, despite recent advances in precision andrology and fundamental spermatology research, sperm count, concentration, morphology, and often but not always, sperm motility, remain the guiding parameters of semen analysis in humans and livestock animals. Male fertility is of paramount importance in animal health, veterinary medicine and reproductive management. Artificial insemination (AI) of livestock has been a staple technology for producers across various species worldwide for over sixty years. This technology allows for greater overall livestock production through enhanced livestock genetic selection while also experiencing an increase in efficiency over the past decades. Though much work has been done to improve the efficiency of AI, there are still many areas in need of advancement including semen analysis protocols, sperm selection techniques, semen sexing technologies, and semen storage methods. These improvements are driven by new technologies and fueled by a deeper understanding of reproductive physiology. Our laboratory has been at the forefront of sperm quality biomarker discovery, validating proteins involved in protein turnover by the ubiquitin-proteasome system, ligands and receptors involved in fertilization, and sperm redox system enzymes defending spermatozoa from damage inflicted by reactive oxygen species within the male and female reproductive tract. We have contributed to these areas of improvement in several ways including increasing the capabilities of semen analysis using image-based flow cytometry (IBFC) in combination with new biomarker probes, such as those that reflect spermatozoas’ zinc ion content and localization. Furthermore, we have explored the role of zinc ions in sperm function and their impact on sperm capacitation and sperm storage. We have also investigated sperm mitochondrial sheath length and its association with boar and bull AI fertility, which may provide a new flow cytometry-based semen analysis method coupled with machine learning to ultimately develop an automated, label-free sperm phenotyping pipeline. As a proof of concept, we have used IBFC to phenotype the sperm quality of commercially available beef and dairy bulls carrying rare, detrimental single nucleotide polymorphism (SNP) mutations within the sperm quality/output influencing genes that contribute to reduced AI fertility. Our laboratory was able to link these fertility issues to identifiable sperm phenotypes and is conducting similar studies on bulls with compromised fertility. Regarding new sperm selection technologies, our laboratory was among the first to explore the use of nanopurification. Peanut agglutinin lectin (PNA) probe coated nanoparticles have been used to cleanse semen samples of damaged/abnormal spermatozoa and tested in field AI trials with favorable results. Our lab also heavily investigates post-fertilization sperm mitophagy and its roles in fertilization, which is becoming ever more important as the recent reports of human heteroplasmy continue to be published. As such, the possibility of naturally occurring and somatic cell nuclear transfer -related livestock heteroplasmy continues to increase. The use of basic research to shift the understanding of paradigms within reproductive physiology, such as is outlined above, will continue to impact the field of andrology, lead to the development of new technologies and increase the efficiency of assisted reproductive technologies such as AI.