High Throughput Phenotypic Screening of The Human Spermatozoon

Despite recent advances in male reproductive health research, there remain many elements of male (in)fertility where our understanding is incomplete. Consequently, diagnostic tools and treatments for men with sperm dysfunction, other than medically assisted reproduction, are limited. On the other hand, the gaps in our knowledge of the mechanisms which underpin sperm function have hampered the development of male non-hormonal contraceptives. The study of mature spermatozoa is inherently difficult. They are a unique and highly specialised cell type which does not actively transcribe or translate proteins and cannot be cultured for long periods of time or matured in vitro. One, large scale, approach to both increasing understanding of sperm function, and the discovery and development of compounds that can modulate sperm function, is to directly observe responses to compounds with phenotypic screening techniques. These target agnostic approaches can be developed into high-throughput screening platforms with the potential to drastically increase advances in the field. Here we discuss the rationale and development of high-throughput phenotypic screening platforms for mature human spermatozoa, and the multiple potential applications these present, as well as the current limitations and leaps in our understanding and capabilities needed to overcome them. Further development and use of these technologies could lead to the identification of compounds which positively or negatively affect sperm cell motility or function, or novel platforms for toxicology or environmental chemical testing among other applications. Ultimately, each of these potential applications is also likely to increase understanding within the field of sperm biology.

N-Methyl-d-aspartic Acid (NMDA) Receptor Is Involved in the Inhibitory Effect of Ketamine on Human Sperm Functions

Ketamine, which used to be widely applied in human and animal medicine as a dissociative anesthetic, has become a popular recreational drug because of its hallucinogenic effect. Our previous study preliminarily proved that ketamine could inhibit human sperm function by affecting intracellular calcium concentration ([Ca2+]i). However, the specific signaling pathway of [Ca2+]i induced by ketamine in human sperm is still not clear yet. Here, the N-methyl-d-aspartic acid (NMDA) receptor was detected in the tail region of human sperm. Its physiological ligand, NMDA (50 μM), could reverse ketamine’s inhibitory effect on human sperm function, and its antagonist, MK801 (100 μM), could restrain the effect of NMDA. The inhibitory effect caused by 4 mM ketamine or 100 μM MK801 on [Ca2+]i, which is a central factor in the regulation of human sperm function, could also be recovered by 50 μM NMDA. The results suggest that the NMDA receptor is probably involved in the inhibitory effect of ketamine on human sperm functions.

X-linked palindromic gene families 4930567H17Rik and Mageb5 are dispensable for male mouse fertility

Mammalian sex chromosomes are enriched for large, nearly-identical, palindromic sequences harboring genes expressed predominately in testicular germ cells. Discerning if individual palindrome-associated gene families are essential for male reproduction is difficult due to challenges in disrupting all copies within a gene family. Here we generate precise, independent, deletions to assess the reproductive roles of two X-linked palindromic gene families with spermatid-predominant expression, 4930567H17Rik or Mageb5. Via sequence comparisons, we find mouse 4930567H17Rik and Mageb5 have human orthologs, 4930567H17Rik is rapidly diverging in rodents and primates, and 4930567H17Rik is harbored in a palindrome in humans and mice, while Mageb5 is not. Mice lacking either 4930567H17Rik or Mageb5 gene families do not have detectable defects in male fertility, fecundity, spermatogenesis, or in gene regulation, but do show differences in sperm head morphology, suggesting a potential role in sperm function. We conclude that while all palindrome-associated gene families are not essential for male fertility, large palindromes influence the evolution of their associated gene families.

Compounds enhancing human sperm motility identified using a high-throughput phenotypic screening platform

Study questionCan a high-throughput screening platform facilitate male fertility drug discovery?Summary answerA high-throughput screening platform identified a large number of compounds that enhanced sperm motility.What is known alreadySeveral efforts to find small molecules modulating sperm function have been performed but not using high-throughput technology.Study design, size, durationHealthy donor semen samples were used and samples were pooled (3-5 donors per pool). Primary screening was performed in singlicate; dose-response screening was performed in duplicate (independent donor pools).Participants/materials, setting, methodsSpermatozoa isolated from healthy donors were prepared by density gradient centrifugation and incubated in 384-well plates with compounds (6.25 uM) to identify those compounds with enhancing effects on motility. A total of ∼17,000 compounds from the following libraries: ReFRAME, Prestwick, Tocris, LOPAC, CLOUD and MMV Pathogen Box were screened. Dose response experiments of screening hits were performed to confirm the enhancing effect on sperm motility. Experiments were performed in a University setting.Main results and the role of chanceFrom our primary single concentration screening, 105 compounds elicited an enhancing effect on sperm motility compared to DMSO treated wells. Confirmed enhancing compounds were grouped based on their annotated targets/target classes. A major target class, phosphodiesterase inhibitors, were identified in particular PDE10A inhibitors as well as number of compounds not previously identified/known to enhance human sperm motility such as those related to GABA signaling.Limitations, reasons for cautionCompounds have been tested with prepared donor spermatozoa and only incubated for a short period of time. Therefore, the effect of compounds on whole semen or with longer incubation time may be different. All experiments were performed in vitro.Wider implications of the findingsThis phenotypic screening assay identified a large number of compounds that increased sperm motility. In addition to furthering our understanding of human sperm function, for example identifying new avenues for discovery, we highlight potential inhibitors as promising start-point for a medicinal chemistry programme for potential enhancement of male infertility. Moreover, with disclosure of the results of screening we present a substantial resource to inform further work in the fieldStudy funding/competing interest(s)This study was supported by the Bill and Melinda Gates Foundation and Scottish Funding Council and Scottish Universities Life Science Alliance.