Sustained soluble adenylyl cyclase (sAC)-generated cAMP is necessary and sufficient for hyperactivated motility in human sperm.
Academic Article
Overview
abstract
STUDY QUESTION: How does soluble adenylyl cyclase (sAC)-generated cyclic AMP (cAMP) control hyperactivated motility in human sperm? SUMMARY ANSWER: sAC-generated cAMP rapidly initiates and is required to maintain hyperactivated motility in human sperm. WHAT IS KNOWN ALREADY: Mouse and human sperm devoid of sAC activity (either genetically or pharmacologically) are immotile and do not undergo capacitation; thus, the HCO3--dependent stimulation of sAC and consequent increase in cAMP is responsible for activating basal motility and initiating capacitation in multiple mammalian species. Among the changes sperm undergo during capacitation is acquisition of hyperactivated motility, which is presumed to be essential for male fertility. STUDY DESIGN, SIZE, DURATION: In this study, the kinetics of cAMP generation and motility were assessed in sperm from healthy semen donors with no known fertility issues subjected to capacitating media components (HCO3- and albumin). Controls included cAMP agonists and adenylyl cyclase inhibitors. PARTICIPANTS/MATERIALS, SETTING, METHODS: The motility of sperm purified from donors' semen samples was analyzed by a Computer-Assisted Sperm Analysis (CASA) system, and the intracellular cAMP was quantified using a cAMP ELISA. MAIN RESULTS AND THE ROLE OF CHANCE: HCO3- stimulates sAC-dependent cAMP production and the transition to hyperactivated motility at the earliest times measured. Sperm hyperactivated motility seems to be a reversible process, as maintaining hyperactivated motility requires sustained sAC activation. LIMITATIONS, REASONS FOR CAUTION: The CASA system, used to measure hyperactivated motility, employs snapshot technology; sperm trajectories are observed for only short segments of time. This is an ex vivo study of sperm motility parameters in aqueous solutions. The conditions used were established for successful IVF, and the capacitation-induced hyperactivated motility studied here is proven essential for IVF and positively correlated with in vivo fertilization competence. However, in vivo, ejaculated sperm must navigate through the female reproductive tract, which is lined by viscous mucus, to reach the site of fertilization. Future studies should examine motility behaviors in solutions whose viscosity more accurately reflects the mucus-lined environment of the female reproductive tract. WIDER IMPLICATIONS OF THE FINDINGS: There are two novel findings presented here; that hyperactivation of human sperm occurs early during capacitation and that hyperactivated motility is reversible. These findings raise the possibility that the rapid, sAC-dependent hyperactivated motility allows human sperm to escape the harsh vaginal environment. Its roles modulating sperm motility define sAC as an optimal target for both male and female contraception. Additionally, sAC inhibitors with different off-rates are shown here to be useful tools enabling us to study the kinetics of sAC activation in a physiological context. STUDY FUNDING/COMPETING INTEREST(S): The research was funded by Male Contraceptive Initiative (to J.B. and L.R.L.) and National Institutes of Health via HD113015 and HD111549 (to J.B. and L.R.L.). C.R. was awarded a Male Contraceptive Initiative fellowship. L.R.L. and J.B. are co-inventors of a panel of in vivo, validated sAC inhibitors (patent PCT/US2022/02652) and are co-founders, co-owners, and members of the Board of Directors of Sacyl Pharmaceuticals Inc., which licensed the sAC inhibitors for development into on-demand male contraceptives. C.R. has been a paid consultant to Sacyl Pharmaceuticals Inc. TRIAL REGISTRATION NUMBER: N/A.
