Soluble adenylyl cyclase inhibition prevents human sperm functions essential for fertilization

Abstract

Soluble adenylyl cyclase (sAC: ADCY10) has been genetically confirmed to be essential for male fertility in mice and humans. In mice, ex vivo studies of dormant, caudal epididymal sperm demonstrated that sAC is required for initiating capacitation and activating motility. We now use an improved sAC inhibitor, TDI-10229, for a comprehensive analysis of sAC function in mouse and human sperm. In contrast to caudal epididymal mouse sperm, human sperm are collected post-ejaculation, after sAC activity has already been stimulated. In addition to preventing the capacitation-induced stimulation of sAC and protein kinase A activities, tyrosine phosphorylation, alkalinization, beat frequency, and acrosome reaction in dormant mouse sperm, sAC inhibitors interrupt each of these capacitation-induced changes in ejaculated human sperm. Furthermore, we show for the first time that sAC is required during acrosomal exocytosis in mouse and human sperm. These data define sAC inhibitors as candidates for non-hormonal, on-demand contraceptives suitable for delivery via intravaginal devices in women.

Conserved Mechanism of Bicarbonate-Induced Sensitization of CatSper Channels in Human and Mouse Sperm

“…Our results are consistent with others’ observations that the sAC and PKA pathways are important in regulating sperm capacitation in many species and that these pathways act, at least in part, by regulating pH i ( Puga Molina et al, 2017 ; Chavez et al, 2019 ; Matamoros-Volante and Trevino, 2020 ; Balbach et al, 2021 ). Carlson et al showed no changes in pH i induced by HCO 3 – in mouse sperm.…”

“…Our observation that the HCO 3 – -induced change in pH i was inhibited by a specific sAC inhibitor ( Balbach et al, 2020 , 2021 ) suggests that the main mechanism of pH i increase is through the sAC/cAMP/PKA pathway. This increase in pHi might further activate sAC, as Xie et al showed that sAC activity increases upon intracellular alkalinization ( Xie et al, 2006 ).…”

“…Second, in a pharmacologic approach, we treated epididymal sperm from wild-type mice with the sAC-specific inhibitor TDI-10229 ( Balbach et al, 2021 ) and found that it prevented an increase in the percentage of sperm responding to high extracellular KCl ( Figures 7C,H ). Treatment with TDI-10229 also reduced the rate of [Ca 2+ ] i increase in responsive sperm ( Figures 7A,B,D,E ).…”

“…Sperm samples were incubated for 60 min in the presence or absence of the soluble adenylyl cyclase inhibitor TDI-10229 (donated by Lonnie Levin and Johen Buck’s labs) ( Balbach et al, 2021 ) in capacitating TYH media or in non-capacitating HS media. After incubation, sperm pH was evaluated as previously described ( Gunderson et al, 2021 ).…”

“…Sperm samples were incubated for 60 min in the presence or absence of the soluble adenylyl cyclase inhibitor TDI-10229 (donated by Lonnie Levin and Johen Buck's labs) (Balbach et al, 2021) in capacitating TYH media or in non-capacitating HS media. After incubation, sperm pH was evaluated as previously described (Gunderson et al, 2021 We first repeated previous experiments on mouse epidydimal sperm (Chavez et al, 2014) and confirmed that, at pH 7.4, KCl induced an increase in [Ca 2+ ] i in 12% of sperm in non-capacitating conditions and 61% of sperm in capacitating conditions (bicarbonate [HCO 3 − ] plus bovine serum albumin).…”