The CatSper channel modulates boar sperm motility during capacitation

Abstract

The cation channel of sperm (CatSper) comprises four transmembrane subunits specifically expressed in human, equine, murine and ovine spermatozoa, apparently implicated in capacitation, hyperactivation and acrosome exocytosis. Western blotting and immunocytochemistry showed hereby that CatSper subunits are also present in boar spermatozoa, primarily over the sperm neck, tail and cytoplasmic droplets; albeit CatSper -1 presented in addition some distribution over the membrane of the acrosome and CatSper -2 and -4 over the membrane of the post-acrosome. The role of the Catsper channel in boar spermatozoa was investigated by extending the spermatozoa in media containing different calcium (Ca) availability and exposure to the capacitation-trigger bicarbonate, to progesterone or CatSper inhibitors (Mibefradil and NNC 55-0396), separately or sequentially, at physiological and toxicological doses. Extracellular Ca availability, combined with bicarbonate exposure (capacitation-inducing conditions) decreased sperm motility, similarly to when spermatozoa incubated in capacitation-inducing conditions was exposed to Mibefradil and NNC 55-0396. Exposure of these spermatozoa to progesterone did not cause significant changes in sperm motility and nor did it revert its decrease induced by CatSper antagonists. In conclusion, the CatSper channel regulates sperm motility during porcine capacitation-related events in vitro.

The achievement of boar spermin vitrocapacitation is related to an increase of disrupted disulphide bonds and intracellular reactive oxygen species levels

“…In this regard, it is worth noting that calcium plays a crucial role during both sperm capacitation and acrosome reaction (Belmonte et al, 2016;Vicente-Carrillo et al, 2017), and that we previously identified two storage calcium sites (head and mid-piece) in boar spermatozoa . Interestingly, both observations are counteracted when GSH is present, which occurs together with changes in other sperm capacitation markers, such as motility, membrane lipid disorder and tyrosine phosphorylation.…”

“…The effects of GSH on specific parameters, such as motility, membrane lipid disorder, mitochondrial membrane potential and intracellular calcium levels, also support the modulating role of GSH on sperm capacitation. In this regard, it is worth noting that calcium plays a crucial role during both sperm capacitation and acrosome reaction (Belmonte et al, 2016;Vicente-Carrillo et al, 2017), and that we previously identified two storage calcium sites (head and mid-piece) in boar spermatozoa . In this study, we observed that the effects of GSH on intracellular calcium levels were more apparent in Flu-o3-stained calcium (mainly located in the mid-piece) than in the 792 Andrology, 2018, 6, 781-797…”

Flagellar hyperactivation of bull and boar spermatozoa

“…Epididymal spermatozoa from male CatSper ‐KO mice are incapable of exhibiting hyperactivation by incubation in the capacitation‐supporting medium . Although the CatSper channels exist in bull and boar ejaculated spermatozoa, further experiments are necessary to demonstrate their functions in the occurrence of hyperactivation.…”

“…Epididymal spermatozoa from male CatSper-KO mice are incapable of exhibiting hyperactivation by incubation in the capacitation-supporting medium 64,66,67. Although the CatSper channels exist in bull and boar ejaculated spermatozoa,68,69 further experiments are necessary to demonstrate their functions in the occurrence of hyperactivation.In bulls, boars, and mice, hyperactivation can be induced immediately in uncapacitated spermatozoa by a short treatment with putative stimulator for IP 3 R "thimerosal." The thimerosal-induced hyperactivation is full-type (bulls and boars)/anti-hock (mice) 38,50,51,70.…”

Membrane Dynamics of Spermatozoa during Capacitation: New Insight in Germ Cells Signalling

“…Interestingly, since in spermatozoa AR is a terminal event that occurs only once in cell life, different from what happens in secreting cells where the complex could be disassembled and recycled for further rounds of fusion, here the SNAREs are associated to form ternary cis-complex unstable and insensitive to neurotoxins. When AR takes place, calmodulin is activated by calcium intracellular concentration peak [39] and promotes the activation of RAB3A, which in turn allows the cis-SNAREs disassembly by SF/a-SNAP. Then, monomeric SNAREs form trans-complexes, causing the irreversible docking of the acrosome to the PM.…”