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Ca2+ signals generated by CatSper and Ca2+ stores regulate different behaviors in human sperm.

Alasmari W, Costello S, Correia J, Oxenham SK, Morris J, Fernandes L, Ramalho-Santos J, Kirkman-Brown J, Michelangeli F, Publicover S, Barratt CL - J. Biol. Chem. (2013)

Bottom Line: Thimerosal had no effect on penetration into methylcellulose. 4-Aminopyridine, a powerful modulator of sperm motility, both raised pHi and mobilized Ca(2+) stored in sperm (and from microsomal membrane preparations). 4-Aminopyridine-induced hyperactivation even in cells suspended in Ca(2+)-depleted medium and also potentiated penetration into methylcellulose.The latter effect was sensitive to NNC55-039, but induction of hyperactivation was not.We conclude that these two components of the [Ca(2+)]i signaling apparatus have strikingly different effects on sperm motility.

View Article: PubMed Central - PubMed

Affiliation: From the Reproductive and Developmental Biology, Medical School, University of Dundee, Ninewells Hospital, Dundee DD1 9SY, Scotland, United Kingdom.

ABSTRACT
[Ca(2+)]i signaling regulates sperm motility, enabling switching between functionally different behaviors that the sperm must employ as it ascends the female tract and fertilizes the oocyte. We report that different behaviors in human sperm are recruited according to the Ca(2+) signaling pathway used. Activation of CatSper (by raising pHi or stimulating with progesterone) caused sustained [Ca(2+)]i elevation but did not induce hyperactivation, the whiplash-like behavior required for progression along the oviduct and penetration of the zona pellucida. In contrast, penetration into methylcellulose (mimicking penetration into cervical mucus or cumulus matrix) was enhanced by activation of CatSper. NNC55-0396, which abolishes CatSper currents in human sperm, inhibited this effect. Treatment with 5 μm thimerosal to mobilize stored Ca(2+) caused sustained [Ca(2+)]i elevation and induced strong, sustained hyperactivation that was completely insensitive to NNC55-0396. Thimerosal had no effect on penetration into methylcellulose. 4-Aminopyridine, a powerful modulator of sperm motility, both raised pHi and mobilized Ca(2+) stored in sperm (and from microsomal membrane preparations). 4-Aminopyridine-induced hyperactivation even in cells suspended in Ca(2+)-depleted medium and also potentiated penetration into methylcellulose. The latter effect was sensitive to NNC55-039, but induction of hyperactivation was not. We conclude that these two components of the [Ca(2+)]i signaling apparatus have strikingly different effects on sperm motility. Furthermore, since stored Ca(2+) at the sperm neck can be mobilized by Ca(2+)-induced Ca(2+) release, we propose that CatSper activation can elicit functionally different behaviors according to the sensitivity of the Ca(2+) store, which may be regulated by capacitation and NO from the cumulus.

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Tentative model for the interacting effects of Ca2+ influx mediated by CatSper (blue box) and release of Ca2+ from the store at the sperm neck (yellow box) based on evidence from this and previous studies. The acrosomal Ca2+ store is also shown (green box). CICR links these two parts of the Ca2+-signaling apparatus in a subset of cells where the Ca2+ store is sensitized (dashed arrow). Agents employed in this study are shown in red. STF is shown acting to enhance capacitation, including sensitization of the Ca2+ store at the sperm neck. Other (endogenous) agents and pathways are shown in black. Question marks indicate effects that are consistent with the model or may be predicted on the basis of studies on other cell types but that have not been established in sperm. Double question marks denote speculation.
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Figure 5: Tentative model for the interacting effects of Ca2+ influx mediated by CatSper (blue box) and release of Ca2+ from the store at the sperm neck (yellow box) based on evidence from this and previous studies. The acrosomal Ca2+ store is also shown (green box). CICR links these two parts of the Ca2+-signaling apparatus in a subset of cells where the Ca2+ store is sensitized (dashed arrow). Agents employed in this study are shown in red. STF is shown acting to enhance capacitation, including sensitization of the Ca2+ store at the sperm neck. Other (endogenous) agents and pathways are shown in black. Question marks indicate effects that are consistent with the model or may be predicted on the basis of studies on other cell types but that have not been established in sperm. Double question marks denote speculation.

Mentions: By selective activation of CatSper and store mobilization, we were able to demonstrate their functionally different effects in regulating motility. How are these two components of Ca2+ signaling (and their effects on sperm behavior) recruited in the female tract? CatSper channels are activated by a range of small organic molecules, including progesterone and prostaglandin E1, and are also sensitive to depolarization, cytoplasmic alkalinization, and probably other aspects of capacitation (38, 39). CatSper thus acts as a polymodal signaling “node” on which many stimuli converge (11). Mobilization of stored Ca2+ at the sperm neck, generating [Ca2+]i oscillations, occurs secondarily to influx of Ca2+ induced pharmacologically or by progesterone-induced activation of CatSper (18, 25) (Fig. 1F). Progesterone does not directly mobilize stored Ca2+ (39), but release at the sperm neck, where both ryanodine receptors (18, 19) and inositol trisphosphate receptors (13) have been described in human sperm, can occur by CICR. The proportion of cells in which oscillations are observed is enhanced by nitric oxide (NO•; a product of the oviduct epithelium and cumulus cells surrounding the oocyte) and by capacitation (25, 26). NO•S-nitrosylates ryanodine receptors in human sperm (59), an action that sensitizes CICR (60). An important component of capacitation may be oxidative stress, which has similar effects (61). NO• facilitates the release of stored Ca2+ in human sperm by low doses of progesterone and enhances the effect of progesterone on flagellar excursion (62, 63). In addition, release of stored Ca2+ may be modulated by exchange proteins activated directly by cyclic AMP (EPACs). These proteins are known to facilitate release of stored Ca2+ and have been detected at the acrosome and neck region in human sperm (64–66). A potential mechanism for mobilization of stored Ca2+ at the sperm neck is thus through CatSper-mediated Ca2+ influx followed by CICR, where CICR is a “gatekeeper,” determining the availability of each cell for recruitment into the hyperactivated population. Sensitization/desensitization through S-nitrosylation and signaling events related to capacitation will regulate this “available” population (Fig. 5). If store mobilization through CICR is supported by CatSper, high levels of spontaneous HA induced by potent capacitating media should be sensitive to blockade of CatSper, and this was the case, the effect of NNC being most marked in cells where the rate of spontaneous hyperactivation was greatest.


Ca2+ signals generated by CatSper and Ca2+ stores regulate different behaviors in human sperm.

Alasmari W, Costello S, Correia J, Oxenham SK, Morris J, Fernandes L, Ramalho-Santos J, Kirkman-Brown J, Michelangeli F, Publicover S, Barratt CL - J. Biol. Chem. (2013)

Tentative model for the interacting effects of Ca2+ influx mediated by CatSper (blue box) and release of Ca2+ from the store at the sperm neck (yellow box) based on evidence from this and previous studies. The acrosomal Ca2+ store is also shown (green box). CICR links these two parts of the Ca2+-signaling apparatus in a subset of cells where the Ca2+ store is sensitized (dashed arrow). Agents employed in this study are shown in red. STF is shown acting to enhance capacitation, including sensitization of the Ca2+ store at the sperm neck. Other (endogenous) agents and pathways are shown in black. Question marks indicate effects that are consistent with the model or may be predicted on the basis of studies on other cell types but that have not been established in sperm. Double question marks denote speculation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585060&req=5

Figure 5: Tentative model for the interacting effects of Ca2+ influx mediated by CatSper (blue box) and release of Ca2+ from the store at the sperm neck (yellow box) based on evidence from this and previous studies. The acrosomal Ca2+ store is also shown (green box). CICR links these two parts of the Ca2+-signaling apparatus in a subset of cells where the Ca2+ store is sensitized (dashed arrow). Agents employed in this study are shown in red. STF is shown acting to enhance capacitation, including sensitization of the Ca2+ store at the sperm neck. Other (endogenous) agents and pathways are shown in black. Question marks indicate effects that are consistent with the model or may be predicted on the basis of studies on other cell types but that have not been established in sperm. Double question marks denote speculation.
Mentions: By selective activation of CatSper and store mobilization, we were able to demonstrate their functionally different effects in regulating motility. How are these two components of Ca2+ signaling (and their effects on sperm behavior) recruited in the female tract? CatSper channels are activated by a range of small organic molecules, including progesterone and prostaglandin E1, and are also sensitive to depolarization, cytoplasmic alkalinization, and probably other aspects of capacitation (38, 39). CatSper thus acts as a polymodal signaling “node” on which many stimuli converge (11). Mobilization of stored Ca2+ at the sperm neck, generating [Ca2+]i oscillations, occurs secondarily to influx of Ca2+ induced pharmacologically or by progesterone-induced activation of CatSper (18, 25) (Fig. 1F). Progesterone does not directly mobilize stored Ca2+ (39), but release at the sperm neck, where both ryanodine receptors (18, 19) and inositol trisphosphate receptors (13) have been described in human sperm, can occur by CICR. The proportion of cells in which oscillations are observed is enhanced by nitric oxide (NO•; a product of the oviduct epithelium and cumulus cells surrounding the oocyte) and by capacitation (25, 26). NO•S-nitrosylates ryanodine receptors in human sperm (59), an action that sensitizes CICR (60). An important component of capacitation may be oxidative stress, which has similar effects (61). NO• facilitates the release of stored Ca2+ in human sperm by low doses of progesterone and enhances the effect of progesterone on flagellar excursion (62, 63). In addition, release of stored Ca2+ may be modulated by exchange proteins activated directly by cyclic AMP (EPACs). These proteins are known to facilitate release of stored Ca2+ and have been detected at the acrosome and neck region in human sperm (64–66). A potential mechanism for mobilization of stored Ca2+ at the sperm neck is thus through CatSper-mediated Ca2+ influx followed by CICR, where CICR is a “gatekeeper,” determining the availability of each cell for recruitment into the hyperactivated population. Sensitization/desensitization through S-nitrosylation and signaling events related to capacitation will regulate this “available” population (Fig. 5). If store mobilization through CICR is supported by CatSper, high levels of spontaneous HA induced by potent capacitating media should be sensitive to blockade of CatSper, and this was the case, the effect of NNC being most marked in cells where the rate of spontaneous hyperactivation was greatest.

Bottom Line: Thimerosal had no effect on penetration into methylcellulose. 4-Aminopyridine, a powerful modulator of sperm motility, both raised pHi and mobilized Ca(2+) stored in sperm (and from microsomal membrane preparations). 4-Aminopyridine-induced hyperactivation even in cells suspended in Ca(2+)-depleted medium and also potentiated penetration into methylcellulose.The latter effect was sensitive to NNC55-039, but induction of hyperactivation was not.We conclude that these two components of the [Ca(2+)]i signaling apparatus have strikingly different effects on sperm motility.

View Article: PubMed Central - PubMed

Affiliation: From the Reproductive and Developmental Biology, Medical School, University of Dundee, Ninewells Hospital, Dundee DD1 9SY, Scotland, United Kingdom.

ABSTRACT
[Ca(2+)]i signaling regulates sperm motility, enabling switching between functionally different behaviors that the sperm must employ as it ascends the female tract and fertilizes the oocyte. We report that different behaviors in human sperm are recruited according to the Ca(2+) signaling pathway used. Activation of CatSper (by raising pHi or stimulating with progesterone) caused sustained [Ca(2+)]i elevation but did not induce hyperactivation, the whiplash-like behavior required for progression along the oviduct and penetration of the zona pellucida. In contrast, penetration into methylcellulose (mimicking penetration into cervical mucus or cumulus matrix) was enhanced by activation of CatSper. NNC55-0396, which abolishes CatSper currents in human sperm, inhibited this effect. Treatment with 5 μm thimerosal to mobilize stored Ca(2+) caused sustained [Ca(2+)]i elevation and induced strong, sustained hyperactivation that was completely insensitive to NNC55-0396. Thimerosal had no effect on penetration into methylcellulose. 4-Aminopyridine, a powerful modulator of sperm motility, both raised pHi and mobilized Ca(2+) stored in sperm (and from microsomal membrane preparations). 4-Aminopyridine-induced hyperactivation even in cells suspended in Ca(2+)-depleted medium and also potentiated penetration into methylcellulose. The latter effect was sensitive to NNC55-039, but induction of hyperactivation was not. We conclude that these two components of the [Ca(2+)]i signaling apparatus have strikingly different effects on sperm motility. Furthermore, since stored Ca(2+) at the sperm neck can be mobilized by Ca(2+)-induced Ca(2+) release, we propose that CatSper activation can elicit functionally different behaviors according to the sensitivity of the Ca(2+) store, which may be regulated by capacitation and NO from the cumulus.

Show MeSH
Related in: MedlinePlus