Cdc42 activity is necessary for the interplay between cAMP/PKA pathway and CatSper function

Abstract

Sperm acquire the ability to fertilize in the female genital tract in a process calledcapacitation. During capacitation, sperm undergo changes in the motility pattern calledhyperactivation, which depends on Ca2+ transport by the sperm-specific Ca2+ channelCatSper. CatSper is essential for fertilization and therefore, it is subjected to a complexregulation that is not fully understood. Recent reports found that mouse CatSper isupregulated by cAMP-dependent activation of protein kinase A (PKA). From amolecular point of view, bicarbonate stimulation of the soluble adenylyl cyclase (sAC)leads to an increase in cAMP, PKA activity and tyrosine phosphorylation of spermproteins. It remains incompletely understood if PKA itself phosphorylates CatSper or ifits activation relays on other intermediary events.By using super-resolution microscopy, we report that similar to CatSper, the smallGTPase Cdc42 distribution in the principal piece is confined to four linear domains andthis localization is disrupted in CatSper-null sperm. Cdc42 inhibition impaired CatSperopening, assessed by different approaches including analysis of downstream signalingevents and membrane potential recordings. Consequently, Cdc42 inhibition abrogatedthe increase in intracellular Ca2+ and other Ca2+- associated events, resulting in asevere compromise of the sperm fertilizing potential: decreased percentage of spermundergoing hyperactivation and in vitro fertilization. We also demonstrate that Cdc42 isessential for CatSper function by modulating cAMP production by sAC, providing a newregulatory mechanism for the upregulation of CatSper by the cAMP/PKA-dependentpathway. These results reveal a broad mechanistic insight into the regulation of Ca2+ inmammalian sperm, a matter of critical importance in male infertility as well as incontraception.