Crosstalk between protein kinase A and C regulates phospholipase D and F-actin formation during sperm capacitation

Abstract

Mammalian spermatozoa should reside in the female reproductive tract for a certain time before gaining the ability to fertilize. During this time, the spermatozoa undergo a series of biochemical processes collectively called capacitation. We recently demonstrated that actin polymerization is a necessary step in the cascade leading to capacitation. We demonstrate here for the first time a role for phospholipase D (PLD) in the induction of actin polymerization and capacitation in spermatozoa. The involvement of PLD is supported by specific inhibition of F-actin formation during sperm capacitation by PLD inhibitors and the stimulation of fast F-actin formation by exogenous PLD or phosphatidic acid (PA). Moreover, PLD activity is enhanced during capacitation before actin polymerization. Protein kinase A (PKA), known to be active in sperm capacitation, and protein kinase C (PKC), involved in the acrosome reaction, can both activate PLD and actin polymerization. We suggest that PKA- and PKC-dependent signal transduction pathways can potentially lead to PLD activation; however, under physiological conditions, actin polymerization depends primarily on PKA activity. Activation of PKA during capacitation causes inactivation of phospholipase C, and as a result, PKC activation is prevented. It appears that PKA activation promotes sperm capacitation whereas early activation of PKC during capacitation would jeopardize this process.

Role and Regulation of Sperm Gelsolin Prior to Fertilization

“…Moreover, phalloidin-FITC staining revealed an increase of F-actin levels in the sperm heads during capacitation that decreased after the AR ( Fig. 2A), as was previously shown in bovine sperm (28). Accordingly, cytochemical and Western blot analysis of separated sperm heads and tails showed that gelsolin translocates from the tail to the head during capacitation (Fig.…”

“…We have shown elsewhere in bovine sperm that before capacitation there is almost no F-actin in the sperm head, as most of it is localized to the tail midpiece, whereas after capacitation, there is a significant increase in F-actin in the head (28). Here, we demonstrated that the amount of F-actin in human sperm heads was low before capacitation, increased in capacitated cells, and was reduced again in acrosome-reacted cells ( Fig.…”

“…Capacitation-In our previous studies, we showed that actin polymerization occurs during sperm capacitation (3,28). Gelsolin, an actin-severing protein, is expected to be localized with the F-actin fraction in the cell when activated.…”

“…In vitro studies have shown that gelsolin modulates the activity of several signaling enzymes, including PLC and phospholipase D through interactions with PIP 2(4,5) (23)(24)(25)(26)(27)). It appears that actin polymerization during sperm capacitation depends on phospholipase D activity, which is regulated by the cross-talk between PKA and protein kinase C (PKC) (1,28). Moreover, we showed elsewhere that PIP 2 (4,5) , the cofactor for phospholipase D activation and F-actin production during sperm capacitation, is mediated by phospha-tidylinositol 4-kinase (PI4K) but not by phosphatidylinositol 3-kinase (PI3K) activity (29).…”

Myoinositol improves sperm parameters and serum reproductive hormones in patients with idiopathic infertility: a prospective double-blind randomized placebo-controlled study

“…In particular, two possible roles for PKC in acrosome reaction have been proposed: the first is to trigger a plasma membrane calcium channel to increase intracellular Ca 2+ (Galizzi et al, 1987;Spungin & Breitbart, 1996); the second one is to activate the phospholipase A 2 (PLA 2 ) that generates arachidonic acid (Roldan et al, 1992). Interestingly, a crosstalk between PKA and PKC during sperm capacitation was highlighted by Cohen and colleagues (Cohen et al, 2004;Breitbart et al, 2005) with a consequent rapid increase in actin polymerization which is followed by fast depolymerization, probably because of the increase in Ca 2+ levels. Therefore, spermatozoa ability to fertilize is tightly associated to a remodeling in cytoskeletal compounds.…”