GABA, progesterone and zona pellucida activation of PLA₂ and regulation by MEK‐ERK1/2 during acrosomal exocytosis in guinea pig spermatozoa

Abstract

We investigated whether GABA activates phospholipase A 2 (PLA 2 ) during acrosomal exocytosis, and if the MEK-ERK1/2 pathway modulates PLA 2 activation initiated by GABA, progesterone or zona pellucida (ZP). In guinea pig spermatozoa prelabelled with [14 C]arachidonic acid or [ 14 C]choline chloride, GABA stimulated a decrease in phosphatidylcholine (PC), and release of arachidonic acid and lysoPC, during exocytosis. These lipid changes are indicative of PLA 2 activation and appear essential for exocytosis since inclusion of aristolochic acid (a PLA 2 inhibitor) abrogated them, along with exocytosis. GABA activation of PLA 2 seems to be mediated, at least in part, by diacylglycerol (DAG) and protein kinase C since inclusion of the DAG kinase inhibitor R59022 enhanced PLA 2 activity and exocytosis stimulated by GABA, whereas exposure to staurosporine decreased both. GABA-, progesterone-and ZP-induced release of arachidonic acid and exocytosis were prevented by U0126 and PD98059 (MEK inhibitors). Taken together, our results suggest that PLA 2 plays a fundamental role in agoniststimulated exocytosis and that MEK-ERK1/2 are involved in PLA 2 regulation during this process.

A-Kinase Anchoring Protein 4 (AKAP4) is an ERK1/2 substrate and a switch molecule between cAMP/PKA and PKC/ERK1/2 in human spermatozoa

“…The above results led us to hypothesize that AKAP4 can play a role in regulating spermatozoa cAMP/PKA and the PKC/ERK1/2 pathways, both known to regulate sperm biology324252627282930373839. We therefore examined the effect of cAMP upon PMA-stimulated ERK1/2 activity in the presence or absence of proAKAP4 in HEK293T cells.…”

Suppression of Progesterone-enhanced Hyperactivation in Hamster Spermatozoa by γ-aminobutyric Acid

“…At the very least, P enhances hamster sperm hyperactivation through both Ca 2+ signals and protein phosphorylations [5, 6, 8, 9, 12, 16, 30]. Moreover, it has been suggested that GABA induces the AR and capacitation in human, ram, rat, guinea pig and bull spermatozoa [19, 21, 23, 33,34,35,36]. Although in these species it is suggested that the effects of GABA on the AR and capacitation are the same as those of P, the regulatory mechanisms vary.…”

“…In human spermatozoa, it has been suggested that both the GABA A and GABA B receptors block stimulation of the AR by follicular fluid [34]. In guinea pig spermatozoa, GABA regulates the AR through activation of phospholipase A 2 , protein kinase C and the mitogen-activated protein kinase cascade [35]. Therefore, it is not possible to propose a universal GABA signal pathway regulating sperm function.…”

Cl− Is Required for HCO3− Entry Necessary for Sperm Capacitation in Guinea Pig: Involvement of a Cl−/HCO3− Exchanger (SLC26A3) and CFTR1

“…All guinea pigs were housed and then euthanized. The spermatozoa from guinea pig vas deferens and cauda epididymis were washed for 18 min at 600 3 g through a Percoll gradient (85%-55%-35%) and were adjusted to 2-3 3 10 7 cells/ml (unless indicated otherwise), resuspended in complete or Cl À -deficient MCM, and incubated at 38.58C for 6 h [29,34]. Sperm capacitation was evaluated by the induction of rapid synchronization of the AR following the addition of 2 mM Ca 2þ and progesterone or ZP [29,35].…”