Zona Pellucida Induces Activation of Phospholipase A2 During Acrosomal Exocytosis in Guinea Pig Spermatozoa1

Abstract

Phospholipase A(2) (PLA(2)) is activated in spermatozoa in response to progesterone and Ca(2+) ionophores, but to our knowledge, no study has yet reported zona pellucida (ZP)-induced activation of PLA(2). We investigated whether PLA(2) is involved in ZP-stimulated acrosomal exocytosis, if Ca(2+) is required for activation of PLA(2), and signal transduction pathways modulating PLA(2) using guinea pig sperm as a model. Spermatozoa were capacitated and labeled in low-Ca(2+) medium with [(14)C]choline chloride or [(14)C]arachidonic acid and were then exposed to millimolar Ca(2+) and various reagents and stimulated with ZP. Precapacitated spermatozoa exposed to millimolar Ca(2+) and stimulated with ZP experienced increases in arachidonic acid (AA) and lysophosphatidylcholine (lysoPC) levels and a parallel decrease in phosphatidylcholine level; these changes are indicative of PLA(2) activation. Simulation with ZP also led to acrosomal exocytosis in a high proportion of spermatozoa. Lipid changes and exocytosis were prevented if spermatozoa were exposed to aristolochic acid, a PLA(2) inhibitor, before treatment with ZP. Stimulation with ZP in medium without added Ca(2+) or in medium with millimolar Ca(2+) and EGTA or La(3+) resulted in no lipid changes or exocytosis. Pretreatment with pertussis toxin, a G(i) protein inhibitor, before stimulation with ZP blocked the release of AA and lysoPC as well as acrosomal exocytosis. Exposure of spermatozoa to the diacylglycerol (DAG) kinase inhibitor R59022 before ZP stimulation led to a significant increase in generation of lysoPC and exocytosis. Taken together, these results indicate very strongly that PLA(2) plays an essential role in ZP-induced exocytosis in spermatozoa, that PLA(2) activation requires Ca(2+) internalization, and that PLA(2) activation is regulated by signal transduction pathways involving G proteins and DAG.

Arylsulfatase A deficiency causes seminolipid accumulation and a lysosomal storage disorder in Sertoli cells

“…Like its analog SGC, SGG may be cytotoxic when present intracellularly at aberrantly high levels ( 16 ). Because Sertoli cells and male germ cells contain lipases (38)(39)(40), lyso-SGG may be produced following the intracellular accumulation of SGG in Arsa Ϫ / Ϫ testes. Lysoglycolipids are believed to be more cytotoxic than the parental lipids ( 18 ).…”

Male Mice That Do Not Express Group VIA Phospholipase A2 Produce Spermatozoa with Impaired Motility and Have Greatly Reduced Fertility

“…Ca 2ϩ signaling in the tail of spermatozoa is involved in regulating flagellar motion, and [Ca 2ϩ ] in the head of spermatozoa is involved in the acrosomal reaction induced in spermatozoa by oocyte zona pellucida (45), a reaction in which iPLA 2 ␤ could participate. A PLA 2 is activated during induction of the acrosomal reaction by zona pellucida and releases arachidonic acid and LPC from spermatozoa membrane phospholipids (46). LPC also induces the acrosome reaction in spermatozoa (30,32), and one species of LPC (2-lysoplasmanylcholine) is the precursor of the platelet-activating factor, which is produced by spermatozoa and is an autocrine inducer of capacitation (47).…”

Calcium-independent phospholipases A2 and their roles in biological processes and diseases

“…Analogous phenotype is exhibited in WT spermatozoa treated with BEL. Based on earlier reports of involvement of LPC in acrosome reaction (197)(198)(199) and induction of capacitation ( 200 ), it was suggested that LPC levels are decreased the rate of [ 3 H]AA incorporation into P388D1 cell PC ( 165,166 ).…”