Progesterone primes zona pellucida-induced activation of phospholipase A2 during acrosomal exocytosis in guinea pig spermatozoa
✍ Scribed by Qi-xian Shi; W.Y. Chen; Y.Y. Yuan; L.Z. Mao; S.Q. Yu; A.J. Chen; Y. Ni; E.R.S. Roldan
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 164 KB
- Volume
- 205
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
We investigated, using guinea‐pig spermatozoa as a model, whether phospholipase A~2~ (PLA~2~) is involved in progesterone or zona pellucida (ZP)‐stimulated acrosomal exocytosis, if progesterone enhances ZP‐induced activation of PLA~2~, and mechanisms underlying PLA~2~ regulation. Spermatozoa were capacitated and labeled in low Ca^2+^ medium with [^14^C]choline chloride or [^14^C]arachidonic acid, washed, and then exposed to millimolar Ca^2+^ and progesterone and/or ZP. Each agonist stimulated decrease of phosphatidylcholine (PC) and release of arachidonic acid and lysoPC, indicative of PLA~2~ activation. Aristolochic acid (a PLA~2~ inhibitor) abrogated lipid changes and exocytosis, indicating that these lipid changes are essential for exocytosis. Exposure of spermatozoa to submaximal concentrations of both progesterone and ZP resulted in a synergistic increase of arachidonic acid and lysoPC releases, and exocytosis, suggesting that, under natural conditions, both agonists interact to bring about acrosomal exocytosis. Progesterone‐induced PLA~2~ activation appears to be mediated by a GABA~A~‐like receptor, because bicuculline (a GABA~A~ receptor antagonist) blocked arachidonic acid release and exocytosis. In agreement with this, GABA mimicked progesterone actions. ZP‐induced activation of PLA~2~ seemed to be transduced via G~i~ proteins because pertussis toxin blocked arachidonic acid release and acrosomal exocytosis. PLA~2~ may be regulated by PKC because progesterone‐ or ZP‐induced release of arachidonic acid was blocked by the PKC inhibitors staurosporine or chelerythrine chloride. PLA~2~ could also be regulated by the cAMP‐PKA pathway; inclusion of the PKA inhibitor 14–22 amide or H‐89 led to a reduction in arachidonic acid release or exocytosis after progesterone or ZP. Taken together, these results suggest that PLA~2~ plays an essential role in progesterone or ZP‐stimulated exocytosis with progesterone priming ZP action. © 2005 Wiley‐Liss, Inc.