Antioxidants stimulate meiosis resumption, but inhibit mitogen-activated protein kinase phosphorylation and further cell cycle progression in porcine oocytes

Abstract

In the present study the effects of two cell-permeant antioxidants,2(3)-tert-butyl-4-hydroxyanisole (BHA) andnordihydroguaiaretic acid (NDGA), on porcine oocyte meiosis resumption,chromatin behaviour and spindle assembly were investigated. The antioxidantsBHA and NDGA stimulated meiosis resumption in a dose-dependent manner in bothcumulus-enclosed and denuded porcine oocytes.Afterin vitro culture for 8 h, few oocytes underwentgerminal vesicle breakdown (GVBD) in control groups, whereas GVBD occurred inhigh percentages of oocytes treated with BHA or NDGA at concentrations thatinhibit GVBD in rodent oocytes, although mitogen-activated protein (MAP)kinase was not phosphorylated as revealed by Western immunoblots. Orceinstaining and fluorescein isothiocyanate-anti-· -tubulin labellingshowed that chromosome and spindle formation, respectively, and furthermeiosis progression were inhibited 20 and 25 h after culture. Instead,chromatin was highly condensed or existed in scattered condensed clusters.Correspondingly, MAP kinase phosphorylation was inhibited by both BHA and NDGAin a dose-dependent manner. The inhibitory effects of BHA on meiosiscompletion and MAP kinase phosphorylation was reversible. These resultssuggest that, unlike in rodent oocytes, antioxidants stimulate GVBD in theabsence of MAP kinase activation, but inhibit MAP kinase phosphorylation,meiotic apparatus formation and thus the further progression of the meiosis ofporcine oocytes.