Effects of oxidative stress and inhibitors of the pentose phosphate pathway on sexually dimorphic production of IFN‐τ by bovine blastocysts

Abstract

Bovine interferon‐tau (IFN‐τ), the anti‐luteolytic factor secreted by conceptuses of pecoran ruminants, is a product of autosomal genes, yet in vitro produced (IVP) female expanded blastocysts (EB) secrete about twice as much IFN‐τ as males. Two possible explanations have been tested here. One is that embryos of one sex are differentially susceptible to oxidative stress. The second is that female EB produce more IFN‐τ because pentose‐phosphate pathway (PPP) activity is elevated as a result of delayed X‐chromosome inactivation. IVP bovine zygotes were cultured to the 8‐cell stage and placed under conditions designed either to promote oxidative stress (±H₂O₂; 20 vs. 5% O₂), or to inhibit glucose 6‐phosphate dehydrogenase (G6PDH) activity (addition of dehydroepiandrosterone, DHEA or 6‐aminonicotinamide, 6‐AN to the medium). At day 8, blastocysts were cultured individually for a further 48 hr to assess IFN‐τ production, and embryo sex determined retrospectively. Blastocyst numbers were reduced (P < 0.05) and their continued development impaired (P < 0.05) in presence of H₂O₂ (200 μM) and 20% O₂, but neither IFN‐τ production nor sexually dimorphic expression of IFN‐τ were affected. IFN‐τ production was reduced, particularly in females (P < 0.05), and sexual dimorphic differences in production were lost in the presence of both DHEA (100 μM) and 6‐AN (1 μM). In the case of 6‐AN, these effects were achieved without a significant decline in blastocyst developmental progression, quality, or cell number. The data suggest that the higher production of IFN‐τ by female EB is an indirect outcome of the increased activity of the oxidative arm of the PPP pathway. Mol. Reprod. Dev. 68: 88–95, 2004.