Effects of Oxidative Stress and Inhibitors of the Pentose Phosphate Pathway on Sexually Dimorphic Production of IFN-τ by Bovine Blastocysts

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 (±H ₂O₂; 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.