Molecular Characterisation of Selenium-Dependent Glutathione Peroxidase Isoforms and Their Functional Significance in Reproductive Failure of Sheep in Kano State, North West Nigeria

Selenium-dependent glutathione peroxidase isoforms play critical roles in protecting spermatozoa, oocytes, and placental tissue from oxidative damage, and their dysregulation in selenium-deficient regions may contribute to the high rates of reproductive failure observed in small ruminants in northern Nigeria. This doctoral study molecularly characterised glutathione peroxidase isoforms 1, 4, and 5 in reproductive tissues of Yankasa sheep with and without reproductive failure in Kano State, North West Nigeria. Eighty ewes and forty rams were enrolled based on reproductive performance history. Reproductive tissues including endometrium, ovarian follicular fluid, spermatozoa, and epididymis were collected post-mortem or by minimally invasive biopsy for analysis. Messenger RNA expression of glutathione peroxidase isoforms 1, 4, and 5 was quantified by real-time PCR, and protein expression confirmed by western immunoblotting. Enzyme activities were measured by fluorometric kinetic assay. Selenium concentrations were determined by atomic absorption spectrophotometry. Reproductive failure ewes had significantly lower selenium in all tissues examined and markedly reduced glutathione peroxidase-4 expression in oocytes and placental tissue. Glutathione peroxidase-5 messenger RNA was the most severely depressed isoform in sperm from infertile rams. Sperm DNA fragmentation was inversely correlated with glutathione peroxidase-4 and 5 activities. Selenium supplementation in a treatment arm restored glutathione peroxidase isoform expression to levels comparable with reproductively normal animals within eight weeks. These original molecular findings establish the functional significance of selenium-glutathione peroxidase networks in sheep reproductive failure in North West Nigeria. Keywords: glutathione peroxidase, selenium, reproductive failure, oxidative stress, Yankasa sheep.