Sperm nuclei glutathione peroxidases and their occurrence in animal species with cysteine-containing protamines

Dynamic alterations in the paternal epigenetic landscape following fertilization

Embryonic development is a complex and dynamic process with frequent changes in gene expression, ultimately leading to cellular differentiation and commitment of various cell lines. These changes are likely preceded by changes to signaling cascades and/or alterations to the epigenetic program in specific cells. The process of epigenetic remodeling begins early in development. In fact, soon after the union of sperm and egg massive epigenetic changes occur across the paternal and maternal epigenetic landscape. The epigenome of these cells includes modifications to the DNA itself, in the form of DNA methylation, as well as nuclear protein content and modification, such as modifications to histones. Sperm chromatin is predominantly packaged by protamines, but following fertilization the sperm pronucleus undergoes remodeling in which maternally derived histones replace protamines, resulting in the relaxation of chromatin and ultimately decondensation of the paternal pronucleus. In addition, active DNA demethylation occurs across the paternal genome prior to the first cell division, effectively erasing many spermatogenesis derived methylation marks. This complex interplay begins the dynamic process by which two haploid cells unite to form a diploid organism. The biology of these events is central to the understanding of sexual reproduction, yet our knowledge regarding the mechanisms involved is extremely limited. This review will explore what is known regarding the post-fertilization epigenetic alterations of the paternal chromatin and the implications suggested by the available literature.

Increased sensitivity to testicular toxicity of transplacental benzo[a]pyrene exposure in male glutamate cysteine ligase modifier subunit knockout (Gclm-/-) mice

Polycyclic aromatic hydrocarbons (PAHs), like benzo[a]pyrene (BaP), are ubiquitous environmental pollutants formed by the incomplete combustion of organic materials. The tripeptide glutathione (GSH) is a major antioxidant and is important in detoxification of PAH metabolites. Mice null for the modifier subunit of glutamate cysteine ligase (Gclm), the rate-limiting enzyme in GSH synthesis, have decreased GSH concentrations. We investigated the effects of Gclm deletion alone on male fertility and spermatogenesis and its effect on the sensitivity of male embryos to the transplacental testicular toxicity of BaP. Gclm-/- males had dramatically decreased testicular and epididymal GCL enzymatic activity and total GSH concentrations compared with Gclm+/+ littermates. Ratios of reduced to oxidized GSH were significantly increased in Gclm-/- testes. GSH reductase enzymatic activity was increased in Gclm-/- epididymides. We observed no changes in fertility, testicular weights, testicular sperm head counts, or testicular histology and subtle changes in cauda epididymal sperm counts, motility, and morphology in Gclm-/- compared with Gclm+/+ males. Prenatal exposure to BaP from gestational day 7 to 16 was dose dependently associated with significantly decreased testicular and epididymal weights, testicular and epididymal sperm counts, and with vacuolated seminiferous tubules at 10 weeks of age. Gclm-/- males exposed prenatally to BaP had greater decreases in testicular weights, testicular sperm head counts, epididymal sperm counts, and epididymal sperm motility than Gclm+/+ littermates. These results show no effects of Gclm deletion alone on male fertility and testicular spermatogenesis and subtle epididymal effects but support increased sensitivity of Gclm-/- males to the transplacental testicular toxicity of BaP.

[Nuclear glutathione and its functions]

During recent years the nuclear localization of glutathione has been confirmed and this fraction has been quantitatively determined. The nuclear GSH and the enzymes of its metabolism realize independent and important functions. They considerably differ from functions of hyaloplasmic and mitochondrial GSH. Glutathione interacts with regulatory pathways, involved into signal transmission into the nucleus.

Selenium in blood, semen, seminal plasma and spermatozoa of stallions and its relationship to sperm quality

The essential trace element selenium is indispensable for male fertility in mammals. Until now, little data existed regarding the relationship between selenium and sperm quality in the stallion. Selenium, or selenium-dependent glutathione peroxidase activity, was determined in red blood cells, semen, seminal plasma and spermatozoa, and the percentages of spermatozoa with progressive motility (PMS), intact membranes (PMI), altered (positive) acrosomal status (PAS) and detectable DNA damage, determined by the sperm chromatin structure assay, were evaluated in 41 healthy stallions (three samples each). The pregnancy rate per oestrus cycle (PRC) served as an estimation of fertility. An adverse effect on stallion fertility caused by low dietary selenium intake was excluded, as all stallions had sufficient selenium levels in their blood. Interestingly, no significant correlations (P > 0.05) between the selenium level in blood and the selenium level in seminal plasma or spermatozoa were found, suggesting that the selenium level in blood is no indicator of an adequate selenium supply for spermatogenesis. The selenium level in spermatozoa (nmol billion–1) was correlated with PMI, PMS and PAS (r = 0.40, r = 0.31 and r = –0.42, respectively; P ≤ 0.05), and the selenium concentration in spermatozoa (nmol g–1) was correlated with PRC (r = 0.40, P < 0.03). The results of the present study show that the determination of an adequate selenium status for the male equine reproduction requires the analysis of selenium in spermatozoa. Furthermore, selenium is associated with improved sperm quality and fertility in the stallion.