Dr Zamira Gibb

Mammalian semen is a physiological fluid composed of a cellular fraction (spermatozoa), and a liquid fraction (seminal plasma). Once delivered to the female genital tract, spermatozoa should be able to capacitate; a process which involves a plethora of biochemical and physiological changes required to fertilize the oocyte. Sperm production (spermatogenesis) occurs in the testes, whereby pluripotent spermatogonia differentiate to form the most morphologically specialized cells in the body. Further maturation of spermatozoa occurs in the epididymis, where they are stored prior to ejaculation. During this whole process, spermatozoa are exposed to different environments and cellular processes which may expose them to substantial levels of oxidative stress. To avoid damage associated with the unchecked production of reactive oxygen species (ROS), both spermatozoa, and the parts of the male genital tract in which they reside, are furnished with a suite of antioxidant molecules which are able to provide protection to these cells, thereby increasing their chance of being able to fertilize the oocyte and deliver an intact paternal genome to the future offspring. However, there are a host of reasons why these antioxidant systems may fail, including nutritional deficiencies, genetics, and disease states, and in these situations, a reduction or abolition of fertilizing capacity may result. This review paper focuses on the endogenous antioxidant defences available to spermatozoa during spermatogenesis and sperm maturation, the site of their production and their physiological role. Furthermore, we revised the causes and effects of antioxidant deficiencies (congenital or acquired during the animal's adulthood) on reproductive function in different animal species.

Reactive oxygen species (ROS) are implicated in all aspects of cellular functions. While the importance of ROS as signalling molecules is well described, ROS are also associated with stress pathologies. Within the reproduction field, there are associations with reduced fertility as a result of lipid peroxidation, protein dysfunction, premature cell death and DNA damage which readily occur in spermatozoa. These oxidative insults can arise in vivo, or in vitro as a result of sperm storage, purification and processing. Following a brief description of the production, homeostasis and functions of ROS in mammalian sperm function, this review paper will focus on describing the predominant sources of ROS in the ejaculate, the effects of ROS on a cellular and molecular level, and the actions of ROS from the whole animal perspective. There is highlighting of some studies, which have revealed the mechanisms for these observations, along with some strategies to ameliorate or prevent the instigation of the oxidative stress cascade before irreversible damage to spermatozoa occurs.

The horse breeding industry relies upon optimal stallion fertility. Conventional sperm assessments provide limited information regarding ejaculate quality and are not individually predictive of fertilizing potential. The aim of this study was to harness mass spectrometry to compare the proteomic profiles of high- and low-quality stallion spermatozoa, with the ultimate goal of identifying fertility biomarker candidates. Extended stallion semen (n = 12) was fractionated using Percoll density gradients to isolate low-quality and high-quality sperm populations. Motility and morphological assessments were carried out, and proteomic analyses was conducted using UHPLC-MS/MS. High-quality spermatozoa recorded higher total (95.2 ± 0.52% vs 70.6 ± 4.20%; P = 0.001) and progressive motilities (43.4 ± 3.42% vs 27.3 ± 4.32%; P = 0.05), and a higher proportion of morphologically normal cells (50.2 ± 4.34% vs 38.8 ± 2.72%; P = 0.05). In total, 1069 proteins were quantified by UHPLC-MS/MS, of which 22 proteins were significantly more abundant in the high-quality sperm population (P = 0.05). A-kinase anchor protein 4 (AKAP4) and Hexokinase 1 (HK1) were considered possible biomarker candidates and their differential expression was confirmed by immunoblot. Protein expression was significantly correlated with total (AKAP4 R2 = 0.38, P = 0.01; HK1 R2 = 0.46, P = 0.001) and progressive motilities (AKAP4 R2 = 0.51, P = 0.001; HK1 R2 = 0.55, P = 0.01), percentage rapid (AKAP4 R2 = 0.29, P = 0.05; HK1 R2 = 0.58, P = 0.001), straight-line velocity (HK1 R2 = 0.50, P = 0.01) and straightness (HK1 R2 = 0.40, P = 0.01). Furthermore, AKAP4 was highly susceptible to adduction by 4-hydroxynonenal (4HNE), which resulted in a global reduction in the phosphorylation profiles following capacitation. In conclusion, the proteomic profiles of high- and low-quality stallion spermatozoa differ substantially, and proteins such as AKAP4 and HK1 could serve as biomarkers of ejaculate quality.

Stallion fertility is a vast subject, with a wide array of permutations that can impact reproductive performance in either positive or negative ways. This review is intended to address a mere segment of the male fertility issue, but the very essence of the male contribution to fertilisation, that of the spermatozoon. Spermatozoal ultrastructure and form-to-function are detailed and spermatozoal metabolism is discussed, with specific reference to distinctive characteristics of stallion spermatozoa. Lastly, methods for assessment of spermatozoal function are considered, with emphasis on spermatozoal motility, the acrosome reaction and spermatozoon-oocyte interactions. Closing comments address the need for development and standardisation of molecular-based assays for use with spermatozoa of stallions whose subfertility cannot be explained with conventional tests.

Stallion spermatozoa continue to present scientific and clinical challenges with regard to the biological mechanisms responsible for their survival and function. In particular, deeper understanding of sperm energy metabolism, defence against oxidative damage and cell-cell interactions should improve fertility assessment and the application of advanced reproductive technologies in the equine species. In this study, we used highly sensitive LC-MS/MS technology and sequence database analysis to identify and characterise the proteome of Percoll-isolated ejaculated equine spermatozoa, with the aim offurthering our understanding of this cell's complex biological machinery. We were able to identify 9883 peptides comprising 1030 proteins, which were subsequently attributed to 975 gene products. Gene ontology analysis for molecular and cellular processes revealed new information about the metabolism, antioxidant defences and receptors of stallion spermatozoa. Mitochondrial proteins and those involved in catabolic processes constituted dominant categories. Several enzymes specific to ß-oxidation of fatty acids were identified, and further experiments were carried out to ascertain their functional significance. Inhibition of carnitine palmitoyl transferase 1, a rate-limiting enzyme of ß-oxidation, reduced motility parameters, indicating that b-oxidation contributes to maintenance of motility in stallion spermatozoa.

The spermatozoa of many stallions do not tolerate being cooled, restricting the commercial viability of these animals and necessitating the development of a chemically defined room temperature (RT) storage medium. This study examined the impact of two major modulators of oxidative phosphorylation, pyruvate (Pyr) and L-carnitine (L-C), on the storage of stallion spermatozoa at RT. Optimal concentrations of Pyr (10 mM) and L-C (50 mM) were first identified and these concentrations were then used to investigate the effects of these compounds on sperm functionality and oxidative stress at RT. Mitochondrial and cytosolic reactive oxygen species, along with lipid peroxidation, were all significantly suppressed by the addition of L-C (48 h MitoSOX Red negative: 46.2% vs. 26.1%; 48 and 72 h dihydroethidium negative: 61.6% vs. 43.1% and 64.4% vs. 46.9%, respectively; 48 and 72 h 4-hydroxynonenal negative: 37.1% vs. 23.8% and 41.6% vs. 25.7%, respectively), while the Pyr + L-C combination resulted in significantly higher motility compared to the control at 72 h (total motility: 64.2% vs. 39.4%; progressive motility: 34.2% vs. 15.2%). In addition, supplementation with L-C significantly reduced oxidative DNA damage at 72 h (9.0% vs. 15.6%). To investigate the effects of LC as an osmolyte, comparisons were made between media that were osmotically balanced with NaCl, choline chloride, or L-C. This analysis demonstrated that spermatozoa stored in the L-C balanced medium had significantly higher total motility (55.0% vs. 39.0%), rapid motility (44.0% vs. 25.7%), and ATP levels (70.9 vs. 12.8 ng/ml) following storage compared with the NaCl treatment, while choline chloride did not significantly improve these parameters compared to the control. Finally, mass spectrometry was used to demonstrate that a combination of Pyr and L-C produced significantly higher acetyl-L-carnitine production than any other treatment (6.7 pg/106 spermatozoa vs. control at 4.0 pg/106 spermatozoa). These findings suggest that Pyr and L-C could form the basis of a novel, effective RT storage medium for equine spermatozoa.

Seminal plasma contains a large protein component which has been implicated in the function, transit and survival of spermatozoa within the female reproductive tract. However, the identity of the majority of these proteins remains unknown and a direct comparison between the major domestic mammalian species has yet to be made. As such, the present study characterized and compared the seminal plasma proteomes of cattle, horse, sheep, pig, goat, camel and alpaca. GeLC-MS/MS and shotgun proteomic analysis by 2D-LC-MS/MS identified a total of 302 proteins in the seminal plasma of the chosen mammalian species. Nucleobindin 1 and RSVP14, a member of the BSP (binder of sperm protein) family, were identified in all species. Beta nerve growth factor (bNGF), previously identified as an ovulation inducing factor in alpacas and llamas, was identified in this study in alpaca and camel (induced ovulators), cattle, sheep and horse (spontaneous ovulators) seminal plasma. These findings indicate that while the mammalian species studied have common ancestry as ungulates, their seminal plasma is divergent in protein composition, which may explain variation in reproductive capacity and function. The identification of major specific proteins within seminal plasma facilitates future investigation of the role of each protein in mammalian reproduction. Biological significance: This proteomic study is the first study to compare the protein composition of seminal plasma from seven mammalian species including two camelid species. Beta nerve growth factor, previously described as the ovulation inducing factor in camelids is shown to be the major protein in alpaca and camel seminal plasma and also present in small amounts in bull, ram, and horse seminal plasma. © 2013.

The low efficiency of flow cytometric sex-sorting of stallion sperm has been attributed to the use of an opaque skim milk-based diluent during Hoechst 33342 (H33342) staining. Three experiments were conducted to formulate an optically clear stallion semen diluent for use during H33342 staining, and to determine whether a clear diluent improved resolution during sorting. For Experiment 1, sperm were incubated at 34 °C in each of five diluents containing either no protein, skim milk, 0.25% Cohn's Fraction V BSA, 0.5% BSA, or 1% BSA, following an 18 h storage (15 °C) period, or shortly after collection. Sperm incubated in both skim milk and 1% BSA-supplemented diluents had equivalent total (47 and 49.5%, respectively) and progressive (4.73 and 5.67%, respectively) sperm motilities after 45 min, and comparable acrosome integrity (65.9 and 67.9%, respectively). For Experiment 2, the protein source was optimised by comparing the characteristics of sperm stored and incubated in five diluents supplemented with skim milk, BSA, fatty acid and endotoxin free BSA (I-BSA), KnockOut¿ Serum Replacement, and ß-lactoglobulin, respectively. The I-BSA diluent was superior to skim milk for motility maintenance during incubation (74.0 vs 63.7%). The effect of diluent on sorting was investigated in Experiment 3 using a range of H33342 concentrations and incubation durations. The clear (1% BSA) diluent improved the split ratio compared with the opaque (skim milk) diluent (0.17 vs 0.08), with an optimum staining time of 45 min using 0.09 mM H33342. In conclusion, a diluent containing 1% fatty acid free, low endotoxin BSA in lieu of skim milk improved the sorting efficiency and motility characteristics of stallion sperm after storage for 18 h. © 2011.