The triple role of glutathione S-transferases in mammalian male fertility

Male idiopathic infertility accounts for 15-25% of reproductive failure. One of the factors that has been linked to this condition is oxidative stress (OS), defined as the imbalance between antioxidants and reactive oxygen species. Amongst the different factors that protect the cell against OS, the members of the glutathione S-transferase (GST) superfamily play an important role. Interestingly, reduction or lack of some GSTs has been associated to infertility in men. Therefore, and to clarify the relationship between GSTs and male fertility, the aim of this work is to describe the role that GSTs play in the male reproductive tract and in sperm physiology. To that end, the present review provides a novel perspective on the triple role of GSTs (detoxification, regulation of cell signalling and fertilisation), and reports their localisation in sperm, seminal plasma and the male reproductive tract. Furthermore, we also tackle the existing correlation between some GST classes and male fertility. Due to the considerable impact of GSTs in human pathology and their tight relationship with fertility, future research should address the specific role of these proteins in male fertility, which could result in new approaches for the diagnosis and/or treatment of male infertility.

Period of Boar Ejaculate Collection Contributes to the Yearly Intra-Male Variability of Seminal Plasma Cytokines

The concentrations of cytokines in seminal plasma (SP) fluctuate over time in healthy males, weakening their practical usefulness as diagnostic tools. This study evaluated the relevance of intra-male variability in SP cytokines and to what extent the period of the year when ejaculate is collected contributes to such variability. Thirteen cytokines (GM-CSF, IFNγ, IL-1α, IL-1β, IL-1ra, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18, and TNFα) were measured using the Luminex xMAP^® technology for 180 SP samples of ejaculate collected over a year from nine healthy and fertile boars. The SP samples were grouped into two annual periods according to decreasing or increasing daylight and ambient temperature. Intra-male variability was higher than inter-male variability for all cytokines. All SP cytokines showed concentration differences between the two periods of the year, showing the highest concentration during the increasing daylength/temperature period, irrespective of the male. Similarly, some cytokines showed differences between daylength/temperature periods when focusing on their total amount in the ejaculate. No strong relationship (explaining more than 50% of the total variance) was found between annual fluctuations in SP-cytokine levels and semen parameters. In conclusion, the period of the year during which ejaculates were collected helps explain the intra-male variability of SP-cytokine levels in breeding boars.

The Transcriptome of Pig Spermatozoa, and Its Role in Fertility

In the study presented here we identified transcriptomic markers for fertility in the cargo of pig ejaculated spermatozoa using porcine-specific micro-arrays (GeneChip^® miRNA 4.0 and GeneChip^® Porcine Gene 1.0 ST). We report (i) the relative abundance of the ssc-miR-1285, miR-16, miR-4332, miR-92a, miR-671-5p, miR-4334-5p, miR-425-5p, miR-191, miR-92b-5p and miR-15b miRNAs, and (ii) the presence of 347 up-regulated and 174 down-regulated RNA transcripts in high-fertility breeding boars, based on differences of farrowing rate (FS) and litter size (LS), relative to low-fertility boars in the (Artificial Insemination) AI program. An overrepresentation analysis of the protein class (PANTHER) identified significant fold-increases for C-C chemokine binding (GO:0019957): CCR7, which activates B- and T-lymphocytes, 8-fold increase), XCR1 and CXCR4 (with ubiquitin as a natural ligand, 1.24-fold increase), cytokine receptor activity (GO:0005126): IL23R receptor of the IL23 protein, associated to JAK2 and STAT3, 3.4-fold increase), the TGF-receptor (PC00035) genes ACVR1C and ACVR2B (12-fold increase). Moreover, two micro-RNAs (miR-221 and mir-621) were down- and up-regulated, respectively, in high-fertility males. In conclusion, boars with different fertility performance possess a wide variety of differentially expressed RNA present in spermatozoa that would be attractive targets as non-invasive molecular markers for predicting fertility.

Proteomics in fresh and preserved pig semen: Recent achievements and future challenges

Proteins in semen, either in spermatozoa (SPZ) or seminal plasma (SP), are directly involved in molecular processes and biological pathways regulating sperm function, including fertilizing ability. Therefore, semen proteins are candidates of choice for biomarkers discovery for fertility and for sperm (dys)function. Mass spectrometry (MS)-based proteomics has opened up a new era for characterizing and quantifying the protein profile of SP and SPZ, as well as for unveiling the complex protein interactions involved in the activation of sperm functionality. This article overviews existing literature on MS-based proteomics regarding porcine semen, with a specific focus on the potential practical application of the results achieved so far. The weaknesses of current studies and the perspectives for future research in MS-based pig semen proteomics are also addressed.

Glutathione S-Transferases Play a Crucial Role in Mitochondrial Function, Plasma Membrane Stability and Oxidative Regulation of Mammalian Sperm

Glutathione S-transferases (GSTs) are essential sperm antioxidant enzymes involved in cell protection against oxidative stress and toxic chemicals, preserving sperm function and fertilising ability. Artificial insemination (AI) in pigs is commonly carried out through the use of liquid-stored semen at 17 °C, which not only reduces sperm metabolic activity but also sperm quality and AI-farrowing rates within the 72 h of storage. While one may reasonably suggest that such enzymes are implicated in the physiology and maintenance of mammalian sperm function during liquid-storage, no previous studies conducted on any species have addressed this hypothesis. Therefore, the objective of the present work was to characterise the presence and function of sperm GSTs in mammalian sperm, using the pig as a model. In this regard, inhibition of such enzymes by ethacrynic acid (EA) during semen storage at 17 °C was performed to evaluate the effects of GSTs in liquid-preserved boar sperm by flow cytometry, immunofluorescence, and immunoblotting analysis. The results of this study have shown, for the first time in mammalian species, that the inhibition of GSTs reduces sperm quality and functionality parameters during their storage at 17 °C. These findings highlight the key role of such enzymes, especially preserving mitochondrial function and maintaining plasma membrane stability. In addition, this study has identified and localised GSTM3 in the tail and equatorial subdomain of the head of boar sperm. Finally, this study has set grounds for future investigations testing supplementation of semen extenders with GSTs, as this may improve fertility outcomes of swine AIs.

Seminal Plasma Cytokines Are Predictive of the Outcome of Boar Sperm Preservation

Background: Boar seminal plasma is rich in cytokines, which could influence the capability of spermatozoa to tolerate preservation. Objectives: To evaluate the involvement of boar seminal plasma cytokines in the changes experienced by boar spermatozoa during their storage, either in liquid or frozen state. Materials and Methods: In two separated experiments, semen samples from healthy and fertile boars were split in two aliquots, one centrifuged twice (1,500 ×g for 10 min) to harvest seminal plasma, whereas the other was either commercially extended (3 × 10⁷ sperm/mL) and liquid-stored at 17°C during 144 h (n = 28, Experiment 1) or frozen-thawed using a standard 0.5 mL protocol (n = 27, Experiment 2). Sixteen cytokines were quantified using Luminex xMAP®. Sperm attributes (CASA-evaluated total and progressive motility; flow cytometry-evaluated sperm viability, production of intracellular H₂O₂ and O 2 • - and levels of lipid peroxidation in viable spermatozoa) were evaluated either at 0, 72, or 144 h of liquid storage (Experiment 1) or before freezing and at 30- and 150-min post-thawing (Experiment 2). Results: Multiple linear regression models, with Bayesian approach for variable selection, revealed that the anti-inflammatory TGF-β2, TGF-β3, IL-1Ra, and IL-4 and the pro-inflammatory IL-8 and IL-18, predicted changes in sperm motility for liquid-stored semen while the anti-inflammatory IFN-γ was included in the models predicting changes in all sperm attributes for cryopreserved semen. Conclusion: Specific boar seminal plasma cytokines would contribute to modulate the structural and metabolic changes shown by spermatozoa during preservation, either in liquid or frozen state.

Total and specific activities of superoxide dismutase (SOD) in seminal plasma are related with the cryotolerance of jackass spermatozoa

This study investigated whether the activities of four antioxidant enzymes present in jackass seminal plasma (SP), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) and glutathione reductase (GSR), are related to the sperm ability to withstand cryopreservation. Eighteen ejaculates from 16 healthy jackasses were collected and split into two aliquots. The first one was centrifuged (3,000×g, 4 °C for 10 min) and used to determine the activities of these four enzymes in SP, whereas the other was diluted in a skim-milk extender and then cryopreserved. Assessment of sperm motility and membrane integrity was performed before and after cryopreservation. Based on the percentages of total motile and viable spermatozoa at post-thaw, samples were classified as good (GFE) or poor (PFE) freezability ejaculates through cluster analyses. Total and specific activities of SOD in seminal plasma were higher (P < 0.05) in GFE than in PFE, whereas no significant differences between GFE and PFE were observed regarding total and specific activities of CAT, GPX and GSR. However, post-thaw sperm parameters were positively correlated with total and specific activities of CAT and negatively correlated with those of GSR. In conclusion, determination of total and specific activities of SOD in the seminal plasma of a given jackass ejaculate may predict the sperm ability to withstand cryopreservation. In addition, our results warrant further research on addressing whether SOD activity in seminal plasma does not only allow predicting the sperm cryotolerance of a given ejaculate but also that of all ejaculates from a given jackass.

Aquaglyceroporins but not orthodox aquaporins are involved in the cryotolerance of pig spermatozoa

Background

Aquaporins (AQPs) are a family of transmembrane water channels that includes orthodox AQPs, aquaglyceroporins (GLPs) and superAQPs. AQP3, AQP7, AQP9 and AQP11 have been identified in boar sperm, and they are crucial for sperm maturation and osmoregulation. Water exchange is an important event in cryopreservation, which is the most efficient method for long-term storage of sperm. However, the freeze-thaw process leads to sperm damage and a loss of fertilizing potential. Assuming that the quality of frozen-thawed sperm partially depends on the regulation of osmolality variations during this process, AQPs might play a crucial role in boar semen freezability. In this context, the aim of this study was to unravel the functional relevance of the different groups of AQPs for boar sperm cryotolerance through three different inhibitors.

Results

Inhibition of different groups of AQPs was found to have different effects on boar sperm cryotolerance. Whereas the use of 1,3-propanediol (PDO), an inhibitor of orthodox AQPs and GLPs, decreased total motility (P < 0.05), it increased post-thaw sperm viability, lowered membrane lipid disorder and increased mitochondrial membrane potential (MMP) (P < 0.05). When acetazolamide (AC) was used as an inhibitor of orthodox AQPs, the effects on post-thaw sperm quality were restricted to a mild increase in MMP in the presence of the intermediate concentration at 30 min post-thaw and an increase in superoxide levels (P < 0.05). Finally, the addition of phloretin (PHL), a GLP inhibitor, had detrimental effects on post-thaw total and progressive sperm motilities, viability and lipid membrane disorder (P < 0.05).

Conclusions

The effects of the different inhibitors suggest that GLPs rather than orthodox AQPs are relevant for boar sperm freezability. Moreover, the positive effect of PDO on sperm quality suggests a cryoprotective role for this molecule.

Extracellular vesicles isolated from porcine seminal plasma exhibit different tetraspanin expression profiles

Seminal extracellular vesicles (EVs) include exosomes (ø 40–120 nm) and microvesicles (MVs, ø 120–1000 nm), which would be involved in multiple functional reproductive roles. The study aimed to establish which EV subtypes are present in pig semen, using a high-resolution flow cytometer to explore differences in their tetraspanin expression profile. The EVs were isolated from 12 pig ejaculates using serial ultracentrifugation and characterized by dynamic light scattering and electron microscopy for size and morphology as well as for tetraspanin expression using flow cytometry with Carboxyfluorescein succinimidyl ester (CFSE) and antibodies against CD9, CD63 and CD81. Pig semen contained a heterogeneous EV-population regarding size and morphology. Flow cytometric analysis demonstrated that the proportion of EVs expressing CD63 and CD9 was higher in MVs (P < 0.001 and P < 0.05, respectively) than in exosomes, while the opposite was true for CD81; higher (P < 0.001) in exosomes than in MVs. In conclusion, (1) the new generation of flow cytometers are able to accurately identify EVs and to gate them in two size-different populations named exosomes and MVs. (2) Tetraspanins CD9, CD63 and CD81 are present in both seminal EVs, albeit with exosomes and MVs differing in expression profiles, suggesting dissimilar cargo and binding affinity.

Levels of activity of superoxide dismutase in seminal plasma do not predict fertility of pig AI-semen doses

Superoxide dismutase (SOD) is a major antioxidant enzyme in boar seminal plasma (SP). This study evaluated how SP-SOD affected sperm attributes when semen of boars of various breeds, included in commercial artificial insemination (AI)-programs, was extended and liquid-stored at 17 °C for AI; as well as their in vivo fertility (farrowing rate and litter size of 10,952 AI-sows). SP-SOD-activity was assessed in 311 ejaculates (100 boars) while sperm motility (by CASA), viability and intracellular H₂O₂ generation in viable spermatozoa (by flow cytometry) were measured at 0 and 72 h of liquid storage. SP-SOD activity was not affected by breed but differed (P < 0.001) between boars (n = 50), ranging from 1.16 ± 0.11 to 7.02 ± 0.75 IU/mL. Semen AI-doses (n = 44) hierarchically grouped (P < 0.001) with low SP-SOD activity showed lower (P < 0.05) sperm motility and intracellular H₂O₂ at 72 h of liquid storage. Fertility did not differ between AI-boars (n = 39) hierarchically grouped (P < 0.001) with high or low SP-SOD activity. In conclusion, SP-SOD activity is boar dependent and positively related with sperm functionality of liquid-stored semen AI-doses. However, this positive effect is not reflected on in vivo fertility post-AI.

GSTM3, but not IZUMO1, is a cryotolerance marker of boar sperm

Background

Cryopreservation is currently the most efficient method for long-term preservation of mammalian gametes and is extensively used in swine artificial insemination (AI) centres. However, it is well-known that cryopreservation procedures induce changes in the water phase in both intra and extracellular compartments, which alter the content and localisation of several proteins and ends up curtailing the structural integrity of functional sperm (i.e., cryoinjuries). Alterations and deficiencies of sperm-oocyte binding proteins during gamete recognition are one of the causes of reproductive failure both in vitro and in vivo. In this sense, characterisation of cryopreservation effects upon oocyte-binding proteins of sperm, such as IZUMO1 and GSTM3, is essential when assessing the impact of this technique in swine reproduction.

Results

Cryopreservation was found to induce changes in the localisation of IZUMO1 and GSTM3 in boar sperm. However, the relative content of both proteins was not altered after thawing. Furthermore, whereas IZUMO1 content was found not to be related to the cryotolerance of boar sperm, GSTM3 content was observed to be higher in poor (PFE) than in good (GFE) freezability ejaculates in both pre-frozen (1.00 INT·mm² ± 0.14 INT·mm² vs. 0.72 INT·mm² ± 0.15 INT·mm²; P < 0.05) and post-thawed (0.96 INT·mm² ± 0.20 INT·mm² vs. 70 INT·mm² ± 0.19 INT·mm²; P < 0.05) samples. Moreover, GSTM3 levels were found to be higher in those spermatozoa that exhibited low mitochondrial activity, high reactive oxygen species (ROS) production, and high membrane lipid disorder post-thaw (P < 0.05).

Conclusions

The difference in GSTM3 content between GFE and PFE, together with this protein having been found to be related to poor sperm quality post-thaw, suggests that it could be used as a cryotolerance marker of boar spermatozoa. Furthermore, both IZUMO1 and GSTM3 relocate during cryopreservation, which could contribute to the reduced fertilising capacity of frozen-thawed boar sperm.

Electronic supplementary material

The online version of this article (10.1186/s40104-019-0370-5) contains supplementary material, which is available to authorized users.

Boar semen proteomics and sperm preservation

Recently numerous proteomic approaches have been undertaken to identify sperm and seminal plasma (SP) proteins that can be used as potential biomarkers for sperm function, including fertilization ability. This review aims firstly to briefly introduce the proteomic technologies and workflows that can be successfully applied for sperm and SP proteomic analysis. Secondly, we summarize the current knowledge about boar SP and the sperm proteome, focusing mainly on its relevance to sperm preservation procedures (liquid storage or cryopreservation) and their outcomes in terms of sperm function and fertility.

Cryopreservation Differentially Alters the Proteome of Epididymal and Ejaculated Pig Spermatozoa

Cryopreservation induces differential remodeling of the proteome in mammalian spermatozoa. How these proteome changes relate to the loss of sperm function during cryopreservation remains unsolved. The present study aimed to clarify this issue evaluating differential changes in the proteome of fresh and frozen-thawed pig spermatozoa retrieved from the cauda epididymis and the ejaculate of the same boars, with clear differences in cryotolerance. Spermatozoa were collected from 10 healthy, sexually mature, and fertile boars, and cryopreserved using a standard 0.5 mL-straw protocol. Total and progressive motility, viability, and mitochondria membrane potential were higher and membrane fluidity and reactive oxygen species generation lower in frozen-thawed (FT) epididymal than ejaculated spermatozoa. Quantitative proteomics of fresh and FT spermatozoa were analyzed using a LC-ESI-MS/MS-based Sequential Window Acquisition of All Theoretical Spectra approach. Cryopreservation quantitatively altered more proteins in ejaculated than cauda epididymal spermatozoa. Differential protein-protein networks highlighted a set of proteins quantitatively altered in ejaculated spermatozoa, directly involved in mitochondrial functionality which would explain why ejaculated spermatozoa deteriorate during cryopreservation.

The Proteome of Pig Spermatozoa Is Remodeled During Ejaculation

Proteins are essential for sperm function, including their fertilizing capacity. Pig spermatozoa, emitted in well-defined ejaculate fractions, vary in their functionality, which could be related to different sperm protein composition. This study aimed (i) to update the porcine sperm proteome and (ii) to identify proteins differentially expressed in mature spermatozoa from cauda epididymis and those delivered in separate ejaculate fractions. Ejaculates from nine mature and fertile boars were manually collected in three separate portions: the first 10 ml of the sperm-rich ejaculate fraction (SRF), the rest of the SRF and the post-SRF. The contents of cauda epididymides of the boars were collected post-mortem by retrograde duct perfusion, generating four different semen sources for each boar. Following centrifugation, the resulting pellets of each semen source were initially pooled and later split to generate two technical replicates per source. The resulting eight sperm samples (two per semen source) were subjected to iTRAQ-based 2D-LC-MS/MS for protein identification and quantification. A total of 1,723 proteins were identified (974 of Sus scrofa taxonomy) and 1,602 of them were also quantified (960 of Sus scrofa taxonomy). After an ANOVA test, 32 Sus scrofa proteins showed quantitative differences (p < 0.01) among semen sources, which was particularly relevant for sperm functionality in the post-SRF. The present study showed that the proteome of boar spermatozoa is remodeled during ejaculation involving proteins clearly implicated in sperm function. The findings provide valuable groundwork for further studies focused on identifying protein biomarkers of sperm fertility.

Is boar sperm freezability more intrinsically linked to spermatozoa than to the surrounding seminal plasma?

This study aimed to elucidate the effect of seminal plasma (SP) from post-SRF on boar sperm freezability and, in addition, to determine the relevance of sperm itself to sustain cryopreservation, regardless of the SP surrounding them. Twelve ejaculates from three boars were manually collected in fractions/portions, P1: the first 10 mL of the SRF, P2: the rest of the SRF and the post-SRF. Immediately, samples were centrifuged to separate spermatozoa from the surrounding SP. Spermatozoa from P1 and P2 were then incubated with its own SP or that from post-SRF, diluted in BTS (1:1, v/v) at 17 °C overnight before being frozen in 0.5 mL straws using a standard protocol. Sperm motility (total and progressive) deteriorated (P < 0.05) when P1- or P2-sperm when incubated overnight in SP from post-SRF, while sperm viability differed between P1 and P2 (P < 0.05) regardless of the SP they were incubated in. Post-thaw sperm quality and functionality differed between P1 and P2, regardless of the SP used for overnight pre-freezing incubation. Post-thaw motility (P < 0.05) and viability (P < 0.01), as well as plasma membrane fluidity (P < 0.05) or lipid peroxidation values (P < 0.01) were best in P1 sperm compared to those of P2. The protein profile of sperm from P1 and P2, analyzed by 2D-PAGE, showed qualitative differences, which suggest that sperm rather than SP would explain differences in sperm freezability between ejaculate fractions/portions. Use of P1 fraction spermatozoa seems thus optimal for cryopreservation.

Seminal plasma antioxidants are directly involved in boar sperm cryotolerance

Boar ejaculates are ejected in fractions with a specific composition in terms of sperm numbers and seminal plasma (SP), which is reflected in the varying sperm cryotolerance observed among different fractions. As boar sperm are particularly sensitive to oxidative stress, this study evaluated the role of SP antioxidants in the observed differences in sperm cryotolerance among ejaculate fractions. Ten ejaculates from five boars were manually collected in fractions: the first 10 mL of the sperm-rich fraction (SRF), the rest of the SRF and the post-SRF. Semen samples comprising the entire ejaculate (EE) were created by proportionally mixing the three fractions described above. Each of the 40 resulting semen samples was split into two aliquots: one was used for sperm cryopreservation following a standard protocol utilizing 0.5-mL straws, and the other was used to collect SP for antioxidant assessment. Frozen-thawed (FT) sperm from the SRF (the first 10 mL of the SRF and the rest of the SRF) and those from post-SRF were of the highest and worst quality, respectively, which was measured in terms of total and objective progressive motility and viability (P < 0.01). Viable FT sperm from the post-SRF generated more reactive oxygen species and experienced more lipid peroxidation than those from the SRF (both the first 10 mL and the rest of the SRF) (P < 0.01). The percentage of FT sperm exhibiting fragmented nuclear DNA did not differ among ejaculate fractions and the EE. Catalase, glutathione peroxidase and glutathione peroxidase 5 (GPx-5) were lowest in SP from the first 10 mL of the SRF (P < 0.001), whereas superoxide dismutase (SOD) and paraoxonase 1 (PON-1) were highest in SP of the SRF (both the first 10 mL and the rest of the SRF) (P < 0.01). Trolox-equivalent antioxidant capacity (TEAC) and the ferric-reducing ability of plasma (FRAP) were highest in SP from the first 10 mL of the SRF and lowest in the post-SRF (P < 0.001), whereas cupric-reducing antioxidant capacity was lowest (P < 0.05) in SP from the first 10 mL of the SRF. Regression analyses indicated that certain SP antioxidants had good predictive value for post-thaw recovery rates of total motility (R² = 54.8%, P < 0.001; including SOD, TEAC and FRAP) and viability (R² = 56.1%, P < 0.001; including SOD, PON-1, GPx-5 and TEAC). These results demonstrated that certain SP antioxidants are positively involved in boar sperm cryotolerance, minimizing the oxidative stress imposed by cryogenic handling.

Profile and reproductive roles of seminal plasma melatonin of boar ejaculates used in artificial insemination programs

Melatonin (MLT) is present in seminal plasma (SP) of mammalian species, including pigs, and it is credited with antioxidant properties. This study aims to identify the sources of variation and the role of boar SP MLT on sperm quality and functionality and in vivo fertilizing ability of liquid-stored semen doses used in AI programs. The SP MLT was measured using an ELISA kit in a total of 219 ejaculates collected from 76 boars, and reproductive records of 5,318 AI sows were recorded. Sperm quality was assessed according to motility (computer-aided sperm analysis) and viability (cytometry evaluation). Sperm functionality was assessed according to the cytometric determination of intracellular HO generation, total and mitochondrial O production, and lipid peroxidation in liquid AI semen samples stored at 17°C over 144 h. The concentration of SP MLT differed among seasons ( < 0.01) and day length periods ( < 0.001) of the year, demonstrating that the ejaculates collected during the increasing day length period (9.80 ± 1.38 pg/mL, range: 2.75-21.94) had lower SP MLT concentrations than those collected during the decreasing day length period (16.32 ± 1.67 pg/mL, range: 5.02-35.61). The SP MLT also differed ( < 0.001) among boars, among ejaculates within boar, and among portions within the ejaculate, demonstrating that SP from the first 10 mL of sperm-rich ejaculate fraction (SRF) exhibited lower MLT concentrations than post-SRF. The SP MLT was negatively related ( < 0.001) to mitochondrial O production in viable sperm. The SP MLT did not differ among AI boars ( = 14) hierarchically grouped according to high and low fertility outcomes. In conclusion, SP MLT concentration in AI boars varies depending on the season of ejaculate collection and differs among boars, ejaculates within boar, and portions within ejaculate. The SP MLT may act at the mitochondrial level of sperm by reducing the generation of O. However, this antioxidant role of SP MLT was not reflected in sperm quality or in vivo fertility outcomes of AI semen doses.

Active paraoxonase 1 is synthesised throughout the internal boar genital organs

The paraoxonase type 1 (PON1) is an enzyme with antioxidant properties recently identified in the seminal plasma (SP) of several species, including the porcine. The aims of the present study were to (1) describe the immunohistochemical localisation of PON1 in the genital organs of fertile boars and (2) evaluate the relationship among PON1 activity and high-density lipoprotein cholesterol (HDL-C) concentration in fluids of the boar genital organs. Immunohistochemical analysis demonstrated that PON1 was present in testis (specifically in Leydig cells, blood vessels, spermatogonia and elongated spermatids), epididymis (specifically in the cytoplasm of the principal epithelial cells, luminal secretion and in the surrounding smooth muscle) and the lining epithelia of the accessory sexual glands (cytoplasmic location in the prostate and membranous in the seminal vesicle and bulbourethral glands). The Western blotting analysis confirmed the presence of PON1 in all boar genital organs, showing in all of them a band of 51 kDa and an extra band of 45 kDa only in seminal vesicles. PON1 showed higher activity levels in epididymal fluid than those in SP of the entire ejaculate or of specific ejaculate portions. A highly positive relationship between PON1 activity and HDL-C concentration was found in all genital fluids. In sum, all boar genital organs contributing to sperm-accompanying fluid/s were able to express PON1, whose activity in these genital fluids is highly dependent on the variable HDL-C concentration present.

Characterization of the porcine seminal plasma proteome comparing ejaculate portions

Full identification of boar seminal plasma (SP) proteins remains challenging. This study aims to provide an extensive proteomic analysis of boar SP and to generate an accessible database of boar SP-proteome. A SP-pool (33entire ejaculates/11 boars; 3ejaculates/boar) was analyzed to characterize the boar SP-proteome. Twenty ejaculates (5 boars, 4ejaculates/boar) collected in portions (P1: first 10mL of sperm rich ejaculate fraction (SRF), P2: rest of SRF and P3: post-SRF) were analyzed to evaluate differentially expressed SP-proteins among portions. SP-samples were analyzed using a combination of SEC, 1-D SDS PAGE and NanoLC-ESI-MS/MS followed by functional bioinformatics. The identified proteins were quantified from normalized LFQ intensity data. A total of 536 SP-proteins were identified, 409 of them in Sus scrofa taxonomy (374 validated with ≥99% confidence). Barely 20 of the identified SP-proteins were specifically implicated in reproductive processes, albeit other SP-proteins could be indirectly involved in functionality and fertility of boar spermatozoa. Thirty-four proteins (16 identified in S. scrofa taxonomy) were differentially expressed among ejaculate portions, 16 being over-expressed and 18 under-expressed in P1-P2 regarding to P3. This major proteome mapping of the boar SP provides a complex inventory of proteins with potential roles as sperm function- and fertility- biomarkers.

BIOLOGICAL SIGNIFICANCE

This proteomic study provides the major characterization of the boar SP-proteome with >250 proteins first reported. The boar SP-proteome is described so that a spectral library can be built for relative 'label free' protein quantification with SWATH approach. This proteomic profiling allows the creation of a publicly accessible database of the boar SP-proteome, as a first step for further understanding the role of SP-proteins in reproductive outcomes as well as for the identification of biomarkers for sperm quality and fertility.