Spermatozoa and seminal plasma small extracellular vesicles miRNAs as biomarkers of boar semen cryotolerance

Recent advances in cryotolerance biomarkers for semen preservation in frozen form-A systematic review

Spermatozoa cryopreservation has been practiced for decades and is a very useful technique for long-term preservation of sperm fertility. The capability for semen cryopreservation varies across species, seasons, latitudes, and even for different ejaculates from the same animal. This article summarizes research results on sperm cryotolerance biomarkers in several species, focusing on three areas: spermatozoa cryotolerance biomarkers, seminal plasma proteins cryotolerance biomarkers, and other cryotolerance biomarkers. We discovered that sperm cryoresistance biomarkers are primarily related to sperm plasma membrane stability, the presence of antioxidant substances in sperm or seminal plasma, sperm cell energy metabolism, water and small molecule transport channels in the sperm plasma membrane, and antistress substances in sperm or seminal plasma. The research conducted using diverse livestock models can be employed to enhance the basic and applied reproduction of other mammals through the study of sperm cryotolerance biomarkers, as well as the substantial similarities between livestock and other organisms, including endangered species.

Effects of Slow Freezing and Vitrification of Human Semen on Post-Thaw Semen Quality and miRNA Expression

Semen cryopreservation has played an important role in medically assisted reproduction for decades. In addition to preserving male fertility, it is sometimes used for overcoming logistical issues. Despite its proven clinical usability and safety, there is a lack of knowledge of how it affects spermatozoa at the molecular level, especially in terms of non-coding RNAs. Therefore, we conducted this study, where we compared slow freezing and vitrification of good- and poor-quality human semen samples by analyzing conventional sperm quality parameters, performing functional tests and analyzing the expression of miRNAs. The results revealed that cryopreservation of normozoospermic samples does not alter the maturity of spermatozoa (protamine staining, hyaluronan binding), although cryopreservation can increase sperm DNA fragmentation and lower motility. On a molecular level, we revealed that in both types of cryopreservation, miRNAs from spermatozoa are significantly overexpressed compared to those in the native semen of normozoospermic patients, but in oligozoospermic samples, this effect is observed only after vitrification. Moreover, we show that expression of selected miRNAs is mostly overexpressed in native oligozoospermic samples compared to normozoospermic samples. Conversely, when vitrified normozoospermic and oligozoospermic samples were compared, we determined that only miR-99b-5p was significantly overexpressed in oligozoospermic sperm samples, and when comparing slow freezing, only miR-15b-5p and miR-34b-3p were significantly under-expressed in oligozoospermic sperm samples. Therefore, our results imply that cryopreservation of normozoospermic sperm samples can modulate miRNA expression profiles in spermatozoa to become comparable to those in oligozoospermic samples.

MicroRNAs in Male Fertility

Around 50% of all occurrences of infertility are attributable to the male factor, which is a significant global public health concern. There are numerous circumstances that might interfere with spermatogenesis and cause the body to produce abnormal sperm. While evaluating sperm, the count, the speed at which they migrate, and their appearance are the three primary characteristics that are analyzed. MicroRNAs, also known as miRNAs, are present in all physiological fluids and tissues. They participate in both physiological and pathological processes. Researches have demonstrated that the expression of microRNA genes differs in infertile men. These genes regulate spermatogenesis at various stages and in several male reproductive cells. Hence, microRNAs have the potential to act as useful indicators in the diagnosis and treatment of male infertility and other diseases affecting male reproduction. Despite this, additional research is necessary to determine the precise miRNA regulation mechanisms.

Emerging role of extracellular vesicles in veterinary practice: novel opportunities and potential challenges

Extracellular vesicles are nanoscale vesicles that transport signals between cells, mediating both physiological and pathological processes. EVs facilitate conserved intercellular communication. By transferring bioactive molecules between cells, EVs coordinate systemic responses, regulating homeostasis, immunity, and disease progression. Given their biological importance and involvement in pathogenesis, EVs show promise as biomarkers for veterinary diagnosis, and candidates for vaccine production, and treatment agents. Additionally, different treatment or engineering methods could be used to boost the capability of extracellular vesicles. Despite the emerging veterinary interest, EV research has been predominantly human-based. Critical knowledge gaps remain regarding isolation protocols, cargo loading mechanisms, in vivo biodistribution, and species-specific functions. Standardized methods for veterinary EV characterization and validation are lacking. Regulatory uncertainties impede veterinary clinical translation. Advances in fundamental EV biology and technology are needed to propel the veterinary field forward. This review introduces EVs from a veterinary perspective by introducing the latest studies, highlighting their potential while analyzing challenges to motivate expanded veterinary investigation and translation.

The effects of boar seminal plasma extracellular vesicles on sperm fertility

Extracellular vesicles (EVs) are abundant in body fluid and are critical in cell interaction. Seminal plasma contains numerous EVs which affecting sperm function via transferring regulatory cargoes to the sperm. However, the mechanism of seminal plasma extracellular vesicles (SP-EVs) is still not clear. The present study aimed to isolate the boar SP-EVs and explore its potential function, then identify the key protein involved in SP-EVs and sperms interaction, and elucidate mechanism of SP-EVs protein on sperms. Here, we successfully isolated and concentrated boar SP-EVs, the SP-EVs showed a typical vesicle structure under transmission electron microscopy, most of their diameters range between 50 and 200 nm and express EVs biomarkers CD9 and CD63. We proved that SP-EVs could inhibit sperm acrosome reaction and in vitro fertility. Through a data-independent acquisition analysis of protein profiles of noncapacitated sperms, normal capacitated sperms and SP-EVs treated capacitated sperms, we identified that EZRIN was one of the active proteins that participated in SP-EVs and sperms interaction. Furthermore, we tested that the inhibition of EZRIN could promote boar sperm fertility, which is in consistence with the function of SP-EVs. The results may facilitate future research of SP-EVs on sperm function and male infertility.

Post-Thaw Storage Temperature Influenced Boar Sperm Quality and Lifespan through Apoptosis and Lipid Peroxidation

Cryopreservation deteriorates boar sperm quality and lifespan, which restricts the use of artificial insemination with frozen-thawed boar semen in field conditions. The objective of this study was to test the effects of post-thaw storage time and temperature on boar sperm survival. Semen ejaculates from five Landrace boars (one ejaculate per boar) were collected and frozen following a 0.5 mL-straw protocol. Straws from the five boars were thawed and diluted 1:1 (v:v) in BTS. The frozen-thawed semen samples were aliquoted into three parts and respectively stored at 5 °C, 17 °C, and 37 °C for up to 6 h. At 0.5, 2, and 6 h of storage, sperm motility, viability, mitochondrial membrane potential, and intracellular reactive oxygen species (ROS) levels and apoptotic changes were measured. Antioxidant and oxidant levels were tested in boar sperm (SPZ) and their surrounding environment (SN) at each timepoint. The results showed significant effects of post-thaw storage time and temperature and an impact on boar sperm quality (total and progressive motility, VCL, viability, acrosome integrity), early and late sperm apoptotic changes, and changes in MDA levels in SPZ and SN. Compared to storage at 5 °C and 37 °C, frozen-thawed semen samples stored at 17 °C displayed better sperm quality, less apoptotic levels, and lower levels of SPZ MDA and SN MDA. Notably, post-thaw storage at 17 °C extended boar sperm lifespan up to 6 h without obvious reduction in sperm quality. In conclusion, storage of frozen-thawed boar semen at 17 °C preserves sperm quality for up to 6 h, which facilitates the use of cryopreserved boar semen for field artificial insemination.

Effects of supplemental antioxidants on in vitro fertility measures for cryopreserved boar spermatozoa

This work aims to evaluate how supplementing a commercial freezing media with butylated hydroxytoluene (BHT), or reduced glutathione (GSH), or their combination affected in-vitro measures of boar sperm after cryopreservation. One ejaculate was collected from 30 high-fertility boars in a weekly collection rotation. Samples were diluted 1:1 in an extender and cooled before overnight shipping at 17 °C to the freezing lab. On arrival, samples were split into the treatments with the following additions before cryopreservation; 1) semen without additional antioxidants (Control), 2) semen with 1 mM BHT, 3) semen with 2 mM GSH, and 4) semen with 1 mM BHT+2 mM GSH. Semen was evaluated for motility kinetics at 30, 120, and 240 min after thawing. Flow cytometry assessments were performed at 60 min after thawing. At all-time points evaluated, total and progressive motility were greater (P ≤ 0.05) in semen cryopreserved with GSH than in Control. No (P > 0.05) differences between Control and other treatment groups were observed in viability, or acrosomal and mitochondrial membrane integrity; however, the proportion of capacitated spermatozoa were reduced (by -21.17%) in semen treated with BHT + GSH compared to Control (P ≤ 0.05). In contrast, there was a higher (P ≤ 0.05, +21.18%) superoxide anion production in the Control than in the BHT + GSH. For IVF, semen cryopreserved with both antioxidants (BHT + GSH) had a negative (P < 0.05) impact on fertilization rate (-54.11%) compared to Control. However, for the blastocysts rate, there were more (+22.75%) blastocysts (P ≤ 0.05) for BHT compared to Control. These results indicate that commercial media supplemented with GSH increased motility but impaired in vitro fertilization rate. On the other hand, media supplemented with BHT improved the in vitro fertilizing ability of the frozen-thawed sperm cells. Therefore, we suggest the supplementation with 1 mM of BHT in the formula of commercial freezing media used in the present experiment.

Extracellular vesicles-encapsulated microRNA in mammalian reproduction: A review

Extracellular vesicles (EVs) are nanoscale cell-derived lipid vesicles that participate in cell-cell communication by delivering cargo, including mRNAs, proteins and non-coding RNAs, to recipient cells. MicroRNA (miRNA), a non-coding RNA typically 22 nucleotides long, is crucial for nearly all developmental and pathophysiological processes in mammals by regulating recipient cells gene expression. Infertility is a worldwide health issue that affects 10-15% of couples during their reproductive years. Although assisted reproductive technology (ART) gives infertility couples hope, the failure of ART is mainly unknown. It is well accepted that EVs-encapsulated miRNAs have a role in different reproductive processes, implying that these EVs-encapsulated miRNAs could optimize ART, improve reproductive rate, and treat infertility. As a result, in this review, we describe the present understanding of EVs-encapsulated miRNAs in reproduction regulation.

Albumin (ALB) and protein disulfide isomerase family A member 4 (PDIA4) are novel markers to predict sperm freezability of Erhualian boar

The frozen semen of Erhualian pig can promote the continuous improvement of commercial pigs, but currently, frozen semen fails to satisfy the practical application requirement. Oxidative damage is one of the crucial factors affecting the quality of frozen semen; besides, there are individual differences in boar sperm freezability. Based on the previous analysis of the proteomic differences of Erhualian boar sperm with different freezability, two differentially abundant proteins (DAPs) in boar sperm, albumin (ALB) and protein disulfide isomerase family A member 4 (PDIA4), were selected as the research objects in the current study. It is assumed that redox-related proteins ALB and PDIA4 can be used as markers to predict Erhualian boar sperm freezability. We cryopreserved the semen of 14 Erhualian boars. According to the difference of frozen semen quality, boars with good and poor freezability ejaculates (GFE and PFE, n = 3) were selected respectively. The relative contents of ALB and PDIA4 in GFE and PFE were analyzed by Western blot, and the localization patterns of ALB and PDIA4 in pre-frozen and frozen-thawed sperm were detected by immunofluorescence. The results showed that the abundances of ALB and PDIA4 in GFE were significantly higher than PFE, and there was a significant correlation between the relative contents of ALB and PDIA4 and frozen-thawed sperm quality parameters. Additionally, the freezing process had no effect on the localization patterns of ALB and PDIA4 in spermatozoa. In conclusion, these results suggest that ALB and PDIA4 are related to boar sperm cryotolerance and may be used as novel freezability markers.

What is the relevance of seminal plasma from a functional and preservation perspective?

When preserving sperm in the liquid or cryopreserved state, seminal plasma (SP) components within ejaculates can alter fertilizing capacity of these gametes. Depending on the species or how semen is collected, volume and concentration of SP components varies considerably. The SP contains substances essential for maintenance of sperm viability and fertility; however, these components can be deleterious depending on quantity, or duration of time before there is removal of SP from sperm in semen processing. Substances that impair (e.g., BSP - bull; HSP-1 - stallion; Major seminal plasma protein PSPI - boar) or improve (e.g., spermadhesin PSP-I - boar) spermatozoa fertilizing capacity have been identified. Depending on individual males, species, and semen collection procedures, SP removal may be beneficial before preservation in the liquid or cryopreserved state. In some cases, SP that is removed can be added back to thawing extender with there being positive effects in thawed sperm and for sperm viability in the female reproductive tract. In this review article, there is a focus on different effects of SP in samples of cooled and cryopreserved semen from four domestic species (pigs, horses, cattle, and sheep) with there being emphasis on how SP modulates the function and morphology of sperm cells before, during, and after preservation in the refrigerated or cryopreserved state. The present review is part of the Festschrift in honor of Dr. Duane Garner who made major contributions to the area of focus in this manuscript as evidenced by the many times his research is cited in this manuscript.

Canine Spermatozoa—Predictability of Cryotolerance

Simple Summary

Semen freezing in dogs is a field of growing interest. The international shipment of cryoconserved semen contributes to the avoidance of long travels and long-term storage of valuable gametes. However, the collection of one semen portion on average results in one to three doses for artificial insemination, which is a poor result in comparison to the outcome in large animals. The costs for the owners are therefore rather high. In individual dogs, the semen quality of raw semen is good; however, it could be suboptimal after thawing. To avoid costly freezing of these low-quality ejaculates, markers of freezability are useful. An abundance of markers are available for large animals, but not for dogs. This review provides an overview on markers for freezability of canine semen.

Abstract

Markers of freezability allow the selection of ejaculates of good freezability. So far, most investigations were conducted in boars, bulls, rams and horses, with high economic interests triggering the efforts. The progress in dogs is comparably slow. A critical evaluation of the methods requires consideration of practicability, with most labs not even possessing a computer assisted sperm analyser (CASA); furthermore, small canine ejaculates mostly do not allow the use of large semen volumes. In dogs, modern markers of freezability no longer assess single membrane constituents or seminal plasma components but comprise tests of cell functionality and adaptability, energy metabolism, cluster analyses of kinetic and morphometric parameters, as well as DNA intactness. Identification of the most efficient combination of tests seems useful. At present, examination by CASA combined with cluster analysis of kinetic subgroups, JC-1 staining and COMET assay or staining with toluidine blue seem most appropriate; however, cell volumetry and other functional tests deserve better attention. A better understanding of spermatozoa energy metabolism might reveal new markers. This review focuses on the requirements and markers of freezability of canine semen, highlighting potential future candidates.

In vitro effects of two different commercial freezing and thawing extenders on boar sperm quality

This study was conducted to evaluate whether there were differences in viability of cryopreserved semen when using two different freezing (Minitube Cryoguard - F1 or Androstar® CryoPlus - F2) and thawing (Minitube Cryoguard Thawing solution - T1 or Androstar® Plus - T2) extenders. Ejaculates were collected, diluted (1:1), and cooled before shipping at 17 °C overnight. Samples were aliquoted in cryopreservation extender F1 or F2. Four straws from each treatment sample were thawed and diluted in T1 or T2, resulting in four treatments (F1-T1, F1-T2, F2-T1, and F2-T2). The sperm in diluted semen were evaluated for motility kinetics at 30, 180, and 360 min after thawing. The integrity assessments of the plasma and acrosomal membranes were performed at 30 and 360 min after thawing. There was no interaction between F × T × Time (P > 0.05), and no interaction between F × T (P > 0.05). The sperm progressive motility (PMOT) as time post-thawing increased was greater (P = 0.015) when dilutions occurred using F1 compared with F2 extender. Sperm thawed in T1 had a greater TMOT (P = 0.008) and PMOT (P = 0.033) at all times evaluated. The sperm plasma and acrosomal membrane integrity (AIMI) were greater (P = 0.009) when samples were preserved in F1 compared to F2 extender. The use of T2, as compared with T1 thawing extender, resulted in an enhanced integrity of the plasma and acrosomal membranes (P = 0.008). It is concluded different combinations of commercial freezing extenders and thawing solutions have effects on the quality of cryopreserved boar semen in vitro.