Deciphering sperm chromatin properties to predict stallion sperm fertility

Association between sperm DNA fragmentation and fertility parameters in farm animals: a systematic review and meta-analysis

BACKGROUND

Accurately predicting male fertility is crucial for the animal breeding industry due to its significant economic implications. Existing literature suggests that mammalian fertility is partially dependent on sperm DNA integrity. However, routine semen analysis often fails to detect DNA damage and does not consistently correlate with field fertility outcomes. While assessing sperm DNA integrity provides valuable biological insights, its role in diagnosing animal infertility remains uncertain.

RESULTS

This meta-analysis evaluated the association between sperm DNA fragmentation (SDF) and fertility in farm animals. Comprehensive searches were conducted using PubMed, Google Scholar, and Springer Link Library, with results stratified by animal species and SDF detection methods. Across 30 studies, the overall correlation coefficient (COR) between SDF and male fertility was -0.46 (95% confidence interval [CI]: -0.54 to -0.37; Z = -8.97; p < 0.001). A significant association was observed in bulls (COR = -0.47; 95% CI: -0.54 to -0.40; Z = -11.13; p < 0.001) and stallions (COR = -0.54; 95% CI: -0.72 to -0.29; Z = -3.83; p < 0.001), whereas no significant relationship was found in boars (COR = -0.19; 95% CI: -0.37 to 0.01; Z = -1.84; p = 0.07). The effect of SDF on male fertility was analyzed in 15 studies, demonstrating significantly higher SDF values in low-fertility animals compared to high-fertility groups (SMD = 0.85; 95% CI: 0.68 to 1.01; Z = 10.07; p < 0.001). This pattern was observed in both bulls (SMD = 1.21; 95% CI: 0.85 to 1.57; Z = 6.59; p < 0.001) and stallions (SMD = 0.64; 95% CI: 0.44 to 0.85; Z = 6.14; p < 0.001) subgroups.

CONCLUSIONS

These findings suggest that incorporating SDF assays into breeding soundness evaluations could enhance the accuracy of selecting high-quality breeding males for artificial breeding programs. However, further research with adequately powered studies, standardized methodologies, and appropriate sample sizes is necessary to fully elucidate the impact of elevated SDF on fertility in farm animals.

Cryopreservation-Induced Changes in Protamine Levels and DNA Fragmentation in Alpaca Spermatozoa

Cryopreservation is known to destabilise spermatozoa and is associated with deficiencies in protamine levels and increased DNA fragmentation, which can reduce fertility in various species. The objective of this study was to evaluate the impact of cryopreservation on protamine levels and DNA fragmentation in alpaca spermatozoa. A total of 108 testicles/epididymides were collected from a slaughterhouse and sperm were recovered from the cauda epididymis. Only samples meeting the criteria of > 10 g in weight, > 3 cm in length, > 30% motility, and > 50 million spermatozoa/mL were processed. Sixty samples (n = 60) were suitable for cryopreservation: 30 were used to assess protamine levels, and 30 to evaluate DNA fragmentation. Assessments were conducted both before and after cryopreservation using imaging flow cytometry. Protamine levels were assessed with chromomycin A3 (CMA3, 0.25 mg/mL), where fluorescence inversely correlates with protamination levels. The TUNEL assay was used to analyse DNA fragmentation, following fixation with 0.4% formaldehyde and permeabilisation with 0.8% Triton X-100. Results showed a significant decrease in CMA3 mean fluorescence after cryopreservation (288.19 ± 145.53 mFL vs. 68.54 ± 51.25 mFL, p < 0.05) and an increase in DNA fragmentation (2.98 ± 2.39 vs. 9.45 ± 15.43, p < 0.05). In conclusion, cryopreservation decreases CMA3 fluorescence, related to a possible increase in protamination, and increases DNA fragmentation in alpaca spermatozoa.

Niosomal nanocarriers loaded with artemisinin has potential to enhance the functional characteristics of cryo-preserved equine spermatozoa

Cryopreservation is a crucial method for the preservation of genetic materials. Nevertheless, this technique can have adverse effects due to cryo-oxidative damage. The primary objective of this study was to investigate the cryo-protective effects of niosomal nanocarriers loaded with artemisinin (NN-Art) on the functional attributes of equine spermatozoa. The parameters examined included sperm motility and kinematics through computer-assisted sperm analysis (CASA), plasma membrane integrity via the hypoosmotic swelling test, viability using the eosin-nigrosin staining technique, morphology with Hancock's solution, and lipid peroxidation through the thiobarbituric acid reactive substances assay. Additionally, flow cytometry was applied to assess mitochondrial membrane potential, reactive oxygen species (ROS) levels, sperm chromatin structure, and apoptotic-like changes. The CASA indicated a greater enhancement in the total and progressive motility and as well straight line velocity following the addition of NN-Art into the cryo-diluent medium compared with the conventional form of artemisinin and control (P < 0.05). Moreover, the incorporation of cryo-diluent medium with NN-Art demonstrated a greater efficiency in the improvement of viability, proportion of spermatozoa abnormality, plasma membrane functionality, and lipid peroxidation (P < 0.05). The flow cytometry assessment demonstrated a significant enhancement in mitochondrial potential activity, a reduction in the level of ROS, and an increase in the proportion of live spermatozoa along with a decrease in late apoptotic stallion post-thawed spermatozoa treated with both Art and specifically NN-Art. The results of this study suggest that NN-Art exhibit enhanced antioxidant capabilities, which are crucial for improving the functional quality of equine spermatozoa by mitigating cryo-oxidative stress.

A combination of biomarkers for predicting stallion sperm fertility

Equine breeding would benefit greatly from reliable biomarkers of stallion or ejaculate fertility. The aim of the study was to investigate how several in vitro sperm characteristics correlate with fertility after artificial insemination, to explore the potential to build a fertility prediction model for stallions. Cooled insemination doses (3-5 per stallion) were obtained from various studs. Sperm membrane integrity, acrosome integrity, chromatin integrity, mitochondrial membrane potential, and reactive oxygen species production were evaluated by flow cytometry 24-30 h after semen collection, and sperm motility was assessed by computer aided sperm analysis. Calcein violet was used to differentiate viable spermatozoa. Per season pregnancy rates for these stallions were available the following year. Positive correlations were found between pregnancy rate and straightness (r = 0.43, p ≤ 0.001), as well as pregnancy rate and the proportion of living hydrogen peroxide positive spermatozoa (r = 0.32, p ≤ 0.05). There were negative correlations between pregnancy rate and amplitude of lateral head displacement (r = -0.26, p ≤ 0.05), and between pregnancy rate and the mean fluorescence of dead superoxide positive spermatozoa (r = -0.46, p < 0.001). Principal component analysis indicated that motility, membrane integrity, DNA fragmentation, and reactive oxygen species production were associated with pregnancy rate. Therefore, a combination of these factors could be used as a biomarker of fertility when assessing ejaculates. However, data from more individuals would be required to construct a model for fertility prediction.

Comparative Study on the Sperm Proteomes of Horses and Donkeys

The reproductive performance of horse sperm and donkey sperm has been reported to differ. Sperm proteins play a crucial role in sperm viability and fertility. Although differences between species are known, no prior study has investigated disparities in the sperm proteome between horses and donkeys. Therefore, this study characterized and compared the sperm proteomes of horses and donkeys using 4D-DIA mass spectrometry technology. We identified 3436 proteins in horse sperm and 3404 proteins in donkey sperm. Of these, 3363 proteins were expressed in both horse and donkey sperm, with 73 proteins being specifically expressed in horse sperm, and 41 in donkey sperm. According to data analysis, donkeys exhibited a greater percentage of motility and progressive movement in straight-line sperm than horses, as well as lower percentages of static and slow sperm than horses. Joint analysis of the results from the horse and donkey sperm proteomes and their CEROS II-read parameters demonstrated a possible association between sperm proteins and their sperm viability patterns. These findings suggest that there are discrepancies in the expression levels and protein compositions of horse and donkey sperm and that certain specific proteins may be responsible for the differences in performance between these two species.

Effect of sperm treatment with lysolecithin on in vitro outcomes of equine intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) in horses is currently employed for clinical and commercial uses, but the protocol could be optimized to improve its efficiency. We have hypothesized that destabilization of plasma and acrosomal membranes prior to injection would positively impact the developmental potential of equine zygotes generated by ICSI. This study evaluated effects of the sperm treatment with lysolecithin on plasma and acrosomal membranes and on oocyte activation ability, initially following heterologous ICSI on bovine oocytes and subsequently employing equine oocytes. The effects of the lysolecithin -treatment on the efficiency of conventional and piezo-assisted equine ICSI were evaluated. To do this, the equine sperm were treated with different concentrations of lysolecithin and the sperm plasma membrane, acrosome and DNA integrity were evaluated by flow cytometry. The results showed that a lysolecithin concentration of 0.08 % destabilized the membranes of all sperm and affected DNA integrity within the range described for the species (8-30 %). In addition, the heterologous ICSI assay showed that lysolecithin treatment was detrimental to the sperm's ability to activate the oocyte, therefore, chemical oocyte activation was used after equine ICSI after injection with lysolecithin -treated sperm. This group showed similar developmental rate to the control group with and without exogenous activation. In conclusion, lysolecithin pre-treatment is not necessary when using ICSI to produce equine embryos in vitro. The results from the current study provide additional insight regarding the factors impacting ICSI in horses.

A critical review of the recent concept of regulatory performance of DNA Methylations, and DNA methyltransferase enzymes alongside the induction of immune microenvironment elements in recurrent pregnancy loss

Recurrent pregnancy Loss (RPL)is a frequent and upsetting condition. Besides the prevalent cause of RPL including chromosomal defects in the embryo,the effect of translational elements like alterations of epigenetics are of great importance. The emergence of epigenetics has offered a fresh outlook on the causes and treatment of RPL by focusing on the examination of DNA methylation. RPL may arise as a result of aberrant DNA methylation of imprinted genes, placenta-specific genes, immune-related genes, and sperm DNA, which may have a direct or indirect impact on embryo implantation, growth, and development. Moreover, the distinct immunological tolerogenic milieu established at the interface between the mother and fetus plays a crucial role in sustaining pregnancy. Given this, there has been a great deal of interest in the regulation of DNA methylation and alterations in the cellular components of the maternal-fetal immunological milieu. The research on DNA methylation's role in RPL incidence and the control of the mother-fetal immunological milieu is summed up in this review.