DNA Fragmentation in Viable and Non-Viable Spermatozoa Discriminates Fertile and Subfertile Subjects with Similar Accuracy

An intracellular, non-oxidative factor activates in vitro chromatin fragmentation in pig sperm

BACKGROUND

In vitro incubation of epididymal and vas deferens sperm with Mn2+ induces Sperm Chromatin Fragmentation (SCF), a mechanism that causes double-stranded breaks in toroid-linker regions (TLRs). Whether this mechanism, thought to require the participation of topoisomerases and/or DNAses and thus far only described in epididymal mouse sperm, can be triggered in ejaculated sperm is yet to be elucidated. The current study aimed to determine if exposure of pig ejaculated sperm to divalent ions (Mn2+ and Mg2+) activates SCF, and whether this has any impact on sperm function and survival. For this purpose, sperm DNA integrity was evaluated through the Comet assay and Pulsed Field Gel Electrophoresis (PFGE); sperm motility and agglutination were assessed with computer assisted sperm analysis (CASA); and sperm viability and levels of total reactive oxygen species (ROS) and superoxides were determined through flow cytometry.

RESULTS

Incubation with Mn2+/Ca2+ activated SCF in a dose-dependent (P < 0.05) albeit not time-dependent manner (P > 0.05); in contrast, Mg2+/Ca2+ only triggered SCF at high concentrations (50 mM). The PFGE revealed that, when activated by Mn2+/Ca2+ or Mg2+/Ca2+, SCF generated DNA fragments of 33-194 Kb, compatible with the size of one or multiple toroids. Besides, Mn2+/Ca2+ affected sperm motility in a dose-dependent manner (P < 0.05), whereas Mg2+/Ca2+ only impaired this variable at high concentrations (P < 0.05). While this effect on motility was concomitant with an increase of agglutination, neither viability nor ROS levels were affected by Mn2+/Ca2+ or Mg2+/Ca2+ treatments.

CONCLUSION

Mn2+/Ca2+ and Mn2+/Ca2+ were observed to induce SCF in ejaculated sperm, resulting in DNA cleavage at TLRs. The activation of this mechanism by an intracellular, non-oxidative factor sheds light on the events taking place during sperm cell death.

Altered DNA methylation in estrogen-responsive repetitive sequences of spermatozoa of infertile men with shortened anogenital distance

BACKGROUND

It has been suggested that antenatal exposure to environmental endocrine disruptors is responsible for adverse trends in male reproductive health, including male infertility, impaired semen quality, cryptorchidism and testicular cancer, a condition known as testicular dysgenesis syndrome. Anogenital distance (AGD) is an anthropomorphic measure of antenatal exposure to endocrine disruptors, with higher exposure levels leading to shortened AGD. We hypothesized that exposure to endocrine disruptors could lead to changes in DNA methylation during early embryonic development, which could then persist in the sperm of infertile men with shortened AGD.

RESULTS

Using fluorescence activated cell sorting based on staining with either YO-PRO-1 (YOPRO) or chromomycin-3 (CMA3), we isolated four sperm fractions from eleven infertile men with short AGD and ten healthy semen donors. We examined DNA methylation in these sorted spermatozoa using reduced representation bisulfite sequencing. We found that fractions of spermatozoa from infertile men stained with CMA3 or YOPRO were more likely to contain transposable elements harboring an estrogen receptor response element (ERE). Abnormal sperm (as judged by high CMA3 or YOPRO staining) from infertile men shows substantial hypomethylation in estrogenic Alu sequences. Conversely, normal sperm fractions (as judged by low CMA3 or YO-PRO-1 staining) of either healthy donors or infertile patients were more likely to contain hypermethylated Alu sequences with ERE.

CONCLUSIONS

Shortened AGD, as related to previous exposure to endocrine disruptors, and male infertility are accompanied by increased presence of hormonal response elements in the differentially methylated regulatory sequences of the genome of sperm fractions characterized by chromatin decondensation and apoptosis.

Testosterone Serum Levels Are Related to Sperm DNA Fragmentation Index Reduction after FSH Administration in Males with Idiopathic Infertility

Purpose: Although a robust physiological rationale supports follicle stimulating hormone (FSH) use in male idiopathic infertility, useful biomarkers to evaluate its efficacy are not available. Thus, the primary aim of the study was to evaluate if testosterone serum levels are related to sperm DNA fragmentation (sDF) index change after FSH administration. The secondary aim was to confirm sDF index validity as a biomarker of FSH administration effectiveness in male idiopathic infertility. Methods: A retrospective, post-hoc re-analysis was performed on prospectively collected raw data of clinical trials in which idiopathic infertile men were treated with FSH and both testosterone serum levels and sDF were reported. Results: Three trials were included, accounting for 251 patients. The comprehensive analysis confirmed FSH’s beneficial effect on spermatogenesis detected in each trial. Indeed, an overall significant sDF decrease (p < 0.001) of 20.2% of baseline value was detected. Although sDF resulted to be unrelated to testosterone serum levels at baseline, a significant correlation was highlighted after three months of FSH treatment (p = 0.002). Moreover, testosterone serum levels and patients’ age significantly correlated with sDF (p = 0.006). Dividing the cohort into responders/not responders to FSH treatment according to sDF change, the FSH effectiveness in terms of sDF improvement was related to testosterone and male age (p = 0.003). Conclusion: Exogenous FSH administration in male idiopathic infertility is efficient in reducing sDF basal levels by about 20%. In terms of sDF reduction, 59.2% of the patients treated were FSH-responders. After three months of FSH administration, a significant inverse correlation between sDF and testosterone was detected, suggesting an association between the FSH-administration-related sDF improvement and testosterone serum levels increase. These observations lead to the hypothesis that FSH may promote communications or interactions between Sertoli cells and Leydig cells.

Complete Chromatin Decondensation of Pig Sperm Is Required to Analyze Sperm DNA Breaks With the Comet Assay

Sperm quality is usually evaluated prior to artificial insemination in farm animals. In addition to conventional semen analysis, other biomarkers, such as mitochondrial activity, integrity and lipid disorder of plasma membrane, generation of reactive oxygen species (ROS) and sperm DNA integrity, have been found to be related to fertility rates in different species. While mounting evidence indicates that the Comet assay is a sensitive method for the detection of DNA breaks, complete sperm chromatin decondensation is required in order to properly analyze the presence of single- and double-strand DNA breaks. In this sense, a previous study showed that longer lysis treatment with proteinase K is needed to achieve complete chromatin decondensation. The current work sought to determine which specific lysis treatment leads to complete chromatin decondensation in pig sperm, as this is needed for the measurement of DNA damage in this species. With this purpose, incubation with a lysis solution containing proteinase K for 0, 30, and 180 min was added to the conventional protocol. The impact of the DNA damage induced by hydrogen peroxide (H₂O₂; 0.01 and 0.1%) and DNAse I (1U and 4U) was also evaluated. Complete chromatin decondensation was only achieved when a long additional lysis treatment (180 min) was included. Furthermore, olive tail moment (OTM) and percentage of tail DNA (TD) indicated that a higher amount of DNA breaks was detected when hydrogen peroxide and DNAse I treatments were applied (P < 0.05). The comparison of treated and control sperm allowed defining the thresholds for OTM; these thresholds revealed that the percentage of sperm with fragmented DNA determined by the alkaline Comet does not depend on chromatin decondensation (P > 0.05). In conclusion, complete chromatin decondensation prior to alkaline and neutral Comet assays is needed to analyze DNA breaks in pig sperm.

Simultaneous detection of sperm membrane integrity and DNA fragmentation by flow cytometry: A novel and rapid tool for sperm analysis

BACKGROUND

Sperm DNA integrity has become one of the most discussed and promising biomarkers for the assessment of male fertility. However, an easy-to-apply method capable of estimating DNA fragmentation in the live fraction of spermatozoa has remained elusive, preventing this parameter from being fully applied in clinical settings.

OBJECTIVES

To validate a novel co-staining for the analysis of DNA fragmentation in membrane-intact spermatozoa.

MATERIALS AND METHODS

Normozoospermic semen samples were used to validate the co-staining consisting of acridine orange (AO) and LIVE/DEAD™ Fixable Blue Dead Cell Stain (LD), against established methods for the evaluation of cell viability, propidium iodide stain (PI), and DNA fragmentation, the sperm chromatin structure assay (SCSA), to rule out cross-interference. Furthermore, the accuracy of the method was tested by the evaluation of samples prepared with different amounts of membrane and DNA damage (20, 40, 60, 80, and 100%).

RESULTS

No significant differences were observed between the co-staining and the established staining procedures (membrane integrity, p = 0.755; DNA fragmentation p = 0.976). Moreover, high R square values were obtained from the analysis of samples of known membrane (R²  = 0.9959) and DNA damage (R²  = 0.9843). The simultaneous assaying of sperm membrane integrity and nuclear DNA fragmentation allowed the analysis of four sperm categories and thereby to assess the proportion of membrane-intact spermatozoa with compromised DNA integrity.

DISCUSSION AND CONCLUSION

This new protocol has the potential to provide clinically relevant information about the DNA fragmentation in membrane-intact spermatozoa. Thus, it has the potential of improving the diagnostic of male infertility and enabling a better understanding of sperm dysfunction.