Influence of p53 zygosity on select sperm parameters of the mouse

p53 Protein Evaluation on Spermatozoa DNA in Fertile and Infertile Males

Introduction and Objectives:

Protein p53 role in the spermatogenesis is demonstrated, it guarantees both the appropriate quality and quantity of mature spermatozoa. In this observational study we evaluate the eventual correlation between “corrected” p53 concentration on human spermatozoa DNA and male fertility potential.

Materials and Methods:

Our work is based on an observational study made of 169 male in a period between March 2012 and February 2017. The entire study group is composed by 208 male partners aged between 26-38 years with ejaculate volume from 0.6 to 5.8 mL and heterogeneous seminal valuation: 86/208 (41,3%) normospermic; 19/208 (9,1%) mild oligospermic; 51/208 (24,5%) moderate oligospermic to; 52/208 (25,1%) with severe oligospermic. The “control” group A includes 39 male partners considered “fertile”, because we did the p53 “corrected” test on their spermatozoa after 28 ± 3,5 days from the positives of their partners pregnancy test (betaHCG> 400 m U/m L). The group B, subdivided in B1, B2 and B3, includes 169 male partners for a observational period of 60 months. This partners don't report previous conceptions, they aren't smokers, don't make use neither of alcohol nor drugs and don't present pathologic varicocele studied with ecoColorDoppler. They are all married or stable cohabitants from a period of 27-39 months and report to have frequent sex without protection with their partners. Determination of p53 procedure: To separate the spermatozoa from seminal fluid we utilized the Differex™ kit System and the DNA IQ™ kit (Promega). For the p53 test we used the direct DuoSet IC kit and quantitative (R&D System). The p53 values were corrected in respect to the spermatozoa concentration expressed in ng/millions of spermatozoa.

Results:

Group A (39 male) presents “correct” p53 values that vary from 0.35 to 3.20 ng/millions of spermatozoa and group B presents values that vary from 0.68 to 14.53. From group B (48 male) in the observational period we have recorded 21 pregnancies with initial “correct” p53 values that vary from a minimum of 0.84 to a maximum of 3.29. In the subgroup B1 we obtained 8 pregnancies from male partners with a “correct” p53 concentration included between 0.84 to 1.34. In the subgroup B2 we obtained 13 pregnancies from male partners with a “correct” p53 concentration included between 1.66 and 3.29. In the subgroup B3 (121 male) there weren't neither pregnancies nor miscarriages and “correct” p53 values were included between 3.58 and 14.53.

Conclusion:

The results show that the member of the group A with values of 'corrected' p53 between 0.35 and 3.20 were considered “Fertile”, although in the observational period 3 miscarriages happened for 3 partners. 36 partners on 39 (92,3%) had a p53 concentration inferior to 1.65, this value were considered as the extreme to identify this group. The member of the group B1 had “corrected” p53 concentration that were included in the group. In the group B2 were observe 13 pregnancies, so its member were considered “potentially fertile” In the group B3 (121 male) weren't observe neither pregnancies nor miscarriages, so its member were considered “potentially infertile”. If further studies confirm these data, we will consider the p53 test ELISA inspected in “correct” p53 as a new and accurate marker of the potential of male fertility.

An miR-200 Cluster on Chromosome 23 Regulates Sperm Motility in Zebrafish

Besides its well-documented roles in cell proliferation, apoptosis, and carcinogenesis, the function of the p53-microRNA axis has been recently revealed in the reproductive system. Recent studies indicated that miR-200 family members are dysregulated in nonobstructive azoospermia patients, whereas their functions remain poorly documented. The aim of this study was to investigate the function of the miR-200 family on zebrafish testis development and sperm activity. There was no substantial difference in testis morphology and histology between wild-type (WT) and knockout zebrafish with deletion of miR-200 cluster on chromosome 6 (chr6-miR-200-KO) or on chromosome 23 (chr23-miR-200-KO). Interestingly, compared with WT zebrafish, the chr6-miR-200-KO zebrafish had no difference on sperm motility, whereas chr23-miR-200-KO zebrafish showed significantly improved sperm motility. Consistently, ectopic expression of miR-429a, miR-200a, and miR-200b, which are located in the miR-200 cluster on chromosome 23, significantly reduced motility traits of sperm. Several sperm motility-related genes, such as amh, wt1a, and srd5a2b have been confirmed as direct targets of miR-200s on chr23. 17α-ethynylestradiol (EE2) exposure resulted in upregulated expression of p53 and miR-429a in testis and impairment of sperm motility. Strikingly, in p53 mutant zebrafish testis, the expression levels of miR-200s on chr23 were significantly reduced and accompanied by a stimulation of sperm motility. Moreover, the upregulation of miR-429a associated with EE2 treatment was abolished in testis with p53 mutation. And the impairment of sperm activity by EE2 treatment was also eliminated when p53 was mutated. Together, our results reveal that miR-200 cluster on chromosome 23 controls sperm motility in a p53-dependent manner.

Effects of boar variability on comet-detected sperm-DNA damage following cryopreservation

Assessment of sperm-DNA integrity is a crucial issue in male fertility. In the present study, parameters derived from the image analysis of comets after single-cell gel electrophoresis were used to analyse the types of DNA damage of frozen–thawed boar spermatozoa. Semen, frozen in a cryoprotectant-free extender or in cryoprotectant-based extenders, was analysed for DNA fragmentation and with the following comet tail measures: percentage DNA in comet tail, comet tail length and olive tail moment. The percentages of sperm DNA damage in the comet tails were classified as Type 0 (no DNA damage), Type I (very low DNA damage), Type II (light DNA damage), Type III (medium DNA damage) and Type IV (heavy DNA damage). Sperm motility characteristics and membrane integrity were assessed in the pre-freeze and frozen–thawed semen samples. Assessment of sperm DNA fragmentation and comet tail measures showed marked inter-boar variability following cryopreservation. However, consistent differences among the boars, with respect to cryo-induced sperm DNA damage, were detected by the comet tail length and olive tail moment. Besides Type IV, all types of DNA damage were detected in the cryoprotectant-based extenders. It was found that the frequency of Type II and Type III of DNA damage of frozen–thawed spermatozoa was significantly greater in the cryoprotectant-based and cryoprotectant-free extenders respectively. Deterioration in the quality of the sperm DNA integrity was concomitant with a marked decline in sperm motility characteristics, reduced plasma membrane integrity and higher lipid peroxidation and aspartate aminotransferase activity after cryopreservation. It can be suggested that the comet-assay parameters, coupled with routine laboratory tests, are useful to improve the sperm evaluations of post-thaw quality of semen from individual boars and would offer more comprehensive information for a better understanding of the degree of cryo-induced sperm-DNA damage.

Nutlin-3a decreases male fertility via UQCRC2

Ubiquinol-cytochrome-c reductase core protein 2 (UQCRC2) is a component of ubiquinol-cytochrome c reductase complex that is known to correlate with male fertility via spermatogenesis. Simultaneously, nutlin-3a is a small molecule antagonist of mouse double minute 2 repressor (MDM2), activate p53 and induce apoptosis responsible for spermatogenesis. To date, however there are no known effects of nutlin-3a on reproduction. Therefore, present study was designed to investigate the effect of nutlin-3a on male fertility via UQCRC2. In this in vitro trial with mice spermatozoa, we utilized CASA, CTC staining, ATP assay, western blotting, and IVF to measure the main study outcome. The short-term exposure of spermatozoa in nutlin-3a decreases sperm motion kinematics, intracellular ATP production, capacitation, the acrosome reaction, UQCRC2, and tyrosine phosphorylation (TYP) of sperm proteins in a dose-dependent manner. Notably, the decreased UQCRC2 and TYP were associated with reduced sperm kinematics, ATP production, and capacitation, which ultimately led to adverse effects on male fertility such as poor fertilization rates and embryo development. Thus, nutlin-3a may be considered as a potential male contraceptive agent due to its ability to decrease fertility secondary to changes in overall sperm physiology and embryonic development. However, the results of this preliminary study have to be confirmed by additional independent trial.

The effect of Trp53 gene-dosage and parent-of-origin of inheritance on mouse gamete and embryo function in vitro

The transformation-related protein 53 (TRP53) has a canonical role as the "guardian of the genome," serving to protect against the propagation of cells with genomic damage. Autocrine trophic signals act to block the accumulation of TRP53 in the normal preimplantation embryo. Culture of the early embryo at limiting dilutions in simple defined media limits autocrine signaling, resulting in the accumulation of TRP53. This TRP53 reduces the rate of development of embryos. In this study we show that deletion of the Trp53 gene improved development in vitro in a dose-dependent manner. Development to morphological blastocysts increased as the dose of Trp53 was reduced, and this was accompanied by a Trp53-dependent increase in the allocation of cells to the inner cell mass. The intermediate developmental response of heterozygous mice provides evidence for haploinsufficiency of this trait. This haploinsufficiency was evident irrespective of the parent-of-origin of the null allele; however, zygotes with paternal inheritance of the Trp53-null allele had better development in vitro than those with maternal inheritance. There was a beneficial effect of the Trp53-null allele on the number of oocytes released by Trp53(+/-) females, and heterozygous males produced higher fertilization rates than controls, although this was independent of the genotype of the fertilizing sperm. The study shows that ovulation induction or culture of embryos in limiting conditions creates conditions that favor the early development of embryos inheriting loss of Trp53 function. This occurs even in the heterozygous state, showing that the conditions provide a potential basis for accelerated accumulation of deleterious mutations within a population.

Semen quality parameters and embryo lethality in mice deficient for Trp53 protein

Trp53 is a protein which is able to control semen parameters in mice, but the extent of that control depends on the genetic background of the mouse strain. Males from C57BL/6Kw, 129/Sv, C57BL×129 -p53+/+ (wild type controls) and C57BL×129-p53-/- (mutants) strains were used in the study, and histology and light microscopy were applied to evaluate the influence of genetic background and Trp53 (p53) genotype on testes morphology and semen quality in male mice. We showed that sperm head morphology, maturity and tail membrane integrity were controlled only by the genetic background of C57BL/6Kw and 129/Sv males, while testes weight and sperm concentration depended on both the genetic background and p53 genotype. Cell accumulation in seminiferous tubules may be responsible for heavier testes of p53-deficient males. In addition, to examine the effect of sex and p53 genotype on embryo lethality, pairs of control (C57BL×129-p53+/+) and heterozygous (C57BL×129-p53+/-) mice were examined. Before day 7 post coitum (dpc), female and male embryos were equally resorbed in both crosses types. After 7 dpc, preferential female embryo lethality in the heterozygote pairs was responsible for the skewed sex ratio in their progeny. Also, mutant female and male newborns were underrepresented in the litters of the heterozygous breeding pairs.

Is p53 controlling spermatogenesis in male mice with the deletion on the Y chromosome?

The aim of the study was to evaluate the influence of the chromosome Y structure and Trp53 genotype on semen quality parameters. Mice with partial deletion of the Y chromosome (B10.BR-Ydel) have severely altered sperm head morphology when compared with males that possess the complete Y chromosome (B10.BR). Control males from B10.BR and B10.BR-Ydel mice, and mutant males from B10.BR-p53−/− and B10.BR-Ydel-p53−/− experimental groups were used. We assessed testis weight, sperm head abnormalities, viability of spermatozoa (eosin test), percentage of motile and immature sperm, and performed a hypo-osmotic test to detect abnormal tail membrane integrity. Sperm morphology and maturation were controlled by the genes within the deleted region of the Y chromosome. Testis weight was higher in the mutants than in the control males, possibly due to cell accumulation in Trp53-deficient males as the concentration of sperm was significantly increased in the mutants. An elevated percentage of abnormal sperm was noted in B10.BR-p53−/− and B10.BR-Ydel-p53−/− male mice. We suggest that, in Trp53-deficient mice, the sperm cells that escape apoptosis are the ones that have abnormal morphology. The only sperm quality parameter affected by the interplay between Trp53 and chromosome Y genes was sperm motility, which was elevated in B10.BR-p53−/− males, but remained unchanged in B10.BR-Ydel-p53−/− males.

Initial insights regarding the role of p53 in maintaining sperm DNA integrity following treatment of mice with ethylnitrosourea or cyclophosphamide

If p53 is essential to eliminate damaged spermatogenic cells, then mutagen exposure in the absence of p53 would increase sperm containing damaged DNA. p53 knockout (-/-, NULL) and wild-type (+/+, WT) mice (five/group) were exposed to ethylnitrosourea (ENU) or cyclophosphamide (CP). In phase I, mice were exposed by gavage to 0 or 60 mg/kg/day ENU or CP for four days and examined on test day (TD) 4, and in phase II, mice were exposed to 0, 6, 20, or 60 mg/kg/day ENU or CP for four days and evaluated on TD 36 when exposed spermatocytes matured. In phase I, mutagens were not directly cytotoxic to mature sperm. In phase II, WT mice were more sensitive to decreases in reproductive organ weights, whereas both genotypes had decreased sperm counts. Testicular histology revealed similar CP responses, but genotype-specific ENU responses (WT mice had depletion of elongating spermatids; NULL mice had late-stage spermatocyte/early stage spermatid loss). Ethylnitrosourea increased DNA strand breaks in WT mice. Thus, mice responded similarly to CP, suggesting a primarily p53-independent response, whereas the ENU response differed by zygosity, suggesting a role for p53. As DNA damage increased at higher ENU doses, compensatory repair pathways may operate in NULL mice.

Chromosome aberrations and telomere length modulation in bone marrow and spleen cells of melphalan-treated p53+/- mice

The p53 gene regulates cell cycle and apoptotic pathways after induction of DNA damage. Telomeres, capping chromosome ends, are involved in maintaining chromosome stability; alterations of their length have been related to increased levels of chromosomal aberrations. To study a possible interaction between chromosome aberrations, telomere dysfunction, and p53, we investigated via painting analysis the induction and persistence of chromosome aberrations in bone marrow and spleen cells of p53+/- (and wild type) mice exposed for 4, 13, or 26 weeks to 2 mg/kg melphalan (MLP), a chemotherapeutic agent with carcinogenic potential. In addition, telomere length was evaluated in bone marrow cells by quantitative fluorescence in situ hybridization (Q-FISH). Chromosome aberrations were significantly increased in both tissues after MLP treatment. The p53 genotype did not influence the response of spleen cells, whereas a slight but significant increase of the aberration frequency was measured in the bone marrow of p53+/- mice exposed to MLP for 13 weeks with respect to the level detected in the matched wild-type group. The main finding of our still preliminary results on telomere length modulation was again a difference between the two genotypes. In bone marrow cells of wild-type mice, MLP treatment was associated with telomere shortening, while in p53+/- mice telomere elongation was the prevalent response to MLP exposure. In agreement with previous literature data, our in vivo study suggests that even the lack of a single functional copy of the p53 gene might have an impact on the quantity and quality of chromosome alterations induced in cycling cells by a clastogenic exposure.

The comet assay in male reproductive toxicology

Due to our lifestyle and the environment we live in, we are constantly confronted with genotoxic or potentially genotoxic compounds. These toxins can cause DNA damage to our cells, leading to an increase in mutations. Sometimes such mutations could give rise to cancer in somatic cells. However, when germ cells are affected, then the damage could also have an effect on the next and successive generations. A rapid, sensitive and reliable method to detect DNA damage and assess the integrity of the genome within single cells is that of the comet or single-cell gel electrophoresis assay. The present communication gives an overview of the use of the comet assay utilising sperm or testicular cells in reproductive toxicology. This includes consideration of damage assessed by protocol modification, cryopreservation vs the use of fresh sperm, viability and statistics. It further focuses on in vivo and in vitro comet assay studies with sperm and a comparison of this assay with other assays measuring germ cell genotoxicity. As most of the de novo structural aberrations occur in sperm and spermatogenesis is functional from puberty to old age, whereas female germ cells are more complicated to obtain, the examination of male germ cells seems to be an easier and logical choice for research and testing in reproductive toxicology. In addition, the importance of such an assay for the paternal impact of genetic damage in offspring is undisputed. As there is a growing interest in the evaluation of genotoxins in male germ cells, the comet assay allows in vitro and in vivo assessments of various environmental and lifestyle genotoxins to be reliably determined.

Deletion of genes implicated in protecting the integrity of male germ cells has differential effects on the incidence of DNA breaks and germ cell loss

BACKGROUND

Infertility affects approximately 20% of couples in Europe and in 50% of cases the problem lies with the male partner. The impact of damaged DNA originating in the male germ line on infertility is poorly understood but may increase miscarriage. Mouse models allow us to investigate how deficiencies in DNA repair/damage response pathways impact on formation and function of male germ cells. We have investigated mice with deletions of ERCC1 (excision repair cross-complementing gene 1), MSH2 (MutS homolog 2, involved in mismatch repair pathway), and p53 (tumour suppressor gene implicated in elimination of germ cells with DNA damage).

PRINCIPAL FINDINGS

We demonstrate for the first time that depletion of ERCC1 or p53 from germ cells results in an increased incidence of unrepaired DNA breaks in pachytene spermatocytes and increased numbers of caspase-3 positive (apoptotic) germ cells. Sertoli cell-only tubules were detected in testes from mice lacking expression of ERCC1 or MSH2 but not p53. The number of sperm recovered from epididymes was significantly reduced in mice lacking testicular ERCC1 and 40% of sperm contained DNA breaks whereas the numbers of sperm were not different to controls in adult Msh2 -/- or p53 -/- mice nor did they have significantly compromised DNA.

CONCLUSIONS

These data have demonstrated that deletion of Ercc1, Msh2 and p53 can have differential but overlapping affects on germ cell function and sperm production. These findings increase our understanding of the ways in which gene mutations can have an impact on male fertility.

Effect of ATM heterozygosity on heritable DNA damage in mice following paternal F0 germline irradiation

The ataxia telangiectasia mutated (ATM) gene product maintains genome integrity and initiates cellular DNA repair pathways following exposures to genotoxic agents. ATM also plays a significant role in meiotic recombination during spermatogenesis. Fertilization with sperm carrying damaged DNA could lead to adverse effects in offspring including developmental defects or increased cancer susceptibility. Currently, there is little information regarding the effect of ATM heterozygosity on germline DNA repair and heritable effects of paternal germline-ionizing irradiation. We used neutral pH comet assays to evaluate spermatozoa 45 days after acute whole-body irradiation of male mice (0.1Gy, attenuated (137)Cs gamma rays) to determine the effect of ATM heterozygosity on delayed DNA damage effects of Type A/B spermatogonial irradiation. Using the neutral pH sperm comet assay, significant irradiation-related differences were found in comet tail length, percent tail DNA and tail extent moment, but there were no observed differences in effect between wild-type and ATM +/- mice. However, evaluation of spermatozoa from third generation descendants of irradiated male mice for heritable chromatin effects revealed significant differences in DNA electrophoretic mobility in the F(3) descendants that were based upon the irradiated F(0) sire's genotype. In this study, radiation-induced chromatin alterations to Type A/B spermatogonia, detected in mature sperm 45 days post-irradiation, led to chromatin effects in mature sperm three generations later. The early cellular response to and repair of DNA damage is critical and appears to be affected by ATM zygosity. Our results indicate that there is potential for heritable genetic or epigenetic changes following Type A/B spermatogonial irradiation and that ATM heterozygosity increases this effect.

Effect of p53 haploinsufficiency on melphalan-induced genotoxic effects in mouse bone marrow and peripheral blood

Mice heterozygous for a p53 null mutation develop tumours induced by genotoxic carcinogens with a shorter latency than wild type mice and have been proposed as an alternate animal model for carcinogenicity testing. Some literature data suggest that p53+/- mice might also be more sensitive to the short-term effects of genotoxic agents and manifest a haploinsufficiency phenotype that could contribute to the higher tumour susceptibility. We have compared the induction of micronuclei in bone marrow and blood of p53+/- and p53+/+ isogenic mice after treatment with a single or multiple doses of melphalan (MLP), a crosslinking genotoxic carcinogen. We have also characterized the mechanism of micronucleus induction with CREST staining of kinetochore proteins to distinguish between chromosome break- and chromosome loss-induced micronuclei. Significant increases of micronucleated bone marrow polychromatic erythrocytes and blood reticulocytes were induced under all MLP exposure conditions. The frequency of micronucleated blood erythrocytes increased linearly with duration of exposure. Micronuclei were essentially a consequence of chromosome break events. After a single MLP dose, a significant reduction of the frequency of polychromatic erythrocytes in bone marrow of p53+/+ animals suggested the induction of cytotoxicity/cell cycle delay. This effect was not observed in p53+/- mice. We believe this finding to provide some evidence of a haploinsufficiency phenotype in the modulation of cell cycle/apoptotic pathways mediated by the p53 protein. In bone marrow of wild type mice, an increased effect of multiple MLP doses was detected over that of a single administration, whereas, in p53+/- mice, no differential effect was found of different exposure durations. Possibly, the probability of micronucleus formation increased under chronic exposure because of increased cell division in response to peripheral anemia and a reduction of p53 protein level had a small effect on cell cycle modulation and on such indirect mechanism of micronucleus induction. However, pairwise comparisons between the frequencies of cells with micronuclei in wild type and p53+/- mice under all exposure conditions did not show statistically significant differences, suggesting that the observed effects of p53 haploinsufficiency were weak and temporary and a higher/faster induction of irreversible chromosome damage could not account for the increased susceptibility of p53+/- mice to MLP-induced tumours.

Effects of age on DNA double-strand breaks and apoptosis in human sperm

OBJECTIVE

This study was designed to explore the relationship between men's age and DNA damage and apoptosis in human spermatozoa.

DESIGN

Semen samples were collected from men between the ages of 20 and 57 years. Sperm DNA double-strand breaks were assessed using the neutral microgel electrophoresis (comet) assay, and apoptosis was estimated using the DNA diffusion assay.

SETTING

Academic medical center.

PATIENT(S)

Sixty-six men aged 20 to 57 years were recruited from infertility laboratory and general populations and consented to donate a semen sample. Recruitment was determined by time and day of analysis; the only exclusions were for azoospermia, prostatitis, or prior cancer therapy.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

DNA damage and apoptosis in human sperm.

RESULT(S)

Age correlated with an increasing percentage of sperm with highly damaged DNA (range: 0-83%) and tended to inversely correlate with percentage of apoptotic sperm (range: 0.3%-23%). For example, percentage of sperm with highly damaged DNA, comet extent, DNA break number, and other comet measures was statistically significantly higher in men aged 36-57 years than in those aged 20-35 years, but percentage apoptosis was statistically significantly lower in the older group. Semen analysis showed percentage motility to be significantly higher in younger age groups.

CONCLUSION(S)

This study clearly demonstrates an increase in sperm double-stranded DNA breaks with age. Our findings also suggest for the first time an age-related decrease in human sperm apoptosis. These novel findings may indicate deterioration of healthy sperm cell selection process with age.

Detection of DNA damage in response to cooling injury in equine spermatozoa using single-cell gel electrophoresis

Single-cell gel electrophoresis (SCGE), or comet assay, has the ability to detect damage at the single cell level and has not been reported for equine sperm. The ability to detect nuclear damage at the single cell level could aid in the advancement of protocols for optimal semen preservation. The goals of these experiments were to adapt this assay for use with equine sperm and to utilize the assay for determining the integrity of equine sperm DNA following treatments with storage at various decreased temperatures (-20 degrees C and 5 degrees C). Results from experiments in which sperm were frozen (-20 degrees C) in the absence of cryoprotectants revealed that significantly more cells with fragmented tails of DNA, or comets, occurred among those exposed to 1, 3, and 5 freeze-thaw cycles (65% +/- 6%, 76% +/- 11%, 92% +/- 6%, respectively) compared with fresh, untreated sperm (19% +/- 16%, P < .05). In addition DNA damage was different (P < .05) between the three freeze-thaw treatments. Sensitivity of SCGE on equine sperm was further tested with known ratios of frozen-thawed and fresh cells. The amount of detectable DNA damage was positively correlated with the percentage of cryo-damaged cells in each treatment (r2 = 0.92, P < .05). Potential damage as a result of cooled storage was also investigated and results revealed that sperm stored for 48 hours (at 5 degrees C) had a higher percentage of comets than that of fresh sperm (63% +/- 13.9% and 28% +/- 15.6%, respectively, P < .05). The percentage of viable sperm also decreased linearly over time and was inversely correlated with percent of comets (r2 = 0.805, P < .001). Detection of sublethal and/or uncompensable fertility factors in semen, such as DNA fragmentation, could be useful for detecting male differences in semen for cooling or cryopreservation potential and could provide a tool for monitoring and preserving fertility for individual stallions.