Alleviation of acrosome reaction prematurity by sperm treatment with egg yolk

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section I

Simple Summary

Male fertility is often estimated by simple sperm assessment, and therefore, it is crucial to establish species-specific baselines for normal sperm parameters. In this paper, sperm physiology, function, and common abnormalities in stallions will be reviewed.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of semen physiology as it applies to overall fertility. This segment of our two-section review will focus on normal sperm parameters, beginning with development and extending through the basic morphology of mature spermatozoa, as well as common issues with male factor infertility in IVP. Ultimately, the relevance of sperm parameters to overall male factor fertility in equine IVP will be assessed.

GIV/Girdin, a non-receptor modulator for Gαi/s, regulates spatiotemporal signaling during sperm capacitation and is required for male fertility

For a sperm to successfully fertilize an egg, it must first undergo capacitation in the female reproductive tract and later undergo acrosomal reaction (AR) upon encountering an egg surrounded by its vestment. How premature AR is avoided despite rapid surges in signaling cascades during capacitation remains unknown. Using a combination of conditional knockout (cKO) mice and cell-penetrating peptides, we show that GIV (CCDC88A), a guanine nucleotide-exchange modulator (GEM) for trimeric GTPases, is highly expressed in spermatocytes and is required for male fertility. GIV is rapidly phosphoregulated on key tyrosine and serine residues in human and murine spermatozoa. These phosphomodifications enable GIV-GEM to orchestrate two distinct compartmentalized signaling programs in the sperm tail and head; in the tail, GIV enhances PI3K→Akt signals, sperm motility and survival, whereas in the head it inhibits cAMP surge and premature AR. Furthermore, GIV transcripts are downregulated in the testis and semen of infertile men. These findings exemplify the spatiotemporally segregated signaling programs that support sperm capacitation and shed light on a hitherto unforeseen cause of infertility in men.

Src family kinases-mediated negative regulation of sperm acrosome reaction in chickens (Gallus gallus domesticus)

The acrosome reaction (AR) is a strictly-regulated, synchronous exocytosis that is required for sperm to penetrate ova. This all-or-nothing process occurs only once in the sperm lifecycle through a sequence of signaling pathways. Spontaneous, premature AR therefore compromises fertilization potential. Although protein kinase A (PKA) pathways play a central role in AR across species, the signaling network used for AR induction is poorly understood in birds. Mechanistic studies of mammalian sperm AR demonstrate that PKA activity is downstreamly regulated by Src family kinases (SFKs). Using SFK inhibitors, our study shows that in chicken sperm, SFKs play a role in the regulation of PKA activity and spontaneous AR without affecting motility. Furthermore, we examined the nature of SFK phosphorylation using PKA and protein tyrosine phosphatase inhibitors, which demonstrated that unlike in mammals, SFK phosphorylation in birds does not occur downstream of PKA and is primarily regulated by calcium-dependent tyrosine phosphatase activity. Functional characterization of SFKs in chicken sperm showed that SFK activation modulates the membrane potential and plays a role in inhibiting spontaneous AR. Employing biochemical isolation, we also found that membrane rafts are involved in the regulation of SFK phosphorylation. This study demonstrates a unique mechanism for regulating AR induction inherent to avian sperm that ensure fertilization potential despite prolonged storage.

Clinical importance of a micro-assay for the evaluation of sperm acrosome reaction using homologous zona pellucida

This study aimed to develop an acrosome reaction assay using microvolumes of solubilized human zonae pellucidae among 35 couples attending an in vitro fertilization programme. The sperm morphology of the men was classified as g-pattern (5-14% normal forms) and/or normal pattern (> 14% normal forms). All the couples had a history of repeated poor or failed in vitro fertilization rates from previous attempts. A zona-induced acrosome reaction test was performed using homologous 0.25 zona pellucida microl-1 incubated with spermatozoa to induce the acrosome reaction. Acrosome reactions were measured with FITC-PSA staining, and expressed as the difference between zona-induced and spontaneous acrosome reaction spermatozoa. The results indicated that microvolumes of solubilized human zona pellucida could successfully be used to determine the acrosome reaction status of spermatozoa. The results were compared with in vitro fertilization rates of metaphase II oocytes, and analysed with the receiver operating characteristics curve. Receiver operating characteristics analyses divided the patients into two groups: i.e. zona-induced acrosome reaction < 15% and > 15%. The sensitivity and specificity for zona-induced acrosome reaction results versus fertilization were 93% and 100%, respectively. The correlation coefficient between zona-induced acrosome reaction and in vitro fertilization was r = 0.94 (P < 0.0001). Zona-induced acrosome reaction data can be used as an indicator for fertilization failure, thus helping clinicians to refine the therapeutic approach for infertile couples prior to the onset of the treatment.

Evaluation of acrosomal status and sperm viability in fresh and cryopreserved specimens by the use of fluorescent peanut agglutinin lectin in conjunction with hypo-osmotic swelling test

OBJECTIVE

In this study, we evaluated whether the hypo-osmotic swelling test (HOST) can be used as a vital marker in combination with peanut agglutinin (PNA) - labeling in fresh and cryopreserved spermatozoa.

MATERIALS AND METHODS

Human sperm populations were exposed to a hypo-osmotic medium for 60 minutes, and then incubated in a 1 microg/mL solution of the fluorescent dye Hoescht 33258 (H33258) for 10 minutes. Excess stain was removed by washing in phosphate-buffered saline (PBS) solution, and the pellet was resuspended in 100 microL of culture medium. Twenty microliters of this solution were subsequently smeared on a microscope slide, and fixed in ice-cold methanol to permeabilize the sperm membranes. The fixed smears were finally incubated in a 40-microg/mL FITC-PNA solution for 20 minutes. Simultaneous assessment of acrosome and viability scores was done in a fluorescent microscope equipped with appropriate filters and phase contrast illumination. The same slide was examined for FITC-PNA labeling, tail swelling, and for Hoechst-33258 staining by interchanging the filters and phase contrast optics.

RESULTS

In fresh specimens, HOST was found to provide viability assessments comparable to those obtained using the H33258 method (r = 0.95). However, the results of HOST and H33258 were not correlated in cryopreserved specimens (r = 0.22). There was no alteration of PNA-labeling due to the HOST or H33258.

CONCLUSIONS

FITC-PNA labeling in conjunction with the visualization of the morphological change induced by exposure to hypo-osmotic solution provides a simple but effective method for establishing the state of acrosomal membrane and viability in fresh human spermatozoa, but this technique is not reliable for cryopreserved ones.

Association between freezing agent and acrosome damage of human spermatozoa from subnormal and normal semen

This experimental study compares the effects of human sperm preservation medium (HSPM) with TEST-yolk buffer (TYB) as cryoprotectants of human spermatozoa with respect to the integrity of the acrosome after the freeze-thawing procedure. Fifty-six semen samples were included in this study; 18 were subnormal (G1) and 38 were normal (G2) based on World Health Organization criteria, except for morphology, which was evaluated according to strict criteria. Each semen sample was divided into two parts: the first part was prepared for cryopreservation by the addition of HSPM (1:1) and the second by addition of TYB (1:1). Freezing was performed in liquid nitrogen vapour. Smears were made before freezing and after the thawing process for evaluation of acrosome integrity using fluorescent-lectin labelling. The mean percentage of spermatozoa with intact acrosomes in the subnormal group was 77.0 +/- 7.2% before freezing and decreased significantly (P < 0.001) after thawing: to 63.7 +/- 8.2% with the use of HSPM and 66.8 +/- 8.7% with the use of TYB. The corresponding values in the normal semen samples were 83.4 +/- 9.2%, 76.0 +/- 8.8% and 77.9 +/- 9.2%, respectively. It is obvious that the decrease in the mean percentage of spermatozoa with intact acrosome was significantly higher when using HSPM in comparison with TYB, not only for G1 (-14.9 +/- 1.9% versus -11.8 +/- 1.4%) but also for G2 samples (-13.8 +/- 1.5% versus -11.9 +/- 1.3%). In conclusion, TYB should be recommended for freeze-thawing of human spermatozoa as the first-choice cryoprotectant, for normal as well as subnormal semen samples, in order to protect the sperm acrosome from the deleterious effects of the freeze-thawing procedure.

Clinical importance of zona pellucida-induced acrosome reaction and its predictive value for IVF

The study aimed to establish zona pellucida induced acrosome reaction response (ZIAR) among 35 couples with normal and G-pattern sperm morphology and repeated poor fertilization results during assisted reproduction treatment. ZIAR tests were performed using 0.25 zona pellucida/microliter co-incubated with spermatozoa for 60 min. Acrosome reactions were measured with FITC-PSA staining, and expressed as the difference between stimulated and unstimulated (spontaneous) sperm populations. Results were compared with IVF rates of metaphase II oocytes. Interactive dot diagrams divided the patients into two groups, i.e. ZIAR <15% and ZIAR > 15%, with mean fertilization rates of 49 and 79% respectively. The sensitivity and specificity for ZIAR results versus fertilization were 93 and 100% respectively. The area under the curve was 99% and the 95% confidence interval did not include 0.5 which implies that the ZIAR test is able to predict fertilization failure among IVF patients. In conclusion, the ZIAR test has diagnostic potential since it can assist the clinician to identify couples that will benefit from intracytoplasmic sperm injection therapy.

Acrosome reaction: methods for detection and clinical significance

The present article reviews the methods for detection and the clinical significance of the acrosome reaction. The best method for the detection of the acrosome reaction is electron microscopy, but it is expensive and labour-intensive and therefore cannot be used routinely. The most widely used methods utilize optical microscopy where spermatozoa are stained for the visualization of their acrosomal status. Different dyes are used for this purpose as well as lectins and antibodies labelled with fluorescence. The acrosome reaction following ionophore challenge (ARIC) can separate spermatozoa that undergo spontaneous acrosome reaction from those that are induced, making the result of the inducible acrosome reaction more meaningful. Many different stimuli have been used for the induction of the acrosome reaction with different results. The ARIC test can provide information on the fertilizing capability of a sample. The ARIC test was also used to evaluate patients undergoing in vitro fertilization since a low percentage of induced acrosome reaction was found to be associated with lower rates of fertilization. The cut-off value that could be used to identify infertile patients is under debate. Therapeutic decisions can also be made on the basis of the value of the ARIC test.

The incidence of spontaneous acrosome reaction in homogeneous populations of hyperactivated human spermatozoa

The incidence of spontaneous acrosome reaction occurring in 1314 individually selected hyperactivated (HA) human spermatozoa was compared to that occurring in 8226 individually selected non-hyperactivated spermatozoa (non-HA) sampled over an incubation time course to allow for capacitation. Two-way analysis of variance showed a significant difference between HA and non-HA spermatozoa for the mean percent acrosome reacted (R), partially acrosome reacted (PR) and combined total (R+PR) (P < 0.001). One-way analysis showed that among the HA spermatozoa there were marked differences among the proportion showing R+PR at the various time points (P = 0.005). Using the same end point, there was no significant evidence of change with time for the non-HA spermatozoa. The overall data indicated that HA human spermatozoa have a greater propensity for spontaneous acrosomal loss than non-HA spermatozoa during incubation in synthetic culture media.

Effect of sperm preparation with TEST yolk buffer on sperm-binding capacity under hemizona assay conditions

The study was conducted to evaluate the diverse effect and clinical significance of TEST yolk buffer treatment on sperm samples of 128 infertile men. Sperm samples were incubated with TEST yolk buffer and control medium (Ham's F-10) at room temperature for 2 h. The hemizona indices (mean +/- SE) of the TEST yolk buffer and medium-treated sperm samples were 29 +/- 2.3% and 22 +/- 1.6%, respectively. Inspection of the individual response of each sperm sample to TEST yolk buffer revealed that 63 samples (49%) improved (double the interassay variation = 28%) their binding to zona pellucida, 36 (28%) remained unchanged, whereas the binding capacity of 29 samples (23%) decreased. Furthermore, TEST yolk buffer treatment of 24 samples (19%) resulted in an increased binding beyond the hemizona index threshold set up at 23%. This level was previously shown to be the cut-off point between fertile and infertile sperm samples. It was concluded that when applied to an unselected group of infertile men, TEST yolk buffer significantly increased sperm binding capacity to the zona pellucida. However, only 19% of the sperm samples showed improvement with clinical significance. The other sperm samples may have improved, remained unchanged or even deteriorated independently on basic sperm variables. Thus, the effect of TEST yolk buffer treatment on sperm binding should be tested prior to its clinical use to avoid possible damage to certain sperm samples.