Enhanced fertility after heat-induced hyperactivation

Thermotaxis of mammalian sperm

Sperm are guided through the female reproductive tract. A temperature difference of about 2 °C exists between the storage site and fertilization site of the mammalian oviduct, leading to the hypothesis that sperm can sense and swim towards the oocyte along a rising temperature gradient, known as thermotaxis. Research over the past two decades has reported that sperm feature a sophisticated thermal detection system to detect and track ambient temperature gradients. More recently, thermotaxis is expected to be added to the microfluidic isolation method based on sperm tactic responses for sperm selection. In this paper, mammalian sperm thermotaxis is discussed, explaining the underlying behavioral mechanisms and molecular basis, according to the latest research. Finally, this paper explores the possible application of sperm thermotaxis in assisted reproductive technologies.

Evaluation of ubiquitination and sumoylation of acrosin inhibitor during in vitro capacitation of porcine sperm

The main objective of this study was to investigate the expression of acrosin inhibitor (AI), ubiquitin (Ub), and small ubiquitin-related modifier 1 (SUMO1) proteins during in vitro capacitation of pig sperm. Duroc pig sperm was divided into fresh sperm and capacitation treatment groups. Protein expression was evaluated using computer-assisted sperm analysis (CASA) systems, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), western blotting, and immunofluorescence. The results showed that the expression of AI (30 kDa) incapacitated sperm was significantly lower than that in fresh sperm (P < 0.05), and that the levels of ubiquitinated and SUMO1-ylated proteins in capacitated sperm were significantly higher than those in fresh sperm (P < 0.05). Immunofluorescence results showed that AI, Ub, and SUMO1 were located in the acrosome region of the fresh and capacitated sperm heads. After capacitation, the fluorescence intensity of AI and SUMO1 decreased, while that of Ub increased. The protein band at 30 kDa represented the AI-Ub-SUMO1 complex, indicating that this complex was involved in sperm capacitation. Furthermore, SUMO1 increased the stability of AI at 30 kDa, preventing its complete decomposition, while at 46 kDa, in the absence of SUMO1, AI is bound to ubiquitin, and was completely degraded.

Thermotaxis of human sperm cells in extraordinarily shallow temperature gradients over a wide range

On the basis of the finding that capacitated (ready to fertilize) rabbit and human spermatozoa swim towards warmer temperatures by directing their movement along a temperature gradient, sperm thermotaxis has been proposed to be one of the processes guiding these spermatozoa to the fertilization site. Although the molecular mechanism underlying sperm thermotaxis is gradually being revealed, basic questions related to this process are still open. Here, employing human spermatozoa, we addressed the questions of how wide the temperature range of thermotaxis is, whether this range includes an optimal temperature or whether spermatozoa generally prefer swimming towards warmer temperatures, whether or not they can sense and respond to descending temperature gradients, and what the minimal temperature gradient is to which they can thermotactically respond. We found that human spermatozoa can respond thermotactically within a wide temperature range (at least 29–41°C), that within this range they preferentially accumulate in warmer temperatures rather than at a single specific, preferred temperature, that they can respond to both ascending and descending temperature gradients, and that they can sense and thermotactically respond to temperature gradients as low as <0.014°C/mm. This temperature gradient is astonishingly low because it means that as a spermatozoon swims through its entire body length (46 µm) it can sense and respond to a temperature difference of <0.0006°C. The significance of this surprisingly high temperature sensitivity is discussed.

Control of hyperactivation in sperm

BACKGROUND

Sperm hyperactivation is critical to fertilization, because it is required for penetration of the zona pellucida. Hyperactivation may also facilitate release of sperm from the oviductal storage reservoir and may propel sperm through mucus in the oviductal lumen and the matrix of the cumulus oophorus. Hyperactivation is characterized by high amplitude, asymmetrical flagellar bending.

METHODS

This is a review of the original literature on the mechanisms that regulate hyperactivation, including physiological factors and signaling pathways.

RESULTS

Computer-assisted semen analysis systems can be used to identify hyperactivated sperm by setting minimum thresholds for curvilinear velocity (VSL) and lateral head movement and a maximum threshold for path linearity. Hyperactivation is triggered by a rise in flagellar Ca(2+) resulting from influx primarily through plasma membrane CatSper channels and possibly also by release of Ca(2+) from a store in the redundant nuclear envelope. It requires increased pH and ATP production. The physiological signals that trigger the rise in Ca(2+) remain elusive, but there is evidence that the increased Ca(2+) acts through a calmodulin/calmodulin kinase pathway. Hyperactivation is considered part of the capacitation process; however, the regulatory pathway that triggers hyperactivation can operate independently from that which prepares sperm to undergo the acrosome reaction. Hyperactivation may be modulated by chemotactic signals to turn sperm toward the oocyte.

CONCLUSIONS

Little is known about exactly what triggers hyperactivation in human sperm. This information could enable clinicians to develop reliable fertility assays to assess normal hyperactivation in human sperm samples.

Compliance in the neck structures of the guinea pig spermatozoon, as indicated by rapid freezing and electron microscopy

Electron microscopy has been used to investigate whether the transversely striated columns of the connecting piece in the neck region of guinea pig spermatozoa, undergo lengthening and shortening as a result of the forces generated during motility. Motile spermatozoa were subjected to near-instantaneous rapid freezing, followed by freeze-substitution fixation and epoxy embedment. Thin sections passing longitudinally through the striated columns revealed that the periodicity was indeed variable. The repeat period, taken to have an unstressed width of 60 nm, could be found extended to 75 nm in some specimens, and reduced to 54 nm in others. The estimates of the coefficients of variation were 6.6% for the width of the 'dense' band and 33.5% for the 'pale' band. The 'pale' band in the extended state showed longitudinal striae. Such variations in length, which - it is suggested - are physiological, and passively induced, would have functional implications for the flagellum - for both bend initiation and bend growth. Also, hypothetically, any mechanism that could increase the degree of compliance in these columns, such as perhaps phosphorylation of the constituent proteins, could permit the flagellum to develop the exaggerated bend angles and asymmetries of the 'hyperactivated' state.

Effect of heat-induced hypermotility on pregnancy rate in intrauterine insemination for male factor infertility associated with asthenospermia: a prospective, randomized, controlled study

OBJECTIVE

To assess the effect of mild heat for the enhancement of sperm fertilizing capacity in intrauterine insemination for male factor infertility associated with asthenospermia.

MATERIAL AND METHOD

Prospective, controlled, clinical study. Male factor infertility associated with asthenozoospermia was the criteria for inclusion. Ninety-seven couples were randomized to the study group while 100 couples were randomized to serve as the control group. Semen samples from the study group were processed with Percoll gradient and were left for incubation at 40 degrees C for 2 h. Semen samples from the control group were processed with Percoll gradient method and were incubated at 37 degrees C. Main outcome measure was the pregnancy rate.

RESULTS

The mean concentration of total motile sperm (TMS) in the study group was 11.20 +/- 4.22 x 10(6) (range 7-18) after wash with Percoll while was increased to 62.41 +/- 12.49 x 10(6) (range 44-71) after heat treatment. The mean concentration of TMS in the control group was 13.90 +/- 5.66 x 10(6) (range 8-19) after wash with Percoll while was increased to 17.73 +/- 3.67 x 10(6) (range 14-22) after incubation at 37 degrees C. The difference in TMS concentrations between the study and the control group after incubation at different temperatures was statistically significant (p < 0.005). There were 24 pregnancies in the study group, providing a pregnancy rate of 24.7%. In the control group eight pregnancies were achieved (8%) (p = 0.001).

CONCLUSION

Mild heat was found remarkably effective in asthenozoospermic males for increasing the concentration of inseminated total motile sperm and the pregnancy rate correspondingly.

Moving to the beat: a review of mammalian sperm motility regulation

Because it is generally accepted that a high percentage of poorly motile or immotile sperm will adversely affect male fertility, analysis of sperm motility is a central part of the evaluation of male fertility. In spite of its importance to fertility, poor sperm motility remains only a description of a pathology whose underlying cause is typically poorly understood. The present review is designed to bring the clinician up to date with the most current understanding of the mechanisms that regulate sperm motility and to raise questions about how aberrations in these mechanisms could be the underlying causes of this pathology.

[Sperm hyperactivated motility: influence of the capacitation medium]

OBJECTIVE

Hyperactivation-associated motility is an important marker of capacitation and a prerequisite to fertilization. Computer-Assisted Sperm Analysis (CASA) is a reproducible method that can be used to predict fertilization success, in addition to the migration and survival test. However, published data are contradictory and preparation methods are heterogeneous. Changing one element in the sperm preparation (capacitation medium) may alter its kinetic parameter values.

MATERIAL AND METHOD

This prospective study with two paired series was performed on sperm considered as normal. The sperm preparation was identical up to the second centrifugation, and there after the centrifugate was divided into two groups and suspended either in the capacitating medium Upgraded B2 INRA Medium(R), or in Ferticult Flushing Medium. Measurements were carried out with a Hamilton Thorne Research Analyzer (IVOS v10.9i).

RESULTS

The analysis of the 87 sperm samples included in the study showed differences between the averages of Straight Line Velocity (SLV, p=0.02), Curvilinear Velocity (CLV, p<0.0001), Amplitude of Lateral Head Displacement (ALH, p<0.0001), and algorithmic calculation of the examined hyperactivation (Hyper 5, p<0.0001).

CONCLUSION

The diagnostic validity of hyperactivation motility cannot be dissociated from the preparation conditions. A standardised preparation is a prerequisite for scientific evaluation and validation of this technique. Although higher motility characteristics seem to be desirable in a therapeutic environment, results will have to be validated by clinical tests.

Modified isocratic capillary electrophoresis detection of cell-free DNA in semen

PURPOSE

The objectives were: i) to analyze semen for the presence of cell-free DNA and ii) to determine the association between sperm parameters and cell-free DNA.

METHODS

Cell-free DNA in semen (N = 25 cases) were detected using the modified capillary gel electrophoresis (CE) procedure. SYBR-Gold was used to stain high (12 Kb) and low (1 Kb) molecular weight DNA fragments and the images analyzed.

RESULTS

The quantity of low-molecular weight cell-free DNA was positively correlated to rapid progression, curvilinear velocity (>40 microm/s), normal strict morphology and capacitation index. High-molecular weight cell-free DNA intensity index was negatively correlated to post-wash hyperactivation. Sperm concentration was not related to cell-free DNA quantity. The sperm freezing process did not increase cell-free DNA but reduced the more labile low-molecular weight cell-free DNA.

CONCLUSIONS

Cell-free DNA present in semen was correlated to important sperm parameters linked to normal sperm function. The data suggested the possible use of cell-free DNA as a marker of semen quality. This study reports on the novel finding of cell-free DNA released along with sperm during each ejaculation.

Hyperactivated motility in sperm

Hyperactivation is a movement pattern seen in sperm at the site and time of fertilization in mammals. It may be critical to the success of fertilization, because it enhances the ability of sperm to detach from the wall of the oviduct, to move around in the labyrinthine lumen of the oviduct, to penetrate mucous substances and, finally, to penetrate the zona pellucida of the oocyte. The movement of hyperactivated sperm appears different under different physical conditions and in different species, but basically it involves an increase in flagellar bend amplitude and, usually, beat asymmetry. Presumably, a signal or signals exist in the oviduct to initiate hyperactivation at the appropriate time; however, none has yet been identified with certainty. While the signal transduction cascade regulating hyperactivation remains to be completely described, it is clear that calcium ions interact with the axoneme of the flagellum to switch on hyperactivation. Although hyperactivation often occurs during the process of capacitation, the two events are regulated by somewhat different pathways.

A simple DNA disc chip in a microarray design based on modified comparative genomic hybridization for sperm DNA analysis

OBJECTIVE

A DNA disc chip assay, based on comparative genomic hybridization, was designed to measure changes in sperm DNA intensities. The objective was to analyze the DNA integrity of hyperactive sperm cells after mild heat treatment.

DESIGN

The assay based on a multiple cell comet assay was used to analyze changes in genomic DNA. Washed sperm DNA were tested on the assay and images stored in a microarray design.

SETTING

Clinical and academic research environment.

PATIENT(S)

Frozen-thawed washed sperm from different donors (n = 7).

INTERVENTION(S)

Discarded sperm leftover from trial washes carried out at 37 degrees and 40 degrees C were frozen and processed for the DNA disc chip assay.

MAIN OUTCOME MEASURE(S)

Fluorescent intensities of DNA disc chips and sperm variables.

RESULT(S)

Heat treatment resulted in more than eightfold increase in sperm hyperactive motility with little degradation in DNA integrity. Sperm with low hyperactivation was associated with alterations in DNA after heat treatment.

CONCLUSION(S)

The DNA disc chip assay was simple, inexpensive, and permitted assisted reproduction technologies laboratories to use comparative genomic hybridization for cytogenotoxicity testing. However, the assay required manual processing, a fluorescent microscope, and computer. The data showed an association between sperm hyperactivation and DNA integrity suggesting that the hyperactivation marker may be used for selecting quality sperm for intracytoplasmic sperm injection. More studies are needed to examine temperature effects on ejaculated human sperm.

Computer assisted semen analyzers in andrology research and veterinary practice

The evaluation of sperm cell motility and morphology is an essential parameter in the examination of sperm quality and in the establishment of correlations between sperm quality and fertility. Computer-assisted sperm analysis (CASA) allows an objective assessment of different cell characteristics: motion, velocity, and morphology. The development and problems related to this technology are raised in this review, paying particular attention to the biases and standardization requirements absolutely needed to obtain useful results. Although some interesting results, mainly in humans, have already been obtained, many questions remain, which have to be answered to allow for further development of this technology in veterinary medicine, clinical fertility settings, physiological, and toxicology research activities. The main problem is related to the standardization and optimization of the equipment and procedures. The different CASA instruments have all demonstrated high levels of precision and reliability using different sperm classification methodology. Their availability gives us a great tool to objectively compare sperm motility and morphology and to improve our knowledge and ability to manipulate spermatozoa.

A comparison of heat-induced hyperactivation in patients' sperm after colloid or pentoxifylline wash methods

OBJECTIVE

Our purpose was to compare kinematic parameters of human sperm after processing through two different wash methods and 40 degrees C heat treatment.

STUDY DESIGN

Sperm specimens (N = 169 cases) were washed by either colloid or pentoxifylline wash methods, and the motility parameters were measured at either 37 degrees C or 40 degrees C at baseline (0 hours) and after 4 hours. Five randomly selected washed specimens with matching 37 degrees C (control) or 40 degrees C heat treatments were assessed for changes in a sentinel gene.

RESULTS

The percentage of sperm hyperactive motility was >5 times higher after the 40 degrees C heat treatment, in comparison with the 37 degrees C treatment, for both the colloid- and the pentoxifylline-washed sperm. The percentages of total motility and progression were equally enhanced in heated sperm for the two wash methods. No changes were detected in the sentinel gene with the heat treatment.

CONCLUSION

Sperm cells mildly heated at 40 degrees C responded with greater motility, progression, and hyperactivation. The data suggest that mild heat is a stimulus for sperm function because greater sperm hyperactivation is associated with increased sperm fertilizing capacity. The absence of change in the sentinel gene in heated sperm suggests that a temperature of 40 degrees C is too low to initiate alterations in the highly condensed sperm chromatin. More studies are needed before mild heating of ejaculated sperm becomes acceptable for use in assisted reproductive technologies.