Effect of two intracellular calcium modulators on sperm motility and heparin-induced capacitation in cryopreserved bovine spermatozoa

Seminal trace elements and their relationship with sperm parameters

Male reproductive problems may derive from many reasons including the environmental toxicants which may either intaken by occupational exposure, nutrition or bad air quality. The increased exposure to these substances due to rapid industrial development and technology has raised the questions: Is there a relationship between sperm parameters and these substances, and if so, in what extent? Results of studies on the subject reported conflicting results, many of which were not investigated in the seminal plasma. The aim of the current study was to evaluate the relationship between 23 metals and trace elements in human seminal plasma and semen parameters many of which were not investigated before. Levels of 23 metals in human seminal plasma were assessed by inductively coupled plasma mass spectrometry (ICP-MS). We examined the differences between subjects with normal ejaculate (normozoospermia) and pathologic ejaculate (with at least one abnormal semen parameter) according to the WHO criteria. The only significant difference was detected for Se while the other element's difference was not statistically significant. Se was statistically significantly increased in normal semen group suggesting the positive effect of this element on semen parameters.

Increased mitochondrial activity upon CatSper channel activation is required for mouse sperm capacitation

To fertilize an oocyte, sperm must undergo several biochemical and functional changes known as capacitation. A key event in capacitation is calcium influx through the cation channel of sperm (CatSper). However, the molecular mechanisms of capacitation downstream of this calcium influx are not completely understood. Capacitation is also associated with an increase in mitochondrial oxygen consumption, and several lines of evidence indicate that regulated calcium entry into mitochondria increases the efficiency of oxidative respiration. Thus, we hypothesized that calcium influx through CatSper during capacitation increases mitochondrial calcium concentration and mitochondrial efficiency and thereby contributes to sperm hyperactivation and fertilization capacity. To test this hypothesis, we used high-resolution respirometry to measure mouse sperm mitochondrial activity. We also measured mitochondrial membrane potential, ATP/ADP exchange during capacitation, and mitochondrial calcium concentration in sperm from wild-type and CatSper knockout mice. We show that the increase in mitochondrial activity in capacitated wild-type sperm parallels the increase in mitochondrial calcium concentration. This effect is blunted in sperm from CatSper knockout mice. Importantly, these mechanisms are needed for optimal hyperactivation and fertilization in wild-type mice, as confirmed by using mitochondrial inhibitors. Thus, we describe a novel mechanism of sperm capacitation. This work contributes to our understanding of the role of mitochondria in sperm physiology and opens the possibility of new molecular targets for fertility treatments and male contraception.

Effects from disruption of mitochondrial electron transport chain function on bull sperm motility

Sperm mitochondrial function is essential for normal physiology and fertility, but the importance of mitochondrial activity to support specific sperm functions, such as motility, varies between species. It was previously believed that mitochondrial function was not necessary for bull sperm motility [1]; however, this theory is contradicted by recently reported findings that the upper fraction of bull sperm swim-up preparations had both high motility and elevated mitochondrial oxygen consumption rates [2]. The objective of this study was to investigate the relationship between mitochondrial function and motility in bull sperm. We hypothesized that sperm motility would be positively correlated with mitochondrial oxygen consumption (MITOX) but unaffected by pharmacological inhibition of electron transport chain (ETC) activity. This was accomplished by monitoring both mitochondrial oxygen consumption and motility parameters in the presence of mitochondrial effector drug treatments. Duplicate ejaculates were collected by electroejaculation from Black Angus bulls (n = 4). Oxygen consumption, as % air saturation (pO_2; oxygen partial pressure), over time was monitored in the presence of 5 drug treatments: vehicle control, FCCP, Antimycin (ANTI), Oligomycin (Oligo), and FCCP + Oligomycin (FCCP + OLIGO). Duplicate aliquots were prepared for concurrent motility assessment by computer-assisted sperm analysis (CASA) at 6 and 30 min post-treatment (t6 and t30). The impact of treatments on pO₂ (in % air saturation) over time were assessed by generalized linear mixed effects modeling (GLMM) which was also used to test for differences in average motility across treatment conditions and time points (t6 and t30). Pearson product-moment correlation was used to investigate relationships between oxygen consumption and motility parameters. Overall, pO₂ differed over time between treatment conditions (p < 0.0001). When compared to the vehicle treatment, ANTI and OLIGO significantly inhibited oxygen consumption (p < 0.05, adjusted), and FCCP stimulated a marked increase in oxygen consumption. No significant differences in motility over time were observed between treatments, so comparison of motility parameters between treatment conditions was performed with pooled timepoints. Motility parameters were only observed to differ significantly from the vehicle with ANTI Treatment, for which significant decreases in numerous parameters, including total motility (p = 0.007), progressive motility (p = 0.01), DAP (p = 0.01), VAP (p = 0.01) and VSL (p = 0.02) were identified. For the vehicle treatment, correlational analysis did not reveal any significant correlations between pO₂ and any motility parameters at t6; however, several significant correlations were identified at t30. Mean pO₂ was negatively correlated with local motility (p < 0.01) and positively correlated with DCL, DAP, and VCL (p < 0.05). Results from this study suggest that bovine sperm motility is impacted by mitochondrial functionality, with ETC inhibition by ANTI causing significant reduction in motility parameters. This study also demonstrates the use of a new technology for the assessment of bovine sperm mitochondrial function. This modality for evaluation of bull sperm mitochondrial function will inform future efforts to understand bull sperm function and fertility and aid investigations into toxicological agents.

cDNA cloning, expression and bioinformatical analysis of Tssk genes in tree shrews

Tree shrews are more closely related to primate animals than rodents in many aspects. In addition, they also possess several advantageous characteristics including small body size, high brain-to-body mass ratio, low cost of feeding and maintenance, short reproductive cycle and life span, which make them promising novel laboratory animals to replace more precious larger primate animals. Testis-specific serine/threonine kinase (Tssk) plays important roles in spermatogenesis and/or the regulation of sperm function. However, studies on Tssk in tree shrews have not been reported yet. In the present study, the full-length sequences of five members of the Tssk family in tree shrews were cloned and their CDS region sequences were analyzed by basic bioinformatics. The phylogenetic tree and prokaryotic protein expression system of Tssk gene of tree shrews were constructed. The mRNA expressions of Tssk genes in 11 tissues/organs from tree shrews were studied. The results showed that: 1. the length of the CDS region of tree shrew Tssk gene for Tssk1B, Tssk2, Tssk3 (variant X1 / X2), Tssk4 (variant X1 / X2) and Tssk6 is 1080bp, 1077bp, 867 / 807bp, 1014 / 984bp, 822bp, respectively, encoding 359, 358, 288/268, 337/327 and 273 amino acids, respectively; the cloned sequences of Tssk genes have been submitted to GenBank with the following accession numbers: KX091161(Tssk1B), KX091162(Tssk2), KX091163(Tssk3 variant X1)/KX091164(Tssk3 variant X2), KX091165(Tssk4variant X1)/KX091166(Tssk4variant X2), KX091160(Tssk6). 2. All tree shrew Tssk proteins distribute in cytoplasm, indicating that they are hydrophilic and non-secretory proteins, with multiple phosphorylation sites of serine and/or threonine. In addition, they are all mixed proteins with similar tertiary structures sharing a highly conserved functional domain of S_TKc (Serine/Threonine protein kinases, catalytic domain). 3.The molecular phylogenetic tree of five Tssk genes in tree shrews indicates that they are neither rodent nor primate animal, but are closely related to primate animals. 4. Five members of the Tssk recombinant proteins in tree shrews were successfully obtained using the constructed prokaryotic protein expression system. 5. Five Tssk genes are specifically expressed in the testis and/or sperm of tree shrews. Additionally, small amount of Tssk1B was expressed in several tissues other than testis and sperm. Limited mRNA levels of Tssk2 and Tssk4 were expressed in the brain, while mRNA of Tssk3 or Tssk6 could only be detected in the testis and sperm. This study will provide fundamental data on reproductive biology of tree shrews, which paves a way for further studying Tssk's biological function in this novel model animal.

Mitochondria: their role in spermatozoa and in male infertility

BACKGROUND

The best-known role of spermatozoa is to fertilize the oocyte and to transmit the paternal genome to offspring. These highly specialized cells have a unique structure consisting of all the elements absolutely necessary to each stage of fertilization and to embryonic development. Mature spermatozoa are made up of a head with the nucleus, a neck, and a flagellum that allows motility and that contains a midpiece with a mitochondrial helix. Mitochondria are central to cellular energy production but they also have various other functions. Although mitochondria are recognized as essential to spermatozoa, their exact pathophysiological role and their functioning are complex. Available literature relative to mitochondria in spermatozoa is dense and contradictory in some cases. Furthermore, mitochondria are only indirectly involved in cytoplasmic heredity as their DNA, the paternal mitochondrial DNA, is not transmitted to descendants.

OBJECTIVE AND RATIONAL

This review aims to summarize available literature on mitochondria in spermatozoa, and, in particular, that with respect to humans, with the perspective of better understanding the anomalies that could be implicated in male infertility.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews pertaining to human spermatozoa and mitochondria. Searches were performed using keywords belonging to three groups: 'mitochondria' or 'mitochondrial DNA', 'spermatozoa' or 'sperm' and 'reactive oxygen species' or 'calcium' or 'apoptosis' or signaling pathways'. These keywords were combined with other relevant search phrases. References from these articles were used to obtain additional articles.

OUTCOMES

Mitochondria are central to the metabolism of spermatozoa and they are implicated in energy production, redox equilibrium and calcium regulation, as well as apoptotic pathways, all of which are necessary for flagellar motility, capacitation, acrosome reaction and gametic fusion. In numerous cases, alterations in one of the aforementioned functions could be linked to a decline in sperm quality and/or infertility. The link between the mitochondrial genome and the quality of spermatozoa appears to be more complex. Although the quantity of mtDNA, and the existence of large-scale deletions therein, are inversely correlated to sperm quality, the effects of mutations seem to be heterogeneous and particularly related to their pathogenicity.

WIDER IMPLICATIONS

The importance of the role of mitochondria in reproduction, and particularly in gamete quality, has recently emerged following numerous publications. Better understanding of male infertility is of great interest in the current context where a significant decline in sperm quality has been observed.

Role of the Calcium-Sensing Receptor (CaSR) in bovine gametes and during in vitro fertilization

Calcium Sensing Receptor (CaSR) is a G-protein coupled receptor which senses extracellular calcium and activates diverse intracellular pathways. The objective of our work was to demonstrate the presence of CaSR in bovine gametes and its possible role in fertilization and embryo development. The location of CaSR was demonstrated by immunofluorescence in bovine gametes; additionally bovine sperm were incubated with 5, 10 and 15 μM of the specific CaSR inhibitor NPS2143 in a Tyrode's Albumin Lactate Pyruvate medium (4 h). Sperm viability was maintained for all concentrations tested while total motility decreased significantly at 10 and 15 μM. Addition of 15 μM of NPS2143 during oocyte in vitro maturation did not alter the maturation rate. When NPS2143 (15 μM) was added to the fertilization medium during sperm-oocyte co-incubation the cleavage, morula and blastocyst rates remained unchanged. To confirm if 15 μM of NPS2143 exerted any effect on embryo development, NPS2143 was added to the embryo culture medium. Cleavage rates remained unchanged when 15 μM of NPS2143 was added to the culture medium (79.1 ± 6.8 vs. 73.7 ± 5.3; mean % ± SEM; p > 0.05, control vs. inhibitor). By contrast, development to the morula (46.6 ± 7.3 vs. 24.3 ± 4.3; mean % ± SEM; p < 0.05) and blastocyst stages (29.9 ± 9.0 vs. 9.9 ± 3.6; mean % ± SEM; p < 0.05) decreased (control vs. inhibitor). Our results demonstrate a key role of CaSR on sperm motility and embryo development but not on oocyte maturation or fertilization in the bovine species.

Low physiological levels of prostaglandins E2 and F2α improve human sperm functions

Prostaglandins (PGs) have been reported to be present in the seminal fluid and cervical mucus, affecting different stages of sperm maturation from spermatogenesis to the acrosome reaction. This study assessed the effects of low physiological PGE2 and PGF2α concentrations on human sperm motility and on the ability of the spermatozoa to bind to the zona pellucida (ZP). Human spermatozoa were isolated from seminal samples with normal concentration and motility parameters and incubated with 1 μM PGE2, 1 μM PGF2α or control solution to determine sperm motility and the ability to bind to human ZP. The effects of both PGs on intracellular calcium levels were determined. Incubation for 2 or 18 h with PGE2 or PGF2α resulted in a significant (P < 0.05) increase in the percentage of spermatozoa with progressive motility. In contrast with PGF2α, PGE2 alone induced an increase in sperm intracellular calcium levels; however, the percentage of sperm bound to the human ZP was doubled for both PGs. These results indicate that incubation of human spermatozoa with low physiological levels of PGE2 or PGF2α increases sperm functions and could improve conditions for assisted reproduction protocols.

Effect of mitochondrial calcium uniporter blocking on human spermatozoa

Calcium (Ca(2+) ) regulates a number of essential processes in spermatozoa. Ca(2+) is taken up by mitochondria via the mitochondrial calcium uniporter (mCU). Oxygen-bridged dinuclear ruthenium amine complex (Ru360) has been used to study mCU because it is a potent and specific inhibitor of this channel. In bovine spermatozoa, it has been demonstrated that mitochondrial calcium uptake inhibition adversely affects the capacitation process. It has been demonstrated in human spermatozoa that mCU blocking, through Ru360, prevents apoptosis; however, the contribution of the mCU to normal human sperm function has not been studied. Therefore, the aim of this study was to evaluate the effect of mCU blocking on human sperm function. Spermatozoa obtained from apparently healthy donors were incubated with 5 and 10 μm Ru360 for 4 h at 37 °C. Viability was assessed using propidium iodide staining; motility was determined by computer-aided sperm analysis, adenosine triphosphate (ATP) levels using a luminescence-based method, mitochondrial membrane potential (ΔΨm) using JC-1 staining and reactive oxygen species (ROS) production using dihydroethidium dye. Our results show that mCU blocking significantly reduced total sperm motility and ATP levels without affecting sperm viability, ΔΨm and ROS production. In conclusion, mCU contributes to the maintenance of sperm motility and ATP levels in human spermatozoa.