Perspective on plasma membrane cholesterol efflux and spermatozoal function

Caffeine attenuates spermatogenic disorders in mice with induced chronic scrotal hyperthermia

OBJECTIVE

Chronic scrotal hyperthermia (SHT) can lead to serious disorders of the male reproductive system, with oxidative stress playing a key role in the onset of these dysfunctions. Thus, we evaluated the impact of caffeine, a potent antioxidant, on cellular and tissue disorders in mice with chronic SHT.

METHODS

In this experimental study, 56 adult male NMRI mice were allocated into seven equal groups. Apart from the non-treated control group, all were exposed to heat stress. Two groups, termed "preventive" and "curative," were orally administered caffeine. The preventive mice began receiving caffeine immediately prior to heat exposure, while for the curative group, a caffeine regimen was initiated 15 consecutive days following cessation of heat exposure. Each treated group was subdivided based on pairing with a positive control (Pre/curative [Cur]+PC) or a vehicle (Pre/Cur+vehicle). Upon conclusion of the study, we assessed sperm characteristics, testosterone levels, stereological parameters, apoptosis, antioxidant and oxidant levels, and molecular markers.

RESULTS

Sperm parameters, testosterone levels, stereological parameters, biochemical factors (excluding malondialdehyde [MDA]), and c-kit gene expression were significantly elevated in the preventive and curative groups, especially the former, relative to the other groups. Conversely, expression levels of the heat shock protein 72 (HSP72) and nuclear factor kappa beta (NF-κβ) genes, MDA levels, and apoptotic cell density were markedly lower in both caffeine-treated groups relative to the other groups, with more pronounced differences observed in the preventive group.

CONCLUSION

Overall, caffeine attenuated cellular and molecular abnormalities induced by heat stress in the testis, particularly in the mice treated under the preventive condition.

Problems of human spermatozoa cryopreservation: research methods, solutions

Cryopreservation of male gametes is one of the most important methods of assisted reproductive technologies, which allows preserving gametes for research or further use. However, the fertilizing ability of spermatozoa after cryopreservation decreases by 30-70%, which makes it urgent to search for new substances with cryoprotective properties. The review considers the main causes of cell damage during cryopreservation. The relevance of methods for assessing the formation of crystals and the physicochemical properties of cryoprotective media depending on various compositions is discussed. The problem of stabilization of the spermatozoa membrane during cryopreservation is considered. A possible solution to the problem of membrane integrity may consist in modification of the basic cryoprotective media with yolk emulsion or development of methods for saturation of the membrane phospholipid layer with cholesterol.

Relative Abundance of Lipid Metabolites in Spermatozoa across Three Compartments

Male fertility, as manifest by the quantity and progressive motility of spermatozoa, is negatively impacted by obesity, dyslipidaemia and metabolic disease. However, the relative distribution of lipids in spermatozoa and the two compartments which supply lipids for spermatogenesis (seminal fluid and blood serum) has not been studied. We hypothesised that altered availability of lipids in blood serum and seminal fluid may affect the lipid composition and progressive motility of sperm. 60 men of age 35 years (median (range 20-45) and BMI 30.4 kg/m² (24-36.5) under preliminary investigation for subfertility were recruited at an NHS clinic. Men provided samples of serum and semen, subject to strict acceptance criteria, for analysis of spermatozoa count and motility. Blood serum (n = 60), spermatozoa (n = 26) and seminal fluid (n = 60) were frozen for batch lipidomics analysis. Spermatozoa and seminal fluid had comparable lipid composition but showed marked differences with the serum lipidome. Spermatozoa demonstrated high abundance of ceramides, very-long-chain fatty acids (C20-22), and certain phospholipids (sphingomyelins, plasmalogens, phosphatidylethanolamines) with low abundance of phosphatidylcholines, cholesterol and triglycerides. Men with spermatozoa of low progressive motility had evidence of fewer concentration gradients for many lipid species between blood serum and spermatozoa compartments. Spermatozoa are abundant in multiple lipid species which are likely to contribute to key cellular functions. Lipid metabolism shows reduced regulation between compartments in men with spermatozoa with reduced progressive motility.

A combination of taurine and caffeine maintains sperm quality in equine semen during chilled storage

Objective

The objective of this study was to evaluate the effects of caffeine and taurine on the motility and viability of chilled equine semen.

Materials and Methods

A total of 12 ejaculates were collected from three mature stallions with proven fertility during the breeding season. The gel-free spermatic fraction of each ejaculate was divided into two aliquots and diluted with a semen extender (either INRA 96® or BotuSemen Gold®). The aliquots were then split and assigned to one of the six treatment groups: control (no supplement), caffeine (2 and 4 mM), taurine (25 and 50 mM), and a combination of caffeine (2 mM) plus taurine (25 mM). Samples were stored at 4°C and analyzed at different time points (0, 24, 48, 72, and 96 h) to evaluate total (TMOT) and progressive (PMOT) motility and viability by computer-assisted sperm analysis.

Results

Regardless of the extender, PMOT and TMOT decreased over time. However, compared with the control, the treatment with 4 mM caffeine significantly mitigated the decrease in PMOT at 72 h. Additionally, semen treated with a combination of caffeine plus taurine maintained a significantly higher PMOT at 96 h, with improved viability at all time points.

Conclusions

The combination of caffeine plus taurine helps maintain chilled equine semen viability and progressive motility up to 96 h independently of the extender used.

Presence of Cholesterol in Non-Animal Organisms: Identification and Quantification of Cholesterol in Crude Seed Oil from Perilla frutescens and Dehydrated Pyropia tenera

Studies have reported that cholesterol, a molecule found mainly in animals, is also present in some plants and algae. This study aimed to determine whether cholesterol exists in three dehydrated algae species, namely, Pyropia tenera, Saccharina japonica, and Undaria pinnatifida, and in one plant species, namely, Perilla frutescens (four perilla seed oil samples were analyzed). These species were chosen for investigation because they are common ingredients in East Asian cuisine. Gas chromatography-flame ionization detection (GC-FID) analysis found that cholesterol was present in P. tenera (14.6 mg/100 g) and in all four perilla seed oil samples (0.3–0.5 mg/100 g). High-performance liquid chromatography with evaporative light-scattering detection (HPLC-ELSD) also demonstrated that cholesterol was present in P. tenera (14.2 mg/100 g) and allowed the separation of cholesterol from its isomer lathosterol. However, cholesterol could not be detected by HPLC-ELSD in the perilla seed oil samples, most likely because it is only present in trace amounts. Moreover, liquid chromatography-tandem mass spectrometry (LC-MS/MS) confirmed the presence of cholesterol in both P. tenera and perilla seed oil. MRM results further suggested that lathosterol (a precursor of cholesterol) was present in P. tenera.

Advancing Semen Evaluation Using Lipidomics

Developing a deeper understanding of biological components of sperm is essential to improving cryopreservation techniques and reproductive technologies. To fully ascertain the functional determinants of fertility, lipidomic methods have come to the forefront. Lipidomics is the study of the lipid profile (lipidome) within a cell, tissue, or organism and provides a quantitative analysis of the lipid content in that sample. Sperm cells are composed of various lipids, each with their unique contribution to the overall function of the cell. Lipidomics has already been used to find new and exciting information regarding the fatty acid content of sperm cells from different species. While the applications of lipidomics are rapidly evolving, gaps in the knowledge base remain unresolved. Current limitations of lipidomics studies include the number of available samples to analyze and the total amount of cells within those samples needed to detect changes in the lipid profiles across different subjects. The information obtained through lipidomics research is essential to systems and cellular biology. This review provides a concise analysis of the most recent developments in lipidomic research. This scientific resource is important because these developments can be used to not only combat the reproductive challenges faced when using cryopreserved semen and artificial reproductive technologies in livestock such as cattle, but also other mammals, such as humans or endangered species.

Individual variation in fresh and frozen semen of Bali bulls (Bos sondaicus)

AIM

This study aimed to analyze the individual factors influencing the sperm quality of Bali bulls at Baturiti Artificial Insemination (AI) center.

MATERIALS AND METHODS

Semen that was ejaculated from nine Bali bulls was collected using artificial vaginas (n=5/bull). Semen ejaculates were evaluated immediately after collection to measure the quality of the fresh semen, including semen volume, sperm concentration, progressive motility, membrane integrity (MI), and abnormal morphology. Frozen semen was evaluated for progressive sperm motility, concentration, viability, MI, abnormal morphology, and deoxyribonucleic acid (DNA) fragmentation. Other secondary data, focusing on semen quantity (semen volume and sperm concentration), were also collected from frozen the semen production data of the Baturiti AI center from 2017 to 2019. Data were analyzed statistically using a completely randomized design, and one-way analysis of variance was applied to find differences among individual bulls.

RESULTS

Significant differences (p<0.05) were found among the bulls in semen volume, sperm motility, concentration, and MI of the fresh semen. Significant differences (p<0.05) were also found among the bulls in sperm motility, viability, MI, abnormal morphology, and DNA fragmentation of the frozen semen.

CONCLUSION

Individual variation in all the tested sperm parameters of the fresh semen of Bali bulls, except sperm viability and abnormalities, was noted. Similarly, individual variation in all the tested sperm parameters in frozen semen, except sperm concentration, was noted. Therefore, individual factors can be used for selecting a superior bull in Bali cattle.

Human Sperm Express the Receptor for Glucagon-like Peptide-1 (GLP-1), Which Affects Sperm Function and Metabolism

AIM

Glucagon-like peptide-1 (GLP-1) produces pleiotropic effects binding to the GLP-1 receptor (GLP1-R), potentiating insulin secretion in the pancreas. GLP1-R is expressed in peripheral tissues and evidence for its role in reproduction has come from knockout mice, although the relationship between GLP-1 and male fertility needs to be clarified. Given that human sperm is an insulin-sensitive and insulin-secreting cell, we hypothesized that the GLP-1/GLP1-R axis may be expressed and functional in these cells.

RESULTS AND DISCUSSION

We revealed the presence of GLP1-R by Western blotting and immunofluorescence analyses. Because Exendin-4 (Ex-4) displays similar functional properties to native GLP-1, we used this agonist to perform a dose-response study on progressive motility and cholesterol efflux, showing that 300 pM Ex-4 was the most effective treatment. These actions are mediated by GLP1-R and independent from sperm-secreted insulin. The exposure to Ex-4 fueled phosphatidylinositol-3-kinase (PI3K)/AKT signaling and was reversed by H89, indicating a protein kinase A (PKA)-dependence of GLP-1/GLP1-R signaling. It emerged that in sperm, insulin secretion regulated by Ex-4 did not occur in a strictly glucose-dependent manner. A stimulatory action of Ex-4/GLP1-R on lactate dehydrogenase and glucose-6-phosphate dehydrogenase (G6PDH) activities was observed. Ex-4/GLP1-R decreased triglycerides content concomitantly to enhanced lipase and acyl-coenzyme A (acyl-CoA) dehydrogenase activities, addressing a lipolytic effect.

CONCLUSION

Collectively, we discovered that human sperm is a new GLP1 incretin target, broadening our knowledge about the effects of the GLP1-R agonist in the male reproductive field. Further findings in humans should be conducted in the future to confirm it and to improve the translational aspect of this study.

Low Density Lipoprotein - important player in increasing cryoprotective efficiency of soybean lecithin-based bull semen extenders

Currently, considering cryopreservation of bull semen, there is no clear consensus over the comparability of cryoprotective efficacy of extenders with soybean lecithin and those based on egg yolk. The objective of this study was to prove the use of Low Density Lipoprotein (LDL) extracted from hen-egg yolk as an enhancing factor for soybean lecithin-based extenders. In total, 35 ejaculates of (seven bulls x five ejaculates per bull) were collected and cryopreserved at a commercial insemination centre. The effect of the LDL addition to the extenders AndroMed^® and Bioxcell^® was tested in a 6% (v/v) concentration on spermatozoa after thawing. Modified extender composition effects were assessed on sperm functional parameters motility, plasma membrane, mitochondrial membrane potential and acrosomal integrity after thawing by CASA, flow cytometry and fluorescent microscopy, respectively. Based on kinematic parameters determined from CASA, k-means cluster analysis was used to classify individual spermatozoon into specific subpopulations (fast, medium fast and slow). A subpopulation of fast spermatozoa was increased in the presence of LDL in both selected extenders (P < 0.05). Moreover, the positive effect of LDL on sperm motility was confirmed by decreasing the percentage of sperm in slow subpopulation (P < 0.05). The effect of LDL addition on the incidence of spermatozoa with intact plasma membrane was not demonstrated in any case of extender used (P > 0.05). The percentage of sperm with intact acrosome was improved when LDL was added to Bioxcell^® extender (P < 0.05). On the other hand, addition of LDL to AndroMed^® extender improved mitochondrial intactness after thawing (P < 0.05). In conclusion, our results showed that adding LDL to selected soybean lecithin-based extenders considerably ameliorated the functional parameters of spermatozoa after thawing and thus this lipoprotein could represent an improving agent for soybean lecithin-based extender for bull semen cryopreservation.

The maturation of murine spermatozoa membranes within the epididymis, a computational biology perspective

To become fertile, mammalian spermatozoa require completing a complex biochemical maturation that begins in the testis and ends within the female oviduct. Here, we paid attention to the events occurring at the membrane level during the epididymal transit. Indeed, in the epididymis, the molecular composition and the physical-chemical proprieties of sperm membranes markedly change, with functional cross talking among the spermatozoa, the epithelium, and the luminal content (particularly the epididymosomes). To study this process, we undertook a biological networks study, representing the involved molecules as nodes and their interactions as links. The analysis of network topology revealed that it has a scale free and small world architecture and it is robust against random failure. That assures a fast and efficient transmission of information and it leads to identifying the molecules exerting a higher level of control on the system, among which cholesterol plays a pivotal role. The reactome enrichment analysis allowed the reconstruction of the biochemical pathways involved in sperm epididymal maturation and STRING analysis permitted the identification of molecular events possibly involved in that process. In conclusion, this approach allows inferring interesting information, thus contributing to the knowledge on this process and suggesting staring points for further research.

Modification of membrane cholesterol and its impact on frozen-thawed chicken sperm characteristics

This study was conducted to determine the changes in chicken sperm plasma membranes fluidity and polarity as lipid packing arrangement induced by cholesterol-loaded cyclodextrin (CLC) and 2-hydroxypropyl-β-cyclodextrin (HBCD) and how sperm cryopreservation outcomes are improved by these changes. Treatment with 2 mg HBCD supported the highest (P < 0.01) percentage of viable spermatozoa compared with the control and CLCs groups after cryopreservation. The percentage of post-thaw progressive and rapid sperm motility was highest in 2 mg HBCD (P < 0.01). After thawing, sperm treated with 1 or 2 mg CLC showed the highest anisotropy at 5, 21, 25 and 40°C (P < 0.01). At 25°C, the lowest anisotropy was observed in the thawed semen from the control group. The highest value (P < 0.01) of generalized polarization (GP) (0.5) at 5°C was observed in the 1 mg CLC treated sample. After 2 h of incubation, the highest percentage of viable spermatozoa was observed in the HBCD group in relation to the other treatments (P < 0.01). Exposure to 1 mg or 2 mg of CLC significantly decreased the percentage of live spermatozoa after thawing (P < 0.01). In conclusion, HBCD appears to play a role in the modification of sperm membranes, increasing their fluidity and preventing them against membrane phase transition to gel, thus minimizing freezing-thaw sperm damage. HBCD treatment enhances chicken sperm viability and motility after cryopreservation and subsequent storage. This novel procedure may be useful for improving the technology for cryopreservation of fowl spermatozoa.

A transcriptomal analysis of bovine oviductal epithelial cells collected during the follicular phase versus the luteal phase of the estrous cycle

BACKGROUND

Reproductive success depends on a functional oviduct for gamete storage, maturation, fertilization, and early embryonic development. The ovarian-derived steroids estrogen and progesterone are key regulators of oviductal function. The objective of this study was to investigate luteal and follicular phase-specific oviductal epithelial cell function by using microarray-based transcriptional profiling, to increase our understanding of mRNAs regulating epithelial cell processes, and to identify novel genes and biochemical pathways that may be found to affect fertility in the future.

METHODS

Six normally cycling Angus heifers were assigned to either luteal phase (LP, n = 3) or follicular phase (FP, n = 3) treatment groups. Heifers in the LP group were killed between day 11 and 12 after estrus. Heifers in the FP group were treated with 25 mg PGF2α (Lutalyse, Pfizer, NY) at 8 pm on day 6 after estrus and killed 36 h later. Transcriptional profiling by microarray and confirmation of selected mRNAs by real-time RT-PCR analyses was performed using total RNA from epithelial cells isolated from sections of the ampulla and isthmus collected from LP and FP treatment groups. Differentially expressed genes were subjected to gene ontology classification and bioinformatic pathway analyses.

RESULTS

Statistical one-way ANOVA using Benjamini-hochberg multiple testing correction for false discovery rate (FDR) and pairwise comparison of epithelial cells in the ampulla of FP versus LP groups revealed 972 and 597 transcripts up- and down-regulated, respectively (P < 0.05). Within epithelial cells of the isthmus in FP versus LP groups, 946 and 817 transcripts were up- and down-regulated, respectively (P < 0.05). Up-regulated genes from both ampulla and isthmus were found to be largely involved in cholesterol biosynthesis and cell cycle pathways, while down-regulated genes were found in numerous inflammatory response pathways.

CONCLUSIONS

Microarray-based transcriptional profiling revealed phase of the cycle-dependent changes in the expression of mRNA within the epithelium of the oviducts' ampulla and isthmus.

A novel acrosomal protein, IQCF1, involved in sperm capacitation and the acrosome reaction

On the basis of the unknown tags in the mature human sperm serial analysis of gene expression library constructed by our laboratory, some transcripts were cloned, including Iqcf1 (IQ motif containing F1). To investigate the function of sperm-retained Iqcf1 in spermatogenesis and fertilization of mice, we investigated the spatial and temporal expression of IQCF1. By using the (transcription activator-like effector nuclease) strategy, Iqcf1-knockout mice were produced, and the phenotypes of the Iqcf1(-/-) mice were analyzed. The results showed that IQCF1 was localized in the acrosome of spermatozoa and spermatids; the expression of IQCF1 in testes was associated with spermatogenic capacity. The Iqcf1(-/-) mice were significantly less fertile than the wild-type mice (p = 0.0057) because of reduced sperm motility (p = 0.0094) and the acrosome reaction (AR) (p = 0.0093). In spermatozoa, IQCF1 interacted with calmodulin (CaM) and possibly participated in the tyrosine phosphorylation of sperm proteins during capacitation. In conclusion, a newly identified acrosomal protein, IQCF1, is closely related to sperm capacitation and AR; in particular, it is involved in tyrosine phosphorylation of sperm proteins through interaction with CaM. Research into the function of IQCF1 during fertilization could facilitate the investigation of the molecular mechanism of capacitation, which is unclear.

Sperm nuclear DNA fragmentation rate is associated with differential protein expression and enriched functions in human seminal plasma

OBJECTIVE

To analyse the proteomic profile of seminal plasma with the aim of identifying the proteins and post-genomic pathways associated with sperm DNA fragmentation.

MATERIALS AND METHODS

A cross-sectional study including 89 subjects from a human reproduction service was carried out. All semen samples were assessed for sperm DNA fragmentation using a comet assay. Results from 60 sperm were analysed using Komet 6.0.1 software and the 'Olive tail moment' variable was used to stratify these into low and high sperm DNA fragmentation groups. Seminal plasma proteins from the two groups were pooled and used for proteomic analysis. Quantitative data were used for functional enrichment studies.

RESULTS

Seventy-two proteins were identified or quantified in seminal plasma. Of these, nine were differentially expressed in the low group and 21 in the high group. Forty-two proteins were conserved between these groups. Functional enrichment analysis indicated that sperm DNA fragmentation was related to functions such as lipoprotein particle remodelling and regulation, fatty acid binding and immune response. Proteins found exclusively in the low group may be involved in correcting spermatogenesis and/or improving sperm function. Proteins in the high group were associated with increased innate immune response, sperm motility and/or maturation and inhibition of mitochondrial apoptosis.

CONCLUSION

Protein expression and post-genomic pathways of seminal plasma differ according to the rate of sperm DNA integrity.

Involvement of ABCB1 and ABCC1 transporters in sea urchin Echinometra lucunter fertilization

Fertilization is an ordered sequence of cellular interactions that promotes gamete fusion to form a new individual. Since the pioneering work of Oskar Hertwig conducted on sea urchins, echinoderms have contributed to the understanding of cellular and molecular aspects of the fertilization processes. Studies on sea urchin spermatozoa reported the involvement of a plasma membrane protein that belongs to the ABC proteins superfamily in the acrosome reaction. ABC transporters are expressed in membranes of eukaryotic and prokaryotic cells, and are associated with the transport of several compounds or ions across biomembranes. We aimed to investigate ABCB1 and ABCC1 transporter activity in sea urchin spermatozoa and their involvement in fertilization. Our results indicate that Echinometra lucunter spermatozoa exhibit a low intracellular calcein accumulation (18.5% stained cells); however, the ABC blockers reversin205, verapamil, and MK571 increased dye accumulation (93.0-96.6% stained cells). We also demonstrated that pharmacologically blocking ABCB1 and ABCC1 decreased spermatozoa fertilizing capacity (70% inhibition), and this phenotype was independent of extracellular calcium. These data suggest that functional spermatozoa ABCB1 and ABCC1 transporters are crucial for a successful fertilization. Additional studies must be performed to investigate the involvement of membrane lipid homeostasis in the fertilization process.

Expression of Tas1 taste receptors in mammalian spermatozoa: functional role of Tas1r1 in regulating basal Ca²⁺ and cAMP concentrations in spermatozoa

BACKGROUND

During their transit through the female genital tract, sperm have to recognize and discriminate numerous chemical compounds. However, our current knowledge of the molecular identity of appropriate chemosensory receptor proteins in sperm is still rudimentary. Considering that members of the Tas1r family of taste receptors are able to discriminate between a broad diversity of hydrophilic chemosensory substances, the expression of taste receptors in mammalian spermatozoa was examined.

METHODOLOGY/PRINCIPAL FINDINGS

The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head. Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities. In addition, a significant increase in spontaneous acrosomal reaction was observed in Tas1r1 null mutant sperm whereas acrosomal secretion triggered by isolated zona pellucida or the Ca²⁺ ionophore A23187 was not different from wild-type spermatozoa. Remarkably, cytosolic Ca²⁺ levels in freshly isolated Tas1r1-deficient sperm were significantly higher compared to wild-type cells. Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes.

CONCLUSIONS/SIGNIFICANCE

Since Ca²⁺ and cAMP control fundamental processes during the sequential process of fertilization, we propose that the identified taste receptors and coupled signaling cascades keep sperm in a chronically quiescent state until they arrive in the vicinity of the egg - either by constitutive receptor activity and/or by tonic receptor activation by gradients of diverse chemical compounds in different compartments of the female reproductive tract.