Exposure of actin on the surface of the human sperm head during in vitro culture relates to sperm morphology, capacitation and zona binding

Identification of potential key genes related to idiopathic male infertility using RNA-sequencing data: an in-silico approach

Among reproductive health problems, idiopathic infertility affects married couples. The current diagnosis of male infertility focuses on the concentration, motility, and morphology of sperm in the ejaculate. Since the molecular mechanism of idiopathic infertility is unknown, identification of Differentially Expressed Genes (DEGs) among the control and idiopathic infertile male can shed light on diagnosis and treatment. Here, we analyzed the dataset GSE65683 to identify DEGs in idiopathic human sperm in three groups of patients: (i) Timed Intercourse (TIC); (ii) Intrauterine Insemination (IUI); and (iii) Assisted Reproductive Technology (ART). The enrichment analysis was carried out using DAVID (Database for Annotation, Visualization and Integrated Discovery) and GeneCodis for the DEGs. Protein-Protein Interaction (PPI) network of these DEGs were constructed using the STRING database. The network parameters such as degree and betweenness were calculated to select the important hubs. In total, 118 DEGs in TIC, 446 in IUI, and 188 in ART were identified. PPI network was constructed and identified critical top hub genes such as ACTB, BTBD6, EIF2S3, EIF3A, EIF4E, POLR2L, RPL4, RPL7, RPS11, RPL13, RPS15, RPL23, RPL27, RPL9, RPLP0 and UBA52 that may play an essential role in idiopathic male infertility. Thus, the identified hub genes may provide an insight into the molecular mechanism and contribute to discovering novel therapeutic targets and developing new strategies for idiopathic male infertility.

Coenzyme Q-10 improves preservation of mitochondrial functionality and actin structure of cryopreserved stallion sperm

Coenzyme Q-10 (CoQ-10) is a cofactor for mitochondrial electron transport chain and may be an alternative to improve sperm quality of cryopreserved equine semen. This work aimed to improve stallion semen quality after freezing by adding CoQ-10 to the cryopreservation protocol. Seven saddle stallions were utilized. Each animal was submitted to five semen collections and freezing procedures. For cryopreservation, each ejaculate was divided in three treatments: 1) Botucrio® diluent (control); 2) 50 μmol CoQ-10 added to Botucrio® diluent; 3) 1 mmol CoQ-10 added to Botucrio® diluent. Semen batches were analyzed for sperm motility characteristics (CASA), plasma and acrosomal membranes integrity and mitochondrial membrane potential (by fluorescence probes propidium iodide, Hoechst 33342, FITC-PSA and JC-1, respectively), alterations in cytoskeletal actin (phalloidin-FITC) and mitochondrial function (diaminobenzidine; DAB). The 1 mmol CoQ-10 treatment presented higher (P<0.05) amount (66.8%) of sperm cells with fully stained midpiece (indicating high mitochondrial activity) and higher (P<0.05) amount (81.6%) of cells without actin reorganization to the post-acrosomal region compared to control group (60.8% and 76.0%, respectively). It was concluded that the addition of 1 mmol CoQ-10 to the freezing diluent was more effective in preserving mitochondria functionality and cytoskeleton of sperm cells submitted to cryopreservation process.

Molecular insights into the divergence and diversity of post-testicular maturation strategies

Competition to achieve paternity has coerced the development of a multitude of male reproductive strategies. In one of the most well-studied examples, the spermatozoa of all mammalian species must undergo a series of physiological changes as they transit the male (epididymal maturation) and female (capacitation) reproductive tracts prior to realizing their potential to fertilize an ovum. However, the origin and adaptive advantage afforded by these intricate processes of post-testicular sperm maturation remain to be fully elucidated. Here, we review literature pertaining to the nature and the physiological role of epididymal maturation and subsequent capacitation in comparative vertebrate taxa including representative species from the avian, reptilian, and mammalian lineages. Such insights are discussed in terms of the framework they provide for helping to understand the evolutionary significance of post-testicular sperm maturation.

Weighted Single-Step Genome-Wide Association Study of Semen Traits in Holstein Bulls of China

Efficient production of high-quality semen is a crucial trait in the dairy cattle breeding due to the widespread use of artificial insemination. However, the genetic architecture (e.g., distributions of causal variants and their corresponding effects) underlying such semen quality traits remains unclear. In this study, we performed genome-wide association studies to identify genes associated with five semen quality traits in Chinese Holstein population, including ejaculate volume, progressive sperm motility, sperm concentration, number of sperm, and number of progressive motile sperm. Our dataset consisted of 2,218 Holstein bulls in China with full pedigree information, representing 12 artificial insemination centers, with 1,508 genotyped using the Illumina BovineSNP50 BeadChip. We used a weighted single-step genome-wide association method with 10 adjacent Single nucleotide polymorphisms (SNPs) as sliding windows, which can make use of individuals without genotypes. We considered the top 10 genomic regions in terms of their explained genomic variants as candidate window regions for each trait. In total, we detected 36 window regions related to one or multiple semen traits across 19 chromosomes. Promising candidate genes of PSMB5, PRMT5, ACTB, PDE3A, NPC1, FSCN1, NR5A2, IQCG, LHX8, and DMRT1 were identified in these window regions for these five semen traits. Our findings provided a solid basis for further research into genetic mechanisms underlying semen quality traits, which may contribute to their accurate genomic prediction in Chinese Holstein population.

Astaxanthin Prevents Human Papillomavirus L1 Protein Binding in Human Sperm Membranes

Astaxanthin (Asta), red pigment of the carotenoid family, is known for its anti-oxidant, anti-cancer, anti-diabetic, and anti-inflammatory properties. In this study, we evaluated the effects of Asta on isolated human sperm in the presence of human papillomavirus (HPV) 16 capsid protein, L1. Sperm, purified by gradient separation, were treated with HPV16-L1 in both a dose and time-dependent manner in the absence or presence of 30 min-Asta pre-incubation. Effects of HPV16-L1 alone after Asta pre-incubation were evaluated by rafts (CTB) and Lyn dislocation, Tyr-phosphorylation (Tyr-P) of the head, percentages of acrosome-reacted cells (ARC) and endogenous reactive oxygen species (ROS) generation. Sperm membranes were also analyzed for the HPV16-L1 content. Results show that HPV16-L1 drastically reduced membrane rearrangement with percentage of sperm showing head CTB and Lyn displacement decreasing from 72% to 15.8%, and from 63.1% to 13.9%, respectively. Accordingly, both Tyr-P of the head and ARC decreased from 68.4% to 10.2%, and from 65.7% to 14.6%, respectively. Asta pre-incubation prevented this drop and restored values of the percentage of ARC up to 40.8%. No alteration was found in either the ROS generation curve or sperm motility. In conclusion, Asta is able to preserve sperm by reducing the amount of HPV16-L1 bound onto membranes.

Extracellular Actin in Health and Disease

This review considers the functions of extracellular actin - cell surface bound, associated with extracellular matrix, or freely circulating. The role of this protein in different pathological processes is analyzed: its toxic effects and involvement in autoimmune diseases as an autoantigen. The extracellular actin clearance system and its role in protection against the negative effects of actin are characterized. Levels of free-circulating actin, anti-actin immunoglobulins, and components of the actin clearance system as prognostic biomarkers for different diseases are reviewed. Experimental approaches to protection against excessive amounts of free-circulating F-actin are discussed.

Dynamics of thrombin-induced exposition of actin on the platelet surface

Platelets play the key role in thrombosis and are also involved in angiogenesis as well as immune and reparative responses. In the function cascade, platelets undergo a complex cell processing, and subcellular fragments, not detectable in the resting state, are exposed on platelet surface after stimulation with agonists. This study has been performed to evaluate dynamic characteristics of actin exposition on the surface of plasma membrane of thrombin-activated platelets. Using flow-cytometric assay, it has been observed that the level of actin presented on activated platelets directly depends on agonist concentration. In the case of platelet stimulation with thrombin in the highest concentration (1.0 U/ml) taken for this study, the level of actin exposed on activated platelets was up to 4.4 times higher as compared with resting cells. Confirmation of the flow cytometry data for cell-surface actin on thrombin-activated platelets was achieved by direct visualization using a confocal laser scanning microscopy. Period of actin exposition appeared to be longer than the time phase corresponding to platelet secretion stage. Functional role of platelet surface actin has required further detailed studying, however, it is thought that superficial actin could interact with various blood plasma proteins, including plasminogen and its activators, serving as a binding site and/or center for their pericellular processing.

Conserved peptide sequences bind to actin and enolase on the surface of Plasmodium berghei ookinetes

The description of Plasmodium ookinete surface proteins and their participation in the complex process of mosquito midgut invasion is still incomplete. In this study, using phage display, a consensus peptide sequence (PWWP) was identified in phages that bound to the Plasmodium berghei ookinete surface and, in selected phages, bound to actin and enolase in overlay assays with ookinete protein extracts. Actin was localized on the surface of fresh live ookinetes by immunofluorescence and electron microscopy using specific antibodies. The overall results indicated that enolase and actin can be located on the surface of ookinetes, and suggest that they could participate in Plasmodium invasion of the mosquito midgut.

The role of ezrin-associated protein network in human sperm capacitation

Membrane modifications in sperm cells represent a key step in sperm capacitation; however, the molecular basis of these modifications is not fully understood. Ezrin is the best-studied member of the ezrin/radixin/merlin family. As a cross-linker between the cortical cytoskeleton and plasma membrane proteins, ezrin contributes to remodeling of the membrane surface structure. Furthermore, activated ezrin and the Rho dissociation inhibitor, RhoGDI, promote the formation of cortical cytoskeleton-polymerized actin through Rho activation. Thus, ezrin, actin, RhoGDI, Rho and plasma membrane proteins form a complicated network in vivo, which contributes to the assembly of the structure of the membrane surface. Previously, we showed that ezrin and RhoGDI1 are expressed in human testes. Thus, we sought to determine whether the ezrin-RhoGDI1-actin-membrane protein network has a role in human sperm capacitation. Our results by Western blot indicate that ezrin is activated by phosphorylation of the threonine567 residue during capacitation. Co-immunoprecipitation studies revealed that, during sperm capacitation, the interaction between ezrin and RhoGDI1 increases, and phosphostaining of two dimensional electrophoresis gels showed that RhoGDI1 is phosphorylated, suggesting that RhoGDI1 dissociates from RhoA and leads to actin polymerization on the sperm head. We speculate that activated ezrin interacts with polymerized actin and the glycosylated membrane protein cd44 after capacitation. Blocking sperm capacitation using ezrin- or actin-specific monoclonal antibodies decreases their acrosome reaction (AR) rate, but has no effect on the AR alone. Taken together, our results show that a network consisting of ezrin, RhoGDI1, RhoA, F-actin and membrane proteins functions to influence the modifications that occur on the membrane of the sperm head during human sperm capacitation.

Cryopreservation-induced alterations in boar spermatozoa mitochondrial function are related to changes in the expression and location of midpiece mitofusin-2 and actin network

The authors analyzed changes in mitochondrial activity of boar semen during a standard cryopreservation protocol. For this purpose, mitochondrial activity was evaluated simultaneously with the rhythm of mitochondrial formation of reactive oxygen species (mROS) through a double MitoTracker Red/proxylfluorescamine stain. Moreover, we analyzed changes in the expression and location of two key regulatory elements of mitochondrial function, namely mitofusin-2 (Mfn2) and actin, during the freezing-thawing protocol. Our results indicate that mitochondrial activity and mROS formation decreased during cyropreservation, with an initial decrease during the cooling phase of the protocol. This decrease was accompanied by an increase in the amount of solubilized Mfn2, which was concomitant with a progressive extension of Mfn2 location from the apical zone of the midpiece to the whole midpiece. Simultaneously, cryopreservation induced a decrease in solubilized actin, which was concurrent with significant changes in the midpiece actin location. The observed changes in the expression and location of both Mfn2 and actin were already present after the cooling phase of the cryopreservation protocol. Our results suggest that freezing-thawing impaired mitochondrial function. This impairment was concomitant with a decrease in the mitochondrial capacity to synthesize mROS. This impairment is attributed to changes in mitochondrial volume as a result of alterations in the expression and location of both Mfn-2 and the actin network. Finally, the alterations of mitochondrial function induced by the cryopreservation protocol were already apparent at the cooling phase. This observation indicates that the cooling phase is a crucial stage in which mitochondrial alterations occur during cryopreservation.

Cl- is required for HCO3- entry necessary for sperm capacitation in guinea pig: involvement of a Cl-/HCO3- exchanger (SLC26A3) and CFTR

Our previous study demonstrated the involvement of cystic fibrosis transmembrane conductance regulator (CFTR) in transporting bicarbonate that is necessary for sperm capacitation; however, whether its involvement is direct or indirect remains unclear. The present study investigated the possibility of a Cl-/HCO3- exchanger (solute carrier family 26, number 3 [SLC26A3]) operating with CFTR during guinea pig sperm capacitation. Incubating sperm in media with various concentrations of Cl- resulted in varied percentages of capacitated sperm in a concentration-dependent manner. Depletion of Cl-, even in the presence of HCO3-, abolished sperm capacitation and vice versa, indicating the involvement of both anions in the process. Capacitation-associated HCO3--dependent events, including increased intracellular pH, cAMP production, and protein tyrosine phosphorylation, also depend on Cl- concentrations. Similar Cl- dependence and inhibitor sensitivity were observed for sperm-hyperactivated motility and for sperm-egg fusion. The expression and localization of CFTR and SLC26A3 were demonstrated using immunostaining and Western blot analysis. Taken together, our results indicate that Cl- is required for the entry of HCO3- that is necessary for sperm capacitation, implicating the involvement of SLC26A3 in transporting HCO3-, with CFTR providing the recycling pathway for Cl-.

Spatial Distribution of Actin and Tubulin in Human Sperm Nuclear Matrix-intermediate Filament Whole Mounts—A New Paradigm

Sperm is a highly differentiated cell streamlined for fertilization. The function is thus heavily dependent on the cytoskeletal organization. Conventional methods limit the appreciation and correlation of this intricate cytoskeletal filament network in the context of an entire sperm. Our recent successful localization of nonmuscle myosin IIA on sperm nuclear matrix-intermediate filament (NM-IF) preparations from fertile men by embedment-free electron microscopy (EF-EM), prompted us to investigate the antigenic distribution of two major cytoskeletal proteins-actin and tubulin. The NM-IF preparations were subjected to a cocktail of buffered paraformaldehyde (2%) with a low concentration of glutaraldehyde (0.05%). These proteins were localized by indirect immunogold technique using EF-EM on sperm NM-IF whole mounts. Ultrastructure analysis revealed well preserved centrioles, outer dense fibers, axonemal filaments, and submitochondrial reticulum in the sperm NM-IF. Immunoreactive actin was localized along the length of the sperm whereas beta-tubulin was present in the axoneme alone. The spatial distribution of actin and tubulin in normal human sperm NM-IF reported here together with that of myosin on whole mount offers a powerful technique to understand sperm cytoskeletal supramolecular structure.

Haplotype analysis of ?-actin gene for its association with sperm quality and boar fertility

beta-actin (ACTB) was examined as a direct functional candidate gene for the possible association with sperm concentration, motility (MOT), semen volume per ejaculate, plasma droplet rate, abnormal sperm rate (ASR) and the fertility traits, non-return rate and number of piglets born alive (NBA). Three polymorphisms in intron 3 (T>C) and one polymorphism in exon 4 (T>C) of porcine ACTB gene were identified by comparative sequencing of animals of the breeds Pietrain and Hampshire. Association analysis revealed that haplotypes affected the variation of the traits MOT, ASR and NBA. The beneficial haplotypes may provide considerable improvement of sperm quality and fertility in the tested commercial boar population.

Critical role of CFTR in uterine bicarbonate secretion and the fertilizing capacity of sperm

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-activated Cl- channel expressed in a wide variety of epithelial cells, mutations of which are responsible for hallmark defective Cl- and HCO3- secretion seen in cystic fibrosis (CF). However, the physiological role of CFTR in reproductive tracts is far from understood although infertility has been observed in CF patients of both sexes. Previously we have demonstrated the expression of CFTR in the female reproductive tract and the involvement of CFTR in mediating anion secretion by the endometrium. Our recent results show that endometrial epithelial cells possess a cAMP-activated HCO3- transport mechanism, which could be impaired with channel blockers known to block CFTR or antisense against CFTR. Co-culture of sperm with CFTR antisense-treated endometrial cells or HCO3- secretion-defective CF epithelial cells resulted in reduced sperm capacitation and egg-fertilizing ability. Addition of HCO3- to the culture media and transfection of wild-type CFTR into CF cells rescued the fertilizing capacity of sperm. Immunostaining and Western blot revealed that CFTR is expressed in rodent sperm and intracellular measurement of pH during sperm capacitation indicated that the entry of HCO3- into sperm could be inhibited by CFTR inhibitor. These results are consistent with a critical role of CFTR in controlling uterine HCO3- secretion and sperm fertilizing capacity, suggesting that CFTR may be a potential target for post-meiotic regulation of fertility.

Identification and characterization of oviductal glycoprotein-binding protein partner on gametes: epitopic similarity to non-muscle myosin IIA, MYH 9

The mammalian estrogen induced oviductal glycoprotein (OGP) has been known to associate with capacitated sperm, oocytes and developing embryos. This study aimed to identify the putative binding partner of OGP on gametes using N-terminal peptide of bonnet monkey (Macaca radiata) OGP, Nmon, as bait. A protein(s) of molecular size approximately 54 kDa was detected by far-western blot analysis of detergent solubilized human sperm proteins. MALDI-TOF mass spectra analysis of approximately 54 kDa tryptic peptides gave a significant hit to non-muscle myosin heavy chain. Biochemical characterization of approximately 54 kDa was done with antibodies specific to non-muscle myosin IIA, MYH9. The approximately 54 kDa protein, possible breakdown product of MYH9, immunoreacted with MYH9 antibody in western blot analysis. OGP binding to approximately 54 kDa could also be demonstrated in far-western blot analysis of detergent solubilized human sperm proteins and nuclear matrix intermediate filament (NM-IF) preparations from human sperm and mouse oocytes. Far-western blot analysis of MYH9 enriched by immunoprecipitation identified the native approximately 220 kDa protein as OGP-binding partner. The identical and characteristic immunogold localization pattern of Nmon and MYH9 on sperm NM-IF preparation substantiated these findings. The results suggest that OGP binds to both gametes through its interaction with MYH9 through the non-glycosylated N-terminal conserved region of OGP, spanning the residues 11-137.