A Kinase Anchor Protein 4 Is Vulnerable to Oxidative Adduction in Male Germ Cells

SUMO1 modification reduces oxidative stress and SUMO1ylated AKAP4 degradation affects frozen-thawed boar sperm quality

Low-temperature injury affects normal physiological function and viability of boar sperm during cryopreservation. Small ubiquitin-like modifier (SUMO) modification of proteins after translation is related to the cell stress response but the relationship between SUMO modification and oxidative stress in freeze-thawed sperm remains unclear. A-kinase ankyrin 4 (AKAP4) and its precursor proAKAP4 are two main proteins in mammalian sperm. Although AKAP4 expression has been studied in many species, its expression in porcine sperm has not been described in detail. In this study, liquid chromatography-mass spectrometry was used to determine the differentially expressed SUMO-modified proteins in porcine sperm after freezen and thawed. The results identified 26 down-regulated SUMO-modified proteins, with AKAP4 identified as one of the target proteins of SUMO1 under sperm stress. In addition, the level of SUMO1 protein increased significantly (P < 0.001) and the level of AKAP4 protein decreased (P < 0.05) after freezing and oxidative stress treatment. Inhibition of SUMO1 modification of AKAP4 protein did not affect its degradation (P > 0.05), indicating that SUMO1 is not involved in the degradation of AKAP4. The inhibition of SUMO1 modification by sperm protein decreased sperm motility (P < 0.05), ATP content, and DNA integrity (P < 0.05). In summary, cryopreservation and oxidative stress can induce SUMO modification of porcine sperm proteins and the modification of sperm protein SUMO1 can help sperm resist oxidative stress; and its role in protecting sperm quality is not via regulating the degradation of AKAP4. These findings provide new insights into the mechanisms underlying SUMO1 modifications during sperm cryopreservation and oxidative stress.

Manipulation of metabolism to improve liquid preservation of mammalian spermatozoa

Reproductive success in mammals hinges on the ability of sperm to generate sufficient energy through cellular metabolism to perform the energy-intensive processes required for fertilisation, including motility, maturation, and oocyte interactions. It is now widely accepted that sperm exhibit metabolic flexibility, utilising a combination of glycolysis and oxidative phosphorylation (supported by the Krebs cycle and other complementary pathways) to meet their energy demands. However, the preferred pathway for energy production varies significantly among species, making it challenging to map species-specific metabolic strategies, particularly in species with high metabolic flexibility, like the ram. Additionally, differences in methodologies used to measure metabolism have led to biased interpretations of species' metabolic strategies, complicating the development of liquid storage methods aimed at preserving spermatozoa by manipulating energy generation based on species-specific requirements. This review examines sperm energy requirements, current methods for assessing metabolic capacity, and the current research on species-specific metabolism. Future research should focus on establishing a standardised approach for determining metabolic preferences to accurately map species-specific strategies, a critical step before developing effective liquid preservation methods. By identifying species-specific regulatory points, strategies can be designed to temporarily inhibit metabolic pathways, conserving resources and reducing the accumulation of metabolic by-products. Alternatively, supplementation with depleted metabolites can be guided by understanding areas of excessive consumption during prolonged metabolism. Applying this knowledge to develop tailored preservation techniques will help minimise sperm damage and improve survival during in vitro processing and liquid storage, ultimately enhancing the success of artificial breeding programs.

Use of a sperm-Hyaluronan binding assay for evaluation of sperm quality in dromedary camels

The objective of this study was to assess the ability of camel spermatozoa to bind in the Hyaluronan Binding Assay (HBA), to determine if conventional sperm quality parameters, in vitro fertilization capacity, and precursor of A-Kinase Anchoring Protein 4 (proAKAP4) values correlate with HBA results. The potential to predict post-thaw fertilization performance from HBA for fresh dromedary camel sperm was also evaluated. Semen samples were collected and assessed both fresh and post thawing, at 0 h and 1.5 h. Conventional semen analysis, HBA, and a proAKAP4 biomarker-test were used to validate sperm quality. A heterologous sperm penetration assay using zona pellucida-free goat oocytes was used to assess in vitro sperm fertilizing capacity. The results showed that dromedary camel spermatozoa bound to hyaluronan with no correlation between results from fresh samples and after thawing. Furthermore, the proAKAP4 test results showed a negative correlation with HBA at 0 h after thawing (r = - 0.62; P = 0.03). In the conventional analysis, only progressive motility (r = 0.65; P = 0.02) and straightness correlated with HBA for fresh semen (r = 0.69; P = 0.01). In the sperm penetration assay, a moderate but non-significant correlation was identified between fresh sperm HBA and penetration (r = 0.52; P = 0.07). In conclusion, results suggested that HBA can be used to assess camel sperm properties, but further investigation is needed to understand its correlation with other sperm quality parameters. The HBA score from fresh dromedary camel sperm was unable to predict post-thaw fertilization performance.

ProAKAP4 as Indicator of Long-Lasting Motility Marker in Post-Thaw Conditions in Stallions

ProAKAP4, a precursor of AKAP4 (A-kinase anchor protein) found in the flagellum of mammalian and non-mammalian spermatozoa, serves as a structural protein with established correlations to motility parameters across diverse species. This study aimed to determine the proAKAP4 level evolution in thawed stallion semen over a 3 h period, examining its correlation with motility descriptors and mitochondrial membrane potential. Utilizing sixteen ejaculates from four French warmblood stallions, this study involved maintaining thawed samples at 37 °C for 3 h, conducting proAKAP4 enzyme-linked immunosorbent assays (ELISA), computer-assisted sperm analysis (CASA), and mitochondrial membrane potential by JC-1 probe and flow cytometry at 0, 1, and 3 h post-thawing. The findings indicate significant positive correlations (p ≤ 0.05) between proAKAP4 levels and sperm total or progressive motility at all time points analyzed. Spermatozoa velocity descriptors (VAP, VCL, VSL) and spermatozoa lateral head displacement (ALH) display positive correlations (p ≤ 0.05) with ProAKAP4 at the 0 h post-thawing. ProAKAP4 concentration exhibits no discernible difference between batches with or without a cryoprotectant. Notably, proAKAP4 consumption remains insignificant within the initial hour after thawing but becomes significant (p ≤ 0.05) between 1 and 3 h post-thawing. In summary, proAKAP4 demonstrates positive correlations with total and progressive motility in stallion semen for up to 3 h after thawing, albeit showing a noticeable decrease starting from the first hour post-thawing, indicating a progressive consumption as a result of spermatozoa motile activity.

Evaluation of a commercial proAKAP4 kit for the assessment of fresh and frozen-thawed feline spermatozoa

ProAKAP4 is gaining increasing attention as a potential marker of semen quality in many species, but while there is a commercial kit for assessing proAKAP4 in the domestic cat, there are no publications about its use. The aim of this study was to evaluate the commercial proAKAP4 kit - Cat 4MID® Kit (SPQI - 4BioDx, Lille, France) for the assessment of feline semen. Semen was collected from 54 male cats by urethral catheterization. After a basic semen evaluation (subjective motility, CASA, viability, morphology), proAKAP4 levels in each sample were assessed using the Cat 4MID® Kit according to the manufacturer's protocol or with some modifications related to incubation time, sample storage conditions and number of spermatozoa used. Finally, the Spearman correlation of proAKAP4 concentration and sperm motility parameters was calculated. The most reliable results (acceptable intraassay coefficient of variation) were obtained with an optimized protocol of overnight incubation and isolation of proAKAP4 protein from 1 × 106 spermatozoa stored at -80°C. For fresh semen, there were no significant correlations between proAKAP4 concentration and sperm motility parameters, despite a strong correlation between motility parameters and sperm viability and morphology. A predominant effect of other sperm parameters and highly variable performance of lysis buffer question the usefulness of Cat 4MID® Kit for the assessment of feline semen. For frozen-thawed semen, there was a moderate, negative correlation between proAKAP4 concentration and two CASA parameters, VAP and VSL. As there were no correlations between proAKAP4 concentration in fresh semen and motility parameters in cryopreserved samples, proAKAP4 cannot be used as freezability marker in cats. More studies are needed to establish potential correlation with long-lasting motility.

Decreased AKAP4/PKA signaling pathway in high DFI sperm affects sperm capacitation

The sperm DNA fragmentation index (DFI) is a metric used to assess DNA fragmentation within sperm. During in vitro fertilization-embryo transfer (IVF-ET), high sperm DFI can lead to a low fertilization rate, poor embryo development, early miscarriage, etc. A kinase anchoring protein (AKAP) is a scaffold protein that can bind protein kinase A (PKA) to subcellular sites of specific substrates and protects the biophosphorylation reaction. Sperm protein antigen 17 (SPA17) can also bind to AKAP. This study intends to explore the reason for the decreased fertilization rate observed in high sperm DFI (H-DFI) patients during IVF-ET. In addition, the study investigates the expression of AKAP, protein kinase A regulatory subunit (PKARII), and SPA17 between H-DFI and low sperm DFI (L-DFI) patients. SPA17 at the transcriptional level is abnormal, the translational level increases in H-DFI patients, and the expression of AKAP4/PKARII protein decreases. H 2 O 2 has been used to simulate oxidative stress damage to spermatozoa during the formation of sperm DFI. It indicates that H 2 O 2 increases the expression of sperm SPA17 protein and suppresses AKAP4/PKARII protein expression. These processes inhibit sperm capacitation and reduce acrosomal reactions. Embryo culture data and IVF outcomes have been documented. The H-DFI group has a lower fertilization rate. Therefore, the results indicate that the possible causes for the decreased fertilization rate in the H-DFI patients have included loss of sperm AKAP4/PKARII proteins, blocked sperm capacitation, and reduced occurrence of acrosome reaction.

RNA sequencing profiles reveals progressively reduced spermatogenesis with progression in adult cryptorchidism

Introduction

The fertility of cryptorchidism patients who didn't perform corrective surgery will decrease with age. Herein, we elucidate the histological alterations and underlying molecular mechanism in patients with an increase in the disease duration from 20 to 40 years.

Methods

Testicular tissues were obtained from three patients with cryptorchidism, ranging in age from 22 to 44 years. Three benign paracancerous testicular samples of matched ages were used as controls. The normal and undescended testicular tissues were stained with hematoxylin and eosin (HE) and immunofluorescence and all six testicular samples were subjected to RNA sequencing. RNA sequencing data were subjected to gene set enrichment analysis (GSEA), Kyoto Encyclopedia of Genes and Genomes (KEGG), protein-protein interaction (PPI) network analysis, and Gene Ontology (GO) searches. Real-time reverse transcriptase polymerase chain reaction was used to confirm the DEGs.

Results

The seminiferous tubules' basement membrane thickens with age in healthy testes. As the period of cryptorchidism in the cryptorchid testis extended, the seminiferous tubules significantly atrophy, the number of spermatogenic cells declines, and the amount of interstitial fibrous tissue increases in comparison to normal tissues. The number of germ cells per cross-section of seminiferous tubules was significantly lower in cryptorchidism than in normal testicular tissues, according to immunofluorescence staining, but the number of Sertoli cells remained stable. RNA sequencing analysis identified 1150 differentially expressed genes (DEGs) between cryptorchidism and normal testicular tissues (fold change >2 and p<0.05), of which 61 genes were noticeably upregulated and 1089 were significantly downregulated. These genes were predominantly linked to sperm development and differentiation, and fertilization, according to GO analysis. Meiosis pathways were significantly downregulated in cryptorchidism, according to KEGG pathway analysis and GSEA (P<0.001). PPI analysis was used to identify the top seven downregulated hub genes (PLCZ1, AKAP4, IZUMO1, SPAG6, CAPZA3, and ROPN1L), which were then further verified by qPCR.

Discussion

By describing the histological changes and differential gene expression patterns in adult cryptorchid patients of different age groups, we discovered the progression mechanisms of undescended testes in adults with aging and identified seven significantly downregulated hub genes (PLCZ1, AKAP4, IZUMO1, SPAG6, CAPZA3, and ROPN1L) in cryptorchid testis compared to normal testicular tissues. These genes played a role in the process of spermgenesis and are directly linked to the steady decline in fertility caused by cryptorchidism. Our study provided a better understanding of the molecular mechanisms underlying the loss of spermatogenesis in adult cryptorchidism, and give support for the development of adult cryptorchidism treatments.

Fibrinogen-Related Protein, Fgl2, of Hamster Cauda Epididymal Fluid: Enzymatic Characterization, and Identification of Fgl2-Binding Proteins and Ligand of Defective Hamster Sperm Organelles

The luminal environment of the mammalian epididymidis performs a dual function; sperm maturation and maintaining sperm viability. We previously identified a secretory protein (260/280KDa oligomers) of hamster cauda epididymal principal cells that binds to nonviable sperm. The 260/280KDa oligomers are composed of 64kDa FGL2 (fibrinogen-like protein-2) and 33kDa FGL1) (fibrinogen-like protein-1). The potential mechanism by which FGL2 binds to degenerative sperm is not clearly demonstrated. In this study, we report the downstream sequence of prothrombinase activity of FGL2, the identification of organelles, and characterize candidate proteins that bind FGL2. The following reaction sequence confirms that FGL2 is a phospholipid-activated serine protease; the conversion of prothrombin to thrombin by FGL2, followed by the conversion of soluble fibrinogen to insoluble fibrin polymers by thrombin. FGL2 binds intensely to tails than heads of de-membranated sperm. A spectrum of polypeptides of cauda sperm tails binds to FGL2. Proteomic analyses of 65KDa, 16kDa, and 13kDa polypeptides of tails correspond to a-Kinase anchor protein 4, glutathione peroxidase 4, and cytochrome c oxidase subunit 4, respectively. Annexin V, a calcium-dependent phosphatidylserine-binding protein localized to the flagellum and co-precipitated with FGL2. We have demonstrated a novel protective mechanism for recognizing and eliminating defective spermatozoa from viable sperm population.

Mechanisms of damage to sperm structure in mice on the zinc-deficient diet

BACKGROUND

Zinc (Zn)is an essential trace element for spermatogenesis and its deficiency causes abnormal spermatogenesis.

OBJECTIVE

The present study was conducted to examine the mechanisms by which Zn-deficient diet impairs sperm morphology and its reversibility.

METHODS

30 SPF grade male Kunming (KM) mice were randomly divided into three groups, 10 mice per group. Zn-normal diet group (ZN group) was given Zn-normal diet（Zn content= 30 mg/kg）for 8 weeks. Zn-deficienct diet group (ZD group) was given Zn-deficienct diet（Zn content< 1 mg/kg）for 8 weeks. Zn-deficient and Zn-normal diet group（ZDN group）was given 4 weeks Zn-deficienct diet followed by 4 weeks Zn-normal diet. After 8 weeks, the overnight fasted mice were sacrificed, and blood and organs were collected for further analysis.

RESULTS

The experimental results showed that Zn-deficienct diet leads to increased abnormal morphology sperm and testicular oxidative stress.The rate of abnormal morphology sperm, chromomycin A3(CMA3), DNA fragmentation index (DFI), malondialdehyde (MDA) were significantly increased, and a-kinase anchor protein 4(AKAP4), dynein axonemal heavy chain 1(DNAH1), sperm associated antigen 6(SPAG6), cilia and flagella associated protein 44(CFAP44), glutathione peroxidase (GSH-PX), superoxide dismutase (SOD), total antioxidant capacity (T-AOC), nuclear factor erythroid 2-related factor (NRF2), NAD(P)H:quinone oxidoreductase 1(NQO1)and heme oxygenase 1(HO1) were significantly decreased in the ZD group mice. While the changes in above indicators caused by Zn-deficient diet were significantly alleviated in the ZDN group.

CONCLUSION

It was concluded that Zn-deficient diet causes abnormal morphology sperm and testicular oxidative stress in male mice. Abnormal morphology sperm caused by Zn-deficient diet are reversible, and Zn-normal diet can alleviate them.

Proteasome-Associated Proteins, PA200 and ECPAS, Are Essential for Murine Spermatogenesis

Proteasomes are highly sophisticated protease complexes that degrade non-lysosomal proteins, and their proper regulation ensures various biological functions such as spermatogenesis. The proteasome-associated proteins, PA200 and ECPAS, are predicted to function during spermatogenesis; however, male mice lacking each of these genes sustain fertility, raising the possibility that these proteins complement each other. To address this issue, we explored these possible roles during spermatogenesis by producing mice lacking these genes (double-knockout mice; dKO mice). Expression patterns and quantities were similar throughout spermatogenesis in the testes. In epididymal sperm, PA200 and ECPAS were expressed but were differentially localized to the midpiece and acrosome, respectively. Proteasome activity was considerably reduced in both the testes and epididymides of dKO male mice, resulting in infertility. Mass spectrometric analysis revealed LPIN1 as a target protein for PA200 and ECPAS, which was confirmed via immunoblotting and immunostaining. Furthermore, ultrastructural and microscopic analyses demonstrated that the dKO sperm displayed disorganization of the mitochondrial sheath. Our results indicate that PA200 and ECPAS work cooperatively during spermatogenesis and are essential for male fertility.

Effect of MnTBAP on sperm ultra-rapid freezing and its proteomics study

MnTBAP is a new synthetic antioxidant that has been used for the cryopreservation of sperm. However, the exact mechanism of its cryoprotection at the molecular level is largely unknown. Therefore, in this study, normal human semen samples were selected and MnTBAP (0, 5, 10, 20, 40 μM) was added to sperm freezing medium to assess changes in kinetics parameters, apoptosis, reactive oxygen species (ROS), and DNA fragmentation index (DFI) after sperm ultra-rapid freezing. The tandem masstagging (TMT) proteomics technique was used to further investigate the changes in proteins after sperm ultra-rapid freezing. The kinetic parameters of sperm after ultra-rapid freezing and thawing were significantly reduced and apoptosis, ROS production and DFI were significantly increased. The addition of 40 μM MnTBAP improved the kinetic parameters, while it reduced apoptosis, ROS production, and DFI of sperm after ultra-rapid freezing and thawing (P < 0.05). Compared with the fresh semen, 1978 differential proteins were identified in the frozen-thawed sperm without MnTBAP and 1888 differential proteins were identified in the frozen-thawed sperm with MnTBAP (40 μM) added. The proteins affected during ultra-rapid freezing were mainly related to sperm metabolism, flagellar structure motility, apoptosis, intracellular signaling, capacitation and fertilization, while the addition of MnTBAP reduced the alterations of these proteins.

Sperm cryopreservation: current status and future developments

The cryopreservation of spermatozoa is an important reproductive technology for the preservation of fertility in man and animals. Since the serendipitous discovery of glycerol as an effective cryoprotectant in 1947, sperm cryopreservation has undergone many changes in terms of the freezing methods employed, the rates at which samples are frozen and thawed, and the media used to preserve sperm functionality and DNA integrity. An extensive literature survey has been conducted addressing the cryoprotectants employed for both animal and human semen and the freezing protocols utilised. The results indicate that glycerol remains the dominant cryoprotective agent, usually incorporated into a balanced salt solution containing energy substrates, buffers, osmolytes and protein in the form of human serum albumin (human) or skimmed milk (animal). Realisation that some of the damage observed in cryostored cells involves the generation of reactive oxygen species during the thawing process, has prompted many studies to assess the relative merits of incorporating antioxidants into the cryopreservation media. However, in the absence of systematic comparisons, there is currently no consensus as to which antioxidant combination might be the most effective. Utilising our fundamental understanding of cryodamage to optimise cryopreservation protocols for each species will be important in the future.

New horizons in human sperm selection for assisted reproduction

Male infertility is a commonly encountered pathology that is estimated to be a contributory factor in approximately 50% of couples seeking recourse to assisted reproductive technologies. Upon clinical presentation, such males are commonly subjected to conventional diagnostic andrological practices that rely on descriptive criteria to define their fertility based on the number of morphologically normal, motile spermatozoa encountered within their ejaculate. Despite the virtual ubiquitous adoption of such diagnostic practices, they are not without their limitations and accordingly, there is now increasing awareness of the importance of assessing sperm quality in order to more accurately predict a male's fertility status. This realization raises the important question of which characteristics signify a high-quality, fertilization competent sperm cell. In this review, we reflect on recent advances in our mechanistic understanding of sperm biology and function, which are contributing to a growing armory of innovative approaches to diagnose and treat male infertility. In particular we review progress toward the implementation of precision medicine; the robust clinical adoption of which in the setting of fertility, currently lags well behind that of other fields of medicine. Despite this, research shows that the application of advanced technology platforms such as whole exome sequencing and proteomic analyses hold considerable promise in optimizing outcomes for the management of male infertility by uncovering and expanding our inventory of candidate infertility biomarkers, as well as those associated with recurrent pregnancy loss. Similarly, the development of advanced imaging technologies in tandem with machine learning artificial intelligence are poised to disrupt the fertility care paradigm by advancing our understanding of the molecular and biological causes of infertility to provide novel avenues for future diagnostics and treatments.

ProAKAP4 Concentration Is Related to Sperm Motility and Motile Sperm Subpopulations in Frozen-Thawed Horse Semen

ProAKAP4 is the precursor of AKAP4 (A-kinase Anchor protein 4), the main structural protein of the fibrous sheath of sperm. The amount of proAKAP4 reflects the ability of spermatozoa to maintain the flagellum activity and functionality up to the site of fertilization and is positively correlated with progressive motility in several mammalian species. The aim of this study was to investigate the relationship between proAKAP4 concentration with horse sperm motility descriptors and spermatic motile subpopulations. For this purpose, a total of 48 ejaculates from 13 different stallions were analyzed. Spermatic motility descriptors were obtained by the CASA system, and four motile subpopulations (SP) with specific motility patterns were statistically identified. ProAKAP4 concentrations were evaluated by ELISA. The relationship between motility descriptors of sperm subpopulations and proAKAP4 concentrations was evaluated. Following a hierarchical cluster statistical analysis, ejaculates were divided into two groups according to their proAKAP4 concentrations, either having low proAKAP4 concentrations (5.06−35.61 ng/10M spz; n = 23) or high (39.92−82.23 ng/10M spz; n = 25) proAKAP4 concentrations (p < 0.001). ProAKAP4 concentrations were positively correlated (p < 0.05) with total and progressive motility, as well as with parameters of velocity. ProAKAP4 amount also showed a negative correlation (p < 0.05) with sperm motile subpopulation number 3, which was the subpopulation with the lowest velocity parameters. In conclusion, proAKAP4 concentration in stallion semen positively reflects sperm progressive motility with the functional velocity kinematic descriptors. Concentrations of proAKAP4 higher than 37.77 ng/10M spz were correlated with a very good quality frozen/thawed stallion semen.

Male infertility and somatic health - insights into lipid damage as a mechanistic link

Over the past decade, mounting evidence has shown an alarming association between male subfertility and poor somatic health, with substantial evidence supporting the increased incidence of oncological disease, cardiovascular disease, metabolic disorders and autoimmune diseases in men who have previously received a subfertility diagnosis. This paradigm is concerning, but might also provide a novel window for a crucial health reform in which the infertile phenotype could serve as an indication of potential pathological conditions. One of the major limiting factors in this association is the poor understanding of the molecular features that link infertility with comorbidities across the life course. Enzymes involved in the lipid oxidation process might provide novel clues to reconcile the mechanistic basis of infertility with incident pathological conditions. Building research capacity in this area is essential to enhance the early detection of disease states and provide crucial information about the disease risk of offspring conceived through assisted reproduction.

Single-cell RNA sequencing of the Mongolia sheep testis reveals a conserved and divergent transcriptome landscape of mammalian spermatogenesis

Spermatogenesis is a highly coordinated and complex process, and is pivotal for transmitting genetic information between mammalian generations. In this study, we investigated the conservation, differences, and biological functions of homologous genes during spermatogenesis in Mongolia sheep, humans, cynomolgus monkey, and mice using single-cell RNA sequencing technology. We compared X chromosome meiotic inactivation events in Mongolia sheep, humans, cynomolgus monkey, and mice to uncover the concerted activity of X chromosome genes. Subsequently, we focused on the dynamics of gene expression, key biological functions, and signaling pathways at various stages of spermatogenesis in Mongolia sheep and humans. Additionally, the ligand-receptor networks of Mongolia sheep and humans in testicular somatic and germ cells at different developmental stages were mapped to reveal conserved germ cell-soma communication using single-cell resolution. These datasets provided novel information and insights to unravel the molecular regulatory mechanisms of Mongolia sheep spermatogenesis and highlight conservation in gene expression during spermatogenesis between Mongolia sheep and humans, providing a foundation for the establishment of a large mammalian disease model of male infertility.

ProAKAP4 Semen Concentrations as a Valuable Marker Protein of Post-Thawed Semen Quality and Bull Fertility: A Retrospective Study

Functional sperm quality markers to predict bull fertility have been actively investigated. Among them, proAKAP4, which is the precursor of AKAP4, the main structural protein in the fibrous sheath of spermatozoa; appears to be promising, especially since spermatozoa lacking AKAP4 expression were shown to be immotile, abnormal, and infertile. In this study, the objective was to evaluate proAKAP4 concentration values with the classic sperm motility descriptors and fertility outcomes (NRR at 90 days) in post-thawed conditions of 10 bulls' semen. ProAKAP4 expression was confirmed by Western blotting and proAKAP4 concentrations were determined by ELISA. Variations in proAKAP4 concentrations were observed independently of the motility sperm descriptors measured using computer-assisted semen analysis (CASA). A ProAKAP4 concentration of 38.67 ± 8.55 ng/10 million spermatozoa was obtained as a statistical mean of all samples. Threshold values of proAKAP4 were then determined between 19.96 to 96.95 ng/10 million spermatozoa. ProAKAP4 concentrations were positively correlated with progressive motility and the linearity coefficient. The sperm showing the lowest progressive motility were the samples exhibiting proAKAP4 concentrations below 20 ng/10 million spermatozoa. Furthermore, proAKAP4 concentrations were significantly higher in bulls with a higher NRR in the field. Our results demonstrate a correlation between the semen concentration of proAKAP4 and NRR-90d (p = 0.05) in post-thawed bull semen, highlighting the potential of proAKAP4 as a predictive marker of bull fertility.

A scRNA-seq Approach to Identifying Changes in Spermatogonial Stem Cell Gene Expression Following in vitro Culture

Spermatogonial stem cell (SSC) function is essential for male fertility, and these cells hold potential therapeutic value spanning from human infertility treatments to wildlife conservation. As in vitro culture is likely to be an integral component of many therapeutic pipelines, we have elected to explore changes in gene expression occurring in undifferentiated spermatogonia in culture that may be intertwined with the temporal reduction in regenerative capacity that they experience. Single cell RNA-sequencing analysis was conducted, comparing undifferentiated spermatogonia retrieved from the adult mouse testis with those that had been subjected to 10 weeks of in vitro culture. Although the majority of SSC signature genes were conserved between the two populations, a suite of differentially expressed genes were also identified. Gene ontology analysis revealed upregulated expression of genes involved in oxidative phosphorylation in cultured spermatogonia, along with downregulation of integral processes such as DNA repair and ubiquitin-mediated proteolysis. Indeed, our follow-up analyses have provided the first depiction of a significant accumulation of ubiquitinated proteins in cultured spermatogonia, when compared to those residing in the testis. The data produced in this manuscript will provide a valuable platform for future studies looking to improve SSC culture approaches and assess their safety for utilisation in therapeutic pipelines.

The Concentration of ProAKAP4 and Other Indicators of Cryopotential of Spermatozoa Cryopreserved in Extender with Holothuroidea Extract Addition

Simple Summary

Scientists are constantly making efforts to determine the fertilization capacity of sperm after ejaculation. The present research proves that the application of Holothuroidea extract to the semen extender improves its cryostability, and has a positive effect on the biological quality of sperm after the freezing process. Moreover, it has been proven that the proAKAP4 biomarker can be successfully used to evaluate the effectiveness of the use of various extenders for semen cryopreservation.

Abstract

The aim of this study was to determine the concentration of proAKAP4 and other indicators of cryopotential of spermatozoa cryopreserved in extender with Holothuroidea extract addition. Nine Holstein Friesian bulls, 3.5 years old, of known health status, were used for the study. The animals were kept and fed equally. Semen was collected once a week using an artificial vagina. The commercially available Holothuroidea extract was used as a supplement to the commercial extender (0, 2, 4 and 6 µL/mL) before the freezing/thawing process. The viability, motility, motion parameters, and acrosome integrity of the sperm were analyzed with (test) or without (control) extract samples. Furthermore, the concentration of the proAKAP4 biomarker in frozen sperm was assessed. It was shown that the addition of 4 and 6 µL of the extract may have a positive effect on the quality parameters of the sperm after thawing. The results indicate that extender supplementation with the above extract modulates (increases) the concentration of proAKAP4 in sperm at all tested levels. Additionally, this indicator has become helpful in identifying sperm of poor biological quality. Moreover, it has been proven that the proAKAP4 biomarker can be successfully used to evaluate the effectiveness of the use of various extenders for semen cryopreservation.

Influence of sperm cryopreservation on sperm motility and proAKAP4 concentration in mice

Background

The protein proAKAP4 is crucial for sperm motility and has been suggested as an indicator of male fertility. We determined the relationship between proAKAP4 concentration and sperm motility parameters in mice, and investigated the effects of cryopreservation on these variables.

Methods

Computer-assisted sperm analysis and ELISA were applied to determine sperm motility and proAKAP4 concentration in fresh and frozen-thawed epididymal sperm of SWISS, B6D2F1, C57BL/6N, and BALB/c mice.

Results

ProAKAP4 levels ranged between 12 and 89 ng/ml and did not differ between fresh and frozen-thawed samples, or between strains. We found a negative relationship between proAKAP4 levels and some sperm motility parameters. Sperm traits differed between strains, and cryopreservation negatively affected sperm velocity but not sperm direction parameters.

Conclusion

ProAKAP4 levels in epididymal mouse spermatozoa were unaffected by cryopreservation, highlighting the robustness of this parameter as a potentially time-independent marker for sperm motility and fertility. The high individual variation in proAKAP4 levels supports the potential role of proAKAP4 as a marker for sperm quality, though we found no positive, and even negative relationships between proAKAP4 levels and some sperm motility parameters. Future studies have to investigate the significance of proAKAP4 as an indicator for fertility in mice.

A new hemizygous missense mutation, c.454T＞C (p.S152P), in AKAP4 gene is associated with asthenozoospermia

Asthenozoospermia (ASZ) is a condition characterized by reduced forward motility of spermatozoa affecting approximately 19% of infertile men. A kinase anchor protein 4 (AKAP4) is an X-linked testis-specific gene and plays a major role in sperm motility and flagella formation. However, few studies have reported its association with ASZ. Here, we sequenced for exonic mutations of human AKAP4 gene by high-fidelity PCR/Sanger sequencing in peripheral blood samples from 150 ASZ patients and 150 fertile men. We reported the identification of three novel hemizygous mutations unique to four ASZ patients, including one patient carrying missense mutation c.454T>C (p.S152P), two patient carrying synonymous mutation c.1173T>C (p.H391H), and one patient carrying synonymous mutation c.2007 A>G (p.R669R). The p.S152P mutation was located in a precursor pro-polypeptide domain of AKAP4 protein, which was predicted to be damaging by SIFT and PolyPhen-2 and could cause the protein accumulation in the cytoplasm of COS-7 cells. The mature protein of AKAP4 was absent in spermatozoa of ASZ patient harboring AKAP4 p.S152P mutation. Further in vitro cellular assays showed that reactive oxygen species (ROS), malondialdehyde (MDA), myeloperoxidase (MPO) levels, and apoptotic cells were increased in GC2-spd cells by AKAP4 p.S152P mutant protein, whereas superoxide dismutase (SOD) level was decreased. AKAP4 p.H391H and p.R669R mutant proteins were coimmunoprecipitated with ribonuclease T2 (RNASET2) protein in GC2-spd cells, whereas no interaction between the AKAP4 p.S152P mutant protein and RNASET2 protein was observed. In addition, AKAP4 p.S152P mutant protein could decrease the activity of PKA/PI3K signaling. Overall, our study identifies a novel AKAP4 p.S152P mutation is associated with ASZ probably through affecting oxidative stress and cell apoptosis by regulating the interaction with RNASET2 and the activity of the PKA/PI3K signaling pathway.

Loss-of-function missense variant of AKAP4 induced male infertility through reduced interaction with QRICH2 during sperm flagella development

Sperm fibrous sheath is closely related to sperm maturation, capacitation and motility, and A-kinase anchor protein 4 (AKAP4) is the most abundant protein in sperm fibrous sheath. Previous studies found incomplete sperm fibrous sheaths and abnormal flagella in Akap4 knockout (KO) mice. Meanwhile, it was reported that the partial deletion in AKAP4 is highly relevant to the dysplasia of the fibrous sheath in an infertile man, and so far, there is no report about male infertility caused by hemizygous AKAP4 variant. Furthermore, the specific mechanisms of how the variant is relevant to the phenotype remain elusive. In this study, we investigated three multiple morphological abnormalities of the sperm flagella (MMAF)-affected men from three independent families (including one consanguine family) carried hemizygous c.C1285T variant in AKAP4. The patients carried thisvariant showed dysplastic sperm fibrous sheath and the protein expression of AKAP4 was decreased in flagella which was further confirmed in HEK-293 T cells in vitro. In addition, the co-localization and interaction between AKAP4 and glutamine-rich protein 2 (QRICH2) on the molecular level were identified by immunofluorescence and Co-immunoprecipitation (CO-IP). The hemizygous c.1285C > T variant in AKAP4 induced decreased protein expression of QRICH2 in spermatozoa. These results suggested that the normal expression of AKAP4 is required for maintaining the expression of QRICH2 and the decreased protein expression of AKAP4 and QRICH2，as well as the interaction between them induced by the hemizygous variant of AKAP4 caused dysplastic fibrous sheath, which eventually led to reduced sperm motility and male infertility.

First results about ProAKAP4 concentration in stallion semen after cryopreservation in two different freezing media

The quality of fresh or thawed sperm in stallions has been generally determined by the viability and total and progressive motility of the sperm. Today, the expression of ProAKAP4, a protein present in the flagellum of spermatozoa, appears to be an innovative and relevant functional marker to assess semen quality and male fertility. This study aims to compare the concentration of ProAKAP4 in the semen from 5 stallions frozen with two different extenders immediately after thawing (T0) and 4 h post-thawing (T4). Viability, total and progressive motility were measured in parallel. Significant differences for sperm viability and total motility were observed between the two extenders, as was the concentration of ProAKAP4 both at T0 and T4. At T4, all quality parameters and ProAKAP4 content significantly decreased compared to T0, but with a considerably slower decrease in one extender than the other. These preliminary results suggest that measuring the concentration of ProAKAP4 is a promising tool for the comparison of different extenders and the selection of the optimal freezing medium for each stallion ejaculate.

Comparative Proteomics and Phosphoproteomics Analysis Reveal the Possible Breed Difference in Yorkshire and Duroc Boar Spermatozoa

Sperm cells are of unique elongated structure and function, the development of which is tightly regulated by the existing proteins and the posttranslational modifications (PTM) of these proteins. Based on the phylogenetic relationships of various swine breeds, Yorkshire boar is believed to be distinctly different from Duroc boar. The comprehensive differential proteomics and phosphoproteomics profilings were performed on spermatozoa from both Yorkshire and Duroc boars. By both peptide and PTM peptide quantification followed by statistical analyses, 167 differentially expressed proteins were identified from 1,745 proteins, and 283 differentially expressed phosphopeptides corresponding to 102 unique differentially phosphorylated proteins were measured from 1,140 identified phosphopeptides derived from 363 phosphorylated proteins. The representative results were validated by Western blots. Pathway enrichment analyses revealed that majority of differential expression proteins and differential phosphorylation proteins were primarily concerned with spermatogenesis, male gamete generation, sperm motility, energy metabolism, cilium morphogenesis, axonemal dynein complex assembly, sperm–egg recognition, and capacitation. Remarkably, axonemal dynein complex assembly related proteins, such as SMCP, SUN5, ODF1, AKAP3, and AKAP4 that play a key regulatory role in the sperm physiological functions, were significantly higher in Duroc spermatozoa than that of Yorkshire. Furthermore, phosphorylation of sperm-specific proteins, such as CABYR, ROPN1, CALM1, PRKAR2A, and PRKAR1A, participates in regulation of the boar sperm motility mainly through the cAMP/PKA signal pathway in different breeds, demonstrating that protein phosphorylation may be an important mechanism underlying the sperm diversity. Protein–protein interaction analysis revealed that the 14 overlapped proteins between differential expression proteins and differential phosphorylation proteins potentially played a key role in sperm development and motility of the flagellum, including the proteins ODF1, SMCP, AKAP4, FSIP2, and SUN5. Taken together, these physiologically and functionally differentially expressed proteins (DEPs) and differentially expressed phosphorylated proteins (DPPs) may constitute the proteomic backgrounds between the two different boar breeds. The validation will be performed to delineate the roles of these PTM proteins as modulators of Yorkshire and Duroc boar spermatozoa.

Proteostasis in the Male and Female Germline: A New Outlook on the Maintenance of Reproductive Health

For fully differentiated, long lived cells the maintenance of protein homeostasis (proteostasis) becomes a crucial determinant of cellular function and viability. Neurons are the most well-known example of this phenomenon where the majority of these cells must survive the entire course of life. However, male and female germ cells are also uniquely dependent on the maintenance of proteostasis to achieve successful fertilization. Oocytes, also long-lived cells, are subjected to prolonged periods of arrest and are largely reliant on the translation of stored mRNAs, accumulated during the growth period, to support meiotic maturation and subsequent embryogenesis. Conversely, sperm cells, while relatively ephemeral, are completely reliant on proteostasis due to the absence of both transcription and translation. Despite these remarkable, cell-specific features there has been little focus on understanding protein homeostasis in reproductive cells and how/whether proteostasis is "reset" during embryogenesis. Here, we seek to capture the momentum of this growing field by highlighting novel findings regarding germline proteostasis and how this knowledge can be used to promote reproductive health. In this review we capture proteostasis in the context of both somatic cell and germline aging and discuss the influence of oxidative stress on protein function. In particular, we highlight the contributions of proteostasis changes to oocyte aging and encourage a focus in this area that may complement the extensive analyses of DNA damage and aneuploidy that have long occupied the oocyte aging field. Moreover, we discuss the influence of common non-enzymatic protein modifications on the stability of proteins in the male germline, how these changes affect sperm function, and how they may be prevented to preserve fertility. Through this review we aim to bring to light a new trajectory for our field and highlight the potential to harness the germ cell's natural proteostasis mechanisms to improve reproductive health. This manuscript will be of interest to those in the fields of proteostasis, aging, male and female gamete reproductive biology, embryogenesis, and life course health.

Decreased expression of AKAP4 and TyrPho proteins in testis, epididymis, and spermatozoa with low sexual performance of mice induced by modified CUMS

The molecular mechanism of chronic stress especially reduced motility, a major cause of male infertility, has not been proved. It is known that A-kinase anchor protein 4 (AKAP4) and tyrosine-phosphorylated (TyrPho) proteins are involved in progressive motility. This study aimed to investigate the effect of chronic unpredictable mild stress (CUMS) on sexual behaviours, sperm quality, and expressions of AKAP4 and TyrPho proteins in testis, epididymis, and spermatozoa. Sixteen male mice were divided into control and CUMS groups (n = 8/group). Animals were induced by a stressor from twelve stressors for 36 days. Sexual behaviours, corticosterone and testosterone, sperm parameters, and histopathology were observed. The expressions of AKAP4 and TyrPho proteins in testis, epididymis, and spermatozoa were examined. Results showed that CUMS significantly increased corticosterone while serum testosterone level was decreased. Sexual behaviours and sperm parameter quality were significantly decreased. CUMS mice showed vacuolisation and pyknotic cells in seminiferous epithelium and less sperm mass was observed within epididymal lumen. CUMS decreased expressions of AKAP4 and TyrPho proteins in testis, epididymis, and spermatozoa. In conclusion, the decreased expression of AKAP4 and TyrPho proteins may be a mechanism associated with low semen qualities particularly decrease of sperm motility in CUMS.

The Male Is Significantly Implicated as the Cause of Unexplained Infertility

Male infertility is recognized as a relatively common, complex condition, generated by a broad array of environmental and genetic factors. Historical reliance on the conventional semen profile has tended to underestimate the true contribution of "the male factor" to human infertility. This review highlights the importance of genetic and epigenetic factors in the etiology of male infertility, identifying a range of mutations responsible for primary testicular failure and impaired fertilizing potential. More than three quarters of all de novo mutations arise in the male germline via mechanisms that involve the inefficient or defective repair of DNA damage. Understanding the range of factors capable of creating genetic turmoil in the paternal germline is essential, if we are to gain a deep understanding of the causes of male infertility, rather than just the symptoms that characterize its presence. High levels of DNA fragmentation induced by oxidative stress are part of this equation. Oxidative stress is, in turn, driven by biological (age, ejaculation frequency, varicocele, infection), lifestyle (smoking, obesity), and environmental factors (heat, other forms of electromagnetic radiation, and toxins) that can impair the fertilizing potential of the spermatozoa and influence the incidence of spontaneous mutations that may cause infertility in the offspring.

ProAKAP4 as Novel Molecular Marker of Sperm Quality in Ram: An Integrative Study in Fresh, Cooled and Cryopreserved Sperm

To improve artificial insemination protocols in ovine species it is crucial to optimize sperm quality evaluation after preservation technologies. Emerging technologies based on novel biomolecules and related to redox balance and proteins involved in sperm motility such as ProAKAP4 could be successfully applied in ram sperm evaluation. In this work, a multiparametric analysis of fresh, cooled, and cryopreserved ram sperm was performed at different complexity levels. Samples were evaluated in terms of motility (total motility, progressive motility, and curvilinear velocity), viability, apoptosis, content of reactive oxygen species, oxidation‒reduction potential, and ProAKAP4 expression and concentration. As expected, cryopreserved samples showed a significant decrease of sperm quality (p < 0.05), evidencing different freezability classes among samples that were detected by ProAKAP4 analyses. However, in cooled sperm no differences were found concerning motility, viability, apoptosis, ROS content, and redox balance compared to fresh sperm that could explain the reported decrease in fertility rates. However, although the proportion of sperm ProAKAP4 positive-cells remained unaltered in cooled sperm compared to fresh control, the concentration of this protein significantly decreased (p < 0.05) in cooled samples. This altered protein level could contribute to the decrease in fertility rates of cooled samples detected by some authors. More importantly, ProAKAP4 can be established as a promising diagnostic parameter of sperm quality allowing us to optimize sperm conservation protocols and finally improve artificial insemination in ovine species.

Molecular Changes Induced by Oxidative Stress that Impair Human Sperm Motility

A state of oxidative stress (OS) and the presence of reactive oxygen species (ROS) in the male reproductive tract are strongly correlated with infertility. While physiological levels of ROS are necessary for normal sperm functioning, elevated ROS production can overwhelm the cell's limited antioxidant defenses leading to dysfunction and loss of fertilizing potential. Among the deleterious pleiotropic impacts arising from OS, sperm motility appears to be particularly vulnerable. Here, we present a mechanistic account for how OS contributes to altered sperm motility profiles. In our model, it is suggested that the abundant polyunsaturated fatty acids (PUFAs) residing in the sperm membrane serve to sensitize the male germ cell to ROS attack by virtue of their ability to act as substrates for lipid peroxidation (LPO) cascades. Upon initiation, LPO leads to dramatic remodeling of the composition and biophysical properties of sperm membranes and, in the case of the mitochondria, this manifests in a dissipation of membrane potential, electron leakage, increased ROS production and reduced capacity for energy production. This situation is exacerbated by the production of cytotoxic LPO byproducts such as 4-hydroxynonenal, which dysregulate molecules associated with sperm bioenergetic pathways as well as the structural and signaling components of the motility apparatus. The impact of ROS also extends to lesions in the paternal genome, as is commonly seen in the defective spermatozoa of asthenozoospermic males. Concluding, the presence of OS in the male reproductive tract is strongly and positively correlated with reduced sperm motility and fertilizing potential, thus providing a rational target for the development of new therapeutic interventions.