Absence of Rnf126 causes male infertility with multiple morphological abnormalities of the sperm flagella

Male infertility is primarily caused by impaired flagella development, reduced sperm count, and decreased motility. Despite the involvement of many genes in spermatogenesis, the precise processes remain unclear. The critical E3 ubiquitin ligase Rnf126 regulates essential cellular processes through ubiquitination-induced protein degradation. It plays a significant role in DNA repair, immune response, and signaling cascades, underscoring its central importance in maintaining cellular homeostasis. However, the mechanisms by which Rnf126 controls spermatogenesis are not fully understood. This research identifies Rnf126 as a crucial component in sperm flagellar biogenesis and germ cell development. Through genetic lineage tracing, we show that RNF126 is highly expressed in sperm cells and weakly expressed in Sertoli cells. The germ epithelium of RNF126 deficiencies is characterized by a loss of germ cells due to an increase in germ cell apoptosis at various stages of development, which ultimately results in vesiculation of the spermatogenic tubule. Targeting Rnf126 results in different types of germ cells reduction, infertility, and microtubule-associated motor activity failure (MMAF), characterized by spermatozoa with truncated, twisted, and malformed flagella. Detailed ultrastructural studies reveal the extent of flagellar damage in the absence of Rnf126, highlighting its critical role in maintaining flagellar stability. An important finding is the interaction between RNF126 and BAG6, which regulates sperm synthesis and germ cell development. Clinically, reduced RNF126 levels in sperm from individuals with oligoasthenoteratospermia are significantly different from those in fertile individuals. Investigating Rnf126 function in spermatogenesis, together with empirical findings on MMAF presentation, may improve our understanding of the developmental processes involved in sperm flagellum formation and contribute to elucidating the causes of male infertility.

Male germ cells with Bag5 deficiency show reduced spermiogenesis and exchange of basic nuclear proteins

Bcl-2 associated athanogene-5 (BAG5) represents a unique BAG cochaperone family member, regulating chaperone activity. We first demonstrated significant differences in Bag5 expression by RNA seq analysis of teratozoospermia and healthy male sperm samples, but the genetic and molecular mechanisms governing this process remain elusive. We further found that BAG5 has highest expression in human and mouse testes. BAG5 expression is elevated in late stage pachytene spermatocytes and spermatids. Targeted Bag5 inactivation in mice induces massive apoptosis in male germ cells and abrogates male infertility. The ordered loading of sperm basic nuclear proteins on chromatin is altered, with lost TNPs and PRMs, resulting in severe sperm head deformity and partial 9 + 2 microtubule structure disorder. In terms of mechanism, immunoprecipitation (IP)-mass spectroscopy (MS) revealed BAG5 interacts with HSPA2, a testis-specific HSP70 family member regulating the transcription of the transition protein TNPs as well as spermatogenesis. RNA-sequencing assessment of Bag5 deficient testis confirmed Bag5 participation in transcriptional repression and revealed significant changes in Hspa2 expression. Bag5 deficiency resulted in decreased levels of HSPA2, germ cell apoptosis and subsequent inappropriate nuclear protein deposition and chromatin condensation. Decreased BAG5 expression levels in patients with non-obstructive azoospermia and oligoasthenospermia were also detected. These results uncovered an intriguing HSPA2-mediated key function of BAG5, which may constitute a potential prognostic biomarker of male infertility.

The proteomic landscape of sperm surface deciphers its maturational and functional aspects in buffalo

Buffalo is a dominant dairy animal in many agriculture-based economies. However, the poor reproductive efficiency (low conception rate) of the buffalo bulls constrains the realization of its full production potential. This in turn leads to economic and welfare issues, especially for the marginal farmers in such economies. The mammalian sperm surface proteins have been implicated in the regulation of survival and function of the spermatozoa in the female reproductive tract (FRT). Nonetheless, the lack of specific studies on buffalo sperm surface makes it difficult for researchers to explore and investigate the role of these proteins in the regulation of mechanisms associated with sperm protection, survival, and function. This study aimed to generate a buffalo sperm surface-specific proteomic fingerprint (LC-MS/MS) and to predict the functional roles of the identified proteins. The three treatments used to remove sperm surface protein viz. Elevated salt, phosphoinositide phospholipase C (PI-PLC) and in vitro capacitation led to the identification of N = 1,695 proteins (≥1 high-quality peptide-spectrum matches (PSMs), p < 0.05, and FDR<0.01). Almost half of these proteins (N = 873) were found to be involved in crucial processes relevant in the context of male fertility, e.g., spermatogenesis, sperm maturation and protection in the FRT, and gamete interaction or fertilization, amongst others. The extensive sperm-surface proteomic repertoire discovered in this study is unparalleled vis-à-vis the depth of identification of reproduction-specific cell-surface proteins and can provide a potential framework for further studies on the functional aspects of buffalo spermatozoa.

Molecular Chaperone HSPA2 Distribution During Hyaluronic Acid Selection in Human Sperm

During fertilization, sperm hyaluronidase activity is essential for spermatozoa to successfully penetrate the hyaluronic acid-enriched extracellular matrix of the cumulus cells. Since molecular chaperones, as the heat shock protein A2, are typically involved in bringing hyaluronic acid receptors to the cell surface, here we evaluated the presence and spatial location of HSPA2 on human spermatozoa based on its hyaluronic acid binding capacity. This study included 16 normozoospermic sperm samples from volunteering donors. The location of HSPA2 was studied in cells before and after 1-h incubation under capacitating conditions, as well as in spermatozoa selected according to their ability of binding to hyaluronic acid. Our results showed no significant differences in HSPA2 immunofluorescent cells before and after 1 h of incubation in capacitating conditions. Nevertheless, after hyaluronic acid selection, the percentage of HSPA2-labelled cells increased significantly, indicating that the interaction with hyaluronic acid may induce the unmasking of HSPA2 epitopes. Furthermore, after swim-up and hyaluronic acid selection, spermatozoa presented a highly immunostained equatorial band with a homogeneous fluorescence throughout the acrosomal region. This distribution has been previously suggested to have important implications in male fertility. Noteworthy, a homogeneous fluorescence among the acrosomal region with a more intense labelling at the apical region was observed only in hyaluronic acid bound sperm cells, which may be associated with primary gamete recognition. Our findings suggest that the hyaluronic acid selection technique and HSPA2 biomarker should be considered candidates to complement the classic seminal analysis before recommending an appropriate assisted reproduction technique.

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.

Proteomic changes in human spermatozoa during in vitro capacitation and acrosome reaction in normozoospermia and asthenozoospermia

BACKGROUND

The cellular and molecular mechanisms of the events that help spermatozoa acquire their fertilizing capability during capacitation and acrosome reaction are not completely understood.

OBJECTIVE

This study was performed with a postulation that the identification of sperm proteins and their changes during in vitro capacitation and acrosome reaction will unravel unknown molecular aspects of fertilization that impact male fertility.

MATERIALS AND METHODS

Spermatozoa collected from sequential conditions, that is, separation of ejaculated spermatozoa by Percoll gradient centrifugation, in vitro capacitation, and acrosome reaction were processed for tandem mass spectrometric analysis, followed by protein identification, label-free quantitation, and statistical analysis.

RESULTS AND DISCUSSION

Collectively, a total of 1088 sperm proteins were identified. In comparison to ejaculated spermatozoa, 44 and 141 proteins were differentially expressed in capacitated and acrosome reacted spermatozoa, respectively. A large number of proteins were found downregulated, including clusterin, pyruvate dehydrogenase E1 component, semenogelin-1 and 2, heat shock protein 90, beta-microseminoprotein, and keratin. It was expected as sperm-membrane-associated proteins are removed during capacitation. There were significant proteomic alterations in asthenozoospermia compared to normozoospermia; however, variation was more noticeable among proteins of acrosome reacted spermatozoa and those released during the acrosome reaction. The processes enriched among downregulated proteins in asthenozoospermia included acrosome assembly, binding of spermatozoa to zona pellucida, nucleosome assembly, flagellated sperm motility, protein folding, oxidative phosphorylation, tricarboxylic acid cycle, chromatin silencing, gluconeogenesis, glycolytic process, and glycolysis.

CONCLUSION

The dynamic information generated about proteomic alterations in spermatozoa during capacitation and acrosome reaction and their variability in asthenozoospermia will contribute not only to enhancing our understanding of processes that prepare spermatozoa to acquire fertilization capability but also help in deciphering novel factors of male infertility.

USP5 enhances SGTA mediated protein quality control

Mislocalised membrane proteins (MLPs) present a risk to the cell due to exposed hydrophobic amino acids which cause MLPs to aggregate. Previous studies identified SGTA as a key component of the machinery that regulates the quality control of MLPs. Overexpression of SGTA promotes deubiqutination of MLPs resulting in their accumulation in cytosolic inclusions, suggesting SGTA acts in collaboration with deubiquitinating enzymes (DUBs) to exert these effects. However, the DUBs that play a role in this process have not been identified. In this study we have identified the ubiquitin specific peptidase 5 (USP5) as a DUB important in regulating the quality control of MLPs. We show that USP5 is in complex with SGTA, and this association is increased in the presence of an MLP. Overexpression of SGTA results in an increase in steady-state levels of MLPs suggesting a delay in proteasomal degradation of substrates. However, our results show that this effect is strongly dependent on the presence of USP5. We find that in the absence of USP5, the ability of SGTA to increase the steady state levels of MLPs is compromised. Moreover, knockdown of USP5 results in a reduction in the steady state levels of MLPs, while overexpression of USP5 increases the steady state levels. Our findings suggest that the interaction of SGTA with USP5 enables specific MLPs to escape proteasomal degradation allowing selective modulation of MLP quality control. These findings progress our understanding of aggregate formation, a hallmark in a range of neurodegenerative diseases and type II diabetes, as well as physiological processes of aggregate clearance.

Targeted Analysis of HSP70 Isoforms in Human Spermatozoa in the Context of Capacitation and Motility

HSP70s constitute a family of chaperones, some isoforms of which appear to play a role in sperm function. Notably, global proteomic studies analyzing proteins deregulated in asthenozoospermia, a main cause of male infertility characterized by low sperm motility, showed the dysregulation of some HSP70 isoforms. However, to date, no clear trend has been established since the variations in the abundance of HSP70 isoforms differed between studies. The HSPA2 isoform has been reported to play a key role in fertilization, but its dysregulation and possible relocation during capacitation, a maturation process making the spermatozoon capable of fertilizing an oocyte, is debated in the literature. The aim of the present study was to investigate the fate of all sperm HSP70 isoforms during capacitation and in relation to sperm motility. Using Multiple-Reaction Monitoring (MRM) mass spectrometry, we showed that the relative abundance of all detected isoforms was stable between non-capacitated and capacitated spermatozoa. Immunofluorescence using two different antibodies also demonstrated the stability of HSP70 isoform localization during capacitation. We also investigated spermatozoa purified from 20 sperm samples displaying various levels of total and progressive sperm motility. We showed that the abundance of HSP70 isoforms is not correlated to sperm total or progressive motility.

BCL2-associated athanogene 6 exon24 contributes to testosterone synthesis and male fertility in mammals

Objectives

BCL2‐associated athanogene 6 (BAG6) plays critical roles in spermatogenesis by maintaining testicular cell survival. Our previous data showed porcine BAG6 exon24‐skipped transcript is highly expressed in immature testes compared with mature testes. The objective of this study is to reveal the functional significance of BAG6 exon24 in mammalian spermatogenesis.

Materials and Methods

CRISPR/Cas9 system was used to generate Bag6 exon24 knockout mice. Testes and cauda epididymal sperm were collected from mice. TMT proteomics analysis was used to discover the protein differences induced by Bag6 exon24 deletion. Testosterone enanthate was injected into mice to generate a high‐testosterone mice model. H&E staining, qRT‐PCR, western blotting, vector/siRNA transfection, immunofluorescence, immunoprecipitation, transmission electron microscopy, TUNEL and ELISA were performed to investigate the phenotypes and molecular basis.

Results

Bag6 exon24 knockout mice show sub‐fertility along with partially impaired blood‐testis barrier, increased apoptotic testicular cell rate and abnormal sperm morphology. Endoplasmic reticulum stress occurs in Bag6 exon24‐deficient testes and sterol regulatory element‐binding transcription factor 2 is activated; as a result, cytochrome P450 family 51 subfamily A member 1 expression is up‐regulated, which causes a high serum testosterone level. Additionally, serine/arginine‐rich splicing factor 1 down‐regulates BAG6 exon24‐skipped transcripts in porcine Sertoli cells by binding to 35–51 nt on BAG6 exon24 via its N‐terminal RNA‐recognition domain.

Conclusions

Our findings reveal the critical roles of BAG6 exon24 in testosterone biosynthesis and male fertility, which provides new insights into the regulation of spermatogenesis and pathogenesis of subfertility in mammals.

Differential gene expression analysis related to sperm storage in spermathecas of Amphioctopus fangsiao

Sperm storage in the female body is an important strategy in animal reproductive behavior. Amphioctopus fangsiao is an economically important cephalopod that has a sperm storage period of up to seven months. There are few studies concerning the mechanism of sperm storage in A. fangsiao. In this study, we performed transcriptome gene expression profiling of the oviductal glands at different phases (presence and absence of sperm storage). In total, 7943 differentially expressed genes (DEGs) comprising 4737 upregulated and 3206 downregulated genes were identified. GO and KEGG enrichment analyses were used to search for sperm storage-related genes. A protein interaction network was constructed to examine the interactions between genes. Nineteen genes associated with immunity, apoptosis, and autophagy were obtained and verified by qRT-PCR. This is the first comprehensive analysis of sperm storage-related genes in A. fangsiao. The results provide basic insights into the complex sperm storage mechanism of A. fangsiao.

Extracellular vesicles derived from human Sertoli cells: characterizations, proteomic analysis, and miRNA profiling

BACKGROUND

Extracellular vesicles (EVs) contain thousands of proteins and nucleic acids, playing an important role in cell-cell communications. Sertoli cells have been essential in the testis as a "nurse cell". However, EVs derived from human Sertoli cells (HSerCs) have not been well investigated.

METHODS

EVs were isolated from HSerCs via ultracentrifugation and characterized by transmission electron microscopy, tunable resistive pulse sensing, and Western blotting. The cargo carried by HSerCs-EVs was measured via liquid chromatography-mass spectrometry and GeneChip miRNA Arrays. Bioinformatic analysis was performed to reveal potential functions of HSerCs-EVs.

RESULTS

A total of 860 proteins with no less than 2 unique peptides and 88 microRNAs with high signal values were identified in HSerCs-EVs. Biological processes related to molecular binding, enzyme activity, and regulation of cell cycle were significantly enriched. Specifically, many proteins in HSerCs-EVs were associated with spermatogenesis and regulation of immune system, including Septins, Large proline-rich protein BAG6, Clusterin, and Galectin-1. Moreover, abundant microRNAs within HSerCs-EVs (miR-638, miR-149-3p, miR-1246, etc.) had a possible impact on male reproductive disorders such as asthenozoospermia and oligozoospermia.

CONCLUSIONS

Our study has shown that HSerCs-EVs contain diverse components such as proteins and microRNAs. Further research is required to evaluate HSerCs-EVs in spermatogenesis, which are underutilized but highly potent resources with particular promise for male infertility.

Evaluation of seminal plasma HSPA2 protein as a biomarker of human spermatogenesis status

In mammals, testicular Heat shock-related 70 kDa protein 2 (HSPA2) is a chaperon strictly linked to spermatogenesis status, whereas its presence in spermatozoa ensures successful oocyte fertilization. However, there is little information on this protein in seminal plasma in infertile males. Based on our previous two independent studies, we have selected HSPA2 to evaluate this seminal plasma protein is a potential biomarker of correct spermatogenesis. Using immunoblotting and mass spectrometry (MS) we have screened human seminal plasma samples for the presence of HSPA2. Samples were obtained from individuals with normozoospermia, cryptozoospermia, non-obstructive and obstructive azoospermia. Our results showed a lack of HSPA2 in seminal plasma in all azoospermic males however, in cryptozoospermia the results were extremely diversified. Additionally, the application of 2-dimensional gel electrophoresis (2-DE) indicated the presence of additional protein isoforms suggesting possible mechanisms underlying the male infertility. Our findings suggest seminal plasma HSPA2 protein as a possible biomarker not only of spermatogenesis status, especially in cryptozoospermic males, but also as a biomarker predicting the success of reproductive treatment including assisted reproductive techniques (ART).

Proteomic Profile of Sperm in Infertile Males Reveals Changes in Metabolic Pathways

The objective of the present study was to investigate the differences in the proteomic profiles of sperm from infertile males with severe oligoasthenoteratozoospermia requiring intracytoplasmic sperm injection (ICSI) and normal control sperm from fertile males. Isobaric tag for relative and absolute quantitation labeling and liquid chromatography-tandem mass spectrometry was performed for identifying proteins in the sperm of infertile and fertile males. Differentially expressed proteins were analyzed via the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases through the Database for Annotation, Visualization, and Integrated Discovery, and protein-protein networks were produced using the Search Tool for Retrieval of Interacting Genes. Immunofluorescence and western blotting verified the differential expression of Y-box-binding protein 1(YBX1), adenylate kinase 1 (AK1), and aconitase 2, mitochondrial (ACO2) proteins. Altogether, 3444 proteins were identified in the sperm of infertile and fertile males, and 938 were differentially expressed between the two groups. Pairwise comparisons revealed that 226 and 712 proteins were significantly upregulated and downregulated in infertile males, respectively. These proteins were significantly enriched in metabolic pathways as per KEGG enrichment analysis. YBX1 expression was upregulated in the sperm heads of patients requiring ICSI treatment, whereas AK1 and ACO2, which are critical enzymes involved in energy metabolism, were downregulated in the sperm tails of the same patients. This result indicates that metabolism may have a crucial role in maintaining normal sperm function. Overall, our results provide insights that will further help in investigating the pathogenic mechanisms of infertility and possible therapeutic strategies.

Stress response pathways in the male germ cells and gametes

The unfolded protein response (UPR) is a conserved and essential cellular pathway involved in protein quality control that is activated in response to several cellular stressors such as diseases states, ageing, infection and toxins. The cytosol, endoplasmic reticulum (ER) and mitochondria are continuously exposed to new proteins and in situations of aberrant protein folding; one of three lines of defence may be activated: (i) heat-shock response, (ii) mitochondrial UPR and (iii) ER UPR. These pathways lead to different signal transduction mechanisms that activate or upregulate transcription factors that, in turn, regulate genes that increase the cell's ability to correct the conformation of poorly folded proteins or, ultimately, lead to apoptosis. Despite the recent progress in understanding such biological processes, few studies have focused on the implications of the UPR in male infertility, highlighting the need for a first approach concerning the presence of these components in the male reproductive system. In testis, there is a high rate of protein synthesis, and the UPR mechanisms are well described. However, the presence of these mechanisms in spermatozoa, apparently transcriptionally inactive cells, is contentious, and it is unclear how sperm cells deal with stress. Here, we review current concepts and mechanisms of the UPR and highlight the relevance of these stress response pathways in male fertility, especially the presence and functional activation of those components in male germinal cells and spermatozoa.

[Localization of Arylsulfatase A during in vitro incubation of human spermatozoa in capacitation media]

OBJECTIVE

To determine the localization and distribution of the ArylsulfataseA receptor (ARSA) in human spermatozoa before and after their incubation in capacitation medium for 1 and 4hours.

MATERIAL AND METHODS

Semen samples were obtained from five normozoospermic donors. Capacitation was by swim-up technique using capacitation medium for 1 and 4hours. Localization of the ARSA receptor was assessed by indirect immunofluorescence using confocal microscopy. A minimum of 200cells were observed in each physiological condition.

RESULTS

Before incubation, no representative pattern was observed among the cells positive for this biomarker (8.61%). This percentage increased significantly after incubation in the capacitation medium for 1 and 4hours (61.86% and 63.38% respectively). A majority pattern was observed among the capacitated cells, with intense labelling in the acrosomal region (27.11% and 28.20% after 1 and 4hours respectively). It should be noted that the pattern corresponding to fluorescence at the level of the periacrosomal region was not observed in the spermatozoa prior to incubation. Only after incubation in capacitation medium for 1 and 4hours, 9.13% and 12.78% of cells with such distribution were detected.

CONCLUSIONS

In vitro capacitation, regardless of time, favours the immunolocalization of ARSA in the cephalic region of the spermatozoa. The most representative subpopulation after this process was the one in which ARSA was intensely and homogeneously distributed in the acrosome region, involved in primary gamete recognition.

Human sperm chaperone HSPA2 distribution during in vitro capacitation

Human fertilization success depends on the ability of the spermatozoa to undergo capacitation. Even though this process can be conducted in vitro, the optimal time for a sperm cell to complete capacitation in vitro is still under discussion due to the lack of proper capacitation biomarkers. Here, we evaluated the influence of in vitro capacitation time on HSPA2 distribution over human sperm head testing this chaperone as a potential capacitation biomarker. The chaperone was assessed in human spermatozoa from 16 normozoospermic donors using indirect immunofluorescence in uncapacitated, one and four-hour capacitated spermatozoa. The percentage of HSPA2 immunofluorescent cells before and after one hour of capacitation did not differ significantly. However, after four hours of capacitation, we observed a significantly higher percentage of HSPA2 labelled cells. In fluorescent cells analysed before capacitation, we could not identify a predominant distribution pattern. Meanwhile, after capacitation, most sperm showed a highly labelled equatorial band accompanied by a homogeneous fluorescence throughout the acrosomal region. Our findings suggest that HSPA2 needs more than one hour of in vitro capacitation for being correctly distributed in the anterior region of the sperm head. In conclusion, the present study provides solid evidences for the utility of HSPA2 as a biomarker of human sperm in vitro capacitation. Due to its importance during egg-sperm recognition, the use of HSPA2 as a biomarker before an artificial reproduction technique may be suggested, in addition to a longer capacitation time during sperm preparation.

Various Anti-HSPA2 Antibodies Yield Different Results in Studies on Cancer-Related Functions of Heat Shock Protein A2

Heat shock proteins (HSPs) constitute a major part of the molecular chaperone system and play a fundamental role in cell proteostasis. The HSPA (HSP70) family groups twelve highly homologous HSPA proteins. Certain HSPAs are regarded as important cancer-related proteins, prospective therapeutic targets for cancer treatment, and also as potential cancer biomarkers. Heat Shock Protein A2 (HSPA2), a testis-enriched chaperone and one of the least characterized members of the HSPA family, has recently emerged as an important cancer-relevant protein with potential biomarker significance. Nevertheless, conflicting conclusions have been recently drawn both according to HSPA2 role in cancer cells, as well as to its prognostic value. In this work we have shown that one of the serious limitations in HSPA2 protein research is cross-reactivity of antibodies marketed as specific for HSPA2 with one or more other HSPA(s). Among non-specific antibodies were also those recently used for HSPA2 detection in functional and biomarker studies. We showed how using non-specific antibodies can generate misleading conclusions on HSPA2 expression in non-stressed cancer cells and tumors, as well as in cancer cells exposed to proteotoxic stress. Our findings addressed concerns on some published studies dealing with HSPA2 as a cancer-related protein.

Transcriptome profiling of porcine testis tissue reveals genes related to sperm hyperactive motility

BACKGROUND

Sperm hyperactive motility has previously been shown to influence litter size in pigs, but little is known about the underlying biological mechanisms. The aim of this study was to use RNA sequencing to investigate gene expression differences in testis tissue from Landrace and Duroc boars with high and low levels of sperm hyperactive motility. Boars with divergent phenotypes were selected based on their sperm hyperactivity values at the day of ejaculation (day 0) (contrasts (i) and (ii) for Landrace and Duroc, respectively) and on their change in hyperactivity between day 0 and after 96 h liquid storage at 18 °C (contrast (iii)).

RESULTS

RNA sequencing was used to measure gene expression in testis. In Landrace boars, 3219 genes were differentially expressed for contrast (i), whereas 102 genes were differentially expressed for contrast (iii). Forty-one differentially expressed genes were identified in both contrasts, suggesting a functional role of these genes in hyperactivity regardless of storage. Zinc finger DNLZ was the most up-regulated gene in contrasts (i) and (iii), whereas the most significant differentially expressed gene for the two contrasts were ADP ribosylation factor ARFGAP1 and solute carrier SLC40A1, respectively. For Duroc (contrast (ii)), the clustering of boars based on their gene expression data did not reflect their difference in sperm hyperactivity phenotypes. No results were therefore obtained for this breed. A case-control analysis of variants identified in the Landrace RNA sequencing data showed that SNPs in NEU3, CHRDL2 and HMCN1 might be important for sperm hyperactivity.

CONCLUSIONS

Differentially expressed genes were identified in Landrace boars with high and low levels of sperm hyperactivity at the day of ejaculate collection and high and low change in hyperactivity after 96 h of sperm storage. The results point towards important candidate genes, biochemical pathways and sequence variants underlying sperm hyperactivity in pigs.

GLIPR1L1 is an IZUMO-binding protein required for optimal fertilization in the mouse

Background

The sperm protein IZUMO1 (Izumo sperm-egg fusion 1) and its recently identified binding partner on the oolemma, IZUMO1R, are among the first ligand-receptor pairs shown to be essential for gamete recognition and adhesion. However, the IZUMO1-IZUMO1R interaction does not appear to be directly responsible for promoting the fusion of the gamete membranes, suggesting that this critical phase of the fertilization cascade requires the concerted action of alternative fusogenic machinery. It has therefore been proposed that IZUMO1 may play a secondary role in the organization and/or stabilization of higher-order heteromeric complexes in spermatozoa that are required for membrane fusion.

Results

Here, we show that fertilization-competent (acrosome reacted) mouse spermatozoa harbor several high molecular weight protein complexes, a subset of which are readily able to adhere to solubilized oolemmal proteins. At least two of these complexes contain IZUMO1 in partnership with GLI pathogenesis-related 1 like 1 (GLIPR1L1). This interaction is associated with lipid rafts and is dynamically remodeled upon the induction of acrosomal exocytosis in preparation for sperm adhesion to the oolemma. Accordingly, the selective ablation of GLIPR1L1 leads to compromised sperm function characterized by a reduced ability to undergo the acrosome reaction and a failure of IZUMO1 redistribution.

Conclusions

Collectively, this study characterizes multimeric protein complexes on the sperm surface and identifies GLIPRL1L1 as a physiologically relevant regulator of IZUMO1 function and the fertilization process.

RNF144A functions as a tumor suppressor in breast cancer through ubiquitin ligase activity-dependent regulation of stability and oncogenic functions of HSPA2

Deregulation of E3 ubiquitin ligases is intimately implicated in breast cancer pathogenesis and progression, but the underlying mechanisms still remain elusive. Here we report that RING finger protein 144A (RNF144A), a poorly characterized member of the RING-in-between-RING family of E3 ubiquitin ligases, functions as a tumor suppressor in breast cancer. RNF144A was  downregulated in a subset of primary breast tumors and restoration of RNF144A suppressed breast cancer cell proliferation, colony formation, migration, invasion in vitro, tumor growth, and lung metastasis in vivo. In contrast, knockdown of RNF144A promoted malignant phenotypes of breast cancer cells. Quantitative proteomics and biochemical analysis revealed that RNF144A interacted with and targeted heat-shock protein family A member 2 (HSPA2), a putative oncoprotein that is frequently upregulated in human cancer and promotes tumor growth and progression, for ubiquitination and degradation. Notably, the ligase activity-defective mutants of RNF144A impaired its ability to induce ubiquitination and degradation of HSPA2, and to suppress breast cancer cell proliferation, migration, and invasion as compared with its wild-type counterpart. Moreover, RNF144A-mediated suppression of breast cancer cell proliferation, migration, and invasion was rescued by ectopic HSPA2 expression. Clinically, low RNF144A and high HSPA2 expression in breast cancer patients was correlated with aggressive clinicopathological characteristics and decreased overall and disease-free survival. Collectively, these findings reveal a previously unappreciated role for RNF144A in suppression of breast cancer growth and metastasis, and identify RNF144A as the first, to our knowledge, E3 ubiquitin ligase for HSPA2 in human cancer.

Investigation into the presence and functional significance of proinsulin C-peptide in the female germline†

Diabetes is associated with poor oocyte quality and the dysregulation of ovarian function and is thus a leading contributor to the increasing prevalence of female reproductive pathologies. Accordingly, it is well-established that insulin fulfills a key role in the regulation of several facets of female reproduction. What remains less certain is whether proinsulin C-peptide, which has recently been implicated in cellular signaling cascades, holds a functional role in the female germline. In the present study, we examined the expression of insulin, C-peptide, and its purported receptor; GPR146, within the mouse ovary and oocyte. Our data establish the presence of abundant C-peptide within follicular fluid and raise the prospect that this bioactive peptide is internalized by oocytes in a G-protein coupled receptor-dependent manner. Further, our data reveal that internalized C-peptide undergoes pronounced subcellular relocalization from the ooplasm to the pronuclei postfertilization. The application of immunoprecipitation analysis and mass spectrometry identified breast cancer type 2 susceptibility protein (BRCA2), the meiotic resumption/DNA repair protein, as a primary binding partner for C-peptide within the oocyte. Collectively, these findings establish a novel accumulation profile for C-peptide in the female germline and provide the first evidence for an interaction between C-peptide and BRCA2. This interaction is particularly intriguing when considering the propensity for oocytes from diabetic women to experience aberrant meiotic resumption and perturbation of traditional DNA repair processes. This therefore provides a clear imperative for further investigation of the implications of dysregulated C-peptide production in these individuals.

The roles of cytosolic quality control proteins, SGTA and the BAG6 complex, in disease

SGTA is a co-chaperone that, in collaboration with the complex of BAG6/UBL4A/TRC35, facilitates the biogenesis and quality control of hydrophobic proteins, protecting them from the aqueous cytosolic environment. This work includes targeting tail-anchored proteins to their resident membranes, sorting of membrane and secretory proteins that mislocalize to the cytoplasm and endoplasmic reticulum-associated degradation of misfolded proteins. Since these functions are all vital for the cell's continued proteostasis, their disruption poses a threat to the cell, with a particular risk of protein aggregation, a phenomenon that underpins many diseases. Although the specific disease implications of machinery involved in quality control of hydrophobic substrates are poorly understood, here we summarize much of the available information on this topic.

Assessing the potential of HSPA2 and ADAM2 as two biomarkers for human sperm selection

Selection of the best sperm, with the least defects, is a critical factor in the success of ART especially in male factor infertility. This study assessed the potential Heat shock protein (HSPA2) and metallopeptidase domain2 (ADAM2) biomarkers for sperm selection. Sperm were obtained from 72 asthenoteratozoospermic and 42 normospermic ejaculates. The semen characteristic, DNA fragmentation (DFI), chromatin maturation index (CMI), ADAM2 and HSPA2 levels on sperm, and their correlation with embryo quality were assessed in both groups. Results showed the significant reduction in HSPA2 and ADAM2 in asthenoteratozoospermic compared to normazoospermic ejaculates regarding the cut-off value of 14 and 13% for these two biomarkers. The specificity of HSPA2 and ADAM2 separately, and the combination of these two biomarkers, were 95.2, 90.5 and 93.5%, respectively, for sperm from normozoospermic ejaculates. However, they were 48.6, 50.0 and 54.5% for asthenoteratozoospermic ones. A significant correlation was observed with HSPA2, ADAM2 and a combination of these two biomarkers with CMI, DFI and embryo quality. Although a combination of these two biomarkers have the potential to be a good choice for selecting sperm with the lowest level of chromatin damage, it seems that selection according to HSPA2 has priority over ADAM2 or a combination of the two.

Proteolytic degradation of heat shock protein A2 occurs in response to oxidative stress in male germ cells of the mouse

STUDY QUESTION

Does oxidative stress compromise the protein expression of heat shock protein A2 (HSPA2) in the developing germ cells of the mouse testis?

SUMMARY ANSWER

Oxidative stress leads to the modification of HSPA2 by the lipid aldehyde 4-hydroxynonenal (4HNE) and initiates its degradation via the ubiquitin-proteasome system.

WHAT IS KNOWN ALREADY

Previous work has revealed a deficiency in HSPA2 protein expression within the spermatozoa of infertile men that have failed fertilization in a clinical setting. While the biological basis of this reduction in HSPA2 remains to be established, we have recently shown that the HSPA2 expressed in the spermatozoa of normozoospermic individuals is highly susceptible to adduction, a form of post-translational modification, by the lipid aldehyde 4HNE that has been causally linked to the degradation of its substrates. This modification of HSPA2 by 4HNE adduction dramatically reduced human sperm-egg interaction in vitro. Moreover, studies in a mouse model offer compelling evidence that the co-chaperone BCL2-associated athanogene 6 (BAG6) plays a key role in regulating the stability of HSPA2 in the testis, by preventing its ubiquitination and subsequent proteolytic degradation.

STUDY DESIGN, SIZE, DURATION

Dose-dependent studies were used to establish a 4HNE-treatment regime for primary culture(s) of male mouse germ cells. The influence of 4HNE on HSPA2 protein stability was subsequently assessed in treated germ cells. Additionally, sperm lysates from infertile patients with established zona pellucida recognition defects were examined for the presence of 4HNE and ubiquitin adducts. A minimum of three biological replicates were performed to test statistical significance.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oxidative stress was induced in pachytene spermatocytes and round spermatids isolated from the mouse testis, as well as a GC-2 cell line, using 50-200 µM 4HNE or hydrogen peroxide (H2O2), and the expression of HSPA2 was monitored via immunocytochemistry and immunoblotting approaches. Using the GC-2 cell line as a model, the ubiquitination and degradation of HSPA2 was assessed using immunoprecipitation techniques and pharmacological inhibition of proteasomal and lysosomal degradation pathways. Finally, the interaction between BAG6 and HSPA2 was examined in response to 4HNE exposure via proximity ligation assays.

MAIN RESULTS AND THE ROLE OF CHANCE

HSPA2 protein levels were significantly reduced compared with controls after 4HNE treatment of round spermatids (P < 0.01) and GC-2 cells (P < 0.001) but not pachytene spermatocytes. Using GC-2 cells as a model, HSPA2 was shown to be both adducted by 4HNE and targeted for ubiquitination in response to cellular oxidative stress. Inhibition of the proteasome with MG132 prevented HSPA2 degradation after 4HNE treatment indicating that the degradation of HSPA2 is likely to occur via a proteasomal pathway. Moreover, our assessment of proteasome activity provided evidence that 4HNE treatment can significantly increase the proteasome activity of GC-2 cells (P < 0.05 versus control). Finally, 4HNE exposure to GC-2 cells resulted in the dissociation of HSPA2 from its regulatory co-chaperone BAG6, a key mediator of HSPA2 stability in male germ cells.

LIMITATIONS, REASONS FOR CAUTION

While these experiments were performed using a mouse germ cell-model system, our analyses of patient sperm lysate imply that these mechanisms are conserved between mouse and human germ cells.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests a causative link between non-enzymatic post-translational modifications and the relative levels of HSPA2 in the spermatozoa of a specific sub-class of infertile males. In doing so, this work enhances our understanding of failed sperm-egg recognition and may assist in the development of targeted antioxidant-based approaches for ameliorating the production of cytotoxic lipid aldehydes in the testis in an attempt to prevent this form of infertility.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Health and Medical Research Council of Australia (APP1101953). The authors have no competing interests to declare.

Treatment of semen samples with α-chymotrypsin alters the expression pattern of sperm functional proteins-a pilot study

Semen hyperviscosity delays the liquefaction of semen sample and is subjected to limited proteolysis by addition of α-chymotrypsin to reduce the viscosity. α-Chymotrypsin is a proteolytic enzyme involved in degradation of the proteins and polypeptides. Even though α-chymotrypsin improves the handling of hyperviscous samples, its effect on the sperm proteins is not clear. This study was aimed to evaluate the alteration in the expression of sperm functional proteins in samples treated with α-chymotrypsin. Among all the proteins examined in both donor and patient samples, HSPA2 (70 KDa), BAG6 (150 KDa), HIST1H2BA (14 KDa), SPA17 (17 KDa formed after cleavage of C-terminal calmodulin-binding domain), and OXPHOS complexes were undetectable in α-chymotrypsin-treated samples, while the expression of the native SPA17 (20 KDa) was significantly decreased in the α-chymotrypsin-treated samples in comparison with controls. The use of α-chymotrypsin for liquefaction of hyperviscous samples degrades functional proteins of spermatozoa. Intracellular proteins, such as OXPHOS complexes and HIST1H2BA, and sperm surface proteins (HSPA2, BAG6, and SPA17) were degraded in all treated samples. Whether treatment of samples with α-chymotrypsin affects the global proteomic outcome is unclear. More in-depth calibration studies are required to determine the appropriate concentration of α-chymotrypsin for processing hyperviscous semen samples without compromising its protein expression and function. Similarly, the effects of altered protein function on assisted reproductive techniques (ART), such as intrauterine insemination (IUI) and in vitro fertilization (IVF) outcome, are not known and require further research.

Oocyte Activation and Fertilisation: Crucial Contributors from the Sperm and Oocyte

This chapter intends to summarise the importance of sperm- and oocyte-derived factors in the processes of sperm-oocyte binding and oocyte activation. First, we describe the initial interaction between sperm and the zona pellucida, with particular regard to acrosome exocytosis. We then describe how sperm and oocyte membranes fuse, with special reference to the discovery of the sperm protein IZUMO1 and its interaction with the oocyte membrane receptor JUNO. We then focus specifically upon oocyte activation, the fundamental process by which the oocyte is alleviated from metaphase II arrest by a sperm-soluble factor. The identity of this sperm factor has been the source of much debate recently, although mounting evidence, from several different laboratories, provides strong support for phospholipase C ζ (PLCζ), a sperm-specific phospholipase. Herein, we discuss the evidence in support of PLCζ and evaluate the potential role of other candidate proteins, such as post-acrosomal WW-binding domain protein (PAWP/WBP2NL). Since the cascade of downstream events triggered by the sperm-borne oocyte activation factor heavily relies upon specialised cellular machinery within the oocyte, we also discuss the critical role of oocyte-borne factors, such as the inositol trisphosphate receptor (IP₃R), protein kinase C (PKC), store-operated calcium entry (SOCE) and calcium/calmodulin-dependent protein kinase II (CaMKII), during the process of oocyte activation. In order to place the implications of these various factors and processes into a clinical context, we proceed to describe their potential association with oocyte activation failure and discuss how clinical techniques such as the in vitro maturation of oocytes may affect oocyte activation ability. Finally, we contemplate the role of artificial oocyte activating agents in the clinical rescue of oocyte activation deficiency and discuss options for more endogenous alternatives.

Heat Shock Protein A2 (HSPA2): Regulatory Roles in Germ Cell Development and Sperm Function

Among the numerous families of heat shock protein (HSP) that have been implicated in the regulation of reproductive system development and function, those belonging to the 70 kDa HSP family have emerged as being indispensable for male fertility. In particular, the testis-enriched heat shock 70 kDa protein 2 (HSPA2) has been shown to be critical for the progression of germ cell differentiation during spermatogenesis in the mouse model. Beyond this developmentally important window, mounting evidence has also implicated HSPA2 in the functional transformation of the human sperm cell during their ascent of the female reproductive tract. Specifically, HSPA2 appears to coordinate the remodelling of specialised sperm domains overlying the anterior region of the sperm head compatible with their principle role in oocyte recognition. The fact that levels of the HSPA2 protein in mature spermatozoa tightly correlate with the efficacy of oocyte binding highlight its utility as a powerful prognostic biomarker of male fertility. In this chapter, we consider the unique structural and biochemical characteristics of HSPA2 that enable this heat shock protein to fulfil its prominent roles in orchestrating the morphological differentiation of male germ cells during spermatogenesis as well as their functional transformation during post-testicular sperm maturation.

Data on the concentrations of etoposide, PSC833, BAPTA-AM, and cycloheximide that do not compromise the vitality of mature mouse oocytes, parthenogencially activated and fertilized embryos

These data document the vitality of mature mouse oocytes (Metaphase II (MII)) and early stage embryos (zygotes) following exposure to the genotoxic chemotherapeutic agent, etoposide, in combination with PSC833, a selective inhibitor of permeability glycoprotein. They also illustrate the vitality of parthenogenetically activated and fertilized embryos following incubation with the calcium chelator BAPTA-AM (1,2-Bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid tetrakis (acetoxymethyl ester)), cycloheximide (an antibiotic that is capable of inhibiting protein synthesis), and hydrogen peroxide (a potent reactive oxygen species). Finally, they present evidence that permeability glycoprotein is not represented in the proteome of mouse spermatozoa. Our interpretation and discussion of these data feature in the article “Identification of a key role for permeability glycoprotein in enhancing the cellular defense mechanisms of fertilized oocytes” (Martin et al., in press) [1].

Spermatogenesis-associated proteins at different developmental stages of buffalo testicular seminiferous tubules identified by comparative proteomic analysis

The testicular seminiferous tubules contain Sertoli cells and different types of spermatogenic cells. They provide the microenvironment for spermatogenesis, but the precise molecular mechanism of spermatogenesis is still not well known. Here, we have employed tandem mass tag coupled to LC-MS/MS with the high-throughput quantitative proteomics technology to explore the protein expression from buffalo testicular seminiferous tubules at three different developmental stages (prepuberty, puberty, and postpuberty). The results show 304 differentially expressed proteins with a ≥2-fold change, and bioinformatics analysis indicates that 27 of these may be associated with spermatogenesis. Expression patterns of seven selected proteins were verified via Western blot and quantitative RT-PCR analysis, and further cellular localizations of these proteins by immunohistochemical or immunofluorescence analysis. Taken together, the results provide potential molecular markers of spermatogenesis and provide a rich resource for further studies on male reproduction regulation.