Proteomic analysis reveals dysregulated cell signaling in ejaculated spermatozoa from infertile men

Insulin‑like growth factor 2 in spermatogenesis dysfunction (Review)

Spermatogenesis dysfunction is characterized by abnormal morphology, destruction, atrophy of seminiferous tubules, blocked differentiation of spermatogenic cells, decreased sperm count and increased sperm abnormalities. Inflammation, oxidative stress, endoplasmic reticulum stress and obesity are important factors leading to spermatogenesis dysfunction. It has been demonstrated that insulin‑like growth factor 2 (IGF2) is closely related to the aforementioned factors. In the present review, the relationship between IGF2 and inflammation, oxidative stress, ER stress and obesity was investigated, providing theoretical and experimental evidence on the role of IGF2 in the prevention and treatment of spermatogenesis dysfunction of male infertility.

Cryoprotectant-specific alterations in the proteome of Siberian sturgeon spermatozoa induced by cryopreservation

Cryopreservation is crucial for conserving genetic diversity in endangered species including the critically endangered group of sturgeons (Acipenseridae), but it can compromise sperm quality and protein profiles. Although cryopreservation with dimethyl sulfoxide (DMSO) and methanol (MeOH) results in the recovery of good post-thaw motility, DMSO-preserved sperm show reduced fertilization ability. This study was conducted in Siberian sturgeon as a model for Acipenserid fishes to explore the effects of DMSO and MeOH on the proteome of semen using advanced proteomics methods-liquid chromatography‒mass spectrometry and two-dimensional difference gel electrophoresis. We analyzed the proteomic profiles of fresh and cryopreserved spermatozoa and their extracellular medium and showed that cryopreservation decreases motility and viability and increases reactive oxygen species levels, membrane fluidity, and acrosome damage. Despite having similar post-thaw semen motility, sperm treated with DMSO had significantly lower fertilization success (6.2%) than those treated with MeOH (51.2%). A total of 224 and 118 differentially abundant proteins were identified in spermatozoa preserved with MeOH and DMSO, respectively. MeOH-related proteins were linked to chromosomal structure and mitochondrial functionality, while DMSO-related proteins impacted fertilization by altering the acrosome reaction and binding of sperm to the zona pellucida and nuclear organization. Additionally, cryopreservation led to alterations in the proacrosin/acrosin system in both cryoprotectants. This study provides the first comprehensive proteomic characterization of Siberian sturgeon sperm after cryopreservation, offering insights into how cryoprotectants impact fertilization ability.

Cancer risk and male Infertility: Unravelling predictive biomarkers and prognostic indicators

In recent years, there has been a global increase in cases of male infertility. There are about 30 million cases of male infertility worldwide and male reproductive health is showing rapid decline in last few decades. It is now recognized as a potential risk factor for developing certain types of cancer, particularly genitourinary malignancies like testicular and prostate cancer. Male infertility is considered a potential indicator of overall health and an early biomarker for cancer. Cases of unexplained male factor infertility have high levels of oxidative stress and oxidative DNA damage and this induces both denovo germ line mutations and epimutations due to build up of 8-hydroxy 2 deoxygunaosine abase which is highly mutagenic and also induces hypomethylation and genomic instability. Consequently, there is growing evidence to explore the various factors contributing to an increased cancer risk. Currently, the available prognostic and predictive biomarkers associated with semen characteristics and cancer risk are limited but gaining significant attention in clinical research for the diagnosis and treatment of elevated cancer risk in the individual and in offspring. The male germ cell being transcriptionally and translationally inert has a highly truncated repair mechanism and has minimal antioxidants and thus most vulnerable to oxidative injury due to environmental factors and unhealthy lifestyle and social habits. Therefore, advancing our understanding requires a thorough evaluation of the pathophysiologic mechanisms at the DNA, RNA, protein, and metabolite levels to identify key biomarkers that may underlie the pathogenesis of male infertility and associated cancer. Advanced methodologies such as genomics, epigenetics, proteomics, transcriptomics, and metabolomics stand at the forefront of cutting-edge approaches for discovering novel biomarkers, spanning from infertility to associated cancer types. Henceforth, in this review, we aim to assess the role and potential of recently identified predictive and prognostic biomarkers, offering insights into the success of assisted reproductive technologies, causes of azoospermia and idiopathic infertility, the impact of integrated holistic approach and lifestyle modifications, and the monitoring of cancer susceptibility, initiation and progression. Comprehending these biomarkers is crucial for providing comprehensive counselling to infertile men and cancer patients, along with their families.

The Effect of Neutral Alpha-Glucosidase on Semen Parameters

INTRODUCTION

The objective of this study was to investigate the relationship between the activity of neutral α-glucosidase in seminal plasma and semen quality and to explore the effect of secretory capability of the epididymis on male fertility.

METHODS

A retrospective analysis of 542 men treated in the Center for Reproductive Medicine and Infertility from February to December 2022, the semen parameters and neutral α-glucosidase were tested and compared among different groups. These 542 men included normozoospermia, oligospermia, asthenospermia, and teratozoospermia.

RESULTS

There was statistical difference in neutral alpha-glucosidase (NAG) level among different groups with different sperm concentration, motility, and morphology (p < 0.001). The NAG activity in seminal plasma was positively correlated with ejaculate volume and sperm concentration; meanwhile, a very weak positive correlation was found between NAG level and sperm motility, sperm morphology, respectively.

CONCLUSIONS

Our results indicated that the secretion of NAG affected the volume, concentration, motility, and morphology of sperm to a certain extent. Given that NAG is a specific and marker enzyme in epididymis, where is the site of sperm maturation, we can conclude that there is a close relationship between NAG and sperm quality. Therefore, seminal plasma NAG has a definite clinical value in helping diagnosis of male infertility.

Decoding the influence of semen collection processes on goat sperm quality from a perspective of seminal plasma proteomics

This study aims to assess the impact of semen collection methods on goat semen quality and seminal plasma (SP) proteomes. Semen was collected by artificial vagina (AV) or electro-ejaculator (EE) and semen parameters were evaluated. Tandem mass tag coupled with liquid chromatography-tandem mass spectrometry was used to screen SP differentially abundant proteins (DAPs) between EE and AV. PRM was used to confirm the reliability of the data. In contrast to EE, a lower volume, higher progressive motility and concentration were observed in AV. No differences were found in total motility, membrane integrity, acrosome integrity, and ROS production between EE and AV. In total, 1692 proteins were identified in SP, including 210 DAPs. Among them, 120 and 90 proteins were down-regulated and up-regulated in AV compared to EE, respectively. The GO annotation showed that DAPs are mainly localized in the membrane, involved in deference responses to bacterium, RNA processing, and related to oxidoreductase activity. KEGG demonstrated tight associations of DAPs with specific amino acids, carbon metabolism, citrate cycle, and propanoate metabolism. In conclusion, this study provides valuable insights into the effects of semen collection on goat semen quality and explores the potential action mechanism based on the modification of SP proteomes. SIGNIFICANCE OF THE STUDY: The quality of fresh semen directly influences the results of artificial insemination and semen cryopreservation in livestock. This study represents the first attempt to evaluate the impact of semen collection methods including electroejaculation and artificial vagina on sperm quality and seminal plasma proteomes in goat. The results of this study demonstrated that semen collection methods directly impacted the quality of goat semen. Then, the proteomic strategy was used to explore the potential action mechanism of semen collection methods on sperm. Some differentially abundant proteins that potentially influence semen quality were identified. Furthermore, this study suggests the possibility of utilizing specific proteins as predictive markers for goat semen quality.

Sperm traits and seminal plasma proteome of locally adapted hairy rams subjected to intermittent scrotal insulation

The present study evaluated the effects of heat stress on reproductive parameters of hairy rams. Six animals were subjected to scrotal insulation during four consecutive nights (6 PM - 6 AM). Day (D) 0 was the first day of insulation. Scrotal circumference increased from 30.5 ± 0.3 cm (at pre-insulation) to 31.8 ± 0.4 cm on D4, decreased 3.9 cm on D28, returning to 30.6 ± 0.6 cm on D57. Sperm concentration decreased from 3.7 ± 0.12 ×109 sperm/mL before insulation to 2.6 ± 0.1 ×109 on D23, returning to normal on D57. Sperm motility averaged 75 ± 2.9% before insulation, was undetectable on D23, and became normal on D77. Sperm with normal morphology reached 5.9 ± 2.6% on D35 but recovered (86.8 ± 2.1%) on D91. Sperm DNA integrity decreased from 86.5 ± 4.7% before insulation to 11.1 ± 3.7% on D63, returning to pre-insulation values on D120. Sperm BSP immunostaining was reduced after scrotal insulation. Variations in seminal protein abundances coincided with changes in sperm parameters. Seminal plasma superoxide dismutase, carboxypeptidase Q-precursor and NPC intracellular cholesterol transporter 2 decreased on D18, returning to normal after D28. Albumin, inhibitor of carbonic anhydrase precursor, EGF-like repeat and discoid I-like domain-containing protein 3 and polymeric immunoglobulin receptor increased after insulation. In summary, intermittent scrotal insulation drastically altered ram sperm attributes and seminal proteins, especially those associated with oxidative stress. Knowledge of animal´s response to thermal stress is vital in the scenario of climate changes.

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

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

Relationship among seminal antigenicity, antioxidant status and metabolically active sperm from Holstein-Friesian (Bos taurus) bulls

Sperm antigenicity has been implicated as a regulatory factor for acquiring fertilizing competence in the female reproductive tract. Overt immune response against the sperm proteins leads to idiopathic infertility. Hence, the aim of the study was to evaluate the influence of the auto-antigenic potential of sperm on the antioxidant status, metabolic activities and reactive oxygen species (ROS) in bovine. Semen from Holstein-Friesian bulls (n = 15) was collected and classified into higher (HA, n = 8) and lower (LA, n = 7) antigenic groups based on micro-titer agglutination assay. The neat semen was subjected to the evaluation of bacterial load, leukocyte count, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lipid peroxidation (LPO) levels. Antioxidant activities in seminal plasma and intracellular ROS levels in the post-thawed sperm were estimated. The number of leukocytes was lower (p < .05) in the HA than the LA semen. The percentage of metabolically active sperm was higher (p < .05) in HA than the LA group. The activities of total non-enzymatic antioxidant, superoxide dismutase (SOD) and catalase (CAT) were higher (p < .05) while glutathione peroxidase activity was lower (p < .05) in the seminal plasma of LA group. The LPO levels of neat sperm and the percentage sperm positive for intracellular ROS in the cryopreserved sample were lower (p < .05) in the HA group. Auto-antigenic levels were positively correlated with the percentage of metabolically active sperm (r = 0.73, p < .01). However, the seminal auto-antigenicity was negatively (p < .05) correlated with the levels of SOD (r=-0.66), CAT (r=-0.72), LPO (r=-0.602) and intracellular ROS (r=-0.835). The findings were represented in graphical abstract. It is inferred that the higher auto-antigenic levels protect the quality of bovine semen by promoting sperm metabolism and lowering ROS and LPO levels.

Mapping the human sperm proteome - novel insights into reproductive research

INTRODUCTION

Spermatozoa are highly specialized cells with unique morphology. In addition, spermatozoa lose a considerable amount of cytoplasm during spermiogenesis, when they also compact their DNA, resulting in a transcriptionally quiescent cell. Throughout the male reproductive tract, sperm will acquire proteins that enable them to interact with the female reproductive tract. After ejaculation, proteins undergo post-translational modifications for sperm to capacitate, hyperactivate and fertilize the oocyte. Many proteins have been identified as predictors of male infertility, and also investigated in diseases that compromise reproductive potential.

AREAS COVERED

In this review we proposed to summarize the recent findings about the sperm proteome and how they affect sperm structure, function, and fertility. A literature search was performed using PubMed and Google Scholar databases within the past 5 years until August 2022.

EXPERT OPINION

Sperm function depends on protein abundance, conformation, and PTMs; understanding the sperm proteome may help to identify pathways essential to fertility, even making it possible to unravel the mechanisms involved in idiopathic infertility. In addition, proteomics evaluation offers knowledge regarding alterations that compromise the male reproductive potential.

Altered ureido protein modification profiles in seminal plasma extracellular vesicles of non-normozoospermic men

INTRODUCTION

Extracellular vesicles (EVs) have been recognized as key players in numerous physiological functions. These vesicles alter their compositions attuned to the health and disease states of the organism. In men, significant changes in the proteomic composition(s) of seminal plasma EVs (sEVs) have already been found to be related to infertility.

METHODS

Methods: In this study, we analyze the posttranslational configuration of sEV proteomes from normozoospermic (NZ) men and non-normozoospermic (non-NZ) men diagnosed with teratozoospermia and/or asthenozoospermia by unbiased, discovery-driven proteomics and advanced bioinformatics, specifically focusing on citrulline (Cit) and homocitrulline (hCit) posttranscriptional residues, both considered product of ureido protein modifications.

RESULTS AND DISCUSSION

Significant increase in the proteome-wide cumulative presence of hCit together with downregulation of Cit in specific proteins related to decisive molecular functions have been encountered in sEVs of non-NZ subjects. These findings identify novel culprits with a higher chance of affecting fundamental aspects of sperm functional quality and define potential specific diagnostic and prognostic non-invasive markers for male infertility.

Paternal factors in recurrent pregnancy loss: an insight through analysis of non-synonymous single-nucleotide polymorphism in human testis-specific chaperone HSPA2 gene

Heat shock protein A2 (HSPA2) is a testis-specific molecular chaperone of the 70 kDa heat shock protein (HSP70) family and reported to play a key role in spermatogenesis as well as in the remodelling of the sperm surface during capacitation. It is established that mice lacking HSPA2 gene are infertile and spermatozoa that fail to interact with the zona pellucida of the oocyte consistently lack HSPA2 protein expression. However, its role in post fertilization events is not fully understood. Owing to the importance of HSPA2 in male reproduction, the present study is undertaken to reveal the association between genetic mutation and phenotypic variation in recurrent pregnancy loss (RPL) patients through an in silico prediction analysis. In this study, we used different computational tools and servers such as SIFT, PolyPhen2, PROVEAN, nsSNPAnalyzer, and SNPs & GO to analyse the functional consequences of the nsSNPs in human HSPA2 gene. The most damaging amino acid variants generated were subjected to I-Mutant 2.0 and ConSurf. Post-translational modifications such as phosphorylation mediated by these deleterious nsSNPs were analysed using NetPhos 2.0, and gene-gene interaction study was conducted using GeneMANIA. Finally, in-depth studies of the nsSNPs were studied through Project HOPE. The findings of the study revealed 18 nsSNPs to be deleterious using a combinatorial bioinformatic approach. Further functional analysis suggests that screening of nsSNP variants of HSPA2 that tend to be conserved and has potential to undergo phosphorylation at critical positions (rs764410231, rs200951589, rs756852956) may be useful for predicting outcome in altered reproductive outcome. The physicochemical alterations and its impact on the structural and functional conformity were determined by Project HOPE. Gene-gene interaction depicts its close association with antioxidant enzyme (SOD1) strongly supporting an inefficient oxidative scavenging regulatory mechanism in the spermatozoa of RPL patients as reported earlier. The present study has thus identified high-risk deleterious nsSNPs of HSPA2 gene and would be beneficial in the diagnosis and prognosis of the paternal effects in RPL patients.

Sperm acquire epididymis-derived proteins through epididymosomes

STUDY QUESTION

Are epididymosomes implicated in protein transfer from the epididymis to spermatozoa?

SUMMARY ANSWER

We characterized the contribution of epididymal secretions to the sperm proteome and demonstrated that sperm acquire epididymal proteins through epididymosomes.

WHAT IS KNOWN ALREADY

Testicular sperm are immature cells unable to fertilize an oocyte. After leaving the testis, sperm transit along the epididymis to acquire motility and fertilizing abilities. It is well known that marked changes in the sperm proteome profile occur during epididymal maturation. Since the sperm is a transcriptional and translational inert cell, previous studies have shown that sperm incorporate proteins, RNA and lipids from extracellular vesicles (EVs), released by epithelial cells lining the male reproductive tract.

STUDY DESIGN, SIZE, DURATION

We examined the contribution of the epididymis to the post-testicular maturation of spermatozoa, via the production of EVs named epididymosomes, released by epididymal epithelial cells. An integrative analysis using both human and mouse data was performed to identify sperm proteins with a potential epididymis-derived origin. Testes and epididymides from adult humans (n = 9) and adult mice (n = 3) were used to experimentally validate the tissue localization of four selected proteins using high-resolution confocal microscopy. Mouse epididymal sperm were co-incubated with carboxyfluorescein succinimidyl ester (CFSE)-labeled epididymosomes (n = 4 mice), and visualized using high-resolution confocal microscopy.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Adult (12-week-old) C57BL/CBAF1 wild-type male mice and adult humans were used for validation purposes. Testes and epididymides from both mice and humans were obtained and processed for immunofluorescence. Mouse epididymal sperm and mouse epididymosomes were obtained from the epididymal cauda segment. Fluorescent epididymosomes were obtained after labeling the epididymal vesicles with CFSE dye followed by epididymosome isolation using a density cushion. Immunofluorescence was performed following co-incubation of sperm with epididymosomes in vitro. High-resolution confocal microscopy and 3D image reconstruction were used to visualize protein localization and sperm-epididymosomes interactions.

MAIN RESULTS AND THE ROLE OF CHANCE

Through in silico analysis, we first identified 25 sperm proteins with a putative epididymal origin that were conserved in both human and mouse spermatozoa. From those, the epididymal origin of four sperm proteins (SLC27A2, EDDM3B, KRT19 and WFDC8) was validated by high-resolution confocal microscopy. SLC27A2, EDDM3B, KRT19 and WFDC8 were all detected in epithelial cells lining the human and mouse epididymis, and absent from human and mouse seminiferous tubules. We found region-specific expression patterns of these proteins throughout the mouse epididymides. In addition, while EDDM3B, KRT19 and WFDC8 were detected in both epididymal principal and clear cells (CCs), SLC27A2 was exclusively expressed in CCs. Finally, we showed that CFSE-fluorescently labeled epididymosomes interact with sperm in vitro and about 12-36% of the epididymosomes contain the targeted sperm proteins with an epididymal origin.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The human and mouse sample size was limited and our results were descriptive. The analyses of epididymal sperm and epididymosomes were solely performed in the mouse model due to the difficulties in obtaining epididymal luminal fluid human samples. Alternatively, human ejaculated sperm and seminal EVs could not be used because ejaculated sperm have already contacted with the fluids secreted by the male accessory sex glands, and seminal EVs contain other EVs in addition to epididymosomes, such as the abundant prostate-derived EVs.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings indicate that epididymosomes are capable of providing spermatozoa with a new set of epididymis-derived proteins that could modulate the sperm proteome and, subsequently, participate in the post-testicular maturation of sperm cells. Additionally, our data provide further evidence of the novel role of epididymal CCs in epididymosome production. Identifying mechanisms by which sperm mature to acquire their fertilization potential would, ultimately, lead to a better understanding of male reproductive health and may help to identify potential therapeutic strategies to improve male infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Spanish Ministry of Economy and Competitiveness (Ministerio de Economía y Competividad; fondos FEDER 'una manera de hacer Europa' PI13/00699 and PI16/00346 to R.O.; and Sara Borrell Postdoctoral Fellowship, Acción Estratégica en Salud, CD17/00109 to J.C.), by National Institutes of Health (grants HD040793 and HD069623 to S.B., grant HD104672-01 to M.A.B.), by the Spanish Ministry of Education, Culture and Sports (Ministerio de Educación, Cultura y Deporte para la Formación de Profesorado Universitario, FPU15/02306 to F.B.), by a Lalor Foundation Fellowship (to F.B. and M.A.B.), by the Government of Catalonia (Generalitat de Catalunya, pla estratègic de recerca i innovació en salut, PERIS 2016-2020, SLT002/16/00337 to M.J.), by Fundació Universitària Agustí Pedro i Pons (to F.B.), and by the American Society for Biochemistry and Molecular Biology (PROLAB Award from ASBMB/IUBMB/PABMB to F.B.). Confocal microscopy and transmission electron microscopy was performed in the Microscopy Core facility of the Massachusetts General Hospital (MGH) Center for Systems Biology/Program in Membrane Biology which receives support from Boston Area Diabetes and Endocrinology Research Center (BADERC) award DK57521 and Center for the Study of Inflammatory Bowel Disease grant DK43351. The Zeiss LSM800 microscope was acquired using an NIH Shared Instrumentation Grant S10-OD-021577-01. The authors have no conflicts of interest to declare.

Proteins involved in mitochondrial metabolic functions and fertilization predominate in stallions with better motility

Even in stallions with sperm quality within normal reference ranges at ejaculation, subtle differences in sperm quality exist that in many cases lead to reduced time frames for conservation of the ejaculate and/or reduced fertility. The spermatozoon is a cell highly suitable for proteomics studies, and the use of this technique is allowing rapid advances in the understanding of sperm biology. The aim of the present study was to investigate differences among stallions of variable sperm quality (based on motility and sperm velocities), although all horses had sperm characteristics within normal ranges. The proteome was studied using UHPLC/MS/MS and posterior bioinformatic and enrichment analysis; data are available via ProteomeXchange with identifier PXD025807. Sperm motility, linear motility and circular, straight line and average velocities (VCL, VSL, VAP) were measured using computer assisted sperm analysis (CASA). In stallions showing better percentages of motility, circular and average velocity predominated mitochondrial proteins with roles in the Citric acid cycle, pyruvate metabolism and oxidative phosphorylation. Interestingly, in stallions with better percentages of total motility, sperm proteins were also enriched in proteins within the gene ontology (G0) terms, single fertilization (G0: 0007338), fertilization (G0: 0009566), and zona pellucida receptor complex (GO:0002199). The enrichment of this proteins in samples with better percentages of total motility may offer a molecular explanation for the link between this parameter and fertility. SIGNIFICANCE: Proteomic analysis identified a high degree of specificity of stallion sperm proteins with discriminant power for motility, linear motility, and sperm velocities (VCL, VAP and VSL). These findings may represent an interesting outcome in relation to the molecular biology regulating the movement of the spermatozoa, and the biological meaning of the measurements that computer assisted sperm analysis (CASA) provide. Of a total of 903 proteins identified in stallion spermatozoa, 24 were related to the percentage of total motility in the sample; interestingly, gene ontology (G0) analysis revealed that these proteins were enriched in terms like single fertilization and fertilization, providing a molecular link between motility and fertility. Field studies indicate that the percentage of total motility is the CASA derived parameter with the best correlation with fertility in stallions.

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.

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.

The sperm centrioles

Centrioles are eukaryotic subcellular structures that produce and regulate massive cytoskeleton superstructures. They form centrosomes and cilia, regulate new centriole formation, anchor cilia to the cell, and regulate cilia function. These basic centriolar functions are executed in sperm cells during their amplification from spermatogonial stem cells during their differentiation to spermatozoa, and finally, after fertilization, when the sperm fuses with the egg. However, sperm centrioles exhibit many unique characteristics not commonly observed in other cell types, including structural remodeling, centriole-flagellum transition zone migration, and cell membrane association during meiosis. Here, we discuss five roles of sperm centrioles: orchestrating early spermatogenic cell divisions, forming the spermatozoon flagella, linking the spermatozoon head and tail, controlling sperm tail beating, and organizing the cytoskeleton of the zygote post-fertilization. We present the historic discovery of the centriole as a sperm factor that initiates embryogenesis, and recent genetic studies in humans and other mammals evaluating the current evidence for the five functions of sperm centrioles. We also examine information connecting the various sperm centriole functions to distinct clinical phenotypes. The emerging picture is that centrioles are essential sperm components with remarkable functional diversity and specialization that will require extensive and in-depth future studies.

Anatomic characteristics of epididymis based on histology, proteomic, and 3D reconstruction

BACKGROUND

The epididymis is a popular research topic in urology and reproduction.

OBJECTIVES

To explore and identify the anatomical characteristics of the epididymis based on histology, proteomics, and 3D reconstruction of epididymal tubules.

MATERIALS AND METHODS

A 3D reconstruction of epididymal tubules was generated based on 7-μm-thick transverse serial sections of an epididymis. The proteins in the subcompartments of the epididymis were obtained and analyzed by non-labeled sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH MS). Protein function, signaling pathways, protein expression, and the histology in different subcompartments were analyzed.

RESULTS

The caput (Cap), corpus (Cor), and cauda (Cau) of the epididymis were divided into 6, 10, and 4 subcompartments, respectively, and the subcompartment between the Cap and Cor is mixed together. A total of 3411 proteins were identified, and 854 proteins were accurately quantified after screening. When the subcompartment Cap 5 transitioned to Cap 6 and Cap 6 to Cap 7, 87 and 52 proteins were upregulated and 14 and 7 proteins were downregulated, respectively. The Cor 9 transition to Cau 1 was marked by 230 proteins that were downregulated, while 74 proteins were upregulated. At the junction of the cauda and the vas deferens, 57 proteins were downregulated, and 410 proteins were upregulated. Cap 6 histology was consistent with that of Cor 1.

DISCUSSION AND CONCLUSION

The epididymis contains distinct connective tissue septa that can be identified under a surgical tabletop microscope, enabling it to be divided into 20 subcompartments.

Alterations of Spermatozoa Proteomic Profile in Men with Hodgkin's Disease Prior to Cancer Therapy

Purpose

Hodgkin's disease (HD) is a type of cancer affecting men in the reproductive age with potential consequences on their fertility status. This study aims to analyze sperm parameters, alterations in proteomic profiles and validate selected protein biomarkers of spermatozoa in men with HD undergoing sperm banking before cancer therapy.

Materials and Methods

Semen analysis was carried out in healthy fertile donors (control, n=42), and patients diagnosed with HD (patients, n=38) before cancer therapy. We compared proteomic profiles of spermatozoa from donors (n=3) and patients (n=3) using LTQ-Orbitrap Elite hybrid MS system.

Results

A total of 1,169 proteins were identified by global proteomic in both groups. The ingenuity pathway analysis revealed that differentially expressed proteins involved in capacitation, acrosome reaction, binding of sperm to the zona pellucida, sperm motility, regulation of sperm DNA damage, and apoptosis were significantly downregulated in HD patients. Validation of proteins implicated in sperm fertility potential by Western Blot demonstrated that peroxiredoxin 2 (PRDX 2) was underexpressed (p=0.015), and transferrin (p=0.045) and SERPIN A5 (p=0.010) protein levels were overexpressed in spermatozoa of men with HD.

Conclusions

Findings of this study indicates that the key proteins involved in sperm fertility potential are significantly altered in men with HD, which provides substantial explanation for the observed low sperm quality in HD subjects prior to cancer therapy. Furthermore, our results suggest PRDX 2, transferrin and SERPIN A5 as possible candidate proteins for assessing sperm quality in HD patients prior to cancer therapy.