Extracellular microRNAs from the epididymis as potential mediators of cell-to-cell communication

Signatures of metabolic diseases on spermatogenesis and testicular metabolism

Diets leading to caloric overload are linked to metabolic disorders and reproductive function impairment. Metabolic and hormonal abnormalities stand out as defining features of metabolic disorders, and substantially affect the functionality of the testis. Metabolic disorders induce testicular metabolic dysfunction, chronic inflammation and oxidative stress. The disruption of gastrointestinal, pancreatic, adipose tissue and testicular hormonal regulation induced by metabolic disorders can also contribute to a state of compromised fertility. In this Review, we will delve into the effects of high-fat diets and metabolic disorders on testicular metabolism and spermatogenesis, which are crucial elements for male reproductive function. Moreover, metabolic disorders have been shown to influence the epigenome of male gametes and might have a potential role in transmitting phenotype traits across generations. However, the existing evidence strongly underscores the unmet need to understand the mechanisms responsible for transgenerational paternal inheritance of male reproductive function impairment related to metabolic disorders. This knowledge could be useful for developing targeted interventions to prevent, counteract, and most of all break the perpetuation chain of male reproductive dysfunction associated with metabolic disorders across generations.

Infertility: Focus on the therapeutic potential of extracellular vesicles

Infertility is a well-known problem that arises from a variety of reproductive diseases. Until now, researchers have tried various methods to restore fertility, including medication specific to the cause, hormone treatments, surgical removals, and assisted reproductive technologies. While these methods do produce results, they do not consistently lead to fertility restoration in every instance. The use of exosome therapy has significant potential in treating infertility in patients. This is because exosomes, microvesicles, and apoptotic bodies, which are different types of vesicles, play a crucial role in transferring bioactive molecules that aid in cell-to-cell communication. Reproductive fluids can transport a variety of molecular cargos, such as miRNAs, mRNAs, proteins, lipids, and DNA molecules. The percentage of these cargos in the fluids can be linked to their physiological and pathological status. EVs are involved in several physiological and pathological processes and offer interesting non-cellular therapeutic possibilities to treat infertility. EVs (extracellular vesicles) transplantation has been shown in many studies to be a key part of regenerating different parts of the reproductive system, including the production of oocytes and the start of sperm production. Nevertheless, the existing evidence necessitates testifying to the effectiveness of injecting EVs in resolving reproductive problems among humans. This review focuses on the current literature about infertility issues in both females and males, specifically examining the potential treatments involving extracellular vesicles (EVs).

MicroRNAs in Male Fertility

Around 50% of all occurrences of infertility are attributable to the male factor, which is a significant global public health concern. There are numerous circumstances that might interfere with spermatogenesis and cause the body to produce abnormal sperm. While evaluating sperm, the count, the speed at which they migrate, and their appearance are the three primary characteristics that are analyzed. MicroRNAs, also known as miRNAs, are present in all physiological fluids and tissues. They participate in both physiological and pathological processes. Researches have demonstrated that the expression of microRNA genes differs in infertile men. These genes regulate spermatogenesis at various stages and in several male reproductive cells. Hence, microRNAs have the potential to act as useful indicators in the diagnosis and treatment of male infertility and other diseases affecting male reproduction. Despite this, additional research is necessary to determine the precise miRNA regulation mechanisms.

Segmental differentiation of the murine epididymis: identification of segment-specific, GM1-enriched vesicles and regulation by luminal fluid factors†

The murine epididymis has 10 distinct segments that provide the opportunity to identify compartmentalized cell physiological mechanisms underlying sperm maturation. However, despite the essential role of the epididymis in reproduction, remarkably little is known about segment-specific functions of this organ. Here, we investigate the dramatic segmental localization of the ganglioside GM1, a glycosphingolipid already known to play key roles in sperm capacitation and acrosome exocytosis. Frozen tissue sections of epididymides from adult mice were treated with the binding subunit of cholera toxin conjugated to AlexaFluor 488 to label GM1. We report that GM1-enriched vesicles were found exclusively in principal and clear cells of segment 2. These vesicles were also restricted to the lumen of segment 2 and did not appear to flow with the sperm into segment 3, within the limits of detection by confocal microscopy. Interestingly, this segment-specific presence was altered in several azoospermic mouse models and in wild-type mice after efferent duct ligation. These findings indicate that a lumicrine factor, itself dependent on spermatogenesis, controls this segmental differentiation. The RNA sequencing results confirmed global de-differentiation of the proximal epididymal segments in response to efferent duct ligation. Additionally, GM1 localization on the surface of the sperm head increased as sperm transit through segment 2 and have contact with the GM1-enriched vesicles. This is the first report of segment-specific vesicles and their role in enriching sperm with GM1, a glycosphingolipid known to be critical for sperm function, providing key insights into the segment-specific physiology and function of the epididymis.

Conditioned medium and secretome from epididymal epithelial cell cultures improve sperm kinetics and capacitation

Background and Aim

Sperm maturation occurs in the epididymis through interactions with existing molecules inside the lumen. However, the mechanism of epididymis molecular transfer is currently unclear. This study was aimed to determine the necessity of the epididymal epithelial cells (EECs) in the process of sperm maturation in terms of sperm kinetics and tyrosine phosphorylation.

Materials and Methods

A true experimental research design was used in this study. The medium tested was a primary culture of mice caput epididymal cells (cells and culture medium), conditioned medium (CM) (supernatant of EECs), and secretome (CM filtered at 0.22 μm). Sperm was cocultured in EEC culture, CM, and secretome for 1, 2, 3, or 4 h. The original culture medium was used as the control. Sperm kinetic analysis was performed after the indicated times using computer-assisted sperm analysis, and tyrosine phosphorylation was detected using the Western blot technique.

Results

A primary culture of caput EECs was successfully generated. The results showed increased sperm motility and progressive movement after 3 h of incubation (p < 0.05). There was a significant decrease in the average path velocity (VAP) values after 4 h of incubation (p < 0.05), but there was no significant change in the 1, 2, and 3 h incubation groups. The EEC culture-CM and secretome groups showed a significant increased progressivity and VAP percentage values compared with the control medium (p < 0.05). In terms of percentage motility, the culture and CM groups were significantly different from the control medium, but the secretome group was not.

Conclusion

The sperm kinetics of sperm cultured in CM, secretome, and EEC were significantly increased after 3 h of incubation, suggesting that CM and secretome can be used to replace EECs, especially when analyzing molecules secreted by the epididymal epithelium during sperm maturation. The results of this study highlight the potential of CM and secretome as therapy mediums for sperm kinetic abnormalities.

Spectacular role of epididymis and bio-active cargo of nano-scale exosome in sperm maturation: A review

The epididymis is responsible for post-testicular sperm maturation as it provides a favorable environment for spermatozoa to gain the ability for movement and fertilization. The recent evidence has shown that, the spermatozoa are vulnerable to dynamic variations driven by various cellular exposure mechanisms mediated by epididymosomes. Exosomes provide new insight into a mechanism of intercellular communication because they provide direct evidence for the transfer of several important bio-active cargo elements (proteins, lipid, DNA, mRNA, microRNA, circular RNA, long noncoding RNA) between epididymis and spermatozoa. In broad sense, proteomic analysis of exosomes from epididymis indicates number of proteins that are involved in sperm motility, acrosomal reaction, prevent pre-mature sperm capacitation and male infertility. Pinpointing, how reproductive disorders are associated with bio-active cargo elements of nano-scale exosome in the male reproductive tract. Therefore, the current review presents evidence regarding the distinctive characteristics and functions of nano-scale exosome in the male reproductive tract in both pathological and physiological developments, and argue that these vesicles serve as an important regulator of male reproduction, fertility, and disease susceptibility.

Expression of SPAG7 and its regulatory microRNAs in seminal plasma and seminal plasma-derived extracellular vesicles of patients with subfertility

Seminal plasma contains a variety of extracellular vesicles (EVs) that deliver RNAs including microRNAs (miRNAs) molecules. However, the roles of these EVs along with their delivered RNAs and their interactions with male infertility are not clear. Sperm-associated antigen 7 (SPAG 7) is expressed in male germ cells and plays a crucial role in several biological functions associated with sperm production and maturation. In this study, we aimed to identify the post-transcriptional regulation of SPAG7 in seminal plasma (SF-Native) and seminal plasma-derived extracellular vesicles (SF-EVs) collected from 87 men undergoing infertility treatment. Among the multiple binding sites for miRNAs within its 3'UTR of SPAG7, we identified the binding of four miRNAs (miR-15b-5p, miR-195-5p, miR-424-5p, and miR-497-5p) to the 3'UTR of SPAG7 by the dual luciferase assays. Analyzing sperm, we found reduced mRNA expression levels of SPAG7 in SF-EVs and SF-Native samples from oligoasthenozoospermic men. By contrast, two miRNAs (miR-424-5p and miR-497-5p) form the SF-Native samples, and four miRNAs (miR-195-5p, miR-424-5p, miR-497-5p, and miR-6838-5p) from the SF-EVs samples showed significantly higher expression levels in oligoasthenozoospermic men. The expression levels of miRNAs and SPAG7 were significantly correlated with basic semen parameters. These findings contribute significantly to our understanding of regulatory pathways in male fertility by showing a direct link between upregulated miRNA, notably miR-424, and downregulated SPAG7 both in seminal plasma and in plasma-derived EVs likely contributing to oligoasthenozoospermia.

Integrative Analysis of Small RNA and mRNA Expression Profiles Identifies Signatures Associated With Chronic Epididymitis

Chronic epididymitis (CE) refers to a long-lasting inflammatory condition of the epididymis, which is considered the most common site of intrascrotal inflammation and an important aetiological factor of male infertility. Recent studies demonstrate that small RNAs secreted from epididymal epithelium modulate embryo development and offspring phenotypes via sperm transmission, and the resulting modifications may lead to transgenerational inheritance. However, to date, the genome-wide analysis of small RNA together with the transcriptomic expression profiles of human epididymis and CE is still lacking. In this study, we facilitated next-generation sequencing and bioinformatics to comprehensively analyze the small RNA and mRNA in an integrative way and identified signatures associated with CE. Both of the small RNA and mRNA expression data demonstrated relatively larger molecular differences among the segmental region of the epididymides, including caput, corpus, and cauda, than that of the inflammatory conditions. By comparing the inflamed caputs to the controls, a total of 1727 genes (1220 upregulated and 507 downregulated; 42 most significant genes, adjusted P <0.05) and 34 miRNAs (23 upregulated and 11 downregulated) were identified as differentially expressed. In silico functional enrichment analysis showed their roles in regulating different biological activities, including leukocyte chemotaxis, extracellular milieu reconstruction, ion channel and transporter-related processes, and nervous system development. Integrative analysis of miRNA and mRNA identified a regulatory network consisting of 22 miRNAs and 31 genes (miRNA-mRNA) which are strong candidates for CE. In addition, analysis about other species of small RNA, including (miRNA), piwi-interacting RNA (piRNA), tRNA-derived small RNA (tsRNA), Y RNA, and rsRNA identified the distinct expression pattern of tsRNA in CE. In summary, our study performed small RNA and miRNA profiling and integrative analysis in human CE. The findings will help to understand the role of miRNA-mRNA in the pathogenesis of CE and provide molecular candidates for the development of potential biomarkers for human CE.

Calcium Homeostasis in the Epididymal Microenvironment: Is Extracellular Calcium a Cofactor for Matrix Gla Protein-Dependent Scavenging Regulated by Vitamins

In the male reproductive tract, the epididymis is an essential organ for sperm maturation, in which sperm cells acquire mobility and the ability to fertilize oocytes while being stored in a protective microenvironment. Epididymal function involves a specialized luminal microenvironment established by the epithelial cells of epididymal mucosa. Low-calcium concentration is a unique feature of this epididymal luminal microenvironment, its relevance and regulation are, however, incompletely understood. In the rat epididymis, the vitamin D-related calcium-dependent TRPV6-TMEM16A channel-coupler has been shown to be involved in fluid transport, and, in a spatially complementary manner, vitamin K2-related γ-glutamyl carboxylase (GGCX)-dependent carboxylation of matrix Gla protein (MGP) plays an essential role in promoting calcium-dependent protein aggregation. An SNP in the human GGCX gene has been associated with asthenozoospermia. In addition, bioinformatic analysis also suggests the involvement of a vitamin B6-axis in calcium-dependent MGP-mediated protein aggregation. These findings suggest that vitamins interact with calcium homeostasis in the epididymis to ensure proper sperm maturation and male fertility. This review article discusses the regulation mechanisms of calcium homeostasis in the epididymis, and the potential role of vitamin interactions on epididymal calcium homeostasis, especially the role of matrix calcium in the epididymal lumen as a cofactor for the carboxylated MGP-mediated scavenging function.

Small Noncoding RNAs in Reproduction and Infertility

Infertility has been reported as one of the most common reproductive impairments, affecting nearly one in six couples worldwide. A large proportion of infertility cases are diagnosed as idiopathic, signifying a deficit in information surrounding the pathology of infertility and necessity of medical intervention such as assisted reproductive therapy. Small noncoding RNAs (sncRNAs) are well-established regulators of mammalian reproduction. Advanced technologies have revealed the dynamic expression and diverse functions of sncRNAs during mammalian germ cell development. Mounting evidence indicates sncRNAs in sperm, especially microRNAs (miRNAs) and transfer RNA (tRNA)-derived small RNAs (tsRNAs), are sensitive to environmental changes and mediate the inheritance of paternally acquired metabolic and mental traits. Here, we review the critical roles of sncRNAs in mammalian germ cell development. Furthermore, we highlight the functions of sperm-borne sncRNAs in epigenetic inheritance. We also discuss evidence supporting sncRNAs as promising biomarkers for fertility and embryo quality in addition to the present limitations of using sncRNAs for infertility diagnosis and treatment.

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section I

Simple Summary

Male fertility is often estimated by simple sperm assessment, and therefore, it is crucial to establish species-specific baselines for normal sperm parameters. In this paper, sperm physiology, function, and common abnormalities in stallions will be reviewed.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of semen physiology as it applies to overall fertility. This segment of our two-section review will focus on normal sperm parameters, beginning with development and extending through the basic morphology of mature spermatozoa, as well as common issues with male factor infertility in IVP. Ultimately, the relevance of sperm parameters to overall male factor fertility in equine IVP will be assessed.

Caput Ligation Renders Immature Mouse Sperm Motile and Capable to Undergo cAMP-Dependent Phosphorylation

Mammalian sperm must undergo two post-testicular processes to become fertilization-competent: maturation in the male epididymis and capacitation in the female reproductive tract. While caput epididymal sperm are unable to move and have not yet acquired fertilization potential, sperm in the cauda epididymis have completed their maturation, can move actively, and have gained the ability to undergo capacitation in the female tract or in vitro. Due to the impossibility of mimicking sperm maturation in vitro, the molecular pathways underlying this process remain largely unknown. We aimed to investigate the use of caput epididymal ligation as a tool for the study of sperm maturation in mice. Our results indicate that after seven days of ligation, caput sperm gained motility and underwent molecular changes comparable with those observed for cauda mature sperm. Moreover, ligated caput sperm were able to activate pathways related to sperm capacitation. Despite these changes, ligated caput sperm were unable to fertilize in vitro. Our results suggest that transit through the epididymis is not required for the acquisition of motility and some capacitation-associated signaling but is essential for full epididymal maturation. Caput epididymal ligation is a useful tool for the study of the molecular pathways involved in the acquisition of sperm motility during maturation.

Seminal plasma miR-210-3p induces spermatogenic cell apoptosis by activating caspase-3 in patients with varicocele

The aim of this study was to investigate the role of seminal plasma miR-210-3p in the impairment of semen quality caused by varicocele. This study included 102 patients whose semen quality was normal when they were diagnosed with varicocele. A 2-year follow-up for included patients was performed, and they were divided into Group A (semen quality became abnormal) and Group B (semen quality remained normal) according to the results of semen analysis during the follow-up. Semen parameters and seminal plasma miR-210-3p expression were investigated by semen analysis and quantitative real-time polymerase chain reaction, respectively. In vitro experiments with GC-2 cells were performed to explore the role of miR-210-3p in spermatogenic cells. The results of quantitative real-time polymerase chain reaction showed that the level of seminal plasma miR-210-3p in Group A was higher than that in Group B both after 2-year follow-up and when they were diagnosed with varicocele (both P < 0.01). Apoptosis and proliferation assays showed that miR-210-3p induces apoptosis of spermatogenic cells by promoting caspase-3 activation. In conclusion, our study indicated that seminal plasma miR-210-3p induces spermatogenic cell apoptosis by activating caspase-3 in patients with varicocele. Seminal plasma miR-210-3p may be a potential biomarker for predicting impaired semen quality caused by varicocele.

Role of Exosomes in the Exchange of Spermatozoa after Leaving the Seminiferous Tubule: A Review

BACKGROUND

Exosomes are extracellular vesicles (EVs) released from cells upon fusion of an intermediate endocytic compartment with the plasma membrane. They refer to the intraluminal vesicles released from the fusion of multivesicular bodies with the plasma membrane. The contents and number of exosomes are related to diseases such as metabolic diseases, cancer and inflammatory diseases. Exosomes have been used in neurological research as a drug delivery tool and also as biomarkers for diseases. Recently, exosomes were observed in the seminal plasma of the one who is asthenozoospermia, which can affect sperm motility and capacitation.

OBJECTIVE

The main objective of this review is to deeply discuss the role of exosomes in spermatozoa after leaving the seminiferous tubule.

METHODS

We conducted an extensive search of the literature available on relationships between exosomes and exosomes in spermatozoa on the bibliographic database.

CONCLUSION

This review thoroughly discussed the role that exosomes play in the exchange of spermatozoa after leaving the seminiferous tubule and its potential as a drug delivery tool and biomarkers for diseases as well.

Network Analyses Predict Small RNAs That Might Modulate Gene Expression in the Testis and Epididymis of Bos indicus Bulls

Spermatogenesis relies on complex molecular mechanisms, essential for the genesis and differentiation of the male gamete. Germ cell differentiation starts at the testicular parenchyma and finishes in the epididymis, which has three main regions: head, body, and tail. RNA-sequencing data of the testicular parenchyma (TP), head epididymis (HE), and tail epididymis (TE) from four bulls (three biopsies per bull: 12 samples) were subjected to differential expression analyses, functional enrichment analyses, and co-expression analyses. The aim was to investigate the co-expression and infer possible regulatory roles for transcripts involved in the spermatogenesis of Bos indicus bulls. Across the three pairwise comparisons, 3,826 differentially expressed (DE) transcripts were identified, of which 384 are small RNAs. Functional enrichment analysis pointed to gene ontology (GO) terms related to ion channel activity, detoxification of copper, neuroactive receptors, and spermatogenesis. Using the regulatory impact factor (RIF) algorithm, we detected 70 DE small RNAs likely to regulate the DE transcripts considering all pairwise comparisons among tissues. The pattern of small RNA co-expression suggested that these elements are involved in spermatogenesis regulation. The 3,826 DE transcripts (mRNAs and small RNAs) were further subjected to co-expression analyses using the partial correlation and information theory (PCIT) algorithm for network prediction. Significant correlations underpinned the co-expression network, which had 2,216 transcripts connected by 158,807 predicted interactions. The larger network cluster was enriched for male gamete generation and had 15 miRNAs with significant RIF. The miRNA bta-mir-2886 showed the highest number of connections (601) and was predicted to down-regulate ELOVL3, FEZF2, and HOXA13 (negative co-expression correlations and confirmed with TargetScan). In short, we suggest that bta-mir-2886 and other small RNAs might modulate gene expression in the testis and epididymis, in Bos indicus cattle.

Adipocyte, Immune Cells, and miRNA Crosstalk: A Novel Regulator of Metabolic Dysfunction and Obesity

Obesity is characterized as a complex and multifactorial excess accretion of adipose tissue (AT) accompanied with alterations in the immune response that affects virtually all age and socioeconomic groups around the globe. The abnormal accumulation of AT leads to several metabolic diseases, including nonalcoholic fatty liver disorder (NAFLD), low-grade inflammation, type 2 diabetes mellitus (T2DM), cardiovascular disorders (CVDs), and cancer. AT is an endocrine organ composed of adipocytes and immune cells, including B-Cells, T-cells and macrophages. These immune cells secrete various cytokines and chemokines and crosstalk with adipokines to maintain metabolic homeostasis and low-grade chronic inflammation. A novel form of adipokines, microRNA (miRs), is expressed in many developing peripheral tissues, including ATs, T-cells, and macrophages, and modulates the immune response. miRs are essential for insulin resistance, maintaining the tumor microenvironment, and obesity-associated inflammation (OAI). The abnormal regulation of AT, T-cells, and macrophage miRs may change the function of different organs including the pancreas, heart, liver, and skeletal muscle. Since obesity and inflammation are closely associated, the dysregulated expression of miRs in inflammatory adipocytes, T-cells, and macrophages suggest the importance of miRs in OAI. Therefore, in this review article, we have elaborated the role of miRs as epigenetic regulators affecting adipocyte differentiation, immune response, AT browning, adipogenesis, lipid metabolism, insulin resistance (IR), glucose homeostasis, obesity, and metabolic disorders. Further, we will discuss a set of altered miRs as novel biomarkers for metabolic disease progression and therapeutic targets for obesity.

Expression and localization of alpha-tubulin N-acetyltransferase 1 in the reproductive system of male mice

The structure of microtubules is essential for the fertilizing ability of spermatozoa. Acetylation of α-tubulin plays an important role in flagellar elongation and spermatozoa motility. Previous reports have suggested that alpha-tubulin N-acetyltransferase 1 (ATAT1) is the main acetyltransferase involved in the acetylation of α-tubulin. Although ATAT1 is reported to express in the testis, no information is available regarding its expression in elongated spermatids, epididymis, and mature spermatozoa. Hence, it remains unclear whether ATAT1 is involved in spermatozoa maturation and capacitation. Therefore, we evaluated the expression of ATAT1 in the mouse male reproductive system using immunostaining and western blotting. Our results showed that ATAT1 was expressed in spermatids during spermiogenesis in mouse testes, but its expression varied according to the seminiferous tubule stage. We observed ATAT1 in the cytoplasm of round spermatids, the flagella of elongated spermatids, and in the cytoplasm of step 16 spermatids, just before its release into the lumen. In addition, ATAT1 was expressed in epithelial cells of the epididymis. In spermatozoa of the cauda epididymis, ATAT1 expression was primarily observed in the midpiece of the spermatozoa. The localization of ATAT1 protein in the male germline was observed during spermiogenesis as well as during spermatozoa maturation. Our results suggest that ATAT1 may be involved in the formation of flagella and in the acetylation process, which has attracted attention in recent years regarding male infertility.

From Sperm Motility to Sperm-Borne microRNA Signatures: New Approaches to Predict Male Fertility Potential

In addition to the paternal genome, spermatozoa carry several intrinsic factors, including organelles (e.g., centrioles and mitochondria) and molecules (e.g., proteins and RNAs), which are involved in important steps of reproductive biology such as spermatogenesis, sperm maturation, oocyte fertilization and embryo development. These factors constitute potential biomarkers of "viable sperm" and male fertility status and may become major assets for diagnosing instances of idiopathic male infertility in both humans and livestock animals. A better understanding of the mechanism of action of these sperm intrinsic factors in the regulation of reproductive and developmental processes still presents a major challenge that must be addressed. This review assembles the main data regarding morpho-functional and intrinsic sperm features that are associated with male infertility, with a particular focus on microRNA (miRNA) molecules.

The Role of the Epididymis and the Contribution of Epididymosomes to Mammalian Reproduction

It is well-established that testicular spermatozoa are immature and acquire motility and fertilization capabilities during transit throughout the epididymis. The epididymis is a duct-like organ that connects the testis to the vas deferens and is comprised of four anatomical regions: the initial segment, caput, corpus, and cauda. Sperm maturation occurs during epididymal transit by the interaction of sperm cells with the unique luminal environment of each epididymal region. In this review we discuss the epididymis as an essential reproductive organ responsible for sperm concentration, maturation (including sperm motility acquisition and fertilizing ability), protection and storage. Importantly, we also discuss specific characteristics and roles of epididymal-derived exosomes (epididymosomes) in establishing sperm competency within the intricate process of reproduction. This review suggests that an increasing body of evidence is working to develop a complete picture of the role of the epididymis in male reproduction, offspring health, and disease susceptibility.

miR-26a is Involved in Glycometabolism and Affects Boar Sperm Viability by Targeting PDHX

miR-26a is associated with sperm metabolism and can affect sperm motility and apoptosis. However, how miR-26a affects sperm motility remains largely unknown. Our previous study indicated that the PDHX gene is predicted to be a potential target of miR-26a, which is responsible for pyruvate oxidative decarboxylation which is considered as a key step for connecting glycolysis with oxidative phosphorylation. In this study, we first reported a potential relationship between miR-26a and PDHX and their expressions in fresh, frozen-thawed, and epididymal boar sperm. Then, sperm viability and survival were determined after transfection of miR-26a. mRNA and protein expression level of PDHX in the liquid-preserved boar sperm after transfection were also determined by RT-qPCR and Western Blot (WB). Our results showed that expression level of PDHX was significantly increased during sperm transit from epididymal caput to corpus and cauda. Similarly, expression of PDHX was significantly higher (P < 0.05) in fresh sperm as compared to epididymal cauda and frozen-thawed sperm. However, the expression of miR-26a in epididymal corpus sperm was significantly higher (P < 0.05) than that of caput and cauda sperm. Furthermore, after transfection of boar sperm with miR-26a mimic and inhibitor under liquid storage, the lowest and highest sperm viability was observed in miR-26a mimic and inhibitor treatment (P < 0.05), respectively. The protein levels of PDHX, after 24 and 48 h of transfection of miR-26a mimics and inhibitor, were notably decreased and increased (P < 0.05), respectively, as compared to negative control (NC) group. In conclusion, the novel and enticing findings of our study provide a reasonable evidence that miR-26a via PDHX, a link between glycolysis and oxidative phosphorylation, could regulate the glycometabolic pathway which eventually affect boar sperm viability and survival.

Region-specific microRNA signatures in the human epididymis

The epithelium of the human epididymis maintains an appropriate luminal environment for sperm maturation that is essential for male fertility. Regional expression of small noncoding RNAs such as microRNAs contributes to segment-specific gene expression and differentiated functions. MicroRNA profiles were reported in human epididymal tissues but not specifically in the epithelial cells derived from those regions. Here, we reveal miRNA signatures of primary cultures of caput, corpus, and cauda epididymis epithelial cells and of the tissues from which they were derived. We identify 324 epithelial cell-derived microRNAs and 259 tissue-derived microRNAs in the epididymis, some of which displayed regionalized expression patterns in cells and/or tissues. Caput cell-enriched miRNAs included miR-573 and miR-155. Cauda cell-enriched miRNAs included miR-1204 and miR-770. Next, we determined the gene ontology pathways associated with in silico predicted target genes of the differentially expressed miRNAs. The effect of androgen receptor stimulation on miRNA expression was also investigated. These data show novel epithelial cell-derived miRNAs that may regulate the expression of important gene networks that are responsible for the regionalized gene expression and function of the epididymis.

Advances in understanding mechanisms of long-term sperm storage-the soft-shelled turtle model

Long-term sperm storage is a special reproductive strategy, which can extend the time window between mating and fertilization in some animal species. Spermatozoa of the soft-shelled turtle, Pelodiscus sinensis, can be stored in the epididymis and oviduct for at least six months and one year, respectively. How spermatozoa can be stored in vivo for such a prolonged period is yet to be explained. We analyze the mechanisms that contribute to long-term sperm storage in P. sinensis, and compare them with other species from three different perspectives: the spermatozoon itself, the storage microenvironment and the interaction between the spermatozoon and microenvironment. Characteristics of soft-shelled turtle spermatozoa itself, such as the huge cytoplasmic droplet with its content of several large lipid droplets (LDs) and onion-like mitochondira, facilitate long-term sperm storage. The microenvironment of reproductive tract, involving in the secretions, structural barriers, exosomes, androgen receptors, Toll-like receptors and survival factor Bcl-2, are important for the maintenance of spermatozoa long-term storage. Sperm heads are always embedded among the oviductal cilia and even intercalate into the apical hollowness of the ciliated cells, indicating that the ciliated cells support the stored spermatozoa. RNA seq is firstly used to detect the molecular mechanism of sperm storage, which shows that autophagy, apoptosis and immune take part in the long-term sperm storage in this species.

MicroRNAs: Recent insights towards their role in male infertility and reproductive cancers

Spermatogenesis is a tightly controlled, multi-step process in which mature spermatozoa are produced. Disruption of regulatory mechanisms in spermatogenesis can lead to male infertility, various diseases of male reproductive system, or even cancer. The spermatogenic impairment in infertile men can be associated with different etiologies, and the exact molecular mechanisms are yet to be determined. MicroRNAs (miRNAs) are a type of non-protein coding RNAs, about 22 nucleotides long, with an essential role in post-transcriptional regulation. miRNAs have been recognized as important regulators of various biological processes, including spermatogenesis. The aim of this review is to summarize the recent literature on the role of miRNAs in spermatogenesis, male infertility and reproductive cancers, and to evaluate their potential in diagnosis, prognosis and therapy of disease. Experimental evidence shows that aberrant expression of miRNAs affects spermatogenesis at multiple stages and in different cell types, most often resulting in infertility. In more severe cases, dysregulation of miRNAs leads to cancer. miRNAs have enormous potential to be used as diagnostic and prognostic markers as well as therapeutic targets in male infertility and reproductive system diseases. However, to exploit this potential fully, we need a better understanding of miRNA-mediated regulation of spermatogenesis, including the characterization of yet unidentified miRNAs and related regulatory mechanisms.

Driving the Next Generation: Paternal Lifetime Experiences Transmitted via Extracellular Vesicles and Their Small RNA Cargo

Epidemiological studies provide strong evidence for the impact of diverse paternal life experiences on offspring neurodevelopmental disease risk. While these associations are well established, the molecular mechanisms underlying these intergenerational transmissions remain elusive, though recent studies focusing on the influence of paternal experience before conception have implicated germ cell epigenetic programming. Any model accounting for the germline transfer of nongenetic information from sire to offspring must include certain components, such as 1) a vector to carry any signal from the paternal compartment to the maternal reproductive tract and future embryo; 2) a molecular signal, encoded by a paternal experience, to carry this memory and enact downstream responses; and 3) a target cell or tissue to receive the signal and convert it into an effect on embryonic development. We explore the current understanding of the potential processes and candidate factors that may serve as these components. We specifically discuss the growing appreciation for the importance of extracellular vesicles in these processes, beginning with their known role in delivering potential signals, including small RNAs, to sperm, the prototypical vector, during their posttesticular maturation. Finally, we explore the possibility that paternal extracellular vesicles could themselves serve as vectors, delivering signals not only to gametes or the zygote but also to tissues of the maternal reproductive tract to influence fetal development.

Roles of microRNAs in mammalian reproduction: from the commitment of germ cells to peri-implantation embryos

MicroRNAs (miRNAs) are active regulators of numerous biological and physiological processes including most of the events of mammalian reproduction. Understanding the biological functions of miRNAs in the context of mammalian reproduction will allow a better and comparative understanding of fertility and sterility in male and female mammals. Herein, we summarize recent progress in miRNA‐mediated regulation of mammalian reproduction and highlight the significance of miRNAs in different aspects of mammalian reproduction including the biogenesis of germ cells, the functionality of reproductive organs, and the development of early embryos. Furthermore, we focus on the gene expression regulatory feedback loops involving hormones and miRNA expression to increase our understanding of germ cell commitment and the functioning of reproductive organs. Finally, we discuss the influence of miRNAs on male and female reproductive failure, and provide perspectives for future studies on this topic.

Molecular changes and signaling events occurring in spermatozoa during epididymal maturation

After leaving the testis, spermatozoa have not yet acquired the ability to move progressively and are unable to fertilize oocytes. To become fertilization competent, they must go through an epididymal maturation process in the male, and capacitation in the female tract. Epididymal maturation can be defined as those changes occurring to spermatozoa in the epididymis that render the spermatozoa the ability to capacitate in the female tract. As part of this process, sperm cells undergo a series of biochemical and physiological changes that require incorporation of new molecules derived from the epididymal epithelium, as well as post-translational modifications of endogenous proteins synthesized during spermiogenesis in the testis. This review will focus on epididymal maturation events, with emphasis in recent advances in the understanding of the molecular basis of this process.

Cellular evidence for nano-scale exosome secretion and interactions with spermatozoa in the epididymis of the Chinese soft-shelled turtle, Pelodiscus sinensis

The epididymis is the location of sperm maturation and sperm storage. Recent studies have shown that nano-scale exosomes play a vital role during these complicated processes. Our aim was to analyze the secretory properties of epididymal exosomes and their ultrastructural interaction with maturing spermatozoa in the Chinese soft-shelled turtle. The exosome marker CD63 was primarily localized to the apices of principal cells throughout the epididymal epithelium. Identification of nano-scale exosomes and their secretory processes were further investigated via transmission electron microscopy. The epithelium secreted epididymal exosomes (50~300 nm in diameter) through apocrine secretion and the multivesicular body (MVB) pathway. Spermatozoa absorbed epididymal exosomes through endocytosis or membrane fusion pathways. This study shows, for the first time, that nano-scale exosomes use two secretion and two absorption pathways in the reptile, which may be contribute to long-term sperm storage.

MicroRNA Signaling in Embryo Development

Expression of microRNAs (miRNAs) is essential for embryonic development and serves important roles in gametogenesis. miRNAs are secreted into the extracellular environment by the embryo during the preimplantation stage of development. Several cell types secrete miRNAs into biological fluids in the extracellular environment. These fluid-derived miRNAs have been shown to circulate the body. Stable transport is dependent on proper packaging of the miRNAs into extracellular vesicles (EVs), including exosomes. These vesicles, which also contain RNA, DNA and proteins, are on the forefront of research on cell-to-cell communication. Interestingly, EVs have been identified in many reproductive fluids, such as uterine fluid, where their miRNA content is proposed to serve as a mechanism of crosstalk between the mother and conceptus. Here, we review the role of miRNAs in molecular signaling and discuss their transport during early embryo development and implantation.

Primate-specific Long Non-coding RNAs and MicroRNAs

Non-coding RNAs (ncRNAs) are critical regulators of gene expression in essentially all life forms. Long ncRNAs (lncRNAs) and microRNAs (miRNAs) are two important RNA classes possessing regulatory functions. Up to date, many primate-specific ncRNAs have been identified and investigated. Their expression specificity to primate lineage suggests primate-specific roles. It is thus critical to elucidate the biological significance of primate or even human-specific ncRNAs, and to develop potential ncRNA-based therapeutics. Here, we have summarized the studies regarding regulatory roles of some key primate-specific lncRNAs and miRNAs.

Dysregulation of an X-linked primate-specific epididymal microRNA cluster in unexplained asthenozoospermia

Asthenoszoopermia, characterized by reduced sperm motility, is one of the primary forms of male infertility. Whereas most cases were diagnosed into unexplained asthenozoospermia (UA) because the etiology cannot be identified. In animal models, epigenetic dysregulation in epididymis can impair sperm maturation and result in asthenozoospermia. However, researches of epididymal epigenetic regulation on humans are impeded by the difficulty in obtaining epididymal tissues. We previously identified cell-free seminal microRNAs predominately derived from epididymis in human ejaculate. In the present study, these microRNAs were used to screen and validate the microRNA dysregulation in men with UA, which were divided into screening set and validation set. The expression of five miRNAs (miR-891b, miR-892b, miR-892a, miR-888 and miR-890) was found and confirmed to be dysregulated in men with UA. Interestingly, these five miRNAs belong to a primate-specific miRNA cluster located on the X chromosome with epididymis specific expression. Moreover, obvious coherent dysregulation of these miRNAs were observed in 13% men with UA. Regression analysis demonstrated that levels of these miRNAs were significantly correlated with progressive sperm motility. Functions and pathways of predicted target genes of this cluster suggested its role in sperm maturation. Dysregulation of this miRNA cluster might be an epigenetic basis for some patients with UA. We also showed a noninvasive and feasible approach to get epigenetic information of human epididymis.

Cell-free and intracellular nucleic acids: new non-invasive biomarkers to explore male infertility

Male infertility is a devastating problem that affects many couples worldwide. However, the molecular mechanisms and causes of idiopathic male infertility remain unclear. Circulating cell-free nucleic acids have an important role in human physiology and emerging evidence suggests that they play a role in male infertility. This review summarizes recent results on cell-free and intracellular nucleic acids in male infertility and discusses their potential use as biomarkers of male infertility in the clinical practice.

Similar Responses of Circulating MicroRNAs to Acute High-Intensity Interval Exercise and Vigorous-Intensity Continuous Exercise

High-intensity interval exercise (HIIE) has been reported to be more beneficial for physical adaptation than low-to-moderate exercise intensity. Recently, it is becoming increasingly evident that circulating miRNAs (c-miRNAs) may distinguish between specific stress signals imposed by variations in the duration, modality, and type of exercise. The aim of this study is to investigate whether or not HIIE is superior to vigorous-intensity continuous exercise (VICE), which is contributing to develop effective fitness assessment. Twenty-six young males were enrolled, and plasma samples were collected prior to exercise and immediately after HIIE or distance-matched VICE. The miRNA level profiles in HIIE were initially determined using TaqMan Low Density Array (TLDA). And the differentially miRNAs levels were validated by stem-loop quantitative reverse-transcription PCR (RT-qPCR). Furthermore, these selective c-miRNAs were measured for VICE. Our results showed that some muscle-related miRNAs levels in the plasma, such as miR-1, miR-133a, miR-133b, and miR-206 significantly increased following HIIE or VICE compared to those at rest (P < 0.05), and there was only a significant reduction in miR-1 level for HIIE compared to VICE (P < 0.05), while no significant differences were observed for other muscle-related miRNAs between both exercises (P > 0.05). In addition, some tissue-related or unknown original miRNA levels, such as miR-485-5p, miR-509-5p, miR-517a, miR-518f, miR-520f, miR-522, miR-553, and miR-888, also significantly increased (P < 0.05) in both exercises compared to rest. However, no significant differences were found between both exercises (P > 0.05). Overall, endurance exercise assessed in this study both led to significant increases in selective c-miRNAs of comparable magnitude, suggesting that both types of endurance exercise have general stress processes. Accordingly, the similar responses to both acute exercises likely indicate both exercises can be used interchangeably. Further work is needed to reveal the functional significance and signaling mechanisms behind changes in c-miRNA turnover during exercise.