Fibronectin modulates the endocannabinoid system through the cAMP/PKA pathway during human sperm capacitation

Research progress on ion channels and their molecular regulatory mechanisms in the human sperm flagellum

The ion channels in sperm tail play an important role in triggering key physiological reactions, e.g., progressive motility, hyperactivation, required for successful fertilization. Among them, CatSper and KSper have been shown to be important ion channels for the transport of Ca2+ and K+ . Moreover, the voltage-gated proton channel Hv1, the sperm-specific sodium-hydrogen exchanger (sNHE), the epithelial sodium channel (ENaC), members of the temperature-sensitive TRP channel family, and the cystic fibrosis transmembrane regulator (CFTR) are also found in the flagellum. This review focuses on the latest advances in ion channels located at the flagellum, describes how they affect sperm physiological function, and summarizes some primary mutual regulation mechanism between ion channels, including PH, membrane potential, and cAMP. These ion channels may be promising targets for clinical application in infertility.

Proteomic Landscape of Human Sperm in Patients with Different Spermatogenic Impairments

Although the proteome of sperm has been characterized, there is still a lack of high-throughput studies on dysregulated proteins in sperm from subfertile men, with only a few studies on the sperm proteome in asthenozoospermic and oligoasthenozoospermic men. Using liquid chromatography–mass spectrometry (LC-MS/MS) along with bioinformatics analyses, we investigated the proteomic landscape of sperm collected from subfertile men (n = 22), i.e., asthenozoospermic men (n = 13), oligoasthenozoospermic men (n = 9) and normozoospermic controls (n = 31). We identified 4412 proteins in human sperm. Out of these, 1336 differentially abundant proteins were identified in 70% of the samples. In subfertile men, 32 proteins showed a lower abundance level and 34 showed a higher abundance level when compared with normozoospermic men. Compared to normozoospermic controls, 95 and 8 proteins showed a lower abundance level, and 86 and 1 proteins showed a higher abundance level in asthenozoospermic and oligoasthenozoospermic men, respectively. Sperm motility and count were negatively correlated with 13 and 35 and positively correlated with 37 and 20 differentially abundant proteins in asthenozoospermic and oligoasthenozoospermic men, respectively. The combination of the proteins APCS, APOE, and FLOT1 discriminates subfertile males from normozoospermic controls with an AUC value of 0.95. Combined APOE and FN1 proteins discriminate asthenozoospermic men form controls with an AUC of 1, and combined RUVBL1 and TFKC oligoasthenozoospermic men with an AUC of 0.93. Using a proteomic approach, we revealed the proteomic landscape of sperm collected from asthenozoospermic or oligoasthenozoospermic men. Identified abundance changes of several specific proteins are likely to impact sperm function leading to subfertility. The data also provide evidence for the usefulness of specific proteins or protein combinations to support future diagnosis of male subfertility.

Effects of phytoestrogens combined with cold stress on sperm parameters and testicular proteomics in rats

Phytoestrogens and cold negatively influence male fertility. However, the combined effects of these two factors on male reproduction remain unknown. Herein, we studied the changes of sperm parameters and identify potential biomarkers involved in testis of rats, which were intervened by phytoestrogens combined with cold stress. Male Sprague-Dawley rats were randomly divided into control and model groups. The rats in the model group were fed an estrogen diet and placed in a climate chamber [10 ± 2°C; humidity of 75 ± 5%] for 12 h/daily. When compared with the control group after 24 weeks, the rats in the model group showed increased food intake, urine and stool outputs, and higher estradiol and follicle-stimulating hormone levels. However, lower sperm concentration, motility, and viability, and reduced testosterone levels were detected. The epithelial cells of the seminiferous tubules and epididymal ducts presented morphological abnormalities. Proteomic analysis showed that 24 testicular proteins were upregulated and 15 were downregulated. The identified proteins were involved in reticulophagy and stress response. Our findings suggest that the phytoestrogens combined with cold stress had negative effects on the reproductive function of male rats and provide the basis for the establishment of "course simulation" type of oligospermia animal model.

TRPV1 channel in spermatozoa is a molecular target for ROS-mediated sperm dysfunction and differentially expressed in both natural and ART pregnancy failure

Bi-directional crosstalk between Ca2+ signaling and ROS modulates physiological processes as a part of a regulatory circuit including sperm function. The role of transient receptor potential vanilloid 1 (TRPV1) in this regard cannot be undermined. This is the first report demonstrating the Ca2+-sensitive TRPV1 channel to be under-expressed in spermatozoa of subfertile men, idiopathic infertile men, and normozoospermic infertile males with high ROS (idiopathic infertility and unilateral varicocele). To study the effect of TRPV1 in determining the fertility outcome, we compared the expression profile of TRPV1 in spermatozoa of male partners who achieved pregnancy by natural conception (NC+, n = 10), IVF (IVF+, n = 23), or ICSI (ICSI +, n = 9) and their respective counterparts with failed pregnancy NC (n = 7), IVF (n = 23), or ICSI (n = 10), by both immunocytochemistry and flow-cytometry. Reduced expression of TRPV1 in sperm of IVF ± and ICSI ± men with respect to that NC+ men imply its role in mediating successful fertilization. Unsuccessful pregnancy outcome with an underexpression of TRPV1 in sperm of NC-/IVF-/ICSI-men suggests its role in conception and maintenance of pregnancy. Since ROS is regarded as one of the major contributors to sperm dysfunction, the effect of H2O2 +/- TRPV1 modulators (RTX/iRTX) on acrosomal reaction and calcium influx was evaluated to confirm TRPV1 as a redox sensor in human sperm. A significant increment in the percentage of acrosome reacted spermatozoa along with augmented Ca2+-influx was observed after H2O2 treatment, both in the presence or absence of TRPV1 agonist resiniferatoxin (RTX). The effect was attenuated by the TRPV1 antagonist iodoresiniferatoxin (iRTX), indicating the involvement of TRPV1 in mediating H2O2 response. Enhancement of motility and triggering of acrosomal reaction post TRPV1 activation suggested that disruption of these signaling cascades in vivo, possibly due to down-regulation of TRPV1 in these subfertile males. Bioinformatic analysis of the crosstalk between TRPV1 with fertility candidate proteins (reported to influence IVF outcome) revealed cell death and survival, cellular compromise, and embryonic development to be the primary networks affected by anomalous TRPV1 expression. We therefore postulate that TRPV1 can act as a redox sensor, and its expression in spermatozoa may serve as a fertility marker.

TRPV1 in male reproductive system: focus on sperm function

The transient receptor potential vanilloid 1 (TRPV1) is a receptor used to perceive external noxious stimuli and participates in the regulation of various pathophysiological mechanisms in vivo by integrating multiple signals. The explosive growth in knowledge of TRPV1 stemmed from research on neuronal pain and heat sensation over the last decades and is being expanded tremendously in peripheral tissue research. The discovery that TRPV1 is functionally active in male animal and human reproductive tissues have attracted increasing attention in recent years. Indeed, many studies have indicated that TRPV1 is an endocannabinoid receptor that mediates Anandamide's regulation of sperm function. Other characteristics of the TRPV1 channel itself, such as calcium penetration and temperature sensitivity, have also been investigated, especially the possibility that TRPV1 could act as a mediator for sperm thermotaxis. In addition, some reproductive diseases appear to be related to the protective effects of TRPV1 on oxidative stress and heat stress. A better understanding of TRPV1 in these areas should provide strategies for tackling male infertility. This paper is the first to review the expression and mechanism of TRPV1 in the male reproductive system from molecular and cellular perspectives. A focus is given on sperm function, including calcium homeostasis, crosstalk with endocannabinoid system, participation in cholesterol-related sperm maturation, and thermotaxis, hoping to capture the current situation of this rapidly developing field.

Diverse role of endocannabinoid system in mammalian male reproduction

Endocannabinoid system (ECS) is known for its modulatory role in numerous physiological processes in the body. Endocannabinoids (eCBs) are endogenous lipid molecules which function both centrally and peripherally. The ECS is best studied in the central nervous system (CNS), immune system as well as in the metabolic system. The role of ECS in male reproductive system is emerging and the presence of a complete enzymatic machinery to synthesize and metabolize eCBs has been demonstrated in male reproductive tract. Endocannabinoid concentrations and alterations in their levels have been reported to affect the functioning of spermatozoa. A dysfunctional ECS has also been linked to the development of prostate cancer, the leading cause of cancer related mortality among male population. This review is an attempt to provide an insight into the significant role of endocannabinoids in male reproduction and further summarize recent findings that demonstrate the manner in which the endocannabinoid system impacts male sexual behavior and fertility.

Role and Modulation of TRPV1 in Mammalian Spermatozoa: An Updated Review

Based on the abundance of scientific publications, the polymodal sensor TRPV1 is known as one of the most studied proteins within the TRP channel family. This receptor has been found in numerous cell types from different species as well as in spermatozoa. The present review is focused on analyzing the role played by this important channel in the post-ejaculatory life of spermatozoa, where it has been described to be involved in events such as capacitation, acrosome reaction, calcium trafficking, sperm migration, and fertilization. By performing an exhaustive bibliographic search, this review gathers, for the first time, all the modulators of the TRPV1 function that, to our knowledge, were described to date in different species and cell types. Moreover, all those modulators with a relationship with the reproductive process, either found in the female tract, seminal plasma, or spermatozoa, are presented here. Since the sperm migration through the female reproductive tract is one of the most intriguing and less understood events of the fertilization process, in the present work, chemotaxis, thermotaxis, and rheotaxis guiding mechanisms and their relationship with TRPV1 receptor are deeply analyzed, hypothesizing its (in)direct participation during the sperm migration. Last, TRPV1 is presented as a pharmacological target, with a special focus on humans and some pathologies in mammals strictly related to the male reproductive system.

Cannabinoid signalling and effects of cannabis on the male reproductive system

Marijuana is the most widely consumed recreational drug worldwide, which raises concerns for its potential effects on fertility. Many aspects of human male reproduction can be modulated by cannabis-derived extracts (cannabinoids) and their endogenous counterparts, known as endocannabinoids (eCBs). These latter molecules act as critical signals in a variety of physiological processes through receptors, enzymes and transporters collectively termed the endocannabinoid system (ECS). Increasing evidence suggests a role for eCBs, as well as cannabinoids, in various aspects of male sexual and reproductive health. Although preclinical studies have clearly shown that ECS is involved in negative modulation of testosterone secretion by acting both at central and testicular levels in animal models, the effect of in vivo exposure to cannabinoids on spermatogenesis remains a matter of debate. Furthermore, inconclusive clinical evidence does not seem to support the notion that plant-derived cannabinoids have harmful effects on human sexual and reproductive health. An improved understanding of the complex crosstalk between cannabinoids and eCBs is required before targeting of ECS for modulation of human fertility becomes a reality.

FAK regulates actin polymerization during sperm capacitation via the ERK2/GEF-H1/RhoA signaling pathway

Actin polymerization is a crucial process during sperm capacitation. We have recently described the participation of FAK during actin polymerization in guinea pig spermatozoa. However, the mechanism by which FAK mediates these processes is unknown. Our previous data have shown that MAPK1 (hereafter referred to as ERK2) is activated during the first minutes of capacitation, and inhibition of ERK2 blocked actin polymerization and the acrosome reaction. In this current study, we found that FAK is involved in ERK2 activation - as FAK was phosphorylated at tyrosine residue 925 and bound to Grb2 - and that inhibition of FAK results in a significant decrease of ERK2 activation. We also confirmed the presence of Rho guanine nucleotide exchange factor 2 (ARHGEF2, hereafter referred to as GEF-H1), which is able to associate with RhoA during capacitation. RhoA activation and its participation in actin polymerization were also analyzed. Inhibition of FAK or ERK1/2 impeded GEF-H1 phosphorylation, RhoA activation, and the association between GEF-H1 and RhoA. Finally, we observed the presence of fibronectin on the sperm surface, its role in sperm-sperm interaction as well as participation of β-integrin in the activation of ERK2. Our results show that the signaling pathway downstream of fibronectin, via integrin, FAK, Grb2, MEK1/2, ERK2, GEF-H1 and RhoA regulates the actin polymerization associated with spermatozoa capacitation.