Molecular and functional insights into Transient Receptor Potential Vanilloid 1 (TRPV1) in bull spermatozoa

Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation

In order to accomplish their primary goal, mammalian spermatozoa must undergo a series of physiological, biochemical, and functional changes crucial for the acquisition of fertilization ability. Spermatozoa are highly polarized cells, which must swiftly respond to ionic changes on their passage through the female reproductive tract, and which are necessary for male gametes to acquire their functional competence. This review summarizes the current knowledge about specific ion channels and transporters located in the mammalian sperm plasma membrane, which are intricately involved in the initiation of changes within the ionic milieu of the sperm cell, leading to variations in the sperm membrane potential, membrane depolarization and hyperpolarization, changes in sperm motility and capacitation to further lead to the acrosome reaction and sperm-egg fusion. We also discuss the functionality of selected ion channels in male reproductive health and/or disease since these may become promising targets for clinical management of infertility in the future.

Effects of cryopreservation in the presence of Natural Deep Eutectic Solvents (NADESs) on sperm parameters

Natural Deep Eutectic Solvents (NADESs) are being considered as a potential alternative to traditional cryoprotective agents (CPAs) in sperm freezing. The study aimed to assess the effects of NADESs as a CPA on human sperm parameters. A total of 32 normozoospermic semen samples were collected from the Alzahra infertility treatment center (Iran) between July 2021 and September 2022. The samples were categorized into eight different groups: 1) a control (nonfrozen), and groups frozen with 2) SpermFreeze Solution, 3) ChX (Choline chloride and Xylitol), 4) ChS (Choline chloride and D-sorbitol), 5) ChG (Choline chloride and Glucose), 6) ChU (Choline chloride and Urea), 7) EtP (Ethylene glycol and l-proline), and 8) GlyP (Glycerol and l-proline). The study also analyzed the quality of sperm parameters, such as chromatin condensation and integrity, acrosome integrity, and survival, along with the expression of some genes that affect sperm fertility (TRPV1, TRPV4, SPACA3, and OGG1). The study found there were notable variations in sperm parameters (such as viability, chromatin condensation and integrity, and acrosome integrity) among frozen groups with some NADESs compared to the SpermFreeze Solution and control groups (P < 0.05). Analysis of gene expression demonstrated that the levels of TRPV1, TRPV4, SPACA3, and OGG1 genes were superior in the GlyP group compared to the other groups (P < 0.05). Additionally, the ChS and ChU groups exhibited preserved expression of these genes compared with the SpermFreeze Solution group. The use of NADESs led to the discovery of a more appropriate CPA that has low toxicity and is highly effective in maintaining the fertility potential of sperm.

Introduction to the pathways involved in the activation and regulation of sperm motility: A review of the relevance of ion channels

To participate in sperm-oocyte fusion, spermatozoa need to be motile. In the testes, spermatozoa are immotile, although these gametes acquire the capacity for motility during the transit through the epididymis. During the period of epididymal transport from the male genital tract to the female genital tract, spermatozoa exhibit various types of motility that are regulated by complex signalling and communication mechanisms. Because motility is very dynamic, it can be affected by small changes in the external or internal environment of spermatozoa within a very short time. This indicates that regulatory membrane proteins, known as sperm ion channels, are involved in the regulation of sperm motility. Research results from studies, where there was use of electrophysiological, pharmacological, molecular and knock-out approaches, indicate ion channels are possibly involved in the regulation of sperm membrane polarisation, intracellular pH, motility, energy homeostasis, membrane integrity, capacitation, hyperactivity, acrosome reaction and fertilisation processes. In this review, there is summarisation of the key functions that ion channels have in the regulation, initiation, maintenance, and modulation of sperm motility. In addition, in this review there is highlighting of novel insights about the pathways of ion channels that are activated in spermatozoa while these gametes are located in the oviduct leading to the fertilisation capacity of these cells.

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.

Interplay mechanisms between progesterone and endocannabinoid receptors in regulating bull sperm capacitation and acrosome reaction

After ejaculation, sperm show a limited capacity for transcription and translation. In the oviduct, most of the signalling in sperm is nongenomic and is mediated through membrane receptors. Studies have shown that the cation channel of sperm (CatSper), cAMP, cGMP, protein kinases, and tyrosine phosphorylation are involved in the nongenomic signalling of progesterone (P4) in sperm. However, it is not known whether there is an interplay between P4 and cannabinoid receptors 1 and 2 (CB1 and CB2), transient receptor potential vanilloid 1 (TRPV1), CatSper channels, cAMP, inositol trisphosphate receptor (IP3R), and mitogen-activated protein kinase (MAPK); these potential regulators are involved in the regulation of capacitation and the acrosome reaction. In the present study, selective blockers of CB1, CB2, TRPV1, CatSper channels, cAMP, protein kinase A (PKA), IP3R, and MAPK were used to identify their involvement in P4-mediated bull sperm capacitation and the acrosome reaction. Selective blocking of any one of the molecules caused a significant reduction in P4 signalling (p < 0.05). Interestingly, blocking these molecules in combination followed by treatment with P4 resulted in the complete absence of capacitation and the acrosome reaction. Blocking a single receptor was not able to eliminate the P4-induced capacitation and the acrosome reaction. In addition to the CB1 and CB2 receptors, there may be other signalling pathways that mediate P4 signalling. In conclusion, P4 signalling exhibited interplay with the cannabinoid receptors. The regulation of sperm capacitation and the acrosome reaction also involved cAMP, PKA, l-type and T-type calcium channels, TRPV1, inositol trisphosphate, and MAPK.

Perspectives on Potential Fatty Acid Modulations of Motility Associated Human Sperm Ion Channels

Human spermatozoan ion channels are specifically distributed in the spermatozoan membrane, contribute to sperm motility, and are associated with male reproductive abnormalities. Calcium, potassium, protons, sodium, and chloride are the main ions that are regulated across this membrane, and their intracellular concentrations are crucial for sperm motility. Fatty acids (FAs) affect sperm quality parameters, reproductive pathologies, male fertility, and regulate ion channel functions in other cells. However, to date the literature is insufficient to draw any conclusions regarding the effects of FAs on human spermatozoan ion channels. Here, we aimed to discern the possible effects of FAs on spermatozoan ion channels and direct guidance for future research. After investigating the effects of FAs on characteristics related to human spermatozoan motility, reproductive pathologies, and the modulation of similar ion channels in other cells by FAs, we extrapolated polyunsaturated FAs (PUFAs) to have the highest potency in modulating sperm ion channels to increase sperm motility. Of the PUFAs, the ω-3 unsaturated fatty acids have the greatest effect. We speculate that saturated and monounsaturated FAs will have little to no effect on sperm ion channel activity, though the possible effects could be opposite to those of the PUFAs, considering the differences between FA structure and behavior.

Structure and Function of Ion Channels Regulating Sperm Motility-An Overview

Sperm motility is linked to the activation of signaling pathways that trigger movement. These pathways are mainly dependent on Ca²⁺, which acts as a secondary messenger. The maintenance of adequate Ca²⁺ concentrations is possible thanks to proper concentrations of other ions, such as K⁺ and Na⁺, among others, that modulate plasma membrane potential and the intracellular pH. Like in every cell, ion homeostasis in spermatozoa is ensured by a vast spectrum of ion channels supported by the work of ion pumps and transporters. To achieve success in fertilization, sperm ion channels have to be sensitive to various external and internal factors. This sensitivity is provided by specific channel structures. In addition, novel sperm-specific channels or isoforms have been found with compositions that increase the chance of fertilization. Notably, the most significant sperm ion channel is the cation channel of sperm (CatSper), which is a sperm-specific Ca²⁺ channel required for the hyperactivation of sperm motility. The role of other ion channels in the spermatozoa, such as voltage-gated Ca²⁺ channels (VGCCs), Ca²⁺-activated Cl-channels (CaCCs), SLO K⁺ channels or voltage-gated H⁺ channels (VGHCs), is to ensure the activation and modulation of CatSper. As the activation of sperm motility differs among metazoa, different ion channels may participate; however, knowledge regarding these channels is still scarce. In the present review, the roles and structures of the most important known ion channels are described in regard to regulation of sperm motility in animals.

The Roles of NO and H2S in Sperm Biology: Recent Advances and New Perspectives

After being historically considered as noxious agents, nitric oxide (NO) and hydrogen sulfide (H2S) are now listed as gasotransmitters, gaseous molecules that play a key role in a variety of cellular functions. Both NO and H2S are endogenously produced, enzymatically or non-enzymatically, and interact with each other in a range of cells and tissues. In spite of the great advances achieved in recent decades in other biological systems, knowledge about H2S function and interactions with NO in sperm biology is in its infancy. Here, we aim to provide an update on the importance of these molecules in the physiology of the male gamete. Special emphasis is given to the most recent advances in the metabolism, mechanisms of action, and effects (both physiological and pathophysiological) of these gasotransmitters. This manuscript also illustrates the physiological implications of NO and H2S observed in other cell types, which might be important for sperm function. The relevance of these gasotransmitters to several signaling pathways within sperm cells highlights their potential use for the improvement and successful application of assisted reproductive technologies.

Functional insights into voltage gated proton channel (Hv1) in bull spermatozoa

Acid extrusion and intracellular alkalisation are the key events during sperm capacitation and these are mediated through proton gated channels (Hv1). Role of Hv1 in regulating sperm motility, capacitation and acrosome reaction has been documented in human spermatozoa; but no such data is available in bull spermatozoa; therefore, the present study was undertaken in Hariana bull spermatozoa. Sixty four ejaculates were collected from four Hariana bulls to investigate the functional involvement of Hv1 in regulation of sperm motility, capacitation and acrosome reaction in bull spermatozoa. Immunoblotting revealed the presence of a single band of 31.8 kDa corresponding to Hv1 in Hariana bull spermatozoa and immunoflourescence confirmed the positive immune-reactivity at principal piece of spermatozoa for Hv1. Functional study was carried out using 200 μM 2-Guanidinobenzimidazole (2-Guanidinobenzimidazole,selective Hv1 blocker) and 1 mM zinc chloride (potent Hv1 blocker), and 0.3 μM Anandamide (AEA), an activator of Hv1. Blocking of Hv1 resulted in significant (P < 0.05) reduction in progressive sperm motility (PSM). Activation of Hv1 with AEA also resulted in significant (P < 0.05) reduction in PSM till 1 h and thereafter, the PSM was restored and reduction was almost similar to that in control. However, during activation and inactivation of Hv1, per cent spermatozoa showing hyperactive motility were found to be markedly increased (20-30%) compared to 10-20% in control. 2-Guanidinobenzimidazole, zinc and AEA treated spermatozoa revealed significant (P < 0.05) increase in B-pattern of spermatozoa indicating induction of capacitation. Downstream signalling of Hv1 activation or inactivation seemed to be mediated through cAMP and PKA pathways. Catsper channels were found to be intimately associated with Hv1 function in regulating sperm motility. Blocking as well as activation of Hv1 resulted in significant (P < 0.05) reduction in sperm livability, spermatozoa having intact membrane, intact acrosome, and high mitochondrial transmembrane potential (MTP). Our findings evidently suggest that Hv1 channels are present in bull spermatozoa and these regulate sperm functions like hypermotility, capacitation and acrosome reaction through complex interplay between different pathways involving cAMP, PKC, and Catsper. Further studies are required to find out the possible relationship between Hv1 channels and other channels in regulating spermatozoa functions.