Testin and actin are key molecular targets of adjudin, an anti-spermatogenic agent, in the testis

Advances in Male Contraception: When Will the Novel Male Contraception be Available?

Many contraceptive methods have been developed over the years due to high demand. However, female contraceptive pills and devices do not work for all females due to health conditions and side effects. Also, the number of males who want to actively participate in family planning is gradually increasing. However, the only contraceptive options currently available to males are condoms and vasectomy. Therefore, many male contraceptive methods, including medication (hormonal and non-hormonal therapy) and mechanical methods, are under development. Reversibility, safety, persistence, degree of invasion, promptness, and the suppression of anti-sperm antibody formation are essential factors in the development of male contraceptive methods. In this paper, male contraceptive methods under development are reviewed according to those essential factors. Furthermore, the timeline for the availability of a new male contraception is discussed.

Cell-Cell Interaction-Mediated Signaling in the Testis Induces Reproductive Dysfunction—Lesson from the Toxicant/Pharmaceutical Models

Emerging evidence has shown that cell-cell interactions between testicular cells, in particular at the Sertoli cell-cell and Sertoli-germ cell interface, are crucial to support spermatogenesis. The unique ultrastructures that support cell-cell interactions in the testis are the basal ES (ectoplasmic specialization) and the apical ES. The basal ES is found between adjacent Sertoli cells near the basement membrane that also constitute the blood-testis barrier (BTB). The apical ES is restrictively expressed at the Sertoli-spermatid contact site in the apical (adluminal) compartment of the seminiferous epithelium. These ultrastructures are present in both rodent and human testes, but the majority of studies found in the literature were done in rodent testes. As such, our discussion herein, unless otherwise specified, is focused on studies in testes of adult rats. Studies have shown that the testicular cell-cell interactions crucial to support spermatogenesis are mediated through distinctive signaling proteins and pathways, most notably involving FAK, Akt1/2 and Cdc42 GTPase. Thus, manipulation of some of these signaling proteins, such as FAK, through the use of phosphomimetic mutants for overexpression in Sertoli cell epithelium in vitro or in the testis in vivo, making FAK either constitutively active or inactive, we can modify the outcome of spermatogenesis. For instance, using the toxicant-induced Sertoli cell or testis injury in rats as study models, we can either block or rescue toxicant-induced infertility through overexpression of p-FAK-Y397 or p-FAK-Y407 (and their mutants), including the use of specific activator(s) of the involved signaling proteins against pAkt1/2. These findings thus illustrate that a potential therapeutic approach can be developed to manage toxicant-induced male reproductive dysfunction. In this review, we critically evaluate these recent findings, highlighting the direction for future investigations by bringing the laboratory-based research through a translation path to clinical investigations.

Aquaporin 4 in Traumatic Brain Injury: From Molecular Pathways to Therapeutic Target

Traumatic brain injury (TBI) is known as an acute degenerative pathology of the central nervous system, and has been shown to increase brain aquaporin 4 (AQP4) expression. Various molecular mechanisms affect AQP4 expression, including neuronal high mobility group box 1, forkhead box O3a, vascular endothelial growth factor, hypoxia-inducible factor-1 α (HIF-1 α) sirtuin 2, NF-κB, Malat1, nerve growth factor and Angiotensin II receptor type 1. In addition, inhibition of AQP4 with FK-506, MK-801 (indirectly by targeting N-methyl-D-aspartate receptor), inactivation of adenosine A2A receptor, levetiracetam, adjudin, progesterone, estrogen, V1aR inhibitor, hypertonic saline, erythropoietin, poloxamer 188, brilliant blue G, HIF-1alpha inhibitor, normobaric oxygen therapy, astaxanthin, epigallocatechin-3-gallate, sesamin, thaliporphine, magnesium, prebiotic fiber, resveratrol and omega-3, as well as AQP4 gene silencing lead to reduced edema upon TBI. This review summarizes current knowledge and evidence on the relationship between AQP4 and TBI, and the potential mechanisms involved.

Emerging approaches to male contraception

Despite significant interests in contraception by men, effective methods of male contraception are limited to vasectomy and condoms. Recently, there have been several promising advances in male contraceptive research. This review will update readers on recent research in both hormonal and nonhormonal approaches to male contraception. Hormonal approaches to male contraception have been stymied by adverse effects, formulations requiring injections or implants, a 5% to10% nonresponse rate, as well as poor understanding of user acceptability. In the last several years, research has focused on novel, orally bioavailable androgens such as dimethandrolone undecanoate and 11β-methyl-19-nor-testosterone. Additionally, combinations of a topical testosterone gel combined with a gel containing segesterone acetate, a potent progestin, have shown promise in clinical trials recently. Simultaneously, significant preclinical progress has been made in several approaches to nonhormonal male contraceptives, including compounds that inhibit sperm motility such as eppin, compounds that inhibit retinoic acid binding or biosynthesis, and reversible approaches to obstruction of the vas deferens. It is imperative for these areas of research to continue making strides so that there is a gamut of contraceptive options for couples to choose from. Some of these approaches will hopefully reach clinical utility soon, greatly improving contraceptive choice for couples.

mTORC1/rpS6 and p-FAK-Y407 signaling regulate spermatogenesis: Insights from studies of the adjudin pharmaceutical/toxicant model

In rodents and humans, the major cellular events at spermatogenesis include self-renewal of spermatogonial stem cells and undifferentiated spermatogonia via mitosis, commitment of spermatogonia to differentiation and transformation to spermatocytes, meiosis, spermiogenesis, and the release of spermatozoa at spermiation. While details of the morphological changes during these cellular events have been delineated, knowledge gap exists between the morphological changes in the seminiferous epithelium and the underlying molecular mechanism(s) that regulate these cellular events. Even though many of the regulatory proteins and biomolecules that modulate spermatogenesis are known based on studies using genetic models, the underlying regulatory mechanism(s), in particular signaling pathways/proteins, remain unexplored since much of the information regarding the signaling regulation is unknown. Studies in the past decade, however, have unequivocally demonstrated that the testis is using several signaling proteins and/or pathways to regulate multiple cellular events to modulate spermatogenesis. These include mTORC1/rpS6/Akt1/2 and p-FAK-Y407. While selective inhibitors and/or agonists and antagonists are available to examine some of these signaling proteins, their use have limitations due to their specificities and also potential systemic cytotoxicity. On the other hand, the use of genetic models has had profound implications for our understanding of the molecular regulation of spermatogenesis, and these knockout (null) models have also revealed the factors that are critical for spermatogenesis. Nonetheless, additional studies using in vitro and in vivo models are necessary to unravel the signaling pathways involved in regulating seminiferous epithelial cycle. Emerging data from studies, such as the use of the adjudin pharmaceutical/toxicant model, have illustrated that this non-hormonal male contraceptive drug is utilizing specific signaling pathways/proteins to induce specific defects in spermatogenesis, yielding mechanistic insights on the regulation of spermatogenesis. We sought to review these recent data in this article, highlighting an interesting approach that can be considered for future studies.

Signaling Proteins That Regulate Spermatogenesis Are the Emerging Target of Toxicant-Induced Male Reproductive Dysfunction

There is emerging evidence that environmental toxicants, in particular endocrine disrupting chemicals (EDCs) such as cadmium and perfluorooctanesulfonate (PFOS), induce Sertoli cell and testis injury, thereby perturbing spermatogenesis in humans, rodents and also widelife. Recent studies have shown that cadmium (e.g., cadmium chloride, CdCl₂) and PFOS exert their disruptive effects through putative signaling proteins and signaling cascade similar to other pharmaceuticals, such as the non-hormonal male contraceptive drug adjudin. More important, these signaling proteins were also shown to be involved in modulating testis function based on studies in rodents. Collectively, these findings suggest that toxicants are using similar mechanisms that used to support spermatogenesis under physiological conditions to perturb Sertoli and testis function. These observations are physiologically significant, since a manipulation on the expression of these signaling proteins can possibly be used to manage the toxicant-induced male reproductive dysfunction. In this review, we highlight some of these findings and critically evaluate the possibility of using this approach to manage toxicant-induced defects in spermatrogenesis based on recent studies in animal models.

Regulation of blood-testis barrier dynamics by the mTORC1/rpS6 signaling complex: An in vitro study

During spermatogenesis, developing germ cells that lack the cellular ultrastructures of filopodia and lamellipodia generally found in migrating cells, such as macrophages and fibroblasts, rely on Sertoli cells to support their transport across the seminiferous epithelium. These include the transport of preleptotene spermatocytes across the blood-testis barrier (BTB), but also the transport of germ cells, in particular developing haploid spermatids, across the seminiferous epithelium, that is to and away from the tubule lumen, depending on the stages of the epithelial cycle. On the other hand, cell junctions at the Sertoli cell–cell and Sertoli–germ cell interface also undergo rapid remodeling, involving disassembly and reassembly of cell junctions, which, in turn, are supported by actin- and microtubule-based cytoskeletal remodeling. Interestingly, the underlying mechanism(s) and the involving biomolecule(s) that regulate or support cytoskeletal remodeling remain largely unknown. Herein, we used an in vitro model of primary Sertoli cell cultures that mimicked the Sertoli BTB in vivo overexpressed with the ribosomal protein S6 (rpS6, the downstream signaling protein of mammalian target of rapamycin complex 1 [mTORC1]) cloned into the mammalian expression vector pCI-neo, namely, quadruple phosphomimetic and constitutively active mutant of rpS6 (pCI-neo/p-rpS6-MT) versus pCI-neo/rpS6-WT (wild-type) and empty vector (pCI-neo/Ctrl) for studies. These findings provide compelling evidence that the mTORC1/rpS6 signal pathway exerted its effects to promote Sertoli cell BTB remodeling. This was mediated through changes in the organization of actin- and microtubule-based cytoskeletons, involving changes in the distribution and/or spatial expression of actin- and microtubule-regulatory proteins.

The dynamics and regulation of microfilament during spermatogenesis

Spermatogenesis is a highly complex physiological process which contains spermatogonia proliferation, spermatocyte meiosis and spermatid morphogenesis. In the past decade, actin binding proteins and signaling pathways which are critical for regulating the actin cytoskeleton in testis had been found. In this review, we summarized 5 actin-binding proteins that have been proven to play important roles in the seminiferous epithelium. Lack of them perturbs spermatids polarity and the transport of spermatids. The loss of Arp2/3 complex, Formin1, Eps8, Palladin and Plastin3 cause sperm release failure suggesting their irreplaceable role in spermatogenesis. Actin regulation relies on multiple signal pathways. The PI3K/Akt signaling pathway positively regulate the mTOR pathway to promote actin reorganization in seminiferous epithelium. Conversely, TSC1/TSC2 complex, the upstream of mTOR, is activated by the LKB1/AMPK pathway to inhibit cell proliferation, differentiation and migration. The increasing researches focus on the function of actin binding proteins (ABPs), however, their collaborative regulation of actin patterns and potential regulatory signaling networks remains unclear. We reviewed ABPs that play important roles in mammalian spermatogenesis and signal pathways involved in the regulation of microfilaments. We suggest that more relevant studies should be performed in the future.

Development of Novel Male Contraceptives

Unintended pregnancy is surprisingly common, accounting for 40-50% of pregnancies worldwide. Contraception is the most effective means of preventing unintended pregnancy. Seventy percent of all contraceptives are used by women; however, some women are unable to use contraceptives due to health conditions or side effects. Many men wish to take a more active role family planning, but currently have only two effective male contraceptive options, condoms and vasectomy. Therefore, work to develop novel male contraceptives analogous to popular female methods, such as daily pills or long-acting shots and implants, is underway. This paper will briefly discuss the pros and cons of condoms and vasectomies, and then review the research into novel methods of male contraception.

Toward Development of the Male Pill: A Decade of Potential Non-hormonal Contraceptive Targets

With the continued steep rise of the global human population, and the paucity of safe and practical contraceptive options available to men, the need for development of effective and reversible non-hormonal methods of male fertility control is widely recognized. Currently there are several contraceptive options available to men, however, none of the non-hormonal alternatives have been clinically approved. To advance progress in the development of a safe and reversible contraceptive for men, further identification of novel reproductive tract-specific druggable protein targets is required. Here we provide an overview of genes/proteins identified in the last decade as specific or highly expressed in the male reproductive tract, with deletion phenotypes leading to complete male infertility in mice. These phenotypes include arrest of spermatogenesis and/or spermiogenesis, abnormal spermiation, abnormal spermatid morphology, abnormal sperm motility, azoospermia, globozoospermia, asthenozoospermia, and/or teratozoospermia, which are all desirable outcomes for a novel male contraceptive. We also consider other associated deletion phenotypes that could impact the desirability of a potential contraceptive. We further discuss novel contraceptive targets underscoring promising leads with the objective of presenting data for potential druggability and whether collateral effects may exist from paralogs with close sequence similarity.

Testin regulates the blood-testis barrier via disturbing occludin/ZO-1 association and actin organization

The blood-testis barrier (BTB) separates the seminiferous epithelium into the apical and basal compartments. The BTB has to operate timely and accurately to ensure the correct migration of germ cells, meanwhile maintaining the immunological barrier. Testin was first characterized from primary Sertoli cells, it is a secretory protein and a sensitive biomarker to monitor junctions between Sertoli and germ cells. Till now, the functions of testin on BTB dynamics and the involving mechanisms are unknown. Herein, testin acts as a regulatory protein on BTB integrity. In vitro testin knockdown by RNAi caused significant damage to the Sertoli cell barrier with no apparent changes in the protein levels of several major tight junction (TJ), adhesion junction, and gap junction proteins. Also, testin RNAi caused the diffusion of two TJ structural proteins, occludin and ZO-1, diffusing away from the Sertoli cell surface into the cytoplasm. Association and colocalization between ZO-1 and occludin were decreased after testin RNAi, examined by Co-IP and coimmunofluorescent staining, respectively. Furthermore, testin RNAi induced a dramatic disruption on the arrangement of actin filament bundles and a reduced F-actin/G-actin ratio. The actin regulatory protein ARP3 appeared at the Sertoli cell interface after testin RNAi without its protein level change, whereas overexpressing testin in Sertoli cells showed no effect on TJ barrier integrity. The above findings suggest that besides as a monitor for Sertoli-germ cell junction integrity, testin is also an essential molecule to maintain Sertoli-Sertoli junctions.

Dynein 1 supports spermatid transport and spermiation during spermatogenesis in the rat testis

In the mammalian testis, spermatogenesis is dependent on the microtubule (MT)-specific motor proteins, such as dynein 1, that serve as the engine to support germ cell and organelle transport across the seminiferous epithelium at different stages of the epithelial cycle. Yet the underlying molecular mechanism(s) that support this series of cellular events remain unknown. Herein, we used RNAi to knockdown cytoplasmic dynein 1 heavy chain (Dync1h1) and an inhibitor ciliobrevin D to inactivate dynein in Sertoli cells in vitro and the testis in vivo, thereby probing the role of dynein 1 in spermatogenesis. Both treatments were shown to extensively induce disruption of MT organization across Sertoli cells in vitro and the testis in vivo. These changes also perturbed the transport of spermatids and other organelles (such as phagosomes) across the epithelium. These changes thus led to disruption of spermatogenesis. Interestingly, the knockdown of dynein 1 or its inactivation by ciliobrevin D also perturbed gross disruption of F-actin across the Sertoli cells in vitro and the seminiferous epithelium in vivo, illustrating there are cross talks between the two cytoskeletons in the testis. In summary, these findings confirm the role of cytoplasmic dynein 1 to support the transport of spermatids and organelles across the seminiferous epithelium during the epithelial cycle of spermatogenesis.

Differential effects of depot formulations of GnRH agonist leuprorelin and antagonist degarelix on the seminiferous epithelium of the rat testis

Despite their pharmacologically opposite actions, long-acting depot formulations of both GnRH agonists and antagonists have been clinically applied for treatment of androgen-sensitive prostate cancer. Sustained treatment with GnRH analogues commonly suppresses both the synthesis and release of gonadotropins, leading to depletion of testicular testosterone. To clarify the underlying differences in the effects of GnRH agonists and antagonists on spermatogenesis, we compared histological changes in the seminiferous epithelium after administration of depot formulations of GnRH agonist leuprorelin and antagonist degarelix to male rats. Testicular weight had markedly declined by 28 days after administration of both GnRH analogues, although the testicular weight was decreased more promptly by leuprorelin compared with degarelix. Shortly after administration, massive exfoliation of premature spermatids and anomalous multinucleated giant cells was observed in seminiferous tubules of leuprorelin-treated rats, probably via the initial hyperstimulatory effects on the hypothalamic-pituitary-testicular axis, whereas no discernible changes were found in those of degarelix-treated rats. Long term treatment with both types of GnRH analogues similarly induced a marked reduction in the height of the epithelium and deformation of apical cytoplasm in Sertoli cells, resulting in premature detachment of spermatids from the epithelium. Lipid droplets had accumulated progressively in Sertoli cells, especially in those of degarelix-treated rats. These findings clearly demonstrate the differences in the effects of GnRH agonists and antagonists on the spermatogenic process. This study suggests that an appropriate choice of GnRH analogues is necessary to minimize their adverse effects on spermatogenesis when reproductive functions should be preserved in patients.

Male contraception

Although female contraceptives are very effective at preventing unintended pregnancy, some women can not use them because of health conditions or side-effects, leaving some couples without effective contraceptive options. In addition, many men wish to take active responsibility for family planning. Thus, there is a great need for male contraceptives to prevent unintended pregnancies, of which 80-90 million occur annually. At present, effective male contraceptive options are condoms and vasectomy, which are not ideal for all men. Therefore, efforts are under way to develop novel male contraceptives. This paper briefly reviews the advantages and disadvantages of condoms and vasectomies and then discusses the research directed toward development of novel methods of male contraception.

Beyond the Condom: Frontiers in Male Contraception

Nearly half of all pregnancies worldwide are unplanned, despite numerous contraceptive options available. No new contraceptive method has been developed for men since the invention of condom. Nevertheless, more than 25% of contraception worldwide relies on male methods. Therefore, novel effective methods of male contraception are of interest. Herein we review the physiologic basis for both male hormonal and nonhormonal methods of contraception. We review the history of male hormonal contraception development, current hormonal agents in development, as well as the potential risks and benefits of male hormonal contraception options for men. Nonhormonal methods reviewed will include both pharmacological and mechanical approaches in development, with specific focus on methods which inhibit the testicular retinoic acid synthesis and action. Multiple hormonal and nonhormonal methods of male contraception are in the drug development pathway, with the hope that a reversible, reliable, safe method of male contraception will be available to couples in the not too distant future.

Regulation of microtubule (MT)-based cytoskeleton in the seminiferous epithelium during spermatogenesis

In rodents and humans, testicular cells, similar to other mammalian cells, are supported by actin-, microtubule (MT)- and intermediate filament-based cytoskeletons. Although the cytoskeletal network of the testis serves an important role in regulating spermatogenesis during the epithelial cycle, most of the published findings in the literature are limited to studies that only visualize these cytoskeletons in the seminiferous epithelium. Few focus on the underlying molecular mechanism that regulates their organization in the epithelium in response to changes in the stages of the epithelial cycle. Functional studies in the last decade have begun to focus on the role of binding proteins that regulate these cytoskeletons, with some interesting findings rapidly emerging in the field. Since the actin- and intermediate filament-based cytoskeletons have been recently reviewed, herein we focus on the MT-based cytoskeleton for two reasons. First, besides serving as a structural support cytoskeleton, MTs are known to serve as the track to support and facilitate the transport of germ cells, such as preleptotene spermatocytes connected in clones and elongating/elongated spermatids during spermiogenesis, across the blood-testis barrier (BTB) and the adluminal compartment, respectively, during spermatogenesis. While these cellular events are crucial to the completion of spermatogenesis, they have been largely ignored in the past. Second, MT-based cytoskeleton is working in concert with the actin-based cytoskeleton to provide structural support for the transport of intracellular organelles across the cell cytosol, such as endosome-based vesicles, and phagosomes, which contain residual bodies detached from spermatids, to maintain the cellular homeostasis in the seminiferous epithelium. We critically evaluate some recent published findings herein to support a hypothesis regarding the role of MT in conferring germ cell transport in the seminiferous epithelium.

Effective Delivery of Male Contraceptives Behind the Blood-Testis Barrier (BTB) - Lesson from Adjudin

The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body. It divides the seminiferous epithelium of the seminiferous tubule, the functional unit of the testis, where spermatogenesis takes place, into the basal and the adluminal (apical) compartments. Functionally, the BTB provides a unique microenvironment for meiosis I/II and post-meiotic spermatid development which take place exclusively in the apical compartment, away from the host immune system, and it contributes to the immune privilege status of testis. However, the BTB also poses major obstacles in developing male contraceptives (e.g., adjudin) that exert their effects on germ cells in the apical compartment, such as by disrupting spermatid adhesion to the Sertoli cell, causing germ cell exfoliation from the testis. Besides the tight junction (TJ) between adjacent Sertoli cells at the BTB that restricts the entry of contraceptives from the microvessels in the interstitium to the adluminal compartment, drug transporters, such as P-glycoprotein and multidrug resistance-associated protein 1 (MRP1), are also present that actively pump drugs out of the testis, limiting drug bioavailability. Recent advances in drug formulations, such as drug particle micronization (<50 μm) and co-grinding of drug particles with ß-cyclodextrin have improved bioavailability of contraceptives via considerable increase in solubility. Herein, we discuss development in drug formulations using adjudin as an example. We also put emphasis on the possible use of nanotechnology to deliver adjudin to the apical compartment with multidrug magnetic mesoporous silica nanoparticles. These advances in technology will significantly enhance our ability to develop effective non-hormonal male contraceptives for men.

Interaction of oligomeric breast cancer resistant protein (BCRP) with adjudin: a male contraceptive with anti-cancer activity

Breast cancer resistant protein (BCRP, ABCG2) is an ATP-binding cassette (ABC) transporter, which together with two other ABC efflux drug pumps, namely P-glycoprotein (P-gp, ABCB1) and multidrug resistance-related protein 1 (MRP1, ABCC1) is the most important multidrug resistance protein foun d in eukaryotic cells including cells in the testis. However, unlike P-gp and MRP1, which are components of the Sertoli cell blood-testis barrier (BTB), BCRP is not expressed at the BTB in rodents and human testes. Instead, BCRP is expressed by peritubular myoid cells and endothelial cells of the lymphatic vessel in the tunica propria, residing outside the BTB. As such, the testis is equipped with two levels of defense against xenobiotics or drugs, preventing these harmful substances from entering the adluminal compartment to perturb meiosis and post-meiotic spermatid development: one at the level of the BTB conferred by P-gp and MRP1 and one at the tunica propria conferred by BCRP. The presence of drug transporters at the tunica propria as well as at the Sertoli cell BTB thus poses significant obstacles in developing non-hormonal contraceptives if these drugs (e.g., adjudin) exert their effects in germ cells behind the BTB, such as in the adluminal (apical) compartment of the seminiferous epithelium. Herein, we summarize recent findings pertinent to adjudin, a non-hormonal male contraceptive, and molecular interactions of adjudin with BCRP so that this information can be helpful to devise delivery strategies to evade BCRP in the tunica propria to improve its bioavailability in the testis.

Toxicants target cell junctions in the testis: Insights from the indazole-carboxylic acid model

There are numerous types of junctions in the seminiferous epithelium which are integrated with, and critically dependent on the Sertoli cell cytoskeleton. These include the basal tight junctions between Sertoli cells that form the main component of the blood–testis barrier, the basal ectoplasmic specializations (basal ES) and basal tubulobulbar complexes (basal TBC) between Sertoli cells; as well as apical ES and apical TBC between Sertoli cells and the developing spermatids that orchestrate spermiogenesis and spermiation. These junctions, namely TJ, ES, and TBC interact with actin microfilament-based cytoskeleton, which together with the desmosomal junctions that interact with the intermediate filament-based cytoskeleton plus the highly polarized microtubule-based cytoskeleton are working in concert to move spermatocytes and spermatids between the basal and luminal aspect of the seminiferous epithelium. In short, these various junctions are structurally complexed with the actin- and microtubule-based cytoskeleton or intermediate filaments of the Sertoli cell. Studies have shown toxicants (e.g., cadmium, bisphenol A (BPA), perfluorooctanesulfonate (PFOS), phthalates, and glycerol), and some male contraceptives under development (e.g., adjudin, gamendazole), exert their effects, at least in part, by targeting cell junctions in the testis. The disruption of Sertoli–Sertoli cell and Sertoli–germ cell junctions, results in the loss of germ cells from the seminiferous epithelium. Adjudin, a potential male contraceptive under investigation in our laboratory, produces loss of spermatids from the seminiferous tubules through disruption of the Sertoli cell spermatid junctions and disruption of the Sertoli cell cytoskeleton. The molecular and structural changes associated with adjudin administration are described, to provide an example of the profile of changes caused by disturbance of Sertoli-germ cell and also Sertoli cell-cell junctions.

The apical ES-BTB-BM functional axis is an emerging target for toxicant-induced infertility

Testes are sensitive to toxicants, such as cadmium and phthalates, which disrupt a local functional axis in the seminiferous epithelium known as the 'apical ectoplasmic specialization (apical ES)-blood-testis barrier (BTB)-basement membrane (BM)'. Following exposure, toxicants contact the basement membrane and activate the Sertoli cell, which perturbs its signaling function. Thus, toxicants can modulate signaling and/or cellular events at the apical ES-BTB-BM axis, perturbing spermatogenesis without entering the epithelium. Toxicants also enter the epithelium via drug transporters to potentiate their damaging effects, and downregulation of efflux transporters by toxicants impedes BTB function such that toxicants remain in the epithelium and efficiently disrupt spermatogenesis. These findings support a novel model of toxicant-induced disruption of spermatogenesis that could be interfered with using small molecules.

Inhibition of sperm capacitation and fertilizing capacity by adjudin is mediated by chloride and its channels in humans

STUDY QUESTION

Does adjudin disrupt chloride ion (Cl⁻) ion transport function in human sperm and impede sperm capacitation and fertilizing ability in vitro?

SUMMARY ANSWER

In this study the results indicate that adjudin is a potent blocker of Cl⁻ channels: disrupting Cl⁻ ion transport function results in a decline in sperm capacitation and fertilizing ability in humans in vitro.

WHAT IS KNOWN ALREADY

Although our previous studies have demonstrated that adjudin exerts its effect by disrupting sertoli-germ cell adhesion junctions, most notably apical ectoplasmic specialization by targeting testin and actin filament bundles that disrupts the actin-based cytoskeleton in sertoli cells, it remains unclear whether adjudin impedes Cl⁻ ion transport function in the human sperm.

STUDY DESIGN, SIZE AND DURATION

Semen samples were obtained from 45 fertile men (aged 25-32). Spermatozoa were isolated from the semen in the human tube fluid (HTF) medium by centrifugation through a discontinuous Percoll gradient, and incubated with adjudin at 10 nM-10 µM and/or other reagents under capacitating conditions for 0-5 h.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We evaluated the effect of adjudin and different reagents on sperm functions with which they were incubated at 37 °C. Sperm motility and hyperactivation were analyzed by a computer-assisted sperm analysis (CASA) system. Sperm capacitation and the acrosome reaction were assessed by chlortetracycline fluorescence staining. Sperm fertilizing ability was evaluated by sperm penetration of zona-free hamster egg assay, and cellular cAMP levels in spermatozoa were quantified by the EIA kit. The proteins tyrosine, serine and threonine phosphorylation in the presence or absence of adjudin were analyzed by means of a immunodetection of spermatozoa, especially, compared the effect of adjudin on sperm hyperactivation and capacitation in the complete HTF medium with the Cl⁻-deficient HTF medium as well as the various Cl⁻ channel blockers.

MAIN RESULTS AND THE ROLE OF CHANCE

Adjudin significantly inhibited sperm hyperactivation but not sperm motility. Adjudin-induced inhibition of sperm capacitation was reversible, and it was found to block the rhuZP₃β- and progesterone-induced acrosome reaction in a dose-dependent manner. Adjudin also blocked sperm penetration of zona-free hamster eggs, and significantly inhibited both forskolin-activated transmembrane adenylyl cyclase and soluble adenylyl cyclase activities leading to a significant decline in the cellular cAMP levels in human spermatozoa. Adjudin failed to reduce sperm protein tyrosine phosphorylation but it did prevent sperm serine and threonine protein phosphorylation. Interestingly, adjudin was found to exert its inhibitory effects on sperm capacitation and capacitation-associated events only in the complete Cl⁻-HTF medium but not Cl⁻-deficient medium, illustrating the likely involvement of Cl⁻. Adjudin inhibits the fertility capacity of human sperm is mediated by disrupting chloride ion and its transport function.

LIMITATIONS, REASONS FOR CAUTION

This study has examined the effect of adjudin only on human sperm capacitation and fertilizing ability in vitro and thus has some limitations. Further investigations in vivo are needed to confirm adjudin is a potent male contraceptive.

WIDER IMPLICATIONS OF THE FINDINGS

Our studies demonstrated that adjudin inhibition of capacitation is reversible and its toxicity is low, opening the door for the examination of adjudin as a mediator of male fertility control. Adjudin may be a safe, efficient and reversible male antifertility agent and applicable to initial clinical trials of adjudin as a male antifertility agent in humans. STUDING FUNDING/COMPETING INTEREST(S): This work was supported by the National Basic Research Program of China (2006CB504002), the Nature Science Foundation of China (Nos. 81000244 and 81170554), Zhejiang Project of Science and Technology (2011C23046), the Nature Science Fund of Zhejiang province (Nos.Y2100058 and Y2090236), the key Science and Technology Innovation Team of Zhejiang Province (No.2012R10048-07) and the National Institutes of Health (NICHD U54 HD029990 project 5), USA. The authors declare no conflict of interest.

New approaches to male non-hormonal contraception

A non-hormonal male contraceptive is a contraceptive that does not involve the administration of hormones or hormone blockers. This review will focus on the use of lonidamine derivatives and inhibitors of retinoic acid biosynthesis and function as approaches to male non-hormonal contraception. Two current lonidamine derivatives, adjudin and H2-gamendazole, are in development as male contraceptives. These potent anti-spermatogenic compounds impair the integrity of the apical ectoplasmic specialization, resulting in premature spermiation and infertility. Another approach to male contraceptive development is the inhibition of retinoic acid in the testes, as retinoic acid signaling is necessary for spermatogenesis. The administration of the retinoic acid receptor antagonist BMS-189453 reversibly inhibits spermatogenesis in mice. Similarly, oral dosing of WIN 18,446, which inhibits testicular retinoic acid biosynthesis, effectively contracepts rabbits. Hopefully, one of these approaches to non-hormonal male contraception will prove to be safe and effective in future clinical trials.

Adjudin disrupts spermatogenesis via the action of some unlikely partners: Eps8, Arp2/3 complex, drebrin E, PAR6 and 14-3-3

Adjudin, 1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide (formerly called AF-2364), is a potent analog of lonidamine [1-(2,4-dichlorobenzyl)-1H-indazole-3-carboxylic acid] known to disrupt germ cell adhesion, most notably elongating and elongated spermatids, in the seminiferous epithelium of adult rat testes and thus, leads to infertility in rats. Since the population of spermatogonia and spermatogonial stem cells (SSCs) in the seminiferous tubules is not significantly reduced by the treatment of rats with adjudin, adjudin-induced infertility is highly reversible, which enables reinitiation of spermatogenesis and germ cell re-population of the voided seminiferous epithelium. Furthermore, adjudin appears to exert its effects at the testis-specific atypical adherens junction (AJ) type known as ectoplasmic specialization (ES), most notably the apical ES at the Sertoli cell-spermatid interface. Thus, the hypothalamic-pituitary-gonadal axis is not unaffected and systemic side-effects are minimal. This also makes adjudin a potential candidate for male contraceptive development. Herein, we critically evaluate recent findings in the field and provide an updated model regarding the mechanism underlying adjudin-induced apical ES disruption. In short, adjudin targets actin filament bundles at the apical ES, the hallmark ultrastructure of this testis-specific junction type not found in any other epithelia/endothelia in mammals, by suppressing the expression of Eps8 (epidermal growth factor receptor pathway substrate 8), an actin capping protein that also plays a role in actin bundling, so that actin filament bundles can no longer be maintained at the apical ES. This is concomitant with a mis-localization of Arp3 (actin-related protein 3, a component of the Arp2/3 complex that induces actin nucleation/branching) recruited by drebrin E, causing "unwanted" actin branching, further destabilizing actin filament bundles at the apical ES. Additionally, adjudin blocks the expression of PAR6 (partitioning defective protein 6) and 14-3-3 (also known as PAR5) considerably at the apical ES, disrupting the homeostasis of endocytic vesicle-mediated protein trafficking, which in turn leads to an increase in protein endocytosis. The net result of these changes destabilizes cell adhesion and induces degeneration of the apical ES, causing premature release of spermatids, mimicking spermiation.

Interactions of laminin β3 fragment with β1-integrin receptor: A revisit of the apical ectoplasmic specialization-blood-testis-barrier-hemidesmosome functional axis in the testis

Recent studies have demonstrated the presence of a functional axis that coordinates the events of spermiation and blood-testis barrier (BTB) restructuring which take place simultaneously at the opposite ends of the seminiferous epithelium at stage VIII of the epithelial cycle of spermatogenesis in the rat testis. In short, the disruption of the apical ectoplasmic specialization (apical ES) at the Sertoli cell-elongated spermatid interface, which facilitates the release of sperm at spermiation near the tubule lumen, is coordinated with restructuring at the BTB to accommodate the transit of preleptotene spermatocytes across the immunological barrier near the basement membrane. These two events are likely coordinated by a functional axis involving hemidesmosome at the Sertoli cell-basement membrane interface, and it was designated the apical ES-BTB-hemidesmosome axis. It was demonstrated that fragments of laminin chains (e.g., laminin β3 or γ3 chains) derived from the α6β1-integrin-laminin333 protein complex at the apical ES, which were likely generated via the action of MMP-2 (matrix metalloprotease-2, MMP2) prior to spermiation, acted as biologically active peptides to perturb the BTB permeability function by accelerating protein endocytosis (e.g., occludin) at the site, thereby destabilizing the BTB integrity to facilitate the transit of preleptotene spermatocytes. These laminin fragments also perturbed hemidesmosome function via their action on β1-integrin, a component of hemidesmosome in the testis, which in turn, sent a signal to further destabilize the BTB function. As such, the events of spermiation and BTB restructuring are coordinated via this functional axis. Recent studies using animal models treated with toxicants, such as mono-(2-ethylhexyl) phthalate (MEHP), or adjudin, a male contraceptive under investigation, have also supported the presence of this functional axis in the mouse. In this short review, we critically evaluate the role of this local functional axis in the seminiferous epithelium in spermatogenesis. We also provide molecular modeling information on the interactions between biologically active laminin fragments and β1-integrin, which will be important to assist in the design of more potent laminin-based peptides to disrupt this axis, thereby perturbing spermatogenesis for male contraception and to understand the underlying biology that coordinates spermiation and BTB restructuring during spermatogenesis.