Cyclic nucleotide phosphodiesterases in human spermatozoa and seminal fluid: Presence of an active PDE10A in human spermatozoa

Computational and in vitro binding studies of theophylline against phosphodiesterases functioning in sperm in presence and absence of pentoxifylline

Fertility is a result of a synergy among the sperm's various functions including capacitation, motility, chemotaxis, acrosome reaction, and, finally, the fertilization of the oocyte. Subpar motility is the most common cause of infertility in males. Cyclic adenosine monophosphate (cAMP) signalling underlies motility and is depleted by the phosphodiesterases (PDEs) in sperm, such as PDE10A, PDE1, and PDE4. Therefore, the PDE inhibitor (PDEI) category of fertility drugs aim to enhance motility in assisted reproduction technologies (ARTs) through inhibition of PDEs, though they might have adverse effects on other physiological variables. For example, the popular drug pentoxifylline (PTX), widely used in ARTs, improves motility but causes premature acrosome reaction and exerts toxicity on the fertilized oocyte. Another xanthine-derived drug, theophylline (TP), has been repurposed for treating infertility, but its mechanism of PDE inhibition remains unexplored. Here, using biophysical and computational approaches, we identified that TP binds to the same binding pocket as PTX with higher affinity than PTX. We also found that PTX and TP co-bind to the same binding pocket, but at different sites.

Comparative Proteomic Identification of Ram Sperm before and after In Vitro Capacitation

Ram sperm undergo a sequence of physiological and biochemical changes collectively termed as capacitation to perform oocyte fertilization. However, the protein changes induced by capacitation remain in need of further exploration. Thus, the present study investigated the comparative proteomic profiling in ram spermatozoa under non-capacitating (NC) and capacitating (CAP) conditions in vitro using a liquid chromatography-tandem mass spectrometry combined with tandem mass tag labeling strategy. As a results, 2050 proteins were identified and quantified; 348 of them were differentially abundant, with 280 of the proteins upregulated and 68 of the proteins downregulated between the CAP and NC spermatozoa, respectively. Functional enrichment analysis indicated that the differentially abundant proteins Prune Exopolyphosphatase 1, Galactose-1-Phosphate Uridylyltransferase, and ATP Citrate Lyase were strictly related to energy production and conversion, and Phosphoglycolate phosphatase, Glucosamine-6-Phosphate Deaminase 1 and 2 were related to metabolism, RNA processing, and vesicular transport pathways. Furthermore, the networks of protein-protein interaction indicated a strong interaction among these differential proteins in annotated pathways such as ubiquitin and transport metabolism. Our findings indicate that capacitation progress might be regulated through different pathways, providing insights into mechanisms involved in ram sperm capacitation and fertility.

Control of intracellular pH and bicarbonate by CO2 diffusion into human sperm

The reaction of CO2 with H2O to form bicarbonate (HCO3-) and H+ controls sperm motility and fertilization via HCO3--stimulated cAMP synthesis. A complex network of signaling proteins participates in this reaction. Here, we identify key players that regulate intracellular pH (pHi) and HCO3- in human sperm by quantitative mass spectrometry (MS) and kinetic patch-clamp fluorometry. The resting pHi is set by amiloride-sensitive Na+/H+ exchange. The sperm-specific putative Na+/H+ exchanger SLC9C1, unlike its sea urchin homologue, is not gated by voltage or cAMP. Transporters and channels implied in HCO3- transport are not detected, and may be present at copy numbers < 10 molecules/sperm cell. Instead, HCO3- is produced by diffusion of CO2 into cells and readjustment of the CO2/HCO3-/H+ equilibrium. The proton channel Hv1 may serve as a unidirectional valve that blunts the acidification ensuing from HCO3- synthesis. This work provides a new framework for the study of male infertility.

Phosphodiesterase 10A inhibitor PF-2545920 as a prospective agent for the clinical promotion of sperm motility

Phosphodiesterase (PDE) inhibitors can improve sperm motility in patients with asthenozoospermia. However, the most commonly reported nonselective PDE inhibitor pentoxifylline and PDE5 inhibitor sildenafil have the disadvantages of requiring a high concentration and destroying sperm integrity. We examined the PDE10A inhibitor PF-2545920 to compare its ability to promote sperm motility with that of pentoxifylline and sildenafil. After seminal plasma was discarded, several semen samples were subjected to four treatments (control, PF-2545920, pentoxifylline, and sildenafil) to evaluate their ability to affect motility, viability, and spontaneous acrosome reactions. Intracellular calcium and adenosine triphosphate (ATP), mitochondrial membrane potential, and penetration through viscous medium were assessed by flow cytometry, luciferase, and hyaluronic acid after treatment with PF-2545920. Statistical analyses were performed using the analysis of variance statistical test. PF-2545920 elevated the percentage of motile spermatozoa compared to the control, pentoxifylline, and sildenafil groups at 10 µmol l -1 ( P < 0.01). It is less toxic to GC-2spd mouse spermatocytes cells and spermatozoa and causes fewer spontaneous acrosomal reactions ( P < 0.05). PF-2545920 also increased mitochondrial membrane potential ( P < 0.001) and altered intracellular calcium ( P < 0.05) in a dose-dependent manner, including increasing sperm hyaluronic acid penetrating ability ( P < 0.05). Therefore, PF-2545920 might be an excellent choice for stimulating the sperm motility.

Once upon a Testis: The Tale of Cyclic Nucleotide Phosphodiesterase in Testicular Cancers

Phosphodiesterases are key regulators that fine tune the intracellular levels of cyclic nucleotides, given their ability to hydrolyze cAMP and cGMP. They are critical regulators of cAMP/cGMP-mediated signaling pathways, modulating their downstream biological effects such as gene expression, cell proliferation, cell-cycle regulation but also inflammation and metabolic function. Recently, mutations in PDE genes have been identified and linked to human genetic diseases and PDEs have been demonstrated to play a potential role in predisposition to several tumors, especially in cAMP-sensitive tissues. This review summarizes the current knowledge and most relevant findings regarding the expression and regulation of PDE families in the testis focusing on PDEs role in testicular cancer development.

Computational, biochemical and ex vivo evaluation of xanthine derivatives against phosphodiesterases to enhance the sperm motility

Enhancing sperm motility in vitro has immensely benefited assisted conception methods. Phosphodiesterases (PDE) break the second messenger cAMP, and therefore, inhibition of their catalytic activity enhances the sperm motility through maintaining cAMP homeostasis in sperm. In view of identifying the molecules that could inhibit PDE functioning in spermatozoa, we aimed to evaluate the phosphodiesterase inhibitors (PDEI) - xanthine derivatives - acefylline, dyphylline and proxyphylline to repurpose them for assisted reproductive technology. These are available in the market as pharmaceutical agents to treat mainly respiratory system diseases. Based on the structure guided in silico studies, we predicted that these molecules bind to the cAMP binding catalytic pocket of PDE enzymes, and further molecular dynamics simulation analysis indicated that these molecules form the stable complexes. Isothermal titration calorimetry studies revealed that acefylline has better affinity towards PDE4A, PDE4D and PDE10A, when compared to dyphylline and proxyphylline. In addition, ex vivo studies corroborated in vitro binding studies that acefylline has much superior sperm motility enhancement property on human ejaculated spermatozoa and mouse testicular spermatozoa compared to dyphylline and proxyphylline.Communicated by Ramaswamy H. Sarma.

Compounds enhancing human sperm motility identified using a high-throughput phenotypic screening platform

STUDY QUESTION

Can a high-throughput screening (HTS) platform facilitate male fertility drug discovery?

SUMMARY ANSWER

An HTS platform identified a large number of compounds that enhanced sperm motility.

WHAT IS KNOWN ALREADY

Several efforts to find small molecules modulating sperm function have been performed but none have used high-throughput technology.

STUDY DESIGN, SIZE, DURATION

Healthy donor semen samples were used and samples were pooled (3-5 donors per pool). Primary screening was performed singly; dose-response screening was performed in duplicate (using independent donor pools).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Spermatozoa isolated from healthy donors were prepared by density gradient centrifugation and incubated in 384-well plates with compounds (6.25 μM) to identify those compounds with enhancing effects on motility. Approximately 17 000 compounds from the libraries, ReFRAME, Prestwick, Tocris, LOPAC, CLOUD and MMV Pathogen Box, were screened. Dose-response experiments of screening hits were performed to confirm the enhancing effect on sperm motility. Experiments were performed in a university setting.

MAIN RESULTS AND THE ROLE OF CHANCE

From our primary single concentration screening, 105 compounds elicited an enhancing effect on sperm motility compared to dimethylsulphoxide-treated wells. Confirmed enhancing compounds were grouped based on their annotated targets/target classes. A major target class, phosphodiesterase inhibitors, were identified, in particular PDE10A inhibitors as well as number of compounds not previously known to enhance human sperm motility, such as those related to GABA signalling.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although this approach provides data about the activity of the compound, it is only a starting point. For example, further substantive experiments are necessary to provide a more comprehensive picture of each compound's activity, the effect on the kinetics of the cell populations and subpopulations, and their potential mechanisms of action. Compounds have been tested with prepared donor spermatozoa, incubated under non-capacitating conditions, and only incubated with compounds for a relatively short period of time. Therefore, the effect of compounds under different conditions, for example in whole semen, for longer incubation times, or using samples from patient groups, may be different and require further study. All experiments were performed in vitro.

WIDER IMPLICATIONS OF THE FINDINGS

This phenotypic screening assay identified a large number of compounds that increased sperm motility. In addition to furthering our understanding of human sperm function, for example identifying new avenues for discovery, we highlight potential compounds as promising start-point for a medicinal chemistry programme for potential enhancement of male fertility. Moreover, with disclosure of the results of screening, we present a substantial resource to inform further work in the field.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Bill and Melinda Gates Foundation, Scottish Funding Council and Scottish Universities Life Science Alliance. C.L.R.B. is Editor for RBMO. C.L.R.B. receives funding from Chief Scientists Office (Scotland), ESHRE and Genus PLC, consulting fees from Exscientia and lecture fees from Cooper Surgical and Ferring. S.M.d.S. is an Associate Editor of Human Reproduction, and an Associate Editor of Reproduction and Fertility. S.M.d.S. receives funding from Cooper Surgical and British Dietetic Society. No other authors declared a COI.

Structure-based redesigning of pentoxifylline analogs against selective phosphodiesterases to modulate sperm functional competence for assisted reproductive technologies

Phosphodiesterase (PDE) inhibitors, such as pentoxifylline (PTX), are used as pharmacological agents to enhance sperm motility in assisted reproductive technology (ART), mainly to aid the selection of viable sperm in asthenozoospermic ejaculates and testicular spermatozoa, prior to intracytoplasmic sperm injection (ICSI). However, PTX is reported to induce premature acrosome reaction (AR) and, exert toxic effects on oocyte function and early embryo development. Additionally, in vitro binding studies as well as computational binding free energy (ΔGbind) suggest that PTX exhibits weak binding to sperm PDEs, indicating room for improvement. Aiming to reduce the adverse effects and to enhance the sperm motility, we designed and studied PTX analogues. Using structure-guided in silico approach and by considering the physico-chemical properties of the binding pocket of the PDEs, designed analogues of PTX. In silico assessments indicated that PTX analogues bind more tightly to PDEs and form stable complexes. Particularly, ex vivo evaluation of sperm treated with one of the PTX analogues (PTXm-1), showed comparable beneficial effect at much lower concentration-slower AR, higher DNA integrity and extended longevity of  spermatozoa and  superior embryo quality. PTXm-1 is proposed to be a better pharmacological agent for ART than PTX for sperm function enhancement.

Efficacy and safety of papaverine as an in vitro motility enhancer on human spermatozoa

PURPOSE

The aim of this study was to examine the ability and safety of papaverine supplementation for in vitro sperm motility enhancement. In addition, sperm motility enhancement of papaverine was compared to pentoxifylline and theophylline. The post-thaw spermatozoa were used as an asthenozoospermia model.

METHODS

Post thaw sperm suspensions were divided into two groups: papaverine (100 μmol/L) and control, and each was investigated in two subgroups of 30- and 60-min exposure times. Detailed motility parameters were detected using a computerized sperm motility analyzer. Acrosomal status, viability, apoptosis, and DNA fragmentation were evaluated by flow cytometry. Furthermore, the motility-enhancing capacity of papaverine, pentoxifylline, and theophylline was compared.

RESULTS

Cryopreservation impaired sperm parameters dramatically but no significant changes occurred in acrosomal status and apoptosis. Supplementation of papaverine enhanced motility parameters consistently at all exposure intervals, significantly. However, viability was lower at the 60th minute compared to the 30th minute (p=0.019). Papaverine did not alter any acrosomal or apoptotic markers at any time points. All of the compounds compared in this study increased the motility parameters, where theophylline supplementation provided significantly better improvement in total motility compared to papaverine and pentoxifylline.

CONCLUSION

Our results suggest that in vitro papaverine treatment for 30 min adequately improves motility of post-thaw sperm, without leading to acrosome reaction, DNA damage, and viability loss. Theophylline's potency on increasing the ratio of total motile spermatozoa was found significantly superior than the two tested compounds. Prospective clinical studies with embryo production, pregnancy, and live birth data should be undertaken.

Proteomic Changes Associated With Sperm Fertilizing Ability in Meat-Type Roosters

The molecular basis of male fertility remains unclear, especially in chickens, where decades of genetic selection increased male fertility variability as a side effect. As transcription and translation are highly limited in sperm, proteins are key molecules defining their functionality, making proteomic approaches one of the most adequate methods to investigate sperm capacity. In this context, it is interesting to combine complementary proteomic approaches to maximize the identification of proteins related to sperm-fertilizing ability. In the present study, we aimed at identifying proteins related to fertility in meat-type roosters, showing fertility variability. Fertile roosters (fertility rates higher than 70% after artificial insemination) differed from subfertile roosters (fertility rates lower than 40%) in their sperm mass motility. Fertile and subfertile sperm protein contents were compared using two complementary label-free quantitative proteomic methods: Intact Cell MALDI-TOF-Mass Spectrometry and GeLC-MS/MS. Combining the two strategies, 57 proteins were identified as differentially abundant. Most of them were described for the first time as differentially abundant according to fertility in this species. These proteins were involved in various molecular pathways including flagellum integrity and movement, mitochondrial functions, sperm maturation, and storage in female tract as well as oocyte-sperm interaction. Collectively, our data improved our understanding of chicken sperm biology by revealing new actors involved in the complexity of male fertility that depends on multiple cell functions to reach optimal rates. This explains the inability of reductionist in vitro fertility testing in predicting male fertility and suggests that the use of a combination of markers is a promising approach.

The synthesis of a novel pentoxifylline derivative with superior human sperm motility enhancement properties

mPTF1 demonstrated lower genotoxicity, higher affinity for PDEs, & reasonable pharmacokinetic, druglikeness & ADMET properties compared to Pentoxifylline.

Cyclic AMP efflux through MRP4 regulates actin dynamics signalling pathway and sperm motility in bovines

Previously we demonstrated that multidrug resistance-associated protein 4 transporter (MRP4) mediates cAMP efflux in bovine spermatozoa and that extracellular cAMP (ecAMP) triggers events associated to capacitation. Here, we deepen the study of the role of MRP4 in bovine sperm function by using MK571, an MRP4 inhibitor. The incubation of spermatozoa with MK571 during 45 min inhibited capacitation-associated events. MRP4 was localized in post-acrosomal region and mid-piece at 15 min capacitation, while at 45 min it was mainly located in the acrosome. After 15 min, MK571 decreased total sperm motility (TM), progressive motility (PM) and several kinematic parameters. The addition of ecAMP rescued MK571 effect and ecAMP alone increased the percentage of motile sperm and kinematics parameters. Since actin cytoskeleton plays essential roles in the regulation of sperm motility, we investigated if MRP4 activity might affect actin polymerization. After 15 min capacitation, an increase in F-actin was observed, which was inhibited by MK571. This effect was reverted by the addition of ecAMP. Furthermore, ecAMP alone increased F-actin levels while no F-actin was detected with ecAMP in the presence of PKA inhibitors. Our results support the importance of cAMP efflux through MRP4 in sperm capacitation and suggest its involvement in the regulation of actin polymerization and motility.

Novel pharmacological actions of trequinsin hydrochloride improve human sperm cell motility and function

BACKGROUND AND PURPOSE

Asthenozoospermia is a leading cause of male infertility, but development of pharmacological agents to improve sperm motility is hindered by the lack of effective screening platforms and knowledge of suitable molecular targets. We have demonstrated that a high-throughput screening (HTS) strategy and established in vitro tests can identify and characterise compounds that improve sperm motility. Here, we applied HTS to identify new compounds from a novel small molecule library that increase intracellular calcium ([Ca²⁺ ]_i ), promote human sperm cell motility, and systematically determine the mechanism of action.

EXPERIMENTAL APPROACH

A validated HTS fluorometric [Ca²⁺ ]_i assay was used to screen an in-house library of compounds. Trequinsin hydrochloride (a PDE3 inhibitor) was selected for detailed molecular (plate reader assays, electrophysiology, and cyclic nucleotide measurement) and functional (motility and acrosome reaction) testing in sperm from healthy volunteer donors and, where possible, patients.

KEY RESULTS

Fluorometric assays identified trequinsin as an efficacious agonist of [Ca²⁺ ]_i , although less potent than progesterone. Functionally, trequinsin significantly increased cell hyperactivation and penetration into viscous medium in all donor sperm samples and cell hyperactivation in 22/25 (88%) patient sperm samples. Trequinsin-induced [Ca²⁺ ]_i responses were cross-desensitised consistently by PGE₁ but not progesterone. Whole-cell patch clamp electrophysiology confirmed that trequinsin activated CatSper and partly inhibited potassium channel activity. Trequinsin also increased intracellular cGMP.

CONCLUSION AND IMPLICATIONS

Trequinsin exhibits a novel pharmacological profile in human sperm and may be a suitable lead compound for the development of new agents to improve patient sperm function and fertilisation potential.

Extracellular cAMP activates molecular signalling pathways associated with sperm capacitation in bovines

STUDY QUESTION

Is extracellular cAMP involved in the regulation of signalling pathways in bovine sperm capacitation?

SUMMARY ANSWER

Extracellular cAMP induces sperm capacitation through the activation of different signalling pathways that involve phospholipase C (PLC), PKC/ERK1-2 signalling and an increase in sperm Ca2+ levels, as well as soluble AC and cAMP/protein kinase A (PKA) signalling.

WHAT IS KNOWN ALREADY

In order to fertilize the oocyte, ejaculated spermatozoa must undergo a series of changes in the female reproductive tract, known as capacitation. This correlates with a number of membrane and metabolic modifications that include an increased influx of bicarbonate and Ca2+, activation of a soluble adenylyl cyclase (sAC) to produce cAMP, PKA activation, protein tyrosine phosphorylation and the development of hyperactivated motility. We previously reported that cAMP efflux by Multidrug Resistance Protein 4 (MRP4) occurs during sperm capacitation and the pharmacological blockade of this inhibits the process. Moreover, the supplementation of incubation media with cAMP abolishes the inhibition and leads to sperm capacitation, suggesting that extracellular cAMP regulates crucial signalling cascades involved in this process.

STUDY DESIGN, SIZE, DURATION

Bovine sperm were selected by the wool glass column method, and washed by centrifugation in BSA-Free Tyrode's Albumin Lactate Pyruvate (sp-TALP). Pellets were resuspended then diluted for each treatment. For in vitro capacitation, 10 to 15 × 106 SPZ/ml were incubated in 0.3% BSA sp-TALP at 38.5°C for 45 min under different experimental conditions. To evaluate the role of extracellular cAMP on different events associated with sperm capacitation, 10 nM cAMP was added to the incubation medium as well as different inhibitors of enzymes associated with signalling transduction pathways: U73122 (PLC inhibitor, 10 μM), Gö6983 (PKC inhibitor, 10 μM), PD98059 (ERK-1/2 inhibitor, 30 μM), H89 and KT (PKA inhibitors, 50 μM and 100 nM, respectively), KH7 (sAC inhibitor, 10 μM), BAPTA-AM (intracellular Ca2+ chelator, 50 μM), EGTA (10 μM) and Probenecid (MRPs general inhibitor, 500 μM). In addition, assays for binding to oviductal epithelial cells and IVF were carried out to test the effect of cAMP compared with other known capacitant agents such as heparin (60 μg/ml) and bicarbonate (40 mM).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Straws of frozen bovine semen (20-25 × 106 spermatozoa/ml) were kindly provided by Las Lilas, CIALE and CIAVT Artificial Insemination Centers. The methods used in this work include western blot, immunohistochemistry, flow cytometry, computer-assisted semen analysis, live imaging of Ca2+ and fluorescence scanning. At least three independent assays with bull samples of proven fertility were carried.

MAIN RESULTS AND THE ROLE OF CHANCE

In the present study, we elucidate the molecular events induced by extracellular cAMP. Our results showed that external cAMP induces sperm capacitation, depending upon the action of PLC. Downstream, this enzyme increased ERK1-2 activation through PKC and elicited a rise in sperm Ca2+ levels (P < 0.01). Moreover, extracellular cAMP-induced capacitation also depended on the activity of sAC and PKA, and increased tyrosine phosphorylation, indicating that the nucleotide exerts a broad range of responses. In addition, extracellular cAMP-induced sperm hyperactivation and concomitantly increased the proportion of spermatozoa with high mitochondrial activity (P < 0.01). Finally, cAMP increased the in vitro fertilization rate compared to control conditions (P < 0.001).

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study performed with bovine cryopreserved spermatozoa. Studies in other species and with fresh samples are needed to extrapolate these data.

WIDER IMPLICATIONS OF THE FINDINGS

These findings strongly suggest an important role of extracellular cAMP in the regulation of the signalling pathways involved in the acquisition of bull sperm fertilizing capability. The data presented here indicate that not only a rise, but also a regulation of cAMP levels is necessary to ensure sperm fertilizing ability. Thus, exclusion of the nucleotide to the extracellular space might be essential to guarantee the achievement of a cAMP tone, needed for all capacitation-associated events to take place. Moreover, the ability of cAMP to trigger such broad and complex signalling events allows us to hypothesize that cAMP is a self-produced autocrine/paracrine factor, and supports the emerging paradigm that spermatozoa do not compete but, in fact, communicate with each other. A precise understanding of the functional competence of mammalian spermatozoa is essential to generate clinical advances in the treatment of infertility and the development of novel contraceptive strategies.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by Consejo Nacional de Investigaciones Científicas y Técnicas [PIP0 496 to S.P.-M.], Agencia Nacional de Promoción Científica y Tecológica [PICT 2012-1195 and PICT2014-2325 to S.P.-M., and PICT 2013-2050 to C.D.], Boehringer Ingelheim Funds, and the Swedish Farmers Foundation [SLF-H13300339 to J.M.]. The authors declare there are no conflicts of interests.