Estrogen suppresses melatonin-enhanced hyperactivation of hamster spermatozoa

Progesterone and estradiol regulate sperm hyperactivation and in vitro fertilization success in mice

Progesterone (P) and 17β-estradiol (Eβ) form the well-known hormone pair that regulates sperm capacitation. Here, we examined the regulatory effects of P and Eβ on sperm hyperactivation in mice and evaluated the in vitro fertilization (IVF) success. Although P enhanced hyperactivation, Eβ dose-dependently suppressed the P-enhanced hyperactivation. Moreover, P increased IVF success, whereas Eβ suppressed the P-induced increase in IVF success in a dose-dependent manner. Thus, P and Eβ competitively regulate hyperactivation and IVF success in mice. Since P and Eβ concentrations generally change during the estrous cycle, sperm are speculated to capacitate in response to the oviductal environment and fertilize the oocyte.

Enhancement of rat spermatozoal hyperactivation by progesterone

Progesterone (P) is a well-known enhancer of hyperactivation which is associated with the success of in vitro fertilization (IVF). In this study, we examined whether P-enhanced hyperactivation affected IVF success in rats. When rat spermatozoa were exposed to 10, 20, and 40 ng/ml P, 20 ng/ml P enhanced hyperactivation via the membrane progesterone receptor. In addition, the enhancement of hyperactivation by 20 ng/ml P was regulated by phospholipase C, transmembrane adenylate cyclase, and protein kinase A. However, 20 ng/ml P did not affect IVF success. These results suggest that 20 ng/ml P enhances rat spermatozoal hyperactivation through non-genomic pathways. Because the concentration of P changes during the estrous cycle, it seems that rat spermatozoa are hyperactivated in response to the oviductal environment. However, the effect of 20 ng/ml P does not seem to fully capacitate spermatozoa.

Effects of aging and oviductal hormones on testes, epididymides, and sperm of hamster

Purpose

Aging is a major cause of decreased fertility. Using hamster, we examined the effects of aging on testes, epididymides, and sperm. Additionally, we examined whether progesterone (P4), melatonin (Mel) and 5-hydroxytryptamine (5-HT) mitigated effects of aging on sperm.

Methods

Young (10-16 weeks), Adult (5-7 months), Aged (13-15 months), and Old (19-22 months) hamsters were used. Weights of bodies, testes, and epididymides were measured. Testes and epididymides were studied by histological microscopy. Sera were obtained to determine testosterone concentrations. Sperm were analyzed by video-microscopy.

Results

By aging, body weights increased but weights of testes and epididymides decreased. Most hamsters were normozoospermia, although several old hamsters were azoospermia. In testes and epididymides, desquamation and structures resembling residual bodies (SRRBs) were observed. Although desquamation was not always related to aging, SRRBs occurred by aging. Testosterone concentrations were not changed in normozoospermic hamsters, but it was significantly reduced in old azoospermic hamster. Aging significantly reduced sperm ability to exhibit hyperactivation. Additionally, aging significantly increased the straight-line velocity (VSL). P4, Mel, and 5-HT lessened the reduction in sperm hyperactivation and the increasing of VSL.

Conclusion

Aging reduces qualities of testes, epididymides, and sperm, and P4, Mel, and 5-HT recover reduced quality of sperm.

Serotonergic signals enhanced hamster sperm hyperactivation

In the present study, we investigated the regulatory mechanisms underlying sperm hyperactivation enhanced by 5-hydroxytryptamine (5-HT) in hamsters. First, we examined the types of 5-HT receptors that regulate hyperactivation. Hyperactivation was significantly enhanced by 5-HT_2A and 5-HT₄ receptor agonists. Moreover, the results of the motility assay revealed that 5-HT_2A, 5-HT₃, and 5-HT₄ receptor agonists significantly decreased the velocity and/or amplitude of sperm. Under 5-HT₂ receptor stimulation, hyperactivation was associated with phospholipase C (PLC), inositol 1,4,5-trisphosphate (IP₃) receptor, soluble adenylate cyclase (sAC), and protein kinase A (PKA). In contrast, under 5-HT₄ receptor stimulation, hyperactivation was associated with transmembrane adenylate cyclase (tmAC), sAC, PKA, and CatSper channels. Accordingly, under the condition that sperm are hyperactivated, 5-HT likely stimulates PLC/IP₃ receptor signals via the 5-HT_2A receptor and tmAC/PKA/CatSper channel signals via the 5-HT₄ receptor. After sAC and PKA are activated by these stimulations, sperm hyperactivation is enhanced.

The in vitro effects of melatonin and Cry gene on the secretion of estradiol from camel ovarian granulosa cells

Bactrian camel as endemic economic species to the Northwest of China, its seasonal reproduction severely limits litter rates. In addition to melatonin, seasonal reproduction of animals is also regulated by the biological clock, but the specific molecular mechanism is not clear. To investigate the effects of melatonin and Cryptochrome (Cry) genes on seasonal reproduction, they were placed in ovarian granulosa cells, and their effects on reproduction were determined by measuring the concentrations of estradiol. Immunohistochemistry revealed that melatonin receptor protein (MT) was expressed in the cytosol and membrane of the ovarian granulosa cells, and the highest levels of CRY were expressed in the nuclei. The concentrations of estradiol in the cell culture supernatant were increased after the addition of exogenous melatonin or overexpression of MT, but these were decreased after MT was over expressed, and exogenous melatonin was added to the cells. In addition, there was a significant increase in the concentrations of estradiol after the Cry genes were overexpressed; however, the estradiol concentrations were decreased after the Cry genes were silenced. Our findings demonstrate that the MT and Cry genes play important roles in ovarian granulosa cell production of estradiol in a seasonally breeding species.

Involvement of progesterone and estrogen receptors in the ram sperm acrosome reaction

The steroid hormones 17-β estradiol (E2) and progesterone (P4) can regulate capacitation, hyperactive motility, and the acrosome reaction (AR) during the sperm transit through the female tract. Moreover, exogenous P4 and E2 can induce the AR in ovine spermatozoa, and progesterone receptor (PR) and estrogen receptors (ERα and ERβ) are present in these cells. Thus, to investigate whether the effects both steroid hormones in ram sperm capacitation and AR are receptor-mediated, we incubated them with receptor agonists (tanaproget 1 μM and 5 μM for PR or resveratrol 5 μM and 10 μM for ER) or antagonists (mifepristone 4 μM and 40 μM for PR or tamoxifen 5 μM and 10 μM for ER) in capacitating conditions. The addition of receptor modulators did not affect sperm viability or total motility, although changes in progressive motility were detected. The incubation with both receptor agonists increased the percentage of acrosome-reacted spermatozoa, evaluated by chlortetracycline staining, when compared with the capacitated nontreated sample (Cap-C, P < 0.001). Moreover, the ER agonist resveratrol 10 μM provoked a greater AR than E2 (P < 0.01). Furthermore, the incubation with the receptor antagonists prevented the induction of the AR by P4 or E2, as the antagonists-treated spermatozoa presented a similar CTC pattern to that of Cap-C. In conclusion, these results confirm that P4 and E2 can induce the AR in ram spermatozoa and that this effect is receptor-mediated.

Melatonin Non-Linearly Modulates Bull Spermatozoa Motility and Physiology in Capacitating and Non-Capacitating Conditions

Bull spermatozoa physiology may be modulated by melatonin. We washed ejaculated spermatozoa free of melatonin and incubated them (4 h, 38 °C) with 0-pM, 1-pM, 100-pM, 10-nM and 1-µM melatonin in TALP-HEPES (non-capacitating) and TALP-HEPES-heparin (capacitating). This range of concentrations encompassed the effects mediated by melatonin receptors (pM), intracellular targets (nM–µM) or antioxidant activity (µM). Treatment effects were assessed as motility changes by computer-assisted sperm analysis (CASA) of motility and physiological changes by flow cytometry. Melatonin effects were more evident in capacitating conditions, with 100 pM reducing motility and velocity (VCL) while increasing a “slow” subpopulation. All concentrations decreased apoptotic spermatozoa and stimulated mitochondrial activity in viable spermatozoa, with 100 pM–1 µM increasing acrosomal damage, 10 nM–1 µM increasing intracellular calcium and 1 pM reducing the response to a calcium-ionophore challenge. In non-capacitating media, 1 µM increased hyperactivation-related variables and decreased apoptotic spermatozoa; 100 pM–1 µM increased membrane disorders (related to capacitation); all concentrations decreased mitochondrial ROS production. Melatonin concentrations had a modal effect on bull spermatozoa, suggesting a capacitation-modulating role and protective effect at physiological concentrations (pM). Some effects may be of practical use, considering artificial reproductive techniques.

Effects of 5-hydroxytryptamine on spermatozoal hyperactivation and in vitro fertilization in mice

In this study, we examined the effects of 5-hydroxytryptamine (5-HT) on the motility and hyperactivation of mouse spermatozoa. In addition, we examined whether 5-HT increases the success of in vitro fertilization (IVF) in mice. Interestingly, 5-HT and agonists of the 5-HT₂, 5-HT₃, 5-HT₄, and 5-HT₇ receptors significantly increased the percentage of hyperactivated spermatozoa but did not affect the percentage of motile spermatozoa. Moreover, agonists of the 5-HT₂, 5-HT₃, and 5-HT₄ receptors significantly affected the velocities, linearity, straightness, wobbler coefficient, amplitude and/or frequency of spermatozoa. In particular, the improvement of hyperactivation by 5-HT was strongly inhibited by antagonists of the receptors 5-HT₄ and 5-HT₇ and was completely inhibited by a mixture of the four 5-HT-receptor antagonists. The increase in hyperactivation by the agonists was significantly inhibited by the corresponding 5-HT-receptor antagonist. Moreover, 5-HT significantly increased the percentage of two-cell embryos. The increase in the IVF success rate by 5-HT was significantly inhibited by a 5-HT₄-receptor antagonist. These results suggest that 5-HT increased hyperactivation through the 5-HT receptors and increased the success of IVF in mice.

Interactions between oestrogen and 1α,25(OH)2-vitamin D3 signalling and their roles in spermatogenesis and spermatozoa functions

Oestrogens and 1α,25(OH)₂-vitamin D₃ (1,25-D₃) are steroids that can provide effects by binding to their receptors localised in the cytoplasm and in the nucleus or the plasma membrane respectively inducing genomic and non-genomic effects. As confirmed notably by invalidation of the genes, coding for their receptors as tested with mice with in vivo and in vitro treatments, oestrogens and 1,25-D₃ are regulators of spermatogenesis. Moreover, some functions of ejaculated spermatozoa as viability, DNA integrity, motility, capacitation, acrosome reaction and fertilizing ability are targets for these hormones. The studies conducted on their mechanisms of action, even though not completely elicited, have allowed the demonstration of putative interactions between their signalling pathways that are worth examining more closely. The present review focuses on the elements regulated by oestrogens and 1,25-D₃ in the testis and spermatozoa as well as the interactions between the signalling pathways of both hormones.

γ-Aminobutyric acid suppresses enhancement of hamster sperm hyperactivation by 5-hydroxytryptamine

Sperm hyperactivation is regulated by hormones present in the oviduct. In hamsters, 5-hydroxytryptamine (5HT) enhances hyperactivation associated with the 5HT₂ receptor and 5HT₄ receptor, while 17β-estradiol (E₂) and γ-aminobutyric acid (GABA) suppress the association of the estrogen receptor and GABA_A receptor, respectively. In the present study, we examined the regulatory interactions among 5HT, GABA, and E₂ in the regulation of hamster sperm hyperactivation. When sperm were exposed to E₂ prior to 5HT exposure, E₂ did not affect 5HT-enhanced hyperactivation. In contrast, GABA partially suppressed 5HT-enhanced hyperactivation when sperm were exposed to GABA prior to 5HT. GABA suppressed 5HT-enhanced hyperactivation associated with the 5HT₂ receptor although it did not suppress 5HT-enhanced hyperactivation associated with the 5HT₄ receptor. These results demonstrate that hamster sperm hyperactivation is regulated by an interaction between the 5HT₂ receptor-mediated action of 5HT and GABA.

Regulation of hamster sperm hyperactivation by extracellular Na+

Mammalian sperm motility has to be hyperactivated to be fertilization-competent. Hyperactivation is regulated by extracellular environment. Osmolality of mammalian semen is higher than that in female reproductive tract; however, the effect of them on hyperactivation has not been investigated. So we investigated the effect of osmotic environment on hyperactivation using hamster spermatozoa at first. Increase in the osmolality of the media (∼370 mOsm) by increasing the concentration of NaCl (∼150 mmol/L) caused the delay of the expression of hyperactivation. When NaCl concentration varied in the same range (75–150 mmol/L) whereas the osmolality was fixed at 370 mOsm by adding mannitol, the delay of hyperactivation occurred dependent on NaCl concentration. Increase in NaCl concentration also caused suppression of curvilinear velocity, bend angle, and sliding velocity of the flagellum at the onset of incubation, suggesting that NaCl concentration affect both activation and hyperactivation in hamster spermatozoa. Hamster sperm intracellular Ca2+ concentration decreased as extracellular NaCl concentration increased, whereas membrane potential and intracellular pH were unaffected by extracellular NaCl concentration. SN-6 and SEA0400, inhibitors of Na+-Ca2+ exchanger (NCX), increased intracellular Ca2+ and accelerated hyperactivation in the presence of 150 mmol/L NaCl. Tyrosine phosphorylation on fibrous sheath proteins was unaffected by extracellular NaCl concentration. These results suggest that extracellular Na+ suppresses hamster sperm hyperactivation by reducing intracellular Ca2+ via an action of NCX in a tyrosine phosphorylation-independent manner. It seems that the removal of suppression by extracellular Na+ leads to the expression of hyperactivated motility.

Non-genomic regulation and disruption of spermatozoal in vitro hyperactivation by oviductal hormones

During capacitation, motility of mammalian spermatozoon is changed from a state of "activation" to "hyperactivation." Recently, it has been suggested that some hormones present in the oviduct are involved in the regulation of this hyperactivation in vitro. Progesterone, melatonin, and serotonin enhance hyperactivation through specific membrane receptors, and 17β-estradiol suppresses this enhancement by progesterone and melatonin via a membrane estrogen receptor. Moreover, γ-aminobutyric acid suppresses progesterone-enhanced hyperactivation through the γ-aminobutyric acid receptor. These hormones dose-dependently affect hyperactivation. Although the complete signaling pathway is not clear, progesterone activates phospholipase C and protein kinases and enhances tyrosine phosphorylation. Moreover, tyrosine phosphorylation is suppressed by 17β-estradiol. This regulation of spermatozoal hyperactivation by steroids is also disrupted by diethylstilbestrol. The in vitro experiments reviewed here suggest that mammalian spermatozoa are able to respond to effects of oviductal hormones. We therefore assume that the enhancement of spermatozoal hyperactivation is also regulated by oviductal hormones in vivo.

Roles of the reproductive tract in modifications of the sperm membrane surface

Successful fertilization requires viable and functional spermatozoa to recognize and fuse with the oocyte. In most mammalian species, mature spermatozoa are not capable of fertilizing the oocytes immediately after ejaculation. However, unlike somatic cells, spermatozoa, after leaving the testis, are transcriptionally and translationally silent; therefore, upon completion of spermiogenesis, spermatozoa carry only a minimal amount of essential proteins on their membranes as well as within their restricted volume of cytoplasm. To develop into a fully functional and competent sperm that is capable of successful fertilization, modifications of the sperm membrane surface during its transit in the reproductive tracts is critical. These post-spermatogenesis modifications advance the maturation of epididymal spermatozoa. In addition, components secreted into the lumen of the reproductive tracts that are later added onto the sperm membrane surface also regulate (inhibit or activate) the functions of the spermatozoa. This acquisition of additional proteins from the reproductive tracts may compensate for the inactivity of morphologically mature spermatozoa. In this review, we discuss the contributions of the male and female genital tracts to modifications of the sperm membrane surface at different stages of fertilization.