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      Estradiol inhibits the effects of extracellular ATP in human sperm by a non genomic mechanism of action

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          Abstract

          Steroid hormones, beside their classical genomic mechanism of action, exert rapid, non genomic effects in different cell types. These effects are mediated by still poorly characterized plasma membrane receptors that appear to be distinct from the classic intracellular receptors. In the present study we evaluated the non genomic effects of estradiol (17βE 2) in human sperm and its effects on sperm stimulation by extracellular ATP, a potent activator of sperm acrosome reaction. In human sperm 17βE 2 induced a rapid increase of intracellular calcium (Ca 2+) concentrations dependent on an influx of Ca 2+ from the extracellular medium. The monitoring of the plasma membrane potential variations induced by 17βE 2 showed that this steroid induces a rapid plasma membrane hyperpolarization that was dependent on the presence of Ca 2+ in the extracellular medium since it was absent in Ca 2+ free-medium. When sperm were pre-incubated in the presence of the K + channel inhibitor tetra-ethylammonium, the 17βE 2 induced plasma membrane hyperpolarization was blunted suggesting the involvement of K + channels in the hyperpolarizing effects of 17βE 2. Extracellular ATP induced a rapid plasma membrane depolarization followed by acrosome reaction. Sperm pre-incubation with 17βE 2 inhibited the effects of extracellular ATP on sperm plasma membrane potential variations and acrosome reaction. The effects of 17βE 2 were specific since its inactive steroisomer 17αE 2 was inactive. Furthermore the effects of 17βE 2 were not inhibited by tamoxifen, an antagonist of the classic 17βE 2 intracellular receptor.

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          Regulation of Sodium Channel Function by Bilayer Elasticity

          Jens Lundbæk, Pia Birn, Anker Hansen … (2004)
          Membrane proteins are regulated by the lipid bilayer composition. Specific lipid–protein interactions rarely are involved, which suggests that the regulation is due to changes in some general bilayer property (or properties). The hydrophobic coupling between a membrane-spanning protein and the surrounding bilayer means that protein conformational changes may be associated with a reversible, local bilayer deformation. Lipid bilayers are elastic bodies, and the energetic cost of the bilayer deformation contributes to the total energetic cost of the protein conformational change. The energetics and kinetics of the protein conformational changes therefore will be regulated by the bilayer elasticity, which is determined by the lipid composition. This hydrophobic coupling mechanism has been studied extensively in gramicidin channels, where the channel–bilayer hydrophobic interactions link a “conformational” change (the monomer↔dimer transition) to an elastic bilayer deformation. Gramicidin channels thus are regulated by the lipid bilayer elastic properties (thickness, monolayer equilibrium curvature, and compression and bending moduli). To investigate whether this hydrophobic coupling mechanism could be a general mechanism regulating membrane protein function, we examined whether voltage-dependent skeletal-muscle sodium channels, expressed in HEK293 cells, are regulated by bilayer elasticity, as monitored using gramicidin A (gA) channels. Nonphysiological amphiphiles (β-octyl-glucoside, Genapol X-100, Triton X-100, and reduced Triton X-100) that make lipid bilayers less “stiff”, as measured using gA channels, shift the voltage dependence of sodium channel inactivation toward more hyperpolarized potentials. At low amphiphile concentration, the magnitude of the shift is linearly correlated to the change in gA channel lifetime. Cholesterol-depletion, which also reduces bilayer stiffness, causes a similar shift in sodium channel inactivation. These results provide strong support for the notion that bilayer–protein hydrophobic coupling allows the bilayer elastic properties to regulate membrane protein function.
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            Estrogen receptor (ER)alpha and ER beta are both expressed in human ejaculated spermatozoa: evidence of their direct interaction with phosphatidylinositol-3-OH kinase/Akt pathway.

            Diego Sisci, Gabrielle Gentile, Vittoria Rago … (2004)
            Human and animal models have evidenced how estrogen insufficiency is associated with abnormal spermatogenesis and male infertility. We previously demonstrated that estradiol is able to influence both capacitation and acrosome reaction in human ejaculated spermatozoa. It remains to be elucidated whether the biochemical changes induced by estradiol, in a rapid nongenomic way, are mediated by a single estrogen receptor (ER) or by the two ER subtypes, ER alpha and ER beta. In the present study, we have first demonstrated the concomitant expression of ER beta and ER alpha in human ejaculated spermatozoa. By RT-PCR and Southern blot, transcripts of both ERs were detected. Western blot analysis showed ER alpha and ER beta proteins at the same size as the "classical" ERs. The localization of ER alpha and ER beta with the immunocytochemistry shows a differential distribution of the two ER subtypes, the former being prevalently located in the midpiece, but the latter being in the tail. Estradiol has been associated with sperm longevity; however, the mechanism through which estradiol acts in sperm survival was never investigated. Upon estradiol exposure, we observed an enhanced phosphorylation of the proteins involved in the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway like PDK1, Akt, GSK-3, Bcl-2, together with ERK1/2, which was also involved in cell survival signals. Moreover, such phosphorylations were reduced in the presence of ICI 182, 780, addressing the role of estradiol and ERs in sperm survival. For instance we have provided, for the first time, a different interaction of the two ERs with the PI3K/Akt pathway, because ER alpha interacts with the p55 regulatory subunit of PI3K, whereas ER beta interacts with Akt1. However, it still remains to be elucidated whether the functional role of each of the ER subtypes in sperm survival signaling is redundant or distinct.
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              Functional consequences of lipid packing stress

              Sergey M. Bezrukov (2000)
              Article 0 comments Cited 27 times – based on 0 reviews     Review now
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                Author and article information

                Contributors
                : +39-049-8218747 , +39-049-8213332 , marco.rossato@unipd.it
                Journal
                Journal ID (nlm-ta): Purinergic Signal
                Title: Purinergic Signalling
                Publisher: Springer Netherlands (Dordrecht )
                ISSN (Print): 1573-9538
                ISSN (Electronic): 1573-9546
                Publication date (Electronic): 3 December 2005
                Publication date (Print): December 2005
                Volume: 1
                Issue: 4
                Pages: 369-375
                Affiliations
                [1 ]Department of Medical and Surgical Sciences, Clinica Medica 3, University of Padova, Italy
                [2 ]Department of Histology, Microbiology and Medical Biotechnologies, Center of Male Gamete Cryopreservation, University of Padova, Padova, Italy
                [3 ]Department of Medical and Surgical Sciences, Clinica Medica 3, University of Padova, Via Ospedale 105, 35128 Padova, Italy
                Article
                Publisher ID: 21172
                DOI: 10.1007/s11302-005-1172-0
                PMC ID: 2096547
                PubMed ID: 18404521
                SO-VID: 38956b0c-da0a-4abc-a9db-f8426d653b90
                Copyright © © Springer 2005
                History
                Date received : 18 March 2005
                Date revision received : 7 July 2005
                Date accepted : 20 July 2005
                Categories
                Subject: Article
                Custom metadata
                issue-copyright-statement © Springer 2005

                ScienceOpen disciplines: Cell biology
                Keywords: calcium,membrane potential,human sperm,atp,estradiol,p2 purinergic receptor
                Data availability:
                ScienceOpen disciplines: Cell biology
                Keywords: calcium, membrane potential, human sperm, atp, estradiol, p2 purinergic receptor

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