Ion fluxes through the progesterone-activated channel of the sperm plasma membrane.
Ontology highlight
ABSTRACT:
SUBMITTER: Foresta C
PROVIDER: S-EPMC1134595 | biostudies-other | 1993 Aug
REPOSITORIES: biostudies-other
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Project description:The female steroid hormone progesterone regulates ovulation and supports pregnancy, but also controls human sperm function within the female reproductive tract. Progesterone causes elevation of sperm intracellular Ca(2+) leading to sperm hyperactivation, acrosome reaction, and perhaps chemotaxis toward the egg. Although it has been suggested that progesterone-dependent Ca(2+) influx into human spermatozoa is primarily mediated by cationic channel of sperm (CatSper), the principal flagellar Ca(2+) channel of sperm, conclusive loss-of-function genetic evidence for activation of CatSper by progesterone has yet to be provided. Moreover, it is not clear whether the responsiveness of CatSper to progesterone is an innate property of human spermatozoa or is acquired as the result of exposure to the seminal plasma. Here, by recording ionic currents from spermatozoa of an infertile CatSper-deficient patient, we demonstrate that CatSper is indeed the principal Ca(2+) channel of human spermatozoa, and that it is strongly potentiated by progesterone. In addition, by recording CatSper currents from human epididymal and testicular spermatozoa, we show that CatSper sensitivity to progesterone arises early in sperm development and increases gradually to a peak when spermatozoa are ejaculated. These results unambiguously establish an important role of CatSper channel in human sperm nongenomic progesterone signaling and demonstrate that the molecular mechanism responsible for activation of CatSper by progesterone arises early in sperm development concurrently with the CatSper channel itself.
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Project description:Abhydrolase domain containing 2-acylglycerol lipase (ABHD2) was recently claimed as the membrane receptor of progesterone (P4) in sperm cells, mediating cell processes such as sperm chemotaxis and acrosome reaction. Here, we investigated the role of membrane cholesterol (Chol) on ABHD2-mediated human sperm chemotaxis. Human sperm cells were obtained from twelve normozoospemic healthy donors. ABHD2-Chol interaction was modelled by computational molecular-modelling (MM). Sperm membrane Chol content was depleted by incubating cells with cyclodextrin (CD) or augmented by the incubation with the complex between CD and Chol (CD:Chol). Cell Chol levels were quantified by liquid chromatography-mass spectrometry. Sperm migration upon P4 gradient was evaluated through the accumulation assay in a specific migration device. Motility parameters were evaluated by sperm class analyzer, whilst intracellular calcium concentration, acrosome reaction and mitochondrial membrane potential were evaluated with calcium orange, FITC-conjugated anti-CD46 antibody and JC-1 fluorescent probes, respectively. MM analysis showed the possible stable binding Chol to ABHD2, resulting in to major impact on the protein backbone flexibility. The treatment with CD was associated with a dose-dependent increase in sperm migration in a 160 nM P4 gradient, together with increase in sperm motility parameters and levels of acrosome reaction. The treatment with CD:Chol was associated with essentially opposite effects. Chol was, thus, suggested to inhibit P4-mediated sperm function through the possible inhibition of ABHD2.
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Project description:Progesterone (P4) acts as a key conserved signalling molecule in vertebrate reproduction. P4 is especially important for mature sperm physiology and subsequent reproductive success. "CatSpermasome", a multi-unit molecular complex, has been suggested to be the main if not the only P4-responsive atypical Ca2+-ion channel present in mature sperm. Altogether, here we analyse the protein sequences of CatSper1-4 from more than 500 vertebrates ranging from early fishes to humans. CatSper1 becomes longer in mammals due to sequence gain mainly at the N-terminus. Overall the conservation of full-length CatSper1-4 as well as the individual TM regions remain low. The lipid-water-interface residues (i.e. a 5 amino acid stretch sequence present on both sides of each TM region) also remain highly diverged. No specific patterns of amino acid distributions were observed. The total frequency of positively charged, negatively charged or their ratios do not follow in any specific pattern. Similarly, the frequency of total hydrophobic, total hydrophilic residues or even their ratios remain random and do not follow any specific pattern. We noted that the CatSper1-4 genes are missing in amphibians and the CatSper1 gene is missing in birds. The high variability of CatSper1-4 and gene-loss in certain clades indicate that the "CatSpermasome" is not the only P4-responsive ion channel. Data indicate that the molecular evolution of CatSper is mostly guided by diverse hydrophobic ligands rather than only P4. The comparative data also suggest possibilities of other Ca2+-channel/s in vertebrate sperm that can also respond to P4.
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Project description:Various pharmacological agents designed to modulate plasma membrane ion channels seem to significantly affect intracellular Ca²⁺ signaling when acting on their target receptor. Some agents could also cross-react (modulate channels or receptors beyond their putative target) with intracellular Ca²⁺ transporters. This study investigated the potential of thirty putative modulators of either plasma membrane K⁺, Na⁺, or transient receptor potential (TRP) channels to cross-react with intracellular Ca²⁺ release channels [i.e., ryanodine receptors (RyRs)] from skeletal muscle sarcoplasmic reticulum (SR). Screening for cross-reactivity of these various agents was performed by measuring the rate of spontaneous Ca²⁺ leak or caffeine-induced Ca²⁺ release from SR microsomes. Four of the agents displayed a strong cross-reactivity and were further evaluated with skeletal RyR (RyR1) reconstituted into planar bilayers. 6,12,19,20,25,26-Hexahydro-5,27:13,18:21,24-trietheno-11,7-metheno-7H-dibenzo [b,n][1,5,12,16]tetraazacyclotricosine-5, 13-diium dibromide (UCL 1684; K⁺ channel antagonist) and lamotrigine (Na⁺ channel antagonist) were found to significantly inhibit the RyR1-mediated caffeine-induced Ca²⁺ release. TRP channel agonists anandamide and (-)menthol were found to inhibit and activate RyR1, respectively. High concentrations of nine other agents produced partial inhibition of RyR1-mediated Ca²⁺ release from SR microsomes. Various pharmacological agents, especially TRP modulators, also inhibited a minor RyR1-independent component of the SR Ca²⁺ leak. Overall, ∼43% of the agents selected cross-reacted with RyR1-mediated and/or RyR1-independent Ca²⁺ leak from intracellular stores. Thus, cross-reactivity should be considered when using these classes of pharmacological agents to determine the role of plasmalemmal channels in Ca²⁺ homeostasis.
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