Kinetic Study of 17α-Estradiol Mechanism during Rat Sperm Capacitation

17α-Estradiol (αE2) is a natural diastereoisomer of 17β-estradiol (E2). It is well known that αE2 can bind to estrogen receptors. However, its biological activity is less than that of E2 and is species and tissue specific. The goal of our study was to propose the mechanism of αE2 hormonal response in rat sperm during their capacitation in vitro and compare it with a previously studied mouse model. Concentration changes in externally added αE2 during capacitation of rat sperm were monitored by the high-performance liquid chromatographic method with tandem mass spectrometric detection (HPLC-MS/MS). The calculated values of relative concentrations B_t were subjected to kinetic analysis. The findings indicated that αE2 in rat sperm did not trigger autocatalytic reaction, in contrast to the mouse sperm, and that the initiation of the hormone penetration through the sperm plasma membrane was substantially faster in rats.

Identifying new sperm Western blot loading controls

The measurement of protein expression level plays a pivotal role in both biological and medical studies. Housekeeping proteins, generally encoded by housekeeping genes are used as loading control proteins to normalize protein expression. Obviously, proper reference standards are essential for adequate analysis of protein expression. However, our study showed that the widely used normalisation proteins, whose expression levels varied greatly among sperm samples, were unsuitable for data standardisation. To uncover the proteins steadily expressed in sperm, we analysed several published transcriptome data of sperm. Seven proteins whose expression levels were relatively stable (co-efficient variation values less than 0.35) were selected and further evaluated by quantitative real-time polymerase chain reaction, Western Blot (WB) and immunocytochemistry. Our results showed that among the classical housekeeping proteins, only β-tubulin remained constant in sperm samples from 85 individuals. Compared with other classical housekeeping proteins such as glyceraldehyde 3-phosphate dehydrogenase, actin and histone H3, Cullin-1 (CUL1) and F-box only protein 7 (FBXO7) seemed to be more suitable to be used as internal controls for WB in sperm protein studies. Combined with the locations of these proteins, CUL1 and FBXO7 were suggested to be used as a housekeeping protein for total proteins.

Reciprocal surface expression of arylsulfatase A and ubiquitin in normal and defective mammalian spermatozoa

Defective mammalian spermatozoa are marked on their surface by proteolytic chaperone ubiquitin. To identify potential ubiquitinated substrates in the defective spermatozoa, we resolved bull sperm protein extracts on a two-dimensional gel and isolated a 64-65-kDa spot (p64) corresponding to one of the major ubiquitin-immunoreactive bands observed in the one-dimensional Western blots. Immune serum raised against this protein recognized a prominent, possibly glycosylated band/spot in the range of 55-68 kDa, consistent with the original spot used for immunization. Internal sequences obtained by Edman degradation of this spot matched the sequence of arylsulfatase A (ARSA), the sperm acrosomal enzyme thought to be important for fertility. By immunofluorescence, a prominent signal was detected on the acrosomal surface (boar and bull) and on the sperm tail principal piece (bull). A second immune serum raised against a synthetic peptide corresponding to an immunogenic internal sequence (GTGKSPRRTL) of the porcine ARSA also labeled sperm acrosome and principal piece. Both sera showed diminished immunoreactivity in the defective bull spermatozoa co-labeled with an anti-ubiquitin antibody. Western blotting and image-based flow cytometry (IBFC) confirmed a reduced ARSA immunoreactivity in the immotile sperm fraction rich in ubiquitinated spermatozoa. Larger than expected ARSA-immunoreactive bands were found in sperm protein extracts immunoprecipitated with anti-ubiquitin antibodies and affinity purified with matrix-bound, recombinant ubiquitin-binding UBA domain. These bands did not show the typical pattern of ARSA glycosylation but overlapped with bands preferentially binding the Lens culinaris agglutinin (LCA) lectin. By both epifluorescence microscopy and IBFC, the LCA binding was increased in the ubiquitinated spermatozoa with diminished ARSA immunoreactivity. ARSA was also found in the epididymal fluid suggesting that in addition to intrinsic ARSA expression in the testis, epididymal spermatozoa take up ARSA on their surface during the epididymal passage. We conclude that sperm surface ARSA is one of the ubiquitinated sperm surface glycoproteins in defective bull spermatozoa. Defective sperm surface thus differs from normal sperm surface by increased ubiquitination, reduced ARSA binding, and altered glycosylation.

New Insight into Sperm Capacitation: A Novel Mechanism of 17β-Estradiol Signalling

17β-estradiol (estradiol) is a natural estrogen regulating reproduction including sperm and egg development, sperm maturation—called capacitation—and sperm–egg communication. High doses can increase germ cell apoptosis and decrease sperm count. Our aim was to answer the biological relevance of estradiol in sperm capacitation and its effect on motility and acrosome reaction to quantify its interaction with estrogen receptors and propose a model of estradiol action during capacitation using kinetic analysis. Estradiol increased protein tyrosine phosphorylation, elevated rate of spontaneous acrosome reaction, and altered motility parameters measured Hamilton-Thorne Computer Assisted Semen Analyzer (CASA) in capacitating sperm. To monitor time and concentration dependent binding dynamics of extracellular estradiol, high-performance liquid chromatography with tandem mass spectrometry was used to measure sperm response and data was subjected to kinetic analysis. The kinetic model of estradiol action during sperm maturation shows that estradiol adsorption onto a plasma membrane surface is controlled by Langmuir isotherm. After, when estradiol passes into the cytoplasm, it forms an unstable adduct with cytoplasmic receptors, which display a signalling autocatalytic pattern. This autocatalytic reaction suggests crosstalk between receptor and non-receptor pathways utilized by sperm prior to fertilization.

Diversity of ejaculated sperm proteins in Moxotó bucks (Capra hircus ) evaluated by multiple extraction methods

This study aimed to develop protocols for the extraction of sperm proteins from Moxotó goats (Capra hircus) and to compare the resulting proteomic maps. The sperm proteins were isolated using an extraction buffer containing 7 M urea and 2 M thiourea, 20 mM DTT, and one of the following detergents: 1% or 4% CHAPS; 1% or 4% SDS; 1% or 4% Triton X-100; or a combination of CHAPS and SDS. The 1-DE and 2-DE profiles of the isolated proteins revealed that the various isolation methods were efficient. Qualitative and quantitative differences in the 1-DE and 2-DE profiles were observed. 2-DE maps indicated that the amount and diversity of proteins visualized depended on the detergent that was used. Furthermore, this work revealed that the combination of detergents increased the resolution of some spots and retained the characteristics of the individual detergents, depending on their concentrations.

Characterization of sperm surface protein patterns of ejaculated and capacitated boar sperm, with the detection of ZP binding candidates

Complementary molecules on the surface of both gametes are responsible for the interaction of sperm protein receptors with zona pellucida (ZP) saccharide structures, and many primary sperm receptors for ZP glycoproteins have been disclosed in various mammals. For our study, proteins were obtained from the surface of ejaculated and in vitro capacitated boar sperm. The isolated proteins were characterized by 1D- and 2D-electrophoretic protein profiles, and by glycoprotein staining. Our results show quantitative and qualitative differences in protein and glycoprotein patterns between ejaculated and capacitated sperm. Far-western blotting with ZP glycoproteins identified 17 interactions in the subproteome of the ejaculated sperm and 14 interactions in the subproteome of the capacitated sperm. High-molecular-mass proteins, coincident with binding to ZP, were sequence-identified. Angiotensin-converting enzyme (ACE), polycystic kidney disease receptor and egg jelly receptor (PKDREJ), and acrosin precursor were successfully identified. This is the first time PKDREJ has been identified on the surface of boar spermatozoa.

In vivo exposure to 17β-estradiol triggers premature sperm capacitation in cauda epididymis

Estrogens play a crucial role in spermatogenesis and estrogen receptor α knock-out male mice are infertile. It has been demonstrated that estrogens significantly increase the speed of capacitation in vitro; however this may lead to the reduction of reproductive potential due to the decreased ability of these sperm to undergo the acrosome reaction. To date the in vivo effect of estrogens on the ability of sperm to capacitate has not been investigated. Therefore, in this study, we exposed mice (n=24) to 17β-estradiol (E2) at the concentration of 20 ng/ml either during puberty from the fourth to seventh week of age (n=8), or continuously from birth for a period of 12 weeks (n=8) at which age the animals from both groups were killed. The capacitation status of epididymal and testicular sperm was analysed by tyrosine phosphorylation (TyrP) antibody (immunofluorescence and western blot) and chlortetracycline (CTC) assay. According to our results, in vivo exposure to increased E2 concentrations caused premature sperm capacitation in the epididymis. The effect of E2, however, seems reversible because after the termination of the exposure premature epididymal sperm capacitation is decreased in animals treated during puberty. Furthermore the changes in epididymal sperm capacitation status detected by TyrP and CTC positively correlate with plasma levels of E2 and the expression of the estrogen-dependent trefoil factor 1 (Tff1) gene in testicular tissue. Therefore, our data implicate that in vivo exposure to E2 under specific conditions leads to the premature capacitation of mouse sperm in epididymis with a potential negative impact on the sperm reproductive fitness in the female reproductive tract.