Gamete therapeutics: recombinant protein adsorption by sperm for increasing fertility via artificial insemination

Contributions of seminal plasma proteins to fertilizing ability of bull sperm: A meta-analytical review

Seminal plasma is a dynamic, intricate combination of fluids from the testicles, epididymides, seminal vesicles, bulbourethral glands, and prostate, containing molecules that modulate sperm functions, post-fertilization events, and the female reproductive tract physiology. Significant variations in sperm parameters and fertility status of bulls relate to differences in the seminal plasma proteome. In this framework, a meta-analytical study was conducted examining 29 studies (published between 1990 and 2021) to ascertain the effects of seminal fluid proteins on parameters associated with bull fertility and the influence of distinct methodologies on such effects. Our results revealed that seminal proteins ameliorate sperm parameters, such as motility, integrity, capacitation, and fertilizing ability, and favours sperm protection. Seminal binder of sperm proteins and beta-defensin 126 highly favoured sperm protection when cells were collected from the epididymis by retrograde flux and analysed under room temperature conditions. Furthermore, seminal proteins improved the motility and quality of Bos taurus sperm collected by artificial vagina, mainly in the presence of heparin-binding proteins. The key limitations faced by this meta-analysis were the paucity of studies evaluating the effects of whole seminal fluid proteins and the limited number of studies conducted in vivo. In conclusion, the present meta-analytical study confirms that seminal proteins improve fertility-related parameters in the bovine species. However, methodological strategies used by authors are diverse, with distinct endpoints and methods. Thus, the translational aspects of seminal plasma research should be taken into consideration to precisely define how seminal proteins can be harnessed to advance reproductive biotechnology.

Production of bioactive recombinant ovine cysteine-rich secretory protein 1 in Escherichia coli

Ovine cysteine-rich secretory protein 1 (CRISP-1) is an acidic glycoprotein of epididymal origin under CRISP, antigen 5, pathogenesis-related protein 1 (CAP) super-family. The aim of the present study was the optimization of bacterial production and partial characterization of putative mature ovine CRISP-1 protein. The cDNA corresponding to T^{23 -} C²⁴² peptide fragment of ovine CRISP-1 protein was cloned into THE pET32b(+) expression vector using E. coli DH5α. Protein expression was carried out in E. coli BL21(DE3) by inducition with 1 mM IPTG at 37°C for 4 h. The recombinant protein was expressed as inclusion bodies and purified by Ni-NTA affinity chromatography using a pH gradient. Further purification of the protein was carried out by gel extraction following zinc sulfate negative staining. SDS-PAGE analysis of the purified recombinant CRISP-1 protein revealed a 43.8 kDa band. Bioactivity of the purified CRISP-1 protein was examined on sperm motility and capacitation. The recombinant ovine CRISP-1 protein at 5 µg/ml caused significant inhibition of sperm motility, and the activity was lost following heating the protein at 100°C for 5 min. The protein also demonstrated decapacitation activity, and at a concentration of 2 µg/ml, it caused a significant (P < 0.05) reduction in sperm capacitation. In conclusion, the thioredoxin-tagged ovine CRISP-1 protein was successfully produced in E. coli and purified in the soluble form by a combination of Ni-NTA affinity chromatography, gel purification, and dialysis. The recombinant protein exhibited both motility-inhibiting and decapacitating activities. Further study is needed to elucidate the mechanism of action and evaluate it's possible use in semen preservation.Abbreviations: CRISP-1: Cysteine-rich secretory protein-1; PCR: polymerase chain reaction; IPTG: isopropyl-β-D-thiogalactopyranoside; LB: Luria Bertani; SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis; EDTA: ethylene diamine tetraacetic acid; Ni-NTA: Nickel nitrilotriacetic acid.

Effects of increased scrotal temperature on semen quality and seminal plasma proteins in Brahman bulls

Environmental temperature has effects on sperm quality with differences in susceptibility between cattle subspecies and breeds, but very little is known about the seminal plasma protein (SPP) changes resulting from testicular heat stress. Scrotal insulation (SI) for 48 hr was applied to Brahman (Bos indicus) bulls. Semen was collected at 3-day intervals from before, until 74 days post-SI. The changes in sperm morphology and motility following SI were comparable to previously reported and differences were detected in measures of sperm chromatin conformation as early as 8 days post-SI. New proteins spots, in the SPP two-dimensional (2-D) gels, were apparent when comparing pre-SI with 74 days post-SI, and SPP identified as associated with mechanisms of cellular repair and protection. Similar trends between 2-D gel and Sequential Window Acquisition of All Theoretical Mass Spectra (SWATH-MS) data was observed, with SWATH-MS able to quantify individual SPP that otherwise were not resolved on 2-D gel. The SPP assessment at peak sperm damage (21-24 days) showed a significant difference in 29 SPP (adjusted p < .05), and identified six proteins with change in abundance in the SI group. In conclusion both spermatozoa and SPP composition of bulls are susceptible to temperature change incurred by SI, and SPP markers for testicular heat insults may be detected.

Review: Recent advances in bovine in vitro embryo production: reproductive biotechnology history and methods

In vitro production (IVP) of embryos and associated technologies in cattle have shown significant progress in recent years, in part driven by a better understanding of the full potential of these tools by end users. The combination of IVP with sexed semen (SS) and genomic selection (GS) is being successfully and widely used in North America, South America and Europe. The main advantages offered by these technologies include a higher number of embryos and pregnancies per unit of time, and a wider range of potential female donors from which to retrieve oocytes (including open cyclic females and ones up to 3 months pregnant), including high index genomic calves, a reduced number of sperm required to produce embryos and increased chances of obtaining the desired sex of offspring. However, there are still unresolved aspects of IVP of embryos that limit a wider implementation of the technology, including potentially reduced fertility from the use of SS, reduced oocyte quality after in vitro oocyte maturation and lower embryo cryotolerance, resulting in reduced pregnancy rates compared to in vivo-produced embryos. Nevertheless, promising research results have been reported, and work is in progress to address current deficiencies. The combination of GS, IVP and SS has proven successful in the commercial field in several countries assisting practitioners and cattle producers to improve reproductive performance, efficiency and genetic gain.

Proteomic landscape of seminal plasma associated with dairy bull fertility

Male fertility is the ability of sperm to fertilize the egg and sustain embryo development. Several factors determine the fertilizing capacity of mammalian sperm, including those intrinsic to sperm and components of the seminal plasma. The present study analyzed the seminal fluid proteome of Bos taurus and potential associations between proteins and fertility scores. Mass spectrometry coupled with nano HPLC allowed the identification of 1,159 proteins in the dairy bull seminal plasma. There were 50 and 29 seminal proteins more abundant in high (HF) low fertility (LF) bulls, respectively. Based on multivariate analysis, C-type natriuretic peptide, TIMP-2, BSP5 and sulfhydryl oxidase indicated relationship with HF bulls. Clusterin, tissue factor pathway inhibitor 2, galectin-3-binding protein and 5′-nucleotidase were associated with LF bulls. Abundance of NAD(P)(+)-arginine ADP-ribosyltransferase, prosaposin and transmembrane protein 2 proteins had the highest positive correlations with fertility ranking. Quantities of vitamin D-binding protein, nucleotide exchange factor SIL1 and galectin-3-binding protein showed the highest negative correlations with fertility ranking. A fertility ranking score was calculated and the relationship with these proteins was significant (Spearman’s rho = 0.94). The present findings represent a major and novel contribution to the study of bovine seminal proteins. Indicators of fertility can be used to improve reproductive biotechnologies.

Supplemented stallion seminal plasma can improve impaired motility due to the dilution effect in chilled Asian elephant sperm

The dilution effect and effect of restoring seminal plasma (SP) proportion in diluted semen were determined in chilled Asian elephant sperm. Semen was collected from eight males, and samples with ≥30% motile sperm were used in the study. Tris-glucose-egg yolk extender (TE) was used for cooled storage at 4°C for 48 hr. In experiment 1 (n = 18), semen was diluted to 1:1, 1:3, 1:7 and 1:15 with TE (volume per volume). There were no significant changes in sperm viability and sperm with normal acrosome integrity among dilutions, but sperm motility and motility velocities were greater (p < .05) in the 1:1 dilution than those of the 1:7 and 1:15 dilutions at 48 hr of storage. In experiment 2, supplemented SP was derived from elephants and stallions. In experiment 2.1, diluted semen (1:7 dilution) was restored with SP to obtain a 1:2 proportion (n = 8). Sperm motility, viability and sperm with normal acrosome integrity were similar among treatments, but motility velocities were greater (p < .05) with stallion SP at 48 hr of storage. In experiment 2.2, diluted semen (1:15 dilution) was restored with SP to obtain a 1:3 proportion (n = 10). Sperm viability and sperm with normal acrosome integrity were similar among treatments at 48 hr of storage. However, sperm motility and motility velocities were greater (p < .05) with stallion SP than those of others. In conclusion, elephant sperm motility was affected by a dilution effect and restoration of SP proportion with stallion SP, but not with elephant SP, could improve motility in chilled highly diluted sperm.

Seminal Plasma Heparin Binding Proteins Improve Semen Quality by Reducing Oxidative Stress during Cryopreservation of Cattle Bull Semen

Heparin binding proteins (HBPs) are produced by accessory glands. These are secreted into the seminal fluid, bind to the spermatozoa at the time of ejaculation, favour capacitation, acrosome reaction, and alter the immune system response toward the sperm. The present study was conducted with an objective to assess the effect of purified seminal plasma-HBPs (SP-HBPs) on cross bred cattle bull sperm attributes during two phases of cryopreservation: Pre freezing and freezing-thawing. SP-HBPs were purified from pooled seminal plasma by heparin affinity chromatography. Three doses of SP-HBPs i.e. 10, 20, 40 μg/mL semen were standardized to find out the optimum dose and 20 μg/mL was found to be an optimum dose. Semen as such and treated with SP-HBPs was diluted with sodium citrate-egg yolk diluter and cryopreserved as per the standard protocol. Sperm parameters i.e. motility, viability, Hypo-osmotic swelling test (HOST), acrosome damage, in vitro capacitation and lipid peroxidation were evaluated in SP-HBP treated and untreated (control) semen at both phases of cryopreservation. A considerable variation in percent sperm motility, viability, membrane integrity (HOST), acrosome damage, acrosome reaction and lipid peroxidation was observed at both phases among the bulls irrespective of the treatment. Incubation of neat semen with 20 μg/mL SP-HBP before processing for cryopreservation enhanced the average motility, viability, membrane integrity by 7.2%, 1.5%, 7.9%, and 5.6%, 6.6%, 7.4% in pre-frozen and frozen-thawed semen in comparison to control. There was also an average increase of 4.1%/3.9% in in vitro capacitation and acrosome reaction in SP-HBPs-treated frozen-thawed semen as compared to control. However, binding of SP-HBPs to the sperm declined acrosome damage and lipid peroxidation by 1.3%/4.1% and 22.1/32.7 μM/10⁹ spermatozoa in SP-HBP treated pre-frozen/frozen-thawed semen as compared to control, respectively. Significant (p<0.05) effects were observed only in motility, HOST and in vitro acrosome reaction. It can be concluded that treatment of neat semen with SP-HBPs before cryopreservation minimized the cryoinjury by decreasing the generation of reactive oxygen species.