Extracellular vesicles in seminal plasma: A safe and relevant tool to improve fertility in livestock?

Cryogenic electron microscopy reveals morphologically distinct subtypes of extracellular vesicles among porcine ejaculate fractions

Seminal plasma (SP) is rich in extracellular vesicles (EVs), which are still poorly studied, especially in livestock species. To better understand their functional role in both spermatozoa and endometrial epithelial cells, proper characterization of EVs is an essential step. The objective was to phenotypically characterize porcine seminal EVs (sEVs) using cryogenic electron microscopy (cryo-EM), which allows visualization of EVs in their native state. Porcine ejaculates are released in fractions, each containing SP from different source. This allows characterization sEVs released from various male reproductive tissues. Two experiments were performed, the first with SP from the entire ejaculate (n:6) and the second with SP from three ejaculate fractions (n:15): the first 10 mL of the sperm-rich ejaculate fraction (SRF-P1) with SP mainly from the epididymis, the remainder of the SRF (SRF-P2) with SP mainly from the prostate, and the post-SRF with SP mainly from the seminal vesicles. The sEVs were isolated by size exclusion chromatography and 1840 cryo-EM sEV images were acquired using a Jeol-JEM-2200FS/CR-EM. The size, electron density, complexity, and peripheral corona layer were measured in each sEV using the ImageJ software. The first experiment showed that sEVs were structurally and morphologically heterogeneous, although most (83.1%) were small (less than 200 nm), rounded, and poorly electrodense, and some have a peripheral coronal layer. There were also larger sEVs (16.9%) that were irregularly shaped, more electrodense, and few with a peripheral coronal layer. The second experiment showed that small sEVs were more common in SRF-P1 and SRF-P2, indicating that they originated mainly from the epididymis and prostate. Large sEVs were more abundant in post-SRF, indicating that they originated mainly from seminal vesicles. Porcine sEVs are structurally and morphologically heterogeneous. This would be explained by the diversity of reproductive organs of origin.

Small and Large Extracellular Vesicles of Porcine Seminal Plasma Differ in Lipid Profile

Seminal plasma contains a heterogeneous population of extracellular vesicles (sEVs) that remains poorly characterized. This study aimed to characterize the lipidomic profile of two subsets of differently sized sEVs, small (S-) and large (L-), isolated from porcine seminal plasma by size-exclusion chromatography and characterized by an orthogonal approach. High-performance liquid chromatography-high-resolution mass spectrometry was used for lipidomic analysis. A total of 157 lipid species from 14 lipid classes of 4 major categories (sphingolipids, glycerophospholipids, glycerolipids, and sterols) were identified. Qualitative differences were limited to two cholesteryl ester species present only in S-sEVs. L-sEVs had higher levels of all quantified lipid classes due to their larger membrane surface area. The distribution pattern was different, especially for sphingomyelins (more in S-sEVs) and ceramides (more in L-sEVs). In conclusion, this study reveals differences in the lipidomic profile of two subsets of porcine sEVs, suggesting that they differ in biogenesis and functionality.

Seminal extracellular vesicles alter porcine in vitro fertilization outcome by modulating sperm metabolism

Porcine seminal plasma (SP) is loaded with a heterogeneous population of extracellular vesicles (sEVs) that modulate several reproductive-related processes. This study investigated the effect of two sEV subsets, small (S-sEVs) and large (L-sEVs), on porcine in vitro fertilization (IVF). The sEVs were isolated from nine SP pools (five ejaculates/pool) using a size-exclusion chromatography-based procedure and characterized for quantity (total protein), morphology (cryogenic electron microscopy), size distribution (dynamic light scattering), purity and EV-protein markers (flow cytometry; albumin, CD81, HSP90β). The characterization confirmed the existence of two subsets of high purity (low albumin content) sEVs that differed in size (S- and L-sEVs). In vitro fertilization was performed with in vitro matured oocytes and frozen-thawed spermatozoa and the IVF medium was supplemented during gamete coincubation (1 h at 38.5 °C, 5 % CO2 in a humidified atmosphere) with three different concentrations of each sEV subset: 0 (control, without sEVs), 0.1, and 0.2 mg/mL. The first experiment showed that sEVs, regardless of subset and concentration, decreased penetration rates and total IVF efficiency (P < 0.0001). In a subsequent experiment, it was shown that sEVs, regardless of subset and concentration, impaired the ability of spermatozoa to bind to the zona pellucida of oocytes (P < 0.0001). The following experiment showed that sEVs, regardless of the subset, bound to frozen-thawed sperm but not to in vitro matured oocytes, indicating that sEVs would affect sperm functionality but not oocyte functionality. The lack of effect on oocytes was confirmed by incubating sEVs with oocytes prior to IVF, achieving sperm-zona pellucida binding results similar to those of control. In the last experiment, conducted under IVF conditions, sperm functionality was analyzed in terms of tyrosine phosphorylation, acrosome integrity and metabolism. The sEVs, regardless of the subset, did not affect sperm tyrosine phosphorylation or acrosome integrity, but did influence sperm metabolism by decreasing sperm ATP production under capacitating conditions. In conclusion, this study demonstrated that the presence of sEVs on IVF medium impairs IVF outcomes, most likely by altering sperm metabolism.

Immunophenotype profile by flow cytometry reveals different subtypes of extracellular vesicles in porcine seminal plasma

BACKGROUND

Porcine seminal plasma (SP) is endowed with a heterogeneous population of extracellular vesicles (sEVs). This study evaluated the immunophenotypic profile by high-sensitivity flow cytometry of eight sEV subpopulations isolated according to their size (small [S-sEVs] and large [L-sEVs]) from four different SP sources, namely three ejaculate fractions (the first 10 mL of the sperm rich fraction [SRF-P1], the remaining SRF [SRF-P2], and the post-SRF [PSRF]) and entire ejaculate (EE).

METHODS

Seminal EVs were isolated using a size exclusion chromatography-based protocol from six SP pools (five ejaculates/pool) of each SP source and characterized using complementary approaches including total protein (BCA™assay), particle size distribution (dynamic light scattering), morphology (transmission electron microscopy), and purity (albumin by Western blot). Expression of CD9, CD63, CD81, CD44 and HSP90β was analyzed in all sEV subpopulations by high-sensitivity flow cytometry according to MIFlowCyt-EV guidelines, including an accurate calibration, controls, and discrimination by CFSE-labelling.

RESULTS

Each sEV subpopulation exhibited a specific immunophenotypic profile. The percentage of sEVs positive for CD9, CD63, CD81 and HSP90β differed between S- and L-sEVs (P < 0.0001). Specifically, the percentage of sEVs positive for CD9 and CD63 was higher and that for CD81 was lower in S- than L-sEVs in the four SP sources. However, the percentage of HSP90β-positive sEVs was lower in S-sEVs than L-sEVs in the SRF-P1 and EE samples. The percentage of sEVs positive for CD9, CD63, and CD44 also differed among the four SP sources (P < 0.0001), being highest in PSRF samples. Notably, virtually all sEV subpopulations expressed CD44 (range: 88.04-98.50%).

CONCLUSIONS

This study demonstrated the utility of high-sensitivity flow cytometry for sEV immunophenotyping, allowing the identification of distinct sEV subpopulations that may have different cellular origin, cargo, functions, and target cells.

Extracellular vesicle-coupled miRNA profiles of chicken seminal plasma and their potential interaction with recipient cells

The presence of EVs in seminal plasma (SPEVs) suggests their involvement on fertility via transmitting information between the original cells and recipient cells. SPEVs-coupled miRNAs have been shown to affect sperm motility, maturation, and capacitation in mammals, but rarely in poultry species. The present study aims to reveal the profile of SPEVs miRNAs and their potential effect on sperm storage and function in poultry. The SPEVs was successfully isolated from 4 different chicken breeds by ultracentrifugation and verified. Deep sequencing of SPEVs small RNA library of each breed identified 1077 miRNAs in total and 563 shared ones. The top 10 abundant miRNAs (such as miR-10-5p, miR-100-5p, and miR-10a-5p etc.) accounted for around 60% of total SPEVs miRNA reads and are highly conserved across species, predisposing their functional significance. Target genes prediction and functional enrichment analysis indicated that the most abundantly expressed miRNAs may regulate pathways like ubiquitin-mediated proteolysis, endocytosis, mitophagy, glycosphingolipid biosynthesis, fatty acid metabolism, and fatty acid elongation. The high abundant SPEVs-coupled miRNAs were found to target 107 and 64 functionally important mRNAs in the potential recipient cells, sperm and sperm storage tubules (SST) cells, respectively. The pathways that enriched by target mRNAs revealed that the SPEVs-coupled miRNA may rule the fertility by affecting the sperm maturation and regulating the female's immune response and lipid metabolism. In summary, this study presents the distinctive repertoire of SPEVs-coupled miRNAs, and extends our understanding about their potential roles in sperm maturation, capacitation, storage, and fertility, and may help to develop new therapeutic strategies for male infertility and sperm storage.

The Cation/Calcium Channel of Sperm (CatSper): A Common Role Played Despite Inter-Species Variation?

The main cation/calcium channel of spermatozoa (CatSper), first identified in 2001, has been thoroughly studied to elucidate its composition and function, while its distribution among species and sperm sources is yet incomplete. CatSper is composed of several subunits that build a pore-forming calcium channel, mainly activated in vivo in ejaculated sperm cells by intracellular alkalinization and progesterone, as suggested by the in vitro examinations. The CatSper channel relevance is dual: to maintain sperm homeostasis (alongside the plethora of membrane channels present) as well as being involved in pre-fertilization events, such as sperm capacitation, hyperactivation of sperm motility and the acrosome reaction, with remarkable species differences. Interestingly, the observed variations in CatSper localization in the plasma membrane seem to depend on the source of the sperm cells explored (i.e., epididymal or ejaculated, immature or mature, processed or not), the method used for examination and, particularly, on the specificity of the antibodies employed. In addition, despite multiple findings showing the relevance of CatSper in fertilization, few studies have studied CatSper as a biomarker to fine-tune diagnosis of sub-fertility in livestock or even consider its potential to control fertilization in plague animals, a more ethically defensible strategy than implicating CatSper to pharmacologically modify male-related fertility control in humans, pets or wild animals. This review describes inter- and intra-species differences in the localization, structure and function of the CatSper channel, calling for caution when considering its potential manipulation for fertility control or improvement.