Plasminogen activation and plasmin inhibition during in vitro fertilization in bovine: implications for fertilization parameters and early embryo development

Components of the plasminogen/plasmin system, known to be present in the oocyte, play a key role in maturation and fertilization. The objective of this study was to examine the effect of plasminogen activation and plasmin inhibition by exogenous supplementation of the IVF medium with streptokinase (SK) or ɛ-aminocaproic acid (ε-ACA), respectively, on fertilization parameters and preimplantation embryo development. After in vitro maturation, bovine cumulus-oocyte complexes (COCs) were inseminated in the presence of SK or ε-ACA. The addition of SK to the IVF medium facilitated the adhesion of the spermatozoa to the zona pellucida without affecting the percentages of monospermy. Cleavage rates and blastocyst yield were similar between the SK and Control groups while they were lower with the ε-ACA treatment. Additionally, we found that the expression levels of embryo quality-related genes (SDHA and DNMT3A) could be modified in blastocysts by the addition of SK or ε-ACA during IVF. The results obtained indicate that supplementation of the IVF medium with SK did not greatly alter the embryonic developmental parameters related to embryo quality in blastocysts. Moreover, we noticed that ε-ACA treatment compromises the success of in vitro embryo development, thus highlighting the importance of the plasminogen/plasmin activity during the early stages of embryogenesis in bovine.

Role of steroid hormones in the maintenance of focal adhesions in bovine oviductal epithelial cells

The oviduct, the organ of the female reproductive system where fertilization and early embryonic development occur, provides an optimal environment for the final maturation of oocytes, storage, and sperm capacitation and transport of gametes and embryos. During the estrous cycle, the oviduct is affected by ovarian sex hormones, resulting in changes aimed at maintaining an appropriate microenvironment. Normal cell migration is tightly regulated, its role being essential for the development and maintenance of organ and tissue functions as well as for regeneration following injury. Due to their involvement in focal contact formations, focal adhesion kinase (PTK2) and paxillin (PXN) are key proteins in the study of cell migration and adhesion. The objective of this work was to compare the expression of PTK2 and PXN in oviductal cells along the estrous cycle and to determine if their expression is regulated by the presence of 17-β estradiol (E2) and/or progesterone (P4). No transcripts of PTK2 or of PXN were detected in cells corresponding to the luteal phase. Additionally, hormonal stimulation experiments on bovine oviductal cell cultures (BOECs) were carried out, where P4 inhibited the expression of both genes. Migration assays demonstrated that P4 reduced BOECs migration capacity. P4 treatment also reduced cell adhesion, while E2 increased the number of adhered cells. In conclusion, the presence of E2 and P4 regulates the expression of genes involved in the formation of focal contacts and modifies the migration and adhesion of BOECs. Understanding the effect of steroid hormones on BOECs is critical to grasp the impact of steroid control on oviductal function and its contribution to establishing successful pregnancies.

A long-term in vitro culture of bovine epithelial cells on collagen rafts

In the present work, we established and characterized a 3D functional polarized primary bovine oviduct epithelial cells (BOECs) culture on free-floating type I collagen hydrogels (rafts) at an air-liquid interface (ALI). Intercellular junctions, ultrastructural cellular morphology and the expression of the OVGP1 closely recapitulated those of the in vivo epithelium lining. These morphological and physiological epithelial cell features were maintained under standard DMEM/F12 with 10% foetal bovine serum culture medium for at least 28 days of ALI culture. The versatility of the BOECs raft cultures should allow testing of toxicity compounds, in vitro evaluation of physiological or pathological oviductal states, and the study of epithelial-mesenchymal interactions that are critical for the maintenance of oviductal homeostasis.

Exogenous activation and inhibition of plasminogen/plasmin activity during in vitro maturation of bovine cumulus-oocyte complexes: A biological and spectroscopic approach

This study deals with the effect of plasminogen/plasmin on the in vitro maturation (IVM) of bovine cumulus-oocyte complexes (COCs). Exogenous plasminogen activator streptokinase (SK) added to the IVM medium revealed similar values of cumulus expansion and oocyte nuclear maturation compared to controls (standard IVM medium). However, a decrease in both determinations was observed in COCs matured with the supplementation of ɛ-aminocaproic acid (ɛ-ACA), a specific plasmin inhibitor. After in vitro fertilization, no differences were observed in either cleavage or blastocyst rates between SK and control groups; however, ε-ACA treatment caused a decrease in both developmental rates. Zona pellucida (ZP) digestion time decreased in the SK group while it increased in the ε-ACA group. Raman microspectroscopy revealed an increase in the intensity of the band corresponding to the glycerol group of sialic acid in the ZP of oocytes matured with SK, whereas ZP spectra of oocytes treated with ɛ-ACA presented similarities with immature oocytes. The results indicate that although treatment with SK did not alter oocyte developmental competence, it induced modifications in the ZP of oocytes that could modify the folding of glycoproteins. Plasmin inhibition impairs oocyte maturation and has an impact on embryo development, thus evidencing the importance of this protease during IVM.

Effect of urokinase type plasminogen activator on in vitro bovine oocyte maturation

This study examines the impacts of the urokinase-type plasminogen activator (uPA) on the in vitro maturation (IVM) of bovine oocytes. Cumulus-oocyte complexes in IVM medium were treated with uPA, amiloride (an uPA inhibitor), dimethyl sulfoxide (DMSO) or left untreated (control group). After 24 h of IVM, oocytes were recovered for testing or were in vitro fertilized and cultured to the blastocyst stage. The factors examined in all groups were: (i) oocyte nuclear maturation (Hoëscht staining); (ii) oocyte cytoplasmic maturation (cortical granules, CGs, distribution assessed by LCA-FITC); (iii) oocyte and cumulus cell (CC) gene expression (RT-qPCR); and (iv) embryo development (cleavage rate and blastocyst yield). Oocytes subjected to uPA treatment showed rates of nuclear maturation and CG distribution patterns similar to controls (P > 0.05), whereas lower rates of oocyte maturation were recorded in the amiloride group (P < 0.05). Both in oocytes and CC, treatment with uPA did not affect the transcription of genes related to apoptosis, cell junctions, cell cycle or serpin protease inhibitors. In contrast, amiloride altered the expression of genes associated with cell junctions, cell cycle, oxidative stress and CC serpins. No differences were observed between the control and uPA group in cleavage rate or in blastocyst yield recorded on Days 7, 8 or 9 post-insemination. However, amiloride led to drastically reduced cleavage rate (28.5% vs 83.2%) and Day 9 embryo production (6.0% vs 21.0%) over the rates recorded for DMSO. These results indicate that the proteolytic activity of uPA is needed for successful oocyte maturation in bovine.

Structural modifications induced by an in vitro maturation process in zona pellucida glycoproteins of bovine oocytes. A Raman microspectroscopy analysis

Raman microspectroscopy is useful for discrimination between immature and in vitro matured bovine oocytes. Modifications in the glycoproteins of the zona pellucida exerted by the maturation methods might influence the process of in vitro production.

199 EFFECT OF UROKINASE TYPE PLASMINOGEN ACTIVATOR DURING IN VITRO MATURATION OF BOVINE OOCYTES AND EARLY EMBRYO PRODUCTION

The study of molecules involved in the oocyte maturation and early embryo development is crucial to improve the conditions of in vitro embryo production. The plasminogen activation system is involved in the initial steps of reproduction and urokinase type plasminogen activator (uPA) is expressed in the granulosa cells (GC) of bovine cumulus-oocyte complexes (COC). The aim of this study was to analyse the effect of uPA in bovine oocyte in vitro maturation (IVM). We have analysed whether the addition of uPA or the inhibition of its proteolytic activity affects IVM. We have evaluated (1) nuclear and cytoplasmic maturation, (2) developmental competence, and (3) oocyte and GC gene expression. Immature COC were obtained by aspiration of ovarian follicles of slaughtered heifers. Selected COC were in vitro-matured in 4 groups: control, 10 nM uPA, dimethyl sulfoxide control, and 100 μg mL–1 amiloride, a specific inhibitor of uPA proteolytic activity (4 replicates). After 24 h of IVM, oocytes of each treatment were either fixed and stained with Hoëscht (to evaluate nuclear maturation) or LCA-FITC to analyse the cortical granules distribution as a marker of cytoplasmic maturation (n = 10/group per treatment per replicate). In addition, pools of 10 oocytes and their separated GC were snap-frozen to analyse by qRT-PCR their profile expression of genes related with apoptosis (BAX, BCL2, TP53, SHC1), cell junctions (GJA1, TJP1), cell cycle (CCNB1), oxidative stress (SOD2, GPX1), oocyte quality (BMP15, GDF9), and serpin proteases inhibitors (SRP1, SRP5), normalised respect 2 housekeeping genes (H2AFZ, ACTB). The remaining COC were fertilised (Day 0) and in vitro cultured to evaluate developmental competence in terms of cleavage rate (Day 2) and blastocyst yield (Days 7–9). All data were analysed by one-way ANOVA. In the presence of amiloride, a significant reduction in the oocyte maturation was observed at both levels; 83.33% of oocytes remained in vesicle stage, and 75.0% showed a cortical granules distribution of type I. The rest of the groups (62.67%, 62.65%, and 60.29%) reached metaphase II (MII), and 51.66%, 32.9%, and 25.44% showed granule distribution of type III. For embryo development, the amiloride group had a cleavage rate and blastocyst yield significantly lower compared with controls (23.23% v. 80.85% and 83.83%; 4.45% v. 25.21% and 25.21%, respectively), whereas uPA treatment had no effect (84.28% and 24.16%). In presence of amiloride, the transcript levels of TJP1, GJA1, and CCNB1 were up-regulated, whereas SOD2, SRP1, and SRP5 were down-regulated in GC compared with all other groups (P < 0.05). No differences were observed in oocytes gene expression between treatments. In conclusion, although the addition of exogenous uPA does not alter oocyte maturation, the specific inhibition of the proteolytic activity of uPA by amiloride reduced IVM of bovine oocytes and altered the expression of genes related to cell junctions, cell cycle, oxidative stress, and serpins of GC, indicating that proteolytic activity of uPA is critical for oocyte IVM in bovines.

Expression of urokinase type plasminogen activator receptor (uPAR) in the bovine oviduct: Relationship with uPA effect on oviductal epithelial cells

Urokinase type plasminogen activator (uPA) is an oviductal fluid component whose activity is regulated by binding to urokinase type plasminogen activator receptor (uPAR). In this study uPAR and uPA gene expression in bovine oviduct were evaluated and similar expression patterns for both uPAR and uPA mRNAs were observed during the estrous cycle. Immunolocalization of uPAR at the apical zone of epithelial cells suggests that uPA action would be focalized in the oviductal lumen, triggering intracellular signaling pathways. As uPAR expression was also observed in in vitro cultures of oviductal epithelial cells, the effect of uPA was explored using this culture model. Real-time RT-PCR demonstrated that c-fos expression in oviductal cell cultures increases under uPA stimulation. These results suggest that uPA/uPAR binding would be involved in signaling pathways that activate transcription factors and would regulate the synthesis of molecules concerned with the arrangement of a particular oviductal microenvironment.

Plasminogen detection in oocytes and plasminogen activator activities in the porcine oviduct during the estrous cycle

Plasminogen activators (PAs) are highly specific serine proteases that convert the extracellular zymogen plasminogen into the active proteinase plasmin. Plasminogen-dependent proteolytic activity was detected by zymography both in the tissue membrane fraction of oviducts and in the oviductal flushing obtained at the preovulatory (Pre-Ov), postovulatory (Post-Ov) and mid-luteal (Mid-L) stages of the estrous cycle. A main proteolytic band, with a relative mobility similar to a human melanoma cell tissue-type plasminogen activator (t-PA), was found in all samples. Two additional components were observed in Pre-Ov and Post-Ov oviductal flushing but not in the tissue membrane fraction. In the oviductal flushing the PA activity was significantly higher in the Post-Ov stage than in the Pre-Ov one. Both urokinase-type plasminogen activator (u-PA, 50 kDa) and t-PA (72 kDa) were detected by Western blot; they showed differences in their relative concentration between Post-Ov and Pre-Ov oviductal flushing. The main PA substrate, plasminogen, was detected by indirect immunofluorescence in the cumulus cell extracellular matrix (ECM) and oocyte zona pellucida (ZP). In denuded oocytes, plasminogen was also detected on the surface of the plasma membrane. It is possible that oviductal PAs may act on the plasminogen present in the cumulus cell ECM and ZP; consequently, the generated plasmin could be involved in the rebuilding or degradation of these oocyte structures during fertilization or early development.