Classification of bovine follicles based on the concentrations of steroids, glucose and lactate in follicular fluid and the status of accompanying follicles

Autophagy is involved in granulosa cell death and follicular atresia in ewe ovaries

In mammalian ovaries, most follicles do not ovulate and are eliminated by atresia, which primarily depends on granulosa cell (GC) apoptosis. Autophagy is an alternative mechanism involved in follicle depletion in mammals through independent or tandem action with apoptosis. However, follicular autophagy has not yet been investigated in sheep; therefore, the present study aimed to investigate the involvement of autophagy in atresia among a pool of growing antral follicles in ewe ovaries. The abundance of the autophagic marker LC3B-II was determined using western blotting in GCs collected from ewe antral follicles. The antral follicles were classified as healthy or atretic based on morphological criteria and steroid measurements in follicular fluid (FF). Immunofluorescence and confocal microscopy analyses were performed on GCs to evaluate the presence of autophagic proteins and their subcellular localisation. Caspase-3 and DNA fragmentation were assessed using western blotting and TUNEL assays, respectively, in the same GC population to investigate the simultaneous apoptosis. The novel results of this study demonstrated enhanced LC3B-II protein expression in GCs of atretic follicles compared to that of healthy ones (1.3-fold increase; P = 0.0001, ANOVA), indicating a correlation between autophagy enhancement in GCs and antral follicular atresia. Autophagy, either functioning independently or in tandem with apoptosis, may be involved in the atresia of growing antral follicles in ewe ovaries because atretic GCs also showed high levels of apoptotic markers. The findings of this study might have important implication on scientific understanding of ovarian follicle dynamics.

Corpus luteum presence in the bovine ovary increase intrafollicular progesterone concentration: consequences in follicular cells gene expression and follicular fluid small extracellular vesicles miRNA contents

BACKGROUND

It is well described that circulating progesterone (P4) plays a key role in several reproductive events such as oocyte maturation. However, during diestrus, when circulating P4 is at the highest concentrations, little is known about its local impact on the follicular cells such as intrafollicular P4 concentration due to corpus luteum (CL) presence within the same ovary. Based on that, our hypothesis is that the CL presence in the ovary during diestrus alters intrafollicular P4 concentrations, oocyte competence acquisition, follicular cells gene expression, and small extracellular vesicles (sEVs) miRNAs contents.

RESULTS

P4 hormonal analysis revealed that ipsilateral to the CL follicular fluid (iFF) presented higher P4 concentration compared to contralateral follicular fluid (cFF). Furthermore, oocyte maturation and miRNA biogenesis pathways transcripts (ADAMTS-1 and AGO2, respectively) were increased in cumulus and granulosa cells of iFF, respectively. Nevertheless, a RT-PCR screening of 382 miRNAs showed that three miRNAs were upregulated and two exclusively expressed in sEVs from iFF and are predicted to regulate cell communication pathways. Similarly, seven miRNAs were higher and two exclusively expressed from cFF sEVs and are predicted to modulate proliferation signaling pathways.

CONCLUSION

In conclusion, intrafollicular P4 concentration is influenced by the presence of the CL and modulates biological processes related to follicular cell development and oocyte competence, which may influence the oocyte quality. Altogether, these results are crucial to improve our knowledge about the follicular microenvironment involved in oocyte competence acquisition.

Follicular fluid meiosis-activating sterol prevents porcine ovarian granulosa cells from hypoxia-induced apoptosis via inhibiting STAT4 expression

Follicular fluid meiosis-activating sterol (FF-MAS) is a small molecule compound found in FF, named for its ability to induce oocyte resumption of meiosis. Granulosa cells (GCs) within the follicle are typically located in a hypoxic environment under physiologic conditions due to limited vascular distribution. Previous research suggests that hypoxia-induced cell cycle arrest and apoptosis in GCs may be crucial triggering factors in porcine follicular atresia. However, the impact of FF-MAS on GCs within follicles has not been explored so far. In this study, we uncovered a novel role of FF-MAS in facilitating GC survival under hypoxic conditions by inhibiting STAT4 expression. We found that STAT4 expression was upregulated in porcine GCs exposed to 1% O2. Both gain and loss of function assays confirmed that STAT4 was required for cell apoptosis under hypoxia conditions, and that the GC apoptosis caused by hypoxia was markedly attenuated following FF-MAS treatment through inhibition of STAT4 expression. Correlation analysis in vivo revealed that GC apoptosis was associated with increased STAT4 expression, while the FF-MAS content in follicular fluid was negatively correlated with STAT4 mRNA levels and cell apoptosis. These findings elucidate a novel role of FF-MAS-mediated protection of GCs by inhibiting STAT4 expression under hypoxia, which might contribute to the mechanistic understanding of follicular development.

Reduced period from follicular wave emergence to luteolysis generated greater steroidogenic follicles and estrus intensity in dairy cows

The onset of productive life in dairy cattle, concomitant to parturition, is accompanied by a substantial decrease in fertility in comparison with non-lactating, nulliparous heifers. Follicular growth patterns differ between parous and nulliparous dairy cattle. Nulliparous heifers ovulate follicles with reduced antral age (RAA). This study aimed to exogenously reduce ovulatory follicle age in lactating dairy cows from 7 to 5 days old. Cows (n = 80) had their estrous cycles synchronized with the Double-Ovsynch program. At the final portion of this program, luteolysis was induced at either 5 (RAA) or 7 (Control) days following follicular wave emergence. RAA outcomes were estimated in comparison with Controls. RAA resulted in smaller follicles 2 days post-treatment. Despite lower serum concentrations of 17β-estradiol before treatment compared with Controls, the rate of increase in this hormone was greater for the RAA treatment. There was no difference in luteolysis rates between treatments. Proestrus (luteolysis onset to estrus onset) was prolonged in RAA cows. Cows with RAA had more intense estruses. Collectively, these results indicate that decreasing the age of the ovulatory follicle may improve the steroidogenic capacity of the dominant follicle and estrus expression intensity in lactating dairy cows.

Preovulatory follicular fluid and serum metabolome profiles in lactating beef cows with thin, moderate, and obese body condition

Extremes in body condition reduce fertility and overall productivity in beef cattle herds, due in part to altered systemic metabolic conditions that influence the intrafollicular and uterine environment. Follicular fluid and serum metabolome profiles are influenced by body composition in women and dairy cattle; however, such information is lacking in beef cattle. We hypothesized that body condition score (BCS)-related alterations in the metabolome of preovulatory follicular fluid and serum may influence oocyte maturation while impacting the oviductal or uterine environment. Therefore, we performed a study with the objective to determine the relationship between BCS and the metabolome of follicular fluid and serum in lactating beef cattle. We synchronized the development of a preovulatory follicle in 130 cows of varying BCS. We collected blood and performed transvaginal follicle aspirations to collect follicular fluid from the preovulatory follicle ~18 h after gonadotropin-releasing hormone administration to stimulate the preovulatory gonadotropin surge. We then selected follicular fluid and serum samples from cows with BCS 4 (Thin; n = 14), BCS 6 (Moderate; n = 18), or BCS >8 (Obese; n = 14) for ultra-high performance liquid chromatography-high resolution mass spectrometry. We identified differences in the follicular fluid or serum of thin, moderate, and obese animals based on multiple linear regression. MetaboAnalyst 5.0 was used for enrichment analysis of significant metabolites. We identified 38 metabolites in follicular fluid and 49 metabolites in serum. There were no significant differences in follicular fluid metabolite content among BCS classifications. There were 5, 22, and 1 serum metabolites differentially abundant between thin-obese, moderate-thin, and moderate-obese classifications, respectively (false discovery rate [FDR] < 0.10). These metabolites were enriched in multiple processes including "arginine biosynthesis," "arginine/proline metabolism," and "D-glutamine/D-glutamate metabolism" (FDR < 0.04). Pathways enriched with serum metabolites associated with BCS indicate potentially increased reactive oxygen species (ROS) in serum of thin cows. ROS crossing the blood follicular barrier may negatively impact the oocyte during oocyte maturation and contribute to the reduced pregnancy rates observed in thin beef cows.

Fatty Acids and Metabolomic Composition of Follicular Fluid Collected from Environments Associated with Good and Poor Oocyte Competence in Goats

In goats, embryo oocyte competence is affected by follicle size regardless the age of the females. In previous studies we have found differences in blastocyst development between oocytes coming of small (<3 mm) and large follicles (>3 mm) in prepubertal (1−2 months-old) goats. Oocyte competence and Follicular Fluid (FF) composition changes throughout follicle growth. The aim of this study was to analyze Fatty Acids (FAs) composition and metabolomic profiles of FF recovered from small and large follicles of prepubertal goats and follicles of adult goats. FAs were analyzed by chromatography and metabolites by 1H-Nuclear Magnetic Resonance (1H-NMR) Spectrometry. The results showed important differences between adult and prepubertal follicles: (a) the presence of α,β-glucose in adult and no detection in prepubertal; (b) lactate, -N-(CH3)3 groups and inositol were higher in prepubertal (c) the percentage of Linolenic Acid, Total Saturated Fatty Acids and n-3 PUFAs were higher in adults; and (d) the percentage of Linoleic Acid, total MUFAs, PUFAs, n-6 PUFAs and n-6 PUFAs: n-3 PUFAs ratio were higher in prepubertal goats. Not significant differences were found in follicle size of prepubertal goats, despite the differences in oocyte competence for in vitro embryo production.

Non-targeted Metabolomics Reveals Metabolic Characteristics of Porcine Atretic Follicles

Follicular atresia is one of the main factors limiting the reproductive power of domestic animals. At present, the molecular mechanisms involved in porcine follicular atresia at the metabolic level remain unclear. In this study, we divided the follicles of Bama Xiang pigs into healthy follicles (HFs) and atretic follicles (AFs) based on the follicle morphology. The expression of genes related to atresia in granulosa cells (GCs) and the concentration of hormones in the follicular fluid (FF) from HFs and AFs were detected. We then used liquid chromatography–mass spectrometry-based non-targeted metabolomic approach to analyze the metabolites in the FF from HFs and AFs. The results showed that the content of estradiol was significantly lower in AFs than in HFs, whereas that of progesterone was significantly higher in AFs than that in HFs. The expression of BCL2, VEGFA, and CYP19A1 was significantly higher in HFs than in AFs. In contrast, the expression of BAX and CASPASE3 was significantly lower in HFs. A total of 18 differential metabolites (DMs) were identified, including phospholipids, bioactive substances, and amino acids. The DMs were involved in 12 metabolic pathways, including arginine biosynthesis and primary bile acid biosynthesis. The levels of eight DMs were higher in the HF group than those in the AF group (p < 0.01), and those of 10 DMs were higher in the AF group than those in the HF group (p < 0.01). These findings indicate that the metabolic characteristics of porcine AFs are lower levels of lipids such as phospholipids and higher levels of amino acids and bile acids than those in HFs. Disorders of amino acid metabolism and cholic acid metabolism may contribute to porcine follicular atresia.

Estrous cycle impacts microRNA content in extracellular vesicles that modulate bovine cumulus cell transcripts during in vitro maturation†

Extracellular vesicles (EVs) are nanoparticles secreted by ovarian follicle cells. Extracellular vesicles are an important form of intercellular communication, since they carry bioactive contents, such as microRNAs (miRNAs), mRNAs, and proteins. MicroRNAs are small noncoding RNA capable of modulating mRNA translation. Thus, EVs can play a role in follicle and oocyte development. However, it is not clear if EV contents vary with the estrous cycle stage. The aim of this study was to investigate the bovine miRNA content in EVs obtained from follicles at different estrous cycle stages, which are associated with different progesterone (P4) levels in the follicular fluid (FF). We collected FF from 3 to 6 mm follicles and evaluated the miRNA profile of the EVs and their effects on cumulus-oocyte complexes during in vitro maturation. We observed that EVs from low P4 group have a higher abundance of miRNAs predicted to modulate pathways, such as MAPK, RNA transport, Hippo, Cell cycle, FoxO, oocyte meiosis, and TGF-beta. Additionally, EVs were taken up by cumulus cells and, thus, affected the RNA global profile 9 h after EV supplementation. Cumulus cells supplemented with EVs from low P4 presented upregulated genes that could modulate biological processes, such as oocyte development, immune responses, and Notch signaling compared with genes of cumulus cells in the EV free media or with EVs from high P4 follicles. In conclusion, our results demonstrate that EV miRNA contents are distinct in follicles exposed to different estrous cycle stage. Supplementation with EVs impacts gene expression and biological processes in cumulus cells.

Local sex steroid hormone milieu in the bovine oviduct ipsilateral and contralateral to preovulatory follicle or corpus luteum during the periovulatory phase

Estradiol-17β (E2) and progesterone (P4) regulate oviductal functions, providing a suitable environment for the transport and maturation of gametes, fertilization, and embryonic development. In addition to the E2 and P4 nuclear receptors, estrogen receptor (ESR) α and β, nuclear progesterone receptor (PGR), nongenomic mechanisms through G protein-coupled estrogen receptor (GPER1), and progesterone receptor membrane component (PGRMC) 1 and 2 mediate E2 and P4 actions. This study aimed to characterize the local endocrine environment of the oviduct by examining the oviductal E2 and P4 concentrations and their receptors' mRNA expression during the periovulatory phase. The bovine oviducts were collected in a slaughterhouse and the days postovulation were estimated according to state of the ovaries and the uterus. Samples of the ampulla and isthmus ipsilateral and contralateral to the preovulatory follicle or corpus luteum were collected on Days 19 to 21, Days 0 to 1, Days 2 to 4, and Days 5 to 7 of the estrous cycle. The effects of the estrous cycle phase and oviductal region (ampulla and isthmus) and side (ipsilateral and contralateral) were analyzed by 3-way ANOVA. Moreover, to clarify the regulatory mechanisms of the mRNA expression of hormone receptors, the effects of E2 and P4 on mRNA expression in the oviduct were examined by multiple linear regression. The oviductal endocrine milieu on Days 19 to 21 was characterized by an E2-dominant environment with high E2 and low P4, high ESR1 and PGR mRNA expression, and low ESR2, GPER1, and PGRMC2 mRNA expression, whereas the corresponding on Days 0 to 1 was characterized by the endocrine milieu without hormone dominance. The environment on Days 2 to 4 and Day 5 to 7 was characterized by opposite tendency of oviductal hormone concentrations and their receptors' mRNA expression to Days 19 to 21. Additionally, the ipsilateral oviduct had the more P4-dominant endocrine milieu, with lower E2 and higher P4 concentrations, and different expression of ESR1/2, GPER1, PGR, and PGRMC2 mRNA when compared with the contralateral oviduct on Days 2 to 4 and Days 5 to 7, except for PGRMC1. Although oviductal E2 and P4 influenced the mRNA expression of ESR1/2, GPER1, PGR, and PGRMC1/2, their effects were different between regions and sides. In summary, the oviductal endocrine milieu varies according to the estrous cycle phase and the oviductal region and side, which may be involved in the estrous cycle phase-specific and oviductal region-specific and side-specific functions.

Expression of genes encoding mineralocorticoid biosynthetic enzymes and the mineralocorticoid receptor, and levels of mineralocorticoids in the bovine follicle and corpus luteum

Unlike sex steroids, mineralocorticoids have attracted limited attention in ovarian physiology. Recent studies on primates have indicated possible local synthesis and action of mineralocorticoids in the ovary. Here, we examined developmental changes in the levels of mineralocorticoids and expression of genes encoding their biosynthetic enzymes and receptor in the bovine ovary. The follicles and corpora lutea (CL) were collected from F1 heifers. Expression levels of 21α-hydroxylase (CYP21A2), 11β-hydroxylase-1 (CYP11B1), and the mineralocorticoid receptor (NR3C2) in granulosa cells (GC), thecal layers (TL), and CL tissues were quantified by real-time PCR, whereas mineralocorticoids in the follicular fluid were measured by enzyme immunoassay (EIA). TL and GC expressed CYP21A2 and NR3C2, whereas CYP11B1 was expressed at very low or undetectable levels. The expression levels of these genes were not significantly different among small/large and healthy/atretic follicles but were higher in TL than in GC. CYP21A2 and NR3C2 were expressed in all CL stages with higher expression observed in the mid-stage. CYP11B1 expression was only apparent in the mid-stage CL. Aldosterone was detected in all follicles, and its concentration was not significantly different among the follicular groups. In paired large-healthy/atretic follicles, the concentration of deoxycorticosterone, a precursor of aldosterone, was approximately ten-fold higher than that of aldosterone and not significantly different between healthy and atretic follicles. In conclusion, the presence of mineralocorticoids and expression of NR3C2 in the bovine follicle together with the developmental change in the expression of CYP21A2, CYP11B1, and NR3C2 in the CL suggest possible endocrine/paracrine/autocrine roles of mineralocorticoids in the bovine ovary.

Possible roles of local oviductal estradiol-17β in luteal formation phase on the function of bovine oviductal epithelium

Oviducts play an important role in the reproductive process, such as in gamete transport, fertilization, and early embryonic development. However, the regulation of oviductal function during luteal formation phase (3−5 days post-ovulation), which is a crucial phase for early embryonic development, remains poorly understood. This study investigated the roles of oviductal estradiol-17β (E2) and progesterone (P4) concentrations on bovine oviductal functions in the luteal formation phase using RT-qPCR for some genes of oviductal epithelial cells. Bovine oviducts ipsilateral to the corpus luteum (CL) in the luteal formation phase were collected from a slaughterhouse. The concentration of oviductal E2 was positively correlated with the mRNA expressions of nuclear P4 receptor (PGR) and protein disulfide isomerase family A member 4 (PDIA4), which is related to protein secretion, in the ampulla and with estrogen receptor α (ESR1) mRNA expression in the isthmus. In contrast, the concentration of oviductal P4 was not correlated with oviductal mRNA expressions in either regions. Furthermore, for the candidate factor related to the oviductal E2 concentration, the CL parameters (CL size and tissue P4 concentration), first-wave dominant follicle (W1DF) parameters (follicle size and intrafollicular E2 concentration), and W1DF location (ipsilateral or contralateral to CL) did not influence the oviductal E2 concentration. In conclusion, our results suggest that the local oviductal E2 is a potential oviductal function regulator during the luteal formation phase.

MicroRNAs in ovarian follicular atresia and granulosa cell apoptosis

MicroRNAs (miRNAs) are short, noncoding RNAs that posttranscriptionally regulate gene expression. In the past decade, studies on miRNAs in ovaries have revealed the key roles of miRNAs in ovarian development and function. In this review, we first introduce the development of follicular atresia research and then summarize genome-wide studies on the ovarian miRNA profiles of different mammalian species. Differentially expressed miRNA profiles during atresia and other biological processes are herein compared. In addition, current knowledge on confirmed functional miRNAs during the follicular atresia process, which is mostly indicated by granulosa cell (GC) apoptosis, is presented. The main miRNA families and clusters, including the let-7 family, miR-23-27-24 cluster, miR-183-96-182 cluster and miR-17-92 cluster, and related pathways that are involved in follicular atresia are thoroughly summarized. A deep understanding of the roles of miRNA networks will not only help elucidate the mechanisms of GC apoptosis, follicular development, atresia and their disorders but also offer new diagnostic and treatment strategies for infertility and other ovarian dysfunctions.

Follicular competition in cows: the selection of dominant follicles as a synergistic effect

The reproductive cycle of mono-ovulatory species such as cows or humans is known to show two or more waves of follicular growth and decline between two successive ovulations. Within each wave, there is one dominant follicle escorted by subordinate follicles of varying number. Under the surge of the luteinizing hormone a growing dominant follicle ovulates. Rarely the number of ovulating follicles exceeds one. In the biological literature, the change of hormonal concentrations and individually varying numbers of follicular receptors are made responsible for the selection of exactly one dominant follicle, yet a clear cause has not been identified. In this paper, we suggest a synergistic explanation based on competition, formulated by a parsimoniously defined system of ordinary differential equations (ODEs) that quantifies the time evolution of multiple follicles and their competitive interaction during one wave. Not discriminating between follicles, growth and decline are given by fixed rates. Competition is introduced via a growth-suppressing term, equally supported by all follicles. We prove that the number of dominant follicles is determined exclusively by the ratio of follicular growth and competition. This number turns out to be independent of the number of subordinate follicles. The asymptotic behavior of the corresponding dynamical system is investigated rigorously, where we demonstrate that the [Formula: see text]-limit set only contains fixed points. When also including follicular decline, our ODEs perfectly resemble ultrasound data of bovine follicles. Implications for the involved but not explicitly modeled hormones are discussed.

Lactate promotes specific differentiation in bovine granulosa cells depending on lactate uptake thus mimicking an early post-LH stage

BACKGROUND

The LH-induced folliculo-luteal transformation is connected with alterations of the gene expression profile in cells of the granulosa layer. It has been described that hypoxic conditions occur during luteinization, thus favoring the formation of L-lactate within the follicle. Despite being a product of anaerobic respiration, L-lactate has been shown to act as a signaling molecule affecting gene expression in neuronal cells. During the present study, we tested the hypothesis that L-lactate may influence differentiation of follicular granulosa cells (GC).

METHODS

In a bovine granulosa cell culture model effects of L- and D-lactate, of increased glucose concentrations and of the lactate transport inhibitor UK5099 were analyzed. Steroid hormone production was analyzed by RIA and the abundance of key transcripts was determined by quantitative real-time RT-PCR.

RESULTS

L-lactate decreased the production of estradiol and significantly affected selected genes of the folliculo-luteal transition as well as genes of the lactate metabolism. CYP19A1, FSHR, LHCGR were down-regulated, whereas RGS2, VNN2, PTX3, LDHA and lactate transporters were up-regulated. These effects could be partly or completely reversed by pre-treatment of the cells with UK5099. The non-metabolized enantiomer D-lactate had even more pronounced effects on gene expression, whereas increased glucose concentrations did not affect transcript abundance.

CONCLUSIONS

In summary, our data suggest that L-lactate specifically alters physiological and molecular characteristics of GC. These effects critically depend on L-lactate uptake, but are not triggered by increased energy supply. Further, we could show that L-lactate has a positive feedback on the lactate metabolism. Therefore, we hypothesize that L-lactate acts as a signaling molecule in bovine and possibly other monovular species supporting differentiation during the folliculo-luteal transformation.

A Metabolomic Overview of Follicular Fluid in Cows

Follicular fluid (FF) protects the oocyte against proteolysis and extrusion during ovulation, providing an appropriate microenvironment that favors proper embryonic development; thereby, FF plays a key role in embryo quality. Being directly related to cattle breeding, studying FF is extremely important in livestock science to measure cattle fertility. This may eventually help to assess the quality of both meat and milk, products widely consumed worldwide. There is an important commercial interest in the evaluation and characterization of compounds present in the FF of livestock that present greater likelihood of pregnancy. Mass spectrometry is a great ally for this type of analysis and can provide quick and efficient screening for molecular markers in biological samples. The present study demonstrated the potential of high-resolution mass spectrometry in analyzing FF samples from two distinct groups of Nellore cows (Bos indicus): high and low fertility, as determined by the number of oocytes produced. We were able to delineate markers of interest for each group, which may ultimately be related to biochemical pathways that lead to higher or lower reproductive performance.

Metabolomic profiling of bovine oviductal fluid across the oestrous cycle using proton nuclear magnetic resonance spectroscopy

In the present study we tested whether regulation of the metabolome in bovine oviductal fluid depended on the stage of the oestrous cycle, the side relative to ovulation and local concentrations of steroid hormones. Luminal fluid samples from both oviducts were collected in the preovulatory, postovulatory, mid- and late luteal phases, from cyclic cows at a local abattoir (18–27 cows per stage and side). The metabolomes were assessed by proton nuclear magnetic resonance spectroscopy (H-NMR). In all, 39 metabolites were identified, among which the amino acid glycine and the energy substrates lactate and myoinositol were the most abundant at all stages. The concentrations of 14 metabolites varied according to the stage of the oestrous cycle in at least one side relative to ovulation, of which four (choline, glucose-1-phosphate, glycine and pyruvate) were correlated with intraoviductal progesterone or oestradiol concentrations. Glucose-1-phosphate was most affected by the stage of the cycle, with four- to sixfold higher levels in luteal than periovulatory stages. These results provide new knowledge on the regulation of secretory activity in the oviduct and may help optimise culture media for gamete maturation, IVF and embryo production.

Evidence of endometrial amino acid metabolism and transport modulation by peri-ovulatory endocrine profiles driving uterine receptivity

Background

In beef cattle, changes in the periovulatory endocrine milieu are associated with fertility and conceptus growth. A large preovulatory follicle (POF) and the resulting elevated concentrations of progesterone (P4) during diestrus positively affect pregnancy rates. Amino acids (AA) are important components of maternally derived secretions that are crucial for embryonic survival before implantation. The hypothesis is that the size of the POF and the concentration of P4 in early diestrus modulate the endometrial abundance of SLC transcripts related to AA transport and metabolism and subsequently impact luminal concentrations of AA. The follicle growth of Nelore cows was manipulated to produce two experimental groups: large POF and CL (LF-LCL group) and small POF and CL (SF-SCL group). On Day 4 (D4; Experiment 1) and Day 7 (D7; Experiment 2) after GnRH-induced ovulation (GnRH treatment = D0), the animals were slaughtered and uterine tissues and uterine washings were collected. qRT-PCR was used to evaluate the expression levels of AA transporters in D4 and D7 endometrial tissues. The concentrations of AA were quantified in D4 and D7 uterine washings by HPLC.

Results

Transcript results show that, on D4, SLC6A6, SLC7A4, SLC17A5, SLC38A1, SLC38A7 and SCLY and on D7 SLC1A4, SLC6A1, SLC6A14, SLC7A4, SLC7A7, SLC7A8, SLC17A5, SLC38A1, SLC38A7, SLC43A2 and DDO were more abundant in the endometria of cows from the LF-LCL group (P < 0.05). In addition, concentrations of AA in the uterine lumen were influenced by the endocrine profiles of the mother. In this context, D4 uterine washings revealed that greater concentrations of taurine, alanine and α-aminobutyric acid were present in SF-SCL (P < 0.05). In contrast, lower concentrations of valine and cystathionine were quantified on D7 uterine washings from SF-SCL cows (P < 0.05).

Conclusion

The present study revealed an association between the abundance of transcripts related to AA transport and metabolism in the endometrium and specific periovulatory endocrine profiles related to the receptive status of the mother. Such insights suggest that AAs are involved in uterine function to support embryo development.

Insulin signalling and glucose transport in the ovary and ovarian function during the ovarian cycle

Data derived principally from peripheral tissues (fat, muscle and liver) show that insulin signals via diverse interconnecting intracellular pathways and that some of the major intersecting points (known as critical nodes) are the IRSs (insulin receptor substrates), PI3K (phosphoinositide kinase)/Akt and MAPK (mitogen-activated protein kinase). Most of these insulin pathways are probably also active in the ovary and their ability to interact with each other and also with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) signalling pathways enables insulin to exert direct modulating influences on ovarian function. The present paper reviews the intracellular actions of insulin and the uptake of glucose by ovarian tissues (granulosa, theca and oocyte) during the oestrous/menstrual cycle of some rodent, primate and ruminant species. Insulin signals through diverse pathways and these are discussed with specific reference to follicular cell types (granulosa, theca and oocyte). The signalling pathways for FSH in granulosa cells and LH in granulosa and theca cells are summarized. The roles of glucose and of insulin-mediated uptake of glucose in folliculogenesis are discussed. It is suggested that glucose in addition to its well-established role of providing energy for cellular function may also have insulin-mediated signalling functions in ovarian cells, involving AMPK (AMP-dependent protein kinase) and/or hexosamine. Potential interactions of insulin signalling with FSH or LH signalling at critical nodes are identified and the available evidence for such interactions in ovarian cells is discussed. Finally the action of the insulin-sensitizing drugs metformin and the thiazolidinedione rosiglitazone on follicular cells is reviewed.

Regulation of the bovine oviductal fluid proteome

Our objective was to investigate the regulation of the proteome in the bovine oviductal fluid according to the stage of the oestrous cycle, to the side relative to ovulation and to local concentrations of steroid hormones. Luminal fluid samples from both oviducts were collected at four stages of the oestrous cycle: pre-ovulatory (Pre-ov), post-ovulatory (Post-ov), and mid- and late luteal phases from adult cyclic cows (18–25 cows/stage). The proteomes were assessed by nanoLC–MS/MS and quantified by label-free method. Totally, 482 proteins were identified including a limited number of proteins specific to one stage or one side. Proportions of differentially abundant proteins fluctuated from 10 to 24% between sides at one stage and from 4 to 20% among stages in a given side of ovulation. In oviductal fluids ipsilateral to ovulation, Annexin A1 was the most abundant protein at Pre-ov compared with Post-ov while numerous heat shock proteins were more abundant at Post-ov compared with Pre-ov. Among differentially abundant proteins, seven tended to be correlated with intra-oviductal concentrations of progesterone. A wide range of biological processes was evidenced for differentially abundant proteins, of which metabolic and cellular processes were predominant. This work identifies numerous new candidate proteins potentially interacting with the oocyte, spermatozoa and embryo to modulate fertilization and early embryo development.

Characterization of blood flow and the effects of exogenous estradiol benzoate on residual follicles formed after ultrasound-guided transvaginal follicle aspiration in cattle

BACKGROUND

Removal of the follicular content by ultrasound-guided transvaginal follicle aspiration (TVFA) may fail to induce immediate atresia and loss of function, resulting in the occurrence of residual follicles (RF). The aims of this study were to characterize the blood flow in RF and to determine the effects of the treatment with estradiol benzoate on RF fate. Lactating, cyclic Holstein-Gir crossbred cows were used. In Experiment 1, follicular wave emergence (D0) was synchronized in cows (n = 10) and follicular growth was then monitored by transrectal ultrasonography from D0 to D8, followed by TVFA of the largest follicle present on the ovaries 24 h later. Color Doppler ultrasound imaging was used to examine blood flow on the follicular wall, which was recorded immediately before and every 12 h after TVFA, up to 72 h. In experiment 2, cows (n = 22) were randomly allocated to receive either 2 mL of saline i.m. (Control group, n = 11) or 2 mL estradiol benzoate i.m. (EB group, n = 11) immediately after TVFA. Ovaries were scanned every 12 h to confirm the presence and to measure the diameter of RF. The contents of the RF, if present, were collected 72 h after the first TVFA, using the same aspiration procedures. Follicular fluid from original follicles and RF were stored at -20 °C until hormonal assays.

RESULTS

In Experiment 1, there was no reduction (P > 0.05) of blood flow in the remaining follicle walls after TVFA and maximum blood flow values were observed at 49.5 ± 19.7 h post-TVFA. In Experiment 2, formation of RF after TVFA was proportionally similar between Controls (5/9) and EB (5/10) cows. Also, RF diameter did not differ between groups (P > 0.05). Nonetheless, the content of RF from cows in the EB group had lower (P = 0.0004) estradiol (E2) concentration and lower (P = 0.0005) E2:P4 ratio compared with Controls.

CONCLUSIONS

In conclusion, 1) the persistence of vascularization in the remaining follicle wall may contribute to the formation of RF after follicle aspiration, and 2) the treatment with estradiol benzoate does not prevent formation of RF, but does reduce their estradiol production.

Steroid hormones in bovine oviductal fluid during the estrous cycle

Ovarian steroid hormones are major regulators of the physiology of the oviduct and reproductive events occurring within the oviduct. To establish a whole steroid profiling of the bovine oviductal fluid (OF) during the estrous cycle, contralateral and ipsilateral (to the corpus luteum or preovulatory follicle) oviducts were classified into four stages of the estrous cycle (n = 18-27 cows per stage): postovulatory (Post-ov), mid-luteal (Mid-lut), late luteal (Late-lut), and preovulatory on the basis of the ovarian morphology and intrafollicular steroid concentrations. Steroids were extracted from pools of 150 to 200 μL OF (three to 10 cows per pool; three to four pools per "stage × side" group), purified, fractioned by high-performance liquid chromatography, and analyzed by gas chromatography coupled with tandem mass spectrometry. The concentrations of progesterone (P4) in ipsilateral OF increased from Post-ov (56.9 ± 13.4 ng/mL) to Mid-lut (120.3 ± 34.3 ng/mL), then decreased from Late-lut (76.7 ± 1.8 ng/mL) to Pre-ov (6.3 ± 1.7 ng/mL), and were four to 16 times higher than in contralateral OF. Most P4 metabolites followed similar patterns of variation. Concentrations of 17beta-estradiol (E2) were significantly higher at Pre-ov (290.5 ± 63.2 pg/mL) compared with all other stages (<118.3 pg/mL), with no difference regarding the side of ovulation. Concentrations of androstenedione displayed a pattern similar to that of E2, whereas other androgens, estrone, and corticoids did not vary between stages or sides. In conclusion, a highly concentrated and fluctuating hormonal environment was evidenced in the bovine OF. These results could be useful to improve media for IVF, embryo development, and culture of oviductal cells.

In vivo collection of follicular fluid and granulosa cells from individual follicles of different diameters in cattle by an adapted ovum pick-up system

BACKGROUND

Most studies on granulosa cell (GC) function in cattle have been performed using GC and follicular fluid (FF) samples collected from slaughterhouse ovaries. Using this approach, the follicular developmental stage and functional status are unknown and indirectly inferred, limiting data interpretation. Ultrasound-guided follicle aspiration has previously been used to recover GC or FF samples, but this was mostly carried out in large follicles or pools of small follicles, without recording the efficiency of recovery. The present study was aimed at adapting and evaluating an ovum pick-up (OPU) system for the in vivo recovery of FF and GC from individual follicles of different diameters.

METHODS

In the first trial, the losses of fluid inside the tubing system were calculated using a conventional or an adapted-OPU system. Blood plasma volumes equivalent to the amount of FF in follicles of different diameters were aspirated using a conventional OPU Teflon circuit. The OPU system was then adapted by connecting 0.25 mL straws to the circuit. A second trial evaluated the efficiency of FF recovery in vivo. Follicles ranging from 4.0 to 16.8 mm in diameter were aspirated individually using the conventional or adapted-OPU systems. A third trial assessed the in vivo recovery of GC and the subsequent amount of RNA obtained from the follicles of different diameters from Holstein and Gir cattle.

RESULTS

In Trial I, the plasma recovery efficiency was similar (P > 0.05) for the volumes expected for 12 and 10 mm follicles, but decreased (P < 0.05) for smaller follicles (45.7+/-4.0%, 12.4+/-4.3% and 0.0+/-0.0% for 8, 6, and 4 mm follicles, respectively). Using the adaptation, the losses intrinsic to the aspiration system were similar for all follicle diameters. In Trial II, the expected and recovered volumes of FF were correlated (r = 0.89) and the efficiency of recovery was similar among follicles <12 mm, while larger follicles had a progressive increase in FF losses that was not related to the tubing system. In Trial III, the number of GC and amount of RNA obtained were not affected (P > 0.05) by follicle size, but differed according to breed (615,054+/-58,122 vs 458,095+/-36,407 for Holstein and Gir, respectively; P < 0.05).

CONCLUSIONS

The adapted-OPU system can be successfully used for the in vivo collection of FF and GC from follicles of different diameters. This will enable further endocrine, cellular, and gene expression analyses.

Estradiol supports in vitro development of bovine early antral follicles

Antrum formation and estradiol (E2) secretion are specific features of oocyte and granulosa cell complexes (OGCs). This study investigates the effect of E2 on the in vitro development of bovine OGCs derived from early antral follicles as well as on the expression of genes in granulosa cells (GCs). The supplementation of culture medium with either E2 or androstenedione (A4) improved the in vitro development of OGCs and the nuclear maturation of enclosed oocytes. When OGCs were cultured in medium containing A4, developmentally competent OGCs secreted more E2 than OGCs that were not competent. In addition, fulvestrant inhibited the effect of both E2 and A4 on OGCs development. Comprehensive gene expression analysis using next-generation sequence technology was conducted for the following three types of GCs: i) GCs of OGCs cultured for 4 days with E2 (1 μg/ml; E2(+)), ii) GCs of OGCs cultured for 4 days without E2 (E2(−)) or iii) OGCs that formed clear antrum after 8 days of in vitro culture in medium containing E2 (1 μg/ml; AF group). GCs of the E2(+) group had a similar gene expression profile to the profile reported previously for the in vivo development of large follicles. This genetic profile included factors implicated in the up-regulation of E2 biosynthesis and down-regulation of cytoskeleton and extracellular matrices. In addition, a novel gene expression profile was found in the AF group. In conclusion, E2 impacts the gene expression profile of GCs to support the in vitro development of OGCs.

Steroid hormones content and proteomic analysis of canine follicular fluid during the preovulatory period

BACKGROUND

Follicular fluid contains substances involved in follicle activity, cell differentiation and oocyte maturation. Studies of its components may contribute to better understanding of the mechanisms underlying follicular development and oocyte quality. The canine species is characterized by several ovarian activity features that are not extensively described such as preovulatory luteinization, oocyte ovulated at the GV stage (prophase 1) and poly-oocytic follicles. In this study, we examined the hypothesis that the preovulatory LH surge is associated with changes in steroid and protein content of canine follicular fluid prior to ovulation.

METHODS

Follicular fluid samples were collected from canine ovaries during the preovulatory phase, before (pre-LH; n = 16 bitches) and after (post-LH; n = 16) the LH surge. Blood was simultaneously collected. Steroids were assayed by radioimmunoassay and proteomic analyses were carried out by 2D-PAGE and mass spectrometry.

RESULTS

The concentrations of 17beta-estradiol and progesterone at the pre-LH stage were 737.2 +/- 43.5 ng/ml and 2630.1 +/- 287.2 ng/ml in follicular fluid vs. 53 +/- 4.1 pg/ml and 3.9 +/- 0.3 ng/ml in plasma, respectively. At that stage, significant positive correlations between follicular size and intra-follicular steroid concentrations were recorded. After the LH peak, the intrafollicular concentration of 17beta-estradiol decreased significantly (48.3 +/- 4.4 ng/ml; p < 0.001), whereas that of progesterone increased (11690.2 +/- 693.6 ng/ml; p < 0.001). Plasmatic concentration of 17beta-estradiol was not modified (49 +/- 9.6 pg/ml) after the LH peak, but that of progesterone significantly increased (9.8 +/- 0.63 ng/ml).Proteomic analysis of canine follicular fluid identified 38 protein spots, corresponding to 21 proteins, some of which are known to play roles in the ovarian physiology. The comparison of 2D-PAGE patterns of follicular fluids from the pre- and post-LH stages demonstrated 3 differentially stained single spot or groups of spots. One of them was identified as complement factor B. A comparison of follicular fluid and plasma protein patterns demonstrated a group of 4 spots that were more concentrated in plasma than in follicular fluid, and a single spot specific to follicular fluid. These proteins were identified as gelsolin and clusterin, respectively.

CONCLUSION

Our results provide the first demonstration of size-related changes in the steroid concentrations in canine follicular fluid associated with the LH surge. 2D protein mapping allowed identification of several proteins that may play a role in follicle physiology and ovarian activity at the preovulatory stage. This may help in the future to explain and to better understand the species specificities that are described in dogs.

Gene expression of 11β-HSD and glucocorticoid receptor in the bovine (Bos taurus) follicle during follicular maturation and atresia: the role of follicular stimulating hormone

Glucocorticoids modulate ovarian function in cattle. However, their regulatory mechanisms have not been fully elucidated. In the present study, we examined gene expression of two glucocorticoid-metabolizing enzymes, a bidirectional 11β-HSD type 1 (11HSD1) and a dehydrogenase 11β-HSD type 2 (11HSD2), and glucocorticoid receptor (GR) in bovine follicles during follicular maturation and atresia. Granulosa cells (GCs) and theca interna layers (TIs) were harvested from follicles classified as small growing, dominant, preovulatory, early atretic and late atretic follicles. The expression levels of 11HSD1, 11HSD2 and GR mRNA were quantified by real-time PCR. In the healthy follicles, expression of 11HSD1 mRNA increased as follicles matured, both in GCs and TIs. A significant negative correlation was found between the concentration of cortisol in follicular fluid and the level of 11HSD1 mRNA in GCs. The expression of 11HSD2 and GR was either very low or largely unchanged during follicular maturation. In the atretic follicles, a drastic increase in the expression of 11HSD2 was observed both in GCs and TIs. To assess the effect of FSH on the expression of 11HSDs and GR, GCs were cultured with FSH (0-100 ng/ml) for up to 6 days. FSH increased 11HSD1 mRNA in a dose-dependent manner, but not 11HSD2, nor GR. Taken together, these results suggest that developmentally-regulated 11HSD1 plays a pivotal role in modulating the local glucocorticoid environment in maturing bovine follicles.