Morphological and functional characteristics of the dominant follicle and corpus luteum in cattle and their influence on ovarian function

Evidence and manipulation of O-GlcNAcylation in granulosa cells of bovine antral follicles†

Glucose is a preferred energy substrate for metabolism by bovine granulosa cells (GCs). O-linked N-acetylglucosaminylation (O-GlcNAcylation), is a product of glucose metabolism that occurs as the hexosamine biosynthesis pathway (HBP) shunts O-GlcNAc sugars to serine and threonine residues of proteins. O-GlcNAcylation through the HBP is considered a nutrient sensing mechanism that regulates many cellular processes. Yet little is known of its importance in GCs. Here, O-GlcNAcylation in GCs and its effects on GC proliferation were determined. Bovine ovaries from a slaughterhouse, staged to the mid-to-late estrous period were used. Follicular fluid and GCs were aspirated from small (3-5 mm) and large (>10 mm) antral follicles. Freshly isolated GCs of small follicles exhibited greater expression of O-GlcNAcylation and O-GlcNAc transferase (OGT) than large follicles. Less glucose and more lactate was detectable in the follicular fluid of small versus large follicles. Culture of GCs revealed that inhibition of the HBP via the glutamine fructose-6-phosphate aminotransferase inhibitor, DON (50 μM), impaired O-GlcNAcylation and GC proliferation, regardless of follicle size. Direct inhibition of O-GlcNAcylation via the OGT inhibitor, OSMI-1 (50 μM), also prevented proliferation, but only in GCs of small follicles. Augmentation of O-GlcNAcylation via the O-GlcNAcase inhibitor, Thiamet-G (2.5 μM), had no effect on GC proliferation, regardless of follicle size. The results indicate GCs of bovine antral follicles undergo O-GlcNAcylation, and O-GlcNAcylation is associated with alterations of glucose and lactate in follicular fluid. Disruption of O-GlcNAcylation impairs GC proliferation. Thus, the HBP via O-GlcNAcylation constitutes a plausible nutrient-sensing pathway influencing bovine GC function and follicular growth.

Applicability of Hyaluronic Acid-Alginate Hydrogel and Ovarian Cells for In Vitro Development of Mouse Preantral Follicles

Objective

In the present study, the applicability of hyaluronic acid-alginate (HAA) hydrogel and ovarian cells (OCs) for the culture of mouse ovarian follicles were investigated and compared with those of alginate (ALG) and fibrin-alginate (FA) hydrogels.

Materials and Methods

In the first step of this experimental study, mechanically isolated preantral follicles from the ovaries of two-week-old mice were encapsulated in the absence or presence of OCs in ALG, HAA, and FA hydrogels and cultured for 14 days. The morphology, diameter, survival and antrum formation rates of the follicles and the maturation and quality of the oocytes were evaluated during culture. In the second step, preantral follicles were cultured similar to the first step, but for 13 days, and their gene expressions and hormonal secretion were assessed on the last day of culture.

Results

In the absence of OCs, higher numbers of ALG- and HAA-encapsulated follicles reached the antral stage compared to FA-encapsulated follicles (P<0.05). However, a higher percentage of HAA-developed oocytes resumed meiosis up to the germinal vesicle breakdown (GVBD)/metaphase II (MII) stages in comparison with ALG-developed oocytes (P<0.05). HAA-encapsulated follicles had significant overexpression of most of the growth and differentiation genes, and secreted higher levels of estradiol (E2) compared to ALG- and FA-encapsulated follicles (P<0.05). The co-culture condition increased the diameter of ALG-encapsulated follicles on day 13 of culture (P<0.05). It also increased the survival and maturation rates of ALG- and FA-encapsulated follicles, respectively (P<0.05). The co-culture condition improved cortical granule distribution in all groups, increased E2 and progesterone (P4) secretions in the ALG and FA groups, and androstenedione (A4) secretion in the FA group (P<0.05).

Conclusion

The present study results show that HAA hydrogel is a promising hydrogel for follicle culture. OCs utilization could ameliorate the culture conditions regardless of the type of hydrogel.

MicroRNA-424/503 cluster members regulate bovine granulosa cell proliferation and cell cycle progression by targeting SMAD7 gene through activin signalling pathway

BACKGROUND

The granulosa cells are indispensable for follicular development and its function is orchestrated by several genes, which in turn posttranscriptionally regulated by microRNAs (miRNA). In our previous study, the miRRNA-424/503 cluster was found to be highly abundant in bovine granulosa cells (bGCs) of preovulatory dominant follicle compared to subordinate counterpart at day 19 of the bovine estrous cycle. Other study also indicated the involvement of miR-424/503 cluster in tumour cell resistance to apoptosis suggesting this miRNA cluster may involve in cell survival. However, the role of miR-424/503 cluster in granulosa cell function remains elusive Therefore, this study aimed to investigate the role of miRNA-424/503 cluster in bGCs function using microRNA gain- and loss-of-function approaches.

RESULTS

The role of miR-424/503 cluster members in granulosa cell function was investigated by overexpressing or inhibiting its activity in vitro cultured granulosa cells using miR-424/503 mimic or inhibitor, respectively. Luciferase reporter assay showed that SMAD7 and ACVR2A are the direct targets of the miRNA-424/503 cluster members. In line with this, overexpression of miRNA-424/503 cluster members using its mimic and inhibition of its activity by its inhibitor reduced and increased, respectively the expression of SMAD7 and ACVR2A. Furthermore, flow cytometric analysis indicated that overexpression of miRNA-424/503 cluster members enhanced bGCs proliferation by promoting G1- to S- phase cell cycle transition. Modulation of miRNA-424/503 cluster members tended to increase phosphorylation of SMAD2/3 in the Activin signalling pathway. Moreover, sequence specific knockdown of SMAD7, the target gene of miRNA-424/503 cluster members, using small interfering RNA also revealed similar phenotypic and molecular alterations observed when miRNA-424/503 cluster members were overexpressed. Similarly, to get more insight about the role of miRNA-424/503 cluster members in activin signalling pathway, granulosa cells were treated with activin A. Activin A treatment increased cell proliferation and downregulation of both miRNA-424/503 members and its target gene, indicated the presence of negative feedback loop between activin A and the expression of miRNA-424/503.

CONCLUSION

This study suggests that the miRNA-424/503 cluster members are involved in regulating bovine granulosa cell proliferation and cell cycle progression. Further, miRNA-424/503 cluster members target the SMAD7 and ACVR2A genes which are involved in the activin signalling pathway.

Comparative analysis of granulosa cell gene expression in association with oocyte competence in FSH-stimulated Holstein cows

Ovarian stimulation with exogenous FSH followed by FSH withdrawal or ‘coasting’ is an effective means of increasing the number of oocytes obtainable for the in vitro production of cattle embryos. However, the quality of the oocytes thus obtained varies considerably from one cow to the next. The aim of the present study was to gain a better understanding of the follicular conditions associated with low oocyte developmental competence. Granulosa cells from 94 Holstein cows in a commercial embryo production facility were collected following ovarian stimulation and coasting. Microarray analysis showed 120 genes expressed with a differential of at least 1.5 when comparing donors of mostly competent with donors of mostly incompetent oocytes. Using ingenuity pathway analysis, we revealed the main biological functions and potential upstream regulators that distinguish donors of mostly incompetent oocytes. These are involved in cell proliferation, apoptosis, lipid metabolism, retinol availability and insulin signalling. In summary, we demonstrated that differences in follicle maturity at collection could explain differences in oocyte competence associated with individual animals. We also revealed deficiencies in lipid metabolism and retinol signalling in granulosa cells from donors of mostly incompetent oocytes.

Global gene expression in granulosa cells of growing, plateau and atretic dominant follicles in cattle

BACKGROUND

The physiological state of the dominant follicle is important as it may be linked to the competence of the oocyte within. The objective of this study was to analyze, by transcriptomic analysis, the changes occurring in granulosa cells from dominant follicles at different phases of follicular growth.

METHODS

Granulosa cells were collected from slaughterhouse dairy cattle follicles with a diameter greater than 9 mm, and were classified at different phases of follicle growth based on flow cytometry profiles of DNA content after staining with propidium iodide. Three phases were identified based on the proportion of cells in -G1 (less than 2n DNA), G0-G1 (2n DNA) or S-M (more than 2n DNA) and follicles were thus allocated to the growing, plateau or atresia group. Between group analysis (BGA) showed clear segregation of the three groups, and the groups were contrasted against each other in a loop design to identify differently expressed genes. Ingenuity Pathway Analysis (IPA) was used to identify the functions and upstream regulators associated with the observed differently expressed genes.

RESULTS

Major differences were observed between the growth phases. Granulosa cells from follicles in the plateau phase had increased expression of TYRO3 and downregulation of JAM2 compared to growing follicles, supporting the idea of a shift from proliferation to differentiation. On the other hand, genes regulating the response to oxidative stress (VNN1) and angiogenesis (ANGPT2) were upregulated in granulosa cells from atretic follicles. While the predicted activated functions in cells at the plateau stage compared to cells at the growing stage included synthesis and transport of molecules, the predictions for atretic follicles relative to plateau ones included an increase in apoptosis and cell death.

CONCLUSION

Consistent with previous studies, these observations allowed us to match the presence of specific gene transcripts to a particular physiological status and consequently to classify follicles. The results also demonstrated that the plateau phase is not a simple 'in between' status between growth and atresia, as several characteristics are unique to this stage.

Ischemia/reperfusion injury in liver resection: a review of preconditioning methods

Ischemic preconditioning is one of the therapeutic interventions aiming at preventing ischemia/reperfusion-related injury. Numerous experimental studies and a few clinical series have shown that during liver resections, ischemic preconditioning is a promising strategy for optimizing the postoperative outcome. Moreover, various types of pharmacological intervention as well as different types of preconditioning, such as remote preconditioning, the use of heat shock, and hyperbaric oxygen, have been developed to attenuate the functional impairment accompanying ischemia/reperfusion injury. This review summarizes the various forms of preconditioning, thus suggesting that close cooperation between surgeons and anesthesiologists paves the way to apply novel strategies to improve the outcome of liver resection.

Hormonal, biochemical, and hematological profiles in female camels (Camelus dromedarius) affected with reproductive disorders

The aim of this study was to assess the blood profiles in female camels affected with common reproductive disorders. Estradiol-17beta (E(2)), progesterone (P(4)), thyroxin (T(4)), zinc (Zn), copper (Cu), calcium (Ca), phosphorus (P), magnesium (Mg), cholesterol, glucose, triglycerides, total protein, albumin, globulin, hematocrite, and total and differential white blood cell counts (WBC) were determined in blood of female camels affected with endometritis (n=15), vaginal adhesions (n=15), and ovarian cysts (n=15). Normal cyclic animals were used as controls (n=15). Diagnosis of reproductive disorders was based on transrectal palpation, ultrasonographic examination, and exploration of the vagina. Increased WBC counts (P=0.03) and a tendency for neutrophelia (P=0.05) were noted in female camels with vaginal adhesions. These animals were also characterized by having higher concentration of serum P(4) (P=0.0001), T(4) (P=0.001) and total protein (P=0.007), in comparison with female camels with endometritis, ovarian cysts, or controls. Animals having ovarian cysts with thin walls and homogenous hypoechogenic contents had greater serum E(2) (P=0.001) and P(4) (P=0.0001) than those having ovarian cysts with thick walls and non-homogenous echogenic contents. Animals with endometritis, vaginal adhesions, and ovarian cysts revealed lower serum Zn concentration than that of control group (P=0.003). Other blood parameters did not differ significantly compared to controls. In conclusion, this is the first report characterizing blood constituents in female camels with various reproductive disorders. These profiles may be valuable in clarifying the etio-pathogenesis of these disorders.

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

A simple and clear means to identify the physiological status of follicles is essential for study of follicular biology. In the present study, we verified a novel classification procedure based on analysis of the follicular population and glucose concentration in follicular fluid (FF) as an alternative method to classify bovine follicles. Paired ovaries were collected from heifers, and the number of follicles and stage of the CL were recorded. Follicles were initially divided into the following 3 groups according to diameter and the ratio of E2 and P4 (E/P): E2 active (E-A: E/P>or=1), E2 inactive (E-I: E/P<1, >or=8.5 mm) and small follicles (E/P<1, <8.5 mm). E-A follicles were easily identified as E2-rich dominant follicles and were further classified according to diameter and stage of the CL as early dominant (EDF: <8.5 mm), dominant (DF: >or=8.5 mm, stages I-III) or preovulatory follicles (POF: >or=8.5 mm, stage IV). E-I follicles were classified as follows based on the status of the accompanying follicles: early atretic (EAF: without an E-A follicle), mid-atretic (MAF: with an EDF or DF) and late atretic follicles (LAF: with an EAF or POF). The follicular P4 concentrations of the MAF and LAF were significantly higher compared with that of the EAF, while follicular glucose concentration of the LAF was lower compared with those of EAF and MAF, indicating that this classification can be used to distinguish early atretic follicles from more advanced atretic follicles. Small follicles were classified as growing (GF: without E-A follicles) and suppressed small follicles (SSF: with E-A follicles). The SSF was easily identifiable by this procedure, but some GF populations likely contained SSF. To identify true GF, the ratio of E2 in the GF and accompanying EAF may be used. In conclusion, analysis of the follicular population in conjunction with biochemical indices such as steroid and glucose concentrations in FF provides a simple and accurate means of classifying bovine follicles.

The mouse follicle microenvironment regulates antrum formation and steroid production: alterations in gene expression profiles

Folliculogenesis is a coordinated process, and the genes that regulate development are difficult to investigate in vivo. In vitro culture systems permit the assessment of individual follicles during development, thereby enabling gene expression patterns to be monitored during follicle development. Mouse multilayered secondary follicles (150-180 microm in diameter) were cultured in three-dimensional matrices of varying physical properties for up to 8 days. During this period of follicle growth in vitro, antrum formation and steroid production were monitored, and mRNA was isolated. The expression levels of genes (Star, Cyp11a1, Cyp17a1, Hsd3b1, Cyp19a1, Fshr, Lhcgr, Aqp7, Aqp8, Aqp9, and Hif1a) were measured and correlated to follicle developmental status. Follicles that developed an antrum and produced appropriate levels of estrogen and progesterone had unchanging expression of Star, Aqp7, Aqp8, and Hif1a and a 34-fold increase in Cyp19a1 expression at Day 8 of culture and had elevated Lhcgr at Days 6 and 8 of culture. Follicles that were healthy but did not form an antrum or produce appropriate levels of steroids, however, demonstrated increasing levels of Star, Aqp7, Aqp8, and Hif1a and a 15-fold increase in Cyp19a1 at Day 8 of culture, and Lhcgr levels were not elevated until Day 8 of culture. To our knowledge, this study provides the first temporal analysis of gene expression using individual culture in alginate hydrogels that correlates growth and steroidogenesis during follicle development and identifies expression patterns in healthy follicles and in developmentally disadvantaged follicles.

Improved superovulatory response in beef cattle following ovarian follicular ablation using a simplified transvaginal device

The influence of the timing for the ablation of dominant follicle(s) prior to superovulatory treatment, and its effect on ovarian follicular growth and embryo yield, still remain elusive in cattle. The present study was designed to evaluate the effects of: (1) the day of the estrous cycle, at mid-diestrus, for the onset of superstimulation of follicular development, (2) the presence or absence of large ovarian follicles (ovary status) and (3) the time of follicular ablation, in hours, prior to the superovulatory treatment, on the superovulatory response in cattle. From a total of 244 superovulatory treatments and embryo collections in nulliparous and multiparous females, 76 were conducted after follicular ablation using a simplified transvaginal puncture cannula. Results from the present study indicated that the presence of large palpable follicle(s) at the onset of superstimulation of follicular development markedly reduced the superovulatory response. In addition, follicular ablation at 0 h or at 24 h prior to the onset of the superstimulation treatment significantly increased the number of total viable embryos. However, superovulatory responses were not affected by the day of the estrous cycle for the onset of follicular superstimulation and by the animal category (heifers or cows). In conclusion, the ablation of palpable follicle(s) 24 h or immediately prior to the onset of gonadotropin treatment, from days 8 to 12 of the estrous cycle (day 0, behavioral estrus), increased the total number of transferable embryos per flushing in cattle.

Seasonal variation of the ovarian follicular dynamics and luteal functions of sheep in the subtropics

This study was undertaken to describe the development of individual follicles and corpora lutea (CL) in Ossimi ewe lambs at different seasons of the year in the subtropics. Seven ewe lambs underwent daily ultrasonographic examination for 20 interovulatory periods (IOP) during spring, winter and autumn. Ovarian follicles >or=2 mm and corpora lutea were counted and measured. Blood samples were taken for progesterone (P(4)) analysis. All ewe lambs included, but one, were cyclic in all seasons studied. Three (65%) and two (35%) follicular waves were detected per estrous cycle. None of the characteristics of the large follicles was affected by season. Follicles >or=2 mm in diameter were significantly higher in winter. The CL developed slowly in autumn. Serum P(4) level was higher in autumn. Double ovulation was observed only in autumn. The data demonstrated that Ossimi sheep in the subtropics were cyclic in most seasons of the year. Season affected mainly the luteal functions with little influences on the follicular characteristics.

Cholesterol side-chain cleavage cytochrome P450 and 3beta-hydroxysteroid dehydrogenase expression and the concentrations of steroid hormones in the follicular fluids of different phenotypes of healthy and atretic bovine ovarian follicles

Bovine ovarian antral follicles exhibit either one or the other of two patterns of granulosa cell death in atresia. Death can commence either from the antrum and progress toward the basal lamina (antral atresia) or the converse (basal atresia). In basal atresia, the remaining live antrally situated cells appeared to continue maturing. Beyond that, little is known about these distinct patterns of atresia. Healthy (nonatretic) follicles also exhibit either one or the other of two patterns of granulosa cell shape, follicular basal lamina ultrastructure or location of younger cells within the membrana granulosa. To examine these different phenotypes, the expression of the steroidogenic enzymes cholesterol side-chain cleavage cytochrome P450 (SCC) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in granulosa cells and concentrations of steroid hormones in follicular fluid were measured in individual histologically classified bovine antral follicles. Healthy follicles first expressed SCC and 3beta-HSD in granulosa cells only when the follicles reached an approximate threshold of 10 mm in diameter. The pattern of expression in antral atretic follicles was the same as healthy follicles. Basal atretic follicles were all <5 mm. In these, the surviving antral granulosa cells expressed SCC and 3beta-HSD. In examining follicles of 3-5 mm, basal atretic follicles were found to have substantially elevated progesterone (P < 0.001) and decreased androstenedione and testosterone compared to healthy and antral atretic follicles. Estradiol was highest in the large healthy follicles, lower in the small healthy follicles, lower still in the antral atretic follicles, and lowest in the basal atretic follicles. Our findings have two major implications. First, the traditional method of identifying atretic follicles by measurement of steroid hormone concentrations may be less valid with small bovine follicles. Second, features of the two forms of follicular atresia are so different as to imply different mechanisms of initiation and regulation.

Ovarian follicular dynamics in buffalo cows (Bubalus bubalis)

Follicular growth in Egyptian buffalo cows was monitored using genital tracts from 200 buffalo cows collected immediately after slaughter. According to the morphological appearance of the corpus luteum (CL), the corresponding oestrous cycle was divided into four stages: A (days 1-4), B (days 5-10), C (days 11-17) and D (days 18-21). Within these stages the follicular population on the ovaries was evaluated and the dominant follicle (DF) determined in all recovered ovaries. The functional status of the DF and the largest sub-dominant follicles was examined by histological examination in 31 cases, and Radio Immunoassay (RIA) analyses for estradiol-17beta (E2) and progesterone (P4) was performed in the follicular fluid in 23 of the DF. The results showed that DFs changed their endocrine character within the stages of the oestrous cycle. The DFs between days 5 and 10 were functionally active (E2-dominant; non-atretic) in most of the cases. Between days 11 and day 17 half of the DFs became functionally inactive (P4-dominant; atretic). At days 18-21 all of the DF became functionally active and non-atretic. In the specimens that carried two large follicles one of them was regularly atretic and P4-dominant whereas the other was non-atretic and E2-dominant. Between days 18 and 21 all ovaries examined showed at least one large follicle. These findings suggest that in most of the cases follicular dynamics occurs in two wave-like patterns in the Egyptian buffalo cows.