Thrombospondin and vascular endothelial growth factor are cyclically expressed in an inverse pattern during bovine ovarian follicle development

Integrative proteomic and transcriptomic analysis in the female goat ovary to explore the onset of puberty

Puberty is considered a prerequisite for affecting reproductive performance and productivity. Little was known about molecular changes in pubertal goat ovaries. Therefore, we measured and performed a correlation analysis of the mRNA and proteins changes in the pre-pubertal and pubertal goat ovaries. The results showed that only six differentially expressed genes and differentially abundant proteins out of 18,139 genes and 7550 proteins quantified had significant correlations. CNTN2 and THBS1, discovered in the mRNA-mRNA interaction network, probably participated in pubertal and reproductive regulation by influencing GnRH receptor signals, follicular development, and ovulation. The predicted core transcription factors may either promote or inhibit the expression of reproductive genes and act synergistically to maintain normal reproductive function in animals. The interaction between PKM and TIMP3 with other proteins may impact animal puberty through energy metabolism and ovarian hormone secretion. Pathway enrichment analyses revealed that the co-associated key pathways between ovarian genes and proteins at puberty included calcium signalling pathway and olfactory transduction. These pathways were associated with gonadotropin-releasing hormone synthesis and secretion, signal transmission, and cell proliferation. In summary, these results enriched the potential molecules and signalling pathways that affect puberty and provided new insights for regulating and promoting the onset of puberty. SIGNIFICANCE: This study conducted the first transcriptomic and proteomic correlation analysis of pre-pubertal and pubertal goat ovaries and identified six significantly correlated molecules at both the gene and protein levels. Meanwhile, we were drawn to several molecules and signalling pathways that may play a regulatory role in the onset of puberty and reproduction by influencing reproductive-related gene expression, GnRH receptor signals, energy metabolism, ovarian hormone secretion, follicular development, and ovulation. This information contributed to identify potential biomarkers in pubertal goat ovaries, which was vital for predicting the onset of puberty and improving livestock performance.

Hormone regulation of thrombospondin-1 mRNA in porcine granulosa cells in vitro

Thrombospondin-1 (THBS1) is involved in the process of angiogenesis and is down-regulated by insulin-like growth factor 1 (IGF1) in porcine granulosa cells (GC), but what other hormones regulate GC THBS1 and its role in follicular growth is unclear. Thus, six experiments were conducted to determine the influence of other hormones on THBS1 gene expression in porcine GC, and to determine if THBS1 mRNA changes during follicular development. For Exp. 1-5, small (1-5 mm) follicles from ovaries of abattoir gilts were aspirated, GC collected and treated with FSH, IGF1, fibroblast growth factor 9 (FGF9), Sonic hedgehog (SHH), estradiol, cortisol, and/or prostaglandin E2 (PGE2). FSH, IGF1 and FGF9 each decreased (P < 0.05) THBS1 mRNA abundance. Alone, PGE2 increased (P < 0.05) THBS1 mRNA abundance. PGE2 significantly attenuated the FSH-induced inhibition of THBS1 mRNA expression. Estradiol, cortisol, and SHH had no effect on THBS1 mRNA abundance. In Exp. 6, small (1-3 mm), medium (4-6 mm) and large (7-14 mm) follicles were aspirated to measure abundance of THBS1 mRNA in GC which did not differ (P > 0.10) between small and medium-sized follicles but was threefold greater (P < 0.05) in large compared to small or medium follicles. We hypothesize that the inhibitory effects of FSH, IGF1 and FGF9 on the antiangiogenic gene THBS1 could contribute to promoting angiogenesis in the developing follicle, while stimulation of THBS1 mRNA by PGE2 may help reduce angiogenesis during the preovulatory period when PGE2 and THBS1 mRNA are at their greatest levels.

Delta-9-tetrahydrocannabinol increases vascular endothelial growth factor (VEGF) secretion through a cyclooxygenase-dependent mechanism in rat granulosa cells

While the effects of delta-9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, have been studied extensively in the central nervous system, there is limited knowledge about its effects on the female reproductive system. The aim of this study was to assess the effect of THC on the expression and secretion of the angiogenic factor vascular endothelial growth factor (VEGF) in the ovary, and to determine if these effects were mediated by prostaglandins. Spontaneously immortalized rat granulosa cells (SIGCs) were exposed to THC for 24hours. Gene expression, proliferation and TNFα-induced apoptosis were evaluated in the cells and concentrations of VEGF and prostaglandin E2 (PGE₂), a known regulator of VEGF production, were determined in the media. To evaluate the role of the prostanoid pathway, cells were pre-treated with cyclooxygenase (COX) inhibitors prior to THC exposure. THC-exposed SIGCs had a significant increase in VEGF and PGE₂ secretion, along with an increase in proliferation and cell survival when challenged with an apoptosis-inducing factor. Pre-treatment with COX inhibitors reversed the THC-induced increase in both PGE₂ and VEGF secretion. Alterations in granulosa cell function, such as the ones observed after THC exposure, may impact essential ovarian processes including folliculogenesis and ovulation, which could in turn affect female reproductive health and fertility. With the ongoing increase in cannabis use and potency, further study on the impact of cannabis and its constituents on female reproductive health is required.

The effects of polycyclic aromatic compounds (PACs) on mammalian ovarian function

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Toxicity of polycyclic aromatic compounds (PACs) is limited to a subset of PACs.

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Exposure to these compounds impact major processes necessary for ovarian function.

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PAC exposure causes follicle loss and aberrant steroid production and angiogenesis.

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PAC exposure may increase the risk for impaired fertility and ovarian pathologies.

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The study of PACs as ovarian toxicants should include additional compounds.

Polycyclic aromatic compounds (PACs) are a broad class of contaminants ubiquitously present in the environment due to natural and anthropogenic activities. With increasing industrialization and reliance on petroleum worldwide, PACs are increasingly being detected in different environmental compartments. Previous studies have shown that PACs possess endocrine disruptive properties as these compounds often interfere with hormone signaling and function. In females, the ovary is largely responsible for regulating reproductive and endocrine function and thus, serves as a primary target for PAC-mediated toxicity. Perturbations in the signaling pathways that mediate ovarian folliculogenesis, steroidogenesis and angiogenesis can lead to adverse reproductive outcomes including polycystic ovary syndrome, premature ovarian insufficiency, and infertility. To date, the impact of PACs on ovarian function has focused predominantly on polycyclic aromatic hydrocarbons like benzo(a)pyrene, 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene. However, investigation into the impact of substituted PACs including halogenated, heterocyclic, and alkylated PACs on mammalian reproduction has been largely overlooked despite the fact that these compounds are found in higher abundance in free-ranging wildlife. This review aims to discuss current literature on the effects of PACs on the ovary in mammals, with a particular focus on folliculogenesis, steroidogenesis and angiogenesis, which are key processes necessary for proper ovarian functions.

Potential of thrombospondin-1 in treatment of polycystic ovary syndrome rat model: a preliminary study

OBJECTIVE

Polycystic ovary syndrome (PCOS) is a common gynecological endocrine disease in reproductive women, and the endocrine levels are also affected by diseases. The aim of this study was to determine the effect of thrombospondin-1 (TSP-1) on PCOS rat model.

METHODS

We established the PCOS rat model, the serum hormones including TSP-1 expression were determined and morphological characteristics were investigated to evaluate the model. These above endocrine and morphological features were investigated again to evaluate the effect of TSP-1 treatment.

RESULTS

In the PCOS model group, the serum hormones change (higher luteinizing hormone, testosterone and estrogen) and decreased TSP-1 expression levels were found compared with the control group. Besides, the morphological characteristics of PCOS were also observed in the model group. After TSP-1 treatment, the higher TSP-1, ANGPT2, PDGFB and PDGFD expression levels, the lower LH and T levels, decreased vessel density as well as VEGFA and ANGPT1 expression levels were found compared with the control group, and the ovary morphological changes were also observed in the TSP-1 experimental group.

CONCLUSIONS

TSP-1 delivery system might be an alternative therapy for PCOS treatment.

Regulation of Female Folliculogenesis by Tsp1a in Nile Tilapia (Oreochromis niloticus)

TSP1 was reported to be involved in multiple biological processes including the activation of TGF-β signaling pathways and the regulation of angiogenesis during wound repair and tumor growth, while its role in ovarian folliculogenesis remains to be elucidated. In the present study, Tsp1a was found to be expressed in the oogonia and granulosa cells of phase I to phase IV follicles in the ovaries of Nile tilapia by immunofluorescence. tsp1a homozygous mutants were generated by CRISPR/Cas9. Mutation of tsp1a resulted in increased oogonia, reduced secondary growth follicles and delayed ovary development. Expression of the cell proliferation marker PCNA was significantly up-regulated in the oogonia of the mutant ovaries. Furthermore, transcriptomic analysis revealed that expressions of DNA replication related genes were significantly up-regulated, while cAMP and MAPK signaling pathway genes which inhibit cell proliferation and promote cell differentiation were significantly down-regulated. In addition, aromatase (Cyp19a1a) expression and serum 17β-estradiol (E2) concentration were significantly decreased in the mutants. These results indicated that lacking tsp1a resulted in increased proliferation and inhibited differentiation of oogonia, which in turn, resulted in increased oogonia, reduced secondary growth follicles and decreased E2. Taken together, our results indicated that tsp1a was essential for ovarian folliculogenesis in Nile tilapia.

FSH promotes the proliferation of sheep granulosa cells by inhibiting the expression of TSP1

Thrombospondin (TSP1) plays an important role as an antiangiogenic factor in the reproductive system of female mammals. However, its expression and function in sheep are still unclear. In the present research, the Altay sheep (a native Chinese breed) was used to analyze the expression of TSP1 in the ovary and its potential function in granulosa cells. TSP1 was widely expressed in most tissues, as shown by qPCR. In the ovary, TSP1 mRNA expression decreased during follicular to luteal growth. The TSP1 protein was expressed in a wide variety of follicles of different diameters and localized to the cytoplasm and nucleus of granulosa cells. In in vitro studies, follicle-stimulating hormone (FSH) significantly inhibited the expression of TSP1 in sheep granulosa cells. Functionally, FSH- and TSP1-specific siRNAs can promote the proliferation of sheep granulosa cells. In contrast, TSP1 mimetic peptide, ABT510, offsets the proliferation of sheep granulosa cells. Different signaling pathway inhibitors all promoted FSH-inhibited TSP1 expression, but each inhibitor had different effects on TSP1. Among them, the PI3K and ERK pathway inhibitors significantly promoted TSP1 expression and inhibited the proliferation of sheep granulosa cells.

Newly Identified Regulators of Ovarian Folliculogenesis and Ovulation

Each follicle represents the basic functional unit of the ovary. From its very initial stage of development, the follicle consists of an oocyte surrounded by somatic cells. The oocyte grows and matures to become fertilizable and the somatic cells proliferate and differentiate into the major suppliers of steroid sex hormones as well as generators of other local regulators. The process by which a follicle forms, proceeds through several growing stages, develops to eventually release the mature oocyte, and turns into a corpus luteum (CL) is known as “folliculogenesis”. The task of this review is to define the different stages of folliculogenesis culminating at ovulation and CL formation, and to summarize the most recent information regarding the newly identified factors that regulate the specific stages of this highly intricated process. This information comprises of either novel regulators involved in ovarian biology, such as Ube2i, Phoenixin/GPR73, C1QTNF, and α-SNAP, or recently identified members of signaling pathways previously reported in this context, namely PKB/Akt, HIPPO, and Notch.

Hypothermic machine perfusion after static cold storage improves ovarian function in rat ovarian tissue transplantation

OBJECTIVE

This study was performed to investigate the effect of hypothermic machine perfusion (HMP) after cold storage (CS) on ovarian transplantation.

METHODS

Rats aged 8-10 weeks were used as the donors and recipients for allotransplantation. Eighteen donor rats were divided into three groups: the fresh control (n = 6), cold storage (CS; n = 6), and hypothermic machine perfusion (HMP; n = 6) groups. The preservation solution contained Dulbecco's modified Eagle's medium/Ham's F-12 (1:1, v/v), 10% fetal bovine serum, 10 μg/ml insulin, 10 μg/ml transferrin, and 50 mIU/ml follicle-stimulating hormone (FSH). The donor ovaries in the CS and HMP groups were excised and then respectively subjected to 4 h of CS and 2 h of CS combined with 2 h of HMP at 4 °C, and then transplanted beneath the recipient's left renal capsule. At 7 days after transplantation, the ovaries were removed and blood samples were obtained for histological analysis, immunohistochemistry for CD31 and Ki67, and serum anti-Mullerian hormone (AMH) level estimation.

RESULTS

The HMP group showed significant increases in serum AMH and CD31-positive areas when compared to these values in the CS group (P < 0.05). However, no differences were noted in the total number of follicles or the Ki67-positive areas among the three groups.

CONCLUSION

Hypothermic machine perfusion after static cold storage is more effective than static CS alone for the short-term preservation of whole ovaries during transport. Whole ovary transplantation with vascular pedicle is our future research direction. Graphical Abstract The black rectangle in the figure shows the place where ligation and disconnection are required, the black dotted line shows the place where vascular forceps are used to clamp, and the black circle shows the place where the cannula is inserted This diagram was made for reviewers to understand more intuitively how my hypothermia mechanical perfusion model was built. Organs obtained in this way can be used for subsequent perfusion and whole ovarian transplantation.

Hormonal regulation of vascular endothelial growth factor A (VEGFA) gene expression in granulosa and theca cells of cattle1

Vascular endothelial growth factor A (VEGFA) stimulates angiogenesis and is associated with increased vascularity in ovarian follicles of cattle. The objectives of this study were to investigate the developmental and hormonal regulation of VEGFA expression in ovarian granulosa and theca cells (TC) of cattle. Bovine ovaries were collected from a local slaughterhouse and granulosa cells (GC) and TC were collected from small (SM; 1 to 5 mm) and large (LG; 8 to 20 mm) follicles. Cells were collected fresh or cultured in serum-free medium and treated with various factors that regulate angiogenesis and follicular development. RNA was collected for analysis of VEGFA mRNA abundance via quantitative PCR. In SM-follicle GC (SMGC), prostaglandin E2 (PGE2) and FSH decreased (P < 0.05) VEGFA mRNA abundance by 30 to 46%, whereas in LG-follicle GC (LGGC), PGE2 and FSH were without effect (P > 0.10). In SMGC, dihydrotestosterone (DHT), sonic hedgehog (SHH), and growth differentiation factor-9 (GDF9) decreased (P < 0.05) VEGFA expression by 30 to 40%. Fibroblast growth factor-9 (FGF9) and estradiol (E2) were without effect (P > 0.10) on VEGFA mRNA in both SMGC and LGGC, whereas progesterone increased (P < 0.05) VEGFA mRNA in LGGC but had no effect in LGTC. Bone morphogenetic protein-4 (BMP4), LH, and FGF9 increased (P < 0.05) abundance of VEGFA mRNA by 1.5- to 1.9-fold in LGTC. Insulin-like growth factor-1 (IGF1) was without effect (P > 0.10) on VEGFA mRNA in both TC and GC. An E2F transcription factor inhibitor, HLM0064741 (E2Fi), dramatically (i.e., 8- to 13-fold) stimulated (P < 0.01) the expression of VEGFA mRNA expression in both SMGC and LGTC. Abundance of VEGFA mRNA was greater (P < 0.05) in LGGC and SMGC than in LGTC. Also, SMTC had greater (P < 0.05) abundance of VEGFA mRNA than LGTC. In conclusion, VEGFA mRNA abundance was greater in GC than TC, and VEGFA expression decreased in TC during follicle development. Some treatments either suppressed, stimulated, or had no effect on VEGFA expression depending on the cell type. The inhibition of E2F transcription factors had the greatest stimulatory effect of all treatments evaluated, and thus, E2Fs may play an important role in regulating angiogenesis during follicle growth in cattle.

MiR-222 inhibits apoptosis in porcine follicular granulosa cells by targeting the THBS1 gene

Apoptosis of granulosa cells affects follicular atresia and reproduction and is regulated by miRNAs and the expression of certain genes. For the present study, we investigated the regulatory relationship between microRNA-222 (miR-222) and THBS1 in porcine follicular granulosa cells (pGCs) and its effects on apoptosis to provide empirical data for developing methods to improve pig fecundity. Results revealed that miR-222 promotes the proliferation of pGCs. MiRNA mimics and luciferase reporter assays revealed that miR-222 functions as an anti-apoptotic factor in pGCs. MiR-222 mimics in pGCs result in the upregulation of the anti-apoptotic BCL-2 gene, down-regulation of the proapoptotic caspase-3 gene, and inhibition of apoptosis. MiR-222 inhibitors reduced BCL-2 and had no significant effect on caspase-3. MiR-222 mimics promoted estrogen levels. Inhibition of THBS1 inhibited pGC apoptosis. Transfection of THBS1-siRNA reduced the proapoptotic BAX gene. MiR-222 can directly target the 3'-untranslated region of the THBS1 gene. MiR-222 mimics suppressed THBS1 mRNA and proteins, but these were upregulated by the miR-222 inhibitor. Transfection of THBS1-siRNA resulted in the inhibition of the miR-222 inhibitor, which suggests that miR-222 inhibits pGC apoptosis by targeting THBS1. These findings suggest that miR-222 and THBS1 play important roles in follicular atresia, ovarian development, and female reproduction.

Ovulation: Parallels With Inflammatory Processes

The midcycle surge of LH sets in motion interconnected networks of signaling cascades to bring about rupture of the follicle and release of the oocyte during ovulation. Many mediators of these LH-induced signaling cascades are associated with inflammation, leading to the postulate that ovulation is similar to an inflammatory response. First responders to the LH surge are granulosa and theca cells, which produce steroids, prostaglandins, chemokines, and cytokines, which are also mediators of inflammatory processes. These mediators, in turn, activate both nonimmune ovarian cells as well as resident immune cells within the ovary; additional immune cells are also attracted to the ovary. Collectively, these cells regulate proteolytic pathways to reorganize the follicular stroma, disrupt the granulosa cell basal lamina, and facilitate invasion of vascular endothelial cells. LH-induced mediators initiate cumulus expansion and cumulus oocyte complex detachment, whereas the follicular apex undergoes extensive extracellular matrix remodeling and a loss of the surface epithelium. The remainder of the follicle undergoes rapid angiogenesis and functional differentiation of granulosa and theca cells. Ultimately, these functional and structural changes culminate in follicular rupture and oocyte release. Throughout the ovulatory process, the importance of inflammatory responses is highlighted by the commonalities and similarities between many of these events associated with ovulation and inflammation. However, ovulation includes processes that are distinct from inflammation, such as regulation of steroid action, oocyte maturation, and the eventual release of the oocyte. This review focuses on the commonalities between inflammatory responses and the process of ovulation.

Application of transcutaneous carbon dioxide improves capillary regression of skeletal muscle in hyperglycemia

The purpose of the present study was to determine the effects of transcutaneous CO2 application on the blood flow and capillary architecture of the soleus muscle in rats with streptozotocin (STZ)-induced hyperglycemia. Wistar rats were randomly divided into four groups: control, control + CO2-treated, STZ-induced hyperglycemia, and STZ-induced hyperglycemia + CO2-treated groups. Blood flow in soleus muscle increased during the transcutaneous CO2 exposure, and continued to increase for 30 min after the treatment. In addition, the transcutaneous CO2 attenuated a decrease in capillary and the expression level of eNOS and VEGF protein, and an increase in the expression level of MDM-2 and TSP-1 protein of soleus muscle due to STZ-induced hyperglycemia. These results indicate that the application of transcutaneous CO2 could improve capillary regression via the change of pro- and anti-angiogenesis factors, which might be induced by an increase in blood flow.

The Interaction Between Nodal, Hypoxia-Inducible Factor 1 Alpha, and Thrombospondin 1 Promotes Luteolysis in Equine Corpus Luteum

The regulation of corpus luteus (CL) luteolysis is a complex process involving a myriad of factors. Previously, we have shown the involvement of Nodal in functional luteolysis in mares. Presently, we ask the extent of which Nodal mediation of luteolysis is done through regulation of angioregression. We demonstrated the interaction between Nodal and hypoxia-inducible factor 1 α (HIF1α) and thrombospondin 1/thrombospondin receptor (TSP1/CD36) systems, could mediate angioregression during luteolysis. First, we demonstrated the inhibitory effect of Nodal on the vascular marker platelet/endothelial cell adhesion molecule 1 (CD31). Also, treatment of mid CL explants with vascular endothelial growth factor A (VEGFA) showed a trend on activin-like kinase 7 (Alk7) protein inhibition. Next, Nodal was also shown to activate HIF1α and in vitro culture of mid CL explants under decreased oxygen level promoted Nodal expression and SMAD family member 3 (Smad3) phosphorylation. In another experiment, the crosstalk between Nodal and TSP1/CD36 was investigated. Indeed, Nodal increased the expression of the anti-angiogenic TSP1 and its receptor CD36 in mid CL explants. Finally, the supportive effect of prostaglandin F2α (PGF2α) on TSP1/CD36 was blocked by SB431542 (SB), a pharmacological inhibitor of Nodal signaling. Thus, we evidenced for the first time the in vitro interaction between Nodal and both HIF1α and TSP1 systems, two conserved pathways previously shown to be involved in vascular regression during luteolysis. Considering the given increased expression of Nodal in mid CL and its role on functional luteolysis, the current results suggest the additional involvement of Nodal in angioregression during luteolysis in the mare, particularly in the activation of HIF1α and TSP1/CD36.

Thrombospondin 1 (THBS1) Promotes Follicular Angiogenesis, Luteinization, and Ovulation in Primates

Angiogenesis is essential to both ovulation and the formation of the corpus luteum. The thrombospondin (THBS) family of glycoproteins plays diverse roles in regulation of angiogenesis, but the role of these vascular regulators in ovulation and luteinization remain to be elucidated. Using the cynomolgus macaque as a model for human ovulation, we demonstrated that levels of THBS1 mRNA and protein in preovulatory follicle granulosa cells increased after the ovulatory gonadotropin surge, with peak levels just before the expected time of ovulation. THBS1 treatment of monkey ovarian microvascular endothelial cells in vitro stimulated migration, proliferation, and capillary sprout formation, consistent with a pro-angiogenic action of THBS1. Injection of an anti-THBS1 antibody into monkey preovulatory follicles reduced rates of follicle rupture and oocyte release in response to an ovulatory gonadotropin stimulus when compared with control IgG-injected follicles. Interestingly, two of three oocytes from anti-THBS1 antibody injected follicles were germinal vesicle intact, indicating that meiosis failed to resume as anticipated. Follicles injected with anti-THBS1 antibody also showed reduced granulosa cell layer expansion, endothelial cell invasion, and capillary formation when compared to control IgG-injected follicles. Overall, these findings support a critical role for THBS1 in follicular angiogenesis, with implications for both successful ovulation and corpus luteum formation.

Low-dose metronomic delivery of cyclophosphamide is less detrimental to granulosa cell viability, ovarian function, and fertility than maximum tolerated dose delivery in the mouse

Chemotherapy can cause early menopause or infertility in women and have a profound negative impact on the quality of life of young female cancer survivors. Various factors are known to influence the risk of chemotherapy-induced ovarian failure, including the drug dose and treatment duration; however, the scheduling of dose administration has not yet been evaluated as an independent risk factor. We hypothesized that low-dose metronomic (LDM) chemotherapy scheduling would be less detrimental to ovarian function than the traditional maximum tolerated dose (MTD) strategy. In vitro, MTD cyclophosphamide exposure resulted in decreased proliferation and increased granulosa cell apoptosis, while cells treated with LDM cyclophosphamide were not different from untreated controls. Treatments of MTD cyclophosphamide induced high levels of follicle atresia and enhanced follicle recruitment in mice. In contrast, LDM delivery of an equivalent dose of cyclophosphamide reduced growing follicle numbers, but was not associated with higher levels of follicle atresia or recruitment. MTD cyclophosphamide induced significant vascular disruption and DNA damage in vivo, while LDM chemotherapy with equal cumulative amounts of cyclophosphamide was not different from controls. MTD chemotherapy also had a negative effect on mouse-fertility outcomes. Our findings suggest that LDM scheduling could potentially minimize the long-term effects of cyclophosphamide on female fertility by preventing follicle depletion from enhanced activation.

Matricellular Proteins: Functional Insights From Non-mammalian Animal Models

The extracellular matrix (ECM) has central roles in tissue integrity and remodeling throughout the life span of animals. While collagens are the most abundant structural components of ECM in most tissues, tissue-specific molecular complexity is contributed by ECM glycoproteins. The matricellular glycoproteins are categorized primarily according to functional criteria and represented predominantly by the thrombospondin, tenascin, SPARC/osteonectin, and CCN families. These proteins do not self-assemble into ECM fibrils; nevertheless, they shape ECM properties through interactions with structural ECM proteins, growth factors, and cells. Matricellular proteins also promote cell migration or morphological changes through adhesion-modulating or counter-adhesive actions on cell-ECM adhesions, intracellular signaling, and the actin cytoskeleton. Typically, matricellular proteins are most highly expressed during embryonic development. In adult tissues, expression is more limited unless activated by cues for dynamic tissue remodeling and cell motility, such as occur during inflammatory response and wound repair. Many insights in the complex roles of matricellular proteins have been obtained from studies of gene knockout mice. However, with the exception of chordate-specific tenascins, these are highly conserved proteins that are encoded in many animal phyla. This review will consider the increasing body of research on matricellular proteins in nonmammalian animal models. These models provide better access to the very earliest stages of embryonic development and opportunities to study biological processes such as limb and organ regeneration. In aggregate, this research is expanding concepts of the functions and mechanisms of action of matricellular proteins.

Localization of thrombospondin-1 and its receptor CD36 in the ovary of the ostrich (Struthio camelus)

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, plays a decisive role for the rapid growth of avian follicles. Compared to mammals, few data on the angiogenesis in the avian ovary are available. However, whereas several pro-angiogenic factors in the avian ovary have been recently studied in detail, little information is available on the localization of anti-angiogenic factors. The aim of this study was to determine the localization and possible function of the anti-angiogenic factor thrombospondin-1 (TSP-1) and its receptor CD36 in the ovary of the ostrich using immunohistochemistry and to correlate the results with ultrastructural data. Whereas the oocytes and granulosa cells of all follicular stages were negative for TSP-1, myofibroblasts of the theca externa and smooth muscle cells of blood vessels showed distinct reactions. A distinctly different staining pattern was observed for CD36. The oocytes were CD36 negative. No immunostaining for CD36 could be observed neither in the granulosa cells nor in the adjacent theca interna of vitellogenic follicles. In the theca externa, blood vessels protruding towards the oocyte showed CD36-positive endothelial cells. In conclusion, a fine balance between angiogenic and anti-angiogenic processes assures that a dense net of blood vessels develops during the rapid growth of a selected follicle. Anti-angiogenic molecules, such as TSP-1 and its receptor CD36 may, after the oocyte has reached its final size, inhibit further angiogenesis and limit the transport of yolk material to the mature oocyte. By this mechanism, the growth of the megalecithal oocyte during folliculogenesis may cease.

Bovine ovarian follicular growth and development correlate with lysophosphatidic acid expression

The basis of successful reproduction is proper ovarian follicular growth and development. In addition to prostaglandins and vascular endothelial growth factor, a number of novel factors are suggested as important regulators of follicular growth and development: PGES, TFG, CD36, RABGAP1, DBI and BTC. This study focuses on examining the expression of these factors in granulosa and thecal cells that originate from different ovarian follicle types and their link with the expression of lysophosphatidic acid (LPA), known local regulator of reproductive functions in the cow. Ovarian follicles were divided into healthy, transitional, and atretic categories. The mRNA expression levels for PGES, TFG, CD36, RABGAP1, DBI and BTC in granulosa and thecal cells in different follicle types were measured by real-time PCR. The correlations among expression of enzymes synthesizing LPA (autotaxin, phospholipase A2), receptors for LPA and examined factors were measured. Immunolocalization of PGES, TFG, CD36, RABGAP1, DBI and BTC was examined by immunohistochemistry. We investigated follicle-type dependent mRNA expression of factors potentially involved in ovarian follicular growth and development, both in granulosa and thecal cells of bovine ovarian follicles. Strong correlations among receptors for LPA, enzymes synthesizing LPA, and the examined factors in healthy and transitional follicles were observed, with its strongest interconnection with TFG, DBI and RABGAP1 in granulosa cells, and TFG in thecal cells; whereas no correlations in atretic follicles were detected. A greater number of correlations were found in thecal cells than in granulosa cells as well as in healthy follicles than in transitional follicles. These data indicate the role of LPA in the growth, development and physiology of the bovine ovarian follicle.

Age-associated changes in granulosa cells and follicular fluid in cows

Age-associated decline in oocyte quality is common in mammals. Oocytes take a long time to reach their full-grown size in large animals, and maternal physical conditions profoundly affect follicle development. Aging affects the oocyte itself as well as the surrounding environment, such as granulosa cells and follicular fluid. This review discusses age-associated changes that occur in granulosa cells and follicular fluid in cows and suggests that age-associated decline in granulosa cells and follicular fluid hampers proper oocyte development.

Transcriptional profiling of porcine granulosa cells exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic man-made chemical compound contaminating the environment. An exposure of living organisms to TCDD may result in numerous disorders, including reproductive pathologies. The aim of the current study was to examine the effects of TCDD on the transcriptome of porcine granulosa cell line AVG-16. By employing next-generation sequencing (NGS) we aimed to identify genes potentially involved in the mechanism of TCDD action and toxicity in porcine granulosa cells. The AVG-16 cells were treated with TCDD (100 nM) for 3, 12 or 24 h, and afterwards total cellular RNA was isolated and sequenced. In TCDD-treated cells we identified 141 differentially expressed genes (DEGs; p_adjusted < 0.05 and log2 fold change ≥1.0). The DEGs were assigned to GO term, covering biological processes, molecular functions and cellular components. Due to the large number of genes with altered expression, in the current study we analyzed only the genes involved in follicular growth, development and functioning. The obtained results showed that TCDD may affect ovarian follicle fate by influencing granulosa cell cycle, proliferation and DNA repair. The demonstrated over-time changes in the quantity and quality of genes being affected by TCDD treatment showed that the effects of TCDD on granulosa cells changed dramatically between 3-, 12- and 24-h of cell culture. This finding indicate that timing of gene expression measurement is critical for drawing correct conclusions on detailed relationships between the TCDD-affected genes and resulting intracellular processes. These conclusions have to be confirmed and extended by research involving proteomic and functional studies.

Expression and localization of members of the thrombospondin family during final follicle maturation and corpus luteum formation and function in the bovine ovary

The aim of this study was to characterize the expression patterns and localization of the thrombospondin family members (THBS1, THBS2) and their receptors (CD36 and CD47) in bovine ovaries. First, the antral follicles were classified into 5 groups based on the follicle size and estradiol-17beta (E2) concentration in the follicular fluid (< 0.5, 0.5-5, 5-40, 40-180 and >180 E2 ng/ml). Second, the corpus luteum (CL) was assigned to the following stages: days 1-2, 3-4, 5-7, 8-12, 13-16 and >18 of the estrous cycle and of pregnancy (month 1-2, 3-4, 6-7 and > 8). Third, the corpora lutea were collected by transvaginal ovariectomy before and 0.5, 2, 4, 12, 24, 48 and 64 h after inducing luteolysis by injecting a prostaglandin F2alpha analog. The mRNA expression of examined factors was measured by RT-qPCR, steroid hormone concentration by EIA, and localization by immunohistochemistry. The mRNA expression of THBS1, THBS2, CD36, and CD47 in the granulosa cells and theca interna was high in the small follicles and reduced in the preovulatory follicles. The mRNA expression of THBS1, THBS2, and CD47 in the CL during the estrous cycle was high, but decreased significantly during pregnancy. After induced luteolysis, thrombospondins increased significantly to reach the maximum level at 12 h for THBS1, 24 h for THBS2, and 48 h for CD36. The temporal expression and localization pattern of the thrombospondins and their specific receptors in the antral follicles and corpora lutea during the different physiological phases of the estrous cycle and induced luteolysis appear to be compatible with their inhibitory role in the control of ovarian angiogenesis.

Age-associated events in bovine oocytes and possible countermeasures

Maternal aging profoundly affects oocyte quality. This has become common knowledge in industrialized countries and extensive studies addressing the causes and possible countermeasures against age-associated deterioration of oocytes suggest that mitochondrial dysfunction is a causal factor in infertility. However, almost all studies addressing age-associated events in oocytes have used mice as an animal model, and the reproductive life of mice is very short, making it difficult to study the gradual decline in fertility observed in humans. In the present review, age-associated changes in the quality and quantity of bovine oocytes and possible countermeasures related to mitochondrial quality control are introduced.

Vascular endothelial growth factor and angiopoietins during hen ovarian follicle development

Growth and maturation of ovarian follicles in the hen (Gallus gallus) requires a network of blood vessels that increases in complexity during development. The present studies investigate expression of vascular endothelial growth factor A (VEGF), angiopoietin1 (ANGPT1) and ANGPT2 mRNAs together with their associated receptors (VEGFR and TIE2, respectively) during maturation. Elevated expression of VEGF and its receptors is associated with healthy, compared to atretic, follicles. Levels of VEGF significantly increase, while antagonistic ANGPT2 decrease, in granulosa cells (GC) at follicle selection. By comparison, levels of VEGF, VEGFR1, VEGFR2, ANGPT1, ANGPT2 and TIE2 within the theca layer do not change (P>0.05) relative to developmental stages surrounding follicle selection (6-8mm versus 9-12mm follicles). Prior to selection, treatment with transforming growth factor β1 (TGFβ1) significantly increases levels of VEGF in undifferentiated GC from prehierarchal (6-8mm) follicles and actively differentiating GC from selected (9-12 and F4) follicles. Moreover, subsequent to selection follicle stimulating hormone (FSH) increases VEGF expression in GC from 9 to 12mm follicles, and eventually luteinizing hormone (LH) promotes VEGF expression in GC from more mature preovulatory follicles. It is concluded that prior to follicle selection VEGF expression is regulated by autocrine and paracrine actions of TGFβ1 (but not FSH), and that a comparatively limited extent of vasculature is sufficient to maintain prehierarchal follicles in a viable and undifferentiated state. At follicle selection, FSH- and subsequently LH-induced VEGF production within the GC layer enhance angiogenesis within the theca layer, which facilitates the rapid growth of preovulatory follicles via enhanced incorporation of yellow yolk.

Luteal angiogenesis and its control

Angiogenesis, the formation of new blood vessels from preexisting ones, is critical to luteal structure and function. In addition, it is a complex and tightly regulated process. Not only does rapid and extensive angiogenesis occur to provide the corpus luteum with an unusually high blood flow and support its high metabolic rate, but in the absence of pregnancy, the luteal vasculature must rapidly regress to enable the next cycle of ovarian activity. This review describes a number of key endogenous stimulatory and inhibitory factors, which act in a delicate balance to regulate luteal angiogenesis and ultimately luteal function. In vitro luteal angiogenesis cultures have demonstrated critical roles for fibroblast growth factor 2 (FGF2) in endothelial cell proliferation and sprouting, although other factors such as vascular endothelial growth factor A (VEGFA) and platelet-derived growth factor were important modulators in the control of luteal angiogenesis. Post-transcriptional regulation by small non-coding microRNAs is also likely to play a central role in the regulation of luteal angiogenesis. Appropriate luteal angiogenesis requires the coordinated activity of numerous factors expressed by several cell types at different times, and this review will also describe the role of perivascular pericytes and the importance of vascular maturation and stability. It is hoped that a better understanding of the critical processes underlying the transition from follicle to corpus luteum and subsequent luteal development will benefit the management of luteal function in the future.

Physiological Capillary Regression is not Dependent on Reducing VEGF Expression

Investigations into physiologically controlled capillary regression report the provocative finding that microvessel regression occurs in the face of persistent elevation of skeletal muscle VEGF expression. TSP-1, a negative angiogenic regulator, is increasingly being observed to temporally correlate with capillary regression, suggesting that increased TSP-1 (and not reduction in VEGF per se) is needed to initiate, and likely regulate, capillary regression. Based on evidence being gleaned from physiologically mediated regression of capillaries, it needs to be recognized that capillary regression (and perhaps capillary rarefaction with disease) is not simply the reversal of factors used to stimulate angiogenesis. Rather, the conceptual understanding that angiogenesis and capillary regression each have specific and unique requirements that are biologically constrained to opposite sides of the balance between positive and negative angioregulatory factors may shed light on why anti-VEGF therapies have not lived up to the promise in reversing angiogenesis and providing the cure that many had hoped toward fighting cancer. Emerging evidence from physiological controlled angiogenesis suggest that cases involving excessive or uncontrolled capillary expansion may be best treated by therapies designed to increase expression of negative angiogenic regulators, whereas those involving capillary rarefaction may benefit from inhibiting negative regulators (like TSP-1).

Localization of Vascular Endothelial Growth Factor and Fibroblast Growth Factor 2 in the Ovary of the Ostrich (Struthio camelus)

Vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF-2) play a paramount role in the regulation of normal and pathologic angiogenesis in the ovary of mammals. Very little is known on the expression of these two growth factors in the avian ovary. The aim of this study was to determine for the first time the localization of VEGF and FGF-2 in the ovary of the ostrich using immunohistochemical techniques to investigate the vascularization of the rapidly growing huge ostrich oocyte. At the oocyte periphery, distinct VEGF-positive granules are visible. In our opinion, the expression of VEGF in the growing oocytes, which does not occur in mammals such as bovines, does not significantly contribute to angiogenesis in the theca interna and externa, where all the original and developing vessels are located, but may contribute to the mitoses and survival of granulosa cells during folliculogenesis. A different immunostaining can be demonstrated for FGF-2: from late pre-vitellogenic follicles, FGF-2 immunopositivity can be observed at the inner perivitelline layer area. In the stroma, the smooth muscle cells of small arteries and the endothelial cells of venules and veins are positively stained for FGF-2. Another interesting finding of this study is the occurrence of a significant number of VEGF- and FGF-2 positive heterophilic granulocytes within the ovarian stroma, which migrate from the periphery of the ovary towards the growing follicles. We assume that the growth factors of the heterophilic granulocytes contribute significantly to the angiogenesis seen in both theca layers.

Differential gene expression in ovaries of Qira black sheep and Hetian sheep using RNA-Seq technique

The Qira black sheep and the Hetian sheep are two local breeds in the Northwest of China, which are characterized by high-fecundity and low-fecundity breed respectively. The elucidation of mRNA expression profiles in the ovaries among different sheep breeds representing fecundity extremes will helpful for identification and utilization of major prolificacy genes in sheep. In the present study, we performed RNA-seq technology to compare the difference in ovarian mRNA expression profiles between Qira black sheep and Hetian sheep. From the Qira black sheep and the Hetian sheep libraries, we obtained a total of 11,747,582 and 11,879,968 sequencing reads, respectively. After aligning to the reference sequences, the two libraries included 16,763 and 16,814 genes respectively. A total of 1,252 genes were significantly differentially expressed at Hetian sheep compared with Qira black sheep. Eight differentially expressed genes were randomly selected for validation by real-time RT-PCR. This study provides a basic data for future research of the sheep reproduction.

Functions and transcriptional regulation of thrombospondins and their interrelationship with fibroblast growth factor-2 in bovine luteal cells

Previously, we showed luteal stage-specific regulation of angiogenesis-modulating factors by prostaglandin F2 alpha (PGF2alpha). Fibroblast growth factor 2 (FGF2) and thrombospondins (THBSs) exhibited the most divergent profile of induction by PGF2alpha. We therefore examined the transcriptional regulation and roles of THBSs in luteal cells and studied their interaction with FGF2. THBSs and their receptors exhibited cell-specific expression: THBS1 was the predominant form in luteal endothelial cells (LEC), whereas luteinized granulosa cells (LGC) expressed mostly THBS2. CD36 was confined to LGC, but CD47 did not exhibit preferential expression between LEC and LGC. THBS1 and THBS2 were both stimulated in vitro by PGF2a and its analog in LGC. In contrast, luteinizing signals (LH and insulin) decreased the expression of THBS1, THBS2, and CD36. Importantly, LH increased FGF2 expression, suggesting that THBSs and FGF2 are conversely regulated. We found that FGF2 inhibited THBS1 and vice versa, and that THBS1 treatment decreased FGF2 expression, suggesting reciprocal inhibition. In agreement, ablation of THBS1 by specific small interference RNAs elevated FGF2 levels. THBS1 reduced LEC numbers and promoted apoptosis by activation of caspase-3. In contrast, FGF2 reduced basal and THBS1-induced caspase-3 levels. Consistent with these findings, small interference RNA silencing of THBS1 in luteal cells reduced the levels of active caspase-3 and improved the survival of cells when challenged with staurosporine. Taken together, these studies suggest that THBSs are suppressed during luteinization but are induced by PGF2alpha in luteolysis. THBS1 has antiangiogenic, proapoptotic properties; these, together with its ability to inhibit FGF2 expression and activity, can promote luteolysis.

Cell density-mediated pericellular hypoxia and the local dynamic regulation of VEGF-a splice variants in ovine ovarian granulosa cells

The primary aims of this study were to utilize a specialized culture system to further elucidate the functional significance of pericellular hypoxia within the granulosa cell (GC) compartment of growing follicles, and to clarify its effects on the production of vascular endothelial growth factor (VEGF)-A isoforms and steroid hormones. Multilaminar clusters formed rapidly in ovine GCs seeded at high density (HD), and Hypoxyprobe-1 protein adducts appeared markedly more abundant and HIF-1 activation significantly (P < 0.001) greater than in cells seeded at low density (LD). Four proangiogenic VEGF mRNA transcript variants were identified in cultured GCs. Most abundant were VEGF120 and VEGF164, but VEGF182 and VEGF188 were also detected. Total VEGF mRNA was shown to be up-regulated transiently in the HD cells (P < 0.001) and VEGF164 mRNA appeared to contribute most to this. The hypoxia mimetic cobalt chloride also induced marked increases in HIF-1 activation (P < 0.01) and total VEGF mRNA (P < 0.01) production. HD cells increased levels of HIF-1alpha (P < 0.001) and VEGF receptor type 1 (P < 0.05), but not VEGF receptor type 2 mRNA, compared to LD cells or cells grown under chemically induced hypoxia. Both 17beta-estradiol (E2) and progesterone (P4) were markedly lower (P < 0.001) in the HD, cells but though cobalt chloride treatment accompanied significantly reduced P4 production (P < 0.05), E2 levels remained similar to those in untreated cells. These outcomes suggest that pericellular hypoxia may be an important mediator of VEGF production in the GCs of growing follicles, but that local regulation is complex and may involve multiple mechanisms such as mediation by steroid hormones and differential variant mRNA production.

Age-associated changes in bovine oocytes and granulosa cell complexes collected from early antral follicles

PURPOSE

To assess the age-associated changes in oocytes and granulosa cells derived from early antral follicles (EAFs).

METHOD

Gene expression analysis of granulosa cells of the EAFs using a genome analyzer (Illumina) and in vitro culture of oocyte-granulosa cell complexes (OGCs) of EAFs (400-700 μm in diameter) collected from ovaries of aged (>120 months) and young (<50 months) cows.

RESULTS

Gene expression profiles in granulosa cells of EAFs of aged cows, which included changes in genes that encode chaperone proteins and antioxidants. In vivo development of EAFs, as determined by oocyte diameter of EAFs and AFs (3-6 mm in diameter), appeared to be impaired in aged cows and the OGCs of aged cows contained low GSH compared to younger counterparts. When the OGCs were cultured in a medium containing low estradiol (E2, 0.1 μg/mL), the ratio of antrum formation was higher for OGCs from aged animals than that from young animals, while higher abnormal fertilization rate and lower total cell number of the blastocysts were observed in the OGCs of aged cows compared with those of young cows. On the contrary, when the OGCs were cultured in a medium containing 10 μg/mL E2, the ratio of antrum formation and fertilization outcome was comparable between the two age groups, whereas the total cell number of the blastocysts was still low in the aged group.

CONCLUSION

Aging affects the gene expression profiles of the granulosa cells, and impairs in vitro developmental ability of OGCs collected from EAFs.

The thrombospondin-1 receptor CD36 is an important mediator of ovarian angiogenesis and folliculogenesis

BACKGROUND

Ovarian angiogenesis is a complex process that is regulated by a balance between pro- and anti-angiogenic factors. Physiological processes within the ovary, such as folliculogenesis, ovulation, and luteal formation are dependent upon adequate vascularization and anything that disrupts normal angiogenic processes may result in ovarian dysfunction, and possibly infertility. The objective of this study was to evaluate the role of the thrombospondin-1 (TSP-1) receptor CD36 in mediating ovarian angiogenesis and regulating ovarian function.

METHODS

The role of CD36 was evaluated in granulosa cells in vitro and ovarian morphology and protein expression were determined in wild type and CD36 null mice.

RESULTS

In vitro, CD36 inhibition increased granulosa cell proliferation and decreased apoptosis. Granulosa cells in which CD36 was knocked down also exhibited an increase in expression of survival and angiogenic proteins. Ovaries from CD36 null mice were hypervascularized, with increased expression of pro-angiogenic vascular endothelial growth factor (VEGF) and its receptor VEGFR-2. Ovaries from CD36 null mice contained an increase in the numbers of pre-ovulatory follicles and decreased numbers of corpora lutea. CD36 null mice also had fewer number of offspring compared to wild type controls.

CONCLUSIONS

The results from this study demonstrate that CD36 is integral to the regulation of ovarian angiogenesis by TSP-1 and the expression of these family members may be useful in the control of ovarian vascular disorders.

Transcriptome profiling of granulosa cells from bovine ovarian follicles during atresia

Background

The major function of the ovary is to produce oocytes for fertilisation. Oocytes mature in follicles surrounded by nurturing granulosa cells and all are enclosed by a basal lamina. During growth, granulosa cells replicate and a large fluid-filled cavity (the antrum) develops in the centre. Only follicles that have enlarged to over 10 mm can ovulate in cows. In mammals, the number of primordial follicles far exceeds the numbers that ever ovulate and atresia or regression of follicles is a mechanism to regulate the number of oocytes ovulated and to contribute to the timing of ovulation. To better understand the molecular basis of follicular atresia, we undertook transcriptome profiling of granulosa cells from healthy (n = 10) and atretic (n = 5) bovine follicles at early antral stages (< 5 mm).

Results

Principal Component Analysis (PCA) and hierarchical classification of the signal intensity plots for the arrays showed primary clustering into two groups, healthy and atretic. These analyses and size-frequency plots of coefficients of variation of signal intensities revealed that the healthy follicles were more heterogeneous. Examining the differentially-expressed genes the most significantly affected functions in atretic follicles were cell death, organ development, tissue development and embryonic development. The overall processes influenced by transcription factor gene TP53 were predicted to be activated, whereas those of MYC were inhibited on the basis of known interactions with the genes in our dataset. The top ranked canonical pathway contained signalling molecules common to various inflammatory/fibrotic pathways such as the transforming growth factor-β and tumour necrosis factor-α pathways. The two most significant networks also reflect this pattern of tissue remodelling/fibrosis gene expression. These networks also contain molecules which are present in the canonical pathways of hepatic fibrosis/hepatic stellate cell activation and transforming growth factor-β signalling and were up regulated.

Conclusions

Small healthy antral follicles, which have a number of growth outcomes, exhibit greater variability in gene expression, particularly in genes associated with cell division and other growth-related functions. Atresia, on the other hand, not only involves cell death but clearly is an active process similar to wound healing.

Differential gene expression of granulosa cells after ovarian superstimulation in beef cattle

Microarray analysis was used to compare the gene expression of granulosa cells from dominant follicles with that of those after superstimulatory treatment. Cows were allocated randomly to two groups (superstimulation and control, n=6/group). A new follicular wave was induced by ablation of follicles ≥5 mm in diameter, and a progesterone-releasing device controlled internal drug release (CIDR) was placed in the vagina. The superstimulation group was given eight doses of 25 mg FSH at 12-h intervals starting from the day of wave emergence (day 0), whereas the control group was not given FSH treatment. Both groups were given prostaglandin F2α twice, 12 h apart, on day 3 and the CIDR was removed at the second injection; 25 mg porcine luteinizing hormone (pLH) was given 24 h after CIDR removal, and cows were ovariectomized 24 h later. Granulosa cells were collected for RNA extraction, amplification, and microarray hybridization. A total of 190 genes were downregulated and 280 genes were upregulated. To validate the microarray results, five genes were selected for real-time PCR (NTS, FOS, THBS1, FN1, and IGF2). Expression of four genes increased significantly in the three different animals tested (NTS, FOS, THBS1, and FN1). The upregulated genes are related to matrix remodeling (i.e. tissue proliferation), disturbance of angiogenesis, apoptosis, and oxidative stress response. We conclude that superstimulation treatment i) results in granulosa cells that lag behind in maturation and differentiation (most of the upregulated genes are markers of the follicular growth stage), ii) activates genes involved with the NFE2L2 oxidative stress response and endoplasmic reticulum stress response, and iii) disturbs angiogenesis.

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.

The effects of whole ovarian perfusion and cryopreservation on endothelial cell-related gene expression in the ovarian medulla and pedicle

Fertility preservation by whole ovarian cryopreservation requires successful cryopreservation of both the ovary and its vascular supply. Previous work has indicated detrimental effects of both perfusion and cryopreservation on the ovarian vasculature. This study assessed the effects of blood perfusion, alone or in combination with cryopreservation, on functional effects in the follicle population and ovarian function in vivo following short-term autotransplantation of the tissue after vascular reanastomosis and measured acute changes in endothelial cell-related gene expression within the ovarian medulla and pedicle. Following autotransplantation for 7 days, primordial, transitional and primary follicle densities were significantly reduced (P < 0.05) and stromal Ki67 and caspase-3 expression significantly increased (P < 0.05) in cryopreserved but not fresh or perfused whole ovaries. There was evidence of clot formation and fluorescent microsphere (FMS) extravasation in the medulla of all cryopreserved ovaries, indicating vascular damage. Utilizing a customized RT-PCR array or conventional RT-PCR, we found that perfusion alone resulted in down-regulation in the expression of caspase 6 and thrombospondin 1 (THBS1) genes in the medulla. Following additional cryopreservation, endothelial nitric oxide synthase (eNOS), endothelin 1, endothelin receptor A and Bcl-2 expression were significantly (P < 0.05) down-regulated. In the pedicle, both perfusion and cryopreservation caused a (P < 0.05) down-regulation of eNOS and THBS1, and an up-regulation in Bax expression. Perfusion also caused a down-regulation of TNF and up-regulation of endothelin-2 expression (P < 0.05). In conclusion, this study has identified a number of endothelial cell-related genes expressed in the medulla which are acutely affected by both cryopreservation and perfusion, supporting the hypothesis that both interventions have deleterious effects on endothelial cell function.

Hormonal regulation of pigment epithelium-derived factor (PEDF) in granulosa cells

Angiogenesis is critical for the development of ovarian follicles. Blood vessels are abrogated from the follicle until ovulation, when they invade it to support the developing corpus luteum. Granulosa cells are known to secrete anti-angiogenic factors that shield against premature vascularization; however, their molecular identity is yet to be defined. In this study we address the physiological role of pigment epithelium-derived factor (PEDF), a well-known angiogenic inhibitor, in granulosa cells. We have shown that human and mouse primary granulosa cells express and secrete PEDF, and characterized its hormonal regulation. Stimulation of granulosa cells with increasing doses of estrogen caused a gradual decrease in the PEDF secretion, while stimulation with progesterone caused an abrupt decrease in its secretion. Moreover, We have shown, by time- and dose-response experiments, that the secreted PEDF and vascular endothelial growth factor (VEGF) were inversely regulated by hCG; namely, PEDF level was nearly undetectable under high doses of hCG, while VEGF level was significantly elevated. The anti-angiogenic nature of the PEDF secreted from granulosa cells was examined by migration, proliferation and tube formation assays in cultures of human umbilical vein endothelial cells. Depleting PEDF from primary granulosa cells conditioned media accelerated endothelial cells proliferation, migration and tube formation. Collectively, the dynamic expression of PEDF that inversely portrays VEGF expression may imply its putative role as a physiological negative regulator of follicular angiogenesis.

Importance of vascular endothelial growth factor (VEGF) in ovarian physiology of mammals

Ovarian folliculogenesis in mammals is a complex process. Several compounds have been tested during in vitro culture of follicular cells for a better understanding of the mechanisms and factors related to ovarian folliculogenesis in mammals. From these compounds, vascular endothelial growth factor (VEGF) can be highlighted, as it is strongly associated with angiogenesis and, in recent years, its presence in ovarian cells has been investigated extensively. Previous studies have shown that the presence of VEGF protein, as well as mRNA expression of its receptor 2 (VEGFR-2) increases during follicular development. Therefore, it is likely that the interaction between VEGF and VEGFR-2 is crucial to promote follicular development. However, few studies on the influence of this factor on follicular development have been reported. This review addresses aspects related to the structural characterization and mechanism of action of VEGF and its receptors, and their biological importance in the ovary of mammals.

The thrombospondins

Thrombospondins are evolutionarily conserved, calcium-binding glycoproteins that undergo transient or longer-term interactions with other extracellular matrix components. They share properties with other matrix molecules, cytokines, adaptor proteins, and chaperones, modulate the organization of collagen fibrils, and bind and localize an array of growth factors or proteases. At cell surfaces, interactions with an array of receptors activate cell-dependent signaling and phenotypic outcomes. Through these dynamic, pleiotropic, and context-dependent pathways, mammalian thrombospondins contribute to wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. We overview the domain organization and structure of thrombospondins, key features of their evolution, and their cell biology. We discuss their roles in vivo, associations with human disease, and ongoing translational applications. In many respects, we are only beginning to appreciate the important roles of these proteins in physiology and pathology.

PPAR Gamma: Coordinating Metabolic and Immune Contributions to Female Fertility

Peroxisome proliferator-activated receptor gamma (PPARG) regulates cellular functions such as adipogenesis and immune cell activation. However, new information has indicated additional roles of PPARG directing the cyclic changes that occur within ovarian tissue of female mammals, including those that facilitate the release of oocytes each estrous cycle. In addition to ovarian PPARG expression and function, many PPARG actions within adipocytes and macrophages have additional direct and indirect implications for ovarian function and female fertility. This encompasses the regulation of lipid uptake and transport, insulin sensitivity, glucose metabolism, and the regulation of inflammatory mediator synthesis and release. This review discusses the developing links between PPARG activity and female reproductive function, and highlights several mechanisms that may facilitate such a relationship.

A thrombospondin-mimetic peptide, ABT-898, suppresses angiogenesis and promotes follicular atresia in pre- and early-antral follicles in vivo

Using a novel in vitro angiogenesis assay, we previously showed that thrombospondin (TSP)-1 has antiangiogenic effects on rat follicles and induces apoptosis in granulosa cells in vitro. ABT-898 is an octapeptide mimetic of TSP-1 closely related to ABT-510. Here, we demonstrate the inhibitory effects of ABT-898 on follicular angiogenesis and its proapoptotic effect on granulosa cells. To investigate the potential of this peptide to inhibit follicular angiogenesis in vivo, marmoset monkeys were treated with 2.5 mg/kg ABT-898 twice daily throughout the follicular phase of the cycle. Although treatment did not block emergence of dominant follicles, angiogenesis was reduced in preantral and early-antral follicles. Furthermore, the incidence of atresia at these follicle stages was increased. To investigate whether treatment with ABT-898 would interfere with the timing or duration of the normal ovulatory rise in plasma progesterone, marmosets were treated with a depot formulation containing 25 mg ABT-898 at the start of the follicular phase, with a second injection after 2 wk. Despite active concentrations of peptide being maintained in the circulation, no apparent effects on the ovulatory cycle were observed. Taken together, these results indicate that ABT-898 is capable of having a dual effect by inhibiting follicular angiogenesis and promoting atresia of antral follicles in vivo but does not prevent ovulation or induce luteolysis, as has been observed with direct vascular endothelial growth factor inhibitors. These results suggest that ABT-898 could be a novel therapeutic to inhibit abnormal angiogenesis and induce atresia of accumulated follicles in polycystic ovary syndrome.

Theca: the forgotten cell of the ovarian follicle

Theca cells function in a diverse range of necessary roles during folliculogenesis; to synthesize androgens, provide crosstalk with granulosa cells and oocytes during development, and provide structural support of the growing follicle as it progresses through the developmental stages to produce a mature and fertilizable oocyte. Thecal cells are thought to be recruited from surrounding stromal tissue by factors secreted from an activated primary follicle. The precise origin and identity of these recruiting factors are currently not clear, but it appears that thecal recruitment and/or differentiation involves not just one signal, but a complex and tightly controlled combination of multiple factors. It is clear that thecal cells are fundamental for follicular growth, providing all the androgens required by the developing follicle(s) for conversion into estrogens by the granulosa cells. Their function is enabled through the establishment of a vascular system providing communication with the pituitary axis throughout the reproductive cycle, and delivering essential nutrients to these highly active cells. During development, the majority of follicles undergo atresia, and the theca cells are often the final follicular cell type to die. For those follicles that do ovulate, the theca cells then undergo hormone-dependent differentiation into luteinized thecal cells of the corpus luteum. While the theca is an essential component of follicle development and ovulation, we do not yet fully understand the control of recruitment and function of theca cells, an important consideration since their function appears to be altered in certain causes of infertility.

WNT4 is required for normal ovarian follicle development and female fertility

To study the role of WNT4 in the postnatal ovary, a mouse strain bearing a floxed Wnt4 allele was created and mated to the Amhr2(tm3(cre)Bhr) strain to target deletion of Wnt4 to granulosa cells. Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had reduced ovary weights and produced smaller litters (P<0.05). Serial follicle counting demonstrated that Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice were born with a normal ovarian reserve and maintained normal numbers of small follicles until puberty but had only 25.2% of the normal number of healthy antral follicles. Some Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had no antral follicles or corpora lutea and underwent premature follicle depletion. RT-PCR analyses of Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) granulosa cells and cultured granulosa cells that overexpress WNT4 demonstrated that WNT4 regulates the expression of Star, Cyp11a1, and Cyp19, steroidogenic genes previously identified as downstream targets of the WNT signaling effector CTNNB1. Decreased serum progesterone levels were found in immature, gonadotropin-treated Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice (P<0.05). WNT4- and CTNNB1-overexpressing cultured granulosa cells were analyzed by microarray for alterations in gene expression, which showed that WNT4 regulates additional genes involved in late follicle development via the WNT/CTNNB1 signaling pathway. Together, these data indicate that WNT4 is required for normal antral follicle development and may act by regulating granulosa cell functions including steroidogenesis.