Angiogenic Activity of Swine Granulosa Cells: Effects of Hypoxia and the Role of VEGF

FOXO1 mediates hypoxia-induced G0/G1 arrest in ovarian somatic granulosa cells by activating the TP53INP1-p53-CDKN1A pathway

The development of ovarian follicles constitutes the foundation of female reproduction. The proliferation of granulosa cells (GCs) is a basic process required to ensure normal follicular development. However, the mechanisms involved in controlling GC cell cycle are not fully understood. Here, by performing gene expression profiling in the domestic pig (Sus scrofa), we showed that cell cycle arrest at G0/G1 phase is highly correlated with pathways associated with hypoxic stress and FOXO signalling. Specifically, the elevated proportion of GCs at the arrested G0/G1 phase was accompanied by increased nuclear translocation of FOXO1 under conditions of hypoxia both in vivo and in vitro. Furthermore, phosphorylation of 14-3-3 by the JNK kinase is required for hypoxia-mediated FOXO1 activation and the resultant G0/G1 arrest. Notably, a FOXO1 mutant without DNA-binding activity failed to induce G0/G1 arrest of GCs during hypoxia. Importantly, we identified a new target gene of FOXO1, namely TP53INP1, which contributes to suppression of the G1-S cell cycle transition in response to hypoxia. Furthermore, we demonstrated that the inhibitory effect of the FOXO1-TP53INP1 axis on the GC cell cycle is mediated through a p53-CDKN1A-dependent mechanism. These findings could provide avenues for the clinical treatment of human infertility caused by impaired follicular development.

Insulin-like growth factor-I prevents hypoxia-inducible factor-1 alpha-dependent G1/S arrest by activating cyclin E/cyclin-dependent kinase2 via the phoshatidylinositol-3 kinase/AKT/forkhead box O1/Cdkn1b pathway in porcine granulosa cells†

As the follicle develops, the thickening of the granulosa compartment leads to progressively deficient supply of oxygen in granulosa cells (GCs) due to the growing distances from the follicular vessels. These conditions are believed to cause hypoxia in GCs during folliculogenesis. Upon hypoxic conditions, several types of mammalian cells have been reported to undergo cell cycle arrest. However, it remains unclear whether hypoxia exerts any impact on cell cycle progression of GCs. On the other hand, although the GCs may live in a hypoxic environment, their mitotic capability appears to be unaffected in growing follicles. It thus raises the question whether there are certain intraovarian factors that might overcome the inhibitory effects of hypoxia. The present study provides the first evidence suggesting that cobalt chloride (CoCl2)-mimicked hypoxia prevented G1-to-S cell cycle progression in porcine GCs. In addition, we demonstrated that the inhibitory effects of CoCl2 on GCs cell cycle are mediated through hypoxia-inducible factor-1 alpha/FOXO1/Cdkn1b pathway. Moreover, we identified insulin-like growth factor-I (IGF-I) as an intrafollicular factor required for cell cycle recovery by binding to IGF-I receptor in GCs suffering CoCl2 stimulation. Further investigations confirmed a role of IGF-I in preserving G1/S progression of CoCl2-treated GCs via activating the cyclin E/cyclin-dependent kinase2 complex through the phoshatidylinositol-3 kinase/protein kinase B (AKT)/FOXO1/Cdkn1b axis. Although the present findings were based on a hypoxia mimicking model by using CoCl2, our study might shed new light on the regulatory mechanism of GCs cell cycle upon hypoxic stimulation.

HIF-1α Protects Granulosa Cells From Hypoxia-Induced Apoptosis During Follicular Development by Inducing Autophagy

Owing to the avascular structure of the ovarian follicle, proliferation of granulosa cells (GCs) and development of follicles occur under hypoxia, which is obviously different from the cell survival requirements of most mammalian cells. We hypothesized that autophagy may exert an inhibitory effect on GC apoptosis. To decipher the underlying mechanism, we constructed a rat follicular development model using pregnant mare serum gonadotropin and a cell culture experiment in hypoxic conditions (3% O₂). The present results showed that the autophagy level was obviously increased and was accompanied by the concomitant elevation of hypoxia inducible factor (HIF)-1α and BNIP3 (Bcl-2/adenovirus E1B 19kDa-interacting protein 3) in GCs during follicular development. The levels of Bax (Bcl2-associated X) and Bcl-2 (B-cell lymphoma-2) were increased, while the activation of caspase-3 exhibited no obvious changes during follicular development. However, inhibition of HIF-1α attenuated the increase in Bcl-2 and promoted the increase in Bax and cleaved caspase-3. Furthermore, we observed the downregulation of BNIP3 and the decrease in autophagy after treatment with a specific HIF-1α activity inhibitor (echinomycin), indicating that HIF-1α/BNIP3 was involved in autophagy regulation in GCs in vivo. In an in vitro study, we also found that hypoxia did not obviously promote GC apoptosis, while it significantly enhanced the activation of HIF-1α/BNIP3 and the induction of autophagy. Expectedly, this effect could be reversed by 3-methyladenine (3-MA) treatment. Taken together, these findings demonstrated that hypoxia drives the activation of HIF-1α/BNIP3 signaling, which induces an increase in autophagy, protecting GC from apoptosis during follicular development.

The distribution and expression of vascular endothelial growth factor A (VEGFA) during follicular development and atresia in the pig

The involvement of vascular endothelial growth factor A (VEGFA) in ovarian physiological processes has been widely reported, but the location and role of VEGFA during follicular atresia remain unknown. This study investigated the distribution and expression of VEGFA during porcine follicular development and atresia. Pig ovaries were obtained, individual medium-sized (3-5mm in diameter) antral follicles were separated and classified into healthy, early atretic or progressively atretic groups. Immunobiology and quantitative techniques were used to investigate the varied follicular distribution of VEGFA at both the morphological and molecular level. The results indicated that VEGFA protein expression peaked in tertiary follicles, mostly distributed in the thecal and inner granulosa layers, during follicular development while VEGFA mRNA was mainly expressed in the inner granulosa layers. Additionally, healthy antral follicles showed a significantly higher expression of VEGFA than atretic follicles in both theca and granulosa cells. Knockdown of VEGFA using siRNA revealed an antiapoptosis effect of VEGFA in cultured pig granulosa cells. Our results increase the knowledge of VEGFA functions in follicles.

miR-361-5p Mediates SMAD4 to Promote Porcine Granulosa Cell Apoptosis through VEGFA

Follicular atresia is an inevitable degenerative process that occurs in mammalian ovarian follicles. The molecular events involved in atresia, particularly granulosa cell apoptosis, have long attracted researchers’ attention. Vascular endothelial growth factor A (VEGFA) is downregulated during follicular atresia in porcine ovaries and serves as an inhibitor of apoptosis in granulosa cells. In addition, transforming growth factor (TGF)-βsignaling has been considered a central trigger in granulosa cell apoptosis. However, the link between TGF-β signaling and VEGFA is unknown. We proved that miR-361-5p is significantly upregulated during the atresia process and that it promotes GC apoptosis by directly targeting the VEGFA 3′UTR. In addition, we revealed that the miR-361-5p coding gene MIR361 was significantly downregulated by SMAD4, the central intracellular mediator of TGF-β signaling, that bound to the MIR361 promoter. In conclusion, our findings expanded what is known about VEGFA posttranscriptional regulation and revealed a complete SMAD4/miR-361-5p/VEGFA regulatory network in ovarian granulosa cell apoptosis. These data provide useful references for follicular atresia and ovarian physiological function studies.

Multiple roles of hypoxia in bovine corpus luteum

There has been increasing interest in the role of hypoxia in the microenvironment of organs, because of the discovery of hypoxia-inducible factor-1 (HIF1), which acts as a transcription factor for many genes activated specifically under hypoxic conditions. The ovary changes day by day during the estrous cycle as it goes through phases of follicular growth, ovulation, and formation and regression of the corpus luteum (CL). These phenomena are regulated by hypothalamic and pituitary hormones, sex steroids, peptides and cytokines, as well as oxygen conditions. Hypoxia strongly induces angiogenesis via transcription of a potent angiogenic factor, vascular endothelial growth factor (VEGF), that is regulated by HIF1. A CL forms with a rapid increase of angiogenesis that is mainly induced by HIF1-VEGF signaling. Hypoxia also contributes to luteolysis by down-regulating progesterone synthesis and by up-regulating apoptosis of luteal cells. This review focuses on recent studies on the roles of hypoxia- and HIF1-regulated genes in the regulation of bovine CL function.

FSH prevents porcine granulosa cells from hypoxia-induced apoptosis via activating mitophagy through the HIF-1α-PINK1-Parkin pathway

In developing follicles, the granulosa cells (GCs) live in a hypoxic environment due to the devoid of blood supply. Upon hypoxic conditions, several types of mammalian cells have been reported to undergo apoptosis. Follicle-stimulating hormone (FSH) is known as the primary survival factor for antral follicles by preventing GCs apoptosis. Mitophagy is a type of organelle-specific autophagy that removes damaged or stressed mitochondria to maintain cellular health. This study provides the first evidence suggesting that FSH-mediated mitophagy protected porcine GCs from hypoxia-induced apoptosis. Our data showed that the GCs apoptosis caused by mitochondrial pathway upon hypoxia stress was markedly attenuated after FSH treatment, which was correlated with enhanced activation of mitophagy. Interestingly, FSH also stimulated mitochondrial biogenesis as suggested by increased expression of mitochondrial transcription factor A and nuclear respiratory factor 1 during hypoxia exposure. Notably, the protein level of hypoxia inducible factor-1α (HIF-1α) was significantly increased in hypoxic GCs following FSH treatment, accompanied by elevated mitophagic activity and dampened apoptotic signaling. Blocking HIF-1α inhibited mitophagy and restored hypoxia-induced apoptosis despite FSH treatment. Importantly, FSH promoted the expression of serine/threonine kinase PTEN induced putative kinase 1 (PINK1) and the E3 ligase Parkin during hypoxia stress through a HIF-1α dependent manner. This induced the mitophagic clearance of damaged mitochondria, hence inhibiting apoptosis by reducing cytochrome c releasing. The inhibition of HIF-1α and/or PINK1 using inhibitor or RNAi further confirmed the role of the FSH-HIF-1α-PINK1-Parkin-mitophagy axis in suppressing GC apoptosis under hypoxic conditions. These findings highlight a novel function of FSH in preserving GCs viability against hypoxic damage by activating HIF-1α-PINK1-Parkin-mediated mitophagy.

Autophagy in hypoxic ovary

Oxygen deprivation affects human health by modulating system as well as cellular physiology. Hypoxia generates reactive oxygen species (ROS), causes oxidative stress and affects female reproductive health by altering ovarian as well as oocyte physiology in mammals. Hypoxic conditions lead to several degenerative changes by inducing various cell death pathways like autophagy, apoptosis and necrosis in the follicle of mammalian ovary. The encircling somatic cell death interrupts supply of nutrients to the oocyte and nutrient deprivation may result in the generation of ROS. Increased level of ROS could induce granulosa cells as well as oocyte autophagy. Although autophagy removes damaged proteins and subcellular organelles to maintain the cell survival, irreparable damages could induce cell death within intra-follicular microenvironment. Hypoxia-induced autophagy is operated through 5' AMP activated protein kinase-mammalian target of rapamycin, endoplasmic reticulum stress/unfolded protein response and protein kinase C delta-c-junN terminal kinase 1 pathways in a wide variety of somatic cell types. Similar to somatic cells, we propose that hypoxia may induce granulosa cell as well as oocyte autophagy and it could be responsible at least in part for germ cell elimination from mammalian ovary. Hypoxia-mediated germ cell depletion may cause several reproductive impairments including early menopause in mammals.

Efficacy and safety of aflibercept in in vitro and in vivo models of retinoblastoma

Background

To evaluate the inhibitory effects of aflibercept on the growth and subretinal invasion of retinoblastoma.

Methods

Xenotransplantation and orthotopic mouse models were created by injecting Y-79 cells subcutaneously and intravitreally, respectively. After induction of retinoblastoma, animals were intraperitoneally injected with aflibercept (25 mg/kg body weight) or saline twice a week for 3 weeks. Tumor size was measured weekly and compared between the two groups. At 4 weeks, animals were sacrificed and an immunohistochemical examination was conducted to compare the microvascular density and degree of apoptosis between groups. In addition, the degree of choroidal invasion was also analyzed in the orthotopic xenotransplantation model. A co-culture system of Y-79 or WERI-Rb-1 cells and human umbilical vein endothelial cells (HUVECs) was used for in vitro experiments, and the anti-angiogenic effect of aflibercept was evaluated by analyzing cell numbers.

Results

In the Y-79 xenotransplantation model, aflibercept treatment significantly inhibited tumor growth at 4 weeks versus baseline compared with saline-injected mice (188.53 ± 118.53 mm³ vs. 747.87 ± 118.83 mm³, respectively, P < 0.001). Tumors isolated from aflibercept-treated mice contained fewer blood vessels (8.59 % ± 7.60 % vs. 14.91 % ± 4.53 %, respectively, P < 0.05) and an increased number of apoptotic cells (15.10 ± 9.13 vs. 4.44 ± 2.24, respectively, P < 0.05). In the orthotopic model, the degree of subretinal invasion of tumor cells was significantly reduced after aflibercept treatment (0.07 ± 0.06 vs. 0.15 ± 0.10, P < 0.05). And addition of aflibercept to co-cultures of HUVECs and Y-79, WERI-Rb-1 cells significantly reduced HUVEC proliferation.

Conclusions

Aflibercept reduced retinoblastoma angiogenesis in association with a significant reduction in tumor growth and invasion. These findings suggest that aflibercept could be used in an adjuvant role together with systemic chemotherapy to reduce tumor size and angiogenesis in retinoblastoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0451-7) contains supplementary material, which is available to authorized users.

Hypoxia-inducible factor-1α overexpression indicates poor clinical outcomes in tongue squamous cell carcinoma

The aim of the present study was to investigate the expression of hypoxia-inducible factor-1α (HIF-1α) in tongue squamous cell carcinoma (TSCC) and to assess its possible impact on prognosis. A total of 49 tumor samples and 15 adjacent non-tumor samples from 49 patients treated between January 2000 and December 2005 at the Department of Oral and Maxillofacial Surgery, Hospital of Stomatology, Tongji University (Shanghai, China) were obtained for investigation with immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). The expression of HIF-1α was detected in 87.76% (43/49) of the TSCC samples and in 33.33% (5/15) of the adjacent non-tumor tissues. The expression of vascular endothelial growth factor (VEGF) was also observed in 83.67% (41/49) of the TSCC samples and in only 20% (3/15) of the adjacent non-tumor samples at a low level. RT-PCR revealed that the mRNA expression of HIF-1α and VEGF was present in the tumor tissues; however, it was barely detected in the corresponding adjacent normal tissues. The overexpression of HIF-1α was significantly associated with T classification (P=0.01), lymphatic metastasis (P=0.05) and histological differentiation (P<0.001). Furthermore, HIF-1α overexpression was significantly associated with poor overall (P=0.001) and disease-free survival rates (P=0.01), independent of T stage and lymphatic metastasis. The Cox proportional hazards regression model demonstrated that the level of HIF-1α expression may be an independent prognostic factor for TSCC. HIF-1α overexpression was observed in TSCC and its overexpression suggests a poor prognosis. HIF-1α may be a molecular marker for predicting the prognosis of TSCC.

Hypoxia stimulates the production of the angiogenesis inhibitor 2-methoxyestradiol by swine granulosa cells

We previously demonstrated the presence of 2-methoxyestradiol (2-ME) in swine follicular fluid. Present study was aimed first of all to investigate if swine granulosa cell produce 2-ME; in addition, we tried to assess a potential effect of hypoxia in modulating 2-ME output. Finally, we explored the effect of 2-ME in an angiogenesis bioassay set up in our lab. Our data show that cultured granulosa cells are able to produce 2-ME; interestingly, the secretion of the hormone appeared to be stimulated by hypoxia. Angiogenesis bioassay points out that 2-ME displays an inhibitory effect on neovascularisation. Therefore our data suggest that 2-ME could be a local effector in determining the fine tuning responsible for follicle angiogenesis. These data deserve special attention since the ovary is a valuable experimental model in angiogenesis research.

Prevention and management of ovarian hyperstimulation syndrome

The Ovarian Hyperstimulation Syndrome (OHSS) represents one of the biggest nightmares of all physicians involved in Assisted Reproductive Technologies (ART). Every year, several hundreds of women are hospitalized and to date several deaths have been reported. The pivotal event in the development of OHSS is the disruption of capillary integrity that results in leakage of intravascular fluid and proteins into third space. On the molecular level, human chorionic godadotropin (HCG) either exogenous or endogenous, functions as the triggering point for the production of vascular endothelial growth factor (VEGF) that is the main mediator to increase permeability on the vascular bed. Spontaneous OHSS has also been reported, either due to inappropriate activation of a mutant FSH receptor or due to very high levels of HCG during pregnancy. The available evidence on the several preventive and therapeutic approaches with special attention to level 1 evidence when available is also presented. OHSS is a self-resolving condition and the main role of the physician is to correct and maintain the intravascular volume, to support renal function and respiration and prevent thrombotic events. An algorithm on the management of OHSS on an outpatient basis and in the hospital is based on the previous mentioned principles.