Co‐ordinated expression of the VEGF system components in granulosa cells to develop a proangiogenic autocrine milieu during ovarian follicle development

Ovarian microenvironment: challenges and opportunities in protecting against chemotherapy-associated ovarian damage

BACKGROUND

Chemotherapy-associated ovarian damage (CAOD) is one of the most feared short- and long-term side effects of anticancer treatment in premenopausal women. Accumulating detailed data show that different chemotherapy regimens can lead to disturbance of ovarian hormone levels, reduced or lost fertility, and an increased risk of early menopause. Previous studies have often focused on the direct effects of chemotherapeutic drugs on ovarian follicles, such as direct DNA damage-mediated apoptotic death and primordial follicle burnout. Emerging evidence has revealed an imbalance in the ovarian microenvironment during chemotherapy. The ovarian microenvironment provides nutritional support and transportation of signals that stimulate the growth and development of follicles, ovulation, and corpus luteum formation. The close interaction between the ovarian microenvironment and follicles can determine ovarian function. Therefore, designing novel and precise strategies to manipulate the ovarian microenvironment may be a new strategy to protect ovarian function during chemotherapy.

OBJECTIVE AND RATIONALE

This review details the changes that occur in the ovarian microenvironment during chemotherapy and emphasizes the importance of developing new therapeutics that protect ovarian function by targeting the ovarian microenvironment during chemotherapy.

SEARCH METHODS

A comprehensive review of the literature was performed by searching PubMed up to April 2024. Search terms included 'ovarian microenvironment' (ovarian extracellular matrix, ovarian stromal cells, ovarian interstitial, ovarian blood vessels, ovarian lymphatic vessels, ovarian macrophages, ovarian lymphocytes, ovarian immune cytokines, ovarian oxidative stress, ovarian reactive oxygen species, ovarian senescence cells, ovarian senescence-associated secretory phenotypes, ovarian oogonial stem cells, ovarian stem cells), terms related to ovarian function (reproductive health, fertility, infertility, fecundity, ovarian reserve, ovarian function, menopause, decreased ovarian reserve, premature ovarian insufficiency/failure), and terms related to chemotherapy (cyclophosphamide, lfosfamide, chlormethine, chlorambucil, busulfan, melphalan, procarbazine, cisplatin, doxorubicin, carboplatin, taxane, paclitaxel, docetaxel, 5-fluorouraci, vincristine, methotrexate, dactinomycin, bleomycin, mercaptopurine).

OUTCOMES

The ovarian microenvironment shows great changes during chemotherapy, inducing extracellular matrix deposition and stromal fibrosis, angiogenesis disorders, immune microenvironment disturbance, oxidative stress imbalances, ovarian stem cell exhaustion, and cell senescence, thereby lowering the quantity and quality of ovarian follicles. Several methods targeting the ovarian microenvironment have been adopted to prevent and treat CAOD, such as stem cell therapy and the use of free radical scavengers, senolytherapies, immunomodulators, and proangiogenic factors.

WIDER IMPLICATIONS

Ovarian function is determined by its 'seeds' (follicles) and 'soil' (ovarian microenvironment). The ovarian microenvironment has been reported to play a vital role in CAOD and targeting the ovarian microenvironment may present potential therapeutic approaches for CAOD. However, the relation between the ovarian microenvironment, its regulatory networks, and CAOD needs to be further studied. A better understanding of these issues could be helpful in explaining the pathogenesis of CAOD and creating innovative strategies for counteracting the effects exerted on ovarian function. Our aim is that this narrative review of CAOD will stimulate more research in this important field.

REGISTRATION NUMBER

Not applicable.

Genome-wide association studies of egg production traits by whole genome sequencing of Laiwu Black chicken

Compared to high-yield commercial laying hens, Chinese indigenous chicken breeds have poor egg laying capacity due to the lack of intensive selection. However, as these breeds have not undergone systematic selection, it is possible that there is a greater abundance of genetic variations related to egg laying traits. In this study, we assessed 5 egg number (EN) traits at different stages of the egg-laying period: EN1 (from the first egg to 23 wk), EN2 (from 23 to 35 wk), EN3 (from 35 to 48 wk), EN4 (from the first egg to 35 wk), and EN5 (from the first egg to 48 wk). To investigate the molecular mechanisms underlying egg number traits in a Chinese local chicken breed, we conducted a genome-wide association study (GWAS) using data from whole-genome sequencing (WGS) of 399 Laiwu Black chickens. We obtained a total of 3.01 Tb of raw data with an average depth of 7.07 × per individual. A total of 86 genome-wide suggestive or significant single-nucleotide polymorphisms (SNP) contained within a set of 45 corresponding candidate genes were identified and found to be associated with stages EN1-EN5. The genes vitellogenin 2 (VTG2), lipase maturation factor 1 (LMF1), calcium voltage-gated channel auxiliary subunit alpha2delta 3 (CACNA2D3), poly(A) binding protein cytoplasmic 1 (PABPC1), programmed cell death 11 (PDCD11) and family with sequence similarity 213 member A (FAM213A) can be considered as the candidate genes associated with egg number traits, due to their reported association with animal reproduction traits. Noteworthy, results suggests that VTG2 and PDCD11 are not only involved in the regulation of EN3, but also in the regulation of EN5, implies that VTG2 and PDCD11 have a significant influence on egg production traits. Our study offers valuable genomic insights into the molecular genetic mechanisms that govern egg number traits in a Chinese indigenous egg-laying chicken breed. These findings have the potential to enhance the egg-laying performance of chickens.

Effects of vascular endothelial growth factor (VEGF) on the viability, apoptosis and steroidogenesis of yak (Bos grunniens) granulosa cells

Vascular endothelial growth factor (VEGF) is crucial for follicle development through the regulation of granulosa cell (GC) function in some mammals, but its mechanism is unclear in yak (Bos grunniens). Therefore, the objectives of this study were to investigate the effects of VEGF on the viability, apoptosis and steroidogenesis of yak GCs. First, we investigated the localization of VEGF and its receptor (VEGFR2) in yak ovaries by immunohistochemistry analysis and evaluated the effect of culture medium containing different VEGF concentrations and culture times on the viability of yak GCs by Cell Counting Kit-8. Then, optimal treatment with 20 ng/mL VEGF for 24 h was selected to analyze the effects of this compound on intracellular reactive oxygen species levels by DCFH-DA kit, cell cycle and apoptosis by flow cytometry, steroidogenesis by ELISA kit and the expression of the related genes by RT‒qPCR. The results showed that VEGF and VEGFR2 were highly coexpressed in GCs and theca cells. GCs cultured in medium containing 20 ng/mL VEGF for 24 h significantly improved cell viability, decreased ROS production, promoted the transition from G1 phase to S phase (P < 0.05), increased the expression of the CCND1 (P < 0.05), CCNE1, CDK2, CDK4, and PCNA genes (P < 0.01) and decreased the expression of the P53 gene (P < 0.05). This treatment significantly reduced GC apoptosis (P < 0.05) by promoting the expression of BCL2 and GDF9 (P < 0.01) and inhibiting the expression of BAX and CASPASE3 (P < 0.05). VEGF promoted progesterone secretion (P < 0.05) accompanied by increased expression of HSD3B, StAR and CYP11A1 (P < 0.05). Taken together, our findings highlight the beneficial influence exerted by VEGF in improving GC viability and reducing ROS production and the apoptosis rate through the modulation of related gene expression.

The vascular endothelial growth factor (VEGF) system as a key regulator of ovarian follicle angiogenesis and growth

The vascular endothelial growth factor-A (VEGFA) system is a complex set of proteins, with multiple isoforms and receptors, including both angiogenic (VEGFxxx, VEGFR2) and antiangiogenic members (VEGFxxxb, VEGFR1 and soluble forms of VEGFR). The members of the VEGF system affect the proliferation, survival, and migration of endothelial and nonendothelial cells and are involved in the regulation of follicular angiogenesis and development. The production of VEGF by secondary follicles stimulates preantral follicular development by directly affecting follicular cells and promoting the acquisition of the follicular vasculature and downstream antrum formation. Additionally, the pattern of expression of the components of the VEGF system may provide a proangiogenic milieu capable of triggering angiogenesis and stimulating follicular cells to promote antral follicle growth, whereas, during atresia, this milieu becomes antiangiogenic and blocks follicular development.

Identifying selection signatures for litter size in Guangxi Bama Xiang pigs

Litter size is an important economic trait in pig production. However, the genetic mechanisms underlying varying litter size in Guangxi Bama Xiang pigs remain unknown. To identify selection signatures for litter size in Guangxi Bama Xiang pigs, we obtained 297 Illumina PorcineSNP50 BeadChip array data and the average born number (ABN) from parity one to nine in Guangxi Bama Xiang pigs. Fixation index (Fst) methods were used to identify the selection signature of the litter size, and three phenotypic gradient differential population pairs (according to the ABN) in individuals were used to reduce the false positives of signature selections. Single nucleotide polymorphisms (SNPs) were identified in the VEGFA promoter and exons. The general linear model was used to analyse the differences in distinct genotypes after they were typed using three-round multiplex PCR technology. Finally, the transcriptome factor and CpG island in the VEGFA promoter were predicted. A total of 328, 328 and 317 significant loci were identified in the 1st, 2nd and 3rd population pairs, respectively. After removing the false positives, 25 SNPs were defined as the selection signatures in relation to litter size. Ten (VEGFA, USP49, USP25, SRPK1, SLC26A8, RPL10A, PPARD, MAPK14, HMGA1 and CHRDL2) out of 52 genes in the selection regions were annotated as the candidate genes of litter size, respectively, VEGFA. There were no SNPs in the VEGFA exon region, but we obtained three SNPs (rs786889605, rs343769603 and rs323942424) in the VEGFA promoter regions. The ABN in CC was significantly higher than that in TT in rs786889605, and the ABN in TT was significantly lower than that in GG in rs323942424. Meanwhile, the mutation of the VEGFA promoter result in the loss of Sp1 and NF-1 and the formation of Oct-1. In summary, we obtained ten candidate genes, and two mutations in the VEGFA promoter that could be important potential molecular biomarkers for litter size in Bama Xiang pigs.

Hypoxia up-regulates VEGF ligand and downregulates VEGF soluble receptor mRNA expression in bovine granulosa cells in vitro

Oxygen concentration (0₂) in antral ovarian follicles is below that found in most tissues, which is important for adequate granulosa cell function. The VEGF system is linked to angiogenesis and responds to changing 0₂ by stimulating neovascularization when levels are low. However, in the avascular granulosa cell layer of the follicle, VEGF action is directed to stimulating cell viability and steroidogenesis. The aim of this study was to examine the effect of 0₂ concentration on granulosa cell expression of the VEGF-system components. Bovine granulosa cells were isolated from medium-sized follicles (4-7 mm in diameter), placed in McCoy 5a medium supplemented with 10 ng/mL of insulin, 1 ng/mL of IGF-I, and 1 ng/mL of FSH, and cultured in four well plates (500 thousand cells per well), on three separate occasions. Culture plates were placed in gas-impermeable jars with a gas mixture containing either 2%, or 5% of O₂, or under atmospheric air condition inside an incubator (20% of 0₂). Media was replaced at 48 h of culture and cells from the plate in each oxygen concentration were pooled for RNA extraction after 96 h. The number of mRNA copies for the VEGF-system components - including ligands (VEGF120, VEGF120b, VEGF165 and VEGF165b), enzymes (cyclin-dependent like kinases-1, CLK1 and serine-arginine protein kinase 1, SRPK1), splicing factors (serine-arginine-rich splicing factors, SRSF1 and SRSF6), and the membrane-bound (VEGFR1, VEGFR2) and soluble forms of the receptors (sVEGFR1 and sVEGFR2) were quantified by qPCR. Granulosa cells cultured with low 0₂ (2%) had a higher expression of VEGF ligands (P < 0.05) when compared to cells cultured at 20% 0₂. VEGF164b mRNA was absent in granulosa cells from all culture conditions. The 2 and 5% 0₂ levels, which coincide with physiological concentrations, in the ovarian follicle, induced higher SRSF6 expression than atmospheric 0₂ concentrations (20%, P < 0.05). In contrast, mRNA copies for SRPK1, CLK1, SRSF1, VEGFR1 or VEGFR2 did not differ between 0₂ culture conditions. (P > 0.05). Nonetheless, mRNA copies for the soluble receptors, sVEGFR1 and sVEGFR2, linearly increased (P < 0.05) with 0₂ concentration. These results suggest that when cultured under hypoxic conditions, granulosa cells may develop an autocrine milieu that favors VEGF's biological effects on their survival and function.