Changes in the Thecal Vasculature During Follicular Atresia in the Ovary of Swamp Buffalo

Integrated transcriptome and proteome revealed that the declined expression of cell cycle-related genes associated with follicular atresia in geese

BACKGROUND

Geese exhibit relatively low reproductive performance, and follicular atresia is an important factor that restricts the egg production of geese. Systematic analysis of the regulation of follicle atresia in geese through transcriptome and proteome levels could provide meaningful information on clarifying the mechanism of follicle atresia in poultry.

RESULT

The granulosa cell layer was loose, disintegrated and showed apoptosis in atretic follicles and remained intact in normal follicles. The hormone levels of FSH and LH were significantly decreased in the atresia follicles compared to the normal follicles (P < 0.05). A total of 954 differentially expressed genes (DEGs, 315 increased and 639 decreased) and 161 differentially expressed proteins (DEPs, 61 increased and 100 decreased) were obtained in atresia follicles compared to normal follicles, of which, 15 genes were differentially expressed in both transcriptome and proteome. The DEGs were mainly enriched in sodium transmembrane transport, plasma membrane, and transmembrane transporter activity based on the GO enrichment analysis and in the cell cycle pathway based on the KEGG enrichment analysis. The DEPs were mainly enriched in localization, lysosome, and phospholipid-binding based on the GO enrichment analysis. Candidate genes Smad2/3, Smad4, Annexin A1 (ANXA1), Stromelysin-1 (MMP3), Serine/threonine-protein kinase (CHK1), DNA replication licensing factor (MCM3), Cyclin-A2 (CCNA2), mitotic spindle assembly checkpoint protein (MAD2), Cyclin-dependent kinase 1 (CDK1), fibroblast growth factor 12 (FGF12), and G1/S-specific cyclin-D1 (CCND1) were possibly responsible for the regulation of atresia.

CONCLUSION

The cell cycle is an important pathway for the regulation of follicular atresia. Sodium outflow and high expression of MMP3 and MMP9 could be responsible for structural destruction and apoptosis of follicular cells.

NORHA, a novel follicular atresia-related lncRNA, promotes porcine granulosa cell apoptosis via the miR-183-96-182 cluster and FoxO1 axis

BACKGROUND

Follicular atresia has been shown to be strongly associated with a low follicle utilization rate and female infertility, which are regulated by many factors such as microRNAs (miRNAs), which constitute a class of noncoding RNAs (ncRNAs). However, little is known about long noncoding RNAs (lncRNAs), which constitute another ncRNA family that regulate follicular atresia.

RESULTS

A total of 77 differentially expressed lncRNAs, including 67 upregulated and 10 downregulated lncRNAs, were identified in early atretic follicles compared to healthy follicles by RNA-Sequencing. We characterized a noncoding RNA that was highly expressed in atretic follicles (NORHA). As an intergenic lncRNA, NORHA was one of the upregulated lncRNAs identified in the atretic follicles. To determine NORHA function, RT-PCR, flow cytometry and western blotting were performed, and the results showed that NORHA was involved in follicular atresia by influencing GC apoptosis with or without oxidative stress. To determine the mechanism of action, bioinformatics analysis, luciferase reporter assay and RNA immunoprecipitation assay were performed, and the results showed that NORHA acted as a 'sponge', that directly bound to the miR-183-96-182 cluster, and thus prevented its targeted inhibition of FoxO1, a major sensor and effector of oxidative stress.

CONCLUSIONS

We provide a comprehensive perspective of lncRNA regulation of follicular atresia, and demonstrate that NORHA, a novel lncRNA related to follicular atresia, induces GC apoptosis by influencing the activities of the miR-183-96-182 cluster and FoxO1 axis.

Deficient Proliferation and Apoptosis in the Granulosa and Theca Interna Cells of the Bovine Cystic Follicle

The aim of the present study was to examine the frequencies of cell proliferation and death of granulosa and theca interna layers during development of cystic follicles in order to understand the mechanisms of cystic follicle formation. Paraffin sections of cystic follicles were immunostained with antibodies against proliferating cell nuclear antigen (PCNA) and cleaved caspase-3 in order to observe proliferating and apoptotic cells, respectively. The concentrations of estradiol-17beta and progesterone in the follicular fluid of these follicles were measured by ELISA. The granulosa and theca interna layers contained both PCNA- and caspase-3-positive cells, although their numbers were limited. There was significant negative correlation between the estradiol-17beta and progesterone concentrations in the follicular fluid. Regression analysis revealed no significant correlation, except for that between the PCNA-positive cells in the theca interna and the caspase-3-positive cells in the granulosa layer. These results indicate that the granulosa and theca interna cells of the cystic follicle show weak proliferative activity and low apoptotic frequency; this implies that the cystic follicle grows slowly and then maintains a static condition without degeneration, which leads to long-term persistence of the follicle.

Regulation of the ovarian follicular vasculature

Angiogenesis is associated with follicular development and is regulated independently within each follicle potentially making the functioning of its vasculature critically important in determining its fate. This review examines the various ways in which follicular angiogenesis may be monitored, describes the follicular localisation and changes in pro- and anti-angiogenic factors that may regulate the process and how antagonists may be used to elucidate their physiological role in vivo. Thus, inhibition of vascular endothelial growth factor (VEGF), VEGF receptor-2, vascular endothelial cell cadherin or interference with the angiopoietin system can inhibit follicular development or prevent ovulation.

Microvascular distribution and vascular endothelial growth factor expression in bovine cystic follicles

The aim of this study was to examine the distribution of microvessels in the theca and the expression of vascular endothelial growth factor (VEGF) in the theca and granulosa of cystic follicles. Paraffin sections of cystic follicles were stained with Bandeiraea simplicifolia-I (BS-I) to visualize the endothelial cells of microvessels. The other sections were immunostained with anti-VEGF antibody. The mRNA expression of VEGF in the theca interna of cystic and healthy follicle was determined by RT-PCR. In the theca interna, cystic follicles with granulosa cells had significantly greater microvessel number density (the number of microvessels per given field) and area (area occupied by microvessels per given area) than healthy follicles in various sizes (<3, 4-8, >9 mm). Loss of granulosa cells from cystic follicles resulted in a similar number density, but significantly smaller area of microvessels in the theca interna. There was no significant difference in the microvessel number density and area of the theca externa between the types of follicle. VEGF protein was expressed in the granulosa and theca interna of healthy and cystic follicles. These results demonstrate that cystic follicles have a highly developed vasculature network in the theca interna, especially in cystic follicles containing granulosa cells. It is also suggested that VEGF is highly expressed in the cystic follicle as well as healthy follicle, which may be associated with advanced vasculature and the accumulation of follicular fluid in cystic follicles.

Apoptosis in the Antral Follicles of Swamp Buffalo and Cattle Ovary: TUNEL and Caspase-3 Histochemistry

The present study was carried out to investigate the pattern of apoptosis in the healthy antral and atretic follicles of Philippine swamp buffaloes (BU) in comparison with Holstein-Friesian (HF) cows. Paraffin sections of healthy follicles and various stages of atretic follicles were stained using the terminal deoxynucleotidyl transferase (TdT)-mediated biotinylated deoxyuridine triphosphates (dUTP) nick end-labelling (TUNEL) method to detect DNA fragmentation and cleaved caspase-3 antibody to detect cells committed to undergo apoptosis. Five equidistant areas of a follicle were counted for the presence of TUNEL- and caspase-3-positive cells. Healthy follicles of BU and HF contained no TUNEL-positive cells in the granulosa and theca layer but showed some caspase-3 positivity. The granulosa layer of advanced atretic follicles showed a significantly higher frequency of caspase-3 positivity than the healthy and early atretic follicles in both breeds. The frequency of caspase-3-positive cells of BU was significantly higher than HF in the granulosa layer of healthy, early atretic and advanced atretic follicles. In the theca interna layer, BU and HF showed a significantly lower and higher frequency of TUNEL-positive cells in the late atretic follicles compared with advanced atretic follicle, respectively. However, the frequency of caspase-3-positive cells of both BU and HF in the late atretic follicles was significantly higher than the advanced atretic follicles in the theca interna layer. These results indicate that caspase-3 and DNA fragmentation is involved in the buffalo ovarian apoptotic process.

Immunolocalization of von Willebrand Factor and Vascular Endothelial Growth Factor during Follicular Atresia in the Swamp Buffalo Ovary

The aim of this study was to investigate the distribution pattern of von Willebrand factor (vWF) and vascular endothelial growth factor (VEGF) in the healthy antral and atretic follicles of Philippine swamp buffaloes (SB) in comparison with Holstein-Friesian cows (HF). Paraffin sections of healthy follicles and atretic follicles at various stages were immunostained with vWF antibody and VEGF antibody. The density of vWF-positive capillary vessels in the theca interna significantly increased as atresia progressed in SB, whereas the density significantly decreased in late atretic follicles compared with advanced ones in HF. On the other hand, the area of vWF-positive capillary vessels in the theca interna significantly increased as atresia progressed in both SB and HF. Immunoreactions of VEGF in the granulosa cells (in all follicle types) were observed in both SB and HF. In the granulosa layer, a reduction in the VEGF immunoreaction was noted as follicles progressed from healthy to advanced atretic follicles in both animals. Granulosa cells (in both SB and HF) showed a higher immunopositive staining than theca cells. In the theca interna, VEGF immunostaining diminished as follicles progressed to the late atretic follicles in both animals. These results indicate that during atresia, changes of vWF expression are the opposite of VEGF expression in SB. Both vWF and VEGF are suggested to be associated with follicular atresia in SB.

Expression of Gap Junction Protein Connexin 43 during Follicular Atresia in the Ovary of Swamp Buffaloes

The present study was performed to detect the presence of gap junction protein connexin 43 (Cx43) and describe the changes in its expression during ovarian follicular atresia in the swamp buffalo in comparison with cattle. Ovaries of Philippine swamp buffaloes (Bubalus bubalis; SB) and Holstein-Friesian cows (Bos taurus; HF) were collected from slaughterhouses, fixed in 10% formalin in PBS and embedded in paraffin. Sections of healthy follicles and at various follicular stages of atresia were immunostained with anti-Cx43 antibody. Cx43 appeared as punctate staining between granulosa cells (healthy to advanced atretic follicles), indicating assembled gap junctions, but was absent in the theca interna. In SB as well as in HF, granulosa cells showed a dense, moderate, and sparse immunoreactivity to Cx43 in healthy, early atretic, and advanced atretic follicles, respectively. Cumulus cells (in the advanced atretic follicle) surrounding oocytes and adjacent granulosa layers retain the Cx43 protein, although there was only a sparse expression of Cx43 observed in the granulosa layers distant from oocytes in the same follicles. The results indicate that gap junction protein Cx43 decreases in association with atresia and supports the concept that a loss of gap junctional communication plays a coordinating role in the process of atresia. Furthermore, the schema of Cx43 immunoreactivity in SB granulosa cells is similar to that of HF.