Evidence for the existence of de novo lipogenesis in goose granulosa cells

Downregulation of FASN in granulosa cells and its impact on ovulatory dysfunction in PCOS

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complicated endocrinological and anovulatory disorder in women. Mice exposed to dihydrotestosterone (DHT) exhibit a PCOS-like phenotype characterized by abnormal steroid hormone production and ovulation dysfunction. The present investigation aims to identify overlapping genes expressed in PCOS patients and a PCOS mouse model induced by DHT and to examine the function of key genes fatty acid synthase (FASN) in hormone production and ovulation dysfunction.

RESULTS

We examined 5 datasets of high-throughput mRNA transcription from the Gene Expression Omnibus (GEO) database, including 4 datasets from individuals with PCOS and 1 dataset from a DHT-induced mouse model. GO and KEGG enrichment analyses revealed these differentially expressed genes (DEGs) are primarily involved in ovarian steroidogenesis and fatty acid metabolism. The PPI network identified 12 hub genes. qRT-PCR verification in human granulosa cells showed differential expression of FASN, SCARB1, FABP5, RIMS2, and RAPGEF4 in PCOS patients (p < 0.05). FASN was downregulated in the granulosa cells (GCs) of PCOS patients (p < 0.05). FASN depletion reduced KGN cell proliferation (p < 0.001), decreased progesterone secretion (p < 0.05), and increased estradiol secretion (p < 0.05). Downregulation of FASN inhibited ovulation by suppressing ERK1/2 phosphorylation and the expression of C/EBPα and C/EBPβ. Lentivirus-mediated FASN downregulation in rat ovaries for one and four weeks impaired the super ovulatory response, reducing oocyte retrieval, estrous cycle, secretion of estrogen and progesterone, and luteinization.

CONCLUSIONS

Our results provide new insights into PCOS pathogenesis and suggest that FASN could be a promising target for treating abnormal steroid hormone production and impaired ovulation in PCOS.

Proteome of granulosa cells lipid droplets reveals mechanisms regulating lipid metabolism at hierarchical and pre-hierarchical follicle in goose

Avian hierarchical follicles are formed by selection and dominance of pre-hierarchical follicles, and lipid metabolism plays a pivotal role in this process. The amount of lipid in goose follicular granulosa cells increases with the increase of culture time, and the neutral lipid in the cells is stored in the form of lipid droplets (LDs). LD-associated proteins (LDAPs) collaborate with LDs to regulate intracellular lipid homeostasis, which subsequently influences avian follicle development. The mechanism by which LDAPs regulate lipid metabolism in goose granulosa cells at different developmental stages is unclear. Therefore, using BODIPY staining, we found that at five time points during in vitro culture, the LD content in hierarchical granulosa cells was significantly higher than that in pre-hierarchical granulosa cells in this study (p < 0.001). Next, we identified LDAPs in both hierarchical and pre-hierarchical granulosa cells, and screened out 1,180, 922, 907, 663, and 1,313 differentially expressed proteins (DEPs) at the respective time points. Subsequently, by performing Clusters of Orthologous Groups (COGs) classification on the DEPs, we identified a large number of proteins related to lipid transport and metabolism. Following this, the potential functions of these DEPs were investigated through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis. Finally, the important pathway of fatty acid degradation and the key protein ACSL3 were screened out using Short Time-series Expression Miner (STEM) and Protein-Protein Interaction (PPI) analysis methods. It is hypothesized that ACSL3 may potentially modulate lipid metabolism through the fatty acid degradation pathway, thereby contributing to the difference in lipid content between hierarchical and pre-hierarchical granulosa cells. These findings will provide a theoretical foundation for further studies on the role of LDs and LDAPs in avian follicle development.

IGF2BP3 curbed by miR-15c-3p restores disrupted lipid storage and progesterone secretion in chicken granulosa cells under oxidative stress through AKT-Raf1-ERK1/2 signaling pathway

For commercial laying hens, the continuous high-intensity ovulation process leads to a significant accumulation of reactive oxygen species (ROS) in the granulosa cells, inducing oxidative stress, which accelerates ovarian aging and shortens the peak laying period. The molecular mechanisms underlying this process remain poorly understood. Therefore, we modeled the processes of oxidative stress and antioxidant in chicken granulosa cells. Small RNA sequencing revealed that miR-15c-3p expression was elevated by oxidative stress induction and attenuated by antioxidant curcumin. Functional validation with miR-15c-3p mimic and inhibitor confirmed the role of miR-15c-3p in exacerbating oxidative stress and resultant suppression of lipid droplet storage and progesterone secretion in chicken granulosa cells by targeting insulin-like growth factor 2 binding protein 3 (IGF2BP3). These regulatory effects were mediated through the sequential downstream signaling cascade of AKT-Raf1-ERK1/2. In conclusion, IGF2BP3 curbed by miR-15c-3p restores disrupted lipid storage and progesterone secretion in chicken granulosa cells under oxidative stress through AKT-Raf1-ERK1/2 signaling pathway. These findings offer new insights into the molecular mechanisms by which oxidative stress damages reproductive capacity and a theoretical basis for mitigating oxidative stress in laying hens through genetic improvement.

Transcriptome Analysis Reveals the Molecular Mechanism of PLIN1 in Goose Hierarchical and Pre-Hierarchical Follicle Granulosa Cells

PLIN1, a member of the PAT family, is expressed in both adipocytes and steroidogenic cells. In this study, we used cell transfection technology combined with transcriptome sequencing to investigate the regulatory mechanism of PLIN1 in goose follicular GCs. Gene Ontology (GO) analysis revealed that in the four groups (phGC: over_vs_over-NC; hGC: over_vs_over-NC; phGC: si_vs_si-NC; hGC: si_vs_si-NC), most differentially expressed genes (DEGs) were significantly enriched (p < 0.05) in pathways related to biological processes (BPs), particularly those associated with the regulation of cellular lipid metabolism and oxidative stress. KEGG analysis further identified significant enrichment (p < 0.05) in pathways related to cell apoptosis and the cell cycle. A joint analysis of KEGG and PPI on the upregulated and downregulated DEGs revealed that the TGF-β signaling pathway was the only pathway significantly enriched among both upregulated and downregulated DEGs after PLIN1 overexpression in hGCs and phGCs. Based on these findings, we hypothesize that PLIN1 overexpression may promote granulosa cell proliferation and apoptosis by activating the TGF-β signaling pathway in goose follicular GCs. Additionally, nine potential candidate genes were identified: PPARγ, MGLL, PTEN, BAMBI, BMPR2, JUN, FST, ACSF3, and ACSL4. These results address a significant research gap concerning the role of this gene in granulosa cells and contribute to the understanding of its molecular regulatory mechanisms.

miR-24-3p inhibits lipid synthesis and progesterone secretion in chicken granulosa cells via ERK1/2 signaling pathway

Normal follicular development is the basis for ovulation in poultry. Our previous sequencing analysis revealed a high expression of miR-24-3p in chicken follicles from degenerated ovaries, suggesting that miR-24-3p may modulate follicular development. Hence, this study investigated the specific mechanisms of miR-24-3p in regulating chicken follicular development. The results revealed that the proliferation, lipid synthesis, and progesterone secretion were significantly inhibited after miR-24-3p overexpression in chicken granulosa cells, vice versa by miR-24-3p knockdown. Dual-specificity phosphatase 16 (DUSP16) and thousand and one amino acid kinase 1 (TAOK1) were identified as potential target genes of miR-24-3p. Further validation revealed that knockdown of DUSP16 and TAOK1 suppressed proliferation, lipid synthesis, and progesterone secretion in chicken granulosa cells. Moreover, we observed that miR-24-3p, along with knockdown of DUSP16 and TAOK1, increased the phosphorylation levels of extracellular signal-regulated kinases 1 and 2 (ERK1/2). Our previous study proved that activation of ERK1/2 inhibited lipid synthesis and progesterone secretion of chicken granulosa cells. In summary, we demonstrated that miR-24-3p targeting DUSP16 and TAOK1 disrupts lipid synthesis and progesterone secretion via ERK1/2 signaling pathway in chicken granulosa cells in vitro. These results may provide a new theoretical basis for resolving miRNAs regulation on reproductive performance of chickens.

tsRNA-00764 Regulates Estrogen and Progesterone Synthesis and Lipid Deposition by Targeting PPAR-γ in Duck Granulosa Cells

Transfer RNA-derived small RNAs (tsRNAs) are novel regulatory small non-coding RNAs that have been found to modulate many life activities in recent years. However, the exact functions of tsRNAs in follicle development remain unclear. Follicle development is a remarkably complex process that follows a strict hierarchy and is strongly associated with reproductive performance in ducks. The process of converting small yellow follicles into hierarchal follicles is known as follicle selection, which directly determines the number of mature follicles. We performed small RNA sequencing during follicle selection in ducks and identified tsRNA-00764 as the target of interest based on tsRNA expression profiles in this study. Bioinformatics analyses and luciferase reporter assays further revealed that peroxisome proliferator-activated receptor-γ (PPAR-γ) was the target gene of tsRNA-00764. Moreover, tsRNA-00764 knockdown promoted estrogen and progesterone synthesis and lipid deposition in duck granulosa cells, while a PPAR-γ inhibitor reversed the above phenomenon. Taken together, these results demonstrate that tsRNA-00764, differentially expressed in pre-hierarchal and hierarchy follicles, modulates estrogen and progesterone synthesis and lipid deposition by targeting PPAR-γ in duck granulosa cells, serving as a potential novel mechanism of follicle selection. Overall, our findings provide a theoretical foundation for further exploration of the molecular mechanisms underlying follicle development and production performance in ducks.

DUSP8-attenuated ERK1/2 signaling mediates lipogenesis and steroidogenesis in chicken granulosa cells

The lipogenesis and steroidogenesis of granulosa cells are crucial during follicular development, yet it remains unclear whether dual-specificity phosphatase 8 (DUSP8) is involved. In this study, the specific role of DUSP8 in lipogenesis and steroidogenesis was investigated through culturing chicken granulosa cells in vitro. The results revealed that the expression levels of adipogenic genes were elevated after DUSP8 overexpression and reduced after knockdown. The same was observed for lipid deposition in granulosa cells. Meanwhile, the steroidogenic gene expression and progesterone synthesis were promoted after DUSP8 overexpression and inhibited after knockdown. In addition, we also found that DUSP8 blocked the phosphorylation of extracellular regulatory kinase 1/2 (ERK1/2). Based on the previous results that activated ERK1/2 signaling inhibited lipid deposition and progesterone synthesis in chicken granulosa cells, we demonstrated that DUSP8 promoted lipid deposition and progesterone synthesis through mediating the ERK1/2 signaling pathway. The results will improve our understanding of the molecular regulatory mechanisms regarding lipid metabolism and progesterone synthesis in chicken granulosa cells.

Attenuated AKT signaling by miR-146a-5p interferes with chicken granulosa cell proliferation, lipid deposition and progesterone biosynthesis

Steroid hormones play a crucial role in the growth and maturation of poultry ovarian follicles, with progesterone secretion by granulosa cells (GC) being essential. According to our previous transcriptome analysis, it apparented that miR-146a-5p expressions were upregulated in the follicles undergoing atresia. In this study, we delved the depth to explore the underlying mechanisms by miR-146a-5p in the regulation of follicle functions in chicken. The study demonstrated that miR-146a-5p suppressed cell growth, lipids accumulation, and progesterone biosynthesis in chicken GC. Through targeting association validations, we identified delta 4-desaturase, sphingolipid 1 (DEGS1) as capable of interacting with miR-146a-5p. Co-transfection experiments further confirmed that DEGS1 reversed the impairment of GC functions by miR-146a-5p. Moreover, we discovered that miR-146a-5p suppressed AKT phosphorylation, while DEGS1 enhanced AKT phosphorylation. Phosphatidylinositol-3 kinase (PI3K) inhibitor (LY294002) studies showed that miR-146a-5p would inhibit AKT phosphorylation by governing the DEGS1/AKT pathway, which in turn regulates GC function. In summary, the findings revealed that miR-146a-5p suppressed cell growth, lipid deposition, and progesterone biosynthesis via the DEGS1/AKT pathway. These results may further enrich our understandings of how non-coding RNA regulates productive performance in chickens.

Estrogen Receptor Gene 1 (ESR1) Mediates Lipid Metabolism in Goose Hierarchical Granulosa Cells Rather than in Pre-Hierarchical Granulosa Cells

(1) Background: The role of estrogen receptor gene 1 (ESR1) in female reproduction and lipid metabolism has been extensively investigated. However, its contribution to lipid metabolism during the development of poultry follicles remains unclear. (2) Methods: This study aimed to explore the function of ESR1 via overexpressing (ESR1^ov) and interfering (ESR1^si) with its expression in pre-hierarchical granulosa cells (phGCs) and hierarchical granulosa cells (poGCs). (3) Results: We successfully cloned and obtained an 1866 bp segment of the full-length CDS region of the Sichuan white goose ESR1 gene. In phGCs of the ESR1^ov and ESR1^si groups, there were no significant changes compared to the control group. However, in poGCs, the ESR1^ov group exhibited decreased lipid deposition, triglycerides, and cholesterol compared to the control group, while the ESR1^si group showed increased lipid deposition, triglycerides, and cholesterol. The expression of APOB and PPARα was significantly reduced in the ESR1^ov group compared to the ESR1^ov-NC group. Moreover, significant changes in the expression of ACCα, DGAT1, SCD, CPT1, and ATGL were observed between the ESR1^si and ESR1^si-NC group. (4) Conclusions: These findings shed light on the function and molecular mechanism of ESR1 in lipid metabolism in goose poGCs, providing a better understanding of the physiological process of goose follicular development.

Transcriptome Profiling of Goose Ovarian Follicle Granulosa Cells Reveals Key Regulatory Networks for Follicle Selection

The selection of follicles determines the reproductive performance of birds, but the process of follicle selection in geese is still elusive. This study focuses on Yangzhou geese during the egg-laying period and divides the follicular development process into three stages: small follicle development, follicle selection, and follicle maturation. Transcriptome sequencing was performed on granulosa cells from large white follicles, small yellow follicles, and F5 and F4 follicles. In addition, we selected the transcripts that remained unchanged during the development and maturation of small follicles but significantly changed during the follicular selection stage as the transcript collection that plays an important role in the follicular selection process. Then, we performed functional analysis on these transcripts and constructed a ceRNA network. The results showed that during the follicular selection stage, the number of differentially expressed mRNAs, miRNAs, and lncRNAs was the highest. In addition, miR-222-3p, miR-2954-3p, miR-126-5p, miR-2478, and miR-425-5p are potential key core regulatory molecules in the selection stage of goose follicles. These results can provide a reference for a better understanding of the basic mechanisms of the goose follicle selection process and potential targets for the precise regulation of goose egg production performance.

miR-128-3p regulates chicken granulosa cell function via 14-3-3β/FoxO and PPAR-γ/LPL signaling pathways

MicroRNAs (miRNAs) are class of 22 nt short RNA sequences which inhibit protein translation through binding to the 3'UTR of its target genes. The continuous ovulatory property of chicken follicle makes it a perfect model for studying granulosa cell (GC) functions. In this study, we found that large number of miRNAs including miR-128-3p, were differentially expressed in the GCs of F1 and F5 follicles of chicken. Subsequently, the results revealed that miR-128-3p inhibited proliferation, the formation of lipid droplets, and hormone secretion in chicken primary GCs through directly targeting YWHAB and PPAR-γ genes. To determine the effects of 14-3-3β (encoded by YWHAB) protein on GCs functions, we overexpressed or inhibited the expression of YWHAB, and the results showed that YWHAB inhibited the function of FoxO proteins. Collectively, we found that miR-128-3p was highly expressed in the chicken F1 follicles compared to the F5 follicles. In addition, the results indicated that miR-128-3p promoted GC apoptosis through 14-3-3β/FoxO pathway via repressing YWHAB, and inhibited lipid synthesis by impeding the PPAR-γ/LPL pathway, as well as reduced the secretion of progesterone and estrogen. Taken together, the results showed that miR-128-3p plays a regulatory role in chicken granulosa cell function via 14-3-3β/FoxO and PPAR-γ/LPL signaling pathways.

miR-202-5p Inhibits Lipid Metabolism and Steroidogenesis of Goose Hierarchical Granulosa Cells by Targeting ACSL3

miRNAs are critical for steroidogenesis in granulosa cells (GCs) during ovarian follicular development. We have previously shown that miR-202-5p displays a stage-dependent expression pattern in GCs from goose follicles of different sizes, suggesting that this miRNA could be involved in the regulation of the functions of goose GCs; therefore, in this study, the effects of miR-202-5p on lipid metabolism and steroidogenesis in goose hierarchical follicular GCs (hGCs), as well as its mechanisms of action, were evaluated. Oil Red O staining and analyses of intracellular cholesterol and triglyceride contents showed that the overexpression of miR-202-5p significantly inhibited lipid deposition in hGCs; additionally, miR-202-5p significantly inhibited progesterone secretion in hGCs. A bioinformatics analysis and luciferase reporter assay indicated that Acyl-CoA synthetase long-chain family member 3 (ACSL3), which activates long-chain fatty acids for the synthesis of cellular lipids, is a potential target of miR-202-5p. ACSL3 silencing inhibited lipid deposition and estrogen secretion in hGCs. These data suggest that miR-202-5p exerts inhibitory effects on lipid deposition and steroidogenesis in goose hGCs by targeting the ACSL3 gene.

Integrated Transcriptome and Metabolome Analysis Reveals the Regulatory Mechanisms of FASN in Geese Granulosa Cells

FASN plays a critical role in lipid metabolism, which is involved in regulating ovarian follicular development. However, the molecular mechanisms of how FASN regulate the function of ovarian follicular cells still remain elusive. In this study, by overexpression or interference of FASN in pre-hierarchical follicle granulosa cells (phGCs) and hierarchical follicle granulosa cells (hGCs), we analyzed their effects on the granulosa cell transcriptome and metabolome profiles using RNA-Seq and LC-MS/MS, respectively. The results showed that overexpression of FASN promoted proinflammatory factors expression by activating TLR3/IRF7 and TLR3/NF-κB pathways in phGCs, but only by activating TLR3/IRF7 pathways in hGCs. Then, necroptosis and apoptosis were triggered through the JAK/STAT1 pathway (induced by inflammatory factors) and BAK/caspase-7 pathway, respectively. The combined analysis of the metabolome and transcriptome revealed that FASN affected the demand of GCs for 5-hydroxytryptamine (5-HT) by activating the neuroactive ligand-receptor interaction pathway in two categorized GCs and only altering the metabolic pathway of tryptophan in phGCs, and ultimately participated in regulating the physiological function of geese GCs. Taken together, this study showed that the mechanisms of FASN regulating the physiological function of geese phGCs and hGCs were similar, but they also had some different characteristics.

Mechanism of SCD Participation in Lipid Droplet-Mediated Steroidogenesis in Goose Granulosa Cells

Stearoyl-CoA desaturase (SCD) is a key enzyme catalyzing the rate-limiting step in monounsaturated fatty acids (MUFAs) production. There may be a mechanism by which SCD is involved in lipid metabolism, which is assumed to be essential for goose follicular development. For this reason, a cellular model of SCD function in goose granulosa cells (GCs) via SCD overexpression and knockdown was used to determine the role of SCD in GC proliferation using flow cytometry. We found that SCD overexpression induced and SCD knockdown inhibited GCs proliferation. Furthermore, ELISA analysis showed that SCD overexpression increased the total cholesterol (TC), progesterone, and estrogen levels in GCs, while SCD knockdown decreased TC, progesterone, and estrogen levels (p < 0.05). Combining these results with those of related multi-omics reports, we proposed a mechanism of SCD regulating the key lipids and differentially expressed gene (DEGs) in glycerophospholipid and glycerolipid metabolism, which participate in steroidogenesis mediated by the lipid droplet deposition in goose GCs. These results add further insights into understanding the lipid metabolism mechanism of goose GCs.

Comparative Transcriptome Analysis Provides Novel Insights into the Effect of Lipid Metabolism on Laying of Geese

Simple Summary

The importance of lipid metabolism in the egg production of poultry has been widely reported. Meanwhile, geese have lower egg production and unique lipid metabolism patterns compared with chicken and duck. It is of great significance to further improve egg laying performance to explore the differences of fat metabolism and the molecular mechanisms in geese with different egg laying performance. This study compared the phenotypic differences of liver and abdominal fat, as well as the transcriptome level differences of liver, abdominal fat, and ovarian stroma among high-, low-, and no-egg production groups. The results reveal that lipid metabolism regulated by the circadian rhythm of the liver may directly or indirectly affect ovarian function through the inflammation and hormone secretion of abdominal fat.

Abstract

The lower egg production of geese (20~60 eggs per year) compared with chicken and duck limits the development of the industry, while the yolk weight and fatty liver susceptibility of geese was higher than that of other poultry. Therefore, the relationship between lipid metabolism and the laying performance of geese remains to be explored. Phenotypically, we observed that the liver fat content of the high-, low-, and no-egg production groups decreased in turn, while the abdominal fat weight increased in turn. For transcriptional regulation, the KEGG pathways related to lipid metabolism were enriched in all pairwise comparisons of abdominal fat and liver through functional analysis. However, some KEGG pathways related to inflammation and the circadian rhythm pathway were enriched by DEGs only in abdominal fat and the liver, respectively. The DEGs in ovarian stroma among different groups enriched some KEGG pathways related to ovarian steroidogenesis and cell adhesion. Our research reveals that lipid metabolism regulated by the circadian rhythm of the liver may directly or indirectly affect ovarian function through the inflammation and hormone secretion of abdominal fat. These results offer new insights into the regulation mechanisms of goose reproductive traits.

Molecular characterization, expression profile and transcriptional regulation of the CYP19 gene in goose ovarian follicles

Cytochrome P450 Family 19 (CYP19) is a crucial enzyme to catalyze the conversion of androgens to estrogens. However, the regulatory mechanism of goose CYP19 gene remains poorly understood. The present study attempted to obtain the full-length coding sequence (CDS) and 5'-flanking sequence of CYP19 gene, to investigate its expression and distribution profiles in different sized follicles, and to analyze the transcriptional regulatory mechanism of CYP19 gene in goose. Results showed that its CDS consisted of 1512 nucleotides and the encoded amino acid sequence contained a classical P450 structural domain. Homology analysis showed that there were high homologies of nucleotide and amino acid sequences between goose and other avian species. Its promoter sequence spanned from -1925 bp to the transcription start site (ATG) and several transcriptional factors were predicted in this region. Further analysis from luciferase assay showed that the luciferase activity was the highest spanning from -118 to -1 bp by constructing deletion promoter reporter vector. In addition, result from quantitative real-time polymerase chain reaction indicated that the mRNA level of CYP19 gene were highly expressed in theca layer of the fifth largest follicle, and the cellular location was in the theca externa cells by immunohistochemistry. Taken together, it could be concluded that the transcription activity of CYP19 gene was activated by transcriptional factors in its proximal region of promoter to promote the synthesis of estrogens, regulating the selection of pre-hierarchical into hierarchical follicle in goose.

Lipidomics profiling of goose granulosa cell model of stearoyl-CoA desaturase function identifies a pattern of lipid droplets associated with follicle development

Background

Despite their important functions and nearly ubiquitous presence in cells, an understanding of the biology of intracellular lipid droplets (LDs) in goose follicle development remains limited. An integrated study of lipidomic and transcriptomic analyses was performed in a cellular model of stearoyl-CoA desaturase (SCD) function, to determine the effects of intracellular LDs on follicle development in geese.

Results

Numerous internalized LDs, which were generally spherical in shape, were dispersed throughout the cytoplasm of granulosa cells (GCs), as determined using confocal microscopy analysis, with altered SCD expression affecting LD content. GC lipidomic profiling showed that the majority of the differentially abundant lipid classes were glycerophospholipids, including PA, PC, PE, PG, PI, and PS, and glycerolipids, including DG and TG, which enriched glycerophospholipid, sphingolipid, and glycerolipid metabolisms. Furthermore, transcriptomics identified differentially expressed genes (DEGs), some of which were assigned to lipid-related Gene Ontology slim terms. More DEGs were assigned in the SCD-knockdown group than in the SCD-overexpression group. Integration of the significant differentially expressed genes and lipids based on pathway enrichment analysis identified potentially targetable pathways related to glycerolipid/glycerophospholipid metabolism.

Conclusions

This study demonstrated the importance of lipids in understanding follicle development, thus providing a potential foundation to decipher the underlying mechanisms of lipid-mediated follicle development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00604-6.

Exploration of the effects of goose TCs on GCs at different follicular stages using a co-culture model

Granulosa cells (GCs) play a critical role in follicular development, which cannot be separated from the assistance of theca cells (TCs). In the present study, we used a transwell system to develop three stages of goose GCs in vitro mono-culture and co-culture models, and we analyzed the morphology, activity, intracellular lipid content and the expression of core genes involved in de novo lipogenesis (DNL), steroidogenesis, proliferation and apoptosis of the GCs. In the co-culture group, the activity of all three stages of GCs showed significant (P<0.01) changes, and they had a strong (P<0.01) correlation with culture time; further, the intracellular lipid deposition of hierarchical GCs was significantly different (P<0.01) between the two methods. Moreover, after co-culture, in pre-hierarchical GCs, the expression of SREBP, CYP11 and 3βHSD was promoted (P<0.01). In hierarchical GCs, the expression of ACC, SREBP, STAR, CYP11, 3βHSD and CCND1 was promoted at 48 h, but they were inhibited (P<0.05) at 96 h. In F1 GCs, the expression of ACC, FAS, SREBP, CYP11, BCL2 and CAS3 was inhibited (P<0.01). The results indicate that goose TCs had complex and time-dependent effects on the biological function of GCs at each corresponding stage, and the effects were distinct in the different stages. In addition, DNL, steroidogenesis, proliferation and apoptosis in hierarchical and F1 GCs might have some synergistic relationships in the effects of TCs on GCs. Furthermore, we speculated that TCs might play an important role in the differentiation and maturation of GCs during follicular development.

Effects of the FABP4 gene on steroid hormone secretion in goose ovarian granulosa cells

1. To investigate the physiological role of FABP4 in the goose ovary, this study determined the effects of overexpressing and siRNA interfering FABP4 on progesterone (P₄) and oestradiol (E₂) production in granulosa cells. Measurements were made by ELISA, real-time qRT-PCR and western blotting. 2. The concentrations of P₄ and E₂ in the FABP4 overexpression granulosa cells were increased compared to the control group (P > 0.05 for P₄; P < 0.05 for E₂). Likewise, the mRNA and protein expression levels of CYP11A1 and CYP19A1 were significantly higher than in the control group (P < 0.05 or P < 0.001). Conversely, the concentrations of P₄ and E₂ in the FABP4 silencing granulosa cells were significantly decreased compared with the control group (P < 0.001). Likewise, the mRNA and protein expression levels of CYP11A1 and CYP19A1 were significantly lower than in the control group (P < 0.001, or P < 0.01). 3. The study indicated that the FABP4 gene may regulate steroid hormone secretion and the expression of the steroidogenic genes in geese ovarian granulosa cells. These results support the possibility that the FABP4 gene mediates ovarian steroid hormone biosynthesis function and reproduction in geese.

Co-culture model reveals the characteristics of theca cells and the effect of granulosa cells on theca cells at different stages of follicular development

Theca cells (TCs) play an important role in follicular development, which cannot be separated from granulosa cells (GCs). However, compared with mammals, the TCs and the effects of GCs on TCs at different follicular development stages (FDSs) have specific characteristics in avian species, but none of them have been clearly defined. In this study, we established an in vitro co-culture (with GC at the corresponding stage) model of goose TCs at different FDSs (pre-hierarchical, hierarchical and F1) by using a transwell system. The properties of TCs in co-culture at the three FDSs, including cell morphology, activity and intracellular lipid content, as well as the expression of key genes involved in de novo lipogenesis, steroidogenesis, proliferation and apoptosis, were examined and defined. We further compared the mono-culture and co-culture groups. After co-culture, the activity of TCs showed significant (p < .01) increases in all stages; moreover, in pre-hierarchical TCs, the expression levels of FAS, SREBP, 3β-HSD and CCND1 were promoted, and PPARγ, CYP19, BCL2 and CAS3 were inhibited (p < .05); in the hierarchical TCs, the expression levels of PPARγ, FAS, CYP19, CCND1 and BCL2 were promoted, and SREBP, STAR, 3β-HSD and CAS3 were inhibited (p < .05), whereas in the F1 TCs, the expression levels of PPARγ, FAS, 3β-HSD, CYP19 and CCND1 were promoted, and STAR and CAS3 were inhibited (p < .05). These results suggested that GCs at the three FDSs have dynamic and complex influences on the physiological characteristics of TCs, and the influences on TCs at the three FDSs were varied.

Dynamic characteristics of lipid metabolism in cultured granulosa cells from geese follicles at different developmental stages

Previous studies have shown that lipid metabolism in granulosa cells (GCs) plays a vital role during mammalian ovarian follicular development. However, little research has been done on lipid metabolism in avian follicular GCs. The goal of the present study was to investigate the dynamic characteristics of lipid metabolism in GCs from geese pre-hierarchical (6–10 mm) and hierarchical (F4-F2 and F1) follicles during a 6-day period of in vitro culture. Oil red O staining showed that with the increasing incubation time, the amount of lipids accumulated in three cohorts of GCs increased gradually, reached the maxima after 96 h of culture, and then decreased. Moreover, the lipid content varied among these three cohorts, with the highest in F1 GCs. The qPCR results showed genes related to lipid synthesis and oxidation were highest expressed in pre-hierarchical GCs, while those related to lipid transport and deposition were highest expressed in hierarchical GCs. These results suggested that the amount of intracellular lipids in GCs increases with both the follicular diameter and culture time, which is accompanied by significant changes in expression of genes related to lipid metabolism. Therefore, it is postulated that the lipid accumulation capacity of geese GCs depends on the stage of follicle development and is finely regulated by the differential expression of genes related to lipid metabolism.

Differential actions of diacylglycerol acyltransferase (DGAT) 1 and 2 in regulating lipid metabolism and progesterone secretion of goose granulosa cells

Accumulating evidence shows that granulosa cells within both mammalian and avian ovaries have the ability to synthesize fatty acids through de novo lipogenesis and to accumulate triglycerides essential for oocyte and ovarian development. However, very little is known about the exact roles of key genes involved in the lipid metabolic pathway in granulosa cells. The goal of this study was to investigate the differential actions of diacylglycerol acyltransferase (DGAT) 1 and 2, which are recognized as the rate-limiting enzymes catalyzing the last step of triglyceride biosynthesis, in regulating lipid metabolism and steroidogenesis in granulosa cells of goose follicles at different developmental stages. It was observed that the mRNAs encoding DGAT1 and DGAT2 were ubiquitous in all examined granulosa cell layers but exhibited distinct expression profiles during follicle development. Notably, the mRNA levels of DGAT1, DGAT2, FSHR, LHR, STAR, CYP11A1, and 3βHSD remained almost constant in all except for 1-2 follicles within the 8-10 mm cohort, followed by an acute increase/decrease in the F5 follicles. At the cellular level, siRNA-mediated downregulation of DGAT1 or DGAT2 did not change the amount of lipids accumulated in both undifferentiated- and differentiated granulosa cells, while overexpression of DGAT2 promoted lipid accumulation and expression of lipogenic-related genes in these cells. Meanwhile, we found that interfering DGAT2 had no effect but interfering DGAT1 or overexpressing DGAT2 stimulated progesterone secretion in undifferentiated granulosa cells; in contrast, interference or overexpression of DGAT1/2 failed to change progesterone levels in differentiated granulosa cells but differently modulated expression of steroidogenic-related genes. Therefore, it could be concluded that DGAT1 is less efficient than DGAT2 in promoting lipid accumulation in both undifferentiated- and differentiated granulosa cells and that DGAT1 negatively while DGAT2 positively regulates progesterone production in undifferentiated granulosa cells.

Metabolomic Analysis of SCD during Goose Follicular Development: Implications for Lipid Metabolism

Stearoyl-CoA desaturase (SCD) is known to be an important rate-limiting enzyme in the production of monounsaturated fatty acids (MUFAs). However, the role of this enzyme in goose follicular development is poorly understood. To investigate the metabolic mechanism of SCD during goose follicular development, we observed its expression patterns in vivo and in vitro using quantitative reverse-transcription (qRT)-PCR. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to determine a cellular model of SCD function in granulosa cells (GCs) via SCD overexpression and knockdown. qRT-PCR analysis showed that SCD was abundantly expressed in the GC layer, and was upregulated in preovulatory follicles. Peak expression was found in F1 and prehierarchal follicles with diameters of 4–6 mm and 8–10 mm, respectively. We further found that mRNA expression and corresponding enzyme activity occur in a time-dependent oscillation pattern in vitro, beginning on the first day of GC culture. By LC-MS/MS, we identified numerous changes in metabolite activation and developed an overview of multiple metabolic pathways, 10 of which were associated with lipid metabolism and enriched in both the overexpressed and knockdown groups. Finally, we confirmed cholesterol and pantothenol or pantothenate as potential metabolite biomarkers to study SCD-related lipid metabolism in goose GCs.

FASN-Mediated Lipid Metabolism Regulates Goose Granulosa Cells Apoptosis and Steroidogenesis

Lipid metabolism participates in regulating the functions of granulosa cells (GCs), which is important for follicular development. In this experiment, goose GCs from pre-hierarchical follicles and hierarchical follicles were selected to be the model for studying the putative regulatory role of lipid metabolism in apoptosis and steroidogenesis, through overexpression and interference with fatty acid synthase (FASN). When FASN was overexpressed, the lipid accumulation was increased in hierarchical GCs (hGCs) and it was increased in the two categorized GCs when FASN was interfered. In addition, the apoptosis of the two categorized GCs was increased when FASN was overexpressed, and their progesterone production was decreased when FASN was interfered. The results of qRT-PCR showed that, when FASN was overexpressed, the expression level of CYP11A1 was decreased in pre-hierarchical GCs (phGCs), while the expression levels of SCD1, DGAT2, APOB, and StAR were increased in hGCs. When FASN was interfered, the expression levels of CPT-1, DGAT2, and StAR were decreased whereas the expression level of CYP11A1 was increased in phGCs, and the expression levels of CPT-1, SCD1, and StAR were decreased in hGCs. These results not only identify the different effects of manipulated FASN expression on lipid metabolism of goose phGCs and hGCs but also demonstrate that FASN-mediated lipid metabolism plays an important role in regulating apoptosis and steroidogenesis of in vitro cultured goose GCs.

mRNA and miRNA Transcriptome Profiling of Granulosa and Theca Layers From Geese Ovarian Follicles Reveals the Crucial Pathways and Interaction Networks for Regulation of Follicle Selection

Follicle development is characterized by the recruitment, growth, selection, and dominance of follicles, and follicle selection determines the lifetime reproductive performance. However, in birds, the molecular mechanisms underlying follicle selection still remain elusive. This study analyzed genome-wide changes in the mRNA and miRNA expression profiles in both the granulosa and theca layers of geese ovarian follicles before selection (4–6- and 8–10-mm follicles) and after selection (F5). The sequencing results showed that a higher number of both differentially expressed (DE) mRNAs and DE miRNAs were identified between 8–10-mm and F5 follicles compared with those between the 4–6- and 8–10-mm follicles, especially in the granulosa layer. Moreover, a Short Time-series Expression Miner analysis identified a large number of DE mRNAs and DE miRNAs that are associated with follicle selection. The functional enrichment analysis showed that DE genes in the granulosa layer during follicle selection were mainly enriched in five pathways related to junctional adhesion and two pathways associated with lipid metabolism. Additionally, an interaction network was constructed to visualize interactions among protein-coding genes, which identified 53 junctional adhesion- and 15 lipid regulation-related protein-coding genes. Then, a co-expression network between mRNAs and miRNAs in relation to junctional adhesion was also visualized and mainly included acy-miR-2954, acy-miR-218, acy-miR-2970, acy-miR-100, acy-miR-1329, acy-miR-199, acy-miR-425, acy-miR-181, and acy-miR-147. Furthermore, miRNA–mRNA interaction pairs related to lipid regulation were constructed including acy-miR-107, acy-miR-138, acy-miR-130, acy-miR-128, and acy-miR-101 during follicular selection. In summary, these data highlight the key roles of junctional adhesion and lipid metabolism during follicular selection and contribute to a better understanding of the mechanisms underlying follicle selection in birds.