Dynamics of apoptosis-related gene expression during follicular development in yak

Molecular characterization and expression profile of the ALDH1A1 gene and its functions in yak luteal cells

The ALDH1A1 gene encodes a cytoplasmic member of the aldehyde dehydrogenase 1 family, which plays an important role in regulating animal reproductive performance, including estrus cycle and embryonic development. The aim of this study was to characterize ALDH1A1 activity in ovaries of 3-5 year-old yaks and to determine its effects on cell proliferation, apoptosis, and progesterone secretion in luteal cells (LCs). The coding sequence (CDS) of the ALDH1A1 gene was cloned by reverse transcription-PCR and immunohistochemical analysis was used to confirm localization of the ALDH1A1 protein in the ovary. To assess the activity of ALDH1A1 in regulating progesterone secretion, si-ALDH1A1 was transfected into LCs in vitro and progesterone levels in LC supernatants were measured by ELISA. The interference efficiency was assessed by real-time quantitative PCR (RT-qPCR) and immunofluorescence staining, and cell proliferation and apoptosis were evaluated by EdU and TUNEL staining, respectively. The cloned ALDH1A1 sequence contained 1462 bp, encoding 487 amino acids. Immunohistochemical analysis showed that ALDH1A1 protein expression, which was significantly higher in LCs, was mainly found in antral follicles and the corpus luteum (CL). The expression of ALDH1A1 mRNA in LCs was effectively inhibited by si-ALDH1A1transfection, and progesterone secretion was markedly decreased along with the significant down-regulation of progesterone pathway-related genes, STAR, CYP11A1, CYP19A1, CYP17A1, 3β-HSD, and HSD17B1. Knockdown of ALDH1A1 mRNA expression decreased cell proliferation and increased apoptosis in LCs. The mRNA expression of the proliferation-related genes, PCNA, CCND1, CCNB1 and CDC25A, was significantly down-regulated, while expression of the apoptosis-promoting CASP3 gene was significantly increased. In summary, we characterized the yak ALDH1A1 gene and revealed that ALDH1A1 knockdown promoted apoptosis, repressed cell proliferation, and decreased progesterone secretion by yak LCs, potentially by regulating the mRNA expression of genes related to proliferation, apoptosis, and progesterone synthesis and secretion.

Small extracellular vesicles derived from lipopolysaccharide-preconditioned dental follicle cells inhibit cell apoptosis and alveolar bone loss in periodontitis

OBJECTIVE

This study aimed to explore the effects of small extracellular vesicles derived from lipopolysaccharide-preconditioned dental follicle cells (L-D-sEV) on periodontal ligament cells from periodontitis affected teeth (p-PDLCs) in vitro and experimental periodontitis in mice.

DESIGN

In vitro, the biological function of p-PDLCs and the underlying molecular mechanism were investigated by flow cytometry, Western blot, and quantitative real-time PCR (qRT-PCR) analysis. Eighteen-eight-week-old male C57BL/6 mice were randomly divided into three groups: control (Con), periodontitis (Peri), and L-D-sEV groups. Mice periodontitis model was induced by placing the 5-0 silk thread (around the maxillary second molar) and P.gingivalis (1 ×107 CFUs per mouse). In vivo, the alveolar bone loss, osteoclast activity, and macrophage polarization were measured by micro-computed tomography and histological analysis.

RESULTS

In vitro, the RANKL/OPG ratio and phosphorylation of JNK and P38 protein levels of p-PDLCs were significantly decreased after L-D-sEV administration. Besides, flow cytometry and qRT-PCR analysis showed that L-D-sEV reduced apoptosis of p-PDLCs, down-regulated apoptosis-related genes Caspase-3 and BCL-2-Associated X expression, and up-regulated B-cell lymphoma-2 gene levels. In vivo, L-D-sEV administration significantly reduced alveolar bone loss, inhibited osteoclast activity, and induced M2 polarization. The histological analysis showed that iNOS/CD206, RANKL/OPG, p-JNK/JNK, and p-P38/P38 ratios were significantly lower in the L-D-sEV group than in the Peri group.

CONCLUSIONS

L-D-sEV administration alleviated alveolar bone loss by mediating RANKL/OPG-related osteoclast activity and M2 macrophage polarization, alleviating p-PDLCs apoptosis and proliferation via the JNK and P38 pathways.

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.

MEL regulates miR-21 and let-7b through the STAT3 cascade in the follicular granulosa cells of Tibetan sheep

Under physiological and pathological conditions, melatonin (MEL) can regulate microRNA (miRNA) expression. However, the mechanisms underlying the regulatory effects of MEL on miRNAs in ovaries are not understood. Firstly, by using fluorescence in situ hybridisation, we found that in ovaries and follicular granulosa cells (FGCs), MT1 co-located with miR-21 and let-7b. Additionally, immunofluorescence revealed that MT1, STAT3, c-MYC and LIN28 proteins co-located. The mRNA and protein levels of STAT3, c-MYC and LIN28 increased under treatment with 10^-7 M MEL. MEL induced an increase in miR-21 and a decrease in let-7b. The LIN28/let-7b and STAT3/miR-21 axes are related to cell differentiation, apoptosis and proliferation. We explored whether the STAT3/c-MYC/LIN28 pathway was involved in miRNA regulation by MEL to explore the putative mechanism of the above relationship. AG490, an inhibitor of the STAT3 pathway, was added before MEL treatment. AG490 inhibited the MEL-induced increases in STAT3, c-MYC, LIN28 and MT1 and changes in miRNA. Through live-cell detection, we discovered that MEL enhanced the proliferation of FGCs. However, the ki67 protein levels decreased when AG490 was added in advance. Furthermore, the dual-luciferase reporter assay verified that STAT3, LIN28 and MT1 were target genes of let-7b. Furthermore, STAT3 and SMAD7 were target genes of miR-21. In addition, the protein levels of the STAT3, c-MYC, LIN28 and MEL receptors decreased when let-7b was overexpressed in FGCs. Overall, MEL might regulate miRNA expression through the STAT3 pathway. In addition, a negative feedback loop between the STAT3 and miR-21 formed; MEL and let-7b antagonized each other in FGCs. These findings may provide a theoretical basis for improving the reproductive performance of Tibetan sheep through MEL and miRNAs.

Role of COX-2/PGE2 signaling pathway in the apoptosis of rat ovarian granulosa cells induced by MEHP

OBJECTIVE

MEHP, as the metabolite of DEHP, is a widely used environmental endocrine disruptor. Ovarian granulosa cells participate in maintaining the function of ovary and COX2/PGE2 pathway may regulate the function of granulosa cells. We aimed to explore how COX-2/PGE2 pathway affects cell apoptosis in ovarian granulosa cells caused by MEHP.

METHODS

Primary rat ovarian granulosa cells were treated with MEHP (0, 200, 250, 300 and 350 μM) for 48 h. Adenovirus was used for over-expression of COX-2 gene. The cell viability was tested with CCK8 kits. The apoptosis level was tested by flow cytometry. The levels of PGE2 were tested with ELISA kits. The expression levels of COX-2/PGE2 pathway related genes, ovulation-related genes and apoptosis-related genes, were measured with RT-qPCR and Western blot.

RESULTS

MEHP decreased the cell viability. After MEHP exposure, the cell apoptosis level increased. The level of PGE2 markedly decreased. The expression levels of COX-2/PGE2 pathway related genes, ovulation-related genes and anti-apoptotic genes decreased; the expression levels of pro-apoptotic genes increased. The apoptosis level was alleviated after over-expression of COX-2, and the level of PGE2 slightly increased. The expression levels of PTGER2 and PTGER4, and the levels of ovulation-related genes increased; the levels of pro-apoptotic genes decreased.

CONCLUSION

MEHP can cause cell apoptosis by down-regulating the levels of ovulation-related genes via COX-2/PGE2 pathway in rat ovarian granulosa cells.

Identification of key genes and biological pathways in different parts of yak oviduct based on transcriptome analysis

The oviduct consists of three parts: the infundibulum (In), ampulla (Am), and isthmus (Is). These have the same histological structure, but different physiological functions. In this study, transcriptomics was used to analyze mRNA in these three parts of yak oviduct. The results showed that there were 325 up-regulated genes and 282 down-regulated genes in the infundibulum and ampulla. Moreover, there were 234 up-regulated genes and 776 down-regulated genes in the isthmus and ampulla, as well as 873 up-regulated genes and 297 down-regulated genes in the infundibulum and isthmus. The expression of C3 in the infundibulum was significantly higher than that in the ampulla and isthmus. The expression of FAU in the isthmus was significantly lower than that in the ampulla and infundibulum, and the expression of EEF1A1 in the ampulla was significantly higher than that in the ampulla and infundibulum. When the infundibulum was compared with the ampulla and isthmus, it was found that the up-regulated genes were enriched in the lysosome, phagosome, staphylococcus aureus infection, and leishmaniasis pathway. When the isthmus was compared with the ampulla and infundibulum, the up-regulated genes were present in the apoptosis pathway, oxidative phosphorylation, and viral myocarditis pathway. When the isthmus was compared with the infundibulum and ampulla, the down-regulated pathways were protein processing in the endoplasmic reticulum and the endocytosis. The Epstein-Barr virus infection pathway was up-regulated according to a comparison of the isthmus and infundibulum and was down-regulated based on a comparison of the isthmus and ampulla. Transcriptional misregulation in the Middle East pathway was up-regulated based on a comparison of the isthmus and ampulla and was down-regulated based on a comparison of the isthmus and infundibulum. ERBB2, JUP, CTNND1, and KRT7 were defined as the hub genes of the yak oviduct. The results of this study provide sufficient omics data for yak fertilization, which is also of great significance to altitude medicine.

Exosomes Derived from Yak Follicular Fluid Increase 2-Hydroxyestradiol Secretion by Activating Autophagy in Cumulus Cells

Exosomes in the follicular fluid can carry and transfer regulatory molecules to recipient cells, thus influencing their biological functions. However, the specific effects of yak follicular fluid exosomes on 2-hydroxyestrodiol (2-OHE₂) secretion remain unknown. Here, we investigated whether yak follicular fluid exosomes can increase 2-OHE₂ secretion through the activation of autophagy in cumulus cells (YCCs). In vitro cultured YCCs were treated with yak follicular fluid exosomes for 6, 12, and 24 h. The effects of yak follicular fluid exosomes on autophagy and 2-OHE₂ secretion were evaluated through real-time quantitative fluorescence PCR (RT-qPCR), Western blotting (WB), transfected with RFP-GFP-LC3, immunohistochemistry, and ELISA. To further investigate whether 2-OHE₂ secretion was related to autophagy, YCCs were administered with yak follicular fluid exosomes, 3-methyladenine (3-MA), and rapamycin (RAPA). The results revealed that treatment with yak follicular fluid exosomes activated autophagy in YCCs and increased 2-OHE₂ secretion. Conversely, the inhibition of autophagy with 3-MA blocked these effects, suggesting that autophagy has an important role in 2-OHE₂ secretion in YCCs. Treatment of YCCs with rapamycin showed similar results with yak follicular fluid exosomes as there was an increase in 2-OHE2 secretion due to the activation of autophagy in the treated cumulus cells. Our results demonstrate that autophagy is enhanced by yak follicular fluid exosomes, and this is associated with an increase in 2-OHE₂ secretion in YCCs.

The mRNA expression of the three major described cold-inducible proteins, including CIRBP, differs in the bovine endometrium and ampulla during the estrous cycle

The cold-inducible proteins (CIPs) are essential for post-transcriptional gene regulation playing diverse tissue-specific roles in maintaining normal cellular function and morphogenesis. The potential implications of CIPs in reproductive events raise questions about their role in the physiology of the bovine reproductive tract. However, the expression changes of CIPs during the bovine estrous cycle have not been studied so far. Here, we hypothesized that the bovine estrous cycle could affect the mRNA expression of the CIPs and other candidate transcripts in the reproductive tract. This study aimed to examine estrous cycle-dependent mRNA expression patterns in the bovine endometrium and ampulla of three of the major described CIPs (CIRBP, RBM3, SRSF5), a set of inflammatory cytokines (IL-10, IL-18, IL-1β), and other candidate genes (IL-10RA, IL-10RB, BCL2, NLRP3, STAT1, STAT3, STAT5A, STAT6). Endometrial and ampullar tissues were assessed by RT-qPCR. Additionally, the mRNA expression levels were correlated among them and with follicular progesterone and estradiol concentrations. The transcript levels of CIPs increased in the endometrium during stage III (Days 11-17) compared to stage I (Days 1-4) and IV (Days 18-20). In the ampulla, the mRNA expression of CIRBP increased during the late luteal phase (stage III), but no differences in the expression of other CIPs were observed. This study expands the current knowledge regarding mRNA expression in the endometrium and oviductal ampulla of cycling heifers, focusing mainly on the CIPs. A better understanding of the mechanisms within the uterus and oviduct during the estrous cycle is crucial to improving the fertility rate.

Targeted metabolomics analysis of bile acids and cell biology studies reveal the critical role of glycodeoxycholic acid in buffalo follicular atresia

The follicular fluid of mammals has a high abundance of bile acids and these have proven to be closely related to the follicular atresia. However, the origin and content of bile acids in follicular fluid and its mechanisms on follicular atresia remain largely unknown. In this work, we analyzed the origin of bile acids in buffalo follicles by using cell biology studies, and quantified the subspecies of bile acids in follicular fluid from healthy follicles (HF) and atretic follicles (AF) by targeted metabolomics. The function of differential bile acids on follicular granulosa cells was also studied. The results showed that the bile acids transporters were abundantly expressed in ovarian tissues, but the rate-limiting enzymes were not, which was consistent with the inability of cultured follicular cells to convert cholesterol into bile acids. Targeted metabolomics analysis revealed thirteen differential subspecies of bile acids between HF and AF. The free bile acids were significant down-regulated and their conjugated forms were significantly up-regulated in AF as compared to HF. Finally, cell biological validation found a specific differentially conjugated bile acid, glycodeoxycholic acid (GDCA), which could promote follicular granulosa cell apoptosis and reduce steroid hormone secretion. In summary, our studies suggest that bile acids in buffalo follicles are transported from the blood rather than being synthesized within the follicles. The conjugated bile acids such as GDCA, accumulate in buffalo follicles, and may accelerate atresia by promoting apoptosis of granulosa cells and inhibiting steroid hormone production. These results will provide new clues for studying the physiological role and mechanism of bile acids involved in buffalo follicular atresia.

miR-21, miR-125b, and let-7b contribute to the involution of atretic follicles and corpus lutea in Tibetan sheep ovaries

Follicular granulosa cells (FGCs) are crucial for ovarian follicle functions, and miRNAs are differentially expressed at various stages of follicular developments. In this study, we confirmed that miR-21, miR-125b, and let-7b were located in FGCs/luteal cells by in situ hybridization experiments. Moreover, miR-21 and miR-125b expressions were upregulated in late corpus lutea (CL) and atretic follicles (AF); let-7b expression was increased in early AF. After transfected with inhibitor or mimic of miRNAs in FGCs, we found that FGCs apoptosis was decreased in the miR-21-mi group but increased in the miR-125b-mi group using flow cytometry. mRNA and protein expression levels were determined for apoptosis-related factors (e.g., Bcl-2 and Bax), the potential target genes of miRNAs (e.g., SMAD7, SP1, and STAT3), hormone receptors (e.g., FSHR and LHR), and genes related to hormone secretion (e.g., CYP19, CYP11, and 3βHSD). The protein levels of SMAD7 were decreased in the miR-21-mi group but opposite to SP1 and FSHR. In the let-7b-mi group, Bcl-2, SMAD7, and FSHR were suppressed but not Bax, CYP11, and 3βHSD. However, hormone secretion was not changed in the supernatant of transfected FGCs. This study provides information about ovarian miRNAs to improve the fertility in Tibetan sheep.

Non-targeted Metabolomics Reveals Metabolic Characteristics of Porcine Atretic Follicles

Follicular atresia is one of the main factors limiting the reproductive power of domestic animals. At present, the molecular mechanisms involved in porcine follicular atresia at the metabolic level remain unclear. In this study, we divided the follicles of Bama Xiang pigs into healthy follicles (HFs) and atretic follicles (AFs) based on the follicle morphology. The expression of genes related to atresia in granulosa cells (GCs) and the concentration of hormones in the follicular fluid (FF) from HFs and AFs were detected. We then used liquid chromatography–mass spectrometry-based non-targeted metabolomic approach to analyze the metabolites in the FF from HFs and AFs. The results showed that the content of estradiol was significantly lower in AFs than in HFs, whereas that of progesterone was significantly higher in AFs than that in HFs. The expression of BCL2, VEGFA, and CYP19A1 was significantly higher in HFs than in AFs. In contrast, the expression of BAX and CASPASE3 was significantly lower in HFs. A total of 18 differential metabolites (DMs) were identified, including phospholipids, bioactive substances, and amino acids. The DMs were involved in 12 metabolic pathways, including arginine biosynthesis and primary bile acid biosynthesis. The levels of eight DMs were higher in the HF group than those in the AF group (p < 0.01), and those of 10 DMs were higher in the AF group than those in the HF group (p < 0.01). These findings indicate that the metabolic characteristics of porcine AFs are lower levels of lipids such as phospholipids and higher levels of amino acids and bile acids than those in HFs. Disorders of amino acid metabolism and cholic acid metabolism may contribute to porcine follicular atresia.