Effects of nonglycosylated and glycosylated prolactin on basal and gonadotropin-stimulated steroidogenesis in chicken ovarian follicles

Comparison of the Effects of Recombinant and Native Prolactin on the Proliferation and Apoptosis of Goose Granulosa Cells

In poultry, prolactin (PRL) plays a key role in the regulation of incubation behavior, hormone secretion, and reproductive activities. However, previous in vitro studies have focused on the actions of PRL in ovarian follicles of poultry, relying on the use of exogenous or recombinant PRL, and the true role of PRL in regulating ovarian granulosa cell (GC) functions in poultry awaits a further investigation using endogenous native PRL. Therefore, in this study, we first isolated and purified recombinant goose PRL protein (rPRL) and native goose PRL protein (nPRL) using Ni-affinity chromatography and rabbit anti-rPRL antibodies-filled immunoaffinity chromatography, respectively. Then, we analyzed and compared the effects of rPRL and nPRL at different concentrations (0, 3, 30, or 300 ng/mL) on the proliferation and apoptosis of both GCs isolated from goose ovarian pre-hierarchical follicles (phGCs) and from hierarchical follicles (hGCs). Our results show that rPRL at lower concentrations increased the viability and proliferation of both phGCs and hGCs, while it exerted anti-apoptotic effects in phGCs by upregulating the expression of Bcl-2. On the other hand, nPRL increased the apoptosis of phGCs in a concentration-dependent manner by upregulating the expressions of caspase-3 and Fas and downregulating the expressions of Bcl-2 and Becn-1. In conclusion, this study not only obtained a highly pure nPRL for the first time, but also suggested a dual role of PRL in regulating the proliferation and apoptosis of goose GCs, depending on its concentration and the stage of follicle development. The data presented here can be helpful in purifying native proteins of poultry and enabling a better understanding of the roles of PRL during the ovarian follicle development in poultry.

Seasonal patterns of prolactin, prolactin receptor, and STAT5 expression in the ovaries of wild ground squirrels (<em>Citellus dauricus</em> Brandt)

Prolactin (PRL) is a hormone crucial for normal reproduction, functioning as an autocrine, paracrine, and endocrine factor. This study aimed to examine the immunolocalization and expression patterns of PRL, prolactin receptor (PRLR), and signal transducer and activator of transcription 5 (STAT5) in the ovaries of wild ground squirrels during both breeding and non-breeding periods. Significant seasonal variations were observed in ovarian weights, with higher values during the breeding season and relatively lower values during the nonbreeding season. PRL, PRLR, STAT5, and p-STAT5 were immunolocalized in granulosa cells and luteal cells during the breeding season, whereas they were exclusively found in granulosa cells during the non-breeding season. The mRNA expression levels of Prl, Prlr, and Stat5 were increased in ovarian tissues during the breeding season compared to the non-breeding season. Moreover, the mean mRNA levels of Prl, Prlr, and Stat5 exhibited a positive correlation with ovarian weights. Both circulating PRL and ovarian PRL concentrations were significantly elevated during the breeding season. Additionally, transcriptomic analysis of ovarian tissues revealed differentially expressed genes possibly associated with ovarian function and mammary gland development, including ovarian follicle development, steroid synthesis, and regulation of reproductive process. These findings suggest that PRL might play an essential endocrine, autocrine, or paracrine role in the regulation of seasonal changes in the ovarian functions in wild ground squirrels.

High Prolactin Concentration Induces Ovarian Granulosa Cell Oxidative Stress, Leading to Apoptosis Mediated by L-PRLR and S-PRLR

High prolactin (PRL) concentration has been shown to induce the apoptosis of ovine ovarian granulosa cells (GCs), but the underlying mechanisms are unclear. This study aimed to investigate the mechanism of apoptosis induced by high PRL concentration in GCs. Trial 1: The optimal concentration of glutathion was determined according to the detected cell proliferation. The results showed that the optimal glutathione concentration was 5 μmol/mL. Trial 2: 500 ng/mL PRL was chosen as the high PRL concentration. The GCs were treated with 0 ng/mL PRL (C group), 500 ng/mL PRL (P group) or 500 ng/mL PRL, and 5 μmol/mL glutathione (P-GSH group). The results indicated that the mitochondrial respiratory chain complex (MRCC) I-V, ATP production, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and thioredoxin peroxidase (TPx) in the C group were higher than those in the P group (p < 0.05), while they were lower than those in the P-GSH group (p < 0.05). Compared to the C group, the P group exhibited elevated levels of reactive oxygen species (ROS) and apoptosis (p < 0.05) and increased expression of ATG7 and ATG5 (p < 0.05). However, MRCC I-V, ATP, SOD, A-TOC, TPx, ROS, and apoptosis were decreased after the addition of glutathione (p < 0.05). The knockdown of either L-PRLR or S-PRLR in P group GCs resulted in a significant reduction (p < 0.05) in MRCC I-V, ATP, T-AOC, SOD and TPx, while the overexpression of either receptor showed an opposite trend (p < 0.05). Our findings suggest that high PRL concentrations induce apoptotic cell death in ovine ovarian GCs by downregulating L-PRLR and S-PRLR, activating oxidative stress and autophagic pathways.

Prolactin Regulates Ovine Ovarian Granulosa Cell Apoptosis by Affecting the Expression of MAPK12 Gene

Prolactin (PRL) has been reported to influence reproductive performance and cell apoptosis. However, its mechanism remains unclear. Hence, in the present study, ovine ovarian granulosa cells (GCs) were used as a cell model to investigate the relationship between PRL concentration and GC apoptosis, as well as its possible mechanisms. We examined the relationship between serum PRL concentration and follicle counts in sexually mature ewes. GCs were isolated from adult ewes and treated with different concentrations of PRL, while 500 ng/mL PRL was selected as the high concentration of prolactin (HPC). Then, we applied the transcriptome sequencing (RNA-Seq) combined with a gene editing approach to explore the HPC contributing to cell apoptosis and steroid hormones. The apoptosis of GCs gradually increased at PRL concentrations above 20 ng/mL, while 500 ng/mL PRL significantly decreased the secretion of steroid hormones and the expression of L-PRLR and S-PRLR. The results indicated that PRL regulates GC development and steroid hormones mainly through the target gene MAPK12. The expression of MAPK12 was increased after knocked-down L-PRLR and S-PRLR, while it decreased after overexpressed L-PRLR and S-PRLR. Cell apoptosis was inhibited and the secretion of steroid hormones increased after interfering with MAPK12, while the overexpression of MAPK12 showed the opposite trend. Overall, the number of follicles gradually decreased with increasing PRL concentration. HPCs promoted apoptosis and inhibited steroid hormone secretion in GCs by upregulating MAPK12 through reducing L-PRLR and S-PRLR.

Molecular characterisation and expression profile of the PRLR gene during goose ovarian follicle development

1. Although PRL-PRLR signalling plays important roles in regulating avian reproduction, there is a paucity of information regarding the functional significance of PRLR in goose ovarian follicle development.2. The full-length 2,496 bp coding sequence of PRLR was obtained from Sichuan White goose (Anser cygnoides) for the first time and was seen to encode a polypeptide containing 831 amino acids. Goose PRLR shares similar sequence characteristics and conserved functional domains to other avian species and was phylogenetically clustered into the avian clade.3. The qPCR results suggested that the mRNA levels of PRLR significantly increased in primary follicles during weeks 3 to 4 of age and were higher in secondary- than in primordial follicles at week 5 post-hatching, which suggested that the PRLR-mediated signalling could be involved in regulation of early folliculogenesis.4. The PRLR mRNA was expressed at the highest levels in the prehierarchical 8-10 mm granulosa layers throughout goose ovarian follicle development, indicating a role for PRLR in the process of follicle selection.5. PRLR mRNA was differentially expressed in the three cohorts of in vitro cultured granulosa cells harvested from different sized goose ovarian follicles, which suggested that PRLR was involved in regulating granulosa cell functions depending on the stage of follicle development. These data provide novel insights into the role of PRLR during goose ovarian follicle development, although the underlying mechanisms await further investigations.

miR-27b-3p inhibits estrogen secretion of goose granulosa cells by targeting CYP1B1 through the AMPK signaling pathway

Although miR-27b-3p has been evidenced to regulate the proliferation, apoptosis, and differentiation of a variety of mammalian cell types, its actions and mechanisms on ovarian cell steroidogenesis remains largely unknown in both mammalian and avian species. In this study, we aimed to determine the expression profiles of miR-27b-3p in granulosa cell layers during goose ovarian follicle development and to reveal its actions on estrogen (E₂) secretion of goose granulosa cells as well as the underlying regulatory mechanisms. It was observed that miR-27b-3p was ubiquitously expressed throughout follicle development but exhibited much higher levels in hierarchical- than in prehierarchical follicles. In cultured granulosa cells from the fourth through second largest preovulatory (F4-F2) follicles of goose, up- and downregulation of miR-27b-3p by using its mimic and inhibitor significantly decreased and increased E₂ secretion, respectively. Meanwhile, the mRNA levels of STAR and CYP19A1 were significantly reduced while those of CYP11A1 and 3βHSD were elevated in the mimic-transfected granulosa cells. By comparison, downregulation of miR-27b-3p enhanced the mRNA levels of STAR but had no significant effects on those of CYP19A1, CYP11A1, and 3βHSD. Results from bioinformatic prediction and luciferase reporter assay demonstrated that CYP1B1 was a downstream target of miR-27b-3p. Although the siRNA-mediated downregulation of CYP1B1 did not significantly change E₂ secretion by goose granulosa cells, it reduced the mRNA levels of STAR and CYP19A1 as well as those of LKB1 and AMPKα, which are involved in the AMPK signaling pathway. Taken together, these data suggest that miR-27b-3p plays an inhibitory role in E₂ secretion by goose F4-F2 granulosa cells, at least in part, by targeting CYP1B1 through the AMPK signaling pathway.

Effect of Heat Stress on Egg Production, Steroid Hormone Synthesis, and Related Gene Expression in Chicken Preovulatory Follicular Granulosa Cells

Simple Summary

The debilitating effects of heat stress on poultry production have been well documented. Heat stress already results in severe economic loss worldwide. Regarding the decline in the reproductive performance of heat-stressed hens, the exact mechanisms involved are still unknown. The present study was conducted to elucidate the molecular mechanisms underlying heat-stress-induced abnormal egg production in laying hens. Our results confirmed that laying hens reared under heat stress had impaired laying performance. Follicular granulosa cells cultured in vitro are sensitive to the effects of heat stress, showing an increase in apoptosis and cellular ultrastructural changes. These effects appeared in the form of heat-stress-elevated progesterone, with the increased expression of steroidogenic acute regulatory protein, cytochrome P450 family 11 subfamily A member 1, and 3b-hydroxysteroid dehydrogenase, along with inhibited estradiol synthesis through the decreased expression of follicle-stimulating hormone receptor and the cytochrome P450 family 19 subfamily A member 1. Collectively, laying hens exposed to high temperatures showed damage to granulosa cells that brought about a decline in egg production. This study provides a molecular mechanism for the abnormal laying performance of hens subjected to heat stress, which may help when developing novel strategies to reverse the adverse impact.

Abstract

This study was conducted to elucidate the molecular mechanisms underlying heat stress (HS)-induced abnormal egg-laying in laying hens. Hy-Line brown laying hens were exposed to HS at 32 °C or maintained at 22 °C (control) for 14 days. In addition, granulosa cells (GCs) from preovulatory follicles were subjected to normal (37 °C) or high (41 °C or 43 °C) temperatures in vitro. Proliferation, apoptosis, and steroidogenesis were investigated, and the expression of estrogen and progesterone synthesis-related genes was detected. The results confirmed that laying hens reared under HS had impaired laying performance. HS inhibited proliferation, increased apoptosis, and altered the GC ultrastructure. HS also elevated progesterone secretion by increasing the expression of steroidogenic acute regulatory protein (StAR), cytochrome P450 family 11 subfamily A member 1 (CYP11A1), and 3b-hydroxysteroid dehydrogenase (3β-HSD). In addition, HS inhibited estrogen synthesis in GCs by decreasing the expression of the follicle-stimulating hormone receptor (FSHR) and cytochrome P450 family 19 subfamily A member 1 (CYP19A1). The upregulation of heat shock 70 kDa protein (HSP70) under HS was also observed. Collectively, laying hens exposed to high temperatures experienced damage to follicular GCs and steroidogenesis dysfunction, which reduced their laying performance. This study provides a molecular mechanism for the abnormal laying performance of hens subjected to HS.

Leptin Modulates the mRNA Expression of Follicle Development Markers in Post-hatch Chicks in an Age-Dependent Manner

Leptin is involved in regulating reproductive function in chickens, and the development of the leptin system is initiated during the early embryonic stage; however, whether leptin has a specific role in regulating the ovarian development in early post-hatch days is still not fully understood. This study investigated the expression of ovarian functional markers in growing juvenile chickens, along with the effects of leptin on gene expression in the hypothalamus–pituitary–gonadal (HPG) axis on specific ovarian-remodeling days. Leptin receptor (LEPR), follicle-stimulating hormone receptor (FSHR), and the mRNA expression of aromatase (CYP19A1) tended to increase with age in the ovaries of growing chicks. In the ovaries of 7-day-old chicks, intraperitoneally injected leptin significantly increased the mRNA expressions of LEPR, FSHR, and CYP19A1, and this resulted in the increased serum estradiol levels. However, leptin had no effect on hypothalamic LEPR, gonadotropin-releasing hormone 1 (GnRH1), or gonadotropin-inhibitory hormone (GnIH) mRNAs; however, in the pituitary gland, leptin significantly increased the mRNA expression of luteinizing hormone beta subunit (LHB) but had no effect on the mRNA expression of follicle-stimulating hormone beta subunit (FSHB). In 28-day-old chicks, hypothalamic and pituitary mRNAs were unaffected by leptin administration, except hypothalamic LEPR mRNA that was upregulated by a high dose of leptin. In the ovary, leptin dose-dependently decreased the mRNA expression of LEPR; low doses of leptin significantly increased the mRNA expression of FSHR, whereas high doses significantly decreased this expression; leptin did not affect the mRNA expression of CYP19A1; and high leptin doses significantly reduced the serum estradiol levels. Collectively, the results of this study show that leptin modulates ovarian development and folliculogenesis marker genes by primarily acting on ovaries on the specific ovarian-remodeling days in post-hatch chicks, which may alter folliculogenesis and ovarian development toward puberty in chicken.

Response of the matrix metalloproteinase system of the chicken ovary to prolactin treatment

The expression and activity of several matrix metalloproteinases (MMPs) has been demonstrated in the chicken ovary during various physiological states; these data indicate that MMPs are involved in the remodeling of the extracellular matrix (ECM) during follicle development, ovulation, atresia, and regression. The regulation of MMPs in the avian ovary, however, remains largely unknown. The present study aimed to examine the effect of recombinant chicken prolactin (chPRL) treatment on the expression of selected MMPs and their tissue inhibitors (TIMPs), as well as MMP-2 and MMP-9 activity in the hen ovary. Real-time polymerase chain reaction revealed changes in the mRNA expression of MMP-2, MMP-7, MMP-9, MMP-10, MMP-13, TIMP-2, and TIMP-3 in the following ovarian follicles: white, yellowish, small yellow, and the largest yellow preovulatory (F3-F1). Western blot analysis showed alterations in the abundance of latent and active forms of the MMP-2 protein, as well as the abundance of the MMP-9 protein. Moreover, minor changes in MMP-2 and MMP-9 total activities were found in ovarian follicles of chPRL-treated hens. The response to chPRL treatment depended upon the stage of follicle development, the layer of follicular wall, and the type of MMPs or TIMPs studied. In general, the results indicate that chPRL, is a positive regulator of MMP expression in the yellow preovulatory follicles. Our findings suggest that PRL participates in the mechanisms orchestrating ECM turnover during ovarian follicular development in the hen ovary via regulating the transcription, translation, and/or activity of some constituents of the MMP system.

Histomorphology and gene expression profiles during early ovarian folliculogenesis in duck and goose

In contrast to the later stages of follicle development, little is known about the characteristics and mechanisms associated with early folliculogenesis in avian species. The objectives of the present study were to examine and compare the histomorphological and molecular changes of primordial, primary, and secondary follicles from duck and goose ovaries during the first 6 post-hatching week. Morphological analysis showed that the length and width of both duck and goose ovaries increased steadily during weeks 1 to 5 but increased acutely at week 6, whereas a greater increment was observed in the ovarian length of ducks than that of geese during weeks 4 to 5. Furthermore, smaller diameters of the 3 categories of follicles were observed in ducks than those in geese at the first appearance, but they reached a similar size at week 6. More importantly, secondary follicles were found in the ovaries of ducks 1 wk earlier than in those of geese. These results indicated a more rapid growth rate for ovarian follicles in ducks than in geese during early post-hatching development. At the molecular level, it was found that the mRNAs encoding follicle stimulating hormone receptor (FSHR), anti-Müllerian hormone (AMH), B-cell leukemia/lymphoma 2, and cysteine-dependent aspartate specific protease 3 (CASPASE3) were ubiquitously expressed in all ovarian follicles of ducks and geese with different expression profiles in each follicular category during the first 6 post-hatching week. Notably, transcript levels of FSHR, AMH, and CASPASE3 changed differently between ducks and geese during weeks 5 to 6, which was postulated to be one of the mechanisms inducing more rapid growth of ovarian follicles in ducks rather than in geese. In conclusion, our results revealed, for the first time, differences in early folliculogenesis, including the rate of growth of each follicular category and the timing of transition of primary to secondary follicles, between ducks and geese, and these differences could result from different expression profiles of FSHR, AMH, and CASPASE3 during early post-hatching development.

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.

Determination of the roles of GREM1 gene in granulosa cell proliferation and steroidogenesis of hen ovarian prehierarchical follicles

Gremlin genes are known members of the DAN family of bone morphogenetic protein (BMP) antagonists, but their functions and regulatory mechanisms in ovarian follicular development of chicken remain unknown. The current study was designed to investigate the mRNA expression patterns of gremlin1 gene (GREM1) and its protein location in the follicles sampled, and to explore the biological effect of GREM1 on the prehierarchical follicular development. This work revealed that chicken GREM1 mRNA exhibits a constant expression level across all the prehierarchical follicles (PFs) from 1-4 mm to 7-8 mm in diameter, and the preovulatory follicles (from F6 to F1) by using RT-qPCR (P > 0.05). The GREM1 protein is predominantly expressed in the oocytes and granulosa cells (GCs) of the PFs by immunohistochemistry. Furthermore, our data demonstrated that siRNA-mediated knockdown of GREM1 in the GCs resulted in a significant reduction in cell proliferation (P < 0.001); conversely, overexpression of GREM1 in the GCs led to a remarkable increase in cell proliferation (P < 0.001). Interestingly, the expression levels of proliferating cell nuclear antigen (PCNA) and cyclin D2 (CCND2) mRNA and proteins were notably increased when GREM1 expression was upregulated in the GCs (P < 0.01), however, the expression levels of CYP11A1 and StAR were markedly downregulated (P < 0.01). The current results showed that GREM1 gene plays a stimulatory role in GC proliferation during growth and development of the prehierarchical follicles in vitro but an inhibitory role in GC differentiation and steroidogenesis of the hen ovary follicles.

Reproductive management of poultry

Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems.

Genistein increases progesterone secretion by elevating related enzymes in chicken granulosa cells

Genistein, a biologically active isoflavone, exists in many soy products. It is well known that genistein binds to both oestrogen receptor alpha (ERα) and oestrogen receptor beta (ERβ), but it has a higher affinity to ERβ. Genistein can also bind to the G protein-coupled receptor 30 (GPR30, also known as G protein-coupled oestrogen receptor 1 or GPER). Furthermore, weak oestrogenic activity has been found in genistein, but the mechanism of action remains unknown. The aim of this study was to investigate the in vitro effects of genistein on the secretion of progesterone (P4) and oestradiol (E2) in chicken granulosa cells harvested from follicles, as well as the mRNA expression of ERs in these cells. In addition, we examined the expression of key enzymes including steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD) in the process of P4 synthesis. The results showed that genistein did not affect the viability of granulosa cells, nor was the proliferating cell nuclear antigen (PCNA) protein changed. Among the 1-, 10-, 100-, and 1,000-nM concentrations tested, treatment with 1 nM genistein for 48 h significantly increased P4 but did not affect E2 secretion. Real-time PCR results showed that the ERβ gene expression in granulosa cells was markedly upregulated by 1 nM genistein treatment for 48 h, but there was no significant difference in ERα and GPR30 expression. Genistein also increased the gene expression of StAR, P450scc and 3β-HSD in the cultured granulosa cells. These results indicate that genistein acts directly on chicken granulosa cells to increase P4 production by upregulating the gene expression of key enzymes through binding in ERβ. It may exert positive effects on the reproduction of late-laying hens and act as an effective and safe feed additive for animals.