Novel regulators of rabbit reproductive functions

Reproductive performance and transcriptome analysis of ovaries at different parities in female rabbits

This study investigated the reproductive performance and ovarian molecular regulation associated with parity in commercial rabbit systems. The pregnancy data of 658 female rabbits from the first to sixth parities (P1 to P6) under the same mating pattern were analyzed, showing a significant decrease in the conception rate in P6. Compared to P1 (N = 120) and P2 (N = 105), P6 (N = 99) had significantly lower performance indices in terms of total litter size, live litter size, survival rate at birth, and weight of 3 and 5 wk old kits (P < 0.05). Using H&E staining, we found that the ovarian primordial follicle reservoir of P6 was significantly lower than that of P1 and P2, and the number of atretic follicles at P6 was significantly higher (P < 0.05). Blood (N = 30 per group) and ovaries (N = 6 per group) in P1, P2, and P6 were collected for measurement of the serum anti-oxidant capacity and indices of ovarian function by ELISA. It was found that serum glutathione, ovarian Klotho protein, and telomeres of P1 and P2 were significantly higher than those of P6 (P < 0.05). The serum levels of ROS and MDA at P1 and P2 were significantly lower than those at P6 (P < 0.05). Additionally, transcriptome analysis showed 213 up-regulated and 747 down-regulated differentially expressed genes (DEGs) between P2 and P6 ovaries. Several DEGs were related to reproduction, including CYP21A2, PTGFR, SGK1, PIK3R6, and SRD5A2. These results demonstrate the influence of parity on reproduction in female rabbits, reflected in a loss of follicle reservoir, disordered levels of anti-oxidants, and indices associated with ovarian function and molecular regulation. This study provides a basis for the strategies to increase reproductive rate in female rabbits.

High temperature impairs rabbit viability, feed consumption, growth and fecundity: examination of endocrine mechanisms

The aim of the present study was to examine the effect of high ambient temperature on rabbit feed consumption, growth, viability, and fecundity, as well as the morphology and endocrine function of gonadal and adrenal cells. Adult does and their offspring were kept at either a comfortable (20°C; control) or high (36°C) temperature throughout pregnancy and up until weaning of pups. Doe mortality and fecundity, and plasma concentrations of hormones were evaluated. In addition, granulosa cells were cultured with and without FSH to assess progesterone production. In the offspring, we assessed mortality, total feed consumption, feed efficiency, growth, plasma hormone concentrations, as well as the microstructure in ovarian granulosa cells, testicular Leydig cells, and adrenocortical cells. We observed greater mortality of both adult animals and offspring at the higher ambient temperature compared with the control. The higher ambient temperature suppressed feed consumption, feed efficiency, and growth of pups. Adult and young females exposed to a high temperature had lower circulating concentrations of progesterone, but not of estradiol, compared with controls. Young males exposed to a high ambient temperature had greater circulating concentrations of testosterone, but not progesterone, compared with controls. High ambient temperature reduced circulating IGF-I concentrations in all the animals. Corticosterone level was increased in plasma of young but not of adult animals. Granulosa cells isolated from the ovaries of does subjected to high temperatures released less progesterone, and they had poorer response to the stimulatory action of FSH than the cells from control does. High temperatures induced fragmentation of nucleoli in ovarian granulosa cells, but they did not alter the state of other organelles in ovarian, testicular, or adrenocortical cells. A negative influence of high temperature on rabbit feed consumption, growth, viability, and fecundity was observed. Taken together, these changes could be due to a decrease in IGF-I and/or progesterone secretion, destruction of ovarian cell nucleoli, and/or impaired ovarian cell response to FSH.

Interrelationships between metabolic hormones, leptin and ghrelin, and oil-related contaminants in control of oxytocin and prostaglandin F release by feline ovaries

We examined the effects of metabolic hormones leptin and ghrelin, and the oil-related environmental contaminants toluene and xylene on the release of ovarian hormones by gravid and non-gravid cats, as well as the functional interrelationships between metabolic hormones and contaminants. Ovarian fragments of non-gravid cats were cultured with and without leptin and toluene. Next, ovarian fragments of either non-gravid or gravid animals were cultured with and without ghrelin and xylene. Oxytocin (OT) and prostaglandin F (PGF) release was measured using ELISA. We confirm ovarian OT and PGF production by feline ovary, demonstrate the involvement of leptin and ghrelin in controlling OT and PGF release, show the direct influence of toluene and xylene on feline ovarian secretory activity, indicate the ability of leptin and ghrelin to mimic and promote the main contaminant effects, demonstrate that oil-related contaminants can prevent and even invert the effects of leptin and ghrelin on the ovary, and suggest the gravidity-associated changes in ability of ghrelin to promote xylene action on PGF (but not to OT), but not in basic ovarian OT and PGF release and their response to ghrelin or xylene.

The phytoestrogen, diosgenin, directly stimulates ovarian cell functions in two farm animal species

The present in vitro study was conducted to examine the direct action of the plant steroidal sapogenin, diosgenin, on basic farm animal ovarian cell functions. As models, we used cultured porcine ovarian granulosa cells, porcine whole follicles, and rabbit ovarian fragments. The effects of diosgenin (0, 1, 10, or 100 μg/mL medium) on the markers of proliferation, cytoplasmic apoptosis, steroid (progesterone: P4, testosterone: T, and estradiol: E2) release, and peptide hormone (insulin-like growth factor I: IGF-I) release were analyzed by quantitative immunocytochemistry and radioimmunoassay. Diosgenin promoted proliferation, apoptosis, and T and E2 release and inhibited P4 output in cultured porcine granulosa cells. Similarly, cultured porcine ovarian follicles showed diosgenin-induced inhibition of P4 and stimulation of T release. In cultured rabbit ovarian fragments, diosgenin stimulated P4 and IGF-I release. This is the first study showing that diosgenin can promote basic ovarian cell functions such as proliferation, apoptosis, and steroid and peptide hormone release. The similar effects of diosgenin on porcine granulosa cells and ovarian follicles suggest that granulosa cells are the primary ovarian target of diosgenin. The contrasting effects of diosgenin on porcine and rabbit ovarian P4 output suggest that diosgenin functions in a species-specific manner. These observations indicate that diosgenin has potential applications for improving female reproduction.

Quercetin directly promotes rabbit ovarian steroidogenesis

<p>The bioflavonoid quercetin is a component of food with numerous biological effects, but its function in reproductive processes remains to be investigated. This study aimed to examine the direct action of quercetin on steroid hormone release in rabbit ovaries. We analysed the effect of quercetin (0, 1, 10, and 100 ng/mL) on cultured rabbit ovarian fragments. The release of progesterone (P4), testosterone (T) and estradiol (E2) were analysed by enzyme immunoassay. Quercetin promoted P4, T, and E2 release by rabbit ovarian fragments. These observations indicate that quercetin can directly stimulate rabbit ovarian steroidogenesis – an essential regulator of reproduction and fecundity. The application of dietary quercetin for control of rabbit reproduction is discussed.</p>

Apoptosis signal-regulating kinase (ASK1) and transcription factor tumor suppressor protein TP53 suppress rabbit ovarian granulosa cell functions

This study was conducted with the aim to understand the roles of apoptosis signal-regulating kinase (ASK1) and transcription factor tumor suppressor protein TP53, as well as the possible interrelationships, in the control of healthy ovarian cell functions. Rabbit ovarian granulosa cells were transfected with constructs encoding ASK1, TP53, or TP53 + ASK1 and cultured with or without insulin-like growth factor 1 (IGF1). The accumulation of ASK1, the cytoplasmic apoptosis regulators BAX and BCL2, and proliferating cell nuclear antigen (PCNA, a cell proliferation marker), as well as progesterone release, were evaluated by quantitative immunocytochemistry and radioimmunoassay. Results indicate both ASK1 and TP53 promoted the accumulation of BAX, but suppressed that of BCL2 and PCNA. Progesterone release was inhibited by ASK1 and promoted by TP53, while TP53 also stimulated ASK1 accumulation. Additionally, IGF1 stimulated PCNA and reduced progesterone release, but did not affect ASK1. Transfection with ASK1, TP53, or TP53 + ASK1 could modify IGF1 activity, however, there was no cumulative effect with co-transfection of TP53 and ASK1. This is the first results that indicate there is ASK1 suppression of healthy ovarian granulosa cell functions, including promoting apoptosis, inhibiting proliferation, and alter progesterone release. There was also TP53 actions in rabbit ovarian granulosa cells, where it stimulated ASK1, apoptosis, and progesterone release, thus suppressing proliferation and responses to IGF1. The similarity of ASK1 and TP53 effects on apoptosis and proliferation, lack of cumulative action of these molecules, and capacity of TP53 to promote ASK1 accumulation suggest that TP53 can suppress some ovarian granulosa cell functions through ASK1 stimulation.

Integrated Analysis of mRNA and miRNA Expression Profiles in the Ovary of Oryctolagus cuniculus in Response to Gonadotrophic Stimulation

Molecular mechanisms responsible for gonadotrophic control of ovarian follicle development and ovulation have not been fully delineated. In this study, prepubertal female rabbits were subjected to a combined PMSG/hCG treatment for the induction of follicle maturation and ovulation. Ovaries of 6 does at different time points during gonadotrophic stimulation were collected for histomorphological examination and genome-wide analysis of miRNA and mRNA transcriptomes, and the plasma were separated for detecting melatonin (MT), prostaglandin E₂ (PGE₂), estradiol (E₂), and progesterone (P₄) levels. The results suggested that PMSG promoted the development of the reproductive tract by decreasing plasma levels of E₂ and slightly increasing those of MT and PGE₂ and that hCG induced ovulation and corpus luteum formation by significantly increasing MT, PGE₂, and P₄ levels. At the transcriptomic level, a total of 1,122 differentially expressed genes (DEGs) and 12 DE miRNAs were identified using three-group comparisons. Meanwhile, pairwise comparisons revealed that 279 and 103 genes as well as 36 and 20 miRNAs were up- and down-regulated during PMSG-stimulated follicle development while 11 and 5 genes as well as 33 and 16 miRNAs were up- and down-regulated during hCG-induced luteinization. KEGG enrichment analysis of the DEGs derived from both three-group- and two-group comparisons as well as the predicted target genes of DE miRNAs highlighted the crucial roles of pathways involving tissue remodeling, energy metabolism, and regulation of cellular functions in mediating gonadotrophin-induced follicle maturation. Specifically, 3 genes including the matrix metallopeptidase 13 (MMP13), protein phosphatase 1 regulatory subunit 3C (PPP1R3C), and solute carrier family 2 member 12 (SLC2A12), together with 2 miRNAs including the miR-205-1 and miR-34c, were predicted to be the promising downstream targets of both PMSG and hCG. Significantly, the miRNA-mRNA interaction pairs containing top 10 up- and down-regulated mRNAs/miRNAs upon PMSG/hCG stimulation were established, and so were those involved in the PI3K-Akt, ECM-receptor interaction, and focal adhesion pathways during PMSG-induced follicle maturation. Finally, qRT-PCR analysis confirmed the results from RNA-Seq and Small RNA-Seq. Our work may contribute to a better understanding of the regulatory mechanisms of gonadotrophins on ovarian follicle development and ovulation.

cAMP response element-binding protein 1 controls porcine ovarian cell proliferation, apoptosis, and FSH and insulin-like growth factor 1 response

The aim of the present study was to examine the role of cAMP response element-binding protein (CREB) and its phosphorylation in the regulation of ovarian cell proliferation and apoptosis, and of the response of proliferation and apoptosis to the upstream hormonal stimulators FSH and insulin-like growth factor (IGF) 1. In the first series of experiments, porcine ovarian granulosa cells, transfected or not with a gene construct encoding wild-type CREB1 (CREB1WT), were cultured with and without FSH (0, 1, 10 or 100 ng mL−1). In the second series of experiments, these cells were transfected or not with CREB1WT or non-phosphorylatable mutant CREB1 (CREB1M1) and cultured with and without FSH (0, 1, 10 or 100 ng mL−1) or IGF1 (0, 1, 10 and 100 ng mL−1). Levels of total and phosphorylated (p-) CREB1, proliferating cell nuclear antigen (PCNA), a marker of proliferation, and BAX, a marker of apoptosis, were evaluated by western immunoblotting and immunocytochemical analysis. Transfection of cells with CREB1WT promoted accumulation of total CREB1 within cells, but p-CREB1 was not detected in any cell group. Both CREB1WT and CREB1M1 reduced cell proliferation and apoptosis. Addition of 10 and 100 ng mL−1 FSH to non-transfected cells promoted CREB1 accumulation and apoptosis, whereas cell proliferation was promoted by all concentrations of FSH tested. FSH activity was not modified in cells transfected with either CREB1WT or CREB1M1. IGF1 at 100 ng mL−1 promoted cell proliferation, whereas all concentrations of IGF1 tested reduced apoptosis. Transfection with either CREB1WT or CREB1M1 did not modify the effects of either FSH or IGF1, although CREB1M1 reversed the effect of IGF1 on apoptosis from inhibitory to stimulatory. These observations suggest that CREB1 is involved in the downregulation of porcine ovarian cell proliferation and apoptosis. The absence of visible CREB1 phosphorylation and the similarity between the effects of CREB1WT and CREB1M1 transfection indicate that phosphorylation is not necessary for CREB1 action on these processes. Furthermore, the observations suggest that FSH promotes both ovarian cell proliferation and apoptosis, whereas IGF1 has proliferation-promoting and antiapoptotic properties. The effect of FSH on CREB1 accumulation and the ability of CREB1M1 to reverse the effects of IGF1 on apoptosis indicate that CREB1 is a mediator of hormonal activity, but the inability of either CREB1WT or CREBM1transfection to modify the primary effects of FSH and IGF1 suggest that CREB1 and its phosphorylation do not mediate the action of these hormones on ovarian cell proliferation and apoptosis.

Effect of turmeric on the viability, ovarian folliculogenesis, fecundity, ovarian hormones and response to luteinizing hormone of rabbits

The present study investigated whether dietary turmeric (Curcuma longa L.) can improve rabbit reproduction, ovarian function, growth, or viability. Female New Zealand White rabbits were either fed a standard diet (n=15) or a diet enriched with 5 g (group E1) or 20 g (group E2) turmeric powder per 100 kg feed mixture (n=16 or 15, respectively). After 295 days, weight gain, conception and kindling rates, pup and mother viability, ovarian macro- and micro-morphometric indices, release of leptin in response to the addition LH, and the release of progesterone, testosterone and leptin by isolated ovarian fragments were analyzed. Dietary turmeric failed to affect ovarian length and weight but did increase the number of primary follicles (E2: 32.5% greater than control group), as well as the diameter of primary (E1: +19.4%, E2: +21.1%), secondary (E2: +41.4%), and tertiary (E1: +97.1%, E2: +205.1%) follicles. Turmeric also increased the number of liveborn (E1: +21.0%) and weaned (E1: +25.0%) pups and decreased the number of stillborn pups (E2: -87.5%) but did not affect weight gain, conception, or kindling rate. Furthermore, dietary turmeric decreased doe mortality during the first reproductive cycle (13.3% in control; 0% in E1; and 6.7% in E2) but not during the second cycle. In vitro, the ovaries of the turmeric-treated rabbits released more progesterone (E1: +85.7%, E2: +90.0%) and less testosterone (E2: -87.0%) and leptin (E2: -29.0%) than the ovaries of control rabbits. Moreover, LH decreased the leptin output of control rabbits but increased that of experimental rabbits. Therefore, it is likely that dietary turmeric improves pup viability and that it could promote rabbit fecundity by either (1) promoting the production of primary ovarian follicles or (2) stimulating the growth of follicles at all stages of folliculogenesis.

Aging influences steroid hormone release by mink ovaries and their response to leptin and IGF-I

The aim of our study was to understand whether ovarian steroid hormones, and their response to the metabolic hormones leptin and IGF-I leptin, could be involved in the control of mink reproductive aging via changes in basal release of ovarian progesterone and estradiol. For this purpose, we compared the release of progesterone and estradiol by ovarian fragments isolated from young (yearlings) and old (3-5 years of age) minks cultured with and without leptin and IGF-I (0, 1, 10 or 100 ng/ml). We observed that isolated ovaries of older animals produced less progesterone but not less estradiol than the ovaries of young animals. Leptin addition stimulated estradiol release by the ovarian tissue of young animals but inhibited it in older females. Leptin did not influence progesterone output by the ovaries of either young or older animals. IGF-I inhibited estradiol output in young but not old animals, whereas progesterone release was inhibited by IGF-I irrespective of the animal age. Our observations demonstrate the involvement of both leptin and IGF-I in the control of mink ovarian steroid hormones release. Furthermore, our findings suggest that reproductive aging in minks can be due to (a) reduction in basal progesterone release and (b) alterations in the response of estradiol but not of progesterone to leptin and IGF-I.

Summary: Both leptin and IGF-I are involved in the control of mink ovarian steroid hormone release. Reproductive aging can be due to (a) reduction in basal progesterone release and (b) alterations in the response of estradiol but not of progesterone to leptin and IGF-I.