Effects of diet and arginine treatment during the luteal phase on ovarian NO/PGC-1α signaling in ewes

Nitric oxide synthase and its function in animal reproduction: an update

Nitric oxide (NO), a free radical labile gas, is involved in the regulation of various biological functions and physiological processes during animal reproduction. Recently, increasing evidence suggests that the biological role and chemical fate of NO is dependent on dynamic regulation of its biosynthetic enzyme, three distinct nitric oxide synthase (NOS) according to their structure, location and function. The impact of NOS isoforms on reproductive functions need to be timely elucidated. Here, we focus on and the basic background and latest studies on the development, structure, importance inhibitor, location pattern, complex functions. Moreover, we summarize the exactly mechanisms which involved some cell signal pathways in the regulation of NOS with cellular and molecular level in the animal reproduction. Therefore, this growing research area provides the new insight into the important role of NOS male and female reproduction system. It also provides the treatment evidence on targeting NOS of reproductive regulation and diseases.

Dietary N-carbamylglutamate or L-arginine improves fetal intestinal amino acid profiles during intrauterine growth restriction in undernourished ewes

Our previous studies demonstrated that prenatal in utero growth restriction impairs postnatal intestinal function. Thus, improving postpartal intestinal absorption capacity and growth by manipulating the maternal diet prepartum is of importance. This work was conducted to determine whether supplementation of N-carbamylglutamate (NCG) or rumen-protected L-arginine (RP-Arg) increased fetal intestinal amino acid (AA) profiles in intrauterine growth retardation (IUGR) fetuses. On d 35 of gestation, Hu ewes (n = 32) carrying twin fetuses were randomized into 4 groups (8 ewes and 16 fetuses in each group), where diets were as follows: 100% of nutrient requirements recommended by National Research Council (NRC, 2007) (CON); 50% of nutrient requirements recommended by NRC (2007) (RES); RES + RP-Arg (20 g/d), (RES + ARG); and RES + NCG (5 g/d), (RES + NCG). On d 110 of gestation, both fetal and maternal tissues were collected and weighed. Compared with RES, solute carrier family 1, member 5 (SLC1A5) was upregulated (P < 0.05) within fetal jejunum, duodenum and ileum when supplementing NCG and RP-Arg. Relative to RES, RP-Arg or NCG supplementation to RES resulted in upregulation (P < 0.05) of peptide transporter 1 protein abundance within the fetal ileum. NCG or RP-Arg supplementation to RES also upregulated phosphorylated mechanistic target of rapamycin (pmTOR)-to-mTOR ratio in the fetal ileum induced by IUGR (P < 0.05). As a result, during IUGR, supplementation of Arg or NCG affected intestinal AA profiles in the fetus in part through controlling mTOR signal transduction as well as AA and peptide transport. Future studies should be conducted to understand the role (if any) of the placenta on the improvement of growth and AA profiles independent of the fetal intestine. This would help demonstrate the relative contribution of intestinal uptake in fetal life.

l-Argine regulates the proliferation, apoptosis and endocrine activity by alleviating oxidative stress in sheep endometrial epithelial cells

l-arginine (L-Arg) is a semiessential amino acid that plays crucial roles in the reproductive performance of animals. This research aimed to investigate the effect of supplementing L-Arg on endometrial epithelial cells (EECs) of Hu sheep. In vivo, female Hu sheep were randomly divided into three groups: control group (n = 5), nutrient-restricted group (n = 5), and L-Arg supplemented nutrient-restricted group (n = 5). Then, the effect of L-Arg on ovine endometrial growth and antioxidant capacity was assessed. We found that L-Arg supplementation promoted the growth of endometrial ductal gland invaginations (DGI), and alleviated oxidative stress in nutrient-restricted sheep. In order to investigate its mechanism, a H₂O₂-induced EECs oxidative stress model was established, and roles of L-Arg in EECs oxidation resistance, proliferation, apoptosis and endocrine activity were studied in vitro. Our results showed that L-Arg markedly decreased the release of reactive oxygen species (ROS) and malonaldehyde (MDA), and enhanced the expression and activity of certain antioxidant enzymes in EECs challenged by the H₂O₂ (p < 0.05). Supplementation of L-Arg significantly reduced the effect of 200 μM H₂O₂ on the viability of EECs (p < 0.05). In addition, EECs treated with L-Arg significantly alleviated the G0/G1-phase cell cycle arrest, apoptosis, and the inhibition of endometrial growth factors expression caused by H₂O₂ (p < 0.05). Overall, the results demonstrate that L-Arg performs crucial roles in maintaining the proliferation of ovine EECs, endocrine activity and inhibiting apoptosis through reducing oxidative stress. This study offers a theoretical basis for using L-Arg to improve sheep the uterine function.

Effect of dietary arginine-to-lysine ratio in lactation on biochemical indices and performance of lactating sows

The present study investigated the effect of optimizing the total dietary arginine (Arg)-to-lysine (Lys) ratios on the metabolism of lactating sows and piglet performance by supplementation with l- Arg during lactation. A total of 200 multiparous sows (three to six parities, Yorkshire × Landrace) were selected and randomly and equally assigned to five groups in lactation, and finally, 36, 34, 35, 36, and 33 dams completed the study in the dietary treatments, respectively, where the diets consisted of five step-up Arg-to-Lys ratios (0.9, 1.0, 1.1, 1.2, and 1.3) by the addition of 0%, 0.10%, 0.20%, 0.30%, and 0.40% Arg. The diets contained 3.37 to 3.38 Mcal of digestible energy/kg energy, 17.73% to 17.75% crude protein, and 0.98% to 1.01% Lys and were fed ad libitum during lactation. The performance of sows and suckling piglets was measured, and plasma and milk samples were collected for analysis. The feed intake of sows as well as litter weight gain during lactation increased linearly (P ≤ 0.05), while maternal backfat and milk composition were not affected (P > 0.05) as the dietary Arg-to-Lys ratios increased. Analyzed plasma biochemical indices, including concentrations of free Arg, Orn, and Glu, and prolactin, insulin, and follicle-stimulating hormone, responded linearly (P ≤ 0.05) to increases in dietary Arg-to-Lys ratios. The dietary Arg-to-Lys ratios of 1.01 and 1.02 were optimal for maternal feed intake and litter weight gain, based on broken-line models. Collectively, the results of this study indicate that increasing total dietary Arg-to-Lys ratios in lactation was beneficial for the performance of lactating sows and suckling piglets, and dietary Arg-to-Lys ratios of 1.01 and 1.02 were optimal, from regression analyses, for the practical feeding of lactating sows.

Arginine infusion rescues ovarian follicular development in feed-restricted Hu sheep during the luteal phase

The aim of this study was to investigate the molecular mechanisms of arginine (Arg) on follicular development of acute feed-restricted ewes during the luteal phase. From day 6 of the estrous cycle, 24 multiparous Hu sheep were randomly assigned into three groups: control group (a maintenance diet; n = 6), feed restriction group (0.5 maintenance diet, saline infusion; n = 9) and Arg treatment group (0.5 maintenance diet, infusion with 155 μmol of Arg-HCl/kg body weight; n = 9). The intravenous administrations were performed three times per day from day 6 to day 15 of the estrous cycle. At the end of treatment, the hypothalamus and pituitary were collected, as well as the follicular fluid (FF) and granulose cells (GCs) in the ≥2.5 mm follicles. The transcription level of NPVF was significantly increased, and the expression level of GNRH was significantly decreased in the hypothalamus with feed restriction. In addition, feed restriction significantly decreased the number of ≥2.5 mm follicles in the ovaries. In the ≥2.5 mm follicles, feed restriction significantly increased estradiol (E₂) level in FF and the expression levels of steroidogenesis related genes (STAR, 3BHSD and CYP19A1) in GCs, while significantly decreased the expressions of FSHR and cell proliferation related genes (YAP1, CCND1 and PCNA) in GCs. Moreover, the activities of glucose metabolism enzymes (PFKP and G6PDH) were significantly decreased in GCs of the ≥2.5 mm follicles with feed restriction. Interestingly, as a precursor of nitric oxide, Arg supplementation can rescue the effects of feed restriction on follicular development by enhancing glucose metabolism and cell proliferation of GCs, and alleviating the abnormal E₂ secretion in the ≥2.5 mm follicles, accompanied with recovering the expressions of NPVF and GNRH in the hypothalamus. These findings will be helpful for understanding the role of nutrition and Arg in sheep follicular development.

Long non-coding RNA366.2 controls endometrial epithelial cell proliferation and migration by upregulating WNT6 as a ceRNA of miR-1576 in sheep uterus

Long non-coding RNAs (lncRNAs) play an important regulatory role in mammalian fecundity. Currently, most studies are primarily concentrated on ovarian lncRNAs, ignoring the influence of uterine lncRNAs on the fecundity of female sheep. In this study, we found a higher density of uterine glands and endometrial microvessel density (MVD) in high prolificacy group of Hu sheep compared to low prolificacy groups (p < 0.05) as well as an increased level of serum placental growth factor (PLGF). Hundreds of differentially expressed (DE) lncRNAs were identified in Hu sheep with different fecundity by RNA sequencing (RNA-seq), and their targets were enriched in some signaling pathways involved in endometrial functions, such as the estrogen signaling pathway, nuclear factor kappa B (NF-κB) signaling pathway, oxytocin signaling pathway, and Wnt signaling pathway. Furthermore, the underlying mechanisms of competitive endogenous RNA (ceRNA) of lncRNA366.2-miR-1576- WNT6 were determined by bioinformatics analysis. Functionally, our results indicated that lncRNA366.2 promoted endometrial epithelial cell (EEC) proliferation, migration, and growth factor expression by sponging miR-1576 to upregulate WNT6 expression and activate the Wnt/β-catenin pathway. Taken together, our research indicated the regulatory mechanism of the lncRNA366.2-miR-1576-WNT6 in EEC proliferation and migration. Furthermore, this study provides a new theoretical reference for the identification of candidate genes related to fecundity.

Rumen-protected arginine in ewe lambs: effects on circulating serum amino acids and carotid artery hemodynamics

Sixty nonpregnant, nulliparous Rambouillet ewes (51 ± 1.4 kg initial body weight) were used in a completely randomized design to determine 1) if rumen-protected l-Arg (RP-ARG) supplementation would increase serum concentrations of amino acids resulting from Arg supplementation and metabolism, and decrease serum concentrations of amino acids that compete with Arg for transporters, 2) if RP-ARG supplementation would alter carotid artery hemodynamics, and 3) the most effective oral dose of RP-ARG to positively increase both circulating amino acids and improve peripheral tissue blood perfusion as measured by carotid hemodynamics. Ewes were penned individually in a temperature-controlled facility. Ewes were randomly assigned to one of four treatments: a control group that received no supplemental Arg (CON; 50 g of finely ground corn, only), or Arg-supplemented groups that received 90 (90), 180 (180), or 360 (360) mg RP-ARG·kg BW-1·d-1 mixed in 50 g of finely ground corn. Supplements were administered once daily for 14 d and fully consumed before the delivery of a total pelleted diet at 0630 and 1830 hours daily. Baseline and final blood samples were collected at days 0 (before treatment initiation) and 15, respectively. Doppler ultrasound was used to assess carotid arterial hemodynamics at 0600 hours on days 0 (before treatment initiation), 5, 8, 12, and 15. After 14 d of supplementation, ewes fed 180 had greater Arg (P = 0.05) and Orn (P = 0.05) and tended (P = 0.08) to have greater Asp in serum than ewes fed 90, and for these amino acids, ewes fed 180 were similar (P ≥ 0.16) compared with ewes fed 360. All supplemented ewes (90, 180, and 360) had a negative change (P = 0.02) from baseline when normalized to CON for the pulsatility and resistance indices, which indicate greater distal tissue blood perfusion and lower vascular resistance of blood flow, respectively. Additionally, there were quadratic responses for the pulsatility and resistance indices (P = 0.03 and 0.01, respectively) where ewes fed 180 had the greatest change from baseline when normalized to CON. Results indicate that Arg supplementation increased serum amino acid concentrations and improved peripheral tissue blood perfusion. The 180 mg·kg BW-1·d-1 RP-ARG dose was determined to be the optimal dose for nonpregnant, nulliparous Rambouillet ewes.

Estradiol-17β regulates proliferation and apoptosis of sheep endometrial epithelial cells by regulating the relative abundance of YAP1

Yes-associated protein 1 (YAP1) transcription regulator of the Hippo protein kinase pathway, serves as a key regulator of tissue growth and organ size by regulating cell proliferation and apoptosis. Effects of YAP1 on proliferation and apoptosis of sheep endometrial epithelial cells (EEC) as a result of estradiol-17β (E₂) treatment, however, remain unclear. In the present study, the abundance of YAP1 protein in the uterine horn was greater than that in the uterine body or cervix. The YAP1 protein was primarily localized in the endometrial luminal and glandular epithelial cells of the uterine horn of ewes on day 2 of the estrous cycle. Compared with control samples, there was a lesser abundance of YAP1 mRNA transcript that was associated with a lesser proliferation and greater apoptosis of EEC. There were also lesser concentrations of epidermal growth factor and insulin-like growth factor 1 in the spent culture medium when there was a lesser abundance of YAP1 mRNA in EEC compared with those in the control group. When there was a greater abundance of YAP1 mRNA transcript, there were greater concentrations of epidermal growth factor and insulin-like growth factor 1 in the spent media. Furthermore, with estradiol-17β treatment the abundance of YAP1 mRNA transcript was similar to that of the control samples. Taken together, estradiol-17β may function as an essential regulator of EEC proliferation and apoptosis by modulation of concentrations of YAP1 protein in the sheep uterus. These results indicate there are molecular mechanisms of estradiol-17β and YAP1 in EEC proliferation and apoptosis of ewes.

Long non-coding RNA LOC105611671 modulates fibroblast growth factor 9 (FGF9) expression by targeting oar-miR-26a to promote testosterone biosynthesis in Hu sheep

Fibroblast growth factors (FGFs) play crucial roles in early gonadal development and germ cell maturation of mammals; FGF9 is involved in mammalian testis steroidogenesis. However, the upstream regulators of FGF9 in ovine testosterone biosynthesis remain unknown. Long non-coding RNAs (lncRNAs) are crucial regulators of multiple biological functions that act by altering gene expression. In the present study, we analysed the role of LOC105611671, a lncRNA upstream of FGF9, in Hu sheep steroidogenesis. We found that LOC105611671 expression increased significantly in Hu sheep testes during sexual maturation (P&lt;0.05). Moreover, levels of FGF9 and testosterone were decreased by LOC105611671 knockdown in Hu sheep Leydig cells (LCs). Results of transient transfection and luciferase assays revealed that FGF9 is a functional target gene of oar-miR-26a in ovine LCs. Further functional validation experiments revealed that LOC105611671 regulates testosterone biosynthesis by targeting oar-miR-26a. Overall, the present study describes the expression profile of LOC105611671 during sexual maturation and demonstrates that LOC105611671 modulates FGF9 expression by targeting oar-miR-26a to promote testis steroidogenesis in Hu sheep. Our research provides a new theoretical basis for genetic and molecular research on testosterone biosynthesis in sheep.

Effect of short-term nutritional supplementation on hormone concentrations in ovarian follicular fluid and steroid regulating gene mRNA abundances in granulosa cells of ewes

This study was conducted to investigate effects of short-term nutritional supplementation on concentrations of reproductive hormones in follicular fluid and on mRNA abundance in granulosa cells (GCs) during the luteal phase of ewes. Eighteen ewes were randomly assigned to treatment or control groups (n = 9, each group). All the ewes were subjected to estrous synchronization using a Controlled Intravaginal Releasing Device (CIDR). From the second to the eleventh day of estrous synchronization, ewes were fed a diet with a relatively greater (treatment group) or a maintenance (control group) energy content. Samples of follicular fluid and GCs were collected from antral follicles of estrous ewes after CIDR removal. The results indicate mean FSH concentration of fluid in small follicles and mean LH concentrations of fluid in large follicles of the ewes in the treatment group were greater (P < 0.05) than that of ewes in the control group. Follicular fluid E₂ concentrations were directly related (P < 0.05) to follicular diameter. The ewes of the treatment group had greater (P < 0.05), compared with the control group, abundances of Follicle Stimulating Hormone Receptor (FSHR) in small and medium follicles, and (P<0.05) Luteinizing Hormone Receptor (LHR), Steroid Acute Regulatory Protein (STAR), cytochrome P450 (CYP17A1, CYP19A1) enzyme and Estrogen Receptor (ESR1) in large follicles. The results of this study provide evidence for a potential mechanism by which short-term nutritional supplementation improves follicular development possibly because of increased expression of steroid synthesis-regulating genes in large follicles.

Effects of l-arginine on endometrial estrogen receptor α/β and progesterone receptor expression in nutrient-restricted sheep

This study aimed to determine the effects of l-arginine (L-Arg) supplementation on steroid hormone receptors in non-pregnant ovine endometrium. All experimental ewes were randomly assigned to either a control group (n = 6), a nutrient-restricted group (n = 6), or an L-Arg supplemented nutrient-restricted group (n = 6). The effects of L-Arg on estrogen receptor α/β (ERα/β) and progesterone receptor (PGR) expression in the ovine endometrium were assessed. Our results showed that levels of ERβ and PGR expression were significantly increased by nutrient restriction, but L-Arg counteracted the effect of nutrient restriction on ERβ and PGR expression (p < 0.05). Also, expression of endometrial ERα was substantially increased (p < 0.05) by L-Arg supplementation. Furthermore, ERα/β and PGR were mainly detected in the endometrial luminal epithelium and glandular epithelium. Therefore, we isolated and identified endometrial epithelial cells (EECs) from sheep. Different concentrations of L-Arg were added to investigate the effects on ERα/β and PGR in EECs. The expression levels of endothelial nitric oxide synthase, ERβ, and PGR were significantly increased in response to low-concentration (200 μmol) L-Arg supplementation, which subsequently decreased with a high concentration (800 μmol) (p < 0.05). Otherwise, ERα expression was remarkably increased at both L-Arg concentrations in EECs (p < 0.05). Overall, the results indicated that L-Arg performed crucial roles in the regulation of ovine steroid hormone receptor expression in the endometrium. The results of this study provide a theoretical basis and technical means for the normal function of endometrium in response to low nutrient levels.