Yixuan Guo

Effects of nutrient restriction and arginine treatment on oxidative stress in the ovarian tissue of ewes during the luteal phase

The aim of this study was to determine whether nutrient restriction and arginine treatment affect energy metabolism changes and oxidative stress through the mitochondrial pathway in the ovarian tissue of ewes during the luteal phase. On days 6-15 of the estrous cycle, 24 multiparous Hu sheep (BW = 43.56 ± 1.53 kg) were randomly assigned to three groups: control group (CG; n = 6), restriction group (RG; n = 9), and l-arginine group (AG; n = 9) administered Arg treatment (or vehicle) three times per day. The ewes were slaughtered at the end of treatment, and blood samples and ovaries were collected for analysis. In this study, the expression levels of antioxidase enzymes (SOD2, CAT and GPX1) and mitochondrial biogenesis-related genes (ESRRA and TFAM), as well as antioxidase activity and mitochondrial function were examined in ovarian tissue. Nutrient restriction resulted in activation of ESRRA and TFAM and an increase in relative mtDNA copy number, whereas arginine treatment led to a pronounced recovery of ovarian tissue. In addition, we observed increased AMPK phosphorylation at Thr172 and SIRT3 levels in nutrient restricted ewes, and these effects decreased with arginine treatment. In conclusion, the present results indicated that short-term nutritional restriction led to changes in energy metabolism and oxidative stress. These changes disrupted the redox balance, thus leading to apoptosis through the mitochondria-dependent apoptosis pathway. Arginine treatment altered gene expression in ovarian tissue and increased the resistance to oxidative stress and the anti-apoptosis capacity. The results presented here suggest a potential method to increase agricultural productivity and economic benefits in the sheep industry by using dietary supplementation with arginine to decrease temporary undernutrition of ewes.

Effects of l-arginine on endometrial microvessel density in nutrient-restricted Hu sheep

Nutrient deficiency in ruminants can lead to estrus cycle disorders, a decreased pregnancy rate, and reduce birth weight. l-arginine (L-Arg), an important amino acid, can improve uterine homeostasis in pregnant sheep and prevent intrauterine growth restriction (IUGR). However, most studies of L-Arg have been conducted on pregnant sheep and few have reported the effects of L-Arg on microvessel density (MVD) in the non-pregnant ovine endometrium. The processes of normal uterine cyclical development and implantation are dependent on a balanced of endometrial MVD. In this study, female Hu sheep 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 MVD in ovine endometrium were then studied. Our results showed that ovine endometrial MVD was significantly increased by nutrient restriction, but L-Arg counteracted the effect of nutrient restriction on MVD (P < 0.05). Levels of angiogenic growth factors (including VEGFA, VEGFR2, and FGF2) had significant increases (P < 0.05) in endometrium of nutrient restriction on sheep, but that L-Arg supplementation substantially decreased (P < 0.05) their expressions in nutrient restriction sheep. Furthermore, oxidative stress caused by nutrient restriction was also alleviated by L-Arg supplementation in the ovine endometrium. Overall, the results suggested that L-Arg has crucial roles in maintaining the balance of endometrial MVD and angiogenic growth factors, and increasing anti-oxidation capability in the endometrium of nutrient-restricted sheep. This study will provide a theoretical basis and technical means for the normal development of endometrial microvessels in low nutrition level.

Dietary rumen-protected arginine and N-carbamylglutamate supplementation enhances fetal growth in underfed ewes

The present study was conducted with an ovine intrauterine growth restriction (IUGR) model to test the hypothesis that dietary rumen-protected l-arginine (RP-Arg) or N-carbamylglutamate (NCG) supplementation in underfed ewes is effective in enhancing fetal growth. Between Days 35 and 110 of pregnancy, 32 multiparous ewes carrying two fetuses were randomly assigned to one of four groups: a control (CG) group (n=8; 100% National Research Council (NRC) requirements for pregnant sheep), a nutrient-restricted (RG) group (n=8; fed 50% NRC requirements, and two treatment (ARG and NCG) groups (n=8 in each group; fed 50% NRC requirements supplemented with 20gday-1 RP-Arg or 5gday-1 NCG. All ewes were killed on Day 110 of pregnancy to determine fetal weight and fetal organ weights, and metabolites and hormones in fetal plasma, amino acid concentrations in the fetal liver and longissimus dorsi muscle, and expression of mRNAs in the somatotropic axis. Maternal and fetal bodyweight and the weight of most fetal organs expressed as a percentage of bodyweight increased in response to ARG and NCG compared with values for fetuses from RG ewes. Fetal plasma concentrations of insulin, insulin-like growth factor 1, total amino acids, lactate, thyroxine, and the thyroxine/tri-iodothyronine ratio were lower in fetuses from RG ewes compared with the other treatment groups, but concentrations of growth hormone, non-esterified fatty acids, and total cholesterol were greater in fetuses from RG ewes. Maternal RP-Arg or NCG supplementation increased concentrations of amino acids in fetal tissues and expression of mRNAs for somatotropic axis proteins in fetuses from RG ewes. These findings suggest that maternal RP-Arg and NCG supplementation of underfed ewes decreases fetal IUGR by improving metabolic homeostasis of fetal endocrinology, increasing the availability of amino acids in the fetal liver and longissimus dorsi muscle and affecting the expression of somatotropic axis genes.

Role of FGF9 in sheep testis steroidogenesis during sexual maturation

Fibroblast growth factor 9 (FGF9) is an important signaling molecule in early gonadal development. Hu sheep are noted for reproductive precociousness and fertility. The present study was conducted to investigate the gene expression and functions of FGF9 in ovine testis steroidogenesis during sexual maturity. A 874 bp cDNA fragment of FGF9 was detected that included a 627 bp coding sequence, encoding 208 amino acids. The FGF9 amino acid sequence of sheep had high homology with this molecule of other mammalian species. Additionally, the abundance of FGF9 in ovine testis was greater (P <  0.05) at 9 months (M) and 24 M of age compared with those at 3 M. Immunohistochemistry further revealed that FGF9 mainly localized in the Leydig cells and that there were small amounts in elongating spermatids. The functions of FGF9 in sheep Leydig cells was investigated using a siRNA-FGF9. Secretion of T and abundance of testosterone synthesis-related enzymes in Leydig cells were inhibited (P <  0.05) by siRNA-FGF9. Thus, these results demonstrated FGF9 is an important regulator of testosterone biosynthesis in rams. Results of the present research provide a new perspective for genetic and molecular research on modulation of physiological mechanisms during sexual maturity in male sheep.

Energy restriction affect liver development in Hu sheep ram lambs through Hippo signaling pathway

This study aimed to evaluate the effects of dietary energy restriction on postnatal liver development in Hu sheep ram lambs. A total of 16 ram lambs were randomly divided into two groups: 100% energy requirements diet and 55% energy requirements diet, which were fed for 75 d. Results showed that the final body and liver weights decreased with energy restriction (p <0.05). Energy restriction caused a significant decrease in the levels of circulating insulin-like growth factor 1 (IGF1) and an increase in growth hormone secretion (p <0.05), which can be explained by the decreased mRNA expression levels of the growth hormone receptor (GHR) and IGF1 (p <0.05). The proliferating cell nuclear antigen (PCNA), Ki-67 and apoptosis-related proteins (BAX and BCL2) were mainly located in the nucleus and the cytoplasm of hepatocytes, respectively. The transcription and protein levels of PCNA and BAX were significantly decreased and increased by energy restriction, respectively (p <0.05). The caspase9 and caspase3 mRNA and activity were increased in energy restriction group (p <0.05). Moreover, Hippo signaling pathway proteins [mammalian sterile 20-like protein kinase 1 (MST1), large tumor suppressor kinase 1 (LATS1), and yes-associated protein 1 (YAP1)] were mainly observed around the hepatic portal area, and the expression levels of their mRNA and proteins were significantly decreased in energy restriction group (p <0.05). In summary, energy restriction in ram lambs impairs liver development by increasing apoptosis, which may occur via the Hippo signaling pathway.