Energy substrate metabolism in skeletal muscle and liver when consuming diets of different energy levels: comparison between Tibetan and Small-tailed Han sheep

Liver Transcriptome Analysis Reveals the Mechanisms of Metabolic Adaptation of Xizang Sheep to Seasonal Changes

Background/Objectives: The Xizang sheep is a unique breed of sheep in the highland regions of China that has gradually developed physiological characteristics adapted to the plate environment through long-term natural selection and artificial breeding. However, little is known about the molecular basis of metabolic adaptation to seasons in Xizang sheep. Methods: In this study, liver tissues from Xizang sheep in summer (SL) and autumn (AL) were selected for transcriptome sequencing to explore the metabolic adaptability of Xizang sheep to seasons. Results: The results showed that a total of 12,046 differentially expressed genes (DEGs) were identified, with 1123 genes significantly upregulated and 951 genes significantly downregulated in autumn. The top five pathways enriched for DEGs were Metabolic pathways, Phagosome, Valine, leucine and isoleucine degradation, Propanoate metabolism, and Fatty acid metabolism, which are involved in immune regulation, fat oxidation, and synthesis. The reduction in lipid synthesis, fatty acid oxidation, and fat breakdown metabolism promotes gluconeogenesis by inhibiting the Peroxisome proliferator-activated receptors (PPAR) and Phosphoinositide 3-kinase- Protein kinase B (PI3K-Akt) signaling pathways. Conclusions: This process helps to maintain the whole-body energy homeostasis of Xizang sheep, facilitating their adaptation to the seasonal changes in the extreme high-altitude environment. These findings provide foundational data for studying the molecular mechanisms of metabolic adaptation to seasons in ruminants.

Quantitative Proteomic Analysis of Tibetan Pig Livers at Different Altitudes

In this study, the differences in protein profiles between the livers of Shannan Tibetan pigs (SNT), Linzhi Tibetan pigs (LZT) and Jiuzhaigou Tibetan pigs (JZT) were comparatively analyzed by tandem mass spectrometry-labeling quantitative proteomics. A total of 6804 proteins were identified: 6471 were quantified and 1095 were screened as differentially expressed proteins (DEPs). Bioinformatics analysis results show that, compared with JZT livers, up-regulated DEPs in SNT and LZT livers mainly promoted hepatic detoxification through steroid hormone biosynthesis and participated in lipid metabolism to maintain body energy homeostasis, immune response and immune regulation, while down-regulated DEPs were mainly involved in lipid metabolism and immune regulation. Three proteases closely related to hepatic fatty acid oxidation were down-regulated in enzymatic activity, indicating higher levels of lipid oxidation in SNT and LZT livers than in JZT livers. Down-regulation of the expression of ten immunoglobulins suggests that JZT are more susceptible to autoimmune diseases. It is highly likely that these differences in lipid metabolism and immune-related proteins are in response to the ecological environment at different altitudes, and the findings contribute to the understanding of the potential molecular link between Tibetan pig livers and the environment.

Diet-induced insulin resistance altered cardiac GLUT4 and FATP/CD36 expression in rats

Background

Altered substrate transport protein expression is central to the effect of insulin resistance on cardiac metabolism. The present study was thus designed to investigate the comparative effects of high fat, high sucrose and salt-induced IR on cardiac expression of fatty acid transporter (FATP) and glucose transporter (GLUT4) in rats.

Results

Rats fed with high fat, high sucrose and salt diets developed impaired glucose tolerance (p > 0.05) and hyperinsulinemia (p < 0.05) compared with control group. Myocardial glucose transporter expression was significantly increased (p < 0.001 for salt-induced IR; p < 0.01 for sucrose-induced IR; p < 0.01 for fat-induced IR) across all IR groups compared with control. Fatty acid transporter expression was also increased (p < 0.001) in high salt diet-induced IR rats, and high fat diet-induced IR rats (p < 0.05).

Conclusions

Our results demonstrate that salt and not caloric excess has a potential role in IR alteration of myocardial substrate transport protein expression in the rat.

Small intestinal morphology and sugar transporters expression when consuming diets of different energy levels: comparison between Tibetan and small-tailed Han sheep

Some non-structural carbohydrates, especially starch, escape ruminal fermentation, are converted into glucose, and are absorbed from the small intestine. This glucose provides an important source of energy, and its usage is more efficient than glucose from carbohydrates which are fermented as short chain fatty acids in the rumen and, subsequently, undergo hepatic gluconeogenesis. Tibetan sheep graze on the harsh Qinghai-Tibetan Plateau (QTP) all year round and their carbohydrate and energy intakes fluctuate greatly with seasonal forage availability. Consequently, a high capacity to absorb glucose from the small intestine would be particularly beneficial for Tibetan sheep to allow them to cope with the inconsistent dietary intakes. This study examined how the small intestinal morphology and sugar transporters' expression of Tibetan and Small-tailed Han (Han) sheep respond to fluctuating energy intakes under the harsh conditions of the QTP. Han sheep graze on the QTP only in summer and are generally raised in feedlots. Twenty-four Tibetan sheep and 24 Han sheep, all wethers, were assigned randomly to four groups (n = 6 per breed/group), with each group offered a diet differing in digestible energy content: 8.21, 9.33, 10.45 and 11.57 MJ/kg DM. After 49 d, all sheep were slaughtered, tissues of the small intestine were collected, and measurements were made of the morphology and glucose transporters and the related regulation gene expressions. At intakes of low energy levels, Tibetan sheep had a greater villus surface area in the duodenum, jejunum and ileum and higher mRNA expression of sodium-dependent glucose transporter 1 in the duodenum and ileum (P < 0.05) than Han sheep. In the glucose transporter 2 (GLUT2) mediated glucose absorption pathway, Tibetan sheep had higher GLUT2 and taste receptor family 1 member 2 and 3 mRNA expressions than Han sheep in the duodenum, jejunum and ileum (P < 0.05). We concluded that the differences between breeds indicated a greater glucose absorption capacity in the small intestine of Tibetan than Han sheep, which would confer an advantage to Tibetan over Han sheep to an inconsistent energy intake on the harsh QTP. These findings suggested that ruminants raised under harsh environmental conditions with highly fluctuating dietary intakes, as is often the case in grazing ruminants worldwide, are able to absorb glucose from the small intestine to a greater extent than ruminants raised under more moderate conditions.

Transcriptomic and Metabolomic Analyses Reveal Inhibition of Hepatic Adipogenesis and Fat Catabolism in Yak for Adaptation to Forage Shortage During Cold Season

Animals have adapted behavioral and physiological strategies to conserve energy during periods of adverse conditions. Hepatic glucose is one such adaptation used by grazing animals. While large vertebrates have been shown to have feed utilization and deposition of nutrients—fluctuations in metabolic rate—little is known about the regulating mechanism that controls hepatic metabolism in yaks under grazing conditions in the cold season. Hence, the objective of this research was to integrate transcriptomic and metabolomic data to better understand how the hepatic responds to chronic nutrient stress. Our analyses indicated that the blood parameters related to energy metabolism (glucose, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, lipoprotein lipase, insulin, and insulin-like growth factor 1) were significantly (p &lt; 0.05) lower in the cold season. The RNA-Seq results showed that malnutrition inhibited lipid synthesis (particularly fatty acid, cholesterol, and steroid synthesis), fatty acid oxidation, and lipid catabolism and promoted gluconeogenesis by inhibiting the peroxisome proliferator-activated receptor (PPAR) and PI3K-Akt signaling pathways. For metabolite profiles, 359 metabolites were significantly altered in two groups. Interestingly, the cold season group remarkably decreased glutathione and phosphatidylcholine (18:2 (2E, 4E)/0:0). Moreover, integrative analysis of the transcriptome and metabolome demonstrated that glycolysis or gluconeogenesis, PPAR signaling pathway, fatty acid biosynthesis, steroid biosynthesis, and glutathione metabolism play an important role in the potential relationship between differential expression genes and metabolites. The reduced lipid synthesis, fatty acid oxidation, and fat catabolism facilitated gluconeogenesis by inhibiting the PPAR and PI3K-Akt signaling pathways to maintain the energy homeostasis of the whole body in the yak, thereby coping with the shortage of forages and adapting to the extreme environment of the Qinghai-Tibetan Plateau (QTP).

RNA-sequencing reveals the metabolism regulation mechanism of sheep skeletal muscle under nutrition deprivation stress

Although the skeletal muscle is one of the main sites of metabolism, little is known about the molecular mechanisms involving its response to nutrition stress. The aim of the study was to screen the transcriptome of sheep muscle to identify the metabolism-related genes under nutrition deprivation stress. Ten healthy adult female Small-tailed Han sheep with similar age and weight were randomly divided into a normal group and fasted group. After 3 days, three sheep were randomly selected from each group and the semitendinosus samples were subjected to RNA-sequencing (RNA-seq) and a series of analyses and function annotations. Compared with the normal group, 391 differentially expressed genes (DEGs) were identified in the fasted group that had obvious weight loss, including 278 down-regulated and 113 up-regulated genes. Gene Ontology enrichment annotation classified 228 DEGs in the metabolic process, 11 of which were new genes and only Sheep_newGene_4578 had been annotated by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. The results of Clusters of Orthologous Groups annotation indicated that 11, 9, and 4 DEGs were respectively classified in lipid transport and metabolism, amino acid transport and metabolism, and carbohydrate transport and metabolism. In addition, KEGG enrichment analysis showed that there were not only pathways which were directly related to metabolisms such as protein digestion and absorption pathway, fatty acid metabolism pathway, and biosynthesis pathway of unsaturated fatty acids, but also PI3K-AKT pathway, AMPK pathway, MAPK pathway, and FoxO pathway which were important to metabolism among the top 20 pathways with the lowest significant Q value. The MCODE analysis of protein-protein interaction revealed that two identified subnetworks with top score were closely associated with metabolism. The correlation analysis showed that the mRNA levels of most of DEGs that might be related in the two subnetworks were significantly correlated respectively, and the mRNA levels of most of 10 metabolism-related DEGs including Sheep_newGene_4578 were significantly correlated. Finally, 16 random and 10 metabolism-related DEGs were chosen for confirmation by quantitative real-time PCR, demonstrating the same expression change as determined by RNA-seq. In conclusion, multiple interrelated metabolism-related DEGs in skeletal muscle contributed to the response of sheep to nutritional deprivation stress.