FASN, SCD1 and ANXA9 gene polymorphism as genetic predictors of the fatty acid profile of sheep milk

Progress of Conjugated Linoleic Acid on Milk Fat Metabolism in Ruminants and Humans

As a valuable nutrient in milk, fat accounts for a significant proportion of the energy requirements of ruminants and is largely responsible for determining milk quality. Fatty acids (FAs) are a pivotal component of milk fat. Conjugated linoleic acid (CLA) is one of the naturally occurring FAs prevalent in ruminant dairy products and meat. Increasing attention has been given to CLA because of its anti-cancer, anti-inflammatory, immune regulation, and lipid metabolism regulation properties, and these benefits potentially contribute to the growth and health of infants. In breast milk, CLA is present in trace amounts, mainly in the form of cis-9, trans-11 CLA. Notably, cis-9, trans-11 CLA improves the milk fat rate while trans-10, cis-12 CLA inhibits it. Apart from having multiple physiological functions, CLA is also a pivotal factor in determining the milk quality of ruminants, especially milk fat rate. In response to growing interest in green and healthy functional foods, more and more researchers are exploring the potential of CLA to improve the production performance of animals and the nutritional value of livestock products. Taken together, it is novel and worthwhile to investigate how CLA regulates milk fat synthesis. It is the purpose of this review to clarify the necessity for studying CLA in ruminant milk fat and breast milk fat.

Polymorphisms at Candidate Genes for Fat Content and Fatty Acids Composition: Effects on Sheep Milk Production and Fatty Acid Profile Using Two Dietary Supplementations

The nutritional value of sheep's milk and its derivatives is influenced by the lipid fraction, which is affected by diet and genetics. This study aimed to explore the genetic variations in the DGAT1 and SCD genes and assessed the impact of the DGAT1 genotype on milk quality in Valle del Belìce sheep, considering diet supplementation with carob pulp and barley grain. Among the potentially polymorphic sites, only DGAT1 g.127 C > A and SCD g.87 C > A showed variability. The DGAT1 genotype did not significantly impact milk yield and composition, except for higher urea content in the CA genotypes than in the CC ones. Carob pulp increased the milk fat content compared to barley grain. Genetic variation in DGAT1 was associated with changes in the milk fatty acid profile; specifically, the CA genotype exhibited higher levels of short-chain fatty acids and lower levels of polyunsaturated fatty acids compared to the CC genotype. Carob pulp supplementation increased saturated fatty acids and reduced unsaturated fractions, leading to milk with higher atherogenic and thrombogenic indices. No significant interaction was found between genotype and diet. This study provides insights into the genetic and dietary factors influencing sheep's milk composition. Further research is needed to understand the impact of these genetic variations on milk production and composition, as well as to determine optimal levels of carob pulp for improving fat percentage and promoting sustainable sheep breeding practices.

Integration of Selection Signatures and Protein Interactions Reveals NR6A1, PAPPA2, and PIK3C2B as the Promising Candidate Genes Underlying the Characteristics of Licha Black Pig

Licha black (LI) pig has the specific characteristics of larger body length and appropriate fat deposition among Chinese indigenous pigs. Body length is one of the external traits that affect production performance, and fat deposition influences meat quality. However, the genetic characteristics of LI pigs have not yet been systematically uncovered. Here, the genomic information from 891 individuals of LI pigs, commercial pigs, and other Chinese indigenous pigs was used to analyze the breed characteristics of the LI pig with runs of homozygosity, haplotype, and FST selection signatures. The results showed the growth traits-related genes (i.e., NR6A1 and PAPPA2) and the fatness traits-related gene (i.e., PIK3C2B) were the promising candidate genes that closely related to the characteristics of LI pigs. In addition, the protein–protein interaction network revealed the potential interactions between the promising candidate genes and the FASN gene. The RNA expression data from FarmGTEx indicated that the RNA expression levels of NR6A1, PAPPA2, PIK3C2B, and FASN were highly correlated in the ileum. This study provides valuable molecular insights into the mechanisms that affect pig body length and fat deposition, which can be used in the further breeding process to improve meat quality and commercial profitability.

Characterization of fatty acid compositions in longissimus thoracis muscle and identification of candidate gene and SNPs related to polyunsaturated fatty acid in Hu sheep

Fatty acid (FA) composition contributes greatly to the quality and nutritional value of lamb meat. In the present study, FA was measured in longissimus thoracis (LT) muscles of 1,085 Hu sheep using gas chromatography. Comparative transcriptomic analysis was conducted in LT muscles to identify differentially expressed genes (DEGs) between six individuals with high polyunsaturated fatty acids (H-PUFA, 15.27% ± 0.42%) and six with low PUFA (L-PUFA, 5.22% ± 0.25%). Subsequently, the single nucleotide polymorphisms (SNPs) in a candidate gene PLIN2 were correlated with FA traits. The results showed a total of 29 FA compositions and 8 FA groups were identified, with the highest content of monounsaturated fatty acids (MUFA, 46.54%, mainly C18:1n9c), followed by saturated fatty acids (SFA, 44.32%, mainly C16:0), and PUFA (8.72%, mainly C18:2n6c), and significant correlations were observed among the most of FA traits. Transcriptomic analyses identified 110 upregulated and 302 downregulated DEGs between H-PUFA and L-PUFA groups. The functional enrichment analysis revealed three significant Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and 17 gene ontology (GO) terms, in which regulation of lipolysis in adipocytes, the AMPK signaling pathway, and the PPAR signaling pathway may play important roles in FA metabolism and biosynthesis. In addition, weighted gene co-expression network analysis (WGCNA) identified 37 module genes associated with PUFA-related traits. In general, PLIN1, LIPE, FABP4, LEP, ACACA, ADIPOQ, SCD, PCK2, FASN, PLIN2, LPL, FABP3, THRSP, and ACADVL may have a great impact on PUFA metabolism and lipid deposition. Four SNPs within PLIN2 were significantly associated with FA. Of those, SNP1 (g.287 G>A) was significantly associated with C18:1n9c and MUFA, and SNP4 (g.7807 T>C) was significantly correlated with PUFA (C18:3n3). In addition, the combined genotype of SNP1 (g.287 G>A), SNP3 (g.7664 T>C), and SNP4 (g.7807 T>C) were significantly correlated with C16:1, C17:0, C18:1C6, PUFA (C18:3n3, C22:6n3), and n-6/n-3 PUFA. These results contribute to the knowledge of the biological mechanisms and genetic markers involved in the composition of FA in Hu sheep.

Lipid metabolism and m6A RNA methylation are altered in lambs supplemented rumen-protected methionine and lysine in a low-protein diet

Background

Methionine or lysine has been reported to influence DNA methylation and fat metabolism, but their combined effects in N6-methyl-adenosine (m⁶A) RNA methylation remain unclarified. The combined effects of rumen-protected methionine and lysine (RML) in a low-protein (LP) diet on lipid metabolism, m⁶A RNA methylation, and fatty acid (FA) profiles in the liver and muscle of lambs were investigated. Sixty-three male lambs were divided into three treatment groups, three pens per group and seven lambs per pen. The lambs were fed a 14.5% crude protein (CP) diet (adequate protein [NP]), 12.5% CP diet (LP), and a LP diet plus RML (LP + RML) for 60 d.

Results

The results showed that the addition of RML in a LP diet tended to lower the concentrations of plasma leptin (P = 0.07), triglyceride (P = 0.05), and non-esterified FA (P = 0.08). Feeding a LP diet increased the enzyme activity or mRNA expression of lipogenic enzymes and decreased lipolytic enzymes compared with the NP diet. This effect was reversed by supplementation of RML with a LP diet. The inclusion of RML in a LP diet affected the polyunsaturated fatty acids (PUFA), n-3 PUFA, and n-6 PUFA in the liver but not in the muscle, which might be linked with altered expression of FA desaturase-1 (FADS1) and acetyl-CoA carboxylase (ACC). A LP diet supplemented with RML increased (P < 0.05) total m⁶A levels in the liver and muscle and were accompanied by decreased expression of fat mass and obesity-associated protein (FTO) and alkB homologue 5 (ALKBH5). The mRNA expressions of methyltransferase-like 3 (METTL3) and methyltransferase-like 14 (METTL14) in the LP + RML diet group were lower than those in the other two groups. Supplementation of RML with a LP diet affected only liver YTH domain family (YTHDF2) proteins (P < 0.05) and muscle YTHDF3 (P = 0.09), which can be explained by limited m⁶A-binding proteins that were mediated in mRNA fate.

Conclusions

Our findings showed that the inclusion of RML in a LP diet could alter fat deposition through modulations of lipogenesis and lipolysis in the liver and muscle. These changes in fat metabolism may be associated with the modification of m⁶A RNA methylation.

Graphical abstract

A systematic graph illustrates the mechanism of dietary methionine and lysine influence on lipid metabolism and M⁶A. The green arrow with triangular heads indicates as activation and brown-wine arrows with flat heads indicates as suppression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00733-z.