Palm kernel meal regulates the expression of genes involved in the amino acid metabolism in the liver of Tibetan sheep

Abstract

Background: Palm kernel meal (PKM) is a by-product of oil palm kernel after oil extraction, which is widely used in animal feeds due to its high energy content. This study aimed to investigate the impact of supplementing Tibetan sheep with PKM on their hepatic phenotype, oxidative stress and immune response. A total of 120 Tibetan lambs (Initial weight = 12.37 ± 0.92 kg) were randomly assigned into four groups: control group (C group, 0% PKM diet), low group (L group, 15% PKM diet), middle group (M group, 18% PKM diet), and high group (H group, 21% PKM diet) on a dry matter basis. The feeding experiment was performed for 130 d, including a 10 d adaption period.

Results: Results showed that the level of GSH-Px were higher in the H and M groups than in the C and L groups (P < 0.05). The levels of IgM and TNF-α were higher in the M group when compared to those on the C group (P < 0.05). The level of IgA was significantly higher in the M group than in the H group (P < 0.05). Additionally, compared with the others groups, the hepatocytes in the M group displayed a radial arrangement, forming hepatic plates that were centered around the central vein. The transcriptome results revealed that proteasome 26 S subunit, ATPase 3 (PSMC3), proteasome 26 S subunit, ATPase 5 (PSMC5), proteasome 26 S subunit ubiquitin receptor, non-ATPase 4 (PSMD4), proteasome activator subunit 1 (PSME1), acyl-CoA dehydrogenase short/branched chain (ACADSB), enoyl-CoA hydratase, short chain 1 (ECHS1), serine dehydratase (SDS), ornithine transcarbamylase (OTC), and phenylalanine hydroxylase (PAH) were the hub genes regulating the amino acid metabolism in the liver.

Conclusions: In summary, dietary 18% PMK supplementation contributed to improve the hepatic phenotype, oxidative stress and immune response through regulating the expression of related genes.

Keywords: Liver; Nutrient; Palm kernel meal; Tibetan sheep; Transcriptome.

Fig. 1

Effect of varying supplement levels of PMK on hepatic phenotypes. C group was supplement of 0% PKM. L group was supplement of 15% PKM. M group was supplement of 18% PKM. H group was supplement of 21% PKM. HE staining, 400x. a: Interlobular veins, b: Interlobular artery, d: Sinus Periphery Gap, e: Hepatic Blood Sinusoids, f: Macrophages

Fig. 2

Gene expression BoxPlot. The horizontal coordinate statistic was derived based on the gene FPKM value. C group was supplement of 0% PKM. L group was supplement of 15% PKM. M group was supplement of 18% PKM. H group was supplement of 21% PKM. P < 0.05 indicates highly significant difference. I: Intergroup gene expression BoxPlot, to analyze the differences between groups. II: Gene expression within group, to analyze within-group uniformities

Fig. 3

PCA Analysis. C group was supplement of 0% PKM. L group was supplement of 15% PKM. M group was supplement of 18% PKM. H group was supplement of 21% PKM. P < 0.05 indicates highly significant difference

Fig. 4

Differential Expressed Genes. Vertical bars shows the number of intersections, lines between points represents specific intersecting groups, and horizontal bars represents the amount of raw data for individual groups. C group was supplement of 0% PKM. L group was supplement of 15% PKM. M group was supplement of 18% PKM. H group was supplement of 21% PKM. III: Differential Expression Genes Venn Diagram, the overlap is co-annotated to the gene. IV: Gene expression UpSet Diagram, The black dots represent the samples, the line connecting the dots represents the sample intersection portion, the vertical bars represent the number of intersections, and the horizontal bars represent the sample raw volume

Fig. 5

Short Time-Series Expression Miner (STEM) Analysis. A box represents a class of gene sets, a colored box represents a gene set with a significant trend, and the same color represents the same expression trend. C group was supplement of 0% PKM. L group was supplement of 15% PKM. M group was supplement of 18% PKM. H group was supplement of 21% PKM.

Fig. 6

Gene sets with significant trends in STEM analysis. The positions of the dots represents a sample, the lines represents gene changes from the previous sample to the subsequent sample, and the lines of different colors represents different genes. C group was supplement of 0% PKM. L group was supplement of 15% PKM. M group was supplement of 18% PKM. H group was supplement of 21% PKM. P < 0.05 indicates highly significant difference

Fig. 7

KEGG Enrichment Analysis. The size of the circle represents the number of genes enriched to the pathway, the larger the circle represents the more number of genes, and the color represents the significance, the deeper the color represents the lesser P value. P < 0.05 indicates significant difference. V: metabolic pathways enriched on 27 and 29 profile, VI: metabolic pathways enriched on 40, 26, 38 and 37 profile, VII: metabolic pathways enriched on 46 and 48 profile

Fig. 8

Protein-protein interaction (PPI) network. The figure is based on the Metabolism of amino acids and derivatives pathway in Reactom. where the pink represent hub genes regulated in liver tissue. PSMC3,PSMC5, PSMD4, PSME1, PSMA3, ACADSB, ECHS1, SDS, OTC, PAH.

Fig. 9

Metabolism of amino acids and derivatives. a: Ubiquitin-dependent protein degradation. b: Glycolysis/gluconeogenesis, glycine, serine, and threonine metabolism. c: Valine, leucine and isoleucine biosynthesis