Analysis of porcine adipose tissue transcriptome reveals differences in de novo fatty acid synthesis in pigs with divergent muscle fatty acid composition

Abstract

Background: In pigs, adipose tissue is one of the principal organs involved in the regulation of lipid metabolism. It is particularly involved in the overall fatty acid synthesis with consequences in other lipid-target organs such as muscles and the liver. With this in mind, we have used massive, parallel high-throughput sequencing technologies to characterize the porcine adipose tissue transcriptome architecture in six Iberian x Landrace crossbred pigs showing extreme phenotypes for intramuscular fatty acid composition (three per group).

Results: High-throughput RNA sequencing was used to generate a whole characterization of adipose tissue (backfat) transcriptome. A total of 4,130 putative unannotated protein-coding sequences were identified in the 20% of reads which mapped in intergenic regions. Furthermore, 36% of the unmapped reads were represented by interspersed repeats, SINEs being the most abundant elements. Differential expression analyses identified 396 candidate genes among divergent animals for intramuscular fatty acid composition. Sixty-two percent of these genes (247/396) presented higher expression in the group of pigs with higher content of intramuscular SFA and MUFA, while the remaining 149 showed higher expression in the group with higher content of PUFA. Pathway analysis related these genes to biological functions and canonical pathways controlling lipid and fatty acid metabolisms. In concordance with the phenotypic classification of animals, the major metabolic pathway differentially modulated between groups was de novo lipogenesis, the group with more PUFA being the one that showed lower expression of lipogenic genes.

Conclusions: These results will help in the identification of genetic variants at loci that affect fatty acid composition traits. The implications of these results range from the improvement of porcine meat quality traits to the application of the pig as an animal model of human metabolic diseases.

Figure 1

Q-Q plot representing the distribution of the p-value. The red line represents the expected distribution of the p-value, while the blue trend represents the distribution observed. X-axis values are Expected –log₁₀ (p-value) and y-axis are the Observed –log₁₀ (p-value).

Figure 2

Representation of the 396 differentially expressed genes (in red) with fold difference ≥ 1.2 and p-value ≤ 0.01. X-axis values are base mean-expression values and y-axis values are the log2 (fold difference).

Figure 3

Networks showing metabolic pathways differentially modulated between H and L groups. A: Diagram of the different expression between H and L groups of the main genes affecting de novo FA synthesis pathway. B: Global IPA network of genes associated with lipid metabolism, nucleic acid metabolism and small molecule biochemistry. Biological association of 35 focus genes as a graphical representation of the molecular relationship (edges) between genes/gene products (nodes). The intensity of the node color indicates the degree of expression: (red) up-regulated and (green) down-regulated in the H group relative to the L group. The shape of nodes indicates the functional classes of the gene products. Genes highlighted in orange are those genes related to lipid metabolism.

Figure 4

Diagram representing the hypothetical causes of the differences in intramuscular and backfat FA composition. Adipocytes incorporate FA from intestine absorption and glucose. Both follow different metabolic pathways that allow FA synthesis by lipogenesis (black arrows). Nevertheless, higher absorption, transport or storage of FA (mainly LA and ALA) produced an inhibitory effect (red lines) on the glucose metabolism and lipogenesis, reducing the content of MUFA and SFA and increasing PUFA content. FA: fatty acids, LA: linoleic acid and ALA: α-linolenic acid.