NEW YORK (GenomeWeb News) – A Spanish research team reported today in BMC Genomics that it has identified gene expression profiles associated with fat-related traits in pigs.
"Our data suggest that selection for increasing intramuscular fat content in pigs would lead to a shift but not disruption of the metabolic homeostasis of muscle cells," senior author Ramona Pena, an animal genetics researcher at Spain's IRTA research institute, and colleagues wrote.
The researchers did microarray analyses on muscle tissue from dozens of Duroc breed pigs, identifying transcriptomic patterns associated with high and low fat-related traits. Their findings indicate that, compared with leaner animals, the chunkiest pigs tend to show enhanced expression of genes involved in fat production and fatty acid uptake and lower expression of certain antigen-related genes.
But the pudgier porkers also seemed to have enhanced fat degradation gene activity, leading the team to propose that these pigs may be perpetually building up and breaking down triacylglycerols. In contrast to obese humans, who tend to have insulin signaling deficits, the high-fat pigs also showed elevated levels of some insulin signaling genes.
Intramuscular fat content is an important trait in pork production because it influences meat tenderness, flavor, and texture, the researchers explained. In addition, they noted, some types of fatty acids produce flavors that please the consumer palate while others tend to be converted to compounds that produce unpleasant, rancid tastes in meat.
In an effort to explore if, and how, selection for animals with a particular fat content and composition might affect pig biology, the researchers assessed transcript patterns in muscle tissue from 68 Duroc pigs that had been phenotyped for growth, food intake, fat content, composition, and distribution, cholesterol levels, and so on.
"Although selection for increased intramuscular fat content is not expected to impair pig health, it might have consequences on muscle lipid metabolism that need to be determined," they explained.
The team selected 35 animals each at the high and low extremes for fat-related phenotypes, generated complementary DNA from RNA isolated from muscle tissues, and evaluated transcript profiles using Affymetrix GeneChip Porcine arrays.
The researchers found 442 differentially expressed genes when they compared data for 34 of the high-fat pigs (which had elevated fat thickness, serum cholesterol, intramuscular fat, and saturated and monounsaturated fatty acid content) and 34 of the low-fat pigs (which were leaner and had increased levels of polyunsaturated fatty acids in their muscle tissue).
These genes were involved in a range of processes, from RNA processing to lipid metabolism. Among the pathways affected: antigen presentation and processing pathways, lipid metabolism pathways, fatty acid biosynthesis and degradation pathways, and several signaling pathways.
For instance, the high-fat pig group showed up-regulation of genes involved in fatty acid uptake, lipogenesis, and lipid deposition genes. Even so, these animals also appear to have increased activity for genes coding for triacylglycerol hydrolysis enzymes.
Based on these expression patterns, the researchers speculated that muscle tissue from high-fat pigs involves "a futile cycle where triacylglycerols are continuously degraded and re-synthesized."
And while the higher fat animals did not have decreased expression of genes involved in insulin signaling and glucose uptake, the team noted, they did show decidedly lower levels of immunity related genes — specifically genes coding for antigen-presenting molecules.
"[S]election for increasing either leanness or intramuscular fat might lead to two extreme phenotypes with divergent muscular metabolic profiles," the researchers concluded. Nevertheless, they argued, "selection for increasing intramuscular fat content in pigs would not lead to a disruption of the metabolic homeostasis of muscle cells."