Dietary lysine affected the expression of genes related to ubiquitin-proteasome protein degradation pathway in skeletal muscle of finishing pigs

Abstract Text:

It has been known that some amino acids, such as leucine, can function as signaling molecules to regulate skeletal muscle growth of pigs. However, which signaling pathway(s) that may be regulated by dietary lysine is unclear. This study was conducted to identify the genes that may be regulated by dietary lysine and responsible for muscle growth of pigs. Nine crossbred barrows (94.4 ± 6.7 kg BW) were randomly allotted to 3 dietary treatments (3 pigs/treatment). Three corn and soybean-meal based diets were formulated to meet the NRC (2012) requirements for nutrients except for lysine, whose concentrations were 0.43, 0.71, and 0.98% (as-fed basis) for the lysine-deficient, lysine-adequate, and lysine-excess diets, respectively. The feeding trial lasted 5 weeks, during which time the pigs were allowed ad libitum access to diets and water. After the trial, all pigs were harvested and muscle samples were collected from longissimus dorsi (between the 10^th and 12^th ribs). Total RNA was extracted from 50 mg of each sample using the TRIzol reagent. Porcine Gene 1.0 ST Array (Affymetrix, Inc.) was used to quantify the expression levels of 19,211 genes. Raw microarray data were normalized with gcRMA algorithm and analyzed with ANOVA using Partek Genomics Suite (Partek Inc.). A total of 674 transcripts were differentially expressed (p < 0.05); 60 out of 131 transcripts (at p < 0.01) belong to 58 genes and 71 were unannotated. Canonical pathway analysis of these 58 genes using the IPA software (Qiagen.com) revealed that the protein ubiquitination pathway was significantly affected (p < 0.01) by dietary lysine level, which involved at least 6 genes. Specifically, when compared to the lysine-adequate group, the expression of DNAJA1, HSP90AB1, and UBE2B was up-regulated in the lysine-deficient group, while the expression of DNAJA1, HSP90AA1, HSPH1, and UBE2D3 was down-regulated in the lysine-excess group. The protein ubiquitination pathway plays a major role in the degradation of short-lived or regulatory proteins by the 26S proteasome complex, affecting a variety of cellular processes including cell cycle, cell proliferation, apoptosis, and transcription regulation. Taken together, decreasing dietary lysine level may activate, while increasing dietary lysine level may inhibit, the ubiquitin-proteasome pathway and regulate protein accretion in skeletal muscle of late-stage finishing pigs. Further studies are needed to elucidate how the proteins coded from these genes influence pig skeletal muscle degradation. (This project is supported by USDA Hatch/Multistate Project 233803)

Keywords: pig, lysine, muscle, protein ubiquitination pathway