Molecular Differences in Hepatic Metabolism between AA Broiler and Big Bone Chickens: A Proteomic Study

Abstract

Identifying the metabolic differences in the livers of modern broilers and local chicken breeds is important for understanding their biological characteristics, and many proteomic changes in their livers are not well characterized. We therefore analyzed the hepatic protein profiles of a commercial breed, Arbor Acres (AA) broilers, and a local dual purpose breed, Big Bone chickens, using two-dimensional electrophoresis combined with liquid chromatography-chip/electrospray ionization-quadruple time-of-flight/mass spectrometry (LC-MS/MS). A total of 145 proteins were identified as having differential abundance in the two breeds at three growth stages. Among them, 49, 63 and 54 belonged to 2, 4, and 6 weeks of age, respectively. The higher abundance proteins in AA broilers were related to the energy production pathways suggesting enhanced energy metabolism and lipid biosynthesis. In contrast, the higher abundance proteins in Big Bone chickens showed enhanced lipid degradation, resulting in a reduction in the abdominal fat percentage. Along with the decrease in fat deposition, flavor substance synthesis in the meat of the Big Bone chickens may be improved by enhanced abundance of proteins involved in glycine metabolism. In addition, the identified proteins in nucleotide metabolism, antioxidants, cell structure, protein folding and transporters may be critically important for immune defense, gene transcription and other biological processes in the two breeds. These results indicate that selection pressure may have shaped the two lines differently resulting in different hepatic metabolic capacities and extensive metabolic differences in the liver. The results from this study may help provide the theoretical basis for chicken breeding.

Fig 1. 2-DE hepatic protein profiles of AA broilers and Big Bone chickens.

Protein spots showing significant differences (2-fold, p < 0.05) were manually excised and identified by LC-Chip-ESI-QTOF-MS. Proteins of differential abundance with known identities were numbered and marked red or blue for increased or decreased abundance, respectively.

Fig 2. Comparisons proteins with higher abundance in the livers between the AA broiler and Big Bone chickens at 2, 4 and 6 weeks, respectively.

A represents the percentage of proteins with increased abundance, B represents the numbers of proteins with increased abundance.

Fig 3. Functional classification of the proteins with differential abundance identified in the livers of AA broiler and Big Bone chickens at 2, 4 and 6 weeks.

Fig 4. Comparisons of functional classification of proteins with higher abundance in the livers between the AA broiler and Big Bone chickens at 2, 4 and 6 weeks.

Fig 5. Quantitative comparisons of differentially expressed proteins in the livers of AA broiler and Big Bone chickens at 2, 4 and 6 weeks.

The ratios of the protein abundance (AA broilers to Big Bone chickens) are transformed, and the protein spots with |log₂ ratio|≥1 (p≤0.05) are selected as the differentially expressed proteins. A, B and C represent differentially expressed proteins at 2, 4 and 6 weeks, respectively.

Fig 6. Functional enrichment analysis of the proteins of differential abundance in the livers between AA broiler and Big Bone chickens at 2, 4 and 6 weeks using ClueGO software.

* and ** mean p < 0.05 and p < 0.01 levels of significance. A, B and C represent enrichment analysis of differentially expressed proteins at 2, 4 and 6 weeks, respectively.

Fig 7. Biological interaction network of the proteins of differential abundance in the livers of AA broiler and Big Bone chickens at 2, 4 and 6 weeks.

Red lines indicate fusion evidence, green lines indicate neighborhood evidence, blue lines indicate co-occurrence evidence, purple lines indicate experimental evidence, yellow lines indicate text mining evidence, light blue lines indicate database evidence and black lines indicate co-expression evidence.

Fig 8. Validation using qPCR of proteins of differential abundance at the mRNA level in the livers between the AA broiler and Big Bone chickens at 2, 4 and 6 weeks.

Samples were normalized with the reference genes β-actin. A, B and C represent differentially expressed proteins at the mRNA level at 2, 4 and 6 weeks, respectively.