Abstract
OBJECTIVES: To identify possible mechanisms involved in the development and progression of NAFLD through protein expression (shotgun proteomics) analysis on liver samples of obese Zucker rats fed with either casein (CAS) or soy protein isolate (SPI) during 8 and 16 weeks. METHODS: 7 weeks old rats (n = 8–9 per group) were randomly assigned to an either CAS-based or a SPI-based diet. Rats were sacrificed after 8 weeks or 16 weeks of SPI feeding. Livers were immediately obtained and stored at −80 C. Ingenuity Pathway Analysis (IPA) software was used to facilitate interpretation of proteomics data. Predictions of activation or inhibition of molecules in the data was made based on activation z-score and P value of overlap (P < 0.05). Activation z-scores > 2.0 indicate that a molecule is activated, whereas activation z-scores of < −2.0 indicate that a target molecule is inhibited. RESULTS: Upstream regulator analysis by IPA revealed 6 molecules predicted to be activated (z-scores between 2 and 2.8) and 9 inhibited (z-scores between −2 and −2.6) in SPI vs CAS-fed rats in proteomics data at 8 weeks of SPI feeding. In contrast, at 16 weeks of SPI feeding there were 12 molecules activated (z-scores between 2 and 2.5) and 18 inhibited (z-scores between −2 and −2.8) in SPI vs CAS-fed. All p values were <0.05. Regulator effects analysis also revealed that some of these molecules would be participating, directly or indirectly, in the inhibition of the immune response of cells (such as IL27 and CSF2) and synthesis of lipids (CEBPA, Ins1 and IRF8) in SPI-fed rats. CONCLUSIONS: These molecules and their downstream target proteins may provide clues by which soy protein produces the observed attenuation of liver steatosis that can be tested in future experiments in this obese rat model. FUNDING SOURCES: This study was supported in part by the College of Medicine's University Medical Group (RH) and the Arkansas Biosciences Institute (WB, RH).