Effect of a western diet and age on liver proteome in male and female rats

Aging combined with an increasingly unbalanced diet in Western societies promote the manifestation of diseases such as obesity and non-alcoholic fatty liver disease. Proteome profiling, including the identification, quantification and qualitative characterization could provide a better understanding of the molecular mechanisms associated with these diseases. The general aim of the present project was to systematically investigate the potential role of diet and age on the liver proteome as a central metabolic organ. To this end, 84 Wistar rats of both sexes were fed with a standard diet (SD) and a moderate Western diet (WD, 36 kcal % fat, 13 kcal % sugar), respectively, up to the age of 26, 52 and 72 weeks. Rats were characterized among other things for weight changes, clinical and functional parameters as well as for liver histology. For proteome analysis, proteins were extracted from rat liver homogenates, digested, labelled using a TMT 11plex system and analyzed using an ion trap mass spectrometer (Quadrupol-Orbitrap QExactivePlus) coupled to liquid chromatography equipment. The collected data were processed using MaxQuant and Perseus. Looking at the global proteome, a total of 28,079 peptides were initially identified and could be assigned to 4,164 proteins. Following processing and refinement, 1,602 and 1,495 proteins were derived for female and male rats, respectively, with 1,310 proteins overlapping between the sexes. Statistical analysis revealed a significant difference in the relative amount of protein between SD and WD in both female and male rats. Taking age into account, results showed significant differences with 206 and 129 (at 26 weeks of age); 141 and 168 (at 52 weeks of age) and 200 and 195 proteins (at 78 weeks of age) between females and males, respectively. Furthermore, pathway enrichment analysis identified regulators of fatty acid metabolism in both sexes, proteins involved in oxidative energy production, carbohydrate and lipid metabolism were predominant in female groups, while in male rats, proteins involved in peroxisome metabolism and the NF-κB signaling pathway were predominantly identified. In addition, an age-dependent change in the relative abundance of proteins was observed for a total of 35 proteins in males compared to only 9 proteins in females. In contrast, no effects of WD could be observed for clinical and histological compounds, except for differences in body weight for males. These results may illustrate a tendency for females to adapt better than males to a Westernized diet as they age. The significant differences observed between the diets in both sexes may further indicate an adaptation in metabolism, and in particular a compensatory regulation prior to a probable clinical manifestation, mainly in the context of the Western diet.