Discovering the Impact of Diet, Genetic, and Sex Effects on Adipose, Skeletal Muscle, and Liver Metabolomes in Mice Using Untargeted Liquid-Chromatography Mass-Spectrometry

The metabolome is the end product of all biochemical reactions in the body and is sensitive to external perturbations, such as diet, genetics, sex, disease, and environment. Understanding the dynamic relationship between metabolites and external inputs is key to delineating the metabolic underpinnings of disease. Mass-spectrometry based metabolomics provides a means through which the metabolome can be systemically and systematically profiled to discern alterations across thousands of metabolites at a time. The research in this dissertation characterized the effects of diet, genetics, and sex on the tissue metabolome. Adipose, skeletal muscle, and liver tissue were chosen due to their role in energy metabolism. In the first study, we characterized the effects of five diets (Japanese, ketogenic, Mediterranean, American, and standard chow) on the tissue metabolome, across both sexes. This study described the metabolic response to diets that altered in macronutrient ratio and composition, independent of genetic differences. Our results revealed that liver tissue was most sensitive to metabolic changes but responded similarly for diet, sex, and sex-by-diet interaction while adipose and muscle remained largely stable. In the second study, we characterized the effects of four strains (A/J, C57BL/6J, FVB/NJ, and NOD/ShiLtJ) on the tissue metabolome, across both sexes. This study assessed the metabolic response to differing genetic backgrounds represented by various predispositions to metabolic disease, independent of diet. Our results showed that strain exerted the largest effect on metabolites across all three tissues. In contrast, sex and sex-by-strain interaction had little effect on adipose, muscle, and liver. The third study characterized the effects of diet, genetics, and sex on the tissue metabolome. We assessed the metabolic response to diet, genetics, sex, and their interactions to determine which factor/s were potentially driving metabolic differences. Strain exerted the largest effect across all tissues. Liver was most sensitive to metabolite changes when all factors and interactions were collectively assessed. Overall, the results in this dissertation aid in the understanding of complex relationships between diet, genetics, and sex at the systems-level. Furthermore, it was shown that tissues responded differentially to the same stimuli highlighting the need to consider sample type when performing metabolomics.