The 15N isotope effect as a means for correlating phenotypic alterations and affected pathways in a trait anxiety mouse model
Stable isotope labeling techniques hold great potential for accurate quantitative proteomics comparisons by MS. To investigate the effect of stable isotopes in vivo, we metabolically labeled high anxiety-related behavior (HAB) mice with the heavy nitrogen isotope 15N. 15Nlabeled HAB mice exhibited behavioral alterations compared to unlabeled (14N) HAB mice in their depression-like phenotype. To correlate behavioral alterations with changes on the molecular level, we explored the 15N isotope effect on the brain proteome by comparing protein expression levels between 15N-labeled and 14N HAB mouse brains using quantitative MS. By implementing two complementary in silico pathway analysis approaches, we were able to identify altered networks in 15N-labeled HAB mice, including major metabolic pathways such as the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. Here, we discuss the affected pathways with regard to their relevance for the behavioral phenotype and critically assess the utility of exploiting the 15N isotope effect for correlating phenotypic and molecular alterations.