The super(15) N 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 super(15) N . super(15) N -labeled HAB mice exhibited behavioral alterations compared to unlabeled ( super(14) N ) HAB mice in their depression-like phenotype. To correlate behavioral alterations with changes on the molecular level, we explored the super(15) N isotope effect on the brain proteome by comparing protein expression levels between super(15) N -labeled and super(14) N HAB mouse brains using quantitative MS . By implementing two complementary in silico pathway analysis approaches, we were able to identify altered networks in super(15) N -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 super(15) N isotope effect for correlating phenotypic and molecular alterations.