Werner syndrome (WS) is a premature aging disorder caused by mutations in a DNA helicase/exonuclease. Mice lacking the helicase domain of the Wrn protein orthologue exhibit transcriptomic and metabolic alterations, some of which are reversed by vitamin C. Recent studies on the liver of these animals indicated that the Wrn mutant protein is associated with the endoplasmic reticulum (ER) resulting in an ER stress response. In this study, we identified liver proteins that exhibit actual level differences in the ER fraction between wild type and Wrn mutant mice using quantitative proteomic profiling with label-free Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Multiple Reaction Monitoring (MRM) and immunoblotting were performed to validate findings in a secondary independent cohort of wild type and Wrn mutant mice in the presence or absence of vitamin C in drinking water. The list of identified proteins showing significant altered expression levels was compared to transcriptomic results that were obtained in previous studies to assess the extent of correlation between the mRNA levels and their corresponding encoded protein levels in the liver of our different mouse cohorts.