Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Recent insights have endorsed the importance of energy metabolism in the pathophysiology, governed by the liver. Previous research by our group links the downregulation of certain metabolic genes in sepsis to a loss of function and reduced DNA-binding activity of HNF4α, a key transcription factor. The transcriptional activity of nuclear receptors highly depends on protein-protein interactions and post-translational modifications. In search of the underlying molecular mechanism of how HNF4α binding and activity changes in sepsis, I will study its interactome, phosphoproteome and other post-translational modifications. I will use a mouse sepsis model and examine liver nuclei by performing immunoprecipitation prior to LC-MS/MS. The set-up will be recapitulated in a human in cellulo sepsis model, and key interactors of HNF4α will be compared in both models. In parallel, the presence of sepsis-specific post-translational modifications of HNF4α or its interaction partners will also be evaluated. To increase the chances of finding relevant differentially interacting protein candidates, I will perform proximity biotinylation combined with LC-MS/MS. Validations will include functional perturbations via mutagenesis of which the impact will be examined both in cellulo and in vivo. My study will provide mechanistic clues on which HNF4α impacting pathways are (in)activated during sepsis.