Understanding the Metabolic Regulation of Trained Immunity by Palmitic Acid

Sepsis is an inflammatory disease that occurs when the body’s response to an infection becomes dysregulated, and infection-fighting processes of the body damage tissues via inflammation, resulting in organ failure and death. Currently, the role for diet in regulating sepsis susceptibility and severity is not fully understood. The Western Diet (WD), the most prevalent diet worldwide, is high in saturated fatty acids (SFAs) and sucrose, and low in fiber. Previously, we have used a lipopolysaccharide (LPS)-induced sepsis mouse model to show that mice fed a Western Diet (WD) or a diet enriched only in SFAs (Ketogenic Diet; KD), experience increased systemic inflammatory disease severity and mortality, compared to mice fed a low-SFA diet. It is unclear how dietary SFAs regulate inflammation during sepsis, however many SFAs have been shown to induce inflammation in monocytes and macrophages, key cell types that regulate inflammation during sepsis. Our preliminary data show that a pre-treatment with a specific dietary SFA, palmitic acid (PA), plays a role in amplifying the inflammatory response of monocytes and macrophages to a secondary challenge with numerous microbial ligands. This PA-induced hyper-inflammation resembles a well-known phenomenon called trained immunity. Trained immunity is a long-term immunological memory induced by a primary stimulus, which leads to hyper-inflammation upon secondary stimulation with a homologous or heterologous ligand. It is mediated by epigenetic and metabolic reprogramming that allows for modification of gene expression and cellular function. It is unknown if PA induces similar metabolic changes required for the induction of trained immunity. The goal of this study is to determine the metabolic pathways within macrophages that are perturbed by PA, and lead to enhanced inflammation upon secondary stimulation with LPS. Specifically, we aim to quantify the expression of three key glycolytic genes within bone-marrow derived mouse macrophages treated with PA, followed by LPS. Slc2a1 encodes for the transmembrane protein GLUT1 that allows glucose to enter the cell, and Hk2 and Pkfp encode for two rate-limiting enzymes in glycolysis. It is known that LPS upregulates glycolysis, and we hypothesize that PA induces trained immunity in macrophages by increasing expression of Slc2a1, Hk2, and Pkfp, and enhancing the inflammatory response to LPS. The capacity for PA to directly impact innate immune metabolism associated with inflammatory pathways may inform dietary interventions and treatments for sepsis patients, and our findings will be important to consider in a high SFA-fed population