Abstract
Metabolic endotoxemia (ME) is associated with bacterial lipopolysaccharide (LPS, endotoxin) and increased levels of saturated fatty acids (SFAs) in the bloodstream, causing systemic inflammation. ME usually accompanies obesity and a diet rich in fats, especially SFAs. Numerous studies confirm the effect of ME-related endotoxin on microglial activation. Our study aimed to assess lipid metabolism and immune response in microglia pre-stimulated with TNFα (Tumor Necrosis Factor α) and then with endotoxin and palmitic acid (PA). Using ELISA, we determined cytokines IL-1β, IL-10, IL-13 (interleukin-1β, -10, -13, and TGFβ (Transforming Growth Factor β) in the culture medium from microglial cells stimulated for 24 h with TNFα and then treated with LPS (10 ng/mL) and PA (200 µM) for 24 h. HMC3 (Human Microglial Cells clone 3) cells produced negligible amounts of IL-1β, IL-10, and IL-13 after stimulation but secreted moderate levels of TGFβ. Changes in lipid metabolism accompanied changes in TREM2 (Triggering Receptor Expressed on Myeloid Cells 2) expression. HMC3 stimulation with endotoxin increased TREM2 expression, while PA treatment decreased it. Endotoxin increased ceramide levels, while PA increased triglyceride levels. These results indicated that pre-stimulation of microglia with TNFα significantly affects its interactions with LPS and PA and modulates lipid metabolism, which may lead to microglial activation silencing and neurodegeneration.