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Published on: November 7, 2019
Lipidomics Analysis of Human HMC3 Microglial Cells in an In Vitro Model of Metabolic Syndrome
Mateusz Chmielarz1, Mariusz Aleksander Bromke2, Mateusz Olbromski3
1Department of Clinical Microbiology, Faculty of Medicine, Wroclaw Medical University, Chalubinskiego 4, 50-368 Wroclaw, Poland.
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.
Insights
Metabolic endotoxemia involves bacterial endotoxin and fatty acids, triggering inflammation. This study shows pre-stimulating microglia with TNFα alters their response to endotoxin and palmitic acid, impacting lipid metabolism and potentially silencing microglial activation.
Area of Science:
- Neuroimmunology
- Cellular Metabolism
Background:
- Metabolic endotoxemia (ME), linked to bacterial lipopolysaccharide (LPS) and saturated fatty acids (SFAs), drives systemic inflammation, often accompanying obesity.
- ME-related endotoxin is known to activate microglia, the immune cells of the central nervous system.
Purpose of the Study:
- To investigate lipid metabolism and immune responses in human microglial cells (HMC3) pre-stimulated with Tumor Necrosis Factor α (TNFα).
- To assess the effects of subsequent endotoxin (LPS) and palmitic acid (PA) treatment on these cells.
Main Methods:
- Human Microglial Cells clone 3 (HMC3) were pre-stimulated with TNFα for 24 hours.
- Cells were then treated with LPS (10 ng/mL) and palmitic acid (PA, 200 µM) for 24 hours.
- Cytokine levels (IL-1β, IL-10, IL-13, TGFβ) were measured using ELISA, and lipid metabolism markers (ceramides, triglycerides) and TREM2 expression were analyzed.
Main Results:
- Pre-stimulation with TNFα modulated microglial responses to LPS and PA.
- LPS increased Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) expression and ceramide levels.
- PA decreased TREM2 expression and increased triglyceride levels, while TGFβ secretion was moderate.
- Negligible levels of IL-1β, IL-10, and IL-13 were observed.
Conclusions:
- TNFα pre-stimulation significantly alters microglial interactions with LPS and PA.
- Modulated lipid metabolism and TREM2 expression suggest a potential silencing of microglial activation.
- This pathway may contribute to neurodegeneration in conditions associated with metabolic endotoxemia.
