Distinct Effects of Escherichia coli,Pseudomonas aeruginosa and Staphylococcus aureus Cell Wall Component-Induced Inflammation on the Iron Metabolism of THP-1 Cells

Abstract

Macrophages are essential immune cells of the innate immune system. They participate in the development and regulation of inflammation. Macrophages play a fundamental role in fighting against bacterial infections by phagocytosis of bacteria, and they also have a specific role in immunomodulation by secreting pro-inflammatory cytokines. In bacterial infection, macrophages decrease the serum iron concentration by removing iron from the blood, acting as one of the most important regulatory cells of iron homeostasis. We examined whether the Gram-positive and Gram-negative cell wall components from various bacterial strains affect the cytokine production and iron transport, storage and utilization of THP-1 monocytes in different ways. We found that S. aureus lipoteichoic acid (LTA) was less effective in activating pro-inflammatory cytokine expression that may related to its effect on fractalkine production. LTA-treated cells increased iron uptake through divalent metal transporter-1, but did not elevate the expression of cytosolic and mitochondrial iron storage proteins, suggesting that the cells maintained iron efflux via the ferroportin iron exporter. E. coli and P. aeruginosa lipopolysaccharides (LPSs) acted similarly on THP-1 cells, but the rates of the alterations of the examined proteins were different. E. coli LPS was more effective in increasing the pro-inflammatory cytokine production, meanwhile it caused less dramatic alterations in iron metabolism. P. aeruginosa LPS-treated cells produced a smaller amount of pro-inflammatory cytokines, but caused remarkable elevation of both cytosolic and mitochondrial iron storage proteins and intracellular iron content compared to E. coli LPS. These results prove that LPS molecules from different bacterial sources alter diverse molecular mechanisms in macrophages that prepossess the outcome of the bacterial infection.

Early-Life Nutrition Interventions Improved Growth Performance and Intestinal Health via the Gut Microbiota in Piglets

“…This was attributed to increased expression of MUC2 , and decreased enteric leakiness which in turn reduced contact of intestinal epithelial cells with harmful substances, and ultimately decreased frequency of inflammation ( 48 ). Previous human and animal studies indicated that LPS is a strong inducer of proinflammatory cytokines, and is produced by harmful microorganisms ( 49 ). LPS stimulation upregulates expression of TNF- α, MCP-1 , and IL-10 ( 50 ).…”

Modulatory Effects of Fractalkine on Inflammatory Response and Iron Metabolism of Lipopolysaccharide and Lipoteichoic Acid-Activated THP-1 Macrophages

“…Monocytes/macrophages can be activated by bacterial compounds such as bacterial cell wall components obtained from both Gram-negative (LPS) and Gram-positive (LTA) bacterial strains [ 2 , 35 ]. It has been proven that LPS or LTA inflammatory mediators from various sources affect differently both the inflammatory response and iron metabolism [ 15 , 36 ].…”

“…This can be explained by the fact that IL-1β undergoes a posttranslational maturation; therefore, the cells can still secrete IL-1β even though the mRNA expression has already decreased [ 40 ]. It can also be concluded that fractalkine may act differently on the regulation of TNFα expression; moreover, the type of inflammatory mediator (whether LPS or LTA) also influences the inflammatory response of THP-1 cells [ 36 ]. We also examined the relative mRNA expression of one additional M1 (INFγ) and four M2 (IL-4, IL-10, TGFβ and CD163) macrophage markers to reveal the possible effects of fractalkine on the polarization of THP-1 cells.…”

“…The presence of fractalkine and/or the inflammatory signal in the THP-1 cells may also assist in iron sequestration via DMT-1 or TfR1 iron importers. Unlike pro-inflammatory cytokine production, fractalkine alone was able to alter the expression of iron transporters and modified their levels in the case of co-treatments suggesting that fractalkine may have a crucial role in the elimination of iron from the circulation in the case of bacterial infections [ 36 ]. The total intracellular iron content of the differently treated cells was in correlation with the protein expression levels of the examined iron transporters Fp, DMT-1 and TfR1.…”

“…The cells were treated with 5 and 10 ng/mL of fractalkine alone for 24 h or 1 µg/mL LPS or LTA alone for 24 h. In the case of co-treatments, the same amount of fractalkine and LPS or LTA were added to the cells at the same time for 24 h. Untreated THP-1 cells were used as controls. The utilized concentrations of LPS/LTA and fractalkine were determined based on our previous article [ 36 ].…”