Background: The first of the two objectives in this study was based on a well demonstrated link between diabetes and chronic low-grade inflammation and the results from the ACCORD study and other studies investigating benefits and drawbacks in intensive glucose therapy in diabetes. Our first objective was therefore to investigate how rapid changes in glucose levels would affect macrophagelike cells.
Recently there has also been revealed g-protein coupled receptors using intermediates in TCA-cycle as ligands. Studies have found several actions of the succinate receptor GPR91 linked to the development of diabetic complications and as part in the immune response in dendritic cells. Our second objective was therefore to find out whether the expression of GPR91 increases during differentiation from THP-1 cells into macrophage-like cells, and what kind of effect a stimulation with succinate would have on these cells.
Methods: Both aims were explored using a model based on cultivating and stimulating cells in vitro, and measuring gene expression with qRT-PCR and Affymetrix gen expression array. TNF-α, IL-6, MCP-1 and caveolin-1 was chosen as markers based on current knowledge upon their role in inflammation and atherosclerosis.
Results: There was not demonstrated any significant changes in the expression (fold change) in any of the markers after change in glucose levels. Analyses of global gene expression showed no abundant changes. The expression of GPR91 was found to increase significantly during phorbol ester induced differentiation of THP-1 cells to macrophage-like cells. Maturation into macrophage-like cells did not lead to any significant increase in expression of TNF-α when stimulating with succinate. Analyses of global gene expression showed no abundant changes after succinate stimulation.
Conclusion: Rapid changes in glucose levels did not seem to affect the macrophagelike cells. On the other hand their expression of GPR91 did increase after PMA stimulation, when compared to the immature THP-1 cells. This strengthens the hypothesis of a role for this receptor in immune responses, even though we did not find any effect upon TNF-α when stimulating with succinate.