Differential Protein Pathways in 1,25-Dihydroxyvitamin D3 and Dexamethasone Modulated Tolerogenic Human Dendritic Cells

Tolerogenic dendritic cells (DC) that are maturation-resistant and locked in a semimature state are promising tools in clinical applications for tolerance induction. Different immunomodulatory agents have been shown to induce a tolerogenic DC phenotype, such as the biologically active form of vitamin D (1,25(OH)2D3), glucocorticoids, and a synergistic combination of both.

In this study, we aimed to characterize the protein profile, function and phenotype of DCs obtained in vitro in the presence of 1,25(OH)2D3, dexamethasone (DEX), and a combination of both compounds (combi). Human CD14+ monocytes were differentiated toward mature DCs, in the presence or absence of 1,25(OH)2D3 and/or DEX.

Cells were prefractionated into cytoplasmic and microsomal fractions and protein samples were separated in two different pH ranges (pH 3–7NL and 6–9), analyzed by 2D-DIGE and differentially expressed spots (p < 0.05) were identified after MALDI-TOF/TOF analysis. In parallel, morphological and phenotypical analyses were performed, revealing that 1,25(OH)2D3- and combi-mDCs are closer related to each other than DEX-mDCs.

This was translated in their protein profile, indicating that 1,25(OH)2D3 is more potent than DEX in inducing a tolerogenic profile on human DCs. Moreover, we demonstrate that combining 1,25(OH)2D3 with DEX induces a unique protein expression pattern with major imprinting of the 1,25(OH)2D3 effect. Finally, protein interaction networks and pathway analysis suggest that 1,25(OH)2D3, rather than DEX treatment, has a severe impact on metabolic pathways involving lipids, glucose, and oxidative phosphorylation, which may affect the production of or the response to ROS generation.

These findings provide new insights on the molecular basis of DC tolerogenicity induced by 1,25(OH)2D3 and/or DEX, which may lead to the discovery of new pathways involved in DC immunomodulation.