Activation of Gingival Fibroblasts by Bacterial Cyclic Dinucleotides and Lipopolysaccharides

Objectives: Cyclic dinucleotides (cyclic di-guanosine monophosphate (c-di-GMP) and cyclic di-adenosine monophosphate (c-di-AMP)) and lipopolysaccharides (LPS) are pathogen-associated molecular patterns (PAMPs) that stimulate an immune response in eukaryotic cells. Although their individual impacts on the selected immune cells have been documented, simultaneous actions of multiple PAMPs on gingival fibroblasts are not studied so far. In the present study, we examined the effects of c-di-GMP and c-di-AMP on cytokine and enzyme response of gingival fibroblasts in the presence and absence of Porphyromonas gingivalis LPS.

Methods: Human gingival fibroblasts were incubated for 24 h with three concentrations of c-di-GMP and c-di-AMP (100 μM, 10 μM, and 1 μM), either in the presence or absence of P. gingivalis LPS. The luminex technique was used to measure the extracellular levels of interleukin (IL)-8, -10, -34, matrix metalloproteinase (MMP)-1, -2, and -3.

Results: Incubating fibroblasts with LPS alone or together with c-di-AMP or c-di-GMP at all tested concentrations elevated IL-8 levels, while incubation with 100 μM of c-di-GMP alone increased extracellular IL-10 levels. The MMP-3 levels were increased when the cells were incubated with c-di-AMP (10 μM) or c-di-GMP (10 and 100 μM) in the presence of LPS. MMP-2 levels were suppressed in the stimultaneous presence of LPS and c-di-GMP (1 μM).

Conclusions: Bacterial cyclic dinucleotides and LPS stimulate gingival fibroblasts to secrete cytokines and enzymes; however, variations in response profile may indicate differences in the activation of response regulatory pathways.