Melatonin exerts anti-fibrinolytic effects by regulating IL-1β-induced changes in uPA, uPAR, and PAI-1 expression/production in human dental pulp cells.

Interleukin-1β (IL-1β) is a pro-inflammatory cytokine and its expression is increased in inflamed dental pulp. IL-1β affects plasminogen activation system molecules, which are crucial for tissue inflammation, fibrinolysis, matrix turnover, and cell adhesion and migration. Melatonin, which provides circadian and seasonal signals, is a physiological endocrine generated by the pineal gland. It has anti-oxidant and anti-inflammatory properties. Studies are warranted to determine whether melatonin prevents IL-1β-induced expression/production of plasminogen system molecules. Human dental pulp cells (HDPCs) were exposed to IL-1β or melatonin alone or to IL-1β with/without pretreatment with melatonin or other inhibitors. The mRNA expression of uPA, uPAR, and PAI-1 was quantified using real-time polymerase chain reaction analysis. The cellular uPA, PAI-1, and soluble uPAR (suPAR) production was determined using an enzyme-linked immunosorbent assay. Signaling molecules' protein expression was analyzed by immunofluorescent staining. We found that IL-1β (0.1-10 ng/mL) stimulated uPA and uPAR expression/production but inhibited PAI-1 expression/ production of HDPCs. Melatonin inhibited uPA but stimulated uPAR/suPAR and PAI-1 expression/production. Intriguingly, melatonin prevented IL-1β-induced uPA mRNA expression/production. Conversely, melatonin enhanced the IL-1β-induced uPAR and PAI-1 mRNA expression/protein production of HDPCs. IL-1β-induced suPAR production was attenuated by U0126 (a MEK/ERK inhibitor), SB203580 (a p38 inhibitor), and 5Z-7oxozeaenol (a TAK1 inhibitor), whereas SB203580 prevented an IL-1β-induced decline of PAI-1 production. Moreover, melatonin attenuated the IL-1β-induced p-ERK, p-p38, p-Akt and p-TAK1. These results revealed the crucial role of IL-1β in the pathogenesis of pulpal inflammation/repair via stimulation of uPA and uPAR and inhibition of PAI-1, which can be differentially regulated by p38, Akt, MEK/ERK, and TAK1. Melatonin exerts an anti-fibrinolytic effect on IL-1β-induced changes in uPA, uPAR, and PAI-1 in HDPCs. Clinically, the melatonin levels of patients may affect pulpal inflammatory response. Melatonin and signal transduction inhibitors may be administered concomitantly for the prevention and treatment of pulpal inflammatory diseases.