Adrenomedullin inhibits CXCL10 production by human gingival fibroblasts

Objectives: Adrenomedullin (AM) is a peptide that has multiple regulatory functions. Several studies indicate that AM could act as an endogenous immunomodulatory factor. Our aim was to elucidate the effects and mechanism of AM on the CXC chemokine ligand (CXCL) 10 production, which are involved in Th1 response by human gingival fibroblasts (HGFs). Methods: The HGFs that grew from three clinically healthy gingival were cultured primarily on plastic dishes in Dulbecco's modified Eagle medium supplemented with 10% fetal bovine serum and antibiotics at 37°C in humidified air with 5% CO₂. Confluent cells were transferred and cultured for use in the present study. We examined the expressions of AM, AM receptors, calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP)2 and 3 in HGFs culture by RT-PCR. HGFs were stimulated with tumor necrosis factor (TNF)-α, AM, folskolin (adenylate cyclase activator) and cyclic AMP (cAMP), and the CXCL10 production by HGFs was evaluated by RT-PCR and/or ELISA. In some experiments, we pre-incubated HGFs with H89 (protein kinase A inhibitor) prior to the stimulation. Results: HGFs expressed AM and AM receptors, CRLR and RAMP2, mRNA constitutively. Meanwhile, RAMP3 mRNA was not expressed in HGFs. AM treatment inhibited CXCL10 production by TNF-α-stimulated HGFs. H89 treatment cancelled the inhibitory effects of AM on CXCL10 produciton from TNF-α-stimulated HGFs. Moreover, folskolin and cAMP suppressed CXCL10 production by TNF-α-stimulated HGFs. Conclusions: From these results, AM inhibited CXCL10 production by TNF-α-stimulated HGFs via cAMP/PKA pathway activation. These findings indicate that the effects of AM on CXCL10 production by HGFs are related to lymphocyte infiltration, particularly Th1-type T cells, into the gingival tissue with periodontal disease. Recently, it has been reported that Th1-type T cells were involved in bone resorption in periodontal diseased tissue. Therefore, AM could play a role as therapeutioc approach to treatment of periodontitis.