Histamine promotes the expression of receptors TLR2 and TLR4 and amplifies sensitivity to lipopolysaccharide and lipoteichoic acid treatment in human gingival fibroblasts.

The vasoactive hydrophilic amine histamine is the most important molecule released by mast cells. However, histamine's role in activating intracellular responses in HGFs (human gingival fibroblasts) has not been evaluated to date. In the present study, we investigated the effect of histamine and of Gram-negative [LPS (lipopolysaccharide)] and Gram-positive [LTA (lipoteichoic acid)] bacterial components on the modulation of the inflammatory response of HGFs. We incubated HGFs with histamine to determine whether this hydrophilic amine regulates overexpression of TLR2 (Toll-like receptor 2) and TLR4, which recognize LTA and LPS respectively. Our experiments demonstrated that histamine increases transcription and translation of TLR2 and TLR4. Incubation with LTA or LPS in the presence of histamine markedly increased expression of COX2 (cyclo-oxygenase 2) and synthesis of prostaglandin E2. These results suggest that histamine plays an important role in modulating the innate immune response, and likewise, that LTA and LPS regulate the adaptive immune response. The present study provides information about the regulation and expression of molecules that promote chronic inflammatory processes leading to the emergence of periodontitis and the consequent loss of the dental organ.

Activation of ERK1/2 by protein kinase C-alpha in response to hydrogen peroxide-induced cell death in human gingival fibroblasts.

Hydrogen peroxide (H(2)O(2)) increases protein tyrosine phosphorylation of numerous proteins in human gingival fibroblasts (HGFs). Two main proteins, with an apparent molecular weight of 44 and 42kDa, were phosphorylated after hydrogen peroxide stimulation of the human gingival fibroblasts. Further analysis identified these two proteins as ERK1/2. Maximum phosphorylation was detected at 10min post-H(2)O(2) treatment. Pretreatment with an MEK inhibitor, PD98059, inhibited H(2)O(2)-stimulated ERK1/2 phosphorylation in a dose-dependent manner. Treatment with H(2)O(2) also induced phosphorylation of protein kinase C-alpha (PKCalpha). Staurosporine, a PKC inhibitor, blocked ERK1/2 phosphorylation induced by H(2)O(2). In addition, H(2)O(2)-induced cell death was prevented by PD98059, SB203580, and calphostin C, which are MEK, p38 and PKC inhibitors, respectively. These results suggest that H(2)O(2) leads to the phosphorylation and activation of ERK1/2 in a PKC-dependent manner. These findings demonstrate that the MAPK signaling pathway plays an active role in mediating the H(2)O(2)-induced decrease in HGF cell viability and ATP depletion.