Histamine-stimulated production of matrix metalloproteinase 1 by human rheumatoid synovial fibroblasts is mediated by histamine H1-receptors.

The purpose of this study was to investigate the role of histamine in human rheumatoid synovial fibroblasts in the production of factors responsible for tissue remodelling and cartilage breakdown in rheumatoid arthritis. We examined the effects of histamine of tritiated thymidine incorporation, production of matrix metalloproteinase-1 (MMP-1), histamine H1-receptor expression, phosphoinositide metabolism and intracellular calcium ion concentration ([Ca2+]i) in human rheumatoid synovial fibroblasts. Tritiated thymidine incorporation studies demonstrated that histamine markedly stimulated the proliferation of rheumatoid synovial fibroblasts. Immunofluorescence and Northern blot analyses revealed that proMMP-1 production was also stimulated by histamine. The levels of inositol phosphates and [Ca2+]i in the cells were elevated in response to histamine, indicating that the cells expressed histamine H1-receptors; and Northern blot analysis indicated that these H1-receptors were up-regulated by histamine. In in situ hybridization, large amounts of histamine H1-receptor mRNA were also detected in rheumatoid synovial tissue. These results suggest that the interaction between H1-receptor expression in rheumatoid synovial fibroblasts and histamine secretion by mast cells and macrophages in the affected sites is an important event responsible for tissue remodelling and joint destruction in rheumatoid arthritis.