Selective induction of matrix metalloproteinases by Borrelia burgdorferi via toll-like receptor 2 in monocytes

Regulation of secretion of matrix metalloproteinase (MMP) underlies the basis of numerous physiological and pathological processes in multicellular organisms. The Toll receptor family, which is conserved from Drosophila species to humans, mediates pattern recognition of a diversity of ligands involved in morphogenesis and innate immunity. Here, we show that secretion of MMP-9 is selectively induced through Toll-like receptor (TLR) 2 in human and murine monocytic cells stimulated with Borrelia burgdorferi. Secretion of MMP-1 was shown to be stimulated through a pathway other than TLR2, under identical conditions. Analysis of nuclear extracts indicated that activator protein (AP)-1 was reduced in TLR2-neutralized monocytic cells, suggesting that AP-1 plays a role in the transcriptional activation of MMP-9 through TLR2. The specific induction of MMP-9 through TLR2 provides direct evidence of a new role for this ancient receptor family in regulating secretion of MMPs and demonstrates evolutionary convergence between invertebrate morphogenesis and the vertebrate innate immune system.