Role of Monocytes in Immunopathology

Dental &Craniofacial Research

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Abstract

The focus of this project is to define factors and signal transduction pathways involved in the modulation of human monocyte functions that may contribute to the immunopathology associated with various disease states. Connective tissue destruction is associated with many diseases in which the monocyte/macrophage is a prominent cell. Since matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) are believed to play a major role in the destruction and remodeling of connective tissue, a major emphasis has been placed on how these enzymes and inhibitors are controlled. Current studies have focused on the specific roles of the mitogen-activated protein kinases (MAPKs) in the regulation of MMP-1 and MMP-9, two major MMPs produced by monocytes. LPS was compared with TNF alpha and GM-CSF to determine if similar MAPK pathways were utilized by these agonists in the induction of MMP-1 and MMP-9. Through the use of specific MAPK inhibitors and phosphorylation studies LPS induction of MMP-1 was shown to occur primarily through the p38 MAPK pathway whereas MMP-9 was regulated mainly by ERK 1/2. In contrast the combination of TNF alpha and GM-CSF induced both MMP-1 and MMP-9 through ERK 1/2. Moreover, these studies demonstrated that p38 inhibition results in significant increase in the phosphorylation of ERK 1/2 and the MMP-1 induced by TNF alpha and GM-CSF. Possible explanations for this increase in ERK1/2 phosphorylation include p38 serving as a negative regulator of ERK1/2 and/or a shunting to the ERK1/2 pathway when the p38 pathway is inhibited. In summary, induction of MMP-1 by LPS occurs through the p38 pathway whereas TNF alpha and GM-CSF utilized ERK 1/2. However, ERK 1/2 is the predominate pathway utilized by both LPS and the cytokines in the induction of MMP-9.