AbstractFibroblasts, a major constituent of gingival connective tissue, can produce immunoregulatory cytokines and proteolytic enzymes that may contribute to tissue destruction. In this study, we evaluated the production of matrix metalloproteinases (MMPs), tissue inhibitors of MMPs (TIMPs), and plasminogen activators by gingival fibroblasts stimulated with lipopolysaccharides (LPS) produced by periodontopathogens, including Actinobacillus actinomycetemcomitans. In addition, changes in the expression and phosphorylation state of fibroblast intracellular signaling proteins induced by A. actinomycetemcomitans LPS were characterized using antibody microarrays. We showed that A. actinomycetemcomitans LPS induced the production of a 50 kDa plasminogen activator, MMP‐2 and, to a lesser extent, MMP‐3 by fibroblasts. The stimulation of fibroblasts with A. actinomycetemcomitans LPS also resulted in the overproduction of TIMP‐1, but had no effect on the production of TIMP‐2. Comparable responses were also obtained with Porphyromonas gingivalis and Fusobacterium nucleatum subsp. nucleatum LPS. The results of the microarray analyses showed that A. actinomycetemcomitans LPS induced changes in the phosphorylation state and expression of gingival fibroblast intracellular signaling proteins. More specifically, they suggested that A. actinomycetemcomitans LPS may induce both Jun N‐terminus protein‐serine kinases (JNK) and mitogen‐activated protein‐serine kinase p38 alpha (p38α MAPK) pathway activation, leading to increased activator protein‐1 (AP‐1) and nuclear factor kappa‐B (NFκB) activities, which in turn can stimulate MMP‐2, MMP‐3, TIMP‐1, and urokinase‐type plasminogen activator (uPA) expression. This may contribute to periodontal connective tissue destruction. J. Cell. Physiol. 212: 189–194, 2007. © 2007 Wiley‐Liss, Inc.