Journal of Cellular Biochemistry 102:453–462 (2007) Constitutive Collagenase-1 Synthesis Through MAPK Pathways Is Mediated, in Part, by Endogenous IL-1a During Fibrotic Repair in Corneal Stroma Jae-Chang Jung, 1 * Man-Il Huh, 1 and M. Elizabeth Fini 2 1 Department of Biology, College of Natural Sciences, Kyungpook National University, Daegu, Korea 2 Evelyn F. and William L. McKnight Vision Research Center, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida Abstract Collagenase-1 is a protease expressed by active fibroblasts that is involved in remodeling of the extracellular matrix (ECM). In this study, we characterize the intracellular signaling mechanism of collagenase-1 production by IL-1a in subcultured normal fibroblasts (NF) from uninjured normal corneas, compared to that in repair wound fibroblasts (WF). In NF, collagenase-1 was induced specifically after the exogenous addition of IL-1a via activation of ERK and p38MAPK. Collagenase-1 expression was strongly suppressed upon treatment with either a MEK or p38MAPK inhibitor. In contrast, repair WF constitutively synthesized both IL-1a and collagenase-1. Combined treatment with both mitogen-activated protein kinase (MAPK) inhibitors dramatically reduced collagenase-1 synthesis, while individual MEK1 or p38 inhibitors weakly modulated the collagenase-1 level. The results indicate that both pathways are crucial in the regulation of collagenase-1 synthesis. Furthermore, an IL-1a receptor antagonist (IL-1ra) could not abolish constitutive collagenase-1 synthesis, even at high doses, suggesting that other cytokines/factors are additionally involved in this process. We propose that induction of collagenase-1 by IL-1a in both WF and NF depends on a unique combination of cell type-specific signaling pathways. J. Cell. Biochem. 102: 453 – 462, 2007. ß 2007 Wiley-Liss, Inc. Key words: collagenase-1; corneal stroma; fibrosis; MAPK; IL-1a The cornea contains three layers, the outer squamous epithelium, inner endothelium, and central stroma containing quiescent stromal cells (keratocytes) embedded within a thick collagenous matrix. Upon ablation wounding, keratocytes located at the wound edge of the stroma begin to undergo mitosis along with morphological and functional changes, trans- form into active fibroblasts, and migrate into the damaged acellular area filled with fibrin clot [Weimar, 1962; Fini and Stramer, 2005]. Active fibroblasts synthesize new extracellular matrix (ECM) molecules distinct from normal unin- jured stroma, as well as collagenase-1, which is not produced by keratocytes of normal corneas [Girard et al., 1993; Fini, 1999]. During the contraction phase of wound healing, fibroblasts transform into myofibroblasts expressing a- smooth muscle actin (a-SMA) that imparts contractile properties to cells [Jester et al., 1994; Jester et al., 1996]. Myofibroblasts gen- erate abundant ECM, and participate in ECM remodeling by producing matrix metalloprotei- nases (MMPs) [Jain et al., 1996; Arthur, 1998; Ramadori et al., 1998]. In corneal wound healing, spontaneous fibroblast activation and myofibroblast transformation results in the deposition of opaque scar tissue, which inter- feres with vision [Fini and Stramer, 2005]. MMPs are zinc endopeptidases characterized by reactivity against all components of the ECM at neutral pH [Yong et al., 2001]. MMPs are sub- classified into the following functional groups: collagenases, gelatinases, stromelysins, matri- lysins, membrane type-MMPs (MT-MMPs), and ß 2007 Wiley-Liss, Inc. Grant sponsor: Korea Research Foundation; Grant num- ber: R05-2003-000-11051-0; Grant sponsor: NIH; Grant number: R01 EY09828; Grant sponsor: Research to Prevent Blindness, Inc. *Correspondence to: Jae-Chang Jung, PhD, Developmental Biology Laboratory, Department of Biology, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Korea. E-mail: jcjung@mail.knu.ac.kr Received 30 September 2006; Accepted 24 January 2007 DOI 10.1002/jcb.21309