030 Inhibition of Mitogen Activated Kinase-Mediated Hyaluronan Expression by Glucocorticoids

Abstract

Background and Objectives: Hyaluronan (HA), a ubiquitous glycosaminoglycan is synthesized by one of three distinct hyaluronan synthases (HAS). The purposes of this study were to determine whether a cause-and-effect relationship exists between the proinflammatory cytokine, interleukin-1β(IL-1β), and hyaluronan expression in normal jejunum-derived mesenchymal cells (JDMCs), to identify possible mechanisms involved and to determine the effects of glucocorticoids, a common therapy for intestinal inflammatory pathologies including Crohn’s disease and ulcerative colitis (UC), on cytokine-mediated hyaluronan expression. Experimental Procedures: JDMCs were stimulated with IL-1β for 20 hr with or without pretreatment for 1 hr with mitogen activated protein kinase (MAPK) inhibitors or dexamethasone. HA levels from culture media were quantified using a slot blotting approach. HAS transcript levels were quantified using RPA. Immunoblotting was used to detect and quantify activation of MAP kinases. Results: Preliminary data of sample tissue from patients with Crohn’s or UC indicated increased HAS transcript levels. Similarly, IL-1β induced an approximate 18-fold increase in both HAS2 steady state transcripts and HA levels. These increases were blocked by dexamethasone (95%). Knockdown with siRNA demonstrated that IL-1β induction of HA expression occurred via HAS2. Immunoblot analysis indicated that IL-1β activated the ERK1/2, p38 and JNK pathways. Inhibitors of the p38 and ERK1/2, but not JNK, blocked the IL-1β induction of HA expression (80 and 90%, repectively). Similarly, dexamethasone was also found to block activation of the ERK1/2 and p38 pathways indicating a mechanism for glucocorticoid steroid regulation of HAS expression. Conclusion: This study provides evidence for proinflammatory cytokine regulation of HA expression in JDMCs. Furthermore, this study provides support for the hypothesis that HA may be one of the targets involved in the treatment of steroid-dependent inflammatory bowel disease. Support: This work was supported by NIH GM 58530.