Abstract 220: Induction of Heme Oxygenase-1 Enhances Matrix Metalloproteinase-9 Secretion and Myocardial Fibrosis

Abstract

Background: Heme oxygenase (HO)-1 is a stress-inducible rate-limiting enzyme in heme catabolism into carbon monoxide, biliverdin and free iron. Whereas HO-1 exerts cardioprotective effect, such as anti-hypertrophic and anti-apoptotic effect in cardiomyocytes, the influence of HO-1 on cardiac fibroblasts has not been clarified. We examined the effect of HO-1 induced by cobalt protoporphyrin IX (CoPPIX) on matrix metalloproteinase (MMP)-9 secretion, a biomarker of cardiac remodeling, in cardiac fibroblasts. Methods and Results: Cardiac fibroblasts were isolated from male Wistar rats. Secreted MMP-9 protein into culture medium and HO-1 expression in cell lysates were measured by Western blotting. CoPPIX (0.1-1 μ M) increased HO-1 expression and enhanced interleukin (IL)-1β (4 ng/ml, 24 h)-induced MMP-9 secretion (n=4). Mn 2 (CO) 10 (0.3-10 μ M), a carbon monoxide donor, increased IL-1β-induced MMP-9 secretion (n=4), although bilirubin (0.3-10 μ M), a metabolite of biliverdin, and FeSO 4 (0.3-10 μ M), a free iron donor, had no effect. Mn 2 (CO) 10 increased reactive oxygen species (ROS) generation and the enhanced effect of Mn 2 (CO) 10 on IL-1β-induced MMP-9 secretion was abolished by an antioxidant EUK-134 (10 μ M, n=4). We also examined the effect of CoPPIX on isoproterenol (5 mg/kg/day, subcutaneous injection, for 1 or 7 days)-induced cardiac remodeling in male Wistar rats. CoPPIX (1 mg/kg) was administered intraperitoneally every 2 days and this treatment increased HO-1 expression. Hearts were excised at the day 2 or day 8. Myocardial fibrosis was evaluated by Azan staining. At the day 8, CoPPIX worsened isoproterenol-induced myocardial fibrosis significantly (n=6), but had no effect on the increase of heart weight. CoPPIX also enhanced isoproterenol-induced MMP-9 expression at the day 2 (n=10). Conclusion: Induction of HO-1 by CoPPIX enhances IL-1β-induced MMP-9 secretion via ROS generation through heme-derived carbon monoxide in cardiac fibroblasts and isoproterenol-induced myocardial fibrosis and MMP-9 expression. These findings suggest that HO-1 induction does not necessarily exert cardioprotective effects.