Antiproliferative and antifibrotic effects of mimosine on adult cardiac fibroblasts

Abstract

Prolyl 4-hydroxylase catalyzes the hydroxylation of collagen pro-α chains for the deposition of cardiac collagen. The effect of prolyl 4-hydroxylase on synthesis and degradation of collagen was studied in cultured adult cardiac fibroblasts using mimosine, a prolyl 4-hydroxylase inhibitor. Mimosine inhibited [ 3H]thymidine incorporation in cultured fibroblasts in a dose-dependent manner (100–600 μM). Immunofluorescence in fibroblasts and biochemical detection of mature type I collagen in culture serum revealed a strong inhibition of synthesis and secretion of mature collagens, respectively, in the presence of 200 μM mimosine. Western blot analysis for procollagen was carried out in cultured fibroblasts, and 200 μM mimosine treatment was associated with increased intracellular accumulation of procollagen from 4.14±0.27 to 10.19±0.37 (arbitrary units). Immunofluorescence studies confirmed a marked increase of intracellular procollagens in fibroblasts treated with mimosine, which suggests a loss of coordinated monomeric procollagen synthesis and secretion of triple helical mature collagens. Modest inhibition of collagen type I mRNA abundance was observed in mimosine-treated fibroblasts, whereas no effect was noted for mRNAs of collagen type III, α-prolyl 4-hydroxylase or β-prolyl 4-hydroxylase when compared to untreated control values. Treatment of fibroblasts with 200 μM mimosine was associated with elevation of matrix metalloproteinase (MMP)-9 activity. The cytotoxicity of mimosine treatment was found minimal at the concentrations indicated above. Thus the antifibrotic effects induced by mimosine on cultured adult cardiac fibroblasts was associated with inhibition of prolyl 4-hydroxylase and diminished extracellular secretion of procollagen, despite the reactive elevation of intracellular procollagen synthesis. We suggest that specific inhibition of prolyl 4-hydroxylase may provide a novel therapeutic approach for the modulation of cardiac fibrosis.