IL‐1β and TNF‐α Differentially Regulate Lysyl Oxidase Expression and Activity in Adult Cardiac Fibroblasts

Abstract

Cardiac fibroblasts constitutively express lysyl oxidase (LOX), an enzyme that catalyzes the crosslinking of collagen and modulates extracellular matrix maturation. Pro‐inflammatory cytokines, IL‐1β and TNF‐α, are elevated during cardiac disease and are known to modulate LOX expression in non‐cardiac cells. However, little is known about the regulation of LOX expression or activity in the heart. We tested the hypothesis that IL‐1β and TNF‐α decrease LOX expression and activity in isolated adult rat cardiac fibroblasts. After incubation in minimal serum media, fibroblasts were treated with TNF‐α (20 ng/ml) or IL‐1β (10 ng/ml) for 48 hrs. Cells were harvested and LOX expression assayed by Western blot. LOX activity was measured in cell culture media using Amplex red assay. Treatment with TNF‐α led to a significant reduction in LOX protein expression. However, IL‐1β did not affect LOX expression. Despite these differences in expression, both TNF‐α and IL‐1β significantly decreased LOX activity (64% and 60% vs. control, respectively). In addition, the TNF‐α regulation of LOX protein occurs in part through a Rho‐associated protein kinase (ROCK) pathway, as incubation of fibroblasts with the ROCK inhibitor, Y‐27632, attenuated the reduction of LOX expression. These findings indicate that the expression and activation of LOX in cardiac fibroblasts is differentially regulated by TNF‐α and IL‐1β.