Chronic exposure of interleukin‐13 suppress the induction of matrix metalloproteinase‐1 by tumour necrosis factor α in normal and scleroderma dermal fibroblasts through protein kinase B/Akt

Summary Peripheral blood mononuclear cells taken from patients with scleroderma express increased levels of interleukin (IL)‐13. Moreover, the expression of matrix metalloproteinase‐1 (MMP‐1) from involved scleroderma skin fibroblasts is refractory to stimulation by tumour necrosis factor (TNF)‐α. To elucidate the mechanism(s) involved, we examined the effect of IL‐13 on TNF‐α‐induced MMP‐1 expression in normal and scleroderma human dermal fibroblast lines and studied the involvement of serine/threonine kinase B/protein kinase B (Akt) in this response. Dermal fibroblast lines were stimulated with TNF‐α in the presence of varying concentrations of IL‐13. Total Akt and pAkt were quantitated using Western blot analyses. Fibroblasts were treated with or without Akt inhibitor VIII in the presence of IL‐13 followed by TNF‐α stimulation. MMP‐1 expression was analysed by real‐time polymerase chain reaction (PCR) and enzyme‐linked immunosorbent assay (ELISA). Statistical analysis was performed using analysis of variance ( anova ) or Student's t ‐test. Upon TNF‐α stimulation, normal dermal fibroblasts secrete more MMP‐1 than systemic sclerosis (SSc) fibroblasts. This increase in MMP‐1 is lost when fibroblasts are co‐incubated with IL‐13 and TNF‐α. IL‐13 induced a significant increase in levels of pAkt in dermal fibroblasts, while Akt inhibitor VIII reversed the suppressive effects of IL‐13 on the response of cultured fibroblasts to TNF‐α, increasing their expression of MMP‐1. We show that IL‐13 suppresses MMP‐1 in TNF‐α‐stimulated normal and scleroderma dermal fibroblast. Akt inhibitor VIII is able to reverse the suppressive effect of IL‐13 on MMP‐1 expression and protein synthesis. Our data suggest that IL‐13 regulates MMP‐1 expression in response to TNF‐α through an Akt‐mediated pathway and may play a role in fibrotic diseases such as scleroderma.