Proteasome blockade exerts an antifibrotic activity by coordinately down‐regulating type I collagen and tissue inhibitor of metalloproteinase‐1 and up‐regulating metalloproteinase‐1 production in human dermal fibroblasts

Abstract

Tissue fibrosis results when dysregulation of extracellular matrix (ECM) turnover favors deposition of collagen and other ECM proteins over degradation. Fibrosis may then lead to organ dysfunction and pathology as observed in systemic sclerosis (SSc). In the present study, we investigated the antifibrotic properties of proteasome blockade. A dose- and time-dependent reduction in type-I collagen and tissue inhibitor of metalloproteinase-1 (TIMP-1) production was observed in normal fibroblasts exposed to proteasome inhibitors (PI). In the same culture conditions, metalloproteinase-1 (MMP-1) protein and the collagenolytic activity on type I collagen was increased. The steady-state mRNA levels of COL1A1, TIMP-1, and MMP-1 paralleled protein levels. These effects were dominant over the profibrotic properties of TGF-beta and were observed with fibroblasts generated from normal and SSc skin. PI decreased type I collagen mRNA levels with kinetics similar to those observed with DRB, a specific RNA polymerase II inhibitor, thus indicating transcriptional inhibition. Of interest, PI induced c-Jun phosphorylation and c-Jun nuclear accumulation. The specific N-terminal Jun-kinase inhibitor SP-600125 selectively abrogated c-Jun phosphorylation and, in a dose-dependent fashion, the up-regulated synthesis of MMP-1 induced by PI. Finally, PI did not affect fibroblast viability. Thus, the coordinated down-regulation of collagen and TIMP-1 and up-regulation of MMP-1 renders proteasome blockade an attractive strategy for treating conditions as SSc, characterized by excessive fibrosis.

Autophagy Promotes Intracellular Degradation of Type I Collagen Induced by Transforming Growth Factor (TGF)-β1

“…In contrast to bafilomycin A 1 , we observed that the inhibition of the proteasome by treatment with MG132 repressed the expression of Col-I ␣1 mRNA in MMC. Similar effect of MG132 has been previously reported in human dermal fibroblasts (43) and rat cardiac fibroblasts (44).…”

“…This negative regulatory effect of MG132, in fact, has been previously shown in human dermal fibroblasts (43) and rat cardiac fibroblasts (44). However the precise mechanism by which proteasome inhibitor MG132 represses Col-I ␣1 mRNA expression remains to be determined.…”

“…The transcriptional regulation of Col-I ␣1 mRNA is known to be highly complex that involves various enhancers and repressors. The studies by Fineschi et al (43), suggest that although JNK is activated by MG132, JNK activity may not be involved in the regulation of Col-I ␣1 mRNA transcription, since inhibition of JNK failed to reverse the negative regulatory effect on Col-I expression.…”

Therapeutic Potential of Immunoproteasome Inhibition in Duchenne Muscular Dystrophy

“…To date, steroids are the most effective and utilized treatment, but new immune-modulatory drugs have been experimented to improve muscle repair by reducing inflammation and fibrosis of DMD animal models as anticytokines (anti-TNFα), 30 IL-6r blockade, 31 TGF-β blocker (suramin and pirfenidone) 32,33 and, more recently, Treg expansion. 13 Several evidences suggested that the proteasome is directly involved in the pathophysiology of organ fibrosis: inhibition of the proteasome could block TGF-β1 induced gene expression in primary human lung fibroblasts from healthy individuals and patients with IPF 34,35 and could reduce lung fibrosis in some animal models. 36,37 Indirectly, fibrosis is augmented by inflammatory pathogenesis that is also influenced by i-proteasome.…”

Membrane type-1 matrix metalloproteinase activity is regulated by the endocytic collagen receptor Endo180

“…Conditioned media from equal cell numbers were concentrated fivefold and analysed for total collagen (types I-V) using a Sircol soluble collagen assay kit as described (Biocolor Ltd) (Fineschi et al, 2006). Collagen was measured by reference to a type-I collagen standard curve.…”