In
systemic sclerosis (SSc), a disease characterized by
fibrosis of the skin and internal organs, the occurrence of
interstitial lung disease is responsible for high morbidity and mortality. We previously demonstrated that
proteasome inhibitors (PI) show anti-fibrotic properties in vitro by reducing
collagen production and favoring
collagen degradation in a
c-jun N-terminal kinase (JNK)-dependent manner in human fibroblasts. Therefore, we tested whether PI could control
fibrosis development
in bleomycin-induced
lung injury, which is preceded by massive
inflammation. We extended the study to test PI in TSK-1/+ mice, where skin
fibrosis develops in the absence of overt
inflammation. C57Bl/6 mice received
bleomycin intratracheally and were treated or not with PI.
Lung inflammation and
fibrosis were assessed by histology and quantification of
hydroxyproline content,
type I collagen mRNA, and
TGF-beta at Days 7, 15, and 21, respectively. Histology was used to detect skin
fibrosis in TSK-1/+mice. The chymotryptic activity of
20S proteasome was assessed in mice blood. JNK and Smad2 phosphorylation were evaluated by Western blot on lung
protein extracts. PI reduced
collagen mRNA levels in murine lung fibroblasts, without affecting their viability in vitro. In addition, PI inhibited the chymotryptic activity of
proteasome and enhanced JNK and
TGF-beta signaling in vivo. PI failed to prevent
bleomycin-induced
lung inflammation and
fibrosis and to attenuate skin
fibrosis in TSK-1/+mice. In conclusion, our results provide direct evidence that, despite promising in vitro results,
proteasome blockade may not be a strategy easily applicable to control
fibrosis development in diseases such as lung
fibrosis and scleroderma.