TSG-6 inhibits hypertrophic scar fibroblast proliferation by regulating IRE1 alpha/TRAF2/NF-kappa B signalling

TNF-stimulated gene (TSG-6) was reported to suppress hypertrophic scar (HS) formation in a rabbit ear model, and the overexpression of TSG-6 in human HS fibroblasts (HSFs) was found to induce their apoptotic death. The molecular basis for these findings, however, remains to be clarified. HSFs were subjected to TSG-6 treatment. Treatment with TSG-6 significantly suppressed HSF proliferation and induced them to undergo apoptosis. Moreover, TSG-6 exposure led to reductions in collagen I, collagen III, and alpha-SMA mRNA and protein levels, with a corresponding drop in proliferating cell nuclear antigen (PCNA) expression indicative of impaired proliferative activity. Endoplasmic reticulum (ER) stress was also suppressed in these HSFs as demonstrated by decreases in Bip and p-IRE1 alpha expression, downstream inositol requiring enzyme 1 alpha (IRE1 alpha) -Tumor necrosis factor receptor associated factor 2 (TRAF2) pathway signalling was inhibited and treated cells failed to induce NF-kappa B, TNF-alpha, IL-1 beta, and IL-6 expression. Overall, ER stress was found to trigger inflammatory activity in HSFs via the IRE1 alpha-TRAF2 axis, as confirmed with the specific inhibitor of IRE1 alpha STF083010. Additionally, the effects of TSG-6 on apoptosis, collagen I, collagen III, alpha-SMA, and PCNA of HSFs were reversed by the IRE1 alpha activator thapsigargin (TG). These data suggest that TSG-6 administration can effectively suppress the proliferation of HSFs in part via the inhibition of IRE1 alpha-mediated ER stress-induced inflammation (IRE1 alpha/TRAF2/NF-kappa B signalling).