AIM:To investigate whether targeting proteasome might reverse intestinal fibrosis in rats.METHODS:Chronic colitis was induced in rats by repeated administration of increasing dose of2,4,6-trinitrobenzene sulfonic acid(TNBS,15,30,45,60,60,60 mg)by rectal injection for 6 wk(from day0 to day 35),while control rats received the vehicle.TNBS+bortezomib(BTZ)rats received intraperitoneal injections of BTZ twice weekly(from day 37 to day44)at a dose of 25 mg/kg,whereas the control and TNBS groups received the same amount of the vehicle.Histologic scoring of inflammation and fibrosis was performed.Colonic production of transforming growth factor(TGF)-βwas measured by ELISA.Colon fibrosisrelated proteins such as phospho-p38,phosphoSMAD2/3,Akt and peroxisome proliferator activated receptorγ(PPARγ)were studied by western blot.Expression of the tight junction proteins,occludin and claudin-1,were assessed by Western blot.Colon proteasome activities(chymotrypsin-like and trypsinlike activities)were assessed.RESULTS:TNBS-treated rats had a higher colon weight/length ratio compared to control rats(P<0.01).Furthermore,fibrosis and inflammation scores were higher in TNBS-treated rats compared to control rats(P<0.01 for both).Colonic production of TGF-βproduction tended to be higher in TNBS-treated rats(P<0.06).Fibrosis-related proteins such as phospho-p38,phospho-SMAD2/3,and PPARγwere significantly higher in TNBS-treated rats compared to control rats(all P<0.05).TNBS rats had a higher expression of Akt compared to control rats(P<0.01).Tight junction proteins were modified by repeated TNBS challenge:colon occludin expression rose significantly(P<0.01),whereas claudin-1 expression fell(P<0.01).Bortezomib inhibition significantly decreased chymotrypsin-like activity(P<0.05),but had no significant effect on trypsin-like activity(P>0.05).In contrast,bortezomib had no effect on other studied parameters such as fibrosis score,TGF-βsignaling,or tight junction expression(P>0.05 for all).CONCLUSION:Rats with TNBS-induced chronic colitis exhibited colon fibrosis associated with higher TGF-βsignaling.Proteasome inhibition by bortezomib had no effect on fibrosis in our experimental conditions. AIM: To investigate whether targeting proteasome might reverse intestinal fibrosis in rats. METHODS: Chronic colitis was induced in rats by repeated administration of increasing dose of 2,4,6-trinitrobenzene sulfonic acid (TNBS, 15, 30, 45, 60, 60, 60 mg) by rectal injection for 6 wk from day 0 to day 35 while control rats received the vehicle. TNBS + bortezomib (BTZ) rats received intraperitoneal injections of BTZ twice weekly from day 37 to day 44 at a dose of 25 mg / kg, while the control and TNBS groups received the same amount of the vehicle. Histologic scoring of inflammation and fibrosis was performed. Colonial production of transforming growth factor (TGF) -β was measured by ELISA. Colon fibrosisrelated proteins such as phospho-p38 , phosphoSMAD2 / 3, Akt and peroxisome proliferator activated receptor gamma (PPARγ) were studied by western blot. Expression of the tight junction proteins, occludin and claudin-1, were assessed by Western blot. Colnomc proteasome activities (chymotrypsin-like and trypsinlike activities) wer F assessed by TNBS-treated rats with a higher colon weight / length ratio compared to control rats (P <0.01 for both ) .Colonic production of TGF-β production tended to be higher in TNBS-treated rats (P <0.06). Fibrosis-related proteins such as phospho-p38, phospho-SMAD2 / 3, and PPARγwere significantly higher in TNBS-treated rats compared to (all P <0.05) .TNB rats had a higher expression of Akt compared to control rats (P <0.01) .Tight junction proteins were modified by repeated TNBS challenge: colon occludin expression rose significantly (P <0.01), while claudin -1 expression fell (P <0.01) .Bortezomib inhibition significantly decreased chymotrypsin-like activity (P <0.05), but had no significant effect on trypsin-like activity (P> 0.05) .In contrast, bortezomib had no effect on other studied parameters such as fibrosis score, TGF-β signaling, or tight junction expression (P> 0.05 for all). CONCLUSION: Rats with TNBS-induced chronic colitis exhibited colon fibrosis associated with higher TGF-β signaling. Proteasome inhibition by bortezomib had no effect on fibrosis in our experimental conditions.