Autocrine loop between TGF-β1 and IL-1β through Smad3- and ERK-dependent pathways in rat pancreatic stellate cells

Abstract

Pancreatic stellate cells (PSCs) are activated during pancreatitis and promote pancreatic fibrosis by producing and secreting ECMs such as collagen and fibronectin. IL-1β has been assumed to participate in pancreatic fibrosis by activating PSCs. Activated PSCs secrete various cytokines that regulate PSC function. In this study, we have examined IL-1β secretion from culture-activated PSCs as well as its regulatory mechanism. RT-PCR and ELISA have demonstrated that PSCs express IL-1β mRNA and secrete IL-1β peptide. Inhibition of TGF-β1 activity secreted from PSCs by TGF-β1-neutralizing antibody attenuated IL-1β secretion from PSCs. Exogenous TGF-β1 increased IL-1β expression and secretion by PSCs in a dose-dependent manner. Adenovirus-mediated expression of dominant-negative (dn)Smad2/3 expression reduced both basal and TGF-β1-stimulated IL-1β expression and secretion by PSCs. Coexpression of Smad3 with dnSmad2/3 restored IL-1β expression and secretion by PSCs, which were attenuated by dnSmad2/3 expression. In contrast, coexpression of Smad2 with dnSmad2/3 did not alter them. Furthermore, inhibition of IL-1β activity secreted from PSCs by IL-1β-neutralizing antibody attenuated TGF-β1 secretion from PSCs. Exogenous IL-1β enhanced TGF-β1 expression and secretion by PSCs. IL-1β activated ERK, and PD-98059, a MEK1 inhibitor, blocked IL-1β enhancement of TGF-β1 expression and secretion by PSCs. We propose that an autocrine loop exists between TGF-β1 and IL-1β in activated PSCs through Smad3- and ERK-dependent pathways.