Cyclooxygenase-2 is required for activated pancreatic stellate cells to respond to proinflammatory cytokines

Abstract

Cyclooxygenase-2 (COX-2) mediates various inflammatory responses and is expressed in pancreatic tissue from patients with chronic pancreatitis. To examine the role of COX-2 in chronic pancreatitis, we investigated its participation in regulating functions of pancreatic stellate cells (PSCs), using isolated rat PSCs. COX-2 was expressed in culture-activated PSCs but not in freshly isolated quiescent PSCs. TGF-β1, IL-1β, and IL-6 enhanced COX-2 expression in activated PSCs, concomitantly increasing the expression of α-smooth muscle actin (α-SMA), a parameter of PSC activation. The COX-2 inhibitor NS-398 blocked culture activation of freshly isolated quiescent PSCs. NS-398 also inhibited the enhancement of α-SMA expression by TGF-β1, IL-1β, and IL-6 in activated PSCs. These data indicate that COX-2 is required for the initiation and promotion of PSC activation. We further investigated the mechanism by which cytokines enhance COX-2 expression in PSCs. Adenovirus-mediated expression of dominant negative Smad2/3 inhibited the increase in expression of COX-2, α-SMA, and collagen-1 mediated by TGF-β1 in activated PSCs. Moreover, dominant negative Smad2/3 expression attenuated the expression of COX-2 and α-SMA enhanced by IL-1β and IL-6. Anti-TGF-β neutralizing antibody also attenuated the increase in COX-2 and α-SMA expression caused by IL-1β and IL-6. IL-6 as well as IL-1β enhanced TGF-β1 secretion from PSCs. These data indicate that Smad2/3-dependent pathway plays a central role in COX-2 induction by TGF-β1, IL-1β, and IL-6. Furthermore, IL-1β and IL-6 promote PSC activation by enhancing COX-2 expression indirectly through Smad2/3-dependent pathway by increasing TGF-β1 secretion from PSCs.