NADPH oxidase 1 mediates caerulein-induced pancreatic fibrosis in chronic pancreatitis

Inflammatory disorders of the pancreas are divided into acute (AP) and chronic (CP) forms. Both states of pancreatitis are a result of pro-inflammatory mediators, including reactive oxygen species (ROS). One of the sources of ROS is NADPH oxidase (Nox). The rodent genome encodes Nox1-4, Duox1 and Duox2. Our purpose was to assess the extent to which Nox enzymes contribute to the pathogenesis of both AP and CP using Nox-deficient mice. Using RT-PCR, Nox1 was found in both isolated mouse pancreatic acini and pancreatic stellate cells (PaSCs). Subsequently, mice with genetically deleted Nox1 were further studied and showed that the histo-morphologic characteristics of caerulein-induced CP, but not caerulein-induced AP, was ameliorated in Nox1 KO mice. We also found that the lack of Nox1 impaired caerulein-induced ROS generation in PaSCs. Using Western blotting, we found that AKT mediates the fibrotic effect of Nox1 in a mouse model of CP. We also found a decrease in phospho-ERK and p38MAPK levels in Nox1 KO mice with CP, but not with AP. Both CP-induced TGF-β up-regulation and NF-ĸB activation were impaired in pancreas from Nox1 KO mice. Western blotting indicated increases in proteins involved in fibrosis and acinar-to-ductal metaplasia in WT mice with CP. No change in those proteins were observed in Nox1 KO mice. The lack of Nox1 lowered mRNA levels of CP-induced matrix metalloproteinase MMP-9 and E-cadherin repressor Twist in PaSCs. Nox1-derived ROS in PaSCs mediate the fibrotic process of CP by activating the downstream redox-sensitive signaling pathways AKT and NF-ĸB, up-regulating MMP-9 and Twist, and producing α-smooth muscle actin and collagen I and III.