Aryl Hydrocarbon Receptor Ligands in Cigarette Smoke Induce Production of Interleukin-22 to Promote Pancreatic Fibrosis in Models of Chronic Pancreatitis

Abstract

BACKGROUND & AIMS Cigarette smoke has been identified as an independent risk factor for chronic pancreatitis (CP). Little is known about the mechanisms by which smoking promotes development of CP. We assessed the effects of aryl hydrocarbon receptor (AhR) ligands found in cigarette smoke on immune cell activation in humans and pancreatic fibrosis in animal models of CP. METHODS We obtained serum samples from patients with CP treated at Stanford University hospital and healthy individuals (controls) and isolated CD4+ T cells. Levels of interleukin-22 (IL22) were measured by enzyme-linked immunosorbent assay and smoking histories were collected. T cells from healthy nonsmokers and smokers were stimulated and incubated with AhR agonists (2,3,7,8-tetrachlorodibenzo-p-dioxin or benzo[a]pyrene) or antagonists and analyzed by flow cytometry. Mice were given intraperitoneal injections of caerulein or saline, with or without lipopolysaccharide, to induce CP. Some mice were given intraperitoneal injections of AhR agonists at the start of caerulein injection, with or without an antibody against IL22 (anti-IL22) starting 2 weeks after the first caerulein injection, or recombinant mouse IL22 or vehicle (control) intraperitoneally 4 weeks after the first caerulein injection. Mice were exposed to normal air or cigarette smoke for 6 h/d for 7 weeks and expression of AhR gene targets was measured. Pancreata were collected from all mice and analyzed by histology and quantitative reverse transcription polymerase chain reaction. Pancreatic stellate cells and T cells were isolated and studied using immunoblot, immunofluorescence, flow cytometry, and enzyme-linked immunosorbent analyses. RESULTS Mice given AhR agonists developed more severe pancreatic fibrosis (based on decreased pancreas size, histology, and increased expression of fibrosis-associated genes) than mice not given agonists after caerulein injection. In mice given saline instead of caerulein, AhR ligands did not induce fibrosis. Pancreatic T cells from mice given AhR agonists and caerulein were activated and expressed IL22, but not IL17 or interferon gamma. Human T cells exposed to AhR agonists up-regulated expression of IL22. In mice given anti-IL22, pancreatic fibrosis did not progress, whereas mice given recombinant IL22 had a smaller pancreas and increased fibrosis. Pancreatic stellate cells isolated from mouse and human pancreata expressed the IL22 receptor IL22RA1. Incubation of the pancreatic stellate cells with IL22 induced their expression of the extracellular matrix genes fibronectin 1 and collagen type I α1 chain, but not α2 smooth muscle actin or transforming growth factor–β. Serum samples from smokers had significantly higher levels of IL22 than those from nonsmokers. CONCLUSIONS AhR ligands found in cigarette smoke increase the severity of pancreatic fibrosis in mouse models of pancreatitis via up-regulation of IL22. This pathway might be targeted for treatment of CP and serve as a biomarker of disease.

Chronic Pancreatitis: Current Status and Challenges for Prevention and Treatment

“…Interestingly, a recent paper showed that smoking, through interaction with the aryl hydrocarbon receptor on T cells, also stimulated PaSCs to promote fibrosis through the IL-22-pathway [66]. These findings again reveal an important interplay between inflammatory cells and PaSCs in CP pathogenesis.…”

“…Other studies have reported increases in matrix metalloproteinase-9 (MMP-9) [68], tumor necrosis factor-α (TNF-α) [68], and soluble fractalkine [69]. Interestingly, IL-22 has also shown to be increased in CP patients who are smokers [66]. Thus, more studies are needed to identify, verify, and validate novel clinical biomarkers of disease activity to aid in early diagnosis of CP.…”

The Combination of Alcohol and Cigarette Smoke Induces Endoplasmic Reticulum Stress and Cell Death in Pancreatic Acinar Cells

“…28 A recent report demonstrated that AhR ligands promote fibrosis in a mouse model of chronic pancreatitis. 29 …”

“…40 In a chronic pancreatitis model, AhR activation in T cells elicited IL-22 secretion associated with promotion of the fibrotic pancreatic stellate cell phenotype. 29 Given the robust activation of AhR by smoking compounds in acinar as well as immune cells, the specific role of AhR on adaptive/inflammatory responses in different cell types participating in smoking-related pancreatic disorders deserves further investigation.…”

Cancer Manipulation of Host Physiology: Lessons from Pancreatic Cancer

“…Moreover, IL-22, a cytokine of the IL-10 family typically produced by CD4 + T cells (often together with IL-17), has been found to be secreted in response to Aryl hydrocarbon receptor (AhR) signaling and to promote tissue repair following acute pancreatitis in mice [64]. By contrast, chronic intraperitoneal administration of AhR ligands in mice with chronic pancreatitis has been shown to lead to high IL-22 production by CD4 + T cells, as well as PSC activation, in addition to exacerbated inflammation and fibrosis [65]. Interestingly, previous work examining Th17 cells in pancreatic oncogenesis also found elevated levels of IL-22 in PDAC-infiltrating CD4 + T cells, suggesting that IL-22 may be contributing to PDAC fibro-inflammatory reaction and might constitute a link between smoking and other activators of AhR signaling, chronic pancreatitis, and PDAC [60].…”