A protective effect of inflammatory bowel disease on the severity of sclerosing cholangitis

Background

Primary sclerosing cholangitis (PSC) is a chronic liver disease marked by inflammation of the bile ducts and results in the development of strictures and fibrosis. A robust clinical correlation exists between PSC and inflammatory bowel disease (IBD). At present, published data are controversial, and it is yet unclear whether IBD drives or attenuates PSC.

Methods

Mdr2-deficient mice or DDC-fed mice were used as experimental models for sclerosing cholangitis. Additionally, colitis was induced in mice with experimental sclerosing cholangitis, either through infection with Citrobacter rodentium or by feeding with DSS. Lastly, fibrosis levels were determined through FibroScan analysis in people with PSC and PSC-IBD.

Results

Using two distinct experimental models of colitis and two models of sclerosing cholangitis, we found that colitis does not aggravate liver pathology, but rather reduces liver inflammation and liver fibrosis. Likewise, people with PSC-IBD have decreased liver fibrosis compared to those with PSC alone.

Conclusions

We found evidence that intestinal inflammation attenuates liver pathology. This study serves as a basis for further research on the pathogenesis of PSC and PSC-IBD, as well as the molecular mechanism responsible for the protective effect of IBD on PSC development. This study could lead to the discovery of novel therapeutic targets for PSC.

Colitis Promotes a Pathological Condition of the Liver in the Absence of Foxp3+ Regulatory T Cells

Inflammatory bowel disease is associated with extraintestinal diseases such as primary sclerosing cholangitis in the liver. Interestingly, it is known that an imbalance between Foxp3⁺ regulatory T cells (Treg) and Th17 cells is involved in inflammatory bowel disease and also in primary sclerosing cholangitis. To explain these associations, one hypothesis is that intestinal inflammation and barrier defects promote liver disease because of the influx of bacteria and inflammatory cells to the liver. However, whether and how this is linked to the Treg and Th17 cell imbalance is unclear. To address this, we used dextran sodium sulfate (DSS) and T cell transfer colitis mouse models. We analyzed the pathological conditions of the intestine and liver on histological, cellular, and molecular levels. We observed bacterial translocation and an influx of inflammatory cells, in particular Th17 cells, to the liver during colitis. In the DSS colitis model, in which Treg were concomitantly increased in the liver, we did not observe an overt pathological condition of the liver. In contrast, the T cell-mediated colitis model, in which Treg are not abundant, was associated with marked liver inflammation and a pathological condition. Of note, upon depletion of Treg in DEREG mice, DSS colitis promotes accumulation of Th17 cells and a pathological condition of the liver. Finally, we studied immune cell migration using KAEDE mice and found that some of these cells had migrated directly from the inflamed intestine into the liver. Overall, these data indicate that colitis can promote a pathological condition of the liver and highlight an important role of Treg in controlling colitis-associated liver inflammation.

A Protective Function of IL-22BP in Ischemia Reperfusion and Acetaminophen-Induced Liver Injury

Acute liver injury can be secondary to a variety of causes, including infections, intoxication, and ischemia. All of these insults induce hepatocyte death and subsequent inflammation, which can make acute liver injury a life-threatening event. IL-22 is a dual natured cytokine which has context-dependent protective and pathogenic properties during tissue damage. Accordingly, IL-22 was shown to promote liver regeneration upon acute liver damage. However, other studies suggest pathogenic properties of IL-22 during chronic liver injury. IL-22 binding protein (IL-22BP, IL-22Ra2) is a soluble inhibitor of IL-22 that regulates IL-22 activity. However, the significance of endogenous IL-22BP in acute liver injury is unknown. We hypothesized that IL-22BP may play a role in acute liver injury. To test this hypothesis, we used Il22bp-deficient mice and murine models of acute liver damage induced by ischemia reperfusion and N-acetyl-p-aminophenol (acetaminophen) administration. We found that Il22bp-deficient mice were more susceptible to acute liver damage in both models. We used Il22 × Il22bp double-deficient mice to show that this effect is indeed due to uncontrolled IL-22 activity. We could demonstrate mechanistically increased expression of Cxcl10 by hepatocytes, and consequently increased infiltration of inflammatory CD11b+Ly6C+ monocytes into the liver in Il22bp-deficient mice upon liver damage. Accordingly, neutralization of CXCL10 reversed the increased disease susceptibility of Il22bp-deficient mice. In conclusion, our data indicate that IL-22BP plays a protective role in acute liver damage, via controlling IL-22-induced Cxcl10 expression.

Dysfunction of hepatic regulatory T cells in experimental sclerosing cholangitis is related to IL-12 signaling

BACKGROUND & AIMS

Reduced numbers of regulatory T cells (Treg) have been reported in patients with primary sclerosing cholangitis (PSC); therefore, Treg expansion might serve as a therapeutic approach. Here, we explored whether treatment with IL-2/IL-2 monoclonal antibody complex (IL-2/IL-2Ab complex) could provide in vivo Treg expansion and treatment of experimental sclerosing cholangitis.

METHODS

Treg were expanded by repeated injection of IL-2/IL-2Ab complex in mouse models of cholangitis (Mdr2^-/-, DDC) or colitis (dextran sulfate sodium [DSS]) as control. In vitro suppressive capacity and gene expression were analyzed in isolated hepatic and splenic Treg.

RESULTS

In vivo expansion resulted in a 5-fold increase in hepatic Treg, which localized within the inflamed portal tracts. However, although Treg expansion was associated with reduced pro-inflammatory IL-17 and increased anti-inflammatory IL-10 production by hepatic lymphocytes, the severity of cholangitis was not reduced. In contrast, DSS-induced colitis could be improved by Treg expansion, suggesting a selectively reduced functionality of intrahepatic Treg. Indeed, hepatic Treg manifested reduced Foxp3 expression and reduced suppressive capacity compared to splenic Treg. Hepatic Treg dysfunction could be linked to increased IL-12 signaling due to an upregulation of the IL-12 receptor. Accordingly, IL-12 receptor beta 2 knockout mice (IL-12rb2^-/-) were able to maintain hepatic Treg functionality.

CONCLUSIONS

Hepatic Treg expanded in vivo failed to improve the course of cholangitis, which was related to the effects of hepatic IL-12 on Treg. Therefore, neutralization of IL-12 should be considered as part of treatment strategies targeting Treg in sclerosing cholangitis.

LAY SUMMARY

Primary sclerosing cholangitis (PSC) is associated with a paucity of regulatory T cells (Treg) that have a particular ability to control immune responses; therefore, in vivo expansion of Treg might serve as a treatment of cholangitis. However, in a mouse model of PSC, we show that Treg enrichment in the liver was not sufficient to provide effective control of cholangitis, as the suppressive functionality of hepatic Treg was significantly limited by IL-12 signals. Thus, neutralization of IL-12 should be considered as part of treatment strategies to improve the efficacy of Treg-based treatments for liver diseases. Data accession number: GSE 87898.