CD44 expression on murine hepatic stellate cells promotes the induction of monocytic and polymorphonuclear myeloid-derived suppressor cells.

In chronic inflammation regulatory immune cells, such as regulatory T cells and myeloid-derived suppressor cells (MDCS) can develop. Local signals in the inflamed tissue, such as cytokines and eicosanoids, but also contact dependent signals, can promote MDSC development. In the liver, hepatic stellate cells (HSC) may provide such signals via the expression of CD44. MDSC generated in the presence of HSC and anti-CD44 antibodies were functionally and phenotypically analyzed. We found that both monocytic (M-) and polymorphonuclear (PMN-) MDSC generated in the presence of αCD44 antibodies were less suppressive towards T cells as measured by T cell proliferation and cytokine production. Moreover, both M- and PMN- MDSC were phenotypically altered. M-MDSC mainly changed their expression of CD80 and CD39, PMN-MDSC showed altered expression of CD80/86, PD-L1 and CCR2. Moreover, both PMN- and M-MDSC lost expression of Nos2 mRNA, whereas M-MDSC showed reduced expression of TGFb mRNA and PMN-MDSC reduced expression of Il10 mRNA. In summary, the presence of CD44 on hepatic stellate cells promotes the induction of both M- and PMN-MDSC, although the mechanisms by which these MDSC may increase suppressive function due to interaction with CD44 is only partially overlapping.

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.

Chronic liver inflammation modifies DNA methylation at the precancerous stage of murine hepatocarcinogenesis.

Chronic liver inflammation precedes the majority of hepatocellular carcinomas (HCC). Here, we explore the connection between chronic inflammation and DNA methylation in the liver at the late precancerous stages of HCC development in Mdr2(-/-) (Mdr2/Abcb4-knockout) mice, a model of inflammation-mediated HCC. Using methylated DNA immunoprecipitation followed by hybridization with "CpG islands" (CGIs) microarrays, we found specific CGIs in 76 genes which were hypermethylated in the Mdr2(-/-) liver compared to age-matched healthy controls. The observed hypermethylation resulted mainly from an age-dependent decrease of methylation of the specific CGIs in control livers with no decrease in mutant mice. Chronic inflammation did not change global levels of DNA methylation in Mdr2(-/-) liver, but caused a 2-fold decrease of the global 5-hydroxymethylcytosine level in mutants compared to controls. Liver cell fractionation revealed, that the relative hypermethylation of specific CGIs in Mdr2(-/-) livers affected either hepatocyte, or non-hepatocyte, or both fractions without a correlation between changes of gene methylation and expression. Our findings demonstrate that chronic liver inflammation causes hypermethylation of specific CGIs, which may affect both hepatocytes and non-hepatocyte liver cells. These changes may serve as useful markers of an increased regenerative activity and of a late precancerous stage in the chronically inflamed liver.

Inhibition of heme oxygenase 1 expression by small interfering RNA decreases orthotopic tumor growth in livers of mice.

Endogenous overexpression of the antiapoptotic protein heme oxygenase 1 (HO-1) has been shown to occur in various cancer diseases and might contribute to cancer progression. We compared the expression levels of HO-1 in human liver to expression levels in hepatocellular carcinoma (HCC), as well as the effect of HO-1 inhibition by small interfering RNA (siRNA) on cellular survival and apoptosis in the mouse hepatoma cell lines Hepa129 and Hepa1-6 and on orthotopic tumor growth in immune-competent C3H/HeN mice. Our results show that HO-1 is frequently overexpressed in human HCC. Downmodulation of HO-1 by siRNA resulted in increased cellular damage and apoptosis, reduced proliferation, reduced growth of orthotopic HCC and reduced angiogenesis. Livers and kidneys of treated animals did not reveal signs of damage by this treatment. In conclusion, a specific knockdown of HO-1 might represent a novel therapeutic approach in HCC therapy.