Beneficial effects on weight gain, hepatic steatosis and expression of lipogenic target genes in a murine obesity model after IL-1 type cytokine inactivation

Background:

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease worldwide and its prevalence is still increasing. NAFLD affects up to one fourth of the normal population and 50 – 75% of these patients are also suffering from obesity or type II diabetes. Although the pathogenesis is yet poorly understood recent studies show that inflammatory cytokines and especially IL-1 alpha and beta play a crucial role in the development of the disease. The overall purpose of this project is to clarify the pathophysiological effect of IL-1 in hepatic lipid accumulation and to assess the suitability of cytokine intervention as a therapeutic target for NAFLD.

Methods:

C57BL6 mice were subcutaneously treated with virus-like particles presenting antigens of IL-1 alpha or beta (Cytos Biotechnology) on their surfaces to overcome the immune system tolerance for self antigens efficiently. Robust anti-IL-1α and anti-IL-1β auto-antibody responses were assessed by ELISA. At w14 mice were fed a high fat/high sucrose diet (HFSD) and were sacrificed at w20. Frozen liver sections were stained with H&E and Sudan III to assess fat accumulation, ballooning and inflammation. Triglycerides were measured by TG assay. Expression patterns of genes involved in bile acid and cholesterol metabolism, lipogenic enzymes, nuclear receptors and several immunologic markers were analysed on mRNA- and protein- level via rt-PCR, Western Blotting and immunohistochemistry.

Results:

Mice vaccinated against Il-1alpha, Il-1beta or both previous to HFSD displayed a significant reduction of body weight gain in comparison with control mice on the same diet. Macroscopic and microscopic analysis of liver tissue showed hepatic steatosis with significant reduction of lipid accumulation by Il-1alpha and Il-1beta with most prominent effects in the combination group. Triglyceride measurement confirms this reduction. Induction of lipogenic enzyme expression (FASN, SCD-1, ACC, ELOVL6) was down regulated upon biological IL-1 inactivation. Simultaneously, expression of IL-1 signalling molecules such as MyD88 and Nfκb (p105) was reduced.

Conclusion:

IL-1beta has been previously shown to mediate chronic inflammation and fibrogenesis in NAFLD. Our study in the HFSD model now shows that biological inactivation of Il-1alpha and Il-1beta affects weight gain and hepatic lipid accumulation thereby exerting further favourable metabolic effects beyond inflammation and fibrogenesis. Mechanistically both cytokines down regulate lipogenic target genes in fatty livers. Our data further highlight the role of Il-1alpha and Il-1beta in the pathogenesis of NAFLD and support further studies in clinical application.