Stat2 is a therapeutic target in liver inflammation

The number of patients dying from liver disease is rising faster than those from any other cause of death in the UK, with mortality rates increasing 400% since 1970. In the UK, alcoholic and non-alcoholic fatty liver diseases (ALD and NAFLD respectively), and viral infections are the common causes of chronic liver injury, which can lead to cirrhosis, cancer and liver failure. The mechanisms that govern this progression are not fully understood, but inflammation is a key early event and is common to the broad range of causes of liver disease. Inflammation is the principal cause of deterioration in patients with chronic liver disease (acute-on-chronic liver failure) and a key feature of acute liver failure.

The only treatment currently available is organ transplantation for a select few who have reached end stage disease and are eligible for this high risk and costly procedure and supportive care for those who are not. For those who have not yet reached end-stage disease, lifestyle and behaviour modification represent the cornerstone of management, but such changes are notoriously difficult to implement and the benefits even harder to maintain. Various strategies have therefore been pursued to prevent progression, but targeting the determining step in the development of liver disease - inflammation - has received little attention so far.

Inflammation involves a series of chemical reactions that results in production of special substance in injured tissues, such as the liver, and their release into the bloodstream. These substances cause white cells to leave the bloodstream and enter injured tissue to begin the healing process. When healing fails or becomes uncontrolled, chronic disease takes hold and in the liver, scarring and cirrhosis ensue. This work aims to understand this process in the liver and builds on Alazawi and colleagues' published work that has identified Stat2 as a key controller of inflammation. Although the protein has been known about for some time, this group is the first to discover its pivotal role in the major chemical reactions that lead to inflammation.

This project builds on the early discovery that the Stat2 protein is an important substance in liver inflammation. It is present at low levels in healthy liver tissue that is not inflamed and is highly expressed in liver tissue from patients with the inflammatory form of NAFLD - non-alcoholic steatohepatitis (NASH). The project will use cutting edge techniques to better understand the role of Stat2 in liver inflammation using established models of liver injury. The researchers aim to understand the key cells in which Stat2 plays its pivotal role and determine the consequences of inhibiting Stat2 loss in these cells. The overall aim of the project is to test the hypothesis that targeting drugs against Stat2 (or the genes and proteins it acts on) can be used to treat liver inflammation. The project will use a relatively new technology to 'silence' genes so that the proteins they encode are no longer made in specific cells to reduce the expression of Stat2 in the liver in experimental models. It is hoped that the work completed in this project will be translated into treatment strategies for patients with inflammatory liver disease.

The number of patients dying from liver disease is rising faster than any other cause of illness or death in the UK, with mortality rates increasing 400% since 1970. Inflammation is a key early event and is common to the broad range of causes of liver disease. However, there are currently no drugs licensed for use in liver disease that target inflammation. The PI's recent work demonstrates a novel and unexpected role for Stat2 in governing outcome from inflammation caused by activation of pattern recognition receptors. Preliminary, unpublished data strongly indicate a role for Stat2 in liver inflammation. STAT2 is upregulated in human liver disease and Stat2 loss protects from acute and chronic inflammation caused by carbon tetrachloride in mouse models. The overall aim of this project is to devise therapeutic strategies based on the mechanisms of Stat2-mediated liver injury, using histology, biochemistry and cytokine/chemokine production as endpoints. Our objectives are
1.To determine the tissue compartment and cell type in which Stat2 acts as an inflammatory mediator. The effects of Stat2 deficiency in circulating versus stromal compartments will be assessed in bone-marrow chimera. The main cell types in which Stat2 is expressed will be identified using double-labelled immunohistochemistry and targeted in conditional (floxed) Stat2 knockouts. The effect of Stat2 deficiency on the composition of the host microbiome and its impact on liver injury will be assessed.
2.To determine the downstream mediators and signaling mechanisms for Stat2-mediated liver injury. Based on preliminary data, we will test 3 hypotheses: (a) Stat2 acts as a type I interferon signaling molecule, (b) Stat2 modulates NF-kB-mediated cytokine production and (c) Stat2 modulates cellular migration into injured liver tissue.
3.To devise therapeutic strategies to treat hepatic inflammation based on silencing Stat2 or its the downstream targets using nanoparticle-based siRNA technology.

Inflammatory liver diseases such as those caused by alcoholic and non-alcoholic fatty liver disease (ALD and NAFLD respectively) are major public health problems worldwide. As the problems of alcohol and obesity impact more and more sectors of society, a significant number of non-governmental organisations and charities have set as their goals the reduction of the disease burden from these conditions. The number of liver-related deaths in the UK rose by 25% between 2001 and 2009 (a time when other causes of death have been falling) with over 60% of these deaths in people under the age of 50. It has been estimated that alcohol and obesity cost the UK NHS £7 billion annually and this disease burden has recently been highlighted by the Lancet Commission. Much work and resource have targeted the causes of these diseases, however such public health measures will take many years to impact on the burden of established liver disease in the population. There are currently no drugs licensed for the treatment of inflammatory liver diseases, therefore the cornerstone of treatment is behavior and lifestyle change, but adherence to such changes is limited and effect on long term outcomes has not been demonstrated. Therefore there is a large unmet clinical need for drugs to target the pathogenic processes that drive inflammatory liver diseases.

The findings from this research will impact upon a range of stakeholders including patients, healthcare professionals and healthcare providers. The attached Pathways to Impact document outlines planned academic, public engagement and education activities. It is likely that there will be commercial exploitation opportunities for the body that funds the research and the PI's experience with this process will help early identification of such opportunities. The project brings to bear novel experimental and therapeutic approaches, using cutting edge in vivo siRNA and nanoparticle technology. The experience of refining and adapting these techniques in a model of human disease will inform future projects in a broad range of disciplines. Furthermore, the strategy to study the mechanisms of inflammation beyond the effect of Stat2 in the liver will identify alternative potential therapeutic targets. Whether new treatments are based on Stat2 itself or on these alternatives, strong partnerships with all the stakeholders, including industry, will be required to develop these targets rapidly and to take them back into the clinic.