Defining The Macrophage-Regulatory T Cell Axis That Promotes Fibrosis Resolution in the Liver

Virtually all long term liver disease, including inborn errors of metabolism and diseases where the immune system attacks the liver through metabolic diseases associated with diabetes, result in scarring of the liver (termed fibrosis) and ultimately advanced scarring (termed cirrhosis). As a result liver scarring is now a common cause of death in the UK and the western world. Indeed, it has been estimated that up to 45% of deaths in the west are the result either directly or indirectly of tissue scarring, including that which occurs in the liver. Previously believed to be irreversible, our laboratory has demonstrated that the scar within the liver is dynamic and, in certain circumstances, is susceptible to break down with a return of a more normal liver architecture and more normal liver function. Critical to this change is a cell called the macrophage. Although the macrophage has been known to promote inflammation and to drive the development of scarring for many years, recently we and others have demonstrated that it is also critical to the breakdown of scar tissue by producing the chemicals which degrade the scar. If we could harness this macrophage function, we would have identified a novel therapeutic approach to the treatment of liver and potentially tissue scarring generically. This application describes a programme of work to further understand what drives the macrophage to become scar degrading and therefore valuable as a therapy. We will study the interaction of the macrophage with another key immune cell type -the regulatory T-cells, which are likely to be important in terminating inflammation and creating the conditions in which resolution of scarring can occur. This work is particularly exciting as, for the first time we will be looking at the cell and molecular "switch" which changes an inflammatory damaging process to one in which remodelling and a return of normal function can take place. We know remarkably little about this switch and yet by piecing together the molecular mechanisms we may open the door to new therapies applicable not just to scarring, but to other disease processes in which inflammation is prominent and damaging. Finally, we will look at a signalling axis within the macrophage for which there are already licensed drugs and which may be amenable to manipulation to achieve our desired tool, the scar degrading macrophage. If we are able to show that existing drugs (currently used for an alternative indication) can drive the macrophages to degrade scars, then these drugs could rapidly come to clinical trials as the important asessments of their effects and side effects are already known, defined as safe and in consequence the drugs are fully licensed.

Liver fibrosis represents the final common pathway of all chronic liver disease. We have identified that post phagocytic Ly6Cint hepatic macrophages, restorative macrophages (RMo) are essential for the resolution of fibrosis expressing both matrix degrading MMPs 9 and 12 and the hepatic mitogens, TWEAK and IGF-I. Our pilot studies show CD25 Foxp3 Tregs are also essential for fibrosis resolution. We will interrogate the Treg-RMo interaction to investigate the hypothesis that inflammatory macrophages promote the local accumulation of Treg. On withdrawal of the inflammatory stimulus these then create a "critical niche" that promotes the development of the RMo programme and, ultimately, remodelling of fibrosis with matrix degradation and architectural restoration. Using gene knockout and transgenic mice in which Tregs and RMo can be specifically depleted; we will use our CCl4 based model of fibrosis resolution in which individual cell populations can be tracked and where necessary extracted from fibrotic liver. These populations can be characterised and mapped to position and activity/function in situ histologically and in vitro after extraction. In turn these populations can be related to whole organ histology during distinct and predictable stages of fibrogenesis and fibrosis resolution. We will characterise the behavioural interactions of Treg and RMo and the mechanisms by which the antifibrotic Treg is recruited (by inflammatory macrophages) and executes its mode of action (via the RMo). Specific attributes of the RMo (upregulation of MMPs 9, 12, TWEAK and IGF-I) may be augmented by phagocytic activity. We will study the role of phagocytosis of apoptotic debris in the development of the RMo. By manipulating macrophage phagocytic activity and consequent cell signalling we will augment the RMo phenotype and enhance resolution of experimental fibrosis in tissue culture and in vivo models; with specific focus on PPARg signalling as a classic drugable target.

Strategic Importance:
The calculated burden of inflammatory disease in Western nations will mean that 45% of deaths are contributed to, or caused by, fibrosis. There is a huge strategic imperative to develop effective antifibrotic strategies. Our research therefore addresses a key area of unmet clinical need and has the potential to translate to clear patient, family and societal benefits and fits with the MRC's mission and strategic objectives.

Who benefits:
We have a strong track record in capitalising on our data to provide palpable benefits to colleagues (see academic benificiaries) and patients. Developing out of Iredale's work in the last 10 years have been: the development of serum markers for liver fibrosis (marketed by iQur and Prometheus);robust models of hepatocyte development from HuESC and iPSC (leading directly to the Edinburgh spinout Fibromed); the identification of relaxin as a potential antifibrotic target (a direct development from activities in Iredales current and previous MRC Programme/Fellowship funding) now in Phase I clinical trial with Novartis. We anticipate therefore beneficiaries will be:

Patients of all age groups who are seeking treatment for liver fibrosis and cirrhosis and potentially those with fibrosis in other organs. As significant numbers of patients with fibrosis and cirrhosis are under 65 there will be a disproportionate positive impact on families/carers and employers, costs saved and significant societal impact.

Patients' families: liver fibrosis has a huge impact on wellbeing and family/social roles. Fibrotic liver diseases affect all age groups from paediatric (inborn areas of metabolism/developmental anomalies) through to those who are retired, but the majority of deaths from cirrhosis occur in the economically active wage earning age group. Furthermore, in the absence of an effective antifibrotic therapy, the only long term solution to end stage fibrosis is organ transplantation, a procedure associated with life long costs and potential morbidity, and currently there are insufficient numbers of organs available for all potential recipients - a demographic which will inexorably worsen.

Employers: fibrosis and cirrhosis have a major impact on the employment capacity of patients, not just through absenteeism (due to illness) but arguably in the case of presenteeism when an individual works, but chronic disease, affects performance/productivity.

The NHS budget: curtailing costs and consultation rates at general practices, clinics and major impact on secondary and tertiary healthcare as a result of the impact of chronic liver disease would result, whether supported from the perspective of symptomatic treatment and treatment of complications or ultimately impacting on the need for transplantation.

Clinicians: currently fibrosis is considered intractable to treat. This dogma has been directly and successfully challenged by the work of Iredale and Forbes amongst others. By demonstrating that fibrosis is dynamic and potentially reversible the PIs have contributed to a renewed interest from Pharma in the development of antifibrotic or pro-resolution treatments. Such developments would be widely welcomed by clinicians involved in the treatment of patients with liver disorders.

Research Community: Our research will benefit the research community; our data will not simply dissect the key events underpinning resolution of fibrosis but will likely identify novel biology with respect to the function macrophages and T-cells. Such observations may well prove common to Treg and macrophage function in tissue other than the liver.

Industry: data generated from our proposal along with our extensive expertise in the field will be crucial for our aim to continue to partner with spinouts, small and big pharma to move to potential commercialisation (see comments on track record above).