Defining functional impacts of macrophages in the formation of surgical adhesions

In this project, we will discover new medical treatments to prevent the formation of internal scars, or 'surgical adhesions'.

People often have to undergo operations which involves opening up their abdomen, for example to remove a tumour or take out an inflamed appendix. A common complication after these operations is the development of adhesions or scars which cause organs such as your intestine to be stuck to the wall of the abdomen. These adhesions are painful and can even cause the bowel to become twisted and blocked and therefore stop working. This then requires a major operation to put things right. Unfortunately, these second operations themselves can lead to more adhesions. Because there are currently no good treatments to stop these scars forming we need to better understand how these adhesions form in order to develop methods that surgeons can use to prevent the process happening. Any new ways to prevent adhesions forming would have enormous benefit for a large number of people.

Macrophages, a type of inflammatory cell, known to be important in scar formation in other conditions, has not been carefully investigated with regard to surgical adhesions. There are several types of macrophages but which ones cause adhesions to form and which ones promote healthy repair are not known. From other tissues, we have evidence that a receptor on the macrophage is important for this process of repair versus scar formation but what role it plays in adhesion formation is unknown. We will work out how cells inside the abdomen form scars after operations and then use this knowledge to help find better ways to block the process.

So, our main aims are to:
1. Find the different types of macrophages that occur inside the abdomen following surgery.
2. Remove each type of macrophage before surgery to see if they help adhesion formation or help with normal healing.
3. Work out how these macrophages instruct repair cells in the abdomen to make adhesions instead of healing the surgical wound.

The results of our project will pave the way for new treatments to prevent crippling adhesions in people who have to undergo surgery.

We hypothesise that specific macrophage subpopulations (resident vs recruited) and IL4/13 receptor signalling are critical players in modulating adhesion formation. Macrophages play a crucial role in orchestrating effective tissue repair and display a dynamic switch in phenotype during this process, with IL4 and IL13 as essential switch factors. Critically, dysregulation in the recruitment, local expansion and IL4Ralpha activation of macrophages is strongly implicated in tissue fibrosis.
Our project comprises three technical objectives:
1. To define the macrophage subpopulations involved in adhesion formation we will use a robust mouse surgical model that generates adhesions which phenocopy the human disease scenario. Furthermore, we will use mouse strains with different susceptibilities to adhesion development. Combining this approach with macrophage depletion protocols and specific gene-deficient mice that show an altered macrophage recruitment profile, we will define the possible contribution of these cells to a fibrotic outcome post-surgery.
2. Having defined the major macrophage subpopulations involved, we will specifically address the contribution of IL4/IL13 in adhesion formation in mice lacking IL4Ralpha. Next, we will limit receptor deficiency to just myeloid cells or tissue resident stromal cells using radiation chimeras. This restricted receptor approach will allow us to unravel which cell type requires IL4Ralpha signalling for adhesion formation and/or healthy repair.
3. To gain a mechanistic insight to the interplay between distinct macrophage subpopulations and peritoneal stromal cells, we will exploit our expertise in peritoneal cell biology and use a 3D co-culture adhesion model and induce peritoneal fibrosis in specific macrophage gene-deficient mice.

Our experimental strategy will not only illuminate the pathobiology of adhesion formation, but also identify novel biological therapies to prevent adhesions forming post-surgery.

Scientific research impact. The basic science behind surgical adhesion formation has been a neglected research field, especially bearing in mind the scale of human morbidity and economic burden associated with the condition. Excitingly, however, an explosion in knowledge and understanding of macrophage biology and their contribution to normal tissue repair and the development of fibrosis has stimulated the need to identify their contribution to adhesion formation. In particular, the heterogeneity of peritoneal macrophage subpopulations and their differential response to inflammatory insults is only now just being realised in other systems such as skin and lung repair. Hence our project is extremely timely and significantly combines the expertise of world leading macrophage immunologists with internationally recognised mesothelial cell biologists underpinned by a massive surgical problem, adhesions. Due to its broad scope, our findings will be of direct relevance to groups with an interest in complex wounds and organ fibrosis as well as clinical teams including surgeons, gynaecologists, and veterinary surgeons. Such a wide ranging network will generate new collaborations and novel innovation raising the profile of the UK R&D capabilities.
Novel technology and translational impact. Findings from this proposal have the potential to identify novel therapies to change the sequence of events that lead to adhesion formation and allow peritoneal regeneration without scarring. They may also reveal the opportunity to piggy back on therapies already under development. For example, macrophage depletion as a therapeutic approach is a growing research area but with the awareness that specific subpopulations need to be targeted to generate a desired outcome. Thus therapies developed for other disorders such as cancer may be applied to adhesions. Biologics that block IL4 and IL13 are already in the clinic and these may prove useful. Alternatively, our findings may suggest that reagents which promote the IL4Ralpha pathway should be developed, an approach already considered for conditions in which accelerated repair would be beneficial. Such therapies will not only translate to patients but also to large animals in particular, horses and cows. Developing a 3D in vitro adhesion model incorporating defined subpopulations of macrophages will be innovative and sharing this new technology with the wider scientific community will be of immediate value. Furthermore, such platform technology sets the stage for the generation of human equivalent in vitro adhesion models resulting in a pipeline of physiologically relevant models that will be of great interest to a number of stakeholders. The model is easily experimentally manipulated and can be scaled up for high throughput screening hence have a huge impact in both academia and industry. Importantly, it will reduce the number of animal studies (3Rs) and may be adapted to address related diseases such as peritonitis by including gut flora and peritoneal metastasis with tumour cells.
Societal and health impact. Surgical adhesions and their associated complications such as severe chronic pain, bowel obstruction and infertility in women, represent a huge health problem world-wide. Surgery is the only way to detect and treat already formed adhesions but surgery itself also causes adhesions. The cost of adhesion-related complications for the NHS is an estimated £152 million each year. At present there are no pharmacological ways of preventing adhesion formation, and current physical therapies such as degradable membranes, fluids and gel barriers, show limited efficacy. Any advance in developing efficient anti-adhesion therapies would have enormous consequences for many surgical specialities. Furthermore, because adhesions are associated with other pathologies such as endometriosis, and cancer-, radiation-, infection, our findings will potentially have widespread benefits for a huge number of patients.