Characterization of cellular and tissue chronic inflammation in Recessive Dystrophic Epidermolysis Bullosa (McGrath16 + Ext)

What did this project achieve?

Two of the most significant problems for people with RDEB are chronic wounds that scar and an increased risk of skin cancer. We know that these may be associated with chronic inflammation in the skin but we don’t know the best way to stop these events happening. This study looked at the different types of inflammatory cells and molecules in the skin and blood of people with RDEB and how these cause inflammation and the subsequent clinical complications. We took samples of RDEB skin from the edge of persistent wounds to see which genes and inflammatory cells are present in incorrect amounts as compared to unwounded skin from the same person and skin from control individuals without EB. We also tested blood from the same people to measure the activity of inflammation-associated molecules and the pattern of inflammatory cells in the circulation. This may help us work out how chronic inflammation leads to scarring in EB and the increased cancer risk as well as giving us clues (‘markers’) to improve how we monitor the skin before any complications occur and how we might develop new treatments that alter the activity and clinical course of RDEB.

We initially used genetic studies to look at the gene fingerprint of chronically wounded RDEB skin. More than 1200 differences were noted compared to the unwounded skin. Of note, we found significantly elevated levels of three matrix metalloproteinases (MMPs) called MMP-11, MMP-2 and MMP-9. These are enzymes that break down fibres and proteins in the skin and they are known to be involved in wound healing. However, they also play a role in the development and progression of some cancers. Little is known about MMPs in RDEB and so this merits further study. We could show in the laboratory that inhibiting MMPs in the test tube had a positive effect on slowing down the movement of RDEB cells. These findings provide encouragement for further research that might lead to people with RDEB taking a tablet to neutralize some MMPs to reduce skin inflammation – but the problem at the moment is that the available drugs that might do this have significant side effects and may not be specific enough to help the skin. However, we will now be monitoring these MMPs in people with RDEB to see how changes in their levels mirror changes in the skin over time.

The study then went on to assess the levels of immune cells in the skin and blood of patients with chronic wounds. We found elevated levels of immune cells called T-lymphocytes, which are often elevated in skin conditions such as eczema and psoriasis. We were expecting to see higher levels of a molecule called TNF-alpha in RDEB skin as it is often seen in skin inflammation, but this was not the case. This finding indicates that the inflammation in RDEB skin is somewhat different from other skin diseases. It is a useful negative finding, however, because some doctors have been considering using new anti-TNF-alpha drugs to treat RDEB – because these are available to prescribe and they do help other inflammatory skin conditions – although they can have a number of side-effects. Our research indicates these drugs are unlikely to be helpful in RDEB. Thus our work may have prevented unnecessary clinical trials for a class of drugs that would not have helped people with RDEB. 

More positively, we did find significantly elevated levels of another molecule called IL (interleukin)-17 in RDEB wounds and also in blood taken from RDEB patients when compared to control patients. IL-17 is another pro-inflammatory molecule that has gained a lot of interest recently, as an imbalance of IL-17 and its related molecules seems to predispose some people to psoriasis. Importantly, specific anti-IL-17 antibody treatment improves psoriasis in clinical trials. Furthermore, IL-17 has also been shown to contribute to both chronic inflammation and some cancers, although the role that IL-17 plays in cancers and tumours is not fully understood. We stained archival skin biopsy sections of RDEB wounds and cancers for IL-17 and found increased staining in both sets of tissues, particularly RDEB-SCC when compared to staining normal tissues. This data tells us that IL-17 may be a key part of the excessive inflammatory response seen in RDEB – and poses the question whether anit-IL-17 treatments might also benefit people living with RDEB. This is something we will follow up in future studies.

Another intriguing point about IL-17 is that some studies have suggested that IL-17 may in fact promote cancer growth by increasing the MMPs. This information, therefore, provides a link between the two sets of findings in this study – increased MMPs and increased IL-17. We designed experiments to look at the effects of IL-17 on the three MMPs in question in RDEB fibroblasts and found that IL-17 treatment increases levels of all three MMPs; we are currently planning more studies exploring these pathways.

Taken together, the experiments have highlighted several MMPs and IL-17 as potential markers that may be useful in the surveillance of chronic RDEB wounds. No studies have previously reported the role of these molecules in EB thus this work offers new, thought-provoking insights for functional studies and novel routes for therapeutic approaches.