Epidermolysis Bullosa

Background

Epidermolysis Bullosa (EB), or ‘butterfly skin’ disease, is a painful condition that affects the surface of the skin.

People who have EB have fragile skin that wounds easily - perhaps just from the friction of clothing or the touch of another person. Around half a million people in the world have EB, and one in 18,000 children born in Ireland is affected.

There are 30 subtypes of EB and symptoms can range in severity from mild to life limiting. EB particularly damages the epidermis, or outer layer of skin, which is there to protect us. In EB, this epidermis blisters and breaks down, and normal protection is compromised.

Wounds are not only painful, they can become infected and pose a serious threat to the health of the person. At the moment there is no cure, and people with EB are treated with wound care, specialised dressing and pain management.

Current Research

At UCD Charles Institute, Dr Wenxin Wang and his team are investigating a form of EB called recessive dystrophic epidermolysis bullosa (RDEB, OMIM ID #226600) with the view of developing gene therapy. Prof Martin Steinhoff and his team are investigating the epidemiology and pathophysiology of the problem of itch or pruritus in patients with EB.

Non-viral gene therapy approach to EB

Professor Wenxin Wang and his team are investigating a form of EB called recessive dystrophic epidermolysis bullosa (RDEB, OMIM ID #226600).

This form of EB can be caused by a variety of changes in a gene called COL7A1. The normal function of this gene is to tell the body to make a substance called type VII collagen, which attaches two layers of skin together: the epidermal basement membrane and the dermal matrix.

If COL7A1 is not working properly, as in RDEB, the skin layers are not strongly anchored and blisters can form easily. Some damage only the top layer of skin, but others can develop into chronic wounds comparable with third degree burns.

Dr Wenxin Wang and his team want to restore COL7A1 function through non-viral gene therapy. The end-goal is to have a material that can be applied topically to the skin and wounds that will deliver a working version of the COL7A1 gene to the site where it is needed and this will improve the structure of the skin, promote wound healing and protect the skin from further blistering.

Delivering the gene

In order to get a working version of the COL7A1 gene into the skin cells where it needs to function, the team are making a polymer-based vector, or carrier. Polymer-based vectors have previously been used for gene therapy and treatment of various diseases, but using them for skin tissue is a new approach.

In order to be effective, the delivery polymer needs to be non-toxic to cells. They have also designed it to be biodegradable, so it will effectively ‘disappear’ safely when its delivery job is done.

The technical description of our gene-delivery platform is a hyperbranched cationic biodegradable polymer, which is being made via one-pot in situ deactivation enhanced atom transfer radical polymerisation (DE-ATRP).

Testing gene delivery

Wang and his team have two methods of testing how well their new gene delivery polymer works - lab-grown ‘skin equivalents’ and preclinical models of RDEB.

Skin equivalents: To test whether the gene delivery system can get the therapeutic COL7A1 gene into cells in a way that it can direct the cells to make type VII collagen, they use isolated human skin cells that are grown in a gel-like matrix so that they slightly resemble the structure of human skin. These are known as skin organotypic cultures, or skin equivalents (SEs), and to make these structures they use healthy human cells and cells donated by people with RDEB.

The team have delivered the therapeutic gene COL7A1 into SEs using their polymer-based delivery system, and have seen that when the gene is delivered, then RDEB keratinocyte cells make type VII collagen.

Preclinical work: Their success with delivering the COL7A1 gene into human cells in the laboratory has given them the confidence to bring the technology forward. They are collaborating with other experienced biologists to test this delivery system in an animal model of human RDEB.

The team have used these polymers to deliver the COL7A1 gene into human skin equivalents on an animal model with some promising results; bands of type VII collagen along the basement membrane zone that remains in the skin for a significant time due to the long half-life of type VII collagen. The Wang group are currently working on assessing how safe our polymer is and how to best apply them in vivo.

Molecular mechanisms of itch in EB

Many recent publications have highlighted the problem of itch in patients with EB where the prevalence is reported to be as high as 85%. Patients have also described it as their 'most bothersome' symptom. Itch has profound effects on the quality-of-life of patients by causing distress and sleeplessness but also by contributing to the development of new skin lesions through scratching and trauma of fragile skin.

The exact pathophysiology of itch in these diseases is unclear. The Steinhoff group aim to identify and characterise the key mediators, receptors and pathways of itch in the major EB subtypes where itch is a significant symptom. By collaborating with partners in the UK, they hope that an understanding of the mechanisms involved will lead to optimised treatment algorithms capable of targeting and alleviating the distress caused by this symptom in patients with EB.

In particular, their human study focusing on identifying the key itch pathway(s) important in EB in vivo and ex vivo is the first-of-its-kind and represents an essential first step towards the development of mechanism-based, subtype-oriented therapies in EB.