Understanding the Regulation of Epidermal Differentiation Genes by Filaggrin in Eczema

Atopic eczema is a common skin condition, affecting up to 20% of children in the UK. Eczema has a major impact on the quality of life of patients and their families, including impaired sleep, missed school days, recurrent skin infections and psychological distress. For many children, eczema persists into adulthood and is a long term, incurable condition. Current treatments for eczema are suboptimal with patients relying on intensive topical (cream or ointment based) skin treatments, which are difficult for patients to adhere to and often have no effect on severe disease. For severe disease there are a range of whole body (systemic) treatments but we don't know yet which patients will respond to what treatment. Although eczema has a very high incidence in children, it is an under-researched disease. There is a large unmet need to understand the mechanism of disease. Rather than one disease, eczema is likely to be a combination of different disease subtypes. It is important to understand these disease subtypes to enable us to recognise which patients will respond to which treatments, as this will ultimately lead to more successful and more personalised treatments.

The skin acts as a barrier, preventing bacteria, toxins and other chemicals from entering the body. The skin is also part of the immune system, as it hosts many immune cells, which respond to microorganisms that breach this barrier. It is becoming increasingly apparent that both disruption of the skin's barrier and the resulting changes in the immune system (the skin's defences against the environment and pathogens) is a key causative factor in eczema. There is a strong genetic component to eczema associated with altered skin barrier function. Mutations in the FLG gene, which codes for filaggrin, a key protein of the skin barrier, are a major predisposing factor for eczema. My preliminary work has shown that when the filaggrin levels are reduced in our laboratory disease models, the levels of other genes that code for proteins that make up the skin barrier (called the epidermal differentiation complex or EDC) are also reduced. We think that we could improve barrier function in eczema by restoring the level of EDC genes to normal.

The main aims to this study are:
1. To see if children/young adults with eczema who have reduced levels of filaggrin also have reduced expression of the other genes of the EDC
2. To understand why loss of filaggrin causes suppression of other EDC genes
3. To see if we can use small molecules and proteins to increase EDC protein levels

I will link into an ongoing project at the Royal London Hospital that aims to assess 1500 Bangladeshi children and young adults with eczema. We will obtain skin samples via tape stripping, and analyse the EDC protein levels. We will correlate the clinical assessment with our EDC analysis and filaggrin status to help identify eczema endotypes (subtypes). We will then create a biological model of eczema by growing skin cells in the laboratory. We will use this to look at how filaggrin levels interact with other proteins of the EDC, and what we could change in skin cells to increase EDC protein levels. Finally, we will see if we can increase EDC protein levels using small molecule drugs that increase filaggrin levels or small molecules that may increase levels of EDC proteins directly, and whether this can restore skin barrier function in our eczema models.

Mutations in the FLG gene which codes for the protein filaggrin are associated with the inherited disease ichthyosis vulgaris and are a major predisposing factor in eczema. FLG is a member of over 60 related genes on chromosome 1q21 called the epidermal differentiation complex, which contains genes that are critical to the barrier function of the skin. It is surprising that only FLG mutations are implicated in eczema, while none of the other genes in the EDC, including the related S100 fused genes are not. To investigate this paradox further we knocked down FLG expression in keratinocytes, and found that there was widespread reduction in EDC gene expression, including key barrier proteins such as loricrin, as well as reduction in key structural keratins 1,2 and 10. We found that BMP signalling proteins were increased in expression. I hypothesise that FLG knockdown leads to reduction in EDC gene expression and this exacerbates the barrier dysfunction in eczema, and that restoring EDC and keratin expression, even without restoring filaggrin, would restore or improve epidermal barrier function.

I will examine patient skin scale for levels of EDC genes and keratins 1,2 and 10 by a combination of western blot, mass spectrometry and qPCR and correlate this to filaggrin mutation status and filaggrin protein level to identify a disease endotype in which reduction of EDC and keratin genes occurs. I will then look at BMP signalling in our FLG knockdown keratinocytes and then determine whether restoring filaggrin levels by rapamycin treatment, or restoring normal BMP signalling can rescue both EDC and keratin expression and consequently restore epidermal barrier function.

This work should give insights into how the skin barrier is regulated in eczema and understanding how to modulate the skin barrier should lead to better treatments.

Atopic Eczema is a common and under researched skin condition, with a huge morbidity for patients. As up to 20% of children in the UK develop eczema and the prevalence in developing and low to middle income countries is increasing, the potential impact of our work is vast. In a recent e-Delphi exercise to generate a list of translational dermatology research questions that are regarded as a priority for further investigations, 6/10 of the inflammatory skin disease research questions were eczema-related. UK TREND (Translational Research Network in Dermatology) has identified the stratification of new and existing systemic treatments as a research priority.

Our project is a translational project that directly links clinical data to laboratory based genetic and protein research. It has the potential to have a significant impact on the way we manage eczema. By identifying clinical and genetic endotypes of eczema, we hope to stratify eczema patients in the clinical environment. In the near future this could be used to predict disease course (ie which patients will grow out of their eczema vs those who will have a chronic debilitating condition) and response to treatments. This will help develop personalised medicine, whereby patients will receive the most effective treatments for them as individuals, based on clinical and genetic information. This will be of great benefit to patients, as this will reduce delays to starting an effective treatment and avoid ineffective and potentially toxic treatments. This will have a financial benefit to the NHS, as it will help direct expensive biologic and systemic medications to patients who will benefit most from them. In the UK the majority of patients with eczema are managed by theirs GPs and only the most severe patients are seen in hospital, namely due to a lack of specialists and long waiting lists. This research will help identify which eczema patients will have a severe and protracted clinical course. This may lead to clinical and genetic markers that allow GPs to identify which patients should be seen by a specialist, improving referral pathways. By making eczema treatments more targeted and efficient, this research could help increase capacity in Dermatology clinics.

Understanding how the expression of proteins and genes of the EDC is altered in eczema, how they interact and how we can pharmacologically manipulate them will be of great benefit to patients. We hope that this research will lead to new targeted therapies to restore the skin's barrier function, through pharmacological manipulation of protein expression or gene therapy. This could lead to novel therapeutics for eczema. Current systemic and biologic therapies for eczema rely on suppressing components of the immune system. Targeted therapies of the skin barrier could offer an alternative targeted therapy. This would be of benefit to patients who do not respond to current conventional therapy. This would also offer a treatment that does not involve modulation of the immune system, as immunosuppressant medications can have significant side effects, including severe infections and cancer, and are contraindicated in many patient groups, such as those with a history of cancer.

Restoring skin barrier function could lead to therapeutics to prevent the development of eczema in high risk children. These treatments may also be used to prevent the development of asthma, hayfever and food allergy, as impaired skin barrier function has also been implicated in the development of these diseases. Aside from patients, the pharmaceutical industry will benefit from our research, as our research will identify novel targets for pharmaceutical modulation and drug development.