SkinDev

Rare genetic skin diseases, i.e. skin diseases with a frequency of below 5 in 10,000 people, are not well understood. Even worse, effective therapies for these diseases are missing. In recent years new genetic technologies have been developed there were very successful to identify causes for such diseases, namely mutations in certain genes that cause monogenic (single-gene) diseases. These achievements resulted in a much better understanding of the molecular basis of these diseases, however, in most cases they did not yet lead to the development of new therapies. A major problem in the development of therapies is the lack of suitable models: any new drugs have to be tested in various model systems, such as cells, artificial organs or animals that show certain characteristics of the human disease. The major goal of the project was the development of innovative cellular models and the study of disease mechanisms in these models and corresponding animal models. The best suitable cellular model for the disease comes from the patient himself/herself: If skin cells, i.e. keratinocytes and other cell types, were cultured in the laboratory, characterized and treated with candidate drugs, we could reveal important information about the development of the disease and the effects of potential drugs. This is true for many cell types, keratinocytes, however, do not survive for a longer period in culture. We have therefore used the technology of induced pluripotent stem (iPS) cells: We have obtained fibroblasts from patients, which can be more easily amplified in culture and “reprogrammed” into a pluripotent state. The iPS cells can then be differentiated into several cell types, including keratinocytes. These can be used to generate and characterize artificial skin, three-dimensional skin models with typical properties of normal or patient-specific disease skin.

As examples we have studied two major groups of rare skin diseases: Ectodermal dysplasias (ED), which can be caused by mutations in TP63, a transcription factor gene active in developing and differentiating keratinocytes, and congenital ichthyosis, which can be either isolated (autosomal recessive congenital ichthyosis) or syndromic (manifest in various organs). We have successfully reprogrammed cells from patients with any of these diseases into iPS cells, and the iPS cells were then differentiated into keratinocytes. We have developed protocols for the successful differentiation, however, unexpectedly the differentiated keratinocytes could not be amplified for a longer time. Therefore we have cultured a large number of these keratinocytes from the beginning and used them to generate skin models. The models were characterized and shown to replicate the respective skin disease of the patient who provided the original cells. We have used the cell models and corresponding mouse models to study mechanisms of p63-related ectodermal dysplasias. The functionality of p63 could be successfully restored with a small compound that recognizes the mutant protein domain. For congenital ichthyosis, 2D and 3D models are being used to study candidate drugs. As the models replicate properties of the disease, for instance artificial substitutes for the mutant proteins are now being tested for their capability to restore the normal function of differentiating keratinocytes, including the formation of the skin barrier function.