Mechanisms contributing to the skin phenotype of ectodermal dysplasias caused by TP63 mutations

Mutations in the transcription factor TP63 underlie ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC), a form of ectodermal dysplasia. The molecular mechanisms underlying skin fragility and epidermal differentiation defects in these patients are not well-understood. Animal models of AEC did not fully recapitulate the AEC patient skin phenotype. We developed a human stem cell-based system that expresses mutant TP63 at physiological levels in a cellular background that is genetically susceptible to AEC. Skin fibroblasts from two AEC patients were reprogrammed into induced pluripotent stem cells (iPSC). Next, we corrected the TP63 mutations in these iPSC using Crispr/Cas, thereby generating conisogenic cell lines that were identical except for the presence or absence of the TP63 mutation. The iPSC were differentiated into keratincoytes (iPSC-K) and subjected to a comparative transcriptome anlaysis. We identified defects in several desmosomal components in AEC iPSC-K. Exposure to calcium revealed abnormal desmosomal assembly and reduced cell adhesion in AEC iPSC-K. We also identified differentiation defects in AEC iPSC-K. These findings are consistent with immunofluorescence staining epxeriments demonstrating reduced and aberrant expression of desmosomal components and differentation markers in AEC patient skin. In addition, our results provide evidence that two desmosome-linked signaling pathways (p38MAPK, Erk) that control keratinocye adhesion and differentiation are deregulated in AEC iPSC-K. We believe that our stem cell-based model provides an excellent tool to further investigate the mechanisms underlying ectodermal dysplasias caused by TP63 mutations.