Whole-transcriptome gene expression profiling in an epidermolysis bullosa simplex Dowling-Meara model keratinocyte cell line uncovered novel, potential therapeutic targets and affected pathways

Human iPSC-derived-keratinocytes, a useful model to identify and explore pathological phenotype of Epidermolysis Bullosa Simplex

Epidermolysis Bullosa Simplex (EBS), an autosomal dominant skin disorder, is characterized by skin fragility. Genetically, majority of cases are related to missense mutations in two keratin genes, KRT5 or KRT14, leading to cytolysis of basal keratinocytes and intraepidermal blistering. Progress towards identification of treatments have been hampered by incomplete understanding of the mechanisms underlying this disease, and availability of relevant and reliable in vitro models recapitulating the physiopathological mechanisms. Recent advances in stem cell field have fueled the prospect that these limitations could be overcome thanks to the availability of disease-specific human induced pluripotent stem cells (hiPSC). Here, we generated hiPSC-derived keratinocytes from patients carrying KRT5 dominant mutations and compared them to non-affected hiPSC-derived keratinocytes as well as their primary counterparts. Our results demonstrated that EBS hiPSC-derived keratinocytes displayed proliferative defects, increased capacity to migrate, alteration of ERK signaling pathway and cytoplasmic keratin filament aggregates as observed in primary EBS keratinocytes. Of interest, EBS hiPSC-derived keratinocytes exhibited a downregulation of hemidesmosomal proteins revealing the different effects of KRT5 mutations on keratin cytoskeletal organization. Combination of culture miniaturization and treatment with the chaperone molecule 4-PBA, our results demonstrated that hiPSC-derived keratinocytes represent a suitable model for identifying novel therapies for EBS.

Keratins as an Inflammation Trigger Point in Epidermolysis Bullosa Simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited keratinopathies that, in most cases, arise due to mutations in keratins and lead to intraepidermal ruptures. The cellular pathology of most EBS subtypes is associated with the fragility of the intermediate filament network, cytolysis of the basal layer of the epidermis, or attenuation of hemidesmosomal/desmosomal components. Mutations in keratins 5/14 or in other genes that encode associated proteins induce structural disarrangements of different strengths depending on their locations in the genes. Keratin aggregates display impaired dynamics of assembly and diminished solubility and appear to be the trigger for endoplasmic reticulum (ER) stress upon being phosphorylated by MAPKs. Global changes in cellular signaling mainly occur in cases of severe dominant EBS mutations. The spectrum of changes initiated by phosphorylation includes the inhibition of proteasome degradation, TNF-α signaling activation, deregulated proliferation, abnormal cell migration, and impaired adherence of keratinocytes. ER stress also leads to the release of proinflammatory danger-associated molecular pattern (DAMP) molecules, which enhance avalanche-like inflammation. Many instances of positive feedback in the course of cellular stress and the development of sterile inflammation led to systemic chronic inflammation in EBS. This highlights the role of keratin in the maintenance of epidermal and immune homeostasis.

Prevalence, pathophysiology and management of itch in epidermolysis bullosa

Epidermolysis bullosa (EB) is a highly diverse group of inherited skin disorders, resulting from mutations in genes encoding proteins of the dermoepidermal junction. Itch (pruritus) is one of the most common symptoms across all EB subtypes. It occurs in blistered or wounded sites, or manifests as a generalized phenomenon, thereby affecting both intact skin and healing wounds. The mechanism of pruritus in EB is unclear. It is likely that skin inflammation secondary to barrier disruption, wound healing cascades and dysregulated activation of epidermal sensory nerve endings are all involved in its pathophysiology on the molecular and cellular level. Understanding these mechanisms in depth is crucial in developing optimized treatments for people with EB and improving quality of life. This review summarizes current evidence on the prevalence, mechanisms and management of itch in EB.