321 A human tissue model of Darier disease reveals MEK as a novel therapeutic target downstream of SERCA2 deficiency

Darier disease results from mutation of the ER calcium pump SERCA2, causing epidermal blistering, painful erosions, and recurrent infections. Since treatments are lacking for this disorder and knockout mice do not phenocopy human pathology, we leveraged CRISPR to generate human epidermal keratinocytes lacking SERCA2 to elucidate Darier disease pathogenesis and identify new potential therapies. Analysis of calcium dynamics using the GCaMP biosensor confirmed that SERCA2 knockout keratinocytes display impaired cytosolic calcium handling. In addition to weakened intercellular adhesion, SERCA2-depleted cells underwent defective cornification in organotypic epidermis. To identify pathogenic drivers downstream of SERCA2 loss, we performed RNA sequencing and proteomic analysis of heterozygous cells to model the genetics of Darier disease. SERCA2-deficient cells exhibited reduced expression of keratin 1/10 and the desmosomal cadherin desmoglein 1 (Dsg1), which may underlie skin fragility in patients; as well, we found elevated MAP kinase signaling, a pathway regulating epidermal differentiation. Importantly, immunostaining patient biopsies substantiated our findings with disease lesions demonstrating reduced keratin 10, mis-localized Dsg1, and excess ERK phosphorylation. Thus, we hypothesized that dampening ERK overactivation could rescue the disease phenotype. A mechanical dissociation assay confirmed that multiple MEK inhibitors were able to recover keratin 1/10 expression and rescued intercellular adhesion in keratinocyte sheets lacking SERCA2 or treated with a SERCA2 inhibitor. In summary, our pre-clinical studies revealed that aberrant MAP kinase signaling due to SERCA2 haploinsufficiency disrupts desmosomal adhesion via Dsg1 and keratin 1/10; further, we identified MEK inhibition, already in clinical use, as a novel strategy to restore epidermal integrity in Darier disease.