Hailey-Hailey disease models reveal impaired cadherin expression and localization along with actin dysregulation as key pathogenic drivers that weaken intercellular adhesion

Summary: Abstract Body: Hailey-Hailey disease (HHD) is characterized by painful skin blisters and erosions due to loss of adhesion between epidermal keratinocytes. Despite being linked to ATP2C1 mutations 25 years ago, this disease has no FDA-approved treatments. Understanding HHD pathogenesis has been hampered by the lack of a pre-clinical model as Atp2c1 knockout mice did not replicate HHD. We utilized CRISPR/Cas9 in TERT-immortalized human keratinocytes to ablate ATP2C1, depleting its encoded Golgi calcium ATPase, SPCA1. In a second model, we used drugs to block SPCA1 in normal human epidermal keratinocytes. Leveraging calcium biosensors in live keratinocytes, we found SPCA1 loss did not alter cytoplasmic, ER, or Golgi calcium. However, both genetic depletion and chemical inhibition of SPCA1 impaired the trafficking of adherens junction and desmosomal components to cell-cell contacts and reduced cadherin levels, which compromised the mechanical strength of keratinocyte sheets. Moreover, in organotypic epidermis, we found loss of SPCA1 induced severing of cell-cell junctions (acantholysis), the key pathologic feature of HHD. To identify causes of cell-cell junction disruption in HHD, we performed RNA sequencing of ATP2C1 heterozygous keratinocytes. Gene ontology analysis revealed differential expression of actin regulators including Rho GTPases, in agreement with RNAseq data from HHD biopsies. Further validating a role for actin in HHD, confocal imaging showed impaired actin organization and increased filopodia in SPCA1-deficient keratinocytes; as well, SPCA1-deficient organotypic epidermis and HHD biopsies exhibited impaired cortical actin bundling. These data support our model in which actin dysregulation impairs localization and stability of adhesive proteins in HHD. Importantly, our results point to druggable actin regulators as potential therapeutic targets to restore epidermal integrity in HHD. Jessica L. Ayers¹, Afua Tiwaa¹, Arti S. Parihar¹, Crystal J. Tam¹, Akshata Aravind¹, Nizhoni Sutter¹, Mrinal K. Sarkar², Johann E. Gudjonsson², Cory L. Simpson¹ 1. Dermatology, University of Washington, Seattle, WA, United States. 2. Dermatology, University of Michigan, Ann Arbor, MI, United States. Genetic Disease, Gene Regulation, Gene Therapy & Epigenetics