Targeting SERCA2 in organotypic epidermis reveals MEK inhibition as a therapeutic strategy for Darier disease

Abstract

Mutation of the ATP2A2 gene encoding sarco-endoplasmic reticulum calcium ATPase 2 (SERCA2) was linked to Darier disease more than two decades ago; however, there remain no targeted therapies for this disorder causing recurrent skin blistering and infections. Since Atp2a2 knockout mice do not phenocopy its pathology, we established a human tissue model of Darier disease to elucidate its pathogenesis and identify potential therapies. Leveraging CRISPR/Cas9, we generated human keratinocytes lacking SERCA2, which replicated features of Darier disease, including weakened intercellular adhesion and defective differentiation in organotypic epidermis. To identify pathogenic drivers downstream of SERCA2 depletion, we performed RNA sequencing and proteomic analysis. SERCA2-deficient keratinocytes lacked desmosomal and cytoskeletal proteins required for epidermal integrity and exhibited excess MAP kinase signaling, which modulates keratinocyte adhesion and differentiation. Immunostaining patient biopsies substantiated these findings with lesions showing keratin deficiency, cadherin mis-localization, and ERK hyper-phosphorylation. Dampening ERK activity with MEK inhibitors rescued adhesive protein expression and restored keratinocyte sheet integrity despite SERCA2 depletion or chemical inhibition. In sum, coupling multi-omic analysis with human organotypic epidermis as a pre-clinical model, we found that SERCA2 haploinsufficiency disrupts critical adhesive components in keratinocytes via ERK signaling and identified MEK inhibition as a treatment strategy for Darier disease.

ERK hyperactivation in epidermal keratinocytes impairs intercellular adhesion and drives Grover disease pathology

“…Up to now, it remained unclear why these two disorders would exhibit such similar findings in biopsies that pathologists cannot consistently distinguish the diagnoses without additional clinical information, such as whether the eruption is known to be hereditary (Darier disease) or spontaneous (Grover disease). Our recent work established an in vitro model of Darier disease and demonstrated that deficiency or chemical inhibition of SERCA2 induced hyperactivation of ERK (22), which we report here as a driver of GD pathology. Further linking these disorders with distinct origins (inherited vs. acquired), some cases of GD were recently found to harbor acquired mutations in the Darier disease-linked gene ATP2A2 encoding SERCA2, a major regulator of calcium, which can activate ERK signaling in keratinocytes (43).…”

“…Paradoxically, sustained B-RAF inhibition has been shown to induce activation of MEK (20, 21), which operates downstream of RAF in the mitogen-activated protein (MAP) kinase pathway, but how this signaling aberration induces the pathologic features of GD in human epidermal keratinocytes remains unknown. In recent work, we linked Darier disease to MEK and ERK overactivation (22), which led us to hypothesize that MEK hyperactivity might also fuel GD pathogenesis. Consistent with this, prior retrospective analysis of patients co-treated with MEK inhibitors, instead of B-RAF inhibitor monotherapy, failed to develop GD as a side effect (23).…”