Impaired store-operated Ca²⁺ entry in mouse epidermis leads to reduced epidermal barrier function via Klk activation

Store-operated Ca²⁺ entry (SOCE) is a mechanism by which STIM1/2 detect calcium depletion in the endoplasmic reticulum (ER) and activate ORAI1/TRPC channels on the cell membrane to induce calcium influx into the cytoplasm. This study aimed to investigate SOCE’s role in the skin epidermis in vivo, using female mice with epithelial tissue-specific Stim1 and Stim2 knockout (Stim1/2 cKO) and control mice (Stim1/2^fl/fl ). Keratinocytes from Stim1/2 cKO mice exhibited reduced Stim1 and Stim2 gene expression levels and impaired SOCE function compared with the controls. Histological analysis revealed hyperkeratosis in the Stim1/2 cKO tissues; however, no significant changes were observed in the proliferation or migration of keratinocytes or wound healing of the back skin. RNA-seq analysis indicated altered keratinization and cell-to-cell adhesion in the Stim1/2 cKO mice. Additionally, transepidermal water loss (TEWL) was increased significantly, and a biotinylated reagent diffused from the subcutaneous area into the granular layer, signifying compromised barrier function in the Stim1/2 cKO mice. The Stim1/2 cKO mice exhibited alterations in desmoglein 1 (Dsg1) and elevated levels of Kallikrein-related peptidase (Klk) 6 and Klk7, leading to increased trypsin- and chymotrypsin-like serine protease activities, respectively. These results suggest that SOCE dysfunction leads to hyperkeratosis and impaired epidermal barrier function via Klk activation without affecting skin cell proliferation in vivo. These novel findings improve understanding of the molecular mechanisms underlying calcium signaling in the epidermis barrier and suggest potential avenues for investigating related skin pathologies linked to calcium homeostasis, such as Hailey–Hailey disease (HHD) and Darier disease (DD).