Chemogenetic Activation of <scp> G ₁₂ </scp> Signaling Thickens the Epidermis With Enhanced Barrier Function

ABSTRACT The epidermis provides the body's outermost barrier, yet how G‐protein‐coupled receptor (GPCR) signaling via the G 12/13 family regulates epidermal homeostasis in vivo remains unclear. Here, we selectively activated G 12 signaling in keratinocytes using a chemogenetic strategy. Activation of a G 12 ‐coupled designer receptor (G 12 D) in mouse epithelial cells induced pronounced epidermal thickening while preserving stratified architecture and avoiding overt inflammatory skin changes. This thickening was accompanied by increased Ki67‐positive cells, expansion of keratin 10‐ and filaggrin‐positive layers, and transcriptomic upregulation of genes related to keratinocyte differentiation, keratinization, and epidermal barrier function. Functionally, G 12 D activation strengthened barrier performance, as shown by blunted transepidermal water loss responses to mechanical barrier disruption. Although alarmin‐related genes were upregulated, cytokine analyses indicated only modest inflammatory changes. Pharmacologic inhibition of TYK2 (deucravacitinib) partially reduced G 12 D‐driven epidermal thickening, whereas mTORC1 inhibition (rapamycin) produced a stronger suppressive effect, suggesting that the mTORC1‐dependent keratinocyte response is a major driver of this phenotype, with a moderate TYK2‐dependent component. Together, these findings identify epidermal G 12 signaling as a regulator that promotes “non‐pathological” epidermal thickening coupled to enhanced barrier function, supporting G 12 ‐coupled GPCRs as potential therapeutic entry points for barrier‐compromised skin disorders.