Chemogenetic Activation of G₁₂ Signaling Thickens the Epidermis With Enhanced Barrier Function

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 G₁₂ signaling in keratinocytes using a chemogenetic strategy. Activation of a G₁₂-coupled designer receptor (G₁₂D) 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, G₁₂D 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 G₁₂D-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 G₁₂ signaling as a regulator that promotes "non-pathological" epidermal thickening coupled to enhanced barrier function, supporting G₁₂-coupled GPCRs as potential therapeutic entry points for barrier-compromised skin disorders.