Inhibition of 3‐Phosphoinositide‐Dependent Kinase 1 Improves Age‐Associated Epidermal Dysfunction

ABSTRACT

Epidermal aging is characterized by impaired homeostasis, including reduced cell proliferation, aberrant differentiation, deterioration of the dermal–epidermal junction (DEJ), and compromised barrier function. Accumulating evidence suggests that these alterations arise not solely from intrinsic stem cell loss but from disruption of regulatory signalling networks governing epidermal function. In this study, we investigate whether inhibition of 3‐phosphoinositide‐dependent kinase‐1 (PDK1), a central regulator of aging‐related AKT/mTOR and NF‐κB signalling, is associated with improved epidermal homeostasis through functional enhancement of autophagy. Using primary normal human epidermal keratinocytes (NHEKs) from young and old donors, 3‐dimensional organotypic epidermal skin equivalents (SE), and chronologically aged human skin, we found that aged epidermis exhibited markedly reduced autophagy activity accompanied by defective differentiation, impaired keratinocyte proliferation, and loss of key stem cell niche components at the DEJ. Pharmacological inhibition of PDK1 using selective PDK1 inhibitors (BX795, GSK2334470) or a plant‐derived inhibitor (kaempferol tetrasaccharide, KT1) formulated as Camellia japonica seed fraction (CF) suppressed AKT/mTOR and NF‐κB signalling in aged keratinocytes, which was accompanied by increased autophagy‐related markers and improved entry into differentiation. In addition, PDK1 inhibition increased basal keratinocyte proliferation, increased epidermal thickness, and improved DEJ components. In a proof‐of‐concept clinical study, topical application of CF, a botanical fraction containing KT1, was associated with improvements in epidermal autophagy, differentiation, DEJ integrity, and barrier function in aged human skin. Collectively, these findings identify a regulatory role of PDK1 within the epidermis and provide proof‐of‐concept evidence that pharmacological modulation of PDK1 activity exhibits potential for mitigating age‐associated epidermal dysfunction.