Cyclopeptide 161 protects human dermal fibroblasts against UV-induced damage via the MEK1/2-ERK1/2 signaling pathway.

INTRODUCTION: Cutaneous homeostasis is constantly perturbed by ultraviolet (UV) irradiation, which triggers extracellular matrix (ECM) structural derangement, fibroblast senescence, and the gradual deterioration of dermal integrity. CP161, a synthetic cyclic hexapeptide, has been documented to upregulate the transcription of collagen genes. Nevertheless, its broader cutaneous bioactivities as well as the precise molecular mechanisms underlying its skin-regulating effects remain largely unelucidated. METHODS: We first characterized the skin-protective potential of CP161 in primary human dermal fibroblasts (HDFs) exposed to ultraviolet radiation, relying on RT-qPCR, Western blot analysis, SA-β-gal staining and intracellular reactive oxygen species quantification for phenotypic validation. We utilized label-free quantitative proteomics to map core biological events and signaling networks altered following CP161 treatment, and adopted CETSA, BLI, molecular docking together with molecular dynamics (MD) simulations to verify whether CP161 can physically bind MAP2K1. We extended our investigation to cultured cholinergic neurons and PTZ-stimulated zebrafish larvae to further dissect CP161 biofunction; we quantified changes in acetylcholine (ACh) secretion and excessive neuromuscular activity in these two models, and similarly deployed CETSA, molecular docking and MD simulation assays to test for direct binding between CP161 and Munc18a. RESULTS: In UVA-irradiated HDFs, CP161 restored COL1A1, COL14A1, and COL16A1 expression, suppressed MMP1 and p21 upregulation, reduced SA-β-gal-positive cells, and lowered intracellular ROS accumulation. Proteomic profiling revealed coordinated remodeling of ECM organization. CP161 attenuated UVA-induced MEK1/2-ERK1/2 phosphorylation, and CETSA, BLI, molecular docking, and MD analyses collectively supported direct interaction between CP161 and MAP2K1. In cholinergic neurons, CP161 reduced evoked ACh release; in PTZ-challenged zebrafish larvae, CP161 dose-dependently attenuated neuromuscular hyperactivity, and convergent biophysical and computational evidence supported direct interaction between CP161 and Munc18a, indicating a complementary activity relevant to contraction-associated mechanical injury of the dermis. CONCLUSION: CP161 protects human dermal fibroblasts from UVA-induced damage through direct interaction with MAP2K1 and attenuation of the MEK1/2-ERK1/2 signaling cascade, thereby preserving ECM homeostasis. These findings establish a mechanistic framework for the skin-protective activity of CP161 and identify the MAP2K1-ERK1/2 axis as the principal pathway through which this cyclic hexapeptide maintains dermal homeostasis.