LL37-induced mitochondrial stress activates the mtDNA/cGAS/STING pathway to promote mast cell-mediated rosacea inflammation

Abstract

Background: Rosacea is a chronic inflammatory skin disease characterized by persistent facial erythema and telangiectasia. The antimicrobial peptide LL37 is a key initiator in rosacea, with mast cells serving as critical inflammatory mediators. However, the precise mechanism underlying LL37-induced mast cell degranulation remains unclear.

Methods: The rosacea RNA-seq dataset GSE65914 was downloaded from the Gene Expression Omnibus (GEO) database and subjected to transcriptome analysis. DCFH-DA staining was performed to detect oxidative stress. Mitochondrial function was evaluated using MitoSOX and JC-1 staining. Calcein AM/Co²⁺ quencher staining was employed to assess mitochondrial permeability transition pore (mPTP) opening. Transmission electron microscopy was utilized to observe mitochondrial ultrastructure. Cytosolic mitochondrial DNA (mtDNA) was evaluated via immunofluorescence and qPCR. Western blotting and CUT&RUN assays were conducted to detect activation of the cGAS/STING/NF-κB axis. Mast cell degranulation was assessed using ELISA. N-acetylcysteine (NAC) was administered to scavenge reactive oxygen species (ROS). Cyclosporin A (CsA) was used to inhibit mPTP opening. SP23 was applied for chemical degradation of STING. A LL37-induced rosacea-like dermatitis mouse model was established and topically treated with applied CsA/SP23 cream.

Results: Transcriptomic profiling reveals significant enrichment of the cGAS/STING signaling pathway in rosacea lesions. LL37 induces oxidative stress-driven mitochondrial damage in mast cells, resulting in the leakage of mtDNA. Cytosolic mtDNA activates the cGAS/STING/NF-κB signaling pathway, inducing mast cell degranulation. ROS scavenging, blockade of mPTP or targeted degradation of STING significantly reduced mast cell activation. Animal experiments demonstrated that topical administration of CsA or SP23 suppressed cGAS/STING/NF-κB signaling in dermal mast cells and alleviated rosacea-like dermatitis.

Conclusion: LL37 promotes mast cell-driven inflammation through mitochondrial stress and innate immune activation and suggest that targeting the mtDNA/cGAS/STING pathway may offer a promising therapeutic strategy for rosacea.

Keywords: Mast cell; Mitochondrial DNA; Oxidative stress; Rosacea; cGAS/STING pathway.