Fibroblast Mitochondrial Ca2+ Overload Drives Skin Fibrosis via mtDNA Leakage and cGAS-STING Activation in Systemic Sclerosis.

Abstract

To explore the clinical relevance of mitochondrial DNA (mtDNA) in systemic sclerosis (SSc) and elucidate the mechanism by which mtDNA leakage drives fibroblast activation. Plasma mtDNA was quantified by qPCR in 50 patients with SSc and 20 healthy controls (HC). Primary dermal fibroblasts from 5 diffuse cutaneous SSc (dcSSc) and 5 HC (n= 5 per group) were analyzed for mitochondrial structure, function and RNA-seq profiling. The opening of mitochondrial permeability transition pore (mPTP) and oligomerization of VDAC1 were examined with Ca²⁺ modulators and inhibitors. STING knockdown (siRNA) was performed for validation. The STING inhibitor H-151 was evaluated in vitro and in a bleomycin-induced skin fibrosis model (n= 6 mice per group). Plasma mtDNA levels were significanly higher in SSc than in HC, negatively correlating with forced vital capacity (FVC)% (r = -0.436, P < 0.01) , and correlating with modified Rodnan skin score (mRSS) ( r = 0.807, P < 0.001 ), IL-6 ( r = 0.667, P < 0.001 ) and TGF-β ( r = 0.678, P < 0.001 ). SSc fibroblasts exhibited abnormal mitochondrial morphology and dysfunction. Increased MCU and VDAC1 promoted mitochondrial Ca²⁺ overload, mPTP opening, VDAC1 oligomerization, cytosolic mtDNA accumulation, which activated the cGAS-STING pathway and triggered profibrotic responses. Pharmacologic blockade of mPTP or VDAC1 reduced cytosolic mtDNA, while H-151 suppressed profibrotic markers in SSc fibroblasts and attenuated dermal thickening and collagen deposition in bleomycin-treated mice. The Ca²⁺-mtDNA-cGAS/STING axis drives fibroblast activation and skin fibrosis in SSc, representing a promising therapeutic target.