Autocrine SFRP2 (secreted frizzled related protein 2) enhances lung myofibroblast fibrogenic activity by suppressing PINK1-mediated mitophagy initiation

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease driven by persistent activation of pulmonary myofibroblasts, but the regulatory mechanisms sustaining this pathological state remain incompletely understood. Using single-cell RNA sequencing (scRNA-seq), we identified SFRP2 (secreted frizzled related protein 2) as a critical mediator of profibrotic myofibroblasts in IPF lungs. Functional studies revealed that SFRP2 acted in an autocrine manner to promote myofibroblast activation and extracellular matrix (ECM) production. Mechanistically, SFRP2 activated FZD5-mediated non-canonical WNT-Ca2+ signaling, leading to PPP3/calcineurin-dependent translocation of PINK1 from the outer to the inner mitochondrial membrane (IMM), where it was degraded, thereby inhibiting PINK1-mediated mitophagy. Furthermore, therapeutic intervention with AAV6-shSfrp2, SFRP2-neutralizing antibody, or the autophagy inducer rapamycin significantly ameliorated lung fibrosis in bleomycin (BLM)-induced mouse models. Our results define a novel autocrine SFRP2-mitophagy regulatory axis that perpetuates myofibroblast activation and represents a promising therapeutic target for pulmonary fibrosis. Abbreviations: AAV: adeno-associated virus; BLM: bleomycin; CQ: chloroquine; ECM: extracellular matrix; FZD5: frizzled class receptor 5; H&E: hematoxylin and eosin; IHC: immunohistochemical; IMM: inner mitochondrial membrane; IPF: idiopathic pulmonary fibrosis; Micro-CT: micro-computed tomography; mtROS: mitochondrial reactive oxygen species; PMLFs: primary mouse lung fibroblasts; qPCR: quantitative real-time PCR; scRNA-seq: single-cell RNA sequencing; SFRP2: secreted frizzled related protein 2; TEM: transmission electron microscopy; ∆Ψm: mitochondrial membrane potential.