Fibrotic lung ECM upregulates SDC4/integrin-αvβ1 interaction and the interfering peptide SDC487-131 and its derivative peptides alleviate pulmonary fibrosis

Fibroblast activation promotes remodeling of the extracellular matrix (ECM), and the fibrotic remodeling ECM further stimulating fibroblast activation and advancing pulmonary fibrosis (PF). syndecan-4 (SDC4) is the key mediator of ECM-cell signaling, but its action in PF remains unclear. Using decellularized lung ECM (dECM), this study found that fibrotic ECM enhanced fibroblast activation via SDC4-regulated integrin-αvβ1 expression and activation, and FAK/AKT phosphorylation. Meanwhile, SDC4 knockdown inhibited fibrotic ECM-induced TGF-β1 synthesis and PKCα activation. A Duolink-proximity ligation assay confirmed extracellular interactions between SDC4 and integrin-αvβ1, and the SDC4 blocking antibody Anti-SDC4_(93-121) prevented this interaction, resulting in an effect consistent with knockdown of SDC4. The interfering peptide SDC4_87-131 diminished the interaction between SDC4 and integrin-αvβ1, subsequently inhibited the activation of FAK/AKT, Smad2/3 and PKCα/NF-κB pathways and exhibited anti-PF activity comparable to that of SDC4 knockdown and Anti-SDC4_(93-121). A docking mode of SDC4_87-131 with the Calf-1/Calf-2 domain of integrin-αv was constructed by using the AlphaFold2-Multimer model, and peptide design was performed to obtain a novel polypeptide chain CS-9 with enhanced anti-PF effect. This study found that the biomaterial, lung ECM, regulates fibroblast activation through the collaboration of SDC4 and integrin-αvβ1, and obtained a novel SDC4_87-131-derived peptide that may prevent fibrotic ECM from promoting PF.