Targeted delivery of Follistatin-like 1 siRNA via biodegradable nanoparticles attenuates bleomycin-induced pulmonary fibrosis in mice

Background Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive interstitial lung disorder that often leads to fatal outcomes, characterized by the aberrant proliferation of myofibroblasts and excessive deposition of extracellular matrix (ECM) components. Follistatin-like 1 (Fstl1), a secreted glycoprotein regulated by transforming growth factor β1 (TGF-β1), has been found to be markedly elevated in the fibrotic lungs of both patients with IPF and mice subjected to bleomycin-induced injury. Studies have shown that Fstl1 haploinsufficiency protects against bleomycin-induced lung injury, implicating Fstl1 as a potential therapeutic target. Here, we investigated the effect of Fstl1 knockdown using small interfering RNA (siRNA) on pulmonary fibrosis in vivo.Methods We designed four siRNA sequences targeting Fstl1 and evaluated their efficiency in mouse embryonic fibroblasts (MEFs). Of these, si-Fstl1-12 achieved maximal Fstl1 knockdown (∼80%) and significantly inhibited TGF-β1-induced upregulation of Fstl1 and ECM proteins in vitro. We used biodegradable poly (D, L-lactic-co-glycolic acid) (PLGA) nanomaterials as carriers for in vivo delivery. Bleomycin-treated mice were administered PLGA-si-Fstl1-12, and lung tissues were analyzed for Fstl1 expression, fibrosis severity, and collagen deposition.Results si-Fstl1-12 markedly suppressed TGF-β1-induced Fstl1 expression and ECM protein synthesis in MEFs in vitro. Treatment with PLGA-si-Fstl1-12 effectively reduced Fstl1 levels in lung tissue, attenuated interstitial fibrosis, and decreased collagen accumulation in bleomycin-challenged mice. Notably, even low doses of PLGA-si-Fstl1-12 achieved significant therapeutic effects, demonstrating efficient and safe siRNA delivery in vivo.Conclusions Targeted Fstl1 inhibition using siRNA significantly mitigated pulmonary fibrosis in a murine bleomycin model. The successful application of PLGA nanomaterials for siRNA delivery underscores their potential for safe and effective in vivo gene silencing. These findings highlight si-Fstl1 as a promising therapeutic candidate for IPF and support further investigation of RNA-based nanomedicine in fibrotic lung diseases.