Lathyrol Exerts Anti-Pulmonary Fibrosis Effects by Activating PPARγ to Inhibit the TGF-β/Smad Pathway

Idiopathic pulmonary fibrosis is a chronic, progressive, interstitial lung disease for which specific and effective drug therapies are still lacking. Lathyrol is a diterpene compound with broad pharmacological activities that can be extracted from the traditional Chinese medicine <i>Leptochloa chinensis</i> (L.) Nees. To investigate the anti-pulmonary fibrosis effect of lathyrol and its underlying mechanism. In vivo, a mouse model of pulmonary fibrosis was induced by bleomycin, treated with intraperitoneal injections of lathyrol. In vitro, myofibroblast conversion was induced in three fibroblast cell lines by stimulating them with TGF-β1, followed by treatment with lathyrol. Transcriptomic analysis was performed to assess the regulation of signaling pathways and gene expression patterns modulated by lathyrol. The effects of lathyrol on PPARγ activation, as well as on the nuclear translocation and ubiquitination of phosphorylated Smad3, were examined. The interaction among Nedd4, PPARγ, and phosphorylated Smad3 was detected. In vivo, lathyrol ameliorated pathological fibrosis in the lungs of mice with pulmonary fibrosis and this effect was blocked by a PPARγ inhibitor. In vitro, lathyrol inhibited the transdifferentiation of fibroblasts into myofibroblasts, and these effects were suppressed by either inhibiting PPARγ activation or specifically silencing the PPARγ gene. Lathyrol inhibited the nuclear translocation of phosphorylated Smad3 and promoted its ubiquitination, while also enhancing the interaction among Nedd4, PPARγ, and phosphorylated Smad3. These effects were abolished following the specific silencing of either PPARγ or Nedd4. In conclusion, Lathyrol inhibits myofibroblast transformation by suppressing TGF-β/Smad pathway activation through PPARγ activation, thereby exerting its anti-pulmonary fibrosis effects.