<b>Supplemental Material: STL1267 Inhibits Myofibroblast Differentiation in a TGFβ1-Driven Human Lung Fibroblast Model</b>

Pulmonary fibrosis is a progressive interstitial lung disease characterized by excessive fibroblast-to-myofibroblast transition (FMT) and extracellular matrix (ECM) deposition, largely driven by transforming growth factor-beta 1 (TGFβ1). Existing therapies offer limited efficacy, particularly in advanced disease. Circadian rhythms have recently emerged as key modulators of lung inflammation and fibrosis. In this study, we developed an <i>in vitro</i> model of chronic fibrotic signaling using adenovirus-mediated TGFβ1 overexpression (Ad-TGFβ1) or human recombinant protein TGFβ1 in primary human lung fibroblasts. Using this model, we investigated the antifibrotic potential of STL1267, a next-generation Rev-erbα agonist with improved potency, specificity, and pharmacokinetic properties. RNA sequencing and pathway analysis revealed that STL1267 significantly reversed Ad-TGFβ1-induced expression of genes associated with ECM remodeling, collagen biosynthesis, and immune suppression. STL1267 also upregulated pathways related to IL-10, IL-4, and IL-13 signaling, which are known to counteract fibrotic responses. Quantitative PCR and immunoblotting confirmed STL1267's ability to downregulate key pro-fibrotic markers, including COL1A1, αSMA, FN1, and FAP, at both gene and protein levels. Comparative studies with other Rev-erbα agonists (GSK4112, SR9009), Saracatinib, and FDA-approved antifibrotic drugs (Pirfenidone, Nintedanib) demonstrated superior efficacy of STL1267 in inhibiting both preventive and post-fibrotic induction models. Moreover, lentiviral overexpression of Rev-erbα suppressed TGFβ1-induced αSMA expression, supporting a direct antifibrotic role. These findings highlight Rev-erbα as a key regulator of myofibroblast differentiation and support both STL1267 and GSK4112 as promising candidates for circadian-based antifibrotic therapy. Future <i>in vivo</i> studies are warranted to evaluate its translational potential in idiopathic pulmonary fibrosis.