Two roads to fibrosis: Contrasting initiating mechanisms of Bleomycin and TGFβ-1 in lung fibroblasts

Pulmonary fibrosis, a progressive and debilitating disease, presents a significant global health challenge. Even though often idiopathic, drug-induced fibrosis is increasing its incidence. Traditional chemical safety assessments, relying on apical endpoints from in-vivo models, are limited in capturing the early molecular events initiating fibrosis, consequently limiting the potential for early diagnosis and mechanism-driven treatment. This study employed a toxicogenomic approach on in-vitro MRC-5 fibroblasts, a crucial cell type involved in fibrosis, to dissect the initiating profibrotic mechanisms of Bleomycin (1, 1.5, 2 μg/mL), a profibrotic triggering stimulus, comparing it with TGFβ-1(5, 10, 15 ng/mL), a known sustaining mediator of fibrosis over 24, 48, and 72 h. Our analysis reveals that while both agents alter matrix-related processes, their initiation mechanisms diverge. Specifically, TGFβ-1 directly induces myofibroblast transition, whereas Bleomycin potentially induces an indirect transition through the establishment of a senescence-associated secretory phenotype (SASP). By capturing the early SASP signature, we identified a critical driver of Bleomycin-induced fibroblast fibrosis, relevant to drug-induced fibrosis where antineoplastic agents are a major concern. This study underscores the critical importance of integrating mechanistic understanding into chemical safety assessment, thereby facilitating the development and implementation of safer, more sustainable chemical development.