Patients with progressive fibrosing interstitial lung diseases (PF-ILDs) carry a poor prognosis and have limited therapeutic options. A hallmark feature is fibroblast resistance to apoptosis, leading to their persistence, accumulation, and excessive deposition of extracellular matrix. A complex balance of the B cell lymphoma 2 (BCL-2) protein family controlling the intrinsic pathway of apoptosis and fibroblast reliance on antiapoptotic proteins has been hypothesized to contribute to this resistant phenotype. Examination of lung tissue from patients with PF-ILD (idiopathic pulmonary fibrosis and silicosis) and mice with PF-ILD (repetitive bleomycin and silicosis) showed increased expression of antiapoptotic BCL-2 family members in α–smooth muscle actin–positive fibroblasts, suggesting that fibroblasts from fibrotic lungs may exhibit increased susceptibility to inhibition of antiapoptotic BCL-2 family members BCL-2, BCL-XL, and BCL-W with the BH3 mimetic ABT-263. We used 2 murine models of PF-ILD to test the efficacy of ABT-263 in reversing established persistent pulmonary fibrosis. Treatment with ABT-263 induced fibroblast apoptosis, decreased fibroblast numbers, and reduced lung collagen levels, radiographic disease, and histologically evident fibrosis. Our studies provide insight into how fibroblasts gain resistance to apoptosis and become sensitive to the therapeutic inhibition of antiapoptotic proteins. By targeting profibrotic fibroblasts, ABT-263 offers a promising therapeutic option for PF-ILDs.

OBJECTIVES/GOALS: Silicosis is a highly fatal progressive fibrotic disease of the lungs characterized by accumulation and persistence of fibroblasts that excessively deposit Collagen1a1. We sought to eliminate Collagen1a1-expressing fibroblasts through a targeted genetic ablation strategy and hypothesized that this would arrest the progression of Silicosis. METHODS/STUDY POPULATION: Silicosis was induced with a single intratracheal (i.t.) instillation of silica particles ( RESULTS/ANTICIPATED RESULTS: Targeted ablation of Col1a1+ fibroblast in established Silicosis resulted in a decrease in: 1) Col1a1+ fibroblasts by flow cytometry and within fibrotic nodules by immunofluorescent staining, 2) total lung collagen content by histology and hydroxyproline assay, 3) tissue-associated disease by microCT and an increase in arterial oxygen saturation by pulse oximetry. Cessation of targeted Col1a1+ fibroblast ablation resulted in a rebound effect in Silicosis disease progression. Following ablation, Col1a1+ fibroblasts expanded by proliferation (Ki67+) and total lung collagen levels returned to pre-ablation levels. DISCUSSION/SIGNIFICANCE: Silicosis is a often fatal disease with no FDA approved therapies. These results suggest that targeted loss of Col1a1+ fibroblasts in Silicosis is sufficient to arrest disease progression. Thus, it is essential to understand how targeted loss of pro-fibrotic fibroblasts can alter disease progression as a tool to develop novel therapeutic strategies.

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