Genome-Wide Transcriptional Response During the Development of Bleomycin-Induced Pulmonary Fibrosis in Sprague-Dawley Rats

Pulmonary fibrosis is a common consequence of many lung diseases and a leading cause of morbidity and mortality. The molecular mechanisms underlying the development of pulmonary fibrosis remain poorly understood. One model used successfully to study pulmonary fibrosis over the past few decades is the bleomycin-induced pulmonary fibrosis model. We aimed to identify the genes associated with fibrogenesis using an Affymetrix GeneChip system in a bleomycin-induced rat model for pulmonary fibrosis. To confirm fibrosis development, several analyses were performed, including cellular evaluations using bronchoalveolar lavage fluid, measurement of lactate dehydrogenase activity, and histopathological examinations. Common aspects of pulmonary fibrosis such as prolonged inflammation, immune cell infiltration, emergence of fibroblasts, and deposition of extracellular matrix and connective tissue elements were observed. Global gene expression analysis revealed significantly altered expression of genes ($\geq$ 1.5-fold, p < 0.05.) in a time-dependent manner during the development of pulmonary fibrosis. Our results are consistent with previous results of well-documented gene expression. Interestingly, the expression of triggering receptor expressed on myeloid cells 2 (Trem2), secreted phosphoprotein 1 (Spp1), and several proteases such as Tpsab1, Mcpt1, and Cma1 was considerably induced in the lung after bleomycin treatment, despite little evidence that they are involved in pulmonary fibrogenesis. These data will aid in our understanding of fibrogenic mechanisms and contribute to the identification of candidate biomarkers of fibrotic disease development.