A74-20 Stiffness-Dependent Alveolar Type II Cell Senescence in Idiopathic Pulmonary Fibrosis

Abstract Background IPF is characterized by the fibrotic response involving abnormally activated ATII cells. A stiffened matrix exerts extrinsic microenvironment-derived forces, leading to mechanical stress and ATII cell dysfunction. However, these mechanisms remain largely unknown. Methods ATII cells were isolated from control organ donors and the explanted lungs of patients with IPF. DNA damage was assessed by the comet assay and Western blotting. TERRA transcripts, the long noncoding RNA telomeric repeat-containing RNA and R-loops, which can impact genome integrity, were analyzed by qPCR. H3K27me3 and H3K9me3 levels were defined by immunofluorescence. ATII cell senescence was determined by Western blotting. Results A significant increase in γH2AX expression and impairment of NHEJ were detected in ATII cells in IPF. The obtained data indicate defective DNA damage response and decreased DNA damage repair capacity in ATII cells in patients with this disease, which can contribute to replication stress, transcription replication conflicts, and genomic instability. Moreover, the increased expression of H3K27me3 and H3K9me3 in ATII cells in IPF suggests repressed transcriptional activity. Nuclear envelope ruptures were identified using emerin by immunofluorescence. These alterations contribute to observed ATII cell senescence. Conclusion This study provides new mechanistic insights into the function of ATII cells and the integrity of the alveolar epithelium under highly stressed conditions in IPF. The data underscore the importance of mechanical stiffness on ATII cell dysfunction and senescence. This abstract is funded by: DoD