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A5752 - Geographic Heterogeneity of Lung Tissue Changes in IPF Is Accompanied by Substantial Transcriptomic Homogeneity
Author Block: S. P. Atamas1, M. V. Salcedo1, M. L. Rojas-Peña2, A. E. Wyman3, J. R. Galvin1, A. Sachdeva1, A. Clerman1, J. Kim1, T. J. Franks4, E. J. Britt1, J. D. Hasday1, S. M. Pham1, A. P. Burke1, N. W. Todd1, I. G. Luzina1; 1University of Maryland School of Medicine, Baltimore, MD, United States, 2Otogenetics Corporation, Atlanta, GA, United States, 3Baltimore VA Medical Center, Baltimore, MD, United States, 4Department of Defense, Joint Pathology Center, Silver Spring, MD, United States.
RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized, among other features, by gross (macroscopic) and histopathologic (microscopic) geographic heterogeneity of lung tissue. Macroscopically, peripheral and basilar regions appear overtly scarred (IPFs), whereas central lung areas often appear normal (IPFn). We have recently reported that despite normal macroscopic appearance, microscopic foci of organizing pneumonia and cellular non-specific interstitial pneumonia are widespread in IPFn tissues. To gain insight into the molecular basis of macroscopic and microscopic differences between IPFn and IPFs tissues, we compared their transcriptomic profiles.
METHODS: Multiple IPFn and IPFs tissue samples from explants of three patients were analyzed by RNASeq and compared to multiple healthy control (HC) lung tissue samples from three separate donors. Overall, 26 tissue samples were analyzed by RNASeq, including ten IPFn, eight IPFs, and eight HC tissues. Three early-passage primary fibroblast cultures, each obtained from an IPFn sample of a separate IPF explant, were compared to three similarly derived and cultured fibroblasts from IPFs tissues. RT-qPCR, immunohistochemistry, and western blotting were used to confirm selected findings.
RESULTS: Profound transcriptomic differences between IPFn and HC tissues were observed, with particularly pronounced elevations in the expression of extracellular matrix-, immunity- and inflammation-related mRNAs in IPFn. The magnitude and statistical significance of these changes were comparable to those in the comparison between IPFs and HC tissues. When directly compared with IPFn, IPFs tissues demonstrated elevated expression of epithelial mucociliary mRNAs. Compared with HC, both IPFn and IPFs tissues demonstrated reduced expression of mRNAs related to solute carrier membrane transport and metabolic processes. Primary fibroblast cultures from IPFn and IPFs tissues were transcriptomically identical.
CONCLUSION: Despite macroscopic and microscopic heterogeneity of tissue changes in IPF lungs, there is substantial transcriptomic homogeneity. Macroscopically normal-appearing IPF tissues demonstrate similar transcriptomic profiles to scarred areas, notably in the expression of genes related to extracellular matrix, as well as immune and inflammatory responses. These data indicate that the macroscopically spared and microscopically less involved areas of IPF lungs are profoundly involved in the disease process at the transcriptomic level. Differences between normal-appearing and scarred tissues are due to cell types other than fibroblasts and notably include enhanced expression of mucociliary genes in scarred areas. The marked architectural differences between normal-appearing and terminally scarred lung in end-stage IPF may be explained by deranged epithelial homeostasis, possibly contributing to alveolar derecruitment with subsequent collapse induration.