Aberrant and Ectopic Cell Populations of the Fibrotic Pushing Border in Restrictive Allograft Syndrome after Lung Transplantation
Authors: Leiber Lena M. , Christian Leonard , Neubert Lavinia , Ruwisch Jannik , Yilmaz Hande , Plucinski Edith K. J. , Langer Linus , Kamp Jan C. , Greer Mark , Haermeyer Bernd , Kühnel Mark , Werlein Christopher , Justet Aurelien , Bergmann Anke K. , Ballmaier Matthias , Salman Jawad , Knudsen Lars , Martin Ulrich , Vanaudenaerde Bart , Yildirim Ali Önder , Ius Fabio , Laenger Florian , Welte Tobias , Falk Christine , Kaminski Naftali , Jonigk Danny D. , Gottlieb Jens , Schupp Jonas C. 
Published: June 2024

Rationale

Restrictive allograft syndrome (RAS) is a major cause of mortality in patients following lung transplantation due to rapid progressive fibrosis in the pulmonary graft. We have only limited knowledge of the cellular and molecular mechanisms that characterize the fibrosis in the RAS lung.

Objective

To elucidate cellularly-resolved transcriptomic and histologic characteristics of the structural cells in human RAS lungs.

Methods

Single-nuclei RNA-sequencing was performed in peripheral lung tissues from 15 RAS patients undergoing lung re-transplantation, and from 9 healthy control lungs. Findings were validated and complemented by various histologic techniques, including immunofluorescence, RNAscope, combined Elastica van Gieson-immunohistochemistry stains, and micro-CT scans.

Measurement and Main results

Differential gene expression analysis of our single-nuclei RNA-sequencing data revealed in human RAS lungs previously undescribed and uniquely distributed aberrant basaloid cells, ectopicCOL15A1+vascular endothelial cells, andCTHRC1+fibrotic fibroblasts, all first characterized in idiopathic pulmonary fibrosis (IPF). In contrast to IPF, RAS lacks the cellular equivalent of bronchiolization. Histologic stains confirmed our transcriptomic discoveries and disclosed distinctive distribution patterns: Aberrant basaloid cells are primarily localized at the edge of the fibrotic pushing border, forming together with the juxtaposedCTHRC1+fibrotic fibroblasts the fibrotic niche of alveolar fibroelastosis (AFE), the histopathological hallmark in RAS lungs. On the endothelial side,PRX+alveolar microvasculature is lost in AFE areas. Micro-CT scans revealed that blood supply, now facilitated by expanded and ectopicCOL15A1+VE cells, changes from pulmonary to systemic perfusion. Last, our data reveals potential therapeutically-modifiable expression patterns in RAS, including genes coding for the integrin subunits αvβ6, activators of TGFβ.

Conclusion

Considering the marked clinical, histologic and etiologic dissimilarities of RAS and IPF, our snRNAseq study revealed a surprising general principle of cellular and molecular pathogenesis in the fibrosing lung: the entity-spanning composition of the fibrotic niche by a) aberrant basaloid cells localized at the fibrotic pushing border, b) ectopicCOL15A1+vascular ECs and c) effectorCTHRC1+fibrotic fibroblasts. This general principle justifies a flexible but cellular pathogenesis-guided transferability of potential therapeutic approaches between progressive fibrotic lung diseases.