Background: Congenital pulmonary airways malformations (CPAM) belong to a group of rare congenital lung anomalies whose pathological origin is still mostly unknown. The current research project aims to study the possible role of the underlying mesenchyme in CPAM pathophysiology by comparing data from fetal tissue and healthy lung with CPAM.

Methods: Tissue samples from CPAM patients and healthy adjacent parts were collected during planned surgical resections. Fetal lung tissue obtained from abortions was also used. The mesenchymal parts of pathological, healthy and fetal lung tissues were analyzed using quantitative proteomic, bulk RNA sequencing and multiplex immunohistochemistry to identify the difference in genes and proteins expressed in CPAM.

Results: When compared to healthy adjacent lung tissue, transcriptomic data of CPAM tissue highlighted downregulation of genes implicated in the transforming-growth factor-β and immune-related signaling pathways. Conversely, epithelial-mesenchymal transition genes were upregulated in CPAM, suggesting an abnormal branching associated with abnormal mesenchyme. Quantitative proteomic results showed that the expression of various proteins implicated in muscle differentiation, such as desmin, calponin1 and α-smooth muscle actin, were decreased in CPAM compared to healthy adjacent lung. Multiplex immunostaining confirmed these results with a more significant difference for CPAM type 1 compared to healthy adjacent tissue or to fetal lung. Several pathways known to be crucial in epithelial proliferation, differentiation or branching such as PI3K-AKT-mTOR pathway were dampened.

Conclusion: Our study reveals the presence of abnormal mesenchyme and muscle in and surrounding cystic tissue. Despite normal lung function during pediatric follow-up, the atypical mesenchyme with possible impaired epithelial-mesenchymal transition could potentially contribute to the development of late adult pathologies such as chronic obstructive pulmonary disease or lung tumors and should be assessed accordingly.