Abstract Rationale The Wnt/β-catenin signaling pathway is recognized for its role in controlling stem cell self-renewal and cell fate during lung development. Earlier studies from our group documented the temporally regulated expression of the biphasic Wnt signaling modulator, Secreted frizzled-related protein 1 (Sfrp1) in murine lung development, and demonstrated that loss of Sfrp1 led to alveolar duct dilation. Recent studies from others have identified SFRP1 as a marker of transitional fibroblasts after injury, and when SFRP1 is downregulated, fibroblasts transition to an invasive myofibroblast subtype. While myofibroblasts contribute to pathogenesis of fibrosis in disease, they are also essential in lung development for alveolar septation. Therefore, using our Sfrp1-/- mice we investigated whether Sfrp1 loss affected alveologenesis through its role in fibroblast signaling. Methods Publicly available single cell RNA sequencing data was analyzed to identify cellular expression of Sfrp1 in early development, and validated with proximity ligation in situ hybridization. Formalin fixed paraffin embedded lung tissue samples from developmental stages (14.5 dpc to postnatal day 30) of Sfrp1-/- and wild type (WT) mice were stained with H 0.05) were analyzed using Gene Ontology (GO) Biological Process enrichment to identify developmental programs. Results Single cell RNA sequencing data analysis revealed expression of Sfrp1 in fibroblasts during early development. Morphometric analysis and immunohistochemical staining of P0 lung tissue demonstrated increased mesenchymal thickness and quantitatively increased PDGFRA protein staining in the Sfrp1-/- mouse, compared to WT. Bulk RNA sequencing analysis identified 454 DEGs between the Sfrp1-/- and WT lung tissue at P0. GO enrichment analysis of DEGs revealed overrepresentation of developmental programs, including cell differentiation, anatomical structure development, and extracellular matrix organization. Bulk RNA sequencing of PDGFRA+ cells at P0 revealed 427 DEGs, which prominently included genes known to be involved in inflammatory and fibrotic response to injury. Conclusions SFRP1, normally expressed by fibroblasts during early development, is required for proper alveolar formation. Genetic ablation leads to increased septal thickness and impaired alveolar formation notable between P0 and P7. Genes involved in response to injury and stress were upregulated in PDGFRA+ cells from Sfrp1-/- lungs suggesting that loss of SFRP1 disrupts fibroblast signaling during development. Further studies to delineate the specific impact of Sfrp1 ablation on fibroblast differentiation in development and injury will be explored. This abstract is funded by: American Thoracic Society, Stony Wold Herbert Foundation, NIH
Rai et al. (Fri,) studied this question.