Transcriptional effect of SPARCL1 treatment on lung alveolar organoids

Lung endothelial cells (ECs) and pericytes are closely juxtaposed with the respiratory epithelium before birth and thus may have instructive roles during development. To test this hypothesis, we screened EC-secreted proteins for their ability to alter cell differentiation in alveolar organoids. We identified SPARCL1 as an extracellular matrix molecule that can promote AT2 cell differentiation in vitro. SPARCL1-treated organoids display lysozyme upregulation and a doubling in the number of differentiated AT2 cells at the expense of intermediate progenitors. SPARCL1 also induces the upregulation of NF-?B target genes, and suppression of NF-?B activation in lung organoids blocked SPARCL1 effects. NF-?B activation by LPS was sufficient to induce AT2 cell differentiation; however, pharmacological inhibition of the pathway alone did not prevent it. These data support a role for SPARCL1 and NF-?B in alveolar cell differentiation and suggest a potential value in targeting this signaling axis to promote alveolar maturation and regeneration. Overall design: Comparative gene expression profiling analysis of RNA-seq data from lung alveolar organoids treated with recombiant SPARCL1 (2 µg/ml for 24h) versus controls.