library_construction_protocol: The young control and bleomycin-injured WT and Sdc1–/– cohort details was published (18). For the aged mouse cohort, freshly harvested bleomycin-injured WT and Sdc1–/–mouse lungs were enzymatically digested with elastase (Worthington Biochemical Corporation, Lakewood, NJ) and liberase (RocheTM, Millipore-Sigma) and mechanically disrupted to generate single cell suspension per previously published protocol (43). Viable lung cell suspension (DAPI¯) was flow-sorted for lung immune cells (CD45+), endothelial cells (CD31+), epithelial cells (CD326+), and stromal cells (CD45¯CD31¯CD326¯). Equal proportions of all four cell types were pooled and subjected to single-cell capture using EvercodeTM WT mini kit v2 for barcoding and library preparation (Parse Bioscience, Seattle, WA) following the manufacturer's protocol. Novaseq SP at 200 cycles, 800 million reads