b1 integrin regulates epithelial proliferation and cell shape during alveolar repair

Integrins are extracellular matrix receptors comprised of an a and b subunit that connect and mediate signaling between cells and the surrounding matrix. In organogenesis of epithelial tissues, the b1 integrin subunit regulates essential epithelial cell functions, but the role of b1 integrin in epithelial repair is poorly understood. To define the role of b1 integrin during alveolar repair, we challenged b1 integrin deficient mice with intratracheal lipopolysaccharide, resulting in increased mortality with emphysematous lungs 21 days following injury. The alveolar barrier was repopulated with an overabundance of type 2 alveolar epithelial cells, with reduced numbers of elongated alveolar type 1 cells, suggesting b1 integrin is required for type 2 to type 1 epithelial transition. Consistent with this finding, b1 deficient type 2 epithelial cells proliferated at increased rates throughout repair, lacked actin-rich cellular protrusions necessary for lateral cellular extension, and exhibited transcriptomic dysregulation of adherens junction and actin polymerization pathways. Finally, we show that b1 integrin balances actin polymerization versus stabilization through GTPase activation. Taken together, these data support a novel role for b1 integrin in re-establishing the alveolar niche after injury through modulation of type 2 epithelial cell proliferation and cytoskeletal-dependent cell shape change. Overall design: Single Cell RNAseq of dissociated adult mouse lungs from either Control (Itgb1 fl/fl) or epithelial iKO Itgb1 mice (Itgb1 iKO). Mice were treated with PBS or LPS, then sequenced 7 or 21 days later. Suspensions were enriched for cells that were CD45 negative, Ter119 negative, and viable. Lungs at 21 days post treatment were enriched for epithelial cells by collecting EPCAM positive cells.