HAS1 and idiopathic pulmonary fibrosis: Interestingly, Col14a1hi/Pi16+ adventitial MCs, which may also represent the murine homologue of the previously identified Has1+ mesenchymal populations described in human IPF (17), were the sole fibroblast population that maintained Ptgfr expression throughout the fibrotic remodeling following induction of mutant SftpcI73T (Supplemental Figure 9), raising the potential that PGF2α signaling could modulate all or part of this trajectory in this population.