RESUMEN
BACKGROUND: The origin of αSMA-positive myofibroblasts, key players within organ fibrosis, is still not fully elucidated. Pericytes have been discussed as myofibroblast progenitors in several organs including the lung. METHODS: Using tamoxifen-inducible PDGFRß-tdTomato mice (PDGFRß-CreERT2; R26tdTomato) lineage of lung pericytes was traced. To induce lung fibrosis, a single orotracheal dose of bleomycin was given. Lung tissue was investigated by immunofluorescence analyses, hydroxyproline collagen assay and RT-qPCR. RESULTS: Lineage tracing combined with immunofluorescence for nitric oxide-sensitive guanylyl cyclase (NO-GC) as marker for PDGFRß-positive pericytes allows differentiating two types of αSMA-expressing myofibroblasts in murine pulmonary fibrosis: (1) interstitial myofibroblasts that localize in the alveolar wall, derive from PDGFRß+ pericytes, express NO-GC and produce collagen 1. (2) intra-alveolar myofibroblasts which do not derive from pericytes (but express PDGFRß de novo after injury), are negative for NO-GC, have a large multipolar shape and appear to spread over several alveoli within the injured areas. Moreover, NO-GC expression is reduced during fibrosis, i.e., after pericyte-to-myofibroblast transition. CONCLUSION: In summary, αSMA/PDGFRß-positive myofibroblasts should not be addressed as a homogeneous target cell type within pulmonary fibrosis.