LAM is rare genetic lung disease caused by the inactivating mutations in TSC1/2 genes, resulting in mTORC1hyperactivation, abnormal LAM cell growth causing cystic lung destruction requiring lung transplantation. We identified expression of pro-fibrotic ACTA2, COL1A1, COL1A2, COL6A1, COL3A1, and TGFB3 transcripts in PDGFRa+ fibroblasts from LAM lung demonstrating their activation, and upregulation of transitional AT2/AT1 cell state, a hallmark of lung injury/repair. To study cell and molecular mechanisms involved in fibroblast activation in LAM lung we utilized a novel Tbx4^LMECreTsc2^KO mice characterized progressive female-specific, age-dependent LAM-like lung structure and function decline. Like in human LAM, we identified fibrotically activated Pdgfra+ fibroblasts and transitional AT2/AT1 cells specifically in female breeder Tbx4^LMECreTsc2^KO lungs. We also observed substantial collagen deposition in female mouse Tbx4^LMECreTsc2^KO lung lesions. Tsc2^KO fibroblasts exhibit transcriptomic changes consistent with the resistance to apoptosis (up-regulation of Tgfb) and induced senescence (up-regulation of Il6, Ccl8, Mmp3) which is a sign of lung injury/repair. We reported that at the early stage of the disease Tsc2^KO fibroblasts stimulate AT2 cell proliferation and transdifferentiation. Our new data suggest that at the late stage of the disease there is an overall decrease in pulmonary healing indicative of the exhaustion of AEC renewal capacity. Our data indicate that abnormal epithelial-mesenchymal crosstalk during injury/repair facilitates fibroblast activation in the LAM lung.

These studies are funded by NIH/NHLBI RO1 HL141462, RO1 HL158737, RO1151647, and UO1HL131022 to V.P.K.