Role of the TGF beta 1-mTOR axis in fibroblast-directed alveolar epithelial regeneration in IPF

Impaired renewal capacity of type 2 alveolar epithelial cells (stem cells of the adult lung), the persistence of extracellular matrix producing myofibroblasts and the highly dysregulated cross-talk between these two cell types are key drivers in idiopathic pulmonary fibrosis (IPF). The profibrotic cytokine TGFβ1 promotes fibroblast to myofibroblast differentiation. We recently reported a key role for mechanistic target of rapamycin complex 1 (mTORC1) in mediating TGFβ1 effects in fibroblasts, yet the impact of TGFβ1/mTOR on myofibroblasts’ ability to support fibroblast-directed epithelial regeneration is unknown. Aim: investigate the TGFβ1-mTOR axis in fibroblast-directed alveolar epithelial regeneration. RNASeq analysis of primary human lung fibroblasts (pHLFs) revealed a dramatic transcriptomic shift (~4200 genes) following TGFβ1 stimulation, including genes that have been shown to orchestrate epithelial regeneration. Inhibition of mTOR with the potent ATP-competitive inhibitor AZD8055, counter-modulated nearly 30% (1186) of the TGFβ1-responsive genes, including notably FGF10, NOG and WNT5A. In a 3D in-vitro model of mouse alveolospheres co-cultured with pHLFs, significantly fewer alveolospheres were formed when pHLFs were pre-treated with TGFβ1 compared with unstimulated cells (p=0.03). Importantly, pre-treatment of pHLFs with TGFβ1 and AZD8055 resulted in a similar number of alveolospheres as observed with unstimulated pHLFs (p=0.0002 TGFβ1 vs TGFβ1+AZD8055). These data suggest that mTOR inhibition in TGFβ1-stimulated fibroblasts restores their ability to support alveolar epithelial regeneration. This strengthens the scientific rationale for exploring ATP-competitive mTOR inhibitors in IPF.