Alveolar epithelial depletion of βPAK-interacting exchange factor drives spontaneous pulmonary fibrosis by impairing stemness.

Aberrant repair/regeneration of alveolar epithelial stem cells is a key driver of pulmonary fibrosis (PF). While βPAK-interacting exchange factor (βPIX) is connected to stem cell signaling, its role in pulmonary fibrosis (PF) remains unknown. Here, we generated conditional βPIX knockout mice to investigate its contribution to PF pathogenesis. Selectively depleting βPIX in alveolar type 2 (AT2) cells led to progressive PF in mice, recapitulating the key features observed in human idiopathic pulmonary fibrosis (IPF), where AT2 cells exhibit significantly reduced βPIX levels. Single-nucleus RNA sequencing of the lungs of βPIX-deficient mice revealed the emergence of progenitor cells in a transitional stem cell state with senescent attributes, along with active, collagen-producing myofibroblasts. Mechanistically, the loss of βPIX impaired AT2 cell stemness by downregulating Wnt/β-catenin signaling. AT2 cells from IPF patients also presented reduced levels of β-catenin and Axin2, confirming the downregulation of Wnt/β-catenin signaling. Treatment with a glycogen synthase kinase-3β inhibitor reactivated Wnt/β-catenin signaling and attenuated fibrosis in βPIX-deficient mice. Our results establish a direct causal link between βPIX deficiency and PF, highlighting βPIX and its downstream pathway as promising therapeutic targets for this devastating disease.