Background: Progressive fibrosing interstitial lung diseases (PF-ILDs) are one of the leading causes of death in patients with rheumatic and musculoskeletal diseases. However, due to the limitations of in vitro organoid models and the self-limitation of in vivo fibrosis models, the link between alveolar repair and fibroblast activation in PF-ILDs remains unclear. The humanized pulmonary fibrosis mouse model reported in recent years is beneficial to understand stromal-epithelial axis.

Objectives: The humanized model was used to simulate the direct effect of PF-ILDs lung fibroblasts on alveolar epithelial cells in vivo , and to observe the abnormal regeneration features of alveolar epithelial stem/progenitor cells, type II alveolar epithelial cells (AT2) cells.

Methods: Human PF-ILDs lung fibroblasts transfected with fluorescent reporter gene were injected into the mice with severe combined immunodeficiency via tail vein to establish a humanized pulmonary fibrosis model. Mice were sacrificed on the 14th and 35th days after injection, respectively, and the degree of fibrosis in the model was evaluated from the imaging and histological aspects. The abnormal differentiation state of AT2 cells in the humanized model was detected by immunohistochemistry, including indicators related to the intermediate state of differentiation, cell senescence, and Epithelial-Mesenchymal transition (EMT).

Results: The humanized mouse model based on PF-ILDs lung fibroblasts (LL29A) was successfully established. After LL29A cells were injected into mice, they mainly colonized the lungs and continued to expand. Pulmonary fibrosis appeared on the 14th day after injection, and the fibrosis was mainly derived from mice. Fibrosis persisted after 35 days and was gradually maintained by collagen secretion from human fibroblasts. PF-ILDs lung fibroblasts can directly induce alveolar epithelial cell damage, and then induce alveolar epithelial cell senescence and EMT, and differentiate into KRT5 ⁺ basal-like cells, which hinders lung regeneration and promotes lung fibrosis.

Conclusion: In this study, we established a mouse model of humanized pulmonary fibrosis and revealed that human PF-ILDs lung fibroblasts lead to aberrant alveolar epithelial cell regeneration in vivo, mainly by generating KRT5 ⁺ basal-like cells and inducing senescence of AT2 cells, EMT phenotypic differentiation, and inhibition of lung regeneration.

Acknowledgements: NIL.

REFERENCES: NIL.

Disclosure of Interests: None declared.