Compound Kushen Injection Mitigates Radiation-Induced Pulmonary Fibrosis by Restoring AT2 Cell Stemness and Alveolar...

To determine whether radiation directly compromises AT2 cell stemness through oxidative and DNA damage, and to evaluate whether Compound Kushen Injection (CKI) protects AT2 cells, restores alveolar regeneration, and mitigates radiation-induced pulmonary fibrosis.

Mice were randomly assigned to a control, irradiated model, or CKI-treated group. CKI (4 mL·kg^-1·d^-1) was administered intraperitoneally from 3 days before irradiation until the designated endpoints. A thoracic irradiation plus left pneumonectomy model was established to mimic clinical scenarios requiring postoperative lung regeneration. Lung function, histopathology, and compensatory growth of the accessory lobe were assessed. AT2 cells proliferation, differentiation, and transitional Krt8⁺ accumulation were evaluated using lineage tracing in Sftpc-CreER and Rosa26-ZsGreen mice. Oxidative stress and DNA damage were examined by immunofluorescence. Transcriptomic profiling of sorted lineage-labeled AT2 cells was conducted to identify radiation- and CKI-responsive genes.

Radiation caused marked oxidative stress and γ H2AX-defined DNA damage in AT2 cells, accompanied by suppression of Sod1 and Parp1 and increased Il6 and Tgfb1 expression (P<0.01). These epithelial-intrinsic injuries led to reduced AT2 proliferation, impaired AT2-to-AT1 differentiation, and long-term accumulation of Krt8⁺ transitional cells. Functionally, irradiation significantly impaired compensatory lung regeneration after pneumonectomy and promoted fibrotic remodeling. CKI markedly alleviated ROS accumulation and DNA damage in AT2 cells, restored Sod1 and Parp1 expression, suppressed inflammatory and profibrotic signaling, rescued AT2 proliferative and differentiative capacities, reduced transitional Krt8+ cell accumulation, and improved both alveolar regeneration and fibrosis (P<0.05).

CKI preserves epithelial integrity by reducing oxidative and DNA damage, restoring AT2 stemness, and enhancing alveolar repair. These findings provide mechanistic support for CKI as a potential epithelial-directed therapeutic strategy for preventing or treating radiation-induced lung fibrosis.