Senescence and Short Telomeres Make IPF Lung Cells Far More Vulnerable to Injury

Idiopathic pulmonary fibrosis is a progressive, irreversible lung disease. It is thought to start with repeated microinjury to the lung's alveolar lining cells, followed by faulty repair. Senescent cells with shortened telomeres accumulate in IPF lungs, and mutations in telomere-maintenance genes raise IPF risk. The standard bleomycin mouse model poorly predicts human drug responses, so patient-derived cell models are needed.

The team isolated alveolar epithelial cells from lung tissue of pulmonary fibrosis patients (predominantly IPF) and from largely cancer-surgery non-fibrotic controls. Cells were grown at an air–liquid interface, a more physiological setup containing about 40% type II alveolar cells plus type I and intermediate cells. They were injured with bleomycin (30 μg/mL) and assessed at 48 and 96 hours by ELISA, qPCR, immunofluorescence and telomere measurement (qPCR and FISH). Further experiments compared upper versus lower lung, added extra cell passages to shorten telomeres, and tested cycloastragenol (a telomerase activator) and four senomorphic drugs.

Patient cells had shorter telomeres at baseline, and bleomycin shortened them further. Bleomycin raised p16, p21 and the DNA-damage marker H2AX, plus inflammatory cytokines (IL-6, IL-36γ, IL-1α), more in patient cells than controls. Type I and II alveolar marker responses were suppressed in patient cells, while keratin 17-positive intermediate cells increased. Those cells had weaker telomere signal in both cultures and patient lung tissue. Cells from the lower lung, which is typically more fibrotic, had shorter telomeres and stronger injury responses than upper-lung cells. Baseline telomere length was inversely related to the p21 response. A single bleomycin dose produced effects that persisted to 96 hours. IL-36γ was found in senescent type II-like cells in fibrotic lung tissue.

Extra passaging shortened telomeres and amplified injury, even without bleomycin. Long-term cycloastragenol lengthened telomeres by about 20%, reduced telomere loss and blunted senescence and cytokine responses. Among senomorphics, resveratrol significantly limited telomere loss, rapamycin reduced p21, and the NF-κB inhibitor iguratimod lowered cytokines and α-SMA. Metformin had no significant effect.

The results support the idea that telomere shortening and senescence make the IPF epithelium more injury-prone, and that targeting these pathways may be protective. The model could help screen senotherapeutics before clinical trials.

Caveats: cultured cells are an artificial environment, sample sizes appear modest, and controls were mostly from cancer patients. The work is preclinical, bleomycin may not mimic the true IPF trigger, and the passaging experiments cannot separate telomere effects from other culture changes.