Inhibition of TGFß1 activation prevents radiation-induced lung fibrosis.

ABSTRACT

BACKGROUND: Radiotherapy is the main treatment modality for thoracic tumours, but it may induce pulmonary fibrosis. Currently, the pathogenesis of radiation-induced pulmonary fibrosis (RIPF) is unclear, and effective treatments are lacking. Transforming growth factor beta 1 (TGFß1) plays a central role in RIPF. We found that activated TGFß1 had better performance for radiation pneumonitis (RP) risk prediction by detecting activated and total TGFß1 levels in patient serum. αv integrin plays key roles in TGFß1 activation, but the role of αv integrin-mediated TGFß1 activation in RIPF is unclear. Here, we investigated the role of αv integrin-mediated TGFß1 activation in RIPF and the application of the integrin antagonist cilengitide to prevent RIPF. METHODS: ItgavloxP/loxP ;Pdgfrb-Cre mice were generated by conditionally knocking out Itgav in myofibroblasts, and wild-type mice were treated with cilengitide or placebo. All mice received 16 Gy of radiation or underwent a sham radiation procedure. Lung fibrosis was measured by a modified Ashcroft score and microcomputed tomography (CT). An enzyme-linked immunosorbent assay (ELISA) was used to measure the serum TGFß1 concentration, and total Smad2/3 and p-Smad2/3 levels were determined via Western blotting. RESULTS: Conditional Itgav knockout significantly attenuated RIPF (p < .01). Hounsfield units (HUs) in the lungs were reduced in the knockout mice compared with the control mice (p < .001). Conditional Itgav knockout decreased active TGFß1 secretion and inhibited fibroblast p-Smad2/3 expression. Exogenous active TGFß1, but not latent TGFß1, reversed these reductions. Furthermore, cilengitide treatment elicited similar results and prevented RIPF. CONCLUSIONS: The present study revealed that conditional Itgav knockout and cilengitide treatment both significantly attenuated RIPF in mice by inhibiting αv integrin-mediated TGFß1 activation. HIGHLIGHTS Activated TGFß1 has a superior capacity in predicting radiation pneumonitis (RP) risk and plays a vital role in the development of radiation-induced pulmonary fibrosis (RIPF). Conditional knock out Itgav in myofibroblasts prevented mice from developing RIPF. Cilengitide alleviated the development of RIPF by inhibiting αv integrin-mediated TGFß1 activation and may be used in targeted approaches for preventing RIPF.