Abnormal matrix viscosity promotes the progression of radiation-induced pulmonary fibrosis through integrin-β1/vinculin/FAK pathway in the presclerotic stage

Stiffened extracellular matrix (ECM) accelerates fibroblast activation as well as fibrosis progression. However, the contribution of ECM to the progression of fibrosis is unclear when the sclerosis of the ECM is not obvious in the early stage of radiation-induced pulmonary fibrosis (RIPF). RIPF was established in mice by thoracic irradiation. Decellularized ECM (dECM) was prepared, and the biomechanical characteristics of dECM and its inducing effect on fibroblast were detected by means of bio-atomic force microscopy (Bio-AFM), matrisome, RNAi of vinculin/integrin-β1 and point mutation of vinculin. Compared with the dECM from normal lung tissue (dECM-Nor), the matrix composition of the dECM from early stage of RIPF (dECM-RIPF) changed, with no increase in stiffness (1.44 kPa vs. 1.35 kPa) but a significant increase in viscosity (85.55 pN vs. 39.35 pN). Using our self-made viscoelastic hydrogel, we demonstrated that high viscosity could promote the activation of fibroblast. dECM-RIPF with high viscosity increased integrin-β1 expression and talin1-vinculin binding, up-regulated FAK activation, and enhanced fibroblast activation. Knockdown of vinculin blocked the above effects of dECM-RIPF, while overexpression of vinculin mutant with structural activation didn't automatically increase talin1-vinculin binding. Knockdown of vinculin expression in lung tissue could inhibit the activation of fibroblast and reduce fibrotic lesions and Collagen deposition, and alleviate the progression of RIPF. Our study proposes that early matrix remodeling in RIPF leads to an increase in ECM viscosity, and the high viscosity promotes the progression of RIPF through integrin-β1/vinculin/FAK pathway.

Extracellular matrix; Focal adhesion kinase; Matrix viscosity; Radiation-induced pulmonary fibrosis; Vinculin.