Soluble TGF-β Type Ⅱ Receptor Gene Therapy Ameliorates Radiation-induced Pulmonary Fibrosis In Rats

ObjectiveTo assess whether in vivo administration of recombinant plasmid, which carries soluble TGF- β type II receptor gene, might reduce the radiation-induced pulmonary fibrosis in rats. And to investigate the probable mechanism and observe the feasibility of gene therapy in radiation-induced pulmonary fibrosis in rats.Methods36 SD male rats were randomly distributed into four groups: (1) control (n=6); (2) RT alone (n= 10, received thoracic irradiation of a single dose of 20 Gy); (3) RT and empty plasmid treatment (n=10, empty plasmid 50 $ g per rat administrated intramuscularly once a week from week 10 to week 12 after irradiation); (4) RT and plasmid with soluble TGF-β type II receptor gene treatment (n= 10, plasmid with soluble TGF-β type II receptor gene 50 $ g per rat administrated intramuscularly once a week from week 10 to week 12 after irradiation). One week after the last therapy serum levels of sTβR- II were measured by means of ELISA and its biological activities were evaluated .14 weeks after irradiation the rats were sacrificed and the serum levels of TGF- β1 were detected by means of ELISA. Made the pathological section with the upper lobe of right lungs fixed by 10% formalin, and then investigated the changes of inflammation and fibrosis in lung tissue after stained with hematoxyline-eosin and Sirus red respectively. The mRNA expression ofCollagen I and III were analyzed by semi-quantitative RT-PCR with β -actin as the control. Results were shown as ratio of target products over β -actin. Meanwhile contents of lung hydroxyproline of the upper lobe of left lungs were also detected.ResultsHistological examination of the lungs revealed that samples from the RT alone (group 2) and the RT and empty plasmid treatment rats (group 3) showed severe interstitial fibrosis containing an accumulation of extracellular fibres. And infiltration of inflammatory cells found in thickened interalveolar septa and adjacent air spaces. In contrast, the RT and plasmid with soluble TGF- β type II receptor gene treatment rats (group 4) had mild to moderate thickening of interalveolar septa and fewer fibrotic lesions and minimal inflammatory cells. The control group showed no noticeable changes. The serum levels of TGF- β1 in group 4 were significantly lower than that in group 2 and 3. Compared with group 2 and group3, the contents of lung hydroxyproline and the mRNA expression of tissue Collagen I and III decreased significantly in group 4. There were no significant changes between group 2 and group 3. After gene therapy serum levels of sTpR-IIin group 4 were higher than that of other three groups and its biological activities were confirmed which could neutralize the cell growth inhibition to CCL-64 of bioactive TGF- β1ConclusionThis study has contributed successfully the radiation-induced pulmonary fibrosis rat model, which received thoracic irradiation of a single dose of 20 Gy.This study demonstrates amelioration of radiation-induced lung injury and pulmonary fibrosis in rats, by the administration of recombinant plasmid that carries soluble TGF- β type II receptor gene therapy, maybe through the mechanism which increase the efficient expression of soluble TGF- β type II receptor in vivo. Soluble TGF- β type II receptor would compete with cell surface receptors foractive TGF- β1.This would ameliorate radiation-induced lung injury and flbrosis by reducing the effects of active TGF- β1...