Therapeutic Effects Of Radiation Induced Lung Fibrosis By Clearance Of Senescent Cells

Ionizing radiation exposure and clinical radiation therapy could result in radiation pneumonia and pulmonary fibrosis.According to the difference of the judgment terminal and the influencing factors,the incidence of radiation-induced pulmonary fibrosis is varied from 1%to 43%.The pathogenesis of radiation-induced pulmonary fibrosis has not been clarified,and the prognosis is very poor.There is still a lack of specific and effective therapeutic drug in clinical.Therefore,it is of great significance to clarify the pathogenesis of radiation-induced pulmonary fibrosis for the treatment of clinical diseases and the development of drugs.To date,no effient treatment has been found for pulmonary fibrosis.Therefore,to elucidate the mechanism of radiation induced pulmonary fibrosis and develop novel drug has been the urgent need.ABT-263(BCL-2 inhibitor)as a drug used in clinical treatment of cancer in recent years,was discovered that it could improve IR induced damage in hematopoietic stem cell.This study investigated the effects of ABT-263 on clearance of senescent AECII and attenuation of lung fibrosis in mice.Part Ⅰ.The role of cellular senescence in radiation-induced pulmonary fibrosis in miceThis study investigated the role of AECII senescence and the senescence-associated secretory phenotype(SASP)in murine lung fibrosis model induced by thoracic X ray exposure.Healthy male C57BL/6 mice were randomly divided into control group and irradiation(IR)group.The right chest of mice in the IR group received 17 Gy irradiationexposure.After 4,8,12,16 and 23 weeks,the organ index at different time points were detected,and the for of the irradiated mice were observed.The lung tissue,collagen formation and expression of β-Gal in mice were observed by immunohistochemistry.The expression of Pro-SPC and P16 was detected by immunofluorescence.The gene expression of pulmonary fibrosis was detected by gene PCR array.Peripheral blood count,HSC/HPC,CFU-GM and T cell proliferation assay were conducted to oberserve the functional damage of hematopoietic immune system at different time points.This study showed that 17Gy right thoracic irradiation can induce the development of pulmonary fibrosis;The right lung local irradiation can significantly increase the number and distribution of β-Gal staining and P16 positive cells in the AEC Ⅱ cells of the irradiated lung tissue.Mouse right lung irradiation can increased the expression of genes related to pulmonary fibrosis,inflammation related cytokines in the 8 weeks significantly,fibrosis related factors in the 23 weeks;Tgf-beta 16 weeks to reach peak;Bcl2 expression was continuously increased,in the 23 week reached the highest;The lung irradiation has a harmful effect on hematopoiesis immune system in mice.The results suggest that the aged cells may be a target for the prevention and treatment of radiation-induced pulmonary fibrosis.Part Ⅱ.Clearance of senescent AECⅡ and attenuation of radiation induced lung fibrosis by ABTTo investigate the effects of ABT on clearance of senescent AECⅡ and attenuation of lung fibrosis in mice,healthy male C57BL/6 mice were divided into control group(Control),ABT administration group(ABT),irradiation group(IR)and treatment group(IR+ABT).Mice received 17Gy on the right side of the chest exposed to X ray irradiation,ABT-263 were administered 50mg/kg,i.g for 5days at 16 weeks post exposure,repeated administered another 5days after 2weeks interval.30 weeks survival rate post IR exposure of mice was observed.After two courses of treatment,mouse lung parenchyma injury was evaluated by CT scan,HE,Msson staning and Immunohistochemistry for detection of β-galactosidase expression.The expression of Prosurfactant Protein C and P16 in lung tissue of lung tissue was detected by immunofluorescence.PCR gene chip technology to detect lung fibrosis related gene expression.Peripheral blood count,bone marrow hematopoietic stem cells and hematopoietic progenitor cell typing test,bone marrow cell colony forming assay and T cell proliferation assay was detected to observe the changes of hematopoietic function in irradiated mice.Our work was the first time to investigate the effects of ABT263 on the pulmonary fibrosis induced by radiation.The result showed that ABT263 could reduce the mortality of mice exposed to 17Gy local irradiation and attenuate the development of pulmonary fibrosis;ABT could also mitigate the damages of hematopoietic cells induced by local irradiation.These effects might attribute to the clearance of senescent type Ⅱ lung epithelial cell,the redcution of lung fibrosis related pathway proteins,and the decreasement of Bcl-2 expression.The data suggested that ABT-263 might play a role in the treatment and mitigation of radiation induced pulmonary fibrosis by inhibiting Bcl-2.The study provided a new approach for treatment of radiation-induced pulmonary fibrosis.