The Role Of DDR2in Pathological Process Of Pulmonary Fibrosis

Pulmonary fibrosis is a chronic interstitial lung disease caused by a varietyof factors. Due to rapid development of industry and increased population ofsmokers as well as agings, pulmonary fibrosis has become one of the commonand frequently occurring diseases in our country. Although scientists have done alot of research on this disease, so far, the etiology and pathogenesis of pulmonaryfibrosis is still unclear. Difficulties in early diagnosis, poor prognosis, and thelack of effective treatment makes pulmonary fibrosis an insurmountable disease,as a result, it needs more in-depth study.DDR2molecule belongs to the tyrosine kinase receptor (Receptor TyrosinKinase, RTK) family. This molecular mediats signal transduction between cellsand extracellular matrix, and broadly participates in physiology and pathologyprocess of cell proliferation and differentiation, individual development. Whenthe ligand binds with DDR2, its tyrosine residues of the intracellular area will bephosphorylated. Phosphorylation sites thus raise the downstream molecules,eventually resulting in activation of the whole signal pathway. Compared withclassic RTKs, the duration of its activation significantly improved, suggesting that DDR2may be involved in slower pathological process in our body.Studies have also shown that, DDR2is only highly expressed in lung,stomach and other tissues. Pulmonary fibrosis can produce a large number ofcollagens, which provide a space for activation of DDR2. In human primaryrecurrent biliary cirrhosis and rat alcoholic liver fibrosis model, DDR2expressionlevel gradually increased during the process of diseases. DDR2also regulates theexpression of collagenases such as MMP-1and MMP13in arthritis, and MMPsare precisely the important molecules in pulmonary fibrosis. Therefore, wespeculate that DDR2inevitably plays an important role in pulmonary fibrosis.We carried out the study on the following aspects:1. Detected DDR2expression levels in human samples of normal lung andpulmonary fibrosis through immunofluorescence staining.2. Established bleom ycin induced murine pulmonary fibrosis model anddetected DDR2expression patterns in the process of pulmonary fibrosisusing Real-time PCR and Western blot.3. Established bleomycin induced pulmonary fibrosis model in DDR2deficientmice, and confirmed the role of DDR2in pulmonary fibrosis with themethods such as HE staining, Masson staining, TUNEL staining, ELISA,immunofluorescence, and gelatinase spectroscopy, etc.4. siDDR2specifically downregulated DDR2expression of lung tissue in wildmice, and HE and Masson staining was taken to observe the change ofpulmonary fibrosis after DDR2was interferenced.5. Real-time PCR and Western blot was adopted to detect expression offibrosis-related genes and DDR2downstream genes in TGF-β1stimulatedmouse primary lung fibroblasts.6. Observation of DDR2-specific small molecule inhibitor’s efficiency in pulmonary fibrosis model.Result: Compared with normal human lung samples, DDR2expressionwas significantly increased in fibrosis samples; DDR2expression level was alsochanged in the process of murine pulmonary fibrosis; Inflammatory invasion andsecretion of MMPs was markedly reduced after deletion of DDR2gene;pulmonary fibrosis was also declined in DDR2deficient mice; hydroxyprolinecontent in lung tissues, the amount of TGF-β1in bronchoalveolar lavage fluidwas significantly higher in DDR2wild mice; apoptotic cells was significantlyreduced in latern fibrosis of DDR2deficient mice; expression of fibrosis-relatedgenes in TGF-β1stimulated mouse primary lung fibroblasts was decreased afterDDR2signaling was blocked; DDR2gene deletion significantly downregulatedphosphorylation of AKT and p38; the number of myofibroblasts induced byTGF-β1was also reduced after DDR2deletion.