Background So far,there is no efficient treatment for pulmonary fibrosis.The objective of this study was to determinewhether intramuscular injection of the hepatocyte growth factor(HGF)plasmid DNA by in vivo electroporation couldprevent bleomycin-induced pulmonary fibrosis in rats,and to investigate the possible mechanisms.Methods Twenty male Wistar rats were randomly divided into four groups:control group(group C),model group(groupM),early intervention group(group Ⅰ)and late intervention group(group Ⅱ).Groups M,Ⅰ and Ⅱ were intratrachealiyinfused with bleomycin,then injected the plasmid pcDNA3.1-hHGF to group Ⅰ on day 7,14 and 21.Group Ⅱ received thesame treatment like Group Ⅰ on day 14 and 21.All the rats were killed on day 28 after bleomycin injection.We detectedHomo HGF expression in the rats with ELISA method and estimated the pathological fibrosis score of lung tissue usinghematoxylin eosin(HE)and Massion staining.The mRNA expression of transforming growth factor-β1(TGF-β1),cycloxygenase-2(COX-2),and rat HGF in rat pulmonary parenchyma were evaluated by RT-PCR.Immunohistochemistry and Western blotting were performed to determine the protein expression of transforming TGF-β1and COX-2 in lung parenchyma.Results The plasmid pcDNA3.1-hHGF could express hHGF in NIH3T3 cells and the hHGF protein is secreted into theculture medium.The expression of hHGF protein could be monitored in quadriceps muscle,plasma and lung in GroupsⅠ and Ⅱ.Pulmonary fibrosis levels of Groups Ⅰ and Ⅱ were obviously lower than that of group M(P<0.05).Expression of TGF-β1 protein and mRNA in lung tissue was markedly decreased in Groups Ⅰ and Ⅱ compared withGroup M(P<0.05).The level of expression of HGF and COX-2 mRNA was higher in Groups Ⅰ and Ⅱ than in Group M(P<0.05).Conclusions Injection of the plasmid pcDNA3.1-hHGF into skeletal muscle with electroporation has a potential role inthe treatment of bleomycin-induced lung fibrosis.Exogenous HGF may inhibit the expression of TGF-β1 and regulate thecrosstalk between AECs and mesenchymal fibroblasts.Chin Med J 2007;120(16):1432-1437 Background So far, there is no efficient treatment for pulmonary fibrosis.The objective of this study was to determinewhether intramuscular injection of the hepatocyte growth factor (HGF) plasmidDNA by in vivo electroporation couldprevent bleomycin-induced pulmonary fibrosis in rats, and to investigate the possible mechanisms. Methods Twenty male Wistar rats were divided into four groups: control group (group C), model group (groupM), early intervention group (group I) and late intervention group (group Ⅱ) were intratrachealiyinfused with bleomycin, then injected the plasmid pcDNA3.1-hHGF to group I on day 7,14 and 21.Group Ⅱ received thesame treatment like Group I on day 14 and 21.All the rats were killed on day 28 after bleomycin injection . We detected Homo HGF expression in the rats with ELISA method and estimated the pathological fibrosis score of lung tissue using hepatoxylin eosin (HE) and Massion staining. The mRNA expression of transforming growth factor-beta 1 (TGF-β1), cycloxygenase-2 (COX-2), and rat HGF in rat pulmonary parenchyma were evaluated by RT-PCR. Immunohistochemistry and Western blotting were performed to determine the protein expression of transforming TGF- β1 and COX-2 in lung parenchyma. Results The plasmid pcDNA3.1-hHGF could express hHGF in NIH3T3 cells and the hHGF protein was secreted into the culture medium. The expression of hHGF protein could be monitored in quadriceps muscle, plasma and lung in Groups I and II. Pulmonary fibrosis levels of Groups I and II were significantly lower than that of group M (P <0.05) .Expression of TGF-β1 protein and mRNA in lung tissue was markedly decreased in Groups I and II compared with Group M (P <0.05). The level of expression of HGF and COX-2 mRNA was higher in Groups I and II than in Group M (P <0.05) .Conclusions Injection of the plasmid pcDNA3.1-hHGF into skeletal muscle with electroporation has a potential role in the treatment of bleomycin-induced lung fibrosis. Exogenous HGF may inhibit the expression of TGF-β1 and regulate thecrosstalk between AECs and mesenchymal fibroblasts. Chin Med J 2007; 120 (16): 1432-1437