Green fluorescent protein as marker in chondrocytes overexpressing human insulin-like growth factor-1 for repair of articular cartilage defects in rabbits

Objective:To label the primary articular chondrocytes overexpressing human insulin-like growth factor (hIGF-1) with green fluorescent protein (GFP) for repair of articular cartilage defects in rabbits. Methods: GFP cDNA was inserted into pcDNA3. 1-hIGF-1 to label the expression vector. The recombinant vector, pcGI, a mammalian expression vector with multiple cloning sites under two respective cytomegalovirus promoters/enhancers, was transfected into the primary articular chondrocytes with the help of lipofectamine. After the positive cell clones were selected by G418, G418-resistant chondrocytes were cultured in medium for 4 weeks. The stable expression of hIGF-1 in the articular chondrocytes was determined by in situ hybridization and immunocytochemical analysis and the GFP was confirmed under a fluorescence microscope. Methyl thiazolyl tetrazolium ( MTT) and flow cytometer methods were employed to determine the effect of transfection on proliferation of chondrocytes. Gray value was used to analyze quantitatively the expression of type II collagen. Results: The expression of hIGF-1 and GFP was confirmed in transfected chondrocytes by in situ hybridization, immunocytochemical analysis and fluorescence microscope observation. Green articular chondrocytes overexpressing hIGF-1 could expand and maintain their chondrogenic phenotypes for more than 4 weeks. After the transfection of IGF-1, the proliferation of chondrocytes was enhanced and the chondrocytes could effectively maintain the expression of typeⅡcollagen. Conclusions: The hIGF-1 eukaryotic expression vector containing GFP marker gene has been successfully constructed. GFP, which can be visualized in real time and in situ, is stably expressed in articular chondrocytes overexpressing hIGF-1. The labeled articular chondrocytes overexpressing hIGF-1 can be applied in cell-mediated gene therapy as well as for other biomedical purposes of transgenic chondrocytes.