ROLE OF VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF) IN PATHOGENESIS OF KNEE OSTEOARTHRITIS

Recent evidences suggest that angiogenesis and inflammation contribute to the development and progression of knee osteoarthritis (OA). Vascular endothelial growth factor (VEGF) is a potential angiogenic factor associated with the pathogenesis of OA. The etiology of OA is poorly understood and many risk factors can influence OA. The purposes of this study was to investigate VEGF mRNA and protein levels in plasma, synovial fluid (SF), and synovial tissue from knee OA patients and in vitro under osteoarthritic-like conditions (hypoxia with or without interleukin-1ß(IL-1ß) treatment) using fibroblast like synoviocytes (FLS) isolated from knee OA patients. Additionally, this study was designed to determine the associations between single nucleotide polymorphisms (SNPs) of the VEGF gene (-2578C/A, -1154G/A, -634G/C, and +936C/T) and the susceptibility of knee OA, as well as to examine the expressions of miR-210 and miR-223 in knee OA patients. The expressions of VEGF mRNA, miR-210, miR-223 were evaluated by real time reverse transcriptase-polymerase chain reaction. The protein levels of VEGF were determined using enzyme-linked immunosorbent assay and immunohistochemistry. The SNPs of VEGF gene were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The VEGF protein was expressed in SF and synovial tissue from OA patients. There was a strong positive correlation between SF VEGF and the disease severity and a weak positive correlation in OA plasma VEGF levels and the disease severity. The expression of VEGF mRNA in OA synovial tissue was not significantly different when compared with non-inflamed anterior cruciate ligament controls. Moreover, the expression of miR-210 and miR-223 in OA synovial tissue were higher than those in controls. However, the expression of VEGF in FLS under hypoxia with IL-1ß treatment was remarkably elevated compared to normoxia. The levels of miR-210 were expressed in the same pattern with VEGF mRNA, whereas no significant difference was observed in the expression of miR-223. No associations between genotype distribution and allelic frequency of VEGF SNPs were found in OA compared with those in controls. The stratify analysis according to the severity of knee OA showed that AA genotype of -2578C/A in early stage was significantly different compared with that in advanced stage. Moreover, plasma VEGF levels were increased in the OA patients carrying the -634CC genotype. These findings indicated that VEGF expression was increased in OA samples and had a positive correlation with the severity of knee OA. The CC genotype of -634G/C was also associated with the VEGF production. The -2578AA was associated with a low risk of OA, therefore the AA genotype may play a protective role against progressive OA. FLS treated with osteoarthritic-like conditions showed elevated VEGF and miR-210 levels. VEGF may be useful for monitoring the OA severity and could play a substantial role in the development and progression of knee OA.