ObjectiveTo study the expressions of Renin, angiotensin converting enzyme (ACE), angiotensin receptor 1 (AT1R), and AT2R in synovial tissue of osteoarthritis (OA) at different stages.MethodsThe patients who were treated with upper knee amputation because of trauma or total knee arthroplasty for OA between January 2018 and December 2018 were enrolled. Among them, 32 patients who met the selection criteria were included in the study. According to the Kellgren-Lawrence (K-L) X-ray classification, they were allocated to normal synovial group (group A, n=9), moderate OA synovial group (group B, n=11, K-L level 3), and advanced OA synovial group (group C, n=12, K-L level 4). The relative expressions of Renin, ACE, AT1R, and AT2R mRNAs and proteins were detected by real-time fluorescence quantitative PCR (qRT-PCR) and Western blot.ResultsThe relative expressions of Renin, ACE, and AT1R mRNAs and proteins were significantly higher in group B and group C than in group A (P<0.05). The relative expressions of ACE and AT1R mRNAs and proteins and Renin protein were significantly higher in group C than in group B (P<0.05). However, the relative expressions of AT2R mRNA and protein were lower in group B and group C than in group A (P<0.05), and in group C than in group B (P<0.05).ConclusionThe expressions of Renin, ACE, and AT1R in synovial tissue of osteoarthritis significantly increase as the K-L level increased, and the expression of AT2R decreases. Renin, ACE, AT1R, and AT2R have a certain degree of correlation with the development of OA.