Abstract: BACKGROUND: Early synovial inflammation plays a crucial role in the onset and progression of knee osteoarthritis and has become a significant focus for research and intervention in joint disorders. Electroacupuncture, as a commonly used physical intervention, lacks a systematic molecular-level explanation of its mechanism in synovial tissue. Analyzing the gene expression profile of synovial tissue using transcriptomic technology helps reveal the key signaling pathways and targets regulated by electroacupuncture, providing a theoretical basis and data support for early intervention in osteoarthritis.
OBJECTIVE: To investigate the effect of electroacupuncture on early synovial inflammation in a rat model of knee osteoarthritis based on transcriptomic sequencing technology.
METHODS: Twenty-four 3-month-old male Sprague-Dawley rats were randomly divided into a control group, a model group, and an electroacupuncture group, with eight rats in each group. The model group and electroacupuncture group underwent anterior cruciate ligament transection to induce the knee osteoarthritis model, while the control group did not. Four weeks after modeling, the electroacupuncture group received electroacupuncture at bilateral “Zusanli” (ST 36), “Xuehai” (SP 10), “Taixi” (KI 3), and “Yanglingquan” (GB 34). The parameters were: sparse-dense wave at 3 Hz/15 Hz, current intensity of 
1 mA, 30 minutes per session, once daily, 5 days per week, for a total of 2 weeks. After the intervention, the synovium of the left knee joint was collected for mRNA sequencing, and the right knee joint was subjected to safranin O-fast green staining and Mankin’s scoring.
RESULTS AND CONCLUSION: (1) Compared with the control group, the model group showed rough cartilage surfaces and disordered synovial cell arrangement, with increased Mankin's scores (P < 0.001). Compared with the model group, the electroacupuncture group exhibited smoother cartilage surfaces, reduced inflammatory infiltration in synovial tissue, and decreased Mankin’s scores (P < 0.05). (2) There were 29 genes upregulated in the synovial tissue of the model group and downregulated in the electroacupuncture group, and 19 genes downregulated in the model group and upregulated in the electroacupuncture group. (3) Gene Ontology analysis indicated that the main functions of these differentially expressed genes were enriched in MHC protein complex binding, protein homodimerization activity, and BH3 domain binding. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the differentially expressed genes were primarily enriched in cell adhesion molecules, the phosphatidylinositol 3-kinase-protein kinase B (PI3K-Akt) signaling pathway, the nuclear factor kappa B signaling pathway, and the peroxisome proliferator-activated receptor signaling pathway. (4) Compared with the control group, the mRNA expression of Myh9, Hmox1, and S100a8 in synovial tissue was significantly increased in the model group (P < 0.001, P < 0.001, P < 0.001), while the mRNA expression of Rack1 and Ddit3 was significantly decreased (P < 0.01, P < 0.001). Compared with the model group, the mRNA expression of Myh9, Hmox1, and S100a8 in synovial tissue was significantly decreased in the electroacupuncture group (P < 0.05, P < 0.001, P < 0.001), while Ddit3 mRNA expression was significantly increased (P < 0.001), and Rack1 mRNA expression showed an increasing trend, but the difference was not statistically significant (P > 0.05). Real-time quantitative PCR results were largely consistent with the gene sequencing results. These findings indicate that electroacupuncture can significantly alleviate early synovial inflammation in rats with knee osteoarthritis, which may be related to inhibiting the expression of Myh9, Hmox1, and S100a8 and promoting the expression of Rack1 and Ddit3 in synovial tissue.

Key words: electroacupuncture, knee osteoarthritis, synovitis, transcriptomics, differentially expressed genes, mRNA sequencing, signaling pathways