Effects of electroacupuncture on autophagy of the synovial tissue in the knee joint of rats with knee osteoarthritis by regulating PI3K/Akt/mTOR pathway

To explore the effect of electroacupuncture (EA) via regulating the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway on autophagy of synovial tissue in rats with knee osteoarthritis (KOA).

Thirty-six male Sprague-Dawley (SD) rats were randomly divided into a normal group, a model group, and an EA group, with 12 rats in each group. The KOA model was replicated by injection of 50 μL sodium monoiodoacetate (MIA) into the right knee joint cavity. After successful establishment of the model, rats in the EA group received EA treatment at "Dubin" (ST35) and "Zusanli" (ST36) on the affected side, 20 min each time, once a day for 3 consecutive weeks. The Lequesne MG behavioral scale was used to evaluate the knee joint function of rats. The pathological morphology of the synovial tissue was observed after hematoxylin-eosin (HE) staining. The ultrastructure of autophagosomes and autolysosomes in the synovium was observed under transmission electron microscopy. The contents of autophagy-related protein 5 (Atg5) and autophagy-related protein 12 (Atg12) in the synovial tissue were detected by ELISA method. The expression levels of PI3K, Akt, and mTOR mRNA in the synovial tissue were detected by qPCR. The relative expression levels of PI3K, Akt, mTOR, UNC-51-like kinase 1 (ULK1), Beclin-1, and microtubule-associated protein light chain 3 (LC3) protein in the synovial tissue were detected by Western blot.

Compared with the normal group, the Lequesne MG score of the knee joint was increased (P < 0.01) in the model group; the synovial collagen fiber proliferated, inflammatory cell infiltration occurred, the number of autophagosomes and autolysosomes increased; contents of Atg5, Atg12, and relative expressions of ULK1, Beclin-1 protein and LC3Ⅱ/LC3Ⅰ ratio in the synovial tissue were increased (P < 0.01), while the expressions of PI3K, Akt, and mTOR mRNA and protein were decreased (P < 0.01). Compared with the model group, the Lequesne MG score of the knee joint in the EA group was decreased (P < 0.01); the proliferation of synovial collagen fiber was alleviated and they were arranged neatly, the inflammatory cell infiltration was reduced, the number of autophagosomes and autolysosomes was decreased; contents of Atg5, Atg12, and the relative expressions of ULK1, Beclin-1 proteins and LC3Ⅱ/LC3Ⅰ ratio in the synovial tissue were decreased (P < 0.01), while the expressions of PI3K, Akt, and mTOR mRNA and protein were increased (P < 0.05, P < 0.01).

EA at ST35 and ST36 can inhibit the autophagy of synovial tissue, improve the knee joint function and the morphological structure of synovial tissue in KOA rats, and its mechanism may be related to the activation of PI3K/Akt/mTOR signaling pathway.