[Effects of acupuncture on the efferocytosis pathway of Mer receptor tyrosine kinase in mice with adjuvant arthritis].

Objectives: To observe the effect of acupuncture at "Zusanli" (ST36) on the expression of Mer receptor tyrosine kinase (MerTK)-related efferocytosis regulatory molecules in mice with adjuvant arthritis induced by complete Freund's adjuvant (CFA), so as to explore the potential mechanism of acupuncture on efferocytosis in adjuvant arthritis.

Methods: C57BL/6J mice were randomly divided into a saline group, a model group, and an acupuncture group (10 mice/group). The right hind footpad of mice in the saline group was injected with 0.9% sodium chloride solution, while those in the model group and the acupuncture group were injected with CFA (50 μL) to establish the model of adjuvant arthritis. Mice in the acupuncture group received acupuncture at bilateral ST36 once a day for a total of 7 times, and mice in the saline group and the model group were fixed in the same way. During the experiment, paw swelling degree and the paw withdrawal thermal latency (PWTL) of mice were measured before modeling, on the day of modeling (D0) and on the 1^st, 3^rd, 5^th and 7^th day of acupuncture (D1, D3, D5, D7) to evaluate paw swelling and pain conditions. The mRNA expressions of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β in spinal cord tissue were detected by real-time quantitative PCR. The protein expressions of MerTK, phosphorylated (p)-signal transducer and activator of transcription 3 (STAT3), STAT3, and programmed death-ligand 1 (PD-L1) in footpad and spinal cord tissue were detected by Western blot.

Results: After modeling, compared with the saline group, the PWTL on D0-D7, the protein expression of PD-L1 in spinal cord and protein expressions of MerTK and PD-L1 in footpad, the phosphorylation level of STAT3 in spinal cord and footpad were decreased (P<0.01) in the model group, while the degree of paw swelling, mRNA expressions of TNF-α, IL-6, and IL-1β in spinal cord tissue were increased (P<0.01, P<0.05). Compared with the model group, the PWTL on D1-D7, the protein expressions of MerTK, PD-L1 and phosphorylation level of STAT3 in spinal cord and footpad were increased (P<0.01) in the acupuncture group after acupuncture intervention, while the degree of paw swelling on D7, the mRNA expressions of TNF-α, IL-6, and IL-1β in spinal cord tissue were significantly decreased(P<0.01, P<0.05).

Conclusions: Acupuncture can improve the symptoms of mice with adjuvant arthritis, which may be related to promoting MerTK-mediated efferocytosis and thus exerting an anti-inflammatory effect.