[Mechanism of electroacupuncture on improving insulin resistance and intestinal mucosal barrier injury via the GLP-1R/PKA signaling pathway in type 2 diabetes mellitus rats].

OBJECTIVE

To observe the effect of electroacupuncture (EA) on the glucagon-like peptide-1 receptor (GLP-1R)/protein kinase A (PKA) signaling pathway in the colon tissue of type 2 diabetes mellitus (T2DM) rats and explore the mechanisms underlying EA's improvement of insulin resistance and intestinal mucosal barrier injury.

METHODS

Among 24 SPF-grade male Wistar rats, 6 rats were randomly assigned to a blank group, and the remaining 18 rats were used to establish the T2DM model through a combination of high-sucrose/high-fat diet feeding and intraperitoneal injection of streptozotocin. Successfully modeled rats were randomly assigned to a model group, an EA group, and an EA+inhibitor group, with 6 rats per group. The EA group received EA at bilateral "Tianshu" (ST25), "Shangjuxu" (ST37), "Pishu" (BL20), and "Weiwanxiashu" (EX-B3); EA was applied to ipsilateral "Shangjuxu" (ST37) and "Weiwanxiashu" (EX-B3) using disperse-dense wave (2 Hz/50 Hz, 1-3 mA) for 20 min per session. The EA+inhibitor group received the same EA treatment combined with intraperitoneal injection of the GLP-1 receptor inhibitor Exenatide. All treatments were administered once daily, six times per week, for 6 weeks. Fasting blood glucose (FBG) was measured before modeling and before/after intervention. After the intervention, serum fasting insulin (FINS) and GLP-1 levels were measured by ELISA, and the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Colon morphology was observed using HE staining. Positive expression of zonula occludens-1 (ZO-1) and Occludin in colon tissue was detected by immunohistochemistry. Protein expression of GLP-1R, PKA, GLP-1, ZO-1, and Occludin in colon tissue was analyzed by Western blot.

RESULTS

After the intervention, compared with the blank group, the model group showed significantly increased FBG, FINS, and HOMA-IR (P<0.01), while serum GLP-1 level was significantly decreased (P<0.01); histologically, the colonic mucosal epithelial cells exhibited shedding, crypt atrophy was observed, the number of goblet cells was markedly reduced, and inflammatory cell infiltration was evident in the lamina propria; the positive expression of ZO-1 and Occludin in colon tissue was significantly reduced (P<0.01, P<0.05), and the protein expression of GLP-1R, PKA, GLP-1, ZO-1, and Occludin was also significantly decreased (P<0.05, P<0.01). Compared with the model group and the EA+inhibitor group, the EA group showed significantly lower levels of FBG, FINS, and HOMA-IR (P<0.01), along with higher serum GLP-1 level (P<0.01); the inflammatory cell infiltration in the colon was reduced, the number of goblet cells was increased, and the structure of the mucosal epithelium and crypts was more normalized; the positive expression of ZO-1 and Occludin in colon tissue was significantly increased (P<0.01, P<0.05), and the protein expression of GLP-1R, PKA, GLP-1, ZO-1, and Occludin was also significantly elevated (P<0.05, P<0.01).

CONCLUSION

EA could reduce blood glucose levels, improve insulin resistance, and repair intestinal mucosal barrier injury in T2DM rats. The underlying mechanism may be related to the activation of the GLP-1R/PKA signaling pathway.