[Electroacupuncture ameliorates skeletal muscle insulin resistance in diabetic rats via PPAR-γ/NF-κB signaling pathway]

To observe the effect of electroacupuncture (EA) at "Sanyinjiao" (SP6) and "Zusanli" (ST36) on the expressions of peroxisome proliferator-activated γ receptor (PPAR-γ), nuclear factor-κB (NF-κB) and glucose transporter 4 (GLUT4) in skeletal muscle of Zucker Diabetic Fatty (ZDF) rats with type 2 diabetes mellitus (T2DM), so as to explore its possible mechanism in improving insulin resistance (IR).

Eighteen male 2-month-old ZDF (Lepr^fa/fa) rats were fed with a high-fat diet for 4 weeks to establish a diabetic model. After the model was confirmed, the rats were randomly divided into model, EA and medication groups, with 6 rats in each group. Additionally, 6 Zucker lean rats (Lepr^+/fa) of the same age were used as the control group. EA (15 Hz, 1 mA) was applied to bilateral SP6 and ST36 for 20 min;the medication group was administered pioglitazone solution (10 mg/kg) via gastric gavage;both groups were treated once daily, 5 d a week for 4 weeks. Fasting body weight (FBW) was measured weekly, fasting blood glucose (FBG) was measured the day before sampling. The levels of serum fasting insulin (FINS), free fatty acid (FFA), low density lipoprotein (LDL), total cholesterol (TC), triglyceride (TG), tumor necrosis factor-α (TNF-α), C peptide and C reactive protein (CRP) were detected by ELISA, and the homeostasis model assessment of insulin resistance (HOMA-IR) index was calculated. HE staining and oil red O staining were used to observe the pathological changes and lipid droplet accumulation of skeletal muscle in rats respectively. The protein expression levels of PPAR-γ, NF-κB and phosphorylated (p) -NF-κB in skeletal muscle tissue of rats were detected by Western blot. The positive expressions of TNF-α and GLUT4 in skeletal muscle of rats were detected by immunofluorescence.

Compared with the control group, the FBW, FBG, HOMA-IR index, the serum levels of FINS, FFA, LDL, TG, TC, TNF-α, C-peptide and CRP, NF-κB phosphorylation level, as well as the positive expression of TNF-α and p-NF-κB/NF-κB in skeletal muscle were increased (P<0.01), while the PPAR-γ expression and the positive expression of GLUT4 in skeletal muscle were decreased (P<0.01) in the model group. Oil red O staining showed a large number of bright red lipid droplets and serious lipid accumulation in skeletal muscle cells, HE staining showed that the skeletal muscle fibers were broken in the model group. Compared with the model group, the FBW of the medication group, the expression levels of PPAR-γ and GLUT4 of both EA and medication groups were increased (P<0.01). Conversely, the levels of FBG, HOMA-IR index, FINS, FFA, LDL, TG, TC, TNF-α, C-peptide and CRP, the phosphorylation level of NF-κB protein and TNF-α expression were decreased (P<0.05, P<0.01) in the EA and medication groups. The oil red O staining showed that the lipid droplets in the skeletal muscle cells were significantly reduced, and the degree of lipid accumulation was alleviated, whereas HE staining showed reduced skeletal-muscle fiber disruption in the EA and medication groups compared to those in the model group.

EA can ameliorate energy metabolism disorders in T2DM rats, reduce ectopic lipid accumulation in skeletal muscle, and alleviate inflammatory responses, which may be related to the regulation of the PPAR-γ/NF-κB signaling pathway.