Metformin inhibits the TLR4/MyD88 signaling pathway in the skeletal muscle of type 2 diabetic rat / 医学研究生学报

ABSTRACT

Objective The pathogenesis of type 2 diabetes mellitus (DM) is complex and its molecular mechanism remains unclear. This study was to explore the effect of metformin on the TLR4/MyD88/NFκB signaling pathway in the skeletal muscle of type 2 DM rats and its anti-inflammation mechanism from the perspective of immune inflammation.Methods Forty SD male rats were equally randomized into four groups, normal diet, type 2 DM model, insulin treatment (DM+INS), and metformin treatment (DM+MET). The DM model was established in the latter three groups by feeding the rats on a diet of high fat and high glucose followed by intraperitoneal injection of STZ at 30 mg/kg at the end of the 8th week. After modeling, the animals of the DM+INS and DM+MET groups were treated by hypodermic injection of insulin at 1 IU/d and intragastrical administration of metformin at 200 mg/（d·kg） respectively for 4 weeks. Then, the Homeostasis Model Assessment-insulin resistance (HOMA-IR) was calculated, the content of serum IL-23 measured by ELISA, the expressions of AMPK, TLR4, MyD88 and NFκB in the skeletal muscle detected by Western blot, and the levels of MyD88 mRNA and TLR4 mRNA determined by RT-PCR.Results HOMA-IR was significantly elevated in the DM model, DM+INS and DM+MET groups as compared with that in the normal diet group (4.55±0.22, 4.32±0.32 and 1.79±0.15 vs 1.56±0.04, P<0.05), lower in the DM+MET than in either the DM model (P<0.05) or the DM+INS group (P<0.05). The content of serum IL-23 was also markedly increased in the DM model, DM+INS and DM+MET groups in comparison with that in the normal diet group (\[2.279±0.472\], \[1.886±0.233\] and \[1.205±0.398\] vs \[0.788±0.193\] μg/L, P<0.05), lower in the DM+MET than in either the DM model (P < 0.05) or the DM+INS group (P<0.05). A positive correlation was found between HOMA-IR and serum IL-23 in both the DM model (r=0.716, P<0.05) and the DM+MET group (r=0.725, P<0.05). The levels of TLR4 mRNA, MyD88 mRNA, TLR4, MyD88, and NFκB were all increased in the DM model, DM+INS and DM+MET groups compared with those in the normal diet group (P<0.05), lower in the DM+INS and DM+MET than in the DM model (P<0.05), and even lower in the DM+MET than in the DM+INS group (P<0.05). The expression of AMPK in the skeletal muscle was remarkably upregulated in the M+MET group as compared with the other three groups (P<0.05).Conclusion Metformin acts against inflammation and improves insulin resistance by activating AMPK, inhibiting the TLR4/MyD88/NFκB signaling pathway in the skeletal muscle and down-regulating the expression of IL-23.