Objective: Neuronal nitric oxide synthase (nNOS) contains PZD domain through which NOS1AP was connected. We reported previously that NOS1AP regulated hepatic insulin sensitivity depending on its PZD binding domain suggesting an involvement of nNOS in NOS1AP effect. Thus, in the present study, we aimed to explore the role of nNOS on hepatic glucose and lipid metabolism, and the mechanism underlined.
Methods: Liver specific nNOS overexpression was achieved by tail-vein-injection of adenovirus-nNOS in C57BL/6 mice fed with a high-fat diet (HFD). nNOS specific inhibitor (L-NPA) was used to change the activity of nNOS. Western blot was used to evaluate the protein expression. Real-time PCR was used to detect the gene expression.
Results: nNOS expressed in livers from humans and mice, and its phosphorylation in Ser1417 increased in the livers of ob/ob and HFD-induced obese mice. Overexpression of nNOS in the livers of HFD-induced obese mice further impaired the glucose tolerance, increased the intrahepatic lipid accumulation, decreased the glycogen storage, and blunted insulin-induced phosphorylation of IRβ and AKT in livers (all P <0.05). Similarly, overexpression of nNOS increased the triglyceride production, decreased the glucose utilization, and insulin-induced phosphorylation of IRβ, AKT and GSK3β in HepG2 cells (all P <0.05). In contrast, inhibition of nNOS with L-NPA in ob/ob mice improved the glucose tolerance and increased insulin-induced phosphorylation of IRβ and AKT in livers (all P <0.05). Moreover, overexpression of nNOS in HepG2 cells increased phosphorylation of P38 MAPK, whereas, inhibition of P38 MAPK with SB203580 significantly reversed the defect in insulin signaling activation -induced by nNOS overexpression.
Conclusions: Hepatic nNOS inhibited insulin signaling pathway through the activation of P38 MAPK, suggesting a role of nNOS as a potential therapeutic target for the prevention and treatment of type 2 diabetes.
C. Wang: None. Q. Li: None. Y. Zhu: None.
National Natural Science Foundation of China (81670707)