Original Article
Copyright ©2014 Baishideng Publishing Group Co., Limited. All rights reserved.
World J Gastroenterol. Apr 28, 2014; 20(16): 4626-4635
Published online Apr 28, 2014. doi: 10.3748/wjg.v20.i16.4626
Gastric nNOS reduction accompanied by natriuretic peptides signaling pathway upregulation in diabetic mice
Hong-Li Lu, Xu Huang, Yi-Song Wu, Chun-Mei Zhang, Xiang-Min Meng, Dong-Hai Liu, Young-chul Kim, Wen-Xie Xu
Hong-Li Lu, Xu Huang, Yi-Song Wu, Chun-Mei Zhang, Xiang-Min Meng, Dong-Hai Liu, Wen-Xie Xu, Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai 200240, China
Young-chul Kim, Department of Physiology, Chungbuk National University College of Medicine, Chungbuk 361-763, South Korea
Author contributions: Lu HL, Huang X and Wu YS performed the majority of the experiments; Zhang CM, Meng XM and Liu DH performed the intracellular recording; Kim Y was involved in editing the manuscript; Xu WX designed the study and wrote the manuscript.
Supported by The National Natural Science Foundation of China, No. 31071011; No. 31171107; and the Shanghai Natural Science Foundation, No. 13ZR1423100
Correspondence to: Wen-Xie Xu, Professor, Department of Physiology, Shanghai Jiaotong University School of Medicine, 800 Dongchuan Road, 328 Wenxuan Medical Building, Shanghai 200240, China. wenxiexu@sjtu.edu.cn
Telephone: +86-21-34205639 Fax: +86-21-34205639
Received: July 4, 2013
Revised: October 14, 2013
Accepted: November 2, 2013
Published online: April 28, 2014
Processing time: 298 Days and 19 Hours
Abstract

AIM: To investigate the relationship between neuronal nitric oxide synthase (nNOS) expression and the natriuretic peptide signaling pathway in the gastric fundus of streptozotocin (STZ)-induced diabetic mice.

METHODS: Diabetic mice were induced by injection of STZ solution. Immunofluorescence labeling of HuC/D, nNOS and natriuretic peptide receptor-A, B, C (NPRs) in the gastric fundus (GF) was used to observe nNOS expression and whether NPRs exist on enteric neurons. The expression levels of nNOS and NPRs in the diabetic GF were examined by western blotting. An isometric force transducer recorded the electric field stimulation (EFS)-induced relaxation and contraction in the diabetic GF. An intracellular recording method assessed EFS-induced inhibitory junction potentials (IJP) on the GF. GF smooth muscles acquired from normal mice were incubated with different concentrations of the NPRs agonist C-type natriuretic peptide (CNP) for 24 h, after which their nNOS expressions were detected by western blotting.

RESULTS: Eight weeks after injection, 43 diabetic mice were obtained from mouse models injected with STZ. Immunofluorescence indicated that the number of NOS neurons was significantly decreased and that nNOS expression was significantly downregulated in the diabetic GF. The results of physiological and electrophysiological assays showed that the EFS-induced relaxation that mainly caused by NO was significantly reduced, while the contraction was enhanced in the diabetic GF. EFS-induced IJP showed that L-NAME sensitive IJP in the diabetic GF was significantly reduced compared with control mice. However, both NPR-A and NPR-B were detected on enteric neurons, and their expression levels were upregulated in the diabetic GF. The nNOS expression level was downregulated dose-dependently in GF smooth muscle tissues exposed to CNP.

CONCLUSION: These findings suggested that upregulation of the NPs signaling pathway may be involved in GF neuropathy caused by diabetes by decreasing nNOS expression.

Keywords: Diabetic gastroparesis; Natriuretic peptides; Nitric oxide synthase; Enteric neuron

Core tip: The results demonstrated that the expressions of neuronal nitric oxide synthase (nNOS) and numbers NOS neurons were significantly downregulated while natriuretic peptides (NPs) and the natriuretic peptide receptor-A, B, C (NPRs) signaling pathway were upregulated. C-type natriuretic peptide, an NPRs agonist, inhibited nNOS expression in cultured gastric fundus tissue. These findings suggested that upregulation of the NPs signaling pathway may be involved in gastric fundus neuropathy caused by diabetes, by decreasing nNOS expression. The results are interesting and may represent a molecular mechanism of diabetic gastroparesis.