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A Sustained Activation of Pancreatic NMDARs Is a Novel Factor of β-Cell Apoptosis and Dysfunction.

Endocrinology (2017-09-25)
Xiao-Ting Huang, Shao-Jie Yue, Chen Li, Yan-Hong Huang, Qing-Mei Cheng, Xiao-Hong Li, Cai-Xia Hao, Ling-Zhi Wang, Jian-Ping Xu, Ming Ji, Chen Chen, Dan-Dan Feng, Zi-Qiang Luo
ABSTRACT

Type 2 diabetes, which features β-cell failure, is caused by the decrease of β-cell mass and insulin secretory function. Current treatments fail to halt the decrease of functional β-cell mass. Strategies to prevent β-cell apoptosis and dysfunction are highly desirable. Recently, our group and others have reported that blockade of N-methyl-d-aspartate receptors (NMDARs) in the islets has been proposed to prevent the progress of type 2 diabetes through improving β-cell function. It suggests that a sustained activation of the NMDARs may exhibit deleterious effect on β-cells. However, the exact functional impact and mechanism of the sustained NMDAR stimulation on islet β-cells remains unclear. Here, we identify a sustained activation of pancreatic NMDARs as a novel factor of apoptotic β-cell death and function. The sustained treatment with NMDA results in an increase of intracellular [Ca2+] and reactive oxygen species, subsequently induces mitochondrial membrane potential depolarization and a decrease of oxidative phosphorylation expression, and then impairs the mitochondrial function of β-cells. NMDA specifically induces the mitochondrial-dependent pathway of apoptosis in β-cells through upregulation of the proapoptotic Bim and Bax, and downregulation of antiapoptotic Bcl-2. Furthermore, a sustained stimulation of NMDARs impairs β-cell insulin secretion through decrease of pancreatic duodenal homeobox-1 (Pdx-1) and adenosine triphosphate synthesis. The activation of nuclear factor-κB partly contributes to the reduction of Pdx-1 expression induced by overstimulation of NMDARs. In conclusion, we show that the sustained stimulation of NMDARs is a novel mediator of apoptotic signaling and β-cell dysfunction, providing a mechanistic insight into the pathological role of NMDARs activation in diabetes.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
N-Methyl-D-aspartic acid, ≥98% (TLC), solid
Sigma-Aldrich
Fluo-3, suitable for fluorescence, ~70%