Insulin secretion profiles are modified by overexpression of glutamate dehydrogenase in pancreatic islets
Insulin secretion profiles are modified by overexpression of glutamate dehydrogenase in pancreatic islets
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DOI：
10.1007/s00125-003-1306-2
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发表时间：
2004-02-01
期刊：
影响因子：
8.2
通讯作者：
Maechler, P
中科院分区：
文献类型：
--
作者：
Carobbio, S;Ishihara, H;Maechler, P
目的/假设。谷氨酸脱氢酶（GDH）是一种线粒体酶，在控制胰岛素分泌中起关键作用。然而，目前尚不清楚β细胞中GDH的表达水平是否是葡萄糖分泌反应的限速因素。GDH还控制谷氨酰胺和谷氨酸氧化代谢，如果GDH不被L-亮氨酸或（+/-）-2-氨基二环-[2，2，1]庚烷-2-羧酸（BCH）变构激活，则其在胰岛中仅是弱的。我们构建了一个腺病毒编码GDH过表达的酶在β细胞系INS-1 E，以及在分离的大鼠和小鼠胰岛。在静态和灌流实验中研究了葡萄糖和谷氨酰胺的分泌反应。平行测定氨基酸浓度和代谢参数。大鼠胰岛中GDH过表达在基础或中等葡萄糖浓度下（分别为2.8和8.3 mmol/l）不改变胰岛素释放，但与对照组（+35%）相比，在高葡萄糖浓度下（16.7 mmol/l）增强分泌反应。对照胰岛暴露于5 mmol/l谷氨酰胺在基础葡萄糖没有增加胰岛素释放，除非BCH被添加，产生2.5倍的反应。在过表达GDH的胰岛中，单独谷氨酰胺刺激胰岛素分泌（2.7倍），通过添加BCH增强2.2倍。在这些条件下，谷氨酰胺引起的分泌反应与增强的细胞代谢相关。GDH可以在葡萄糖诱导的胰岛素分泌中限速，因为GDH过表达增强分泌反应。此外，GDH过表达使胰岛对谷氨酰胺有反应，表明在生理条件下，这种酶作为看门人防止氨基酸成为不适当的有效促分泌素。
Aims/hypothesis. Glutamate dehydrogenase (GDH) is a mitochondrial enzyme playing a key role in the control of insulin secretion. However, it is not known whether GDH expression levels in beta cells are rate-limiting for the secretory response to glucose. GDH also controls glutamine and glutamate oxidative metabolism, which is only weak in islets if GDH is not allosterically activated by L-leucine or (+/-)-2-aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH).Methods. We constructed an adenovirus encoding for GDH to overexpress the enzyme in the beta-cell line INS-1E, as well as in isolated rat and mouse pancreatic islets. The secretory responses to glucose and glutamine were studied in static and perifusion experiments. Amino acid concentrations and metabolic parameters were measured in parallel.Results. GDH overexpression in rat islets did not change insulin release at basal or intermediate glucose (2.8 and 8.3 mmol/l respectively), but potentiated the secretory response at high glucose concentrations (16.7 mmol/l) compared to controls (+35%). Control islets exposed to 5 mmol/l glutamine at basal glucose did not increase insulin release, unless BCH was added with a resulting 2.5-fold response. In islets overexpressing GDH glutamine alone stimulated insulin secretion (2.7-fold), which was potentiated 2.2-fold by adding BCH. The secretory responses evoked by glutamine under these conditions correlated with enhanced cellular metabolism.Conclusions/interpretation. GDH could be rate-limiting in glucose-induced insulin secretion, as GDH overexpression enhanced secretory responses. Moreover, GDH overexpression made islets responsive to glutamine, indicating that under physiological conditions this enzyme acts as a gatekeeper to prevent amino acids from being inappropriate efficient secretagogues.