A study on the beta-Cell glucose sensors in insulin secretion : The relationship between dysfunction of glucose sensors and development of diabetes mellitus

遗传因素和环境因素在非胰岛素依赖型糖尿病(NIDDM)的发病机制中起重要作用。最近的研究表明，单基因突变可能在糖尿病的发病机制中起到一定的作用。在日本的NIDDM患者中，葡萄糖诱导的胰岛素分泌在发病早期就受到了损害。在此，我们报道了NIDDM患者葡萄糖传感器候选基因的突变。首先，我们检测了GLUT2基因的突变，发现了一个核苷酸替代Phe^&lt；479&gt；(TTT-&gt；TTC)。该等位基因的纯合子仅见于NIDDM患者，且NIDDM患者该等位基因频率显著高于对照组。其次，研究了电压依赖性钙通道基因(CACNL1A2)的突变。外显子1的聚合酶链式反应-单链构象多态性分析显示，NIDDM患者的ATG三核苷酸重复数由7个变为8个，导致氨基末端增加了蛋氨酸。第三，我们用聚合酶链式反应-单链构象多态性方法对胃抑制多肽受体(GIPR)基因的整个编码区进行了研究，发现了Gly^&lt；198&gt；-&Gt；Cys(Gly198Cys)外显子7和Glu^&lt；354&gt；-&gt；对这两个突变的GIPR的功能分析表明，Gly198Cys表达GIPR的中国仓鼠卵巢细胞对GIP诱导的cAMP反应的半最大刺激值显著高于野生型，而Glu354Gln表达GIPR的中国仓鼠卵巢细胞与野生型GIPR的cAMP反应无显著差异。NIDDM患者Glu354Gln等位基因频率与正常对照组无明显差异，而Gly198Cys纯合子仅在NIDDM患者中检出，上述突变可能是NIDDM发病机制的一部分，其余机制有待进一步研究。

Genetic factors play important roles in pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM) as well as environmental factors. Recent studies showed that single gene mutation might have a causative effect in pathogenesis of diabetes mellitus. In Japanese patients with NIDDM,the insulin secretion induced by glucose is impaired in early stage of pathogenesis. Here, we report the mutations of candidate genes for glucose sensor in NIDDM subjects.First, we examined the mutations of the GLUT2 gene and found a nucleotide substitution Phe^<479> (TTT->TTC). Although it was a silent mutaion, homozygote of this allele was found only in NIDDM subjects, and allelic frequency of this allele was significantly higher in NIDDM subjects than in controls.Second, the mutations of voltage-dependent calcium channel gene (CACNL1A2) was studied. The PCR-SSCP procedure of exon 1 revealed a change from 7 to 8 ATG trinucleotide repeats in a patient with NIDDM,resulting in an addition of methionine at the amino-terminus. This change was not found in normal controls.Third, we investigated the entire coding region of the gastric inhibitory poltpeptide receptor (GIPR) gene by PCR-SSCP.We identified two missence mutations, Gly^<198>->Cys (Gly198Cys) in exon 7 and Glu^<354>->Gln (Glu354Gln) in exon 12. Functional analysis of the GIPR with either of these mutations revealed that half-maximal stimulation value of GIP-induced cAMP response in Chinese hamster ovary cells expressing the GIPR with Gly198Cys was considerably higher than that of the wild type, whereas that of the GIPR with Glu354Gln was not significantly different from that of wild type. While allelic frequency of Glu354Gln in NIDDM subjects was not different from that in normal control, homozygotes of the Gly198Cys was detected only in NIDDM subjects.Mutations described here might be part of mechanisms which contribute to the pathogenesis of NIDDM,and further studies will reveal the rest.