Impaired insulin secretion in pancreatic β-cells lacking the sphingosine-1-phosphate_1 receptor

胰岛β细胞在葡萄糖刺激下分泌胰岛素。为了阐明S1P_1是如何参与胰岛素分泌的，我们研究了胰岛β细胞从产生胰岛素到通过S1P_1分泌胰岛素的全过程。首先，对S1P_1基因敲除小鼠(S1P_1KO)的胰岛形态及胰岛激素含量进行了测定，并与对照组进行了比较。结果1、S1P_1KO的形态分析与对照组无明显差异。免疫组织化学染色显示胰岛素、Glukagon、生长抑素和IPAA在两组中的染色模式相似。2.光镜下观察两组大鼠胰岛β细胞器形态相似。与质膜对接的β细胞颗粒数无统计学差异。3.S1P_1通过磷酸化ERK的配体--鞘氨醇-1-磷酸(S1P)使其磷酸化。用S1P刺激的磷酸化ERK抗体进行蛋白质印迹分析，发现S1P1KO胰岛ERK的磷酸化程度比对照组弱。4.S1P_1受体属于G蛋白偶联受体家族，仅与Gi蛋白偶联。S1P_1KO胰岛在GLP-1刺激下产生的cAMP高于对照胰岛cAMP特异性ELISA。结论1.S1P_1对胰岛质量和胰岛细胞组成比无明显影响。2.胰岛β细胞中的S1P_1偶联Gi蛋白。

Pancreatic islet beta cells secrete insulin in response to glucouse stimulation. To elucidate how S1P_1 is involved in such insulin secretion, whole process from insulin generation to its secretion through S1P_1 on pancreatic beta cell was investigated. First, Morphological study of pancreatic islet and islet hormones contents of S1P_1 knocked out mouse (S1P_1KO) were measured compared to Control litter mate.Results 1. Morphological analysis of S1P_1KO showed no clear difference compared to Control. Immunohistochemistry using antibody for Insulin, Glukagon, Somatostatin and IPAA showed similar staining pattern in both groups. 2. Beta cell organelle showed similar morphology using electronic microscopy in both groups. Also, the number of docking beta cell granules to the plasma membrane reached no statistic difference. 3. S1P_1 phosphorylates ERK kinase in response to its ligand, sphingosin-1-phosphate (S1P). Western brotting analysis using phosph-ERK anti-body by S1P stimulatin revealed weaker phosphrylation of ERK in S1P_1KO islet than in Control. 4. S1P_1 receptor belongs to the family of G protein coupled receptor and couples Gi protein exclusively. S1P_1KO islet showed higher cAMP production in response to GLP-1 stimulation than Control islet cAMP specific ELISA.Conclusions 1. S1P_1 had no apparent effect for islet mass and ratio of islet cell composition. 2. S1P_1 in pancreatic beta cell coupled Gi protein.