Low Jiun T, Zavortink Michael, Mitchell Justin M, Gan Wan J, Do Oanh Hoang, Schwiening Christof J, Gaisano Herbert Y, Thorn Peter
School of Biomedical Sciences, University of Queensland, St Lucia, QLD, 4072, Australia.
Diabetologia. 2014 Aug;57(8):1655-63. doi: 10.1007/s00125-014-3252-6. Epub 2014 May 5.
AIMS/HYPOTHESIS: We set out to test the hypothesis that insulin secretion from beta cells is targeted towards the vasculature.
The spatial location of granule fusion was identified by live-cell two-photon imaging of mouse pancreatic beta cells within intact islets, using sulforhodamine B labelling. Three-dimensional (3D) immunofluorescence of pancreatic slices was used to identify the location of proteins associated with neuronal synapses.
We demonstrated an asymmetric, non-random, distribution of sites of insulin granule fusion in response to glucose and focal targeting of insulin granule secretion to the beta cell membrane facing the vasculature. 3D immunofluorescence of islets showed that structural proteins, such as liprin, piccolo and Rab2-interacting molecule, normally associated with neuronal presynaptic targeting, were present in beta cells and enriched at the vascular face. In contrast, we found that syntaxin 1A and synaptosomal-associated protein 25 kDa (SNAP25) were relatively evenly distributed across the beta cells.
CONCLUSIONS/INTERPRETATION: Our results show that beta cells in situ, within intact islets, are polarised and target insulin secretion. This evidence for an 'endocrine synapse' has wide implications for our understanding of stimulus-secretion coupling in healthy islets and in disease.
目的/假设：我们着手检验β细胞分泌的胰岛素以脉管系统为靶标的假设。
利用磺罗丹明B标记，通过对完整胰岛内的小鼠胰腺β细胞进行活细胞双光子成像，确定颗粒融合的空间位置。使用胰腺切片的三维（3D）免疫荧光来确定与神经元突触相关的蛋白质的位置。
我们证明了胰岛素颗粒融合位点对葡萄糖的反应呈不对称、非随机分布，且胰岛素颗粒分泌集中靶向面向脉管系统的β细胞膜。胰岛的3D免疫荧光显示，通常与神经元突触前靶向相关的结构蛋白，如脂联蛋白、小突触泡蛋白和Rab2相互作用分子，存在于β细胞中，并在血管面富集。相比之下，我们发现 syntaxin 1A和25 kDa突触体相关蛋白（SNAP25）在β细胞中分布相对均匀。
结论/解读：我们的结果表明，完整胰岛内的原位β细胞是极化的，且胰岛素分泌具有靶向性。这种“内分泌突触”的证据对于我们理解健康胰岛和疾病状态下的刺激-分泌偶联具有广泛的意义。
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