Fye Margret, Sangowdar Pranoy, Jayathilake Anissa, Noguchi Pi'ilani, Gu Guoqiang, Kaverina Irina
Cell & Developmental Biology, Vanderbilt University School of Medicine.
bioRxiv. 2025 Mar 27:2024.10.31.621333. doi: 10.1101/2024.10.31.621333.
To maintain normal blood glucose levels, pancreatic beta cells secrete insulin into the bloodstream at specialized regions at the cell periphery, often called secretion hot spots. While many secretory machinery components are located all over the cell membrane, directed secretion relies on distinct cortical patches of the scaffolding protein ELKS and the microtubule (MT)-anchoring protein LL5β. However, using TIRF microscopy of intact mouse islets to precisely localize secretion events within ELKS/LL5β patches, we now show that secretion is restricted to only 5% of ELKS/LL5β patch area. Moreover, the majority of secretion occurs at the margins of ELKS patches. This suggests that additional factor(s) must be responsible for hot spot definition. Because the MT cytoskeleton plays a regulatory role in the insulin secretion process via both delivery and removal of secretory granules from the secretion sites, we test whether local MT organization defines secretory activity at hot spots. We find that the majority of secretion events occur at regions devoid of MTs. Based on our findings, we present a model in which local MT disassembly and optimal ELKS content are strong predictors of directed insulin secretion.
为维持正常血糖水平，胰腺β细胞在细胞周边的特定区域（常被称为分泌热点）将胰岛素分泌到血液中。虽然许多分泌机制组件分布于整个细胞膜，但定向分泌依赖于支架蛋白ELKS和微管（MT）锚定蛋白LL5β形成的独特皮质斑块。然而，通过对完整小鼠胰岛进行全内反射荧光显微镜（TIRF）观察，以精确确定ELKS/LL5β斑块内的分泌事件，我们现在发现分泌仅局限于ELKS/LL5β斑块面积的5%。此外，大多数分泌发生在ELKS斑块的边缘。这表明必定有其他因素负责定义热点。由于MT细胞骨架通过从分泌位点递送和移除分泌颗粒在胰岛素分泌过程中发挥调节作用，我们测试局部MT组织是否决定了热点处的分泌活性。我们发现大多数分泌事件发生在没有MT的区域。基于我们的发现，我们提出了一个模型，其中局部MT解聚和最佳ELKS含量是定向胰岛素分泌的有力预测指标。
