Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, 1000, Ljubljana, Slovenia.
Celica Biomedical, 1000, Ljubljana, Slovenia.
Adv Exp Med Biol. 2019;1175:93-115. doi: 10.1007/978-981-13-9913-8_4.
Astrocytes are secretory cells, actively participating in cell-to-cell communication in the central nervous system (CNS). They sense signaling molecules in the extracellular space, around the nearby synapses and also those released at much farther locations in the CNS, by their cell surface receptors, get excited to then release their own signaling molecules. This contributes to the brain information processing, based on diffusion within the extracellular space around the synapses and on convection when locales relatively far away from the release sites are involved. These functions resemble secretion from endocrine cells, therefore astrocytes were termed to be a part of the gliocrine system in 2015. An important mechanism, by which astrocytes release signaling molecules is the merger of the vesicle membrane with the plasmalemma, i.e., exocytosis. Signaling molecules stored in astroglial secretory vesicles can be discharged into the extracellular space after the vesicle membrane fuses with the plasma membrane. This leads to a fusion pore formation, a channel that must widen to allow the exit of the Vesiclal cargo. Upon complete vesicle membrane fusion, this process also integrates other proteins, such as receptors, transporters and channels into the plasma membrane, determining astroglial surface signaling landscape. Vesiclal cargo, together with the whole vesicle can also exit astrocytes by the fusion of multivesicular bodies with the plasma membrane (exosomes) or by budding of vesicles (ectosomes) from the plasma membrane into the extracellular space. These astroglia-derived extracellular vesicles can later interact with various target cells. Here, the characteristics of four types of astroglial secretory vesicles: synaptic-like microvesicles, dense-core vesicles, secretory lysosomes, and extracellular vesicles, are discussed. Then machinery for vesicle-based exocytosis, second messenger regulation and the kinetics of exocytotic vesicle content discharge or release of extracellular vesicles are considered. In comparison to rapidly responsive, electrically excitable neurons, the receptor-mediated cytosolic excitability-mediated astroglial exocytotic vesicle-based transmitter release is a relatively slow process.
星形胶质细胞是分泌细胞，它们积极参与中枢神经系统（CNS）中的细胞间通讯。它们通过细胞表面受体感知细胞外空间、附近突触周围以及 CNS 中更远位置释放的信号分子，然后兴奋地释放自己的信号分子。这有助于大脑信息处理，基于突触周围细胞外空间中的扩散以及涉及较远释放部位的对流。这些功能类似于内分泌细胞的分泌，因此星形胶质细胞在 2015 年被称为神经胶质分泌系统的一部分。星形胶质细胞释放信号分子的一个重要机制是囊泡膜与质膜融合，即胞吐作用。储存在星形胶质细胞分泌囊泡中的信号分子可以在囊泡膜与质膜融合后排出到细胞外空间。这导致融合孔形成，该通道必须扩大以允许囊泡货物的排出。在完全融合囊泡膜后，这个过程还将其他蛋白质（如受体、转运体和通道）整合到质膜中，决定了星形胶质细胞表面信号景观。囊泡货物连同整个囊泡也可以通过多泡体与质膜融合（外泌体）或通过质膜从囊泡出芽（胞外体）离开星形胶质细胞。这些星形胶质细胞衍生的细胞外囊泡可以随后与各种靶细胞相互作用。在这里，讨论了四种类型的星形胶质细胞分泌囊泡的特征：突触样微囊泡、致密核心囊泡、分泌溶酶体和细胞外囊泡。然后考虑了基于囊泡的胞吐作用、第二信使调节以及胞吐性囊泡内容物排出或细胞外囊泡释放的动力学。与快速响应、电兴奋的神经元相比，受体介导的细胞质兴奋性介导的星形胶质细胞胞吐性囊泡基于递质释放是一个相对较慢的过程。
