Heparan Sulfated Glypican-4 Is Released from Astrocytes by Proteolytic Shedding and GPI-Anchor Cleavage Mechanisms.
Heparan Sulfated Glypican-4 Is Released from Astrocytes by Proteolytic Shedding and GPI-Anchor Cleavage Mechanisms.
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DOI：
10.1523/eneuro.0069-21.2021
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发表时间：
2021-07-01
期刊：
影响因子：
3.4
通讯作者：
Park, Sungjin
中科院分区：
文献类型：
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作者：
Huang, Kevin;Park, Sungjin
星形胶质细胞为神经元提供促进突触形成和成熟的扩散因子。特别是，星形胶质细胞释放的Glypcan-4/GPC4促进兴奋性突触的成熟。与其他分泌因子不同，GPC4含有C端的GPI锚定信号。然而，膜系GPC4从星形胶质细胞释放的机制尚不清楚。利用小鼠原代星形胶质细胞培养和基于荧光素酶的定量释放实验，我们证明GPC4通过GPI锚定在星形胶质细胞表面表达。可溶性GPC4主要通过蛋白水解性脱落从星形胶质细胞释放出来，少量通过GPI锚点裂解释放，但不是通过囊泡释放。药理学、过度表达和功能缺失筛选表明，ADAM9部分介导了星形胶质细胞释放GPC4。释放的GPC4含有硫酸乙酰肝素侧链，表明这些释放机制提供了促进突触成熟和功能的活性形式。总之，我们的研究确定了星形胶质细胞中GPC4的释放机制和主要的释放酶，并将为理解星形胶质细胞如何调控突触的形成和成熟提供见解。
Astrocytes provide neurons with diffusible factors that promote synapse formation and maturation. In particular, glypican-4/GPC4 released from astrocytes promotes the maturation of excitatory synapses. Unlike other secreted factors, GPC4 contains the C-terminal GPI-anchorage signal. However, the mechanism by which membrane-tethered GPC4 is released from astrocytes is unknown. Using mouse primary astrocyte cultures and a quantitative luciferase-based release assay, we show that GPC4 is expressed on the astrocyte surface via a GPI-anchorage. Soluble GPC4 is robustly released from the astrocytes largely by proteolytic shedding and, to a lesser extent, by GPI-anchor cleavage, but not by vesicular release. Pharmacological, overexpression, and loss of function screens showed that ADAM9 in part mediates the release of GPC4 from astrocytes. The released GPC4 contains the heparan sulfate side chain, suggesting that these release mechanisms provide the active form that promotes synapse maturation and function. Overall, our studies identified the release mechanisms and the major releasing enzyme of GPC4 in astrocytes and will provide insights into understanding how astrocytes regulate synapse formation and maturation.