Bragina Luca, Conti Fiorenzo
Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy.
Center for Neurobiology of Aging, IRCCS INRCA, Ancona, Italy.
Front Neuroanat. 2018 Sep 11;12:74. doi: 10.3389/fnana.2018.00074. eCollection 2018.
Neurofilaments (NFs) are neuron-specific heteropolymers that have long been considered as structural proteins. However, it has recently been documented that they may play a functional role at synapses. Indeed, the four NF subunits-NFL, NFM, NFH and α-internexin-are integral components of synapses in the striatum and hippocampus, since their elimination disrupts synaptic plasticity and impairs social memory, an observation that might have important implications for some neuropsychiatric diseases. Here, we studied NFs localization in VGLUT1-, VGLUT2-, VGAT-, PSD-95- and gephyrin-positive (+) puncta, and in glutamatergic and GABAergic synapses in the cerebral cortex of adult rats. Synapses were identified by pre- and postsynaptic markers: glutamatergic synapses by VGLUT1+ or VGLUT2+ puncta contacting PSD-95+ puncta; and GABAergic synapses by VGAT+ puncta contacting gephyrin+ puncta. In VGLUT1 glutamatergic synapses NF showed a greater expression in the compartment labeled by postsynaptic markers (20%-30%) than in those labeled by presynaptic markers (10%-20%), whereas in GABAergic synapses a similar expression was detected in both compartments (20%-30%). Moreover, NF expression was higher in the GABAergic (20%-30%) than in the glutamatergic (10%-15%) compartments labeled by presynaptic markers. Finally, a higher colocalization of VGLUT1+, VGLUT2+ and VGAT+ puncta with NFs was seen when presynaptic puncta contacted elements labeled by postsynaptic markers. These findings show that the four NF subunits are expressed at some neocortical synapses, and contribute to glutamatergic and GABAergic synapse heterogeneity.
神经丝（NFs）是神经元特异性异源聚合物，长期以来一直被视为结构蛋白。然而，最近有文献记载它们可能在突触中发挥功能作用。事实上，四种神经丝亚基——神经丝轻链（NFL）、神经丝中链（NFM）、神经丝重链（NFH）和α-连环蛋白——是纹状体和海马体中突触的组成成分，因为它们的缺失会破坏突触可塑性并损害社会记忆，这一观察结果可能对某些神经精神疾病具有重要意义。在这里，我们研究了成年大鼠大脑皮质中神经丝在囊泡谷氨酸转运体1（VGLUT1）、囊泡谷氨酸转运体2（VGLUT2）、囊泡GABA转运体（VGAT）、突触后密度蛋白95（PSD-95）和gephyrin阳性（+）小点以及谷氨酸能和γ-氨基丁酸能（GABAergic）突触中的定位。通过突触前和突触后标记物来识别突触：谷氨酸能突触通过VGLUT1+或VGLUT2+小点与PSD-95+小点接触来识别；GABA能突触通过VGAT+小点与gephyrin+小点接触来识别。在VGLUT1谷氨酸能突触中，神经丝在突触后标记物标记的区域表达更高（20%-30%），而在突触前标记物标记的区域表达较低（10%-20%），而在GABA能突触中，两个区域的表达相似（20%-30%）。此外，在突触前标记物标记的区域中，GABA能区域（20%-30%）的神经丝表达高于谷氨酸能区域（10%-15%）。最后，当突触前小点与突触后标记物标记的元件接触时，观察到VGLUT1+、VGLUT2+和VGAT+小点与神经丝的共定位更高。这些发现表明，四种神经丝亚基在某些新皮质突触中表达，并有助于谷氨酸能和GABA能突触的异质性。
