Abundant distribution of TARP γ-8 in synaptic and extrasynaptic surface of hippocampal neurons and its major role in AMPA receptor expression on spines and dendrites
Abundant distribution of TARP γ-8 in synaptic and extrasynaptic surface of hippocampal neurons and its major role in AMPA receptor expression on spines and dendrites
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DOI：
10.1111/j.1460-9568.2006.05081.x
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发表时间：
2006-10-01
影响因子：
3.4
通讯作者：
Sakimura, Kenji
中科院分区：
文献类型：
--
作者：
Fukaya, Masahiro;Tsujita, Mika;Sakimura, Kenji
跨膜α-氨基-3-羟基-5-异恶唑丙酸酯(AMPA)受体调节蛋白(TARP)在AMPA受体转运和门控中起着关键作用。在这里，我们研究了TARP-8在小鼠大脑中的细胞和亚细胞分布。免疫印迹和免疫荧光显示，海马区的伽马-8浓度最高。免疫金电镜示γ-8密集分布于海马神经元突触和突触外表面，细胞内标记很低。在神经元表面，γ-8在锥体细胞和中间神经元的非对称性突触上分布水平最高，而它们的对称性突触选择性地缺乏免疫金标记物。然后，利用伽马-8基因缺陷的突变小鼠，研究了伽马-8在海马区AMPA受体表达中的作用。在突变的山角(CA)1区，突触和突触外的AMPA受体在树突和棘上严重减少到对照水平的35-37%，而在躯体上的突触外受体的减少很轻微(74%)，而脊髓内的细胞内受体没有明显的减少。在突变型CA3区，突触AMPA受体在放射层的非对称性突触处轻度减少(为对照的67%)，而在苔藓状纤维-CA3突触处无明显减少。因此，γ-8广泛分布于海马兴奋性突触和突触外膜上，在增加突触和突触外突触的AMPA受体数量中起重要作用，尤其是在CA1区。不同程度的减少进一步表明，根据海马亚区、输入源和神经元隔间的不同，其他TARP也可能以不同的强度介导这一功能。
Transmembrane alpha-amino-3-hydroxyl-5-isoxazolepropionate (AMPA) receptor regulatory proteins (TARPs) play pivotal roles in AMPA receptor trafficking and gating. Here we examined cellular and subcellular distribution of TARP gamma-8 in the mouse brain. Immunoblot and immunofluorescence revealed the highest concentration of gamma-8 in the hippocampus. Immunogold electron microscopy demonstrated dense distribution of gamma-8 on the synaptic and extrasynaptic surface of hippocampal neurons with very low intracellular labeling. Of the neuronal surface, gamma-8 was distributed at the highest level on asymmetrical synapses of pyramidal cells and interneurons, whereas their symmetrical synapses selectively lacked immunogold labeling. Then, the role of gamma-8 in AMPA receptor expression was pursued in the hippocampus using mutant mice defective in the gamma-8 gene. In the mutant cornu ammonis (CA)1 region, synaptic and extrasynaptic AMPA receptors on dendrites and spines were severely reduced to 35-37% of control levels, whereas reduction was mild for extrasynaptic receptors on somata (74%) and no significant decrease was seen for intracellular receptors within spines. In the mutant CA3 region, synaptic AMPA receptors were reduced mildly at asymmetrical synapses in the stratum radiatum (67% of control level), and showed no significant decrease at mossy fiber-CA3 synapses. Therefore, gamma-8 is abundantly distributed on hippocampal excitatory synapses and extrasynaptic membranes, and plays an important role in increasing the number of synaptic and extrasynaptic AMPA receptors on dendrites and spines, particularly, in the CA1 region. Variable degrees of reduction further suggest that other TARPs may also mediate this function at different potencies depending on hippocampal subregions, input sources and neuronal compartments.