Tafoya Lawrence C R, Shuttleworth C William, Yanagawa Yuchio, Obata Kunihiko, Wilson Michael C
Department of Neurosciences, University of New Mexico Health Sciences Center, Albuquerque, USA.
BMC Neurosci. 2008 Oct 29;9:105. doi: 10.1186/1471-2202-9-105.
The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, comprised of SNAP-25, syntaxin 1A, and VAMP-2, has been shown to be responsible for action potential (AP)-dependent, calcium-triggered release of several neurotransmitters. However, this basic fusogenic protein complex may be further specialized to suit the requirements for different neurotransmitter systems, as exemplified by neurons and neuroendocrine cells. In this study, we investigate the effects of SNAP-25 ablation on spontaneous neuronal activity and the expression of functionally distinct isoforms of this t-SNARE in GABAergic and glutamatergic neurons of the adult brain.
We found that neurons cultured from Snap25 homozygous null mutant (Snap25-/-) mice failed to develop synchronous network activity seen as spontaneous AP-dependent calcium oscillations and were unable to trigger glial transients following depolarization. Voltage-gated calcium channel (VGCC) mediated calcium transients evoked by depolarization, nevertheless, did not differ between soma of SNAP-25 deficient and control neurons. Furthermore, we observed that although the expression of SNAP-25 RNA transcripts varied among neuronal populations in adult brain, the relative ratio of the transcripts encoding alternatively spliced SNAP-25 variant isoforms was not different in GABAergic and glutamatergic neurons.
We propose that the SNAP-25b isoform is predominantly expressed by both mature glutamatergic and GABAergic neurons and serves as a fundamental component of SNARE complex used for fast synaptic communication in excitatory and inhibitory circuits required for brain function. Moreover, SNAP-25 is required for neurons to establish AP-evoked synchronous network activity, as measured by calcium transients, whereas the loss of this t-SNARE does not affect voltage-dependent calcium entry.
可溶性N - 乙基马来酰亚胺敏感因子附着蛋白受体（SNARE）复合体由SNAP - 25、 syntaxin 1A和VAMP - 2组成，已被证明负责动作电位（AP）依赖性、钙触发的多种神经递质释放。然而，这种基本的融合蛋白复合体可能会进一步特化以适应不同神经递质系统的需求，成年大脑中的神经元和神经内分泌细胞就是例证。在本研究中，我们调查了SNAP - 25缺失对成年大脑中γ-氨基丁酸能（GABAergic）和谷氨酸能神经元自发神经活动以及这种t - SNARE功能不同亚型表达的影响。
我们发现，从Snap25纯合无效突变（Snap25 - / -）小鼠培养的神经元无法产生同步网络活动，即自发的AP依赖性钙振荡，并且在去极化后无法触发胶质细胞瞬变。然而，去极化诱发的电压门控钙通道（VGCC）介导的钙瞬变在SNAP - 25缺陷神经元和对照神经元的胞体之间并无差异。此外，我们观察到，尽管成年大脑中不同神经元群体间SNAP - 25 RNA转录本的表达有所不同，但编码选择性剪接的SNAP - 25变异亚型的转录本相对比例在GABA能和谷氨酸能神经元中并无差异。
我们提出，SNAP - 25b亚型主要由成熟的谷氨酸能和GABA能神经元表达，并作为SNARE复合体的基本组成部分，用于大脑功能所需的兴奋性和抑制性回路中的快速突触通讯。此外，SNAP - 25是神经元建立如通过钙瞬变测量的AP诱发同步网络活动所必需的，而这种t - SNARE的缺失并不影响电压依赖性钙内流。
