Dharmasri Poorna A, DeMarco Emily M, Anderson Michael C, Levy Aaron D, Blanpied Thomas A
Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA.
Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA.
bioRxiv. 2024 Jan 12:2024.01.12.574705. doi: 10.1101/2024.01.12.574705.
Nanoscale protein organization within the active zone (AZ) and post-synaptic density (PSD) influences synaptic transmission. Nanoclusters of presynaptic Munc13-1 are associated with readily releasable pool size and neurotransmitter vesicle priming, while postsynaptic PSD-95 nanoclusters coordinate glutamate receptors across from release sites to control their opening probability. Nanocluster number, size, and protein density vary between synapse types and with development and plasticity, supporting a wide range of functional states at the synapse. Whether or how the receptors themselves control this critical architecture remains unclear. One prominent PSD molecular complex is the NMDA receptor (NMDAR). NMDARs coordinate several modes of signaling within synapses, giving them the potential to influence synaptic organization through direct protein interactions or through signaling. We found that loss of NMDARs results in larger synapses that contain smaller, denser, and more numerous PSD-95 nanoclusters. Intriguingly, NMDAR loss also generates retrograde reorganization of the active zone, resulting in denser, more numerous Munc13-1 nanoclusters, more of which are aligned with PSD-95 nanoclusters. Together, these changes to synaptic nanostructure predict stronger AMPA receptor-mediated transmission in the absence of NMDARs. Notably, while prolonged antagonism of NMDAR activity increases Munc13-1 density within nanoclusters, it does not fully recapitulate these trans-synaptic effects. Thus, our results confirm that NMDARs play an important role in maintaining pre- and postsynaptic nanostructure and suggest that both decreased NMDAR expression and suppressed NMDAR activity may exert distinct effects on synaptic function, yet through unique architectural mechanisms.
活性区（AZ）和突触后致密区（PSD）内的纳米级蛋白质组织会影响突触传递。突触前Munc13-1的纳米簇与易于释放的囊泡池大小和神经递质囊泡的启动相关，而突触后PSD-95纳米簇则协调释放位点对面的谷氨酸受体以控制其开放概率。纳米簇的数量、大小和蛋白质密度在不同的突触类型之间以及随着发育和可塑性而变化，支持突触处广泛的功能状态。受体本身是否以及如何控制这种关键结构仍不清楚。一个突出的PSD分子复合物是N-甲基-D-天冬氨酸受体（NMDAR）。NMDAR协调突触内的几种信号传导模式，使其有可能通过直接的蛋白质相互作用或通过信号传导来影响突触组织。我们发现NMDAR的缺失会导致更大的突触，这些突触包含更小、更密集且数量更多的PSD-95纳米簇。有趣的是，NMDAR的缺失还会导致活性区的逆行重组，从而产生更密集、数量更多的Munc13-1纳米簇，其中更多的与PSD-95纳米簇对齐。这些突触纳米结构的变化共同预示着在没有NMDAR的情况下，α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPA受体）介导的传递会更强。值得注意的是，虽然对NMDAR活性的长期拮抗会增加纳米簇内Munc13-1的密度，但它并不能完全重现这些跨突触效应。因此，我们的结果证实NMDAR在维持突触前和突触后纳米结构中起重要作用，并表明NMDAR表达的降低和NMDAR活性的抑制可能对突触功能产生不同的影响，但通过独特的结构机制。
