Tröger Jessica, Seemann Eric, Heintzmann Rainer, Kessels Michael M, Qualmann Britta
Institute of Biochemistry I, Jena University Hospital/Friedrich Schiller University Jena, Jena 07743, Germany.
Leibniz Institute of Photonic Technology, Jena 07745, Germany.
J Neurosci. 2022 Aug 31;42(35):6706-6723. doi: 10.1523/JNEUROSCI.2060-21.2022.
Glycine receptor-mediated inhibitory neurotransmission is key for spinal cord function. Recent observations suggested that by largely elusive mechanisms also glycinergic synapses display synaptic plasticity. We imaged receptor fields at ultrahigh-resolution at freeze-fractured membranes, tracked surface and internalized glycine receptors (GlyR), and studied differential regulations of GlyRβ interactions with the scaffold protein gephyrin and the F-BAR domain protein syndapin I and thereby reveal key principles of this process. S403 phosphorylation of GlyRβ, known to be triggered by synaptic signaling, caused a decoupling from gephyrin scaffolds but simultaneously promoted association of syndapin I with GlyRβ. In line, kainate treatments used to trigger rearrangements of glycine receptors in murine KO spinal cords (mixed sex) showed even more severe receptor field fragmentation than already observed in untreated KO spinal cords. Syndapin I deficiency furthermore resulted in more dispersed receptors and increased receptor mobility, also pointing out an important contribution of syndapin I to the organization of GlyRβ fields. Strikingly, KO also led to a complete disruption of kainate-induced GlyRβ internalization. Accompanying quantitative ultrahigh-resolution studies in dissociated spinal cord neurons proved that the defects in GlyR internalization observed in KO spinal cords are neuron-intrinsic defects caused by syndapin I deficiency. Together, our results unveiled important mechanisms organizing and altering glycine receptor fields during both steady state and particularly also as a consequence of kainate-induced synaptic rearrangement - principles organizing and fine-tuning synaptic efficacy and plasticity of glycinergic synapses in the spinal cord. Initial observations suggested that also glycinergic synapses, key for spinal cord and brainstem functions, may display some form of synaptic plasticity. Imaging receptor fields at ultrahigh-resolution at freeze-fractured membranes, tracking surface and internalized glycine receptors (GlyR) and studying regulations of GlyRβ interactions, we here reveal key principles of these kainate-inducible adaptations. A switch from gephyrin-mediated receptor scaffolding to syndapin I-mediated GlyRβ scaffolding and internalization allows for modulating synaptic receptor availability. In line, kainate-induced GlyRβ internalization was completely disrupted and GlyRβ receptor fields were distorted by KO. These results unveiled important mechanisms during both steady-state and kainate-induced alterations of synaptic GlyR fields, principles underlying synaptic efficacy and plasticity of synapses in the spinal cord.
甘氨酸受体介导的抑制性神经传递对脊髓功能至关重要。最近的观察表明，通过很大程度上难以捉摸的机制，甘氨酸能突触也表现出突触可塑性。我们在冷冻断裂的膜上以超高分辨率对受体场进行成像，追踪表面和内化的甘氨酸受体（GlyR），并研究GlyRβ与支架蛋白gephyrin和F-BAR结构域蛋白syndapin I相互作用的差异调节，从而揭示这一过程的关键原则。已知由突触信号触发的GlyRβ的S403磷酸化导致与gephyrin支架解偶联，但同时促进syndapin I与GlyRβ的结合。相应地，用于触发小鼠KO脊髓（混合性别）中甘氨酸受体重排的海藻酸盐处理显示出比未处理的KO脊髓中已经观察到的更严重的受体场碎片化。此外，syndapin I缺陷导致受体更分散且受体流动性增加，这也指出了syndapin I对GlyRβ场组织的重要贡献。引人注目的是，KO还导致海藻酸盐诱导的GlyRβ内化完全破坏。在解离的脊髓神经元中进行的伴随定量超高分辨率研究证明，在KO脊髓中观察到的GlyR内化缺陷是由syndapin I缺陷引起的神经元内在缺陷。总之，我们的结果揭示了在稳态期间以及特别是由于海藻酸盐诱导的突起重排而组织和改变甘氨酸受体场的重要机制——这些原则组织和微调脊髓中甘氨酸能突触的突触效能和可塑性。最初的观察表明，对脊髓和脑干功能至关重要的甘氨酸能突触也可能表现出某种形式的突触可塑性。我们在冷冻断裂的膜上以超高分辨率对受体场进行成像，追踪表面和内化的甘氨酸受体（GlyR）并研究GlyRβ相互作用的调节，在此揭示了这些海藻酸盐诱导适应性的关键原则。从gephyrin介导的受体支架转换为syndapin I介导的GlyRβ支架和内化允许调节突触受体的可用性。相应地，海藻酸盐诱导的GlyRβ内化被完全破坏，并且GlyRβ受体场因KO而扭曲。这些结果揭示了在稳态和海藻酸盐诱导的突触GlyR场改变期间的重要机制，这些是脊髓中突触效能和可塑性的基础原则。
