School of Life Sciences, University of Warwick, Coventry, UK.
Bradford School of Pharmacy and Medical Sciences, University of Bradford, Bradford, UK.
Epilepsia. 2024 Jul;65(7):2152-2164. doi: 10.1111/epi.17981. Epub 2024 May 28.
Pathological forms of neural activity, such as epileptic seizures, modify the expression pattern of multiple proteins, leading to persistent changes in brain function. One such protein is activity-regulated cytoskeleton-associated protein (Arc), which is critically involved in protein-synthesis-dependent synaptic plasticity underlying learning and memory. In the present study, we have investigated how the expression of ArcKR, a form of Arc in which the ubiquitination sites have been mutated, resulting in slowed Arc degradation, modifies group I metabotropic glutamate receptor-mediated long-term depression (G1-mGluR-LTD) following seizures.
We used a knock-in mice line that express ArcKR and two hyperexcitation models: an in vitro model, where hippocampal slices were exposed to zero Mg, 6 mM K; and an in vivo model, where kainic acid was injected unilaterally into the hippocampus. In both models, field excitatory postsynaptic potentials (fEPSPs) were recorded from the CA1 region of hippocampal slices in response to Schaffer collateral stimulation and G1-mGluR-LTD was induced chemically with the group 1 mGluR agonist DHPG.
In the in vitro model, ArcKR expression enhanced the effects of seizure activity and increased the magnitude of G1-mGluR LTD, an effect that could be blocked with the mGluR5 antagonist MTEP. In the in vivo model, fEPSPs were significantly smaller in slices from ArcKR mice and were less contaminated by population spikes. In this model, the amount of G1-mGluR-LTD was significantly less in epileptic slices from ArcKR mice as compared to wildtype (WT) mice.
We have shown that expression of ArcKR, a form of Arc in which degradation is reduced, significantly modulates the magnitude of G1-mGluR-LTD following epileptic seizures. However, the effect of ArcKR on LTD depends on the epileptic model used, with enhancement of LTD in an in vitro model and a reduction in the kainate mouse model.
病理性神经活动形式，如癫痫发作，会改变多种蛋白质的表达模式，导致大脑功能的持续变化。活性调节细胞骨架相关蛋白（Arc）就是这样一种蛋白质，它在学习和记忆所依赖的蛋白合成依赖性突触可塑性中起着至关重要的作用。在本研究中，我们研究了 ArcKR 的表达如何改变 I 型代谢型谷氨酸受体介导的长时程抑制（G1-mGluR-LTD），ArcKR 是一种 Arc 的形式，其泛素化位点发生突变，导致 Arc 降解减慢。
我们使用了一种表达 ArcKR 的敲入小鼠系和两种超兴奋性模型：一种是体外模型，其中海马切片暴露在零镁、6mM K 中；另一种是体内模型，其中单侧注射海人酸到海马中。在这两种模型中，通过 Schaffer 侧支刺激记录海马切片中的场兴奋性突触后电位（fEPSP），并用 1 型 mGluR 激动剂 DHPG 化学诱导 G1-mGluR-LTD。
在体外模型中，ArcKR 的表达增强了癫痫活动的作用，并增加了 G1-mGluR LTD 的幅度，这种作用可以被 mGluR5 拮抗剂 MTEP 阻断。在体内模型中，ArcKR 小鼠的 fEPSP 明显较小，且受群体峰的污染较小。在这种模型中，与野生型（WT）小鼠相比，ArcKR 小鼠的癫痫切片中的 G1-mGluR-LTD 量明显较少。
我们已经表明，ArcKR 的表达，一种降解减少的 Arc 形式，显著调节了癫痫发作后 G1-mGluR-LTD 的幅度。然而，ArcKR 对 LTD 的影响取决于所使用的癫痫模型，在体外模型中增强了 LTD，而在海人酸小鼠模型中则减少了 LTD。
