Parkinsons-linked LRRK2-G2019S derails AMPAR trafficking, mobility and composition in striatum with cell-type and subunit specificity

Parkinsons (PD) is a multi-factorial disease that affects multiple brain systems and circuits. While defined by motor symptoms caused by degeneration of brainstem dopamine neurons, debilitating non-motor abnormalities in fronto-striatal based cognitive function are common, appear early and are initially independent of dopamine. Young adult mice expressing the PD-associated G2019S missense mutation in Lrrk2 also exhibit deficits in fronto-striatal-based cognitive tasks. In mice and humans, cognitive functions require dynamic adjustments in glutamatergic synapse strength through cell-surface trafficking of AMPA-type glutamate receptors (AMPARs), but it is unknown how LRRK2 mutation impacts dynamic features of AMPAR trafficking in striatal projection neurons (SPNs). Here, we used Lrrk2G2019S knockin mice to show that surface AMPAR subunit stoichiometry is altered biochemically and functionally in mutant SPNs in dorsomedial striatum to favor incorporation of GluA1 over GluA2. GluA1-containing AMPARs were resistant to internalization from the cell surface, leaving an excessive accumulation of GluA1 on the surface within and outside synapses. This negatively impacted trafficking dynamics that normally support synapse strengthening, as GluA1-containing AMPARs failed to increase at synapses in response to a potentiating stimulus and showed significantly reduced surface mobility. Surface GluA2-containing AMPARs were expressed at normal levels in synapses, indicating subunit-selective impairment. Abnormal surface accumulation of GluA1 was independent of PKA activity and was limited to D1R SPNs. Since LRRK2 mutation is thought to be part of a common PD pathogenic pathway, our data suggest that sustained, striatal cell-type specific changes in AMPAR composition and trafficking contribute to cognitive or other impairments associated with PD. We used bulk RNAseq to compare expression in dorsal striatum of Lrrk2G2019S knockin and wildtype control mice at postnatal day (P) 21.帕金森病（Parkinsons, PD）是一种多因素疾病，可累及多个脑系统与神经环路。尽管该病以脑干多巴胺能神经元变性引发的运动症状为核心定义，但额纹状体环路相关认知功能的致残性非运动异常亦十分常见，且早期即可出现，初始阶段与多巴胺能系统无关。在Lrrk2基因中携带PD相关G2019S错义突变的青年成年小鼠，同样会在额纹状体依赖的认知任务中表现出认知缺损。在小鼠与人类中，认知功能需要通过AMPA型谷氨酸受体（AMPA-type glutamate receptors, AMPARs）的细胞表面转运，对谷氨酸能突触强度进行动态调控，但目前尚不清楚LRRK2突变如何影响纹状体投射神经元（striatal projection neurons, SPNs）中AMPAR转运的动态特征。本研究使用Lrrk2G2019S敲入小鼠，结果显示：背内侧纹状体的突变型SPNs中，表面AMPAR亚基计量比发生了生化与功能层面的改变，表现为GluA1的整合相较于GluA2更占优势。含GluA1的AMPAR难以从细胞表面发生内吞，导致突触内外的细胞表面出现过量的GluA1蓄积。这对正常情况下协助突触强化的转运动态产生了负面影响——含GluA1的AMPAR无法在强化刺激下于突触处富集，且其表面迁移能力显著降低。而突触处含GluA2的AMPAR表达水平正常，表明该损伤具有亚基选择性。GluA1的异常表面蓄积不依赖于蛋白激酶A（Protein Kinase A, PKA）活性，且仅发生于D1型多巴胺受体阳性纹状体投射神经元（D1R SPNs）。鉴于LRRK2突变被认为是常见PD致病通路的组成部分，本研究数据表明，纹状体中细胞类型特异性的AMPAR组成与转运的持续性改变，参与了PD相关的认知或其他功能缺损。本研究通过批量RNA测序（bulk RNAseq），比较了出生后第21天（P21）的Lrrk2G2019S敲入小鼠与野生型对照小鼠背侧纹状体的基因表达差异。