Matikainen-Ankney Bridget A, Kezunovic Nebojsa, Mesias Roxana E, Tian Yuan, Williams Frances M, Huntley George W, Benson Deanna L
Department of Neuroscience, Friedman Brain Institute and the Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029, and.
Eli Lilly and Company, Indianapolis, Indiana 46285.
J Neurosci. 2016 Jul 6;36(27):7128-41. doi: 10.1523/JNEUROSCI.3314-15.2016.
Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) can cause Parkinson's disease (PD), and the most common disease-associated mutation, G2019S, increases kinase activity. Because LRRK2 expression levels rise during synaptogenesis and are highest in dorsal striatal spiny projection neurons (SPNs), we tested the hypothesis that the LRRK2-G2019S mutation would alter development of excitatory synaptic networks in dorsal striatum. To circumvent experimental confounds associated with LRRK2 overexpression, we used mice expressing LRRK2-G2019S or D2017A (kinase-dead) knockin mutations. In whole-cell recordings, G2019S SPNs exhibited a fourfold increase in sEPSC frequency compared with wild-type SPNs in postnatal day 21 mice. Such heightened neural activity was increased similarly in direct- and indirect-pathway SPNs, and action potential-dependent activity was particularly elevated. Excitatory synaptic activity in D2017A SPNs was similar to wild type, indicating a selective effect of G2019S. Acute exposure to LRRK2 kinase inhibitors normalized activity, supporting that excessive neural activity in G2019S SPNs is mediated directly and is kinase dependent. Although dendritic arborization and densities of excitatory presynaptic terminals and postsynaptic dendritic spines in G2019S SPNs were similar to wild type, G2019S SPNs displayed larger spines that were matched functionally by a shift toward larger postsynaptic response amplitudes. Acutely isolating striatum from overlying neocortex normalized sEPSC frequency in G2019S mutants, supporting that abnormal corticostriatal activity is involved. These findings indicate that the G2019S mutation imparts a gain-of-abnormal function to SPN activity and morphology during a stage of development when activity can permanently modify circuit structure and function.
Mutations in the kinase domain of leucine-rich repeat kinase 2 (LRRK2) follow Parkinson's disease (PD) heritability. How such mutations affect brain function is poorly understood. LRRK2 expression levels rise after birth at a time when synapses are forming and are highest in dorsal striatum, suggesting that LRRK2 regulates development of striatal circuits. During a period of postnatal development when activity plays a large role in permanently shaping neural circuits, our data show how the most common PD-causing LRRK2 mutation dramatically alters excitatory synaptic activity and the shape of postsynaptic structures in striatum. These findings provide new insight into early functional and structural aberrations in striatal connectivity that may predispose striatal circuitry to both motor and nonmotor dysfunction later in life.
富含亮氨酸重复激酶2（LRRK2）基因的突变可导致帕金森病（PD），最常见的与疾病相关的突变G2019S会增加激酶活性。由于LRRK2表达水平在突触形成过程中升高，且在背侧纹状体棘状投射神经元（SPN）中最高，我们检验了以下假设：LRRK2 - G2019S突变会改变背侧纹状体中兴奋性突触网络的发育。为避免与LRRK2过表达相关的实验混淆因素，我们使用了表达LRRK2 - G2019S或D2017A（激酶失活）敲入突变的小鼠。在全细胞记录中，与出生后第21天的野生型SPN相比，G2019S SPN的微小兴奋性突触后电流（sEPSC）频率增加了四倍。在直接通路和间接通路的SPN中，这种增强的神经活动同样增加，且动作电位依赖性活动尤其升高。D2017A SPN中的兴奋性突触活动与野生型相似，表明G2019S具有选择性作用。急性暴露于LRRK2激酶抑制剂可使活动恢复正常，支持G2019S SPN中过度的神经活动是直接介导的且依赖于激酶。尽管G2019S SPN中的树突分支以及兴奋性突触前终末和突触后树突棘的密度与野生型相似，但G2019S SPN显示出更大的棘，其功能上表现为向更大的突触后反应幅度转变。将纹状体与上方的新皮层急性分离可使G2019S突变体中的sEPSC频率恢复正常，支持异常的皮质纹状体活动参与其中。这些发现表明，G2019S突变在发育阶段赋予SPN活动和形态异常功能增强，在此阶段活动可永久改变电路结构和功能。
富含亮氨酸重复激酶2（LRRK2）激酶结构域的突变遵循帕金森病（PD）的遗传模式。此类突变如何影响脑功能尚不清楚。LRRK2表达水平在出生后突触形成时升高，且在背侧纹状体中最高，这表明LRRK2调节纹状体回路的发育。在出生后发育阶段，活动在永久塑造神经回路中起重要作用，我们的数据显示了最常见的导致PD的LRRK2突变如何显著改变纹状体中兴奋性突触活动和突触后结构的形状。这些发现为纹状体连接性的早期功能和结构异常提供了新的见解，这些异常可能使纹状体回路在生命后期易患运动和非运动功能障碍。
