Kurnellas Michael P, Lee Amanda K, Li Hong, Deng Longwen, Ehrlich Debra J, Elkabes Stella
Department of Neurology and Neuroscience, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
Mol Cell Neurosci. 2007 Feb;34(2):178-88. doi: 10.1016/j.mcn.2006.10.010. Epub 2006 Dec 5.
PMCA2, a major calcium pump, is expressed at particularly high levels in Purkinje neurons. Accordingly, PMCA2-null mice exhibit ataxia suggesting cerebellar pathology. It is not yet known how changes in PMCA2 expression or activity affect molecular pathways in Purkinje neurons. We now report that the levels of metabotropic glutamate receptor 1 (mGluR1), which plays essential roles in motor coordination, synaptic plasticity, and associative learning, are reduced in the cerebellum of PMCA2-null mice as compared to wild type littermates. The levels of inositol 1,4,5-triphosphate receptor type 1 (IP3R1), an effector downstream to mGluR1, which mediates intracellular calcium signaling, and the expression of Homer 1b/c and Homer 3, scaffold proteins that couple mGluR1 to IP3R1, are also reduced in somata and dendrites of some Purkinje cell subpopulations. In contrast, no alterations occur in the levels of mGluR1 and its downstream effectors in the hippocampus, indicating that the changes are region specific. The reduction in cerebellar mGluR1, IP3R1 and Homer 3 levels are neither due to a generic decrease in Purkinje proteins nor extensive dendritic loss as immunoreactivity to total and non-phosphorylated neurofilament H (NFH) is increased in Purkinje dendrites and microtubule associated protein 2 (MAP2) staining reveals a dense dendritic network in the molecular layer of the PMCA2-null mouse cerebellum. PMCA2 coimmunoprecipitates with mGluR1, Homer 3 and IP3R1, suggesting that the calcium pump is a constituent of the mGluR1 signaling complex. Our results suggest that the decrease in the expression of mGluR1 and its downstream effectors and perturbations in the mGluR1 signaling complex in the absence of PMCA2 may cumulatively result in aberrant metabotropic glutamate receptor signaling in Purkinje neurons leading to cerebellar deficits in the PMCA2-null mouse.
质膜钙泵2（PMCA2）是一种主要的钙泵，在浦肯野神经元中表达水平特别高。因此，PMCA2基因敲除小鼠表现出共济失调，提示存在小脑病变。目前尚不清楚PMCA2表达或活性的变化如何影响浦肯野神经元中的分子通路。我们现在报告，与野生型同窝小鼠相比，PMCA2基因敲除小鼠小脑中代谢型谷氨酸受体1（mGluR1）的水平降低，mGluR1在运动协调、突触可塑性和联想学习中起重要作用。1,4,5-三磷酸肌醇受体1型（IP3R1）是mGluR1下游的效应器，介导细胞内钙信号传导，其水平以及将mGluR1与IP3R1偶联的支架蛋白Homer 1b/c和Homer 3在一些浦肯野细胞亚群的胞体和树突中的表达也降低。相比之下，海马中mGluR1及其下游效应器的水平没有改变，表明这些变化具有区域特异性。小脑mGluR1、IP3R1和Homer 3水平的降低既不是由于浦肯野蛋白的普遍减少，也不是由于广泛的树突丢失，因为浦肯野树突中对总神经丝H（NFH）和非磷酸化神经丝H的免疫反应性增加，并且微管相关蛋白2（MAP2）染色显示PMCA2基因敲除小鼠小脑分子层中有密集的树突网络。PMCA2与mGluR1、Homer 3和IP3R1共免疫沉淀，表明钙泵是mGluR1信号复合物的一个组成部分。我们的结果表明，在没有PMCA2的情况下，mGluR1及其下游效应器表达的降低以及mGluR1信号复合物的扰动可能会累积导致浦肯野神经元中代谢型谷氨酸受体信号异常，从而导致PMCA2基因敲除小鼠出现小脑缺陷。
