Regulation of brain functions by Ca^<2+>/calmodulin-dependent protein kinase II activity

Ca^<2+>/calmodulin-dependent protein kinase II （CaMKII）是中枢神经系统中最丰富的蛋白激酶之一，是细胞内Ca^<2+>对各种刺激反应的关键介质。CaMKII参与许多神经元功能，包括突触可塑性和高级脑功能。然而，CaMKII的哪种蛋白质功能，即蛋白激酶活性，钙调素结合能力或与其他蛋白质相互作用的多聚体结构，负责这些神经元功能仍有待确定。为了明确CaMKII蛋白激酶活性及其底物蛋白磷酸化的作用，我们通过用Arg-42取代Lys-42来设计CaMKII失活亚基的敲入小鼠。正如预期的那样，CaMKII活性选择性降低，而CaMKII亚基蛋白水平与纯合突变体的野生型对照相当。原位杂交显示CaMKII亚基mRNA的正常表达模式，包括纯合突变体中CaMKIIα mRNA的树突状定位。急性海马切片电生理分析和培养海马神经元细胞生物学研究显示，纯合突变体海马突触可塑性异常，但基底突触传递正常。此外，在这些小鼠中还观察到海马体依赖性学习缺陷。这些结果表明，CaMKIIα蛋白激酶活性及其底物蛋白磷酸化对维持正常海马功能至关重要。这种功能缺陷CaMKIIα突变小鼠将作为寻找活动依赖性突触可塑性分子细节的有力工具。

Ca^<2+>/calmodulin-dependent protein kinase II (CaMKII) is one of the most abundant protein kinase in the central nervous system and a key mediator of intracellular Ca^<2+> in response to various stimuli. CaMKII is involved in many neuronal functions including synaptic plasticity and higher brain functions. However, which protein function of CaMKII, i.e., protein kinase activity, calmodulin-binding capacity or multimeric structure interacting with other proteins, is responsible for such neuronal functions remains to be determined yet. To clarify specifically the role of protein kinase activity of CaMKII and its substrate protein phosphorylation, we engineered knock-in mice with the inactivated a subunit of CaMKII by replacing Lys-42 with Arg-42. As expected, CaMKII activity was selectively reduced, while CaMKII subunit protein levels were comparable to those of wild type controls in homozygous mutants. In situ hybridization revealed normal expression patterns of CaMKII subunit mRNAs, including dendritic localization of CaMKIIα mRNA in homozygous mutants. Electrophysiological analysis using acute hippocampal slices and cell biological study using cultured hippocampal neurons revealed abnormal synaptic plasticity but normal basal synaptic transmission in hippocampus in homozygous mutants. In addition, hippocampus-dependent learning deficit was also observed in these mice. These results indicate that protein kinase activity of CaMKIIα and its substrate protein phosphorylation are essential for maintaining normal hippocampal functions. Such a functionally deficient CaMKIIα mutant mouse will serve as a powerful tool in search for molecular details for activity-dependent synaptic plasticity.