Yamagata Y, Imoto K, Obata K
Laboratory of Neurochemistry National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan.
Neuroscience. 2006 Jul 7;140(3):981-92. doi: 10.1016/j.neuroscience.2006.02.054. Epub 2006 Apr 24.
Seizure is a form of excessive neuronal excitation and seizure-induced neuronal damage has profound effects on the prognosis of epilepsy. In various seizure models, the inactivation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) occurs during seizure activity preceding neuronal cell death. CaMKII is a multifunctional protein kinase enriched in the brain and involved in various ways the regulation of neuronal activity. CaMKII inactivation during seizure activity may modify neuronal cell survival after seizure. However, the mechanism for CaMKII inactivation and its consequence after seizure recovery remain to be elucidated yet. In the present study, we employed a prolonged seizure model by systemic injection of kainic acid into rats and biochemically examined the activity state of CaMKII. In status epilepticus induced by kainic acid, not only the inactivation of CaMKII in brain homogenate, but also a shift in the distribution of CaMKII protein from the soluble to particulate fraction occurred in both hippocampus and parietal cortex. The particulate CaMKII showed a large decrease in the specific activity and a concurrent large increase in the autophosphorylation ratio at Thr-286 (alpha) and at Thr-287 (beta). In contrast, the soluble CaMKII showed normal or rather decreased specific activity and autophosphorylation ratio. After 24 h of recovery from kainic acid-induced status epilepticus, all such changes had disappeared. On the other hand, the total amount of CaMKII was decreased by 35% in hippocampus and 20% in parietal cortex, but the existing CaMKII was indistinguishable from those of controls in terms of the autonomous activity ratio, specific activity and autophosphorylation ratio. Thus, CaMKII inactivation in kainic acid-induced status epilepticus seems to be derived not from simple degradation of the enzyme, but from the formation of the autophosphorylated, inactivated and sedimentable CaMKII. Such a form of CaMKII may be important during pathological conditions in vivo in preventing excessive CaMKII activation due to Ca2+ overload.
癫痫发作是神经元过度兴奋的一种形式，癫痫发作诱导的神经元损伤对癫痫的预后有深远影响。在各种癫痫发作模型中，Ca2+/钙调蛋白依赖性蛋白激酶II（CaMKII）的失活发生在神经元细胞死亡之前的癫痫发作活动期间。CaMKII是一种在大脑中富集的多功能蛋白激酶，以多种方式参与神经元活动的调节。癫痫发作活动期间CaMKII失活可能会改变癫痫发作后神经元细胞的存活情况。然而，癫痫发作恢复后CaMKII失活的机制及其后果仍有待阐明。在本研究中，我们通过向大鼠全身注射海藻酸建立了一个长时间癫痫发作模型，并对CaMKII的活性状态进行了生化检测。在海藻酸诱导的癫痫持续状态中，不仅脑匀浆中的CaMKII失活，而且海马和顶叶皮质中CaMKII蛋白的分布也从可溶性部分转移到了颗粒部分。颗粒状CaMKII的比活性大幅下降，同时苏氨酸-286（α）和苏氨酸-287（β）处的自磷酸化比率大幅增加。相比之下，可溶性CaMKII的比活性正常或略有下降，自磷酸化比率也降低。从海藻酸诱导的癫痫持续状态恢复24小时后，所有这些变化都消失了。另一方面，海马中CaMKII的总量减少了35%，顶叶皮质中减少了20%，但就自主活性比率、比活性和自磷酸化比率而言，现存的CaMKII与对照组的没有区别。因此，海藻酸诱导的癫痫持续状态中CaMKII失活似乎并非源于该酶的简单降解，而是源于自磷酸化、失活且可沉淀的CaMKII的形成。这种形式的CaMKII在体内病理条件下对于防止因Ca2+过载导致的CaMKII过度激活可能很重要。
