Cao Lei, Tian Ye, Jiang Yi, Zhang Ge-Juan, Lei Hui, Di Zheng-Li
Department of Neurological Disease, Xi'an Central Hospital, Xi'an Jiaotong University, Xi'an, Shaanxi, China.
Cell Physiol Biochem. 2015;35(4):1633-42. doi: 10.1159/000373977. Epub 2015 Mar 18.
Homer is a family of post synaptic density proteins functionally and physically attached to target proteins at proline-rich sequences. Reducing Homer1b/c expression has been shown in previous studies to be protective against excitotoxic insults, implicating Homer1b/c in the physiological regulation of aberrant neuronal excitability.
To test the efficacy of a Homer1b/c reducing therapy for disorders with a detrimental hyperexcitability profile in mice, we used small interfere RNA (siRNA) to decrease endogenous Homer1b/c expression in mouse hippocampus. The baseline motor and cognitive behavior was measured by sensorimotor tests, Morris water maze and elevated plus maze tasks. The anti-epileptic effects of Homer1b/c knockdown were determined in two chemically induced seizure models induced by Picrotoxin (PTX) or pentylenetetrazole (PTZ) administration.
The results of sensorimotor tests, Morris water maze and elevated plus maze tasks showed that Homer1b/c reduction had no effect on baseline motor or cognitive behavior. In two chemically induced seizure models, mice with reduced Homerb/c protein had less severe seizures than control mice. Total Homer1b/c protein levels and seizure severity were highly correlated, such that those mice with the most severe seizures also had the highest levels of Homer1b/c. In addition, the phosphorylation of mammalian target of rapamycin (mTOR) and its target protein S6 was significantly inhibited in Homer1b/c down-regulated mice. Homer1b/c knockdown-induced inhibition of mTOR pathway was partially ablated by the metabotropic glutamate receptor 5 (mGluR5) agonist CHPG.
Our results demonstrate that endogenous Homer1b/c is integral for regulating neuronal hyperexcitability in adult animals and suggest that reduction of Homer1b/c could protect against chemically induced seizures through inhibition mTOR pathway.
Homer是一个突触后致密蛋白家族，在富含脯氨酸的序列上与靶蛋白在功能和物理上相连。先前的研究表明，降低Homer1b/c的表达可预防兴奋性毒性损伤，这表明Homer1b/c参与了异常神经元兴奋性的生理调节。
为了测试降低Homer1b/c的疗法对小鼠中具有有害性过度兴奋特征的疾病的疗效，我们使用小干扰RNA（siRNA）来降低小鼠海马体中内源性Homer1b/c的表达。通过感觉运动测试、莫里斯水迷宫和高架十字迷宫任务来测量基线运动和认知行为。在由苦味毒（PTX）或戊四氮（PTZ）诱导的两种化学诱导癫痫模型中确定敲低Homer1b/c的抗癫痫作用。
感觉运动测试、莫里斯水迷宫和高架十字迷宫任务的结果表明，降低Homer1b/c对基线运动或认知行为没有影响。在两种化学诱导癫痫模型中，Homerb/c蛋白降低的小鼠癫痫发作比对照小鼠轻。Homer1b/c总蛋白水平与癫痫发作严重程度高度相关，因此癫痫发作最严重的小鼠Homer1b/c水平也最高。此外，在Homer1b/c下调的小鼠中，雷帕霉素哺乳动物靶标（mTOR）及其靶蛋白S6的磷酸化被显著抑制。代谢型谷氨酸受体5（mGluR5）激动剂CHPG部分消除了敲低Homer1b/c诱导的mTOR通路抑制。
我们的结果表明，内源性Homer1b/c是调节成年动物神经元过度兴奋所必需的，并表明降低Homer1b/c可通过抑制mTOR通路预防化学诱导的癫痫发作。
