OBJECTIVETo investigate the effect of mammalian target of rapamycin(mTOR) inhibitor-rapamycin on cognitive function after chronic cerebral ischemia in mice and its molecular mechanism.

METHODSThe chronic cerebral ischemia model was induced by ligation of right common carotid artery (rUCCAO) in 6-week-old ICR mice. The expressions of mTOR, S6K, S6 and corresponding phosphorylated proteins were detected by Western blotting at different time interval (1 h, 3 h, 6 h, 24 h, 3 d, 7 d, 2 w, 4 w, 6 w) after rUCCAO to determine the changes of mTOR signaling pathway. Rapamycin was administrated i.p. at the dose of 3.0 mg/kg 24 h after rUCCAO. Fluoro Jade B staining was used to detect the apoptotic cells. The expressions of Beclin and LC3-Ⅱ were detected by Western blotting to determine the status of autophagy. Morris water maze test and Y maze test were performed to evaluate cognitive functions.

RESULTSThe mTOR signaling pathway was abnormally activated from 6 h to 6 w after rUCCAO in mouse cortex. The activation of mTOR signaling pathway induced by rUCCAO was reversed by administration of rapamycin, and the apoptotic cell number was significantly decreased (146.1±16.3 vs 84.5±9.6,<0.05). Meanwhile, the elevation of Beclin and LC3-Ⅱ protein induced by rUCCAO was reversed by rapamycin administration. Furthermore, compared with vehicle-treated mice, the latent period[(11.1±2.3) s vs (8.1±1.8) s,<0.05] and swimming distance[(672.8±128.5) cm vs (558.2±124.9) cm,<0.05] were significantly decreased and the number of crossing the platform quadrant in Morris water maze increased(2.8±0.9 vs 5.2±0.8,<0.05) in rapamycin-treated mice. Correct response rate in the Y maze was also increased significantly in rapamycin-treated mice[(38.5±9.2)% vs (64.9±7.9)%,<0.05].

CONCLUSIONSInhibiting mTOR pathway by rapamycin reverses the rUCCAO-induced cognitive impairment partly through the suppression of apoptosis and autophagy.

Accumulating data have revealed that abnormal activity of the mTOR (mammalian target of rapamycin) pathway plays an important role in epileptogenesis triggered by various factors. We previously reported that pretreatment with perifosine, an inhibitor of Akt (also called protein kinase B), abolishes the rapamycin-induced paradoxical increase of S6 phosphorylation in a rat model induced by kainic acid (KA). Since Akt is an upstream target in the mTOR signaling pathway, we set out to determine whether perifosine has a preventive effect on epileptogenesis. Here, we explored the effect of perifosine on the model of temporal epilepsy induced by KA in rats and found that pretreatment with perifosine had no effect on the severity or duration of the KA-induced status epilepticus. However, perifosine almost completely inhibited the activation of p-Akt and p-S6 both acutely and chronically following the KA-induced status epilepticus. Perifosine pretreatment suppressed the KA-induced neuronal death and mossy fiber sprouting. The frequency of spontaneous seizures was markedly decreased in rats pretreated with perifosine. Accordingly, rats pretreated with perifosine showed mild impairment in cognitive functions. Collectively, this study provides novel evidence in a KA seizure model that perifosine may be a potential drug for use in anti-epileptogenic therapy.
Animals ; Anticonvulsants ; pharmacology ; Brain ; drug effects ; pathology ; Convulsants ; toxicity ; Disease Models, Animal ; Epilepsy, Temporal Lobe ; chemically induced ; pathology ; Kainic Acid ; toxicity ; Male ; Neurons ; drug effects ; pathology ; Phosphorylcholine ; analogs & derivatives ; pharmacology ; Protein Kinase Inhibitors ; pharmacology ; Proto-Oncogene Proteins c-akt ; antagonists & inhibitors ; Rats ; Rats, Sprague-Dawley ; Status Epilepticus ; chemically induced ; pathology