Inhibition of the mammalian target of rapamycin blocks epilepsy progression in NS-Pten conditional knockout mice

The Cain Foundation Laboratories and The Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030, USA.
Epilepsia (Impact Factor: 4.58). 11/2011; 52(11):2065-75. DOI: 10.1111/j.1528-1167.2011.03280.x
Source: PubMed

ABSTRACT Increased activity of mTOR Complex 1 (mTORC1) has been demonstrated in cortical dysplasia and tuberous sclerosis complex, as well as in animal models of epilepsy. Recent studies in such models revealed that inhibiting mTORC1 with rapamycin effectively suppressed seizure activity. However, seizures can recur after treatment cessation, and continuous rapamycin exposure can adversely affect animal growth and health. Here, we evaluated the efficacy of an intermittent rapamycin treatment protocol on epilepsy progression using neuron subset-specific-Pten (NS-Pten) conditional knockout mice.
NS-Pten knockouts were treated with a single course of rapamycin during postnatal weeks 4 and 5, or intermittently over a period of 5 months. Epileptiform activity was monitored using video-electroencephalography (EEG) recordings, and mossy fiber sprouting was evaluated using Timm staining. Survival and body weight were assessed in parallel.
NS-Pten knockouts treated with a single course of rapamycin had recurrence of epilepsy 4-7 weeks after treatment ended. In contrast, epileptiform activity remained suppressed, and survival increased if knockout mice received additional rapamycin during weeks 10-11 and 16-17. Aberrant mossy fiber sprouting, present by 4 weeks of age and progressing in parallel with epileptiform activity, was also blocked by rapamycin.
These findings demonstrate that a single course of rapamycin treatment suppresses epileptiform activity and mossy fiber sprouting for several weeks before epilepsy recurs. However, additional intermittent treatments with rapamycin prevented this recurrence and enhanced survival without compromising growth. Therefore, these studies add to the growing body of evidence implicating an important role for mTORC1 signaling in epilepsy.

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Available from: C Nicole Sunnen, Aug 16, 2015
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    • "Recent data support a role for the mammalian target of rapamycin (mTOR) signaling pathway in the pathogenesis of impaired sociability in ASD (Crino, 2011). The mTOR signaling pathway is expressed in brain and plays a major role in brain development by regulating neuronal cell proliferation, synaptogenesis and development of dendrites and axons (Ehninger and Silva, 2011; Ehninger, 2013; Garelick and Kennedy, 2011; Sunnen et al., 2011). mTOR is a serine/threonine kinase that complexes with other proteins to form the mTOR complex 1 (mTORC1), which regulates cellular energy metabolism, cell growth and proliferation, autophagy, and affects protein synthesis and translation through downstream targets such as ribosomal protein p70S6 kinase 1 (S6K1), ribosomal S6 protein (S6), and eukaryotic translation initiation factor 4E (eIF4E) (Ehninger, 2013; Talos et al., 2012). "
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    ABSTRACT: Overactivation of the mammalian target of rapamycin (mTOR) has been implicated in the pathogenesis of syndromic forms of autism spectrum disorders (ASDs), such as tuberous sclerosis complex, neurofibromatosis 1, and fragile X syndrome. Administration of mTORC1 (mTOR complex 1) inhibitors (e.g. rapamycin) in syndromic mouse models of ASDs improved behavior, cognition, and neuropathology. However, since only a minority of ASDs are due to the effects of single genes (∼10%), there is a need to explore inhibition of mTOR activity in mouse models that may be more relevant to the majority of nonsyndromic presentations, such as the genetically inbred BTBR T(+) Itpr3(tf)/J (BTBR) mouse model of ASDs. BTBR mice have social impairment and exhibit increased stereotypic behavior, which may be due to an upregulation of Raf/ERK, upstream intermediates in mTOR signaling. In prior work, D-cycloserine, a partial glycineB site agonist that targets the N-methyl-D-aspartate (NMDA) receptor, was shown to improve sociability in both Balb/c and BTBR mouse models of ASDs. Importantly, NMDA receptor activation regulates mTOR signaling activity. The current study investigated the ability of rapamycin (10mg/kg, i.p. x four days), an mTORC1 inhibitor, to improve sociability and stereotypic behavior in BTBR mice. Using a standard paradigm to assess mouse social behavior, rapamycin improved several measures of sociability in the BTBR mouse, suggesting that mTOR overactivation represents a therapeutic target that mediates or contributes to impaired sociability in the BTBR mouse model of ASDs. Interestingly, there was no effect of rapamycin on stereotypic behaviors in this mouse model.
    Brain research bulletin 11/2013; 100. DOI:10.1016/j.brainresbull.2013.11.005 · 2.97 Impact Factor
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    • "The functional implications of the paradoxical mTOR activation are also uncertain. In previous studies of animal models of epilepsy, rapamycin inhibited mTOR activation and correspondingly had anticonvulsant or antiepileptogenic actions (Zeng et al., 2008, 2009; Huang et al., 2010; Raffo et al., 2011; Sunnen et al., 2011; Talos et al., 2012; van Vliet et al., 2012). In the present study in the KA model, the paradoxical mTOR activation by rapamycin was associated with more severe SE, characterized by higher seizure score and longer duration. "
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    ABSTRACT: Purpose:  Accumulating data have demonstrated that seizures induced by kainate (KA) or pilocarpine activate the mammalian target of rapamycin (mTOR) pathway and that mTOR inhibitor rapamycin can inhibit mTOR activation, which subsequently has potential antiepileptic effects. However, a preliminary study showed a paradoxical exacerbation of increased mTOR pathway activity reflected by S6 phosphorylation when rapamycin was administrated within a short period before KA injection. In the present study, we examined this paradoxical effect of rapamycin in more detail, both in normal rats and KA-injected animals. Methods:  Normal rats or KA-treated rats pretreated with rapamycin at different time intervals were sacrificed at various time points (1, 3, 6, 10, 15, and 24 h) after rapamycin administration or seizure onset for western blotting analysis. Phosphorylation of mTOR signaling target of Akt, mTOR, Rictor, Raptor, S6K, and S6 were analyzed. Seizure activity was monitored behaviorally and graded according to a modified Racine scale (n = 6 for each time point). Neuronal cell death was detected by Fluoro-Jade B staining. Key Findings:  In normal rats, we found that rapamycin showed the expected dose-dependent inhibition of S6 phosphorylation 3-24 h after injection, whereas a paradoxical elevation of S6 phosphorylation was observed 1 h after rapamycin. Similarly, pretreatment with rapamycin over 10 h before KA inhibited the KA seizure-induced mTOR activation. In contrast, rapamycin administered 1-6 h before KA caused a paradoxical increase in the KA seizure-induced mTOR activation. Rats pretreated with rapamycin 1 h prior to KA exhibited an increase in severity and duration of seizures and more neuronal cell death as compared to vehicle-treated groups. In contrast, rapamycin pretreated 10 h prior to KA had no effect on the seizures and decreased neuronal cell death. The paradoxical effect of rapamycin on S6 phosphorylation was correlated with upstream mTOR signaling and was reversed by pretreatment of perifosine, an Akt inhibitor. Significance:  These data indicate the complexity of S6 regulation and its effect on epilepsy. Paradoxical effects of rapamycin need to be considered in clinical applications, such as for potential treatment for epilepsy and other neurologic disorders.
    Epilepsia 11/2012; 53(11):2026-33. DOI:10.1111/epi.12013 · 4.58 Impact Factor
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    • "Importantly, rapamycin administered to chronically epileptic rats following kainic acid (KA; Zeng et al., 2009) or pilocarpine (Huang et al., 2010) treatment has been shown to suppress acquired epilepsy, even though these results have not been replicated in mice (Buckmaster and Lew, 2011). However, some authors pointed out that rapamycin treatment in animal models is still far to be optimal, since seizures may reappear after treatment cessation , and continuous rapamycin exposure might severely affect animal growth and health (Sunnen et al., 2011). In this respect, valid alternative strategies might be represented by a high-dose pulse treatment (Raffo et al., 2011) or even prenatal exposure (to be applied in cases of familial TSC predisposition; Anderl et al., 2011), that have been successfully tested in rodents. "
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    Frontiers in Psychiatry 03/2012; 3:19. DOI:10.3389/fpsyt.2012.00019
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