mTORC1-S6K1 inhibition or mTORC2 activation improves hippocampal synaptic plasticity and learning in Angelman syndrome mice

Nuclear and membrane estrogen receptor antagonists induce similar mTORC2 activation-reversible changes in synaptic protein expression and actin polymerization in the mouse hippocampus

AIMS

Estrogens play pivotal roles in hippocampal synaptic plasticity through nuclear receptors (nERs; including ERα and ERβ) and the membrane receptor (mER; also called GPR30), but the underlying mechanism and the contributions of nERs and mER remain unclear. Mammalian target of rapamycin complex 2 (mTORC2) is involved in actin cytoskeleton polymerization and long-term memory, but whether mTORC2 is involved in the regulation of hippocampal synaptic plasticity by ERs is unclear.

METHODS

We treated animals with nER antagonists (MPP/PHTPP) or the mER antagonist (G15) alone or in combination with A-443654, an activator of mTORC2. Then, we examined the changes in hippocampal SRC-1 expression, mTORC2 signaling (rictor and phospho-AKTSer473), actin polymerization (phospho-cofilin and profilin-1), synaptic protein expression (GluR1, PSD95, spinophilin, and synaptophysin), CA1 spine density, and synapse density.

RESULTS

All of the examined parameters except synaptophysin expression were significantly decreased by MPP/PHTPP and G15 treatment. MPP/PHTPP and G15 induced a similar decrease in most parameters except p-cofilin, GluR1, and spinophilin expression. The ER antagonist-induced decreases in these parameters were significantly reversed by mTORC2 activation, except for the change in SRC-1, rictor, and synaptophysin expression.

CONCLUSIONS

nERs and mER contribute similarly to the changes in proteins and structures associated with synaptic plasticity, and mTORC2 may be a novel target of hippocampal-dependent dementia such as Alzheimer's disease as proposed by previous studies.

Insulin-Like Growth Factor II Targets the mTOR Pathway to Reverse Autism-Like Phenotypes in Mice

Autism spectrum disorder (ASD) is a developmental disability characterized by impairments in social interaction and repetitive behavior, and is also associated with cognitive deficits. There is no current treatment that can ameliorate most of the ASD symptomatology; thus, identifying novel therapies is urgently needed. We used male BTBR T⁺Itpr3^tf /J (BTBR) mice, a model that reproduces most of the core behavioral phenotypes of ASD, to test the effects of systemic administration of insulin-like growth factor II (IGF-II), a polypeptide that crosses the blood-brain barrier and acts as a cognitive enhancer. We show that systemic IGF-II treatments reverse the typical defects in social interaction, cognitive/executive functions, and repetitive behaviors reflective of ASD-like phenotypes. In BTBR mice, IGF-II, via IGF-II receptor, but not via IGF-I receptor, reverses the abnormal levels of the AMPK-mTOR-S6K pathway and of active translation at synapses. Thus, IGF-II may represent a novel potential therapy for ASD.SIGNIFICANCE STATEMENT Currently, there is no effective treatment for autism spectrum disorder (ASD), a developmental disability affecting a high number of children. Using a mouse model that expresses most of the key core as well as associated behavioral deficits of ASD, that are, social, cognitive, and repetitive behaviors, we report that a systemic administration of the polypeptide insulin-like growth factor II (IGF-II) reverses all these deficits. The effects of IGF-II occur via IGF-II receptors, and not IGF-I receptors, and target both basal and learning-dependent molecular abnormalities found in several ASD mice models, including those of identified genetic mutations. We suggest that IGF-II represents a potential novel therapeutic target for ASD.

Estrogen receptor alpha and beta regulate actin polymerization and spatial memory through an SRC-1/mTORC2-dependent pathway in the hippocampus of female mice

Aging-related decline of estrogens, especially 17β-estradiol (E2), has been shown to play an important role in the impairment of learning and memory in dementias, such as Alzheimer's disease (AD), but the underlying molecular mechanisms are poorly understood. In this study, we first demonstrated decreases in E2 signaling (aromatase, classic estrogen receptor ERα and ERβ and their coactivator SRC-1), mTORC2 signaling (Rictor and phospho-AKTser473) and actin polymerization (phospho-Cofilin, Profilin-1 and the F-actin/G-actin ratio) in the hippocampus of old female mice compared with those levels detected in the adult hippocampus. We then showed that ERα and ERβ antagonists induced a significant decrease in SRC-1, mTORC2 signaling, actin polymerization, and CA1 spine density, as well as impairments of learning and memory; however, ovariectomy-induced changes of these parameters could be significantly reversed by treatment with ER agonists. We further showed that expression of SRC-1, mTORC2 signaling and actin polymerization could be upregulated by E2 treatment, and the effects of E2 were blocked by the ER antagonists but mimicked by the agonists. We also showed that the lentivirus-mediated SRC-1 knockdown significantly inhibited the agonist-activated mTORC2 signaling and actin polymerization, and the lentivirus-mediated Rictor knockdown also significantly inhibited the agonist-activated actin polymerization. Finally, we demonstrated that the ERα and ERβ antagonists induced a disruption in actin polymerization and an impairment of spatial memory, which were rescued by activation of mTORC2. Taken together, the above results clearly demonstrated an mTORC2-dependent regulation of actin polymerization that contributed to the effects of ERα and ERβ on spatial learning, which may provide a novel target for the prevention and treatment of E2-related dementia in the aged population.

Postnatal calpain inhibition elicits cerebellar cell death and motor dysfunction

Calpain-1 deletion elicits neurodevelopmental disorders, such as ataxia. However, the function of calpain in postnatal neurodevelopment and its mechanisms remain unknown. In this study, we revealed that postnatal intraperitoneal injection of various calpain inhibitors attenuated cerebellar cytosolic calpain activity. Moreover, postnatal application of calpeptin (2 mg/kg) apparently reduced spectrin breakdown, promoted suprachiasmatic nucleus circadian oscillatory protein (SCOP) accumulation in cerebellar tissue. In addition, application of calpeptin decreased phosphorylated protein kinase B (p-AKT) level (p<0.05), as well as total AKT level (p<0.05). We also evidenced that administration of calpeptin obviously increased phosphorylation of mammalian target of rapamycin (p-mTor) (p<0.01). Apoptosis of granular cells and activation of caspase-3 (p<0.01) were facilitated after calpain inhibition. Importantly, cell numbers of granular cells were reduced and motor function was remarkably impaired in 4-month-old rats receiving postnatal calpain inhibition. Taken together, our data implicated that calpain activity in the postnatal period was critical for the cerebellar development. Postnatal calpain inhibition causes cerebellar granular cell apoptosis and motor dysfunction, likely through SCOP/AKT and p-mTor signaling pathways.

Dysfunctional mTORC1 Signaling: A Convergent Mechanism between Syndromic and Nonsyndromic Forms of Autism Spectrum Disorder?

Whereas autism spectrum disorder (ASD) exhibits striking heterogeneity in genetics and clinical presentation, dysfunction of mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway has been identified as a molecular feature common to several well-characterized syndromes with high prevalence of ASD. Additionally, recent findings have also implicated mTORC1 signaling abnormalities in a subset of nonsyndromic ASD, suggesting that defective mTORC1 pathway may be a potential converging mechanism in ASD pathology across different etiologies. However, the mechanistic evidence for a causal link between aberrant mTORC1 pathway activity and ASD neurobehavioral features varies depending on the ASD form involved. In this review, we first discuss six monogenic ASD-related syndromes, including both classical and potentially novel mTORopathies, highlighting their contribution to our understanding of the neurobiological mechanisms underlying ASD, and then we discuss existing evidence suggesting that aberrant mTORC1 signaling may also play a role in nonsyndromic ASD.

Genetic and Pharmacological Reversibility of Phenotypes in Mouse Models of Autism Spectrum Disorder

As autism spectrum disorder (ASD) is largely regarded as a neurodevelopmental condition, long-time consensus was that its hallmark features are irreversible. However, several studies from recent years using defined mouse models of ASD have provided clear evidence that in mice neurobiological and behavioural alterations can be ameliorated or even reversed by genetic restoration or pharmacological treatment either before or after symptom onset. Here, we review findings on genetic and pharmacological reversibility of phenotypes in mouse models of ASD. Our review should give a comprehensive overview on both aspects and encourage future studies to better understand the underlying molecular mechanisms that might be translatable from animals to humans.

Angelman syndrome: Current and emerging therapies in 2016

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by a loss of the maternally-inherited UBE3A; the paternal UBE3A is silenced in neurons by a mechanism involving an antisense transcript (UBE3A-AS) at the unmethylated paternal locus. We reviewed all published information on the clinical trials that have been completed as well as the publicly available information on ongoing trials of therapies in AS. To date, all clinical trials that strove to improve neurodevelopment in AS have been unsuccessful. Attempts at hypermethylating the maternal locus through dietary compounds were ineffective. The results of an 8-week open-label trial using minocycline as a matrix metalloproteinase-9 inhibitor were inconclusive, while a subsequent randomized placebo-controlled trial suggested that treatment with minocycline for 8 weeks did not result in any neurodevelopmental gains. A 1-year randomized placebo-controlled trial using levodopa to alter the phosphorylation of calcium/calmodulin-dependent kinase II did not lead to any improvement in neurodevelopment. Topoisomerase inhibitors and antisense oligonucleotides are being developed to directly inhibit UBE3A-AS. Artificial transcription factors are being developed to "super activate" UBE3A or inhibit UBE3A-AS. Other strategies targeting specific pathways are briefly discussed. We also reviewed the medications that are currently used to treat seizures and sleep disturbances, which are two of the more common complications of AS. © 2016 Wiley Periodicals, Inc.