mGluR7 allosteric modulator AMN082 corrects protein synthesis and pathological phenotypes in FXS.

Fragile X syndrome (FXS) is the leading cause of inherited autism and intellectual disabilities. Aberrant protein synthesis due to the loss of fragile X messenger ribonucleoprotein (FMRP) is the major defect in FXS, leading to a plethora of cellular and behavioral abnormalities. However, no treatments are available to date. In this study, we found that activation of metabotropic glutamate receptor 7 (mGluR7) using a positive allosteric modulator named AMN082 represses protein synthesis through ERK1/2 and eIF4E signaling in an FMRP-independent manner. We further demonstrated that treatment of AMN082 leads to a reduction in neuronal excitability, which in turn ameliorates audiogenic seizure susceptibility in Fmr1 KO mice, the FXS mouse model. When evaluating the animals' behavior, we showed that treatment of AMN082 reduces repetitive behavior and improves learning and memory in Fmr1 KO mice. This study uncovers novel functions of mGluR7 and AMN082 and suggests the activation of mGluR7 as a potential therapeutic approach for treating FXS.

Withaferin A Induces Heat Shock Response and Ameliorates Disease Progression in a Mouse Model of Huntington's Disease.

Impairment of proteostasis network is one of the characteristic features of many age-related neurodegenerative disorders including autosomal dominantly inherited Huntington's disease (HD). In HD, N-terminal portion of mutant huntingtin protein containing expanded polyglutamine repeats accumulates as inclusion bodies and leads to progressive deterioration of various cellular functioning including proteostasis network. Here we report that Withaferin A (a small bioactive molecule derived from Indian medicinal plant, Withania somnifera) partially rescues defective proteostasis by activating heat shock response (HSR) and delays the disease progression in a HD mouse model. Exposure of Withaferin A activates HSF1 and induces the expression of HSP70 chaperones in an in vitro cell culture system and also suppresses mutant huntingtin aggregation in a cellular model of HD. Withaferin A treatment to HD mice considerably increased their lifespan as well as restored progressive motor behavioral deficits and declined body weight. Biochemical studies confirmed the activation of HSR and global decrease in mutant huntingtin aggregates load accompanied with improvement of striatal function in Withaferin A-treated HD mouse brain. Withaferin A-treated HD mice also exhibit significant decrease in inflammatory processes as evident from the decreased microglial activation. These results indicate immense potential of Withaferin A for the treatment of HD and related neurodegenerative disorders involving protein misfolding and aggregation.

Hyperexcitability and Homeostasis in Fragile X Syndrome.

Fragile X Syndrome (FXS) is a leading inherited cause of autism and intellectual disability, resulting from a mutation in the FMR1 gene and subsequent loss of its protein product FMRP. Despite this simple genetic origin, FXS is a phenotypically complex disorder with a range of physical and neurocognitive disruptions. While numerous molecular and cellular pathways are affected by FMRP loss, there is growing evidence that circuit hyperexcitability may be a common convergence point that can account for many of the wide-ranging phenotypes seen in FXS. The mechanisms for hyperexcitability in FXS include alterations to excitatory synaptic function and connectivity, reduced inhibitory neuron activity, as well as changes to ion channel expression and conductance. However, understanding the impact of FMR1 mutation on circuit function is complicated by the inherent plasticity in neural circuits, which display an array of homeostatic mechanisms to maintain activity near set levels. FMRP is also an important regulator of activity-dependent plasticity in the brain, meaning that dysregulated plasticity can be both a cause and consequence of hyperexcitable networks in FXS. This makes it difficult to separate the direct effects of FMR1 mutation from the myriad and pleiotropic compensatory changes associated with it, both of which are likely to contribute to FXS pathophysiology. Here we will: (1) review evidence for hyperexcitability and homeostatic plasticity phenotypes in FXS models, focusing on similarities/differences across brain regions, cell-types, and developmental time points; (2) examine how excitability and plasticity disruptions interact with each other to ultimately contribute to circuit dysfunction in FXS; and (3) discuss how these synaptic and circuit deficits contribute to disease-relevant behavioral phenotypes like epilepsy and sensory hypersensitivity. Through this discussion of where the current field stands, we aim to introduce perspectives moving forward in FXS research.

Simvastatin Restores HDAC1/2 Activity and Improves Behavioral Deficits in Angelman Syndrome Model Mouse.

Angelman syndrome (AS) is a neurodevelopmental disorder categorized by severe disability in intellectual functions and affected by the loss of function of maternally inherited UBE3A gene. Mice deficient for the maternal Ube3a recapitulates many distinguishing behavioral features of the AS and is used as a typical model system to understand the disease pathogenic mechanism. Here, we first show a significant increase in HDAC1 and HDAC2 activities in AS mice brain from as early as embryonic day 16(E16). In depth study further reveals that the deficiency of Ube3a leads to transcriptional up-regulation of both HDAC1 and HDAC2. Restoration of HDAC1 and HDAC2 activities (as evident from the increased acetylation of histones H3 and H4) using simvastatin significantly improves the cognitive deficit and social interaction behavior in AS mice. Simvastatin treatment also restores the reduced level of BDNF in AS mice brain. Finally, we demonstrate that the treatment of simvastatin to primary cortical neuronal culture prepared from AS mice embryo also rescues altered acetylation of histones H3 and H4 and the level of BDNF. These results suggest that simvastatin could be a promising drug for the treatment of AS.

Down-Regulation of miRNA-708 Promotes Aberrant Calcium Signaling by Targeting Neuronatin in a Mouse Model of Angelman Syndrome.

The expression of ubiquitin ligase UBE3A is paternally imprinted in neurons and loss of function of maternally inherited UBE3A causes Angelman syndrome (AS), a neurodevelopmental disorder characterized by severe intellectual disability and motor disturbances. Over activation of UBE3A is also linked with autism. Mice deficient for maternal Ube3a (AS mice) exhibit various behavioral features of AS including cognitive and motor deficits although the underlying molecular mechanism is poorly understood. Here, we investigated possible involvement of miRNA in AS pathogenesis and identified miR-708 as one of the down-regulated miRNA in the brain of AS mice. This miR-708 targets endoplasmic reticulum resident protein neuronatin (a developmentally regulated protein in the brain) leading to decrease in intracellular Ca2+. Suppression of miR-708 or ectopic expression of neuronatin increased the level of intracellular Ca2+ and phosphorylation of CaMKIIα at Thr286. Neuronatin level was significantly increased in various brain regions of AS mice during embryonic and early postnatal days as well as in parvalbumin-positive GABAergic neurons during adulthood with respect to age-matched wild type controls. Differentiated cultured primary cortical neurons obtained from AS mice brain also exhibited higher expression of neuronatin, increased intracellular basal Ca2+ along with augmented phosphorylation of CaMKIIα at Thr286. These results indicate that miR-708/neuronatin mediated aberrant calcium signaling might be implicated in AS pathogenesis.

Glycogen synthase protects neurons from cytotoxicity of mutant huntingtin by enhancing the autophagy flux.

Healthy neurons do not store glycogen while they do possess the machinery for the glycogen synthesis albeit at an inactive state. Neurons in the degenerating brain, however, are known to accumulate glycogen, although its significance was not well understood. Emerging reports present contrasting views on neuronal glycogen synthesis; a few reports demonstrate a neurotoxic effect of glycogen while a few others suggest glycogen to be neuroprotective. Thus, the specific role of glycogen and glycogen synthase in neuronal physiology is largely unexplored. Using cellular and animal models of Huntington's disease, we show here that the overexpression of cytotoxic mutant huntingtin protein induces glycogen synthesis in the neurons by activating glycogen synthase and the overexpressed glycogen synthase protected neurons from the cytotoxicity of the mutant huntingtin. Exposure of neuronal cells to proteasomal blockade and oxidative stress also activate glycogen synthase to induce glycogen synthesis and to protect against stress-induced neuronal death. We show that the glycogen synthase plays an essential and inductive role in the neuronal autophagic flux, and helps in clearing the cytotoxic huntingtin aggregate. We also show that the increased neuronal glycogen inhibits the aggregation of mutant huntingtin, and thus could directly contribute to its clearance. Finally, we demonstrate that excessive autophagy flux is the molecular basis of cell death caused by the activation of glycogen synthase in unstressed neurons. Taken together, our results thus provide a novel function for glycogen synthase in proteolytic processes and offer insight into the role of glycogen synthase and glycogen in both survival and death of the neurons.

Azadiradione Restores Protein Quality Control and Ameliorates the Disease Pathogenesis in a Mouse Model of Huntington's Disease.

Huntington's disease (HD) is an autosomal dominantly inherited neurodegenerative disorder caused by expansion of CAG repeats in the coding area of huntingtin gene. In the HD brain, mutant huntingtin protein goes through proteolysis, and its amino-terminal portion consisting of polyglutamine repeats accumulate as inclusions that result in progressive impairment of cellular protein quality control system. Here, we demonstrate that partial rescue of the defective protein quality control in HD model mouse by azadiradione (a bioactive limonoids found in the seed of Azadirachta indica) could potentially improve the disease pathology. Prolonged treatment of azadiradione to HD mice significantly improved the progressive deterioration in body weight, motor functioning along with extension of lifespan. Azadiradione-treated HD mice brain also exhibited considerable decrease in mutant huntingtin aggregates load and improvement of striatal pathology in comparison with age-matched saline-treated HD controls. Biochemical analysis further revealed upregulation and activation of not only HSF1 (master regulator of protein folding) but also Ube3a (an ubiquitin ligase involved in the clearance of mutant huntingtin) in azadiradione-treated mice. Our results indicate that azadiradione-mediated enhanced folding and clearance of mutant huntingtin might underlie improved disease pathology in HD mice and suggests that it could be a potential therapeutic molecule to delay the progression of HD.

Ube3a deficiency inhibits amyloid plaque formation in APPswe/PS1δE9 mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive decline in memory and cognitive function. Pathological hallmark of AD includes aberrant aggregation of amyloid beta (Aß) peptide, which is produced upon sequential cleavage of amyloid precursor protein (APP) by ß- and γ -secretases. On the contrary, α-secretase cleaves APP within the Aß sequence and thereby prevents Aß generation. Here, we investigated the role of ubiquitin ligase Ube3a (involved in synaptic function and plasticity) in the pathogenesis of AD using APPswe/PS1δE9 transgenic mouse model and first noticed that soluble pool of Ube3a was age-dependently decreased in AD mouse in comparison with wild type controls. To further explore the role of Ube3a in AD patho-mechanism, we generated brain Ube3a-deficient AD mice that exhibited accelerated cognitive and motor deficits compared with AD mice. Interestingly, these Ube3a-deficient AD mice were excessively obese from their age of 12 months and having shorter lifespan. Biochemical analysis revealed that the Ube3a-deficient AD mice had significantly reduced level of Aß generation and amyloid plaque formation in their brain compared with age-matched AD mice and this effect could be due to the increased activity of α-secretase, ADAM10 (a disintegrin and metalloproteinase-10) that shift the proteolysis of APP towards non-amyloidogenic pathway. These findings suggest that aberrant function of Ube3a could influence the progression of AD and restoring normal level of Ube3a might be beneficial for AD.

Rescue of altered HDAC activity recovers behavioural abnormalities in a mouse model of Angelman syndrome.

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by severe intellectual and developmental disabilities. The disease is caused by the loss of function of maternally inherited UBE3A, a gene that exhibits paternal-specific imprinting in neuronal tissues. Ube3a-maternal deficient mice (AS mice) display many classical features of AS, although, the underlying mechanism of these behavioural deficits is poorly understood. Here we report that the absence of Ube3a in AS mice brain caused aberrant increase in HDAC1/2 along with decreased acetylation of histone H3/H4. Partial knockdown of Ube3a in cultured neuronal cells also lead to significant up-regulation of HDAC1/2 and consequent down-regulation of histones H3/H4 acetylation. Treatment of HDAC inhibitor, sodium valproate, to AS mice showed significant improvement in social, cognitive and motor impairment along with restoration of various proteins linked with synaptic function and plasticity. Interestingly, HDAC inhibitor also significantly increased the expression of Ube3a in cultured neuronal cells and in the brain of wild type mice but not in AS mice. These results indicate that anomalous HDAC1/2 activity might be linked with synaptic dysfunction and behavioural deficits in AS mice and suggests that HDAC inhibitors could be potential therapeutic molecule for the treatment of the disease.

Topoisomerase 1 inhibitor topotecan delays the disease progression in a mouse model of Huntington's disease.

Huntington's disease (HD) is a dominantly inherited progressive neurodegenerative disorder caused by the accumulation of polyglutamine expanded mutant huntingtin as inclusion bodies primarily in the brain. After the discovery of the HD gene, considerable progress has been made in understanding the disease pathogenesis and multiple drug targets have been identified, even though currently there is no effective therapy. Here, we demonstrate that the treatment of topotecan, a brain-penetrating topoisomerase 1 inhibitor, to HD transgenic mouse considerably improved its motor behavioural abnormalities along with a significant extension of lifespan. Improvement of behavioural deficits are accompanied with the significant rescue of their progressively decreased body weight, brain weight and striatal volume. Interestingly, topotecan treatment also significantly reduced insoluble mutant huntingtin load in the HD mouse brain. Finally, we show that topotecan treatment to HD mouse not only inhibits the expression of transgenic mutant huntingtin, but also at the same time induces the expression of Ube3a, an ubiquitin ligase linked to the clearance of mutant huntingtin. These findings suggest that topotecan could be a potential therapeutic molecule to delay the progression of HD.

Environmental Enrichment Improves Behavioral Abnormalities in a Mouse Model of Angelman Syndrome.

Angelman syndrome (AS) is a neurodevelopmental disorder largely caused by the loss of function of maternally inherited UBE3A. UBE3A-maternal deficient mice (AS mice) exhibit many typical features of AS including cognitive and motor deficits but the underlying mechanism of these behavioral abnormalities is poorly understood. Here, we demonstrate that rearing of AS mice in the enriched environment for prolonged period significantly improved their cognitive and motor dysfunction. Enriched environment also restored elevated serum corticosterone level and reduced anxiety-like behaviors in these mice. Biochemical analysis further revealed restoration of altered levels of brain-derived neurotrophic factor, glucocorticoid receptor, and phoshphorylated calcium/calmodulin-dependent protein kinase IIα in the hippocampus of AS mice maintained in the enriched environment. Enriched environment also significantly increased the number of parvalbumin-positive GABAergic interneuron in the hippocampus and basolateral amygdala of AS mice. These results indicate potential beneficial effect of enriched environment in the reversal of AS phenotype.

Efficient Inhibition of Protein Aggregation, Disintegration of Aggregates, and Lowering of Cytotoxicity by Green Tea Polyphenol-Based Self-Assembled Polymer Nanoparticles.

Green tea polyphenol epigallocatechin-3-gallate (EGCG) is known for its antiamyloidogenic property, and it is observed that molecular EGCG binds with amyloid structure, redirects fibrillation kinetics, remodels mature fibril, and lowers the amyloid-derived toxicity. However, this unique property of EGCG is difficult to utilize because of their poor chemical stability and substandard bioavailability. Here we report a nanoparticle form of EGCG of 25 nm size (nano-EGCG) which is 10-100 times more efficient than molecular EGCG in inhibiting protein aggregation, disintegrating mature protein aggregates, and lowering amyloidogenic cytotoxicity. The most attractive advantage of nano-EGCG is that it efficiently protects neuronal cells from the toxic effect of extracellular amyloid beta or intracellular mutant huntingtin protein aggregates by preventing their aggregation. We found that the better performance of nano-EGCG is due to the combined effect of increased chemical stability of EGCG against degradation, stronger binding with protein aggregates, and efficient entry into the cell for interaction with aggregated protein structure. This result indicates that the nanoparticle form of antiamyloidogenic molecules can be more powerful in prevention and curing of protein aggregation derived diseases.

Deficiency of Ube3a in Huntington's disease mice brain increases aggregate load and accelerates disease pathology.

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by abnormal expansion of CAG repeats in the gene encoding huntingtin. Mutant huntingtin undergoes proteolytic processing and its N-terminal fragment containing polyglutamine repeat accumulates as inclusion not only in nucleus but also in cytoplasm and neuronal processes. Here, we demonstrate that removal of ubiquitin ligase Ube3a selectively from HD mice brain resulted in accelerated disease phenotype and shorter lifespan in comparison with HD mice. The deficiency of Ube3a in HD mice brain also caused significant increase in global aggregates load, and these aggregates were less ubiquitinated when compared with age-matched HD mice. These Ube3a-maternal deficient HD mice also showed drastic reduction of DARPP-32, a dopamine-regulated phoshphoprotein in their striatum. These results emphasize the crucial role of Ube3a in the progression of HD and its immense potential as therapeutic target.