ADAR2-dependent RNA editing of GluR2 is involved in thiamine deficiency-induced alteration of calcium dynamics

Orchestration of a blood-derived and ADARB1-centred network in Alzheimer's and Parkinson's disease

The peripheral immune system is thought to influence the pathogenesis of the central nervous system in Alzheimer's disease (AD) and Parkinson's disease (PD). This study aimed to investigate the characteristics of peripheral leukocytes in AD and PD by comprehensively analyzing the transcriptomic and metabolic features in the blood (NCONTROL = 15; NAD = 11; NPD = 13). The study found an ADARB1-centered module that was associated with diagnosis, phenethylamine, and glutamate. The module consisted of ADARB1, a vital RNA-editing enzyme, LINC02960, and 109 miRNAs. The study also predicted that the ADARB1 and involved regulators were targeted by miRNAs in the ADARB1 module. The integrated analysis of transcriptome and metabolic panel revealed a central role of ADARB1, miR-199b-5p, miR-26a, miR-450b-5p, miR-34c-5p, glutamate and phenethylamine in the regulatory relationships. The study highlights a set of synergetic non-coding RNA related to ADARB1 in the blood ecosystem of AD and PD with dynamic glutamate and phenethylamine, providing new insights into the pathogenesis of these diseases.

Risperidone impedes glutamate excitotoxicity in a valproic acid rat model of autism: Role of ADAR2 in AMPA GluA2 RNA editing

Several reports indicate a plausible role of calcium (Ca2+) permeable AMPA glutamate receptors (with RNA hypo-editing at the GluA2 Q/R site) and the subsequent excitotoxicity-mediated neuronal death in the pathogenesis of a wide array of neurological disorders including autism spectrum disorder (ASD). This study was designed to examine the effects of chronic risperidone treatment on the expression of adenosine deaminase acting on RNA 2 (Adar2), the status of AMPA glutamate receptor GluA2 editing, and its effects on oxidative/nitrosative stress and excitotoxicity-mediated neuronal death in the prenatal valproic acid (VPA) rat model of ASD. Prenatal VPA exposure was associated with autistic-like behaviors accompanied by an increase in the apoptotic marker "caspase-3" and a decrease in the antiapoptotic marker "BCL2" alongside a reduction in the Adar2 relative gene expression and an increase in GluA2 Q:R ratio in the hippocampus and the prefrontal cortex. Risperidone, at doses of 1 and 3 mg, improved the VPA-induced behavioral deficits and enhanced the Adar2 relative gene expression and the subsequent GluA2 subunit editing. This was reflected on the cellular level where risperidone impeded VPA-induced oxidative/nitrosative stress and neurodegenerative changes. In conclusion, the present study confirms a possible role for Adar2 downregulation and the subsequent hypo-editing of the GluA2 subunit in the pathophysiology of the prenatal VPA rat model of autism and highlights the favorable effect of risperidone on reversing the RNA editing machinery deficits, giving insights into a new possible mechanism of risperidone in autism.

RNA editing of ion channels and receptors in physiology and neurological disorders

Adenosine-to-inosine (A-to-I) RNA editing is a post-transcriptional modification that diversifies protein functions by recoding RNA or alters protein quantity by regulating mRNA level. A-to-I editing is catalyzed by adenosine deaminases that act on RNA. Millions of editing sites have been reported, but they are mostly found in non-coding sequences. However, there are also several recoding editing sites in transcripts coding for ion channels or transporters that have been shown to play important roles in physiology and changes in editing level are associated with neurological diseases. These editing sites are not only found to be evolutionary conserved across species, but they are also dynamically regulated spatially, developmentally and by environmental factors. In this review, we discuss the current knowledge of A-to-I RNA editing of ion channels and receptors in the context of their roles in physiology and pathological disease. We also discuss the regulation of editing events and site-directed RNA editing approaches for functional study that offer a therapeutic pathway for clinical applications.

GRIA2/ENPP3 Regulates the Proliferation and Migration of Vascular Smooth Muscle Cells in the Restenosis Process Post-PTA in Lower Extremity Arteries

Restenosis is the main restriction on the long-term efficacy of percutaneous transluminal angioplasty (PTA) therapy for peripheral artery disease (PAD). Interventions to prevent restenosis are poor, and the exact mechanism is unclear. Here, we aimed to elucidate the role of GRIA2 in the restenosis process post-PTA in lower extremity arteries. We searched the differentially expressed genes (DEGs) between atherosclerotic and restenotic artery plaques in the Gene Expression Omnibus (GEO), and five DEGs were identified. Combined with Gene Ontology (GO) enrichment analysis, GRIA2 was significantly correlated with the restenosis process. Tissue samples were used to examine GRIA2 expression by immunofluorescence staining of atherosclerotic and restenotic artery plaques. The regulation of GRIA2 in vascular smooth muscle cells (VSMCs) was confirmed by lentiviral transfection. Overexpression of GRIA2 promoted the proliferation and migration of VSMCs. Using Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and protein–protein interaction (PPI) network, a strong connection between ENPP3 and GRIA2 was discovered. In vitro results showed that the high expression of GRIA2 in VSMCs enhanced the expression of ENPP3, while downregulation of GRIA2 downregulated ENPP3. GRIA2 is highly differentially expressed in restenotic arterial plaques, promoting the proliferation and migration of VSMCs through upregulation of ENPP3. These discoveries will help us to obtain a better understanding of restenosis in lower extremity arteries.

Exogenous insulin-like growth factor 1 attenuates acute ischemic stroke-induced spatial memory impairment via modulating inflammatory response and tau phosphorylation

Acute ischemic stroke is one of the main causes of mortality and morbidity worldwide. The present study aimed to explore the effects of exogenous insulin-like growth factor 1 (IGF-1) on the cognitive injuries induced by acute ischemic stroke and the underlying mechanisms. Acute ischemic stroke rat model was established via transient occlusion of the left middle cerebral artery to male Sprague-Dawley rats. IGF-1 was administered intravenously every other day 24 h after surgery for 14 days. Cognitive functions were determined by Morris water maze assay. Cerebral infarction and edema were determined by riphenyltetrazolium chloride staining and cerebral water content measurement. ELISA and Western blot were performed to detect concentrations of target proteins. Ischemic stroke rats exhibited reduced plasma IGF-1 level and impaired cognitive functions. Intravenous IGF-1 delivery increased the IGF-1 levels in plasma, ischemic amygdala, hippocampus and cortex, improved the neurological dysfunction, cognitive deficits, cerebral infarction and brain edema. Furthermore, IGF-1 relieved the systemic and cerebral inflammatory response by inhibiting the secretion of pro-inflammatory cytokines, interleukin (IL)-6, IL-1β, and tumor necrosis factor alpha (TNF-α), in serum and ischemic hippocampus of ischemic rats. Additionally, IGF-1 attenuated tau phosphorylation in ischemic hippocampus. In short, intravenous IGF-1 administration attenuates acute ischemic stroke-induced cognitive injuries in the experimental rat model possibly via modulating inflammatory response and tau phosphorylation, and might be of promising therapeutic value to ischemic stroke in the future.

mGluR5 Tunes NGF/TrkA Signaling to Orient Spiny Stellate Neuron Dendrites Toward Thalamocortical Axons During Whisker-Barrel Map Formation

Neurons receive and integrate synaptic inputs at their dendrites, thus dendritic patterning shapes neural connectivity and behavior. Aberrant dendritogenesis is present in neurodevelopmental disorders such as Down's syndrome and autism. Abnormal glutamatergic signaling has been observed in these diseases, as has dysfunction of the metabotropic glutamate receptor 5 (mGluR5). Deleting mGluR5 in cortical glutamatergic neurons disrupted their coordinated dendritic outgrowth toward thalamocortical axons and perturbed somatosensory circuits. Here we show that mGluR5 loss-of-function disrupts dendritogenesis of cortical neurons by increasing mRNA levels of nerve growth factor (NGF) and fibroblast growth factor 10 (FGF10), in part through calcium-permeable AMPA receptors (CP-AMPARs), as the whisker-barrel map is forming. Postnatal NGF and FGF10 expression in cortical layer IV spiny stellate neurons differentially impacted dendritic patterns. Remarkably, NGF-expressing neurons exhibited dendritic patterns resembling mGluR5 knockout neurons: increased total dendritic length/complexity and reduced polarity. Furthermore, suppressing the kinase activity of TrkA, a major NGF receptor, prevents aberrant dendritic patterning in barrel cortex of mGluR5 knockout neurons. These results reveal novel roles for NGF-TrkA signaling and CP-AMPARs for proper dendritic development of cortical neurons. This is the first in vivo demonstration that cortical neuronal NGF expression modulates dendritic patterning during postnatal brain development.

AMPA receptor GluA2 subunit defects are a cause of neurodevelopmental disorders

AMPA receptors (AMPARs) are tetrameric ligand-gated channels made up of combinations of GluA1-4 subunits encoded by GRIA1-4 genes. GluA2 has an especially important role because, following post-transcriptional editing at the Q607 site, it renders heteromultimeric AMPARs Ca2+-impermeable, with a linear relationship between current and trans-membrane voltage. Here, we report heterozygous de novo GRIA2 mutations in 28 unrelated patients with intellectual disability (ID) and neurodevelopmental abnormalities including autism spectrum disorder (ASD), Rett syndrome-like features, and seizures or developmental epileptic encephalopathy (DEE). In functional expression studies, mutations lead to a decrease in agonist-evoked current mediated by mutant subunits compared to wild-type channels. When GluA2 subunits are co-expressed with GluA1, most GRIA2 mutations cause a decreased current amplitude and some also affect voltage rectification. Our results show that de-novo variants in GRIA2 can cause neurodevelopmental disorders, complementing evidence that other genetic causes of ID, ASD and DEE also disrupt glutamatergic synaptic transmission.

SRSF9 selectively represses ADAR2-mediated editing of brain-specific sites in primates

Adenosine-to-inosine (A-to-I) RNA editing displays diverse spatial patterns across different tissues. However, the human genome encodes only two catalytically active editing enzymes (ADAR1 and ADAR2), suggesting that other regulatory factors help shape the editing landscape. Here, we show that the splicing factor SRSF9 selectively controls the editing of many brain-specific sites in primates. SRSF9 is more lowly expressed in the brain than in non-brain tissues. Gene perturbation experiments and minigene analysis of candidate sites demonstrated that SRSF9 could robustly repress A-to-I editing by ADAR2. We found that SRSF9 biochemically interacted with ADAR2 in the nucleus via its RRM2 domain. This interaction required the presence of the RNA substrate and disrupted the formation of ADAR2 dimers. Transcriptome-wide location analysis and RNA sequencing revealed 1328 editing sites that are controlled directly by SRSF9. This regulon is significantly enriched for brain-specific sites. We further uncovered a novel motif in the ADAR2-dependent SRSF9 binding sites and provided evidence that the splicing factor prevents loss of cell viability by inhibiting ADAR2-mediated editing of genes involved in proteostasis, energy metabolism, the cell cycle and DNA repair. Collectively, our results highlight the importance of SRSF9 as an editing regulator and suggest potential roles for other splicing factors.

Developmental perfluorooctane sulfonate exposure inhibits long-term potentiation by affecting AMPA receptor trafficking

Both animal study and epidemiological survey revealed the associations between defects of cognitive function and the developmental exposure to perfluorooctane sulfonate (PFOS), while the mechanism is not well known. The SD rats were exposed PFOS at 1.7, 5 and 15 mg/L by drinking water from gestation to the adulthood of the pups for evaluating the effects of PFOS exposure on long-term potentiation (LTP) and the role of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors trafficking. Whole-life exposure of PFOS beginning in utero to adulthood significantly inhibited the induction and expression of LTP, and the input/output curve (I/O) and paired-pulse facilitation (PPF) were moderately suppressed, suggesting that PFOS might affect the synaptic transmission and plasticity both in pre- and post-synaptic cells. Meanwhile, PFOS decreased the mRNA levels of AMPA receptor subunits GluA1 and GluA2, and the protein amounts in the membrane, with the total GluA1 and GluA2 protein amounts increased, indicating the internalization of AMPA receptors. Furthermore, tests in the primary hippocampal neurons also support the decreased mRNA levels of GluA1 and GluA2 induced by PFOS. After the pretreatment of AMPA antagonist (NBQX), PFOS decreased the expression of GluA1 and GluA2 and increased internal cellular calcium at much lower levels than that in the neurons without NBQX treatment. The results provide electrophysiological evidence for the impaired cognitive function induced by PFOS exposure and revealed the critical role of AMPA receptor involved.

A-to-I RNA editing in the rat brain is age-dependent, region-specific and sensitive to environmental stress across generations

BACKGROUND

Adenosine-to-inosine (A-to-I) RNA editing is an epigenetic modification catalyzed by adenosine deaminases acting on RNA (ADARs), and is especially prevalent in the brain. We used the highly accurate microfluidics-based multiplex PCR sequencing (mmPCR-seq) technique to assess the effects of development and environmental stress on A-to-I editing at 146 pre-selected, conserved sites in the rat prefrontal cortex and amygdala. Furthermore, we asked whether changes in editing can be observed in offspring of stress-exposed rats. In parallel, we assessed changes in ADARs expression levels.

RESULTS

In agreement with previous studies, we found editing to be generally higher in adult compared to neonatal rat brain. At birth, editing was generally lower in prefrontal cortex than in amygdala. Stress affected editing at the serotonin receptor 2c (Htr2c), and editing at this site was significantly altered in offspring of rats exposed to prereproductive stress across two generations. Stress-induced changes in Htr2c editing measured with mmPCR-seq were comparable to changes measured with Sanger and Illumina sequencing. Developmental and stress-induced changes in Adar and Adarb1 mRNA expression were observed but did not correlate with editing changes.

CONCLUSIONS

Our findings indicate that mmPCR-seq can accurately detect A-to-I RNA editing in rat brain samples, and confirm previous accounts of a developmental increase in RNA editing rates. Our findings also point to stress in adolescence as an environmental factor that alters RNA editing patterns several generations forward, joining a growing body of literature describing the transgenerational effects of stress.

Thiamine deficiency induces endoplasmic reticulum stress and oxidative stress in human neurons derived from induced pluripotent stem cells

Thiamine (vitamin B1) deficiency (TD) plays a major role in the etiology of Wernicke's encephalopathy (WE) which is a severe neurological disorder. TD induces selective neuronal cell death, neuroinflammation, endoplasmic reticulum (ER) stress and oxidative stress in the brain which are commonly observed in many aging-related neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and progressive supranuclear palsy (PSP). However, the underlying cellular and molecular mechanisms remain unclear. The progress in this line of research is hindered due to the lack of appropriate in vitro models. The neurons derived for the human induced pluripotent stem cells (hiPSCs) provide a relevant and powerful tool for the research in pharmaceutical and environmental neurotoxicity. In this study, we for the first time used human induced pluripotent stem cells (hiPSCs)-derived neurons (iCell neurons) to investigate the mechanisms of TD-induced neurodegeneration. We showed that TD caused a concentration- and duration-dependent death of iCell neurons. TD induced ER stress which was evident by the increase in ER stress markers, such as GRP78, XBP-1, CHOP, ATF-6, phosphorylated eIF2α, and cleaved caspase-12. TD also triggered oxidative stress which was shown by the increase in the expression 2,4-dinitrophenyl (DNP) and 4-hydroxynonenal (HNE). ER stress inhibitors (STF-083010 and salubrinal) and antioxidant N-acetyl cysteine (NAC) were effective in alleviating TD-induced death of iCell neurons, supporting the involvement of ER stress and oxidative stress. It establishes that the iCell neurons are a novel tool to investigate cellular and molecular mechanisms for TD-induced neurodegeneration.

Thiamine Deficiency and Neurodegeneration: the Interplay Among Oxidative Stress, Endoplasmic Reticulum Stress, and Autophagy

Thiamine (vitamin B1) is an essential nutrient and indispensable for normal growth and development of the organism due to its multilateral participation in key biochemical and physiological processes. Humans must obtain thiamine from their diet since it is synthesized only in bacteria, fungi, and plants. Thiamine deficiency (TD) can result from inadequate intake, increased requirement, excessive deletion, and chronic alcohol consumption. TD affects multiple organ systems, including the cardiovascular, muscular, gastrointestinal, and central and peripheral nervous systems. In the brain, TD causes a cascade of events including mild impairment of oxidative metabolism, neuroinflammation, and neurodegeneration, which are commonly observed in neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Thiamine metabolites may serve as promising biomarkers for neurodegenerative diseases, and thiamine supplementations exhibit therapeutic potential for patients of some neurodegenerative diseases. Experimental TD has been used to model aging-related neurodegenerative diseases. However, to date, the cellular and molecular mechanisms underlying TD-induced neurodegeneration are not clear. Recent research evidence indicates that TD causes oxidative stress, endoplasmic reticulum (ER) stress, and autophagy in the brain, which are known to contribute to the pathogenesis of various neurodegenerative diseases. In this review, we discuss the role of oxidative stress, ER stress, and autophagy in TD-mediated neurodegeneration. We propose that it is the interplay of oxidative stress, ER stress, and autophagy that contributes to TD-mediated neurodegeneration.

Thiamine Deficiency in Tropical Pediatrics: New Insights into a Neglected but Vital Metabolic Challenge

In humans, thiamine is a micronutrient prone to depletion that may result in severe clinical abnormalities. This narrative review summarizes current knowledge on thiamine deficiency (TD) and bridges the gap between pathophysiology and clinical presentation by integrating thiamine metabolism at subcellular level with its function to vital organs. The broad clinical spectrum of TD is outlined, with emphasis on conditions encountered in tropical pediatric practice. In particular, TD is associated with type B lactic acidosis and classic forms of beriberi in children, but it is often unrecognized. Other severe acute conditions are associated with hypermetabolism, inducing a functional TD. The crucial role of thiamine in infant cognitive development is also highlighted in this review, along with analysis of the potential impact of TD in refeeding syndrome during severe acute malnutrition (SAM). This review aims to increase clinical awareness of TD in tropical settings where access to diagnostic tests is poor, and advocates for an early therapeutic thiamine challenge in resource-limited settings. Moreover, it provides evidence for thiamine as treatment in critical conditions requiring metabolic resuscitation, and gives rationale to the consideration of increased thiamine supplementation in therapeutic foods for malnourished children.

Thiamine Deficiency Increases Ca2+ Current and CaV1.2 L-type Ca2+ Channel Levels in Cerebellum Granular Neurons

Thiamine (vitamin B1) is co-factor for three pivotal enzymes for glycolytic metabolism: pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and transketolase. Thiamine deficiency leads to neurodegeneration of several brain regions, especially the cerebellum. In addition, several neurodegenerative diseases are associated with impairments of glycolytic metabolism, including Alzheimer's disease. Therefore, understanding the link between dysfunction of the glycolytic pathway and neuronal death will be an important step to comprehend the mechanism and progression of neuronal degeneration as well as the development of new treatment for neurodegenerative states. Here, using an in vitro model to study the effects of thiamine deficiency on cerebellum granule neurons, we show an increase in Ca²⁺ current density and Ca_V1.2 expression. These results indicate a link between alterations in glycolytic metabolism and changes to Ca²⁺ dynamics, two factors that have been implicated in neurodegeneration.

Ligand-directed delivery of fluorophores to track native calcium-permeable AMPA receptors in neuronal cultures

Subcellular trafficking of neuronal receptors is known to play a key role in synaptic development, homeostasis, and plasticity. We have developed a ligand-targeted and photo-cleavable probe for delivering a synthetic fluorophore to AMPA receptors natively expressed in neurons. After a receptor is bound to the ligand portion of the probe molecule, a proteinaceous nucleophile reacts with an electrophile on the probe, covalently bonding the two species. The ligand may then be removed by photolysis, returning the receptor to its non-liganded state while leaving intact the new covalent bond between the receptor and the fluorophore. This strategy was used to label polyamine-sensitive receptors, including calcium-permeable AMPA receptors, in live hippocampal neurons from rats. Here, we describe experiments where we examined specificity, competition, and concentration on labeling efficacy as well as quantified receptor trafficking. Pharmacological competition during the labeling step with either a competitive or non-competitive glutamate receptor antagonist prevented the majority of labeling observed without a blocker. In other experiments, labeled receptors were observed to alter their locations and we were able to track and quantify their movements. We used a small molecule, ligand-directed probe to deliver synthetic fluorophores to endogenously expressed glutamate receptors for the purpose of tracking these receptors on live, hippocampal neurons. We found that clusters of receptors appear to move at similar rates to previous studies. We also found that the polyamine toxin pharmacophore likely binds to receptors in addition to calcium-permeable AMPA receptors.

Acquisition of conditioned fear is followed by region-specific changes in RNA editing of glutamate receptors

Adenosine (A) to inosine (I) RNA editing is a post-transcriptional modification process that can affect synaptic function. Transcripts encoding the kainate GRIK1 and AMPA GluA2 glutamate receptor subunits undergo editing that leads to a glycine/arginine (Q/R) exchange and reduced Ca(2+) permeability. We hypothesized that editing at these sites could be experience-dependent, temporally dynamic and region-specific. We trained C57/Bl6 mice in trace and contextual fear conditioning protocols, and examined editing levels at GRIK1 and GluA2 Q/R sites in the amygdala (CeA) and hippocampus (CA1 and CA3), at two time points after training. We also examined experience-dependent changes in the expression of RNA editing enzymes and editing targets. Animals trained in the trace fear conditioning protocol exhibited a transient increase in unedited GRIK1 RNA in the amygdala, and their learning efficiency correlated with unedited RNA levels in CA1. In line with previous reports, GluA2 RNA editing levels were nearly 100%. Additionally, we observed experience-dependent changes in mRNA expression of the RNA editing enzymes ADAR2 and ADAR1 in amygdala and hippocampus, and a learning-dependent increase in the alternatively spliced inactive form of ADAR2 in the amygdala. Since unedited transcripts code for Ca(2+)-permeable receptor subunits, these findings suggest that RNA editing at Q/R sites of glutamate receptors plays an important role in experience-dependent synaptic modification processes.

Down-regulation of the RNA editing enzyme ADAR2 contributes to RGC death in a mouse model of glaucoma

Glaucoma is a progressive neurodegenerative disease of retinal ganglion cells (RGCs) associated with characteristic axon degeneration in the optic nerve. Excitotoxic damage due to increased Ca(2+) influx, possibly through NMDA-type glutamate receptors, has been proposed to be a cause of RGC dysfunction and death in glaucoma. Recent work has found that expression of another potentially critical receptor, the Ca(2+)-permeable AMPA receptor (CP-AMPAR), is elevated during various pathological conditions (including ALS and ischemia), resulting in increased neuronal death. Here we test the hypothesis that CP-AMPARs contribute to RGC death due to elevated Ca(2+) influx in glaucoma. AMPA receptors are impermeable to Ca(2+) if the tetrameric receptor contains a GluA2 subunit that has undergone Q/R RNA editing at a site in the pore region. The activity of ADAR2, the enzyme responsible for this RNA editing, generally ensures that the vast majority of GluA2 proteins are edited. Here, we demonstrate that ADAR2 levels decrease in a mouse model of glaucoma in which IOP is chronically elevated. Furthermore, using an in vitro model of RGCs, we find that knockdown of ADAR2 using siRNA increased the accumulation of Co(2+) in response to glutamate, and decreased the rectification index of AMPA currents detected electrophysiologically, indicating an increased Ca(2+) permeability through AMPARs. The RGCs in primary culture also exhibited increased excitotoxic cell death following knock down of ADAR2. Furthermore, cell death was reversed by NASPM, a specific blocker for CP-AMPARs. Together, our data suggest that chronically elevated IOP in adult mice reduces expression of the ADAR2 enzyme, and the loss of ADAR2 editing and subsequent disruption of GluA2 RNA editing might potentially play a role in promoting RGC neuronal death as observed in glaucoma.

Thiamine deficiency induces anorexia by inhibiting hypothalamic AMPK

Obesity and eating disorders are prevailing health concerns worldwide. It is important to understand the regulation of food intake and energy metabolism. Thiamine (vitamin B1) is an essential nutrient. Thiamine deficiency (TD) can cause a number of disorders in humans, such as Beriberi and Wernicke-Korsakoff syndrome. We demonstrated here that TD caused anorexia in C57BL/6 mice. After feeding a TD diet for 16days, the mice displayed a significant decrease in food intake and an increase in resting energy expenditure (REE), which resulted in a severe weight loss. At the 22nd day, the food intake was reduced by 69% and 74% for male and female mice, respectively in TD group. The REE increased by ninefolds in TD group. The loss of body weight (17-24%) was similar between male and female animals and mainly resulted from the reduction of fat mass (49% decrease). Re-supplementation of thiamine (benfotiamine) restored animal's appetite, leading to a total recovery of body weight. The hypothalamic adenosine monophosphate-activated protein kinase (AMPK) is a critical regulator of food intake. TD inhibited the phosphorylation of AMPK in the arcuate nucleus (ARN) and paraventricular nucleus (PVN) of the hypothalamus without affecting its expression. TD-induced inhibition of AMPK phosphorylation was reversed once thiamine was re-supplemented. In contrast, TD increased AMPK phosphorylation in the skeletal muscle and upregulated the uncoupling protein (UCP)-1 in brown adipose tissues which was consistent with increased basal energy expenditure. Re-administration of thiamine stabilized AMPK phosphorylation in the skeletal muscle as well as energy expenditure. Taken together, TD may induce anorexia by inhibiting hypothalamic AMPK activity. With a simultaneous increase in energy expenditure, TD caused an overall body weight loss. The results suggest that the status of thiamine levels in the body may affect food intake and body weight.

Hippocampus-specific deficiency in RNA editing of GluA2 in Alzheimer's disease

Adenosine to inosine (A-to-I) RNA editing is a base recoding process within precursor messenger RNA, catalyzed by members of the adenosine deaminase acting on RNA (ADAR) family. A notable example occurs at the Q/R site of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptor subunit GluA2. Abnormally, low editing at this site leads to excessive calcium influx and cell death. We studied hippocampus and caudate samples from Alzheimer's disease (AD) patients and age-matched healthy controls, using direct sequencing and a high accuracy primer-extension technique to assess RNA editing at the Q/R GluA2 site. Both techniques revealed lower, more variable RNA editing in AD, specific to the hippocampus and the GluA2 site. Deficient editing also characterized the hippocampus of apolipoprotein ε4 allele carriers, regardless of clinical diagnosis. In AD, messenger RNA expression of neuronal markers was decreased in the hippocampus, and expression of the Q/R-site editing enzyme ADAR2 was decreased in caudate. These findings provide a link between neurodegenerative processes and deficient RNA editing of the GluA2 Q/R site, and may contribute to both diagnosis and treatment of AD.

Autophagy alleviates neurodegeneration caused by mild impairment of oxidative metabolism

Thiamine deficiency (TD) causes mild impairment of oxidative metabolism and region-selective neuronal loss in the brain, which may be mediated by neuronal oxidative stress, endoplasmic reticulum (ER) stress, and neuroinflammation. TD-induced brain damage is used to model neurodegenerative disorders, and the mechanism for the neuronal death is still unclear. We hypothesized that autophagy might be activated in the TD brain and play a protective role in TD-induced neuronal death. Our results demonstrated that TD induced the accumulation of autophagosomes in thalamic neurons measured by transmission electron microscopy, and the up-regulation of autophagic markers LC3-II, Atg5, and Beclin1 as measured with western blotting. TD also increased the expression of autophagic markers and induced LC3 puncta in SH-SY5Y neuroblastoma cells. TD-induced expression of autophagic markers was reversed once thiamine was re-administered. Both inhibition of autophagy by wortmannin and Beclin1 siRNA potentiated TD-induced death of SH-SY5Y cells. In contrast, activation of autophagy by rapamycin alleviated cell death induced by TD. Intraperitoneal injection of rapamycin stimulated neuronal autophagy and attenuated TD-induced neuronal death and microglia activation in the submedial thalamus nucleus (SmTN). TD inhibited the phosphorylation of p70S6 kinase, suggesting mTOR/p70S6 kinase pathway was involved in the TD-induced autophagy. These results suggest that autophagy is neuroprotective in response to TD-induced neuronal death in the central nervous system. This opens a potential therapeutic avenue for neurodegenerative diseases caused by mild impairment of oxidative metabolism. Autophagy is neuroprotective in response to thiamine deficiency (TD)-induced neuronal death. TD caused neuronal damage and induced the formation of autophagosome, and increased the expression of autophagy-related proteins. Autophagy sequestered damaged and dysfunctional organelles/protein, and transported them to lysosomes for degradation/recycling. This process provided nutrients for injured neurons. Wortmannin and knockdown of Beclin1 inhibited autophagy, and exacerbated TD-induced cell death, while activation of autophagy by rapamycin offered protection against TD neurotoxicity.

RNA-interacting proteins act as site-specific repressors of ADAR2-mediated RNA editing and fluctuate upon neuronal stimulation

RNA editing by adenosine deaminases that act on RNA (ADARs) diversifies the transcriptome by changing adenosines to inosines. In mammals, editing levels vary in different tissues, during development, and also in pathogenic conditions. From a screen for repressors of editing we have isolated three proteins that repress ADAR2-mediated RNA editing. The three proteins RPS14, SFRS9 and DDX15 interact with RNA. Overexpression or depletion of these proteins can decrease or increase editing levels by 15%, thus allowing a modulation of RNA editing up to 30%. Interestingly, the three proteins alter RNA editing in a substrate-specific manner that correlates with their RNA binding preferences. In mammalian cells, SFRS9 significantly affects editing of the two substrates CFLAR and cyFIP2, while the ribosomal protein RPS14 mostly inhibits editing of cyFIP2 messenger RNA. The helicase DDX15, in turn, has a strong effect on editing in Caenorhabditis elegans.

Expression of the three factors decreases during mouse brain development. Moreover, expression levels of SFRS9 and DDX15 respond strongly to neuronal stimulation or repression, showing an inverse correlation with editing levels.

Colocalization and immunoprecipitation studies demonstrate a direct interaction of SFRS9 and RPS14 with ADAR2, while DDX15 associates with other helicases and splicing factors. Our data show that different editing sites can be specifically altered in their editing pattern by changing the local RNP landscape.

A-to-I RNA editing modulates the pharmacology of neuronal ion channels and receptors

The regulation of neuronal excitability is complex, as ion channels and neurotransmitter receptors are underlying a large variety of modulating effects. Alterations in the expression patterns of receptors or channel subunits as well as differential splicing contribute to the regulation of neuronal excitability. RNA editing is another and more recently explored mechanism to increase protein diversity, as the genomic recoding leads to new gene products with novel functional and pharmacological properties. In humans A-to-I RNA editing targets several neuronal receptors and channels, including GluR2/5/6 subunits, the Kv1.1 channel, and the 5-HT(2C) receptor. Our review summarizes that RNA editing of these proteins does not only change protein function, but also the pharmacology and presumably the drug therapy in human diseases.

GluA2 AMPA glutamate receptor subunit exhibits codon 607 Q/R RNA editing in the lens

Regulated GluA2 AMPA receptor subunit expression, RNA editing, and membrane localization are fundamental determinants of neuronal Ca(2+) influx, and underlie basic functions such as memory and the primary brain disorder epilepsy. Consistent with this, AMPARs, and specifically GluA2, are targets of common antiepileptic drugs (AEDs) and antidepressants. Recently, epidemiological associations between epilepsy and increased cataract prevalence were found comparable to cataract links with diabetes and smoking. Similarly, use of AEDs and several antidepressants also showed links with increased cataract. Here, we demonstrated GluA2 in lenses, consistent with REST/NRSF and REST4 we described previously in lenses, as well as GluA1 and ADAR2 in the lens. Surprisingly, we found predominant neuron-like Q/R editing of GluA2 RNAs also occurs in the lens and evidence of lens GluA2 phosphorylation and STEP phosphatases linked with GluA2 membrane localization in neurons. This study is among the first to show GluA2 expression and predominant Q/R RNA editing in a non-neural cell. Our results suggest GluA2 AMPARs have related roles in lens physiology and disease processes, and provide evidence these anticonvulsant and antidepressant drug targets also occur in the lens.

Research advances at the Institute for Nutritional Sciences at Shanghai, China

Nutrition-related health issues have emerged as a major threat to public health since the rebirth of the economy in China starting in the 1980s. To meet this challenge, the Chinese Academy of Sciences established the Institute for Nutritional Sciences (INS) at Shanghai, China ≈ 8 y ago. The mission of the INS is to apply modern technologies and concepts in nutritional research to understand the molecular mechanism and provide means of intervention in the combat against nutrition-related diseases, including type 2 diabetes, metabolic syndrome, obesity, cardiovascular diseases, and many types of cancers. Through diligent and orchestrated efforts by INS scientists, graduate students, and research staff in the past few years, the INS has become the leading institution in China in the areas of basic nutritional research and metabolic regulation. Scientists at the INS have made important progress in many areas, including the characterization of genetic and nutritional properties of the Chinese population, metabolic control associated with nutrient sensing, molecular mechanisms underlying glucose and lipid metabolism, regulation of metabolism by adipokines and inflammatory pathways, disease intervention using functional foods or extracts of Chinese herbs, and many biological studies related to carcinogenesis. The INS will continue its efforts in understanding the optimal nutritional needs for Chinese people and the molecular causes associated with metabolic diseases, thus paving the way for effective and individualized intervention in the future. This review highlights the major research endeavors undertaken by INS scientists in recent years.