This editorial highlights a study by Rodriguez, Sanchez‐Moran et al. (2019) in the current issue of the Journal of Neurochemistry, in which the authors describe a microcephalic boy carrying the novel heterozygous de novo missense mutation c.560A> G; p.Asp187Gly in Cdh1/Fzr1 encoding the APC/C E3‐ubiquitin ligase cofactor CDH1. A functional characterization of mutant APC/CCDH1 confirms an aberrant division of neural progenitor cells, a condition known to determine the mouse brain cortex size. These data suggest that APC/CCDH1 may contribute to the regulation of the human brain size.
Insulin receptor (IR) in the brain plays a role in synaptic plasticity and cognitive functions. Phosphorylation of α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) receptors GluR1 subunit at Serine 831 is regulated by calcium–calmodulin‐dependent protein kinase II and protein kinase C that underlie long‐term potentiation and learning/memory. Recent studies have shown that the novel Protein Kinase M zeta (PKMζ) underlies synaptic plasticity and may regulate AMPAr. In this study, we show that insulin induces phosphorylation of Serine 831 GluR1 subunit of AMPAr and induces over‐expression of PKMζ; pre‐treatment with either the IR inhibitor 3‐Bromo‐5‐t‐butyl‐4‐hydroxy‐benzylidenemalonitrile (AG1024) or PKMζ inhibitor protein kinase C zeta pseudo‐substrate inhibitor returned the phosphorylation value of GluR1 to control level. Amyloid beta (Aβ) peptide in the form of oligomers interferes with IR signaling. Pre‐treating neuronal cultures with Aβ following incubation with insulin, we found a reduction of insulin‐dependent PKMζ over‐expression and MAPK/Erk (1/2) phosphorylation, i.e., signaling pathways involved in synaptic plasticity and learning/memory. These results indicate a new intracellular insulin signaling pathway, and, additionally, that insulin resistance in Alzheimer's disease is a response to the production and accumulation of Aβ.
Inflammation is a key part of central nervous system pathophysiology. However, inflammatory factors are now thought to have both beneficial and deleterious effects. Here, we examine the hypothesis that lipocalin‐2 (LCN2), an inflammatory molecule that can be up‐regulated in the distressed central nervous system, may enhance angiogenesis in brain endothelial cells. Adding LCN2 (0.5–2.0 μg/mL) to RBE (Rat brain endothelial cells). 4 rat brain endothelial cells significantly increased matrigel tube formation and scratch migration, and also elevated levels of iron and reactive oxygen species. Co‐treatment with a radical scavenger (U83836E), a Nox inhibitor (apocynin) and an iron chelating agent (deferiprone) significantly dampened the ability of LCN2 to enhance tube formation and scratch migration in brain endothelial cells. These findings provide in vitro proof of the concept that LCN2 can promote angiogenesis via iron‐ and reactive oxygen species‐related pathways, and support the idea that LCN2 may contribute to the neurovascular recovery aspects of inflammation.
The function of amyloid precursor protein (APP) is unknown, although the discovery that it contributes to the regulation of surface expression of N‐methyl‐d ‐aspartate (NMDA) receptors has afforded new insights into its functional significance. Since APP is a member of a gene family that contains two other members, amyloid precursor‐like proteins 1 and 2 (APLP1 and APLP2), it is important to determine if the related APP proteins possess the same properties as APP with respect to their interactions with NMDA receptors. Following expression in mammalian cells, both APLP1 and APLP2 behaved similarly to APP in that they both co‐immunoprecipitated with the two major NMDA receptor subtypes, GluN1/GluN2A and GluN1/GluN2B, via interaction with the obligatory GluN1 subunit. Immunoprecipitations from detergent extracts of adult mammalian brain showed co‐immunoprecipitation of APLP1 and APLP2 with GluN2A‐ and GluN2B‐containing NMDA receptors. Furthermore, similarly to APP, APLP1 and APLP2 both enhanced GluN1/GluN2A and GluN1/GluN2B cell surface expression. Thus, all the three members of the APP gene family behave similarly in that they each contribute to the regulation of cell surface NMDA receptor homoeostasis.
In vitro and in vivo studies have suggested that reduced astrocytic uptake of neuronally released glutamate, alterations in expression of glial fibrillary acidic protein (GFAP) and aquaporin‐4 (AQP‐4) contribute to brain edema in acute liver failure (ALF). However, there is no evidence to date to suggest that these alterations occur in patients with ALF. We analyzed the mRNA expression of excitatory amino acid transporters (EAAT‐1, EAAT‐2), GFAP, and AQP‐4 in the cerebral cortex obtained at autopsy from eight patients with ALF and from seven patients with no evidence of hepatic or neurological disorders by real‐time PCR, and protein expression was assessed using immunoblotting and immunohistochemistry. We demonstrated a significant decrease in GFAP mRNA and protein levels in ALF patients compared to controls. While the loss of EAAT‐2 protein in ALF samples was post‐translational in nature, EAAT‐1 protein remained within normal limits. Immunohistochemistry confirmed that, in all cases, the losses of EAAT‐2 and GFAP were uniquely astrocytic in their localization. AQP‐4 mRNA expression was significantly increased and its immunohistochemistry demonstrated increased AQP‐4 immunoreactivity in the glial end‐feet process surrounding the microvessels. These findings provide evidence of selective alterations in the expression of genes coding for key astrocytic proteins implicated in central nervous system (CNS) excitability and brain edema in human ALF.
Autonomic control of heart rate is mediated by cardioinhibitory parasympathetic cholinergic neurons located in the brainstem and stimulatory sympathetic noradrenergic neurons. During embryonic development the survival and cholinergic phenotype of brainstem autonomic neurons is promoted by brain‐derived neurotrophic factor (BDNF). We now provide evidence that BDNF regulates heart rate by a mechanism involving increased brainstem cardioinhibitory parasympathetic activity. Mice with a BDNF haploinsufficiency exhibit elevated resting heart rate, and infusion of BDNF intracerebroventricularly reduces heart rate in both wild‐type and BDNF+/? mice. The atropine‐induced elevation of heart rate is diminished in BDNF+/? mice and is restored by BDNF infusion, whereas the atenolol‐induced decrease in heart rate is unaffected by BDNF levels, suggesting that BDNF signaling enhances parasympathetic tone which is diminished with BDNF haploinsufficiency. Whole‐cell recordings from pre‐motor cholinergic cardioinhibitory vagal neurons in the nucleus ambiguus indicate that BDNF haploinsufficiency reduces cardioinhibitory vagal neuron activity by increased inhibitory GABAergic and diminished excitatory glutamatergic neurotransmission to these neurons. Our findings reveal a previously unknown role for BDNF in the control of heart rate by a mechanism involving increased activation of brainstem cholinergic parasympathetic neurons
Protein aggregation is a common feature of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. How protein aggregates are formed and contribute to neurodegeneration, however, is not clear. Mutation of Ubiquilin 2 (UBQLN2) has recently been linked to ALS and frontotemporal lobar degeneration. Therefore, we examined the effect of ALS‐linked UBQLN2 mutation on endoplasmic reticulum‐associated protein degradation (ERAD). Compared to its wild‐type counterpart, mutated UBQLN2 caused greater accumulation of the ERAD substrate Hong Kong variant of α‐1‐antitrypsin, although ERAD was disturbed by both UBQLN2 over‐expression and knockdown. Also, UBQLN2 interacted with ubiquitin regulatory X domain‐containing protein 8 (UBXD8) in vitro and in vivo, and this interaction was impaired by pathogenic mutation of UBQLN2. As UBXD8 is an endoplasmic membrane protein involved in the translocation of ubiquitinated ERAD substrates, UBQLN2 likely cooperates with UBXD8 to transport defective proteins from the endoplasmic reticulum to the cytosol for degradation, and this cell‐protective function is disturbed by pathogenic mutation of UBQLN2.
Tuberous sclerosis complex (TSC ) is an autosomal dominant neurogenetic disorder affecting about 1 in 6000 people and is caused by mutations in either TSC 1 or TSC 2 . This disorder is characterized by increased activity of mammalian target of rapamycin complex 1 (mTORC 1), which is involved in regulating ribosomal biogenesis and translation initiation. We measured the effects of Tsc2 haploinsufficiency (Tsc2 +/? ) in 3‐month‐old male mice on regional rates of cerebral protein synthesis (rCPS ) by means of the in vivo L‐[1‐14C]leucine method. This quantitative autoradiographic method includes an estimate of the integrated specific activity of the tracer amino acid in brain tissue. The estimate accounts for recycling of unlabeled amino acids from tissue protein breakdown by means of a factor (λ) that was determined in control and Tsc2 +/? mice. The value of λ was higher in Tsc2 +/? mice, indicating that a greater fraction of leucine in the tissue precursor pool for protein synthesis is derived from the plasma compared to controls, consistent with reduced rates of protein degradation. We determined rCPS in freely moving, awake male Tsc2 +/? and control mice, and we used the determined values of λ in the calculation of rCPS . Unexpectedly, we found that rCPS were significantly decreased in 16 of the 17 brain regions analyzed in Tsc2 +/? mice compared to controls. Our results indicate a complex role of mTORC 1 in the regulation of cerebral protein synthesis that has not been previously recognized.
Secondary neuronal death is a serious stroke complication. This process is facilitated by the conversion of glial cells to the reactive pro‐inflammatory phenotype that induces neurodegeneration. Therefore, regulation of glial activation is a compelling strategy to reduce brain damage after stroke. However, drugs have difficulties to access the CNS , and to specifically target glial cells. In the present work, we explored the use core‐shell polyamidoamine tecto‐dendrimer (G5G2.5 PAMAM ) and studied its ability to target distinct populations of stroke‐activated glial cells. We found that G5G2.5 tecto‐dendrimer is actively engulfed by primary glial cells in a time‐ and dose‐dependent manner showing high cellular selectivity and lysosomal localization. In addition, oxygen‐glucose deprivation or lipopolysaccharides exposure in vitro and brain ischemia in vivo increase glial G5G2.5 uptake; not being incorporated by neurons or other cell types. We conclude that G5G2.5 tecto‐dendrimer is a highly suitable carrier for targeted drug delivery to reactive glial cells in vitro and in vivo after brain ischemia.
Cocaine is a recreational drug of abuse that binds to the dopamine transporter, preventing reuptake of dopamine into pre‐synaptic terminals. The increased presence of synaptic dopamine results in stimulation of both pre‐ and post‐synaptic dopamine receptors, considered an important mechanism by which cocaine elicits its reinforcing properties. However, the effects of acute cocaine administration on pre‐synaptic dopamine function remain unclear. Non‐invasive imaging techniques such as positron emission tomography have revealed impaired pre‐synaptic dopamine function in chronic cocaine users. Similar impairments have been seen in animal studies, with microdialysis experiments indicating decreased basal dopamine release. Here we use micro positron emission tomography imaging techniques in mice to measure dopamine synthesis capacity and determine the effect of acute cocaine administration of pre‐synaptic dopamine function. We show that a dose of 20 mg/kg cocaine is sufficient to elicit hyperlocomotor activity, peaking 15–20 min post treatment (p < 0.001). However, dopamine synthesis capacity in the striatum was not significantly altered by acute cocaine treatment (: 0.0097 per min vs. 0.0112 per min in vehicle controls, p > 0.05). Furthermore, expression levels of two key enzymes related to dopamine synthesis, tyrosine hydroxylase and aromatic l ‐amino acid decarboxylase, within the striatum of scanned mice were not significantly affected by acute cocaine pre‐treatment (p > 0.05). Our findings suggest that while the regulation of dopamine synthesis and release in the striatum have been shown to change with chronic cocaine use, leading to a reduced basal tone, these adaptations to pre‐synaptic dopaminergic neurons are not initiated following a single exposure to the drug.
High serum/plasma cholesterol levels have been suggested as a risk factor for Alzheimer's disease (AD). Some reports, mostly retrospective epidemiological studies, have observed a decreased prevalence of AD in patients taking the cholesterol lowering drugs, statins. The strongest evidence causally linking cholesterol to AD is provided by experimental studies showing that adding/reducing cholesterol alters amyloid precursor protein (APP) and amyloid beta‐protein (Aβ) levels. However, there are problems with the cholesterol‐AD hypothesis. Cholesterol levels in serum/plasma and brain of AD patients do not support cholesterol as a causative factor in AD. Prospective studies on statins and AD have largely failed to show efficacy. Even the experimental data are open to interpretation given that it is well‐established that modification of cholesterol levels has effects on multiple proteins, not only amyloid precursor protein and Aβ. The purpose of this review, therefore, was to examine the above‐mentioned issues, discuss the pros and cons of the cholesterol‐AD hypothesis, involvement of other lipids in the mevalonate pathway, and consider that AD may impact cholesterol homeostasis.
The functional roles of the orphan nuclear receptor, Nurr1, have been extensively studied and well established in the development and survival of midbrain dopamine neurons. As Nurr1 and other NR4A members are widely expressed in the brain in overlapping and distinct manners, it has been an open question whether Nurr1 has important function(s) in other brain areas. Recent studies suggest that up‐regulation of Nurr1 expression is critical for cognitive functions and/or long‐term memory in forebrain areas including hippocampal formation. Questions remain about the association between Nurr1 expression and Alzheimer's disease (AD) brain pathology. Here, using our newly developed Nurr1‐selective antibody, we report that Nurr1 protein is prominently expressed in brain areas with Aβ accumulation, that is, the subiculum and the frontal cortex, in the 5XFAD mouse and that Nurr1 is highly co‐expressed with Aβ at early stages. Furthermore, the number of Nurr1‐expressing cells significantly declines in the 5XFAD mouse in an age‐dependent manner, accompanied by increased plaque deposition. Thus, our findings suggest that altered expression of Nurr1 is associated with AD progression.
Compelling evidence indicates that type 2 diabetes mellitus, insulin resistance (IR), and metabolic syndrome are often accompanied by cognitive impairment. However, the mechanistic link between these metabolic abnormalities and CNS dysfunction requires further investigations. Here, we evaluated whether adipose tissue IR and related metabolic alterations resulted in CNS changes by studying synapse lipid composition and function in the adipocyte‐specific ecto‐nucleotide pyrophosphate phosphodiesterase over‐expressing transgenic (AtENPP1‐Tg) mouse, a model characterized by white adipocyte IR, systemic IR, and ectopic fat deposition. When fed a high‐fat diet, AtENPP1‐Tg mice recapitulate essential features of the human metabolic syndrome, making them an ideal model to characterize peripherally induced CNS deficits. Using a combination of gas chromatography and western blot analysis, we found evidence of altered lipid composition, including decreased phospholipids and increased triglycerides (TG) and free fatty acid in hippocampal synaptosomes isolated from high‐fat diet‐fed AtENPP1‐Tg mice. These changes were associated with impaired basal synaptic transmission at the Schaffer collaterals to hippocampal cornu ammonis 1 (CA1) synapses, decreased phosphorylation of the GluN1 glutamate receptor subunit, down‐regulation of insulin receptor expression, and up‐regulation of the free fatty acid receptor 1.
Adropin is expressed in the CNS and plays a crucial role in the development of stroke. However, little is currently known about the effects of adropin on the blood‐brain barrier (BBB) function after intracerebral hemorrhage (ICH). In this study, the role of adropin in collagenase‐induced ICH was investigated in mice. At 1‐h post‐ICH, mice were administered with recombinant human adropin by intranasal. Brain water +content, BBB permeability, and neurological function were measured at different time intervals. Proteins were quantified using western blot analysis, and the localizations of adropin and Notch1 were visualized via immunofluorescence staining. It is shown that adropin reduced brain water content and improved neurological functions. Adropin preserved the functionality of BBB by increasing N‐cadherin expression and reducing extravasation of albumin. Moreover, in vivo knockdown of Notch1 and Hes1 both abolished the protective effects of adropin. Taken together, our data demonstrate that adropin constitutes a potential treatment value for ICH by preserving BBB and improving functional outcomes through the Notch1 signaling pathway.
The central process in energy production is the oxidation of acetyl‐CoA to CO2 by the tricarboxylic acid (TCA, Krebs, citric acid) cycle. However, this cycle functions also as a biosynthetic pathway from which intermediates leave to be converted primarily to glutamate, GABA, glutamine and aspartate and to a smaller extent to glucose derivatives and fatty acids in the brain. When TCA cycle ketoacids are removed, they must be replaced to permit the continued function of this essential pathway, by a process termed anaplerosis. Since the TCA cycle cannot act as a carbon sink, anaplerosis must be coupled with cataplerosis; the exit of intermediates from the TCA cycle. The role of anaplerotic reactions for cellular metabolism in the brain has been studied extensively. However, the coupling of this process with cataplerosis and the roles that both pathways play in the regulation of amino acid, glucose, and fatty acid homeostasis have not been emphasized. The concept of a linkage between anaplerosis and cataplerosis should be underscored, because the balance between these two processes is essential. The hypothesis that cataplerosis in the brain is achieved by exporting the lactate generated from the TCA cycle intermediates into the blood and perivascular area is presented. This shifts the generally accepted paradigm of lactate generation as simply derived from glycolysis to that of oxidation and might present an alternative explanation for aerobic glycolysis.
Kiss1, a neuropeptide predominantly expressed in the habenula, modulates the serotonin (5‐HT) system to decrease odorant cue [alarm substance (AS)]‐evoked fear behaviour in the zebrafish. The purpose of this study was to assess the interaction of Kiss1 with the 5‐HT system as well as to determine the involvement of the 5‐HT receptor subtypes in AS‐evoked fear. We utilized 0. 28 mg/kg WAY 100635 (WAY), a selective 5‐HT1A receptor antagonist, to observe the effects of Kiss1 administration on AS‐evoked fear. We found WAY significantly inhibited the anxiolytic effects of Kiss1 (p <0.001) with an exception of freezing behaviour. Based on this, we utilized 92.79 mg/kg methysergide, a 5‐HT1 and 5‐HT2 receptor antagonist, and found that methysergide significantly blocked the anxiolytic effects of Kiss1 in the presence of the AS (p <0.001). From this, we conclude that Kiss1 modulates AS‐evoked fear responses mediated by the 5‐HT1A and 5‐HT2 receptors.
Alcohol exposure affects neuronal plasticity in the adult and developing brain. Astrocytes play a major role in modulating neuronal plasticity and are a target of ethanol. Tissue plasminogen activator (tPA) is involved in modulating neuronal plasticity by degrading the extracellular matrix proteins including fibronectin and laminin and is up‐regulated by ethanol in vivo. In this study we explored the hypothesis that ethanol affects DNA methylation in astrocytes thereby increasing expression and release of tPA. It was found that ethanol increased tPA mRNA levels, an effect mimicked by an inhibitor of DNA methyltransferase (DNMT) activity. Ethanol also increased tPA protein expression and release, and inhibited DNMT activity with a corresponding decrease in DNA methylation levels of the tPA promoter. Furthermore, it was observed that protein levels of DNMT3A, but not DNMT1, were reduced in astrocytes after ethanol exposure. These novel studies show that ethanol inhibits DNA methylation in astrocytes leading to increased tPA expression and release; this effect may be involved in astrocyte‐mediated inhibition of neuronal plasticity by alcohol.
A set of specific precursor microRNAs (pre‐miRNAs) are reported to localize into neuronal dendrites, where they could be processed locally to control synaptic protein synthesis and plasticity. However, it is not clear whether specific pre‐miRNAs are also transported into distal axons to autonomously regulate intra‐axonal protein synthesis. Here, we show that a subset of pre‐miRNAs, whose mature miRNAs are enriched in axonal compartment of sympathetic neurons, are present in axons of neurons both in vivo and in vitro by quantitative PCR and by in situ hybridization. Some pre‐miRNAs (let 7c‐a and pre‐miRs‐16, 23a, 25, 125b‐1, 433, and 541) showed elevated axonal levels, while others (pre‐miRs‐138‐2, 185, and 221) were decreased in axonal levels following injury. Dicer and KSRP proteins are also present in distal axons, but Drosha is found restricted to the cell body. These findings suggest that specific pre‐miRNAs are selected for localization into distal axons of sensory neurons and are presumably processed to mature miRNAs in response to extracellular stimuli. This study supports the notion that local miRNA biogenesis effectively provides another level of temporal control for local protein synthesis in axons.
Glutamate is involved in cerebral ischemic injury, but its role has not been completely clarified and studies are required to understand how to minimize its detrimental effects, contemporarily boosting the positive ones. In fact, glutamate is not only a neurotransmitter, but primarily a key metabolite for brain bioenergetics. Thus, we investigated the relationships between glutamate and brain energy metabolism in an in vivo model of complete cerebral ischemia of 15 min and during post‐ischemic recovery after 1, 24, 48, 72, and 96 h in 1‐year‐old adult and 2‐year‐old aged rats. The maximum rates (V max) of glutamate dehydrogenase (GlDH ), glutamate‐oxaloacetate transaminase, and glutamate‐pyruvate transaminase were assayed in somatic mitochondria (FM ) and in intra‐synaptic ‘Light’ mitochondria and intra‐synaptic ‘Heavy’ mitochondria ones purified from cerebral cortex, distinguishing post‐ and pre‐synaptic compartments. During ischemia, none of the enzymes were modified in adult animals. In aged ones, glutamate‐oxaloacetate transaminase was increased in FM and GlDH in intra‐synaptic ‘Heavy’ mitochondria, stimulating glutamate catabolism. During post‐ischemic recovery, FM did not show modifications at both ages while, in intra‐synaptic mitochondria of adult animals, glutamate catabolism was increased after 1 h of recirculation and decreased after 48 and 72 h, whereas it remained decreased up to 96 h in aged rats. These results, with those previously published about Krebs’ cycle and Electron Transport Chain (Villa et al ., [2013] Neurochem. Int . 63, 765–781), demonstrate that: (i) V max of energy‐linked enzymes are different in the various cerebral mitochondria, which (ii) respond differently to ischemia and post‐ischemic recovery, also (iii) with respect to aging.
下载免费PDF全文