Single cocaine exposure does not alter striatal pre‐synaptic dopamine function in mice: an [18F]‐FDOPA PET study

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.

     

Caveolin‐1 mediates tissue plasminogen activator‐induced MMP‐9 up‐regulation in cultured brain microvascular endothelial cells

Thrombolysis with tissue plasminogen activator (tPA) increases matrix metalloproteinase‐9 (MMP‐9) activity in the ischemic brain, which exacerbates blood‐brain barrier injury and increases the risk of symptomatic cerebral hemorrhage. The mechanism through which tPA enhances MMP‐9 activity is not well understood. Here we report an important role of caveolin‐1 in mediating tPA‐induced MMP‐9 synthesis. Brain microvascular endothelial cell line bEnd3 cells were incubated with 5 or 20 μg/ml tPA for 24 hrs before analyzing MMP‐9 levels in the conditioned media and cellular extracts by gelatin zymography. tPA at a dose of 20 μg/mL tPA, but not 5 μg/mL, significantly increased MMP‐9 level in cultured media while decreasing it in cellular extracts. Concurrently, tPA treatment induced a 2.3‐fold increase of caveolin‐1 protein levels in endothelial cells. Interestingly, knockdown of Cav‐1 with siRNA inhibited tPA‐induced MMP‐9 mRNA up‐regulation and MMP‐9 increase in the conditioned media, but did not affect MMP‐9 decrease in cellular extracts. These results suggest that caveolin‐1 critically contributes to tPA‐mediated MMP‐9 up‐regulation, but may not facilitate MMP‐9 secretion in endothelial cells.

     

News and ISN

• Did you know Journal of Neurochemistry offers authors the option to publish Open Access ? ISN members receive a reduced fee ($1,000 USD compared to the regular fee of $3,000 USD, less than most other journals charge).
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• A virtual issue on Neuroinflammation in nervous system disorders, edited by Tammy Kielian, is now available: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1471-4159/homepage/virtual_issues.htm#neuroinflammation

     

BNIP3 mediates pre‐myelinating oligodendrocyte cell death in hypoxia and ischemia

Developing oligodendrocytes, collectively termed ‘pre‐myelinating oligodendrocytes’ (preOLs), are vulnerable to hypoxic or ischemic insults. The underlying mechanism of this vulnerability remains unclear. Previously, we showed that Bcl‐2?E1B‐19K‐interacting protein 3 (BNIP3), a proapoptotic member of the Bcl‐2 family proteins, induced neuronal death in a caspase‐independent manner in stroke. In this study, we investigated the role of BNIP3 in preOL cell death induced by hypoxia or ischemia. In primary oligodendrocyte progenitor cell (OPC) cultures exposed to oxygen–glucose deprivation, we found that BNIP3 was upregulated and levels of BNIP3 expression correlated with the death of OPCs. Up‐regulation of BNIP3 was observed in preOLs in the white matter in a neonatal rat model of stroke. Knockout of BNIP3 significantly reduced death of preOLs in the middle cerebral artery occlusion model in mice. Our results demonstrate a role of BNIP3 in mediating preOLs cell death induced by hypoxia or ischemia, and suggest that BNIP3 may be a new target for protecting oligodendrocytes from death after stroke.

     

Adropin preserves the blood‐brain barrier through a Notch1/Hes1 pathway after intracerebral hemorrhage in mice

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.

     

Reduced blood‐brain barrier expression of fatty acid‐binding protein 5 is associated with increased vulnerability of APP/PS1 mice to cognitive deficits from low omega‐3 fatty acid diets

Lower levels of the cognitively beneficial docosahexaenoic acid (DHA) are often observed in Alzheimer's disease (AD) brains. Brain DHA levels are regulated by the blood‐brain barrier (BBB) transport of plasma‐derived DHA, a process facilitated by fatty acid‐binding protein 5 (FABP5). This study reports a 42.1 ± 12.6% decrease in the BBB transport of ¹⁴C‐DHA in 8‐month‐old AD transgenic mice (APPswe,PSEN1?E9) relative to wild‐type mice, associated with a 34.5 ± 6.7% reduction in FABP5 expression in isolated brain capillaries of AD mice. Furthermore, short‐term spatial and recognition memory deficits were observed in AD mice on a 6‐month n‐3 fatty acid‐depleted diet, but not in AD mice on control diet. This intervention led to a dramatic reduction (41.5 ± 11.9%) of brain DHA levels in AD mice. This study demonstrates FABP5 deficiency and impaired DHA transport at the BBB are associated with increased vulnerability to cognitive deficits in mice fed an n‐3 fatty acid‐depleted diet, in line with our previous studies demonstrating a crucial role of FABP5 in BBB transport of DHA and cognitive function.

     

G5G2.5 core‐shell tecto‐dendrimer specifically targets reactive glia in brain ischemia

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.

     

Vesicular GABA transporter (VGAT) transports β‐alanine

Vesicular GABA transporter (VGAT) is expressed in GABAergic and glycinergic neurons, and is responsible for vesicular storage and subsequent exocytosis of these inhibitory amino acids. In this study, we show that VGAT recognizes β‐alanine as a substrate. Proteoliposomes containing purified VGAT transport β‐alanine using Δψ but not ΔpH as a driving force. The Δψ‐driven β‐alanine uptake requires Cl^?. VGAT also facilitates Cl^? uptake in the presence of β‐alanine. A previously described VGAT mutant (Glu213Ala) that disrupts GABA and glycine transport similarly abrogates β‐alanine uptake. These findings indicated that VGAT transports β‐alanine through a mechanism similar to those for GABA and glycine, and functions as a vesicular β‐alanine transporter.

     

News & ISN April 2019

We are very sad that the ISN lost its President Kazuhiro Ikenaka, Professor and Chairman at National Institute for Physiological Sciences (NIPS), Director of Okazaki Institute of Integrative Biology. JNeurochem published an Obituary to value his outstanding achievements: Akio Wanaka et al. (2019) OBITUARY Kazuhiro Ikenaka (1952‐2018). https://doi.org/10.1111/jnc.14679

     

Machado–Joseph disease/spinocerebellar ataxia type 3: lessons from disease pathogenesis and clues into therapy

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/C^CDH1 confirms an aberrant division of neural progenitor cells, a condition known to determine the mouse brain cortex size. These data suggest that APC/C^CDH1 may contribute to the regulation of the human brain size.

     

Wnt signaling loss accelerates the appearance of neuropathological hallmarks of Alzheimer's disease in J20‐APP transgenic and wild‐type mice

Alzheimer's disease (AD ) is a neurodegenerative pathology characterized by aggregates of amyloid‐β (Aβ) and phosphorylated tau protein, synaptic dysfunction, and spatial memory impairment. The Wnt signaling pathway has several key functions in the adult brain and has been associated with AD , mainly as a neuroprotective factor against Aβ toxicity and tau phosphorylation. However, dysfunction of Wnt/β‐catenin signaling might also play a role in the onset and development of the disease. J20 APP swInd transgenic (Tg) mouse model of AD was treated i.p. with various Wnt signaling inhibitors for 10 weeks during pre‐symptomatic stages. Then, cognitive, biochemical and histochemical analyses were performed. Wnt signaling inhibitors induced severe changes in the hippocampus, including alterations in Wnt pathway components and loss of Wnt signaling function, severe cognitive deficits, increased tau phosphorylation and Aβ_1–42 peptide levels, decreased Aβ42/Aβ40 ratio and Aβ_1–42 concentration in the cerebral spinal fluid, and high levels of soluble Aβ species and synaptotoxic oligomers in the hippocampus, together with changes in the amount and size of senile plaques. More important, we also observed severe alterations in treated wild‐type (WT ) mice, including behavioral impairment, tau phosphorylation, increased Aβ_1–42 in the hippocampus, decreased Aβ_1–42 in the cerebral spinal fluid, and hippocampal dysfunction. Wnt inhibition accelerated the development of the pathology in a Tg AD mouse model and contributed to the development of Alzheimer's‐like changes in WT mice. These results indicate that Wnt signaling plays important roles in the structure and function of the adult hippocampus and suggest that inhibition of the Wnt signaling pathway is an important factor in the pathogenesis of AD .

Read the Editorial Highlight for this article on page 356 .

     

Astrocytes with previous chronic exposure to amyloid β‐peptide fragment 1–40 suppress excitatory synaptic transmission

Synaptic dysfunction and neuronal death are responsible for cognitive and behavioral deficits in Alzheimer's disease (AD). It is well known that such neurological abnormalities are preceded by long‐term exposure of amyloid β‐peptide (Aβ) and/or hyperphosphorylated tau prior. In addition to the neurological deficit, astrocytes as a major glial cell type in the brain, significantly participate in the neuropathogenic mechanisms underlying synaptic modulation. Although astrocytes play a significant key role in modulating synaptic transmission, little is known on whether astrocyte dysfunction caused by such long‐term Aβ exposure affects synapse formation and function. Here, we show that synapse formation and synaptic transmission are attenuated in hippocampal‐naïve neurons co‐cultured with astrocytes that have previously experienced chronic Aβ_1‐40 exposure. In this abnormal astrocytic condition, hippocampal neurons exhibit decrements of evoked excitatory post‐synaptic currents (EPSCs) and miniature EPSC frequency. Furthermore, size of readily releasable synaptic pools and number of excitatory synapses were also significantly decreased. Contrary to these negative effects, release probability at individual synapses was significantly increased in the same astrocytic condition. Taken together, our data indicate that lower synaptic transmission caused by astrocytes previously, and chronically, exposed to Aβ1–40 is attributable to a small number of synapses with higher release probability.

     

The high‐affinity D2/D3 agonist D512 protects PC12 cells from 6‐OHDA‐induced apoptotic cell death and rescues dopaminergic neurons in the MPTP mouse model of Parkinson's disease

In this study, in vitro and in vivo experiments were carried out with the high‐affinity multifunctional D2/D3 agonist D‐512 to explore its potential neuroprotective effects in models of Parkinson's disease and the potential mechanism(s) underlying such properties. Pre‐treatment with D‐512 in vitro was found to rescue rat adrenal Pheochromocytoma PC12 cells from toxicity induced by 6‐hydroxydopamine administration in a dose‐dependent manner. Neuroprotection was found to coincide with reductions in intracellular reactive oxygen species, lipid peroxidation, and DNA damage. In vivo, pre‐treatment with 0.5 mg/kg D‐512 was protective against neurodegenerative phenotypes associated with systemic administration of MPTP, including losses in striatal dopamine, reductions in numbers of DAergic neurons in the substantia nigra (SN), and locomotor dysfunction. These observations strongly suggest that the multifunctional drug D‐512 may constitute a novel viable therapy for Parkinson's disease.

     

The role of glutamate signaling in incentive salience: second‐by‐second glutamate recordings in awake Sprague‐Dawley rats

The attribution of incentive salience to reward‐predictive stimuli has been shown to be associated with substance abuse‐like behavior such as increased drug taking. Evidence suggests that glutamate neurotransmission and sequential N‐methyl‐D‐aspartate (NMDA) activation are involved in the attribution of incentive salience. Here, we further explore the role of second‐by‐second glutamate neurotransmission in the attribution of incentive salience to reward‐predictive stimuli by measuring sign‐tracking behavior during a Pavlovian conditioned approach procedure using ceramic‐based microelectrode arrays configured for sensitive measures of extracellular glutamate in awake behaving Sprague‐Dawley rats. Specifically, we show that there is an increase in extracellular glutamate levels in the prelimbic cortex (PrL) and the nucleus accumbens core (NAcC) during sign‐tracking behavior to a food‐predictive conditioned stimulus (CS+) compared to the presentation of a non‐predictive conditioned stimulus (CS?). Furthermore, the results indicate greater increases in extracellular glutamate levels in the PrL compared to NAcC in response to the CS+, including differences in glutamate release and signal decay. Taken together, the present research suggests that there is differential glutamate signaling in the NAcC and PrL during sign‐tracking behavior to a food‐predictive CS+.

     

Calmodulin‐like skin protein protects against spatial learning impairment in a mouse model of Alzheimer disease

Humanin and calmodulin‐like skin protein (CLSP) inhibits Alzheimer disease (AD)‐related neuronal cell death via the heterotrimeric humanin receptor in vitro . It has been suggested that CLSP is a central agonist of the heterotrimeric humanin receptor in vivo . To investigate the role of CLSP in the AD pathogenesis in vivo , we generated mouse CLSP‐1 transgenic mice, crossed them with the APPswe/PSEN1dE9 mice, a model mouse of AD, and examined the effect of CLSP over‐expression on the pathological phenotype of the AD mouse model. We found that over‐expression of the mouse CLSP‐1 gene attenuated spatial learning impairment, the loss of a presynaptic marker synaptophysin, and the inactivation of STAT3 in the APPswe/PSEN1dE9 mice. On the other hand, CLSP over‐expression did not affect levels of Aβ, soluble Aβ oligomers, or gliosis. These results suggest that the CLSP‐mediated attenuation of memory impairment and synaptic loss occurs in an Aβ‐independent manner. The results of this study may serve as a hint to the better understanding of the AD pathogenesis and the development of AD therapy.

     

Use of cysteine‐reactive cross‐linkers to probe conformational flexibility of human DJ‐1 demonstrates that Glu18 mutations are dimers

The oxidation of a key cysteine residue (Cys106) in the parkinsonism‐associated protein DJ‐1 regulates its ability to protect against oxidative stress and mitochondrial damage. Cys106 interacts with a neighboring protonated Glu18 residue, stabilizing the Cys106‐SO₂^? (sulfinic acid) form of DJ‐1. To study this important post‐translational modification, we previously designed several Glu18 mutations (E18N, E18D, E18Q) that alter the oxidative propensity of Cys106. However, recent results suggest these Glu18 mutations cause loss of DJ‐1 dimerization, which would severely compromise the protein's function. The purpose of this study was to conclusively determine the oligomerization state of these mutants using X‐ray crystallography, NMR spectroscopy, thermal stability analysis, circular dichroism spectroscopy, sedimentation equilibrium ultracentrifugation, and cross‐linking. We found that all of the Glu18 DJ‐1 mutants were dimeric. Thiol cross‐linking indicates that these mutant dimers are more flexible than the wild‐type protein and can form multiple cross‐linked dimeric species due to the transient exposure of cysteine residues that are inaccessible in the wild‐type protein. The enhanced flexibility of Glu18 DJ‐1 mutants provides a parsimonious explanation for their lower observed cross‐linking efficiency in cells. In addition, thiol cross‐linkers may have an underappreciated value as qualitative probes of protein conformational flexibility.