Rhesus monkeys exhibiting spontaneous ritualistic behaviors resembling obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic and debilitating psychiatric disorder that affects ∼2%-3% of the population globally. Studying spontaneous OCD-like behaviors in non-human primates may improve our understanding of the disorder. In large rhesus monkey colonies, we found 10 monkeys spontaneously exhibiting persistent sequential motor behaviors (SMBs) in individual-specific sequences that were repetitive, time-consuming and stable over prolonged periods. Genetic analysis revealed severely damaging mutations in genes associated with OCD risk in humans. Brain imaging showed that monkeys with SMBs had larger gray matter (GM) volumes in the left caudate nucleus and lower fractional anisotropy of the corpus callosum. The GM volume of the left caudate nucleus correlated positively with the daily duration of SMBs. Notably, exposure to a stressor (human presence) significantly increased SMBs. In addition, fluoxetine, a serotonergic medication commonly used for OCD, decreased SMBs in these monkeys. These findings provide a novel foundation for developing better understanding and treatment of OCD.

CDKL5 deficiency in adult glutamatergic neurons alters synaptic activity and causes spontaneous seizures via TrkB signaling

CDKL5 deficiency disorder (CDD) is a severe epileptic encephalopathy resulting from pathological mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene. Despite significant progress in understanding the neuronal function of CDKL5, the molecular mechanisms underlying CDD-associated epileptogenesis are unknown. Here, we report that acute ablation of CDKL5 from adult forebrain glutamatergic neurons leads to elevated neural network activity in the dentate gyrus and the occurrence of early-onset spontaneous seizures via tropomyosin-related kinase B (TrkB) signaling. We observe increased expression of brain-derived neurotrophic factor (BDNF) and enhanced activation of its receptor TrkB in the hippocampus of Cdkl5-deficient mice prior to the onset of behavioral seizures. Moreover, reducing TrkB signaling in these mice rescues the altered synaptic activity and suppresses recurrent seizures. These results suggest that TrkB signaling mediates epileptogenesis in a mouse model of CDD and that targeting this pathway might be effective for treating epilepsy in patients affected by CDKL5 mutations.

Repeated methamphetamine exposure decreases plasma brain-derived neurotrophic factor levels in rhesus monkeys

Background

Brain-derived neurotrophic factor (BDNF) is known to prevent methamphetamine (METH)-induced neurotoxicity and plays a role in various stages of METH addiction. However, there is a lack of research with longitudinal design on changes in plasma BDNF levels in active METH-dependent individuals.

Aims

The aim of the study was to investigate changes in BDNF levels during METH self-administration in monkeys.

Methods

This study measured plasma BDNF levels in three male rhesus monkeys with continuous METH exposure and four male control rhesus monkeys without METH exposure. Changes in plasma BDNF levels were then assessed longitudinally during 40 sessions of METH self-administration in the three monkeys.

Results

Repeated METH exposure decreased plasma BDNF levels. Additionally, plasma BDNF decreased with long-term rather than short-term accumulation of METH during METH self-administration.

Conclusions

These findings may indicate that the changes in peripheral BDNF may reflect the quantity of accumulative METH intake during a frequent drug use period.

A high-fidelity RNA-targeting Cas13 restores paternal Ube3a expression and improves motor functions in Angelman syndrome mice

Angelman syndrome (AS) is a rare neurodevelopmental disorder caused by loss of function mutations in maternally expressed UBE3A. No gene-specific treatment is available for patients so far. Although intact and transcriptionally active, paternally inherited UBE3A is silenced by elongation of antisense long noncoding RNA UBE3A-ATS in neurons. Here, we demonstrated that RNA targeting of paternal Ube3a-ATS with a high-fidelity CRISPR-Cas13 (hfCas13x.1) system could restore Ube3a expression to similar levels as that of maternal Ube3a in the cultured mouse neurons. Furthermore, injection into lateral ventricles with neuron-specific hSyn1 promoter-driven hfCas13x.1 packaged in adeno-associated virus (AAV-PHP.eb) could restore paternal Ube3a expression in cortex and hippocampus of neonatal AS mice for up to 4 months after treatment. Behavioral tests showed that expression of paternal Ube3a significantly alleviated AS-related symptoms, including obesity and motor function. Our results suggested that hfCas13x.1-mediated suppression of the Ube3a-ATS lncRNA potentially serves as a promising targeted intervention for AS.

Low-intensity ultrasound directly modulates neural activity of the cerebellar cortex

BACKGROUND

Low-intensity ultrasound is a noninvasive neuromodulation technique with the potential to focally manipulate deep brain activity at millimeter-scale resolution. However, there have been controversies over the direct influence of ultrasound on neurons, due to an indirect auditory activation. Besides, the capacity of ultrasound to stimulate the cerebellum remains underestimated.

OBJECTIVE

To validate the direct neuromodulation effects of ultrasound on the cerebellar cortex from both cellular and behavioral levels.

METHODS

Two-photon calcium imaging were used to measure the neuronal responses of cerebellar granule cells (GrCs) and Purkinje cells (PCs) to ultrasound application in awake mice. And a mouse model of paroxysmal kinesigenic dyskinesia (PKD), in which direct activation of the cerebellar cortex leads to dyskinetic movements, was used to assess the ultrasound-induced behavioral responses.

RESULTS

Low-intensity ultrasound stimulus (0.1 W/cm2) evoked rapidly increased and sustained neural activity in GrCs and PCs at targeted region, while no significant changes in calcium signals were observed responding to off-target stimulus. The efficacy of ultrasonic neuromodulation relies on acoustic dose modified by ultrasonic duration and intensity. In addition, transcranial ultrasound reliably triggered dyskinesia attacks in proline-rich transmembrane protein 2 (Prrt2) mutant mice, suggesting that the intact cerebellar cortex were activated by ultrasound.

CONCLUSION

Low-intensity ultrasound directly activates the cerebellar cortex in a dose-dependent manner, and thus serves as a promising tool for cerebellar manipulation.

Loss of function of CMPK2 causes mitochondria deficiency and brain calcification

Brain calcification is a critical aging-associated pathology and can cause multifaceted neurological symptoms. Cerebral phosphate homeostasis dysregulation, blood-brain barrier defects, and immune dysregulation have been implicated as major pathological processes in familial brain calcification (FBC). Here, we analyzed two brain calcification families and identified calcification co-segregated biallelic variants in the CMPK2 gene that disrupt mitochondrial functions. Transcriptome analysis of peripheral blood mononuclear cells (PBMCs) isolated from these patients showed impaired mitochondria-associated metabolism pathways. In situ hybridization and single-cell RNA sequencing revealed robust Cmpk2 expression in neurons and vascular endothelial cells (vECs), two cell types with high energy expenditure in the brain. The neurons in Cmpk2-knockout (KO) mice have fewer mitochondrial DNA copies, down-regulated mitochondrial proteins, reduced ATP production, and elevated intracellular inorganic phosphate (Pi) level, recapitulating the mitochondrial dysfunction observed in the PBMCs isolated from the FBC patients. Morphologically, the cristae architecture of the Cmpk2-KO murine neurons was also impaired. Notably, calcification developed in a progressive manner in the homozygous Cmpk2-KO mice thalamus region as well as in the Cmpk2-knock-in mice bearing the patient mutation, thus phenocopying the calcification pathology observed in the patients. Together, our study identifies biallelic variants of CMPK2 as novel genetic factors for FBC; and demonstrates how CMPK2 deficiency alters mitochondrial structures and functions, thereby highlighting the mitochondria dysregulation as a critical pathogenic mechanism underlying brain calcification.

CHIP control degradation of mutant ETF:QO through ubiquitylation in late-onset multiple acyl-CoA dehydrogenase deficiency

Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is the most common form of lipid storage myopathy. The disease is mainly caused by mutations in electron-transfer flavoprotein dehydrogenase gene (ETFDH), which leads to decreased levels of ETF:QO in skeletal muscle. However, the specific underlying mechanisms triggering such degradation remain unknown. We constructed expression plasmids containing wild type ETF:QO and mutants ETF:QO-A84T, R175H, A215T, Y333C, and cultured patient-derived fibroblasts containing the following mutations in ETFDH: c.250G>A (p.A84T), c.998A>G (p.Y333C), c.770A>G (p.Y257C), c.1254_1257delAACT (p. L418TfsX10), c.524G>A (p.R175H), c.380T>A (p.L127P), and c.892C>T (p.P298S). We used in vitro expression systems and patient-derived fibroblasts to detect stability of ETF:QO mutants then evaluated their interaction with Hsp70 interacting protein CHIP with active/inactive ubiquitin E3 ligase carboxyl terminus using western blot and immunofluorescence staining. This interaction was confirmed in vitro and in vivo by co-immunoprecipitation and immunofluorescence staining. We confirmed the existence two ubiquitination sites in mutant ETF:QO using mass spectrometry (MS) analysis. We found that mutant ETF:QO proteins were unstable and easily degraded in patient fibroblasts and in vitro expression systems by ubiquitin-proteasome pathway, and identified the specific ubiquitin E3 ligase as CHIP, which forms complex to control mutant ETF:QO degradation through poly-ubiquitination. CHIP-dependent degradation of mutant ETF:QO proteins was confirmed by MS and site-directed mutagenesis of ubiquitination sites. Hsp70 is directly involved in this process as molecular chaperone of CHIP. CHIP plays an important role in ubiquitin-proteasome pathway dependent degradation of mutant ETF:QO by working as a chaperone-assisted E3 ligase, which reveals CHIP's potential role in pathological mechanisms of late-onset MADD.

CDKL5 deficiency in forebrain glutamatergic neurons results in recurrent spontaneous seizures

OBJECTIVE

Mutations of the cyclin-dependent kinase-like 5 (CDKL5) gene cause severe neurodevelopmental disorders characterized by intractable epilepsy, intellectual disability, and autism. Multiple mouse models generated for mechanistic studies have exhibited phenotypes similar to some human pathological features, but none of the models has developed one of the major symptoms affecting CDKL5 deficiency disorder (CDD) patients: intractable recurrent seizures. As disrupted neuronal excitation/inhibition balance is closely associated with the activity of glutamatergic and γ-aminobutyric acidergic (GABAergic) neurons, our aim was to study the effect of the loss of CDKL5 in different types of neurons on epilepsy.

METHODS

Using the Cre-LoxP system, we generated conditional knockout (cKO) mouse lines allowing CDKL5 deficiency in glutamatergic or GABAergic neurons. We employed noninvasive video recording and in vivo electrophysiological approaches to study seizure activity in these Cdkl5 cKO mice. Furthermore, we conducted Timm staining to confirm a morphological alteration, mossy fiber sprouting, which occurs with limbic epilepsy in both human and mouse brains. Finally, we performed whole-cell patch clamp in dentate granule cells to investigate cell-intrinsic properties and synaptic excitatory activity.

RESULTS

We demonstrate that Emx1- or CamK2α-derived Cdkl5 cKO mice manifest high-frequency spontaneous seizure activities recapitulating the epilepsy of CDD patients, which ultimately led to sudden death in mice. However, Cdkl5 deficiency in GABAergic neurons does not generate such seizures. The seizures were accompanied by typical epileptic features including higher amplitude spikes for epileptiform discharges and abnormal hippocampal mossy fiber sprouting. We also found an increase in spontaneous and miniature excitatory postsynaptic current frequencies but no change in amplitudes in the dentate granule cells of Emx1-cKO mice, indicating enhanced excitatory synaptic activity.

SIGNIFICANCE

Our study demonstrates that Cdkl5 cKO mice, serving as an animal model to study recurrent spontaneous seizures, have potential value for the pathological study of CDD-related seizures and for therapeutic innovation.

Stop-gain mutations in UBAP1 cause pure autosomal-dominant spastic paraplegia

Hereditary spastic paraplegias refer to a heterogeneous group of neurodegenerative disorders resulting from degeneration of the corticospinal tract. Clinical characterization of patients with hereditary spastic paraplegias represents progressive spasticity, exaggerated reflexes and muscular weakness. Here, to expand on the increasingly broad pools of previously unknown hereditary spastic paraplegia causative genes and subtypes, we performed whole exome sequencing for six affected and two unaffected individuals from two unrelated Chinese families with an autosomal dominant hereditary spastic paraplegia and lacking mutations in known hereditary spastic paraplegia implicated genes. The exome sequencing revealed two stop-gain mutations, c.247_248insGTGAATTC (p.I83Sfs*11) and c.526G>T (p.E176*), in the ubiquitin-associated protein 1 (UBAP1) gene, which co-segregated with the spastic paraplegia. We also identified two UBAP1 frameshift mutations, c.324_325delCA (p.H108Qfs*10) and c.425_426delAG (p.K143Sfs*15), in two unrelated families from an additional 38 Chinese pedigrees with autosomal dominant hereditary spastic paraplegias and lacking mutations in known causative genes. The primary disease presentation was a pure lower limb predominant spastic paraplegia. In vivo downregulation of Ubap1 in zebrafish causes abnormal organismal morphology, inhibited motor neuron outgrowth, decreased mobility, and shorter lifespan. UBAP1 is incorporated into endosomal sorting complexes required for transport complex I and binds ubiquitin to function in endosome sorting. Patient-derived truncated form(s) of UBAP1 cause aberrant endosome clustering, pronounced endosome enlargement, and cytoplasmic accumulation of ubiquitinated proteins in HeLa cells and wild-type mouse cortical neuron cultures. Biochemical and immunocytochemical experiments in cultured cortical neurons derived from transgenic Ubap1flox mice confirmed that disruption of UBAP1 leads to dysregulation of both early endosome processing and ubiquitinated protein sorting. Strikingly, deletion of Ubap1 promotes neurodegeneration, potentially mediated by apoptosis. Our study provides genetic and biochemical evidence that mutations in UBAP1 can cause pure autosomal dominant spastic paraplegia.

HAP1 is an in vivo UBE3A target that augments autophagy in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by maternal mutation and paternal imprinting of the gene encoding UBE3A, an E3 ubiquitin ligase. Although several potential target proteins of UBE3A have been reported, how these proteins regulate neuronal development remains unclear. We performed a large-scale quantitative proteomic analysis using stable-isotope labeling of amino acids in mammals (SILAM) in mice with maternal Ube3a mutation. We identified huntingtin (Htt)-associated protein (HAP1), a protein that is involved in Huntington's disease (HD), as a new target of UBE3A. We demonstrate that HAP1 regulates autophagy at the initiation stage by promoting PtdIns3K complex formation and enhancing its activity. HAP1 also co-localized with MAP1LC3 (LC3) and other proteins involved in autophagosome expansion. As a result, HAP1 increased autophagy flux. Strikingly, knocking down of HAP1 alleviated aberrant autophagy in primary neurons from AS mice. Concordantly, treatment of AS neurons with an autophagy inhibitor alleviated the reduction in density of dendritic spines. Furthermore, autophagy inhibition in AS mice partially alleviated a social interaction deficit as shown in open field test. Thus, our results identify HAP1 as an in vivo UBE3A target that contributes to deregulated autophagy and synaptic dysfunction in the central nervous system of AS mouse.

Adhesion to pharyngeal epithelium and modulation of immune response: Lactobacillus salivarius AR809, a potential probiotic strain isolated from the human oral cavity

Microbiome modulators such as probiotics are known to modulate oral diseases. Very few probiotics are commercially available for use in the oral cavity. In this context, we selected human-origin Lactobacillus salivarius AR809 as a promising oropharyngeal probiotic and characterized its functional and immunomodulatory properties. Results demonstrated that AR809 could efficiently adhere to pharyngeal epithelial FaDu cells, antagonize Staphylococcus aureus, adapt to the oral environment, and modulate host innate immunity by inducing potentially protective effects. Particularly, AR809 diminished proinflammatory activity by enhancing the production of IL10 and inhibiting the expression of tumor necrosis factor-α, IL1B, inducible nitric oxide synthase, and RELA. Finally, we observed that AR809 grew efficiently when cultured in milk, suggesting that the preparation of a fermented milk product containing AR809 could be a practical way to administer this probiotic to humans. In conclusion, AR809 has high potential to adhere to the pharyngeal mucosa and could be applied in novel milk-based probiotic fermented food products.

XPO1 inhibitor KPT-330 synergizes with Bcl-xL inhibitor to induce cancer cell apoptosis by perturbing rRNA processing and Mcl-1 protein synthesis

XPO1 (exportin1) mediates nuclear export of proteins and RNAs and is frequently overexpressed in cancers. In this study, we show that the orally bioavailable XPO1 inhibitor KPT-330 reduced Mcl-1 protein level, by which it synergized with Bcl-xL inhibitor A-1331852 to induce apoptosis in cancer cells. KPT-330/A-1331852 combination disrupted bindings of Mcl-1 and Bcl-xL to Bax, Bak, and/or Bim, elicited mitochondrial outer membrane permeabilization, and triggered apoptosis. KPT-330 generally mitigated mRNA expression and protein synthesis rather than mRNA nuclear export or protein stability of Mcl-1. KPT-330 inhibited mTORC1/4E-BP1 and Mnk1/eIF4E axes, which disrupted the eIF4F translation initiation complex but was dispensable for Mcl-1 reduction and KPT-330/A-1331852 combination-induced apoptosis. Mature rRNAs are integral components of the ribosome that determines protein synthesis ability. KPT-330 impeded nucleolar rRNA processing and reduced total levels of multiple mature rRNAs. Reconstitution of XPO1 by expressing degradation-resistant C528S mutant retained rRNA amount, Mcl-1 expression, and Bcl-xL inhibitor resistance upon KPT-330 treatment. KPT-330/A-1331852 combination suppressed growth and enhanced apoptosis of non-small cell lung cancer xenografts. Therefore, we clarify the reason of apoptosis resistance of cancer cells to XPO1 inhibition and develop a potential strategy for treating solid tumors.

Molecular and Synaptic Bases of CDKL5 Disorder

The X-linked gene cyclin-dependent kinase-like 5 (CDKL5) encodes a serine/threonine kinase abundantly expressed in the brain. Mutations in CDKL5 have been associated with neurodevelopmental disorders characterized by early-onset epileptic encephalopathy and severe intellectual disability, suggesting that CDKL5 plays important roles in brain development and function. Recent studies using cultured neurons, knockout mice, and human iPSC-derived neurons have demonstrated that CDKL5 regulates axon outgrowth, dendritic morphogenesis, and synapse formation. The role of CDKL5 in maintaining synaptic function in the mature brain has also begun to emerge. Moreover, mouse models that are deficient for CDKL5 recapitulate some of the key clinical phenotypes in human patients. Here we review these findings related to the function of CDKL5 in the brain and discuss the underlying molecular and cellular mechanisms.

Biallelic Mutations in MYORG Cause Autosomal Recessive Primary Familial Brain Calcification

Primary familial brain calcification (PFBC) is a genetically heterogeneous disorder characterized by bilateral calcifications in the basal ganglia and other brain regions. The genetic basis of this disorder remains unknown in a significant portion of familial cases. Here, we reported a recessive causal gene, MYORG, for PFBC. Compound heterozygous or homozygous mutations of MYORG co-segregated completely with PFBC in six families, with logarithm of odds (LOD) score of 4.91 at the zero recombination fraction. In mice, Myorg mRNA was expressed specifically in S100β-positive astrocytes, and knockout of Myorg induced the formation of brain calcification at 9 months of age. Our findings provide strong evidence that loss-of-function mutations of MYORG cause brain calcification in humans and mice.

KPNB1 inhibition disrupts proteostasis and triggers unfolded protein response-mediated apoptosis in glioblastoma cells

The nuclear import receptor karyopherin β1 (KPNB1) is involved in the nuclear import of most proteins and in the regulation of multiple mitotic events. Upregulation of KPNB1 has been observed in cancers including glioblastoma. Depletion of KPNB1 induces mitotic arrest and apoptosis in cancer cells, but the underlying mechanism is not clearly elucidated. Here, we found that downregulation and functional inhibition of KPNB1 in glioblastoma cells induced growth arrest and apoptosis without apparent mitotic arrest. KPNB1 inhibition upregulated Puma and Noxa and freed Mcl-1-sequestered Bax and Bak, leading to mitochondrial outer membrane permeabilization (MOMP) and apoptosis. Moreover, combination of Bcl-xL inhibitors and KPNB1 inhibition enhanced apoptosis in glioblastoma cells. KPNB1 inhibition promoted cytosolic retention of its cargo and impaired cellular proteostasis, resulting in elevated polyubiquitination, formation of aggresome-like-induced structure (ALIS), and unfolded protein response (UPR). Ubiquitination elevation and UPR activation in KPNB1-deficient cells were reversed by KPNB1 overexpression or inhibitors of protein synthesis but aggravated by inhibitors of autophagy-lysosome or proteasome, indicating that rebalance of cytosolic/nuclear protein distribution and alleviation of protein overload favor proteostasis and cell survival. Chronic activation of eIF2α/ATF4 cascade of UPR was responsible for the upregulation of Puma and Noxa, apoptosis and ABT-263 sensitivity. Taken together, our findings demonstrate that KPNB1 is required for proteostasis maintenance and its inhibition induces apoptosis in glioblastoma cells through UPR-mediated deregulation of Bcl-2 family members.

PRRT2 deficiency induces paroxysmal kinesigenic dyskinesia by regulating synaptic transmission in cerebellum

Mutations in the proline-rich transmembrane protein 2 (PRRT2) are associated with paroxysmal kinesigenic dyskinesia (PKD) and several other paroxysmal neurological diseases, but the PRRT2 function and pathogenic mechanisms remain largely obscure. Here we show that PRRT2 is a presynaptic protein that interacts with components of the SNARE complex and downregulates its formation. Loss-of-function mutant mice showed PKD-like phenotypes triggered by generalized seizures, hyperthermia, or optogenetic stimulation of the cerebellum. Mutant mice with specific PRRT2 deletion in cerebellar granule cells (GCs) recapitulate the behavioral phenotypes seen in Prrt2-null mice. Furthermore, recording made in cerebellar slices showed that optogenetic stimulation of GCs results in transient elevation followed by suppression of Purkinje cell firing. The anticonvulsant drug carbamazepine used in PKD treatment also relieved PKD-like behaviors in mutant mice. Together, our findings identify PRRT2 as a novel regulator of the SNARE complex and provide a circuit mechanism underlying the PRRT2-related behaviors.

China Brain Project: Basic Neuroscience, Brain Diseases, and Brain-Inspired Computing

The China Brain Project covers both basic research on neural mechanisms underlying cognition and translational research for the diagnosis and intervention of brain diseases as well as for brain-inspired intelligence technology. We discuss some emerging themes, with emphasis on unique aspects.

One-step generation of complete gene knockout mice and monkeys by CRISPR/Cas9-mediated gene editing with multiple sgRNAs

The CRISPR/Cas9 system is an efficient gene-editing method, but the majority of gene-edited animals showed mosaicism, with editing occurring only in a portion of cells. Here we show that single gene or multiple genes can be completely knocked out in mouse and monkey embryos by zygotic injection of Cas9 mRNA and multiple adjacent single-guide RNAs (spaced 10-200 bp apart) that target only a single key exon of each gene. Phenotypic analysis of F0 mice following targeted deletion of eight genes on the Y chromosome individually demonstrated the robustness of this approach in generating knockout mice. Importantly, this approach delivers complete gene knockout at high efficiencies (100% on Arntl and 91% on Prrt2) in monkey embryos. Finally, we could generate a complete Prrt2 knockout monkey in a single step, demonstrating the usefulness of this approach in rapidly establishing gene-edited monkey models.

ADAM10-Initiated Release of Notch Intracellular Domain Regulates Microtubule Stability and Radial Migration of Cortical Neurons

Proper neuronal migration is orchestrated by combined membrane signal paradigms, whereas the role and mechanism of regulated intramembrane proteolysis (RIP) remain to be illustrated. We show here that the disintegrin and metalloprotease-domain containing protein 10 (ADAM10) regulates cortical neurons migration by initiating the RIP of Notch. We found that Notch intracellular domain (NICD) significantly rescued the migration defect of ADAM10-deficient neurons. Moreover, ADAM10 deficiency led to reduced neuronal motility and disrupted microtubule (MT) structure, which were associated with downregulated expression of acetylated tubulin and MT-associated proteins. Specifically, the NICD/RBPJ complex bound directly to the promoter, and regulated the neuronal expression level of doublecortin (DCX), a modulator of the MT cytoskeleton. Functionally, DCX overexpression largely restored neuron motility and reversed migration defect caused by ADAM10 knockout. Taken together, these findings demonstrate the direct requirement of ADAM10 in cortical radial migration and reveal the underlying mechanism by linking ADAM10-initiated RIP of Notch to the regulation of MT cytoskeleton through transcriptional control of Dcx expression.

Angelman Syndrome Protein Ube3a Regulates Synaptic Growth and Endocytosis by Inhibiting BMP Signaling in Drosophila

Altered expression of the E3 ubiquitin ligase UBE3A, which is involved in protein degradation through the proteasome-mediated pathway, is associated with neurodevelopmental and behavioral defects observed in Angelman syndrome (AS) and autism. However, little is known about the neuronal function of UBE3A and the pathogenesis of UBE3A-associated disorders. To understand the in vivo function of UBE3A in the nervous system, we generated multiple mutations of ube3a, the Drosophila ortholog of UBE3A. We found a significantly increased number of total boutons and satellite boutons in conjunction with compromised endocytosis in the neuromuscular junctions (NMJs) of ube3a mutants compared to the wild type. Genetic and biochemical analysis showed upregulation of bone morphogenetic protein (BMP) signaling in the nervous system of ube3a mutants. An immunochemical study revealed a specific increase in the protein level of Thickveins (Tkv), a type I BMP receptor, but not other BMP receptors Wishful thinking (Wit) and Saxophone (Sax), in ube3a mutants. Ube3a was associated with and specifically ubiquitinated lysine 227 within the cytoplasmic tail of Tkv, and promoted its proteasomal degradation in Schneider 2 cells. Negative regulation of Tkv by Ube3a was conserved in mammalian cells. These results reveal a critical role for Ube3a in regulating NMJ synapse development by repressing BMP signaling. This study sheds new light onto the neuronal functions of UBE3A and provides novel perspectives for understanding the pathogenesis of UBE3A-associated disorders.

Interactions between N-Ethylmaleimide-sensitive factor and GluA2 contribute to effects of glucocorticoid hormones on AMPA receptor function in the rodent hippocampus

Glucocorticoid hormones, via activation of their receptors, promote memory consolidation, but the exact underlying mechanisms remain elusive. We examined how corticosterone regulates AMPA receptor (AMPAR) availability in the synapse, which is important for synaptic plasticity and memory formation. Peptides which specifically block the interaction between N-Ethylmaleimide-Sensitive Factor (NSF) and the AMPAR-subunit GluA2 prevented the increase in synaptic transmission and surface expression of AMPARs known to occur after corticosterone application to hippocampal neurons. Combining a live imaging Fluorescence Recovery After Photobleaching (FRAP) approach with the use of the pH-sensitive GFP-AMPAR tagging revealed that this NSF/GluA2 interaction was also essential for the increase of the mobile fraction and reduction of the diffusion of AMPARs after treating hippocampal neurons with corticosterone. We conclude that the interaction between NSF and GluA2 contributes to the effects of corticosterone on AMPAR function. © 2016 Wiley Periodicals, Inc.

mTOR is essential for corticosteroid effects on hippocampal AMPA receptor function and fear memory

Glucocorticoid hormones, via activation of their receptors, promote memory consolidation, but the exact underlying mechanisms remain elusive. We examined how corticosterone regulates AMPA receptors (AMPARs), which are crucial for synaptic plasticity and memory formation. Combining a live imaging fluorescent recovery after photobleaching approach with the use of the pH-sensitive GFP-AMPAR tagging revealed that corticosterone enhances the AMPAR mobile fraction and increases synaptic trapping of AMPARs in hippocampal cells. In parallel, corticosterone-enhanced AMPAR-mediated synaptic transmission. Blocking the mammalian target of rapamycin (mTOR) pathway prevented the effects of corticosterone on both AMPAR trapping—but not on the mobile fraction—and synaptic transmission. Blocking the mTOR pathway also prevented the memory enhancing effects of corticosterone in a contextual fear-conditioning paradigm. We conclude that activation of the mTOR pathway is essential for the effects of corticosterone on synaptic trapping of AMPARs and, possibly as a consequence, fearful memory formation.

DSTYK kinase domain ablation impaired the mice capabilities of learning and memory in water maze test

DSTYK (Dual serine/threonine and tyrosine protein kinase) is a putative dual Ser/Thr and Tyr protein kinase with unique structural features. It is proposed that DSTYK may play important roles in brain because of its high expression in most brain areas. In the present study, a DSTYK knockout (KO) mouse line with the ablation of C-terminal of DSTYK including the kinase domain was generated to study the physiological function of DSTYK. The DSTYK KO mice are fertile and have no significant morphological defects revealed by Nissl staining compared with wildtype mice. Open field test and rotarod test showed there is no obvious difference in basic motor and balance capacity between the DSTYK homozygous KO mice and DSTYK heterozygous KO mice. In water maze test, however, the DSTYK homozygous KO mice show impaired capabilities of learning and memory compared with the DSTYK heterozygous KO mice.

ZFX knockdown inhibits growth and migration of non-small cell lung carcinoma cell line H1299

ZFX (zinc finger transcription factor, X chromosome-linked) contributes to the maintenance of different types of stem cells and the progression of various cancers. We have previously reported that ZFX knockdown inhibits proliferation of glioma in vitro and in vivo. Since overexpression of ZFX in lung cancer tissue correlates with lymph node metastasis, we hypothesized that ZFX may play a role in lung cancer. In this study, we identified ZFX as a promoter of lung cancer growth and migration in a NSCLC (non-small cell lung carcinoma) cell line H1299. ZFX knockdown caused proliferation inhibition determined by MTT assay and colony formation assay, G0/G1 arrest of cell cycle and slightly increased proportion of apoptotic cells assessed by flow cytometry assay, decreased population of migrating cells showed by wound-healing assay, increased cell senescence evidenced by senescence-associated β-galactosidase staining. ZFX knockdown also led to decreased proportion of tumor bearing mice and reduced mean tumor volume in a subcutaneous tumor model. In addition, western blot showed that ZFX knockdown down regulated a set of proteins involved in proliferation, survival and motility. Altogether, these results suggest that ZFX may be a potential therapeutic target for NSCLC.

PRRT2 c.649dupC mutation derived from de novo in paroxysmal kinesigenic dyskinesia

AIMS

PRRT2 was recently identified as a causative gene for paroxysmal kinesigenic dyskinesia (PKD), and the c.649dupC mutation was shown to be a "high frequency" mutation. This mutation was also identified in many sporadic cases. This might be attributed to the incomplete penetrance of c.649dupC. Alternatively, c.649dupC might derive from de novo. The aim of this study is to elucidate the possibility concerning de novo mutagenesis of PRRT2 mutations in PKD.

METHODS

Nine sporadic Chinese PKD patients including one Mongolian patient were recruited. Direct sequencing of PRRT2 was performed in them and their parents. Haplotype analysis was conducted to confirm the biological relationship.

RESULTS

A novel mutation, c.133_136delCCAG, was identified in one Han patient and his unaffected mother. The c.649dupC mutation was detected in another Han patient and his unaffected father. To our interest, c.649dupC was detected in the Mongolian patient but not in his parents. Haplotype analysis confirmed the biological relationship among the trio. No mutations were identified in the remaining six patients.

CONCLUSION

These findings demonstrate the heterogeneity of PKD, and the de novo mutagenesis of PRRT2 gene might indicate the genetic instability of this region.

Neuron-restrictive silencer factor is not required for the antiepileptic effect of the ketogenic diet

PURPOSE

The ketogenic diet (KD) has been used as an effective antiepileptic treatment for nearly a century. Inhibition of glycolysis and increased levels of ketone bodies are both known to contribute to the antiepileptic effects of the KD. Neuron-restrictive silencer factor (NRSF), also known as RE-1 silencing transcription factor (REST), is implicated in the antiepileptic effects of the glycolytic inhibitor 2-deoxy-d-glucose (2DG). Glycolytic inhibition is a common feature of the KD and 2DG treatment, leading to the hypothesis that NRSF might also be involved in the antiepileptic effect of the KD. To test this hypothesis, the present study was designed to investigate the role of NRSF in the antiepileptic effect of 2DG, the KD, and acetone in vivo.

METHODS

Kindling was used as a model to test the antiepileptic effects of 2DG, the KD, and acetone on control and NRSF conditional knockout mice (NRSF-cKO; from the intercross of CamKIIα-iCre and NRSF exon 2 floxed mice). After recovery from electrode implantation, adult mice were stimulated twice a day at afterdischarge threshold (ADT) current intensity. In the 2DG- (500 mg/kg) and acetone- (10 mmol/kg) treated groups, drugs were injected intraperitoneally 20 min before each stimulus. In the 2DG group, mice were pretreated with intraperitoneal injections for 3 days in addition to the injections administered before the regular kindling stimulation. In the KD group, mice were fed the KD instead of a control diet until the end of stimulations.

KEY FINDINGS

Compared with control mice, the antiepileptic effect of 2DG was abolished in NRSF-cKO mice, indicating that NRSF is required for the antiepileptic effect of 2DG. In the KD-fed group, kindling development was retarded in both control and NRSF-cKO mice. In the acetone-treated group, inhibition of kindling-induced epileptogenesis was observed in both control and NRSF-cKO mice, similar to the action of the KD.

SIGNIFICANCE

These findings imply that NRSF repression complex is not essential for the antiepileptic effect of the ketogenic diet.

Serum inducible kinase is a positive regulator of cortical dendrite development and is required for BDNF-promoted dendritic arborization

Serum inducible kinase (SNK), also known as polo-like kinase 2 (PLK2), is a known regulator of mitosis, synaptogenesis and synaptic homeostasis. However, its role in early cortical development is unknown. Herein, we show that snk is expressed in the cortical plate from embryonic day 14, but not in the ventricular/subventricular zones (VZ/SVZ), and SNK protein localizes to the soma and dendrites of cultured immature cortical neurons. Loss of SNK impaired dendritic but not axonal arborization in a dose-dependent manner and overexpression had opposite effects, both in vitro and in vivo. Overexpression of SNK also caused abnormal branching of the leading process of migrating cortical neurons in electroporated cortices. The kinase activity was necessary for these effects. Extracellular signal-regulated kinase (ERK) pathway activity downstream of brain-derived neurotrophic factor (BDNF) stimulation led to increases in SNK protein expression via transcriptional regulation, and this upregulation was necessary for the growth-promoting effect of BDNF on dendritic arborization. Taken together, our results indicate that SNK is essential for dendrite morphogenesis in cortical neurons.

Conditional deletion of NRSF in forebrain neurons accelerates epileptogenesis in the kindling model

Neuron-restrictive silencer factor (NRSF), also known as repressor element-1 silencing transcription factor, is a transcriptional repressor that plays important roles in embryonic development and neurogenesis. Recent findings show that NRSF is upregulated after seizures activity however, the link between NRSF and epileptogenesis remains poorly understood. To investigate the role of NRSF in epilepsy, we employed a Cre-loxp system to specifically delete NRSF in excitatory neurons of the postnatal mouse forebrain. In the kindling model of epileptogenesis, conditional NRSF knockout (NRSF-cKO) mice exhibited dramatically accelerated seizure progression and prolonged afterdischarge duration compared with control mice. Moreover, seizures activity-induced mossy fiber sprouting was enhanced in the NRSF-cKO mice. The degree of upregulation of Fibroblast growth factor 14 and Brain-derived neurotrophic factor (BDNF) following kainic acid-induced status epilepticus was significantly increased in the cortex of NRSF-cKO mice compared with control mice. Furthermore, the derepression of BDNF was associated by activation of PLCγ and PI(3)K signaling pathways. These findings indicate that NRSF functions as an intrinsic repressor of limbic epileptogenesis.

Pulse labeling and long-term tracing of newborn neurons in the adult subgranular zone

Research over the past decades has demonstrated that adult brain produces neural progenitor cells which proliferate and differentiate to newborn neurons that integrate into the existing circuit. However, detailed differentiation processes and underlying mechanisms of newly generated neurons are largely unknown due to the limitation of available methods for labeling and manipulating neural progenitor cells and newborn neurons. In this study, we designed a tightly controlled, noninvasive system based on Cre/loxP recombination to achieve long-term tracing and genetic manipulation of adult neurons in vivo. In this system, tamoxifen-inducible recombinase, CreER(T2), was driven by BAC-based promoter of doublecortin (DCX, a marker of newborn neurons). By crossing this Cre line with reporter mouse, we found that newborn neurons in the dentate gyrus (DG) could be selectively pulse-labeled by tamoxifen-induced expression of yellow fluorescent protein (YFP). YFP-positive neurons were identified by coimmunostaining with cell type-specific markers and characterized by electrophysiological recording. Furthermore, analysis of the migration of these neurons showed that the majority of these labeled neurons migrated to the inner part of granule cell layer. Moreover, spine growth of inner molecular layer of newborn granule neurons takes a dynamic pattern of invert U-shape, in contrast to the wedge-shaped change in the outer molecular layer. Our transgenic tool provides an efficient way to selectively label and manipulate newborn neuron in adult mouse DG.

A-type GABA receptor as a central target of TRPM8 agonist menthol

Menthol is a widely-used cooling and flavoring agent derived from mint leaves. In the peripheral nervous system, menthol regulates sensory transduction by activating TRPM8 channels residing specifically in primary sensory neurons. Although behavioral studies have implicated menthol actions in the brain, no direct central target of menthol has been identified. Here we show that menthol reduces the excitation of rat hippocampal neurons in culture and suppresses the epileptic activity induced by pentylenetetrazole injection and electrical kindling in vivo. We found menthol not only enhanced the currents induced by low concentrations of GABA but also directly activated GABA_A receptor (GABA_AR) in hippocampal neurons in culture. Furthermore, in the CA1 region of rat hippocampal slices, menthol enhanced tonic GABAergic inhibition although phasic GABAergic inhibition was unaffected. Finally, the structure-effect relationship of menthol indicated that hydroxyl plays a critical role in menthol enhancement of tonic GABA_AR. Our results thus reveal a novel cellular mechanism that may underlie the ambivalent perception and psychophysical effects of menthol and underscore the importance of tonic inhibition by GABA_ARs in regulating neuronal activity.

Limbic epileptogenesis in a mouse model of fragile X syndrome

Fragile X syndrome (FXS), caused by silencing of the Fmr1 gene, is the most common form of inherited mental retardation. Epilepsy is reported to occur in 20-25% of individuals with FXS. However, no overall increased excitability has been reported in Fmr1 knockout (KO) mice, except for increased sensitivity to auditory stimulation. Here, we report that kindling increased the expressions of Fmr1 mRNA and protein in the forebrain of wild-type (WT) mice. Kindling development was dramatically accelerated in Fmr1 KO mice, and Fmr1 KO mice also displayed prolonged electrographic seizures during kindling and more severe mossy fiber sprouting after kindling. The accelerated rate of kindling was partially repressed by inhibiting N-methyl-D-aspartic acid receptor (NMDAR) with MK-801 or mGluR5 receptor with 2-methyl-6-(phenylethynyl)-pyridine (MPEP). The rate of kindling development in WT was not effected by MPEP, however, suggesting that FMRP normally suppresses epileptogenic signaling downstream of metabolic glutamate receptors. Our findings reveal that FMRP plays a critical role in suppressing limbic epileptogenesis and predict that the enhanced susceptibility of patients with FXS to epilepsy is a direct consequence of the loss of an important homeostatic factor that mitigates vulnerability to excessive neuronal excitation.

Differential roles of NMDA receptor subtypes in ischemic neuronal cell death and ischemic tolerance

BACKGROUND AND PURPOSE

Activation of NMDA subtypes of glutamate receptors is implicated in cell damage induced by ischemia as well as for the establishment of ischemic tolerance after ischemic preconditioning in animal models. We investigated the contributions of NR2A- and NR2B-containing NMDA receptors to ischemic cell death and ischemic tolerance in a rat model of transient global ischemia.

METHODS

Transient global ischemia was produced in rats by 4-vessel occlusion. Neuronal injury was analyzed by Fluoro-Jade B and Nissl staining. Phosphorylation of CREB was detected by Western blotting and immunohistochemistry. In situ hybridization and reverse transcriptase-polymerase chain reaction were used to evaluate the mRNA level of cpg15 and bdnf.

RESULTS

NR2A subtype-specific antagonist NVP-AAM077 enhanced neuronal death after transient global ischemia and abolished the induction of ischemic tolerance. In contrast, NR2B subtype-specific antagonist ifenprodil attenuated ischemic cell death and enhanced preconditioning-induced neuroprotection. Furthermore, selectively blocking NR2A-, but not NR2B-, containing NMDA receptors inhibited ischemia-induced phosphorylation of CREB and the subsequent upregulation of CREB target genes such as cpg15 and bdnf.

CONCLUSIONS

We found that NR2A- and NR2B-containing NMDA receptor subtypes play differential roles in ischemic neuronal death and ischemic tolerance, suggesting attractive new strategies for the development of drugs for patients with stroke.

Brain-derived neurotrophic factor-tropomyosin-related kinase B signaling contributes to activity-dependent changes in synaptic proteins

The ability of synapses to undergo changes in structure and function in response to alterations of neuronal activity is an essential property of neural circuits. One way that this is achieved is through global changes in the molecular composition of the synapse; however, it is not clear how these changes are coupled to the dynamics of neuronal activity. Here we found that, in cultured rat cortical neurons, bidirectional changes of neuronal activity led to corresponding alterations in the expression of brain-derived neurotrophic factor (BDNF) and phosphorylation of its receptor tropomyosin-related kinase B (TrkB), as well as in the level of synaptic proteins. Exogenous BDNF reversed changes in synaptic proteins induced by chronic activity blockade, while inhibiting Trk kinase activity or depleting endogenous BDNF abolished the concentration changes induced by chronic activity elevation. Both tetrodotoxin and bicuculline had significant, but opposite, effects on synaptic protein ubiquitination in a time-dependent manner. Furthermore, exogenous BDNF was sufficient to increase ubiquitination of synaptic proteins, whereas scavenging endogenous BDNF or inhibiting Trk kinase activity prevented the ubiquitination of synaptic proteins induced by chronic elevation of neuronal activity. Inhibiting the proteasome or blocking protein polyubiquitination mimicked the effect of tetrodotoxin on the levels of synaptic proteins and canceled the effects of BDNF. Our study indicates that BDNF-TrkB signaling acts upstream of the ubiquitin proteasome system, linking neuronal activity to protein turnover at the synapse.

Zinc-mediated transactivation of TrkB potentiates the hippocampal mossy fiber-CA3 pyramid synapse

The receptor tyrosine kinase, TrkB, is critical to diverse functions of the mammalian nervous system in health and disease. Evidence of TrkB activation during epileptogenesis in vivo despite genetic deletion of its prototypic neurotrophin ligands led us to hypothesize that a non-neurotrophin, the divalent cation zinc, can transactivate TrkB. We found that zinc activates TrkB through increasing Src family kinase activity by an activity-regulated mechanism independent of neurotrophins. One subcellular locale at which zinc activates TrkB is the postsynaptic density of excitatory synapses. Exogenous zinc potentiates the efficacy of the hippocampal mossy fiber (mf)-CA3 pyramid synapse by a TrkB-requiring mechanism. Long-term potentiation of this synapse is impaired by deletion of TrkB, inhibition of TrkB kinase activity, and by CaEDTA, a selective chelator of zinc. The activity-dependent activation of synaptic TrkB in a neurotrophin-independent manner provides a mechanism by which this receptor can regulate synaptic plasticity.

Clathrin-dependent endocytosis is required for TrkB-dependent Akt-mediated neuronal protection and dendritic growth

Endocytosis of Trk (tropomyosin-related kinase) receptors is critical for neurotrophin signal transduction and biological functions. However, the mechanism governing endocytosis of TrkB (tropomyosin-related kinase B) and the specific contributions of TrkB endocytosis to downstream signaling are unknown. In this study, we report that blocking clathrin, dynamin, or AP2 in cultured neurons of the central nervous system inhibited brain-derived neurotrophic factor (BDNF)-induced activation of Akt but not ERK. Treating neurons with the clathrin inhibitor monodansylcadaverine or a peptide that blocks dynamin function specifically abrogated Akt pathway activation in response to BDNF but did not affect the response of other downstream effectors or the up-regulation of immediate early genes neuropeptide Y and activity-regulated cytoskeleton-associated protein. Similar effects were found in neurons expressing small interfering RNA to silence AP2 or a dominant negative form of dynamin that inhibits clathrin-mediated endocytosis. In PC12 cells, ERK but not Akt activation required TrkA endocytosis following stimulation with nerve growth factor, whereas the opposite was true when TrkA-expressing neurons were stimulated with nerve growth factor in the central nervous system. Thus, the specific effects of internalized Trk receptors probably depend on the presence of cell type-specific modulators of neurotrophin signaling and not on differences inherent to Trk receptors themselves. Endocytosis-dependent activation of Akt in neurons was found to be critical for BDNF-supported survival and dendrite outgrowth. Together, these results demonstrate the functional requirement of clathrin- and dynamin-dependent endocytosis in generating the full intracellular response of neurons to BDNF in the central nervous system.

Transducer of regulated CREB and late phase long-term synaptic potentiation

In the central nervous system, long-term adaptive responses to changes in the environment, such as the processes involved in learning and memory, require the conversion of extracellular stimuli into intracellular signals. Many of these signals involve the induction of gene expression. The late, transcription- and translation-dependent phase of long-term synaptic potentiation (L-LTP) is an attractive cellular model for long-lasting memory formation. The transcription factor cAMP response element-binding protein (CREB) plays an essential role in the maintenance of L-LTP. However, how synaptic signals propagate to the nucleus to initiate CREB-target gene expression is unclear. Recent studies indicate that the CREB transducer of regulated CREB activity 1 coactivator undergoes neuronal activity-dependent translocation from the cytoplasm to the nucleus, a process required for CRE-dependent gene expression and the maintenance of L-LTP in the hippocampus.

Differential roles of NR2A- and NR2B-containing NMDA receptors in activity-dependent brain-derived neurotrophic factor gene regulation and limbic epileptogenesis

Fleeting activation of NMDA receptors (NMDARs) induces long-term modification of synaptic connections and refinement of neuronal circuits, which may underlie learning and memory and contribute to pathogenesis of a diversity of neurological diseases, including epilepsy. Here, we found that NR2A and NR2B subunit-containing NMDARs were coupled to distinct intracellular signaling, resulting in differential BDNF expression and extracellular signal-regulated kinase 1/2 (ERK1/2) activation. Selective activation of NR2A-containing NMDARs increased BDNF gene expression. Activation of NR2B-containing NMDARs led to ERK1/2 phosphorylation. Furthermore, selectively blocking NR2A-containing NMDARs impaired epileptogenesis and the development of mossy fiber sprouting in the kindling and pilocarpine rat models of limbic epilepsy, whereas inhibiting NR2B-containing NMDARs had no effects in epileptogenesis and mossy fiber sprouting. Interestingly, blocking either NR2A- or NR2B-containing NMDARs decreased status epilepticus-induced neuronal cell death. The specific requirement of NR2A and its downstream signaling for epileptogenesis implicates attractive new targets for the development of drugs that prevent epilepsy in patients with brain injury.

Requirement of TORC1 for late-phase long-term potentiation in the hippocampus

Late-phase long-term potentiation (L-LTP) and long-term memory depend on the transcription of mRNA of CRE-driven genes and synthesis of proteins. However, how synaptic signals propagate to the nucleus is unclear. Here we report that the CREB coactivator TORC1 (transducer of regulated CREB activity 1) undergoes neuronal activity-induced translocation from the cytoplasm to the nucleus, a process required for CRE-dependent gene expression and L-LTP. Overexpressing a dominant-negative form of TORC1 or down-regulating TORC1 expression prevented activity-dependent transcription of CREB target genes in cultured hippocampal neurons, while overexpressing a wild-type form of TORC1 facilitated basal and activity-induced transcription of CREB target genes. Furthermore, overexpressing the dominant-negative form of TORC1 suppressed the maintenance of L-LTP without affecting early-phase LTP, while overexpressing the wild-type form of TORC1 facilitated the induction of L-LTP in hippocampal slices. Our results indicate that TORC1 is essential for CRE-driven gene expression and maintenance of long-term synaptic potentiation.

The timing of endocytosis after activation of a G-protein-coupled receptor in a sensory neuron

Endocytosis is a fundamental cellular event in membrane retrieval after exocytosis and in the regulation of receptor-mediated signal transduction. In contrast to the well-studied depolarization-induced membrane recycling, little is known about the kinetics of ligand-induced endocytosis of G-protein-coupled receptors in neurons. Here we investigated the kinetics of ligand-receptor binding-induced endocytosis in rat sensory neurons using a membrane capacitance assay. The time constant of ADP-induced endocytosis of P2Y-receptors was determined as 1.7 s. The ADP-induced endocytosis was blocked by antagonists against P2Y, phosphorylation, and clathrin. However, block of dynamin was without effect. The ADP-induced endocytosis was confirmed independently by a single vesicle image technique using a styryl FM2-10. Finally, the receptors were internalized in response to ADP, as determined by GFP-labeled P2Y. We conclude that ligand-receptor binding leads to rapid endocytosis in the cytoplasm of rat dorsal root ganglion neurons.

Formation of complement membrane attack complex in mammalian cerebral cortex evokes seizures and neurodegeneration

The complement system consists of >30 proteins that interact in a carefully regulated manner to destroy invading bacteria and prevent the deposition of immune complexes in normal tissue. This complex system can be activated by diverse mechanisms proceeding through distinct pathways, yet all converge on a final common pathway in which five proteins assemble into a multimolecular complex, the membrane attack complex (MAC). The MAC inserts into cell membranes to form a functional pore, resulting in ion flux and ultimately osmotic lysis. Immunohistochemical evidence of the MAC decorating neurons in cortical gray matter has been identified in multiple CNS diseases, yet the deleterious consequences, if any, of MAC deposition in the cortex of mammalian brain in vivo are unknown. Here we demonstrate that the sequential infusion of individual proteins of the membrane attack pathway (C5b6, C7, C8, and C9) into the hippocampus of awake, freely moving rats induced both behavioral and electrographic seizures as well as cytotoxicity. The onset of seizures occurred during or shortly after the infusion of C8/C9. Neither seizures nor cytotoxicity resulted from the simultaneous infusion of all five proteins premixed in vitro. The requirement for the sequential infusion of all five proteins together with the temporal relationship of seizure onset to infusions of C8/C9 implies that the MAC was formed in vivo and triggered both seizures and cytotoxicity. Deposition of the complement MAC in cortical gray matter may contribute to epileptic seizures and cell death in diverse diseases of the human brain.

Fas(t) balls and Lou Gehrig disease. A clue to selective vulnerability of motor neurons?

The molecular basis of the selective death of motor neurons in amyotrophic lateral sclerosis (ALS) has been an enigma since its description by Charcot in 1869. In this issue of Neuron, demonstrate a motor neuron-specific death pathway which involves Fas and NO. Remarkably, motor neurons from mice carrying ALS-linked mutant forms of superoxide dismutase 1 (SOD1) exhibit an increased sensitivity to death triggered by Fas but not other insults. These data suggest new insights into the mechanisms of, and potential therapeutic strategies for, death of motor neurons in ALS.