Disease-associated polyalanine expansion mutations impair UBA6-dependent ubiquitination.

Expansion mutations in polyalanine stretches are associated with a growing number of diseases sharing a high degree of genotypic and phenotypic commonality. These similarities prompted us to query the normal function of physiological polyalanine stretches and to investigate whether a common molecular mechanism is involved in these diseases. Here, we show that UBA6, an E1 ubiquitin-activating enzyme, recognizes a polyalanine stretch within its cognate E2 ubiquitin-conjugating enzyme USE1. Aberrations in this polyalanine stretch reduce ubiquitin transfer to USE1 and, subsequently, polyubiquitination and degradation of its target, the ubiquitin ligase E6AP. Furthermore, we identify competition for the UBA6-USE1 interaction by various proteins with polyalanine expansion mutations in the disease state. The deleterious interactions of expanded polyalanine tract proteins with UBA6 in mouse primary neurons alter the levels and ubiquitination-dependent degradation of E6AP, which in turn affects the levels of the synaptic protein Arc. These effects are also observed in induced pluripotent stem cell-derived autonomic neurons from patients with polyalanine expansion mutations, where UBA6 overexpression increases neuronal resilience to cell death. Our results suggest a shared mechanism for such mutations that may contribute to the congenital malformations seen in polyalanine tract diseases.

Kinase Inhibitors with Antiepileptic Properties Identified with a Novel in Vitro Screening Platform.

Kinase signaling plays an important role in acquired epilepsy, but only a small percentage of the total kinome has been investigated in this context. A major roadblock that prevents the systematic investigation of the contributions of kinase signaling networks is the slow speed of experiments designed to test the chronic effects of target inhibition in epilepsy models. We developed a novel in vitro screening platform based on microwire recordings from an organotypic hippocampal culture model of acquired epilepsy. This platform enables the direct, parallel determination of the effects of compounds on spontaneous epileptiform activity. The platform also enables repeated recordings from the same culture over two-week long experiments. We screened 45 kinase inhibitors and quantified their effects on seizure duration, the frequency of paroxysmal activity, and electrographic load. We identified several inhibitors with previously unknown antiepileptic properties. We also used kinase inhibition profile cross-referencing to identify kinases that are inhibited by seizure-suppressing compounds, but not by compounds that had no effect on seizures.

Evolution of Network Synchronization during Early Epileptogenesis Parallels Synaptic Circuit Alterations.

In secondary epilepsy, a seizure-prone neural network evolves during the latent period between brain injury and the onset of spontaneous seizures. The nature of the evolution is largely unknown, and even its completeness at the onset of seizures has recently been challenged by measures of gradually decreasing intervals between subsequent seizures. Sequential calcium imaging of neuronal activity, in the pyramidal cell layer of mouse hippocampal in vitro preparations, during early post-traumatic epileptogenesis demonstrated rapid increases in the fraction of neurons that participate in interictal activity. This was followed by more gradual increases in the rate at which individual neurons join each developing seizure, the pairwise correlation of neuronal activities as a function of the distance separating the pair, and network-wide measures of functional connectivity. These data support the continued evolution of synaptic connectivity in epileptic networks beyond the latent period: early seizures occur when recurrent excitatory pathways are largely polysynaptic, while ongoing synaptic remodeling after the onset of epilepsy enhances intranetwork connectivity as well as the onset and spread of seizure activity.

Perfused drop microfluidic device for brain slice culture-based drug discovery.

Living slices of brain tissue are widely used to model brain processes in vitro. In addition to basic neurophysiology studies, brain slices are also extensively used for pharmacology, toxicology, and drug discovery research. In these experiments, high parallelism and throughput are critical. Capability to conduct long-term electrical recording experiments may also be necessary to address disease processes that require protein synthesis and neural circuit rewiring. We developed a novel perfused drop microfluidic device for use with long term cultures of brain slices (organotypic cultures). Slices of hippocampus were placed into wells cut in polydimethylsiloxane (PDMS) film. Fluid level in the wells was hydrostatically controlled such that a drop was formed around each slice. The drops were continuously perfused with culture medium through microchannels. We found that viable organotypic hippocampal slice cultures could be maintained for at least 9 days in vitro. PDMS microfluidic network could be readily integrated with substrate-printed microelectrodes for parallel electrical recordings of multiple perfused organotypic cultures on a single MEA chip. We expect that this highly scalable perfused drop microfluidic device will facilitate high-throughput drug discovery and toxicology.

Multi-electrode array capable of supporting precisely patterned hippocampal neuronal networks.

Accurate positioning of primary mouse hippocampal neurons on electrodes enables the recording from and stimulation of specified individual neurons on a multi-electrode array (MEA). In this work, positive dielectrophoresis (DEP) is applied to actively recruit hippocampal neurons to the electrodes of a MEA, whereas microstructures such as chambers and trenches are created to effectively define a patterned neuronal network. We present here the effective pretreatment methods, to improve cytocompatibility of cured thin SU-8 epoxy, commonly used in the fabrication of MEAs. The functionality of our novel MEA is proven by the successful recording of spontaneous and stimulated neuronal potentials from primary hippocampal neurons, including the propagation of evoked neuronal bursts between electrodes.

PI3K-Akt signaling activates mTOR-mediated epileptogenesis in organotypic hippocampal culture model of post-traumatic epilepsy.

mTOR is activated in epilepsy, but the mechanisms of mTOR activation in post-traumatic epileptogenesis are unknown. It is also not clear whether mTOR inhibition has an anti-epileptogenic, or merely anticonvulsive effect. The rat hippocampal organotypic culture model of post-traumatic epilepsy was used to study the effects of long-term (four weeks) inhibition of signaling pathways that interact with mTOR. Ictal activity was quantified by measurement of lactate production and electrical recordings, and cell death was quantified with lactate dehydrogenase (LDH) release measurements and Nissl-stained neuron counts. Lactate and LDH measurements were well correlated with electrographic activity and neuron counts, respectively. Inhibition of PI3K and Akt prevented activation of mTOR, and was as effective as inhibition of mTOR in reducing ictal activity and cell death. A dual inhibitor of PI3K and mTOR, NVP-BEZ235, was also effective. Inhibition of mTOR with rapamycin reduced axon sprouting. Late start of rapamycin treatment was effective in reducing epileptic activity and cell death, while early termination of rapamycin treatment did not result in increased epileptic activity or cell death. The conclusions of the study are as follows: (1) the organotypic hippocampal culture model of post-traumatic epilepsy comprises a rapid assay of anti-epileptogenic and neuroprotective activities and, in this model (2) mTOR activation depends on PI3K-Akt signaling, and (3) transient inhibition of mTOR has sustained effects on epilepsy.

Device for detection of activity-dependent changes in neural spheroids at MHz and GHz frequencies.

Intracellular processes triggered by neural activity include changes in ionic concentrations, protein release, and synaptic vesicle cycling. These processes play significant roles in neurological disorders. The beneficial effects of brain stimulation may also be mediated through intracellular changes. There is a lack of label-free techniques for monitoring activity-dependent intracellular changes. Electromagnetic (EM) waves at frequencies larger than 1 × 106 Hz (1 MHz) were previously used to probe intracellular contents of cells, as cell membrane becomes "invisible" at this frequency range. EM waves interact with membranes of intracellular organelles, proteins, and water in the MHz - GHz range. In this work, we developed a device for probing the interaction between active neurons' intracellular contents and EM waves. The device used an array of grounded coplanar waveguides (GCPWs) to deliver EM waves to a three-dimensional (3D) spheroid of rat cortical neurons. Neural activity was evoked using optogenetics, with synchronous detection of propagation of EM waves. Broadband measurements were conducted in the MHz-GHz range to track changes in transmission coefficients. Neuronal activity was found to reversibly alter EM wave transmission. Pharmacological suppression of neuronal activity abolished changes in transmission. Time constants of changes in transmission were in the seconds - tens of seconds range, suggesting the presence of relatively slow, activity-dependent intracellular processes. This study provides the first evidence that EM transmission through neuronal tissue is activity-dependent in MHz - GHz range. Device developed in this work may find future applications in studies of the mechanisms of neurological disorders and the development of new therapies.

3D models of glioblastoma interaction with cortical cells.

Introduction: Glioblastoma (GBM) invasiveness and ability to infiltrate deep into the brain tissue is a major reason for the poor patient prognosis for this type of brain cancer. Behavior of glioblastoma cells, including their motility, and expression of invasion-promoting genes such as matrix metalloprotease-2 (MMP2), are strongly influenced by normal cells found in the brain parenchyma. Cells such as neurons may also be influenced by the tumor, as many glioblastoma patients develop epilepsy. In vitro models of glioblastoma invasiveness are used to supplement animal models in a search for better treatments, and need to combine capability for high-throughput experiments with capturing bidirectional interactions between GBM and brain cells. Methods: In this work, two 3D in vitro models of GBM-cortical interactions were investigated. A matrix-free model was created by co-culturing GBM and cortical spheroids, and a matrix-based model was created by embedding cortical cells and a GBM spheroid in Matrigel. Results: Rapid GBM invasion occurred in the matrix-based model, and was enhanced by the presence of cortical cells. Little invasion occurred in the matrix-free model. In both types of models, presence of GBM cells resulted in a significant increase in paroxysmal neuronal activity. Discussion: Matrix-based model may be better suited for studying GBM invasion in an environment that includes cortical cells, while matrix-free model may be useful in investigation of tumor-associated epilepsy.

Acoustofluidic Engineering of Functional Vessel-on-a-Chip.

Construction of in vitro vascular models is of great significance to various biomedical research, such as pharmacokinetics and hemodynamics, and thus is an important direction in the tissue engineering field. In this work, a standing surface acoustic wave field was constructed to spatially arrange suspended endothelial cells into a designated acoustofluidic pattern. The cell patterning was maintained after the acoustic field was withdrawn within the solidified hydrogel. Then, interstitial flow was provided to activate vessel tube formation. In this way, a functional vessel network with specific vessel geometry was engineered on-chip. Vascular function, including perfusability and vascular barrier function, was characterized by microbead loading and dextran diffusion, respectively. A computational atomistic simulation model was proposed to illustrate how solutes cross the vascular membrane lipid bilayer. The reported acoustofluidic methodology is capable of facile and reproducible fabrication of the functional vessel network with specific geometry and high resolution. It is promising to facilitate the development of both fundamental research and regenerative therapy.

Acoustofluidic Engineering Functional Vessel-on-a-Chip.

Construction of in vitro vascular models is of great significance to various biomedical research, such as pharmacokinetics and hemodynamics, thus is an important direction in tissue engineering. In this work, a standing surface acoustic wave field was constructed to spatially arrange suspended endothelial cells into a designated patterning. The cell patterning was maintained after the acoustic field was withdrawn by the solidified hydrogel. Then, interstitial flow was provided to activate vessel tube formation. Thus, a functional vessel-on-a-chip was engineered with specific vessel geometry. Vascular function, including perfusability and vascular barrier function, was characterized by beads loading and dextran diffusion, respectively. A computational atomistic simulation model was proposed to illustrate how solutes cross vascular lipid bilayer. The reported acoustofluidic methodology is capable of facile and reproducible fabrication of functional vessel network with specific geometry. It is promising to facilitate the development of both fundamental research and regenerative therapy.

Oculopharyngeal muscular dystrophy mutations link the RNA-binding protein HNRNPQ to autophagosome biogenesis.

Autophagy is an intracellular degradative process with an important role in cellular homeostasis. Here, we show that the RNA binding protein (RBP), heterogeneous nuclear ribonucleoprotein Q (HNRNPQ)/SYNCRIP is required to stimulate early events in autophagosome biogenesis, in particular the induction of VPS34 kinase by ULK1-mediated beclin 1 phosphorylation. The RBPs HNRNPQ and poly(A) binding protein nuclear 1 (PABPN1) form a regulatory network that controls the turnover of distinct autophagy-related (ATG) proteins. We also show that oculopharyngeal muscular dystrophy (OPMD) mutations engender a switch from autophagosome stimulation to autophagosome inhibition by impairing PABPN1 and HNRNPQ control of the level of ULK1. The overexpression of HNRNPQ in OPMD patient-derived cells rescues the defective autophagy in these cells. Our data reveal a regulatory mechanism of autophagy induction that is compromised by PABPN1 disease mutations, and may thus further contribute to their deleterious effects.

Brain-Targeted Liposomes Loaded with Monoclonal Antibodies Reduce Alpha-Synuclein Aggregation and Improve Behavioral Symptoms in Parkinson's Disease.

Monoclonal antibodies (mAbs) hold promise in treating Parkinson's disease (PD), although poor delivery to the brain hinders their therapeutic application. In the current study, it is demonstrated that brain-targeted liposomes (BTL) enhance the delivery of mAbs across the blood-brain-barrier (BBB) and into neurons, thereby allowing the intracellular and extracellular treatment of the PD brain. BTL are decorated with transferrin to improve brain targeting through overexpressed transferrin-receptors on the BBB during PD. BTL are loaded with SynO4, a mAb that inhibits alpha-synuclein (AS) aggregation, a pathological hallmark of PD. It is shown that 100-nm BTL cross human BBB models intact and are taken up by primary neurons. Within neurons, SynO4 is released from the nanoparticles and bound to its target, thereby reducing AS aggregation, and enhancing neuronal viability. In vivo, intravenous BTL administration results in a sevenfold increase in mAbs in brain cells, decreasing AS aggregation and neuroinflammation. Treatment with BTL also improve behavioral motor function and learning ability in mice, with a favorable safety profile. Accordingly, targeted nanotechnologies offer a valuable platform for drug delivery to treat brain neurodegeneration.

Compartmentalization of the GABAB receptor signaling complex is required for presynaptic inhibition at hippocampal synapses.

Presynaptic inhibition via G-protein-coupled receptors (GPCRs) and voltage-gated Ca(2+) channels constitutes a widespread regulatory mechanism of synaptic strength. Yet, the mechanism of intermolecular coupling underlying GPCR-mediated signaling at central synapses remains unresolved. Using FRET spectroscopy, we provide evidence for formation of spatially restricted (<100 Å) complexes between GABA(B) receptors composed of GB(1a)/GB(2) subunits, Gα(o)ß(1)γ(2) G-protein heterotrimer, and Ca(V)2.2 channels in hippocampal boutons. GABA release was not required for the assembly but for structural reorganization of the precoupled complex. Unexpectedly, GB(1a) deletion disrupted intermolecular associations within the complex. The GB(1a) proximal C-terminal domain was essential for association of the receptor, Ca(V)2.2 and Gßγ, but was dispensable for agonist-induced receptor activation and cAMP inhibition. Functionally, boutons lacking this complex-formation domain displayed impaired presynaptic inhibition of Ca(2+) transients and synaptic vesicle release. Thus, compartmentalization of the GABA(B1a) receptor, Gßγ, and Ca(V)2.2 channel in a signaling complex is required for presynaptic inhibition at hippocampal synapses.

Interictal spikes, seizures and ictal cell death are not necessary for post-traumatic epileptogenesis in vitro.

Clinical studies indicate that phenytoin prevents acute post-traumatic seizures but not subsequent post-traumatic epilepsy. We explored this phenomenon using organotypic hippocampal slice cultures as a model of severe traumatic brain injury. Hippocampal slices were cultured for up to eight weeks, during which acute and chronic electrical recordings revealed a characteristic evolution of spontaneous epileptiform discharges, including interictal spikes, seizure activity and electrical status epilepticus. Cell death exhibited an early peak immediately following slicing, and a later secondary peak that coincided with the peak of seizure-like activity. The secondary peak in neuronal death was abolished by either blockade of glutamatergic transmission with kynurenic acid or by elimination of ictal activity and status epilepticus with phenytoin. Withdrawal of kynurenic acid or phenytoin was followed by a sharp increase in spontaneous seizure activity. Phenytoin's anticonvulsant and neuroprotective effects failed after four weeks of continuous administration. These data support the clinical findings that after brain injury, anticonvulsants prevent seizures but not epilepsy or the development of anticonvulsant resistance. We extend the clinical data by showing that secondary neuronal death is correlated with ictal but not interictal activity, and that blocking all three of these sequelae of brain injury does not prevent epileptogenesis in this in vitro model.

A prenylated p47phox-p67phox-Rac1 chimera is a Quintessential NADPH oxidase activator: membrane association and functional capacity.

The superoxide-generating NADPH oxidase complex of resting phagocytes includes cytochrome b(559), a membrane-associated heterodimer composed of two subunits (Nox2 and p22(phox)), and four cytosolic proteins (p47(phox), p67(phox), Rac, and p40(phox)). Upon stimulation, the cytosolic components translocate to the membrane, as the result of a series of interactions among the cytosolic components and among the cytosolic components and cytochrome b(559) and its phospholipid environment. We described the construction of a tripartite chimera (trimera) consisting of strategic domains of p47(phox), p67(phox), and Rac1, in which interactions among cytosolic components were replaced by fusion (Berdichevsky, Y., Mizrahi, A., Ugolev, Y., Molshanski-Mor, S., and Pick, E. (2007) J. Biol. Chem. 282, 22122-22139). We now fused green fluorescent protein (GFP) to the N terminus of the trimera and found the following. 1) The GFP-p47(phox)-p67(phox)-Rac1 trimera activates the oxidase in amphiphile-dependent and -independent (anionic phospholipid-enriched membrane) cell-free systems. 2) Geranylgeranylation of the GFP-trimera makes it a potent oxidase activator in unmodified (native) membranes and in the absence of amphiphile. 3) Prenylated GFP-trimera binds spontaneously to native membranes (as assessed by gel filtration and in-line fluorometry), forming a tight complex capable of NADPH-dependent, activator-independent superoxide production at rates similar to those measured in canonical cell-free systems. 4) Prenylation of the GFP-trimera supersedes completely the dependence of oxidase activation on the p47(phox) phox homology domain and, partially, on the Rac1 polybasic domain, but the requirement for Trp(193) in p47(phox) persists. Prenylated GFP-p47(phox)-p67(phox)-Rac1 trimera acts as a quintessential single molecule oxidase activator of potential use in high throughput screening of inhibitors.

Neuron and astrocyte aggregation and sorting in three-dimensional neuronal constructs.

Aggregation and self-sorting of cells in three dimensional cultures have been described for non-neuronal cells. Despite increased interest in engineered neural tissues for treating brain injury or for modeling neurological disorders in vitro, little data is available on collective cell movements in neuronal aggregates. Migration and sorting of cells may alter these constructs' morphology and, therefore, the function of their neural circuitry. In this work, linear, adhered rat and human 3D neuronal-astrocyte cultures were developed to enable the study of aggregation and sorting of these cells. An in silico model of the contraction, clustering, and cell sorting in the 3D cultures was also developed. Experiments and computational modeling showed that aggregation was mainly a neuron mediated process, and formation of astrocyte-rich sheaths in 3D cultures depended on differential attraction between neurons and astrocytes. In silico model predicted formation of self-assembled neuronal layers in disk-shaped 3D cultures. Neuronal activity patterns were found to correlate with local morphological differences. This model of neuronal and astrocyte aggregation and sorting may benefit future design of neuronal constructs.

The molecular basis of Rac-GTP action-promoting binding of p67phox to Nox2 by disengaging the ß hairpin from downstream residues.

p67phox fulfils a key role in the assembly/activation of the NADPH oxidase by direct interaction with Nox2. We proposed that Rac-GTP serves both as a carrier of p67phox to the membrane and an inducer of a conformational change enhancing its affinity for Nox2. This study provides evidence for the latter function: (i) oxidase activation was inhibited by p67phox peptides (106-120) and (181-195), corresponding to the ß hairpin and to a downstream region engaged in intramolecular bonds with the ß hairpin, respectively; (ii) deletion of residues 181-193 and point mutations Q115R or K181E resulted in selective binding of p67phox to Nox2 peptide (369-383); (iii) both deletion and point mutations led to a change in p67phox , expressed in increased apparent molecular weights; (iv) p67phox was bound to p67phox peptide (181-195) and to a cluster of peptides (residues 97-117), supporting the participation of selected residues within these sequences in intramolecular bonds; (v) p67phox failed to bind to Nox2 peptide (369-383), following interaction with Rac1-GTP, but a (p67phox -Rac1-GTP) chimera exhibited marked binding to the peptide, similar to that of p67phox deletion and point mutants; and (vi) size exclusion chromatography of the chimera revealed its partition in monomeric and polymeric forms, with binding to Nox2 peptide (369-383) restricted to polymers. The molecular basis of Rac-GTP action entails unmasking of a previously hidden Nox2-binding site in p67phox , following disengagement of the ß hairpin from more C-terminal residues. The domain in Nox2 binding the "modified" p67phox comprises residues within the 369-383 sequence in the cytosolic dehydrogenase region.

p67phox -derived self-assembled peptides prevent Nox2 NADPH oxidase activation by an auto-inhibitory mechanism.

Activation of the Nox2-dependent NADPH oxidase is the result of a conformational change in Nox2 induced by interaction with the cytosolic component p67phox . In preliminary work we identified a cluster of overlapping 15-mer synthetic peptides, corresponding to p67phox residues 259-279, which inhibited oxidase activity in an in vitro, cell-free assay, but the results did not point to a competitive mechanism. We recently identified an auto-inhibitory intramolecular bond in p67phox , one extremity of which was located within the 259-279 sequence, and we hypothesized that inhibition by exogenous peptides might mimic intrinsic auto-inhibition. In this study, we found that: (i) progressive N- and C-terminal truncation of inhibitory p67phox peptides, corresponding to residues 259-273 and 265-279, revealed that inhibitory ability correlated with the presence of residues 265 NIVFVL270 , exposed at either the N- or C-termini of the peptides; (ii) inhibition of oxidase activity was associated exclusively with self-assembled peptides, which pelleted upon centrifugation at 12,000 ×g; (iii) self-assembled p67phox peptides inhibited oxidase activity by specific binding of p67phox and the ensuing depletion of this component, essential for interaction with Nox2; and (iv) peptides subjected to scrambling or reversing the order of residues in NIVFVL retained the propensity for self-assembly, oxidase inhibitory ability, and specific binding of p67phox , indicating that the dominant parameter was the hydrophobic character of five of the six residues. This appears to be the first description of inhibition of oxidase activity by self-assembled peptides derived from an oxidase component, acting by an auto-inhibitory mechanism.

Microdevice for directional axodendritic connectivity between micro 3D neuronal cultures.

Neuronal cultures are widely used in neuroscience research. However, the randomness of circuits in conventional cultures prevents accurate in vitro modeling of cortical development and of the pathogenesis of neurological and psychiatric disorders. A basic feature of cortical circuits that is not captured in standard cultures of dissociated cortical cells is directional connectivity. In this work, a polydimethylsiloxane (PDMS)-based device that achieves directional connectivity between micro 3D cultures is demonstrated. The device consists of through-holes for micro three-dimensional (µ3D) clusters of cortical cells connected by microtrenches for axon and dendrite guidance. The design of the trenches relies in part on the concept of axonal edge guidance, as well as on the novel concept of specific dendrite targeting. This replicates dominant excitatory connectivity in the cortex, enables the guidance of the axon after it forms a synapse in passing (an "en passant" synapse), and ensures that directional selectivity is preserved over the lifetime of the culture. The directionality of connections was verified morphologically and functionally. Connections were dependent on glutamatergic synapses. The design of this device has the potential to serve as a building block for the reconstruction of more complex cortical circuits in vitro.

Deubiquitylating enzymes in neuronal health and disease.

Ubiquitylation and deubiquitylation play a pivotal role in protein homeostasis (proteostasis). Proteostasis shapes the proteome landscape in the human brain and its impairment is linked to neurodevelopmental and neurodegenerative disorders. Here we discuss the emerging roles of deubiquitylating enzymes in neuronal function and survival. We provide an updated perspective on the genetics, physiology, structure, and function of deubiquitylases in neuronal health and disease.