Fragile X mental retardation protein controls ion channel expression and activity

Fragile X-associated disorders are a family of genetic conditions resulting from the partial or complete loss of fragile X mental retardation protein (FMRP). Among these disorders is fragile X syndrome, the most common cause of inherited intellectual disability and autism. FMRP is an RNA-binding protein involved in the control of local translation, which has pleiotropic effects, in particular on synaptic function. Analysis of the brain FMRP transcriptome has revealed hundreds of potential mRNA targets encoding postsynaptic and presynaptic proteins, including a number of ion channels. FMRP has been confirmed to bind voltage-gated potassium channels (Kv3.1 & Kv4.2) mRNAs and regulates their expression in somatodendritic compartments of neurons. Recent studies have uncovered a number of additional roles for FMRP besides RNA-regulation. FMRP was shown to directly interact with, and modulate, a number of ion channel complexes. The sodium-activated potassium (Slack) channel was the first ion channel shown to directly interact with FMRP; this interaction alters the single-channel properties of Slack channel. FMRP was also shown to interact with the auxiliary 4 subunit of the calcium-activated potassium (BK) channel; this interaction increases calcium-dependent activation of the BK channel. More recently, FMRP was shown to directly interact with the voltage-gated calcium channel, Cav2.2, and reduce its trafficking to the plasma membrane. Studies performed on animal models of fragile X syndrome have revealed links between modifications of ion channel activity and changes in neuronal excitability, suggesting that these modifications could contribute to the phenotypes observed in patients with fragile X-associated disorders

Effect of knockout of α2δ-1 on action potentials in mouse sensory neurons

Gene deletion of the voltage-gated calcium channel auxiliary subunit α2δ-1 has been shown previously to have a cardiovascular phenotype, and a reduction in mechano- and cold sensitivity, coupled with delayed development of neuropathic allodynia. We have also previously shown that dorsal root ganglion (DRG) neuron calcium channel currents were significantly reduced in α2δ-1 knockout mice. To extend our findings in these sensory neurons, we have examined here the properties of action potentials (APs) in DRG neurons from α2δ-1 knockout mice in comparison to their wild-type (WT) littermates, in order to dissect how the calcium channels that are affected by α2δ-1 knockout are involved in setting the duration of individual APs and their firing frequency. Our main findings are that there is reduced Ca(2+) entry on single AP stimulation, particularly in the axon proximal segment, reduced AP duration and reduced firing frequency to a 400 ms stimulation in α2δ-1 knockout neurons, consistent with the expected role of voltage-gated calcium channels in these events. Furthermore, lower intracellular Ca(2+) buffering also resulted in reduced AP duration, and a lower frequency of AP firing in WT neurons, mimicking the effect of α2δ-1 knockout. By contrast, we did not obtain any consistent evidence for the involvement of Ca(2+)-activation of large conductance calcium-activated potassium (BK) and small conductance calcium-activated potassium (SK) channels in these events. In conclusion, the reduced Ca(2+) elevation as a result of single AP stimulation is likely to result from the reduced duration of the AP in α2δ-1 knockout sensory neurons.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'

FMRP regulates presynaptic localization of neuronal voltage gated calcium channels

Fragile X syndrome (FXS), the most common form of inherited intellectual disability and autism, results from the loss of fragile X mental retardation protein (FMRP). We have recently identified a direct interaction of FMRP with voltage-gated Ca2+ channels that modulates neurotransmitter release. In the present study we used a combination of optophysiological tools to investigate the impact of FMRP on the targeting of voltage-gated Ca2+ channels to the active zones in neuronal presynaptic terminals. We monitored Ca2+ transients at synaptic boutons of dorsal root ganglion (DRG) neurons using the genetically-encoded Ca2+ indicator GCaMP6f tagged to synaptophysin. We show that knock-down of FMRP induces an increase of the amplitude of the Ca2+ transient in functionally-releasing presynaptic terminals, and that this effect is due to an increase of N-type Ca2+ channel contribution to the total Ca2+ transient. Dynamic regulation of CaV2.2 channel trafficking is key to the function of these channels in neurons. Using a CaV2.2 construct with an α-bungarotoxin binding site tag, we further investigate the impact of FMRP on the trafficking of CaV2.2 channels. We show that forward trafficking of CaV2.2 channels from the endoplasmic reticulum to the plasma membrane is reduced when co-expressed with FMRP. Altogether our data reveal a critical role of FMRP on localization of CaV channels to the presynaptic terminals and how its defect in a context of FXS can profoundly affect synaptic transmission

Proteolytic maturation of α2δ controls the probability of synaptic vesicular release

Auxiliary α2δ subunits are important proteins for trafficking of voltage-gated calcium channels (CaV) at the active zones of synapses. We have previously shown that the post-translational proteolytic cleavage of α2δ is essential for their modulatory effects on the trafficking of N-type (CaV2.2) calcium channels (Kadurin et al. 2016). We extend these results here by showing that the probability of presynaptic vesicular release is reduced when an uncleaved α2δ is expressed in rat neurons and that this inhibitory effect is reversed when cleavage of α2δ is restored. We also show that asynchronous release is influenced by the maturation of α2δ-1, highlighting the role of CaV channels in this component of vesicular release. We present additional evidence that CaV2.2 co-immunoprecipitates preferentially with cleaved wild-type α2δ. Our data indicate that the proteolytic maturation increases the association of α2δ-1 with CaV channel complex and is essential for its function on synaptic release

Protective effect of tomato-oleoresin supplementation on oxidative injury recoveries cardiac function by improving β-adrenergic response in a diet-obesity induced model

The system redox imbalance is one of the pathways related to obesity-related cardiac dysfunction. Lycopene is considered one of the best antioxidants. The aim of this study was to test if the tomato-oleoresin would be able to recovery cardiac function by improving \u3b2-adrenergic response due its antioxidant effect. A total of 40 animals were randomly divided into two experimental groups to receive either the control diet (Control, n = 20) or a high sugar-fat diet (HSF, n = 20) for 20 weeks. Once cardiac dysfunction was detected by echocardiogram in the HSF group, animals were re- divided to begin the treatment with Tomato-oleoresin or vehicle, performing four groups: Control (n = 6); (Control + Ly, n = 6); HSF (n = 6) and (HSF + Ly, n = 6). Tomato oleoresin (10 mg lycopene/kg body weight (BW) per day) was given orally every morning for a 10-week period. The analysis included nutritional and plasma biochemical parameters, systolic blood pressure, oxidative parameters in plasma, heart, and cardiac analyses in vivo and in vitro. A comparison among the groups was performed by two-way analysis of variance (ANOVA). Results: The HSF diet was able to induce obesity, insulin-resistance, cardiac dysfunction, and oxidative damage. However, the tomato-oleoresin supplementation improved insulin-resistance, cardiac remodeling, and dysfunction by improving the \u3b2-adrenergic response. It is possible to conclude that tomato-oleoresin is able to reduce the oxidative damage by improving the system\u2019s \u3b2-adrenergic response, thus recovering cardiac function

New SOS diode pumping circuit based on an all-solid-state spiral generator for high-voltage nanosecond applications

Semiconductor opening switch (SOS) diodes are capable to switch currents with a density of more than 1 kA/cm 2 and withstand nanosecond pulses with an amplitude of up to 1 MV. SOS diodes, however, require a specific pumping circuit that must simultaneously provide forward and reverse pumping currents with a time of ∼ 500 and ∼ 100 ns, respectively. Such a pumping circuit with energies > 1 J typically requires a gas-discharge switch or a low-efficient solid-state solution. This study proposes a novel approach to pumping SOS diodes based on a spiral generator (SG) (also known as a vector inversion generator). Due to its wave characteristics, the SG produces a bipolar current discharge that meets the time duration and current amplitude required to pump an SOS diode. Moreover, the initial pulse from the spiral typically has a relatively low current amplitude compared to the opposite polarity secondary pulse, so the SOS diode can operate at very high efficiencies. This idea has been tested using an all-solid-state SG coupled with large-area SOS diodes (1 cm 2 ). With this combination, a voltage pulse of 62 kV having a rise time of only 11 ns was obtained on an open circuit load (3 pF, 1 M Ω ). The experiments were highly repeatable, with no damage to the components despite multiple tests. There is significant scope to further improve the results, with simple alterations to the SG

Label-Free Characterization of Organic Nanocarriers Reveals Persistent Single Molecule Cores For Hydrocarbon Sequestration

Self-assembled molecular nanostructures embody an enormous potential for new technologies, therapeutics, and understanding of molecular biofunctions. Their structure and function are dependent on local environments, necessitating in-situ/operando investigations for the biggest leaps in discovery and design. However, the most advanced of such investigations involve laborious labeling methods that can disrupt behavior or are not fast enough to capture stimuli-responsive phenomena. We utilize X-rays resonant with molecular bonds to demonstrate an in-situ nanoprobe that eliminates the need for labels and enables data collection times within seconds. Our analytical spectral model quantifies the structure, molecular composition, and dynamics of a copolymer micelle drug delivery platform using resonant soft X-rays. We additionally apply this technique to a hydrocarbon sequestrating polysoap micelle and discover that the critical organic-capturing domain does not coalesce upon aggregation but retains distinct single-molecule cores. This characteristic promotes its efficiency of hydrocarbon sequestration for applications like oil spill remediation and drug delivery. Such a technique enables operando, chemically sensitive investigations of any aqueous molecular nanostructure, label-free

Status of DIII-D plasma control

A key component of the DIII-D Advanced Tokamak and Radiative Divertor Programs is the development and implementation of methods to actively control a large number of plasma parameters. These parameters include plasma shape and position, total stored energy, density, rf loading resistance, radiated power and more detailed control of the current profile. To support this research goal, a flexible and easily expanded digital control system has been developed and implemented. We have made parallel progress in modeling of the plasma, poloidal coils, vacuum vessel, and power system dynamics and in ensuring the integrity of diagnostic and command circuits used in control. Recent activity has focused on exploiting the mature digital control platform through the implementation of simple feedback controls of more exotic plasma parameters such as enhanced divertor radiation, neutral pressure and Marfe creation and more sophisticated identification and digital feedback control algorithms for plasma shape, vertical position, and safety factor on axis (q{sub 0}). A summary of recent progress in each of these areas will be presented