Emanuele Schiavon

Neuropsin cleaves EphB2 in the amygdala to control anxiety

A minority of individuals experiencing traumatic events develop anxiety disorders. The reason for the lack of correspondence between the prevalence of exposure to psychological trauma and the development of anxiety is unknown. Extracellular proteolysis contributes to fear-associated responses by facilitating neuronal plasticity at the neuron–matrix interface. Here we show in mice that the serine protease neuropsin is critical for stress-related plasticity in the amygdala by regulating the dynamics of the EphB2–NMDA-receptor interaction, the expression of Fkbp5 and anxiety-like behaviour. Stress results in neuropsin-dependent cleavage of EphB2 in the amygdala causing dissociation of EphB2 from the NR1 subunit of the NMDA receptor and promoting membrane turnover of EphB2 receptors. Dynamic EphB2–NR1 interaction enhances NMDA receptor current, induces Fkbp5 gene expression and enhances behavioural signatures of anxiety. On stress, neuropsin-deficient mice do not show EphB2 cleavage and its dissociation from NR1 resulting in a static EphB2–NR1 interaction, attenuated induction of the Fkbp5 gene and low anxiety. The behavioural response to stress can be restored by intra-amygdala injection of neuropsin into neuropsin-deficient mice and disrupted by the injection of either anti-EphB2 antibodies or silencing the Fkbp5 gene in the amygdala of wild-type mice. Our findings establish a novel neuronal pathway linking stress-induced proteolysis of EphB2 in the amygdala to anxiety.

Lipocalin-2 controls neuronal excitability and anxiety by regulating dendritic spine formation and maturation

Psychological stress causes adaptive changes in the nervous system directed toward maintaining homoeostasis. These biochemical and structural mechanisms regulate animal behavior, and their malfunction may result in various forms of affective disorders. Here we found that the lipocalin-2 (Lcn2) gene, encoding a secreted protein of unknown neuronal function, was up-regulated in mouse hippocampus following psychological stress. Addition of lipocalin-2 to cultured hippocampal neurons reduced dendritic spine actins mobility, caused retraction of mushroom spines, and inhibited spine maturation. These effects were further enhanced by inactivating iron-binding residues of Lcn-2, suggesting that they were facilitated by the iron-free form of Lcn-2. Concurrently, disruption of the Lcn2 gene in mice promoted stress-induced increase in spine density and caused an increase in the proportion of mushroom spines. The above changes correlated with higher excitability of CA1 principal neurons and with elevated stress-induced anxiety in Lcn-2−/− mice. Our study demonstrates that lipocalin-2 promotes stress-induced changes in spine morphology and function to regulate neuronal excitability and anxiety.

Resurgent Current and Voltage Sensor Trapping Enhanced Activation by a β-Scorpion Toxin Solely in Nav1.6 Channel SIGNIFICANCE IN MICE PURKINJE NEURONS

Resurgent currents are functionally crucial in sustaining the high frequency firing of cerebellar Purkinje neurons expressing Nav1.6 channels. β-Scorpion toxins, such as CssIV, induce a left shift in the voltage-dependent activation of Nav1.2 channels by “trapping” the IIS4 voltage sensor segment. We found that the dangerous Cn2 β-scorpion peptide induces both the left shift voltage-dependent activation and a transient resurgent current only in human Nav1.6 channels (among 1.1-1.7), whereas CssIV did not induce the resurgent current. Cn2 also produced both actions in mouse Purkinje cells. These findings suggest that only distinct β-toxins produce resurgent currents. We suggest that the novel and unique selectivity of Cn2 could make it a model drug to replace deep brain stimulation of the subthalamic nucleus in patients with Parkinson disease.

Target promiscuity and heterogeneous effects of tarantula venom peptides affecting Na+ and K+ ion channels.

Venom-derived peptide modulators of ion channel gating are regarded as essential tools for understanding the molecular motions that occur during the opening and closing of ion channels. In this study, we present the characterization of five spider toxins on 12 human voltage-gated ion channels, following observations about the target promiscuity of some spider toxins and the ongoing revision of their “canonical” gating-modifying mode of action. The peptides were purified de novo from the venom of Grammostola rosea tarantulas, and their sequences were confirmed by Edman degradation and mass spectrometry analysis. Their effects on seven tetrodotoxin-sensitive Na+ channels, the three human ether-à-go-go (hERG)-related K+ channels, and two human Shaker-related K+ channels were extensively characterized by electrophysiological techniques. All the peptides inhibited ion conduction through all the Na+ channels tested, although with distinctive patterns. The peptides also affected the three pharmaceutically relevant hERG isoforms differently. At higher concentrations, all peptides also modified the gating of the Na+ channels by shifting the activation to more positive potentials, whereas more complex effects were recorded on hERG channels. No effects were evident on the two Shaker-related K+ channels at concentrations well above the IC50 value for the affected channels. Given the sequence diversity of the tested peptides, we propose that tarantula toxins should be considered both as multimode and target-promiscuous ion channel modulators; both features should not be ignored when extracting mechanistic interpretations about ion channel gating. Our observations could also aid in future structure-function studies and might help the development of novel ion channel-specific drugs.

Novel α-conotoxins from Conus spurius and the α-conotoxin EI share high-affinity potentiation and low-affinity inhibition of nicotinic acetylcholine receptors

α‐Conotoxins from marine snails are known to be selective and potent competitive antagonists of nicotinic acetylcholine receptors. Here we describe the purification, structural features and activity of two novel toxins, SrIA and SrIB, isolated from Conus spurius collected in the Yucatan Channel, Mexico. As determined by direct amino acid and cDNA nucleotide sequencing, the toxins are peptides containing 18 amino acid residues with the typical 4/7‐type framework but with completely novel sequences. Therefore, their actions (and that of a synthetic analog, [γ15E]SrIB) were compared to those exerted by the α4/7‐conotoxin EI from Conus ermineus, used as a control. Their target specificity was evaluated by the patch‐clamp technique in mammalian cells expressing α1β1γδ, α4β2 and α3β4 nicotinic acetylcholine receptors. At high concentrations (10 µm), the peptides SrIA, SrIB and [γ15E]SrIB showed weak blocking effects only on α4β2 and α1β1γδ subtypes, but EI also strongly blocked α3β4 receptors. In contrast to this blocking effect, the new peptides and EI showed a remarkable potentiation of α1β1γδ and α4β2 nicotinic acetylcholine receptors if briefly (2–15 s) applied at concentrations several orders of magnitude lower (EC50, 1.78 and 0.37 nm, respectively). These results suggest not only that the novel α‐conotoxins and EI can operate as nicotinic acetylcholine receptor inhibitors, but also that they bind both α1β1γδ and α4β2 nicotinic acetylcholine receptors with very high affinity and increase their intrinsic cholinergic response. Their unique properties make them excellent tools for studying the toxin–receptor interaction, as well as models with which to design highly specific therapeutic drugs.

Electroclinical Features of a Family with Simple Febrile Seizures and Temporal Lobe Epilepsy Associated with SCN1A Loss‐of‐Function Mutation

Summary:  Purpose: To report in detail the electroclinical features of a large family in which we recently identified a missense mutation (M145T) of a well‐conserved amino acid in the first transmembrane segment of domain I of the human SCN1A. We showed that the mutation is associated with a loss of SCN1A function.

Sound localization ability and glycinergic innervation of the superior olivary complex persist after genetic deletion of the medial nucleus of the trapezoid body

The medial nucleus of the trapezoid body (MNTB) in the superior olivary complex (SOC) is an inhibitory hub considered critical for binaural sound localization. We show that genetic ablation of MNTB neurons in mice only subtly affects this ability by prolonging the minimum time required to detect shifts in sound location. Furthermore, glycinergic innervation of the SOC is maintained without an MNTB, consistent with the existence of parallel inhibitory inputs. These findings redefine the role of MNTB in sound localization and suggest that the inhibitory network is more complex than previously thought.

Voltage-dependent Nav1.7 sodium channels: multiple roles in adrenal chromaffin cells and peripheral nervous system

Voltage‐dependent Na+ channels consist of the principal α‐subunit (∼260 kDa), without or with auxiliary β‐subunit (∼38 kDa). Nine α‐subunit isoforms (Nav1.1–Nav1.9) are encoded in nine different genes (SCN1A–SCN5A and SCN8A–SCN11A). Besides initiating and propagating action potentials in established neuronal circuit, Na+ channels engrave, maintain and repair neuronal network in the brain throughout the life. Adrenal chromaffin cells express Nav1.7 encoded in SCN9A, which is widely distributed among peripheral autonomic and sensory ganglia, neuroendocrine cells, as well as prostate cancer cell lines. In chromaffin cells, Nav1.7‐specific biophysical properties have been characterized; physiological stimulation by acetylcholine produces muscarinic receptor‐mediated hyperpolarization followed by nicotinic receptor‐mediated depolarization. In human patients with Nav1.7 channelopathies, gain‐of‐pathological function mutants (i.e. erythermalgia and paroxysmal extreme pain disorder) or loss‐of‐physiological function mutant (channelopathy‐associated insensivity to pain) proved the causal involvement of mutant Nav1.7 in generating intolerable pain syndrome, Nav1.7 being the first molecular target convincingly identified for pain treatment. Importantly, aberrant upregulation/hyperactivity of even the native Nav1.7 produces pain associated with inflammation, nerve injury and diabetic neuropathy in rodents. Various extra‐ and intracellular signals, as well as therapeutic drugs modulate the activity of Nav1.7, and also cause up‐ and downregulation of Nav1.7. Nav1.7 seems to play an increasing number of crucial roles in health, disease and therapeutics.

Negative-shift activation, current reduction and resurgent currents induced by β-toxins from Centruroides scorpions in sodium channels.

The β-toxins purified from the New World scorpion venoms of the Centruroides species affect several voltage-gated sodium channels (VGSCs) and thus are essential tools not only for the discrimination of different channel sub-types but also for studying the structure-function relationship between channels and toxins. This communication reports the results obtained with four different peptides purified from three species of Centruroides scorpions and assayed on seven distinct isoforms of VGSC (Na(v)1.1-Na(v)1.7) by specific functional analysis conducted through single cell electrophysiology. The toxins studied were CssII from Centruroides suffusus suffusus, Cll1 and Cll2 from Centruroides limpidus limpidus and a novel toxin from Centruroides noxius, which was characterized for the first time here. It has 67 amino acid residues and four disulfide bridges with a molecular mass of 7626 Da. Three different functional features were identified: current reduction of macroscopic conductance, left shift of the voltage-dependent activation and induction of resurgent currents at negative voltages following brief, strong depolarizations. The isoforms which revealed to be more affected resulted to be Na(v)1.6 > 1.1 > 1.2 and, for the first time, a β-toxin is here shown to induce resurgent current also in isoforms different from Na(v)1.6. Additionally, these results were analyzed with molecular modelling. In conclusion, although the four toxins have a high degree of identity, they display tri-modal function, each of which shows selectivity among the different sub-types of Na+ -channels. Thus, they are invaluable as tools for structure-function studies of β-toxins and offer a basis for the design of novel ion channel-specific drugs.

Voltage‐gated sodium channel isoform‐specific effects of pompilidotoxins

Pompilidotoxins (PMTXs, α and β) are small peptides consisting of 13 amino acids purified from the venom of the solitary wasps Anoplius samariensis (α‐PMTX) and Batozonellus maculifrons (β‐PMTX). They are known to facilitate synaptic transmission in the lobster neuromuscular junction, and to slow sodium channel inactivation. By using β‐PMTX, α‐PMTX and four synthetic analogs with amino acid changes, we conducted a thorough study of the effects of PMTXs on sodium current inactivation in seven mammalian voltage‐gated sodium channel (VGSC) isoforms and one insect VGSC (DmNav1). By evaluating three components of which the inactivating current is composed (fast, slow and steady‐state components), we could distinguish three distinct groups of PMTX effects. The first group concerned the insect and Nav1.6 channels, which showed a large increase in the steady‐state current component without any increase in the slow component. Moreover, the dose‐dependent increase in this steady‐state component was correlated with the dose‐dependent decrease in the fast component. A second group of effects concerned the Nav1.1, Nav1.2, Nav1.3 and Nav1.7 isoforms, which responded with a large increase in the slow component, and showed only a small steady‐state component. As with the first group of effects, the slow component was dose‐dependent and correlated with the decrease in the fast component. Finally, a third group of effects concerned Nav1.4 and Nav1.5, which did not show any change in the slow or steady‐state component. These data shed light on the complex and intriguing behavior of VGSCs in response to PMTXs, helping us to better understand the molecular determinants explaining isoform‐specific effects.