Neuregulin 1 (NRG-1) and its receptor ErbB4 have emerged as biologically plausible schizophrenia risk factors, modulators of GABAergic and dopaminergic neurotransmission, and as potent regulators of glutamatergic synaptic plasticity. NRG-1 acutely depotentiates LTP in hippocampal slices, and blocking ErbB kinase activity inhibits LTP reversal by theta pulse stimuli (TPS), an activity-dependent reversal paradigm. NRG-1/ErbB4 signaling in parvalbumin (PV) interneurons has been implicated in inhibitory transmission onto pyramidal neurons. However, the role of ErbB4, in particular in PV interneurons, for LTP reversal has not been investigated. Here we show that ErbB4 null (ErbB4-/-) and PV interneuron-restricted mutant (PV-Cre;ErbB4) mice, as well as NRG-1 hypomorphic mice, exhibit increased hippocampal LTP. Moreover, both ErbB4-/- and PV-Cre;ErbB4 mice lack TPS-mediated LTP reversal. A comparative behavioral analysis of full and conditional ErbB4 mutant mice revealed that both exhibit hyperactivity in a novel environment and deficits in pre-pulse inhibition of the startle response. Strikingly, however, only ErbB4-/- mice exhibit reduced anxiety-like behaviors in the elevated plus maze task and deficits in cued and contextual fear conditioning. These results suggest that aberrant NRG-1/ErbB4 signaling in PV interneurons accounts for some but not all behavioral abnormalities observed in ErbB4-/- mice. Consistent with the observation that PV-Cre;ErbB4 mice exhibit normal fear conditioning, we find that ErbB4 is broadly expressed in the amygdala, largely by cells negative for PV. These findings are important to better understand ErbB4's role in complex behaviors and warrant further analysis of ErbB4 mutant mice lacking the receptor in distinct neuron types.

Cellular migration and contractility are fundamental processes that are regulated by a variety of concerted mechanisms such as cytoskeleton rearrangements, focal adhesion turnover, and Ca2+ oscillations. TRPM4 is a Ca2+-activated non-selective cationic channel (Ca2+-NSCC) that conducts monovalent but not divalent cations. Here, we used a mass spectrometry-based proteomics approach to identify putative TRPM4-associated proteins. Interestingly, the largest group of these proteins has actin cytoskeleton-related functions, and among these nine are specifically annotated as focal adhesion-related proteins. Consistent with these results, we found that TRPM4 localizes to focal adhesions in cells from different cellular lineages. We show that suppression of TRPM4 in MEFs impacts turnover of focal adhesions, serum-induced Ca2+ influx, focal adhesion kinase (FAK) and Rac activities, and results in reduced cellular spreading, migration and contractile behavior. Finally, we demonstrate that the inhibition of TRPM4 activity alters cellular contractility in vivo, affecting cutaneous wound healing. Together, these findings provide the first evidence, to our knowledge, for a TRP channel specifically localized to focal adhesions, where it performs a central role in modulating cellular migration and contractility.

Necrosis is associated with an increase in plasma membrane permeability, cell swelling, and loss of membrane integrity with subsequent release of cytoplasmic constituents. The transient receptor potential (TRP) 5 ion channel superfamily comprises a broad variety of cation-selective channels key to many physiological processes, including sensation, cell proliferation, and cell death (1, 2). TRPM4 is a Ca 2ϩ -activated and voltage-dependent monovalent cation selective channel corresponding to the melastatin subfamily of TRP channels (3).A distinct feature of TRPM4, as well as TRPM5 channels is that upon activation by intracellular Ca 2ϩ

Numerous genetic and functional studies implicate variants of Neuregulin-1 and its neuronal receptor ErbB4 in schizophrenia and many of its endophenotypes. While the neurophysiological and behavioral phenotypes of NRG1 mutant mice have been investigated extensively, practically nothing is known about the function of NRG2, the closest NRG1 homologue. We found that NRG2 expression in the adult rodent brain does not overlap with NRG1 and is more extensive than originally reported, including expression in the striatum and medial prefrontal cortex (mPFC), and therefore generated NRG2 knockout mice (KO) to study its function. NRG2 KOs have higher extracellular dopamine levels in the dorsal striatum but lower levels in the mPFC; a pattern with similarities to dopamine dysbalance in schizophrenia. Like ErbB4 KO mice, NRG2 KOs performed abnormally in a battery of behavioral tasks relevant to psychiatric disorders. NRG2 KOs exhibit hyperactivity in a novelty-induced open field, deficits in prepulse inhibition, hypersensitivity to amphetamine, antisocial behaviors, reduced anxiety-like behavior on the elevated plus-maze and deficits on the T-maze alteration reward test - a task dependent on hippocampal and mPFC function. Acute administration of clozapine rapidly increased extracellular dopamine levels in the mPFC and improved alternation T-maze performance. Similar to mice treated chronically with NMDAR antagonists, we demonstrate that NMDA receptor synaptic currents in NRG2 KOs are augmented at hippocampal glutamatergic synapses and are more sensitive to ifenprodil, indicating an increased contribution of GluN2B-containing NMDA receptors. Our findings reveal a novel role for NRG2 in the modulation of behaviors with relevance to psychiatric disorders.

TRPM4 is a Ca2+-activated non-selective cationic channel that conducts monovalent cations. TRPM4 has been proposed to contribute to burst firing and sustained activity in several brain regions, however, the cellular and subcellular pattern of TRPM4 expression in medial prefrontal cortex (mPFC) during postnatal development has not been elucidated. Here, we use multiplex immunofluorescence labeling of brain sections to characterize the postnatal developmental expression of TRPM4 in the mouse mPFC. We also performed electrophysiological recordings to correlate the expression of TRPM4 immunoreactivity with the presence of TRPM4-like currents. We found that TRPM4 is expressed from the first postnatal day, with expression increasing up to postnatal day 35. Additionally, in perforated patch clamp experiments, we found that TRPM4-like currents were active at resting membrane potentials at all postnatal ages studied. Moreover, TRPM4 is expressed in both pyramidal neurons and interneurons. TRPM4 expression is localized in the soma and proximal dendrites, but not in the axon initial segment of pyramidal neurons. This subcellular localization is consistent with a reduction in the basal current only when we locally perfused 9-Phenanthrol in the soma, but not upon perfusion in the medial or distal dendrites. Our results show a specific localization of TRPM4 expression in neurons in the mPFC and that a 9-Phenanthrol sensitive current is active at resting membrane potential, suggesting specific functional roles in mPFC neurons during postnatal development and in adulthood.

Volume-sensitive outwardly rectifying (VSOR) Cl^- channels participate in several physiological processes such as regulatory volume decrease, cell cycle regulation, proliferation and apoptosis. Recent evidence points to a significant role of hydrogen peroxide (H₂O₂) in VSOR Cl^- channel activation. The aim of this study was to determine the signalling pathways responsible for H₂O₂-induced VSOR Cl^- channel activation. In rat hepatoma (HTC) cells, H₂O₂ elicited a transient increase in tyrosine phosphorylation of phospholipase Cγ1 (PLCγ1) that was blocked by PP2, a Src-family protein kinases inhibitor. Also, H₂O₂ triggered an increase in cytosolic [Ca²⁺] that paralleled the time course of PLCγ1 phosphorylation. The H₂O₂-induced [Ca²⁺]_i rise was prevented by the generic phospholipase C (PLC) inhibitor U73122 and the inositol 1,4,5-trisphosphate-receptor (IP₃R) blocker 2-APB. In line with these results, manoeuvres that prevented PLCγ1 activation and/or [Ca²⁺]_i rise, abolished H₂O₂-induced VSOR Cl^- currents. Furthermore, in cells that overexpress a phosphorylation-defective dominant mutant of PLCγ1, H₂O₂ did not induce activation of VSOR Cl^- currents. All these H₂O₂-induced effects were independent of extracellular Ca²⁺. Our findings suggest that activation of PLCγ1 and subsequent Ca²⁺_i mobilisation mediate H₂O₂-induced VSOR Cl^- currents, indicating that H₂O₂ operates via redox-sensitive signalling pathways akin to those activated by osmotic challenges.

The Neuregulin 1 (NRG1)/ErbB4 signaling pathway has been genetically and functionally implicated in the etiology underlying schizophrenia, and in the regulation of glutamatergic pyramidal neuron function and plasticity. However, ErbB4 receptors are expressed in subpopulations of GABAergic interneurons, but not in hippocampal or cortical pyramidal neurons, indicating that NRG1 effects on principal neurons are indirect. Consistent with these findings, NRG1 effects on hippocampal long-term potentiation at CA1 pyramidal neuron synapses in slices are mediated indirectly by dopamine. Here we studied whether NRG/ErbB signaling directly regulates interneuron intrinsic excitability by pharmacologically isolating ErbB4-expressing neurons in rat dissociated hippocampal cultures, which lack dopaminergic innervation. We found that NRG1 acutely attenuates ErbB4-expressing interneuron excitability by depolarizing the firing threshold; neurons treated with the pan-ErbB inhibitor PD158780 or negative for ErbB4 were unaffected. These effects of NRG1 are primarily attributable to decreased voltage-gated sodium channel activity, as current density was attenuated by ~60%. In stark contrast, NRG1 had minor effects on whole-cell potassium currents. Our data reveal the direct actions of NRG1 signaling in ErbB4-expressing interneurons, and offer novel insight into how NRG1/ErbB4 signaling can impact hippocampal activity.

Transient receptor potential melastatin 4 (TRPM4) is a Ca2+‐activated nonselective cationic channel involved in a wide variety of physiologic and pathophysiological processes. Bioinformatics analyses of the primary sequence of TRPM4 allowed us to identify a putative motif for interaction with end‐binding (EB) proteins, which are microtubule plus‐end tracking proteins. Here, we provide novel data suggesting that TRPM4 interacts with EB proteins. We show that mutations of the putative EB binding motif abolish the TRPM4‐EB interaction, leading to a reduced expression of the mature population of the plasma membrane channel and instead display an endoplasmic reticulum‐associated distribution. Furthermore, we demonstrate that EB1 and EB2 proteins are required for TRPM4 trafficking and functional activity. Finally, we demonstrated that the expression of a soluble fragment containing the EB binding motif of TRPM4 reduces the plasma membrane expression of the channel and affects TRPM4‐dependent focal adhesion disassembly and cell invasion processes.—Blanco, C., Morales, D., Mogollones, I., Vergara‐Jaque, A., Vargas, C., Álvarez, A., Riquelme, D., Leiva‐Salcedo, E., González, W., Morales, D., Maureira, D., Aldunate, I., Cáceres, M., Varela, D., Cerda, O. EB1‐ and EB2‐dependent anterograde trafficking of TRPM4 regulates focal adhesion turnover and cell invasion. FASEB J. 33, 9434–9452 (2019). http://www.fasebj.org