Kidins220/ARMS is a novel modulator of short-term synaptic plasticity in hippocampal GABAergic neurons

The Co-Expression Pattern of Calcium-Binding Proteins with γ-Aminobutyric Acid and Glutamate Transporters in the Amygdala of the Guinea Pig: Evidence for Glutamatergic Subpopulations

The amygdala has large populations of neurons utilizing specific calcium-binding proteins such as parvalbumin (PV), calbindin (CB), or calretinin (CR). They are considered specialized subsets of γ-aminobutyric acid (GABA) interneurons; however, many of these cells are devoid of GABA or glutamate decarboxylase. The neurotransmitters used by GABA-immunonegative cells are still unknown, but it is suggested that a part may use glutamate. Thus, this study investigates in the amygdala of the guinea pig relationships between PV, CB, or CR-containing cells and GABA transporter (VGAT) or glutamate transporter type 2 (VGLUT2), markers of GABAergic and glutamatergic neurons, respectively. The results show that although most neurons using PV, CB, and CR co-expressed VGAT, each of these populations also had a fraction of VGLUT2 co-expressing cells. For almost all neurons using PV (~90%) co-expressed VGAT, while ~1.5% of them had VGLUT2. The proportion of neurons using CB and VGAT was smaller than that for PV (~80%), while the percentage of cells with VGLUT2 was larger (~4.5%). Finally, only half of the neurons using CR (~53%) co-expressed VGAT, while ~3.5% of them had VGLUT2. In conclusion, the populations of neurons co-expressing PV, CB, and CR are in the amygdala, primarily GABAergic. However, at least a fraction of neurons in each of them co-express VGLUT2, suggesting that these cells may use glutamate. Moreover, the number of PV-, CB-, and CR-containing neurons that may use glutamate is probably larger as they can utilize VGLUT1 or VGLUT3, which are also present in the amygdala.

GABAergic and Glutamatergic Phenotypes of Neurons Expressing Calcium-Binding Proteins in the Preoptic Area of the Guinea Pig

The mammalian preoptic area (POA) has large populations of calbindin (CB), calretinin (CR) and parvalbumin (PV) neurons, but phenotypes of these cells are unknown. Therefore, the question is whether neurons expressing CB, CR, and/or PV are GABAergic or glutamatergic. Double-immunofluorescence staining followed by epifluorescence and confocal microscopy was used to determine the coexpression patterns of CB, CR and PV expressing neurons with vesicular GABA transporters (VGAT) as specific markers of GABAergic neurons and vesicular glutamate transporters (VGLUT 2) as specific markers of glutamatergic neurons. The guinea pig was adopted as, like humans, it has a reproductive cycle with a true luteal phase and a long gestation period. The results demonstrated that in the guinea pig POA of both sexes, ~80% of CB+ and ~90% of CR+ neurons coexpress VGAT; however, one-fifth of CB+ neurons and one-third of CR+ cells coexpress VGLUT. About two-thirds of PV+ neurons express VGAT, and similar proportion of them coexpress VGLUT. Thus, many CB+, CR+ and PV+ neurons may be exclusively GABAergic (VGAT-expressing cells) or glutamatergic (VGLUT-expressing cells); however, at least a small fraction of CR+ cells and at least one-third of PV+ cells are likely neurons with a dual GABA/glutamate phenotype that may coexpress both transporters.

Kidins220/ARMS modulates brain morphology and anxiety-like traits in adult mice

Kinase D interacting substrate of 220 kDa (Kidins220), also known as ankyrin repeat-rich membrane spanning (ARMS), is a transmembrane scaffold protein that participates in fundamental aspects of neuronal physiology including cell survival, differentiation, and synaptic plasticity. The Kidins220 constitutive knockout line displays developmental defects in the nervous and cardiovascular systems that lead to embryonic lethality, which has so far precluded the study of this protein in the adult. Moreover, Kidins220 mRNA is tightly regulated by alternative splicing, whose impact on nervous system physiology has not yet been addressed in vivo. Here, we have asked to what extent the absence of Kidins220 splicing and the selective knockout of Kidins220 impact on adult brain homeostasis. To answer this question, we used a floxed line that expresses only the full-length, non-spliced Kidins220 mRNA, and a forebrain-specific, CaMKII-Cre driven Kidins220 conditional knockout (cKO) line. Kidins220 cKO brains are characterized by enlarged ventricles in the absence of cell death, and by deficient dendritic arborization in several cortical regions. The deletion of Kidins220 leads to behavioral changes, such as reduced anxiety-like traits linked to alterations in TrkB-BDNF signaling and sex-dependent alterations of hippocampal-dependent spatial memory. Kidins220 floxed mice present similarly enlarged brain ventricles and increased associative memory. Thus, both the absolute levels of Kidins220 expression and its splicing pattern are required for the correct brain development and related expression of behavioral phenotypes. These findings are relevant in light of the increasing evidence linking mutations in the human KIDINS220 gene to the onset of severe neurodevelopmental disorders.

A developmental stage- and Kidins220-dependent switch in astrocyte responsiveness to brain-derived neurotrophic factor

Astroglial cells are key to maintain nervous system homeostasis. Neurotrophins are known for their pleiotropic effects on neuronal physiology but also exert complex functions to glial cells. Here, we investigated (i) the signaling competence of mouse embryonic and postnatal primary cortical astrocytes exposed to brain-derived neurotrophic factor (BDNF) and, (ii) the role of kinase D-interacting substrate of 220 kDa (Kidins220), a transmembrane scaffold protein that mediates neurotrophin signaling in neurons. We found a shift from a kinase-based response in embryonic cells to a response predominantly relying on intracellular Ca2+ transients [Ca2+]i within postnatal cultures, associated with a decrease in the synthesis of full-length BDNF receptor TrkB, with Kidins220 contributing to the BDNF-activated kinase and [Ca2+]i pathways. Finally, Kidins220 participates in the homeostatic function of astrocytes by controlling the expression of the ATP-sensitive inward rectifier potassium channel 10 (Kir4.1) and the metabolic balance of embryonic astrocytes. Overall, our data contribute to the understanding of the complex role played by astrocytes within the central nervous system, and identify Kidins220 as a novel actor in the increasing number of pathologies characterized by astrocytic dysfunctions. This article has an associated First Person interview with the first authors of the paper.

High neural activity accelerates the decline of cognitive plasticity with age in Caenorhabditis elegans

The ability to learn progressively declines with age. Neural hyperactivity has been implicated in impairing cognitive plasticity with age, but the molecular mechanisms remain elusive. Here, we show that chronic excitation of the Caenorhabditis elegans O₂-sensing neurons during ageing causes a rapid decline of experience-dependent plasticity in response to environmental O₂ concentration, whereas sustaining lower activity of O₂-sensing neurons retains plasticity with age. We demonstrate that neural activity alters the ageing trajectory in the transcriptome of O₂-sensing neurons, and our data suggest that high-activity neurons redirect resources from maintaining plasticity to sustaining continuous firing. Sustaining plasticity with age requires the K⁺-dependent Na⁺/Ca²⁺ (NCKX) exchanger, whereas the decline of plasticity with age in high-activity neurons acts through calmodulin and the scaffold protein Kidins220. Our findings demonstrate directly that the activity of neurons alters neuronal homeostasis to govern the age-related decline of neural plasticity and throw light on the mechanisms involved.

Kidins220/ARMS controls astrocyte calcium signaling and neuron-astrocyte communication

Through their ability to modulate synaptic transmission, glial cells are key regulators of neuronal circuit formation and activity. Kidins220/ARMS (kinase-D interacting substrate of 220 kDa/ankyrin repeat-rich membrane spanning) is one of the key effectors of the neurotrophin pathways in neurons where it is required for differentiation, survival, and plasticity. However, its role in glial cells remains largely unknown. Here, we show that ablation of Kidins220 in primary cultured astrocytes induced defects in calcium (Ca2+) signaling that were linked to altered store-operated Ca2+ entry and strong overexpression of the transient receptor potential channel TRPV4. Moreover, Kidins220-/- astrocytes were more sensitive to genotoxic stress. We also show that Kidins220 expression in astrocytes is required for the establishment of proper connectivity of cocultured wild-type neurons. Altogether, our data reveal a previously unidentified role for astrocyte-expressed Kidins220 in the control of glial Ca2+ dynamics, survival/death pathways and astrocyte-neuron communication.

PARK14 (D331Y) PLA2G6 Causes Early-Onset Degeneration of Substantia Nigra Dopaminergic Neurons by Inducing Mitochondrial Dysfunction, ER Stress, Mitophagy Impairment and Transcriptional Dysregulation in a Knockin Mouse Model

PARK14 patients with homozygous (D331Y) PLA2G6 mutation display motor deficits of pure early-onset Parkinson's disease (PD). The aim of this study is to investigate the pathogenic mechanism of mutant (D331Y) PLA2G6-induced PD. We generated knockin (KI) mouse model of PARK14 harboring homozygous (D331Y) PLA2G6 mutation. Then, we investigated neuropathological and neurological phenotypes of PLA2G6^D331Y/D331Y KI mice and molecular pathogenic mechanisms of (D331Y) PLA2G6-induced degeneration of substantia nigra (SN) dopaminergic neurons. Six-or nine-month-old PLA2G6^D331Y/D331Y KI mice displayed early-onset cell death of SNpc dopaminergic neurons. Lewy body pathology was found in the SN of PLA2G6^D331Y/D331Y mice. Six-or nine-month-old PLA2G6^D331Y/D331Y KI mice exhibited early-onset parkinsonism phenotypes. Disrupted cristae of mitochondria were found in SNpc dopaminergic neurons of PLA2G6^D331Y/D331Y mice. PLA2G6^D331Y/D331Y mice displayed mitochondrial dysfunction and upregulated ROS production, which may lead to activation of apoptotic cascade. Upregulated protein levels of Grp78, IRE1, PERK, and CHOP, which are involved in activation of ER stress, were found in the SN of PLA2G6^D331Y/D331Y mice. Protein expression of mitophagic proteins, including parkin and BNIP3, was downregulated in the SN of PLA2G6^D331Y/D331Y mice, suggesting that (D331Y) PLA2G6 mutation causes mitophagy dysfunction. In the SN of PLA2G6^D331Y/D331Y mice, mRNA levels of eight genes that are involved in neuroprotection/neurogenesis were decreased, while mRNA levels of two genes that promote apoptotic death were increased. Our results suggest that PARK14 (D331Y) PLA2G6 mutation causes degeneration of SNpc dopaminergic neurons by causing mitochondrial dysfunction, elevated ER stress, mitophagy impairment, and transcriptional abnormality.

Stepping Out of the Shade: Control of Neuronal Activity by the Scaffold Protein Kidins220/ARMS

The correct functioning of the nervous system depends on the exquisitely fine control of neuronal excitability and synaptic plasticity, which relies on an intricate network of protein-protein interactions and signaling that shapes neuronal homeostasis during development and in adulthood. In this complex scenario, Kinase D interacting substrate of 220 kDa/ankyrin repeat-rich membrane spanning (Kidins220/ARMS) acts as a multi-functional scaffold protein with preferential expression in the nervous system. Engaged in a plethora of interactions with membrane receptors, cytosolic signaling components and cytoskeletal proteins, Kidins220/ARMS is implicated in numerous cellular functions including neuronal survival, neurite outgrowth and maturation and neuronal activity, often in the context of neurotrophin (NT) signaling pathways. Recent studies have highlighted a number of cell- and context-specific roles for this protein in the control of synaptic transmission and neuronal excitability, which are at present far from being completely understood. In addition, some evidence has began to emerge, linking alterations of Kidins220 expression to the onset of various neurodegenerative diseases and neuropsychiatric disorders. In this review, we present a concise summary of our fragmentary knowledge of Kidins220/ARMS biological functions, focusing on the mechanism(s) by which it controls various aspects of neuronal activity. We have tried, where possible, to discuss the available evidence in the wider context of NT-mediated regulation, and to outline emerging roles of Kidins220/ARMS in human pathologies.

Functional Interaction between the Scaffold Protein Kidins220/ARMS and Neuronal Voltage-Gated Na+ Channels

Kidins220 (kinase D-interacting substrate of 220 kDa)/ankyrin repeat-rich membrane spanning (ARMS) acts as a signaling platform at the plasma membrane and is implicated in a multitude of neuronal functions, including the control of neuronal activity. Here, we used the Kidins220(-/-) mouse model to study the effects of Kidins220 ablation on neuronal excitability. Multielectrode array recordings showed reduced evoked spiking activity in Kidins220(-/-) hippocampal networks, which was compatible with the increased excitability of GABAergic neurons determined by current-clamp recordings. Spike waveform analysis further indicated an increased sodium conductance in this neuronal subpopulation. Kidins220 association with brain voltage-gated sodium channels was shown by co-immunoprecipitation experiments and Na(+) current recordings in transfected HEK293 cells, which revealed dramatic alterations of kinetics and voltage dependence. Finally, an in silico interneuronal model incorporating the Kidins220-induced Na(+) current alterations reproduced the firing phenotype observed in Kidins220(-/-) neurons. These results identify Kidins220 as a novel modulator of Nav channel activity, broadening our understanding of the molecular mechanisms regulating network excitability.

Synapsin II desynchronizes neurotransmitter release at inhibitory synapses by interacting with presynaptic calcium channels

In the central nervous system, most synapses show a fast mode of neurotransmitter release known as synchronous release followed by a phase of asynchronous release, which extends over tens of milliseconds to seconds. Synapsin II (SYN2) is a member of the multigene synapsin family (SYN1/2/3) of synaptic vesicle phosphoproteins that modulate synaptic transmission and plasticity, and are mutated in epileptic patients. Here we report that inhibitory synapses of the dentate gyrus of Syn II knockout mice display an upregulation of synchronous neurotransmitter release and a concomitant loss of delayed asynchronous release. Syn II promotes γ-aminobutyric acid asynchronous release in a Ca²⁺-dependent manner by a functional interaction with presynaptic Ca²⁺ channels, revealing a new role in synaptic transmission for synapsins.

The arrival of action potentials at nerve terminals often leads to synchronous neurotransmitter release. Medrihan and colleagues use electrophysiology on mouse hippocampal neurons to show that the vesicle protein Synapsin II promotes GABAergic asynchronous release by interacting with calcium channels.

Kidins220/ARMS as a functional mediator of multiple receptor signalling pathways

An increasing body of evidence suggests that several membrane receptors--in addition to activating distinct signalling cascades--also engage in substantial crosstalk with each other, thereby adjusting their signalling outcome as a function of specific input information. However, little is known about the molecular mechanisms that control their coordination and integration of downstream signalling. A protein that is likely to have a role in this process is kinase-D-interacting substrate of 220 kDa [Kidins220, also known as ankyrin repeat-rich membrane spanning (ARMS), hereafter referred to as Kidins220/ARMS]. Kidins220/ARMS is a conserved membrane protein that is preferentially expressed in the nervous system and interacts with the microtubule and actin cytoskeleton. It interacts with neurotrophin, ephrin, vascular endothelial growth factor (VEGF) and glutamate receptors, and is a common downstream target of several trophic stimuli. Kidins220/ARMS is required for neuronal differentiation and survival, and its expression levels modulate synaptic plasticity. Kidins220/ARMS knockout mice show developmental defects mainly in the nervous and cardiovascular systems, suggesting a crucial role for this protein in modulating the cross talk between different signalling pathways. In this Commentary, we summarise existing knowledge regarding the physiological functions of Kidins220/ARMS, and highlight some interesting directions for future studies on the role of this protein in health and disease.