Role In Synapse Formation Research Articles

Illana Gozes: From the pivotal discovery of activity-dependent neuroprotective protein (ADNP) through its investigational drug davunetide: brain molecular medicine providing hope for autism, schizophrenia, and Alzheimer's disease

Professor Illana Gozes, Ph.D., is a faculty member at Tel Aviv University. Formerly holding the Lily and Avraham Gildor Chair for the Investigation of Growth Factors, she now directs the Dr. Diana and Zelma Elton Laboratory for Molecular Neuroendocrinology. A world-renowned neurochemist, Professor Gozes currently serves as the President of the European Society for Neurochemistry and Vice President of Drug Development at ExoNavis Therapeutics Ltd. Her groundbreaking research began in the late 1970s and early 1980s when she discovered multiple tubulin forms within a single neuron. She demonstrated that these forms evolve with brain development, play a crucial role in synapse formation, and can be identified using monoclonal tubulin antibodies. At the forefront of molecular neuroscience in the 1980s, Professor Gozes became the first to clone the gene encoding vasoactive intestinal peptide (VIP), a key regulatory neuropeptide in the brain. Her research revealed increased VIP expression during synapse formation. In her quest to identify proteins activated by VIP and facilitate neuro-glial interaction, the Gozes laboratory discovered and cloned a novel protein: activity-dependent neuroprotective protein (ADNP). Subsequent research established ADNP's essential role in brain formation and function. Through a series of highly cited articles, Professor Gozes demonstrated that ADNP regulates thousands of essential genes during brain development in a sex-dependent manner and associates with an intricate array of vital proteins. She uncovered ADNP's key role in autophagy and schizophrenia, revealed a fundamental shared mechanism in autism involving critical binding of ADNP with SHANK3 and actin, and showed ADNP's regulation of microtubule dynamics and Tau interaction, which protects against tauopathy. Furthermore, she discovered somatic mutations in ADNP and related genes in Alzheimer's disease, paralleling tauopathy. Her pioneering work on ADNP-deficient mouse models predicted the ADNP syndrome, an autistic/intellectual disability syndrome driven by de novo mutations in ADNP and presenting with tauopathy. Professor Gozes took a reductionist approach to discover an active site in ADNP, leading to the development of the investigational drug davunetide (NAP). This compound has shown promise in protecting against ADNP deficiency/mutations in animal models and in clinical trials. It has been tested in women suffering from progressive supranuclear palsy (PSP), a pure tauopathy, and in individuals with prodromal Alzheimer's disease, demonstrating effects in a sex-dependent manner. Further promise was shown in schizophrenia patients, suggesting improvement in real-world problem solving and task performance. We are honored that Professor Gozes has agreed to share her life's journey with our readers in this Genomic Press Interview.

Human microglial cells as a therapeutic target in a neurodevelopmental disease model

Although microglia are macrophages of the central nervous system, their involvement is not limited to immune functions. The roles of microglia during development in humans remain poorly understood due to limited access to fetal tissue. To understand how microglia can impact human neurodevelopment, the methyl-CpG binding protein 2 (MECP2) gene was knocked out in human microglia-like cells (MGLs). Disruption of the MECP2 in MGLs led to transcriptional and functional perturbations, including impaired phagocytosis. The co-culture of healthy MGLs with MECP2-knockout (KO) neurons rescued synaptogenesis defects, suggesting a microglial role in synapse formation. A targeted drug screening identified ADH-503, a CD11b agonist, restored phagocytosis and synapse formation in spheroid-MGL co-cultures, significantly improved disease progression, and increased survival in MeCP2-null mice. These results unveil a MECP2-specific regulation of human microglial phagocytosis and identify a novel therapeutic treatment for MECP2-related conditions.

Synaptic cell adhesion molecules contribute to the pathogenesis and progression of fragile X syndrome.

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and a monogenic cause of autism spectrum disorders. Deficiencies in the fragile X messenger ribonucleoprotein, encoded by the FMR1 gene, lead to various anatomical and pathophysiological abnormalities and behavioral deficits, such as spine dysmorphogenesis and learning and memory impairments. Synaptic cell adhesion molecules (CAMs) play crucial roles in synapse formation and neural signal transmission by promoting the formation of new synaptic contacts, accurately organizing presynaptic and postsynaptic protein complexes, and ensuring the accuracy of signal transmission. Recent studies have implicated synaptic CAMs such as the immunoglobulin superfamily, N-cadherin, leucine-rich repeat proteins, and neuroligin-1 in the pathogenesis of FXS and found that they contribute to defects in dendritic spines and synaptic plasticity in FXS animal models. This review systematically summarizes the biological associations between nine representative synaptic CAMs and FMRP, as well as the functional consequences of the interaction, to provide new insights into the mechanisms of abnormal synaptic development in FXS.

Molecular Organization and Regulation of the Mammalian Synapse by the Post-Translational Modification SUMOylation.

Neurotransmission occurs within highly specialized compartments forming the active synapse where the complex organization and dynamics of the interactions are tightly orchestrated both in time and space. Post-translational modifications (PTMs) are central to these spatiotemporal regulations to ensure an efficient synaptic transmission. SUMOylation is a dynamic PTM that modulates the interactions between proteins and consequently regulates the conformation, the distribution and the trafficking of the SUMO-target proteins. SUMOylation plays a crucial role in synapse formation and stabilization, as well as in the regulation of synaptic transmission and plasticity. In this review, we summarize the molecular consequences of this protein modification in the structural organization and function of the mammalian synapse. We also outline novel activity-dependent regulation and consequences of the SUMO process and explore how this protein modification can functionally participate in the compartmentalization of both pre- and post-synaptic sites.

Astrocyte Development in the Rodent.

Astrocytes have gained increasing recognition as key elements of a broad array of nervous system functions. These include essential roles in synapse formation and elimination, synaptic modulation, maintenance of the blood-brain barrier, energetic support, and neural repair after injury or disease of the nervous system. Nevertheless, our understanding of mechanisms underlying astrocyte development and maturation remains far behind that of neurons and oligodendrocytes. Early efforts to understand astrocyte development focused primarily on their specification from embryonic progenitors and the molecular mechanisms driving the switch from neuron to glial production. Considerably, less is known about postnatal stages of astrocyte development, the period during which they are predominantly generated and mature. Notably, this period is coincident with synapse formation and the emergence of nascent neural circuits. Thus, a greater understanding of astrocyte development is likely to shed new light on the formation and maturation of synapses and circuits. Here, we highlight key foundational principles of embryonic and postnatal astrocyte development, focusing largely on what is known from rodent studies.

Plk2 promotes synaptic destabilization through disruption of N-cadherin adhesion complexes during homeostatic adaptation to hyperexcitation.

Synaptogenesis in the brain is highly organized and orchestrated by synaptic cellular adhesion molecules (CAMs) such as N-cadherin and amyloid precursor protein (APP) that contribute to the stabilization and structure of synapses. Although N-cadherin plays an integral role in synapse formation and synaptic plasticity, its function in synapse dismantling is not as well understood. Synapse weakening and loss are prominent features of neurodegenerative diseases, and can also be observed during homeostatic compensation to neuronal hyperexcitation. Previously, we have shown that during homeostatic synaptic plasticity, APP is a target for cleavage triggered by phosphorylation by Polo-like kinase 2 (Plk2). Here, we found that Plk2 directly phosphorylates N-cadherin, and during neuronal hyperexcitation Plk2 promotes N-cadherin proteolytic processing, degradation, and disruption of complexes with APP. We further examined the molecular mechanisms underlying N-cadherin degradation. Loss of N-cadherin adhesive function destabilizes excitatory synapses and promotes their structural dismantling as a prerequisite to eventual synapse elimination. This pathway, which may normally help to homeostatically restrain excitability, could also shed light on the dysregulated synapse loss that occurs in cognitive disorders.

Delaying the GABA Shift Indirectly Affects Membrane Properties in the Developing Hippocampus.

During the first two postnatal weeks, intraneuronal chloride concentrations in rodents gradually decrease, causing a shift from depolarizing to hyperpolarizing GABA responses. The postnatal GABA shift is delayed in rodent models for neurodevelopmental disorders and in human patients, but the impact of a delayed GABA shift on the developing brain remains obscure. Here we examine the direct and indirect consequences of a delayed postnatal GABA shift on network development in organotypic hippocampal cultures made from 6- to 7-d-old mice by treating the cultures for 1 week with VU0463271, a specific inhibitor of the chloride exporter KCC2. We verified that VU treatment delayed the GABA shift and kept GABA signaling depolarizing until DIV9. We found that the structural and functional development of excitatory and inhibitory synapses at DIV9 was not affected after VU treatment. In line with previous studies, we observed that GABA signaling was already inhibitory in control and VU-treated postnatal slices. Surprisingly, 14 d after the VU treatment had ended (DIV21), we observed an increased frequency of spontaneous inhibitory postsynaptic currents in CA1 pyramidal cells, while excitatory currents were not changed. Synapse numbers and release probability were unaffected. We found that dendrite-targeting interneurons in the stratum radiatum had an elevated resting membrane potential, while pyramidal cells were less excitable compared with control slices. Our results show that depolarizing GABA signaling does not promote synapse formation after P7, and suggest that postnatal intracellular chloride levels indirectly affect membrane properties in a cell-specific manner.SIGNIFICANCE STATEMENT During brain development, the action of neurotransmitter GABA shifts from depolarizing to hyperpolarizing. This shift is a thought to play a critical role in synapse formation. A delayed shift is common in rodent models for neurodevelopmental disorders and in human patients, but its consequences for synaptic development remain obscure. Here, we delayed the GABA shift by 1 week in organotypic hippocampal cultures and carefully examined the consequences for circuit development. We find that delaying the shift has no direct effects on synaptic development, but instead leads to indirect, cell type-specific changes in membrane properties. Our data call for careful assessment of alterations in cellular excitability in neurodevelopmental disorders.

Regulation of Presynaptic Release Machinery by Cell Adhesion Molecules.

The synapse is a highly specialized asymmetric structure that transmits and stores information in the brain. The size of pre- and postsynaptic structures and function is well coordinated at the individual synapse level. For example, large postsynaptic dendritic spines have a larger postsynaptic density with higher α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) number on their surface, while juxtaposing presynaptic terminals have a larger active zone and higher release probability. This indicates that pre- and postsynaptic domains bidirectionally communicate to coordinate assembly of specific molecules on both sides of the synaptic cleft. Cell adhesion molecules (CAMs) that localize at synapses form transsynaptic protein interactions across the synaptic cleft and play important roles in synapse formation and regulation. The extracellular domain of CAMs is essential for specific synapse formation and function. In contrast, the intracellular domain is necessary for binding with synaptic molecules and signal transduction. Therefore, CAMs play an essential role on synapse function and structure. In fact, ample evidence indicates that transsynaptic CAMs instruct and modulate functions at presynaptic sites. This chapter focuses on transsynaptic protein interactions that regulate presynaptic functions emphasizing the role of neuronal CAMs and the intracellular mechanism of their regulation.

Erratic and blood vessel-guided migration of astrocyte progenitors in the cerebral cortex

Astrocytes are one of the most abundant cell types in the mammalian brain. They play essential roles in synapse formation, maturation, and elimination. However, how astrocytes migrate into the gray matter to accomplish these processes is poorly understood. Here, we show that, by combinational analyses of in vitro and in vivo time-lapse observations and lineage traces, astrocyte progenitors move rapidly and irregularly within the developing cortex, which we call erratic migration. Astrocyte progenitors also adopt blood vessel-guided migration. These highly motile progenitors are generated in the restricted prenatal stages and differentiate into protoplasmic astrocytes in the gray matter, whereas postnatally generated progenitors do not move extensively and differentiate into fibrous astrocytes in the white matter. We found Cxcr4/7, and integrin β1 regulate the blood vessel-guided migration, and their functional blocking disrupts their positioning. This study provides insight into astrocyte development and may contribute to understanding the pathogenesis caused by their defects.

Comparison of serum IGF1, IGF2 and IGFBP1-6 concentration in the children with different stages of autism spectrum disorders

Aim of the studyAutism spectrum disorder (ASD) is a neurodevelopmental condition considered by early-onset difficulties in social communication. Insulin-like growth factors (IGFs) play crucial roles in synapse formation. Most of circulating IGFs are bound to IGF-binding proteins (IGFBPs) that modify IGF action. IGFBPs prolong the plasma half-life of IGFs. In this project we studied the association of IGF1/2 and IGFBP1-6 serum concentration with the severity of ASD (Levels 1-3; Mild, Moderate and severe, respectively).Subject or material and methodsA hundred and eighty patients with ASD (Mild; n=69, Moderate; n=58 and Severe; n=53) and 118 controls age matched were used in this project and IGF1/2 and IGFBP1-6 serum concentration were measured by ELISA.ResultsThe results demonstrated that IGF1, IGF2 and IGFBP1-6 were present in all serum samples. The results showed that the concentration of IGF1 and IGF2 was significantly higher in ASD patients when compared to controls, starting from stages I to III ASD, a significant increase of IGF1 and IGF2 serum concentration was observed. Results obtained also showed that IGFBP1-6 concentration in the ASD group were lower when compared to controls and low serum IGFBP1-6 concentration is associated with advanced stages of ASD.DiscussionIGFs plays important role in synapse formation and changes in IGFs expression may be important in the pathogenesis of ASD.ConclusionsIt is suggested that IGFs and IGFBPs may be involved in the pathogenesis of ASD. Therefore, the detection of serum soluble IGFs and IGFBPs may be useful in classifying ASD.

Neuronal Roles of the Multifunctional Protein Dipeptidyl Peptidase-like 6 (DPP6).

The concerted action of voltage-gated ion channels in the brain is fundamental in controlling neuronal physiology and circuit function. Ion channels often associate in multi-protein complexes together with auxiliary subunits, which can strongly influence channel expression and function and, therefore, neuronal computation. One such auxiliary subunit that displays prominent expression in multiple brain regions is the Dipeptidyl aminopeptidase-like protein 6 (DPP6). This protein associates with A-type K+ channels to control their cellular distribution and gating properties. Intriguingly, DPP6 has been found to be multifunctional with an additional, independent role in synapse formation and maintenance. Here, we feature the role of DPP6 in regulating neuronal function in the context of its modulation of A-type K+ channels as well as its independent involvement in synaptic development. The prevalence of DPP6 in these processes underscores its importance in brain function, and recent work has identified that its dysfunction is associated with host of neurological disorders. We provide a brief overview of these and discuss research directions currently underway to advance our understanding of the contribution of DPP6 to their etiology.

Tissue-Specific Expression of Neurexin-1α Isoforms in Rat Organs

—Neurexins are a family of synaptic adhesion proteins that play a key role in synapse formation and maintenance. Neurexins undergo extensive alternative splicing at six sites (SS1–SS6) resulting in expression of multiplicity of different isoforms. Alternative splicing regulates the functional activity of neurexins in different types of tissues and cells and presumably plays a key role in determining the specificity of the interaction of various neurons. In this study, we have investigated the pattern of tissue expression of neurexin-1α mRNA isoforms including an insert in the recently discovered splice site SS6 using TaqMan Real-Time PCR in different organs of Wistar rats. The isoform containing the insert in the SS6 site was found only in neural tissues suggesting its potential functional importance. Position of the SS6 insert in the hinge region between the LNS5 and LNS6 domains increases variability of possible conformations of the molecule which may represent an additional mechanism for regulating functional activity of the neurexin-1α in the brain.

Mechanisms and Consequences of Cerebellar Purkinje Cell Disinhibition in a Mouse Model of Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD), the most common form of childhood muscular dystrophy, is caused by mutations in the dystrophin gene. In addition to debilitating muscle degeneration, patients display a range of cognitive deficits thought to result from the loss of dystrophin normally expressed in the brain. While the function of dystrophin in muscle tissue is well characterized, its role in the brain is still poorly understood. The highest expression of dystrophin in the mouse brain is in cerebellar Purkinje cells (PCs), where it colocalizes with GABAA receptor clusters. Using ex vivo electrophysiological recordings from connected molecular layer interneuron (MLI)-PC pairs, we investigated changes in inhibitory synaptic transmission caused by dystrophin deficiency. In male mdx mice (which lack long-form dystrophin), we found that responses at MLI-PC pairs were reduced by ∼60% because of both decreased quantal response amplitude and a reduced number of functional vesicle release sites. Using electron microscopy, we found significantly fewer and smaller anatomically defined inhibitory synapses contacting the soma of PCs in mdx mice, suggesting that dystrophin may play a critical role in synapse formation and/or maintenance. Functionally, we found reduced MLI-evoked pauses in PC firing in acute slices. In vivo recordings from awake mdx mice showed increased sensory-evoked simple spike firing in positively modulating PCs, consistent with reduced feedforward inhibition, but no change in negatively modulating PCs. These data suggest that dystrophin deficiency in PCs disrupts inhibitory signaling in the cerebellar circuit and PC firing patterns, potentially contributing to cognitive and motor deficits observed in mdx mice and DMD patients.SIGNIFICANCE STATEMENT Duchenne muscular dystrophy (DMD) is primarily characterized by progressive muscle weakening caused by genetic mutations in the gene for dystrophin. Dystrophin is also normally expressed in the CNS, and DMD patients experience a range of nonprogressive cognitive deficits. The pathophysiology of CNS neurons resulting from loss of dystrophin and the function of dystrophin in neurons are still poorly understood. Using cerebellar PCs as a model, we found that the loss of dystrophin specifically disrupts the number and strength of inhibitory synaptic connections, suggesting that dystrophin participates in formation and/or maintenance of these synapses. This work provides insight into the function of dystrophin in the CNS and establishes neuronal and synaptic dysfunction, which may underlie cognitive deficits in DMD.

Neuroinflammation-mediated mitochondrial dysregulation involved in postoperative cognitive dysfunction

Neuroinflammation following peripheral surgery is a pivotal pathogenic mechanism of postoperative cognitive dysfunction (POCD). However, the key site of inflammation-mediated neural damage remains unclear. Impaired mitochondrial function is a vital feature of degenerated neurons. Dynamin-related protein 1 (DRP1), a crucial regulator of mitochondrial dynamics, has been shown to play an essential role in synapse formation. Here, we designed experiments to assess whether Drp1-regulated mitochondrial dynamics and function are involved in the pathological processes of POCD and elucidate its relationship with neuroinflammation. Aged mice were subjected to experimental laparotomy under isoflurane anesthesia. Primary neurons and SH-SY5Y cells were exposed to tumor necrosis factor (TNF). We found an increase in Drp1 activation as well as mitochondrial fragmentation both in the hippocampus of mice after surgery and primary neurons after TNF exposure. Pretreatment with Mdivi-1, a Drp1 specific inhibitor, reduced this mitochondrial fragmentation. Drp1 knockdown with small interfering RNA blocked TNF-induced mitochondrial fragmentation in SH-SY5Y cells. However, the application of Mdivi-1 exhibited a negative impact on mitochondrial function and neurite growth in primary neurons. Calcineurin activity was increased in primary neurons after TNF exposure and contributed to the Drp1 activation. The calcineurin inhibitor FK506 exhibited a Drp1-independent function that mitigated mitochondrial dysfunction. Finally, we found that FK506 pretreatment ameliorated the neurite growth in neurons treated with TNF and the learning ability of mice after surgery. Overall, our research indicated a crucial role of mitochondrial function in the pathological processes of POCD, and neuronal metabolic modulation may represent a novel and important target for POCD.

Neuroligin-3 and neuroligin-4X form nanoscopic clusters and regulate growth cone organization and size.

The cell-adhesion proteins neuroligin-3 and neuroligin-4X (NLGN3/4X) have well described roles in synapse formation. NLGN3/4X are also expressed highly during neurodevelopment. However, the role these proteins play during this period is unknown. Here we show that NLGN3/4X localized to the leading edge of growth cones where it promoted neuritogenesis in immature human neurons. Super-resolution microscopy revealed that NLGN3/4X clustering induced growth cone enlargement and influenced actin filament organization. Critically, these morphological effects were not induced by autism spectrum disorder (ASD)-associated NLGN3/4X variants. Finally, actin regulators p21-activated kinase 1 and cofilin were found to be activated by NLGN3/4X and involved in mediating the effects of these adhesion proteins on actin filaments, growth cones and neuritogenesis. These data reveal a novel role for NLGN3 and NLGN4X in the development of neuronal architecture, which may be altered in the presence of ASD-associated variants.

Liprin-α-Mediated Assemblies and Their Roles in Synapse Formation.

Brain’s functions, such as memory and learning, rely on synapses that are highly specialized cellular junctions connecting neurons. Functional synapses orchestrate the assembly of ion channels, receptors, enzymes, and scaffold proteins in both pre- and post-synapse. Liprin-α proteins are master scaffolds in synapses and coordinate various synaptic proteins to assemble large protein complexes. The functions of liprin-αs in synapse formation have been largely uncovered by genetic studies in diverse model systems. Recently, emerging structural and biochemical studies on liprin-α proteins and their binding partners begin to unveil the molecular basis of the synaptic assembly. This review summarizes the recent structural findings on liprin-αs, proposes the assembly mechanism of liprin-α-mediated complexes, and discusses the liprin-α-organized assemblies in the regulation of synapse formation and function.

Trans-Synaptic Regulation of Metabotropic Glutamate Receptors by Elfn Proteins in Health and Disease.

Trans-regulation of G protein-coupled receptors (GPCRs) by leucine-rich repeat (LRR) transmembrane proteins has emerged as a novel type of synaptic molecular interaction in the last decade. Several studies on LRR–GPCR interactions have revealed their critical role in synapse formation and in establishing synaptic properties. Among them, LRR–GPCR interactions between extracellular LRR fibronectin domain-containing family proteins (Elfn1 and Elfn2) and metabotropic glutamate receptors (mGluRs) are particularly interesting as they can affect a broad range of synapses through the modulation of signaling by glutamate, the principal excitatory transmitter in the mammalian central nervous system (CNS). Elfn–mGluR interactions have been investigated in hippocampal, cortical, and retinal synapses. Postsynaptic Elfn1 in the hippocampus and cerebral cortex mediates the tonic regulation of excitatory input onto somatostatin-positive interneurons (INs) through recruitment of presynaptic mGluR7. In the retina, presynaptic Elfn1 binds to mGluR6 and is necessary for synapse formation between rod photoreceptor cells and rod-bipolar cells. The repertoire of binding partners for Elfn1 and Elfn2 includes all group III mGluRs (mGluR4, mGluR6, mGluR7, and mGluR8), and both Elfn1 and Elfn2 can alter mGluR-mediated signaling through trans-interaction. Importantly, both preclinical and clinical studies have provided support for the involvement of the Elfn1–mGluR7 interaction in attention-deficit hyperactivity disorder (ADHD), post-traumatic stress disorder (PTSD), and epilepsy. In fact, Elfn1–mGluR7-associated disorders may reflect the altered function of somatostatin-positive interneuron inhibitory neural circuits, the mesolimbic and nigrostriatal dopaminergic pathway, and habenular circuits, highlighting the need for further investigation into this interaction.

Astrocyte-induced synapse formation and ischemic stroke.

Astrocytes are closely associated with the regulation of synapse formation and function. In addition, astrocytes have been shown to block certain brain impairments, including synaptic damage from stroke and other diseases of the central nervous system (CNS). Although astrocytes do not completely prevent synaptic damage, they appear to be protective and to restore synaptic function following damage. The purpose of this study is to discuss the role of astrocytes in synaptogenesis and synaptic damage in ischemic stroke. I detail the mechanism of action of the multiple factors secreted by astrocytes that are involved in synapse formation. In particular, I describe the characteristics and role in synapse formation of each secreted molecule related to synaptic structure and function. Furthermore, I discuss the effect of astrocytes on synaptogenesis and repair in ischemic stroke and in other CNS diseases. Astrocytes release molecules such as thrombospondin, hevin, secreted protein acidic rich in cysteine, etc., due to activation by ischemia to induce synaptic structure and function, an effect associated with protection of the brain from synaptic damage in ischemic stroke. In conclusion, I show that astrocytes may regulate synaptic transmission while having the potential to block and repair synaptic dysfunction in stroke-associated brain damage.

How to Build and to Protect the Neuromuscular Junction: The Role of the Glial Cell Line-Derived Neurotrophic Factor.

The neuromuscular junction (NMJ) is at the crossroad between the nervous system (NS) and the muscle. Following neurotransmitter release from the motor neurons (MNs), muscle contraction occurs and movement is generated. Besides eliciting muscle contraction, the NMJ represents a site of chemical bidirectional interplay between nerve and muscle with the active participation of Schwann cells. Indeed, signals originating from the muscle play an important role in synapse formation, stabilization, maintenance and function, both in development and adulthood. We focus here on the contribution of the Glial cell line-Derived Neurotrophic Factor (GDNF) to these processes and to its potential role in the protection of the NMJ during neurodegeneration. Historically related to the maintenance and survival of dopaminergic neurons of the substantia nigra, GDNF also plays a fundamental role in the peripheral NS (PNS). At this level, it promotes muscle trophism and it participates to the functionality of synapses. Moreover, compared to the other neurotrophic factors, GDNF shows unique peculiarities, which make its contribution essential in neurodegenerative disorders. While describing the known structural and functional changes occurring at the NMJ during neurodegeneration, we highlight the role of GDNF in the NMJ–muscle cross-talk and we review its therapeutic potential in counteracting the degenerative process occurring in the PNS in progressive and severe diseases such as Alzheimer’s disease (AD), Amyotrophic Lateral Sclerosis (ALS) and Spinal Muscular Atrophy (SMA). We also describe functional 3D neuromuscular co-culture systems that have been recently developed as a model for studying both NMJ formation in vitro and its involvement in neuromuscular disorders.

Precise levels of nectin-3 are required for proper synapse formation in postnatal visual cortex

BackgroundDeveloping cortical neurons express a tightly choreographed sequence of cytoskeletal and transmembrane proteins to form and strengthen specific synaptic connections during circuit formation. Nectin-3 is a cell-adhesion molecule with previously described roles in synapse formation and maintenance. This protein and its binding partner, nectin-1, are selectively expressed in upper-layer neurons of mouse visual cortex, but their role in the development of cortical circuits is unknown.MethodsHere we block nectin-3 expression (via shRNA) or overexpress nectin-3 in developing layer 2/3 visual cortical neurons using in utero electroporation. We then assay dendritic spine densities at three developmental time points: eye opening (postnatal day (P)14), one week following eye opening after a period of heightened synaptogenesis (P21), and at the close of the critical period for ocular dominance plasticity (P35).ResultsKnockdown of nectin-3 beginning at E15.5 or ~ P19 increased dendritic spine densities at P21 or P35, respectively. Conversely, overexpressing full length nectin-3 at E15.5 decreased dendritic spine densities when all ages were considered together. The effects of nectin-3 knockdown and overexpression on dendritic spine densities were most significant on proximal secondary apical dendrites. Interestingly, an even greater decrease in dendritic spine densities, particularly on basal dendrites at P21, was observed when we overexpressed nectin-3 lacking its afadin binding domain.ConclusionThese data collectively suggest that the proper levels and functioning of nectin-3 facilitate normal synapse formation after eye opening on apical and basal dendrites in layer 2/3 of visual cortex.