scholarly journals Pathophysiological Roles of Abnormal Axon Initial Segments in Neurodevelopmental Disorders

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 2110
Author(s):  
Masashi Fujitani ◽  
Yoshinori Otani ◽  
Hisao Miyajima
Keyword(s):  
Cell Body ◽  
Neurodevelopmental Disorders ◽  
Neuronal Excitability ◽  
Neural Circuit ◽  
Network Activity ◽  
High Plasticity ◽  
Pathophysiological Role ◽  
Human Mutation ◽  
New Treatment

The 20–60 μm axon initial segment (AIS) is proximally located at the interface between the axon and cell body. AIS has characteristic molecular and structural properties regulated by the crucial protein, ankyrin-G. The AIS contains a high density of Na+ channels relative to the cell body, which allows low thresholds for the initiation of action potential (AP). Molecular and physiological studies have shown that the AIS is also a key domain for the control of neuronal excitability by homeostatic mechanisms. The AIS has high plasticity in normal developmental processes and pathological activities, such as injury, neurodegeneration, and neurodevelopmental disorders (NDDs). In the first half of this review, we provide an overview of the molecular, structural, and ion-channel characteristics of AIS, AIS regulation through axo-axonic synapses, and axo−glial interactions. In the second half, to understand the relationship between NDDs and AIS, we discuss the activity-dependent plasticity of AIS, the human mutation of AIS regulatory genes, and the pathophysiological role of an abnormal AIS in NDD model animals and patients. We propose that the AIS may provide a potentially valuable structural biomarker in response to abnormal network activity in vivo as well as a new treatment concept at the neural circuit level.

scholarly journals Pathophysiological Roles of Abnormal Axon Initial Segments in Neurodevelopmental Disorders

2021 ◽  
Author(s):  
Masashi Fujitani ◽  
Yoshinori Otani ◽  
Hisao Miyajima
Keyword(s):  
Cell Body ◽  
Neurodevelopmental Disorders ◽  
Neuronal Excitability ◽  
Neural Circuit ◽  
Network Activity ◽  
High Plasticity ◽  
Pathophysiological Role ◽  
Human Mutation ◽  
New Treatment

The 20–60-μm axon initial segment (AIS) is proximally located at the interface between the axon and cell body. AIS has characteristic molecular and structural properties regulated by the crucial protein, ankyrin-G. The AIS contains a high density of Na+ channels relative to the cell body, which allows low thresholds for initiation of action potential (AP). Molecular and physiological studies have shown that the AIS is also a key domain for the control of neuronal excitability by homeostatic mechanisms. The AIS has high plasticity in normal developmental processes and pathological activities such as injury, neurodegeneration, and neurodevelopmental disorders (NDDs). In the first half of this review, we provide an overview of the molecular, structural, and ion-channel characteristics of AIS, AIS regulation through axo-axonic synapses, and axo-glial interactions. In the second half, to understand the relationship between NDDs and AIS, we discuss the activity-dependent plasticity of AIS, the human mutation of AIS regulatory genes, and the pathophysiological role of the abnormal AIS in the NDD model animals and patients. We propose that AIS may provide a potentially valuable structural biomarker in response to abnormal network activity in vivo as well as a new treatment concept at the neural circuit level.

scholarly journals The formin Fmn2 is required for the development of an excitatory interneuron module in the zebrafish acoustic startle circuit

2020 ◽  
Author(s):  
Dhriti Nagar ◽  
Tomin K James ◽  
Ratnakar Mishra ◽  
Shrobona Guha ◽  
Aurnab Ghose
Keyword(s):  
Growth Cone ◽  
Neurodevelopmental Disorders ◽  
High Speed ◽  
Neural Circuits ◽  
Neural Circuit ◽  
Video Recording ◽  
Acoustic Startle ◽  
Neuronal Cultures

ABSTRACTThe formin family member, Fmn2, is a neuronally enriched cytoskeletal remodelling protein conserved across vertebrates. Recent studies have implicated Fmn2 in neurodevelopmental disorders, including sensory processing dysfunction and intellectual disability in humans. Cellular characterization of Fmn2 in primary neuronal cultures has identified its function in the regulation of cell-substrate adhesion and consequently growth cone translocation. However, the role of Fmn2 in the development of neural circuits in vivo, and its impact on associated behaviours have not been tested.Using automated analysis of behaviour and systematic investigation of the associated circuitry, we uncover the role of Fmn2 in zebrafish neural circuit development. As reported in other vertebrates, the zebrafish ortholog of Fmn2 is also enriched in the developing zebrafish nervous system. We find that Fmn2 is required for the development of an excitatory interneuron pathway, the spiral fiber neuron, which is an essential circuit component in the regulation of the Mauthner cell-mediated acoustic startle response. Consistent with the loss of the spiral fiber neurons tracts, high-speed video recording revealed a reduction in the short latency escape events while responsiveness to the stimuli was unaffected.Taken together, this study provides evidence for a circuit-specific requirement of Fmn2 in eliciting an essential behaviour in zebrafish. Our findings underscore the importance of Fmn2 in neural development across vertebrate lineages and highlight zebrafish models in understanding neurodevelopmental disorders.SIGNIFICANCE STATEMENTFmn2 is a neuronally enriched cytoskeletal remodelling protein linked to neurodevelopment and cognitive disorders in humans. Recent reports have characterized its function in growth cone motility and chemotaxis in cultured primary neurons. However, the role of Fmn2 in the development of neural circuits in vivo and its implications in associated behaviours remain unexplored. This study shows that Fmn2 is required for the development of neuronal processes in the acoustic startle circuit to ensure robust escape responses to aversive stimuli in zebrafish. Our study underscores the crucial role of the non-diaphanous formin, Fmn2, in establishing neuronal connectivity and related behaviour in zebrafish.

scholarly journals Elevated serotonergic signaling amplifies synaptic noise and facilitates the emergence of epileptiform network oscillations

2014 ◽  
Vol 112 (10) ◽  
pp. 2357-2373 ◽  
Author(s):  
Pavel A. Puzerey ◽  
Michael J. Decker ◽  
Roberto F. Galán
Keyword(s):  
Computational Model ◽  
Cortical Neurons ◽  
Neuronal Excitability ◽  
Network Activity ◽  
Cortical Dynamics ◽  
Synaptic Excitation ◽  
Network Oscillations ◽  
Synaptic Noise ◽  
Serotonin Signaling

Serotonin fibers densely innervate the cortical sheath to regulate neuronal excitability, but its role in shaping network dynamics remains undetermined. We show that serotonin provides an excitatory tone to cortical neurons in the form of spontaneous synaptic noise through 5-HT3 receptors, which is persistent and can be augmented using fluoxetine, a selective serotonin re-uptake inhibitor. Augmented serotonin signaling also increases cortical network activity by enhancing synaptic excitation through activation of 5-HT2 receptors. This in turn facilitates the emergence of epileptiform network oscillations (10–16 Hz) known as fast runs. A computational model of cortical dynamics demonstrates that these two combined mechanisms, increased background synaptic noise and enhanced synaptic excitation, are sufficient to replicate the emergence fast runs and their statistics. Consistent with these findings, we show that blocking 5-HT2 receptors in vivo significantly raises the threshold for convulsant-induced seizures.

Statistical Model Relating CA3 Burst Probability to Recovery From Burst-Induced Depression at Recurrent Collateral Synapses

2001 ◽  
Vol 86 (6) ◽  
pp. 2736-2747 ◽  
Author(s):  
Kevin J. Staley ◽  
Jaideep S. Bains ◽  
Audrey Yee ◽  
Jennifer Hellier ◽  
J. Mark Longacher
Keyword(s):  
Time Constant ◽  
Neuronal Excitability ◽  
Pyramidal Cells ◽  
Network Activity ◽  
Interval Change ◽  
Epileptiform Discharges ◽  
Recurrent Collateral ◽  
Pace Maker

When neuronal excitability is increased in area CA3 of the hippocampus in vitro, the pyramidal cells generate periodic bursts of action potentials that are synchronized across the network. We have previously provided evidence that synaptic depression at the excitatory recurrent collateral synapses in the CA3 network terminates each population burst so that the next burst cannot begin until these synapses have recovered. These findings raise the possibility that burst timing can be described in terms of the probability of recovery of this population of synapses. Here we demonstrate that when neuronal excitability is changed in the CA3 network, the mean and variance of the interburst interval change in a manner that is consistent with a timing mechanism comprised of a pool of exponentially relaxing pacemakers. The relaxation time constant of these pacemakers is the same as the time constant describing the recovery from activity-dependent depression of recurrent collateral synapses. Recovery was estimated from the rate of spontaneous transmitter release versus time elapsed since the last CA3 burst. Pharmacological and long-term alterations of synaptic strength and network excitability affected CA3 burst timing as predicted by the cumulative binomial distribution if the burst pace-maker consists of a pool of recovering recurrent synapses. These findings indicate that the recovery of a pool of synapses from burst-induced depression is a sufficient explanation for burst timing in the in vitro CA3 neuronal network. These findings also demonstrate how information regarding the nature of a pacemaker can be derived from the temporal pattern of synchronous network activity. This information could also be extracted from less accessible networks such as those generating interictal epileptiform discharges in vivo.

scholarly journals MEF2C regulates cortical inhibitory and excitatory synapses and behaviors relevant to neurodevelopmental disorders

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Adam J Harrington ◽  
Aram Raissi ◽  
Kacey Rajkovich ◽  
Stefano Berto ◽  
Jaswinder Kumar ◽  
...  
Keyword(s):  
Genetic Variants ◽  
Neurodevelopmental Disorders ◽  
Network Activity ◽  
Excitatory Synapses ◽  
Dramatic Reduction ◽  
Excitatory Neurons ◽  
Synapse Density ◽  
A Cell ◽  
Differential Gene

Numerous genetic variants associated with MEF2C are linked to autism, intellectual disability (ID) and schizophrenia (SCZ) – a heterogeneous collection of neurodevelopmental disorders with unclear pathophysiology. MEF2C is highly expressed in developing cortical excitatory neurons, but its role in their development remains unclear. We show here that conditional embryonic deletion of Mef2c in cortical and hippocampal excitatory neurons (Emx1-lineage) produces a dramatic reduction in cortical network activity in vivo, due in part to a dramatic increase in inhibitory and a decrease in excitatory synaptic transmission. In addition, we find that MEF2C regulates E/I synapse density predominantly as a cell-autonomous, transcriptional repressor. Analysis of differential gene expression in Mef2c mutant cortex identified a significant overlap with numerous synapse- and autism-linked genes, and the Mef2c mutant mice displayed numerous behaviors reminiscent of autism, ID and SCZ, suggesting that perturbing MEF2C function in neocortex can produce autistic- and ID-like behaviors in mice.

scholarly journals Inhibitory Effects of a Reengineered Anthrax Toxin on Canine Oral Mucosal Melanomas

Toxins ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 157 ◽  
Author(s):  
Adriana Tomoko Nishiya ◽  
Marcia Kazumi Nagamine ◽  
Ivone Izabel Mackowiak da Fonseca ◽  
Andrea Caringi Miraldo ◽  
Nayra Villar Scattone ◽  
...  
Keyword(s):  
Tumor Cells ◽  
Evaluation Criteria ◽  
Anthrax Toxin ◽  
Treatment Modalities ◽  
Inhibitory Effects ◽  
Upa Receptor ◽  
New Treatment ◽  
Oral Malignancy

Canine oral mucosal melanomas (OMM) are the most common oral malignancy in dogs and few treatments are available. Thus, new treatment modalities are needed for this disease. Bacillus anthracis (anthrax) toxin has been reengineered to target tumor cells that express urokinase plasminogen activator (uPA) and metalloproteinases (MMP-2), and has shown antineoplastic effects both, in vitro and in vivo. This study aimed to evaluate the effects of a reengineered anthrax toxin on canine OMM. Five dogs bearing OMM without lung metastasis were included in the clinical study. Tumor tissue was analyzed by immunohistochemistry for expression of uPA, uPA receptor, MMP-2, MT1-MMP and TIMP-2. Animals received either three or six intratumoral injections of the reengineered anthrax toxin prior to surgical tumor excision. OMM samples from the five dogs were positive for all antibodies. After intratumoral treatment, all dogs showed stable disease according to the canine Response Evaluation Criteria in Solid Tumors (cRECIST), and tumors had decreased bleeding. Histopathology has shown necrosis of tumor cells and blood vessel walls after treatment. No significant systemic side effects were noted. In conclusion, the reengineered anthrax toxin exerted inhibitory effects when administered intratumorally, and systemic administration of this toxin is a promising therapy for canine OMM.

Dementia with Lewy bodies—associated ß-synuclein mutations V70M and P123H cause mutation-specific neuropathological lesions

2021 ◽  
Author(s):  
Maryna Psol ◽  
Sofia Guerin Darvas ◽  
Kristian Leite ◽  
Sameehan U Mahajani ◽  
Mathias Bähr ◽  
...  
Keyword(s):  
Neuronal Network ◽  
Dementia With Lewy Bodies ◽  
Lewy Bodies ◽  
Sporadic Case ◽  
Network Activity ◽  
Proteinase K ◽  
Neuronal Network Activity ◽  
Distinct Disease

Abstract ß-Synuclein (ß-Syn) has long been considered to be an attenuator for the neuropathological effects caused by the Parkinson’s disease-related α-Synuclein (α-Syn) protein. However, recent studies demonstrated that overabundant ß-Syn can form aggregates and induce neurodegeneration in CNS neurons in vitro and in vivo, albeit at a slower pace as compared to α-Syn. Here we demonstrate that ß-Syn mutants V70M, detected in a sporadic case of Dementia with Lewy Bodies (DLB), and P123H, detected in a familial case of DLB, robustly aggravate the neurotoxic potential of ß-Syn. Intriguingly, the two mutations trigger mutually exclusive pathways. ß-Syn V70M enhances morphological mitochondrial deterioration and degeneration of dopaminergic and non-dopaminergic neurons, but has no influence on neuronal network activity. Conversely, ß-Syn P123H silences neuronal network activity, but does not aggravate neurodegeneration. ß-Syn WT, V70M and P123H formed proteinase K (PK) resistant intracellular fibrils within neurons, albeit with less stable C-termini as compared to α-Syn. Under cell free conditions, ß-Syn V70M demonstrated a much slower pace of fibril formation as compared to WT ß-Syn, and P123H fibrils present with a unique phenotype characterized by large numbers of short, truncated fibrils. Thus, it is possible that V70M and P123H cause structural alterations in ß-Syn, that are linked to their distinct neuropathological profiles. The extent of the lesions caused by these neuropathological profiles is almost identical to that of overabundant α-Syn, and thus likely to be directly involved into etiology of DLB. Over all, this study provides insights into distinct disease mechanisms caused by mutations of ß-Syn.

scholarly journals YAP1 overexpression contributes to the development of enzalutamide resistance by induction of cancer stemness and lipid metabolism in prostate cancer

Oncogene ◽  
2021 ◽  
Author(s):  
Hsiu-Chi Lee ◽  
Chien-Hui Ou ◽  
Yun-Chen Huang ◽  
Pei-Chi Hou ◽  
Chad J. Creighton ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Lipid Metabolism ◽  
Critical Issue ◽  
Castration Resistant Prostate Cancer ◽  
Cancer Stemness ◽  
New Treatment ◽  
Underlying Mechanisms ◽  
Transcriptional Complex

AbstractMetastatic castration-resistant prostate cancer (mCRPC) is a malignant and lethal disease caused by relapse after androgen-deprivation (ADT) therapy. Since enzalutamide is innovated and approved by US FDA as a new treatment option for mCRPC patients, drug resistance for enzalutamide is a critical issue during clinical usage. Although several underlying mechanisms causing enzalutamide resistance were previously identified, most of them revealed that drug resistant cells are still highly addicted to androgen and AR functions. Due to the numerous physical functions of AR in men, innovated AR-independent therapy might alleviate enzalutamide resistance and prevent production of adverse side effects. Here, we have identified that yes-associated protein 1 (YAP1) is overexpressed in enzalutamide-resistant (EnzaR) cells. Furthermore, enzalutamide-induced YAP1 expression is mediated through the function of chicken ovalbumin upstream promoter transcription factor 2 (COUP-TFII) at the transcriptional and the post-transcriptional levels. Functional analyses reveal that YAP1 positively regulates numerous genes related to cancer stemness and lipid metabolism and interacts with COUP-TFII to form a transcriptional complex. More importantly, YAP1 inhibitor attenuates the growth and cancer stemness of EnzaR cells in vitro and in vivo. Finally, YAP1, COUP-TFII, and miR-21 are detected in the extracellular vesicles (EVs) isolated from EnzaR cells and sera of patients. In addition, treatment with EnzaR-EVs induces the abilities of cancer stemness, lipid metabolism and enzalutamide resistance in its parental cells. Taken together, these results suggest that YAP1 might be a crucial factor involved in the development of enzalutamide resistance and can be an alternative therapeutic target in prostate cancer.

scholarly journals Aη-α and Aη-β peptides impair LTP ex vivo within the low nanomolar range and impact neuronal activity in vivo

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Maria Mensch ◽  
Jade Dunot ◽  
Sandy M. Yishan ◽  
Samuel S. Harris ◽  
Aline Blistein ◽  
...  
Keyword(s):  
Neuronal Activity ◽  
Ex Vivo ◽  
Long Term Potentiation ◽  
Network Activity ◽  
Strongly Correlated ◽  
App Processing ◽  
Term Potentiation ◽  
Hippocampal Network

Abstract Background Amyloid precursor protein (APP) processing is central to Alzheimer’s disease (AD) etiology. As early cognitive alterations in AD are strongly correlated to abnormal information processing due to increasing synaptic impairment, it is crucial to characterize how peptides generated through APP cleavage modulate synapse function. We previously described a novel APP processing pathway producing η-secretase-derived peptides (Aη) and revealed that Aη–α, the longest form of Aη produced by η-secretase and α-secretase cleavage, impaired hippocampal long-term potentiation (LTP) ex vivo and neuronal activity in vivo. Methods With the intention of going beyond this initial observation, we performed a comprehensive analysis to further characterize the effects of both Aη-α and the shorter Aη-β peptide on hippocampus function using ex vivo field electrophysiology, in vivo multiphoton calcium imaging, and in vivo electrophysiology. Results We demonstrate that both synthetic peptides acutely impair LTP at low nanomolar concentrations ex vivo and reveal the N-terminus to be a primary site of activity. We further show that Aη-β, like Aη–α, inhibits neuronal activity in vivo and provide confirmation of LTP impairment by Aη–α in vivo. Conclusions These results provide novel insights into the functional role of the recently discovered η-secretase-derived products and suggest that Aη peptides represent important, pathophysiologically relevant, modulators of hippocampal network activity, with profound implications for APP-targeting therapeutic strategies in AD.

scholarly journals The Ncoa7 locus regulates V-ATPase formation and function, neurodevelopment and behaviour

2020 ◽  
Author(s):  
Enrico Castroflorio ◽  
Joery den Hoed ◽  
Daria Svistunova ◽  
Mattéa J. Finelli ◽  
Alberto Cebrian-Serrano ◽  
...  
Keyword(s):  
Neurodevelopmental Disorders ◽  
Regulatory Protein ◽  
Molecular Function ◽  
Neuronal Connectivity ◽  
Nuclear Receptor Coactivator ◽  
Lysm Domain ◽  
Behavioural Assessment ◽  
And Function ◽  
The Brain

Abstract Members of the Tre2/Bub2/Cdc16 (TBC), lysin motif (LysM), domain catalytic (TLDc) protein family are associated with multiple neurodevelopmental disorders, although their exact roles in disease remain unclear. For example, nuclear receptor coactivator 7 (NCOA7) has been associated with autism, although almost nothing is known regarding the mode-of-action of this TLDc protein in the nervous system. Here we investigated the molecular function of NCOA7 in neurons and generated a novel mouse model to determine the consequences of deleting this locus in vivo. We show that NCOA7 interacts with the cytoplasmic domain of the vacuolar (V)-ATPase in the brain and demonstrate that this protein is required for normal assembly and activity of this critical proton pump. Neurons lacking Ncoa7 exhibit altered development alongside defective lysosomal formation and function; accordingly, Ncoa7 deletion animals exhibited abnormal neuronal patterning defects and a reduced expression of lysosomal markers. Furthermore, behavioural assessment revealed anxiety and social defects in mice lacking Ncoa7. In summary, we demonstrate that NCOA7 is an important V-ATPase regulatory protein in the brain, modulating lysosomal function, neuronal connectivity and behaviour; thus our study reveals a molecular mechanism controlling endolysosomal homeostasis that is essential for neurodevelopment. Graphic abstract

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