Ankyrin-R Links Kv3.3 to the Spectrin Cytoskeleton and Is Required for Purkinje Neuron Survival

Unveiling DNA methylation in Alzheimer's disease: a review of array-based human brain studies

The intricacies of Alzheimer's disease pathogenesis are being increasingly illuminated by the exploration of epigenetic mechanisms, particularly DNA methylation. This review comprehensively surveys recent human-centered studies that investigate whole genome DNA methylation in Alzheimer's disease neuropathology. The examination of various brain regions reveals distinctive DNA methylation patterns that associate with the Braak stage and Alzheimer's disease progression. The entorhinal cortex emerges as a focal point due to its early histological alterations and subsequent impact on downstream regions like the hippocampus. Notably, ANK1 hypermethylation, a protein implicated in neurofibrillary tangle formation, was recurrently identified in the entorhinal cortex. Further, the middle temporal gyrus and prefrontal cortex were shown to exhibit significant hypermethylation of genes like HOXA3, RHBDF2, and MCF2L, potentially influencing neuroinflammatory processes. The complex role of BIN1 in late-onset Alzheimer's disease is underscored by its association with altered methylation patterns. Despite the disparities across studies, these findings highlight the intricate interplay between epigenetic modifications and Alzheimer's disease pathology. Future research efforts should address methodological variations, incorporate diverse cohorts, and consider environmental factors to unravel the nuanced epigenetic landscape underlying Alzheimer's disease progression.

Age-dependent regulation of axoglial interactions and behavior by oligodendrocyte AnkyrinG

The bipolar disorder (BD) risk gene ANK3 encodes the scaffolding protein AnkyrinG (AnkG). In neurons, AnkG regulates polarity and ion channel clustering at axon initial segments and nodes of Ranvier. Disruption of neuronal AnkG causes BD-like phenotypes in mice. During development, AnkG is also expressed at comparable levels in oligodendrocytes and facilitates the efficient assembly of paranodal junctions. However, the physiological roles of glial AnkG in the mature nervous system, and its contributions to BD-like phenotypes, remain unexplored. Here, we generated oligodendroglia-specific AnkG conditional knockout mice and observed the destabilization of axoglial interactions in aged but not young adult mice. In addition, these mice exhibited profound histological, electrophysiological, and behavioral pathophysiologies. Unbiased translatomic profiling revealed potential compensatory machineries. These results highlight the critical functions of glial AnkG in maintaining proper axoglial interactions throughout aging and suggests a previously unrecognized contribution of oligodendroglial AnkG to neuropsychiatric disorders.

Native-state proteomics of Parvalbumin interneurons identifies unique molecular signatures and vulnerabilities to early Alzheimer's pathology

Dysfunction in fast-spiking parvalbumin interneurons (PV-INs) may represent an early pathophysiological perturbation in Alzheimer's Disease (AD). Defining early proteomic alterations in PV-INs can provide key biological and translationally-relevant insights. We used cell-type-specific in-vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state PV-IN proteomes. PV-IN proteomic signatures include high metabolic and translational activity, with over-representation of AD-risk and cognitive resilience-related proteins. In bulk proteomes, PV-IN proteins were associated with cognitive decline in humans, and with progressive neuropathology in humans and the 5xFAD mouse model of Aβ pathology. PV-IN CIBOP in early stages of Aβ pathology revealed signatures of increased mitochondria and metabolism, synaptic and cytoskeletal disruption and decreased mTOR signaling, not apparent in whole-brain proteomes. Furthermore, we demonstrated pre-synaptic defects in PV-to-excitatory neurotransmission, validating our proteomic findings. Overall, in this study we present native-state proteomes of PV-INs, revealing molecular insights into their unique roles in cognitive resiliency and AD pathogenesis.

Widespread alternative splicing dysregulation occurs presymptomatically in CAG expansion spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are a group of dominantly inherited neurodegenerative diseases, several of which are caused by CAG expansion mutations (SCAs 1, 2, 3, 6, 7 and 12) and more broadly belong to the large family of over 40 microsatellite expansion diseases. While dysregulation of alternative splicing is a well defined driver of disease pathogenesis across several microsatellite diseases, the contribution of alternative splicing in CAG expansion SCAs is poorly understood. Furthermore, despite extensive studies on differential gene expression, there remains a gap in our understanding of presymptomatic transcriptomic drivers of disease. We sought to address these knowledge gaps through a comprehensive study of 29 publicly available RNA-sequencing datasets. We identified that dysregulation of alternative splicing is widespread across CAG expansion mouse models of SCAs 1, 3 and 7. These changes were detected presymptomatically, persisted throughout disease progression, were repeat length-dependent, and were present in brain regions implicated in SCA pathogenesis including the cerebellum, pons and medulla. Across disease progression, changes in alternative splicing occurred in genes that function in pathways and processes known to be impaired in SCAs, such as ion channels, synaptic signalling, transcriptional regulation and the cytoskeleton. We validated several key alternative splicing events with known functional consequences, including Trpc3 exon 9 and Kcnma1 exon 23b, in the Atxn1154Q/2Q mouse model. Finally, we demonstrated that alternative splicing dysregulation is responsive to therapeutic intervention in CAG expansion SCAs with Atxn1 targeting antisense oligonucleotide rescuing key splicing events. Taken together, these data demonstrate that widespread presymptomatic dysregulation of alternative splicing in CAG expansion SCAs may contribute to disease onset, early neuronal dysfunction and may represent novel biomarkers across this devastating group of neurodegenerative disorders.

Cerebellar dysfunction in rodent models with dystonia, tremor, and ataxia

Dystonia is a movement disorder characterized by involuntary co- or over-contractions of the muscles, which results in abnormal postures and movements. These symptoms arise from the pathophysiology of a brain-wide dystonia network. There is mounting evidence suggesting that the cerebellum is a central node in this network. For example, manipulations that target the cerebellum cause dystonic symptoms in mice, and cerebellar neuromodulation reduces these symptoms. Although numerous findings provide insight into dystonia pathophysiology, they also raise further questions. Namely, how does cerebellar pathophysiology cause the diverse motor abnormalities in dystonia, tremor, and ataxia? Here, we describe recent work in rodents showing that distinct cerebellar circuit abnormalities could define different disorders and we discuss potential mechanisms that determine the behavioral presentation of cerebellar diseases.

Transcriptomic cytoarchitecture reveals principles of human neocortex organization

Variation in cytoarchitecture is the basis for the histological definition of cortical areas. We used single cell transcriptomics and performed cellular characterization of the human cortex to better understand cortical areal specialization. Single-nucleus RNA-sequencing of 8 areas spanning cortical structural variation showed a highly consistent cellular makeup for 24 cell subclasses. However, proportions of excitatory neuron subclasses varied substantially, likely reflecting differences in connectivity across primary sensorimotor and association cortices. Laminar organization of astrocytes and oligodendrocytes also differed across areas. Primary visual cortex showed characteristic organization with major changes in the excitatory to inhibitory neuron ratio, expansion of layer 4 excitatory neurons, and specialized inhibitory neurons. These results lay the groundwork for a refined cellular and molecular characterization of human cortical cytoarchitecture and areal specialization.

Increased Actin Binding Is a Shared Molecular Consequence of Numerous SCA5 Mutations in β-III-Spectrin

Spinocerebellar ataxia type 5 (SCA5) is a neurodegenerative disease caused by mutations in the SPTBN2 gene encoding the cytoskeletal protein β-III-spectrin. Previously, we demonstrated that a L253P missense mutation, localizing to the β-III-spectrin actin-binding domain (ABD), causes increased actin-binding affinity. Here we investigate the molecular consequences of nine additional ABD-localized, SCA5 missense mutations: V58M, K61E, T62I, K65E, F160C, D255G, T271I, Y272H, and H278R. We show that all of the mutations, similar to L253P, are positioned at or near the interface of the two calponin homology subdomains (CH1 and CH2) comprising the ABD. Using biochemical and biophysical approaches, we demonstrate that the mutant ABD proteins can attain a well-folded state. However, thermal denaturation studies show that all nine mutations are destabilizing, suggesting a structural disruption at the CH1-CH2 interface. Importantly, all nine mutations cause increased actin binding. The mutant actin-binding affinities vary greatly, and none of the nine mutations increase actin-binding affinity as much as L253P. ABD mutations causing high-affinity actin binding, with the notable exception of L253P, appear to be associated with an early age of symptom onset. Altogether, the data indicate that increased actin-binding affinity is a shared molecular consequence of numerous SCA5 mutations, which has important therapeutic implications.

Native-state proteomics of Parvalbumin interneurons identifies novel molecular signatures and metabolic vulnerabilities to early Alzheimer's disease pathology

One of the earliest pathophysiological perturbations in Alzheimer's Disease (AD) may arise from dysfunction of fast-spiking parvalbumin (PV) interneurons (PV-INs). Defining early protein-level (proteomic) alterations in PV-INs can provide key biological and translationally relevant insights. Here, we use cell-type-specific in vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state proteomes of PV interneurons. PV-INs exhibited proteomic signatures of high metabolic, mitochondrial, and translational activity, with over-representation of causally linked AD genetic risk factors. Analyses of bulk brain proteomes indicated strong correlations between PV-IN proteins with cognitive decline in humans, and with progressive neuropathology in humans and mouse models of Aβ pathology. Furthermore, PV-IN-specific proteomes revealed unique signatures of increased mitochondrial and metabolic proteins, but decreased synaptic and mTOR signaling proteins in response to early Aβ pathology. PV-specific changes were not apparent in whole-brain proteomes. These findings showcase the first native state PV-IN proteomes in mammalian brain, revealing a molecular basis for their unique vulnerabilities in AD.

Increased actin binding is a shared molecular consequence of numerous spinocerebellar ataxia mutations in β-III-spectrin

Spinocerebellar ataxia type 5 (SCA5) is a neurodegenerative disease caused by mutations in the SPTBN2 gene encoding the cytoskeletal protein β-III-spectrin. Previously, we demonstrated that a L253P missense mutation, localizing to the β-III-spectrin actin-binding domain (ABD), causes increased actin-binding affinity. Here we investigate the molecular consequences of nine additional ABD-localized, SCA5 missense mutations: V58M, K61E, T62I, K65E, F160C, D255G, T271I, Y272H, and H278R. We show that all of the mutations, similar to L253P, are positioned at or near the interface of the two calponin homology subdomains (CH1 and CH2) comprising the ABD. Using biochemical and biophysical approaches, we demonstrate that the mutant ABD proteins can attain a well-folded state. However, thermal denaturation studies show that all nine mutations are destabilizing, suggesting a structural disruption at the CH1-CH2 interface. Importantly, all nine mutations cause increased actin binding. The mutant actin-binding affinities vary greatly, and none of the nine mutations increase actin-binding affinity as much as L253P. ABD mutations causing high-affinity actin binding, with the notable exception of L253P, appear to be associated with early age of symptom onset. Altogether, the data indicate increased actin-binding affinity is a shared molecular consequence of numerous SCA5 mutations, which has important therapeutic implications.

Pleiotropic Ankyrins: Scaffolds for Ion Channels and Transporters

The ankyrin proteins (Ankyrin-R, Ankyrin-B, and Ankyrin-G) are a family of scaffolding, or membrane adaptor proteins necessary for the regulation and targeting of several types of ion channels and membrane transporters throughout the body. These include voltage-gated sodium, potassium, and calcium channels in the nervous system, heart, lungs, and muscle. At these sites, ankyrins recruit ion channels, and other membrane proteins, to specific subcellular domains, which are then stabilized through ankyrin's interaction with the submembranous spectrin-based cytoskeleton. Several recent studies have expanded our understanding of both ankyrin expression and their ion channel binding partners. This review provides an updated overview of ankyrin proteins and their known channel and transporter interactions. We further discuss several potential avenues of future research that would expand our understanding of these important organizational proteins.

Influence of data sampling methods on the representation of neural spiking activity in vivo

In vivo single-unit recordings distinguish the basal spiking properties of neurons in different experimental settings and disease states. Here, we examined over 300 spike trains recorded from Purkinje cells and cerebellar nuclei neurons to test whether data sampling approaches influence the extraction of rich descriptors of firing properties. Our analyses included neurons recorded in awake and anesthetized control mice, and disease models of ataxia, dystonia, and tremor. We find that recording duration circumscribes overall representations of firing rate and pattern. Notably, shorter recording durations skew estimates for global firing rate variability toward lower values. We also find that only some populations of neurons in the same mouse are more similar to each other than to neurons recorded in different mice. These data reveal that recording duration and approach are primary considerations when interpreting task-independent single neuron firing properties. If not accounted for, group differences may be concealed or exaggerated.

Research Hotspots and Trends of Peripheral Nerve Injuries Based on Web of Science From 2017 to 2021: A Bibliometric Analysis

Background

Peripheral nerve injury (PNI) is very common in clinical practice, which often reduces the quality of life of patients and imposes a serious medical burden on society. However, to date, there have been no bibliometric analyses of the PNI field from 2017 to 2021. This study aimed to provide a comprehensive overview of the current state of research and frontier trends in the field of PNI research from a bibliometric perspective.

Methods

Articles and reviews on PNI from 2017 to 2021 were extracted from the Web of Science database. An online bibliometric platform, CiteSpace, and VOSviewer software were used to generate viewable views and perform co-occurrence analysis, co-citation analysis, and burst analysis. The quantitative indicators such as the number of publications, citation frequency, h-index, and impact factor of journals were analyzed by using the functions of “Create Citation Report” and “Journal Citation Reports” in Web of Science Database and Excel software.

Results

A total of 4,993 papers was identified. The number of annual publications in the field remained high, with an average of more than 998 publications per year. The number of citations increased year by year, with a high number of 22,272 citations in 2021. The United States and China had significant influence in the field. Johns Hopkins University, USA had a leading position in this field. JESSEN KR and JOURNAL OF NEUROSCIENCE were the most influential authors and journals in the field, respectively. Meanwhile, we found that hot topics in the field of PNI focused on dorsal root ganglion (DRG) and satellite glial cells (SGCs) for neuropathic pain relief and on combining tissue engineering techniques and controlling the repair Schwann cell phenotype to promote nerve regeneration, which are not only the focus of research now but is also forecast to be of continued focus in the future.

Conclusion

This is the first study to conduct a comprehensive bibliometric analysis of publications related to PNI from 2017 to 2021, whose bibliometric results can provide a reliable source for researchers to quickly understand key information in this field and identify potential research frontiers and hot directions.

Kv3.3 subunits control presynaptic action potential waveform and neurotransmitter release at a central excitatory synapse

Kv3 potassium currents mediate rapid repolarisation of action potentials (APs), supporting fast spikes and high repetition rates. Of the four Kv3 gene family members, Kv3.1 and Kv3.3 are highly expressed in the auditory brainstem and we exploited this to test for subunit-specific roles at the calyx of Held presynaptic terminal in the mouse. Deletion of Kv3.3 (but not Kv3.1) reduced presynaptic Kv3 channel immunolabelling, increased presynaptic AP duration and facilitated excitatory transmitter release; which in turn enhanced short-term depression during high-frequency transmission. The response to sound was delayed in the Kv3.3KO, with higher spontaneous and lower evoked firing, thereby reducing signal-to-noise ratio. Computational modelling showed that the enhanced EPSC and short-term depression in the Kv3.3KO reflected increased vesicle release probability and accelerated activity-dependent vesicle replenishment. We conclude that Kv3.3 mediates fast repolarisation for short precise APs, conserving transmission during sustained high-frequency activity at this glutamatergic excitatory synapse.