Dendritic Spine Pathology in Neurodegenerative Diseases

Lead exposure disrupts cytoskeletal arrangement and perturbs glucose metabolism in nerve cells through activation of the RhoA/ROCK signaling pathway

Lead (Pb) is a heavy metal environmental pollutant with strong biological toxicity. Our previous study suggested that Pb may impair learning and memory by disrupting cytoskeletal structure and inhibiting the expression of synaptic plasticity-related proteins in mice. However, the exact mechanism of Pb-induced cytoskeletal damage remains unclear. In this study, Neuro-2a cells and Kunming mice were used to explore the neurotoxic mechanism of Pb. The actin dynamics were observed via laser confocal microscopy. The ATP levels and ATPase activity in Neuro-2a cells was measured. In addition, the mRNA and protein expression levels of RhoA/ROCK/Cofilin signaling pathway in brain tissues and Neuro-2a cells was measured, and the mRNA expression levels of glucose metabolism rate-limiting enzymes were detected. Our results showed that Pb induces nerve cell damage and cytoskeletal abnormalities. Western blot and qRT-PCR analyses revealed that Pb activated the RhoA/ROCK/Cofilin signaling pathway. Additionally, ATPase activity significantly decreased following Pb treatment, whereas ATP levels markedly increased in the 50 μM Pb group. In addition, Pb disrupts brain glucose metabolism through affect the transcription of rate-limiting enzymes of glucose metabolism. Overall, these findings suggest that Pb activates the RhoA/ROCK/Cofilin signaling pathway, leading to cytoskeletal damage. Moreover, Pb exposure alters glucose metabolism enzyme activity and ATP production, disrupting the balance between F-actin and G-actin and ultimately affecting neuronal structure and function. These results may provide a better understanding of lead-induced nerve damage.

SFRP1 upregulation causes hippocampal synaptic dysfunction and memory impairment

Impaired neuronal and synaptic function are hallmarks of early Alzheimer's disease (AD), preceding other neuropathological traits and cognitive decline. We previously showed that SFRP1, a glial-derived protein elevated in AD brains from preclinical stages, contributes to disease progression, implicating glial factors in early pathogenesis. Here, we generate and analyze transgenic mice overexpressing astrocytic SFRP1. SFRP1 accumulation causes early dendritic and synaptic defects in adult mice, followed by impaired synaptic long-term potentiation and cognitive decline, evident only when the animals age, thereby mimicking AD's structural-functional temporal distinction. This phenotype correlates with proteomic changes, including increased structural synaptic proteins like neurexin, which localizes in close proximity with SFRP1 in cultured hippocampal neurons. We conclude that excessive SFRP1 hinders synaptic protein turnover, reducing synaptic plasticity-a mechanism that may underlie the synaptopathy observed in the brains of prodromal AD patients.

Effect of stress on neuronal cell: Morphological to molecular approach

Stress can be characterized as any perceived or actual threat that necessitates compensatory actions to maintain homeostasis. It can alter an organism's behavior over time by permanently altering the composition and functionality of brain circuitry. The amygdala and prefrontal cortex are two interrelated brain regions that have been the focus of initial research on stress and brain structural and functional plasticity, with the hippocampus serving as the entry point for most of this knowledge. Prolonged stress causes significant morphological alterations in important brain regions such as the hippocampus, amygdala, and prefrontal cortex. Memory, learning, and emotional regulation are among the cognitive functions that are adversely affected by these changes, including neuronal shrinkage, dendritic retraction, and synaptic malfunction. Stress perturbs the equilibrium of neurotransmitters, neuronal plasticity, and mitochondrial function at the molecular level. On the other hand, chronic stress negatively impacts physiology and can result in neuropsychiatric diseases. Recent molecular research has linked various epigenetic processes, such as DNA methylation, histone modifications, and noncoding RNAs, to the dysregulation of genes in the impacted brain circuits responsible for the pathophysiology of chronic stress. Numerous disorders, including neurodegenerative diseases (NDDs) including Alzheimer's, amyotrophic lateral sclerosis, Friedreich's ataxia, Huntington's disease, multiple sclerosis, and Parkinson's disease, have been linked to oxidative stress as a possible cause.

The Role of Autophagy in Excitotoxicity, Synaptic Mitochondrial Stress and Neurodegeneration

Brain and nervous system functions depend upon maintaining the integrity of synaptic structures over the lifetime. Autophagy, a key homeostatic quality control system, plays a central role not only in neuronal development and survival/cell death, but also in regulating synaptic activity and plasticity. Glutamate is the major excitatory neurotransmitter that activates downstream targets, with a key role in learning and memory. However, an excess of glutamatergic stimulation is pathological in stroke, epilepsy and neurodegeneration, triggering excitotoxic cell death or a sublethal process of excitatory mitochondrial calcium toxicity (EMT) that triggers dendritic retraction. Markers of autophagy and mitophagy are often elevated following excitatory neuronal injuries, with the potential to influence cell death or neurodegenerative outcomes of these injuries. Interestingly, leucine-rich repeat kinase 2 (LRRK2) and PTEN-induced kinase 1 (PINK1), two kinases linked to autophagy, mitophagy and Parkinson disease, play important roles in regulating mitochondrial calcium handling, synaptic density and function, and maturation of dendritic spines. Mutations in LRRK2, PINK1, or proteins linked to Alzheimer's disease perturb mitochondrial calcium handling to sensitize neurons to excitatory injury. While autophagy and mitophagy can play both protective and harmful roles, studies in various excitotoxicity and stroke models often implicate autophagy in a pathogenic role. Understanding the role of autophagic degradation in regulating synaptic loss and cell death following excitatory neuronal injuries has important therapeutic implications for both acute and chronic neurological disorders.

RESPAN: A Deep Learning Pipeline for Accurate and Automated Restoration, Segmentation, and Quantification of Dendritic Spines

Quantification of dendritic spines is essential for studying synaptic connectivity, yet most current approaches require manual adjustments or the combination of multiple software tools for optimal results. Here, we present Restoration Enhanced SPine And Neuron Analysis (RESPAN), an open-source pipeline integrating state-of-the-art deep learning for image restoration, segmentation, and analysis in an easily deployable, user-friendly interface. Leveraging content-aware restoration to enhance signal, contrast, and isotropic resolution further enhances RESPAN's robust detection of spines, dendritic branches, and soma across a wide variety of samples, including challenging datasets such as those from live imaging and in vivo 2-photon microscopy with limited signal. Extensive validation against expert annotations and comparison with other software demonstrates RESPAN's superior accuracy and reproducibility across multiple imaging modalities. RESPAN offers significant improvements in usability over currently available approaches, streamlining and democratizing access to a combination of advanced capabilities through an accessible resource for the neuroscience community.

Developmental deficits, synapse and dendritic abnormalities in a Clcn4 KO autism mice model: endophenotypic target for ASD

Autism spectrum disorder (ASD) is linked to ion channel dysfunction, including chloride voltage-gated channel-4 (CLCN4). We generated Clcn4 knockout (KO) mice by deleting exon 5 of chromosome 7 in the C57BL/6 mice. Clcn4 KO exhibited reduced social interaction and increased repetitive behaviors assessed using three-chamber and marble burying tests. Surprisingly, these symptoms were improved by Risperidone treatment, a drug commonly used to treat ASD. RNA sequencing data from mouse neural progenitor cells (mNPCs) showed that the genes regulating trans-synaptic signaling, transmembrane transport, and neuronal projection development were significantly decreased in Clcn4 knockdown (KD) cells compared to wild type (WT). Moreover, Risperidone treatment increased the genes related to the ion transmembrane transport, membrane potential, and neuron projection development in Clcn4 KD. Abnormalities in synaptic plasticity and dendritic spine formation were also observed in Clcn4 KO compared to WT. We observed that phosphorylation of SYNAPSIN, PSD95, ERK and CREB, as well as the expression of CDK5, were reduced in the brains of Clcn4 KO mice. In Clcn4 KO cortical neurons, the phosphorylation of SYNAPSIN and PSD95 expressions also decreased compared to WT, indicating disrupted synaptic function. Additionally, Sholl analysis revealed a reduction in dendritic branching and neuronal projection length in both mouse and human CLCN4 KD neurons. Finally, the decreased phosphorylation of SYNAPSIN and expression of PSD95 along with dendrite abnormalities were restored after Risperidone treatment. These data suggest that dendritic outgrowth and synapse remodeling may serve as endophenotypic targets for drug efficacy in ASD.

Adolescent mice exposed to TBI developed PD-like pathology in middle age

Traumatic brain injury (TBI) is identified as a risk factor for Parkinson's disease (PD), which is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra (SN). However, the precise mechanism by which chronic TBI initiates PD pathogenesis is not yet fully understood. In our present study, we assessed the chronic progression and pathogenesis of PD-like behavior at different intervals in TBI mice. More than half of the mice exhibited PD-like behavior at 6 months post injury. PD-like behavioral dysfunction and pathological changes were aggravated with the injured time extension in chronic phase of TBI. The loss of tyrosine hydroxylase positive (TH+) neurons in the SN were partly associated with the accumulation of misfolded a-Synuclein and the cytoplasmic translocation of TDP-43 from nuclear. Moreover, the present of chronic inflammation was observed in SN of TBI mice, as evidenced by the enhancement of proinflammatory cytokines and reactive astrocytes and microgliosis post lesion. The enhanced phagocytosis of reactive microglia accounted for the reduction of dendrite spines. Our results revealed that chronic inflammation associated with the damage of TH+ neurons and the development of progressive PD-like pathology after chronic TBI in mice. Our study shed new light on the TBI-triggered molecular events on PD-like pathology. Additional research is required to have a deeper understanding of the molecular factors underlying the impairment of dopaminergic neurons following TBI.

The Alzheimer's Disease Risk Gene CD2AP Functions in Dendritic Spines by Remodeling F-Actin

CD2-associated protein (CD2AP) was identified as a genetic risk factor for late-onset Alzheimer's disease (LOAD). However, it is unclear how CD2AP contributes to LOAD synaptic dysfunction underlying AD memory deficits. We have shown that loss of CD2AP function increases β-amyloid (Aβ) endocytic production, but it is unknown whether it contributes to synapse dysfunction. As CD2AP is an actin-binding protein, it may also function in F-actin-rich dendritic spines, which are the excitatory postsynaptic compartments. Here, we demonstrate that CD2AP colocalizes with F-actin in dendritic spines of primary mouse cortical neurons of both sexes. Cell-autonomous depletion of CD2AP specifically reduces spine density and volume, resulting in a functional decrease in synapse formation and neuronal network activity. Postsynaptic reexpression of CD2AP, but not blocking Aβ production, is sufficient to rescue spine density. CD2AP overexpression increases spine density, volume, and synapse formation, while a rare LOAD CD2AP mutation induces aberrant F-actin spine-like protrusions without functional synapses. CD2AP controls postsynaptic actin turnover, with the LOAD mutation in CD2AP decreasing F-actin dynamicity. Our data support that CD2AP risk variants could contribute to LOAD synapse dysfunction by disrupting spine formation and growth by deregulating actin dynamics.

The lemur tail kinase family in neuronal function and disfunction in neurodegenerative diseases

The complex neuronal architecture and the long distance of synapses from the cell body require precisely orchestrated axonal and dendritic transport processes to support key neuronal functions including synaptic signalling, learning and memory formation. Protein phosphorylation is a major regulator of both intracellular transport and synaptic functions. Some kinases and phosphatases such as cyclin dependent kinase-5 (cdk5)/p35, glycogen synthase kinase-3β (GSK3β) and protein phosphatase-1 (PP1) are strongly involved in these processes. A primary pathological hallmark of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis/frontotemporal dementia, is synaptic degeneration together with disrupted intracellular transport. One attractive possibility is that alterations to key kinases and phosphatases may underlie both synaptic and axonal transport damages. The brain enriched lemur tail kinases (LMTKs, formerly known as lemur tyrosine kinases) are involved in intracellular transport and synaptic functions, and are also centrally placed in cdk5/p35, GSK3β and PP1 signalling pathways. Loss of LMTKs is documented in major neurodegenerative diseases and thus can contribute to pathological defects in these disorders. However, whilst function of their signalling partners became clearer in modulating both synaptic signalling and axonal transport progress has only recently been made around LMTKs. In this review, we describe this progress with a special focus on intracellular transport, synaptic functions and neurodegenerative diseases.

Upregulation of cholinergic modulators Lypd6 and Lypd6b associated with autism drives anxiety and cognitive decline

Intellectual disability and autistic features are associated with chromosome region 2q23.q23.2 duplication carrying LYPD6 and LYPD6B genes. Here, we analyzed LYPD6 and LYPD6B expression in patients with different neuropsychiatric disorders. Increased LYPD6 and LYPD6B expression was revealed in autism and other disorders. To study possible consequences of Lypd6 and Lypd6b overexpression in the brain, we used a mouse model with intracerebroventricular delivery of recombinant analogs of these proteins. A two-week infusion evoked significant memory impairment and acute stress. Both modulators downregulated hippocampal and amygdala dendritic spine density. No changes in synaptic plasticity were observed. Intracerebroventricular administration by both proteins downregulated hippocampal expression of Lypd6, Lypd6b, and α7 nicotinic acetylcholine receptor (nAChR). Similar to Lypd6, Lypd6b targeted different nAChR subtypes in the brain with preferential inhibition of α7- and α4β2-nAChRs. Thus, increased Lypd6 and Lypd6b level in the brain are linked to cholinergic system depression, neuronal atrophy, memory decline, and anxiety.

Dendrite injury triggers neuroprotection in Drosophila models of neurodegenerative disease

Dendrite defects and loss are early cellular alterations observed across neurodegenerative diseases that play a role in early disease pathogenesis. Dendrite degeneration can be modeled by expressing pathogenic polyglutamine disease transgenes in Drosophila neurons in vivo. Here, we show that we can protect against dendrite loss in neurons modeling neurodegenerative polyglutamine diseases through injury to a single primary dendrite branch. We find that this neuroprotection is specific to injury-induced activation of dendrite regeneration: neither injury to the axon nor injury just to surrounding tissues induces this response. We show that the mechanism of this regenerative response is stabilization of the actin (but not microtubule) cytoskeleton. We also demonstrate that this regenerative response may extend to other neurodegenerative diseases. Together, we provide evidence that activating dendrite regeneration pathways has the potential to slow-or even reverse-dendrite loss in neurodegenerative disease.

Therapeutic approaches targeting aging and cellular senescence in Huntington's disease

Huntington's disease (HD) is a devastating neurodegenerative disease that is manifested by a gradual loss of physical, cognitive, and mental abilities. As the disease advances, age has a major impact on the pathogenic signature of mutant huntingtin (mHTT) protein aggregation. This review aims to explore the intricate relationship between aging, mHTT toxicity, and cellular senescence in HD. Scientific data on the interplay between aging, mHTT, and cellular senescence in HD were collected from several academic databases, including PubMed, Google Scholar, Google, and ScienceDirect. The search terms employed were "AGING," "HUNTINGTON'S DISEASE," "MUTANT HUNTINGTIN," and "CELLULAR SENESCENCE." Additionally, to gather information on the molecular mechanisms and potential therapeutic targets, the search was extended to include relevant terms such as "DNA DAMAGE," "OXIDATIVE STRESS," and "AUTOPHAGY." According to research, aging leads to worsening HD pathophysiology through some processes. As a result of the mHTT accumulation, cellular senescence is promoted, which causes DNA damage, oxidative stress, decreased autophagy, and increased inflammatory responses. Pro-inflammatory cytokines and other substances are released by senescent cells, which may worsen the neuronal damage and the course of the disease. It has been shown that treatments directed at these pathways reduce some of the HD symptoms and enhance longevity in experimental animals, pointing to a new possibility of treating the condition. Through their amplification of the harmful effects of mHTT, aging and cellular senescence play crucial roles in the development of HD. Comprehending these interplays creates novel opportunities for therapeutic measures targeted at alleviating cellular aging and enhancing HD patients' quality of life.

Ubiquitin ligase RFWD2 promotes dendritic spine and synapse formation by activating the ERK/PEA3/c-Jun pathway in rat cerebral cortical neurons

The regulation of protein degradation through the ubiquitin-proteasome system is essential for normal brain development, axon growth, synaptic growth and plasticity. The E3 ubiquitin ligase RFWD2 plays a key role in the onset and development of neurological diseases, including the pathogenesis of Alzheimer's disease (AD), but the mechanisms controlling the homeostasis of neuronal synaptic proteins are still poorly understood. Here, we showed that the expression level of RFWD2 gradually decreased with the age of the rats and was negatively correlated with the development of cerebral cortical neurons and dendrites in vivo. RFWD2 was shown to localize to presynaptic terminals and some postsynaptic sides of both excitatory synapses and inhibitory synapses via colocalization with neuronal synaptic proteins (SYN, PSD95, Vglut1 and GAD67). Overexpression of RFWD2 promoted dendrite development and dendritic spine formation and markedly decreased the expression of synaptophysin and PSD95 by reducing the expression of ETV1, ETV4, ETV5 and c-JUN in vitro. Furthermore, the whole-cell membrane slice clamp results showed that RFWD2 overexpression resulted in greater membrane capacitance in neuronal cells, inadequate cell repolarization, and a longer time course for neurons to emit action potentials with decreased excitability. RFWD2 regulates dendritic development and plasticity, dendritic spine formation and synaptic function in rat cerebral cortex neurons by activating the ERK/PEA3/c-Jun pathway via a posttranslational regulatory mechanism and can be used as an efficient treatment target for neurological diseases.

MicroRNAs: pioneering regulators in Alzheimer's disease pathogenesis, diagnosis, and therapy

This article delves into Alzheimer's disease (AD), a prevalent neurodegenerative condition primarily affecting the elderly. It is characterized by progressive memory and cognitive impairments, severely disrupting daily life. Recent research highlights the potential involvement of microRNAs in the pathogenesis of AD. MicroRNAs (MiRNAs), short non-coding RNAs comprising 20-24 nucleotides, significantly influence gene regulation by hindering translation or promoting degradation of target genes. This review explores the role of specific miRNAs in AD progression, focusing on their impact on β-amyloid (Aβ) peptide accumulation, intracellular aggregation of hyperphosphorylated tau proteins, mitochondrial dysfunction, neuroinflammation, oxidative stress, and the expression of the APOE4 gene. Our insights contribute to understanding AD's pathology, offering new avenues for identifying diagnostic markers and developing novel therapeutic targets.

Tau-mediated synaptic dysfunction is coupled with HCN channelopathy

INTRODUCTION

In tauopathies, altered tau processing correlates with impairments in synaptic density and function. Changes in hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contribute to disease-associated abnormalities in multiple neurodegenerative diseases.

METHODS

To investigate the link between tau and HCN channels, we performed histological, biochemical, ultrastructural, and functional analyses of hippocampal tissues from Alzheimer's disease (AD), age-matched controls, Tau35 mice, and/or Tau35 primary hippocampal neurons.

RESULTS

Expression of specific HCN channels is elevated in post mortem AD hippocampus. Tau35 mice develop progressive abnormalities including increased phosphorylated tau, enhanced HCN channel expression, decreased dendritic branching, reduced synapse density, and vesicle clustering defects. Tau35 primary neurons show increased HCN channel expression enhanced hyperpolarization-induced membrane voltage "sag" and changes in the frequency and kinetics of spontaneous excitatory postsynaptic currents.

DISCUSSION

Our findings are consistent with a model in which pathological changes in tauopathies impact HCN channels to drive network-wide structural and functional synaptic deficits.

HIGHLIGHTS

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are functionally linked to the development of tauopathy. Expression of specific HCN channels is elevated in the hippocampus in Alzheimer's disease and the Tau35 mouse model of tauopathy. Increased expression of HCN channels in Tau35 mice is accompanied by hyperpolarization-induced membrane voltage "sag" demonstrating a detrimental effect of tau abnormalities on HCN channel function. Tau35 expression alters synaptic organization, causing a loosened vesicle clustering phenotype in Tau35 mice.

Automatic dendritic spine segmentation in widefield fluorescence images reveal synaptic nanostructures distribution with super-resolution imaging

Dendritic spines are the main sites for synaptic communication in neurons, and alterations in their density, size, and shapes occur in many brain disorders. Current spine segmentation methods perform poorly in conditions with low signal-to-noise and resolution, particularly in the widefield images of thick (10 μm) brain slices. Here, we combined two open-source machine-learning models to achieve automatic 3D spine segmentation in widefield diffraction-limited fluorescence images of neurons in thick brain slices. We validated the performance by comparison with manually segmented super-resolution images of spines reconstructed from direct stochastic optical reconstruction microscopy (dSTORM). Lastly, we show an application of our approach by combining spine segmentation from diffraction-limited images with dSTORM of synaptic protein PSD-95 in the same field-of-view. This allowed us to automatically analyze and quantify the nanoscale distribution of PSD-95 inside the spine. Importantly, we found the numbers, but not the average sizes, of synaptic nanomodules and nanodomains increase with spine size.

Repeated diagnostic ultrasound exposure modifies the structural properties of CA1 dendrites and alters the hippocampal transcriptome

The development of neurons is regulated by several spatiotemporally changing factors, which are crucial to give the ability of neurons to form functional networks. While external physical stimuli may impact the early developmental stages of neurons, the medium and long-term consequences of these influences have yet to be thoroughly examined. Using an animal model, this study focuses on the morphological and transcriptome changes of the hippocampus that may occur as a consequence of fetal ultrasound examination. We selectively labeled CA1 neurons of the hippocampus with in-utero electroporation to analyze their morphological features. Furthermore, certain samples also went through RNA sequencing after repetitive ultrasound exposure. US exposure significantly changed several morphological properties of the basal dendritic tree. A notable increase was also observed in the density of spines on the basal dendrites, accompanied by various alterations in individual spine morphology. Transcriptome analysis revealed several up or downregulated genes, which may explain the molecular background of these alterations. Our results suggest that US-derived changes in the dendritic trees of CA1 pyramidal cells might be connected to modification of the transcriptome of the hippocampus and may lead to an increased dendritic input.

Comprehensive software suite for functional analysis and synaptic input mapping of dendritic spines imaged in vivo

Significance

Advances in genetically encoded sensors and two-photon imaging have unlocked functional imaging at the level of single dendritic spines. Synaptic activity can be measured in real time in awake animals. However, tools are needed to facilitate the analysis of the large datasets acquired by the approach. Commonly available software suites for imaging calcium transients in cell bodies are ill-suited for spine imaging as dendritic spines have structural characteristics distinct from those of the cell bodies. We present an automated tuning analysis tool (AUTOTUNE), which provides analysis routines specifically developed for the extraction and analysis of signals from subcellular compartments, including dendritic subregions and spines.

Aim

Although the acquisition of in vivo functional synaptic imaging data is increasingly accessible, a hurdle remains in the computation-heavy analyses of the acquired data. The aim of this study is to overcome this barrier by offering a comprehensive software suite with a user-friendly interface for easy access to nonprogrammers.

Approach

We demonstrate the utility and effectiveness of our software with demo analyses of dendritic imaging data acquired from layer 2/3 pyramidal neurons in mouse V1 in vivo. A user manual and demo datasets are also provided.

Results

AUTOTUNE provides a robust workflow for analyzing functional imaging data from neuronal dendrites. Features include source image registration, segmentation of regions-of-interest and detection of structural turnover, fluorescence transient extraction and smoothing, subtraction of signals from putative backpropagating action potentials, and stimulus and behavioral parameter response tuning analyses.

Conclusions

AUTOTUNE is open-source and extendable for diverse functional synaptic imaging experiments. The ease of functional characterization of dendritic spine activity provided by our software can accelerate new functional studies that complement decades of morphological studies of dendrites, and further expand our understanding of neural circuits in health and in disease.

Stimulating VAPB-PTPIP51 ER-mitochondria tethering corrects FTD/ALS mutant TDP43 linked Ca2+ and synaptic defects

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are clinically linked major neurodegenerative diseases. Notably, TAR DNA-binding protein-43 (TDP43) accumulations are hallmark pathologies of FTD/ALS and mutations in the gene encoding TDP43 cause familial FTD/ALS. There are no cures for FTD/ALS. FTD/ALS display damage to a broad range of physiological functions, many of which are regulated by signaling between the endoplasmic reticulum (ER) and mitochondria. This signaling is mediated by the VAPB-PTPIP51 tethering proteins that serve to recruit regions of ER to the mitochondrial surface so as to facilitate inter-organelle communications. Several studies have now shown that disrupted ER-mitochondria signaling including breaking of the VAPB-PTPIP51 tethers are features of FTD/ALS and that for TDP43 and other familial genetic FTD/ALS insults, this involves activation of glycogen kinase-3β (GSK3β). Such findings have prompted suggestions that correcting damage to ER-mitochondria signaling and the VAPB-PTPIP51 interaction may be broadly therapeutic. Here we provide evidence to support this notion. We show that overexpression of VAPB or PTPIP51 to enhance ER-mitochondria signaling corrects mutant TDP43 induced damage to inositol 1,4,5-trisphosphate (IP3) receptor delivery of Ca2+ to mitochondria which is a primary function of the VAPB-PTPIP51 tethers, and to synaptic function. Moreover, we show that ursodeoxycholic acid (UDCA), an FDA approved drug linked to FTD/ALS and other neurodegenerative diseases therapy and whose precise therapeutic target is unclear, corrects TDP43 linked damage to the VAPB-PTPIP51 interaction. We also show that this effect involves inhibition of TDP43 mediated activation of GSK3β. Thus, correcting damage to the VAPB-PTPIP51 tethers may have therapeutic value for FTD/ALS and other age-related neurodegenerative diseases.

Specific inhibition of TET1 in the spinal dorsal horn alleviates inflammatory pain in mice by regulating synaptic plasticity

DNA demethylation mediated by ten-eleven translocation 1 (TET1) is a critical epigenetic mechanism in which gene expression is regulated via catalysis of 5-methylcytosine to 5-hydroxymethylcytosine. Previously, we demonstrated that TET1 is associated with the genesis of chronic inflammatory pain. However, how TET1 participates in enhanced nociceptive responses in chronic pain remains poorly understood. Here, we report that conditional knockout of Tet1 in dorsal horn neurons via intrathecal injection of rAAV-hSyn-Cre in Tet1fl/fl mice not only reversed the inflammation-induced upregulation of synapse-associated proteins (post-synaptic density protein 95 (PSD95) and synaptophysin (SYP)) in the dorsal horn but also ameliorated abnormalities in dendritic spine morphology and alleviated pain hypersensitivities. Pharmacological blockade of TET1 by intrathecal injection of a TET1-specific inhibitor-Bobcat 339-produced similar results, as did knockdown of Tet1 by intrathecal injection of siRNA. Thus, our data strongly suggest that increased TET1 expression during inflammatory pain upregulates the expression of multiple synapse-associated proteins and dysregulates synaptic morphology in dorsal horn neurons, suggesting that Tet1 may be a potential target for analgesic strategies.

Akt activation ameliorates deficits in hippocampal-dependent memory and activity-dependent synaptic protein synthesis in an Alzheimer's disease mouse model

Protein kinase-B (Akt) and the mechanistic target of rapamycin (mTOR) signaling pathways are implicated in Alzheimer's disease (AD) pathology. Akt/mTOR signaling pathways, activated by external inputs, enable new protein synthesis at the synapse and synaptic plasticity. The molecular mechanisms impeding new protein synthesis at the synapse in AD pathogenesis remain elusive. Here, we aimed to understand the molecular mechanisms prior to the manifestation of histopathological hallmarks by characterizing Akt1/mTOR signaling cascades and new protein synthesis in the hippocampus of WT and amyloid precursor protein/presenilin-1 (APP/PS1) male mice. Intriguingly, compared to those in WT mice, we found significant decreases in pAkt1, pGSK3β, pmTOR, pS6 ribosomal protein, and p4E-BP1 levels in both post nuclear supernatant and synaptosomes isolated from the hippocampus of one-month-old (presymptomatic) APP/PS1 mice. In synaptoneurosomes prepared from the hippocampus of presymptomatic APP/PS1 mice, activity-dependent protein synthesis at the synapse was impaired and this deficit was sustained in young adults. In hippocampal neurons from C57BL/6 mice, downregulation of Akt1 precluded synaptic activity-dependent protein synthesis at the dendrites but not in the soma. In three-month-old APP/PS1 mice, Akt activator (SC79) administration restored deficits in memory recall and activity-dependent synaptic protein synthesis. C57BL/6 mice administered with an Akt inhibitor (MK2206) resulted in memory recall deficits compared to those treated with vehicle. We conclude that dysregulation of Akt1/mTOR and its downstream signaling molecules in the hippocampus contribute to memory recall deficits and loss of activity-dependent synaptic protein synthesis. In AD mice, however, Akt activation ameliorates deficits in memory recall and activity-dependent synaptic protein synthesis.

Overlap in synaptic neurological condition susceptibility pathways and the neural pannexin 1 interactome revealed by bioinformatics analyses

Many neurological conditions exhibit synaptic impairments, suggesting mechanistic convergence. Additionally, the pannexin 1 (PANX1) channel and signaling scaffold is linked to several of these neurological conditions and is an emerging regulator of synaptic development and plasticity; however, its synaptic pathogenic contributions are relatively unexplored. To this end, we explored connections between synaptic neurodevelopmental disorder and neurodegenerative disease susceptibility genes discovered by genome-wide association studies (GWASs), and the neural PANX1 interactome (483 proteins) identified from mouse Neuro2a (N2a) cells. To identify shared susceptibility genes, we compared synaptic suggestive GWAS candidate genes amongst autism spectrum disorders, schizophrenia, Parkinson's disease, and Alzheimer's disease. To further probe PANX1 signaling pathways at the synapse, we used bioinformatics tools to identify PANX1 interactome signaling pathways and protein-protein interaction clusters. To shed light on synaptic disease mechanisms potentially linking PANX1 and these four neurological conditions, we performed additional cross-analyses between gene ontologies enriched for the PANX1 synaptic and disease-susceptibility gene sets. Finally, to explore the regional specificity of synaptic PANX1-neurological condition connections, we identified brain region-specific elevations of synaptic PANX1 interactome and GWAS candidate gene set transcripts. Our results confirm considerable overlap in risk genes for autism spectrum disorders and schizophrenia and identify potential commonalities in genetic susceptibility for neurodevelopmental disorders and neurodegenerative diseases. Our findings also pinpointed novel putative PANX1 links to synaptic disease-associated pathways, such as regulation of vesicular trafficking and proteostasis, warranting further validation.

NOX-induced oxidative stress is a primary trigger of major neurodegenerative disorders

Neurodegenerative diseases (NDDs) causing cognitive impairment and dementia are difficult to treat due to the lack of understanding of primary initiating factors. Meanwhile, major sporadic NDDs share many risk factors and exhibit similar pathologies in their early stages, indicating the existence of common initiation pathways. Glucose hypometabolism associated with oxidative stress is one such primary, early and shared pathology, and a likely major cause of detrimental disease-associated cascades; targeting this common pathology may therefore be an effective preventative strategy for most sporadic NDDs. However, its exact cause and trigger remain unclear. Recent research suggests that early oxidative stress caused by NADPH oxidase (NOX) activation is a shared initiating mechanism among major sporadic NDDs and could prove to be the long-sought ubiquitous NDD trigger. We focus on two major NDDs - Alzheimer's disease (AD) and Parkinson's disease (PD), as well as on acquired epilepsy which is an increasingly recognized comorbidity in NDDs. We also discuss available data suggesting the relevance of the proposed mechanisms to other NDDs. We delve into the commonalities among these NDDs in neuroinflammation and NOX involvement to identify potential therapeutic targets and gain a deeper understanding of the underlying causes of NDDs.

Synaptic Compensatory Plasticity in Alzheimer's Disease

The loss of excitatory synapses is known to underlie the cognitive deficits in Alzheimer's disease (AD). Although much is known about the mechanisms underlying synaptic loss in AD, how neurons compensate for this loss and whether this provides cognitive benefits remain almost completely unexplored. In this review, we describe two potential compensatory mechanisms implemented following synaptic loss: the enlargement of the surviving neighboring synapses and the regeneration of synapses. Because dendritic spines, the postsynaptic site of excitatory synapses, are easily visualized using light microscopy, we focus on a range of microscopy approaches to monitor synaptic loss and compensation. Here, we stress the importance of longitudinal dendritic spine imaging, as opposed to fixed-tissue imaging, to gain insights into the temporal dynamics of dendritic spine compensation. We believe that understanding the molecular mechanisms behind these and other forms of synaptic compensation and regeneration will be critical for the development of therapeutics aiming at delaying the onset of cognitive deficits in AD.

Hippocampal LIMK1-mediated Structural Synaptic Plasticity in Neurobehavioral Deficits Induced by a Low-dose Heavy Metal Mixture

Humans are commonly exposed to the representative neurotoxic heavy metals lead (Pb), cadmium (Cd), and mercury (Hg). These three substances can be detected simultaneously in the blood of the general population. We have previously shown that a low-dose mixture of these heavy metals induces rat learning and memory impairment at human exposure levels, but the pathogenic mechanism is still unclear. LIM kinase 1 (LIMK1) plays a critical role in orchestrating synaptic plasticity during brain function and dysfunction. Hence, we investigated the role of LIMK1 activity in low-dose heavy metal mixture-induced neurobehavioral deficits and structural synaptic plasticity disorders. Our results showed that heavy metal mixture exposure altered rat fear responses and spatial learning at general population exposure levels and that these alterations were accompanied by downregulation of LIMK1 phosphorylation and structural synaptic plasticity dysfunction in rat hippocampal tissues and cultured hippocampal neurons. In addition, upregulation of LIMK1 phosphorylation attenuated heavy metal mixture-induced structural synaptic plasticity, dendritic actin dynamics, and cofilin phosphorylation damage. The potent LIMK1 inhibitor BMS-5 yielded similar results induced by heavy metal mixture exposure and aggravated these impairments. Our findings demonstrate that LIMK1 plays a crucial role in neurobehavioral deficits induced by low-dose heavy metal mixture exposure by suppressing structural synaptic plasticity.

Co-exposure to low-dose lead, cadmium, and mercury promotes memory deficits in rats: Insights from the dynamics of dendritic spine pruning in brain development

Lead (Pb), cadmium (Cd), and mercury (Hg) are environmentally toxic heavy metals that can be simultaneously detected at low levels in the blood of the general population. Although our previous studies have demonstrated neurodevelopmental toxicity upon co-exposure to these heavy metals at these low levels, the precise mechanisms remain largely unknown. Dendritic spines are the structural foundation of memory and undergo significant dynamic changes during development. This study focused on the dynamics of dendritic spines during brain development following Pb, Cd, and Hg co-exposure-induced memory impairment. First, the dynamic characteristics of dendritic spines in the prefrontal cortex were observed throughout the life cycle of normal rats. We observed that dendritic spines increased rapidly from birth to their peak value at weaning, followed by significant pruning and a decrease during adolescence. Dendritic spines tended to be stable until their loss in old age. Subsequently, a rat model of low-dose Pb, Cd, and Hg co-exposure from embryo to adolescence was established. The results showed that exposure to low doses of heavy metals equivalent to those detected in the blood of the general population impaired spatial memory and altered the dynamics of dendritic spine pruning from weaning to adolescence. Proteomic analysis of brain and blood samples suggested that differentially expressed proteins upon heavy metal exposure were enriched in dendritic spine-related cytoskeletal regulation and axon guidance signaling pathways and that cofilin was enriched in both of these pathways. Further experiments confirmed that heavy metal exposure altered actin cytoskeleton dynamics and disturbed the dendritic spine pruning-related LIM domain kinase 1-cofilin pathway in the rat prefrontal cortex. Our findings demonstrate that low-dose Pb, Cd, and Hg co-exposure may promote memory impairment by perturbing dendritic spine dynamics through dendritic spine pruning-related signaling pathways.

The Role of IgLON Cell Adhesion Molecules in Neurodegenerative Diseases

In the brain, cell adhesion molecules (CAMs) are critical for neurite outgrowth, axonal fasciculation, neuronal survival and migration, and synapse formation and maintenance. Among CAMs, the IgLON family comprises five members: Opioid Binding Protein/Cell Adhesion Molecule Like (OPCML or OBCAM), Limbic System Associated Membrane Protein (LSAMP), neurotrimin (NTM), Neuronal Growth Regulator 1 (NEGR1), and IgLON5. IgLONs exhibit three N-terminal C2 immunoglobulin domains; several glycosylation sites; and a glycosylphosphatidylinositol anchoring to the membrane. Interactions as homo- or heterodimers in cis and in trans, as well as binding to other molecules, appear critical for their functions. Shedding by metalloproteases generates soluble factors interacting with cellular receptors and activating signal transduction. The aim of this review was to analyse the available data implicating a role for IgLONs in neuropsychiatric disorders. Starting from the identification of a pathological role for antibodies against IgLON5 in an autoimmune neurodegenerative disease with a poorly understood mechanism of action, accumulating evidence links IgLONs to neuropsychiatric disorders, albeit with still undefined mechanisms which will require future thorough investigations.

SpineTool is an open-source software for analysis of morphology of dendritic spines

Dendritic spines form most excitatory synaptic inputs in neurons and these spines are altered in many neurodevelopmental and neurodegenerative disorders. Reliable methods to assess and quantify dendritic spines morphology are needed, but most existing methods are subjective and labor intensive. To solve this problem, we developed an open-source software that allows segmentation of dendritic spines from 3D images, extraction of their key morphological features, and their classification and clustering. Instead of commonly used spine descriptors based on numerical metrics we used chord length distribution histogram (CLDH) approach. CLDH method depends on distribution of lengths of chords randomly generated within dendritic spines volume. To achieve less biased analysis, we developed a classification procedure that uses machine-learning algorithm based on experts' consensus and machine-guided clustering tool. These approaches to unbiased and automated measurements, classification and clustering of synaptic spines that we developed should provide a useful resource for a variety of neuroscience and neurodegenerative research applications.

Cerebral Semaphorin3D is a novel risk factor for age-associated cognitive impairment

BACKGROUND

We previously reported that miR-195 exerts neuroprotection by inhibiting Sema3A and cerebral miR-195 levels decreased with age, both of which urged us to explore the role of miR-195 and miR-195-regulated Sema3 family members in age-associated dementia.

METHODS

miR-195a KO mice were used to assess the effect of miR-195 on aging and cognitive functions. Sema3D was predicted as a miR-195 target by TargetScan and then verified by luciferase reporter assay, while effects of Sema3D and miR-195 on neural senescence were assessed by beta-galactosidase and dendritic spine density. Cerebral Sema3D was over-expressed by lentivirus and suppressed by si-RNA, and effects of over-expression of Sema3D and knockdown of miR-195 on cognitive functions were assessed by Morris Water Maze, Y-maze, and open field test. The effect of Sema3D on lifespan was assessed in Drosophila. Sema3D inhibitor was developed using homology modeling and virtual screening. One-way and two-way repeated measures ANOVA were applied to assess longitudinal data on mouse cognitive tests.

RESULTS

Cognitive impairment and reduced density of dendritic spine were observed in miR-195a knockout mice. Sema3D was identified to be a direct target of miR-195 and a possible contributor to age-associated neurodegeneration as Sema3D levels showed age-dependent increase in rodent brains. Injection of Sema3D-expressing lentivirus caused significant memory deficits while silencing hippocampal Sema3D improved cognition. Repeated injections of Sema3D-expressing lentivirus to elevate cerebral Sema3D for 10 weeks revealed a time-dependent decline of working memory. More importantly, analysis of the data on the Gene Expression Omnibus database showed that Sema3D levels were significantly higher in dementia patients than normal controls (p < 0.001). Over-expression of homolog Sema3D gene in the nervous system of Drosophila reduced locomotor activity and lifespan by 25%. Mechanistically, Sema3D might reduce stemness and number of neural stem cells and potentially disrupt neuronal autophagy. Rapamycin restored density of dendritic spines in the hippocampus from mice injected with Sema3D lentivirus. Our novel small molecule increased viability of Sema3D-treated neurons and might improve autophagy efficiency, which suggested Sema3D could be a potential drug target. Video Abstract CONCLUSION: Our results highlight the importance of Sema3D in age-associated dementia. Sema3D could be a novel drug target for dementia treatment.

Neurodegeneration and inflammation crosstalk: Therapeutic targets and perspectives

Glia, which was formerly considered to exist just to connect neurons, now plays a key function in a wide range of physiological events, including formation of memory, learning, neuroplasticity, synaptic plasticity, energy consumption, and homeostasis of ions. Glial cells regulate the brain's immune responses and confers nutritional and structural aid to neurons, making them an important player in a broad range of neurological disorders. Alzheimer's, ALS, Parkinson's, frontotemporal dementia (FTD), and epilepsy are a few of the neurodegenerative diseases that have been linked to microglia and astroglia cells, in particular. Synapse growth is aided by glial cell activity, and this activity has an effect on neuronal signalling. Each glial malfunction in diverse neurodegenerative diseases is distinct, and we will discuss its significance in the progression of the illness, as well as its potential for future treatment.

A novel rhein-huprine hybrid ameliorates disease-modifying properties in preclinical mice model of Alzheimer's disease exacerbated with high fat diet

BACKGROUND

Alzheimer's disease (AD) is characterized by a polyetiological origin. Despite the global burden of AD and the advances made in AD drug research and development, the cure of the disease remains elusive, since any developed drug has demonstrated effectiveness to cure AD. Strikingly, an increasing number of studies indicate a linkage between AD and type 2 diabetes mellitus (T2DM), as both diseases share some common pathophysiological features. In fact, β-secretase (BACE1) and acetylcholinesterase (AChE), two enzymes involved in both conditions, have been considered promising targets for both pathologies. In this regard, due to the multifactorial origin of these diseases, current research efforts are focusing on the development of multi-target drugs as a very promising option to derive effective treatments for both conditions. In the present study, we evaluated the effect of rhein-huprine hybrid (RHE-HUP), a synthesized BACE1 and AChE inhibitor, both considered key factors not only in AD but also in metabolic pathologies. Thus, the aim of this study is to evaluate the effects of this compound in APP/PS1 female mice, a well-established familial AD mouse model, challenged by high-fat diet (HFD) consumption to concomitantly simulate a T2DM-like condition.

RESULTS

Intraperitoneal treatment with RHE-HUP in APP/PS1 mice for 4 weeks reduced the main hallmarks of AD, including Tau hyperphosphorylation, Aβ₄₂ peptide levels and plaque formation. Moreover, we found a decreased inflammatory response together with an increase in different synaptic proteins, such as drebrin 1 (DBN1) or synaptophysin, and in neurotrophic factors, especially in BDNF levels, correlated with a recovery in the number of dendritic spines, which resulted in memory improvement. Notably, the improvement observed in this model can be attributed directly to a protein regulation at central level, since no peripheral modification of those alterations induced by HFD consumption was observed.

CONCLUSIONS

Our results suggest that RHE-HUP could be a new candidate for the treatment of AD, even for individuals with high risk due to peripheral metabolic disturbances, given its multi-target profile which allows for the improvement of some of the most important hallmarks of the disease.

NCK1 Modulates Neuronal Actin Dynamics and Promotes Dendritic Spine, Synapse, and Memory Formation

Memory formation and maintenance is a dynamic process involving the modulation of the actin cytoskeleton at synapses. Understanding the signaling pathways that contribute to actin modulation is important for our understanding of synapse formation and function, as well as learning and memory. Here, we focused on the importance of the actin regulator, noncatalytic region of tyrosine kinase adaptor protein 1 (NCK1), in hippocampal dependent behaviors and development. We report that male mice lacking NCK1 have impairments in both short-term and working memory, as well as spatial learning. Additionally, we report sex differences in memory impairment showing that female mice deficient in NCK1 fail at reversal learning in a spatial learning task. We find that NCK1 is expressed in postmitotic neurons but is dispensable for neuronal proliferation and migration in the developing hippocampus. Morphologically, NCK1 is not necessary for overall neuronal dendrite development. However, neurons lacking NCK1 have lower dendritic spine and synapse densities in vitro and in vivo EM analysis reveal increased postsynaptic density (PSD) thickness in the hippocampal CA1 region of NCK1-deficient mice. Mechanistically, we find the turnover of actin-filaments in dendritic spines is accelerated in neurons that lack NCK1. Together, these findings suggest that NCK1 contributes to hippocampal-dependent memory by stabilizing actin dynamics and dendritic spine formation.SIGNIFICANCE STATEMENT Understanding the molecular signaling pathways that contribute to memory formation, maintenance, and elimination will lead to a better understanding of the genetic influences on cognition and cognitive disorders and will direct future therapeutics. Here, we report that the noncatalytic region of tyrosine kinase adaptor protein 1 (NCK1) adaptor protein modulates actin-filament turnover in hippocampal dendritic spines. Mice lacking NCK1 show sex-dependent deficits in hippocampal memory formation tasks, have altered postsynaptic densities, and reduced synaptic density. Together, our work implicates NCK1 in the regulation of actin cytoskeleton dynamics and normal synapse development which is essential for memory formation.

Getting sharper: the brain under the spotlight of super-resolution microscopy

Brain cells such as neurons and astrocytes exhibit an extremely elaborate morphology, and their functional specializations like synapses and glial processes often fall below the resolution limit of conventional light microscopy. This is a huge obstacle for neurobiologists because the nanoarchitecture critically shapes fundamental functions like synaptic transmission and Ca²⁺ signaling. Super-resolution microscopy can overcome this problem, offering the chance to visualize the structural and molecular organization of brain cells in a living and dynamic tissue context, unlike traditional methods like electron microscopy or atomic force microscopy. This review covers the basic principles of the main super-resolution microscopy techniques in use today and explains how their specific strengths can illuminate the nanoscale mechanisms that govern brain physiology.

Dendritic spine loss deep in the neocortex and dendrite distortion with diffusion disturbances occur early in experimental pneumococcal meningitis

Introduction

Streptococcus pneumoniae (pneumococcus) meningitis is a serious disease with substantial lethality and long-term disability in survivors. Loss of synaptic staining in the superficial layers of the neocortex in rodent models and in humans, and pneumolysin (a major pneumococcal toxin)-dependent dendritic spine collapse in brain slices have been described. It remains unclear how deep in the neocortex more discrete changes are present, how soon after disease onset these changes occur, and whether other properties of dendrites are also affected.

Methods

Using a mouse model of pneumococcal meningitis, we studied changes in the neocortex shortly (3-6 h) after the onset of clinical symptoms via modified Golgi-Cox silver staining.

Results

Dendritic changes were present in areas with otherwise unchanged cell numbers and no signs of necrosis or other apparent neuronal pathology. Mature dendritic spines were reduced in the pyramidal neurons running through layers 1-5. Additionally, spine morphology changes (swelling, spine neck distortion), were also observed in the deeper layers 4 and 5 of the neocortex. Immature spines (filopodia) remained unchanged between groups, as well as the dendritic arborization of the analyzed neurons. In a third of the animals with meningitis, massive mechanical distortion of the primary dendrites of most of the pyramidal neurons through layers 1-5 was observed. This distortion was reproduced in acute brain slices after exposure to pneumolysin-containing bacterial lysates (S. pneumoniae D39 strain), but not to lysates of pneumolysin-deficient bacteria, which we explain by the tissue remodeling effect of the toxin. Experimental mechanical dendrite distortion in primary neural cultures demonstrated diminished FRAP diffusion of neuronally-expressed enhanced green fluorescent protein (eGFP), indicative of disturbed dendritic diffusion.

Discussion

Our work extends earlier knowledge of synaptic loss in the superficial cortical layers during meningitis to deeper layers. These changes occurred surprisingly early in the course of the disease, substantially limiting the effective therapeutic window. Methodologically, we demonstrate that the dendritic spine collapse readout is a highly reliable and early marker of neural damage in pneumococcal meningitis models, allowing for reduction of the total number of animals used per a group due to much lower variation among animals.

miR-101a-3p Impairs Synaptic Plasticity and Contributes to Synucleinopathy

BACKGROUND

Synucleinopathies are disorders characterized by the abnormal accumulation of α-synuclein (aSyn). Synaptic compromise is observed in synucleinopathies parallel to aSyn aggregation and is accompanied by transcript deregulation.

OBJECTIVE

We sought to identify microRNAs associated with synaptic processes that may contribute to synaptic dysfunction and degeneration in synucleinopathies.

METHODS

We performed small RNA-sequencing of midbrain from 6-month-old transgenic mice expressing A30P mutant aSyn, followed by comparative expression analysis. We then used real-time quantitative polymerase chain reaction (qPCR) for validation. Functional analysis was performed in primary neurons by biochemical assays and imaging.

RESULTS

We found several deregulated biological processes linked to the synapse. miR-101a-3p was validated as a synaptic miRNA upregulated in aSyn Tg mice and in the cortex of dementia with Lewy bodies patients. Mice and primary cultured neurons overexpressing miR-101a-3p showed downregulation of postsynaptic proteins GABA Ab2 and SAPAP3 and altered dendritic morphology resembling synaptic plasticity impairments and/or synaptic damage. Interestingly, primary cultured neuron exposure to recombinant wild-type aSyn species efficiently increased miR-101a-3p levels. Finally, a dynamic role of miR-101a-3p in synapse plasticity was shown by identifying downregulation of miR-101a-3p in a condition of enhanced synaptic plasticity modelled in Wt animals housed in enriched environment.

CONCLUSION

To conclude, we correlated pathologic aSyn with high levels of miR-101a-3p and a novel dynamic role of the miRNA in synaptic plasticity.

Neural mechanism underlies CYLD modulation of morphology and synaptic function of medium spiny neurons in dorsolateral striatum

Although the deubiquitinase cylindromatosis (CYLD), an abundant protein in the postsynaptic density fraction, plays a crucial role in mediating the synaptic activity of the striatum, the precise molecular mechanism remains largely unclear. Here, using a Cyld-knockout mouse model, we demonstrate that CYLD regulates dorsolateral striatum (DLS) neuronal morphology, firing activity, excitatory synaptic transmission, and plasticity of striatal medium spiny neurons via, likely, interaction with glutamate receptor 1 (GluA1) and glutamate receptor 2 (GluA2), two key subunits of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs). CYLD deficiency reduces levels of GluA1 and GluA2 surface protein and increases K63-linked ubiquitination, resulting in functional impairments both in AMPAR-mediated excitatory postsynaptic currents and in AMPAR-dependent long-term depression. The results demonstrate a functional association of CYLD with AMPAR activity, which strengthens our understanding of the role of CYLD in striatal neuronal activity.

Steroid Hormone Interaction with Dendritic Spines: Implications for Neuropsychiatric Disease

Dendritic spines, key sites for neural plasticity, are influenced by gonadal steroids. In this chapter, we review the effects of gonadal steroids on dendritic spine density in areas important to cognitive function, the hippocampus, and prefrontal cortex. Most of these animal model studies investigated the effects of estrogen in females, but we also include more recent data on androgen effects in both males and females. The underlying genomic and non-genomic mechanisms related to gonadal steroid-induced spinogenesis are also reviewed. Subsequently, we discuss possible reasons for the observed sex differences in many neuropsychiatric diseases, which appear to be caused, in part, by aberrant synaptic connections that may involve dendritic spine pathology. Overall, knowledge concerning the regulation of dendritic spines by gonadal hormones has grown since the initial discoveries in the 1990s, and current research points to a potential role for aberrant spine functioning in many neuropsychiatric disorders.

Morphological Features of Human Dendritic Spines

Dendritic spine features in human neurons follow the up-to-date knowledge presented in the previous chapters of this book. Human dendrites are notable for their heterogeneity in branching patterns and spatial distribution. These data relate to circuits and specialized functions. Spines enhance neuronal connectivity, modulate and integrate synaptic inputs, and provide additional plastic functions to microcircuits and large-scale networks. Spines present a continuum of shapes and sizes, whose number and distribution along the dendritic length are diverse in neurons and different areas. Indeed, human neurons vary from aspiny or "relatively aspiny" cells to neurons covered with a high density of intermingled pleomorphic spines on very long dendrites. In this chapter, we discuss the phylogenetic and ontogenetic development of human spines and describe the heterogeneous features of human spiny neurons along the spinal cord, brainstem, cerebellum, thalamus, basal ganglia, amygdala, hippocampal regions, and neocortical areas. Three-dimensional reconstructions of Golgi-impregnated dendritic spines and data from fluorescence microscopy are reviewed with ultrastructural findings to address the complex possibilities for synaptic processing and integration in humans. Pathological changes are also presented, for example, in Alzheimer's disease and schizophrenia. Basic morphological data can be linked to current techniques, and perspectives in this research field include the characterization of spines in human neurons with specific transcriptome features, molecular classification of cellular diversity, and electrophysiological identification of coexisting subpopulations of cells. These data would enlighten how cellular attributes determine neuron type-specific connectivity and brain wiring for our diverse aptitudes and behavior.

Introduction: What Are Dendritic Spines?

Dendritic spines are cellular specializations that greatly increase the connectivity of neurons and modulate the "weight" of most postsynaptic excitatory potentials. Spines are found in very diverse animal species providing neural networks with a high integrative and computational possibility and plasticity, enabling the perception of sensorial stimuli and the elaboration of a myriad of behavioral displays, including emotional processing, memory, and learning. Humans have trillions of spines in the cerebral cortex, and these spines in a continuum of shapes and sizes can integrate the features that differ our brain from other species. In this chapter, we describe (1) the discovery of these small neuronal protrusions and the search for the biological meaning of dendritic spines; (2) the heterogeneity of shapes and sizes of spines, whose structure and composition are associated with the fine-tuning of synaptic processing in each nervous area, as well as the findings that support the role of dendritic spines in increasing the wiring of neural circuits and their functions; and (3) within the intraspine microenvironment, the integration and activation of signaling biochemical pathways, the compartmentalization of molecules or their spreading outside the spine, and the biophysical properties that can affect parent dendrites. We also provide (4) examples of plasticity involving dendritic spines and neural circuits relevant to species survival and comment on (5) current research advancements and challenges in this exciting research field.

Characterizing Relevant MicroRNA Editing Sites in Parkinson's Disease

MicroRNAs (miRNAs) are extensively edited in human brains. However, the functional relevance of the miRNA editome is largely unknown in Parkinson's disease (PD). By analyzing small RNA sequencing profiles of brain tissues of 43 PD patients and 88 normal controls, we found that the editing levels of five A-to-I and two C-to-U editing sites are significantly correlated with the ages of normal controls, which is disrupted in PD patients. We totally identified 362 miRNA editing sites with significantly different editing levels in prefrontal cortices of PD patients (PD-PC) compared to results of normal controls. We experimentally validated that A-to-I edited miR-497-5p, with significantly higher expression levels in PD-PC compared to normal controls, directly represses OPA1 and VAPB. Furthermore, overexpression of A-to-I edited miR-497-5p downregulates OPA1 and VAPB in two cell lines, and inhibits proliferation of glioma cells. These results suggest that the hyperediting of miR-497-5p in PD contributes to enhanced progressive neurodegeneration of PD patients. Our results provide new insights into the mechanistic understanding, novel diagnostics, and therapeutic clues of PD.

Modulation of striatal glutamatergic, dopaminergic and cholinergic neurotransmission pathways concomitant with motor disturbance in rats with kaolin-induced hydrocephalus

BACKGROUND

Hydrocephalus is characterized by abnormal accumulation of cerebrospinal fluid in the cerebral ventricles and causes motor impairments. The mechanisms underlying the motor changes remain elusive. Enlargement of ventricles compresses the striatum of the basal ganglia, a group of nuclei involved in the subcortical motor circuit. Here, we used a kaolin-injection juvenile rat model to explore the effects of acute and chronic hydrocephalus, 1 and 5 weeks post-treatment, respectively on the three major neurotransmission pathways (glutamatergic, dopaminergic and cholinergic) in the striatum.

METHODS

Rats were evaluated for motor impairments. Expressions of presynaptic and postsynaptic protein markers related to the glutamatergic, dopaminergic, and cholinergic connections in the striatum were evaluated. Combined intracellular dye injection and substance P immunohistochemistry were used to distinguish between direct and indirect pathway striatal medium spiny neurons (d and i-MSNs) for the analysis of their dendritic spine density changes.

RESULTS

Hydrocephalic rats showed compromised open-field gait behavior. However, male but not female rats displayed stereotypic movements and compromised rotarod performance. Morphologically, the increase in lateral ventricle sizes was greater in the chronic than acute hydrocephalus conditions. Biochemically, hydrocephalic rats had significantly decreased striatal levels of synaptophysin, vesicular glutamate transporter 1, and glutamatergic postsynaptic density protein 95, suggesting a reduction of corticostriatal excitation. The expression of GluR2/3 was also reduced suggesting glutamate receptor compositional changes. The densities of dendritic spines, morphological correlates of excitatory synaptic foci, on both d and i-MSNs were also reduced. Hydrocephalus altered type 1 (DR1) and 2 (DR2) dopamine receptor expressions without affecting tyrosine hydroxylase level. DR1 was decreased in acute and chronic hydrocephalus, while DR2 only started to decrease later during chronic hydrocephalus. Since dopamine excites d-MSNs through DR1 and inhibits i-MSNs via DR2, our findings suggest that hydrocephalus downregulated the direct basal ganglia neural pathway persistently and disinhibited the indirect pathway late during chronic hydrocephalus. Hydrocephalus also persistently reduced the striatal choline acetyltransferase level, suggesting a reduction of cholinergic modulation.

CONCLUSIONS

Hydrocephalus altered striatal glutamatergic, dopaminergic, and cholinergic neurotransmission pathways and tipped the balance between the direct and indirect basal ganglia circuits, which could have contributed to the motor impairments in hydrocephalus.

Human cortical amygdala dendrites and spines morphology under open‐source three‐dimensional reconstruction procedures

Visualizing nerve cells has been fundamental for the systematic description of brain structure and function in humans and other species. Different approaches aimed to unravel the morphological features of neuron types and diversity. The inherent complexity of the human nervous tissue and the need for proper histological processing have made studying human dendrites and spines challenging in postmortem samples. In this study, we used Golgi data and open-source software for 3D image reconstruction of human neurons from the cortical amygdaloid nucleus to show different dendrites and pleomorphic spines at different angles. Procedures required minimal equipment and generated high-quality images for differently shaped cells. We used the "single-section" Golgi method adapted for the human brain to engender 3D reconstructed images of the neuronal cell body and the dendritic ramification by adopting a neuronal tracing procedure. In addition, we elaborated 3D reconstructions to visualize heterogeneous dendritic spines using a supervised machine learning-based algorithm for image segmentation. These tools provided an additional upgrade and enhanced visual display of information related to the spatial orientation of dendritic branches and for dendritic spines of varied sizes and shapes in these human subcortical neurons. This same approach can be adapted for other techniques, areas of the central or peripheral nervous system, and comparative analysis between species.

Sagacious confucius’ pillow elixir ameliorates Dgalactose induced cognitive injury in mice via estrogenic effects and synaptic plasticity

Alzheimer’s disease (AD) is a growing concern in modern society, and there is currently a lack of effective therapeutic drugs. Sagacious Confucius’ Pillow Elixir (SCPE) has been studied for the treatment of neurodegenerative diseases such as AD. This study aimed to reveal the key components and mechanisms of SCPE’s anti-AD effect by combining Ultra-high Performance Liquid Chromatography-electrostatic field Orbitrap combined high-resolution Mass Spectrometry (UPLC-LTQ/Orbitrap-MS) with a network pharmacology approach. And the mechanism was verified by in vivo experiments. Based on UPLC-LTQ/Orbitrap-MS technique identified 9 blood components from rat serum containing SCPE, corresponding to 113 anti-AD targets, and 15 of the 113 targets had high connectivity. KEGG pathway enrichment analysis showed that estrogen signaling pathway and synaptic signaling pathway were the most significantly enriched pathways in SCPE anti-AD, which has been proved by in vivo experiments. SCPE can exert estrogenic effects in the brain by increasing the amount of estrogen in the brain and the expression of ERα receptors. SCPE can enhance the synaptic structure plasticity by promoting the release of brain-derived neurotrophic factor (BDNF) secretion and improving actin polymerization and coordinates cofilin activity. In addition, SCPE also enhances synaptic functional plasticity by increasing the density of postsynaptic densified 95 (PSD95) proteins and the expression of functional receptor AMPA. SCPE is effective for treatment of AD and the mechanism is related to increasing estrogenic effects and improving synaptic plasticity. Our study revealed the synergistic effect of SCPE at the system level and showed that SCPE exhibits anti-AD effects in a multi-component, multi-target and multi-pathway manner. All these provide experimental support for the clinical application and drug development of SCPE in the prevention and treatment of AD.

Pridopidine Promotes Synaptogenesis and Reduces Spatial Memory Deficits in the Alzheimer's Disease APP/PS1 Mouse Model

Sigma-1 receptor agonists have recently gained a great deal of interest due to their anti-amnesic, neuroprotective, and neurorestorative properties. Compounds such as PRE-084 or pridopidine (ACR16) are being studied as a potential treatment against cognitive decline associated with neurodegenerative disease, also to include Alzheimer's disease. Here, we performed in vitro experiments using primary neuronal cell cultures from rats to evaluate the abilities of ACR16 and PRE-084 to induce new synapses and spines formation, analyzing the expression of the possible genes and proteins involved. We additionally examined their neuroprotective properties against neuronal death mediated by oxidative stress and excitotoxicity. Both ACR16 and PRE-084 exhibited a concentration-dependent neuroprotective effect against NMDA- and H2O2-related toxicity, in addition to promoting the formation of new synapses and dendritic spines. However, only ACR16 generated dendritic spines involved in new synapse establishment, maintaining a more expanded activation of MAPK/ERK and PI3K/Akt signaling cascades. Consequently, ACR16 was also evaluated in vivo, and a dose of 1.5 mg/kg/day was administered intraperitoneally in APP/PS1 mice before performing the Morris water maze. ACR16 diminished the spatial learning and memory deficits observed in APP/PS1 transgenic mice via PI3K/Akt pathway activation. These data point to ACR16 as a pharmacological tool to prevent synapse loss and memory deficits associated with Alzheimer's disease, due to its neuroprotective properties against oxidative stress and excitotoxicity, as well as the promotion of new synapses and spines through a mechanism that involves AKT and ERK signaling pathways.

Identification of potential key circular RNAs related to cognitive impairment after chronic constriction injury of the sciatic nerve

Chronic neuropathic pain is commonly accompanied by cognitive impairment. However, the underlying mechanism in the occurrence of cognitive deficits under constant nociceptive irritation remains elusive. Herein, we established a chronic neuropathic pain model by chronic constriction injury (CCI) of the unilateral sciatic nerve in rats. Behavioral tests indicated that CCI rats with long-term nociceptive threshold decline developed significant dysfunction of working memory and recognitive memory starting at 14 days and lasting for at least 21 days. Afterward, circRNA expression profiles in the hippocampus of CCI and sham rats were analyzed via high-throughput sequencing to explore the potential key factors associated with cognitive impairment induced by ongoing nociception, which showed 76 differentially expressed circRNAs, 39 upregulated and 37 downregulated, in the CCI group. These differentially expressed circRNA host genes were validated to be primarily associated with inflammation and apoptotic signaling pathways according to GO/KEGG analysis and the circRNA-miRNA-mRNA network, which was also confirmed through the analysis of neuroinflammation and neuronal apoptosis. Consequently, we assumed that enhanced neuroinflammation and neuronal apoptosis might act as potential regulators of cognitive impairment induced by chronic neuropathic pain. The identification of the regulatory mechanism would provide promising clinical biomarkers or therapeutic targets in the diagnostic prediction and intervention treatment of memory deficits under neuropathic pain conditions.

Principles of risk decision-making

Risk management decisions in public health require consideration of a number of complex, often conflicting factors. The aim of this review was to propose a set of 10 fundamental principles to guide risk decision-making. Although each of these principles is sound in its own right, the guidance provided by different principles might lead the decision-maker in different directions. For example, where the precautionary principle advocates for preemptive risk management action under situations of scientific uncertainty and potentially catastrophic consequences, the principle of risk-based decision-making encourages decision-makers to focus on established and modifiable risks, where a return on the investment in risk management is all but guaranteed in the near term. To evaluate the applicability of the 10 principles in practice, one needs to consider 10 diverse risk issues of broad concern and explore which of these principles are most appropriate in different contexts. The 10 principles presented here afford substantive insight into the process of risk management decision-making, although decision-makers will ultimately need to exercise judgment in reaching appropriate risk decisions, accounting for all of the scientific and extra-scientific factors relevant to the risk decision at hand.

Gestational iron supplementation reverses depressive-like behavior in post-partum Sprague Dawley rats: Evidence from behavioral and neurohistological studies

Background

Postpartum depression is a mood disorder that affects about 9–20% of women after child birth. Reports suggest that gestational iron deficiency can cause a deficit in behavioral, cognitive and affective functions and can precipitate depressive symptoms in mothers during the postpartum period. The present study examined the effect of iron supplementation on depressive behavior during postpartum period in a rat model.

Method

Female Sprague-Dawley rats were crossed. Pregnant rats received iron, fluoxetine, desferrioxamine or vehicle throughout the period of gestation. During the postpartum period, mothers from all groups were taken through the open field test (OFT), forced swim test (FST), novelty-induced hypophagia (NIH) and sacrificed for histological examination of the brains.

Results

Results showed that rats treated with iron-chelating agent, desferrioxamine, and vehicle during gestation exhibited increased immobility scores in the FST, increased latency to feed and reduced feeding in the NIH with corresponding decreased number of neurons and dendritic branches in the cortex of the brain. These depression-related effects were attenuated by perinatal iron supplementation which showed decreased immobility scores in the FST comparable to rats treated with fluoxetine, a clinically effective antidepressant. Iron treatment also decreased latency to feeding while increasing feeding behavior in the NIH. Iron-treated dams had a higher number of neurons with dendritic connections in the frontal cortex compared to vehicle- and desferrioxamine-treated groups.

Conclusion

The results suggest that, iron supplementation during gestation exerts an antidepressant-like effect in postpartum Sprague-Dawley rats, attenuates neuronal loss associated with depression and increases dendritic spine density.

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Iron supplementation during gestation exerts an antidepressant-like effect in postpartum Sprague-Dawley rats.

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Iron supplementation during gestation attenuates neuronal loss associated with depression.

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Iron-treated dams had a higher number of neurons with dendritic connections in the frontal cortex.

The prion protein and its ligands: Insights into structure-function relationships

The prion protein is a multifunctional protein that exists in at least two different folding states. It is subject to diverse proteolytic processing steps that lead to prion protein fragments some of which are membrane-bound whereas others are soluble. A multitude of ligands bind to the prion protein and besides proteinaceous binding partners, interaction with metal ions and nucleic acids occurs. Although of great importance, information on structural and functional consequences of prion protein binding to its partners is limited. Here, we will reflect on the structure-function relationship of the prion protein and its binding partners considering the different folding states and prion protein fragments.

Abnormal synaptic plasticity and impaired cognition in schizophrenia

Schizophrenia (SCZ) is a severe mental illness that affects several brain domains with relation to cognition and behaviour. SCZ symptoms are typically classified into three categories, namely, positive, negative, and cognitive. The etiology of SCZ is thought to be multifactorial and poorly understood. Accumulating evidence has indicated abnormal synaptic plasticity and cognitive impairments in SCZ. Synaptic plasticity is thought to be induced at appropriate synapses during memory formation and has a critical role in the cognitive symptoms of SCZ. Many factors, including synaptic structure changes, aberrant expression of plasticity-related genes, and abnormal synaptic transmission, may influence synaptic plasticity and play vital roles in SCZ. In this article, we briefly summarize the morphology of the synapse, the neurobiology of synaptic plasticity, and the role of synaptic plasticity, and review potential mechanisms underlying abnormal synaptic plasticity in SCZ. These abnormalities involve dendritic spines, postsynaptic density, and long-term potentiation-like plasticity. We also focus on cognitive dysfunction, which reflects impaired connectivity in SCZ. Additionally, the potential targets for the treatment of SCZ are discussed in this article. Therefore, understanding abnormal synaptic plasticity and impaired cognition in SCZ has an essential role in drug therapy.

Plasticity-Related Gene 5 Is Expressed in a Late Phase of Neurodifferentiation After Neuronal Cell-Fate Determination

During adult neurogenesis, neuronal stem cells differentiate into mature neurons that are functionally integrated into the existing network. One hallmark during the late phase of this neurodifferentiation process is the formation of dendritic spines. These morphological specialized structures form the basis of most excitatory synapses in the brain, and are essential for neuronal communication. Additionally, dendritic spines are affected in neurological disorders, such as Alzheimer’s disease or schizophrenia. However, the mechanisms underlying spinogenesis, as well as spine pathologies, are poorly understood. Plasticity-related Gene 5 (PRG5), a neuronal transmembrane protein, has previously been linked to spinogenesis in vitro. Here, we analyze endogenous expression of the PRG5 protein in different mouse brain areas, as well as on a subcellular level. We found that native PRG5 is expressed dendritically, and in high abundance in areas characterized by their regenerative capacity, such as the hippocampus and the olfactory bulb. During adult neurogenesis, PRG5 is specifically expressed in a late phase after neuronal cell-fate determination associated with dendritic spine formation. On a subcellular level, we found PRG5 not to be localized at the postsynaptic density, but at the base of the synapse. In addition, we showed that PRG5-induced formation of membrane protrusions is independent from neuronal activity, supporting a possible role in the morphology and stabilization of spines.