Microglia Mediate Early Corticostriatal Synapse Loss and Cognitive Dysfunction in Huntington’s Disease Through Complement-Dependent Mechanisms

Sporadic, late-onset Alzheimer disease (AD) constitutes the most frequent cause of dementia in the elderly population. AD-related pathology is often accompanied by vascular changes. The predominant vascular lesions in AD are cerebral amyloid angiopathy (CAA) and arteriosclerosis/lipohyalinosis (AS/LH). The present study was carried out to examine the coincidence of these small vessel pathologies during the development of cognitive deficits, amyloid beta-protein (A beta) deposition, and neurofibrillary tangle (NFT) formation in sporadic late-onset AD. We correlated the clinical dementia rating (CDR) score, the sequential extension of AD-related A beta deposition into different parts of the brain, and the extension of NFTs to involve more brain regions with the distribution of CAA and AS/LH in 52 human autopsy brains. The extension of CAA and AS/LH to involve different areas of the brain was associated with a rise of CDR scores and an increase in the extension of A beta deposition and NFT generation. AD cases showed a higher number of regions with CAA and AS/LH compared to nondemented patients with AD-related pathology and controls. Moreover, we demonstrated a hierarchical sequence in which the different regions of the brain exhibited CAA and AS/LH-affected vessels, allowing the distinction of 3 stages in the development of CAA and AS/LH. The first stage of CAA involved leptomeningeal and neocortical vessels. The second stage was characterized by additional A beta deposition in allocortical and midbrain vessels. Finally, in a third stage, CAA was observed in the basal ganglia, the thalamus, and in the lower brainstem. In contrast, AS/LH initially affected the basal ganglia in stage A. In stage B this pathology made inroads into the deep white matter, the leptomeningeal arteries of the cortex, the cerebellum, and into the thalamus. Stage C was characterized by AS/LH in brainstem vessels. Our results demonstrate widespread CAA and AS/LH to be associated with the development of cognitive deficits in AD. A combination of both CAA and AS/LH may, therefore, contribute to neurodegeneration in AD. These data also suggest that small vessel disease due to arteriosclerosis and fibrolipohyalinosis is a potential target for the treatment of AD.

Cerebrovascular diseases belong to a group of the major causes of cognitive impairments, in the elderly in particular. The paper presents current ideas on the etiology and pathogenesis of vascular cognitive impairments (VCI). The etiological factors of VCI may be divided into genetic, sociodemographic, and common risk factors for vascular and other diseases. The pathogenesis of VCI is multifactorial; cognitive function decrement results from brain damage due to cerebral circulatory disorders. Damage to the deep white matter portions and basal ganglions plays a leading role in the development of cognitive deficit in cerebral circulatory insufficiency, disrupting the connections between the frontal lobes and subcortical structures (a dissociation phenomenon). Regulatory functions are impaired; instability of volitional attention develops; the speed of thinking processes and the performance of professional and everyday skills are suffered, mnestic functions being impaired to a lesser extent. Impairments in other higher cortical functions, such as speech, gnosis, praxis, thinking, generally occur in the later stages of cognitive deficit. The comprehensive approach to examining patients with cognitive dysfunctions, which encompasses physical examination with a mandatory evaluation of neurological symptoms, neuropsychological testing, laboratory studies, instrumental diagnostic methods, and structural and functional neuroimaging techniques, are most justified now. VCI therapy is a challenging task requiring the specific features of different types of cognitive deficit to be analyzed, by providing a rationale for the choice of medications. Therapeutic effectiveness may be enhanced by rational combined multimodal therapy, by keeping in mind a variety of factors for the pathogenesis of VCI.

Corticotrophin releasing factor receptor 1 antagonists prevent chronic stress-induced behavioral changes and synapse loss in aged rats

BackgroundExpansion of a polyglutamine repeat at the amino-terminus of huntingtin is the probable cause for Huntington's disease, a lethal progressive autosomal-dominant neurodegenerative disorders characterized by impaired motor performance and severe brain atrophy. The expanded polyglutamine repeat changes the conformation of huntingtin and initiates a range of pathogenic mechanisms in neurons including intracellular huntingtin aggregates, transcriptional dysregulation, energy metabolism deficits, synaptic dystrophy and ultimately neurodegeneration. It is unclear how these events relate to each other or if they can be reversed by pharmacological intervention. Here, we describe neuronal cell lines expressing inducible fragments of normal and mutant huntingtin.ResultsIn HN10 cells, the expression of wild type and mutant huntingtin fragments was dependent on the induction time as well as on the concentration of the RheoSwitch® inducing ligand. In order to analyze the effect of mutant huntingtin expression on cellular functions we concentrated on the 72Q exon1 huntingtin expressing cell line and found that upon induction, it was possible to carefully dissect mutant huntingtin-induced phenotypes as they developed over time. Dysregulation of transcription as a result of mutant huntingtin expression showed a transcription signature replicating that reported in animal models and Huntington's disease patients. Crucially, triggering of neuronal differentiation in mutant huntingtin expressing cell resulted in the appearance of additional pathological hallmarks of Huntington's disease including cell death.ConclusionWe developed neuronal cell lines with inducible expression of wild type and mutant huntingtin. These new cell lines represent a reliable in vitro system for modeling Huntington's disease and should find wide use for high-throughput screening application and for investigating the biology of mutant huntingtin.

Pathological gambling (PG) is a behavioral addiction characterized by an inability to stop gambling despite the negative consequences, which may be mediated by cognitive flexibility deficits. Indeed, impaired cognitive flexibility has previously been linked to PG and also to reduced integrity of white matter connections between the basal ganglia and the prefrontal cortex. It remains unclear, however, how white matter integrity problems relate to cognitive inflexibility seen in PG. We used a cognitive switch paradigm during functional magnetic resonance imaging in pathological gamblers (PGs; n = 26) and healthy controls (HCs; n = 26). Cognitive flexibility performance was measured behaviorally by accuracy and reaction time on the switch task, while brain activity was measured in terms of blood oxygen level-dependent responses. We also used diffusion tensor imaging on a subset of data (PGs = 21; HCs = 21) in combination with tract-based spatial statistics and probabilistic fiber tracking to assess white matter integrity between the basal ganglia and the dorsolateral prefrontal cortex. Although there were no significant group differences in either task performance, related neural activity or tract-based spatial statistics, PGs did show decreased white matter integrity between the left basal ganglia and prefrontal cortex. Our results complement and expand similar findings from a previous study in alcohol-dependent patients. Although we found no association between white matter integrity and task performance here, decreased white matter connections may contribute to a diminished ability to recruit prefrontal networks needed for regulating behavior in PG. Hence, our findings could resonate an underlying risk factor for PG, and we speculate that these findings may extend to addiction in general.

Huntington’s disease is associated with increased CAG repeat resulting in an expanded polyglutamine tract in the protein Huntingtin (HTT) leading to its aggregation resulting in neurodegeneration. Previous studies have shown that N-terminal HTT with 46Q aggregated in the stationary phase but not the logarithmic phase in the yeast model of HD. We carried out a metabolomic analysis of logarithmic and stationary phase yeast model of HD expressing different polyQ lengths attached to N-terminal HTT tagged with enhanced green fluorescent protein (EGFP). The results show significant changes in the metabolic profile and deregulated pathways in stationary phase cells compared to logarithmic phase cells. Comparison of metabolic pathways obtained from logarithmic phase 46Q versus 25Q with those obtained for presymptomatic HD patients from our previous study and drosophila model of HD showed considerable overlap. The arginine biosynthesis pathway emerged as one of the key pathways that is common in stationary phase yeast compared to logarithmic phase and HD patients. Treatment of yeast with arginine led to a significant decrease, while transfer to arginine drop-out media led to a significant increase in the size of protein aggregates in both logarithmic and stationary phase yeast model of HD. Knockout of arginine transporters in the endoplasmic reticulum and vacuole led to a significant decrease in mutant HTT aggregation. Overall our results highlight arginine as a critical metabolite that modulates the aggregation of mutant HTT and disease progression in HD. Communicated by Ramaswamy H. Sarma

Dopamine system dysfunction and altered glucose metabolism are implicated in Huntington's disease (HD), a neurological disease caused by mutant huntingtin (mHTT) expression. The aim was to characterize alterations in cerebral dopamine D2 /D3 receptor density and glucose utilization in a newly developed AAV-mediated NHP model of HD that expresses mHTT throughout numerous brain regions. Positron emission tomography (PET) imaging was performed using [18 F]fallypride to quantify D2 /D3 receptor density and 2-[18 F]fluoro-2-deoxy-d-glucose ([18 F]FDG) to measure cerebral glucose utilization in these HD macaques. Compared to controls, HD macaques showed significantly reduced dopamine D2 /D3 receptor densities in basal ganglia (P < 0.05). In addition, HD macaques displayed significant glucose hypometabolism throughout the cortico-basal ganglia network (P < 0.05). [18 F]Fallypride and [18 F]FDG are PET imaging biomarkers of mHTT-mediated disease progression that can be used as noninvasive outcome measures in future therapeutic studies with this AAV-mediated HD macaque model. © 2022 International Parkinson and Movement Disorder Society.

BackgroundComplement component C3, an innate immune molecule, is important for removing pathogens and eliminating synapses during brain development, aging, and Alzheimer’s disease (AD). Previously, our group demonstrated that C3 deficiency protected against synapse loss during normal aging in wild‐type and APPswe/PS1dE9 mice. Induction of C3 deficiency after normal brain development will help inform whether its inhibition in aging or early stages of AD may serve as a future therapeutic strategy.MethodWe crossed C3fl/fl mice with an inducible, global Cre line (Rosa26‐Cre‐ERT2+/‐) for 2 generations to generate novel inducible C3 conditional knockout C3fl/fl; Rosa26‐Cre‐ERT2+/‐ mice (C3iKO). In one cohort, four‐to‐five‐month‐old mice were injected with tamoxifen (TAM) or corn oil (CO) daily for 5 days. Behavioral tasks were performed when these mice reached 16‐17 months of age. In another study, three‐to‐four‐month‐old female mice were injected with either CO/TAM and electrophysiological recording of long‐term potentiation (LTP) was conducted in hippocampal slices of TAM‐treated and CO‐treated mice at 7‐8 months of age following incubation of the slices with neurotoxic Aβ S26 dimers.ResultC3iKO mice had a significant 85‐95% reduction in serum C3 levels compared to controls, which was consistent at all timepoints analyzed (from Day 7 to Day 365). In this cohort, behavioral testing for hippocampal‐dependent spatial memory, object memory, and object location was performed when TAM‐treated and CO‐treated mice reached 16‐17 months of age. C3iKO+TAM mice performed significantly better than C3iKO+CO‐treated mice in these behavioral tasks, indicating that C3 lowering after brain development protected mice from age‐related cognitive decline. In the second study, we found that C3 lowering in adult mice protected hippocampal synapses from Aβ S26 dimer‐mediated LTP impairment.ConclusionGlobal C3 depletion in C3iKO young adult mice protected against hippocampal dysfunction as they aged, suggesting that C3 lowering may be an effective therapeutic strategy for aging and possibly, AD. Future studies are underway to investigate the C3‐mediated mechanisms of synaptic dysfunction in the hippocampus.

A key question in Huntington's disease (HD) is what underlies the early cognitive deficits that precede the motor symptoms and the characteristic neuronal death observed in HD. The mechanisms underlying cognitive symptoms in HD remain unknown. Postmortem HD brain and animal model studies demonstrate pathologies in dendritic spines and abnormal synaptic plasticity before motor symptoms and neurodegeneration. Experience-dependent synaptic plasticity caused by mechanisms such as LTP or novel sensory experience potentiates synaptic strength, enhances new dendritic spine formation and stabilization, and may contribute to normal cognitive processes, such as learning and memory. We have previously reported that under baseline conditions (without any sensory manipulation) neuronal circuitry in HD (R6/2 mouse model) was highly unstable, which led to a progressive loss of persistent spines in these mice, and that mutant huntingtin was directly involved in the process. Here, we investigated whether pathological processes of HD interfere with the normal experience-dependent plasticity of dendritic spines in the R6/2 model. Six weeks of two-photon in vivo imaging before and after whisker trimming revealed that sensory deprivation exacerbates loss of persistent-type, stable spines in R6/2 mice compared with wild-type littermates. In addition, sensory deprivation leads to impaired transformation of newly generated spines into persistent spines in R6/2 mice. As a consequence, reduced synaptic density and decreased PSD-95 protein levels are evident in their barrel cortical neurons. These data suggest that mutant huntingtin is implicated in maladaptive synaptic plasticity, which could be one of the plausible mechanisms underlying early cognitive deficits in HD.

The brain’s oxytocin system has been implicated in the neurobiology of autism (ASD), given the role of oxytocin in modulating social function in humans and animals more broadly. Previous work from members of our group reported dysregulation in oxytocin receptor (OXTR) binding in postmortem tissue from the basal forebrain in donors with autism compared to unaffected control donors. This study follows up on those findings by investigating the potential genetic and gene expression changes that could be driving those differences. We used adjacent sections from the same specimens from our previous study and performed duplex fluorescence in situ hybridization to visualize and quantify OXTR mRNA in the ventral pallidum (VP) and in the cholinergic magnocellular neurons of the nucleus basalis of Meynert (NBM), visualized with choline acetyltransferase (ChAT). We genotyped the brain samples using a SNP microarray on extracted DNA. We then used regression models to test associations between OXTR binding density, OXTR mRNA levels, and relevant OXTR SNPs. Additionally, we tested for correlations between age and OXTR mRNA. ASD specimens showed significantly greater OXTR mRNA than unaffected donors in both the VP and the NBM. Furthermore, this is the first demonstration of OXTR expression in the cholinergic neurons of the human basal forebrain; 73% of OXTR signal in the images of the ChAT+ neurons were colocalized with the cholinergic neurons. OXTR binding levels from our previous study were positively associated with OXTR mRNA in the NBM but only in the ChAT+ neurons there. OXTR binding levels were not associated with OXTR mRNA in the VP. We genotyped all specimens for three common SNPs in the OXTR gene that have been associated with ASD in the literature, but none significantly predicted levels of OXTR binding or gene expression in the NBM or VP. OXTR mRNA levels were strongly positively correlated with donor age across regions, which was driven by ASD specimens. Taken together, our results contribute to a more nuanced picture triangulating variation in OXTR gene sequence, gene expression, protein levels, and human behavior. Clinical trial number: not applicable.

Human immunodeficiency virus (HIV)-1 infection of the CNS produces changes in dendritic morphology that correlate with cognitive decline in patients with HIV-1 associated dementia (HAD). Here, we investigated the effects of HIV-1 transactivator of transcription (Tat), a protein released by virus-infected cells, on synapses between hippocampal neurons using an imaging-based assay that quantified clusters of the scaffolding protein postsynaptic density 95 fused to green fluorescent protein (PSD95-GFP). Tat (24 h) decreased the number of PSD95-GFP puncta by 50 +/- 7%. The decrease was concentration-dependent (EC(50) = 6 +/- 2 ng/ml) and preceded cell death. Tat acted via the low-density lipoprotein receptor-related protein (LRP) because the specific LRP blocker, receptor associated protein (RAP), prevented the Tat-induced decrease in the number of PSD95-GFP puncta. Ca(2+) influx through the NMDA receptor was necessary for Tat-induced synapse loss. Expression of an ubiquitin ligase inhibitor protected synapses, implicating the ubiquitin-proteasome pathway. In contrast to synapse loss, Tat induced cell death (48 h) required activation of nitric oxide synthase. The ubiquitin ligase-inhibitor nutlin-3 prevented synapse loss but not cell death induced by Tat. Thus, the pathways diverged, consistent with the hypothesis that synapse loss is a mechanism to reduce excess excitatory input rather than a symptom of the neuron's demise. Furthermore, application of RAP to cultures treated with Tat for 16 h reversed synapse loss. These results suggest that the impaired network function and decreased neuronal survival produced by Tat involve distinct mechanisms and that pharmacologic targets, such as LRP, might prove useful in restoring function in HAD patients.

White matter (WM) abnormalities have already been shown in presymptomatic (Pre-HD) and symptomatic HD subjects using Magnetic Resonance Imaging (MRI). In the present study, we examined the microstructure of the long-range large deep WM tracts by applying two different MRI approaches: Diffusion Tensor Imaging (DTI) -based tractography, and T2*weighted (iron sensitive) imaging. We collected Pre-HD subjects (n = 25), HD patients (n = 25) and healthy control subjects (n = 50). Results revealed increased axial (AD) and radial diffusivity (RD) and iron levels in Pre-HD subjects compared to controls. Fractional anisotropy decreased between the Pre-HD and HD phase and AD/RD increased and although impairment was pervasive in HD, degeneration occurred in a pattern in Pre-HD. Furthermore, iron levels dropped for HD patients. As increased iron levels are associated with remyelination, the data suggests that Pre-HD subjects attempt to repair damaged deep WM years before symptoms occur but this process fails with disease progression.

Huntington's disease (HD) is a genetically neurodegenerative disease, affecting the central nervous system and leading to mental and motor dysfunctions. To date, there is no cure for HD; as a result, HD patients gradually suffer devastating symptoms, such as chorea, weight loss, depression and mood swings, until death. According to previous studies, the exon 1 region of the huntingtin (HTT) gene with expanded CAG trinucleotide repeats plays a critical role in causing HD. In vitro studies using exon 1 of HTT fused with green fluorescent protein (GFP) gene have facilitated discovering several mechanisms of HD. However, whether this chimera construct exerts similar functions in vivo is still not clear. Here, we report the generation of transgenic mice carrying GFP fused with mutant HTT exon 1 containing 84 CAG trinucleotide repeats, and the evaluation of phenotypes via molecular, neuropathological and behavioral analyses. Results show that these transgenic mice not only displayed neuropathological characteristics, observed either by green fluorescent signals or by immunohistochemical staining, but also progressively developed pathological and behavioral symptoms of HD. Most interestingly, these transgenic mice showed significantly differential expression levels of nuclear aggregates between cortex and striatum regions, highly mimicking selective expression of mutant HTT in HD patients. To the best of our knowledge, this is the first report showing different nuclear diffusion profiling in mouse models with transgenic mice carrying the exon 1 region of mutant HTT. Our model will be beneficial for tracing the expression of mutant HTT and accelerating the understanding of selective pathological progression in HD.

Acute exposure to chlorpyrifos caused NADPH oxidase mediated oxidative stress and neurotoxicity in a striatal cell model of Huntington’s disease

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin (HTT) protein. The expression of mutant HTT in the baker’s yeast Saccharomyces cerevisiae recapitulates many of the cellular phenotypes observed in mammalian HD models. Mutant HTT aggregation and toxicity in yeast is influenced by the presence of the Rnq1p and Sup35p prions, as well as other glutamine/asparagine-rich aggregation-prone proteins. Here we investigated the ability of a subset of these proteins to modulate mutant HTT aggregation and to substitute for the prion form of Rnq1p. We find that overexpression of either the putative prion Ybr016wp or the Sup35p prion restores aggregation of mutant HTT in yeast cells lacking the Rnq1p prion. These results indicate that an interchangeable suite of aggregation-prone proteins regulates mutant HTT aggregation dynamics in yeast, which may have implications for mutant HTT aggregation in human cells.