White matter changes in Alzheimer's disease: a focus on myelin and oligodendrocytes

Integrative transcriptome- and DNA methylation analysis of brain tissue from the temporal pole in suicide decedents and their controls

Suicide rates have increased steadily world-wide over the past two decades, constituting a serious public health crisis that creates a significant burden to affected families and the society as a whole. Suicidal behavior involves a multi-factorial etiology, including psychological, social and biological factors. Since the molecular neural mechanisms of suicide remain vastly uncharacterized, we examined transcriptional- and methylation profiles of postmortem brain tissue from subjects who died from suicide as well as their neurotypical healthy controls. We analyzed temporal pole tissue from 61 subjects, largely free from antidepressant and antipsychotic medication, using RNA-sequencing and DNA-methylation profiling using an array that targets over 850,000 CpG sites. Expression of NPAS4, a key regulator of inflammation and neuroprotection, was significantly downregulated in the suicide decedent group. Moreover, we identified a total of 40 differentially methylated regions in the suicide decedent group, mapping to seven genes with inflammatory function. There was a significant association between NPAS4 DNA methylation and NPAS4 expression in the control group that was absent in the suicide decedent group, confirming its dysregulation. NPAS4 expression was significantly associated with the expression of multiple inflammatory factors in the brain tissue. Overall, gene sets and pathways closely linked to inflammation were significantly upregulated, while specific pathways linked to neuronal development were suppressed in the suicide decedent group. Excitotoxicity as well as suppressed oligodendrocyte function were also implicated in the suicide decedents. In summary, we have identified central nervous system inflammatory mechanisms that may be active during suicidal behavior, along with oligodendrocyte dysfunction and altered glutamate neurotransmission. In these processes, NPAS4 might be a master regulator, warranting further studies to validate its role as a potential biomarker or therapeutic target in suicidality.

Noninvasive Gamma Sensory Stimulation May Reduce White Matter and Myelin Loss in Alzheimer's Disease

BACKGROUND

Patients with Alzheimer's disease (AD) demonstrate progressive white matter atrophy and myelin loss. Restoring myelin content or preventing demyelination has been suggested as a therapeutic approach for AD.

OBJECTIVE

Herein, we investigate the effects of non-invasive, combined visual and auditory gamma-sensory stimulation on white matter atrophy and myelin content loss in patients with AD.

METHODS

In this study, we used the magnetic resonance imaging (MRI) data from the OVERTURE study (NCT03556280), a randomized, controlled, clinical trial in which active treatment participants received daily, non-invasive, combined visual and auditory, 40 Hz stimulation for six months. A subset of OVERTURE participants who meet the inclusion criteria for detailed white matter (N = 38) and myelin content (N = 36) assessments are included in the analysis. White matter volume assessments were performed using T1-weighted MRI, and myelin content assessments were performed using T1-weighted/T2-weighted MRI. Treatment effects on white matter atrophy and myelin content loss were assessed.

RESULTS

Combined visual and auditory gamma-sensory stimulation treatment is associated with reduced total and regional white matter atrophy and myelin content loss in active treatment participants compared to sham treatment participants. Across white matter structures evaluated, the most significant changes were observed in the entorhinal region.

CONCLUSIONS

The study results suggest that combined visual and auditory gamma-sensory stimulation may modulate neuronal network function in AD in part by reducing white matter atrophy and myelin content loss. Furthermore, the entorhinal region MRI outcomes may have significant implications for early disease intervention, considering the crucial afferent connections to the hippocampus and entorhinal cortex.

Transcriptomic Profiling Reveals Neuroinflammation in the Corpus Callosum of a Transgenic Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a widespread neurodegenerative disorder characterized by progressive cognitive decline, affecting a significant portion of the aging population. While the cerebral cortex and hippocampus have been the primary focus of AD research, accumulating evidence suggests that white matter lesions in the brain, particularly in the corpus callosum, play an important role in the pathogenesis of the disease.

OBJECTIVE

This study aims to investigate the gene expression changes in the corpus callosum of 5xFAD transgenic mice, a widely used AD mouse model.

METHODS

We conducted behavioral tests for spatial learning and memory in 5xFAD transgenic mice and performed RNA sequencing analyses on the corpus callosum to examine transcriptomic changes.

RESULTS

Our results show cognitive decline and demyelination in the corpus callosum of 5xFAD transgenic mice. Transcriptomic analysis reveals a predominance of upregulated genes in AD mice, particularly those associated with immune cells, including microglia. Conversely, downregulation of genes related to chaperone function and clock genes such as Per1, Per2, and Cry1 is also observed.

CONCLUSIONS

This study suggests that activation of neuroinflammation, disruption of chaperone function, and circadian dysfunction are involved in the pathogenesis of white matter lesions in AD. The findings provide insights into potential therapeutic targets and highlight the importance of addressing white matter pathology and circadian dysfunction in AD treatment strategies.

A rat model established by simulating genetic-environmental interactions recapitulates human Alzheimer's disease pathology

BACKGROUND

In humans, Alzheimer's disease (AD) is typically sporadic in nature, and its pathology is usually influenced by extensive factors. The study established a rat model based on the genetic-environmental interaction.

METHODS

A rat model was established by transduction of an adeno-associated virus combined with acrolein treatment. Rats were assigned to the normal control (NC), acrolein group, AAV (-) group, AAV-APP group, and AAV-APP/acrolein group. The success of model construction was verified in multiple ways, including by assessing cognitive function, examining microstructural changes in the brain in vivo, and performing immunohistochemistry. The contribution of genetic (APP mutation) and environmental (acrolein) factors to AD-like phenotypes in the model was explored by factorial analysis.

RESULTS

1) The AAV-APP/acrolein group showed a decline in cognitive function, as indicated by a reduced gray matter volume in key cognition-related brain areas, lower FA values in the hippocampus and internal olfactory cortex, and Aβ deposition in the cortex and hippocampus. 2) The AAV-APP group also showed a decline in cognitive function, although the group exhibited atypical brain atrophy in the gray matter and insignificant Aβ deposition. 3) The acrolein group did not show any significant changes in Aβ levels, gray matter volume, or cognitive function. 4) The genetic factor (APP mutation) explained 39.74% of the AD-like phenotypes in the model factors, and the environmental factor (acrolein exposure) explained 33.3%.

CONCLUSIONS

The genetic-environmental interaction rat model exhibited a phenotype that resembled the features of human AD and will be useful for research on AD.

EAAT3 impedes oligodendrocyte remyelination in chronic cerebral hypoperfusion-induced white matter injury

BACKGROUND

Chronic cerebral hypoperfusion-induced demyelination causes progressive white matter injury, although the pathogenic pathways are unknown.

METHODS

The Single Cell Portal and PanglaoDB databases were used to analyze single-cell RNA sequencing experiments to determine the pattern of EAAT3 expression in CNS cells. Immunofluorescence (IF) was used to detect EAAT3 expression in oligodendrocytes and oligodendrocyte progenitor cells (OPCs). EAAT3 levels in mouse brains were measured using a western blot at various phases of development, as well as in traumatic brain injury (TBI) and intracerebral hemorrhage (ICH) mouse models. The mouse bilateral carotid artery stenosis (BCAS) model was used to create white matter injury. IF, Luxol Fast Blue staining, and electron microscopy were used to investigate the effect of remyelination. 5-Ethynyl-2-Deoxy Uridine staining, transwell chamber assays, and IF were used to examine the effects of OPCs' proliferation, migration, and differentiation in vivo and in vitro. The novel object recognition test, the Y-maze test, the rotarod test, and the grid walking test were used to examine the impact of behavioral modifications.

RESULTS

A considerable amount of EAAT3 was expressed in OPCs and mature oligodendrocytes, according to single-cell RNA sequencing data. During multiple critical phases of mouse brain development, there were no substantial changes in EAAT3 levels in the hippocampus, cerebral cortex, or white matter. Furthermore, neither the TBI nor ICH models significantly affected the levels of EAAT3 in the aforementioned brain areas. The chronic white matter injury caused by BCAS, on the other hand, resulted in a strikingly high level of EAAT3 expression in the oligodendroglia and white matter. Correspondingly, blocking EAAT3 assisted in the recovery of cognitive and motor impairment as well as the restoration of cerebral blood flow following BCAS. Furthermore, EAAT3 suppression was connected to improved OPCs' survival and proliferation in vivo as well as faster OPCs' proliferation, migration, and differentiation in vitro. Furthermore, this study revealed that the mTOR pathway is implicated in EAAT3-mediated remyelination.

CONCLUSIONS

Our findings provide the first evidence that abnormally high levels of oligodendroglial EAAT3 in chronic cerebral hypoperfusion impair OPCs' pro-remyelination actions, hence impeding white matter repair and functional recovery. EAAT3 inhibitors could be useful in the treatment of ischemia demyelination.

Improved myelin water fraction mapping with deep neural networks using synthetically generated 3D data

We introduce a generative model for synthesis of large scale 3D datasets for quantitative parameter mapping of myelin water fraction (MWF). Our model combines a MR physics signal decay model with an accurate probabilistic multi-component parametric T2 model. We synthetically generate a wide variety of high quality signals and corresponding parameters from a wide range of naturally occurring prior parameter values. To capture spatial variation, the generative signal decay model is combined with a generative spatial model conditioned on generic tissue segmentations. Synthesized 3D datasets can be used to train any convolutional neural network (CNN) based architecture for MWF estimation. Our source code is available at: https://github.com/quin-med-harvard-edu/synthmap Reduction of acquisition time at the expense of lower SNR, as well as accuracy and repeatability of MWF estimation techniques, are key factors that affect the adoption of MWF mapping in clinical practice. We demonstrate that the synthetically trained CNN provides superior accuracy over the competing methods under the constraints of naturally occurring noise levels as well as on the synthetically generated images at low SNR levels. Normalized root mean squared error (nRMSE) is less than 7% on synthetic data, which is significantly lower than competing methods. Additionally, the proposed method yields a coefficient of variation (CoV) that is at least 4x better than the competing method on intra-session test-retest reference dataset.

Aβ Amyloid Scaffolds the Accumulation of Matrisome and Additional Proteins in Alzheimer's Disease

We report a highly significant correlation in brain proteome changes between Alzheimers disease (AD) and CRND8 APP695NL/F transgenic mice. However, integrating protein changes observed in the CRND8 mice with co-expression networks derived from human AD, reveals both conserved and divergent module changes. For the most highly conserved module (M42, matrisome) we find many proteins accumulate in plaques, cerebrovascular amyloid (CAA), dystrophic processes, or a combination thereof. Overexpression of two M42 proteins, midkine (Mdk) and pleiotrophin (PTN), in CRND8 mice brains leads to increased accumulation of A β ; in plaques and in CAA; further, recombinant MDK and PTN enhance A β ; aggregation into amyloid. Multiple M42 proteins, annotated as heparan sulfate binding proteins, bind to fibrillar A β 42 and a non-human amyloid fibril in vitro. Supporting this binding data, MDK and PTN co-accumulate with transthyretin (TTR) amyloid in the heart and islet amyloid polypeptide (IAPP) amyloid in the pancreas. Our findings establish several critical insights. Proteomic changes in modules observed in human AD brains define an A β ; amyloid responsome that is well conserved from mouse model to human. Further, distinct amyloid structures may serve as scaffolds, facilitating the co-accumulation of proteins with signaling functions. We hypothesize that this co-accumulation may contribute to downstream pathological sequalae. Overall, this contextualized understanding of proteomic changes and their interplay with amyloid deposition provides valuable insights into the complexity of AD pathogenesis and potential biomarkers and therapeutic targets.

Associations of infections and vaccines with Alzheimer's disease point to a major role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been linked to Alzheimer's disease (AD) indicating a possibility that the culprit may be compromised immunity rather than particular microbe. If true, then vaccines with broad beneficial effects on immunity might be protective against AD.

METHODS

We estimated associations of common adult infections, including herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses, as well as vaccinations against shingles and pneumonia, with the risk of AD in a pseudorandomized sample of the Health and Retirement Study.

RESULTS

Shingles, pneumonia, and mycoses diagnosed between ages 65-75, were all associated with higher risk of AD later in life, by 16%-42%. Pneumococcal and shingles vaccines received between ages 65-75 both lowered the risk of AD, by 15%-21%.

DISCUSSION

Our results support the idea that the connection between AD and infections involves compromised immunity rather than specific pathogen. We discuss mechanisms by which the declining immune surveillance may promote AD, and the role of biological aging in it. Repurposing of vaccines with broad beneficial effects on immunity could be a reasonable approach to AD prevention. Pneumococcal and zoster vaccines are promising candidates for such repurposing.

Preserving cognitive function in patients with Alzheimer's disease: The Alzheimer's disease neuroprotection research initiative (ADNRI)

The global trend toward aging populations has resulted in an increase in the occurrence of Alzheimer's disease (AD) and associated socioeconomic burdens. Abnormal metabolism of amyloid-β (Aβ) has been proposed as a significant pathomechanism in AD, supported by results of recent clinical trials using anti-Aβ antibodies. Nonetheless, the cognitive benefits of the current treatments are limited. The etiology of AD is multifactorial, encompassing Aβ and tau accumulation, neuroinflammation, demyelination, vascular dysfunction, and comorbidities, which collectively lead to widespread neurodegeneration in the brain and cognitive impairment. Hence, solely removing Aβ from the brain may be insufficient to combat neurodegeneration and preserve cognition. To attain effective treatment for AD, it is necessary to (1) conduct extensive research on various mechanisms that cause neurodegeneration, including advances in neuroimaging techniques for earlier detection and a more precise characterization of molecular events at scales ranging from cellular to the full system level; (2) identify neuroprotective intervention targets against different neurodegeneration mechanisms; and (3) discover novel and optimal combinations of neuroprotective intervention strategies to maintain cognitive function in AD patients. The Alzheimer's Disease Neuroprotection Research Initiative's objective is to facilitate coordinated, multidisciplinary efforts to develop systemic neuroprotective strategies to combat AD. The aim is to achieve mitigation of the full spectrum of pathological processes underlying AD, with the goal of halting or even reversing cognitive decline.

Multi-Scale Label-Free Human Brain Imaging with Integrated Serial Sectioning Polarization Sensitive Optical Coherence Tomography and Two-Photon Microscopy

The study of aging and neurodegenerative processes in the human brain requires a comprehensive understanding of cytoarchitectonic, myeloarchitectonic, and vascular structures. Recent computational advances have enabled volumetric reconstruction of the human brain using thousands of stained slices, however, tissue distortions and loss resulting from standard histological processing have hindered deformation-free reconstruction. Here, the authors describe an integrated serial sectioning polarization-sensitive optical coherence tomography (PSOCT) and two photon microscopy (2PM) system to provide label-free multi-contrast imaging of intact brain structures, including scattering, birefringence, and autofluorescence of human brain tissue. The authors demonstrate high-throughput reconstruction of 4 × 4 × 2cm3 sample blocks and simple registration between PSOCT and 2PM images that enable comprehensive analysis of myelin content, vascular structure, and cellular information. The high-resolution 2PM images provide microscopic validation and enrichment of the cellular information provided by the PSOCT optical properties on the same sample, revealing the densely packed fibers, capillaries, and lipofuscin-filled cell bodies in the cortex and white matter. It is  shown that the imaging system enables quantitative characterization of various pathological features in aging process, including myelin degradation, lipofuscin accumulation, and microvascular changes, which opens up numerous opportunities in the study of neurodegenerative diseases in the future.

Cerebrovascular disease drives Alzheimer plasma biomarker concentrations in adults with Down syndrome

Importance

By age 40 years over 90% of adults with Down syndrome (DS) have Alzheimer's disease (AD) pathology and most progress to dementia. Despite having few systemic vascular risk factors, individuals with DS have elevated cerebrovascular disease (CVD) markers that track with the clinical progression of AD, suggesting a role for CVD that is hypothesized to be mediated by inflammatory factors.

Objective

To examine the pathways through which small vessel CVD contributes to AD-related pathophysiology and neurodegeneration in adults with DS.

Design

Cross sectional analysis of neuroimaging, plasma, and clinical data.

Setting

Participants were enrolled in Alzheimer's Biomarker Consortium - Down Syndrome (ABC-DS), a multisite study of AD in adults with DS.

Participants

One hundred eighty-five participants (mean [SD] age=45.2 [9.3] years) with available MRI and plasma biomarker data were included. White matter hyperintensity (WMH) volumes were derived from T2-weighted FLAIR MRI scans and plasma biomarker concentrations of amyloid beta (Aβ42/Aβ40), phosphorylated tau (p-tau217), astrocytosis (glial fibrillary acidic protein, GFAP), and neurodegeneration (neurofilament light chain, NfL) were measured with ultrasensitive immunoassays.

Main Outcomes and Measures

We examined the bivariate relationships of WMH, Aβ42/Aβ40, p-tau217, and GFAP with age-residualized NfL across AD diagnostic groups. A series of mediation and path analyses examined causal pathways linking WMH and AD pathophysiology to promote neurodegeneration in the total sample and groups stratified by clinical diagnosis.

Results

There was a direct and indirect bidirectional effect through GFAP of WMH on p-tau217 concentration, which was associated with NfL concentration in the entire sample. Among cognitively stable participants, WMH was directly and indirectly, through GFAP, associated with p-tau217 concentration, and in those with MCI, there was a direct effect of WMH on p-tau217 and NfL concentrations. There were no associations of WMH with biomarker concentrations among those diagnosed with dementia.

Conclusions and Relevance

The findings suggest that among individuals with DS, CVD promotes neurodegeneration by increasing astrocytosis and tau pathophysiology in the presymptomatic phases of AD. This work joins an emerging literature that implicates CVD and its interface with neuroinflammation as a core pathological feature of AD in adults with DS.

Cellular underpinnings of the selective vulnerability to tauopathic insults in Alzheimer's disease

Neurodegenerative diseases such as Alzheimer's disease (AD) exhibit pathological changes in the brain that proceed in a stereotyped and regionally specific fashion, but the cellular and molecular underpinnings of regional vulnerability are currently poorly understood. Recent work has identified certain subpopulations of neurons in a few focal regions of interest, such as the entorhinal cortex, that are selectively vulnerable to tau pathology in AD. However, the cellular underpinnings of regional susceptibility to tau pathology are currently unknown, primarily because whole-brain maps of a comprehensive collection of cell types have been inaccessible. Here, we deployed a recent cell-type mapping pipeline, Matrix Inversion and Subset Selection (MISS), to determine the brain-wide distributions of pan-hippocampal and neocortical neuronal and non-neuronal cells in the mouse using recently available single-cell RNA sequencing (scRNAseq) data. We then performed a robust set of analyses to identify general principles of cell-type-based selective vulnerability using these cell-type distributions, utilizing 5 transgenic mouse studies that quantified regional tau in 12 distinct PS19 mouse models. Using our approach, which constitutes the broadest exploration of whole-brain selective vulnerability to date, we were able to discover cell types and cell-type classes that conferred vulnerability and resilience to tau pathology. Hippocampal glutamatergic neurons as a whole were strongly positively associated with regional tau deposition, suggesting vulnerability, while cortical glutamatergic and GABAergic neurons were negatively associated. Among glia, we identified oligodendrocytes as the single-most strongly negatively associated cell type, whereas microglia were consistently positively correlated. Strikingly, we found that there was no association between the gene expression relationships between cell types and their vulnerability or resilience to tau pathology. When we looked at the explanatory power of cell types versus GWAS-identified AD risk genes, cell type distributions were consistently more predictive of end-timepoint tau pathology than regional gene expression. To understand the functional enrichment patterns of the genes that were markers of the identified vulnerable or resilient cell types, we performed gene ontology analysis. We found that the genes that are directly correlated to tau pathology are functionally distinct from those that constitutively embody the vulnerable cells. In short, we have demonstrated that regional cell-type composition is a compelling explanation for the selective vulnerability observed in tauopathic diseases at a whole-brain level and is distinct from that conferred by risk genes. These findings may have implications in identifying cell-type-based therapeutic targets.

Microglial function, INPP5D/SHIP1 signaling, and NLRP3 inflammasome activation: implications for Alzheimer's disease

Recent genetic studies on Alzheimer's disease (AD) have brought microglia under the spotlight, as loci associated with AD risk are enriched in genes expressed in microglia. Several of these genes have been recognized for their central roles in microglial functions. Increasing evidence suggests that SHIP1, the protein encoded by the AD-associated gene INPP5D, is an important regulator of microglial phagocytosis and immune response. A recent study from our group identified SHIP1 as a negative regulator of the NLRP3 inflammasome in human iPSC-derived microglial cells (iMGs). In addition, we found evidence for a connection between SHIP1 activity and inflammasome activation in the AD brain. The NLRP3 inflammasome is a multiprotein complex that induces the secretion of pro-inflammatory cytokines as part of innate immune responses against pathogens and endogenous damage signals. Previously published studies have suggested that the NLRP3 inflammasome is activated in AD and contributes to AD-related pathology. Here, we provide an overview of the current understanding of the microglial NLRP3 inflammasome in the context of AD-related inflammation. We then review the known intracellular functions of SHIP1, including its role in phosphoinositide signaling, interactions with microglial phagocytic receptors such as TREM2 and evidence for its intersection with NLRP3 inflammasome signaling. Through rigorous examination of the intricate connections between microglial signaling pathways across several experimental systems and postmortem analyses, the field will be better equipped to tailor newly emerging therapeutic strategies targeting microglia in neurodegenerative diseases.

Glutamate delta-1 receptor regulates oligodendrocyte progenitor cell differentiation and myelination in normal and demyelinating conditions

In this study, we investigated the role of glutamate delta 1 receptor (GluD1) in oligodendrocyte progenitor cell (OPC)-mediated myelination during basal (development) and pathophysiological (cuprizone-induced demyelination) conditions. Initially, we sought to determine the expression pattern of GluD1 in OPCs and found a significant colocalization of GluD1 puncta with neuron-glial antigen 2 (NG2, OPC marker) in the motor cortex and dorsal striatum. Importantly, we found that the ablation of GluD1 led to an increase in the number of myelin-associated glycoprotein (MAG+) cells in the corpus callosum and motor cortex at P40 without affecting the number of NG2+ OPCs, suggesting that GluD1 loss selectively facilitates OPC differentiation rather than proliferation. Further, deletion of GluD1 enhanced myelination in the corpus callosum and motor cortex, as indicated by increased myelin basic protein (MBP) staining at P40, suggesting that GluD1 may play an essential role in the developmental regulation of myelination during the critical window period. In contrast, in cuprizone-induced demyelination, we observed reduced MBP staining in the corpus callosum of GluD1 KO mice. Furthermore, cuprizone-fed GluD1 KO mice showed more robust motor deficits. Collectively, our results demonstrate that GluD1 plays a critical role in OPC regulation and myelination in normal and demyelinating conditions.

APOE4 allele-specific associations between diet, multimodal biomarkers, and cognition among Puerto Rican adults in Massachusetts

Background

Apolipoprotein E (APOE) is the strongest genetic risk factor for sporadic Alzheimer's Disease (AD), and the ε4 allele (APOE4) may interact with lifestyle factors that relate to brain structural changes, underlying the increased risk of AD. However, the exact role of APOE4 in mediating interactions between the peripheral circulatory system and the central nervous system, and how it may link to brain and cognitive aging requires further elucidation. In this analysis, we investigated the association between APOE4 carrier status and multimodal biomarkers (diet, blood markers, clinical diagnosis, brain structure, and cognition) in the context of gene-environment interactions.

Methods

Participants were older adults from a longitudinal observational study, the Boston Puerto Rican Health Study (BPRHS), who self-identified as of Puerto Rican descent. Demographics, APOE genotype, diet, blood, and clinical data were collected at baseline and at approximately 12th year, with the addition of multimodal brain magnetic resonance imaging (MRI) (T1-weighted and diffusion) and cognitive testing acquired at 12-year. Measures were compared between APOE4 carriers and non-carriers, and associations between multimodal variables were examined using correlation and multivariate network analyses within each group.

Results

A total of 156 BPRHS participants (mean age at imaging = 68 years, 77% female, mean follow-up 12.7 years) with complete multimodal data were included in the current analysis. APOE4 carriers (n = 43) showed reduced medial temporal lobe (MTL) white matter (WM) microstructural integrity and lower mini-mental state examination (MMSE) score than non-carriers (n = 113). This pattern was consistent with an independent sample from the Alzheimer's Disease Neuroimaging Initiative (ADNI) of n = 283 non-Hispanic White adults without dementia (mean age = 75, 40% female). Within BPRHS, carriers showed distinct connectivity patterns between multimodal biomarkers, characterized by stronger direct network connections between baseline diet/blood markers with 12-year blood/clinical measures, and between blood markers (especially lipids and cytokines) and WM. Cardiovascular burden (i.e., hypertension and diabetes status) was associated with WM integrity for both carriers and non-carriers.

Conclusion

APOE4 carrier status affects interactions between dietary factors, multimodal blood biomarkers, and MTL WM integrity across ~12 years of follow-up, which may reflect increased peripheral-central systems crosstalk following blood-brain barrier breakdown in carriers.

Oligodendrocyte progenitor cells in Alzheimer's disease: from physiology to pathology

Oligodendrocyte progenitor cells (OPCs) play pivotal roles in myelin formation and phagocytosis, communicating with neighboring cells and contributing to the integrity of the blood-brain barrier (BBB). However, under the pathological circumstances of Alzheimer's disease (AD), the brain's microenvironment undergoes detrimental changes that significantly impact OPCs and their functions. Starting with OPC functions, we delve into the transformation of OPCs to myelin-producing oligodendrocytes, the intricate signaling interactions with other cells in the central nervous system (CNS), and the fascinating process of phagocytosis, which influences the function of OPCs and affects CNS homeostasis. Moreover, we discuss the essential role of OPCs in BBB formation and highlight the critical contribution of OPCs in forming CNS-protective barriers. In the context of AD, the deterioration of the local microenvironment in the brain is discussed, mainly focusing on neuroinflammation, oxidative stress, and the accumulation of toxic proteins. The detrimental changes disturb the delicate balance in the brain, impacting the regenerative capacity of OPCs and compromising myelin integrity. Under pathological conditions, OPCs experience significant alterations in migration and proliferation, leading to impaired differentiation and a reduced ability to produce mature oligodendrocytes. Moreover, myelin degeneration and formation become increasingly active in AD, contributing to progressive neurodegeneration. Finally, we summarize the current therapeutic approaches targeting OPCs in AD. Strategies to revitalize OPC senescence, modulate signaling pathways to enhance OPC differentiation, and explore other potential therapeutic avenues are promising in alleviating the impact of AD on OPCs and CNS function. In conclusion, this review highlights the indispensable role of OPCs in CNS function and their involvement in the pathogenesis of AD. The intricate interplay between OPCs and the AD brain microenvironment underscores the complexity of neurodegenerative diseases. Insights from studying OPCs under pathological conditions provide a foundation for innovative therapeutic strategies targeting OPCs and fostering neurodegeneration. Future research will advance our understanding and management of neurodegenerative diseases, ultimately offering hope for effective treatments and improved quality of life for those affected by AD and related disorders.

Palmitate and glucose increase amyloid precursor protein in extracellular vesicles: Missing link between metabolic syndrome and Alzheimer's disease

The metabolic syndrome (MetS) and Alzheimer's disease share several pathological features, including insulin resistance, abnormal protein processing, mitochondrial dysfunction and elevated inflammation and oxidative stress. The MetS constitutes elevated fasting glucose, obesity, dyslipidaemia and hypertension and increases the risk of developing Alzheimer's disease, but the precise mechanism remains elusive. Insulin resistance, which develops from a diet rich in sugars and saturated fatty acids, such as palmitate, is shared by the MetS and Alzheimer's disease. Extracellular vesicles (EVs) are also a point of convergence, with altered dynamics in both the MetS and Alzheimer's disease. However, the role of palmitate- and glucose-induced insulin resistance in the brain and its potential link through EVs to Alzheimer's disease is unknown. We demonstrate that palmitate and high glucose induce insulin resistance and amyloid precursor protein phosphorylation in primary rat embryonic cortical neurons and human cortical stem cells. Palmitate also triggers insulin resistance in oligodendrocytes, the supportive glia of the brain. Palmitate and glucose enhance amyloid precursor protein secretion from cortical neurons via EVs, which induce tau phosphorylation when added to naïve neurons. Additionally, EVs from palmitate-treated oligodendrocytes enhance insulin resistance in recipient neurons. Overall, our findings suggest a novel theory underlying the increased risk of Alzheimer's disease in MetS mediated by EVs, which spread Alzheimer's pathology and insulin resistance.

Diagnostic performance of MRI radiomics for classification of Alzheimer's disease, mild cognitive impairment, and normal subjects: a systematic review and meta-analysis

BACKGROUND

Alzheimer's disease (AD) is a debilitating neurodegenerative disease. Early diagnosis of AD and its precursor, mild cognitive impairment (MCI), is crucial for timely intervention and management. Radiomics involves extracting quantitative features from medical images and analyzing them using advanced computational algorithms. These characteristics have the potential to serve as biomarkers for disease classification, treatment response prediction, and patient stratification. Of note, Magnetic resonance imaging (MRI) radiomics showed a promising result for diagnosing and classifying AD, and MCI from normal subjects. Thus, we aimed to systematically evaluate the diagnostic performance of the MRI radiomics for this task.

METHODS AND MATERIALS

A comprehensive search of the current literature was conducted using relevant keywords in PubMed/MEDLINE, Embase, Scopus, and Web of Science databases from inception to August 5, 2023. Original studies discussing the diagnostic performance of MRI radiomics for the classification of AD, MCI, and normal subjects were included. Method quality was evaluated with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) and the Radiomics Quality Score (RQS) tools.

RESULTS

We identified 13 studies that met the inclusion criteria, involving a total of 5448 participants. The overall quality of the included studies was moderate to high. The pooled sensitivity and specificity of MRI radiomics for differentiating AD from normal subjects were 0.92 (95% CI [0.85; 0.96]) and 0.91 (95% CI [0.85; 0.95]), respectively. The pooled sensitivity and specificity of MRI radiomics for differentiating MCI from normal subjects were 0.74 (95% CI [0.60; 0.85]) and 0.79 (95% CI [0.70; 0.86]), respectively. Also, the pooled sensitivity and specificity of MRI radiomics for differentiating AD from MCI were 0.73 (95% CI [0.64; 0.80]) and 0.79 (95% CI [0.64; 0.90]), respectively.

CONCLUSION

MRI radiomics has promising diagnostic performance in differentiating AD, MCI, and normal subjects. It can potentially serve as a non-invasive and reliable tool for early diagnosis and classification of AD and MCI.

Quantitative imaging of three-dimensional fiber orientation in the human brain via two illumination angles using polarization-sensitive optical coherence tomography

The accurate measurement of three-dimensional (3D) fiber orientation in the brain is crucial for reconstructing fiber pathways and studying their involvement in neurological diseases. Optical imaging methods such as polarization-sensitive optical coherence tomography (PS-OCT) provide important tools to directly quantify fiber orientation at micrometer resolution. However, brain imaging based on the optic axis by PS-OCT so far has been limited to two-dimensional in-plane orientation, preventing the comprehensive study of connectivity in 3D. In this work, we present a novel method to obtain the 3D fiber orientation in full angular space with only two illumination angles. We measure the optic axis orientation and the apparent birefringence by PS-OCT from a normal and a 15 deg tilted illumination, and then apply a computational method yielding the 3D optic axis orientation and true birefringence. We verify that our method accurately recovers a large range of through-plane orientations from -85 deg to 85 deg with a high angular precision. We further present 3D fiber orientation maps of entire coronal sections of human cerebrum and brainstem with 10 μm in-plane resolution, revealing unprecedented details of fiber configurations. We envision that further development of our method will open a promising avenue towards large-scale 3D fiber axis mapping in the human brain and other complex fibrous tissues at microscopic level.

Lethal adulthood myelin breakdown by oligodendrocyte-specific Ddx54 knockout

Multiple sclerosis (MS) is a leading disease that causes disability in young adults. We have previously shown that a DEAD-box RNA helicase Ddx54 binds to mRNA and protein isoforms of myelin basic protein (MBP) and that Ddx54 siRNA blocking abrogates oligodendrocyte migration and myelination. Herein, we show that MBP-driven Ddx54 knockout mice (Ddx54 fl/fl;MBP-Cre), after the completion of normal postnatal myelination, gradually develop abnormalities in behavioral profiles and learning ability, inner myelin sheath breakdown, loss of myelinated axons, apoptosis of oligodendrocytes, astrocyte and microglia activation, and they die within 7 months but show minimal peripheral immune cell infiltration. Myelin in Ddx54fl/fl;MBP-Cre is highly vulnerable to the neurotoxicant cuprizone and Ddx54 knockdown greatly impairs myelination in vitro. Ddx54 expression in oligodendrocyte-lineage cells decreased in corpus callosum of MS patients. Our results demonstrate that Ddx54 is indispensable for myelin homeostasis, and they provide a demyelinating disease model based on intrinsic disintegration of adult myelin.

The diamagnetic component map from quantitative susceptibility mapping (QSM) source separation reveals pathological alteration in Alzheimer's disease-driven neurodegeneration

A sensitive and accurate imaging technique capable of tracking the disease progression of Alzheimer's Disease (AD) driven amnestic dementia would be beneficial. A currently available method for pathology detection in AD with high accuracy is Positron Emission Tomography (PET) imaging, despite certain limitations such as low spatial resolution, off-targeting error, and radiation exposure. Non-invasive MRI scanning with quantitative magnetic susceptibility measurements can be used as a complementary tool. To date, quantitative susceptibility mapping (QSM) has widely been used in tracking deep gray matter iron accumulation in AD. The present work proposes that by compartmentalizing quantitative susceptibility into paramagnetic and diamagnetic components, more holistic information about AD pathogenesis can be acquired. Particularly, diamagnetic component susceptibility (DCS) can be a powerful indicator for tracking protein accumulation in the gray matter (GM), demyelination in the white matter (WM), and relevant changes in the cerebrospinal fluid (CSF). In the current work, voxel-wise group analysis of the WM and the CSF regions show significantly lower |DCS| (the absolute value of DCS) value for amnestic dementia patients compared to healthy controls. Additionally, |DCS| and τ PET standardized uptake value ratio (SUVr) were found to be associated in several GM regions typically affected by τ deposition in AD. Therefore, we propose that the separated diamagnetic susceptibility can be used to track pathological neurodegeneration in different tissue types and regions of the brain. With the initial evidence, we believe the usage of compartmentalized susceptibility demonstrates substantive potential as an MRI-based technique for tracking AD-driven neurodegeneration.

Inflammasome assembly in neurodegenerative diseases

Neurodegenerative disorders are characterized by the progressive dysfunction and death of selectively vulnerable neuronal populations, often associated with the accumulation of aggregated host proteins. Sustained brain inflammation and hyperactivation of inflammasome complexes have been increasingly demonstrated to contribute to neurodegenerative disease progression. Here, we review molecular mechanisms leading to inflammasome assembly in neurodegeneration. We focus primarily on four degenerative brain disorders in which inflammasome hyperactivation has been well documented: Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and the spectrum of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). We discuss shared and divergent principles of inflammasome assembly across these disorders, and underscore the differences between neurodegeneration-associated inflammasome activation pathways and their peripheral-immune counterparts. We examine how aberrant assembly of inflammasome complexes may amplify pathology in neurodegeneration, including misfolded protein aggregation, and highlight prospects for neurotherapeutic interventions based on targeting inflammasome pathways.

Oligodendrocyte pathology in Huntington's disease: from mechanisms to therapeutics

Oligodendrocytes (OLGs), highly specialized glial cells that wrap axons with myelin sheaths, are critical for brain development and function. There is new recognition of the role of OLGs in the pathogenesis of neurodegenerative diseases (NDDs), including Huntington's disease (HD), a prototypic NDD caused by a polyglutamine tract expansion in huntingtin (HTT), which results in gain- and loss-of-function effects. Clinically, HD is characterized by a constellation of motor, cognitive, and psychiatric disturbances. White matter (WM) structures, representing myelin-rich regions of the brain, are profoundly affected in HD, and recent findings reveal oligodendroglia dysfunction as an early pathological event. Here, we focus on mechanisms that underlie oligodendroglial deficits and dysmyelination in the progression of the disease, highlighting the pathogenic contributions of mutant HTT (mHTT). We also discuss potential therapeutic implications involving these molecular pathways.

Cellular specificity is key to deciphering epigenetic changes underlying Alzheimer's disease

Different cell types in the brain play distinct roles in Alzheimer's disease (AD) progression. Late onset AD (LOAD) is a complex disease, with a large genetic component, but many risk loci fall in non-coding genome regions. Epigenetics implicates the non-coding genome with control of gene expression. The epigenome is highly cell-type specific and dynamically responds to the environment. Therefore, epigenetic mechanisms are well placed to explain genetic and environmental factors that are associated with AD. However, given this cellular specificity, purified cell populations or single cells need to be profiled to avoid effect masking. Here we review the current state of cell-type specific genome-wide profiling in LOAD, covering DNA methylation (CpG, CpH, and hydroxymethylation), histone modifications, and chromatin changes. To date, these data reveal that distinct cell types contribute and react differently to AD progression through epigenetic alterations. This review addresses the current gap in prior bulk-tissue derived work by spotlighting cell-specific changes that govern the complex interplay of cells throughout disease progression and are critical in understanding and developing effective treatments for AD.

Fatigue in Alzheimer's disease: biological basis and clinical management-a narrative review

BACKGROUND

Fatigue is a common symptom in neurodegenerative diseases and is associated with decreased cognitive performances. A full knowledge of the causes and physiopathological pathways leading to fatigue in Alzheimer's disease could help treating this symptom and obtain positive effects on cognitive functions.

OBJECTIVES

To provide an overview of the clinical conditions and the biological mechanisms leading to fatigue in Alzheimer's disease patients. To review the recent advances on fatigue management and describe the landscape of future possibilities.

METHODS

We performed a narrative review including all type of studies (e.g. cross-sectional and longitudinal analysis, reviews, clinical trials).

RESULTS

We found very few studies considering the symptom fatigue in Alzheimer's disease patients. Populations, designs, and objectives varied across studies rendering comparability across studies difficult to perform. Results from cross-sectional and longitudinal analysis suggest that the amyloid cascade may be involved in the pathogenesis of fatigue and that fatigue may be a prodromal manifestation of Alzheimer's disease. Fatigue and neurodegeneration of Alzheimer's disease could share common brain signatures (i.e. hippocampal atrophy and periventricular leukoaraiosis). Some mechanisms of aging (i.e. inflammation, mitochondrial dysfunction, telomere shortening) may be proposed to play a common underlying role in Alzheimer's disease neurodegeneration and muscle fatigability. Considering treatments, donepezil has been found to reduce cognitive fatigue in a 6-week randomized controlled study. Fatigue is frequently reported as an adverse event in patients treated by anti-amyloid agents in clinical trials.

CONCLUSION

The literature is actually inconclusive about the main causes of fatigue in Alzheimer's disease individuals and its potential treatments. Further research is needed to disentangle the role of several components such as comorbidities, depressive symptoms, iatrogenic factors, physical decline and neurodegeneration itself. Given the clinical relevance of this symptom, it seems to be important to systematically assess fatigue by validated tools in Alzheimer's disease clinical trials.

Recurrent Transient Ischemic Attack Induces Neural Cytoskeleton Modification and Gliosis in an Experimental Model

Transient ischemic attack (TIA) presents a high risk for subsequent stroke, Alzheimer's disease (AD), and related dementia (ADRD). However, the neuropathophysiology of TIA has been rarely studied. By evaluating recurrent TIA-induced neuropathological changes, our study aimed to explore the potential mechanisms underlying the contribution of TIA to ADRD. In the current study, we established a recurrent TIA model by three times 10-min middle cerebral artery occlusion within a week in rat. Neither permanent neurological deficit nor apoptosis was observed following recurrent TIA. No increase of AD-related biomarkers was indicated after TIA, including increase of tau hyperphosphorylation and β-site APP cleaving enzyme 1 (BACE1). Neuronal cytoskeleton modification and neuroinflammation was found at 1, 3, and 7 days after recurrent TIA, evidenced by the reduction of microtubule-associated protein 2 (MAP2), elevation of neurofilament-light chain (NFL), and increase of glial fibrillary acidic protein (GFAP)-positive astrocytes and ionized calcium binding adaptor molecule 1 (Iba1)-positive microglia at the TIA-affected cerebral cortex and basal ganglion. Similar NFL, GFAP and Iba1 alteration was found in the white matter of corpus callosum. In summary, the current study demonstrated that recurrent TIA may trigger neuronal cytoskeleton change, astrogliosis, and microgliosis without induction of cell death at the acute and subacute stage. Our study indicates that TIA-induced neuronal cytoskeleton modification and neuroinflammation may be involved in the vascular contribution to cognitive impairment and dementia.

Co-administration of dl-3-n-butylphthalide and neprilysin is neuroprotective in Alzheimer disease associated with mild traumatic brain injury

dl-3-n-Butylphthalide is a potent synthetic Chinese celery extract that is highly efficient in inducing neuroprotection in concussive head injury (CHI), Parkinson's disease, Alzheimer's disease, stroke as well as depression, dementia, anxiety and other neurological diseases. Thus, there are reasons to believe that dl-3-n-butylphthalide could effectively prevent Alzheimer's disease brain pathology. Military personnel during combat operation or veterans are often the victims of brain injury that is a major risk factor for developing Alzheimer's disease in their later lives. In our laboratory we have shown that CHI exacerbates Alzheimer's disease brain pathology and reduces the amyloid beta peptide (AβP) inactivating enzyme neprilysin. We have used TiO2 nanowired-dl-3-n-butylphthalide in attenuating Parkinson's disease brain pathology exacerbated by CHI. Nanodelivery of dl-3-n-butylphthalide appears to be more potent as compared to the conventional delivery of the compound. Thus, it would be interesting to examine the effects of nanowired dl-3-n-butylphthalide together with nanowired delivery of neprilysin in Alzheimer's disease model on brain pathology. In this investigation we found that nanowired delivery of dl-3-n-butylphthalide together with nanowired neprilysin significantly attenuated brain pathology in Alzheimer's disease model with CHI, not reported earlier. The possible mechanism and clinical significance is discussed based on the current literature.

Sex Chromosomes and Gonads Shape the Sex-Biased Transcriptomic Landscape in Tlr7-Mediated Demyelination During Aging

Demyelination occurs in aging and associated diseases, including Alzheimer's disease. Several of these diseases exhibit sex differences in prevalence and severity. Biological sex primarily stems from sex chromosomes and gonads releasing sex hormones. To dissect mechanisms underlying sex differences in demyelination of aging brains, we constructed a transcriptomic atlas of cell type-specific responses to illustrate how sex chromosomes, gonads, and their interaction shape responses to demyelination. We found that sex-biased oligodendrocyte and microglial responses are driven by interaction of sex chromosomes and gonads prior to myelin loss. Post demyelination, sex chromosomes mainly guide microglial responses, while gonadal composition influences oligodendrocyte signaling. Significantly, ablation of the X-linked gene Toll-like receptor 7 (Tlr7), which exhibited sex-biased expression during demyelination, abolished the sex-biased responses and protected against demyelination.

Proteomic analysis across patient iPSC-based models and human post-mortem hippocampal tissue reveals early cellular dysfunction and progression of Alzheimer's disease pathogenesis

The hippocampus is a primary region affected in Alzheimer's disease (AD). Because AD postmortem brain tissue is not available prior to symptomatic stage, we lack understanding of early cellular pathogenic mechanisms. To address this issue, we examined the cellular origin and progression of AD pathogenesis by comparing patient-based model systems including iPSC-derived brain cells transplanted into the mouse brain hippocampus. Proteomic analysis of the graft enabled the identification of pathways and network dysfunction in AD patient brain cells, associated with increased levels of Aβ-42 and β-sheet structures. Interestingly, the host cells surrounding the AD graft also presented alterations in cellular biological pathways. Furthermore, proteomic analysis across human iPSC-based models and human post-mortem hippocampal tissue projected coherent longitudinal cellular changes indicative of early to end stage AD cellular pathogenesis. Our data showcase patient-based models to study the cell autonomous origin and progression of AD pathogenesis.

Lysosomal TMEM106B interacts with galactosylceramidase to regulate myelin lipid metabolism

TMEM106B is an endolysosomal transmembrane protein not only associated with multiple neurological disorders including frontotemporal dementia, Alzheimer's disease, and hypomyelinating leukodystrophy but also potentially involved in COVID-19. Additionally, recent studies have identified amyloid fibrils of C-terminal TMEM106B in both aged healthy and neurodegenerative brains. However, so far little is known about physiological functions of TMEM106B in the endolysosome and how TMEM106B is involved in a wide range of human conditions at molecular levels. Here, we performed lipidomic analysis of the brain of TMEM106B-deficient mice. We found that TMEM106B deficiency significantly decreases levels of two major classes of myelin lipids, galactosylceramide and its sulfated derivative sulfatide. Subsequent co-immunoprecipitation assay showed that TMEM106B physically interacts with galactosylceramidase. We also found that galactosyceramidase activity was significantly increased in TMEM106B-deficient brains. Thus, our results reveal a novel function of TMEM106B interacting with galactosyceramidase to regulate myelin lipid metabolism and have implications for TMEM106B-associated diseases.

Alleviating early demyelination in ischaemia/reperfusion by inhibiting sphingosine-1-phosphate receptor 2 could protect visual function from impairment

Retinal ischaemia/reperfusion (I/R) injury is a common cause of retinal ganglion cell (RGC) apoptosis and axonal degeneration, resulting in irreversible visual impairment. However, there are no available neuroprotective and neurorestorative therapies for retinal I/R injury, and more effective therapeutic approaches are needed. The role of the myelin sheath of the optic nerve after retinal I/R remains unknown. Here, we report that demyelination of the optic nerve is an early pathological feature of retinal I/R and identify sphingosine-1-phosphate receptor 2 (S1PR2) as a therapeutic target for alleviating demyelination in a model of retinal I/R caused by rapid changes in intraocular pressure. Targeting the myelin sheath via S1PR2 protected RGCs and visual function. In our experiment, we observed early damage to the myelin sheath and persistent demyelination accompanied by S1PR2 overexpression after injury. Blockade of S1PR2 by the pharmacological inhibitor JTE-013 reversed demyelination, increased the number of oligodendrocytes, and inhibited microglial activation, contributing to the survival of RGCs and alleviating axonal damage. Finally, we evaluated the postoperative recovery of visual function by recording visual evoked potentials and assessing the quantitative optomotor response. In conclusion, this study is the first to reveal that alleviating demyelination by inhibiting S1PR2 overexpression may be a therapeutic strategy for retinal I/R-related visual impairment.

Role of cytokines and reactive oxygen species in brain aging

Aging is a complex process that produces profound effects on the brain. Although a number of external factors can promote the initiation and progression of brain aging, peripheral and central changes in the immune cells with time, also play an important role. Immunosenescence, which is an age-associated decline in immune function and Inflammaging, a low-grade inflammatory state in the aging brain contribute to an elevation in cytokine and reactive oxygen species production. In this review, we focus on the pro-inflammatory state that is established in the brain as a consequence of these two phenomena and the resulting detrimental changes in brain structure, function and repair that lead to a decline in central and neuroendocrine function.

Astrocytic response mediated by the CLU risk allele inhibits OPC proliferation and myelination in a human iPSC model

The C allele of rs11136000 variant in the clusterin (CLU) gene represents the third strongest known genetic risk factor for late-onset Alzheimer's disease. However, whether this single-nucleotide polymorphism (SNP) is functional and what the underlying mechanisms are remain unclear. In this study, the CLU rs11136000 SNP is identified as a functional variant by a small-scale CRISPR-Cas9 screen. Astrocytes derived from isogenic induced pluripotent stem cells (iPSCs) carrying the "C" or "T" allele of the CLU rs11136000 SNP exhibit different CLU expression levels. TAR DNA-binding protein-43 (TDP-43) preferentially binds to the "C" allele to promote CLU expression and exacerbate inflammation. The interferon response and CXCL10 expression are elevated in cytokine-treated C/C astrocytes, leading to inhibition of oligodendrocyte progenitor cell (OPC) proliferation and myelination. Accordingly, elevated CLU and CXCL10 but reduced myelin basic protein (MBP) expression are detected in human brains of C/C carriers. Our study uncovers a mechanism underlying reduced white matter integrity observed in the CLU rs11136000 risk "C" allele carriers.

Metabolic syndrome and adiposity: Risk factors for decreased myelin in cognitively healthy adults

Metabolic syndrome (MetS) is a cluster of conditions that affects ∼25% of the global population, including excess adiposity, hyperglycemia, dyslipidemia, and elevated blood pressure. MetS is one of major risk factors not only for chronic diseases, but also for dementia and cognitive dysfunction, although the underlying mechanisms remain poorly understood. White matter is of particular interest in the context of MetS due to the metabolic vulnerability of myelin maintenance, and the accumulating evidence for the importance of the white matter in the pathophysiology of dementia. Therefore, we investigated the associations of MetS risk score and adiposity (combined body mass index and waist circumference) with myelin water fraction measured with myelin water imaging. In 90 cognitively and neurologically healthy adults (20-79 years), we found that both high MetS risk score and adiposity were correlated with lower myelin water fraction in late-myelinating prefrontal and associative fibers, controlling for age, sex, race, ethnicity, education and income. Our findings call for randomized clinical trials to establish causality between MetS, adiposity, and myelin content, and to explore the potential of weight loss and visceral adiposity reduction as means to support maintenance of myelin integrity throughout adulthood, which could open new avenues for prevention or treatment of cognitive decline and dementia.

Oligodendrocytes in human induced pluripotent stem cell-derived cortical grafts remyelinate adult rat and human cortical neurons

Neuronal loss and axonal demyelination underlie long-term functional impairments in patients affected by brain disorders such as ischemic stroke. Stem cell-based approaches reconstructing and remyelinating brain neural circuitry, leading to recovery, are highly warranted. Here, we demonstrate the in vitro and in vivo production of myelinating oligodendrocytes from a human induced pluripotent stem cell (iPSC)-derived long-term neuroepithelial stem (lt-NES) cell line, which also gives rise to neurons with the capacity to integrate into stroke-injured, adult rat cortical networks. Most importantly, the generated oligodendrocytes survive and form myelin-ensheathing human axons in the host tissue after grafting onto adult human cortical organotypic cultures. This lt-NES cell line is the first human stem cell source that, after intracerebral delivery, can repair both injured neural circuitries and demyelinated axons. Our findings provide supportive evidence for the potential future use of human iPSC-derived cell lines to promote effective clinical recovery following brain injuries.

Splenium tract projections of the corpus callosum to the parietal cortex classifies Alzheimer's disease and mild cognitive impairment

The corpus callosum (CC) is the largest bundle of white matter tracts in the brain connecting the left and right cerebral hemispheres. The posterior region of the CC, known as the splenium, seems to be relatively preserved throughout the lifespan and is regularly examined for indications of various pathologies, including Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI). However, the splenium has rarely been investigated in terms of its distinct inter-hemispheric tract bundles that project to bilateral occipital, parietal and temporal areas of the cortex. The aim of the present study was to determine if any of these sub-splenium tract bundles are specifically affected by individuals with AD and MCI compared to normal controls. Diffusion Tensor Imaging was used to directly examine the integrity of these distinct tract bundles and their diffusion metrics were compared between groups of MCI, AD, and control individuals. Results revealed that differences between MCI, AD, and controls were particularly evident at parietal tracts of the CC splenium and were consistent with an interpretation of compromised white matter integrity. Combined parietal tract diffusivity and density information strongly discriminated between AD patients and controls with an accuracy (AUC) of 97.19%. Combined parietal tract diffusivity parameters correctly classified MCI subjects against controls with an accuracy of 74.97%. These findings demonstrated the potential of examining the CC splenium in terms of its distinct inter-hemispheric tract bundles for the diagnosis of AD and MCI.

Axonal energy metabolism, and the effects in aging and neurodegenerative diseases

Human studies consistently identify bioenergetic maladaptations in brains upon aging and neurodegenerative disorders of aging (NDAs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis. Glucose is the major brain fuel and glucose hypometabolism has been observed in brain regions vulnerable to aging and NDAs. Many neurodegenerative susceptible regions are in the topological central hub of the brain connectome, linked by densely interconnected long-range axons. Axons, key components of the connectome, have high metabolic needs to support neurotransmission and other essential activities. Long-range axons are particularly vulnerable to injury, neurotoxin exposure, protein stress, lysosomal dysfunction, etc. Axonopathy is often an early sign of neurodegeneration. Recent studies ascribe axonal maintenance failures to local bioenergetic dysregulation. With this review, we aim to stimulate research in exploring metabolically oriented neuroprotection strategies to enhance or normalize bioenergetics in NDA models. Here we start by summarizing evidence from human patients and animal models to reveal the correlation between glucose hypometabolism and connectomic disintegration upon aging/NDAs. To encourage mechanistic investigations on how axonal bioenergetic dysregulation occurs during aging/NDAs, we first review the current literature on axonal bioenergetics in distinct axonal subdomains: axon initial segments, myelinated axonal segments, and axonal arbors harboring pre-synaptic boutons. In each subdomain, we focus on the organization, activity-dependent regulation of the bioenergetic system, and external glial support. Second, we review the mechanisms regulating axonal nicotinamide adenine dinucleotide (NAD+) homeostasis, an essential molecule for energy metabolism processes, including NAD+ biosynthetic, recycling, and consuming pathways. Third, we highlight the innate metabolic vulnerability of the brain connectome and discuss its perturbation during aging and NDAs. As axonal bioenergetic deficits are developing into NDAs, especially in asymptomatic phase, they are likely exaggerated further by impaired NAD+ homeostasis, the high energetic cost of neural network hyperactivity, and glial pathology. Future research in interrogating the causal relationship between metabolic vulnerability, axonopathy, amyloid/tau pathology, and cognitive decline will provide fundamental knowledge for developing therapeutic interventions.

The Potential of Fasting-Mimicking Diet as a Preventive and Curative Strategy for Alzheimer's Disease

This review examines the potential of fasting-mimicking diets (FMDs) in preventing and treating Alzheimer's disease (AD). FMDs are low-calorie diets that mimic the physiological and metabolic effects of fasting, including the activation of cellular stress response pathways and autophagy. Recent studies have shown that FMDs can reduce amyloid-beta accumulation, tau phosphorylation, and inflammation, as well as improve cognitive function in animal models of AD. Human studies have also reported improvements in AD biomarkers, cognitive functions, and subjective well-being measures following FMDs. However, the optimal duration and frequency of FMDs and their long-term safety and efficacy remain to be determined. Despite these uncertainties, FMDs hold promise as a non-pharmacological approach to AD prevention and treatment, and further research in this area is warranted.

Analyzing the glial proteome in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, memory loss, and changes in behavior. Accumulating evidence indicates that dysfunction of glial cells, including astrocytes, microglia, and oligodendrocytes, may contribute to the development and progression of AD. Large-scale analysis of glial proteins sheds light on their roles in cellular processes and diseases. In AD, glial proteomics has been utilized to understand glia-based pathophysiology and identify potential biomarkers and therapeutic targets.

AREA COVERED

In this review, we provide an updated overview of proteomic analysis of glia in the context of AD. Additionally, we discuss current challenges in the field, involving glial complexity and heterogeneity, and describe some cutting-edge proteomic technologies to address them.

EXPERT OPINION

Unbiased comprehensive analysis of glial proteomes aids our understanding of the molecular and cellular mechanisms of AD pathogenesis. These investigations highlight the crucial role of glial cells and provide novel insights into the mechanisms of AD pathology. A deeper understanding of the AD-related glial proteome could offer a repertoire of potential biomarkers and therapeutics. Further technical advancement of glial proteomics will enable us to identify proteins within individual cells and specific cell types, thus significantly enhancing our comprehension of AD pathogenesis.

Central nervous system sulfatide deficiency as a causal factor for bladder disorder in Alzheimer's disease

BACKGROUND

Despite being a brain disorder, Alzheimer's disease (AD) is often accompanied by peripheral organ dysregulations (e.g., loss of bladder control in late-stage AD), which highly rely on spinal cord coordination. However, the causal factor(s) for peripheral organ dysregulation in AD remain elusive.

METHODS

The central nervous system (CNS) is enriched in lipids. We applied quantitative shotgun lipidomics to determine lipid profiles of human AD spinal cord tissues. Additionally, a CNS sulfatide (ST)-deficient mouse model was used to study the lipidome, transcriptome and peripheral organ phenotypes of ST loss.

RESULTS

We observed marked myelin lipid reduction in the spinal cord of AD subjects versus cognitively normal individuals. Among which, levels of ST, a myelin-enriched lipid class, were strongly and negatively associated with the severity of AD. A CNS myelin-specific ST-deficient mouse model was used to further identify the causes and consequences of spinal cord lipidome changes. Interestingly, ST deficiency led to spinal cord lipidome and transcriptome profiles highly resembling those observed in AD, characterized by decline of multiple myelin-enriched lipid classes and enhanced inflammatory responses, respectively. These changes significantly disrupted spinal cord function and led to substantial enlargement of urinary bladder in ST-deficient mice.

CONCLUSIONS

Our study identified CNS ST deficiency as a causal factor for AD-like lipid dysregulation, inflammation response and ultimately the development of bladder disorders. Targeting to maintain ST levels may serve as a promising strategy for the prevention and treatment of AD-related peripheral disorders.

The contribution of DNA methylation to the (dys)function of oligodendroglia in neurodegeneration

Neurodegenerative diseases encompass a heterogeneous group of conditions characterised by the progressive degeneration of the structure and function of the central or peripheral nervous systems. The pathogenic mechanisms underlying these diseases are not fully understood. However, a central feature consists of regional aggregation of proteins in the brain, such as the accumulation of β-amyloid plaques in Alzheimer's disease (AD), inclusions of hyperphosphorylated microtubule-binding tau in AD and other tauopathies, or inclusions containing α-synuclein in Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Various pathogenic mechanisms are thought to contribute to disease, and an increasing number of studies implicate dysfunction of oligodendrocytes (the myelin producing cells of the central nervous system) and myelin loss. Aberrant DNA methylation, the most widely studied epigenetic modification, has been associated with many neurodegenerative diseases, including AD, PD, DLB and MSA, and recent findings highlight aberrant DNA methylation in oligodendrocyte/myelin-related genes. Here we briefly review the evidence showing that changes to oligodendrocytes and myelin are key in neurodegeneration, and explore the relevance of DNA methylation in oligodendrocyte (dys)function. As DNA methylation is reversible, elucidating its involvement in pathogenic mechanisms of neurodegenerative diseases and in dysfunction of specific cell-types such as oligodendrocytes may bring opportunities for therapeutic interventions for these diseases.

The toxic metal hypothesis for neurological disorders

Multiple sclerosis and the major sporadic neurogenerative disorders, amyotrophic lateral sclerosis, Parkinson disease, and Alzheimer disease are considered to have both genetic and environmental components. Advances have been made in finding genetic predispositions to these disorders, but it has been difficult to pin down environmental agents that trigger them. Environmental toxic metals have been implicated in neurological disorders, since human exposure to toxic metals is common from anthropogenic and natural sources, and toxic metals have damaging properties that are suspected to underlie many of these disorders. Questions remain, however, as to how toxic metals enter the nervous system, if one or combinations of metals are sufficient to precipitate disease, and how toxic metal exposure results in different patterns of neuronal and white matter loss. The hypothesis presented here is that damage to selective locus ceruleus neurons from toxic metals causes dysfunction of the blood-brain barrier. This allows circulating toxicants to enter astrocytes, from where they are transferred to, and damage, oligodendrocytes, and neurons. The type of neurological disorder that arises depends on (i) which locus ceruleus neurons are damaged, (ii) genetic variants that give rise to susceptibility to toxic metal uptake, cytotoxicity, or clearance, (iii) the age, frequency, and duration of toxicant exposure, and (iv) the uptake of various mixtures of toxic metals. Evidence supporting this hypothesis is presented, concentrating on studies that have examined the distribution of toxic metals in the human nervous system. Clinicopathological features shared between neurological disorders are listed that can be linked to toxic metals. Details are provided on how the hypothesis applies to multiple sclerosis and the major neurodegenerative disorders. Further avenues to explore the toxic metal hypothesis for neurological disorders are suggested. In conclusion, environmental toxic metals may play a part in several common neurological disorders. While further evidence to support this hypothesis is needed, to protect the nervous system it would be prudent to take steps to reduce environmental toxic metal pollution from industrial, mining, and manufacturing sources, and from the burning of fossil fuels.

Regional contribution of vascular dysfunction in white matter dementia: clinical and neuropathological insights

The maintenance of adequate blood supply and vascular integrity is fundamental to ensure cerebral function. A wide range of studies report vascular dysfunction in white matter dementias, a group of cerebral disorders characterized by substantial white matter damage in the brain leading to cognitive impairment. Despite recent advances in imaging, the contribution of vascular-specific regional alterations in white matter dementia has been not extensively reviewed. First, we present an overview of the main components of the vascular system involved in the maintenance of brain function, modulation of cerebral blood flow and integrity of the blood-brain barrier in the healthy brain and during aging. Second, we review the regional contribution of cerebral blood flow and blood-brain barrier disturbances in the pathogenesis of three distinct conditions: the archetypal white matter predominant neurocognitive dementia that is vascular dementia, a neuroinflammatory predominant disease (multiple sclerosis) and a neurodegenerative predominant disease (Alzheimer's). Finally, we then examine the shared landscape of vascular dysfunction in white matter dementia. By emphasizing the involvement of vascular dysfunction in the white matter, we put forward a hypothetical map of vascular dysfunction during disease-specific progression to guide future research aimed to improve diagnostics and facilitate the development of tailored therapies.

Alzheimer's disease and multiple sclerosis: a possible connection through the viral demyelinating neurodegenerative trigger (vDENT)

Alzheimer's disease (AD) and multiple sclerosis (MS) are two CNS disorders affecting millions of people, for which no cure is available. AD is usually diagnosed in individuals age 65 and older and manifests with accumulation of beta amyloid in the brain. MS, a demyelinating disorder, is most commonly diagnosed in its relapsing-remitting (RRMS) form in young adults (age 20-40). The lack of success in a number of recent clinical trials of immune- or amyloid-targeting therapeutics emphasizes our incomplete understanding of their etiology and pathogenesis. Evidence is accumulating that infectious agents such as viruses may contribute either directly or indirectly. With the emerging recognition that demyelination plays a role in risk and progression of AD, we propose that MS and AD are connected by sharing a common environmental factor (a viral infection such as HSV-1) and pathology (demyelination). In the viral DEmyelinating Neurodegenerative Trigger (vDENT) model of AD and MS, the initial demyelinating viral (e.g., HSV-1) infection provokes the first episode of demyelination that occurs early in life, with subsequent virus reactivations/demyelination and associated immune/inflammatory attacks resulting in RRMS. The accumulating damage and/or virus progression deeper into CNS leads to amyloid dysfunction, which, combined with the inherent age-related defects in remyelination, propensity for autoimmunity, and increased blood-brain barrier permeability, leads to the development of AD dementia later in life. Preventing or diminishing vDENT event(s) early in life, thus, may have a dual benefit of slowing down the progression of MS and reducing incidence of AD at an older age.

Artificial Intelligence as a Tool for the Diagnosis and Treatment of Neurodegenerative Diseases

While humans have much in common biologically with other mammalian species, they are largely distinguished by their innate intelligence, specifically, their ability to generate complex and sophisticated tools [...].

Predictive value of hypercholesterolemia, vegetarian diet, and hypertension for incident dementia among elderly Taiwanese individuals with low educational levels

Objective

Early management of modifiable dementia-related factors is seen as a novel approach to preventing dementia onset; however, these efforts are often hindered by the complexity of interactions among these factors. In addition, different modifiable dementia-related factors may contribute to different etiologies of dementia.

Design

The current study investigated the effects of common modifiable dementia-related factors on prediction of incident dementia, dementia of the Alzheimer's type (DAT), and vascular dementia (VaD).

Methods

Vascular- and lifestyle-related factors were used as predictors of incident dementia, DAT, and VaD among 1,285 elderly individuals without obvious signs of dementia or mild cognitive impairment. Cox proportional hazard models were used to evaluate the risks associated with each modifiable factor.

Results

After controlling for factors other than stroke-related factors, hypercholesterolemia was correlated with a relatively low risk of all-cause incident dementia and DAT, whereas a vegetarian diet was correlated with an elevated risk of all-cause incident dementia and VaD. Hypertension was correlated with incident VaD. After controlling for stroke-related factors, a vegetarian diet was correlated with an elevated risk of all-cause dementia. A history of myocardiac infarction and the use of anti-platelet medication were, respectively, associated with a reduced risk of DAT and elevated risk of VaD. The use of anti-hypertensives was associated with a reduced risk of all-cause dementia, whereas the use of anti-lipid agents was associated with slow progression DAT (i.e. exceeding the average conversion time). Hypercholesterolemia was associated with an elevated risk for slow progression DAT.

Conclusion

These findings could perhaps be used as clinical markers in predicting and preventing incident dementia, DAT, and VaD.

Cerebral white matter rarefaction has both neurodegenerative and vascular causes and may primarily be a distal axonopathy

Cerebral white matter rarefaction (CWMR) was considered by Binswanger and Alzheimer to be due to cerebral arteriolosclerosis. Renewed attention came with CT and MR brain imaging, and neuropathological studies finding a high rate of CWMR in Alzheimer disease (AD). The relative contributions of cerebrovascular disease and AD to CWMR are still uncertain. In 1181 autopsies by the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND), large-format brain sections were used to grade CWMR and determine its vascular and neurodegenerative correlates. Almost all neurodegenerative diseases had more severe CWMR than the normal control group. Multivariable logistic regression models indicated that Braak neurofibrillary stage was the strongest predictor of CWMR, with additional independently significant predictors including age, cortical and diencephalic lacunar and microinfarcts, body mass index, and female sex. It appears that while AD and cerebrovascular pathology may be additive in causing CWMR, both may be solely capable of this. The typical periventricular pattern suggests that CWMR is primarily a distal axonopathy caused by dysfunction of the cell bodies of long-association corticocortical projection neurons. A consequence of these findings is that CWMR should not be viewed simply as "small vessel disease" or as a pathognomonic indicator of vascular cognitive impairment or vascular dementia.

Epigenetic regulation of human-specific gene expression in the prefrontal cortex

BACKGROUND

Changes in gene expression levels during brain development are thought to have played an important role in the evolution of human cognition. With the advent of high-throughput sequencing technologies, changes in brain developmental expression patterns, as well as human-specific brain gene expression, have been characterized. However, interpreting the origin of evolutionarily advanced cognition in human brains requires a deeper understanding of the regulation of gene expression, including the epigenomic context, along the primate genome. Here, we used chromatin immunoprecipitation sequencing (ChIP-seq) to measure the genome-wide profiles of histone H3 lysine 4 trimethylation (H3K4me3) and histone H3 lysine 27 acetylation (H3K27ac), both of which are associated with transcriptional activation in the prefrontal cortex of humans, chimpanzees, and rhesus macaques.

RESULTS

We found a discrete functional association, in which ^H3K4me3HP gain was significantly associated with myelination assembly and signaling transmission, while ^H3K4me3HP loss played a vital role in synaptic activity. Moreover, ^H3K27acHP gain was enriched in interneuron and oligodendrocyte markers, and ^H3K27acHP loss was enriched in CA1 pyramidal neuron markers. Using strand-specific RNA sequencing (ssRNA-seq), we first demonstrated that approximately 7 and 2% of human-specific expressed genes were epigenetically marked by ^H3K4me3HP and ^H3K27acHP, respectively, providing robust support for causal involvement of histones in gene expression. We also revealed the co-activation role of epigenetic modification and transcription factors in human-specific transcriptome evolution. Mechanistically, histone-modifying enzymes at least partially contribute to an epigenetic disturbance among primates, especially for the H3K27ac epigenomic marker. In line with this, peaks enriched in the macaque lineage were found to be driven by upregulated acetyl enzymes.

CONCLUSIONS

Our results comprehensively elucidated a causal species-specific gene-histone-enzyme landscape in the prefrontal cortex and highlighted the regulatory interaction that drove transcriptional activation.

Multi-Scale Label-free Human Brain Imaging with Integrated Serial Sectioning Polarization Sensitive Optical Coherence Tomography and Two-Photon Microscopy

The study of neurodegenerative processes in the human brain requires a comprehensive understanding of cytoarchitectonic, myeloarchitectonic, and vascular structures. Recent computational advances have enabled volumetric reconstruction of the human brain using thousands of stained slices, however, tissue distortions and loss resulting from standard histological processing have hindered deformation-free reconstruction of the human brain. The development of a multi-scale and volumetric human brain imaging technique that can measure intact brain structure would be a major technical advance. Here, we describe the development of integrated serial sectioning Polarization Sensitive Optical Coherence Tomography (PSOCT) and Two Photon Microscopy (2PM) to provide label-free multi-contrast imaging, including scattering, birefringence and autofluorescence of human brain tissue. We demonstrate that high-throughput reconstruction of 4×4×2cm3 sample blocks and simple registration of PSOCT and 2PM images enable comprehensive analysis of myelin content, vascular structure, and cellular information. We show that 2μm in-plane resolution 2PM images provide microscopic validation and enrichment of the cellular information provided by the PSOCT optical property maps on the same sample, revealing the sophisticated capillary networks and lipofuscin filled cell bodies across the cortical layers. Our method is applicable to the study of a variety of pathological processes, including demyelination, cell loss, and microvascular changes in neurodegenerative diseases such as Alzheimer's disease (AD) and Chronic Traumatic Encephalopathy (CTE).