Distinct characteristics of limbic-predominant age-related TDP-43 encephalopathy in Lewy body disease

Cytoplasmic expression of trans-active response DNA-binding protein-43 in aged mice display hippocampal sclerosis-like degeneration and neuronal loss with reduced lifespan

Trans-active response DNA-binding protein-43 (TDP-43) is the major pathological protein in motor neuron disease and TDP-43 pathology has been described in the brains of up to 50% of patients with Alzheimer disease (AD). Hippocampal sclerosis of aging (HS-A), an age-related neuropathology characterized by severe neuronal loss and gliosis in CA1 and/or subiculum, is found in ∼80% of cases that are positive for phosphorylated TDP-43. HS-A is seen as a co-pathology in cases with AD, limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC), and frontotemporal degeneration. To understand the pathogenetic relationships between HS-A and LATE-NC, mice that selectively express human TDP-43 and TDP-43 with a defective nuclear localization signal (ΔNLS) in the hippocampus, alone or in an APP/PSEN1 background, were evaluated using histology, HALO software's object recognition algorithms, and protein expression assays. Twenty-four-month-old mice expressing cytosolic TDP-43 displayed marked neuronal loss and atrophy in the hippocampus, decreased β-amyloid plaque deposition and modulation of microglia and intermediate filament activation. TDP-43ΔNLS-expressing mice survived to only ∼24 months of age whether or not they had an APP/PSEN1 background. This HS-A-like model may provide insights into the pathogenesis of neurodegeneration seen in HS-A and in other TDP-43 proteinopathies.

Co-pathologies modify hippocampal protein accumulation patterns in neurodegenerative diseases

INTRODUCTION

Limited research has extensively analyzed neurodegenerative disease-related protein deposition patterns in the hippocampus.

METHODS

This study examined the distribution of proteins in hippocampal subregions across major neurodegenerative diseases and explored their relation to each other. The area density of phosphorylated tau (p-tau), amyloid beta (Aβ), α-synuclein, and phosphorylated TDP-43 protein deposits together with pyramidal cell density in each hippocampal subregion, including CA1-4, prosubiculum (ProS), and subiculum was assessed in 166 cases encompassing various neurodegenerative diseases.

RESULTS

Alzheimer's disease-associated p-tau predominated in ProS, Aβ in the CA1, and Lewy body-related α-synuclein in the CA2. The area density of protein deposits increased with the pathological stage until a peak, then decreased in cases with high pathology stages along with pyramidal cell density. Comorbid protein pathology influenced protein deposition patterns.

DISCUSSION

This comprehensive evaluation reveals characteristic neurodegenerative disease-related protein accumulation patterns in hippocampal subregions modified by co-pathologies.

HIGHLIGHTS

Alzheimer's disease-related phosphorylated tau predominates in the prosubiculum. Amyloid beta predominates in the CA1 and Lewy body-related α-synuclein in the CA2. The area density of protein deposition increases with the disease stage up to a peak. In the high pathology stage, protein deposition and pyramidal cell density decreases. Comorbid protein pathology affects the pattern of protein accumulation.

Medial temporal atrophy predicts the limbic comorbidities in lewy body disease

PURPOSE

Although neuropathological comorbidities, including Alzheimer's disease neuropathological change (AD-NC) and limbic-predominant age-related TAR DNA-binding protein 43encephalopathy neuropathological change (LATE-NC), are associated with medial temporal atrophy in patients with Lewy body disease (LBD), the diagnostic performance of magnetic resonance imaging (MRI)-derived indices remains unclear. This study aimed to investigate the diagnostic performance of MRI-derived indices representing medial temporal atrophy in differentiating between LBD with AD-NC and/or LATE-NC (mixed LBD [mLBD]) and without these comorbidities (pure LBD [pLBD]).

METHODS

This study included 24 and 16 patients with pathologically confirmed mLBD and pLBD, respectively. In addition to the well-known medial temporal atrophy and entorhinal cortex atrophy (ERICA) scores, the cross-sectional areas of the bilateral entorhinal cortices/parahippocampal gyri (ABEP) were segmented manually.

RESULTS

Even incorporating various covariates such as age at MRI examination, sex, argyrophilic grain, the MRI-derived indices, especially ABEP, significantly correlated with the severity of AD-NC, and showed a trend of correlation with LATE-NC. For the differentiation between all mLBD and pLBD, the ERICA score and ABEP demonstrated higher diagnostic performance (area under the receiver-operating-characteristic curve [AUC] of 0.80 and 0.87, respectively). Additionally, the highest diagnostic performance for ABEP (AUC, 0.94; sensitivity, 100%; specificity, 88.9%; accuracy, 96%) was observed in differentiating between pLBD and mLBD with two comorbidities (AD-NC and LATE-NC).

CONCLUSION

In patients with pathologically confirmed LBD, medial temporal atrophy was significantly correlated with AD-NC, and showed a trend of correlation with LATE-NC. Moreover, MRI-derived indices indicative of medial temporal atrophy were useful in diagnosing these comorbidities.

Pure LATE-NC: Frequency, clinical impact, and the importance of considering APOE genotype when assessing this and other subtypes of non-Alzheimer's pathologies

Pure limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (pure LATE-NC) is a term used to describe brains with LATE-NC but lacking intermediate or severe levels of Alzheimer's disease neuropathologic changes (ADNC). Focusing on pure LATE-NC, we analyzed data from the National Alzheimer's Coordinating Center (NACC) Neuropathology Data Set, comprising clinical and pathological information aggregated from 32 NIH-funded Alzheimer's Disease Research Centers (ADRCs). After excluding subjects dying with unusual conditions, n = 1,926 autopsied subjects were included in the analyses. For > 90% of these participants, apolipoprotein E (APOE) allele status was known; 46.5% had at least one APOE 4 allele. In most human populations, only 15-25% of people are APOE ε4 carriers. ADRCs with higher documented AD risk allele (APOE or BIN1) rates had fewer participants lacking ADNC, and correspondingly low rates of pure LATE-NC. Among APOE ε4 non-carries, 5.3% had pure LATE-NC, 37.0% had pure ADNC, and 3.6% had pure neocortical Lewy body pathology. In terms of clinical impact, participants with pure LATE-NC tended to die after having received a diagnosis of dementia: 56% died with dementia among APOE ε4 non-carrier participants, comparable to 61% with pure ADNC. LATE-NC was associated with increased Clinical Dementia Rating Sum of Boxes (CDR-SOB) scores, i.e. worsened global cognitive impairments, in participants with no/low ADNC and no neocortical Lewy body pathology (p = 0.0023). Among pure LATE-NC cases, there was a trend for higher LATE-NC stages to be associated with worse CDR-SOB scores (p = 0.026 for linear trend of LATE-NC stages). Pure LATE-NC was not associated with clinical features of disinhibition or primary progressive aphasia. In summary, LATE-NC with no or low levels of ADNC was less frequent than pure ADNC but was not rare, particularly among individuals who lacked the APOE 4 allele, and in study cohorts with APOE 4 frequencies similar to those in most human populations.

Cytoplasmic aggregation of TDP43 and topographic correlation with tau and α-synuclein accumulation in the rTg4510 mouse model of tauopathy

In patients with TDP43 proteinopathy, phosphorylated TDP43 (p-TDP43) accumulates in the cytoplasm of neurons. The accumulation of p-TDP43 has also been reported in patients with tauopathy and α-synucleinopathy. We investigated spatiotemporal changes in p-TDP43 accumulation in the brains of rTg4510 mice that overexpressed human mutant tau (P301L) and exhibited hyperphosphorylated tau (hp-tau) and phosphorylated αSyn (p-αSyn) accumulation. Immunohistochemically, p-TDP43 aggregates were observed in the cytoplasm of neurons, which increased with age. A significant positive correlation was observed between the number of cells with p-TDP43 aggregates and hp-tau and p-αSyn aggregates. Suppression of the human mutant tau (P301L) expression by doxycycline treatment reduces the accumulation of p-TDP43, hp-tau, and p-αSyn. Proteinase K-resistant p-TDP43 aggregates were found in regions with high hp-tau, and p-αSyn accumulation. Western blotting of the sarkosyl-insoluble fraction revealed bands of monomeric TDP43 and p-TDP43. These results indicate that the accumulation of mouse p-TDP43 is associated with the accumulation of human mutant tau (P301L) in rTg4510 mouse brains. The accumulation of hp-tau and p-αSyn may promote sarkosyl-insoluble p-TDP43 aggregates that are resistant to proteinase K. The synergistic effects of tau, TDP43, and αSyn may be involved in the pathology of proteinopathies, leading to the accumulation of multiple abnormal proteins.

Network proteomics of the Lewy body dementia brain reveals presynaptic signatures distinct from Alzheimer's disease

Lewy body dementia (LBD), a class of disorders comprising Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB), features substantial clinical and pathological overlap with Alzheimer's disease (AD). The identification of biomarkers unique to LBD pathophysiology could meaningfully advance its diagnosis, monitoring, and treatment. Using quantitative mass spectrometry (MS), we measured over 9,000 proteins across 138 dorsolateral prefrontal cortex (DLPFC) tissues from a University of Pennsylvania autopsy collection comprising control, Parkinson's disease (PD), PDD, and DLB diagnoses. We then analyzed co-expression network protein alterations in those with LBD, validated these disease signatures in two independent LBD datasets, and compared these findings to those observed in network analyses of AD cases. The LBD network revealed numerous groups or "modules" of co-expressed proteins significantly altered in PDD and DLB, representing synaptic, metabolic, and inflammatory pathophysiology. A comparison of validated LBD signatures to those of AD identified distinct differences between the two diseases. Notably, synuclein-associated presynaptic modules were elevated in LBD but decreased in AD relative to controls. We also found that glial-associated matrisome signatures consistently elevated in AD were more variably altered in LBD, ultimately stratifying those LBD cases with low versus high burdens of concurrent beta-amyloid deposition. In conclusion, unbiased network proteomic analysis revealed diverse pathophysiological changes in the LBD frontal cortex distinct from alterations in AD. These results highlight the LBD brain network proteome as a promising source of biomarkers that could enhance clinical recognition and management.

LATE-NC in Alzheimer's disease: Molecular aspects and synergies

Alzheimer's disease (AD) is classically characterized by senile plaques and neurofibrillary tangles (NFTs). However, multiple copathologies can be observed in the AD brain and contribute to the development of cognitive decline. Limbic-predominant age-related TDP-43 encephalopathy neuropathological changes (LATE-NC) accumulates in the majority of AD cases and leads to more severe cognitive decline compared with AD pathology alone. In this review, we focus on the synergistic relationship between LATE-NC and tau in AD, highlighting the aggravating role of TDP-43 aggregates on tau pathogenesis and its impact on the clinical picture and therapeutic strategies. Additionally, we discuss to what extent the molecular patterns of LATE-NC in AD differ from frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP) neuropathological changes. Thus, we highlight the importance of tau and TDP-43 synergies for subtyping AD patients, which may respond differently to therapeutic interventions depending on the presence of comorbid LATE-NC.

Limbic-predominant age-related TDP-43 encephalopathy (LATE-NC): Co-pathologies and genetic risk factors provide clues about pathogenesis

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is detectable at autopsy in more than one-third of people beyond age 85 years and is robustly associated with dementia independent of other pathologies. Although LATE-NC has a large impact on public health, there remain uncertainties about the underlying biologic mechanisms. Here, we review the literature from human studies that may shed light on pathogenetic mechanisms. It is increasingly clear that certain combinations of pathologic changes tend to coexist in aging brains. Although "pure" LATE-NC is not rare, LATE-NC often coexists in the same brains with Alzheimer disease neuropathologic change, brain arteriolosclerosis, hippocampal sclerosis of aging, and/or age-related tau astrogliopathy (ARTAG). The patterns of pathologic comorbidities provide circumstantial evidence of mechanistic interactions ("synergies") between the pathologies, and also suggest common upstream influences. As to primary mediators of vulnerability to neuropathologic changes, genetics may play key roles. Genes associated with LATE-NC include TMEM106B, GRN, APOE, SORL1, ABCC9, and others. Although the anatomic distribution of TDP-43 pathology defines the condition, important cofactors for LATE-NC may include Tau pathology, endolysosomal pathways, and blood-brain barrier dysfunction. A review of the human phenomenology offers insights into disease-driving mechanisms, and may provide clues for diagnostic and therapeutic targets.

A transient protein folding response targets aggregation in the early phase of TDP-43-mediated neurodegeneration

Understanding the mechanisms that drive TDP-43 pathology is integral to combating amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD) and other neurodegenerative diseases. Here we generated a longitudinal quantitative proteomic map of the cortex from the cytoplasmic TDP-43 rNLS8 mouse model of ALS and FTLD, and developed a complementary open-access webtool, TDP-map ( https://shiny.rcc.uq.edu.au/TDP-map/ ). We identified distinct protein subsets enriched for diverse biological pathways with temporal alterations in protein abundance, including increases in protein folding factors prior to disease onset. This included increased levels of DnaJ homolog subfamily B member 5, DNAJB5, which also co-localized with TDP-43 pathology in diseased human motor cortex. DNAJB5 over-expression decreased TDP-43 aggregation in cell and cortical neuron cultures, and knockout of Dnajb5 exacerbated motor impairments caused by AAV-mediated cytoplasmic TDP-43 expression in mice. Together, these findings reveal molecular mechanisms at distinct stages of ALS and FTLD progression and suggest that protein folding factors could be protective in neurodegenerative diseases.

Network Proteomics of the Lewy Body Dementia Brain Reveals Presynaptic Signatures Distinct from Alzheimer's Disease

Lewy body dementia (LBD), a class of disorders comprising Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB), features substantial clinical and pathological overlap with Alzheimer's disease (AD). The identification of biomarkers unique to LBD pathophysiology could meaningfully advance its diagnosis, monitoring, and treatment. Using quantitative mass spectrometry (MS), we measured over 9,000 proteins across 138 dorsolateral prefrontal cortex (DLPFC) tissues from a University of Pennsylvania autopsy collection comprising control, Parkinson's disease (PD), PDD, and DLB diagnoses. We then analyzed co-expression network protein alterations in those with LBD, validated these disease signatures in two independent LBD datasets, and compared these findings to those observed in network analyses of AD cases. The LBD network revealed numerous groups or "modules" of co-expressed proteins significantly altered in PDD and DLB, representing synaptic, metabolic, and inflammatory pathophysiology. A comparison of validated LBD signatures to those of AD identified distinct differences between the two diseases. Notably, synuclein-associated presynaptic modules were elevated in LBD but decreased in AD relative to controls. We also found that glial-associated matrisome signatures consistently elevated in AD were more variably altered in LBD, ultimately stratifying those LBD cases with low versus high burdens of concurrent beta-amyloid deposition. In conclusion, unbiased network proteomic analysis revealed diverse pathophysiological changes in the LBD frontal cortex distinct from alterations in AD. These results highlight the LBD brain network proteome as a promising source of biomarkers that could enhance clinical recognition and management.

α-Synuclein emulsifies TDP-43 prion-like domain-RNA liquid droplets to promote heterotypic amyloid fibrils

Many neurodegenerative diseases including frontotemporal lobar degeneration (FTLD), Lewy body disease (LBD), multiple system atrophy (MSA), etc., show colocalized deposits of TDP-43 and α-synuclein (αS) aggregates. To understand whether these colocalizations are driven by specific molecular interactions between the two proteins, we previously showed that the prion-like C-terminal domain of TDP-43 (TDP-43PrLD) and αS synergistically interact to form neurotoxic heterotypic amyloids in homogeneous buffer conditions. However, it remains unclear if αS can modulate TDP-43 present within liquid droplets and biomolecular condensates called stress granules (SGs). Here, using cell culture and in vitro TDP-43PrLD - RNA liquid droplets as models along with microscopy, nanoscale AFM-IR spectroscopy, and biophysical analyses, we uncover the interactions of αS with phase-separated droplets. We learn that αS acts as a Pickering agent by forming clusters on the surface of TDP-43PrLD - RNA droplets. The aggregates of αS on these clusters emulsify the droplets by nucleating the formation of heterotypic TDP-43PrLD amyloid fibrils, structures of which are distinct from those derived from homogenous solutions. Together, these results reveal an intriguing property of αS to act as a Pickering agent while interacting with SGs and unmask the hitherto unknown role of αS in modulating TDP-43 proteinopathies.

Limbic-predominant age-related TDP43 encephalopathy (LATE) neuropathological change in neurodegenerative diseases

TAR DNA-binding protein 43 (TDP43) is a focus of research in late-onset dementias. TDP43 pathology in the brain was initially identified in amyotrophic lateral sclerosis and frontotemporal lobar degeneration, and later in Alzheimer disease (AD), other neurodegenerative diseases and ageing. Limbic-predominant age-related TDP43 encephalopathy (LATE), recognized as a clinical entity in 2019, is characterized by amnestic dementia resembling AD dementia and occurring most commonly in adults over 80 years of age. Neuropathological findings in LATE, referred to as LATE neuropathological change (LATE-NC), consist of neuronal and glial cytoplasmic TDP43 localized predominantly in limbic areas with or without coexisting hippocampal sclerosis and/or AD neuropathological change and without frontotemporal lobar degeneration or amyotrophic lateral sclerosis pathology. LATE-NC is frequently associated with one or more coexisting pathologies, mainly AD neuropathological change. The focus of this Review is the pathology, genetic risk factors and nature of the cognitive impairments and dementia in pure LATE-NC and in LATE-NC associated with coexisting pathologies. As the clinical and cognitive profile of LATE is currently not easily distinguishable from AD dementia, it is important to develop biomarkers to aid in the diagnosis of this condition in the clinic. The pathogenesis of LATE-NC should be a focus of future research to form the basis for the development of preventive and therapeutic strategies.

α-Synuclein emulsifies TDP-43 prion-like domain - RNA liquid droplets to promote heterotypic amyloid fibrils

Many neurodegenerative diseases including frontotemporal lobar degeneration (FTLD), Lewy body disease (LBD), multiple system atrophy (MSA), etc., show colocalized deposits of TDP-43 and α-synuclein (αS) aggregates. To understand whether these colocalizations are driven by specific molecular interactions between the two proteins, we previously showed that the prion-like C-terminal domain of TDP-43 (TDP-43PrLD) and αS synergistically interact to form neurotoxic heterotypic amyloids in homogeneous buffer conditions. However, it remains unclear whether and how αS modulates TDP-43 present within liquid droplets and biomolecular condensates called stress granules (SGs). Here, using cell culture and in vitro TDP-43PrLD - RNA liquid droplets as models along with microscopy, nanoscale spatially-resolved spectroscopy, and other biophysical analyses, we uncover the interactions of αS with phase-separated droplets. We learn that αS acts as a Pickering agent by forming clusters on the surface of TDP-43PrLD - RNA droplets and emulsifying them. The 'hardening' of the droplets that follow by αS aggregates on the periphery, nucleates the formation of heterotypic TDP-43PrLD amyloid fibrils with structures distinct from those derived from homogenous solutions. Together, these results reveal an intriguing property of αS as a Pickering agent in interacting with SGs and unmask the hitherto unknown role of αS in modulating TDP-43 proteinopathies.

Hippocampal sclerosis of aging at post-mortem is evident on MRI more than a decade prior

INTRODUCTION

Hippocampal sclerosis of aging (HS) is an important component of combined dementia neuropathology. However, the temporal evolution of its histologically-defined features is unknown. We investigated pre-mortem longitudinal hippocampal atrophy associated with HS, as well as with other dementia-associated pathologies.

METHODS

We analyzed hippocampal volumes from MRI segmentations in 64 dementia patients with longitudinal MRI follow-up and post-mortem neuropathological evaluation, including HS assessment in the hippocampal head and body.

RESULTS

Significant HS-associated hippocampal volume changes were observed thoughout the evaluated timespan, up to 11.75 years before death. These changes were independent of age and Alzheimer’s Disease (AD) burden, and specifically driven by CA1 and subiculum. AD burden, but not HS, significantly associated with the rate of hippocampal atrophy.

DISCUSSION

HS-associated volume changes are detectable on MRI earlier than 10 years before death. These findings could contribute to the derivation of volumetric cut-offs for in vivo differentiation between HS and AD.

The unique neuropathological vulnerability of the human brain to aging

Alzheimer's disease (AD)-related neurofibrillary tangles (NFT), argyrophilic grain disease (AGD), aging-related tau astrogliopathy (ARTAG), limbic predominant TDP-43 proteinopathy (LATE), and amygdala-predominant Lewy body disease (LBD) are proteinopathies that, together with hippocampal sclerosis, progressively appear in the elderly affecting from 50% to 99% of individuals aged 80 years, depending on the disease. These disorders usually converge on the same subject and associate with additive cognitive impairment. Abnormal Tau, TDP-43, and α-synuclein pathologies progress following a pattern consistent with an active cell-to-cell transmission and abnormal protein processing in the host cell. However, cell vulnerability and transmission pathways are specific for each disorder, albeit abnormal proteins may co-localize in particular neurons. All these alterations are unique or highly prevalent in humans. They all affect, at first, the archicortex and paleocortex to extend at later stages to the neocortex and other regions of the telencephalon. These observations show that the phylogenetically oldest areas of the human cerebral cortex and amygdala are not designed to cope with the lifespan of actual humans. New strategies aimed at reducing the functional overload of the human telencephalon, including optimization of dream repair mechanisms and implementation of artificial circuit devices to surrogate specific brain functions, appear promising.

LATE-NC staging in routine neuropathologic diagnosis: an update

An international consensus report in 2019 recommended a classification system for limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC). The suggested neuropathologic staging system and nomenclature have proven useful for autopsy practice and dementia research. However, some issues remain unresolved, such as cases with unusual features that do not fit with current diagnostic categories. The goal of this report is to update the neuropathologic criteria for the diagnosis and staging of LATE-NC, based primarily on published data. We provide practical suggestions about how to integrate available genetic information and comorbid pathologies [e.g., Alzheimer's disease neuropathologic changes (ADNC) and Lewy body disease]. We also describe recent research findings that have enabled more precise guidance on how to differentiate LATE-NC from other subtypes of TDP-43 pathology [e.g., frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS)], and how to render diagnoses in unusual situations in which TDP-43 pathology does not follow the staging scheme proposed in 2019. Specific recommendations are also made on when not to apply this diagnostic term based on current knowledge. Neuroanatomical regions of interest in LATE-NC are described in detail and the implications for TDP-43 immunohistochemical results are specified more precisely. We also highlight questions that remain unresolved and areas needing additional study. In summary, the current work lays out a number of recommendations to improve the precision of LATE-NC staging based on published reports and diagnostic experience.

Clinicopathological diversity of semantic dementia: Comparisons of patients with early-onset versus late-onset, left-sided versus right-sided temporal atrophy, and TDP-type A versus type C pathology

Semantic dementia (SD) is a unique clinicopathological entity associated with TDP-type C pathology. We present four cases of SD that illustrate the clinicopathological diversity of TDP-43 pathology, including early-onset cases of TDP-type C with corticospinal tract (CST) and motor neuron pathology and late-onset cases of TDP-type A with combined pathology. Case 1 was a 62-year-old man with semantic variant of primary progressive aphasia (svPPA) with left-predominant temporal atrophy and TDP-type C pathology with low Alzheimer's disease neuropathologic changes (ADNC). Case 2 was a 63-year-old woman with right-predominant temporal atrophy and TDP-type C pathology who had prosopagnosia and personality changes. Phosphorylated(p)-TDP-43-positive long dystrophic neurites (DNs) were observed throughout the cerebral cortex; they were more abundant in the relatively spared cortices and less so in the severely degenerated cortices. We observed CST degeneration with TDP-43 pathology in the upper and lower motor neurons, without apparent motor symptoms, in SD with TDP-type C pathology. Case 3 was a 76-year-old man who had svPPA and personality changes, with left-predominant temporal atrophy and TDP-type A pathology with high ADNC and argyrophilic grain (AG) stage 3. Case 4 was an 82-year-old man who had prosopagnosia and later developed symptoms of dementia with Lewy bodies (DLB) with right-predominant temporal atrophy and TDP-type A pathology with high ADNC, DLB of diffuse neocortical type, and AG stage 3. The distribution of p-TDP-43-positive NCIs and short DNs was localized in the anterior and inferior temporal cortices. An inverse relationship between the extent of TDP pathology and neuronal loss was also observed in SD with TDP-type A pathology. In contrast, the extent of AD, DLB, and AG pathology was greater in severely degenerated regions. CST degeneration was either absent or very mild in SD with TDP-type A. Understanding the clinicopathological diversity of SD will help improve its diagnosis and treatment.

Diverse limbic comorbidities cause limbic and temporal atrophy in lewy body disease

BACKGROUND

In contrast to Alzheimer's disease (AD)-related pathology, the influence of comorbid limbic-predominant age-related TDP-43 encephalopathy neuropathological change (LATE-NC) or argyrophilic grains (AG) on structural imaging in Lewy body disease (LBD) has seldom been evaluated.

OBJECTIVE

This study aimed to investigate whether non-AD limbic comorbidities, including LATE-NC and AG, cause cortical atrophy in LBD.

METHODS

Seventeen patients with pathologically confirmed LBD with lower Braak neurofibrillary tangle stage (<IV) and 10 healthy controls (HC) were included. Based on the presence of comorbid LATE-NC or AG, LBD patients were subdivided into nine patients with these proteinopathies (mixed LBD [mLBD]) and eight without (pure LBD [pLBD]). In addition to clinical feature evaluation, gray matter atrophy on voxel-based morphometry was compared between the two LBD and HC groups.

RESULTS

The mean age at antemortem magnetic resonance imaging of the mLBD patients was higher than that of the pLBD patients (84.3 ± 3.9 vs. 76.5 ± 10.5; p = .046). Irrespective of the presence or absence of comorbid LATE-NC or AG, all patients were clinically diagnosed with probable dementia with Lewy bodies or Parkinson's disease with dementia, respectively. Compared to the pLBD group, the mLBD group showed more conspicuous cortical atrophy of the bilateral hippocampus, amygdala, and temporal pole.

CONCLUSIONS

Non-AD limbic comorbidities, including LATE-NC and AG, are associated with limbic and temporal atrophy in older patients with LBD. Therefore, the possibility of non-AD limbic comorbidities should be considered in the diagnosis of elderly patients with dementia with clinical symptoms of LBD and medial temporal atrophy.

TREM2 risk variants are associated with atypical Alzheimer's disease

Alzheimer's disease (AD) has multiple clinically and pathologically defined subtypes where the underlying causes of such heterogeneity are not well established. Rare TREM2 variants confer significantly increased risk for clinical AD in addition to other neurodegenerative disease clinical phenotypes. Whether TREM2 variants are associated with atypical clinical or pathologically defined subtypes of AD is not known. We studied here the clinical and pathological features associated with TREM2 risk variants in an autopsy-confirmed cohort. TREM2 variant cases were more frequently associated with non-amnestic clinical syndromes. Pathologically, TREM2 variant cases were associated with an atypical distribution of neurofibrillary tangle density with significantly lower hippocampal NFT burden relative to neocortical NFT accumulation. In addition, NFT density but not amyloid burden was associated with an increase of dystrophic microglia. TREM2 variant cases were not associated with an increased prevalence, extent, or severity of co-pathologies. These clinicopathological features suggest that TREM2 variants contribute to clinical and pathologic AD heterogeneity by altering the distribution of neurofibrillary degeneration and tau-dependent microglial dystrophy, resulting in hippocampal-sparing and non-amnestic AD phenotypes.

Limbic-Predominant Age-Related TDP-43 Encephalopathy: LATE-Breaking Updates in Clinicopathologic Features and Biomarkers

PURPOSE OF REVIEW

Limbic-predominant age-related TDP-43 encephalopathy (LATE) is a recently defined neurodegenerative disease characterized by amnestic phenotype and pathological inclusions of TAR DNA-binding protein 43 (TDP-43). LATE is distinct from rarer forms of TDP-43 diseases such as frontotemporal lobar degeneration with TDP-43 but is also a common copathology with Alzheimer's disease (AD) and cerebrovascular disease and accelerates cognitive decline. LATE contributes to clinicopathologic heterogeneity in neurodegenerative diseases, so it is imperative to distinguish LATE from other etiologies.

RECENT FINDINGS

Novel biomarkers for LATE are being developed with magnetic resonance imaging (MRI) and positron emission tomography (PET). When cooccurring with AD, LATE exhibits identifiable patterns of limbic-predominant atrophy on MRI and hypometabolism on 18F-fluorodeoxyglucose PET that are greater than expected relative to levels of local AD pathology. Efforts are being made to develop TDP-43-specific radiotracers, molecularly specific biofluid measures, and genomic predictors of TDP-43. LATE is a highly prevalent neurodegenerative disease distinct from previously characterized cognitive disorders.

Distinct neurotoxic TDP-43 fibril polymorphs are generated by heterotypic interactions with α-Synuclein

Amyloid aggregates of specific proteins constitute important pathological hallmarks in many neurodegenerative diseases, defining neuronal degeneration and disease onset. Recently, increasing numbers of patients show comorbidities and overlaps between multiple neurodegenerative diseases, presenting distinct phenotypes. Such overlaps are often accompanied by colocalizations of more than one amyloid protein, prompting the question of whether direct interactions between different amyloid proteins could generate heterotypic amyloids. To answer this question, we investigated the effect of α-synuclein (αS) on the DNA-binding protein TDP-43 aggregation inspired by their coexistence in pathologies such as Lewy body dementia and limbic predominant age-related TDP-43 encephalopathy. We previously showed αS and prion-like C-terminal domain (PrLD) of TDP-43 synergistically interact to generate toxic heterotypic aggregates. Here, we extend these studies to investigate whether αS induces structurally and functionally distinct polymorphs of PrLD aggregates. Using αS-PrLD heterotypic aggregates generated in two different stoichiometric proportions, we show αS can affect PrLD fibril forms. PrLD fibrils show distinctive residue level signatures determined by solid state NMR, dye-binding capability, proteinase K (PK) stability, and thermal stability toward SDS denaturation. Furthremore, by gold nanoparticle labeling and transmission electron microscopy, we show the presence of both αS and PrLD proteins within the same fibrils, confirming the existence of heterotypic amyloid fibrils. We also observe αS and PrLD colocalize in the cytosol of neuroblastoma cells and show that the heterotypic PrLD fibrils selectively induce synaptic dysfunction in primary neurons. These findings establish the existence of heterotypic amyloid and provide a molecular basis for the observed overlap between synucleinopathies and TDP-43 proteinopathies.

Discrepancy between distribution of alpha-synuclein oligomers and Lewy-related pathology in Parkinson's disease

The pathological hallmarks of Parkinson’s disease (PD) are α-synuclein (αSYN)-positive inclusions referred to as Lewy bodies and Lewy neurites, collectively referred to as Lewy-related pathology (LRP). LRP is thought to propagate in an ascending manner throughout the brain as the disease progresses. LRP is visible with histologic methods and is thought to represent a later stage of the disease process, while αSYN oligomers, which are not visible with routine histologic methods, are considered earlier. There is increasing evidence to suggest that αSYN oligomers may be more toxic than visible LRP. Detecting αSYN oligomers requires special techniques, and their distribution and association with clinical features are important research objectives. In this report, we describe the distribution of αSYN oligomers in multiple cortical and subcortical regions of PD using a proximity ligation assay (PLA). We observe widespread distribution of αSYN oligomers with PLA and more restricted distribution of LRP with αSYN immunohistochemistry. The distribution of αSYN oligomers differed from LRP in that αSYN oligomer burden was significantly greater in the neocortex, while LRP was greater in vulnerable subcortical regions, including the brainstem. We also found that cognitive impairment was associated with αSYN oligomers in the hippocampus. These results suggest that αSYN oligomers may be widely distributed in PD early in the disease process and that they may contribute to cognitive impairment in PD.

Neurovascular Dysfunction in Diverse Communities With Health Disparities-Contributions to Dementia and Alzheimer's Disease

Alzheimer's disease and related dementias (ADRD) are an expanding worldwide crisis. In the absence of scientific breakthroughs, the global prevalence of ADRD will continue to increase as more people are living longer. Racial or ethnic minority groups have an increased risk and incidence of ADRD and have often been neglected by the scientific research community. There is mounting evidence that vascular insults in the brain can initiate a series of biological events leading to neurodegeneration, cognitive impairment, and ADRD. We are a group of researchers interested in developing and expanding ADRD research, with an emphasis on vascular contributions to dementia, to serve our local diverse community. Toward this goal, the primary objective of this review was to investigate and better understand health disparities in Alabama and the contributions of the social determinants of health to those disparities, particularly in the context of vascular dysfunction in ADRD. Here, we explain the neurovascular dysfunction associated with Alzheimer's disease (AD) as well as the intrinsic and extrinsic risk factors contributing to dysfunction of the neurovascular unit (NVU). Next, we ascertain ethnoregional health disparities of individuals living in Alabama, as well as relevant vascular risk factors linked to AD. We also discuss current pharmaceutical and non-pharmaceutical treatment options for neurovascular dysfunction, mild cognitive impairment (MCI) and AD, including relevant studies and ongoing clinical trials. Overall, individuals in Alabama are adversely affected by social and structural determinants of health leading to health disparities, driven by rurality, ethnic minority status, and lower socioeconomic status (SES). In general, these communities have limited access to healthcare and healthy food and other amenities resulting in decreased opportunities for early diagnosis of and pharmaceutical treatments for ADRD. Although this review is focused on the current state of health disparities of ADRD patients in Alabama, future studies must include diversity of race, ethnicity, and region to best be able to treat all individuals affected by ADRD.

Parallel Appearance of Polyglutamine and Transactivation-Responsive DNA-Binding Protein 43 and Their Complementary Subcellular Localization in Brains of Patients With Spinocerebellar Ataxia Type 2

Spinocerebellar ataxia type 2 (SCA2) is caused by mutations in the ATXN2 gene in which toxic effects are triggered by expanded polyglutamine repeats within ataxin-2. SCA2 is accompanied by motor neuron degeneration as occurs in amyotrophic lateral sclerosis (ALS). We investigated the distribution patterns of ataxin-2 and transactivation-responsive DNA-binding protein 43 (TDP-43), a major disease-related protein in ALS, in the CNS of 3 SCA2 patients. Phosphorylated TDP-43 (pTDP-43)-positive lesions were widely distributed throughout the CNS and generally overlapped with 1C2 (expanded polyglutamine)-immunoreactive lesions. This distribution pattern is different from the pattern in limbic-predominant age-related TDP-43 encephalopathy. In SCA2, double immunostaining of TDP-43 and 1C2 in motor neurons revealed 3 staining patterns: cytoplasmic 1C2 and nuclear TDP-43, nucleocytoplasmic 1C2 and nuclear TDP-43, and nuclear 1C2 and cytoplasmic TDP-43, which reflect the early, active, and final stages of pathological change, respectively. The translocation of TDP-43 from the nucleus to the cytoplasm along with the translocation of 1C2 in the opposite direction indicates that nuclear accumulation of the disease-specific protein ataxin-2 affects the intracellular dynamics of TDP-43. Such a close interrelationship between mutant ataxin-2 and TDP-43 in the cell might account for the similarity of their distribution in the CNS of patients with SCA2.

Patterns of amygdala region pathology in LATE-NC: subtypes that differ with regard to TDP-43 histopathology, genetic risk factors, and comorbid pathologies

Transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) pathology is a hallmark of limbic-predominant age-related TDP-43 encephalopathy (LATE). The amygdala is affected early in the evolution of LATE neuropathologic change (LATE-NC), and heterogeneity of LATE-NC in amygdala has previously been observed. However, much remains to be learned about how LATE-NC originates and progresses in the brain. To address this, we assessed TDP-43 and other pathologies in the amygdala region of 184 autopsied subjects (median age = 85 years), blinded to clinical diagnoses, other neuropathologic diagnoses, and risk genotype information. As previously described, LATE-NC was associated with older age at death, cognitive impairment, and the TMEM106B risk allele. Pathologically, LATE-NC was associated with comorbid hippocampal sclerosis (HS), myelin loss, and vascular disease in white matter (WM). Unbiased hierarchical clustering of TDP-43 inclusion morphologies revealed discernable subtypes of LATE-NC with distinct clinical, genetic, and pathologic associations. The most common patterns were: Pattern 1, with lamina II TDP-43 + processes and preinclusion pathology in cortices of the amygdala region, and frequent LATE-NC Stage 3 with HS; Pattern 2, previously described as type-β, with neurofibrillary tangle-like TDP-43 neuronal cytoplasmic inclusions (NCIs), high Alzheimer's disease neuropathologic change (ADNC), frequent APOE ε4, and usually LATE-NC Stage 2; Pattern 3, with round NCIs and thick neurites in amygdala, younger age at death, and often comorbid Lewy body disease; and Pattern 4 (the most common pattern), with tortuous TDP-43 processes in subpial and WM regions, low ADNC, rare HS, and lower dementia probability. TDP-43 pathology with features of patterns 1 and 2 were often comorbid in the same brains. Early and mild TDP-43 pathology was often best described to be localized in the "amygdala region" rather than the amygdala proper. There were also important shared attributes across patterns. For example, all four patterns were associated with the TMEM106B risk allele. Each pattern also demonstrated the potential to progress to higher LATE-NC stages with confluent anatomical and pathological patterns, and to contribute to dementia. Although LATE-NC showed distinct patterns of initiation in amygdala region, there was also apparent shared genetic risk and convergent pathways of clinico-pathological evolution.

Peripheral Pathways to Neurovascular Unit Dysfunction, Cognitive Impairment, and Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of dementia. It was first described more than a century ago, and scientists are acquiring new data and learning novel information about the disease every day. Although there are nuances and details continuously being unraveled, many key players were identified in the early 1900’s by Dr. Oskar Fischer and Dr. Alois Alzheimer, including amyloid-beta (Aβ), tau, vascular abnormalities, gliosis, and a possible role of infections. More recently, there has been growing interest in and appreciation for neurovascular unit dysfunction that occurs early in mild cognitive impairment (MCI) before and independent of Aβ and tau brain accumulation. In the last decade, evidence that Aβ and tau oligomers are antimicrobial peptides generated in response to infection has expanded our knowledge and challenged preconceived notions. The concept that pathogenic germs cause infections generating an innate immune response (e.g., Aβ and tau produced by peripheral organs) that is associated with incident dementia is worthwhile considering in the context of sporadic AD with an unknown root cause. Therefore, the peripheral amyloid hypothesis to cognitive impairment and AD is proposed and remains to be vetted by future research. Meanwhile, humans remain complex variable organisms with individual risk factors that define their immune status, neurovascular function, and neuronal plasticity. In this focused review, the idea that infections and organ dysfunction contribute to Alzheimer’s disease, through the generation of peripheral amyloids and/or neurovascular unit dysfunction will be explored and discussed. Ultimately, many questions remain to be answered and critical areas of future exploration are highlighted.