Brains with medial temporal lobe neurofibrillary tangles but no neuritic amyloid plaques are a diagnostic dilemma but may have pathogenetic aspects distinct from Alzheimer disease

Prevalence and clinicopathological features of primary age-related tauopathy (PART): A large forensic autopsy study

INTRODUCTION

Primary age-related tauopathy (PART), often regarded as a minimally symptomatic pathology of old age, lacks comprehensive cohorts across various age groups.

METHODS

We examined PART prevalence and clinicopathologic features in 1589 forensic autopsy cases (≥40 years old, mean age ± SD 70.2 ± 14.2 years).

RESULTS

PART cases meeting criteria for argyrophilic grain diseases (AGD) were AGD+PART (n = 181). The remaining PART cases (n = 719, 45.2%) were classified as comorbid conditions (PART-C, n = 90) or no comorbid conditions (pure PART, n = 629). Compared to controls (n = 208), Alzheimer's disease (n = 133), and AGD+PART, PART prevalence peaked in the individuals in their 60s (65.5%) and declined in the 80s (21.5%). No significant clinical background differences were found (excluding controls). However, PART-C in patients inclusive of age 80 had a higher suicide rate than pure PART (p < 0.05), and AGD+PART showed more dementia (p < 0.01) and suicide (p < 0.05) than pure PART.

DISCUSSION

Our results advocate a reevaluation of the PART concept and its diagnostic criteria.

HIGHLIGHTS

We investigated 1589 forensic autopsy cases to investigate the features of primary age-related tauopathy (PART). PART peaked in people in their 60s in our study. Many PART cases over 80s had comorbid pathologies in addition to neurofibrillary tangles pathology. Argyrophilic grain disease and Lewy pathology significantly affected dementia and suicide rates in PART. Our results suggest that the diagnostic criteria of PART need to be reconsidered.

Mapping the lipidome in mitochondria-associated membranes (MAMs) in an in vitro model of Alzheimer's disease

The disruption of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) plays a relevant role in Alzheimer's disease (AD). MAMs have been implicated in neuronal dysfunction and death since it is associated with impairment of functions regulated in this subcellular domain, including lipid synthesis and trafficking, mitochondria dysfunction, ER stress-induced unfolded protein response (UPR), apoptosis, and inflammation. Since MAMs play an important role in lipid metabolism, in this study we characterized and investigated the lipidome alterations at MAMs in comparison with other subcellular fractions, namely microsomes and mitochondria, using an in vitro model of AD, namely the mouse neuroblastoma cell line (N2A) over-expressing the APP familial Swedish mutation (APPswe) and the respective control (WT) cells. Phospholipids (PLs) and fatty acids (FAs) were isolated from the different subcellular fractions and analyzed by HILIC-LC-MS/MS and GC-MS, respectively. In this in vitro AD model, we observed a down-regulation in relative abundance of some phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE) species with PUFA and few PC with saturated and long-chain FA. We also found an up-regulation of CL, and antioxidant alkyl acyl PL. Moreover, multivariate analysis indicated that each organelle has a specific lipid profile adaptation in N2A APPswe cells. In the FAs profile, we found an up-regulation of C16:0 in all subcellular fractions, a decrease of C18:0 levels in total fraction (TF) and microsomes fraction, and a down-regulation of 9-C18:1 was also found in mitochondria fraction in the AD model. Together, these results suggest that the over-expression of the familial APP Swedish mutation affects lipid homeostasis in MAMs and other subcellular fractions and supports the important role of lipids in AD physiopathology.

Cytotoxic Effect of Amyloid-β1-42 Oligomers on Endoplasmic Reticulum and Golgi Apparatus Arrangement in SH-SY5Y Neuroblastoma Cells

Amyloid-β oligomers are a cytotoxic structure that is key for the establishment of the beginning stages of Alzheimer's disease (AD). These structures promote subcellular alterations that cause synaptic dysfunction, loss of cell communication, and even cell death, generating cognitive deficits. The aim of this study was to investigate the cytotoxic effects of amyloid-β1-42 oligomers (AβOs) on the membranous organelles involved in protein processing: the endoplasmic reticulum (ER) and Golgi apparatus (GA). The results obtained with 10 μM AβOs in SH-SY5Y neuroblastoma cells showed that oligomeric structures are more toxic than monomers because they cause cell viability to decrease as exposure time increases. Survivor cells were analyzed to further understand the toxic effects of AβOs on intracellular organelles. Survivor cells showed morphological alterations associated with abnormal cytoskeleton modification 72-96 h after exposure to AβOs. Moreover, the ER and GA presented rearrangement throughout the cytoplasmic space, which could be attributed to a lack of constitutive protein processing or to previous abnormal cytoskeleton modification. Interestingly, the disorganization of both ER and GA organelles exposed to AβOs is likely an early pathological alteration that could be related to aberrant protein processing and accumulation in AD.

Significance of a positive tau PET scan with a negative amyloid PET scan

INTRODUCTION

The implications of positive tau positron emission tomography (T) with negative beta amyloid positron emission tomography (A) are not well understood. We investigated cognitive performance in participants who were T+ but A-.

METHODS

We evaluated 98 participants from the Mayo Clinic who were T+ and A-. Participants were matched 2:1 to A- and T- cognitively unimpaired (CU) controls. Cognitive test scores were compared between different groups.

RESULTS

The A-T+ group demonstrated lower performance than the A-T- group on the Mini-Mental Status Exam (MMSE) (p < 0.001), Wechsler Memory Scale-Revised Logical Memory I (p < 0.001) and Logical Memory II (p < 0.001), Auditory Verbal Learning Test (AVLT) delayed recall (p = 0.004), category fluency (animals p = 0.005; vegetables p = 0.021), Trail Making Test A and B (p < 0.001), and others. There were no significant differences in demographic features or apolipoprotein E (APOE) e4 genotype between CU A-T+ and CI A-T+.

DISCUSSION

A-T+ participants show an association with lower cognitive performance.

Early CA2 Tau Inclusions Do Not Distinguish an Age-Related Tauopathy from Early Alzheimer's Disease

Background

Neuropathologic studies of brains from autopsy series show tau inclusions (pretangles, neuropils threads, neurofibrillary tangles) are detectable more than a decade before amyloid-β (Aβ) deposition in Alzheimer's disease (AD) and develop in a characteristic manner that forms the basis for AD staging. An alternative position views pathological tau without Aβ deposition as a 'primary age-related tauopathy' (PART) rather than prodromal AD. Recently, an early focus of tau inclusions in the Ammon's horn second sector (CA2) with relative sparing of CA1 that occurs before tau inclusions develop in the entorhinal cortex (EC) was proposed as an additional feature of PART.

Objective

To test the 'definite PART' hypothesis.

Methods

We used AT8-immunohistochemistry in 100μm sections to examine the EC, transentorhinal cortex (TRE), and Ammon's horn in 325 brains with tau inclusions lacking Aβ deposits (average age at death 66.7 years for females, 66.4 years for males).

Results

100% of cases displayed tau inclusions in the TRE. In 89% of cases, the CA1 tau rating was greater than or equal to that in CA2. In 25%, CA2 was devoid of tau inclusions. Only 4% displayed a higher tau score in CA2 than in the TRE, EC, and CA1. The perforant path also displayed early tau changes. APOE genotyping was available for 199/325 individuals. Of these, 44% had an ɛ4 allele that placed them at greater risk for developing later NFT stages and, therefore, clinical AD.

Conclusions

Our new findings call into question the PART hypothesis and are consistent with the idea that our cases represent prodromal AD.

Illustrated Neuropathologic Diagnosis of Alzheimer's Disease

As of 2022, the prevalence of Alzheimer's disease (AD) among individuals aged 65 and older is estimated to be 6.2 million in the United States. This figure is predicted to grow to 13.8 million by 2060. An accurate assessment of neuropathologic changes represents a critical step in understanding the underlying mechanisms in AD. The current method for assessing postmortem Alzheimer's disease neuropathologic change follows version 11 of the National Alzheimer's Coordinating Center (NACC) coding guidebook. Ambiguity regarding steps in the ABC scoring method can lead to increased time or inaccuracy in staging AD. We present a concise overview of how this postmortem diagnosis is made and relate it to the evolving understanding of antemortem AD biomarkers.

Neurodegenerative pathologies associated with behavioral and psychological symptoms of dementia in a community-based autopsy cohort

In addition to the memory disorders and global cognitive impairment that accompany neurodegenerative diseases, behavioral and psychological symptoms of dementia (BPSD) commonly impair quality of life and complicate clinical management. To investigate clinical-pathological correlations of BPSD, we analyzed data from autopsied participants from the community-based University of Kentucky Alzheimer's Disease Research Center longitudinal cohort (n = 368 research volunteers met inclusion criteria, average age at death 85.4 years). Data assessing BPSD were obtained approximately annually, including parameters for agitation, anxiety, apathy, appetite problems, delusions, depression, disinhibition, hallucinations, motor disturbance, and irritability. Each BPSD was scored on a severity scale (0-3) via the Neuropsychiatric Inventory Questionnaire (NPI-Q). Further, Clinical Dementia Rating (CDR)-Global and -Language evaluations (also scored on 0-3 scales) were used to indicate the degree of global cognitive and language impairment. The NPI-Q and CDR ratings were correlated with neuropathology findings at autopsy: Alzheimer's disease neuropathological changes (ADNC), neocortical and amygdala-only Lewy bodies (LBs), limbic predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC), primary age-related tauopathy (PART), hippocampal sclerosis, and cerebrovascular pathologies. Combinations of pathologies included the quadruple misfolding proteinopathy (QMP) phenotype with co-occurring ADNC, neocortical LBs, and LATE-NC. Statistical models were used to estimate the associations between BPSD subtypes and pathologic patterns. Individuals with severe ADNC (particularly those with Braak NFT stage VI) had more BPSD, and the QMP phenotype was associated with the highest mean number of BPSD symptoms: > 8 different BPSD subtypes per individual. Disinhibition and language problems were common in persons with severe ADNC but were not specific to any pathology. "Pure" LATE-NC was associated with global cognitive impairment, apathy, and motor disturbance, but again, these were not specific associations. In summary, Braak NFT stage VI ADNC was strongly associated with BPSD, but no tested BPSD subtype was a robust indicator of any particular "pure" or mixed pathological combination.

Honey and Alzheimer's Disease-Current Understanding and Future Prospects

Alzheimer's disease (AD), a leading cause of dementia, has been a global concern. AD is associated with the involvement of the central nervous system that causes the characteristic impaired memory, cognitive deficits, and behavioral abnormalities. These abnormalities caused by AD is known to be attributed by extracellular aggregates of amyloid beta plaques and intracellular neurofibrillary tangles. Additionally, genetic factors such as abnormality in the expression of APOE, APP, BACE1, PSEN-1, and PSEN-2 play a role in the disease. As the current treatment aims to treat the symptoms and to slow the disease progression, there has been a continuous search for new nutraceutical agent or medicine to help prevent and cure AD pathology. In this quest, honey has emerged as a powerful nootropic agent. Numerous studies have demonstrated that the high flavonoids and phenolic acids content in honey exerts its antioxidant, anti-inflammatory, and neuroprotective properties. This review summarizes the effect of main flavonoid compounds found in honey on the physiological functioning of the central nervous system, and the effect of honey intake on memory and cognition in various animal model. This review provides a new insight on the potential of honey to prevent AD pathology, as well as to ameliorate the damage in the developed AD.

Clear-headed into old age: Resilience and resistance against brain aging-A PET imaging perspective

With the advances in modern medicine and the adaptation towards healthier lifestyles, the average life expectancy has doubled since the 1930s, with individuals born in the millennium years now carrying an estimated life expectancy of around 100 years. And even though many individuals around the globe manage to age successfully, the prevalence of aging-associated neurodegenerative diseases such as sporadic Alzheimer's disease has never been as high as nowadays. The prevalence of Alzheimer's disease is anticipated to triple by 2050, increasing the societal and economic burden tremendously. Despite all efforts, there is still no available treatment defeating the accelerated aging process as seen in this disease. Yet, given the advances in neuroimaging techniques that are discussed in the current Review article, such as in positron emission tomography (PET) or magnetic resonance imaging (MRI), pivotal insights into the heterogenous effects of aging-associated processes and the contribution of distinct lifestyle and risk factors already have and are still being gathered. In particular, the concepts of resilience (i.e. coping with brain pathology) and resistance (i.e. avoiding brain pathology) have more recently been discussed as they relate to mechanisms that are associated with the prolongation and/or even stop of the progressive brain aging process. Better understanding of the underlying mechanisms of resilience and resistance may one day, hopefully, support the identification of defeating mechanism against accelerating aging.

Comparison of Clinical, Genetic, and Pathologic Features of Limbic and Diffuse Transactive Response DNA-Binding Protein 43 Pathology in Alzheimer's Disease Neuropathologic Spectrum

BACKGROUND

Increasing evidence suggests that TAR DNA-binding protein 43 (TDP-43) pathology in Alzheimer's disease (AD), or AD-TDP, can be diffuse or limbic-predominant. Understanding whether diffuse AD-TDP has genetic, clinical, and pathological features that differ from limbic AD-TDP could have clinical and research implications.

OBJECTIVE

To better characterize the clinical and pathologic features of diffuse AD-TDP and differentiate it from limbic AD-TDP.

METHODS

363 participants from the Mayo Clinic Study of Aging, Alzheimer's Disease Research Center, and Neurodegenerative Research Group with autopsy confirmed AD and TDP-43 pathology were included. All underwent genetic, clinical, neuropsychologic, and neuropathologic evaluations. AD-TDP pathology distribution was assessed using the Josephs 6-stage scale. Stages 1-3 were classified as Limbic, those 4-6 as Diffuse. Multivariable logistic regression was used to identify clinicopathologic features that independently predicted diffuse pathology.

RESULTS

The cohort was 61% female and old at onset (median: 76 years [IQR:70-82]) and death (median: 88 years [IQR:82-92]). Fifty-four percent were Limbic and 46% Diffuse. Clinically, ∼10-20% increases in odds of being Diffuse associated with 5-year increments in age at onset (p = 0.04), 1-year longer disease duration (p = 0.02), and higher Neuropsychiatric Inventory scores (p = 0.03), while 15-second longer Trailmaking Test-B times (p = 0.02) and higher Block Design Test scores (p = 0.02) independently decreased the odds by ~ 10-15%. There was evidence for association of APOEɛ4 allele with limbic AD-TDP and of TMEM106B rs3173615 C allele with diffuse AD-TDP. Pathologically, widespread amyloid-β plaques (Thal phases: 3-5) decreased the odds of diffuse TDP-43 pathology by 80-90%, while hippocampal sclerosis increased it sixfold (p < 0.001).

CONCLUSION

Diffuse AD-TDP shows clinicopathologic and genetic features different from limbic AD-TDP.

TDP-43 Proteinopathy and Tauopathy: Do They Have Pathomechanistic Links?

Transactivation response DNA binding protein 43 kDa (TDP-43) and tau are major pathological proteins of neurodegenerative disorders, of which neuronal and glial aggregates are pathological hallmarks. Interestingly, accumulating evidence from neuropathological studies has shown that comorbid TDP-43 pathology is observed in a subset of patients with tauopathies, and vice versa. The concomitant pathology often spreads in a disease-specific manner and has morphological characteristics in each primary disorder. The findings from translational studies have suggested that comorbid TDP-43 or tau pathology has clinical impacts and that the comorbid pathology is not a bystander, but a part of the disease process. Shared genetic risk factors or molecular abnormalities between TDP-43 proteinopathies and tauopathies, and direct interactions between TDP-43 and tau aggregates, have been reported. Further investigations to clarify the pathogenetic factors that are shared by a broad spectrum of neurodegenerative disorders will establish key therapeutic targets.

Frontotemporal neurofibrillary tangles and cerebrovascular lesions are associated with autism spectrum behaviors in late-life dementia

BACKGROUND AND OBJECTIVES

The pathologic substrates or neuroanatomic regions responsible for similarities in behavioral features seen in autism spectrum disorder and late-life dementia remain unknown. The present study examined the neuropathologic features of late-life dementia in research volunteers with and without antemortem behaviors characteristic of autism spectrum disorders.

METHODS

Antemortem cross-sectional assessment of autistic spectrum behaviors proximal to death in persons with diagnosis of mild cognitive impairment or dementia was completed using the Gilliam Autism Rating Scale, 2nd edition (GARS-2), followed by postmortem quantitative and semiquantitative neuropathologic assessment. All individuals who completed the GARS-2 prior to autopsy were included (n = 56) and we note that no participants had known diagnosis of autism spectrum disorder. The GARS-2 was used as an antemortem screening tool to stratify participants into two groups: "Autism Possible/Very Likely" or "Autism Unlikely." Data were analyzed using nonparametric statistics comparing location and scale to evaluate between-group differences in pathologic features.

RESULTS

Neurofibrillary tangles (NFT; p = 0.028) density and tau burden (p = 0.032) in the frontal region, the NFT density (p = 0.048) and neuritic plaque burden (p = 0.042), and the tau burden (p = 0.032) of the temporal region, were significantly different in scale between groups. For measures with significant group differences, the medians of the Autism Possible/Very Likely group were roughly equal to the 75th percentile of the Autism Unlikely group (i.e., the distributions were shifted to the right).

DISCUSSION

This study links behaviors characteristic of autism to increased pathologic tau burden in the frontal and temporal lobes in persons with late-life dementia. Additional studies are needed to determine causal factors and treatment options for behaviors characteristic of autism behaviors in late-life dementias.

TDP-43 Pathology Exacerbates Cognitive Decline in Primary Age-Related Tauopathy

OBJECTIVE

Primary age-related tauopathy (PART) refers to tau neurofibrillary tangles restricted largely to the medial temporal lobe in the absence of significant beta-amyloid plaques. PART has been associated with cognitive impairment, but contributions from concomitant limbic age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) are underappreciated.

METHODS

We compare prevalence of LATE-NC and vascular copathologies in age- and Braak-matched patients with PART (n = 45, Braak stage I-IV, Thal phase 0-2) or early stage Alzheimer disease neuropathologic change (ADNC; n = 51, Braak I-IV, Thal 3-5), and examine their influence on clinical and cognitive decline.

RESULTS

Concomitant LATE-NC and vascular pathology were equally common, and cognition was equally impaired, in PART (Mini-Mental State Examination [MMSE] = 24.8 ± 6.9) and ADNC (MMSE = 24.2 ± 6.0). Patients with LATE-NC were more impaired than those without LATE-NC on the MMSE (by 5.8 points, 95% confidence interval [CI] = 3.0-8.6), Mattis Dementia Rating Scale (DRS; 17.5 points, 95% CI = 7.1-27.9), Clinical Dementia Rating, sum of boxes scale (CDR-sob; 5.2 points, 95% CI = 2.1-8.2), memory composite (0.8 standard deviations [SD], 95% CI = 0.1-1.6), and language composite (1.1 SD, 95% CI = 0.2-2.0), and more likely to receive a dementia diagnosis (odds ratio = 4.8, 95% CI = 1.5-18.0). Those with vascular pathology performed worse than those without on the DRS (by 10.2 points, 95% CI = 0.1-20.3) and executive composite (1.3 SD, 95% CI = 0.3-2.3). Cognition declined similarly in PART and ADNC over the 5 years preceding death; however, LATE-NC was associated with more rapid decline on the MMSE (β = 1.9, 95% CI = 0.9-3.0), DRS (β = 7.8, 95% CI = 3.4-12.7), CDR-sob (β = 1.9, 95% CI = 0.4-3.7), language composite (β = 0.5 SD, 95% CI = 0.1-0.8), and vascular pathology with more rapid decline on the DRS (β = 5.2, 95% CI = 0.6-10.2).

INTERPRETATION

LATE-NC, and to a lesser extent vascular copathology, exacerbate cognitive impairment and decline in PART and early stage ADNC. ANN NEUROL 2022;92:425-438.

Neuropathology of Dementia Disorders

PURPOSE OF REVIEW

This article provides an overview of the neuropathology of common age-related dementing disorders, focusing on the pathologies that underlie Alzheimer disease (AD) and related dementias, including Lewy body dementias, frontotemporal dementia, vascular dementia, limbic-predominant age-related transactive response DNA-binding protein 43 (TDP-43) encephalopathy (LATE), and mixed-etiology dementias. This article also discusses the underlying proteinopathies of neurodegenerative diseases (eg, amyloid-β, paired helical filament tau, α-synuclein, and TDP-43 pathology) and vascular pathologies, including tissue injury (eg, infarcts, hemorrhages) with or without vessel disease.

RECENT FINDINGS

New criteria for AD pathologic diagnosis highlight amyloid-β as the sine qua non of AD; they require molecular markers of amyloid and establish a minimum threshold of Braak neurofibrillary tangle stage 3. Pathologic diagnosis is separated from clinical disease (ie, pathologic diagnosis no longer requires dementia). TDP-43 pathology, a major pathology in a frontotemporal dementia subtype, was found as a central pathology in LATE, a newly named amnestic disorder. Multiple pathologies (often co-occurring with AD) contribute to dementia and add complexity to the clinical picture. Conversely, Lewy body, LATE, and vascular dementias often have accompanying AD pathology. Pathology and biomarker studies highlight subclinical pathologies in older people without cognitive impairment. This resilience to brain pathology is common and is known as cognitive reserve.

SUMMARY

The pathologies of dementia in aging are most commonly amyloid, tangles, Lewy bodies, TDP-43, hippocampal sclerosis, and vascular pathologies. These pathologies often co-occur (mixed pathologies), which may make specific clinical diagnoses difficult. In addition, dementia-related pathologies are often subclinical, suggesting varying levels of resilience in older people.

Microglia phenotypes are associated with subregional patterns of concomitant tau, amyloid-β and α-synuclein pathologies in the hippocampus of patients with Alzheimer's disease and dementia with Lewy bodies

The cellular alterations of the hippocampus lead to memory decline, a shared symptom between Alzheimer’s disease (AD) and dementia with Lewy Bodies (DLB) patients. However, the subregional deterioration pattern of the hippocampus differs between AD and DLB with the CA1 subfield being more severely affected in AD. The activation of microglia, the brain immune cells, could play a role in its selective volume loss. How subregional microglia populations vary within AD or DLB and across these conditions remains poorly understood. Furthermore, how the nature of the hippocampal local pathological imprint is associated with microglia responses needs to be elucidated. To this purpose, we employed an automated pipeline for analysis of 3D confocal microscopy images to assess CA1, CA3 and DG/CA4 subfields microglia responses in post-mortem hippocampal samples from late-onset AD (n = 10), DLB (n = 8) and age-matched control (CTL) (n = 11) individuals. In parallel, we performed volumetric analyses of hyperphosphorylated tau (pTau), amyloid-β (Aβ) and phosphorylated α-synuclein (pSyn) loads. For each of the 32,447 extracted microglia, 16 morphological features were measured to classify them into seven distinct morphological clusters. Our results show similar alterations of microglial morphological features and clusters in AD and DLB, but with more prominent changes in AD. We identified two distinct microglia clusters enriched in disease conditions and particularly increased in CA1 and DG/CA4 of AD and CA3 of DLB. Our study confirms frequent concomitance of pTau, Aβ and pSyn loads across AD and DLB but reveals a specific subregional pattern for each type of pathology, along with a generally increased severity in AD. Furthermore, pTau and pSyn loads were highly correlated across subregions and conditions. We uncovered tight associations between microglial changes and the subfield pathological imprint. Our findings suggest that combinations and severity of subregional pTau, Aβ and pSyn pathologies transform local microglia phenotypic composition in the hippocampus. The high burdens of pTau and pSyn associated with increased microglial alterations could be a factor in CA1 vulnerability in AD.

Advances in Deep Neuropathological Phenotyping of Alzheimer Disease: Past, Present, and Future

Alzheimer disease (AD) is a neurodegenerative disorder characterized pathologically by the presence of neurofibrillary tangles and amyloid beta (Aβ) plaques in the brain. The disease was first described in 1906 by Alois Alzheimer, and since then, there have been many advancements in technologies that have aided in unlocking the secrets of this devastating disease. Such advancements include improving microscopy and staining techniques, refining diagnostic criteria for the disease, and increased appreciation for disease heterogeneity both in neuroanatomic location of abnormalities as well as overlap with other brain diseases; for example, Lewy body disease and vascular dementia. Despite numerous advancements, there is still much to achieve as there is not a cure for AD and postmortem histological analyses is still the gold standard for appreciating AD neuropathologic changes. Recent technological advances such as in-vivo biomarkers and machine learning algorithms permit great strides in disease understanding, and pave the way for potential new therapies and precision medicine approaches. Here, we review the history of human AD neuropathology research to include the notable advancements in understanding common co-pathologies in the setting of AD, and microscopy and staining methods. We also discuss future approaches with a specific focus on deep phenotyping using machine learning.

Genome-wide association study and functional validation implicates JADE1 in tauopathy

Primary age-related tauopathy (PART) is a neurodegenerative pathology with features distinct from but also overlapping with Alzheimer disease (AD). While both exhibit Alzheimer-type temporal lobe neurofibrillary degeneration alongside amnestic cognitive impairment, PART develops independently of amyloid-β (Aβ) plaques. The pathogenesis of PART is not known, but evidence suggests an association with genes that promote tau pathology and others that protect from Aβ toxicity. Here, we performed a genetic association study in an autopsy cohort of individuals with PART (n = 647) using Braak neurofibrillary tangle stage as a quantitative trait. We found some significant associations with candidate loci associated with AD (SLC24A4, MS4A6A, HS3ST1) and progressive supranuclear palsy (MAPT and EIF2AK3). Genome-wide association analysis revealed a novel significant association with a single nucleotide polymorphism on chromosome 4 (rs56405341) in a locus containing three genes, including JADE1 which was significantly upregulated in tangle-bearing neurons by single-soma RNA-seq. Immunohistochemical studies using antisera targeting JADE1 protein revealed localization within tau aggregates in autopsy brains with four microtubule-binding domain repeats (4R) isoforms and mixed 3R/4R, but not with 3R exclusively. Co-immunoprecipitation in post-mortem human PART brain tissue revealed a specific binding of JADE1 protein to four repeat tau lacking N-terminal inserts (0N4R). Finally, knockdown of the Drosophila JADE1 homolog rhinoceros (rno) enhanced tau-induced toxicity and apoptosis in vivo in a humanized 0N4R mutant tau knock-in model, as quantified by rough eye phenotype and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) in the fly brain. Together, these findings indicate that PART has a genetic architecture that partially overlaps with AD and other tauopathies and suggests a novel role for JADE1 as a modifier of neurofibrillary degeneration.

Primary Age‐Related Tauopathy (PART) in a Finnish Population‐Based Study of the Oldest Old (Vantaa 85+)

Aims

Few studies have investigated primary age‐related tauopathy (PART) in a population‐based setting. Here, we assessed its prevalence, genetic background, comorbidities and features of cognitive decline in an unselected elderly population.

Methods

The population‐based Vantaa 85+ study includes all 601 inhabitants of Vantaa aged ≥ 85 years in 1991. Neuropathological assessment was possible in 301. Dementia (DSM IIIR criteria) and Mini‐Mental State Examination (MMSE) scores were assessed at the baseline of the study and follow‐ups. PART subjects were identified according to the criteria by Crary et al and were compared with subjects with mild and severe Alzheimer's disease (AD) neuropathological changes. The effects of other neuropathologies were taken into account using multivariate and sensitivity assays. Genetic analyses included APOE genotypes and 29 polymorphisms of the MAPT 3′ untranslated region (3′UTR region).

Results

The frequency of PART was 20% (n = 61/301, definite PART 5%). When PART subjects were compared with those with severe AD pathology, dementia was less common, its age at onset was higher and duration shorter. No such differences were seen when compared with those with milder AD pathology. However, both AD groups showed a steeper decline in MMSE scores in follow‐ups compared with PART. APOE ε4 frequency was lower, and APOE ε2 frequency higher in the PART group compared with each AD group. The detected nominally significant associations between PART and two MAPT 3′UTR polymorphisms and haplotypes did not survive Bonferroni correction.

Conclusions

PART is common among very elderly. PART subjects differ from individuals with AD‐type changes in the pattern of cognitive decline, associated genetic and neuropathological features.

Cerebral amyloid load determination in a clinical setting: interpretation of amyloid biomarker discordances aided by tau and neurodegeneration measurements

BACKGROUND

Alzheimer's disease (AD) diagnosis can be hindered by amyloid biomarkers discordances.

OBJECTIVE

We aim to interpret discordances between amyloid positron emission tomography (Amy-PET) and cerebrospinal fluid (CSF) (Aβ₄₂ and Aβ_42/40), using Amy-PET semiquantitative analysis, [¹⁸F]fluorodeoxyglucose (FDG)-PET pattern, and CSF assays.

METHOD

Thirty-six subjects with dementia or mild cognitive impairment, assessed by neuropsychological tests, structural and functional imaging, and CSF assays (Aβ₄₂, Aβ_42/40, p-tau, t-tau), were retrospectively examined. Amy-PET and FDG-PET scans were analyzed by visual assessment and voxel-based analysis. SUVR were calculated on Amy-PET scans.

RESULTS

Groups were defined basing on the agreement among CSF Aβ₄₂ (A), CSF Aβ_42/40 Ratio (R), and Amy-PET (P) dichotomic results ( ±). In discordant groups, CSF assays, Amy-PET semiquantification, and FDG-PET patterns supported the diagnosis suggested by any two agreeing amyloid biomarkers. In groups with discordant CSF Aβ₄₂, the ratio always agrees with Amy-PET results, solving both false-negative and false-positive Aβ₄₂ results, with Aβ₄₂ levels close to the cut-off in A + R-P- subjects. The A + R + P- group presented high amyloid deposition in relevant areas, such as precuneus, posterior cingulate cortex (PCC) and dorsolateral frontal inferior cortex at semiquantitative analysis.

CONCLUSION

The amyloid discordant cases could be overcome by combining CSF Aβ₄₂, CSF ratio, and Amy-PET results. The concordance of any 2 out of the 3 biomarkers seems to reveal the remaining one as a false result. A cut-off point review could avoid CSF Aβ₄₂ false-negative results. The regional semiquantitative Amy-PET analysis in AD areas, such as precuneus and PCC, could increase the accuracy in AD diagnosis.

Renin-Angiotensin System Alterations in the Human Alzheimer's Disease Brain

BACKGROUND

Understanding Alzheimer's disease (AD) in terms of its various pathophysiological pathways is essential to unravel the complex nature of the disease process and identify potential therapeutic targets. The renin-angiotensin system (RAS) has been implicated in several brain diseases, including traumatic brain injury, ischemic stroke, and AD.

OBJECTIVE

This study was designed to evaluate the protein expression levels of RAS components in postmortem cortical and hippocampal brain samples obtained from AD versus non-AD individuals.

METHODS

We analyzed RAS components in the cortex and hippocampus of postmortem human brain samples by western blotting and immunohistochemical techniques in comparison with age-matched non-demented controls.

RESULTS

The expression of AT1R increased in the hippocampus, whereas AT2R expression remained almost unchanged in the cortical and hippocampal regions of AD compared to non-AD brains. The Mas receptor was downregulated in the hippocampus. We also detected slight reductions in ACE-1 protein levels in both the cortex and hippocampus of AD brains, with minor elevations in ACE-2 in the cortex. We did not find remarkable differences in the protein levels of angiotensinogen and Ang II in either the cortex or hippocampus of AD brains, whereas we observed a considerable increase in the expression of brain-derived neurotrophic factor in the hippocampus.

CONCLUSION

The current findings support the significant contribution of RAS components in AD pathogenesis, further suggesting that strategies focusing on the AT1R and AT2R pathways may lead to novel therapies for the management of AD.

ER stress associated TXNIP-NLRP3 inflammasome activation in hippocampus of human Alzheimer's disease

Although the exact etiology of Alzheimer's disease (AD) is poorly understood, experimental and clinical evidences suggest the contribution of neuroinflammation in the pathogenesis of AD. Pathologically, AD brain is characterized by an imbalance in redox status, elevated endoplasmic reticulum (ER) stress, synaptic dysfunction, inflammation, and progressive neurodegeneration. It has been noted that continuous accumulation of amyloid-beta (Aβ) and intracellular neurofibrillary tangles (NFTs) in AD brain trigger ER stress, which contributes to neurodegeneration. Similarly, experimental evidences supports the hypothesis that thioredoxin-interacting protein (TXNIP), an endogenous regulator of redox regulator thioredoxin (TRX), is activated by ER stress and contributes to activation of NLRP3 (NOD-like receptor protein 3) inflammatory cascade in hippocampus of the AD brain. Hippocampus of postmortem human AD and aged matched non-AD controls were analyzed for the expression ER stress markers and TXNIP-NLRP3 inflammasome at cellular and molecular levels. We found higher expression of TXNIP at protein and transcript levels in close association with pathological markers of AD such as Aβ and NFTs in AD hippocampus. In addition, our results demonstrated that TXNIP was co-localized in neurons and microglia. Moreover, expression of binding immunoglobulin protein (BiP), activated eukaryotic initiation factor-2α (eIf2α) and C/EBP homology protein (CHOP), proteins involved the development of ER stress, were elevated in AD hippocampus. Further, elevated expression of effector molecules of NLRP3 inflammasome activation such as apoptosis associated speck-like protein (ASC), cleaved caspase-1 and cleaved interleukin-1β were observed in the AD hippocampus. The study suggests that TXNIP could be a link that connect ER stress with neuroinflammation. Thus, TXNIP can be a possible therapeutic target to mitigate the progression of neuroinflammation in the pathogenesis of AD.

Structural and Functional Alterations in Mitochondria-Associated Membranes (MAMs) and in Mitochondria Activate Stress Response Mechanisms in an In Vitro Model of Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the accumulation of extracellular plaques composed by amyloid-β (Aβ) and intracellular neurofibrillary tangles of hyperphosphorylated tau. AD-related neurodegenerative mechanisms involve early changes of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) and impairment of cellular events modulated by these subcellular domains. In this study, we characterized the structural and functional alterations at MAM, mitochondria, and ER/microsomes in a mouse neuroblastoma cell line (N2A) overexpressing the human amyloid precursor protein (APP) with the familial Swedish mutation (APPswe). Proteins levels were determined by Western blot, ER-mitochondria contacts were quantified by transmission electron microscopy, and Ca²⁺ homeostasis and mitochondria function were analyzed using fluorescent probes and Seahorse assays. In this in vitro AD model, we found APP accumulated in MAM and mitochondria, and altered levels of proteins implicated in ER-mitochondria tethering, Ca²⁺ signaling, mitochondrial dynamics, biogenesis and protein import, as well as in the stress response. Moreover, we observed a decreased number of close ER-mitochondria contacts, activation of the ER unfolded protein response, reduced Ca²⁺ transfer from ER to mitochondria, and impaired mitochondrial function. Together, these results demonstrate that several subcellular alterations occur in AD-like neuronal cells, which supports that the defective ER-mitochondria crosstalk is an important player in AD physiopathology.

Asymmetry of Hippocampal Tau Pathology in Primary Age-Related Tauopathy and Alzheimer Disease

Primary age-related tauopathy (PART) is a neurodegenerative entity defined as neurofibrillary degeneration generally restricted to the medial temporal region (Braak stage I-IV) with complete or near absence of diffuse and neuritic plaques. Symptoms range in severity but are generally milder and later in onset than in Alzheimer disease (AD). Recently, an early predilection for neurofibrillary degeneration in the hippocampal CA2 subregion has been demonstrated in PART, whereas AD neuropathologic change (ADNC) typically displays relative sparing of CA2 until later stages. In this study, we utilized a semiquantitative scoring system to evaluate asymmetry of neurofibrillary degeneration between left and right hippocampi in 67 PART cases and 17 ADNC cases. 49% of PART cases demonstrated asymmetric findings in at least one hippocampal subregion, and 79% of the asymmetric cases displayed some degree of CA2 asymmetry. Additionally, 19% of cases revealed a difference in Braak score between the right and left hippocampi. There was a significant difference in CA2 neurofibrillary degeneration (p = 0.0006) and CA2/CA1 ratio (p < 0.0001) when comparing the contralateral sides, but neither right nor left was more consistently affected. These data show the importance of analyzing bilateral hippocampi in the diagnostic evaluation of PART and potentially of other neurodegenerative diseases.

Aluminum and Tau in Neurofibrillary Tangles in Familial Alzheimer's Disease

BACKGROUND

Familial Alzheimer's disease (fAD) is driven by genetic predispositions affecting the expression and metabolism of the amyloid-β protein precursor. Aluminum is a non-essential yet biologically-reactive metal implicated in the etiology of AD. Recent research has identified aluminum intricately and unequivocally associated with amyloid-β in senile plaques and, more tentatively, co-deposited with neuropil-like threads in the brains of a Colombian cohort of donors with fAD.

OBJECTIVE

Herein, we have assessed the co-localization of aluminum to immunolabelled phosphorylated tau to probe the potential preferential binding of aluminum to senile plaques or neurofibrillary tangles in the same Colombian kindred.

METHODS

Herein, we have performed phosphorylated tau-specific immunolabelling followed by aluminum-specific fluorescence microscopy of the identical brain tissue sections via a sequential labelling method.

RESULTS

Aluminum was co-localized with immunoreactive phosphorylated tau in the brains of donors with fAD. While aluminum was predominantly co-located to neurofibrillary tangles in the temporal cortex, aluminum was more frequently co-deposited with cortical senile plaques.

CONCLUSION

These data suggest that the co-deposition of aluminum with amyloid-β precedes that with neurofibrillary tangles. Extracellularly deposited amyloid-β may also be more immediately available to bind aluminum versus intracellular aggregates of tau. Therapeutic approaches to reduce tau have demonstrated the amelioration of its synergistic interactions with amyloid-β, ultimately reducing tau pathology and reducing neuronal loss. These data support the intricate associations of aluminum in the neuropathology of fAD, of which its subsequent reduction may further therapeutic benefits observed in ongoing clinical trials in vivo.

Limbic-predominant age-related TDP-43 encephalopathy differs from frontotemporal lobar degeneration

TAR-DNA binding protein-43 (TDP-43) proteinopathy is seen in multiple brain diseases. A standardized terminology was recommended recently for common age-related TDP-43 proteinopathy: limbic-predominant, age-related TDP-43 encephalopathy (LATE) and the underlying neuropathological changes, LATE-NC. LATE-NC may be co-morbid with Alzheimer's disease neuropathological changes (ADNC). However, there currently are ill-defined diagnostic classification issues among LATE-NC, ADNC, and frontotemporal lobar degeneration with TDP-43 (FTLD-TDP). A practical challenge is that different autopsy cohorts are composed of disparate groups of research volunteers: hospital- and clinic-based cohorts are enriched for FTLD-TDP cases, whereas community-based cohorts have more LATE-NC cases. Neuropathological methods also differ across laboratories. Here, we combined both cases and neuropathologists' diagnoses from two research centres-University of Pennsylvania and University of Kentucky. The study was designed to compare neuropathological findings between FTLD-TDP and pathologically severe LATE-NC. First, cases were selected from the University of Pennsylvania with pathological diagnoses of either FTLD-TDP (n = 33) or severe LATE-NC (mostly stage 3) with co-morbid ADNC (n = 30). Sections from these University of Pennsylvania cases were cut from amygdala, anterior cingulate, superior/mid-temporal, and middle frontal gyrus. These sections were stained for phospho-TDP-43 immunohistochemically and evaluated independently by two University of Kentucky neuropathologists blinded to case data. A simple set of criteria hypothesized to differentiate FTLD-TDP from LATE-NC was generated based on density of TDP-43 immunoreactive neuronal cytoplasmic inclusions in the neocortical regions. Criteria-based sensitivity and specificity of differentiating severe LATE-NC from FTLD-TDP cases with blind evaluation was ∼90%. Another proposed neuropathological feature related to TDP-43 proteinopathy in aged individuals is 'Alpha' versus 'Beta' in amygdala. Alpha and Beta status was diagnosed by neuropathologists from both universities (n = 5 raters). There was poor inter-rater reliability of Alpha/Beta classification (mean κ = 0.31). We next tested a separate cohort of cases from University of Kentucky with either FTLD-TDP (n = 8) or with relatively 'pure' severe LATE-NC (lacking intermediate or severe ADNC; n = 14). The simple criteria were applied by neuropathologists blinded to the prior diagnoses at University of Pennsylvania. Again, the criteria for differentiating LATE-NC from FTLD-TDP was effective, with sensitivity and specificity ∼90%. If more representative cases from each cohort (including less severe TDP-43 proteinopathy) had been included, the overall accuracy for identifying LATE-NC was estimated at >98% for both cohorts. Also across both cohorts, cases with FTLD-TDP died younger than those with LATE-NC (P < 0.0001). We conclude that in most cases, severe LATE-NC and FTLD-TDP can be differentiated by applying simple neuropathological criteria.

Influence of APOE genotype in primary age-related tauopathy

The term “Primary age-related tauopathy” (PART) was coined in 2014 to describe the common neuropathological observation of neurofibrillary tangles without associated beta-amyloid (Aβ) pathology. It is possible for PART pathology to be present in both cognitively normal and cognitively impaired individuals. Genetically, Apolipoprotein E (APOE) ε4 has been shown to occur less commonly in PART than in Alzheimer’s disease (AD). Here, we investigate the relationships between PART, AD and those pathologically normal for age, with an emphasis on APOE and cognition, using 152 selected participants from The University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age and the Manchester arm of the Brains for Dementia Research cohort. APOE genotype differed between PART and AD with APOE ε2 more common in the former and APOE ε4 more common in the latter. Individuals with definite PART were less likely to be cognitively impaired than those with AD and those with pathology considered pathologically normal for age. We postulate that the lack of Aβ in definite PART cases may be due either to an increased frequency of APOE ε2 or decreased frequency of APOE ε4 as their resulting protein isoforms have differing binding properties in relation to Aβ. Similarly, an increased frequency of APOE ε2 or decreased frequency of APOE ε4 may lead to decreased levels of cognitive impairment, which raises questions regarding the impact of Aβ pathology on overall cognition in elderly subjects. We suggest that it may be possible to use the increased frequency of APOE ε2 in definite PART to assist neuropathological diagnosis.

Primary Age-Related Tauopathy (PART): Addressing the Spectrum of Neuronal Tauopathic Changes in the Aging Brain

PURPOSE OF REVIEW

Primary age-related tauopathy (PART) was recently proposed as a pathologic diagnosis for brains that harbor neurofibrillary tangles (Braak stage ≤ 4) with little, if any, amyloid burden. We sought to review the clinicopathologic findings related to PART.

RECENT FINDINGS

Most adult human brains show at least focal tauopathic changes, and the majority of individuals with PART do not progress to dementia. Older age and cognitive impairment correlate with increased Braak stage, and multivariate analyses suggest that the rate of cognitive decline is less than matched patients with Alzheimer disease (AD). It remains unclear whether PART is a distinct tauopathic entity separate from AD or rather represents an earlier histologic stage of AD. Cognitive decline in PART is usually milder than AD and correlates with tauopathic burden. Biomarker and ligand-based radiologic studies will be important to define PART antemortem and prospectively follow its natural history.

The influence of Aβ-dependent and independent pathways on TDP-43 proteinopathy in Alzheimer's disease: a possible connection to LATE-NC

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that results from the accumulation of plaques by cleaved Aβ₄₂ peptides as well as neurofibrillary tangles of tau proteins. This accumulation triggers a complex cascade of cytotoxic, neuroinflammatory, and oxidative stresses that lead to neuronal death throughout the progression of the disease. Much of research in AD focused on the 2 pathologic proteins. Interestingly, another form of dementia with similar clinical manifestations of AD, but preferentially affected much older individuals, was termed as limbic-predominant age-related transactive response DNA-binding protein 43 (TDP-43) encephalopathy (LATE) and involved the cytotoxic intraneuronal deposition of phosphorylated TDP-43. TDP-43 proteinopathy was also found to be involved in AD pathology leading to the possibility that AD and LATE may share a common upstream etiology. This paper discusses the roles molecular pathways known in AD may have on influencing TDP-43 proteinopathy and the development of AD, LATE, or the 2 being comorbid with each other.

Positron Emission Tomography Imaging With [18F]flortaucipir and Postmortem Assessment of Alzheimer Disease Neuropathologic Changes

Importance

Positron emission tomography (PET) may increase the diagnostic accuracy and confirm the underlying neuropathologic changes of Alzheimer disease (AD).

Objective

To determine the accuracy of antemortem [18F]flortaucipir PET images for predicting the presence of AD-type tau pathology at autopsy.

Design, Setting, and Participants

This diagnostic study (A16 primary cohort) was conducted from October 2015 to June 2018 at 28 study sites (27 in US sites and 1 in Australia). Individuals with a terminal illness who were older than 50 years and had a projected life expectancy of less than 6 months were enrolled. All participants underwent [18F]flortaucipir PET imaging, and scans were interpreted by 5 independent nuclear medicine physicians or radiologists. Supplemental autopsy [18F]flortaucipir images and pathological samples were also collected from 16 historically collected cases. A second study (FR01 validation study) was conducted from March 26 to April 26, 2019, in which 5 new readers assessed the original PET images for comparison to autopsy.

Main Outcomes and Measures

[18F]flortaucipir PET images were visually assessed and compared with immunohistochemical tau pathology. An AD tau pattern of flortaucipir retention was assessed for correspondence with a postmortem B3-level (Braak stage V or VI) pathological pattern of tau accumulation and to the presence of amyloid-β plaques sufficient to meet the criteria for high levels of AD neuropathological change. Success was defined as having at least 3 of the 5 readers above the lower bounds of the 95% CI for both sensitivity and specificity of 50% or greater.

Results

A total of 156 patients were enrolled in the A16 study and underwent [18F]flortaucipir PET imaging. Of these, 73 died during the study, and valid autopsies were performed for 67 of these patients. Three autopsies were evaluated as test cases and removed from the primary cohort (n = 64). Of the 64 primary cohort patients, 34 (53%) were women and 62 (97%) were white; mean (SD) age was 82.5 (9.6) years; and 49 (77%) had dementia, 1 (2%) had mild cognitive impairment, and 14 (22%) had normal cognition. Prespecified success criteria were met for the A16 primary cohort. The flortaucipir PET scans predicted a B3 level of tau pathology, with sensitivity ranging from 92.3% (95% CI, 79.7%-97.3%) to 100.0% (95% CI, 91.0%-100.0%) and specificity ranging from 52.0% (95% CI, 33.5%-70.0%) to 92.0% (95% CI, 75.0%-97.8%). A high level of AD neuropathological change was predicted with sensitivity of 94.7% (95% CI, 82.7%-98.5%) to 100.0% (95% CI, 90.8%-100.0%) and specificity of 50.0% (95% CI, 32.1%-67.9%) to 92.3% (95% CI, 75.9%-97.9%). The FR01 validation study also met prespecified success criteria. Addition of the supplemental autopsy data set and 3 test cases, which comprised a total of 82 patients and autopsies for both the A16 and FR01 studies, resulted in improved specificity and comparable overall accuracy. Among the 156 enrolled participants, 14 (9%) experienced at least 1 treatment-emergent adverse event.

Conclusions and Relevance

This study's findings suggest that PET imaging with [18F]flortaucipir could be used to identify the density and distribution of AD-type tau pathology and the presence of high levels of AD neuropathological change, supporting a neuropathological diagnosis of AD.

Diffuse Amyloid-β Plaques, Neurofibrillary Tangles, and the Impact of APOE in Elderly Persons' Brains Lacking Neuritic Amyloid Plaques

Data from a large autopsy series were analyzed to address questions pertinent to primary age-related tauopathy (PART) and Alzheimer's disease (AD): what factors are associated with increased severity of neurofibrillary degeneration in brains that lack neuritic amyloid plaques?; is there an association between Apolipoprotein E (APOE) alleles and PART pathologic severity independent of amyloid-β (Aβ) deposits?; and, how do the stains used to detect plaques and tangles impact the experimental results? Neuropathologic data were evaluated from elderly research volunteers whose brain autopsies were performed at University of Kentucky Alzheimer's Disease Center (UK-ADC; N = 145 subjects). All of the included subjects' brains lacked neuritic amyloid plaques according to the CERAD diagnostic criteria and the average final MMSE score before death was 26.8±4.6 stdev. The study incorporated evaluation of tissue with both silver histochemical stains and immunohistochemical stains to compare results; the immunohistochemical stains (Aβ and phospho-tau) were scanned and quantified using digital pathologic methods. Immunohistochemical stains provided important advantages over histochemical stains due to sensitivity and detectability via digital methods. When AD-type pathology was in its presumed earliest phases, neocortical parenchymal Aβ deposits were associated with increased medial temporal lobe neurofibrillary tangles. The observation supports the NIA-AA consensus recommendation for neuropathologic diagnoses, because even these "diffuse" Aβ deposits signal that AD pathobiologic mechanisms are occurring. Further, the data were most compatible with the hypothesis that the APOEɛ4 allele exerts its effect(s) via driving Aβ deposition, i.e., an "upstream" influence, rather than being associated directly with Aβ- independent PART pathology.

Co-Expression of Glia Maturation Factor and Apolipoprotein E4 in Alzheimer's Disease Brain

Apolipoprotein E4 (ApoE4) is a major genetic risk factor for Alzheimer's disease (AD). The E4 allele of ApoE plays a crucial role in the inflammatory and neurodegenerative processes associated with AD. This is evident from the multiple effects of the ApoE isoforms in amyloid-β (Aβ) aggregation. Glia maturation factor (GMF) is a brain-specific neuroinflammatory protein that we have previously demonstrated to be significantly upregulated in various regions of AD brains compared to non-AD control brains and that it induces neurodegeneration. We have previously reported that GMF is predominantly expressed in the reactive astrocytes surrounding amyloid plaques (APs) in AD brain. In the present study, using immunohistochemical and dual immunofluorescence staining, we show the expression and colocalization of GMF and ApoE4 in AD brains. Our results show that ApoE4 is present within the APs of AD brain. Further, we found that GMF and ApoE4 were strongly expressed and co-associated in APs and in the reactive astrocytes surrounding APs in AD. An increased expression of GMF in APs and neurofibrillary tangles in the AD brain, and the co-localization of GMF and ApoE4 in APs suggest that GMF and ApoE4 together should be contributing to the neuropathological changes associated with AD.

Thioredoxin-Interacting Protein (TXNIP) Associated NLRP3 Inflammasome Activation in Human Alzheimer's Disease Brain

Alzheimer's disease (AD) is the most common form of age-associated dementia characterized by amyloid-β plaques and neurofibrillary tangles. Recent studies have demonstrated that thioredoxin-interacting protein (TXNIP), an endogenous regulator of redox/glucose induced stress and inflammation, is now known to be upregulated in stroke, traumatic brain injury, diabetes and AD. We hypothesized that TXNIP overexpression sustains neurodegeneration through activation of the nucleotide binding and oligomerization domain-like receptor protein 3 in human AD brains. We analyzed TXNIP and the components of the NLRP3 inflammasome in the cortex of postmortem human brain samples by western blotting, real-time PCR, and immunohistochemical techniques in comparison with age-matched non-demented controls. Our results demonstrate that TXNIP protein as well as its mRNA levels in the cortex was significantly upregulated in AD compared to control brains. Moreover, using double immunofluorescence staining, TXNIP and interlukin-1β (IL-1β) were co-localized near Aβ plaques and p-tau. These results suggest an association between TXNIP overexpression levels and AD pathogenesis. Further, a significant increased expression of cleaved caspase-1 and IL-1β, the products of inflammasome activation, was detected in the cortex of AD brains. Together, these findings suggest that TXNIP, an upstream promising new therapeutic target, is a molecular link between inflammation and AD. The significant contribution of TXNIP to AD pathology suggests that strategies focusing on specific targeting of the TXNIP-NLRP3 inflammasome may lead to novel therapies for the management of AD and other age-related dementias.

Neuropathologic, genetic, and longitudinal cognitive profiles in primary age-related tauopathy (PART) and Alzheimer's disease

INTRODUCTION

Primary age-related tauopathy (PART) is a recently described entity that can cause cognitive impairment in the absence of Alzheimer's disease (AD). Here, we compared neuropathological features, tau haplotypes, apolipoprotein E (APOE) genotypes, and cognitive profiles in age-matched subjects with PART and AD pathology.

METHODS

Brain autopsies (n = 183) were conducted on participants 85 years and older from the Baltimore Longitudinal Study of Aging and Johns Hopkins Alzheimer's Disease Research Center. Participants, normal at enrollment, were followed with periodic cognitive evaluations until death.

RESULTS

Compared with AD, PART subjects showed significantly slower rates of decline on measures of memory, language, and visuospatial performance. They also showed lower APOE ε4 allele frequency (4.1% vs. 17.6%, P = .0046).

DISCUSSION

Our observations suggest that PART is separate from AD and its distinction will be important for the clinical management of patients with cognitive impairment and for public health care planning.

Changes in concentrations of tau-reactive antibodies are dependent on sex in Alzheimer's disease patients

The presence of pre-existing natural antibodies against Alzheimer's disease (AD) pathological proteins might interfere with immune responses to therapeutic vaccination with these proteins. We aimed to compare levels of antibodies in CSF and serum: We observed higher reactivity of natural tau-reactive antibodies towards phosphorylated bovine tau protein than to human recombinant (non-phosphorylated) tau protein. Males with MCI-AD had higher amounts of these antibodies than corresponding controls. Concentrations of antibodies were lower in females with the MCI-AD than in control females. These findings may have implications for tau vaccination trials.

Early Alzheimer-type lesions in cognitively normal subjects

Amyloid deposits and tau-immunoreactive neurofibrillary tangles, together with neuronal and synaptic loss, are the neuropathological hallmarks of Alzheimer's disease (AD). Both proteins are present in the normal brain during aging. However, the temporal sequence of their involvement in the onset of AD pathology remains controversial. To define whether amyloid β protein deposits or tau protein lesions appear first during normal brain aging, we performed an immunohistological study on serial sections from 105 autopsy brains (age range: 40-104 years) from patients free of clinical signs of cognitive decline, using anti-tau (AT8) and anti-amyloid (4G8) antibodies in the hippocampus, entorhinal cortex, inferior temporal cortex (Brodmann area 20), prefrontal cortex (Brodmann area 9), occipital cortex (Brodmann areas 17 and 18), and in the brainstem. All cases older than 48 years displayed at least a few neurofibrillary tangles, which appeared more frequently in the entorhinal than in the transentorhinal cortex. Tau pathology in these areas preceded tau inclusions in the brainstem. Furthermore, the first site of the apparition of tau pathology is inconsistent, being the entorhinal cortex in most cases, and in fewer cases, the transentorhinal region. There was no case presenting with amyloid deposition in the absence of neurofibrillary tangles, lending evidence to the fact that neurofibrillary tangles appear earlier than amyloid plaques during normal brain aging. However, the role of amyloid in promoting tau deposition cannot be excluded in some cases but may not represent the sole mechanism of disease induction and progression.

The Amygdala as a Locus of Pathologic Misfolding in Neurodegenerative Diseases

Over the course of most common neurodegenerative diseases the amygdala accumulates pathologically misfolded proteins. Misfolding of 1 protein in aged brains often is accompanied by the misfolding of other proteins, suggesting synergistic mechanisms. The multiplicity of pathogenic processes in human amygdalae has potentially important implications for the pathogenesis of Alzheimer disease, Lewy body diseases, chronic traumatic encephalopathy, primary age-related tauopathy, and hippocampal sclerosis, and for the biomarkers used to diagnose those diseases. Converging data indicate that the amygdala may represent a preferential locus for a pivotal transition from a relatively benign clinical condition to a more aggressive disease wherein multiple protein species are misfolded. Thus, understanding of amygdalar pathobiology may yield insights relevant to diagnoses and therapies; it is, however, a complex and imperfectly defined brain region. Here, we review aspects of amygdalar anatomy, connectivity, vasculature, and pathologic involvement in neurodegenerative diseases with supporting data from the University of Kentucky Alzheimer's Disease Center autopsy cohort. Immunohistochemical staining of amygdalae for Aβ, Tau, α-synuclein, and TDP-43 highlight the often-coexisting pathologies. We suggest that the amygdala may represent an "incubator" for misfolded proteins and that it is possible that misfolded amygdalar protein species are yet to be discovered.

Comorbidities

The term comorbidities or mixed pathologies is used when brain tissue, a surgical sample, or postmortem brain displays a mixture of protein alterations or other pathologies. Most of the alterations when seen in sufficient extent are considered causative, are related to a certain clinical phenotype, i.e., when hyperphosphorylated τ (HPτ) is observed in occipital cortex concomitant with β-amyloid (Aβ), the diagnosis is Alzheimer disease (AD). When HPτ is observed in hippocampal structures in a subject with extensive and widespread α-synuclein pathology, a Lewy body disease (LBD), the HPτ pathology is considered as a concomitant alteration. There are numerous reports indicating that when "concomitant" pathologies are seen in a subject with certain neurodegenerative diseases, the clinical phenotype might be altered. In addition there are those cases where many alterations are seen in a sparse extent, but jointly they lead to a clinical syndrome. Thus today it is not sufficient to confirm a certain pathology to be seen, i.e., AD- or LBD-related; in addition the concomitant aging-related alterations have to be looked for.

Comparison of symptomatic and asymptomatic persons with primary age-related tauopathy

OBJECTIVE

To conduct a clinicopathologic study to characterize clinical and neuropathologic features associated with cognitive impairment in participants with no neuritic amyloid plaques (primary age-related tauopathy [PART] definite) and sparse neuritic plaques (amyloid sparse).

METHODS

Using the National Alzheimer's Coordinating Center database, we identified 377 individuals who were PART definite (n = 170) or amyloid sparse (n = 207), clinically examined within 1 year of death, and autopsied at 1 of 26 National Institute on Aging-funded Alzheimer's Disease Centers. Factors associated with the odds of being symptomatic (global Clinical Dementia Rating [CDR] score >0) were identified with multivariable logistic regression.

RESULTS

PART-definite participants less often had a high Braak neurofibrillary tangle stage V or VI (4%) compared to amyloid sparse participants (28%, p < 0.001). Of the PART-definite participants, 98 were symptomatic and 72 asymptomatic according to their global CDR scores. PART-definite participants were less often symptomatic (58%) compared with amyloid sparse participants (80%, p < 0.001). Within the PART-definite group, independent predictors of symptomatic status included depression (adjusted odds ratio [aOR] 4.20, 95% confidence interval [CI] 2.15-8.19), Braak stage (aOR 1.42, 95% CI 1.04-1.95), and history of stroke (aOR 8.09, 95% CI 2.63-24.82). Within the amyloid sparse group, independent predictors of symptomatic status included education (aOR 0.80, 95% CI 0.65-0.99), Braak stage (aOR 1.91, 95% CI 1.07-3.43), and amyloid angiopathy (aOR 2.75, 95% CI 1.14-6.64).

CONCLUSIONS

These findings support the hypothesis that participants with PART have an amyloid-independent dementing Alzheimer disease-like temporal lobe tauopathy.

Bidirectional interplay of HSF1 degradation and UPR activation promotes tau hyperphosphorylation

The unfolded protein response (UPR) in the endoplasmic reticulum (ER) and the cytoplasmic heat stress response are two major stress response systems necessary for maintaining proteostasis for cellular health. Failure of either of these systems, such as in sustained UPR activation or in insufficient heat shock response activation, can lead to the development of neurodegeneration. Alleviation of ER stress and enhancement of heat shock response through heat shock factor 1 (HSF1) activation have previously been considered as attractive potential therapeutic targets for Alzheimer’s disease (AD)—a prevalent and devastating tauopathy. Understanding the interplay of the two aforementioned systems and their cooperative role in AD remain elusive. Here we report studies in human brain and tau pathogenic mouse models (rTg4510, PS19, and rTg21221), identifying HSF1 degradation and UPR activation as precursors of aberrant tau pathogenesis. We demonstrate that chemical ER stress inducers caused autophagy-lysosomal HSF1 degradation, resulting in tau hyperphosphorylation in rat primary neurons. In addition, permanent HSF1 loss reversely causes chronic UPR activation, leading to aberrant tau phosphorylation and aggregation in the hippocampus of aged HSF1 heterozygous knock-out mice. The deleterious interplay of UPR activation and HSF1 loss is exacerbated in N2a cells stably overexpressing a pro-aggregation mutant Tau_RD ΔK280 (N2a-Tau_RD ΔK280). We provide evidence of how these two stress response systems are intrinsically interweaved by showing that the gene encoding C/EBP-homologous protein (CHOP) activation in the UPR apoptotic pathway facilitates HSF1 degradation, which likely further contributes to prolonged UPR via ER chaperone HSP70 a5 (BiP/GRP78) suppression. Upregulating HSF1 relieves the tau toxicity in N2a-Tau_RD ΔK280 by reducing CHOP and increasing HSP70 a5 (BiP/GRP78). Our work reveals how the bidirectional crosstalk between the two stress response systems promotes early tau pathology and identifies HSF1 being one likely key player in both systems.

Tauopathy including Alzheimer’s disease (AD) is characterized by a build-up of tau aggregates in the brain, highly associated with failure of cellular protein homeostasis. Proteostasis can be achieved by protein quality control system to cope with numerous stresses such as proteotoxic stress from misfolded proteins. This cellular protective system includes heat shock response regulated by heat shock factor 1 (HSF1) activation and unfolded protein response in ER. Despite the importance of stress response in maintaining proteostasis, their role in neurodegenerative diseases like tauopathy is not clearly understood. The current study reports how the interplay between the two stress response systems, unfolded protein response and HSF1 promotes early tau pathology and identifies HSF1 protein degradation being one likely key player in both human AD and tau transgenic mouse AD models. We identify aging-associated AD-like neuropathological changes in the hippocampus of HSF1 heterozygous knock-out mice. We speculate that that HSF1 loss may constitute a mechanistic connection between ER stress and tau hyperphosphorylation in tau pathology. This study demonstrates the potential therapeutic significance of stabilizing HSF1 protein in treating AD.

Suspected non-Alzheimer's pathology - Is it non-Alzheimer's or non-amyloid?

Neurodegeneration, the progressive loss of neurons, is a major process involved in dementia and age-related cognitive impairment. It can be detected clinically using currently available biomarker tests. Suspected Non-Alzheimer Pathology (SNAP) is a biomarker-based concept that encompasses a group of individuals with neurodegeneration, but no evidence of amyloid deposition (thereby distinguishing it from Alzheimer's disease (AD)). These individuals may often have a clinical diagnosis of AD, but their clinical features, genetic susceptibility and progression can differ significantly, carrying crucial implications for precise diagnostics, clinical management, and efficacy of clinical drug trials. SNAP has caused wide interest in the dementia research community, because it is still unclear whether it represents distinct pathology separate from AD, or whether in some individuals, it could represent the earliest stage of AD. This debate has raised pertinent questions about the pathways to AD, the need for biomarkers, and the sensitivity of current biomarker tests. In this review, we discuss the biomarker and imaging trials that first recognized SNAP. We describe the pathological correlates of SNAP and comment on the different causes of neurodegeneration. Finally, we discuss the debate around the concept of SNAP, and further unanswered questions that are emerging.

Monoaminergic neuropathology in Alzheimer's disease

None of the proposed mechanisms of Alzheimer's disease (AD) fully explains the distribution patterns of the neuropathological changes at the cellular and regional levels, and their clinical correlates. One aspect of this problem lies in the complex genetic, epigenetic, and environmental landscape of AD: early-onset AD is often familial with autosomal dominant inheritance, while the vast majority of AD cases are late-onset, with the ε4 variant of the gene encoding apolipoprotein E (APOE) known to confer a 5-20 fold increased risk with partial penetrance. Mechanisms by which genetic variants and environmental factors influence the development of AD pathological changes, especially neurofibrillary degeneration, are not yet known. Here we review current knowledge of the involvement of the monoaminergic systems in AD. The changes in the serotonergic, noradrenergic, dopaminergic, histaminergic, and melatonergic systems in AD are briefly described. We also summarize the possibilities for monoamine-based treatment in AD. Besides neuropathologic AD criteria that include the noradrenergic locus coeruleus (LC), special emphasis is given to the serotonergic dorsal raphe nucleus (DRN). Both of these brainstem nuclei are among the first to be affected by tau protein abnormalities in the course of sporadic AD, causing behavioral and cognitive symptoms of variable severity. The possibility that most of the tangle-bearing neurons of the LC and DRN may release amyloid β as well as soluble monomeric or oligomeric tau protein trans-synaptically by their diffuse projections to the cerebral cortex emphasizes their selective vulnerability and warrants further investigations of the monoaminergic systems in AD.

Elevation of brain glucose and polyol-pathway intermediates with accompanying brain-copper deficiency in patients with Alzheimer's disease: metabolic basis for dementia

Impairment of brain-glucose uptake and brain-copper regulation occurs in Alzheimer's disease (AD). Here we sought to further elucidate the processes that cause neurodegeneration in AD by measuring levels of metabolites and metals in brain regions that undergo different degrees of damage. We employed mass spectrometry (MS) to measure metabolites and metals in seven post-mortem brain regions of nine AD patients and nine controls, and plasma-glucose and plasma-copper levels in an ante-mortem case-control study. Glucose, sorbitol and fructose were markedly elevated in all AD brain regions, whereas copper was correspondingly deficient throughout (all P < 0.0001). In the ante-mortem case-control study, by contrast, plasma-glucose and plasma-copper levels did not differ between patients and controls. There were pervasive defects in regulation of glucose and copper in AD brain but no evidence for corresponding systemic abnormalities in plasma. Elevation of brain glucose and deficient brain copper potentially contribute to the pathogenesis of neurodegeneration in AD.

"New Old Pathologies": AD, PART, and Cerebral Age-Related TDP-43 With Sclerosis (CARTS)

The pathology-based classification of Alzheimer's disease (AD) and other neurodegenerative diseases is a work in progress that is important for both clinicians and basic scientists. Analyses of large autopsy series, biomarker studies, and genomics analyses have provided important insights about AD and shed light on previously unrecognized conditions, enabling a deeper understanding of neurodegenerative diseases in general. After demonstrating the importance of correct disease classification for AD and primary age-related tauopathy, we emphasize the public health impact of an underappreciated AD "mimic," which has been termed "hippocampal sclerosis of aging" or "hippocampal sclerosis dementia." This pathology affects >20% of individuals older than 85 years and is strongly associated with cognitive impairment. In this review, we provide an overview of current hypotheses about how genetic risk factors (GRN, TMEM106B, ABCC9, and KCNMB2), and other pathogenetic influences contribute to TDP-43 pathology and hippocampal sclerosis. Because hippocampal sclerosis of aging affects the "oldest-old" with arteriolosclerosis and TDP-43 pathologies that extend well beyond the hippocampus, more appropriate terminology for this disease is required. We recommend "cerebral age-related TDP-43 and sclerosis" (CARTS). A detailed case report is presented, which includes neuroimaging and longitudinal neurocognitive data. Finally, we suggest a neuropathology-based diagnostic rubric for CARTS.

Altered Proteins in the Aging Brain

We assessed the prevalence of common altered brain proteins in 296 cognitively unimpaired subjects ranging from age 50 to 102 years. The incidence and the stage of hyperphosphorylated-τ (HPτ), β-amyloid, α-synuclein (αS), and transactive response DNA (TDP) binding protein 43 (TDP43)-immunoreactivity (-IR) increased with age. HPτ-IR was observed in 98% of the subjects; the locus coeruleus was solely affected in 46%, and 79% of the subjects were in Braak stages a to II. β-Amyloid was seen in 47% of subjects and the Thal phase correlated with the HPτ Braak stage and age. Intermediate Alzheimer disease-related pathology (ADRP) was seen in 12%; 52% of the subjects with HPτ-IR fulfilled criteria for definite primary age-related tauopathy (PART). The incidence of concomitant pathology (αS, TDP43) did not differ between those with PART and those with ADRP but the former were younger. TDP43-IR was observed in 36%; the most frequently affected region was the medulla; αS-IR was observed in 19% of subjects. In 41% of the subjects from 80 to 89 years at death, 3 altered proteins were seen in the brain. Thus, altered proteins are common in the brains of cognitively unimpaired aged subjects; this should be considered while developing diagnostic biomarkers, particularly for identifying subjects at early stages of neurodegenerative diseases.

Oxidative stress and hippocampal synaptic protein levels in elderly cognitively intact individuals with Alzheimer's disease pathology

Neuritic amyloid plaques and neurofibrillary tangles are hallmarks of Alzheimer's disease (AD) and are major components used for the clinical diagnosis of this disorder. However, many individuals with no cognitive impairment (NCI) also present at autopsy with high levels of these AD pathologic hallmarks. In this study, we evaluated 15 autopsy cases from NCI individuals with high levels of AD-like pathology (high pathology no cognitive impairment) and compared them to age- and postmortem-matched cohorts of individuals with amnestic mild cognitive impairment and NCI cases with low AD-like pathology (low pathology no cognitive impairment [LPNCI]). Individuals classified as high pathology no cognitive impairment or amnestic mild cognitive impairment had a significant loss of both presynaptic and postsynaptic proteins in the hippocampus compared with those in the LPNCI cohort. In addition, these 2 groups had a significant increase in 3 different markers of oxidative stress compared with that in the LPNCI group. The changes in levels of synaptic proteins are strongly associated with levels of oxidative stress. These data suggest that cognitively older subjects without dementia but with increased levels of AD-like pathology may represent a very early preclinical stage of AD.

Association of APOE with tau-tangle pathology with and without β-amyloid

This study tested the hypothesis that the association of apolipoprotein E (APOE) with paired helical filament tau (PHF-tau) tangle pathology differs in brains with and without β-amyloid. Participants were 1056 autopsied individuals from 2 clinical-pathologic cohort studies of aging and Alzheimer's disease (AD), the Religious Orders Study, and the Rush Memory and Aging Project. Neuropathologic measures were obtained using immunohistochemistry targeting β-amyloid and PHF-tau tangles in 8 brain regions. Linear regression was used to compare the relation of APOE ε4 and ε2 to PHF-tau-tangle density in persons with β-amyloid relative to persons without β-amyloid. We found an interaction between APOE ε4 carriers and presence of β-amyloid (β = -0.968, p = 0.013) such that the association of APOE ε4 with PHF-tau tangles was much stronger in brains with β-amyloid. Stratified analysis shows that the association of APOE ε4 with PHF-tau tangles was considerably stronger among those with β-amyloid (β = 0.757, p = 1.1 × 10(-15)) compared to those without β-amyloid which was not significant (β = -0.201, p = 0.424). Separately, APOE ε2 was associated with fewer tangles in brains with β-amyloid (β = -0.425, p = 7.6 × 10(-4)) compared to those without β-amyloid which was not significant (β = -0.102, p = 0.506). Thus, the presence of APOE ε4 and ε2 alleles was not associated with PHF-tau tangles in the absence of β-amyloid. The data provide additional evidence that PHF-tau tangles in the absence of β-amyloid may reflect a pathologic process distinct from Alzheimer's disease.

Tau positron emission tomographic imaging in aging and early Alzheimer disease

OBJECTIVE

Detection of focal brain tau deposition during life could greatly facilitate accurate diagnosis of Alzheimer disease (AD), staging and monitoring of disease progression, and development of disease-modifying therapies.

METHODS

We acquired tau positron emission tomography (PET) using (18)F T807 (AV1451), and amyloid-β PET using (11)C Pittsburgh compound B (PiB) in older clinically normal individuals, and symptomatic patients with mild cognitive impairment or mild AD dementia.

RESULTS

We found abnormally high cortical (18)F T807 binding in patients with mild cognitive impairment and AD dementia compared to clinically normal controls. Consistent with the neuropathology literature, the presence of elevated neocortical (18)F T807 binding particularly in the inferior temporal gyrus was associated with clinical impairment. The association of cognitive impairment was stronger with inferior temporal (18)F T807 than with mean cortical (11)C PIB. Regional (18)F T807 was correlated with mean cortical (11)C PiB among both impaired and control subjects.

INTERPRETATION

These findings suggest that (18)F T807 PET could have value as a biomarker that reflects both the progression of AD tauopathy and the emergence of clinical impairment.

Brain pathologies in extreme old age

With an emphasis on evolving concepts in the field, we evaluated neuropathologic data from very old research volunteers whose brain autopsies were performed at the University of Kentucky Alzheimer's Disease Center, incorporating data from the Georgia Centenarian Study (n = 49 cases included), Nun Study (n = 17), and University of Kentucky Alzheimer's Disease Center (n = 11) cohorts. Average age of death was 102.0 (range: 98-107) years overall. Alzheimer's disease pathology was not universal (62% with "moderate" or "frequent" neuritic amyloid plaque densities), whereas frontotemporal lobar degeneration was absent. By contrast, some hippocampal neurofibrillary tangles (including primary age-related tauopathy) were observed in every case. Lewy body pathology was seen in 16.9% of subjects and hippocampal sclerosis of aging in 20.8%. We describe anatomic distributions of pigment-laden macrophages, expanded Virchow-Robin spaces, and arteriolosclerosis among Georgia Centenarians. Moderate or severe arteriolosclerosis pathology, throughout the brain, was associated with both hippocampal sclerosis of aging pathology and an ABCC9 gene variant. These results provide fresh insights into the complex cerebral multimorbidity, and a novel genetic risk factor, at the far end of the human aging spectrum.