Here we review progress by the Penn Biomarker Core in the Alzheimer's disease Neuroimaging Initiative (ADNI) towards developing a pathological cerebrospinal fluid (CSF) and plasma biomarker signature for mild Alzheimer's disease (AD) as well as a biomarker profile that predicts conversion of mild cognitive impairment (MCI) and/or normal control (NC) subjects to AD. The Penn Biomarker Core also collaborated with other ADNI Cores to integrate data across ADNI to temporally order changes in clinical measures, imaging data and chemical biomarkers that serve as mileposts and predictors of the conversion of NC to MCI as well as MCI to AD, and the progression of AD.
Initial CSF studies by the ADNI Biomarker Core revealed a pathological CSF biomarker signature of AD defined by the combination of Aβ1-42 and total tau (T-tau) that effectively delineates mild AD in the large multisite prospective clinical investigation conducted in ADNI. This signature appears to predict conversion from MCI to AD. Data fusion efforts across ADNI Cores generated a model for the temporal ordering of AD biomarkers which suggests that Aβ amyloid biomarkers become abnormal first, followed by changes in neurodegenerative biomarkers (CSF tau, FDG-PET, MRI) and the onset of clinical symptoms. The timing of these changes varies in individual patients due to genetic and environmental factors that increase or decrease an individual's resilience in response to progressive accumulations of AD pathologies. Further studies in ADNI will refine this model and render the biomarkers studied in ADNI more applicable to routine diagnosis and to clinical trials of disease modifying therapies.
Alzheimer's disease; cerebrospinal fluid; plasma; biomarkers; mild cognitive impairment
Cerebrovascular disease and vascular risk factors are associated with Alzheimer’s disease, but the evidence for their association with other neurodegenerative disorders is limited. Therefore, we compared the prevalence of cerebrovascular disease, vascular pathology and vascular risk factors in a wide range of neurodegenerative diseases and correlate them with dementia severity. Presence of cerebrovascular disease, vascular pathology and vascular risk factors was studied in 5715 cases of the National Alzheimer’s Coordinating Centre database with a single neurodegenerative disease diagnosis (Alzheimer’s disease, frontotemporal lobar degeneration due to tau, and TAR DNA-binding protein 43 immunoreactive deposits, α-synucleinopathies, hippocampal sclerosis and prion disease) based on a neuropathological examination with or without cerebrovascular disease, defined neuropathologically. In addition, 210 ‘unremarkable brain’ cases without cognitive impairment, and 280 cases with pure cerebrovascular disease were included for comparison. Cases with cerebrovascular disease were older than those without cerebrovascular disease in all the groups except for those with hippocampal sclerosis. After controlling for age and gender as fixed effects and centre as a random effect, we observed that α-synucleinopathies, frontotemporal lobar degeneration due to tau and TAR DNA-binding protein 43, and prion disease showed a lower prevalence of coincident cerebrovascular disease than patients with Alzheimer’s disease, and this was more significant in younger subjects. When cerebrovascular disease was also present, patients with Alzheimer’s disease and patients with α-synucleinopathy showed relatively lower burdens of their respective lesions than those without cerebrovascular disease in the context of comparable severity of dementia at time of death. Concurrent cerebrovascular disease is a common neuropathological finding in aged subjects with dementia, is more common in Alzheimer’s disease than in other neurodegenerative disorders, especially in younger subjects, and lowers the threshold for dementia due to Alzheimer’s disease and α-synucleinopathies, which suggests that these disorders should be targeted by treatments for cerebrovascular disease.
Alzheimer’s disease; frontotemporal lobar degeneration; vascular disease; dementia; epidemiology; neuropathology
Parkinsons disease; Head trauma; Traumatic Brain injury; Alpha-synuclein; Neurodegeneration
To see if the distribution patterns of phosphorylated 43-kDa TAR DNA-binding protein (pTDP-43) intraneuronal inclusions in amyotrophic lateral sclerosis (ALS) permit recognition of neuropathological stages.
pTDP-43 immunohistochemistry was performed on 70 μm sections from ALS autopsy cases (N=76) classified by clinical phenotype and genetic background.
ALS cases with the lowest burden of pTDP-43 pathology were characterized by lesions in the agranular motor cortex, brainstem motor nuclei of cranial nerves XII-X, VII, V, and spinal cord α-motoneurons (stage 1). Increasing burdens of pathology showed involvement of the prefrontal neocortex (middle frontal gyrus), brainstem reticular formation, precerebellar nuclei, and the red nucleus (stage 2). In stage 3, pTDP-43 pathology involved the prefrontal (gyrus rectus and orbital gyri) and then postcentral neocortex and striatum. Cases with the greatest burden of pTDP-43 lesions showed pTDP-43 inclusions in anteromedial portions of the temporal lobe, including the hippocampus (stage 4). At all stages, these lesions were accompanied by pTDP-43 oligodendroglial aggregates. Ten cases with C9orf72 repeat expansion displayed the same sequential spreading pattern as non-expansion cases but a greater regional burden of lesions, indicating a more fulminant dissemination of pTDP-43 pathology.
pTDP-43 pathology in ALS possibly disseminates in a sequential pattern that permits recognition of four neuropathological stages consistent with the hypothesis that pTDP-43 pathology is propagated along axonal pathways. Moreover, the fact that pTDP-43 pathology develops in the prefrontal cortex as part of an ongoing disease process could account for the development of executive cognitive deficits in ALS.
Dementia is increasingly being recognized in cases of Parkinson's disease (PD); such cases are termed PD dementia (PDD). The spread of fibrillar α-synuclein (α-syn) pathology from the brainstem to limbic and neocortical structures seems to be the strongest neuropathological correlate of emerging dementia in PD. In addition, up to 50% of patients with PDD also develop sufficient amyloid-β plaques and tau-containing neurofibrillary tangles for a secondary diagnosis of Alzheimer's disease (AD), and these pathologies may act synergistically with α-syn pathology to confer a worse prognosis. Understanding the relationships between these three distinct pathologies and their resultant clinical phenotypes are crucial to the development of effective disease-modifying treatments for PD and PDD.
Aggregation of TDP-43 proteins to form intracellular inclusions is the primary pathology in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) with TDP-43 inclusions (FTLD-TDP). Histologically, in the cerebral cortex and limbic regions of affected ALS and FTLD-TDP patients, these pathologies occur as a variety of cytoplasmic, neuritic and intranuclear TDP-43 inclusions. In the spinal cord and lower brainstem of ALS patients, the lesions form cytoplasmic dashes or complex filamentous and spherical profiles in addition to skein-like inclusions (SLI). Ultrastructurally, the morphology of TDP-43 inclusions is heterogeneous but mainly composed of loose bundles of 10–20 nm diameter straight filaments associated with electron dense granular material. All of these TDP-43 inclusions are generally described as disordered amorphous aggregations unlike the amyloid fibrils that characterize protein accumulations in neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease.
We here report that Thioflavin-S positive SLI are present in a subset of ALS cases, while TDP-43 inclusions outside the spinal cord lack the chemical properties of amyloid. Further, we examine the differential enrichment of fibrillar profiles in SLI of ALS cases by TDP-43 immuno-electron microscopy (immuno-EM). The demonstration that pathological TDP-43 can be amyloidogenic in situ suggests the following conclusions: 1) the conformational changes associated with TDP-43 aggregation are more complex than previously thought; 2) Thioflavin-S positive SLI may be composed primarily of filamentous ultrastructures.
TDP-43; amyloid; skein; amyotrophic lateral sclerosis; ALS; frontotemporal lobar degeneration; FTLD-TDP
To examine the neuropathological substrates of cognitive dysfunction and dementia in Parkinson’s disease (PD).
140 patients with a clinical diagnosis of PD and either normal cognition or onset of dementia two or more years after motor symptoms (PDD) were studied. Patients with a clinical diagnosis of dementia with Lewy bodies were excluded.
Autopsy records of genetic data and semi-quantitative scores for the burden of neurofibrillary tangles (NFTs), senile plaques (SPs), Lewy body (LB/LN) and other pathologies were used to develop a multivariate logistic regression model to determine the independent association of these variables with dementia. Correlates of co-morbid Alzheimer’s disease (PDD+AD) were also examined.
92 PD patients developed dementia and 48 remained cognitively normal. Severity of cortical LB/LN (CLB/LN) pathology was positively associated with dementia (p<0.001), with an odds-ratio (OR) of 4.06 (CI95%1.87–8.81), as was Apolipoprotein E4 (APOE4) genotype (p=0.018,OR4.19 CI95% 1.28–13.75). 28.6% of all PD cases had sufficient pathology for co-morbid AD, of which 89.5% were demented. The neuropathological diagnosis of PDD+AD correlated with an older age of PD onset (p=0.001,OR1.12 CI95%1.04–1.21), higher CLB/LN burden (p=0.037,OR 2.48 CI95%1.06–5.82), and cerebral amyloid angiopathy severity (p=0.032, OR4.16 CI95%1.13–15.30).
CLB/LN pathology is the most significant correlate of dementia in PD. Additionally, APOE4 genotype may independently influence the risk of dementia in PD. AD pathology was abundant in a subset of patients, and may modify the clinical phenotype. Thus, therapies that target α-synuclein, tau, or Aβ could potentially improve cognitive performance in PD.
Growing evidence of cell-to-cell transmission of neurodegenerative disease (ND)–associated proteins (NDAPs) (ie, tau, Aβ, and α-synuclein) suggests possible similarities in the infectious prion protein (PrPsc) in spongiform encephalopathies. There are limited data on the potential human-to-human transmission of NDAPs associated with Alzheimer disease (AD) and other non-PrPsc ND.
To examine evidence for human-to-human transmission of AD, Parkinson disease (PD), and related NDAPs in cadaveric human growth hormone (c-hGH) recipients.
We conducted a detailed immunohistochemical analysis of pathological NDAPs other than PrPsc in human pituitary glands. We also searched for ND in recipients of pituitary-derived c-hGH by reviewing the National Hormone and Pituitary Program (NHPP) cohort database and medical literature.
University-based academic center and agencies of the US Department of Health and Human Services.
Thirty-four routine autopsy subjects (10 non-ND controls and 24 patients with ND) and a US cohort of c-hGH recipients in the NHPP.
Main Outcome Measures
Detectable NDAPs in human pituitary sections and death certificate reports of non-PrPsc ND in the NHPP database.
We found mild amounts of pathological tau, Aβ, and α-synuclein deposits in the adeno/neurohypophysis of patients with ND and control patients. No cases of AD or PD were identified, and 3 deaths attributed to amyotrophic lateral sclerosis (ALS) were found among US NHPP c-hGH recipients, including 2 of the 796 decedents in the originally confirmed NHPP c-hGH cohort database.
Conclusions and Relevance
Despite the likely frequent exposure of c-hGH recipients to NDAPs, and their markedly elevated risk of PrPsc-related disease, this population of NHPP c-hGH recipients does not appear to be at increased risk of AD or PD. We discovered 3 ALS cases of unclear significance among US c-hGH recipients despite the absence of pathological deposits of ALS-associated proteins (TDP-43, FUS, and ubiquilin) in human pituitary glands. In this unique in vivo model of human-to-human transmission, we found no evidence to support concerns that NDAPs underlying AD and PD transmit disease in humans despite evidence of their cell-to-cell transmission in model systems of these disorders. Further monitoring is required to confirm these conclusions.
The microtubule-binding protein, tau, is the major component of neurofibrillary inclusions characteristic of Alzheimer's disease and related neurodegenerative tauopathies. When tau fibrillizes, it undergoes abnormal post-translational modifications resulting in decreased solubility and altered microtubule-stabilizing properties. Recently, we reported that the abnormal acetylation of tau at lysine residue 280 is a novel, pathological post-translational modification. Here, we performed detailed immunohistochemistry to further examine acetylated-tau expression in Alzheimer's disease and other major tauopathies. Immunohistochemistry using a polyclonal antibody specific for acetylated-tau at lysine 280 was conducted on 30 post-mortem central nervous system regions from patients with Alzheimer's disease (10 patients), corticobasal degeneration (5 patients), and progressive supranuclear palsy (5 patients). Acetylated-tau pathology was compared with the sequential emergence of other tau modifications in the Alzheimer's disease hippocampus using monoclonal antibodies to multiple well-characterized tau epitopes. All cases studied showed significant acetylated-tau pathology in a distribution pattern similar to hyperphosphorylated-tau. Acetylated-tau pathology was largely in intracellular, thioflavin-S-positive tau inclusions in Alzheimer's disease, and also thioflavin-S-negative pathology in corticobasal degeneration and progressive supranuclear palsy. Acetylated-tau was present throughout all stages of Alzheimer's disease pathology, but was more prominently associated with pathological tau epitopes in moderate to severe-stage cases. These temporal and morphological immunohistochemical features suggest acetylation of tau at this epitope is preceded by early modifications, including phosphorylation, and followed by later truncation events and cell death in Alzheimer's disease. Acetylation of tau at lysine 280 is a pathological modification that may contribute to tau-mediated neurodegeneration by both augmenting losses of normal tau properties (reduced solubility and microtubule assembly) as well as toxic gains of function (increased tau fibrillization). Thus, inhibiting tau acetylation could be a disease-modifying target for drug discovery target in tauopathies.
Alzheimer's disease; tauopathy; acetylation; post-translational modification; tau
Filamentous tau pathologies are hallmark lesions of several neurodegenerative tauopathies including Alzheimer’s disease (AD) and corticobasal degeneration (CBD) which show cell type-specific and topographically distinct tau inclusions. Growing evidence supports templated transmission of tauopathies through functionally interconnected neuroanatomical pathways suggesting that different self-propagating strains of pathological tau could account for the diverse manifestations of neurodegenerative tauopathies. Here, we describe the rapid and distinct cell type-specific spread of pathological tau following intracerebral injections of CBD or AD brain extracts enriched in pathological tau (designated CBD-Tau and AD-Tau, respectively) in young human mutant P301S tau transgenic (Tg) mice (line PS19) ~6–9 months before they show onset of mutant tau transgene-induced tau pathology. At 1 month post-injection of CBD-Tau, tau inclusions developed predominantly in oligodendrocytes of the fimbria and white matter near the injection sites with infrequent intraneuronal tau aggregates. In contrast, injections of AD-Tau in young PS19 mice induced tau pathology predominantly in neuronal perikarya with little or no oligodendrocyte involvement 1 month post-injection. With longer post-injection survival intervals of up to 6 months, CBD-Tau- and AD-Tau-induced tau pathology spread to different brain regions distant from the injection sites while maintaining the cell type-specific pattern noted above. Finally, CA3 neuron loss was detected 3 months post-injection of AD-Tau but not CBD-Tau. Thus, AD-Tau and CBD-Tau represent specific pathological tau strains that spread differentially and may underlie distinct clinical and pathological features of these two tauopathies. Hence, these strains could become targets to develop disease-modifying therapies for CBD and AD.
Alzheimer’s disease; Corticobasal degeneration; Seeded transmission of pathological tau; Frontotemporal degeneration
The progression of many neurodegenerative diseases is thought to be driven by the template-directed misfolding, seeded aggregation and cell–cell transmission of characteristic disease-related proteins, leading to the sequential dissemination of pathological protein aggregates. Recent evidence strongly suggests that the anatomical connections made by neurons — in addition to the intrinsic characteristics of neurons, such as morphology and gene expression profile — determine whether they are vulnerable to degeneration in these disorders. Notably, this common pathogenic principle opens up opportunities for pursuing novel targets for therapeutic interventions for these neurodegenerative disorders. We review recent evidence that supports the notion of neuron–neuron protein propagation, with a focus on neuropathological and positron emission tomography imaging studies in humans.
Alzheimer’s disease (AD) affects more than twenty-five million people worldwide and is the most common form of dementia. Symptomatic treatments have been developed, but effective intervention to alter disease progression is needed. Targets have been identified for disease-modifying drugs, but the results of clinical trials have been disappointing. Peripheral biomarkers of disease state may improve clinical trial design and analysis, increasing the likelihood of successful drug development. Amyloid-related measures, presumably reflecting principal pathology of AD, are among the leading cerebrospinal fluid and neuroimaging biomarkers, and measurement of plasma levels of amyloid peptides has been the focus of much investigation. In this review, we discuss recent data on plasma β-amyloid (Aβ) and examine the issues that have arisen in establishing it as a reliable biomarker of AD.
Alzheimer’s disease; Protein biomarker; Plasma amyloid
Previous studies demonstrated that members of the aminothienopyridazine (ATPZ) class of tau aggregation inhibitors exhibit a promising combination of in vitro activity as well as favorable pharmacokinetic properties (i.e., brain-penetration and oral bioavailability). Here we report the synthesis and evaluation of several new analogues. These studies indicate that the thienopyridazine core is essential for inhibition of tau fibrillization in vitro, while the choice of the appropriate scaffold decoration is critical to impart desirable ADME-PK properties. Among the active, brain-penetrant ATPZ inhibitors evaluated, 5-amino-N-cyclopropyl-3-(4-fluorophenyl)-4-oxo-3,4-dihydrothieno[3,4-d]pyridazine-1-carboxamide (43) was selected to undergo maximum tolerated dose and one-month tolerability testing in mice. The latter studies revealed that this compound is well-tolerated with no notable side-effects at an oral dose of 50 mg/kg/day.
Alzheimer’s disease; Tauopathy; Aminothienopyridazine; Tau aggregation inhibitor; K18PL
Neuronal insulin signaling abnormalities have been associated with Alzheimer's disease (AD). However, the specificity of this association and its underlying mechanisms have been unclear. This study investigated the expression of abnormal serine phosphorylation of insulin receptor substrate 1 (IRS1) in 157 human brain autopsy cases that included AD, tauopathies, α-synucleinopathies, TDP-43 proteinopathies, and normal aging. IRS1-pS616, IRS1-pS312 and downstream target Akt-pS473 measures were most elevated in AD but were also significantly increased in the tauopathies: Pick's disease, corticobasal degeneration and progressive supranuclear palsy. Double immunofluorescence labeling showed frequent co-expression of IRS1-pS616 with pathologic tau in neurons and dystrophic neurites. To further investigate an association between tau and abnormal serine phosphorylation of IRS1, we examined the presence of abnormal IRS1-pS616 expression in pathological tau-expressing transgenic mice and demonstrated that abnormal IRS1-pS616 frequently co-localizes in tangle-bearing neurons. Conversely, we observed increased levels of hyperphosphorylated tau in the high-fat diet-fed mouse, a model of insulin resistance. These results provide confirmation and specificity that abnormal phosphorylation of IRS1 is a pathological feature of AD and other tauopathies, and provide support for an association between insulin resistance and abnormal tau as well as amyloid-β.
Alzheimer's disease; Tau; Synuclein; TDP-43; Insulin resistance; Insulin receptor substrate 1
Neurofibrillary tangles composed of hyperphosphorylated fibrillized tau are found in numerous tauopathies including Alzheimer's disease. Increasing evidence suggests that tau pathology can be transmitted from cell-to-cell; however the mechanisms involved in the initiation of tau fibrillization and spreading of disease linked to progression of tau pathology are poorly understood. We show here that intracerebral injections of preformed synthetic tau fibrils into the hippocampus or frontal cortex of young tau transgenic mice expressing mutant human P301L tau induces tau hyperphosphorylation and aggregation around the site of injection, as well as a time-dependent propagation of tau pathology to interconnected brain areas distant from the injection site. Furthermore, we show that the tau pathology as a consequence of injection of tau preformed fibrils into the hippocampus induces selective loss of CA1 neurons. Together, our data confirm previous studies on the seeded induction and the spreading of tau pathology in a different tau transgenic mouse model and reveals neuronal loss associated with seeded tau pathology in tau transgenic mouse brain. These results further validate the utility of the tau seeding model in studying disease transmission, and provide a more complete in vivo tauopathy model with associated neurodegeneration which can be used to investigate the mechanisms involved in tau aggregation and spreading, as well as aid in the search for disease modifying treatments for Alzheimer's disease and related tauopathies.
Seeding; Spreading; Tau pathology; Cell death
Treatment of Alzheimer’s disease (AD) is significantly hampered by the lack of easily accessible biomarkers that can detect disease presence and predict disease risk reliably. Fluid biomarkers of AD currently provide indications of disease stage; however, they are not robust predictors of disease progression or treatment response, and most are measured in cerebrospinal fluid, which limits their applicability. With these aspects in mind, the aim of this article is to underscore the concerted efforts of the Blood-Based Biomarker Interest Group, an international working group of experts in the field. The points addressed include: (1) the major challenges in the development of blood-based biomarkers of AD, including patient heterogeneity, inclusion of the “right” control population, and the blood– brain barrier; (2) the need for a clear definition of the purpose of the individual markers (e.g., prognostic, diagnostic, or monitoring therapeutic efficacy); (3) a critical evaluation of the ongoing biomarker approaches; and (4) highlighting the need for standardization of preanalytical variables and analytical methodologies used by the field.
APOE ε4’s role as a modulator of the relationship between soluble plasma beta-amyloid (Aβ) and fibrillar brain Aβ measured by Pittsburgh Compound-B positron emission tomography ([11C]PiB PET) has not been assessed.
Ninety-six Alzheimer’s Disease Neuroimaging Initiative participants with [11C]PiB scans and plasma Aβ1-40 and Aβ1-42 measurements at time of scan were included. Regional and voxel-wise analyses of [11C]PiB data were used to determine the influence of APOE ε4 on association of plasma Aβ1-40, Aβ1-42, and Aβ1-40/Aβ1-42 with [11C]PiB uptake.
In APOE ε4− but not ε4+ participants, positive relationships between plasma Aβ1-40/Aβ1-42 and [11C]PiB uptake were observed. Modeling the interaction of APOE and plasma Aβ1-40/Aβ1-42 improved the explained variance in [11C]PiB binding compared to using APOE and plasma Aβ1-40/Aβ1-42 as separate terms.
The results suggest that plasma Aβ is a potential Alzheimer’s disease biomarker and highlight the importance of genetic variation in interpretation of plasma Aβ levels.
Alzheimer’s disease (AD); mild cognitive impairment (MCI); Alzheimer’s Disease Neuroimaging Initiative (ADNI); beta-amyloid (Aβ); plasma beta-amyloid; positron emission tomography (PET); Pittsburgh Compound-B ([11C]PiB); Apolipoprotein E (APOE)
An understanding of the anatomic distributions of major neurodegenerative disease lesions is important to appreciate the differential clinical profiles of these disorders and to serve as neuropathological standards for emerging molecular neuroimaging methods. To address these issues, here we present a comparative survey of the topographical distribution of the defining molecular neuropathological lesions among ten neurodegenerative diseases from a large and uniformly assessed brain collection. Ratings of pathological severity in sixteen brain regions from 671 cases with diverse neurodegenerative diseases were summarized and analyzed. These included: a) amyloid-β and tau lesions in Alzheimer’s disease, b) tau lesions in three other tauopathies including Pick’s disease, progressive supranuclear palsy and corticobasal degeneration, c) α-synuclein inclusion ratings in four synucleinopathies including Parkinson’s disease, Parkinson’s disease with dementia, dementia with Lewy bodies and multiple system atrophy, and d) TDP-43 lesions in two TDP-43 proteinopathies, including frontotemporal lobar degeneration associated with TDP-43 and amyotrophic lateral sclerosis. The data presented graphically and topographically confirm and extend previous pathological anatomic descriptions and statistical comparisons highlight the lesion distributions that either overlap or distinguish the diseases in each molecular disease category.
Alzheimer’s disease; Pick’s disease; corticobasal degeneration; progressive supranuclear palsy; Parkinson’s disease; Parkinson’s disease dementia; dementia with Lewy bodies; multiple system atrophy; frontotemporal lobar degeneration - TDP; amyotrophic lateral sclerosis; amyloid-β; Tau α-synuclein; TDP-43
Since over-activation of the hypothalamic-pituitary-adrenal (HPA) axis occurs in Alzheimer’s disease (AD), dysregulation of stress neuromediators may play a mechanistic role in the pathophysiology of AD. However, the effects of stress on tau phosphorylation are poorly understood and the relationship between corticosterone and corticotropin-releasing factor (CRF) on both Aβ and tau pathology remain unclear. Therefore, we first established a model of chronic stress which exacerbates Aβ accumulation in Tg2576 mice and then extended this stress paradigm to a tau transgenic mouse model with the P301S mutation (PS19) which displays tau hyperphosphorylation, insoluble tau inclusions and neurodegeneration. We show for the first time that both Tg2576 and PS19 mice demonstrate a heightened HPA stress profile in the unstressed state. In Tg2576 mice, one month of restraint/isolation (RI) stress increased Aβ levels, suppressed microglial activation, and worsened spatial and fear memory compared to non-stressed mice. In PS19 mice, RI stress promoted tau hyperphosphorylation, insoluble tau aggregation, neurodegeneration and fear-memory impairments. These effects were not mimicked by chronic corticosterone administration but were prevented by pre-stress administration of a CRF receptor type 1 (CRF1) antagonist. The role for a CRF1-dependent mechanism was further supported by the finding that mice over-expressing CRF had increased hyperphosphorylated tau compared to wildtype littermates. Together, these results implicate HPA dysregulation in AD neuropathogenesis and suggest that prolonged stress may increase Aβ and tau hyperphosphorylation. These studies also implicate CRF in AD pathophysiology and suggest that pharmacological manipulation of this neuropeptide may be a potential therapeutic strategy for AD.
stress; corticosterone; corticotropin-releasing factor; hypothalamic-pituitary-adrenal axis; Alzheimer’s disease; β-amyloid; tau
Most people with Parkinson's disease (PD) eventually develop cognitive impairment (CI). However, neither the timing of onset nor the severity of cognitive symptoms can be accurately predicted. We sought plasma-based biomarkers for CI in PD.
A discovery cohort of 70 PD patients was recruited. Cognitive status was evaluated with the Mattis Dementia Rating Scale-2 (DRS) at baseline and on annual follow-up visits, and baseline plasma levels of 102 proteins were determined with a bead-based immunoassay. Using linear regression, we identified biomarkers of CI in PD, i.e. proteins whose levels correlated with cognitive performance at baseline and/or cognitive decline at follow-up. We then replicated the association between cognitive performance and levels of the top biomarker, using a different technical platform, with a separate cohort of 113 PD patients.
Eleven proteins exhibited plasma levels correlating with baseline cognitive performance in the discovery cohort. The best candidate was epidermal growth factor (EGF, p<0.001); many of the other 10 analytes co-varied with EGF across samples. Low levels of EGF not only correlated with poor cognitive test scores at baseline, but also predicted an eightfold greater risk of cognitive decline to dementia-range DRS scores at follow-up for those with intact baseline cognition. A weaker, but still significant, relationship between plasma EGF levels and cognitive performance was found in an independent replication cohort of 113 PD patients.
Our data suggest that plasma EGF may be a biomarker for progression to CI in PD.
Epidermal growth factor; EGF; Parkinson's Disease; Parkinson's Disease with Dementia; Biomarker; Plasma
We examined agreement and disagreement between two biomarkers of Aβ deposition (amyloid PET and CSF Aβ1-42) in normal aging and dementia in a large multicenter study.
Concurrently acquired florbetapir-PET and CSF Aβ were measured in cognitively normal, mild cognitive impairment (MCI), and Alzheimer’s disease (AD) participants (N=374) from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). We also compared Aβ measurements in a separate group with serial CSF measurements over 3.1 +/− 0.8 yrs that preceded a single florbetapir session. Additional biomarker and cognitive data allowed us to further examine profiles of discordant cases.
Florbetapir and CSF Aβ were inversely correlated across all diagnostic groups, and dichotomous measurements were in agreement in 86% of subjects. Among subjects showing the most disagreement, the two discordant groups had different profiles: the florbetapir+/CSF Aβ− group was larger (N=13) and was made up of only normal and early MCI subjects; while the florbetapir−/CSF Aβ+ group was smaller (N=7), had poorer cognitive function and higher CSF tau, but no ApoE4 carriers. In the longitudinal sample, we observed both stable longitudinal CSF Aβ trajectories and those actively transitioning from normal to abnormal, but the final CSF Aβ measurements were in good agreement with florbetapir cortical retention.
CSF and amyloid-PET measurements of Aβ were consistent in the majority of subjects in the cross-sectional and longitudinal populations. Based on our analysis of discordant subjects, the available evidence did not show that CSF Aβ regularly becomes abnormal prior to fibrillar Aβ accumulation early in the course of disease.
Alexander disease (AxD) is a rare neurodegenerative disorder characterized pathologically by the presence of eosinophilic inclusions known as Rosenthal fibers (RFs) within astrocytes, and is caused by dominant mutations in the coding region of the gene encoding glial fibrillary acidic protein (GFAP). GFAP is the major astrocytic intermediate filament, and in AxD patient brain tissue GFAP is a major component of RFs. TAR DNA binding protein of 43 kDa (TDP-43) is the major pathological protein in almost all cases of the neurodegenerative disease amyotrophic lateral sclerosis (ALS) and ∼50% of frontotemporal lobar degeneration (FTLD), designated as FTLD-TDP. In ALS and FTLD-TDP, TDP-43 becomes insoluble, ubiquitinated, and pathologically phosphorylated and accumulates in cytoplasmic inclusions in both neurons and glia of affected brain and spinal cord regions. Previously, TDP-43 was detected in RFs of human pilocytic astrocytomas; however, involvement of TDP-43 in AxD has not been determined. Here we show that TDP-43 is present in RFs in AxD patient brains, and that insoluble phosphorylated full-length and high molecular weight TDP-43 accumulates in white matter of such brains. Phosphorylated TDP-43 also accumulates in the detergent-insoluble fraction from affected brain regions of GfapR236H/+ knock-in mice, which harbor a GFAP mutation homologous to one that causes AxD in humans, and TDP-43 colocalizes with astrocytic RF pathology in GfapR236H/+ mice and transgenic mice overexpressing human wild-type GFAP. These findings suggest common pathogenic mechanisms in ALS, FTLD, and AxD, and this is the first report of TDP-43 involvement in a neurological disorder primarily affecting astrocytes.
Alexander disease; astrocyte; GFAP; mouse models; neurodegeneration; TDP-43
Apolipoprotein E (APOE) ε2 carriers may be protected from dementia because of reduced levels of cortical β-amyloid. In the oldest-old, however, APOE ε2 carriers have high β-amyloid plaque scores and preserved cognition. We compared different measures of β-amyloid pathology across APOE genotypes in the oldest-old, and their relationship with dementia.
The study included 96 participants from The 90+ Study. Using all information, dementia diagnoses were made. Neuropathological examination included staging for amyloid plaques and β-amyloid cortical percent area stained by NAB228 antibody.
Both APOE ε2 and APOE ε4 carriers had high Consortium to Establish a Registry for Alzheimer's Disease plaque scores. However, APOE ε2 carriers had low cortical β-amyloid percent areas. β-amyloid percent area was associated with dementia across APOE genotypes.
Lower levels of percent area in APOE ε2 carriers may reflect lower total β-amyloid and may contribute to APOE ε2 carriers' decreased risk of dementia, despite high β-amyloid plaque scores. The relationship between β-amyloid plaques and dementia in the oldest-old may vary by APOE genotype.
Alzheimer; Apolipoprotein E; Beta-amyloid; Dementia; Oldest-old
Alzheimer's disease (AD) and Lewy body diseases (LBD), e.g. Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB), are common causes of geriatric cognitive impairments. In addition, AD and LBD are often found in the same patients at autopsy; therefore, biomarkers that can detect the presence of both pathologies in living subjects are needed. In this investigation, we report the assessment of α-synuclein (α-syn) in cerebrospinal fluid (CSF) and its association with CSF total tau (t-tau), phosphorylated tau181 (p-tau181), and amyloid beta1-42 (Aβ1-42) in subjects of the Alzheimer's Disease Neuroimaging Initiative (ADNI; n=389), with longitudinal clinical assessments. A strong correlation was noted between α-syn and t-tau in controls, as well as in patients with AD and mild cognitive impairment (MCI). However, the correlation is not specific to subjects in the ADNI cohort, as it was also seen in PD patients and controls enrolled in the Parkinson's Progression Markers Initiative (PPMI; n=102). A bimodal distribution of CSF α-syn levels was observed in the ADNI cohort, with high levels of α-syn in the subjects with abnormally increased t-tau values. Although a correlation was also noted between α-syn and p-tau181, there was a mismatch (α-syn-p-tau181-Mis), i.e. higher p-tau181 levels accompanied by lower α-syn levels in a subset of ADNI patients. We hypothesize that this α-syn-p-tau181-Mis is a CSF signature of concomitant LBD pathology in AD patients. Hence, we suggest that inclusion of measures of CSF α-syn and calculation of α-syn-p-tau181-Mis improves the diagnostic sensitivity/specificity of classic CSF AD biomarkers and better predicts longitudinal cognitive changes.
Alzheimer's disease; Parkinson's disease; dementia with Lewy body; Cerebrospinal fluid; Amyloid β; tau; α-synuclein
The dynamics of cerebrospinal fluid (CSF) tau and Aβ biomarkers over time in Alzheimer’s disease (AD) patients from prodromal pre-symptomatic to severe stages of dementia have not been clearly defined and recent studies, most of which are cross-sectional, present conflicting findings. To clarify this issue, we analyzed the longitudinal CSF tau and Aβ biomarker data from 142 of the AD Neuroimaging Initiative (ADNI) study subjects [18 AD, 74 mild cognitive impairment (MCI), and 50 cognitively normal subjects (CN)]. Yearly follow-up CSF collections and studies were conducted for up to 48 months (median = 36 months) for CSF Aβ1–42, phosphorylated tau (p-tau181), and total tau (t-tau). An unsupervised analysis of longitudinal measurements revealed that for Aβ1–42 and p-tau181 biomarkers there was a group of subjects with stable longitudinal CSF biomarkers measures and a group of subjects who showed a decrease (Aβ1–42, mean = −9.2 pg/ml/year) or increase (p-tau181, mean = 5.1 pg/ml/year) of these biomarker values. Low baseline Aβ1–42 values were associated with longitudinal increases in p-tau181. Conversely, high baseline p-tau181 values were not associated with changes in Aβ1–42 levels. When the subjects with normal baseline biomarkers and stable concentrations during follow-up were excluded, the expected time to reach abnormal CSF levels and the mean AD values was significantly shortened. Thus, our data demonstrate for the first time that there are distinct populations of ADNI subjects with abnormal longitudinal changes in CSF p-tau181 and Aβ1–42 levels, and our longitudinal results favor the hypothesis that Aβ1–42 changes precede p-tau181 changes.
Alzheimer’s disease; Amyloid beta; Tau; Cerebrospinal fluid; Longitudinal; Dementia; Mild cognitive impairment