The Interplay of Tau Protein and β-Amyloid: While Tauopathy Spreads More Profoundly Than Amyloidopathy, Both Processes Are Almost Equally Pathogenic

Strategies for measuring concentrations and forms of amyloid-β peptides

Alzheimer's disease (AD) is affecting more and more people worldwide without the effective treatment, while the existed pathological mechanism has been confirmed barely useful in the treatment. Amyloid-β peptide (Aβ), a main component of senile plaque, is regarded as the most promising target in AD treatment. Aβ clearance from AD brain seems to be a reliably therapeutic strategy, as the two exited drugs, GV-971 and aducanumab, are both developed based on it. However, doubt still exists. To exhaustive expound on the pathological mechanism of Aβ, rigorous analyses on the concentrations and aggregation forms are essential. Thus, it is attracting broad attention these years. However, most of the sensors have not been used in pathological studies, as the lack of the bridge between analytical chemist and pathologists. In this review, we made a brief introduce on Aβ-related pathological mechanism included in β-amyloid hypothesis to elucidate the detection conditions of sensor methods. Furthermore, a summary of the sensor methods was made, which were based on Aβ concentrations and form detections that have been developed in the past 10 years. As the greatest number of the sensors were built on fluorescent spectroscopy, electrochemistry, and Roman spectroscopy, detailed elucidation on them was made. Notably, the aggregation process is another important factor in revealing the progress of AD and developing the treatment methods, so the sensors on monitoring Aβ aggregation processes were also summarized.

The psychiatric symptoms in anti-IgLON5 disease: Case report and literature review

Immunotherapy may be ineffective in the advanced stages of anti-IgLON5 disease with psychiatric symptoms. The psychiatric symptoms in advanced stages of anti-IgLON5 disease may be associated with neurodegeneration.

Computationally Designed Small Molecules Disassemble Both Soluble Oligomers and Protofibrils of Amyloid β-Protein Responsible for Alzheimer's Disease

Alzheimer's disease (AD) is one of the world's most pressing health crises. AD is an incurable disease affecting more than 6.5 million Americans, predominantly the elderly, and in its later stages, leads to memory loss, dementia, and death. Amyloid β (Aβ) protein aggregates have been one of the pathological hallmarks of AD since its initial characterization. The early stages of Aβ accumulation and aggregation involve the formation of oligomers, which are considered neurotoxic and play a key role in further aggregation into fibrils that eventually appear in the brain as amyloid plaques. We have recently shown by combining ion mobility mass spectrometry (IM-MS) and atomic force microscopy (AFM) that Aβ42 rapidly forms dodecamers (12-mers) as the terminal oligomeric state, and these dodecamers seed the early formation of Aβ42 protofibrils. The link between soluble oligomers and fibril formation is one of the essential aspects for understanding the root cause of the disease state and is critical to developing therapeutic interventions. Utilizing a joint pharmacophore space (JPS) method, potential drugs have been designed specifically for amyloid-related diseases. These small molecules were generated based on crucial chemical features necessary for target selectivity. In this paper, we utilize our combined IM-MS and AFM methods to investigate the impact of three second-generation JPS small-molecule inhibitors, AC0201, AC0202, and AC0203, on dodecamer as well as fibril formation in Aβ42. Our results indicate that AC0201 works well as an inhibitor and remodeler of both dodecamers and fibril formation, AC0203 behaves less efficiently, and AC0202 is ineffective.

Intra-hippocampal cis-P tau microinjection induces long-term changes in behavior and synaptic plasticity in mice

BACKGROUND

Alzheimer's disease is accompanied by an abnormal high accumulation of cis-P tau. However, the long-term changes in behavior following tau accumulation remains under debate. The present study investigated the long-term effects of tauopathy on learning and memory, synaptic plasticity, and hippocampal cell numbers.

RESULTS

Cis-P tau was microinjected into the dorsal hippocampus to generate Alzheimer's like-disease model in C57BL/6 mice. Cis-P tau injected animals showed a significant impairment in learning and memory in Y-maze and Barnes maze tests. In another group of animals, the generation of long-term potentiation (LTP) was evaluated in hippocampal slices 7 months after cis-P tau injection. LTP induction was disrupted only in the dorsal but not ventral hippocampal slices. The basal synaptic transmission was also reduced in dorsal hippocampal slices. In addition, hippocampal sampling was done, and the number of cells was assessed by Nissl staining. Obtained results indicated that the number of survived cells was significantly reduced in the dorsal and ventral hippocampus of cis P-tau injected animals compared to the animals in control group. However, the decrement of cell number was higher in the dorsal compared to the ventral hippocampus.

CONCLUSIONS

In conclusion, intra-hippocampal cis-P tau injection produced learning and memory impairment at 7 months after its injection. This impairment might result from LTP disruption and a significant decrease in the number of neurons in the dorsal hippocampus.

Tau Aggregation Inhibiting Peptides as Potential Therapeutics for Alzheimer Disease

Alzheimer disease (AD) is the most common progressive neurodegenerative disorder. AD causes enormous personal and economic burden to society as currently only limited palliative therapeutic options are available. The pathological hallmarks of the disease are extracellular plaques, composed of fibrillar amyloid-β (Aβ), and neurofibrillary tangles inside neurons, composed of Tau protein. Until recently, the search for AD therapeutics was focussed more on the Aβ peptide and its pathology, but the results were unsatisfying. As an alternative, Tau might be a promising therapeutic target as its pathology is closely correlated to clinical symptoms. In addition, pathological Tau aggregation occurs in a large group of diseases, called Tauopathies, and in most of them Aβ aggregation does not play a role in disease pathogenesis. The formation of Tau aggregates is triggered by two hexapeptide motifs within Tau; PHF6* and PHF6. Both fragments are interesting targets for the development of Tau aggregation inhibitors (TAI). Peptides represent a unique class of pharmaceutical compounds and are reasonable alternatives to chemical substances or antibodies. They are attributed with high biological activity, valuable specificity and low toxicity, and often are developed as drug candidates to interrupt protein-protein interactions. The preparation of peptides is simple, controllable and the peptides can be easily modified. However, their application may also have disadvantages. Currently, a few peptide compounds acting as TAI are described in the literature, most of them developed by structure-based design or phage display. Here, we review the current state of research in this promising field of AD therapy development.

Earlier Detection of Alzheimer's Disease Based on a Novel Biomarker cis P-tau by a Label-Free Electrochemical Immunosensor

Early detection of cis phosphorylated tau (cis P-tau) may help as an effective treatment to control the progression of Alzheimer's disease (AD). Recently, we introduced for the first time a monoclonal antibody (mAb) with high affinity against cis P-tau. In this study, the cis P-tau mAb was utilized to develop a label-free immunosensor. The antibody was immobilized onto a gold electrode and the electrochemical responses to the analyte were acquired by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The immunosensor was capable of selective detection of cis P-tau among non-specific targets like trans P-tau and major plasma proteins. A wide concentration range (10 × 10^-14 M-3.0 × 10^-9 M) of cis P-tau was measured in PBS and human serum matrices with a limit of detection of 0.02 and 0.05 pM, respectively. Clinical applicability of the immunosensor was suggested by its long-term storage stability and successful detection of cis P-tau in real samples of cerebrospinal fluid (CSF) and blood serum collected from human patients at different stages of AD. These results suggest that this simple immunosensor may find great application in clinical settings for early detection of AD which is an unmet urgent need in today's healthcare services.

Plasma p-tau181 associated with structural changes in mild cognitive impairment

Alzheimer's disease (AD) is a progressive neurodegenerative disease associated with dementia and is a serious concern for the health of individuals and government health care systems worldwide. Gray matter atrophy and white matter damage are major contributors to cognitive deficits in AD patients, as demonstrated by magnetic resonance imaging (MRI). Many of these brain changes associated with AD begin to occur about 15 years before the onset of initial clinical symptoms. Therefore, it is critical to find biomarkers reflective of these brain changes associated with AD to identify this disease and monitor its prognosis and development. The increased plasma level of hyperphosphorylated tau 181 (p-tau181) has been recently considered a novel biomarker for the diagnosis of AD, preclinical AD, and mild cognitive impairment (MCI). In the current study, we examined the association of cerebrospinal fluid (CSF) and plasma levels of p-tau181 with structural brain changes in cortical thickness, cortical volume, surface area, and subcortical volume in MCI patients. In this cross-sectional study, we included the information of 461 MCI patients from the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. The results of voxel-wise partial correlation analyses showed a significant negative correlation between the increased levels of plasma p-tau181, CSF total tau, and CSF p-tau181 with structural changes in widespread brain regions. These results provide evidence for the use of plasma p-tau181 as a diagnostic marker for structural changes in the brain associated with the early stages of AD and neurodegeneration.

Quantitative susceptibility mapping as an imaging biomarker for Alzheimer’s disease: The expectations and limitations

Alzheimer’s disease (AD) is the most common type of dementia and a distressing diagnosis for individuals and caregivers. Researchers and clinical trials have mainly focused on β-amyloid plaques, which are hypothesized to be one of the most important factors for neurodegeneration in AD. Meanwhile, recent clinicopathological and radiological studies have shown closer associations of tau pathology rather than β-amyloid pathology with the onset and progression of Alzheimer’s symptoms. Toward a biological definition of biomarker-based research framework for AD, the 2018 National Institute on Aging–Alzheimer’s Association working group has updated the ATN classification system for stratifying disease status in accordance with relevant pathological biomarker profiles, such as cerebral β-amyloid deposition, hyperphosphorylated tau, and neurodegeneration. In addition, altered iron metabolism has been considered to interact with abnormal proteins related to AD pathology thorough generating oxidative stress, as some prior histochemical and histopathological studies supported this iron-mediated pathomechanism. Quantitative susceptibility mapping (QSM) has recently become more popular as a non-invasive magnetic resonance technique to quantify local tissue susceptibility with high spatial resolution, which is sensitive to the presence of iron. The association of cerebral susceptibility values with other pathological biomarkers for AD has been investigated using various QSM techniques; however, direct evidence of these associations remains elusive. In this review, we first briefly describe the principles of QSM. Second, we focus on a large variety of QSM applications, ranging from common applications, such as cerebral iron deposition, to more recent applications, such as the assessment of impaired myelination, quantification of venous oxygen saturation, and measurement of blood– brain barrier function in clinical settings for AD. Third, we mention the relationships among QSM, established biomarkers, and cognitive performance in AD. Finally, we discuss the role of QSM as an imaging biomarker as well as the expectations and limitations of clinically useful diagnostic and therapeutic implications for AD.

Plasma neurofilament light levels correlate with white matter damage prior to Alzheimer's disease: results from ADNI

BACKGROUND

The blood biomarker neurofilament light (NFL) is one of the most widely used for monitoring Alzheimer's disease (AD). According to recent research, a higher NFL plasma level has a substantial predictive value for cognitive deterioration in AD patients. Diffusion tensor imaging (DTI) is an MRI-based approach for detecting neurodegeneration, white matter (WM) disruption, and synaptic damage. There have been few studies on the relationship between plasma NFL and WM microstructure integrity.

AIMS

The goal of the current study is to assess the associations between plasma levels of NFL, CSF total tau, phosphorylated tau181 (P-tau181), and amyloid-β (Aβ) with WM microstructural alterations.

METHODS

We herein have investigated the cross-sectional association between plasma levels of NFL and WM microstructural alterations as evaluated by DTI in 92 patients with mild cognitive impairment (MCI) provided by Alzheimer's Disease Neuroimaging Initiative (ADNI) participants. We analyzed the potential association between plasma NFL levels and radial diffusivity (RD), axial diffusivity (AxD), mean diffusivity (MD), and fractional anisotropy (FA) in each region of the Montreal Neurological Institute and Hospital (MNI) atlas, using simple linear regression models stratified by age, sex, and APOE ε4 genotype.

RESULTS

Our findings demonstrated a significant association between plasma NFL levels and disrupted WM microstructure across the brain. In distinct areas, plasma NFL has a negative association with FA in the fornix, fronto-occipital fasciculus, corpus callosum, uncinate fasciculus, internal capsule, and corona radiata and a positive association with RD, AxD, and MD values in sagittal stratum, corpus callosum, fronto-occipital fasciculus, corona radiata, internal capsule, thalamic radiation, hippocampal cingulum, fornix, and cingulum. Lower FA and higher RD, AxD, and MD values are related to demyelination and degeneration in WM.

CONCLUSION

Our findings revealed that the level of NFL in the blood is linked to WM alterations in MCI patients. Plasma NFL has the potential to be a biomarker for microstructural alterations. However, further longitudinal studies are necessary to validate the predictive role of plasma NFL in cognitive decline.

Tau nuclear translocation is a leading step in tau pathology process through P53 stabilization and nucleolar dispersion

Tau protein abnormalities are associated with various neurodegenerative disorders, including Alzheimer's disease (AD) and traumatic brain injury (TBI). In tau-overexpressing SHSY5Y cells and iPSC-derived neuron models of frontotemporal dementia (FTD), axonal tau translocates into the nuclear compartment, resulting in neuronal dysfunction. Despite extensive research, the mechanisms by which tau translocation results in neurodegeneration remain elusive thus far. We studied the nuclear displacement of different P-tau species [Cis phosphorylated Thr231-tau (cis P-tau), phosphorylated Ser202/Thr205-tau (AT8 P-tau), and phosphorylated Thr212/Ser214-tau (AT100 P-tau)] at various time points using starvation in primary cortical neurons and single severe TBI (ssTBI) in male mouse cerebral cortices as tauopathy models. While all P-tau species translocated into the somatodendritic compartment in response to stress, cis P-tau did so more rapidly than the other species. Notably, nuclear localization of P-tau was associated with p53 apoptotic stabilization and nucleolar stress, both of which resulted in neurodegeneration. In summary, our findings indicate that P-tau nuclear translocation results in p53-dependent apoptosis and nucleolar dispersion, which is consistent with neurodegeneration.