The role of tau in neurodegeneration

Decreased anterograde transport coupled with sustained retrograde transport contributes to reduced axonal mitochondrial density in tauopathy neurons

Mitochondria are essential organelle required for neuronal homeostasis. Mitochondria supply ATP and buffer calcium at synaptic terminals. However, the complex structural geometry of neurons poses a unique challenge in transporting mitochondria to synaptic terminals. Kinesin motors supply mitochondria to the axonal compartments, while cytoplasmic dynein is required for retrograde transport. Despite the importance of presynaptic mitochondria, how and whether axonal mitochondrial transport and distribution are altered in tauopathy neurons remain poorly studied. In the current study, we have shown that anterograde transport of mitochondria is reduced in P301L neurons, while there is no change in the retrograde transport. Consistently, axonal mitochondrial abundance is reduced in P301L neurons. We further studied the possible role of two opposing motor proteins on mitochondrial transport and found that mitochondrial association of kinesin is decreased significantly in P301L cells. Interestingly, fitting our experimental data into mathematical equations suggested a possible rise in dynein activity to maintain retrograde flux in P301L cells. Our data indicate that decreased kinesin-mediated transport coupled with sustained retrograde transport might reduce axonal mitochondria in tauopathy neurons, thus contributing to the synaptic deficits in Alzheimer’s disease (AD) and other tauopathies.

APOE in the bullseye of neurodegenerative diseases: impact of the APOE genotype in Alzheimer’s disease pathology and brain diseases

ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell–cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.

Substituent Orchestration in Dimethylquinoxaline Derivatives: A Tool for Fishing Out Appropriate CDK5 Inhibitors as Potential Therapeutics for Alzheimer's

A set of new heterocyclic analogs (Compounds I-IX), comprising of 6,7 dimethyl Quinoxalines were found to be active against the receptor GSK3β (Compounds IV-V) (Chem. Biodiversity 2021, 18, e2100364). In an effort to modulate effective CDK5 inhibitors herein our hypothesis underpinned to fish out an appropriate derivative from the same quinoxaline series, as these two targets GSK3β and CDK5 shared structural resemblance with each other. Aligned to the goal we have synthesized Compounds I-IX, characterized them using a combination of spectroscopic techniques and evaluated their activities against CDK5. Our analysis reflected that the adjacently located alkoxy/hydroxy functionality derivatives namely Compounds III and VI, to be the most potent (micromolar) amongst others in the series, backed by Density Functional Theory (DFT) calculations and molecular modelling studies. Also, the efficacy of the Compounds I-IX, were monitored in few other members of the CMGC family namely DYRK1A, CLK1and CK1δ that have been known to be directly involved in hyperphosphorylation of Tau. But unfortunately in none of the targets, our quinoxaline series were active. In a nut shell further optimisation of these intelligent nucleus, would not only lead to the discovery of novel pharmacophores, but also marked selectivity against a pool of kinases, thereby implementing a distinct roadmap towards the design of potential therapeutics against Alzheimer's.

Identification and characterization of a MAPT-targeting locked nucleic acid antisense oligonucleotide therapeutic for tauopathies

Tau is a microtubule-associated protein (MAPT, tau) implicated in the pathogenesis of tauopathies, a spectrum of neurodegenerative disorders characterized by accumulation of hyperphosphorylated, aggregated tau. Because tau pathology can be distinct across diseases, a pragmatic therapeutic approach may be to intervene at the level of the tau transcript, as it makes no assumptions to mechanisms of tau toxicity. Here we performed a large library screen of locked-nucleic-acid (LNA)-modified antisense oligonucleotides (ASOs), where careful tiling of the MAPT locus resulted in the identification of hot spots for activity in the 3′ UTR. Further modifications to the LNA design resulted in the generation of ASO-001933, which selectively and potently reduces tau in primary cultures from hTau mice, monkey, and human neurons. ASO-001933 was well tolerated and produced a robust, long-lasting reduction in tau protein in both mouse and cynomolgus monkey brain. In monkey, tau protein reduction was maintained in brain for 20 weeks post injection and corresponded with tau protein reduction in the cerebrospinal fluid (CSF). Our results demonstrate that LNA-ASOs exhibit excellent drug-like properties and sustained efficacy likely translating to infrequent, intrathecal dosing in patients. These data further support the development of LNA-ASOs against tau for the treatment of tauopathies.

PTK2 regulates tau-induced neurotoxicity via phosphorylation of p62 at Ser403

Tau is a microtubule-associated protein that forms insoluble filaments that accumulate as neurofibrillary tangles in neurodegenerative diseases such as Alzheimer's disease and other related tauopathies. A relationship between abnormal Tau accumulation and ubiquitin-proteasome system impairment has been reported. However, the molecular mechanism linking Tau accumulation and ubiquitin proteasome system (UPS) dysfunction remains unclear. Here, we show that overexpression of wild-type or mutant (P301L) Tau increases the abundance of polyubiquitinated proteins and activates the autophagy-lysosome pathway in mammalian neuronal cells. Previous studies found that PTK2 inhibition mitigates toxicity induced by UPS impairment. Thus, we investigated whether PTK2 inhibition can attenuate Tau-induced UPS impairment and cell toxicity. We found that PTK2 inhibition significantly reduces Tau-induced death in mammalian neuronal cells. Moreover, overexpression of WT or mutant Tau increased the phosphorylation levels of PTK2 and p62. We also confirmed that PTK2 inhibition suppresses Tau-induced phosphorylation of PTK2 and p62. Furthermore, PTK2 inhibition significantly attenuated the climbing defect and shortened the lifespan in the Drosophila model of tauopathy. In addition, we observed that phosphorylation of p62 is markedly increased in Alzheimer's disease patients with tauopathies. Taken together, our results indicate that the UPS dysfunction induced by Tau accumulation might contribute directly to neurodegeneration in tauopathies and that PTK2 could be a promising therapeutic target for tauopathies.

ER stress and UPR in Alzheimer's disease: mechanisms, pathogenesis, treatments

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by gradual loss of memory and cognitive function, which constitutes a heavy burden on the healthcare system globally. Current therapeutics to interfere with the underlying disease process in AD is still under development. Although many efforts have centered on the toxic forms of Aβ to effectively tackle AD, considering the unsatisfactory results so far it is vital to examine other targets and therapeutic approaches as well. The endoplasmic reticulum (ER) stress refers to the build-up of unfolded or misfolded proteins within the ER, thus, perturbing the ER and cellular homeostasis. Emerging evidence indicates that ER stress contributes to the onset and development of AD. A thorough elucidation of ER stress machinery in AD pathology may help to open up new therapeutic avenues in the management of this devastating condition to relieve the cognitive dementia symptoms. Herein, we aim at deciphering the unique role of ER stress in AD pathogenesis, reviewing key findings, and existing controversy in an attempt to summarize plausible therapeutic interventions in the management of AD pathophysiology.

Recent advances in pre-clinical diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia with currently no known cures or disease modifying treatments (DMTs), despite much time and effort from the field. Diagnosis and intervention of AD during the early pre-symptomatic phase of the disease is thought to be a more effective strategy. Therefore, the detection of biomarkers has emerged as a critical tool for monitoring the effect of new AD therapies, as well as identifying patients most likely to respond to treatment. The establishment of the amyloid/tau/neurodegeneration (A/T/N) framework in 2018 has codified the contexts of use of AD biomarkers in neuroimaging and bodily fluids for research and diagnostic purposes. Furthermore, a renewed drive for novel AD biomarkers and innovative methods of detection has emerged with the goals of adding additional insight to disease progression and discovery of new therapeutic targets. The use of biomarkers has accelerated the development of AD drugs and will bring new therapies to patients in need. This review highlights recent methods utilized to diagnose antemortem AD.

Oxidative Stress in Tauopathies: From Cause to Therapy

Oxidative stress (OS) is the result of an imbalance between the production of reactive oxygen species (ROS) and the antioxidant capacity of cells. Due to its high oxygen demand, the human brain is highly susceptible to OS and, thus, it is not a surprise that OS has emerged as an essential component of the pathophysiology of several neurodegenerative diseases, including tauopathies. Tauopathies are a heterogeneous group of age-related neurodegenerative disorders characterized by the deposition of abnormal tau protein in the affected neurons. With the worldwide population aging, the prevalence of tauopathies is increasing, but effective therapies have not yet been developed. Since OS seems to play a key role in tauopathies, it has been proposed that the use of antioxidants might be beneficial for tau-related neurodegenerative diseases. Although antioxidant therapies looked promising in preclinical studies performed in cellular and animal models, the antioxidant clinical trials performed in tauopathy patients have been disappointing. To develop effective antioxidant therapies, the molecular mechanisms underlying OS in tauopathies should be completely understood. Here, we review the link between OS and tauopathies, emphasizing the causes of OS in these diseases and the role of OS in tau pathogenesis. We also summarize the antioxidant therapies proposed as a potential treatment for tauopathies and discuss why they have not been completely translated to clinical trials. This review aims to provide an integrated perspective of the role of OS and antioxidant therapies in tauopathies. In doing so, we hope to enable a more comprehensive understanding of OS in tauopathies that will positively impact future studies.

NMDA and AMPA Receptors at Synapses: Novel Targets for Tau and α-Synuclein Proteinopathies

A prominent feature of neurodegenerative diseases is synaptic dysfunction and spine loss as early signs of neurodegeneration. In this context, accumulation of misfolded proteins has been identified as one of the most common causes driving synaptic toxicity at excitatory glutamatergic synapses. In particular, a great effort has been placed on dissecting the interplay between the toxic deposition of misfolded proteins and synaptic defects, looking for a possible causal relationship between them. Several studies have demonstrated that misfolded proteins could directly exert negative effects on synaptic compartments, altering either the function or the composition of pre- and post-synaptic receptors. In this review, we focused on the physiopathological role of tau and α-synuclein at the level of postsynaptic glutamate receptors. Tau is a microtubule-associated protein mainly expressed by central nervous system neurons where it exerts several physiological functions. In some cases, it undergoes aberrant post-translational modifications, including hyperphosphorylation, leading to loss of function and toxic aggregate formation. Similarly, aggregated species of the presynaptic protein α-synuclein play a key role in synucleinopathies, a group of neurological conditions that includes Parkinson’s disease. Here, we discussed how tau and α-synuclein target the postsynaptic compartment of excitatory synapses and, specifically, AMPA- and NMDA-type glutamate receptors. Notably, recent studies have reported their direct functional interactions with these receptors, which in turn could contribute to the impaired glutamatergic transmission observed in many neurodegenerative diseases.

Spinal Cord Injury Causes Prominent Tau Pathology Associated with Brain Post-Injury Sequela

Spinal cord injury (SCI) can result in significant neurological impairment and functional and cognitive deficits. It is well established that SCI results in focal neurodegeneration that gradually spreads to other cord areas. On the other hand, traumatic brain injury (TBI) is strongly associated with tau protein pathology and neurodegeneration that can spread in areas throughout the brain. Tau is a microtubule-associated protein abundant in neurons and whose abnormalities result in neuronal cell death. While SCI and TBI have been extensively studied, there is limited research on the relationship between SCI and brain tau pathology. As a result, in this study, we examined tau pathology in spinal cord and brain samples obtained from severe SCI mouse models at various time points. The effects of severe SCI on locomotor function, spatial memory, anxiety/risk-taking behavior were investigated. Immunostaining and immunoblotting confirmed a progressive increase in tau pathology in the spinal cord and brain areas. Moreover, we used electron microscopy to examine brain samples and observed disrupted mitochondria and microtubule structure following SCI. SCI resulted in motor dysfunction, memory impairment, and abnormal risk-taking behavior. Notably, eliminating pathogenic cis P-tau via systemic administration of appropriate monoclonal antibodies restored SCI's pathological and functional consequences. Thus, our findings suggest that SCI causes severe tauopathy that spreads to brain areas, indicating brain dysfunction. Additionally, tau immunotherapy with an anti-cis P-tau antibody could suppress pathogenic outcomes in SCI mouse models, with significant clinical implications for SCI patients. SCI induces profound pathogenic cis p-tau, which diffuses into the brain through CSF, resulting in brain neurodegeneration and cognitive decline.

Alzheimer’s Disease and Tau Self-Assembly: In the Search of the Missing Link

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease characterized by progressive cognitive impairment, apathy, and neuropsychiatric disorders. Two main pathological hallmarks have been described: neurofibrillary tangles, consisting of tau oligomers (hyperphosphorylated tau) and Aβ plaques. The influence of protein kinases and phosphatases on the hyperphosphorylation of tau is already known. Hyperphosphorylated tau undergoes conformational changes that promote its self-assembly. However, the process involving these mechanisms is yet to be elucidated. In vitro recombinant tau can be aggregated by the action of polyanions, such as heparin, arachidonic acid, and more recently, the action of polyphosphates. However, how that process occurs in vivo is yet to be understood. In this review, searching the most accurate and updated literature on the matter, we focus on the precise molecular events linking tau modifications, its misfolding and the initiation of its pathological self-assembly. Among these, we can identify challenges regarding tau phosphorylation, the link between tau heteroarylations and the onset of its self-assembly, as well as the possible metabolic pathways involving natural polyphosphates, that may play a role in tau self-assembly.

The NLRP3 inflammasome modulates tau pathology and neurodegeneration in a tauopathy model

An active role of neuroinflammation and the NLRP3 inflammasome in Alzheimer's disease and related tauopathies is increasingly identified, supporting NLRP3 as an interesting therapeutic target. However, its effect on tau‐associated neurodegeneration, a key‐process in tauopathies, remains unknown. While tau pathology and neurodegeneration are closely correlated, different tau forms may act as culprits in both characteristics and NLRP3‐dependent microglial processes may differently affect both processes, indicating the need to study the role of NLRP3 in both processes concomitantly. To study the role of NLRP3 on tau pathology, prion‐like propagation and tau‐associated neurodegeneration we generated crosses of NLRP3 deficient mice with tauP301S (PS19) transgenic mice. In this model we studied non‐seeded tau pathology and hippocampal atrophy, reminiscent characteristics of tauopathies. Tau pathology in hippocampus and cortex was significantly decreased in tau.NLRP3−/− versus tau.NLRP3+/+ mice. Importantly, tau.NLRP3−/− mice also displayed significantly decreased hippocampal atrophy, indicating a role of NLRP3 in neurodegeneration. We furthermore assessed the effect of NLRP3 deficiency on tau propagation and associated hippocampal atrophy. NLRP3 deficiency significantly decreased prion‐like seeding and propagation of tau pathology, reflected in decreased tau pathology in ipsi‐ and contralateral hippocampus and cortex in tau.NLRP3−/− following tau seeding. Most importantly, hippocampal atrophy was significantly less in tau‐seeded tau.NLRP3−/− mice at 8 months. We here demonstrate for the first time that NLRP3 activation affects tau‐associated neurodegeneration and seeded and non‐seeded tau pathology, hence affecting key molecular processes in tauopathies. Our data thereby provide key‐information in the validation of NLRP3 inflammasome as therapeutic target for AD and related tauopathies.

A Review of the Common Neurodegenerative Disorders: Current Therapeutic Approaches and the Potential Role of Nanotherapeutics

Neurodegenerative disorders are primarily characterized by neuron loss. The most common neurodegenerative disorders include Alzheimer’s and Parkinson’s disease. Although there are several medicines currently approved for managing neurodegenerative disorders, a large majority of them only help with associated symptoms. This lack of pathogenesis-targeting therapies is primarily due to the restrictive effects of the blood–brain barrier (BBB), which keeps close to 99% of all “foreign substances” out of the brain. Since their discovery, nanoparticles have been successfully used for targeted delivery into many organs, including the brain. This review briefly describes the pathophysiology of Alzheimer’s, Parkinson’s disease, and amyotrophic lateral sclerosis, and their current management approaches. We then highlight the major challenges of brain-drug delivery, followed by the role of nanotherapeutics for the diagnosis and treatment of various neurological disorders.

Regulation of Neurodegeneration-associated Protein Fragments by the N-degron Pathways

Among the most salient features that underpin the development of aging-related neurodegenerative disorders are the accumulation of protein aggregates and the decrease in cellular degradation capacity. Mammalian cells have evolved sophisticated quality control mechanisms to repair or eliminate the otherwise abnormal or misfolded proteins. Chaperones identify unstable or abnormal conformations in proteins and often help them regain their correct conformation. However, if repair is not an option, abnormal proteins are selectively degraded to prevent undesired interactions with other proteins or oligomerization into toxic multimeric complexes. The autophagic-lysosomal system and the ubiquitin-proteasome system mediate the selective and targeted degradation of abnormal or aberrant protein fragments. Despite an increasing understanding regarding the molecular responses that counteract the formation and clearance of dysfunctional protein aggregates, the role of N-degrons in these processes is poorly understood. Previous work demonstrated that the Arg-N-end rule degradation pathway (Arg-N-degron pathway) mediates the degradation of neurodegeneration-associated proteins, thereby regulating crucial signaling hubs that modulate the progression of neurodegenerative diseases. Herein, we discuss the functional interconnection between N-degron pathways and proteins associated with neurodegenerative disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease. We also highlight some future prospects related to how the molecular insights gained from these processes will help unveil novel therapeutic approaches.

Broad activation of the Parkin pathway induces synaptic mitochondrial deficits in early tauopathy

Mitochondrial defects are a hallmark of early pathophysiology in Alzheimer's disease, with pathologically phosphorylated tau reported to induce mitochondrial toxicity. Mitophagy constitutes a key pathway in mitochondrial quality control by which damaged mitochondria are targeted for autophagy. However, few details are known regarding the intersection of mitophagy and pathologies in tauopathy. Here, by applying biochemical and cell biological approaches including time-lapse confocal imaging in live tauopathy neurons, combined with gene rescue experiments via stereotactic injections of adeno-associated virus particles into tauopathy mouse brains, electrophysiological recordings and behavioural tests, we demonstrate for the first time that mitochondrial distribution deficits at presynaptic terminals are an early pathological feature in tauopathy brains. Furthermore, Parkin-mediated mitophagy is extensively activated in tauopathy neurons, which accelerates mitochondrial Rho GTPase 1 (Miro1) turnover and consequently halts Miro1-mediated mitochondrial anterograde movement towards synaptic terminals. As a result, mitochondrial supply at tauopathy synapses is disrupted, impairing synaptic function. Strikingly, increasing Miro1 levels restores the synaptic mitochondrial population by enhancing mitochondrial anterograde movement and thus reverses tauopathy-associated synaptic failure. In tauopathy mouse brains, overexpression of Miro1 markedly elevates synaptic distribution of mitochondria and protects against synaptic damage and neurodegeneration, thereby counteracting impairments in learning and memory as well as synaptic plasticity. Taken together, our study reveals that activation of the Parkin pathway triggers an unexpected effect-depletion of mitochondria from synaptic terminals, a characteristic feature of early tauopathy. We further provide new mechanistic insights into how parkin activation-enhanced Miro1 degradation and impaired mitochondrial anterograde transport drive tauopathy-linked synaptic pathogenesis and establish a foundation for future investigations into new therapeutic strategies to prevent synaptic deterioration in Alzheimer's disease and other tauopathies.

Therapeutic Potential of Vital Transcription Factors in Alzheimer's and Parkinson's Disease With Particular Emphasis on Transcription Factor EB Mediated Autophagy

Autophagy is an important cellular self-digestion and recycling pathway that helps in maintaining cellular homeostasis. Dysregulation at various steps of the autophagic and endolysosomal pathway has been reported in several neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington disease (HD) and is cited as a critically important feature for central nervous system (CNS) proteostasis. Recently, another molecular target, namely transcription factor EB (TFEB) has been explored globally to treat neurodegenerative disorders. This TFEB, is a key regulator of autophagy and lysosomal biogenesis pathway. Multiple research studies suggested therapeutic potential by targeting TFEB to treat human diseases involving autophagy-lysosomal dysfunction, especially neurodegenerative disorders. A common observation involving all neurodegenerative disorders is their poor efficacy in clearing and recycle toxic aggregated proteins and damaged cellular organelles due to impairment in the autophagy pathway. This dysfunction in autophagy characterized by the accumulation of toxic protein aggregates leads to a progressive loss in structural integrity/functionality of neurons and may even result in neuronal death. In recent years TFEB, a key regulator of autophagy and lysosomal biogenesis, has received considerable attention. It has emerged as a potential therapeutic target in numerous neurodegenerative disorders like AD and PD. In various neurobiology studies involving animal models, TFEB has been found to ameliorate neurotoxicity and rescue neurodegeneration. Since TFEB is a master transcriptional regulator of autophagy and lysosomal biogenesis pathway and plays a crucial role in defining autophagy activation. Studies have been done to understand the mechanisms for TFEB dysfunction, which may yield insights into how TFEB might be targeted and used for the therapeutic strategy to develop a treatment process with extensive application to neurodegenerative disorders. In this review, we explore the role of different transcription factor-based targeted therapy by some natural compounds for AD and PD with special emphasis on TFEB.

Consequences of Hyperphosphorylated Tau in the Locus Coeruleus on Behavior and Cognition in a Rat Model of Alzheimer's Disease

BACKGROUND

The locus coeruleus (LC) is one of the earliest brain regions to accumulate hyperphosphorylated tau, but a lack of animal models that recapitulate this pathology has hampered our understanding of its contributions to Alzheimer's disease (AD) pathophysiology.

OBJECTIVE

We previously reported that TgF344-AD rats, which overexpress mutant human amyloid precursor protein and presenilin-1, accumulate early endogenous hyperphosphorylated tau in the LC. Here, we used TgF344-AD rats and a wild-type (WT) human tau virus to interrogate the effects of endogenous hyperphosphorylated rat tau and human tau in the LC on AD-related neuropathology and behavior.

METHODS

Two-month-old TgF344-AD and WT rats received bilateral LC infusions of full-length WT human tau or mCherry control virus driven by the noradrenergic-specific PRSx8 promoter. Rats were subsequently assessed at 6 and 12 months for arousal (sleep latency), anxiety-like behavior (open field, elevated plus maze, novelty-suppressed feeding), passive coping (forced swim task), and learning and memory (Morris water maze and fear conditioning). Hippocampal microglia, astrocyte, and AD pathology were evaluated using immunohistochemistry.

RESULTS

In general, the effects of age were more pronounced than genotype or treatment; older rats displayed greater hippocampal pathology, took longer to fall asleep, had reduced locomotor activity, floated more, and had impaired cognition compared to younger animals. TgF344-AD rats showed increased anxiety-like behavior and impaired learning and memory. The tau virus had negligible influence on most measures.

CONCLUSION

Effects of hyperphosphorylated tau on AD-like neuropathology and behavioral symptoms were subtle. Further investigation of different forms of tau is warranted.

Review of Current Strategies for Delivering Alzheimer's Disease Drugs Across the Blood-Brain Barrier

(Appeared originally in the International Journal of Molecular Sciences 2019; 20:381) Reprinted under Creative Commons CC-BY license.

Roflumilast ameliorates cognitive deficits in a mouse model of amyloidogenesis and tauopathy: Involvement of nitric oxide status, Aβ extrusion transporter ABCB1, and reversal by PKA inhibitor H89

The biological cascade of second messenger-cyclic adenosine monophosphate (cAMP) -as a molecular mechanism implicated in memory and learning regulation has captured the attention of neuroscientists worldwide. cAMP triggers its foremost effector, protein kinase A (PKA), resulting in the activation of innumerable downstream targets. Roflumilast (ROF), a phosphodiesterase 4 inhibitor, has demonstrated a greater efficiency in enhancing cAMP signaling in various neurological disorders. This study was conducted to identify various downstream targets of PKA as mechanistic tools through which ROF could hinder the progressive cognitive impairment following central streptozotocin (STZ) administration in mice. Animals were injected with STZ (3 mg/kg/i.c.v) once. Five hours later, mice received ROF (0.4 mg/kg) with or without the PKA inhibitor, H89, for 21 days. ROF highly preserved the structure of hippocampal neurons. It improved the ability of mice to develop short-term memories and retrieve spatial memories in Y-maze and Morris water maze tests, respectively. ROF enhanced the gene expression of ABCB1 transporters and pregnane X receptors (PXR), and hampered Aβ accumulation in hippocampus. Simultaneously, it interfered with the processes of tau phosphorylation and nitration. This effect was associated with an upsurge in hippocampal arginase activity as well as a decline in glycogen synthase kinase-3β activity, nitric oxide synthase (NOS) activity, and inducible NOS expression. Contrariwise, ROF's beneficial effects were utterly abolished by co-administration of H89. In conclusion, boosting PKA, by ROF, modulated PXR/ABCB1 expression and arginase/NOS activities to restrict the main post-translational modifications of tau, Aβ deposition and, accordingly, cognitive deterioration of sporadic Alzheimer's disease.

Revisiting the grammar of Tau aggregation and pathology formation: how new insights from brain pathology are shaping how we study and target Tauopathies

Converging evidence continues to point towards Tau aggregation and pathology formation as central events in the pathogenesis of Alzheimer's disease and other Tauopathies. Despite significant advances in understanding the morphological and structural properties of Tau fibrils, many fundamental questions remain about what causes Tau to aggregate in the first place. The exact roles of cofactors, Tau post-translational modifications, and Tau interactome in regulating Tau aggregation, pathology formation, and toxicity remain unknown. Recent studies have put the spotlight on the wide gap between the complexity of Tau structures, aggregation, and pathology formation in the brain and the simplicity of experimental approaches used for modeling these processes in research laboratories. Embracing and deconstructing this complexity is an essential first step to understanding the role of Tau in health and disease. To help deconstruct this complexity and understand its implication for the development of effective Tau targeting diagnostics and therapies, we firstly review how our understanding of Tau aggregation and pathology formation has evolved over the past few decades. Secondly, we present an analysis of new findings and insights from recent studies illustrating the biochemical, structural, and functional heterogeneity of Tau aggregates. Thirdly, we discuss the importance of adopting new experimental approaches that embrace the complexity of Tau aggregation and pathology as an important first step towards developing mechanism- and structure-based therapies that account for the pathological and clinical heterogeneity of Alzheimer's disease and Tauopathies. We believe that this is essential to develop effective diagnostics and therapies to treat these devastating diseases.

Mechanism by Which Aluminum Regulates the Abnormal Phosphorylation of the Tau Protein in Different Cell Lines

Aluminum (Al) is an environmental neurotoxin to which humans are extensively exposed; however, the molecular mechanism of aluminum toxicity is unclear. Several studies have indicated that exposure to aluminum can cause abnormal phosphorylation of the tau protein. The purpose of this study was to investigate respectively the special molecular mechanism of abnormal regulation on synthesis and degradation of the tau protein induced by AlCl₃ in cells of different species. The results of tau protein showed that the sites of abnormal tau phosphorylation induced by AlCl₃ are Thr231, Ser262, and Ser396 in N2a cells. Meanwhile, the expressions of Thr181, Thr231, and Ser262 increased abnormally in SH-SY5Y cells. The result of the study showed that PP2A expression was high in N2a cells, while GSK-3β and PP2A in SH-SY5Y cells were involved in the synthesis process of abnormal tau phosphorylation induced by AlCl₃. In N2a cells, the ubiquitin-proteasome pathway (UPP) mainly regulated tau phosphorylation at Ser262 and Ser396. Meanwhile, in SH-SY5Y cells, the UPP mainly regulated tau phosphorylation at Thr231 and Ser396. In summary, the UPP is involved in the degradation of Tau that is abnormally phosphorylated induced by AlCl₃, but this process is site-specific and differs in cells of different species.

Novel genetic variants in MAPT and alterations in tau phosphorylation in amyotrophic lateral sclerosis post-mortem motor cortex and cerebrospinal fluid

Although the molecular mechanisms underlying amyotrophic lateral sclerosis (ALS) are not yet fully understood, several studies report alterations in tau phosphorylation in both sporadic and familial ALS. Recently, we have demonstrated that phosphorylated tau at S396 (pTau‐S396) is mislocalized to synapses in ALS motor cortex (mCTX) and contributes to mitochondrial dysfunction. Here, we demonstrate that while there was no overall increase in total tau, pTau‐S396, and pTau‐S404 in ALS post‐mortem mCTX, total tau and pTau‐S396 were increased in C9ORF72‐ALS. Additionally, there was a significant decrease in pTau‐T181 in ALS mCTX compared controls. Furthermore, we leveraged the ALS Knowledge Portal and Project MinE data sets and identified ALS‐specific genetic variants across MAPT, the gene encoding tau. Lastly, assessment of cerebrospinal fluid (CSF) samples revealed a significant increase in total tau levels in bulbar‐onset ALS together with a decrease in CSF pTau‐T181:tau ratio in all ALS samples, as reported previously. While increases in CSF tau levels correlated with a faster disease progression as measured by the revised ALS functional rating scale (ALSFRS‐R), decreases in CSF pTau‐T181:tau ratio correlated with a slower disease progression, suggesting that CSF total tau and pTau‐T181 ratio may serve as biomarkers of disease in ALS. Our findings highlight the potential role of pTau‐T181 in ALS, as decreases in CSF pTau‐T181:tau ratio may reflect the significant decrease in pTau‐T181 in post‐mortem mCTX. Taken together, these results indicate that tau phosphorylation is altered in ALS post‐mortem mCTX as well as in CSF and, importantly, the newly described pathogenic or likely pathogenic variants identified in MAPT in this study are adjacent to T181 and S396 phosphorylation sites further highlighting the potential role of these tau functional domains in ALS.

Although the molecular mechanisms underlying amyotrophic lateral sclerosis (ALS) are not yet fully understood, recent studies report alterations in tau phosphorylation in ALS. Our study builds on these findings and demonstrates that tau phosphorylation is altered in post‐mortem ALS motor cortex and highlights new and ALS‐specific variants in MAPT, the gene encoding tau. Lastly, we report alterations in phosphorylated tau in ALS cerebrospinal fluid that may function as a predictive biomarker for ALS.

A Review of miRNAs as Biomarkers and Effect of Dietary Modulation in Obesity Associated Cognitive Decline and Neurodegenerative Disorders

There has been a progressive increase in the prevalence of obesity and its comorbidities such as type 2 diabetes and cardiovascular diseases worldwide. Recent studies have suggested that the crosstalk between adipose tissue and central nervous system (CNS), through cellular mediators and signaling pathways, may causally link obesity with cognitive decline and give rise to neurodegenerative disorders. Several mechanisms have been proposed in obesity, including inflammation, oxidative stress, insulin resistance, altered lipid and cholesterol homeostasis, which may result in neuroinflammation, altered brain insulin signaling, amyloid-beta (Aβ) deposition and neuronal cell death. Since obesity is associated with functional and morphological alterations in the adipose tissues, the resulting peripheral immune response augments the development and progression of cognitive decline and increases susceptibility of neurodegenerative disorders, such as Alzheimer's Disease (AD) and Parkinson's Disease (PD). Studies have also elucidated an important role of high fat diet in the exacerbation of these clinical conditions. However, the underlying factors that propel and sustain this obesity associated cognitive decline and neurodegeneration, remains highly elusive. Moreover, the mechanisms linking these phenomena are not well-understood. The cumulative line of evidence have demonstrated an important role of microRNAs (miRNAs), a class of small non-coding RNAs that regulate gene expression and transcriptional changes, as biomarkers of pathophysiological conditions. Despite the lack of utility in current clinical practices, miRNAs have been shown to be highly specific and sensitive to the clinical condition being studied. Based on these observations, this review aims to assess the role of several miRNAs and aim to elucidate underlying mechanisms that link obesity with cognitive decline and neurodegenerative disorders. Furthermore, this review will also provide evidence for the effect of dietary modulation which can potentially ameliorate cognitive decline and neurodegenerative diseases associated with obesity.

TFEB regulates lysosomal exocytosis of tau and its loss of function exacerbates tau pathology and spreading

Neurofibrillary tangles (NFTs) composed of hyperphosphorylated and misfolded tau protein are a pathological hallmark of Alzheimer's disease and other tauopathy conditions. Tau is predominantly an intraneuronal protein but is also secreted in physiological and pathological conditions. The extracellular tau has been implicated in the seeding and propagation of tau pathology and is the prime target of the current tau immunotherapy. However, truncated tau species lacking the microtubule-binding repeat (MTBR) domains essential for seeding have been shown to undergo active secretion and the mechanisms and functional consequences of the various extracellular tau are poorly understood. We report here that the transcription factor EB (TFEB), a master regulator of lysosomal biogenesis, plays an essential role in the lysosomal exocytosis of selected tau species. TFEB loss of function significantly reduced the levels of interstitial fluid (ISF) tau in PS19 mice expressing P301S mutant tau and in conditioned media of mutant tau expressing primary neurons, while the secretion of endogenous wild-type tau was not affected. Mechanistically we found that TFEB regulates the secretion of truncated mutant tau lacking MTBR and this process is dependent on the lysosomal calcium channel TRPML1. Consistent with the seeding-incompetent nature of the truncated tau and supporting the concept that TFEB-mediated lysosomal exocytosis promotes cellular clearance, we show that reduced ISF tau in the absence of TFEB is associated with enhanced intraneuronal pathology and accelerated spreading. Our results support the idea that TFEB-mediated tau exocytosis serves as a clearance mechanism to reduce intracellular tau under pathological conditions and that effective tau immunotherapy should devoid targeting these extracellular tau species.

Astrocytes in Down Syndrome Across the Lifespan

Down Syndrome (DS) is the most common genetic cause of intellectual disability in which delays and impairments in brain development and function lead to neurological and cognitive phenotypes. Traditionally, a neurocentric approach, focusing on neurons and their connectivity, has been applied to understanding the mechanisms involved in DS brain pathophysiology with an emphasis on how triplication of chromosome 21 leads to alterations in neuronal survival and homeostasis, synaptogenesis, brain circuit development, and neurodegeneration. However, recent studies have drawn attention to the role of non-neuronal cells, especially astrocytes, in DS. Astrocytes comprise a large proportion of cells in the central nervous system (CNS) and are critical for brain development, homeostasis, and function. As triplication of chromosome 21 occurs in all cells in DS (with the exception of mosaic DS), a deeper understanding of the impact of trisomy 21 on astrocytes in DS pathophysiology is warranted and will likely be necessary for determining how specific brain alterations and neurological phenotypes emerge and progress in DS. Here, we review the current understanding of the role of astrocytes in DS, and discuss how specific perturbations in this cell type can impact the brain across the lifespan from early brain development to adult stages. Finally, we highlight how targeting, modifying, and/or correcting specific molecular pathways and properties of astrocytes in DS may provide an effective therapeutic direction given the important role of astrocytes in regulating brain development and function.

Small Neuron-Derived Extracellular Vesicles from Individuals with Down Syndrome Propagate Tau Pathology in the Wildtype Mouse Brain

Individuals with Down syndrome (DS) exhibit Alzheimer's disease (AD) pathology at a young age, including amyloid plaques and neurofibrillary tangles (NFTs). Tau pathology can spread via extracellular vesicles, such as exosomes. The cargo of neuron-derived small extracellular vesicles (NDEVs) from individuals with DS contains p-Tau at an early age. The goal of the study was to investigate whether NDEVs isolated from the blood of individuals with DS can spread Tau pathology in the brain of wildtype mice. We purified NDEVs from the plasma of patients with DS-AD and controls and injected small quantities using stereotaxic surgery into the dorsal hippocampus of adult wildtype mice. Seeding competent Tau conformers were amplified in vitro from DS-AD NDEVs but not NDEVs from controls. One month or 4 months post-injection, we examined Tau pathology in mouse brains. We found abundant p-Tau immunostaining in the hippocampus of the mice injected with DS-AD NDEVs compared to injections of age-matched control NDEVs. Double labeling with neuronal and glial markers showed that p-Tau staining was largely found in neurons and, to a lesser extent, in glial cells and that p-Tau immunostaining was spreading along the corpus callosum and the medio-lateral axis of the hippocampus. These studies demonstrate that NDEVs from DS-AD patients exhibit Tau seeding capacity and give rise to tangle-like intracellular inclusions.

Identification of retinoblastoma binding protein 7 (Rbbp7) as a mediator against tau acetylation and subsequent neuronal loss in Alzheimer's disease and related tauopathies

Evidence indicates that tau hyper-phosphorylation and subsequent neurofibrillary tangle formation contribute to the extensive neuronal death in Alzheimer's disease (AD) and related tauopathies. Recent work has identified that increased tau acetylation can promote tau phosphorylation. Tau acetylation occurs at lysine 280 resulting from increased expression of the lysine acetyltransferase p300. The exact upstream mechanisms mediating p300 expression remain elusive. Additional work highlights the role of the epigenome in tau pathogenesis, suggesting that dysregulation of epigenetic proteins may contribute to acetylation and hyper-phosphorylation of tau. Here, we identify and focus on the histone-binding subunit of the Nucleosome Remodeling and Deacetylase (NuRD) complex: Retinoblastoma-Binding Protein 7 (Rbbp7). Rbbp7 chaperones chromatin remodeling proteins to their nuclear histone substrates, including histone acetylases and deacetylases. Notably, Rbbp7 binds to p300, suggesting that it may play a role in modulating tau acetylation. We interrogated Rbbp7 in post-mortem brain tissue, cell lines and mouse models of AD. We found reduced Rbbp7 mRNA expression in AD cases, a significant negative correlation with CERAD (neuritic plaque density) and Braak Staging (pathogenic tau inclusions) and a significant positive correlation with post-mortem brain weight. We also found a neuron-specific downregulation of Rbbp7 mRNA in AD patients. Rbbp7 protein levels were significantly decreased in 3xTg-AD and PS19 mice compared to NonTg, but no decreases were found in APP/PS1 mice that lack tau pathology. In vitro, Rbbp7 overexpression rescued TauP301L-induced cytotoxicity in immortalized hippocampal cells and primary cortical neurons. In vivo, hippocampal Rbbp7 overexpression rescued neuronal death in the CA1 of PS19 mice. Mechanistically, we found that increased Rbbp7 reduced p300 levels, tau acetylation at lysine 280 and tau phosphorylation at AT8 and AT100 sites. Collectively, these data identify a novel role of Rbbp7, protecting against tau-related pathologies, and highlight its potential as a therapeutic target in AD and related tauopathies.

Linking Oxidative Stress and Proteinopathy in Alzheimer's Disease

Proteinopathy and excessive production of reactive oxygen species (ROS), which are the principal features observed in the Alzheimer’s disease (AD) brain, contribute to neuronal toxicity. β-amyloid and tau are the primary proteins responsible for the proteinopathy (amyloidopathy and tauopathy, respectively) in AD, which depends on ROS production; these aggregates can also generate ROS. These mechanisms work in concert and reinforce each other to drive the pathology observed in the aging brain, which primarily involves oxidative stress (OS). This, in turn, triggers neurodegeneration due to the subsequent loss of synapses and neurons. Understanding these interactions may thus aid in the identification of potential neuroprotective therapies that could be clinically useful. Here, we review the role of β-amyloid and tau in the activation of ROS production. We then further discuss how free radicals can influence structural changes in key toxic intermediates and describe the putative mechanisms by which OS and oligomers cause neuronal death.

Hippocampal subfield imaging and fractional anisotropy show parallel changes in Alzheimer's disease tau progression using simultaneous tau-PET/MRI at 3T

INTRODUCTION

Alzheimer's disease (AD) is the most common form of dementia, characterized primarily by abnormal aggregation of two proteins, tau and amyloid beta. We assessed tau pathology and white matter connectivity changes in subfields of the hippocampus simultaneously in vivo in AD.

METHODS

Twenty-four subjects were scanned using simultaneous time-of-flight 18F-PI-2620 tau positron emission tomography/3-Tesla magnetic resonance imaging and automated segmentation.

RESULTS

We observed extensive tau elevation in the entorhinal/perirhinal regions, intermediate tau elevation in cornu ammonis 1/subiculum, and an absence of tau elevation in the dentate gyrus, relative to controls. Diffusion tensor imaging showed parahippocampal gyral fractional anisotropy was lower in AD and mild cognitive impairment compared to controls and strongly correlated with early tau accumulation in the entorhinal and perirhinal cortices.

DISCUSSION

This study demonstrates the potential for quantifiable patterns of 18F-PI2620 binding in hippocampus subfields, accompanied by diffusion and volume metrics, to be valuable markers of AD.

Femtomolar Biodetection by a Compact Core-Shell 3D Chiral Metamaterial

Advanced sensing tools, detecting extremely low concentrations of circulating biomarkers, can open unexplored routes toward early diagnostics and diseases progression monitoring. Here, we demonstrate the sensing capabilities of a chip-based metamaterial, combining 3D chiral geometry with a functional core-shell nanoarchitecture. The chiral metamaterial provides a circular polarization-dependent optical response, allowing analysis in a complex environment without significant background interferences. The functional nanoarchitecture, based on the conformal coating with a polymer shell, modifies the chiral metamaterial near- and far-field optical response because of the energy transfer between dielectric shell polarization charges and plasmonic core free electrons, leading to efficient interaction with biomolecules. The system sensitivity slope is 27 nm/pM, in the detection of TAR DNA-binding protein 43, clinically relevant for neurodegenerative diseases. Measurements were performed in spiked solution and in human serum with concentrations from 1 pM down to 10 fM, which is a range not accessible with common immunological assays, opening new perspectives for next-generation biomedical systems.

Amyotrophic Lateral Sclerosis (ALS): Stressed by Dysfunctional Mitochondria-Endoplasmic Reticulum Contacts (MERCs)

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which there is currently no cure. Progress in the characterization of other neurodegenerative mechanisms has shifted the spotlight onto an intracellular structure called mitochondria-endoplasmic reticulum (ER) contacts (MERCs) whose ER portion can be biochemically isolated as mitochondria-associated membranes (MAMs). Within the central nervous system (CNS), these structures control the metabolic output of mitochondria and keep sources of oxidative stress in check via autophagy. The most relevant MERC controllers in the ALS pathogenesis are vesicle-associated membrane protein-associated protein B (VAPB), a mitochondria-ER tether, and the ubiquitin-specific chaperone valosin containing protein (VCP). These two systems cooperate to maintain mitochondrial energy output and prevent oxidative stress. In ALS, mutant VAPB and VCP take a central position in the pathology through MERC dysfunction that ultimately alters or compromises mitochondrial bioenergetics. Intriguingly, both proteins are targets themselves of other ALS mutant proteins, including C9orf72, FUS, or TDP-43. Thus, a new picture emerges, where different triggers cause MERC dysfunction in ALS, subsequently leading to well-known pathological changes including endoplasmic reticulum (ER) stress, inflammation, and motor neuron death.

Autophagy deficiency modulates microglial lipid homeostasis and aggravates tau pathology and spreading

The autophagy-lysosomal pathway plays a critical role in intracellular clearance and metabolic homeostasis. While neuronal autophagy is known to participate in the degradation of neurofibrillary tangles composed of hyperphosphorylated and misfolded tau protein in Alzheimer's disease and other tauopathies, how microglial-specific autophagy regulates microglial intrinsic properties and neuronal tau pathology is not well understood. We report here that Atg7, a key mediator of autophagosome biogenesis, plays an essential role in the regulation of microglial lipid metabolism and neuroinflammation. Microglia-specific deletion of Atg7 leads to the transition of microglia to a proinflammatory status in vivo and to inflammasome activation in vitro. Activation of ApoE and lipid efflux attenuates the lipid droplets accumulation and inhibits cytokine production in microglial cells with Atg7 deficiency. Functionally, we show that the absence of microglial Atg7 enhances intraneuronal tau pathology and its spreading. Our results reveal an essential role for microglial autophagy in regulating lipid homeostasis, neuroinflammation, and tau pathology.

Contribution of the Nrf2 Pathway on Oxidative Damage and Mitochondrial Failure in Parkinson and Alzheimer's Disease

The increase in human life expectancy has become a challenge to reduce the deleterious consequences of aging. Nowadays, an increasing number of the population suffer from age-associated neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD). These disorders present different signs of neurodegeneration such as mitochondrial dysfunction, inflammation, and oxidative stress. Accumulative evidence suggests that the transcriptional factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a vital defensive role orchestrating the antioxidant response in the brain. Nrf2 activation promotes the expression of several antioxidant enzymes that exert cytoprotective effects against oxidative damage and mitochondrial impairment. In this context, several studies have proposed a role of Nrf2 in the pathogenesis of PD and AD. Thus, we consider it important to summarize the ongoing literature related to the effects of the Nrf2 pathway in the context of these diseases. Therefore, in this review, we discuss the mechanisms involved in Nrf2 activity and its connection with mitochondria, energy supply, and antioxidant response in the brain. Furthermore, we will lead our discussion to identify the participation of the Nrf2 pathway in mitochondrial impairment and neurodegeneration present in PD and AD. Finally, we will discuss the therapeutic effects that the Nrf2 pathway activation could have on the cognitive impairment, neurodegeneration, and mitochondrial failure present in PD and AD.

Phosphorylated tau targeted small-molecule PROTACs for the treatment of Alzheimer's disease and tauopathies

Tau is a microtubule-stabilizing protein that plays an important role in the formation of axonal microtubules in neurons. Phosphorylated tau (p-Tau) has received great attention in the field of Alzheimer's disease (AD) as a potential therapeutic target due to its involvement with synaptic damage and neuronal dysfunction. Mounting evidence suggests that amyloid beta (Aβ)-targeted clinical trials continuously failed; therefore, it is important to consider alternative therapeutic strategies such as p-tau-PROTACs targeted small molecules for AD and other tauopathies. The present article describes the characteristics of tau biology, structure, and function in both healthy and pathological states in AD. It also explains data from studies that have identified the involvement of p-tau in neuronal damage and synaptic and cognitive functions in AD. Current article also covers several aspects, including small molecule inhibitors, and the development of p-tau-PROTACs targeted drug molecules to treat patients with AD and other tauopathies.

Elucidating the Neuropathologic Mechanisms of SARS-CoV-2 Infection

The current pandemic caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a public health emergency. To date, March 1, 2021, coronavirus disease 2019 (COVID-19) has caused about 114 million accumulated cases and 2.53 million deaths worldwide. Previous pieces of evidence suggest that SARS-CoV-2 may affect the central nervous system (CNS) and cause neurological symptoms in COVID-19 patients. It is also known that angiotensin-converting enzyme-2 (ACE2), the primary receptor for SARS-CoV-2 infection, is expressed in different brain areas and cell types. Thus, it is hypothesized that infection by this virus could generate or exacerbate neuropathological alterations. However, the molecular mechanisms that link COVID-19 disease and nerve damage are unclear. In this review, we describe the routes of SARS-CoV-2 invasion into the central nervous system. We also analyze the neuropathologic mechanisms underlying this viral infection, and their potential relationship with the neurological manifestations described in patients with COVID-19, and the appearance or exacerbation of some neurodegenerative diseases.

Early alterations of neurovascular unit in the retina in mouse models of tauopathy

The retina, as the only visually accessible tissue in the central nervous system, has attracted significant attention for evaluating it as a biomarker for neurodegenerative diseases. Yet, most of studies focus on characterizing the loss of retinal ganglion cells (RGCs) and degeneration of their axons. There is no integrated analysis addressing temporal alterations of different retinal cells in the neurovascular unit (NVU) in particular retinal vessels. Here we assessed NVU changes in two mouse models of tauopathy, P301S and P301L transgenic mice overexpressing the human tau mutated gene, and evaluated the therapeutic effects of a tau oligomer monoclonal antibody (TOMA). We found that retinal edema and breakdown of blood-retina barrier were observed at the very early stage of tauopathy. Leukocyte adhesion/infiltration, and microglial recruitment/activation were constantly increased in the retinal ganglion cell layer of tau transgenic mice at different ages, while Müller cell gliosis was only detected in relatively older tau mice. Concomitantly, the number and function of RGCs progressively decreased during aging although they were not considerably altered in the very early stage of tauopathy. Moreover, intrinsically photosensitive RGCs appeared more sensitive to tauopathy. Remarkably, TOMA treatment in young tau transgenic mice significantly attenuated vascular leakage, inflammation and RGC loss. Our data provide compelling evidence that abnormal tau accumulation can lead to pathology in the retinal NVU, and vascular alterations occur more manifest and earlier than neurodegeneration in the retina. Oligomeric tau-targeted immunotherapy has the potential to treat tau-induced retinopathies. These data suggest that retinal NVU may serve as a potential biomarker for diagnosis and staging of tauopathy as well as a platform to study the molecular mechanisms of neurodegeneration.

An Analysis of the Neurological and Molecular Alterations Underlying the Pathogenesis of Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by amyloid beta (Aβ) plaques, neurofibrillary tangles, and neuronal loss. Unfortunately, despite decades of studies being performed on these histological alterations, there is no effective treatment or cure for AD. Identifying the molecular characteristics of the disease is imperative to understanding the pathogenesis of AD. Furthermore, uncovering the key causative alterations of AD can be valuable in developing models for AD treatment. Several alterations have been implicated in driving this disease, including blood–brain barrier dysfunction, hypoxia, mitochondrial dysfunction, oxidative stress, glucose hypometabolism, and altered heme homeostasis. Although these alterations have all been associated with the progression of AD, the root cause of AD has not been identified. Intriguingly, recent studies have pinpointed dysfunctional heme metabolism as a culprit of the development of AD. Heme has been shown to be central in neuronal function, mitochondrial respiration, and oxidative stress. Therefore, dysregulation of heme homeostasis may play a pivotal role in the manifestation of AD and its various alterations. This review will discuss the most common neurological and molecular alterations associated with AD and point out the critical role heme plays in the development of this disease.

Chinese herbs and acupuncture to improve cognitive function in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a variety of causes. Traditional Chinese medicine (TCM), which includes the two main approaches of acupuncture and herbal medication, views the human body as a self-controlled system network. Fundamental theories, including "qi," the five elements, and the theory of viscera, form the basis for classification. Diseases in humans are considered to be caused by an imbalance of "yang qi" and "yin qi" that lead to the nonhomeostasis of organs. Acupuncture is derived from 12 main meridians and 365 acupuncture points characterized by "blood and qi." Needling of different positions corresponds to specific disease treatments to increase qi. Treatment with Chinese herbal medicines is based on syndrome differentiation characterized as "Zheng" which differs from the cause orientation approach of Western medicine. In this article, we review basic and clinical research studies that describe TCM herbs and acupuncture for the treatment of AD. Moreover, we propose that these two approaches be integrated to improve the outcomes for AD patients.

Onset of hippocampal network aberration and memory deficits in P301S tau mice are associated with an early gene signature

Hyperphosphorylation and deposition of tau in the brain characterizes frontotemporal dementia and Alzheimer's disease. Disease-associated mutations in the tau-encoding MAPT gene have enabled the generation of transgenic mouse models that recapitulate aspects of human neurodegenerative diseases, including tau hyperphosphorylation and neurofibrillary tangle formation. Here, we characterized the effects of transgenic P301S mutant human tau expression on neuronal network function in the murine hippocampus. Onset of progressive spatial learning deficits in P301S tau transgenic TAU58/2 mice were paralleled by long-term potentiation deficits and neuronal network aberrations during electrophysiological and EEG recordings. Gene-expression profiling just prior to onset of apparent deficits in TAU58/2 mice revealed a signature of immediate early genes that is consistent with neuronal network hypersynchronicity. We found that the increased immediate early gene activity was confined to neurons harbouring tau pathology, providing a cellular link between aberrant tau and network dysfunction. Taken together, our data suggest that tau pathology drives neuronal network dysfunction through hyperexcitation of individual, pathology-harbouring neurons, thereby contributing to memory deficits.

Isoform-selective decrease of glycogen synthase kinase-3-beta (GSK-3β) reduces synaptic tau phosphorylation, transcellular spreading, and aggregation

It has been suggested that aberrant activation of glycogen synthase kinase-3-beta (GSK-3β) can trigger abnormal tau hyperphosphorylation and aggregation, which ultimately leads to neuronal/synaptic damage and impaired cognition in Alzheimer disease (AD). We examined if isoform-selective partial reduction of GSK-3β can decrease pathological tau changes, including hyperphosphorylation, aggregation, and spreading, in mice with localized human wild-type tau (hTau) expression in the brain. We used adeno-associated viruses (AAVs) to express hTau locally in the entorhinal cortex of wild-type and GSK-3β hemi-knockout (GSK-3β-HK) mice. GSK-3β-HK mice had significantly less accumulation of hyperphosphorylated tau in synapses and showed a significant decrease of tau protein spread between neurons. In primary neuronal cultures from GSK-3β-HK mice, the aggregation of exogenous FTD-mutant tau was also significantly reduced. These results show that a partial decrease of GSK-3β significantly represses tau-initiated neurodegenerative changes in the brain, and therefore is a promising therapeutic target for AD and other tauopathies.

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Genetic reduction of GSK-3β decreases synaptic accrual of GSK-3β and p-Tau in mice

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Reduction of GSK-3β lowers the trans-cellular spread of tau in vivo and in vitro

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Reduction of GSK-3β diminishes the formation of tau aggregates in vitro

Tau in Alzheimer's Disease: Pathological Alterations and an Attractive Therapeutic Target

Alzheimer's disease (AD) is an age-related neurodegenerative disease with two major hallmarks: extracellular amyloid plaques made of amyloid-β (Aβ) and intracellular neurofibrillary tangles (NFTs) of abnormally hyperphosphorylated tau. The number of NFTs correlates positively with the severity of dementia in AD patients. However, there is still no efficient therapy available for AD treatment and prevention so far. A deeper understanding of AD pathogenesis has identified novel strategies for the generation of specific therapies over the past few decades. Several studies have suggested that the prion-like seeding and spreading of tau pathology in the brain may be a key driver of AD. Tau protein is considered as a promising candidate target for the development of therapeutic interventions due to its considerable pathological role in a variety of neurodegenerative disorders. Abnormal tau hyperphosphorylation plays a detrimental pathological role, eventually leading to neurodegeneration. In the present review, we describe the recent research progresses in the pathological mechanisms of tau protein in AD and briefly discuss tau-based therapeutic strategies.

Partial Inhibition of Mitochondrial Complex I Reduces Tau Pathology and Improves Energy Homeostasis and Synaptic Function in 3xTg-AD Mice

Background:

Accumulation of hyperphosphorylated tau (pTau) protein is associated with synaptic dysfunction in Alzheimer’s disease (AD). We previously demonstrated that neuroprotection in familial mouse models of AD could be achieved by targeting mitochondria complex I (MCI) and activating the adaptive stress response. Efficacy of this strategy on pTau-related pathology remained unknown.

Objective:

To investigate the effect of specific MCI inhibitor tricyclic pyrone compound CP2 on levels of human pTau, memory function, long term potentiation (LTP), and energy homeostasis in 18-month-old 3xTg-AD mice and explore the potential mechanisms.

Methods:

CP2 was administered to male and female 3xTg-AD mice from 3.5–18 months of age. Cognitive function was assessed using the Morris water maze. Glucose metabolism was measured in periphery using a glucose tolerance test and in the brain using fluorodeoxyglucose F18 positron-emission tomography (FDG-PET). LTP was evaluated using electrophysiology in the hippocampus. The expression of key proteins associated with neuroprotective mechanisms were assessed by western blotting.

Results:

Chronic CP2 treatment restored synaptic activity in female 3xTg-AD mice; cognitive function, levels of synaptic proteins, glucose metabolism, and energy homeostasis were improved in male and female 3xTg-AD mice. Significant reduction of human pTau in the brain was associated with increased activity of protein phosphatase of type 2A (PP2A), and reduced activity of cyclin-dependent kinase 5 (CDK5) and glycogen synthase kinase 3β (GSK3β).

Conclusion:

CP2 treatment protected against synaptic dysfunction and memory impairment in symptomatic 3xTg-AD mice, and reduced levels of human pTau, indicating that targeting mitochondria with small molecule specific MCI inhibitors represents a promising strategy for treating AD.

Brain Α-Tocopherol Concentration is Inversely Associated with Neurofibrillary Tangle Counts in Brain Regions Affected in Earlier Braak Stages: A Cross-Sectional Finding in the Oldest Old

Objectives

Higher vitamin E status has been associated with lower risk of Alzheimer's disease (AD). However, evidence of the association of vitamin E concentration in neural tissue with AD pathologies is limited.

Design

The cross-sectional relationship between the human brain concentrations of α- and γ-tocopherol and the severity of AD pathologies - neurofibrillary tangle (NFT) and neuritic plaque (NP) - was investigated.

Setting & Participants

Brains from 43 centenarians (≥ 98 years at death) enrolled in the Phase III of the Georgia Centenarian Study were collected at autopsy.

Measurements

Brain α- and γ-tocopherol concentrations (previously reported) were averaged from frontal, temporal, and occipital cortices. NP and NFT counts (previously reported) were assessed in frontal, temporal, parietal, entorhinal cortices, amygdala, hippocampus, and subiculum. NFT topological progression was assessed using Braak staging. Multiple linear regression was performed to assess the relationship between tocopherol concentrations and NP or NFT counts, with and without adjustment for covariates.

Results

Brain α-tocopherol concentrations were inversely associated with NFT but not NP counts in amygdala (β = -2.67, 95% CI [-4.57, -0.79]), entorhinal cortex (β = -2.01, 95% CI [-3.72, -0.30]), hippocampus (β = -2.23, 95% CI [-3.82, -0.64]), and subiculum (β = -2.52, 95% CI [-4.42, -0.62]) where NFT present earlier in its topological progression, but not in neocortices. Subjects with Braak III-IV had lower α-tocopherol (median = 69,622 pmol/g, IQR = 54,389-72,155 pmol/g) than those with Braak I-II (median = 72,108 pmol/g, IQR = 64,056-82,430 pmol/g), but the difference was of borderline significance (p = 0.063). γ-Tocopherol concentrations were not associated with either NFT or NP counts in any brain regions assessed.

Conclusions

Higher brain α-tocopherol level is specifically associated with lower NFT counts in brain structures affected in earlier Braak stages. Our findings emphasize the possible importance of α-tocopherol intervention timing in tauopathy progression and warrant future clinical trials.

Relationship Between Oxidative Stress, Tau Level and Antioxidant Mechanisms of the KEAP-1/NRF-2/HO-1 in Children with Hydrocephalus

BACKGROUND

Hydrocephalus is a complex neurologic disorder which has a widespread impact on the central nervous system, and a multifactor disease which effect the CSF dynamics and causes severe neurological impairments in children. The pathophysiology of hydrocephalus is not fully understood. However, increasing evidence suggests that oxidative stress may be an important factor in the pathogenesis of hydrocephalus.

OBJECTIVE

The purpose of this study is to investigate the relationship of KEAP-1/NRF-2/HO-1 pathway, one of the main regulators of the antioxidant system in the hydrocephalus pathology, on oxidative stress and tau protein level.

METHODS

The study included 32 patients with hydrocephalus and 32 healthy controls. KEAP-1, NRF-2, HO-1, TAU, and MPO levels are measured using ELISA method TAS, TOS, Total THIOL colorimetric method.

RESULTS

KEAP-1, TAS, Total THIOL levels were found significantly low in the hydrocephalus group compared to the control group. Nevertheless, it is identified in the hydrocephalus group that the NRF-2, HO-1, TAU, MPO, TOS, and OSI levels were significantly elevated.

CONCLUSION

In conclusion, although KEAP-1/NRF-2/HO-1 pathway is activated in patients with hydrocephalus, it is identified that the antioxidant defense system is insufficient, and ultimately leads to elevated oxidative stress. The elevation in the tau level may be an indicator of oxidative stress induced neurodegenerative damage.

New Insights Into Drug Discovery Targeting Tau Protein

Microtubule-associated protein tau is characterized by the fact that it is an intrinsically disordered protein due to its lack of a stable conformation and high flexibility. Intracellular inclusions of fibrillar forms of tau with a β-sheet structure accumulate in the brain of patients with Alzheimer's disease and other tauopathies. Accordingly, detachment of tau from microtubules and transition of tau from a disordered state to an abnormally aggregated state are essential events preceding the onset of tau-related diseases. Many reports have shown that this transition is caused by post-translational modifications, including hyperphosphorylation and acetylation. The misfolded tau is self-assembled and forms a tau oligomer before the appearance of tau inclusions. Animal and pathological studies using human samples have demonstrated that tau oligomer formation contributes to neuronal loss. During the progression of tauopathies, tau seeds are released from cells and incorporated into other cells, leading to the propagation of pathological tau aggregation. Accumulating evidence suggests several potential approaches for blocking tau-mediated toxicity: (1) direct inhibition of pathological tau aggregation and (2) inhibition of tau post-translational modifications that occur prior to pathological tau aggregation, (3) inhibition of tau propagation and (4) stabilization of microtubules. In addition to traditional low-molecular-weight compounds, newer drug discovery approaches such as the development of medium-molecular-weight drugs (peptide- or oligonucleotide-based drugs) and high-molecular-weight drugs (antibody-based drugs) provide alternative pathways to preventing the formation of abnormal tau. Of particular interest are recent studies suggesting that tau droplet formation by liquid-liquid phase separation may be the initial step in aberrant tau aggregation, as well results that implicate roles for tau in dendritic and nuclear functions. Here, we review the mechanisms through which drugs can target tau and consider recent clinical trials for the treatment of tauopathies. In addition, we discuss the utility of these newer strategies and propose future directions for research on tau-targeted therapeutics.

The Crosstalk Between Pathological Tau Phosphorylation and Mitochondrial Dysfunction as a Key to Understanding and Treating Alzheimer's Disease

Alzheimer's disease (AD) is the most common progressive neurodegenerative disorder. A defining hallmark of the AD brain is the presence of intraneuronal neurofibrillary tangles (NFTs) which are made up of abnormally modified tau, with aberrant phosphorylation being the most studied posttranslational modification (PTM). Although the accumulation of tau as NFTs is an invariant feature of the AD brain, it has become evident that these insoluble aggregates are likely not the primary pathogenic form of tau, rather soluble forms of tau with abnormal PTMs are the mediators of toxicity. The most prevalent PTM on tau is phosphorylation, with the abnormal modification of specific residues on tau playing a key role in its toxicity. Even though it is widely accepted that tau with aberrant PTMs facilitates neurodegeneration, the precise cellular mechanisms remain unknown. Nonetheless, there is an evolving conceptual framework that an important contributing factor may be selective pathological tau species compromising mitochondrial biology. Understanding the mechanisms by which tau with site-specific PTM impacts mitochondria is crucial for understanding the role tau plays in AD. Here, we provide a brief introduction to tau and its phosphorylation and function in a physiological context, followed by a discussion of the impact of soluble phosphorylated tau species on neuronal processes in general and mitochondria more specifically. We also discuss how therapeutic strategies that attenuate pathological tau species in combination with treatments that improve mitochondrial biology could be a potential therapeutic avenue to mitigate disease progression in AD and other tauopathies.

The role of wild-type tau in Alzheimer's disease and related tauopathies

Tau oligomers have recently emerged as the principal toxic species in Alzheimer's disease (AD) and tauopathies. Tau oligomers are spontaneously self-assembled soluble tau proteins that are formed prior to fibrils, and they have been shown to play a central role in neuronal cell death and in the induction of neurodegeneration in animal models. As the therapeutic paradigm shifts to targeting toxic tau oligomers, this suggests the focus to study tau oligomerization in species that are less susceptible to fibrillization. While truncated and mutation containing tau as well as the isolated repeat domains are particularly prone to fibrillization, the wild-type (WT) tau proteins have been shown to be resistant to fibril formation in the absence of aggregation inducers. In this review, we will summarize and discuss the toxicity of WT tau both in vitro and in vivo, as well as its involvement in tau oligomerization and cell-to-cell propagation of pathology. Understanding the role of WT tau will enable more effective biomarker development and therapeutic discovery for treatment of AD and tauopathies.

Role of Phosphorylated Tau and Glucose Synthase Kinase 3 Beta in Huntington's Disease Progression

The purpose of our article is to critically assess the role of phosphorylated tau in Huntington's disease (HD) progression and pathogenesis. HD is a fatal and pure genetic disease, characterized by chorea, seizures, involuntary movements, dystonia, cognitive decline, intellectual impairment, and emotional disturbances. HD is caused by expanded polyglutamine (polyQ or CAG) repeats within the exon 1 of the HD gene. HD has an autosomal dominant pattern of inheritance with genetic anticipation. Although the HD gene was discovered 26 years ago, there is no complete understanding of how mutant huntingtin (mHTT) selectively targets medium spiny projection neurons in the basal ganglia of the brain in patients with HD. Several years of intense research revealed that multiple cellular changes are involved in disease process, including transcriptional dysregulation, mitochondrial abnormalities and impaired bioenergetics, defective axonal transport, calcium dyshomeostasis, synaptic damage and caspase, and NMDAR activations. Recent research also revealed that phosphorylated tau and defective GSK-3β signaling are strongly linked to progression of the disease. This article summarizes the recent developments of cellular and pathological changes in disease progression of HD. This article also highlights recent developments in phosphorylated tau and defective GSK-3β signaling and the involvement of calcineurin in HD progression and pathogenesis.

Cofilin, a Master Node Regulating Cytoskeletal Pathogenesis in Alzheimer's Disease

 The defining pathological hallmarks of Alzheimer’s disease (AD) are proteinopathies marked by the amyloid-β (Aβ) peptide and hyperphosphorylated tau. In addition, Hirano bodies and cofilin-actin rods are extensively found in AD brains, both of which are associated with the actin cytoskeleton. The actin-binding protein cofilin known for its actin filament severing, depolymerizing, nucleating, and bundling activities has emerged as a significant player in AD pathogenesis. In this review, we discuss the regulation of cofilin by multiple signaling events impinging on LIM kinase-1 (LIMK1) and/or Slingshot homolog-1 (SSH1) downstream of Aβ. Such pathophysiological signaling pathways impact actin dynamics to regulate synaptic integrity, mitochondrial translocation of cofilin to promote neurotoxicity, and formation of cofilin-actin pathology. Other intracellular signaling proteins, such as β-arrestin, RanBP9, Chronophin, PLD1, and 14-3-3 also impinge on the regulation of cofilin downstream of Aβ. Finally, we discuss the role of activated cofilin as a bridge between actin and microtubule dynamics by displacing tau from microtubules, thereby destabilizing tau-induced microtubule assembly, missorting tau, and promoting tauopathy.