Structural determinants of Tau aggregation inhibitor potency

Disrupting pathologic phase transitions in neurodegeneration

Solid-like protein deposits found in aged and diseased human brains have revealed a relationship between insoluble protein accumulations and the resulting deficits in neurologic function. Clinically diverse neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis, exhibit unique and disease-specific biochemical protein signatures and abnormal protein depositions that often correlate with disease pathogenesis. Recent evidence indicates that many pathologic proteins assemble into liquid-like protein phases through the highly coordinated process of liquid-liquid phase separation. Over the last decade, biomolecular phase transitions have emerged as a fundamental mechanism of cellular organization. Liquid-like condensates organize functionally related biomolecules within the cell, and many neuropathology-associated proteins reside within these dynamic structures. Thus, examining biomolecular phase transitions enhances our understanding of the molecular mechanisms mediating toxicity across diverse neurodegenerative diseases. This Review explores the known mechanisms contributing to aberrant protein phase transitions in neurodegenerative diseases, focusing on tau and TDP-43 proteinopathies and outlining potential therapeutic strategies to regulate these pathologic events.

Reversal of Tau-Dependent Cognitive Decay by Blocking Adenosine A1 Receptors: Comparison of Transgenic Mouse Models with Different Levels of Tauopathy

The accumulation of tau is a hallmark of several neurodegenerative diseases and is associated with neuronal hypoactivity and presynaptic dysfunction. Oral administration of the adenosine A₁ receptor antagonist rolofylline (KW-3902) has previously been shown to reverse spatial memory deficits and to normalize the basic synaptic transmission in a mouse line expressing full-length pro-aggregant tau (Tau^ΔK) at low levels, with late onset of disease. However, the efficacy of treatment remained to be explored for cases of more aggressive tauopathy. Using a combination of behavioral assays, imaging with several PET-tracers, and analysis of brain tissue, we compared the curative reversal of tau pathology by blocking adenosine A1 receptors in three mouse models expressing different types and levels of tau and tau mutants. We show through positron emission tomography using the tracer [¹⁸F]CPFPX (a selective A1 receptor ligand) that intravenous injection of rolofylline effectively blocks A₁ receptors in the brain. Moreover, when administered to Tau^ΔK mice, rolofylline can reverse tau pathology and synaptic decay. The beneficial effects are also observed in a line with more aggressive tau pathology, expressing the amyloidogenic repeat domain of tau (TauRD^ΔK) with higher aggregation propensity. Both models develop a progressive tau pathology with missorting, phosphorylation, accumulation of tau, loss of synapses, and cognitive decline. TauRD^ΔK causes pronounced neurofibrillary tangle assembly concomitant with neuronal death, whereas Tau^ΔK accumulates only to tau pretangles without overt neuronal loss. A third model tested, the rTg4510 line, has a high expression of mutant Tau^P301L and hence a very aggressive phenotype starting at ~3 months of age. This line failed to reverse pathology upon rolofylline treatment, consistent with a higher accumulation of tau-specific PET tracers and inflammation. In conclusion, blocking adenosine A1 receptors by rolofylline can reverse pathology if the pathological potential of tau remains below a threshold value that depends on concentration and aggregation propensity.

Tau-aggregation inhibitors derived from Streptomyces tendae MCCC 1A01534 protect HT22 cells against okadaic acid-induced damage

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by tau aggregating into neurofibrillary tangles. Targeting tau aggregation is one of the most critical strategies for AD treatment and prevention. Herein, a high-throughput screening of tau-aggregation inhibitors was performed by thioflavin T (ThT) fluorescence assay and tauR3 peptides. According to bioactivity-guided isolation, homoprejadomycin (1) was obtained from the marine bacterium Streptomyces tendae MCCC 1A01534. Two new stable derivatives, 2 and 3, were yielded in a one-step reaction. By ThT assay, transmission electron microscopy, and circular dichroism, we demonstrated that the angucyclinones 2 and 3 inhibited tau aggregation and disaggregated tau fibrils. In the presence of 2, native tauR3 peptides maintained the disorder conformation, whereas the tauR3 aggregates reduced β-sheet structures. And compound 2 was confirmed to inhibit the aggregation of full-length 2N4R tau protein. Furthermore, 2 with low cytotoxicity protected HT22 cells from okadaic acid-induced damage by suppressing tau aggregates. These results indicated that 2 was a promising lead structure with tau therapeutic potency for AD treatment.

DJ-1 Molecular Chaperone Activity Depresses Tau Aggregation Propensity through Interaction with Monomers

Tau aggregate-bearing lesions are pathological markers and potential mediators of tauopathic neurodegenerative diseases, including Alzheimer's disease. The molecular chaperone DJ-1 colocalizes with tau pathology in these disorders, but it has been unclear what functional link exists between them. In this study, we examined the consequences of tau/DJ-1 interaction as isolated proteins in vitro. When added to full-length 2N4R tau under aggregation-promoting conditions, DJ-1 inhibited both the rate and extent of filament formation in a concentration-dependent manner. Inhibitory activity was low affinity, did not require ATP, and was not affected by substituting oxidation incompetent missense mutation C106A for wild-type DJ-1. In contrast, missense mutations previously linked to familial Parkinson's disease and loss of α-synuclein chaperone activity, M26I and E64D, displayed diminished tau chaperone activity relative to wild-type DJ-1. Although DJ-1 directly bound the isolated microtubule-binding repeat region of tau protein, exposure of preformed tau seeds to DJ-1 did not diminish seeding activity in a biosensor cell model. These data reveal DJ-1 to be a holdase chaperone capable of engaging tau as a client in addition to α-synuclein. Our findings support a role for DJ-1 as part of an endogenous defense against the aggregation of these intrinsically disordered proteins.

Exploring the inhibitory effects of liquiritigenin against tau fibrillation and related neurotoxicity as a model of preventive care in Alzheimer's disease

Aggregation of tau protein into the form of insoluble amyloid fibrils is linked with Alzheimer's disease. The identification of potential small molecules that can inhibit tau protein from undergoing aggregation has received a great deal of interest, recently. In the present study, the possible inhibitory effects of liquiritigenin as a member of chiral flavanone family on tau amyloid fibrils formation and their resulting neurotoxicity were assessed by different biophysical and cellular assays. The inhibitory effect of the liquiritigenin against tau amyloid formation was investigated using thioflavin T (ThT) and 1-Anilino-8-naphthalene sulfonate (ANS) fluorescence spectroscopy, Congo red (CR) binding assays, transmission electron microscopy (TEM) analysis, and circular dichroism (CD) spectroscopy. Neurotoxicity assays were also performed against neuron-like cells (SH-SY5Y) using 3-(4,5-Dimethylthiazol)-2,5-diphenyltetrazolium bromide (MTT) reduction, reactive oxygen species (ROS), catalase (CAT) and caspase-3 activity measurements. We found that liquiritigenin served as an efficient inhibitor of tau amyloid fibrils formation through prevention of structural transition in tau structure, exposure of hydrophobic patches and their associated neurotoxicity mediated by decrease in the production of ROS and caspase-3 activity and elevation of CAT activity. These data may finally find applications in the development of promising inhibitors against amyloid fibril formation and treatment of Alzheimer's disease.

The structure and phase of tau: from monomer to amyloid filament

Tau is a microtubule-associated protein involved in regulation of assembly and spatial organization of microtubule in neurons. However, in pathological conditions, tau monomers assemble into amyloid filaments characterized by the cross-β structures in a number of neurodegenerative diseases known as tauopathies. In this review, we summarize recent progression on the characterization of structures of tau monomer and filament, as well as the dynamic liquid droplet assembly. Our aim is to reveal how post-translational modifications, amino acid mutations, and interacting molecules modulate the conformational ensemble of tau monomer, and how they accelerate or inhibit tau assembly into aggregates. Structure-based aggregation inhibitor design is also discussed in the context of dynamics and heterogeneity of tau structures.

Pharmacological Modulators of Tau Aggregation and Spreading

Tauopathies are neurodegenerative disorders characterized by the deposition of aggregates composed of abnormal tau protein in the brain. Additionally, misfolded forms of tau can propagate from cell to cell and throughout the brain. This process is thought to lead to the templated misfolding of the native forms of tau, and thereby, to the formation of newer toxic aggregates, thereby propagating the disease. Therefore, modulation of the processes that lead to tau aggregation and spreading is of utmost importance in the fight against tauopathies. In recent years, several molecules have been developed for the modulation of tau aggregation and spreading. In this review, we discuss the processes of tau aggregation and spreading and highlight selected chemicals developed for the modulation of these processes, their usefulness, and putative mechanisms of action. Ultimately, a stronger understanding of the molecular mechanisms involved, and the properties of the substances developed to modulate them, will lead to the development of safer and better strategies for the treatment of tauopathies.

Tau Protein Aggregation in Alzheimer's Disease: Recent Advances in the Development of Novel Therapeutic Agents

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Major research in Alzheimer’s disease (AD) related to disease-modifying agents is concentrated on pharmacological approaches related to diagnostic markers, neurofibrillary tangles and amyloid plaques. Although most studies focus on anti-amyloid strategies, investigations on tau protein have produced significant advances in the modulation of the pathophysiology of several neurodegenerative diseases. Since the discovery of phenothiazines as tau protein aggregation inhibitors (TAGIs), many additional small molecule inhibitors have been discovered and characterized in biological model systems, which exert their interaction effects by covalent and noncovalent means. In this paper, we summarize the latest advances in the discovery and development of tau aggregation inhibitors using a specialized approach in their chemical classes. The design of new TAGIs and their encouraging use in in vivo and clinical trials support their potential therapeutic use in AD.

Toxic Tau Oligomers Modulated by Novel Curcumin Derivatives

The pathological aggregation and accumulation of tau, a microtubule-associated protein, is a common feature amongst more than 18 different neurodegenerative diseases that are collectively known as tauopathies. Recently, it has been demonstrated that the soluble and hydrophobic tau oligomers are highly toxic in vitro due to their capacity towards seeding tau misfolding, thereby propagating the tau pathology seen across different neurodegenerative diseases. Modulating the aggregation state of tau oligomers through the use of small molecules could be a useful therapeutic strategy to target their toxicity, regardless of other factors involved in their formation. In this study, we screened and tested a small library of newly synthesized curcumin derivatives against preformed recombinant tau oligomers. Our results show that the curcumin derivatives affect and modulate the tau oligomer aggregation pathways, converting to a more aggregated non-toxic state as assessed in the human neuroblastoma SH-SY5Y cell line and primary cortical neuron cultures. These results provide insight into tau aggregation and may become a basis for the discovery of new therapeutic agents, as well as advance the diagnostic field for the detection of toxic tau oligomers.

Pathogenic Tau Protein Species: Promising Therapeutic Targets for Ocular Neurodegenerative Diseases

Tau is a microtubule-associated protein, which is highly expressed in the central nervous system as well as ocular neurons and stabilizes microtubule structure. It is a phospho-protein being moderately phosphorylated under physiological conditions but its abnormal hyperphosphorylation or some post-phosphorylation modifications would result in a pathogenic condition, microtubule dissociation, and aggregation. The aggregates can induce neuroinflammation and trigger some pathogenic cascades, leading to neurodegeneration. Taking these together, targeting pathogenic tau employing tau immunotherapy may be a promising therapeutic strategy in fighting with cerebral and ocular neurodegenerative disorders.

The role of annealing and fragmentation in human tau aggregation dynamics

Alzheimer's disease pathogenesis is associated with the conversion of monomeric tau protein into filamentous aggregates. Because both toxicity and prion-like spread of pathogenic tau depend in part on aggregate size, the processes that underlie filament formation and size distribution are of special importance. Here, using a combination of biophysical and computational approaches, we investigated the fibrillation dynamics of the human tau isoform 2N4R. We found that tau filaments engage in a previously uncharacterized secondary process involving end-to-end annealing and that rationalization of empirical aggregation data composed of total protomer concentrations and fibril length distributions requires inclusion of this process along with filament fragmentation. We noted that annealing of 2N4R tau filaments is robust, with an intrinsic association rate constant of a magnitude similar to that mediating monomer addition and consistent with diffusion-mediated protein-protein interactions in the absence of long-range attractive forces. In contrast, secondary nucleation on the surface of tau filaments did not detectably contribute to tau aggregation dynamics. These results indicate that tau filament ends engage in a range of homotypic interactions involving monomers, oligomers, and filaments. They further indicate that, in the case of tau protein, fibril annealing and fragmentation along with primary nucleation and elongation are the major processes controlling filament size distribution.

Azure C Targets and Modulates Toxic Tau Oligomers

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder affecting millions of people worldwide. Therefore, finding effective interventions and therapies is extremely important. AD is one of over 20 different disorders known as tauopathies, characterized by the pathological aggregation and accumulation of tau, a microtubule-associated protein. Tau aggregates are heterogeneous and can be divided into two major groups: large metastable fibrils, including neurofibrillary tangles, and oligomers. The smaller, soluble and dynamic tau oligomers have been shown to be more toxic with more proficient seeding properties for the propagation of tau pathology as compared to the fibrillar Paired Helical Filaments (PHFs). Therefore, developing small molecules that target and interact with toxic tau oligomers can be beneficial to modulate their aggregation pathways and toxicity, preventing progression of the pathology. In this study, we show that Azure C (AC) is capable of modulating tau oligomer aggregation pathways at micromolar concentrations and rescues tau oligomers-induced toxicity in cell culture. We used both biochemical and biophysical in vitro techniques to characterize preformed tau oligomers in the presence and absence of AC. Interestingly, AC prevents toxicity not by disassembling the oligomers but rather by converting them into clusters of aggregates with nontoxic conformation.

Glycogen synthase kinase-3 (GSK-3) activity regulates mRNA methylation in mouse embryonic stem cells

Glycogen synthase kinase-3 (GSK-3) activity regulates multiple signal transduction pathways and is also a key component of the network responsible for maintaining stem cell pluripotency. Genetic deletion of Gsk-3α and Gsk-3β or inhibition of GSK-3 activity via small molecules promotes stem cell pluripotency, yet the mechanism underlying the role for GSK-3 in this process remains ambiguous. Another cellular process that has been shown to affect stem cell pluripotency is mRNA methylation (m⁶A). Here, we describe an intersection between these components, the regulation of m⁶A by GSK-3. We find that protein levels for the RNA demethylase, FTO (fat mass and obesity-associated protein), are elevated in Gsk-3α;Gsk-3β-deficient mouse embryonic stem cells (ESCs). FTO is normally phosphorylated by GSK-3, and MS identified the sites on FTO that are phosphorylated in a GSK-3-dependent fashion. GSK-3 phosphorylation of FTO leads to polyubiquitination, but in Gsk-3 knockout ESCs, that process is impaired, resulting in elevated levels of FTO protein. As a consequence of altered FTO protein levels, mRNAs in Gsk-3 knockout ESCs have 50% less m⁶A than WT ESCs, and m⁶A-Seq analysis reveals the specific mRNAs that have reduced m⁶A modifications. Taken together, we provide the first evidence for how m⁶A demethylation is regulated in mammalian cells and identify a putative novel mechanism by which GSK-3 activity regulates stem cell pluripotency.

Tau peptides and tau mutant protein aggregation inhibition by cationic polyethyleneimine and polyarginine

Tau protein plays a major role in Alzheimer's disease. The tau protein loses its functionality by self-aggregation due to the two six-amino acid sequences VQIVYK and VQIINK of the protein. Hence it is imperative to find therapeutics that could inhibit the self-aggregation of this tau peptide fragments. Here, we study the inhibitory potential of a cationic polymer polyethyleneimine (PEI) and a cationic polypeptide arginine (Arg) on the aggregation of VQIVYK, and GKVQIINKLDL peptides, and tau mutant protein (P301L), found frequently in taupathy. Various characterization methods are employed including thioflavin S, transmission electron microscopy, and dynamic light scattering to study the aggregation/inhibition process in vitro. Results show that PEI and Arg significantly inhibit tau peptides and protein aggregation. The study could be applied to understand tau protein aggregation mechanism in the presence of cationic polymers.

Tau-based therapeutics for Alzheimer's disease: active and passive immunotherapy

Pharmacological manipulation of tau protein in Alzheimer's disease included microtubule-stabilizing agents, tau protein kinase inhibitors, tau aggregation inhibitors, active and passive immunotherapies and, more recently, inhibitors of tau acetylation. Animal studies have shown that both active and passive approaches can remove tau pathology and, in some cases, improve cognitive function. Two active vaccines targeting either nonphosphorylated (AAD-vac1) and phosphorylated tau (ACI-35) have entered Phase I testing. Notwithstanding, the recent discontinuation of the monoclonal antibody RG7345 for Alzheimer's disease, two other antitau antibodies, BMS-986168 and C2N-8E12, are also currently in Phase I testing for progressive supranuclear palsy. After the recent impressive results in animal studies obtained by salsalate, the dimer of salicylic acid, inhibitors of tau acetylation are being actively pursued.

Interactions between Microtubule-Associated Protein Tau (MAPT) and Small Molecules

Tau aggregation is linked to multiple neurodegenerative disorders that are collectively termed tauopathies. Small molecules are powerful probes of the aggregation process, helping to reveal the key steps and serving as diagnostics and reporters. Moreover, some of these small molecules may have potential as therapeutics. This review details how small molecules and chemical biology have helped to elucidate the mechanisms of tau aggregation and how they are being used to detect and prevent tau aggregation. In addition, we comment on how new insights into tau prions are changing the approach to small molecule discovery.

Tau-directed approaches for the treatment of Alzheimer's disease: focus on leuco-methylthioninium

Small molecular weight compounds able to inhibit formation of tau oligomers and fibrils have already been tested for Alzheimer's disease (AD) treatment. The most advanced tau aggregation inhibitor (TAI) is methylthioninium (MT), a drug existing in equilibrium between a reduced (leuco-methylthioninium) and oxidized form (MT(+)). MT chloride (also known as methylene blue) was investigated in a 24-week Phase II study in 321 mild-to-moderate AD patients at the doses of 69, 138, and 228 mg/day. This trial failed to show significant positive effects of MT in the overall patient population. The dose of 138 mg/day showed potential benefits on cognitive performance of moderately affected patients and cerebral blood flow in mildly affected patients. A follow-up compound (TRx0237) claimed to be more bioavailable and less toxic than MT, is now being developed. Phase III clinical trials on this novel TAI in AD and in the behavioral variant of frontotemporal dementia are underway.

Expression and purification of tau protein and its frontotemporal dementia variants using a cleavable histidine tag

Recombinant tau protein is widely used to study the biochemical, cellular and pathological aspects of tauopathies, including Alzheimer's disease and frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTPD-17). Pure tau in high yield is a requirement for in vitro evaluation of the protein's physiological and toxic functions. However, the preparation of recombinant tau is complicated by the protein's propensity to aggregate and form truncation products, necessitating the use of multiple, time-consuming purification methods. In this study, we investigated parameters that influence the expression of wild type and FTPD-17 pathogenic tau, in an attempt to identify ways to maximise expression yield. Here, we report on the influence of the choice of host strain, induction temperature, duration of induction, and media supplementation with glucose on tau expression in Escherichia coli. We also describe a straightforward process to purify the expressed tau proteins using immobilised metal affinity chromatography, with favourable yields over previous reports. An advantage of the described method is that it enables high yield production of functional oligomeric and monomeric tau, both of which can be used to study the biochemical, physiological and toxic properties of the protein.

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Factors influencing the expression of wild type and FTPD-17 pathogenic tau were investigated in an attempt to maximise yield.

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Soluble monomeric tau expression level was highest at 37 °C compared to 20 °C and 25 °C.

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Media supplementation with 0.2% glucose did not significantly influence monomeric tau expression levels.

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Circular dichroism confirmed that the purified tau proteins were mostly unfolded, with negative peaks around 200 nm.

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The circular dichroism peaks shifted towards 220 nm following the preparation of Alzheimer-like filaments, suggesting secondary structure re-orientation towards β-sheets.

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The tau proteins adopted classical fibrillisation similar to filaments isolated from the brains of Alzheimer's disease patients.

Tau-Centric Targets and Drugs in Clinical Development for the Treatment of Alzheimer's Disease

The failure of several Phase II/III clinical trials in Alzheimer's disease (AD) with drugs targeting β-amyloid accumulation in the brain fuelled an increasing interest in alternative treatments against tau pathology, including approaches targeting tau phosphatases/kinases, active and passive immunization, and anti-tau aggregation. The most advanced tau aggregation inhibitor (TAI) is methylthioninium (MT), a drug existing in equilibrium between a reduced (leuco-methylthioninium) and oxidized form (MT⁺). MT chloride (methylene blue) was investigated in a 24-week Phase II clinical trial in 321 patients with mild to moderate AD that failed to show significant positive effects in mild AD patients, although long-term observations (50 weeks) and biomarker studies suggested possible benefit. The dose of 138 mg/day showed potential benefits on cognitive performance of moderately affected AD patients and cerebral blood flow in mildly affected patients. Further clinical evidence will come from the large ongoing Phase III trials for the treatment of AD and the behavioral variant of frontotemporal dementia on a new form of this TAI, more bioavailable and less toxic at higher doses, called TRx0237. More recently, inhibitors of tau acetylation are being actively pursued based on impressive results in animal studies obtained by salsalate, a clinically used derivative of salicylic acid.

A Fragment-Based Method of Creating Small-Molecule Libraries to Target the Aggregation of Intrinsically Disordered Proteins

The aggregation process of intrinsically disordered proteins (IDPs) has been associated with a wide range of neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. Currently, however, no drug in clinical use targets IDP aggregation. To facilitate drug discovery programs in this important and challenging area, we describe a fragment-based approach of generating small-molecule libraries that target specific IDPs. The method is based on the use of molecular fragments extracted from compounds reported in the literature to inhibit of the aggregation of IDPs. These fragments are used to screen existing large generic libraries of small molecules to form smaller libraries specific for given IDPs. We illustrate this approach by describing three distinct small-molecule libraries to target, Aβ, tau, and α-synuclein, which are three IDPs implicated in Alzheimer's and Parkinson's diseases. The strategy described here offers novel opportunities for the identification of effective molecular scaffolds for drug discovery for neurodegenerative disorders and to provide insights into the mechanism of small-molecule binding to IDPs.

Analyzing Tau Aggregation with Electron Microscopy

Conversion of monomeric tau protein into filamentous aggregates is a defining event in the pathogenesis of Alzheimer's disease. To gain insight into disease pathogenesis, the mechanisms that trigger and mediate tau aggregation are under intense investigation. Characterization efforts have relied primarily on recombinant tau protein preparations and high-throughput solution-based detection methods such as thioflavin-dye fluorescence and laser-light-scattering spectroscopies. Transmission electron microscopy (TEM) is a static imaging tool that complements these approaches by detecting individual tau filaments at nanometer resolution. In doing so, it can provide unique insight into the quality, quantity, and composition of synthetic tau filament populations. Here we describe protocols for analysis of tau filament populations by TEM for purposes of dissecting aggregation mechanism.

Inhibitory effect of corcin on aggregation of 1N/4R human tau protein in vitro

OBJECTIVES

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder. One of the hallmarks of AD is an abnormal accumulation of fibril forms of tau protein which is known as a microtubule associated protein. In this regard, inhibition of tau aggregation has been documented to be a potent therapeutic approach in AD and tauopathies. Unfortunately, the available synthetic drugs have modest beneficial efficacy with several side effects. Therefore, pipeline drugs from natural sources with anti-aggregation properties can be useful in the prevention and treatment of AD. Among medicinal plants, saffron (Crocus sativus, L.), as a traditional herbal medicine has different pharmacological properties and can be used as treatment for several nervous system impairment including depression and dementia. Crocin as a major constituent of saffron is the glycosylated form of crocetin.

MATERIALS AND METHODS

In this study, we investigated the inhibitory effect of crocin on aggregation of recombinant human tau protein 1N/4R isoform using biochemical methods and cell culture.

RESULTS

Results revealed that tau protein under the fibrillation condition and in the presence of crocin had enough stability with low tendency for aggregation. Crocin inhibited tau aggregation with IC50 of 100 µg/ml. Furthermore, transmission electron microscopy images confirmed that crocin could suppress the formation of tau protein filaments.

CONCLUSION

Inhibitory effect of crocin could be related to its interference with nucleation phase that led to increases in monomer species of tau protein. Based on our results, crocin is recommended as a proper candidate to be used in AD treatment.

Advances in therapeutics for neurodegenerative tauopathies: moving toward the specific targeting of the most toxic tau species

Neurodegenerative disease is one of the greatest health concerns today and with no effective treatment in sight, it is crucial that researchers find a safe and successful therapeutic. While neurofibrillary tangles are considered the primary tauopathy hallmark, more evidence continues to come to light to suggest that soluble, intermediate tau aggregates--tau oligomers--are the most toxic species in disease. These intermediate tau species may also be responsible for the spread of pathology, suggesting that oligomeric tau may be the best therapeutic target. Here, we summarize results for the modulation of tau by molecular chaperones, small molecules and aggregation inhibitors, post-translational modifications, immunotherapy, other techniques, and future directions.

Use of genetically modified mesenchymal stem cells to treat neurodegenerative diseases

The transplantation of mesenchymal stem cells (MSCs) for treating neurodegenerative disorders has received growing attention recently because these cells are readily available, easily expanded in culture, and when transplanted, survive for relatively long periods of time. Given that such transplants have been shown to be safe in a variety of applications, in addition to recent findings that MSCs have useful immunomodulatory and chemotactic properties, the use of these cells as vehicles for delivering or producing beneficial proteins for therapeutic purposes has been the focus of several labs. In our lab, the use of genetic modified MSCs to release neurotrophic factors for the treatment of neurodegenerative diseases is of particular interest. Specifically, glial cell-derived neurotrophic factor (GDNF), nerve growth factor (NGF), and brain derived neurotrophic factor (BDNF) have been recognized as therapeutic trophic factors for Parkinson's, Alzheimer's and Huntington's diseases, respectively. The aim of this literature review is to provide insights into: (1) the inherent properties of MSCs as a platform for neurotrophic factor delivery; (2) the molecular tools available for genetic manipulation of MSCs; (3) the rationale for utilizing various neurotrophic factors for particular neurodegenerative diseases; and (4) the clinical challenges of utilizing genetically modified MSCs.