Tau deletion impairs intracellular β-amyloid-42 clearance and leads to more extracellular plaque deposition in gene transfer models

A nonhuman primate model with Alzheimer's disease-like pathology induced by hippocampal overexpression of human tau

BACKGROUND

Alzheimer's disease (AD) is one of the most burdening diseases of the century with no disease-modifying treatment at this time. Nonhuman primates (NHPs) share genetic, anatomical, and physiological similarities with humans, making them ideal model animals for investigating the pathogenesis of AD and potential therapies. However, the use of NHPs in AD research has been hindered by the paucity of AD monkey models due to their long generation time, ethical considerations, and technical challenges in genetically modifying monkeys.

METHODS

Here, we developed an AD-like NHP model by overexpressing human tau in the bilateral hippocampi of adult rhesus macaque monkeys. We evaluated the pathological features of these monkeys with immunostaining, Nissl staining, cerebrospinal fluid (CSF) analysis, magnetic resonance imaging (MRI), positron emission tomography (PET), and behavioural tests.

RESULTS

We demonstrated that after hippocampal overexpression of tau protein, these monkeys displayed multiple pathological features of AD, including 3-repeat (3R)/4-repeat (4R) tau accumulation, tau hyperphosphorylation, tau propagation, neuronal loss, hippocampal atrophy, neuroinflammation, Aβ clearance deficits, blood vessel damage, and cognitive decline. More interestingly, the accumulation of both 3R and 4R tau is specific to NHPs but not found in adult rodents.

CONCLUSIONS

This work establishes a tau-induced AD-like NHP model with many key pathological and behavioural features of AD. In addition, our model may potentially become one of the AD NHP models adopted by researchers worldwide since it can be generated within 2 ~ 3 months through a single injection of AAVs into the monkey brains. Hence, our model NHPs may facilitate mechanistic studies and therapeutic treatments for AD.

Inhibition of discoidin domain receptor (DDR)-1 with nilotinib alters CSF miRNAs and is associated with reduced inflammation and vascular fibrosis in Alzheimer's disease

Discoidin Domain Receptor (DDR)-1 is activated by collagen. Nilotinib is a tyrosine kinase inhibitor that is FDA-approved for leukemia and potently inhibits DDR-1. Individuals diagnosed with mild-moderate Alzheimer's disease (AD) treated with nilotinib (versus placebo) for 12 months showed reduction of amyloid plaque and cerebrospinal fluid (CSF) amyloid, and attenuation of hippocampal volume loss. However, the mechanisms are unclear. Here, we explored unbiased next generation whole genome miRNA sequencing from AD patients CSF and miRNAs were matched with their corresponding mRNAs using gene ontology. Changes in CSF miRNAs were confirmed via measurement of CSF DDR1 activity and plasma levels of AD biomarkers. Approximately 1050 miRNAs are detected in the CSF but only 17 miRNAs are specifically altered between baseline and 12-month treatment with nilotinib versus placebo. Treatment with nilotinib significantly reduces collagen and DDR1 gene expression (upregulated in AD brain), in association with inhibition of CSF DDR1. Pro-inflammatory cytokines, including interleukins and chemokines are reduced along with caspase-3 gene expression. Specific genes that indicate vascular fibrosis, e.g., collagen, Transforming Growth Factors (TGFs) and Tissue Inhibitors of Metalloproteases (TIMPs) are altered by DDR1 inhibition with nilotinib. Specific changes in vesicular transport, including the neurotransmitters dopamine and acetylcholine, and autophagy genes, including ATGs, indicate facilitation of autophagic flux and cellular trafficking. Inhibition of DDR1 with nilotinib may be a safe and effective adjunct treatment strategy involving an oral drug that enters the CNS and adequately engages its target. DDR1 inhibition with nilotinib exhibits multi-modal effects not only on amyloid and tau clearance but also on anti-inflammatory markers that may reduce cerebrovascular fibrosis.

Circular RNAs: New players involved in the regulation of cognition and cognitive diseases

Circular RNAs (circRNAs), a type of covalently closed endogenous single-stranded RNA, have been regarded as the byproducts of the aberrant splicing of genes without any biological functions. Recently, with the development of high-throughput sequencing and bioinformatics, thousands of circRNAs and their differential biological functions have been identified. Except for the great advances in identifying circRNA roles in tumor progression, diagnosis, and treatment, accumulated evidence shows that circRNAs are enriched in the brain, especially in the synapse, and dynamically change with the development or aging of organisms. Because of the specific roles of synapses in higher-order cognitive functions, circRNAs may not only participate in cognitive functions in normal physiological conditions but also lead to cognition-related diseases after abnormal regulation of their expression or location. Thus, in this review, we summarized the progress of studies looking at the role of circRNA in cognitive function, as well as their involvement in the occurrence, development, prognosis, and treatment of cognitive-related diseases, including autism, depression, and Alzheimer's diseases.

FDA-Approved Kinase Inhibitors in Preclinical and Clinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases. We previously developed a new concept termed "Aberrant Cell Cycle Diseases" (ACCD), revealing that these two diseases share a common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncogene activation and tumor suppressor inactivation, which are hallmarks of both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase inhibition, tumor suppressor elevation) can be leveraged for neurological treatments. The United States Food and Drug Administration (US FDA) has so far approved 74 kinase inhibitors, with numerous other kinase inhibitors in clinical trials, mostly for the treatment of cancers. In contrast, there are dire unmet needs of FDA-approved drugs for neurological treatments, such as Alzheimer's disease (AD), intracerebral hemorrhage (ICH), ischemic stroke (IS), traumatic brain injury (TBI), and others. In this review, we list these 74 FDA-approved kinase-targeted drugs and identify those that have been reported in preclinical and/or clinical trials for neurological disorders, with a purpose of discussing the feasibility and applicability of leveraging these cancer drugs (FDA-approved kinase inhibitors) for neurological treatments.

Amyloid Cascade Hypothesis for the Treatment of Alzheimer's Disease: Progress and Challenges

The amyloid cascade hypothesis has always been a research focus in the therapeutic field of Alzheimer's disease (AD) since it was put forward. Numerous researchers attempted to find drugs for AD treatment based on this hypothesis. To promote the research of anti-AD drugs development, the current hypothesis and pathogenesis were reviewed with expounding of β-amyloid generation from its precursor protein and related transformations. Meanwhile, the present drug development strategies aimed at each stage in this hypothesis were also summarized. Several strategies especially immunotherapy showed the optimistic results in clinical trials, but only a small percentage of them eventually succeeded. In this review, we also tried to point out some common problems of drug development in preclinical and clinical studies which might be settled through multidisciplinary cooperation as well as the understanding that reinforces the amyloid cascade hypothesis.

Enhancing autophagy in Alzheimer's disease through drug repositioning

Alzheimer's disease (AD) is one of the biggest human health threats due to increases in aging of the global population. Unfortunately, drugs for treating AD have been largely ineffective. Interestingly, downregulation of macroautophagy (autophagy) plays an essential role in AD pathogenesis. Therefore, targeting autophagy has drawn considerable attention as a therapeutic approach for the treatment of AD. However, developing new therapeutics is time-consuming and requires huge investments. One of the strategies currently under consideration for many diseases is "drug repositioning" or "drug repurposing". In this comprehensive review, we have provided an overview of the impact of autophagy on AD pathophysiology, reviewed the therapeutics that upregulate autophagy and are currently used in the treatment of other diseases, including cancers, and evaluated their repurposing as a possible treatment option for AD. In addition, we discussed the potential of applying nano-drug delivery to neurodegenerative diseases, such as AD, to overcome the challenge of crossing the blood brain barrier and specifically target molecules/pathways of interest with minimal side effects.

Treatment of Dementia With Bosutinib: An Open-Label Study of a Tyrosine Kinase Inhibitor

OBJECTIVE

The pursuit of an effective therapeutic intervention for dementia has inspired interest in the class of medications known as tyrosine kinase inhibitors such as bosutinib.

METHODS

Thirty-one patients with probable Alzheimer dementia or Parkinson spectrum disorder with dementia completed 12 months of bosutinib therapy and an additional 12 months of follow-up. The Clinical Dementia Rating scale (as estimated by the Quick Dementia Rating System [QDRS]) was the primary cognitive status outcome measure. Secondary outcome measures included the Repeatable Battery Assessment of Neuropsychological Status (RBANS) and the Montreal Cognitive Assessment. Cox regression methods were used to compare results with population-based estimates of cognitive decline.

RESULTS

The present article reports on cognitive outcomes obtained at 12 months for 31 participants and up to 24 months for a 16-participant subset. Safety and tolerability of bosutinib were confirmed among the study population (Mage = 73.7 years, SDage = 14 years). Bosutinib was associated with less worsening in Clinical Dementia Rating (CDR) scores (hazard ratio = -0.62, p < 0.001, 95% confidence interval [CI]: -1.02 to -0.30) and less decline in RBANS performance (hazard ratio = -3.42, p < 0.001, 95% CI: -3.59 to -3.72) during the year of treatment than population-based estimates of decline. In the 24-month follow-up, wherein 16 patients were observed after 1 year postintervention, 31.2% of participants exhibited worsened CDR levels compared with their 12-month performances.

CONCLUSIONS

Results support an overall positive outcome after 1 year of bosutinib. Future studies should explore the relationship between tyrosine kinases and neurodegenerative pathology as well as related avenues of treatment.

Regulatory Role of Ubiquitin Specific Protease-13 (USP13) in Misfolded Protein Clearance in Neurodegenerative Diseases

Ubiquitin Specific Protease (USP)-13 is a de-ubiquitinase member of the cysteine-dependent protease superfamily that cleaves ubiquitin off protein substrates to reverse ubiquitin-mediated protein degradation. Several findings implicate USPs in neurodegeneration. Ubiquitin targets proteins to major degradation pathways, including the proteasome and the lysosome. In melanoma cells, USP13 regulates the degradation of several proteins primarily via ubiquitination and de-ubiquitination. However, the significance of USP13 in regulating protein clearance in neurodegeneration is largely unknown. This mini-review summarizes the most recent evidence pertaining to the role of USP13 in protein clearance via autophagy and the proteasome in neurodegenerative diseases.

Disrupted ubiquitin proteasome system underlying tau accumulation in Alzheimer's disease

Accumulation of phosphorylated tau (p-tau) has long been an underappreciated hallmark of Alzheimer's disease. Tau is one of the major components of microtubule networks in neurons, and its abnormal phosphorylation and aggregation are closely related to the impairment of axonal transport. Abnormalities in axonal transport can impede autophagy in neurons, interrupting the autophagic clearance of amyloid beta. The ubiquitin proteasome system (UPS) maintains intracellular proteostasis by degrading abnormal or redundant proteins. Ever-mounting evidence suggests that UPS deficits contribute to p-tau accumulation. And targeting UPS attenuates tau pathology. This review endeavors to exam the potential role of UPS in p-tau aggregation, and how pathogenic tau may inflict other abnormalities such as amyloid beta accumulation in Alzheimer's disease.

Long-Term Safety and Clinical Effects of Nilotinib in Parkinson's Disease

BACKGROUND

Nilotinib is US Food and Drug Administration-approved for leukemia, and this open-label study investigated the safety, tolerability, and potential clinical effects of nilotinib in medically optimized patients with Parkinson's disease.

OBJECTIVES

Safety and tolerability were the primary objectives, and clinical outcomes were exploratory.

METHODS

A total of 63 patients completed a 15-month phase 2, double-blind, placebo-controlled study and were rerandomized 1:1 into an open-label study of nilotinib 150 mg versus 300 mg for 12 months.

RESULTS

Nilotinib was safe and tolerated, and no adverse effects seemed to be related to the drug, and no differences in adverse events were observed between groups. Exploratory clinical outcomes showed that nilotinib 300 mg was remarkably stable from baseline to 27 months using partial and total Unified Parkinson's Disease Scale (UPDRS). Nilotinib 150 mg versus 300 mg, significantly declined using partial or the sum of UPDRS Parts I and II. There was no significant difference in nilotinib 150 mg versus 300 mg using UPDRS Part III (on levodopa) and total UPDRS Parts I to III. Subgroup analysis showed that late-start nilotinib 150 mg significantly worsened using the sum of UPDRS Parts II + III and total UPDRS Parts I to III compared with late-start nilotinib 300 mg. Quality of life using the Parkinson's Disease Questionnaire in nilotinib 150 mg significantly declined between 15 and 27 months compared with nilotinib 300 mg, and there was no change in cognition using the Montreal Cognitive Assessment between groups.

CONCLUSIONS

This study provides evidence that nilotinib is safe and tolerated in Parkinson's disease. The exploratory clinical data will inform an adequately powered larger study to evaluate the efficacy of nilotinib 300 mg in Parkinson's disease. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Traditional Chinese medicine compounds regulate autophagy for treating neurodegenerative disease: A mechanism review

Neurodegenerative diseases (NDs) are common chronic diseases related to progressive damage of the nervous system. Globally, the number of people with an ND is dramatically increasing consistent with the fast aging of society and one of the common features of NDs is the abnormal aggregation of diverse proteins. Autophagy is the main process by which misfolded proteins and damaged organelles are removed from cells. It has been found that the impairment of autophagy is associated with many NDs, suggesting that autophagy has a vital role in the neurodegeneration process. Recently, more and more studies have reported that autophagy inducers display a protective role in different ND experimental models, suggesting that enhancement of autophagy could be a potential therapy for NDs. In this review, the evidence for beneficial effects of traditional Chinese medicine (TCM) regulate autophagy in the models of Alzheimer's disease (AD), Parkinson's disease (PD), and other NDs are presented and common autophagy-related mechanisms are identified. The results demonstrate that TCM which regulate autophagy are potential therapeutic candidates for ND treatment.

Nilotinib Effects on Safety, Tolerability, and Biomarkers in Alzheimer's Disease

OBJECTIVE

Preclinical evidence with nilotinib, a US Food and Drug Administration (FDA)-approved drug for leukemia, indicates improvement in Alzheimer's disease phenotypes. We investigated whether nilotinib is safe, and detectable in cerebrospinal fluid, and alters biomarkers and clinical decline in Alzheimer's disease.

METHODS

This single-center, phase 2, randomized, double-blind, placebo-controlled study investigated the safety, tolerability, and pharmacokinetics of nilotinib, and measured biomarkers in participants with mild to moderate dementia due to Alzheimer's disease. The diagnosis was supported by cerebrospinal fluid or amyloid positron emission tomography biomarkers. Nilotinib 150 mg versus matching placebo was taken orally once daily for 26 weeks followed by nilotinib 300 mg versus placebo for another 26 weeks.

RESULTS

Of the 37 individuals enrolled, 27 were women and the mean (SD) age was 70.7 (6.48) years. Nilotinib was well-tolerated, although more adverse events, particularly mood swings, were noted with the 300 mg dose. In the nilotinib group, central nervous system (CNS) amyloid burden was significantly reduced in the frontal lobe compared to the placebo group. Cerebrospinal fluid Aβ40 was reduced at 6 months and Aβ42 was reduced at 12 months in the nilotinib group compared to the placebo. Hippocampal volume loss was attenuated (-27%) at 12 months and phospho-tau-181 was reduced at 6 months and 12 months in the nilotinib group.

INTERPRETATION

Nilotinib is safe and achieves pharmacologically relevant cerebrospinal fluid concentrations. Biomarkers of disease were altered in response to nilotinib treatment. These data support a larger, longer, multicenter study to determine the safety and efficacy of nilotinib in Alzheimer's disease. ANN NEUROL 2020 ANN NEUROL 2020;88:183-194.

Exploring the bi-directional relationship between autophagy and Alzheimer's disease

Alzheimer's disease (AD) is characterized by β-amyloid (Aβ) deposition and Tau phosphorylation, in which its pathogenesis has not been cleared so far. The metabolism of Aβ and Tau is critically affected by the autophagy. Abnormal autophagy is thought to be involved in the pathogenesis of AD, regulating autophagy may become a new strategy for AD treatment. In the early stage of AD, the presence of Aβ and Tau can induce autophagy to promote their clearance by means of mTOR-dependent and independent manners. As AD progress, the autophagy goes aberrant. As a result, Aβ and Tau generate continually, which aggravates both autophagy dysfunction and AD. Besides, several related genes and proteins of AD can also adapt autophagy to make an effect on the AD development. There seems to be a bi-directional relationship between AD pathology and autophagy. At present, this article reviews this relationship from these aspects: (a) the signaling pathways of regulating autophagy; (b) the relationships between the autophagy and the processing of Aβ; (c) Aβ and Tau cause autophagy dysfunction; (d) normal autophagy promotes the clearance of Aβ and Tau; (e) the relationships between the autophagy and both genes and proteins related to AD: TFEB, miRNAs, Beclin-1, Presenilin, and Nrf2; and (f) the small molecules regulating autophagy on AD therapy. All of the above may help to further elucidate the pathogenesis of AD and provide a theoretical basis for clinical treatment of AD.

Ubiquitin specific protease-13 independently regulates parkin ubiquitination and alpha-synuclein clearance in alpha-synucleinopathies

Ubiquitin specific proteases (USPs) are de-ubiquitinases (DUBs) that control protein ubiquitination cycle. The role of DUBs is poorly understood in neurodegenerative diseases. We found that USP13 is overexpressed in post-mortem Parkinson's disease (PD) brains. We investigated whether changes in USP13 levels can affect two molecules, parkin and alpha-synuclein, that are implicated in PD pathogenesis. Parkin is an E3 ubiquitin ligase that is regulated by ubiquitination and targets certain proteins for degradation, and alpha-synuclein may be ubiquitinated and recycled in the normal brain. We found that USP13 independently regulates parkin and alpha-synuclein ubiquitination in models of alpha-synucleinopathies. USP13 shRNA knockdown increases alpha-synuclein ubiquitination and clearance, in a parkin-independent manner. Furthermore, USP13 overexpression counteracts the effects of a tyrosine kinase inhibitor, Nilotinib, while USP13 knockdown facilitates Nilotinib effects on alpha-synculein clearance, suggesting that alpha-synuclein ubiquitnation is important for its clearance. These studies provide novel evidence of USP13 effects on parkin and alpha-synuclein metabolism and suggest that USP13 is a potential therapeutic target in the alpha-synucleinopathies.

Pharmacokinetics and pharmacodynamics of a single dose Nilotinib in individuals with Parkinson's disease

Nilotinib is a broad-based tyrosine kinase inhibitor with the highest affinity to inhibit Abelson (c-Abl) and discoidin domain receptors (DDR1/2). Preclinical evidence indicates that Nilotinib reduces the level of brain alpha-synuclein and attenuates inflammation in models of Parkinson's disease (PD). We previously showed that Nilotinib penetrates the blood-brain barrier (BBB) and potentially improves clinical outcomes in individuals with PD and dementia with Lewy bodies (DLB). We performed a physiologically based population pharmacokinetic/pharmacodynamic (popPK/PD) study to determine the effects of Nilotinib in a cohort of 75 PD participants. Participants were randomized (1:1:1:1:1) into five groups (n = 15) and received open-label random single dose (RSD) 150:200:300:400 mg Nilotinib vs placebo. Plasma and cerebrospinal fluid (CSF) were collected at 1, 2, 3, and 4 hours after Nilotinib administration. The results show that Nilotinib enters the brain in a dose-independent manner and 200 mg Nilotinib increases the level of 3,4-Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), suggesting alteration to dopamine metabolism. Nilotinib significantly reduces plasma total alpha-synuclein and appears to reduce CSF oligomeric: total alpha-synuclein ratio. Furthermore, Nilotinib significantly increases the CSF level of triggering receptors on myeloid cells (TREM)-2, suggesting an anti-inflammatory effect. Taken together, 200 mg Nilotinib appears to be an optimal single dose that concurrently reduces inflammation and engages surrogate disease biomarkers, including dopamine metabolism and alpha-synuclein.

Sulforaphane metabolites inhibit migration and invasion via microtubule-mediated Claudins dysfunction or inhibition of autolysosome formation in human non-small cell lung cancer cells

Both sulforaphane-cysteine (SFN-Cys) and sulforaphane-N-acetyl-l-cysteine (SFN-NAC) inhibited cancer migration and invasion, but the underlying mechanisms were not clear. Here we uncovered via tissue microarray assay that high expression of invasion-associated Claudin-5 was correlated to malignant grades in human non-small cell lung cancer (NSCLC) cells. Further, SFN-Cys (10 µM) induced the accumulated phosphorylation of ERK1/2, leading to downregulation of Claudin-5 and upregulation of Claudin-7, and the decrease of Claudin-1 in SK-1 cells and increase of Claudin-1 in A549 cells; knockdown of Claudin-5 significantly reduced invasion, whereas knockdown of Claudin-7 increased invasion; knockdown of Claudin-1 reduced invasion in SK-1 cells, whereas it increased invasion in A549 cells, indicating that SFN-Cys regulated Claudins and inhibited invasion depending on Claudin isotypes and cell types. Furthermore, immunofluorescence staining showed that SFN-Cys triggered microtubule disruption and knockdown of α-tubulin downregulated Claudin-1, 5, and 7, and inhibited migration and invasion, indicating that microtubule disruption contributed to invasive inhibition. Co-immunoprecipitation and confocal microscopy observation showed that SFN-Cys lowered the interaction between α-tubulin and Claudin-1 or 5, or 7. Meanwhile, Western blotting and immunofluorescence staining showed that SFN-NAC (15 µM) downregulated α-tubulin resulting in microtubule disruption; knockdown of α-tubulin increased SFN-NAC-induced LC3 II accumulation in SK-1 cells. Combined with the inhibitor of autolysosome formation, Bafilomycin A1 (100 nM), SFN-NAC inhibited invasion via accumulating LC3 II and blocking formation of autolysosome. Further, SFN-NAC upregulated microtubule-stabilizing protein Tau; knockdown of Tau reduced LC3 II/LC3 I inhibiting migration and invasion. These results indicated that SFN-Cys inhibited invasion via microtubule-mediated Claudins dysfunction, but SFN-NAC inhibited invasion via microtubule-mediated inhibition of autolysosome formation in human NSCLC cells.

Ubiquitin Specific Protease 13 Regulates Tau Accumulation and Clearance in Models of Alzheimer's Disease

Ubiquitin Specific Protease-13 (USP13) is a de-ubiquinating enzyme that regulates protein ubiquitination and clearance. The role of USP13 is largely unknown in neurodegeneration. In this study we aim to demonstrate whether tau accumulation and/or clearance depends on ubiquitination/de-ubiquitination via USP-13. We used transgenic animal models of human amyloid precursor protein (APP) or P301L tau mutations and genetically knocked-down USP13 expression via shRNA to determine USP13 effects on tau ubiquitination and levels. We found a two-fold increase of USP13 levels in postmortem Alzheimer's disease (AD) brains. USP13 knockdown significantly increased the activity of the 20S proteasome and reduced the levels of hyper-phosphorylated tau (p-tau) in primary cortical neurons. USP13 knockdown also reduced the levels of amyloid and increased p-tau ubiquitination and clearance in transgenic animal models that overexpress murine tau as a result of the expression of familial APP mutations (TgAPP) and the human mutant P301L tau (rTg4510), respectively. Clearance of p-tau appears to be mediated by autophagy in these animal models. Taken together, these data suggest that USP13 knockdown reduces p-tau accumulation via regulation of ubiquitination/de-ubiquitination and mediates its clearance via autophagy and/or the proteasome. These results suggest that USP13 inhibition may be a therapeutic strategy to reduce accumulation of plaques and toxic p-tau in AD and human tauopathies.

KIT as a therapeutic target for non-oncological diseases

KIT is a receptor tyrosine kinase that after binding to its ligand stem cell factor activates signaling cascades linked to biological processes such as proliferation, differentiation, migration and cell survival. Based on studies performed on SCF and/or KIT mutant animals that presented anemia, sterility, and/or pigmentation disorders, KIT signaling was mainly considered to be involved in the regulation of hematopoiesis, gametogenesis, and melanogenesis. More recently, novel animal models and ameliorated cellular and molecular techniques have led to the discovery of a widen repertoire of tissue compartments and functions that are being modulated by KIT. This is the case for the lung, heart, nervous system, gastrointestinal tract, pancreas, kidney, liver, and bone. For this reason, the tyrosine kinase inhibitors that were originally developed for the treatment of hemato-oncological diseases are being currently investigated for the treatment of non-oncological disorders such as asthma, rheumatoid arthritis, and alzheimer's disease, among others. The beneficial effects of some of these tyrosine kinase inhibitors have been proven to depend on KIT inhibition. This review will focus on KIT expression and regulation in healthy and pathologic conditions other than cancer. Moreover, advances in the development of anti-KIT therapies, including tyrosine kinase inhibitors, and their application will be discussed.

Tau clearance improves astrocytic function and brain glutamate-glutamine cycle

Tau hyperphosphorylation is a critical factor in neurodegenerative diseases, including dementia and Parkinsonism. Existing animal models of tauopathies express tau in neurons within the forebrain and do not often show tau accumulation in the brainstem and astrocytes. This study aims to understand the effects of differential regional expression of tau on neurotransmitter balance in the brain. To obtain an animal model that expresses tau in the brainstem, we bred hemizygous mice that express P301L tau (TauP301L) and detected hyper-phosphorylated tau (p-tau) predominantly in the hippocampus, cortex, brainstem and thalamus. We previously demonstrated that TauP301L mice [26] express tau under the control of a prion promoter in both neurons and astrocytes, reminiscent of human tauopathies. We treated TauP301L mice with tyrosine kinase inhibitors (TKIs) to determine the effects of tau clearance on neurotransmitter balance and astrocytic function. ¹³C/¹H MRS reveals astrocytic dysfunction via reduced glial aspartate and impaired glutamate-glutamine cycle. An increase in glutamate and GABA and decrease in glutamine were observed in homozygous mice compared to hemizygous and control littermates. Daily treatment with TKIs, nilotinib or bosutinib led to p-tau clearance via autophagy and reversal of neurotransmitter imbalance. These data suggest that accumulation of p-tau in the brainstem does not alter dopamine metabolism but may trigger glutamate toxicity and astrocytic dysfunction in the TauP301L mouse. TKIs reverse tau effects via reversal of neurotransmitter imbalance.

Two novel blood-based biomarker candidates measuring degradation of tau are associated with dementia: A prospective study

BACKGROUND

Truncated tau appears to be specifically related to disease pathology and recent studies have shown the presence and elevation of several truncated tau species in Cerebrospinal fluid (CSF) of subjects with Alzheimer's disease (AD); however, the relevance of truncated Tau measurements in blood is still being studied.

OBJECTIVE

The aim of the current study was to assess the longitudinal associations between baseline levels of two novel blood biomarker candidates measuring truncated tau, Tau-A and Tau-C, and the risk of incident dementia and AD in elderly women.

METHODS

Using solid phase competitive ELISA, two tau fragments were detected in serum of 5,309 women from the Prospective Epidemiological Risk Factor study. The study was an observational, prospective study of Danish postmenopausal women. Subjects were followed with registry-linkage for up to 15 years (median follow-up time 13.7 years). Cox regression was used to assess the utility of the biomarker candidates in relation to dementia and AD.

RESULTS

High levels of Tau-A and Tau-C (above the median) in blood were associated with lower risk of dementia and AD (Tau-A: Dementia HR[95% CI] = 0.85[0.70-1.04]; AD 0.71[0.52-0.98] and Tau-C: Dementia 0.84[0.70-1.00]; AD 0.78[0.60-1.03]). Tau-C gave a very modest increase in the AUC in a 5-year prediction horizon as compared to a reference model with age and education, while a combination of the two did not improve their predictive capacity.

CONCLUSIONS

Measurement of tau in serum is feasible. The serological tau turnover profile may be related to the diagnosis and development of dementia and AD. The exact processing and profile in serum in relation to cognitive disorders remains to be further assessed to provide simple non-invasive tests to identify subjects with progressive cognitive disorders.

Pazopanib Reduces Phosphorylated Tau Levels and Alters Astrocytes in a Mouse Model of Tauopathy

Hyperphosphorylation and aggregation of tau protein is a critical factor in many neurodegenerative diseases. These diseases are increasing in prevalence, and there are currently no cures. Previous work from our group and others has shown that tyrosine kinase inhibitors (TKIs) can stimulate autophagy, decrease pathological proteins, and improve symptoms in models of neurodegeneration. Here we examined the role of pazopanib in mouse models that express either human mutant P301L tau (TauP301L) or triple mutant amyloid precursor protein (3x-AβPP). The TauP301L mouse expresses P301L tau under the control of a prion promoter in both neurons and astrocytes, reminiscent of some human tauopathies. Pazopanib crosses the blood-brain barrier with no detectable peripheral off-side effects, and decreases p-tau in TauP301L mice. Pazopanib reaches a brain concentration sufficient for inhibition of several tyrosine kinases, including vascular endothelial growth factor receptors (VEGFRs). Further, pazopanib does not affect microglia but reduces astrocyte levels toward nontransgenic controls in TauP301L mice. Pazopanib does not alter amyloid beta levels or astrocytes in 3x-AβPP mice but modulates a number of inflammatory markers (IP-10, MIP-1α, MIP-1β, and RANTES). These data suggest that pazopanib may be involved in p-tau clearance and modulation of astrocytic activity in models of tauopathies.

Prospects for strain-specific immunotherapy in Alzheimer's disease and tauopathies

With increasing age, as the incidence of Alzheimer's disease is increasing, finding a therapeutic intervention is becoming critically important to either prevent or slow down the progression of the disease. Passive immunotherapy has been demonstrated as a successful way of reducing large aggregates and improving cognition in animal models of both tauopathies and Alzheimer's disease. However, with all the continuous attempts and significant success of immunotherapy in preclinical studies, finding a successful clinical therapy has been a great challenge, possibly indicating a lack of accuracy in targeting the toxic species. Both active and passive immunotherapy approaches in transgenic animals have been demonstrated to have pros and cons. Passive immunotherapy has been favored and many mechanisms have been shown to clear toxic amyloid and tau aggregates and improve memory. These mechanisms may differ depending on the antibodie's' target and administration route. In this regard, deciding on affinity vs. specificity of the antibodies plays a significant role in terms of avoiding the clearance of the physiological forms of the targeted proteins and reducing adverse side effects. In addition, knowing that a single protein can exist in different conformational states, termed as strains, with varying degrees of neurotoxicity and seeding properties, presents an additional level of complexity. Therefore, immunotherapy targeting specifically the toxic strains will aid in developing potential strategies for intervention. Moreover, an approach of combinatorial immunotherapies against different amyloidogenic proteins, at distinct levels of the disease progression, might offer an effective therapy in many neurodegenerative diseases.

Beta-secretase inhibitors in phase I and phase II clinical trials for Alzheimer's disease

INTRODUCTION

BACE 1 is a protease that cleaves the transmembrane amyloid precursor protein and generates amyloid-β peptides that accumulate in AD brains. No known mutations are identified in the gene encoding BACE1 in AD. However, enzyme levels are elevated in AD and a single residue mutation in amyloid precursor protein protects against protein cleavage by BACE1, suggesting BACE involvement in disease pathogenesis. Drugs that can inhibit BACE1 would theoretically prevent Aβ accumulation and halt AD onset and progression. Areas covered: This review discusses clinical developments of BACE1 inhibitors and focuses on what is learned about these inhibitors as a potential treatment. Expert opinion: BACE1 inhibition as a therapeutic strategy to improve cognition in AD has been challening. Brain-penetrant BACE1 inhibitors have been developed and clinical trials are underway, both safety and efficacy are questionable. Several clinical trials suggest that BACE1 inhibition and other immunotherapies to reduce brain Aβ are insufficient to improve cognition in AD. This may be due to the emphasis on the amyloid hypothesis despite big failures. We may have to seriously consider shifting attention to therapeutic strategies other than BACE1 inhibition or reduction of Aβ alone and pay more attention to simultaneous clearance of tau and Aβ.

Discoidin domain receptor inhibition reduces neuropathology and attenuates inflammation in neurodegeneration models

The role of cell surface tyrosine kinase collagen-activated receptors known as discoidin domain receptors (DDRs) is unknown in neurodegenerative diseases. We detect up-regulation in DDRs level in post-mortem Alzheimer and Parkinson brains. Lentiviral shRNA knockdown of DDR1 and DDR2 reduces the levels of α-synuclein, tau, and β-amyloid and prevents cell loss in vivo and in vitro. DDR1 and DDR2 knockdown alters brain immunity and significantly reduces the level of triggering receptor expressed on myeloid cells (TREM)-2 and microglia. These studies suggest that DDR1 and DDR2 inhibition is a potential target to clear neurotoxic proteins and reduce inflammation in neurodegeneration.

Future Therapeutics in Alzheimer's Disease: Development Status of BACE Inhibitors

Alzheimer's disease (AD) is the primary cause of dementia in the elderly. It remains incurable and poses a huge socio-economic challenge for developed countries with an aging population. AD manifests by progressive decline in cognitive functions and alterations in behaviour, which are the result of the extensive degeneration of brain neurons. The AD pathogenic mechanism involves the accumulation of amyloid beta peptide (Aβ), an aggregating protein fragment that self-associates to form neurotoxic fibrils that trigger a cascade of cellular events leading to neuronal injury and death. Researchers from academia and the pharmaceutical industry have pursued a rational approach to AD drug discovery and targeted the amyloid cascade. Schemes have been devised to prevent the overproduction and accumulation of Aβ in the brain. The extensive efforts of the past 20 years have been translated into bringing new drugs to advanced clinical trials. The most progressed mechanism-based therapies to date consist of immunological interventions to clear Aβ oligomers, and pharmacological drugs to inhibit the secretase enzymes that produce Aβ, namely β-site amyloid precursor-cleaving enzyme (BACE) and γ-secretase. After giving an update on the development and current status of new AD therapeutics, this review will focus on BACE inhibitors and, in particular, will discuss the prospects of verubecestat (MK-8931), which has reached phase III clinical trials.

Nilotinib Effects in Parkinson's disease and Dementia with Lewy bodies

BACKGROUND

We evaluated the effects of low doses of the tyrosine kinase Abelson (Abl) inhibitor Nilotinib, on safety and pharmacokinetics in Parkinson's disease dementia or dementia with Lewy bodies.

OBJECTIVES

The primary outcomes of this study were safety and tolerability; pharmacokinetics and target engagement were secondary, while clinical outcomes were exploratory.

METHODS

Twelve subjects were randomized into 150 mg (n = 5) or 300 mg (n = 7) groups and received Nilotinib orally every day for 24 weeks.

RESULTS

This study shows that 150 mg and 300 mg doses of Nilotinib appear to be safe and tolerated in subjects with advanced Parkinson's disease. Nilotinib is detectable in the cerebrospinal fluid (CSF) and seems to engage the target Abl. Motor and cognitive outcomes suggest a possible beneficial effect on clinical outcomes. The CSF levels of homovanillic acid are significantly increased between baseline and 24 weeks of treatment. Exploratory CSF biomarkers were measured.

CONCLUSIONS

This small proof-of-concept study lacks a placebo group and participants were not homogenous, resulting in baseline differences between and within groups. This limits the interpretations of the biomarker and clinical data, and any conclusions should be drawn cautiously. Nonetheless, the collective observations suggest that it is warranted to evaluate the safety and efficacy of Nilotinib in larger randomized, double-blind, placebo-controlled trials.

Yeast Model of Amyloid-β and Tau Aggregation in Alzheimer's Disease

The amyloid-β peptide (Aβ) and the phosphorylated protein tau have been widely implicated in Alzheimer's disease and are the focus of most research. Both agents have been extensively studied in mammalian cell culture and in animal studies, but new research is focusing on yeast models. Yeast are eukaryotes, just like us, and are amenable to effects and expression of Aβ and tau and appear able to 'report' with considerable relevance on the effects of these biomolecules. The use of yeast enables powerful new approaches to understanding how to overcome the effects of Aβ and tau, and such advances could lead to new therapies to prevent the progression of Alzheimer's disease.

Alzheimer's disease genes and autophagy

Autophagy is a process to degrade and recycle cellular constituents via the lysosome for regulating cellular homeostasis. Its dysfunction is now considered to be involved in many diseases, including neurodegenerative diseases. Many features reflecting autophagy impairment, such as autophagosome accumulation and lysosomal dysfunction, have been also revealed to be involved in Alzheimer's disease (AD). Recent genetic studies such as genome-wide association studies in AD have identified a number of novel genes associated with AD. Some of the identified genes have demonstrated dysfunction in autophagic processes in AD, while others remain under investigation. Since autophagy is strongly regarded to be one of the major pathogenic mechanisms of AD, it is necessary to review how the AD-associated genes are related to autophagy. We anticipate our current review to be a starting point for future studies regarding AD-associated genes and autophagy. This article is part of a Special Issue entitled SI:Autophagy.

Implications of GABAergic Neurotransmission in Alzheimer's Disease

Alzheimer's disease (AD) is characterized pathologically by the deposition of β-amyloid peptides (Aβ) and the accumulation of neurofibrillary tangles (NFTs) composed of hyper-phosphorylated tau. Regardless of the pathological hallmarks, synaptic dysfunction is widely accepted as a causal event in AD. Of the two major types of synapses in the central nervous system (CNS): glutamatergic and GABAergic, which provide excitatory and inhibitory outputs respectively, abundant data implicate an impaired glutamatergic system during disease progression. However, emerging evidence supports the notion that disrupted default neuronal network underlies impaired memory, and that alterations of GABAergic circuits, either plays a primary role or as a compensatory response to excitotoxicity, may also contribute to AD by disrupting the overall network function. The goal of this review is to provide an overview of the involvement of Aβ, tau and apolipoprotein E4 (apoE4), the major genetic risk factor in late-onset AD (LOAD), in GABAergic neurotransmission and the potential of modulating the GABAergic function as AD therapy.

Genetic perspective on the role of the autophagy-lysosome pathway in Parkinson disease

Parkinson disease (PD), once considered as a prototype of a sporadic disease, is now known to be considerably affected by various genetic factors, which interact with environmental factors and the normal process of aging, leading to PD. Large studies determined that the hereditary component of PD is at least 27%, and in some populations, single genetic factors are responsible for more than 33% of PD patients. Interestingly, many of these genetic factors, such as LRRK2, GBA, SMPD1, SNCA, PARK2, PINK1, PARK7, SCARB2, and others, are involved in the autophagy-lysosome pathway (ALP). Some of these genes encode lysosomal enzymes, whereas others correspond to proteins that are involved in transport to the lysosome, mitophagy, or other autophagic-related functions. Is it possible that all these factors converge into a single pathway that causes PD? In this review, we will discuss these genetic findings and the role of the ALP in the pathogenesis of PD and will try to answer this question. We will suggest a novel hypothesis for the pathogenic mechanism of PD that involves the lysosome and the different autophagy pathways.