Inhibition of microtubule assembly competent tubulin synthesis leads to accumulation of phosphorylated tau in neuronal cell bodies

Maintaining essential microtubule bundles in meter-long axons: a role for local tubulin biogenesis?

Axons are the narrow, up-to-meter long cellular processes of neurons that form the biological cables wiring our nervous system. Most axons must survive for an organism's lifetime, i.e. up to a century in humans. Axonal maintenance depends on loose bundles of microtubules that run without interruption all along axons. The continued turn-over and the extension of microtubule bundles during developmental, regenerative or plastic growth requires the availability of α/β-tubulin heterodimers up to a meter away from the cell body. The underlying regulation in axons is poorly understood and hardly features in past and contemporary research. Here we discuss potential mechanisms, particularly focussing on the possibility of local tubulin biogenesis in axons. Current knowledge might suggest that local translation of tubulin takes place in axons, but far less is known about the post-translational machinery of tubulin biogenesis involving three chaperone complexes: prefoldin, CCT and TBC. We discuss functional understanding of these chaperones from a range of model organisms including yeast, plants, flies and mice, and explain what is known from human diseases. Microtubules across species depend on these chaperones, and they are clearly required in the nervous system. However, most chaperones display a high degree of functional pleiotropy, partly through independent functions of individual subunits outside their complexes, thus posing a challenge to experimental studies. Notably, we found hardly any studies that investigate their presence and function particularly in axons, thus highlighting an important gap in our understanding of axon biology and pathology.

Characterization of gene expression patterns in mild cognitive impairment using a transcriptomics approach and neuroimaging endophenotypes

INTRODUCTION

Identification of novel therapeutics and risk assessment in early stages of Alzheimer's disease (AD) is a crucial aspect of addressing this complex disease. We characterized gene-expression patterns at the mild cognitive impairment (MCI) stage to identify critical mRNA measures and gene clusters associated with AD pathogenesis.

METHODS

We used a transcriptomics approach, integrating magnetic resonance imaging (MRI) and peripheral blood-based gene expression data using persistent homology (PH) followed by kernel-based clustering.

RESULTS

We identified three clusters of genes significantly associated with diagnosis of amnestic MCI. The biological processes associated with each cluster were mitochondrial function, NF-kB signaling, and apoptosis. Cluster-level associations with cortical thickness displayed canonical AD-like patterns. Driver genes from clusters were also validated in an external dataset for prediction of amyloidosis and clinical diagnosis.

DISCUSSION

We found a disease-relevant transcriptomic signature sensitive to prodromal AD and identified a subset of potential therapeutic targets associated with AD pathogenesis.

Tubulin Cytoskeleton in Neurodegenerative Diseases–not Only Primary Tubulinopathies

Neurodegenerative diseases represent a large group of disorders characterized by gradual loss of neurons and functions of the central nervous systems. Their course is usually severe, leading to high morbidity and subsequent inability of patients to independent functioning. Vast majority of neurodegenerative diseases is currently untreatable, and only some symptomatic drugs are available which efficacy is usually very limited. To develop novel therapies for this group of diseases, it is crucial to understand their pathogenesis and to recognize factors which can influence the disease course. One of cellular structures which dysfunction appears to be relatively poorly understood in the light of neurodegenerative diseases is tubulin cytoskeleton. On the other hand, its changes, both structural and functional, can considerably influence cell physiology, leading to pathological processes occurring also in neurons. In this review, we summarize and discuss dysfunctions of tubulin cytoskeleton in various neurodegenerative diseases different than primary tubulinopathies (caused by mutations in genes encoding the components of the tubulin cytoskeleton), especially Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, prion diseases, and neuronopathic mucopolysaccharidoses. It is also proposed that correction of these disorders might attenuate the progress of specific diseases, thus, finding newly recognized molecular targets for potential drugs might become possible.

Hypoparathyroidism-retardation-dysmorphism syndrome-Clinical insights from a large longitudinal cohort in a single medical center

BACKGROUND

Hypoparathyroidism, retardation, and dysmorphism (HRD) Syndrome is a rare disease composed of hypoparathyroidism, retardation of both growth and development, and distinctive dysmorphic features. Here, we describe the long-term morbidity and mortality in a large cohort of HRD patients and suggest recommendations for follow up and treatment.

METHODS

Medical records of 63 HRD syndrome patients who were followed at Soroka Medical Center during 1989-2019 were reviewed retrospectively. Information regarding demographics, medical complications, laboratory findings, and imaging studies was collected.

RESULTS

The mortality rate was 52%. The main causes of death were infectious diseases including pneumonia, septic shock, and meningitis. Multiple comorbidities were found including brain anomalies in 90% of examined patients (basal ganglia calcifications, tightening of corpus callosum, Chiari malformation, hydrocephalous, and brain atrophy), seizures in 62%, nephrocalcinosis and/or nephrolithiasis in 47%, multiple eye anomalies were recorded in 40%, bowel obstructions in 9.5%, and variable expression of both conductive and senso-neural hearing loss was documented in 9.5%.

CONCLUSION

HRD is a severe multisystem disease. Active surveillance is indicated to prevent and treat complications associated with this rare syndrome.

Broadening the spectrum phenotype of TBCE-related neuron neurodegeneration

BACKGROUND

Severe loss of TBCE function has been related to two well-known dysmorphic syndromes, while TBCE hypomorphic variants have been linked to neurodegenerative conditions due to perturbed microtubule dynamics and homeostasis, with signs of central and peripheral nervous system involvement.

METHOD

We report on an Italian female originating from Southern Italy who presented early-onset regression and neurodegeneration, with neurological features of tetraparesis and signs of peripheral nervous system involvement. Her brain MRI revealed white matter involvement.

RESULTS

Analyzing all known hypomyelination leukodystrophies related genes, two mutations in TBCE (NM_001079515) were detected: the missense variant c.464 T > A; p. (Ile155Asn) and the frameshift variant c.924del; p. (Leu309Ter), in compound heterozygosity, already reported in the literature in patients coming from the same geographical area. The clinical phenotype of the proposita was more severe and with an earlier onset than the majority of the patients reported so far.

CONCLUSIONS

Next Generation Sequencing is becoming increasingly necessary to assess unusual phenotypes, with the opportunity to establish prognosis and disease mechanisms, and facilitating differential diagnosis.

Protective effects of a small molecule inhibitor ligand against hyperphosphorylated tau-induced mitochondrial and synaptic toxicities in Alzheimer disease

The purpose of our study is to understand the protective effects of small molecule ligands for phosphorylated tau (p-tau) in Alzheimer's disease (ad) progression. Many reports show evidence that p-tau is reported to be an important contributor to the formation of paired helical filaments (PHFs) and neurofibrillary tangles (NFTs) in ad neurons. In ad, glycogen synthase kinase-3 beta (GSK3β), cyclin-dependent kinase- 5 (CDK5) and dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A), are the three important kinases responsible for tau hyperphosphorylation. Currently, there are no drugs and/or small molecules that reduce the toxicity of p-tau in ad. In the present study, we rationally selected and validated small molecule ligands that binds to the phosphorylated tau at SER23 (Ser 285). We also assessed the molecular dynamics and validated molecular docking sites for the three best ligands. Based on the best docking scores -8.09, -7.9 and - 7.8 kcal/mol, we found that ligand 1 binds to key hyperphosphorylation residues of p-tau that inhibit abnormal PHF-tau, DYRK1A, and GKS3β that reduce p-tau levels in ad. Using biochemical, molecular, immunoblotting, immunofluorescence, and transmission electron microscopy analyses, we studied the ligand 1 inhibition as well as mitochondrial and synaptic protective effects in immortalized primary hippocampal neuronal (HT22) cells. We found interactions between NAT10-262501 (ligand 1) and p-tau at key phosphorylation sites and these ligand-based inhibitions decreased PHF-tau, DYRK1A and GSK3β levels. We also found increased mitochondrial biogenesis, mitochondrial fusion and synaptic activities and reduced mitochondrial fission in ligand 1-treated mutant tau HT22 cells. Based on these results, we cautiously conclude that p-tau NAT10-262501 (ligand 1) reduces hyperphosphorylation of tau based GKS3β and CDK5 kinase regulation in ad, and aids in the maintenance of neuronal structure, mitochondrial dynamics, and biogenesis with a possible therapeutic drug target for ad.

Quantitative fractionation of tissue microtubules with distinct biochemical properties reflecting their stability and lability

Microtubules form a major cytoskeleton and exhibit dynamic instability through the repetitive polymerization/depolymerization of tubulin dimers. Although microtubule stability should be precisely controlled to maintain various cellular functions, it has been difficult to assess its status in vivo. Here, we propose a tubulin fractionation method reflecting the stability of microtubules in mouse tissues. Analyses of tubulin fractionated by two-step of ultracentrifugation demonstrated three distinct pools of tubulin, that appeared to be stable microtubule, labile microtubule, and free tubulin. Using this method, we were able to show the specific binding of different microtubule-associated proteins onto each pool of microtubules. Also, there were clear differences in the population of stable microtubule among tissues depending on the proliferative capacity of the constituent cells. These findings indicate that this method is useful for broad analysis of microtubule stability in physiological and pathological conditions.

Disulfide bond formation in microtubule-associated tau protein promotes tau accumulation and toxicity in vivo

Accumulation of microtubule-associated tau protein is thought to cause neuron loss in a group of neurodegenerative diseases called tauopathies. In diseased brains, tau molecules adopt pathological structures that propagate into insoluble forms with disease-specific patterns. Several types of posttranslational modifications in tau are known to modulate its aggregation propensity in vitro, but their influence on tau accumulation and toxicity at the whole-organism level has not been fully elucidated. Herein, we utilized a series of transgenic Drosophila models to compare systematically the toxicity induced by five tau constructs with mutations or deletions associated with aggregation, including substitutions at seven disease-associated phosphorylation sites (S7A and S7E), deletions of PHF6 and PHF6* sequences (ΔPHF6 and ΔPHF6*), and substitutions of cysteine residues in the microtubule binding repeats (C291/322A). We found that substitutions and deletions resulted in different patterns of neurodegeneration and accumulation, with C291/322A having a dramatic effect on both tau accumulation and neurodegeneration. These cysteines formed disulfide bonds in mouse primary cultured neurons and in the fly retina, and stabilized tau proteins. Additionally, they contributed to tau accumulation under oxidative stress. We also found that each of these cysteine residues contributes to the microtubule polymerization rate and microtubule levels at equilibrium, but none of them affected tau binding to polymerized microtubules. Since tau proteins expressed in the Drosophila retina are mostly present in the early stages of tau filaments self-assembly, our results suggest that disulfide bond formation by these cysteine residues could be attractive therapeutic targets.

Colchicine Blocks Tubulin Heterodimer Recycling by Tubulin Cofactors TBCA, TBCB, and TBCE

Colchicine has been used to treat gout and, more recently, to effectively prevent autoinflammatory diseases and both primary and recurrent episodes of pericarditis. The anti-inflammatory action of colchicine seems to result from irreversible inhibition of tubulin polymerization and microtubule (MT) assembly by binding to the tubulin heterodimer, avoiding the signal transduction required to the activation of the entire NLRP3 inflammasome. Emerging results show that the MT network is a potential regulator of cardiac mechanics. Here, we investigated how colchicine impacts in tubulin folding cofactors TBCA, TBCB, and TBCE activities. We show that TBCA is abundant in mouse heart insoluble protein extracts. Also, a decrease of the TBCA/β-tubulin complex followed by an increase of free TBCA is observed in human cells treated with colchicine. The presence of free TBCA is not observed in cells treated with other anti-mitotic agents such as nocodazole or cold shock, neither after translation inhibition by cycloheximide. In vitro assays show that colchicine inhibits tubulin heterodimer dissociation by TBCE/TBCB, probably by interfering with interactions of TBCE with tubulin dimers, leading to free TBCA. Manipulation of TBCA levels, either by RNAi or overexpression results in decreased levels of tubulin heterodimers. Together, these data strongly suggest that TBCA is mainly receiving β-tubulin from the dissociation of pre-existing heterodimers instead of newly synthesized tubulins. The TBCE/TBCB+TBCA system is crucial for controlling the critical concentration of free tubulin heterodimers and MT dynamics in the cells by recycling the tubulin heterodimers. It is conceivable that colchicine affects tubulin heterodimer recycling through the TBCE/TBCB+TBCA system producing the known benefits in the treatment of pericardium inflammation.

Milrinone Ameliorates the Neuroinflammation and Memory Function of Alzheimer's Disease in an APP/PS1 Mouse Model

PURPOSE

Alzheimer's disease (AD) is a complex neurodegenerative disorder, which is characterized by memory loss and cognitive deficits. The neuroprotective role of milrinone on the injury of spinal cord or cerebral ischemia-reperfusion has been confirmed. However, the accurate function of milrinone on AD pathogeny is still unclear.

METHODS

APP/PS1 transgenic mouse was used to explore the role of milrinone in behaviour tests, and the effects on histopathologic features of AD such as the formation of neuronal amyloid-β (Aβ) plaque, microglial activation, tau protein hyperphosphorylation, oxidative stress, and neuroinflammation. Lipopolysaccharide (LPS)/Aβ-treated BV-2 cells were used to understand the anti-inflammation mechanism of milrinone on AD in vitro.

RESULTS

Our in vivo results showed that milrinone ameliorates the memory functions of AD mice. Meanwhile, milrinone reduced Aβ deposits, repressed microglial activation and tau protein hyperphosphorylation, attenuated the oxidative stress, and decreased the levels of inflammatory cytokines. The in vitro results demonstrated that milrinone could inhibit the secretion of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α via regulation of NLRP3 inflammasomes and TLR4/MyD88/NF-κB signalling pathway.

CONCLUSION

Overall, milrinone could ameliorate the memory loss and cognitive deficits through repressing the multiple pathological processes of AD, suggesting that milrinone may be an underlying and effective drug for treating AD clinically.

Modulatory Effects of Autophagy on APP Processing as a Potential Treatment Target for Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the formation of intracellular aggregate composed of heavily phosphorylated tau protein and extracellular deposit of amyloid-β (Aβ) plaques derived from proteolysis cleavage of amyloid precursor protein (APP). Autophagy refers to the lysosomal-mediated degradation of cytoplasmic constituents, which plays a critical role in maintaining cellular homeostasis. Importantly, recent studies reported that dysregulation of autophagy is associated in the pathogenesis of AD, and therefore, autophagy modulation has gained attention as a promising approach to treat AD pathogenesis. In AD, both the maturation of autolysosomes and its retrograde transports have been obstructed, which causes the accumulation of autophagic vacuoles and eventually leads to degenerating and dystrophic neurites function. However, the mechanism of autophagy modulation in APP processing and its pathogenesis have not yet been fully elucidated in AD. In the early stage of AD, APP processing and Aβ accumulation-mediated autophagy facilitate the removal of toxic protein aggregates via mTOR-dependent and -independent pathways. In addition, a number of autophagy-related genes (Atg) and APP are thought to influence the development of AD, providing a bidirectional link between autophagy and AD pathology. In this review, we summarized the current observations related to autophagy regulation and APP processing in AD, focusing on their modulation associated with the AD progression. Moreover, we emphasizes the application of small molecules and natural compounds to modulate autophagy for the removal and clearance of APP and Aβ deposits in the pathological condition of AD.