RESUMEN
Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to a lack of appropriate human models. Here, we engineered human induced pluripotent stem cell (hiPSC)-derived neuronal lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes including shared transcriptomic signatures, autophagic body accumulation, and reduced neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of seeding-induced Tau propagation, including retromer VPS29 and genes in the UFMylation cascade. In progressive supranuclear palsy (PSP) and Alzheimer's Disease (AD) brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade in vitro and in vivo suppressed seeding-induced Tau propagation. This model provides a robust platform to identify novel therapeutic strategies for 4R tauopathy.
Asunto(s)
Células Madre Pluripotentes Inducidas , Neuronas , Tauopatías , Proteínas tau , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Proteínas tau/metabolismo , Tauopatías/metabolismo , Tauopatías/patología , Neuronas/metabolismo , Neuronas/patología , Animales , Ratones , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Enfermedad de Alzheimer/genética , Encéfalo/metabolismo , Encéfalo/patología , Parálisis Supranuclear Progresiva/metabolismo , Parálisis Supranuclear Progresiva/patología , Parálisis Supranuclear Progresiva/genética , Diferenciación Celular , Mutación , AutofagiaRESUMEN
Recent Aß-immunotherapy trials have yielded the first clear evidence that removing aggregated Aß from the brains of symptomatic patients can slow the progression of Alzheimer's disease. The clinical benefit achieved in these trials has been modest, however, highlighting the need for both a deeper understanding of disease mechanisms and the importance of intervening early in the pathogenic cascade. An immunoprevention strategy for Alzheimer's disease is required that will integrate the findings from clinical trials with mechanistic insights from preclinical disease models to select promising antibodies, optimize the timing of intervention, identify early biomarkers, and mitigate potential side effects.
Asunto(s)
Enfermedad de Alzheimer , Humanos , Enfermedad de Alzheimer/tratamiento farmacológico , Enfermedad de Alzheimer/inmunología , Enfermedad de Alzheimer/prevención & control , Enfermedad de Alzheimer/terapia , Péptidos beta-Amiloides , Anticuerpos/uso terapéutico , Inmunoterapia , AnimalesRESUMEN
Tau (MAPT) drives neuronal dysfunction in Alzheimer disease (AD) and other tauopathies. To dissect the underlying mechanisms, we combined an engineered ascorbic acid peroxidase (APEX) approach with quantitative affinity purification mass spectrometry (AP-MS) followed by proximity ligation assay (PLA) to characterize Tau interactomes modified by neuronal activity and mutations that cause frontotemporal dementia (FTD) in human induced pluripotent stem cell (iPSC)-derived neurons. We established interactions of Tau with presynaptic vesicle proteins during activity-dependent Tau secretion and mapped the Tau-binding sites to the cytosolic domains of integral synaptic vesicle proteins. We showed that FTD mutations impair bioenergetics and markedly diminished Tau's interaction with mitochondria proteins, which were downregulated in AD brains of multiple cohorts and correlated with disease severity. These multimodal and dynamic Tau interactomes with exquisite spatial resolution shed light on Tau's role in neuronal function and disease and highlight potential therapeutic targets to block Tau-mediated pathogenesis.
Asunto(s)
Mitocondrias/metabolismo , Degeneración Nerviosa/metabolismo , Mapas de Interacción de Proteínas , Sinapsis/metabolismo , Proteínas tau/metabolismo , Enfermedad de Alzheimer/genética , Aminoácidos/metabolismo , Biotinilación , Encéfalo/metabolismo , Encéfalo/patología , Núcleo Celular/metabolismo , Progresión de la Enfermedad , Metabolismo Energético , Demencia Frontotemporal/genética , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Proteínas Mutantes/metabolismo , Mutación/genética , Degeneración Nerviosa/patología , Neuronas/metabolismo , Unión Proteica , Dominios Proteicos , Proteómica , Índice de Severidad de la Enfermedad , Fracciones Subcelulares/metabolismo , Tauopatías/genética , Proteínas tau/químicaRESUMEN
Protein aggregation is a hallmark of multiple human pathologies. Autophagy selectively degrades protein aggregates via aggrephagy. How selectivity is achieved has been elusive. Here, we identify the chaperonin subunit CCT2 as an autophagy receptor regulating the clearance of aggregation-prone proteins in the cell and the mouse brain. CCT2 associates with aggregation-prone proteins independent of cargo ubiquitination and interacts with autophagosome marker ATG8s through a non-classical VLIR motif. In addition, CCT2 regulates aggrephagy independently of the ubiquitin-binding receptors (P62, NBR1, and TAX1BP1) or chaperone-mediated autophagy. Unlike P62, NBR1, and TAX1BP1, which facilitate the clearance of protein condensates with liquidity, CCT2 specifically promotes the autophagic degradation of protein aggregates with little liquidity (solid aggregates). Furthermore, aggregation-prone protein accumulation induces the functional switch of CCT2 from a chaperone subunit to an autophagy receptor by promoting CCT2 monomer formation, which exposes the VLIR to ATG8s interaction and, therefore, enables the autophagic function.
Asunto(s)
Chaperonina con TCP-1 , Macroautofagia , Agregado de Proteínas , Animales , Ratones , Proteínas Reguladoras de la Apoptosis/metabolismo , Autofagia/fisiología , Proteínas Portadoras/metabolismo , Chaperonina con TCP-1/metabolismo , Proteína Sequestosoma-1/metabolismoRESUMEN
Traumatic brain injury (TBI) is the largest non-genetic, non-aging related risk factor for Alzheimer's disease (AD). We report here that TBI induces tau acetylation (ac-tau) at sites acetylated also in human AD brain. This is mediated by S-nitrosylated-GAPDH, which simultaneously inactivates Sirtuin1 deacetylase and activates p300/CBP acetyltransferase, increasing neuronal ac-tau. Subsequent tau mislocalization causes neurodegeneration and neurobehavioral impairment, and ac-tau accumulates in the blood. Blocking GAPDH S-nitrosylation, inhibiting p300/CBP, or stimulating Sirtuin1 all protect mice from neurodegeneration, neurobehavioral impairment, and blood and brain accumulation of ac-tau after TBI. Ac-tau is thus a therapeutic target and potential blood biomarker of TBI that may represent pathologic convergence between TBI and AD. Increased ac-tau in human AD brain is further augmented in AD patients with history of TBI, and patients receiving the p300/CBP inhibitors salsalate or diflunisal exhibit decreased incidence of AD and clinically diagnosed TBI.
Asunto(s)
Enfermedad de Alzheimer/etiología , Enfermedad de Alzheimer/prevención & control , Lesiones Traumáticas del Encéfalo/complicaciones , Neuroprotección , Proteínas tau/metabolismo , Acetilación , Enfermedad de Alzheimer/metabolismo , Animales , Antiinflamatorios no Esteroideos/uso terapéutico , Biomarcadores/sangre , Biomarcadores/metabolismo , Lesiones Traumáticas del Encéfalo/metabolismo , Línea Celular , Diflunisal/uso terapéutico , Femenino , Gliceraldehído-3-Fosfato Deshidrogenasa (Fosforilante) , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Neuronas/metabolismo , Salicilatos/uso terapéutico , Sirtuina 1/metabolismo , Factores de Transcripción p300-CBP/antagonistas & inhibidores , Factores de Transcripción p300-CBP/metabolismo , Proteínas tau/sangreRESUMEN
Components of the proteostasis network malfunction in aging, and reduced protein quality control in neurons has been proposed to promote neurodegeneration. Here, we investigate the role of chaperone-mediated autophagy (CMA), a selective autophagy shown to degrade neurodegeneration-related proteins, in neuronal proteostasis. Using mouse models with systemic and neuronal-specific CMA blockage, we demonstrate that loss of neuronal CMA leads to altered neuronal function, selective changes in the neuronal metastable proteome, and proteotoxicity, all reminiscent of brain aging. Imposing CMA loss on a mouse model of Alzheimer's disease (AD) has synergistic negative effects on the proteome at risk of aggregation, thus increasing neuronal disease vulnerability and accelerating disease progression. Conversely, chemical enhancement of CMA ameliorates pathology in two different AD experimental mouse models. We conclude that functional CMA is essential for neuronal proteostasis through the maintenance of a subset of the proteome with a higher risk of misfolding than the general proteome.
Asunto(s)
Envejecimiento/metabolismo , Enfermedad de Alzheimer/metabolismo , Encéfalo/metabolismo , Autofagia Mediada por Chaperones/fisiología , Neuronas/metabolismo , Proteostasis , Envejecimiento/patología , Enfermedad de Alzheimer/patología , Animales , Encéfalo/patología , Quinasa de la Caseína I/genética , Autofagia Mediada por Chaperones/genética , Modelos Animales de Enfermedad , Femenino , Masculino , Ratones , Neuronas/patología , ProteomaRESUMEN
Dysregulated microglia are intimately involved in neurodegeneration, including Alzheimer's disease (AD) pathogenesis, but the mechanisms controlling pathogenic microglial gene expression remain poorly understood. The transcription factor CCAAT/enhancer binding protein beta (c/EBPß) regulates pro-inflammatory genes in microglia and is upregulated in AD. We show expression of c/EBPß in microglia is regulated post-translationally by the ubiquitin ligase COP1 (also called RFWD2). In the absence of COP1, c/EBPß accumulates rapidly and drives a potent pro-inflammatory and neurodegeneration-related gene program, evidenced by increased neurotoxicity in microglia-neuronal co-cultures. Antibody blocking studies reveal that neurotoxicity is almost entirely attributable to complement. Remarkably, loss of a single allele of Cebpb prevented the pro-inflammatory phenotype. COP1-deficient microglia markedly accelerated tau-mediated neurodegeneration in a mouse model where activated microglia play a deleterious role. Thus, COP1 is an important suppressor of pathogenic c/EBPß-dependent gene expression programs in microglia.
Asunto(s)
Proteína beta Potenciadora de Unión a CCAAT/metabolismo , Ligasas/metabolismo , Microglía/metabolismo , Ubiquitina-Proteína Ligasas/metabolismo , Ubiquitina/genética , Enfermedad de Alzheimer/metabolismo , Animales , Línea Celular , Técnicas de Cocultivo/métodos , Femenino , Expresión Génica/fisiología , Regulación de la Expresión Génica/fisiología , Células HEK293 , Humanos , Inflamación/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Neuronas/metabolismoRESUMEN
Tau aggregation into insoluble filaments is the defining pathological hallmark of tauopathies. However, it is not known what controls the formation and templated seeding of strain-specific structures associated with individual tauopathies. Here, we use cryo-electron microscopy (cryo-EM) to determine the structures of tau filaments from corticobasal degeneration (CBD) human brain tissue. Cryo-EM and mass spectrometry of tau filaments from CBD reveal that this conformer is heavily decorated with posttranslational modifications (PTMs), enabling us to map PTMs directly onto the structures. By comparing the structures and PTMs of tau filaments from CBD and Alzheimer's disease, it is found that ubiquitination of tau can mediate inter-protofilament interfaces. We propose a structure-based model in which cross-talk between PTMs influences tau filament structure, contributing to the structural diversity of tauopathy strains. Our approach establishes a framework for further elucidating the relationship between the structures of polymorphic fibrils, including their PTMs, and neurodegenerative disease.
Asunto(s)
Procesamiento Proteico-Postraduccional , Tauopatías/metabolismo , Proteínas tau/química , Anciano , Microscopía por Crioelectrón , Femenino , Humanos , Masculino , Persona de Mediana Edad , Agregación Patológica de Proteínas/metabolismo , Agregación Patológica de Proteínas/patología , Tauopatías/patología , Proteínas tau/metabolismoRESUMEN
Most common neurodegenerative diseases feature deposition of protein amyloids and degeneration of brain networks. Amyloids are ordered protein assemblies that can act as templates for their own replication through monomer addition. Evidence suggests that this characteristic may underlie the progression of pathology in neurodegenerative diseases. Many different amyloid proteins, including Aß, tau, and α-synuclein, exhibit properties similar to those of infectious prion protein in experimental systems: discrete and self-replicating amyloid structures, transcellular propagation of aggregation, and transmissible neuropathology. This review discusses the contribution of prion phenomena and transcellular propagation to the progression of pathology in common neurodegenerative diseases such as Alzheimer's and Parkinson's. It reviews fundamental events such as cell entry, amplification, and transcellular movement. It also discusses amyloid strains, which produce distinct patterns of neuropathology and spread through the nervous system. These concepts may impact the development of new diagnostic and therapeutic strategies.
Asunto(s)
Enfermedades Neurodegenerativas/metabolismo , Agregación Patológica de Proteínas , Amiloide , Animales , Humanos , Enfermedades Neurodegenerativas/etiología , Enfermedades Neurodegenerativas/patología , Proteínas tauRESUMEN
The expression of some proteins in the autophagy pathway declines with age, which may impact neurodegeneration in diseases, including Alzheimer's Disease. We have identified a novel non-canonical function of several autophagy proteins in the conjugation of LC3 to Rab5+, clathrin+ endosomes containing ß-amyloid in a process of LC3-associated endocytosis (LANDO). We found that LANDO in microglia is a critical regulator of immune-mediated aggregate removal and microglial activation in a murine model of AD. Mice lacking LANDO but not canonical autophagy in the myeloid compartment or specifically in microglia have a robust increase in pro-inflammatory cytokine production in the hippocampus and increased levels of neurotoxic ß-amyloid. This inflammation and ß-amyloid deposition were associated with reactive microgliosis and tau hyperphosphorylation. LANDO-deficient AD mice displayed accelerated neurodegeneration, impaired neuronal signaling, and memory deficits. Our data support a protective role for LANDO in microglia in neurodegenerative pathologies resulting from ß-amyloid deposition.
Asunto(s)
Enfermedad de Alzheimer/patología , Péptidos beta-Amiloides/metabolismo , Endocitosis , Proteínas Asociadas a Microtúbulos/metabolismo , Enfermedad de Alzheimer/metabolismo , Animales , Proteína 5 Relacionada con la Autofagia/deficiencia , Proteína 5 Relacionada con la Autofagia/genética , Proteínas Relacionadas con la Autofagia/deficiencia , Proteínas Relacionadas con la Autofagia/genética , Antígenos CD36/metabolismo , Citocinas/metabolismo , Modelos Animales de Enfermedad , Hipocampo/metabolismo , Péptidos y Proteínas de Señalización Intracelular/deficiencia , Péptidos y Proteínas de Señalización Intracelular/genética , Glicoproteínas de Membrana/metabolismo , Ratones , Ratones Transgénicos , Microglía/citología , Microglía/metabolismo , Células RAW 264.7 , Receptores Inmunológicos/metabolismo , Receptor Toll-Like 4/metabolismoRESUMEN
Class 2 CRISPR-Cas systems endow microbes with diverse mechanisms for adaptive immunity. Here, we analyzed prokaryotic genome and metagenome sequences to identify an uncharacterized family of RNA-guided, RNA-targeting CRISPR systems that we classify as type VI-D. Biochemical characterization and protein engineering of seven distinct orthologs generated a ribonuclease effector derived from Ruminococcus flavefaciens XPD3002 (CasRx) with robust activity in human cells. CasRx-mediated knockdown exhibits high efficiency and specificity relative to RNA interference across diverse endogenous transcripts. As one of the most compact single-effector Cas enzymes, CasRx can also be flexibly packaged into adeno-associated virus. We target virally encoded, catalytically inactive CasRx to cis elements of pre-mRNA to manipulate alternative splicing, alleviating dysregulated tau isoform ratios in a neuronal model of frontotemporal dementia. Our results present CasRx as a programmable RNA-binding module for efficient targeting of cellular RNA, enabling a general platform for transcriptome engineering and future therapeutic development.
Asunto(s)
Sistemas CRISPR-Cas , Biología Computacional/métodos , Ingeniería Genética/métodos , Ingeniería de Proteínas/métodos , ARN/análisis , Empalme Alternativo , Animales , Proteínas Bacterianas/metabolismo , Diferenciación Celular , Escherichia coli/metabolismo , Perfilación de la Expresión Génica , Células HEK293 , Humanos , Células Madre Pluripotentes Inducidas/citología , Lentivirus/genética , Ratones , Interferencia de ARN , ARN Guía de Kinetoplastida/genética , Ruminococcus , Análisis de Secuencia de ARN , TranscriptomaRESUMEN
Phase separation can concentrate biomolecules and accelerate reactions. However, the mechanisms and principles connecting this mesoscale organization to signaling dynamics are difficult to dissect because of the pleiotropic effects associated with disrupting endogenous condensates. To address this limitation, we engineered new phosphorylation reactions within synthetic condensates. We generally found increased activity and broadened kinase specificity. Phosphorylation dynamics within condensates were rapid and could drive cell-cycle-dependent localization changes. High client concentration within condensates was important but not the main factor for efficient phosphorylation. Rather, the availability of many excess client-binding sites together with a flexible scaffold was crucial. Phosphorylation within condensates was also modulated by changes in macromolecular crowding. Finally, the phosphorylation of the Alzheimer's-disease-associated protein Tau by cyclin-dependent kinase 2 was accelerated within condensates. Thus, condensates enable new signaling connections and can create sensors that respond to the biophysical properties of the cytoplasm.
Asunto(s)
Transducción de Señal , Proteínas tau , Quinasa 2 Dependiente de la Ciclina/metabolismo , Citoplasma/metabolismo , Humanos , Sustancias Macromoleculares/metabolismo , Proteínas tau/genética , Proteínas tau/metabolismoRESUMEN
The microtubule-associated protein tau oligomerizes, but the actions of oligomeric tau (oTau) are unknown. We have used Cry2-based optogenetics to induce tau oligomers (oTau-c). Optical induction of oTau-c elicits tau phosphorylation, aggregation, and a translational stress response that includes stress granules and reduced protein synthesis. Proteomic analysis identifies HNRNPA2B1 as a principle target of oTau-c. The association of HNRNPA2B1 with endogenous oTau was verified in neurons, animal models, and human Alzheimer brain tissues. Mechanistic studies demonstrate that HNRNPA2B1 functions as a linker, connecting oTau with N6-methyladenosine (m6A) modified RNA transcripts. Knockdown of HNRNPA2B1 prevents oTau or oTau-c from associating with m6A or from reducing protein synthesis and reduces oTau-induced neurodegeneration. Levels of m6A and the m6A-oTau-HNRNPA2B1 complex are increased up to 5-fold in the brains of Alzheimer subjects and P301S tau mice. These results reveal a complex containing oTau, HNRNPA2B1, and m6A that contributes to the integrated stress response of oTau.
Asunto(s)
Adenosina/análogos & derivados , Enfermedad de Alzheimer/metabolismo , Corteza Cerebral/metabolismo , Corteza Cerebral/patología , Ribonucleoproteína Heterogénea-Nuclear Grupo A-B/metabolismo , Procesamiento Postranscripcional del ARN , ARN/metabolismo , Proteínas tau/metabolismo , Adenosina/metabolismo , Anciano , Anciano de 80 o más Años , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/patología , Animales , Estudios de Casos y Controles , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Femenino , Células HEK293 , Ribonucleoproteína Heterogénea-Nuclear Grupo A-B/genética , Humanos , Masculino , Metilación , Ratones Endogámicos C57BL , Ratones Transgénicos , Persona de Mediana Edad , Agregado de Proteínas , Agregación Patológica de Proteínas , ARN/genética , Índice de Severidad de la Enfermedad , Proteínas tau/genéticaRESUMEN
Tubulin posttranslational modifications have been predicted to control cytoskeletal functions by coordinating the molecular interactions between microtubules and their associating proteins. A prominent tubulin modification in neurons is polyglutamylation, the deregulation of which causes neurodegeneration. Yet, the underlying molecular mechanisms have remained elusive. Here, using in-vitro reconstitution, we determine how polyglutamylation generated by the two predominant neuronal polyglutamylases, TTLL1 and TTLL7, specifically modulates the activities of three major microtubule interactors: the microtubule-associated protein Tau, the microtubule-severing enzyme katanin and the molecular motor kinesin-1. We demonstrate that the unique modification patterns generated by TTLL1 and TTLL7 differentially impact those three effector proteins, thus allowing for their selective regulation. Given that our experiments were performed with brain tubulin from mouse models in which physiological levels and patterns of polyglutamylation were altered by the genetic knockout of the main modifying enzymes, our quantitative measurements provide direct mechanistic insight into how polyglutamylation could selectively control microtubule interactions in neurons.
Asunto(s)
Tubulina (Proteína) , Animales , Ratones , Citoesqueleto/metabolismo , Cinesinas/metabolismo , Microtúbulos/metabolismo , Tubulina (Proteína)/metabolismo , Péptido Sintasas , Proteínas Asociadas a MicrotúbulosRESUMEN
Many neurodegenerative diseases, including Alzheimer's, originate from the conversion of proteins into pathogenic conformations. The microtubule-associated protein tau converts into ß-sheet-rich amyloid conformations, which underlie pathology in over 25 related tauopathies. Structural studies of tau amyloid fibrils isolated from human tauopathy tissues have revealed that tau adopts diverse structural polymorphs, each linked to a different disease. Molecular chaperones play central roles in regulating tau function and amyloid assembly in disease. New data supports the model that chaperones selectively recognize different conformations of tau to limit the accumulation of proteotoxic species. The challenge now is to understand how chaperones influence disease processes across different tauopathies, which will help guide the development of novel conformation-specific diagnostic and therapeutic strategies.
Asunto(s)
Enfermedad de Alzheimer , Tauopatías , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Amiloide/química , Humanos , Chaperonas Moleculares/metabolismo , Conformación Proteica en Lámina beta , Tauopatías/metabolismo , Tauopatías/patología , Proteínas tau/química , Proteínas tau/metabolismoRESUMEN
Microtubule-associated protein tau is a central factor in Alzheimer's disease and other tauopathies. However, the physiological functions of tau are unclear. Here, we used proximity-labelling proteomics to chart tau interactomes in primary neurons and mouse brains in vivo. Tau interactors map onto pathways of cytoskeletal, synaptic vesicle and postsynaptic receptor regulation and show significant enrichment for Parkinson's, Alzheimer's and prion disease. We find that tau interacts with and dose-dependently reduces the activity of N-ethylmaleimide sensitive fusion protein (NSF), a vesicular ATPase essential for AMPA-type glutamate receptor (AMPAR) trafficking. Tau-deficient (tau-/- ) neurons showed mislocalised expression of NSF and enhanced synaptic AMPAR surface levels, reversible through the expression of human tau or inhibition of NSF. Consequently, enhanced AMPAR-mediated associative and object recognition memory in tau-/- mice is suppressed by both hippocampal tau and infusion with an NSF-inhibiting peptide. Pathologic mutant tau from mouse models or Alzheimer's disease significantly enhances NSF inhibition. Our results map neuronal tau interactomes and delineate a functional link of tau with NSF in plasticity-associated AMPAR-trafficking and memory.
Asunto(s)
Enfermedad de Alzheimer , Receptores AMPA , Proteínas tau/metabolismo , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Animales , Hipocampo/metabolismo , Humanos , Memoria , Ratones , Proteínas Sensibles a N-Etilmaleimida/genética , Proteínas Sensibles a N-Etilmaleimida/metabolismo , Neuronas/metabolismo , Transporte de Proteínas , Receptores AMPA/genética , Receptores AMPA/metabolismoRESUMEN
Accumulation of aggregates of the microtubule-binding protein Tau is a pathological hallmark of Alzheimer's disease. While Tau is thought to primarily associate with microtubules, it also interacts with and localizes to the plasma membrane. However, little is known about how Tau behaves and organizes at the plasma membrane of live cells. Using quantitative, single-molecule imaging, we show that Tau exhibits spatial and kinetic heterogeneity near the plasma membrane of live cells, resulting in the formation of nanometer-sized hot spots. The hot spots lasted tens of seconds, much longer than the short dwell time (â¼ 40 ms) of Tau on microtubules. Pharmacological and biochemical disruption of Tau/microtubule interactions did not prevent hot spot formation, suggesting that these are different from the reported Tau condensation on microtubules. Although cholesterol removal has been shown to reduce Tau pathology, its acute depletion did not affect Tau hot spot dynamics. Our study identifies an intrinsic dynamic property of Tau near the plasma membrane that may facilitate the formation of assembly sites for Tau to assume its physiological and pathological functions.
Asunto(s)
Microtúbulos , Imagen Individual de Molécula , Membrana Celular/metabolismo , Cinética , Microtúbulos/metabolismo , Proteínas tau/metabolismoRESUMEN
Direct binding of netrin receptors with dynamic microtubules (MTs) in the neuronal growth cone plays an important role in netrin-mediated axon guidance. However, how netrin-1 (NTN1) regulates MT dynamics in axon turning remains a major unanswered question. Here, we show that the coupling of netrin-1 receptor DCC with tau (MAPT)-regulated MTs is involved in netrin-1-promoted axon attraction. Tau directly interacts with DCC and partially overlaps with DCC in the growth cone of primary neurons. Netrin-1 induces this interaction and the colocalization of DCC and tau in the growth cone. The netrin-1-induced interaction of tau with DCC relies on MT dynamics and TUBB3, a highly dynamic ß-tubulin isotype in developing neurons. Netrin-1 increased cosedimentation of DCC with tau and TUBB3 in MTs, and knockdown of either tau or TUBB3 mutually blocked this effect. Downregulation of endogenous tau levels by tau shRNAs inhibited netrin-1-induced axon outgrowth, branching and commissural axon attraction in vitro, and led to defects in spinal commissural axon projection in vivo. These findings suggest that tau is a key MT-associated protein coupling DCC with MT dynamics in netrin-1-promoted axon attraction.
Asunto(s)
Axones , Conos de Crecimiento , Netrina-1 , Neuronas , MicrotúbulosRESUMEN
Association of tau (encoded by Mapt) with microtubules causes them to be labile, whereas association of MAP6 with microtubules causes them to be stable. As axons differentiate and grow, tau and MAP6 segregate from one another on individual microtubules, resulting in the formation of stable and labile domains. The functional significance of the yin-yang relationship between tau and MAP6 remains speculative, with one idea being that such a relationship assists in balancing morphological stability with plasticity. Here, using primary rodent neuronal cultures, we show that tau depletion has opposite effects compared to MAP6 depletion on the rate of neuronal development, the efficiency of growth cone turning, and the number of neuronal processes and axonal branches. Opposite effects to those seen with tau depletion were also observed on the rate of neuronal migration, in an in vivo assay, when MAP6 was depleted. When tau and MAP6 were depleted together from neuronal cultures, the morphological phenotypes negated one another. Although tau and MAP6 are multifunctional proteins, our results suggest that the observed effects on neuronal development are likely due to their opposite roles in regulating microtubule stability.
Asunto(s)
Proteínas Asociadas a Microtúbulos , Microtúbulos , Neuronas , Proteínas tau , Proteínas tau/metabolismo , Animales , Neuronas/metabolismo , Proteínas Asociadas a Microtúbulos/metabolismo , Proteínas Asociadas a Microtúbulos/genética , Microtúbulos/metabolismo , Neurogénesis , Ratas , Células Cultivadas , Axones/metabolismo , Ratones , Movimiento Celular , Conos de Crecimiento/metabolismoRESUMEN
Alzheimer's disease (AD) is characterized by several neuropathological changes, mainly extracellular amyloid aggregates (plaques), intraneuronal inclusions of phosphorylated tau (tangles), as well as neuronal and synaptic degeneration, accompanied by tissue reactions to these processes (astrocytosis and microglial activation) that precede neuronal network disturbances in the symptomatic phase of the disease. A number of biomarkers for these brain tissue changes have been developed, mainly using immunoassays. In this review, we discuss how targeted mass spectrometry (TMS) can be used to validate and further characterize classes of biomarkers reflecting different AD pathologies, such as tau- and amyloid-beta pathologies, synaptic dysfunction, lysosomal dysregulation, and axonal damage, and the prospect of using TMS to measure these proteins in clinical research and diagnosis. TMS advantages and disadvantages in relation to immunoassays are discussed, and complementary aspects of the technologies are discussed.