RESUMO
Myostatin (or growth/differentiation factor 8 (GDF8)) is a member of the transforming growth factor ß superfamily of growth factors and negatively regulates skeletal muscle growth. Its dysregulation is implicated in muscle wasting diseases. SRK-015 is a clinical-stage mAb that prevents extracellular proteolytic activation of pro- and latent myostatin. Here we used integrated structural and biochemical approaches to elucidate the molecular mechanism of antibody-mediated neutralization of pro-myostatin activation. The crystal structure of pro-myostatin in complex with 29H4-16 Fab, a high-affinity variant of SRK-015, at 2.79 Å resolution revealed that the antibody binds to a conformational epitope in the arm region of the prodomain distant from the proteolytic cleavage sites. This epitope is highly sequence-divergent, having only limited similarity to other closely related members of the transforming growth factor ß superfamily. Hydrogen/deuterium exchange MS experiments indicated that antibody binding induces conformational changes in pro- and latent myostatin that span the arm region, the loops contiguous to the protease cleavage sites, and the latency-associated structural elements. Moreover, negative-stain EM with full-length antibodies disclosed a stable, ring-like antigen-antibody structure in which the two Fab arms of a single antibody occupy the two arm regions of the prodomain in the pro- and latent myostatin homodimers, suggesting a 1:1 (antibody:myostatin homodimer) binding stoichiometry. These results suggest that SRK-015 binding stabilizes the latent conformation and limits the accessibility of protease cleavage sites within the prodomain. These findings shed light on approaches that specifically block the extracellular activation of growth factors by targeting their precursor forms.
Assuntos
Anticorpos Monoclonais/química , Anticorpos Neutralizantes/química , Simulação de Acoplamento Molecular , Miostatina/química , Anticorpos Monoclonais/imunologia , Anticorpos Neutralizantes/imunologia , Sítios de Ligação , Humanos , Miostatina/antagonistas & inibidores , Miostatina/imunologia , Ligação Proteica , Estabilidade ProteicaRESUMO
OBJECTIVE: Cerebrospinal fluid (CSF) tau is an excellent surrogate marker for assessing neuropathological changes that occur in Alzheimer's disease (AD) patients. However, whether the elevated tau in AD CSF is just a marker of neurodegeneration or, in fact, a part of the disease process is uncertain. Moreover, it is unknown how CSF tau relates to the recently described soluble high-molecular-weight (HMW) species that is found in the postmortem AD brain and can be taken up by neurons and seed aggregates. METHODS: We have examined seeding and uptake properties of brain extracellular tau from various sources, including interstitial fluid (ISF) and CSF from an AD transgenic mouse model and postmortem ventricular and antemortem lumbar CSF from AD patients. RESULTS: We found that brain ISF and CSF tau from the AD mouse model can be taken up by cells and induce intracellular aggregates. Ventricular CSF from AD patients contained a rare HMW tau species that exerted a higher seeding activity. Notably, the HMW tau species was also detected in lumbar CSF from AD patients, and its levels were significantly elevated compared to control subjects. HMW tau derived from CSF of AD patients was seed competent in vitro. INTERPRETATION: These findings suggest that CSF from an AD brain contains potentially bioactive HMW tau species, giving new insights into the role of CSF tau and biomarker development for AD. Ann Neurol 2016;80:355-367.
Assuntos
Doença de Alzheimer/líquido cefalorraquidiano , Encéfalo/metabolismo , Proteínas tau/líquido cefalorraquidiano , Idoso , Animais , Biomarcadores/líquido cefalorraquidiano , Líquido Extracelular/metabolismo , Feminino , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Pessoa de Meia-IdadeRESUMO
Accumulating evidence from epidemiological studies suggest that type 2 diabetes is linked to an increased risk of Alzheimer's disease (AD). However, the consequences of type 2 diabetes on AD pathologies, such as tau hyperphosphorylation, are not well understood. Here, we evaluated the impact of type 2 diabetes on tau phosphorylation in db/db diabetic mice aged 4 and 26weeks. We found increased tau phosphorylation at the CP13 epitope correlating with a deregulation of c-Jun. N-terminal kinase (JNK) and Protein Phosphatase 2A (PP2A) in 4-week-old db/db mice. 26-week-old db/db mice displayed tau hyperphosphorylation at multiple epitopes (CP13, AT8, PHF-1), but no obvious change in kinases or phosphatases, no cleavage of tau, and no deregulation of central insulin signaling pathways. In contrast to younger animals, 26-week-old db/db mice were hypothermic and restoration of normothermia rescued phosphorylation at most epitopes. Our results suggest that, at early stages of type 2 diabetes, changes in tau phosphorylation may be due to deregulation of JNK and PP2A, while at later stages hyperphosphorylation is mostly a consequence of hypothermia. These results provide a novel link between diabetes and tau pathology, and underlie the importance of recording body temperature to better understand the relationship between diabetes and AD.
Assuntos
Envelhecimento/fisiologia , Diabetes Mellitus Tipo 2/terapia , Hipotermia Induzida , Proteínas tau/metabolismo , Análise de Variância , Animais , Glicemia , Peso Corporal/genética , Peso Corporal/fisiologia , Encéfalo/metabolismo , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/patologia , Modelos Animais de Doenças , Regulação da Expressão Gênica/genética , Índice Glicêmico , Resistência à Insulina/genética , Leptina/deficiência , Leptina/genética , MAP Quinase Quinase 4/metabolismo , Masculino , Camundongos , Camundongos Mutantes , Fosforilação/genética , Transdução de Sinais/genéticaRESUMO
Neurofibrillary tangles (NFTs), a marker of neuronal alterations in Alzheimer's disease (AD) and other tauopathies, are comprised of aggregates of hyperphosphorylated tau protein. We recently studied the formation of NFTs in the entorhinal cortex (EC) and their subsequent propagation through neural circuits in the rTgTauEC mouse model (de Calignon et al., 2012). We now examine the consequences of suppressing transgene expression with doxycycline on the NFT-associated pathological features of neuronal system deafferentation, NFT progression and propagation, and neuronal loss. At 21 months of age we observe that EC axonal lesions are associated with an abnormal sprouting response of acetylcholinesterase (AChE)-positive fibers, a phenotype reminiscent of human AD. At 24 months, NFTs progress, tau inclusions propagate to the dentate gyrus, and neuronal loss is evident. Suppression of the transgene expression from 18 to 24 months led to reversal of AChE sprouting, resolution of Gallyas-positive and Alz50-positive NFTs, and abrogation of progressive neuronal loss. These data suggest that propagation of NFTs, as well as some of the neural system consequences of NFTs, can be reversed in an animal model of NFT-associated toxicity, providing proof in principle that these lesions can be halted, even in established disease.
Assuntos
Doença de Alzheimer/patologia , Córtex Entorrinal/patologia , Emaranhados Neurofibrilares/patologia , Proteínas tau/metabolismo , Acetilcolinesterase , Doença de Alzheimer/metabolismo , Animais , Western Blotting , Modelos Animais de Doenças , Córtex Entorrinal/metabolismo , Humanos , Imuno-Histoquímica , Camundongos , Camundongos Transgênicos , Fenótipo , Reação em Cadeia da Polimerase em Tempo Real , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Análise Serial de Tecidos , Proteínas tau/genéticaRESUMO
Neurofibrillary tangles (NFTs), a hallmark of Alzheimer's disease, are intracellular silver and thioflavin S-staining aggregates that emerge from earlier accumulation of phospho-tau in the soma. Whether soluble misfolded but nonfibrillar tau disrupts neuronal function is unclear. Here we investigate if soluble pathological tau, specifically directed to the entorhinal cortex (EC), can cause behavioral or synaptic deficits. We studied rTgTauEC transgenic mice, in which P301L mutant human tau overexpressed primarily in the EC leads to the development of tau pathology, but only rare NFT at 16 months of age. We show that the early tau lesions are associated with nearly normal performance in contextual fear conditioning, a hippocampal-related behavior task, but more robust changes in neuronal system activation as marked by Arc induction and clear electrophysiological defects in perforant pathway synaptic plasticity. Electrophysiological changes were likely due to a presynaptic deficit and changes in probability of neurotransmitter release. The data presented here support the hypothesis that misfolded and hyperphosphorylated tau can impair neuronal function within the entorhinal-hippocampal network, even prior to frank NFT formation and overt neurodegeneration.
Assuntos
Doença de Alzheimer/metabolismo , Doença de Alzheimer/fisiopatologia , Córtex Entorrinal/metabolismo , Terminações Pré-Sinápticas/fisiologia , Proteínas tau/metabolismo , Animais , Proteínas do Citoesqueleto/metabolismo , Modelos Animais de Doenças , Fenômenos Eletrofisiológicos/fisiologia , Córtex Entorrinal/fisiopatologia , Hipocampo/metabolismo , Hipocampo/fisiopatologia , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Proteínas do Tecido Nervoso/metabolismo , Plasticidade Neuronal/fisiologiaRESUMO
Inhibitors of the transforming growth factor-ß (TGF-ß) pathway are potentially promising antifibrotic therapies, but nonselective simultaneous inhibition of all three TGF-ß homologs has safety liabilities. TGF-ß1 is noncovalently bound to a latency-associated peptide that is, in turn, covalently bound to different presenting molecules within large latent complexes. The latent TGF-ß-binding proteins (LTBPs) present TGF-ß1 in the extracellular matrix, and TGF-ß1 is presented on immune cells by two transmembrane proteins, glycoprotein A repetitions predominant (GARP) and leucine-rich repeat protein 33 (LRRC33). Here, we describe LTBP-49247, an antibody that selectively bound to and inhibited the activation of TGF-ß1 presented by LTBPs but did not bind to TGF-ß1 presented by GARP or LRRC33. Structural studies demonstrated that LTBP-49247 recognized an epitope on LTBP-presented TGF-ß1 that is not accessible on GARP- or LRRC33-presented TGF-ß1, explaining the antibody's selectivity for LTBP-complexed TGF-ß1. In two rodent models of kidney fibrosis of different etiologies, LTBP-49247 attenuated fibrotic progression, indicating the central role of LTBP-presented TGF-ß1 in renal fibrosis. In mice, LTBP-49247 did not have the toxic effects associated with less selective TGF-ß inhibitors. These results establish the feasibility of selectively targeting LTBP-bound TGF-ß1 as an approach for treating fibrosis.
Assuntos
Matriz Extracelular , Fibrose , Proteínas de Ligação a TGF-beta Latente , Fator de Crescimento Transformador beta1 , Fator de Crescimento Transformador beta1/metabolismo , Animais , Humanos , Proteínas de Ligação a TGF-beta Latente/metabolismo , Proteínas de Ligação a TGF-beta Latente/antagonistas & inibidores , Matriz Extracelular/metabolismo , Camundongos , Masculino , Nefropatias/metabolismo , Nefropatias/patologia , Nefropatias/tratamento farmacológico , Progressão da Doença , Rim/patologia , Rim/metabolismo , Rim/efeitos dos fármacos , Camundongos Endogâmicos C57BLRESUMO
Proteases are one of the most important and historically utilized classes of drug targets. To effectively interrogate this class of proteins, which encodes nearly 2% of the human proteome, it is necessary to develop effective and cost-efficient methods that report on their activity both in vitro and in vivo. We have developed a robust reporter of caspase proteolytic activity, called caspase-activatable green fluorescent protein (CA-GFP). The caspases play central roles in homeostatic regulation, as they execute programmed cell death, and in drug design, as caspases are involved in diseases ranging from cancer to neurodegeneration. CA-GFP is a genetically encoded dark-to-bright fluorescent reporter of caspase activity in in vitro, cell-based, and animal systems. Based on the CA-GFP platform, we developed reporters that can discriminate the activities of caspase-6 and -7, two highly related proteases. A second series of reporters, activated by human rhinovirus 3C protease, demonstrated that we could alter the specificity of the reporter by reengineering the protease recognition sequence. Finally, we took advantage of the spectrum of known fluorescent proteins to generate green, yellow, cyan, and red reporters, paving the way for multiplex protease monitoring.
Assuntos
Caspases/metabolismo , Ensaios Enzimáticos/métodos , Proteínas de Fluorescência Verde/metabolismo , Sondas Moleculares/metabolismo , Engenharia de Proteínas , Proteínas de Fluorescência Verde/química , Proteínas de Fluorescência Verde/genética , Humanos , Modelos Moleculares , Sondas Moleculares/química , Sondas Moleculares/genética , Estrutura Secundária de Proteína , ProteóliseRESUMO
Fluorescent proteins have revolutionized modern biology with their ability to report the presence of tagged proteins in living systems. Although several fluorescent proteins have been described in which the excitation and emission properties can be modulated by external triggers, no fluorescent proteins have been described that can be activated from a silent dark state to a bright fluorescent state directly by the activity of an enzyme. We have developed a version of GFP in which fluorescence is completely quenched by appendage of a hydrophobic quenching peptide that tetramerizes GFP and prevents maturation of the chromophore. The fluorescence can be fully restored by catalytic removal of the quenching peptide, making it a robust reporter of proteolysis. We have demonstrated the utility of this uniquely dark state of GFP as a genetically encoded apoptosis reporter that monitors the function of caspases, which catalyze the fate-determining step in programmed cell death. Caspase Activatable-GFP (CA-GFP) can be activated both in vitro and in vivo, resulting in up to a 45-fold increase in fluorescent signal in bacteria and a 3-fold increase in mammalian cells. We used CA-GFP successfully to monitor real-time apoptosis in mammalian cells. This dark state of GFP may ultimately serve as a useful platform for probes of other enzymatic processes.
Assuntos
Apoptose , Caspases/metabolismo , Genes Reporter , Proteínas de Fluorescência Verde/metabolismo , Proteólise , Animais , Caspases/genética , Catálise , Proteínas de Fluorescência Verde/genética , Camundongos , Microscopia de Fluorescência/métodos , Células NIH 3T3RESUMO
We report gas-phase electronic structure calculations on helical peptides that act as scaffolds for imidazole-based hydrogen-bonding networks (proton wires). We have modeled various 21-residue polyalanine peptides substituted at regular intervals with histidines (imidazole-bearing amino acids), using a hybrid approach with a semiempirical method (AM1) for peptide scaffolds and density functional theory (B3LYP) for proton wires. We have computed energy landscapes including barriers for Grotthuss-shuttling-type proton motions though wires supported on 3(10)-, α- and π-helical structures, showing the 3(10)- and α-helices to be attractive targets in terms of high proton affinities, low Grotthuss shuttling barriers, and high stabilities. Moreover, bias forces provided by the helical dipole moments were found to promote unidirectional proton translocation.
Assuntos
Peptídeos/química , Prótons , Modelos Moleculares , Estrutura Secundária de Proteína , Teoria QuânticaRESUMO
Since the first approval of the anti-CD3 recombinant monoclonal antibody (mAb), muromonab-CD3, a mouse antibody for the prevention of transplant rejection, by the US Food and Drug Administration (FDA) in 1986, mAb therapeutics have become increasingly important to medical care. A wealth of information about mAbs regarding their structure, stability, post-translation modifications, and the relationship between modification and function has been reported. Yet, substantial resources are still required throughout development and commercialization to have appropriate control strategies to maintain consistent product quality, safety, and efficacy. A typical feature of mAbs is charge heterogeneity, which stems from a variety of modifications, including modifications that are common to many mAbs or unique to a specific molecule or process. Charge heterogeneity is highly sensitive to process changes and thus a good indicator of a robust process. It is a high-risk quality attribute that could potentially fail the specification and comparability required for batch disposition. Failure to meet product specifications or comparability can substantially affect clinical development timelines. To mitigate these risks, the general rule is to maintain a comparable charge profile when process changes are inevitably introduced during development and even after commercialization. Otherwise, new peaks or varied levels of acidic and basic species must be justified based on scientific knowledge and clinical experience for a specific molecule. Here, we summarize the current understanding of mAb charge variants and outline risk-based control strategies to support process development and ultimately commercialization.
RESUMO
In Alzheimer's disease and other tauopathies, tau displays several abnormal post-translation modifications such as hyperphosphorylation, truncation, conformation, and oligomerization. Mouse monoclonal antibodies have been raised against such tau modifications for research, diagnostic, and therapeutic purposes. However, many of these primary antibodies are at risk of giving nonspecific signals in common Western blotting procedures. Not because they are unspecific, but because the secondary antibodies used to detect them will also detect the heavy chain of endogenous mouse immunoglobulins (Igs), and give a nonspecific signal at the same molecular weight than tau protein (around 50 kDa). Here, we propose the use of anti-light chain secondary antibodies as a simple and efficient technique to prevent nonspecific Igs signals at around 50 kDa. We demonstrate the efficacy of this method by removing artifactual signals when using monoclonal antibodies directed at tau phosphorylation (AT100, 12E8, AT270), tau truncation (TauC3), tau oligomerization (TOMA), or tau abnormal conformation (Alz50), in wild-type, 3×Tg-AD, and tau knockout mice.
Assuntos
Anticorpos Monoclonais/metabolismo , Encéfalo/metabolismo , Proteínas tau/metabolismo , Animais , Especificidade de Anticorpos , Western Blotting , Cadeias Leves de Imunoglobulina/metabolismo , Camundongos , Camundongos Knockout , Fosforilação , Mutação Puntual , Proteínas tau/genéticaRESUMO
The spread of neurofibrillary tangle (NFT) pathology through the human brain is a hallmark of Alzheimer's disease (AD), which is thought to be caused by the propagation of "seeding" competent soluble misfolded tau. "TauC3", a C-terminally truncated form of tau that is generated by caspase-3 cleavage at D421, has previously been observed in NFTs and has been implicated in tau toxicity. Here we show that TauC3 is found in the seeding competent high molecular weight (HMW) protein fraction of human AD brain. Using a specific TauC3 antibody, we were able to substantially block the HMW tau seeding activity of human AD brain extracts in an in vitro tau seeding FRET assay. We propose that TauC3 could contribute to the templated tau misfolding that leads to NFT spread in AD brains.
Assuntos
Doença de Alzheimer/metabolismo , Anticorpos/metabolismo , Encéfalo/metabolismo , Proteínas tau/imunologia , Idoso de 80 Anos ou mais , Especificidade de Anticorpos , Caspase 3/metabolismo , Linhagem Celular , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Emaranhados Neurofibrilares/metabolismo , Dobramento de Proteína , Proteínas tau/químicaRESUMO
INTRODUCTION: In early stages of Alzheimer's disease (AD), neurofibrillary tangles (NFT) are largely restricted to the entorhinal cortex and medial temporal lobe. At later stages, when clinical symptoms generally occur, NFT involve widespread limbic and association cortices. At this point in the disease, amyloid plaques are also abundantly distributed in the cortex. This observation from human neuropathological studies led us to pose two alternative hypotheses: that amyloid in the cortex is permissive for the spread of tangles from the medial temporal lobe, or that these are co-occurring but not causally related events simply reflecting progression of AD pathology. RESULTS: We now directly test the hypothesis that cortical amyloid acts as an accelerant for spreading of tangles beyond the medial temporal lobe. We crossed rTgTauEC transgenic mice that demonstrate spread of tau from entorhinal cortex to other brain structures at advanced age with APP/PS1 mice, and examined mice with either NFTs, amyloid pathology, or both. We show that concurrent amyloid deposition in the cortex 1) leads to a dramatic increase in the speed of tau propagation and an extraordinary increase in the spread of tau to distal brain regions, and 2) significantly increases tau-induced neuronal loss. CONCLUSIONS: These data strongly support the hypothesis that cortical amyloid accelerates the spread of tangles throughout the cortex and amplifies tangle-associated neural system failure in AD.
Assuntos
Doença de Alzheimer/patologia , Amiloide/metabolismo , Encéfalo/patologia , Emaranhados Neurofibrilares/patologia , Neurônios/patologia , Proteínas tau/metabolismo , Envelhecimento/metabolismo , Envelhecimento/patologia , Doença de Alzheimer/metabolismo , Amiloide/toxicidade , Animais , Encéfalo/metabolismo , Córtex Cerebral/patologia , Modelos Animais de Doenças , Progressão da Doença , Hipocampo/patologia , Humanos , Camundongos , Camundongos Transgênicos , Emaranhados Neurofibrilares/metabolismo , Lobo Temporal/patologiaRESUMO
Tau pathology is known to spread in a hierarchical pattern in Alzheimer's disease (AD) brain during disease progression, likely by trans-synaptic tau transfer between neurons. However, the tau species involved in inter-neuron propagation remains unclear. To identify tau species responsible for propagation, we examined uptake and propagation properties of different tau species derived from postmortem cortical extracts and brain interstitial fluid of tau-transgenic mice, as well as human AD cortices. Here we show that PBS-soluble phosphorylated high-molecular-weight (HMW) tau, though very low in abundance, is taken up, axonally transported, and passed on to synaptically connected neurons. Our findings suggest that a rare species of soluble phosphorylated HMW tau is the endogenous form of tau involved in propagation and could be a target for therapeutic intervention and biomarker development.
Assuntos
Doença de Alzheimer/metabolismo , Encéfalo/metabolismo , Neurônios/metabolismo , Proteínas tau/metabolismo , Idoso , Idoso de 80 Anos ou mais , Animais , Sobrevivência Celular , Feminino , Células HEK293 , Humanos , Masculino , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Técnicas Analíticas Microfluídicas , FosforilaçãoRESUMO
Caspases are a family of integral proteases playing a role in apoptosis. The importance of apoptosis in disease has made these proteases not only an attractive drug target but also a focal point for measuring apoptosis in vivo. The critical role caspases play in determining cell death has led to the development of a wide array of technologies to measure caspase activity in vivo, ranging from small molecule PET imaging reagents to fluorescent and luminescent protein-based reporters used in whole animal and cell-based applications. This chapter reviews this wide range of technologies available as well as the most appropriate applications for each reagent and the mechanism of how it measures caspase activity in vivo.
Assuntos
Caspases/metabolismo , Ativação Enzimática , Animais , Apoptose , Caspases/análise , Ensaios Enzimáticos/métodos , Transferência Ressonante de Energia de Fluorescência/métodos , Corantes Fluorescentes/análise , Proteínas de Fluorescência Verde/análise , Proteínas de Fluorescência Verde/genética , Humanos , Tomografia por Emissão de Pósitrons/métodosRESUMO
Apoptosis is critical for organismal homeostasis and a wide variety of diseases. Caspases are the ultimate executors of the apoptotic programmed cell death pathway. As caspases play such a central role in apoptosis, there is significant demand for technologies to monitor caspase function. We recently developed a caspase activatable-GFP (CA-GFP) reporter. CA-GFP is unique due to its "dark" state, where chromophore maturation of the GFP is inhibited by the presence of a C-terminal peptide. Here we show that chromophore maturation is prevented because CA-GFP does not fold into the robust ß-barrel of GFP until the peptide has been cleaved by active caspase. Both CA-GFP and GFP1â10 , a split form of GFP lacking the 11th strand, have similar secondary structure, different from mature GFP. A similar susceptibility to proteolytic digestion indicates that this shared structure is not the robust, fully formed GFP ß-barrel. We have developed a model that suggests that as CA-GFP is translated in vivo it follows the same folding path as wild-type GFP; however, the presence of the appended peptide does not allow CA-GFP to form the barrel of the fully matured GFP. CA-GFP is therefore held in a "pro-folding" intermediate state until the peptide is released, allowing it to continue folding into the mature barrel geometry. This new understanding of the structural basis of the dark state of the CA-GFP reporter will enable manipulation of this mechanism in the development of reporter systems for any number of cellular processes involving proteases and potentially other enzymes.
Assuntos
Caspases/metabolismo , Fluorescência , Corantes Fluorescentes/química , Proteínas de Fluorescência Verde/química , Apoptose , Western Blotting , Caspases/genética , Cromatografia Líquida de Alta Pressão , Dicroísmo Circular , Corantes Fluorescentes/metabolismo , Genes Reporter , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Cinética , Modelos Moleculares , Peso Molecular , Proteínas Mutantes/química , Proteínas Mutantes/metabolismo , Ressonância Magnética Nuclear Biomolecular , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Fragmentos de Peptídeos/metabolismo , Dobramento de Proteína , Estrutura Secundária de Proteína , Proteólise , Proteínas Recombinantes , Espectrometria de FluorescênciaRESUMO
Accumulation and aggregation of the microtubule-associated protein tau are a pathological hallmark of neurodegenerative disorders such as Alzheimer's disease (AD). In AD, tau becomes abnormally phosphorylated and forms inclusions throughout the brain, starting in the entorhinal cortex and progressively affecting additional brain regions as the disease progresses. Formation of these inclusions is thought to lead to synapse loss and cell death. Tau is also found in the cerebrospinal fluid (CSF), and elevated levels are a biomarker for AD. Until recently, it was thought that the presence of tau in the CSF was due to the passive release of aggregated tau from dead or dying tangle-bearing neurons. However, accumulating evidence from different AD model systems suggests that tau is actively secreted and transferred between synaptically connected neurons. Transgenic mouse lines with localized expression of aggregating human tau in the entorhinal cortex have demonstrated that, as these animals age, tau becomes mislocalized from axons to cell bodies and dendrites and that human tau-positive aggregates form first in the entorhinal cortex and later in downstream projection targets. Numerous in vitro and in vivo studies have provided insight into the mechanisms by which tau may be released and internalized by neurons and have started to provide insight into how tau pathology may spread in AD. In this review, we discuss the evidence for regulated tau release and its specific uptake by neurons. Furthermore, we identify possible therapeutic targets for preventing the propagation of tau pathology, as inhibition of tau transfer may restrict development of tau tangles in a small subset of neurons affected in early stages of AD and therefore prevent widespread neuron loss and cognitive dysfunction associated with later stages of the disease.