Tau Protein Modifications and Interactions: Their Role in Function and Dysfunction (original) (raw)

Review Tau Protein Modifications and Interactions: Their Role in Function and Dysfunction

2014

Abstract: Tau protein is abundant in the central nervous system and involved in microtubule assembly and stabilization. It is predominantly associated with axonal microtubules and present at lower level in dendrites where it is engaged in signaling functions. Post-translational modifications of tau and its interaction with several proteins play an important regulatory role in the physiology of tau. As a consequence of abnormal modifications and expression, tau is redistributed from neuronal processes to the soma and forms toxic oligomers or aggregated deposits. The accumulation of tau protein is increasingly recognized as the neuropathological hallmark of a number of dementia disorders known as tauopathies. Dysfunction of tau protein may contribute to collapse of cytoskeleton, thereby causing improper anterograde and retrograde movement of motor proteins and their cargos on microtubules. These disturbances in intraneuronal signaling may compromise synaptic transmission as well as tr...

Tau protein in neurodegenerative diseases - a review

2017

The study of rare, inherited forms of different diseases resulted in the discovery of gene defects that cause inherited variants of the respective diseases. The defective genes were found to encode major molecular players leading to the neuropathological lesions or factors that characterize these diseases. The exact role of the tau protein in the neurodegenerative process is still under debate. It is very important to understand the normal biological roles of tau and the specific events that induce tau to become neurotoxic. Tau is the major microtubule-associated protein (MAP) of a mature neuron. The other neuronal MAPs are MAP1 and MAP2. These three MAPs perform similar function, promoting assembly and stability of microtubules. Tau protein was isolated as a microtubule-associated factor in the porcine brain. It was isolated as a protein that co-purified with tubulin and had the ability to promote microtubule assembly in vitro. Normal adult human brain tau contains 2-3 moles phosph...

Brief update on different roles of tau in neurodegeneration

IUBMB Life, 2011

Both Alzheimer's disease (AD) and almost every second case of frontotemporal lobar degeneration (FTLD) are characterized by the deposition of hyperphosphorylated forms of the microtubule-associated protein tau in neurons and/or glia. This unifying pathology led to coining the umbrella term ''tauopathies'' for these conditions. While the deposition of tau ultimately results in the formation of typical histopathological lesions, such as the neurofibrillary tangles (NFTs) in AD, it is now well accepted that tau interferes with normal functions in neurons already before its deposition. Together with the identification of pathogenic mutations in the tau-encoding gene MAPT in FTLD and evidence from a rising number of in vivo animal models a central role of tau in neurodegeneration has emerged. Here, we review the role of pathological tau in axonal transport, mitochondrial respiration, and in mediating amyloid-b toxicity in AD. Furthermore, we review recent findings regarding the spreading of tau pathology throughout the brain as disease progresses.

Tau in Alzheimer Disease and Related Tauopathies

Current Alzheimer Research, 2010

Tau is the major microtubule associated protein (MAP) of a mature neuron. The other two neuronal MAPs are MAP1 and MAP2. An established function of MAPs is their interaction with tubulin and promotion of its assembly into microtubules and stabilization of the microtubule network. The microtubule assembly promoting activity of tau, a phosphoprotein, is regulated by its degree of phosphorylation. Normal adult human brain tau contains 2-3 moles phosphate/mole of tau protein. Hyperphosphorylation of tau depresses this biological activity of tau. In Alzheimer disease (AD) brain tau is ~three to four-fold more hyperphosphorylated than the normal adult brain tau and in this hyperphosphorylated state it is polymerized into paired helical filaments ([PHF) admixed with straight filaments (SF) forming neurofibrillary tangles. Tau is transiently hyperphosphorylated during development and during anesthesia and hypothermia but not to the same state as in AD brain. The abnormally hyperphosphorylated tau in AD brain is distinguished from transiently hyperphosphorylated tau by its ability (1) to sequester normal tau, MAP1 and MAP2 and disrupt microtubules, and (2) to self-assemble into PHF/SF. The cytosolic abnormally hyperphosphorylated tau, because of oligomerization, unlike normal tau, is sedimentable and on self-assembly into PHF/SF, loses its ability to sequester normal MAPs. Some of the tau in AD brain is truncated which also promotes its self-assembly. Tau mutations found in frontotemporal dementia apparently promote its abnormal hyperphosphorylation. Thus, the AD abnormally hyperphosphorylated tau (1) is distinguishable from both normal and transiently hyperphosphorylated taus, and is inhibitory when in a cytosolic/oligomeric state but not when it is self-assembled into PHF/SF. Inhibition of abnormal hyperphosphorylation of tau offers a promising therapeutic target for AD and related tauopathies.

Tau pathology in Alzheimer disease and other tauopathies

Biochimica Et Biophysica Acta-molecular Basis of Disease, 2005

Just as neuronal activity is essential to normal brain function, microtubule-associated protein tau appears to be critical to normal neuronal activity in the mammalian brain, especially in the evolutionary most advanced species, the homo sapiens. While the loss of functional tau can be compensated by the other two neuronal microtubule-associated proteins, MAP1A/MAP1B and MAP2, it is the dysfunctional, i.e., the toxic tau, which forces an affected neuron in a long and losing battle resulting in a slow but progressive retrograde neurodegeneration. It is this pathology which is characteristic of Alzheimer disease (AD) and other tauopathies. To date, the most established and the most compelling cause of dysfunctional tau in AD and other tauopathies is the abnormal hyperphosphorylation of tau. The abnormal hyperphosphorylation not only results in the loss of tau function of promoting assembly and stabilizing microtubules but also in a gain of a toxic function whereby the pathological tau sequesters normal tau, MAP1A/MAP1B and MAP2, and causes inhibition and disruption of microtubules. This toxic gain of function of the pathological tau appears to be solely due to its abnormal hyperphosphorylation because dephosphorylation converts it functionally into a normal-like state. The affected neurons battle the toxic tau both by continually synthesizing new normal tau and as well as by packaging the abnormally hyperphosphorylated tau into inert polymers, i.e., neurofibrillary tangles of paired helical filaments, twisted ribbons and straight filaments. Slowly but progressively, the affected neurons undergo a retrograde degeneration. The hyperphosphorylation of tau results both from an imbalance between the activities of tau kinases and tau phosphatases and as well as changes in tau's conformation which affect its interaction with these enzymes. A decrease in the activity of protein phosphatase-2A (PP-2A) in AD brain and certain missense mutations seen in frontotemporal dementia promotes the abnormal hyperphosphorylation of tau. Inhibition of this tau abnormality is one of the most promising therapeutic approaches to AD and other tauopathies.

Post-translational modifications of tau protein in Alzheimer’s disease

Journal of Neural Transmission, 2005

Microtubule-associated protein tau undergoes several post-translational modifications and aggregates into paired helical filaments (PHFs) in Alzheimer's disease (AD) and other tauopathies. These modifications of tau include hyperphosphorylation, glycosylation, ubiquitination, glycation, polyamination, nitration, and proteolysis. Hyperphosphorylation and glycosylation are crucial to the molecular pathogenesis of neurofibrillary degeneration of AD. The others appear to represent failed mechanisms for neurons to remove damaged, misfolded, and aggregated proteins. This review summarizes the abnormal posttranslational modifications of tau and discusses the pathophysiological relevance of hyperphosphorylation and glycosylation of tau. Total tau and phosphorylated tau levels in cerebrospinal fluid as a diagnostic biomarkers are also reviewed. Analyses of the current advances in tau modifications suggest that intervention addressing these abnormalities may offer promising therapeutic opportunities to prevent and treat neurofibrillary degeneration of AD and other tauopathies.

Tau Proteolysis in the Pathogenesis of Tauopathies: Neurotoxic Fragments and Novel Biomarkers

Journal of Alzheimer's disease : JAD, 2018

With predictions showing that 131.5 million people worldwide will be living with dementia by 2050, an understanding of the molecular mechanisms underpinning disease is crucial in the hunt for novel therapeutics and for biomarkers to detect disease early and/or monitor disease progression. The metabolism of the microtubule-associated protein tau is altered in different dementias, the so-called tauopathies. Tau detaches from microtubules, aggregates into oligomers and neurofibrillary tangles, which can be secreted from neurons, and spreads through the brain during disease progression. Post-translational modifications exacerbate the production of both oligomeric and soluble forms of tau, with proteolysis by a range of different proteases being a crucial driver. However, the impact of tau proteolysis on disease progression has been overlooked until recently. Studies have highlighted that proteolytic fragments of tau can drive neurodegeneration in a fragment-dependent manner as a result ...

Untangling the tauopathies: Current concepts of tau pathology and neurodegeneration

Parkinsonism & Related Disorders, 2017

Tau is the most common misfolded protein responsible for human neurodegenerative diseases. The identification of mutations in MAPT, the gene that encodes tau, causing dementia and parkinsonism established the notion that tau aggregation is responsible for the development of disease. An increased understanding of the pathway leading from conformational changes in tau protein and tau propagation to neuronal dysfunction, cell death and clinical manifestation will be the key for the development mechanism-based therapeutic strategies for tauopathies.