@article {46646, title = {Actin-mediated microglial chemotaxis via G-protein coupled purinergic receptor in alzheimer{\textquoteright}s disease}, journal = {Neuroscience}, volume = {448}, year = {2020}, month = {NOV }, pages = {325-336}, type = {Review}, abstract = {

Alzheimer{\textquoteright}s disease (AD) is a neurodegenerative disease mainly associated with aging, oxidative stress and genetic mutations. There are two pathological proteins involved in AD; Amyloid-beta peptide and microtubule-associated protein Tau (MAPT). The beta- and gamma-secretase enzyme cleaves the Amyloid precursor protein, which results in the formation of extracellular plaques in brain. While, Tau undergoes hyperphosphorylation and other post-translational modifications (PTMs), which eventually generates Tau oligomers, and intracellular neurofibrillary tangles (NFTs) in neurons. Moreover, the brain-resident glia and infiltrated macrophages elevate the level of CNS inflammation, which trigger the oxidative damage of neuronal circuits by reactive oxygen species (ROS) and Nitric oxide (NO). Microglia is the primary immune cell in the CNS, which is continuously surveilling the neuronal synapses and pathogen invasion. Microglia in the resting state is called {\textquoteleft}Ramified{\textquoteright}, which possess long surveilling extensions with a small cell body. But, upon activation, microglia retracts the cellular extensions and transform into round migratory cells, called as {\textquoteleft}Amoeboid{\textquoteright} state. Activated microglia undergoes actin remodeling by forming lamellipodia and filopodia, which directs the migratory axis while podosomes formed are involved in extracellular matrix degradation for invasion. Protein-aggregates in malfunctioning synapses and in CNS milieu can be detected by microglia, which results in its activation and migration. Subsequently, the phagocytosis of synapses leads to the inflammatory burst and memory loss. The extracellular nucleotides released from damaged neurons and the cytokine-chemokine gradients allow the neighboring microglia and macrophages to migrate-infiltrate at the site of neuronal-damage. The ionotropic (P2XR) and metabotropic (P2YR) purinergic receptor recognize extracellular ATP/ADP, which propagates through the intracellular calcium signaling, chemotaxis, phagocytosis and inflammation. The P2Y receptors give {\textquoteleft}find me{\textquoteright} or {\textquoteleft}eat me{\textquoteright} signals to microglia to either migrate or phagocytose cellular debris. Further, the actin cytoskeleton helps microglia to mediate directed chemotaxis and neuronal repair during neurodegeneration. Hence, we aim to emphasize the connection between purinergic signaling and actin-driven mechanical movements of microglia for migration and inflammation in AD. (C) 2020 IBRO. Published by Elsevier Ltd. All rights reserved.

}, keywords = {actin remodeling, Alzheimer{\textquoteright}s disease, microglia, P2Y signaling, purinergic GPCRs, Tauopathy}, issn = {0306-4522}, doi = {10.1016/j.neuroscience.2020.09.024}, author = {Das, Rashmi and Chinnathambi, Subashchandrabose} } @article {46842, title = {Effect of melatonin on tau aggregation and tau-mediated cell surface morphology}, journal = {International Journal of Biological Macromolecules}, volume = {152}, year = {2020}, month = {JUN }, pages = {30-39}, type = {Article}, abstract = {

Aggregation of Microtubule-associated protein Tau and its deposition in the form of neurofibrillary tangles (NFTs) is one of the pathological hallmarks of Alzheimer{\textquoteright}s disease (AD). Tau aggregation inhibition has been targeted in various studies including natural compounds and synthetic small molecules. Here, we have studied neurohormone- Melatonin against in vitro Tau aggregation and observed its effect on membrane topology, tubulin network and Tau phosphorylation in Neuro2A and N9 cell lines. The aggregation and conformation of Tau was determined by ThT fluorescence and CD spectroscopy respectively. The morphology of Tau aggregates in presence and absence of Melatonin was studied by transmission electron microscopy. Melatonin was found to reduce the formation of higher order oligomeric structures without affecting the overall aggregation kinetics of Tau. Melatonin also modulates and helps to maintain membrane morphology, independent on tubulin network as evidenced by FE-SEM and immunofluorescence analysis. Overall, Melatonin administration shows mild anti-aggregation and cytoprotective effects. (C) 2020 Elsevier B.V. All rights reserved.

}, keywords = {Alzheimer{\textquoteright}s disease, Cell surface morphology, melatonin, Paired helical filaments, tau protein, Tauopathies}, issn = {0141-8130}, doi = {10.1016/j.ijbiomac.2020.01.296}, author = {Das, Rashmi and Balmik, Abhishek Ankur and Chinnathambi, Subashchandrabose} } @article {46710, title = {Interaction of Tau with the chemokine receptor, CX3CR1 and its effect on microglial activation, migration and proliferation}, journal = {Cell and Bioscience}, volume = {10}, year = {2020}, month = {SEP}, pages = {109}, type = {Review}, abstract = {

Alzheimer{\textquoteright}s disease (AD) is a neurodegenerative disease that leads to progressive loss of memory and dementia. The pathological hallmarks of AD include extracellular accumulation of amyloid-beta peptides forming senile plaques and intracellular accumulation of Tau oligomers and filamentous species. Tau is a microtubule-binding protein that stabilizes tubulin to form microtubules under physiological condition. In AD/ pathological condition, Tau detaches from microtubules and aggregates to form oligomers of different sizes and filamentous species such as paired helical filaments. Microglia are the resident brain macrophages that are involved in the phagocytosis of microbes, cellular debris, misfolded and aggregated proteins. Chemokine receptor, CX3CR1 is mostly expressed on microglia and is involved in maintaining the microglia in a quiescent state by binding to its ligand, fractalkine (CX3CL1), which is expressed in neurons as both soluble or membrane-bound state. Hence, under physiological conditions, the CX3CR1/CX3CL1 axis plays a significant role in maintaining the central nervous system (CNS) homeostasis. Further, CX3CR1/CX3CL1 signalling is involved in the synthesis of anti-inflammatory cytokines and also has a significant role in cytoskeletal rearrangement, migration, apoptosis and proliferation. In AD brain, the expression level of fractalkine is reduced, and hence Tau competes to interact with its receptor, CX3CR1. In microglia, phagocytosis and internalization of extracellular Tau species occurs in the presence of a chemokine receptor, CX3CR1 which binds directly to Tau and promotes its internalization. In this review, the pathophysiological roles of CX3CR1/fractalkine signalling in microglia and neurons at different stages of Alzheimer{\textquoteright}s disease and the possible role of CX3CR1/Tau signalling has been widely discussed.

}, keywords = {Alzheimer{\textquoteright}s disease, CX3CR1 receptor, Fractalkine, microglia, Neuron, Tau}, doi = {10.1186/s13578-020-00474-4}, author = {Chidambaram, Hariharakrishnan and Das, Rashmi and Chinnathambi, Subashchandrabose} } @article {46945, title = {Melatonin interacts with repeat domain of Tau to mediate disaggregation of paired helical filaments}, journal = {Biochimica Et Biophysica Acta-General Subjects}, volume = {1864}, year = {2020}, month = {MAR}, pages = {129467}, type = {Article}, abstract = {

Tau is the major neuronal protein involved in the stabilization of microtubule assembly. In Alzheimer{\textquoteright}s disease, Tau self-assembles to form intracellular protein aggregates which are toxic to cells. Various methods have been tried and tested to restrain the aggregation of Tau. Most of the agents tested for this purpose have limitations in their effectiveness and availability to neuronal cells. We have tested melatonin, a neurohormone secreted by pineal gland and a well-known anti-oxidant, for its ability to interact with the repeat domain of Tau using ITC and NMR. In aggregation inhibition and disaggregation studies of repeat Tau, melatonin was found to modulate the aggregation propensity of repeat Tau at a concentration of 5000 mu M and was more effective in dissolving preformed aggregates rather than acting as an aggregation inhibitor. However, there were no major conformational changes in Tau in presence of melatonin as observed by CD spectroscopy. On the basis of our findings, we are proposing a mechanism by which melatonin can interact with the repeat domain of Tau and exhibit its disaggregation effect.

}, keywords = {Alzheimer{\textquoteright}s disease, Disaggregation, melatonin, Paired helical filaments, tau protein, Tauopathies}, issn = {0304-4165}, doi = {10.1016/j.bbagen.2019.129467}, author = {Balmik, Abhishek Ankur and Das, Rashmi and Dangi, Abha and Gorantla, Nalini Vijay and Marelli, Udaya Kiran and Chinnathambi, Subashchandrabose} } @article {47005, title = {Phagocytosis of full-length Tau oligomers by Actin-remodeling of activated microglia}, journal = {Journal of Neuroinflammation}, volume = {17}, year = {2020}, month = {JAN }, pages = {10}, type = {Article}, abstract = {

Background Alzheimer{\textquoteright}s disease is associated with the accumulation of intracellular Tau tangles within neurons and extracellular amyloid-beta plaques in the brain parenchyma, which altogether results in synaptic loss and neurodegeneration. Extracellular concentrations of oligomers and aggregated proteins initiate microglial activation and convert their state of synaptic surveillance into a destructive inflammatory state. Although Tau oligomers have fleeting nature, they were shown to mediate neurotoxicity and microglial pro-inflammation. Due to the instability of oligomers, in vitro experiments become challenging, and hence, the stability of the full-length Tau oligomers is a major concern. Methods In this study, we have prepared and stabilized hTau40(WT) oligomers, which were purified by size-exclusion chromatography. The formation of the oligomers was confirmed by western blot, thioflavin-S, 8-anilinonaphthaalene-1-sulfonic acid fluorescence, and circular dichroism spectroscopy, which determine the intermolecular cross-beta sheet structure and hydrophobicity. The efficiency of N9 microglial cells to phagocytose hTau40(WT) oligomer and subsequent microglial activation was studied by immunofluorescence microscopy with apotome. The one-way ANOVA was performed for the statistical analysis of fluorometric assay and microscopic analysis. Results Full-length Tau oligomers were detected in heterogeneous globular structures ranging from 5 to 50 nm as observed by high-resolution transmission electron microscopy, which was further characterized by oligomer-specific A11 antibody. Immunocytochemistry studies for oligomer treatment were evidenced with A11(+) Iba1(high) microglia, suggesting that the phagocytosis of extracellular Tau oligomers leads to microglial activation. Also, the microglia were observed with remodeled filopodia-like actin structures upon the exposure of oligomers and aggregated Tau. Conclusion The peri-membrane polymerization of actin filament and co-localization of Iba1 relate to the microglial movements for phagocytosis. Here, these findings suggest that microglia modified actin cytoskeleton for phagocytosis and rapid clearance of Tau oligomers in Alzheimer{\textquoteright}s disease condition.

}, keywords = {Actin, activation, Alzheimer{\textquoteright}s disease, microglia, migration, neurodegeneration, Tau Oligomers, Tauopathy}, doi = {10.1186/s12974-019-1694-y}, author = {Das, Rashmi and Balmik, Abhishek Ankur and Chinnathambi, Subashchandrabose} } @article {46759, title = {Transition metal nickel prevents Tau aggregation in Alzheimer{\textquoteright}s disease}, journal = {International Journal of Biological Macromolecules}, volume = {156}, year = {2020}, month = {AUG }, pages = {1359-1365}, type = {Article}, abstract = {

Alzheimer{\textquoteright}s disease is the leading cause of dementia, effecting majority of aged people worldwide. The multifaceted effectors of Alzheimer{\textquoteright}s disease primarily include Tau, amyloid-beta along with hyper activation of kinases, oxidative stress and mutations etc., makes it challenging to design therapeutics. Tau is a microtubule-associating protein, which is subjected to cellular stress resulting in the formation of neurofibrillary tangles, leading to loss of affinity for microtubules. This causes loss of microtubule stability and in turn alters axonal integrity. In the present work, emphasis towards understanding interaction of nickel with Tau was made. Metals such as iron, zinc, copper and lead etc., are known to modulate Tau conformation and enhance its aggregation. Our results showed the deliverance of Tau aggregation by nickel and its synthetic morpholine conjugate. Nickel prevents aggregation by inducing degradation of Tau as evidenced by SDS-PAGE and TEM. Nickel and the synthetic conjugate being non toxic to neuro2a cells and prevent Tau aggregation, might direct these complexes to overcome AD. (C) 2019 Published by Elsevier B.V.

}, keywords = {Aggregation, Alzheimer{\textquoteright}s disease, metals, Morpholine, Nickel chloride, Tau}, issn = {0141-8130}, doi = {10.1016/j.ijbiomac.2019.11.176}, author = {Gorantla, Nalini Vijay and Das, Rashmi and Balaraman, Ekambaram and Chinnathambi, Subashchandrabose} } @article {48361, title = {G-protein coupled purinergic P2Y12 receptor interacts and internalizes Tau(RD)-mediated by membrane-associated actin cytoskeleton remodeling in microglia}, journal = {European Journal of Cell Biology}, volume = {101}, year = {2022}, month = {APR}, pages = {151201}, type = {Article}, abstract = {

In Alzheimer{\textquoteright}s disease, the microtubule-associated protein, Tau misfolds to form aggregates and filaments in the intra- and extracellular region of neuronal cells. Microglial cells are the resident brain macrophage cells involved in constant surveillance and activated by the extracellular deposits. Purinergic receptors are involved in the chemotactic migration of microglial cells towards the site of inflammation. From our recent study, we have observed that the microglial P2Y12 receptor is involved in phagocytosis of full-length Tau species such as monomers, oligomers and aggregates by actin-driven chemotaxis. This study shows the interaction of repeat-domain of Tau (Tau(RD)) with the microglial P2Y12 receptor and the corresponding residues for interaction have been analysed by various in-silico approaches. In the cellular studies, Tau(RD) was found to interact with microglial P2Y12R and induces its cellular expression confirmed by co-immunoprecipitation and western blot analysis. Furthermore, the P2Y12R-mediated Tau(RD) internalization has demonstrated activation of microglia with an increase in the Iba1 level, and Tau(RD) becomes accumulated at the peri-nuclear region for the degradation. Similarly, immunofluorescence microscopic studies emphasized that Tau(RD) is phagocytosed by microglial P2Y12R via the membrane-associated actin remodeling as filopodia extension. Upon internalization, we have demonstrated the P2Y12R signaling-mediated degradation of accumulated Tau(RD) by lysosomal pathway. Altogether, microglial P2Y12R interacts with Tau(RD) and mediates directed migration and activation for its internalization and degradation.

}, keywords = {Alzheimer{\textquoteright}s disease, Internalization, microglia, P2Y12R, Phagocytosis, Tau(RD)}, issn = {0171-9335}, doi = {10.1016/j.ejcb.2022.151201}, author = {Chidambaram, Hariharakrishnan and Das, Rashmi and Chinnathambi, Subashchandrabose} }