@article {46933, title = {Basic limonoid modulates chaperone-mediated proteostasis and dissolve Tau fibrils}, journal = {Scientific Reports}, volume = {10}, year = {2020}, month = {MAR}, pages = {4023}, type = {Article}, abstract = {

The Alzheimer{\textquoteright}s disease pathology is associated with accumulation of intracellular neurofibrillary tangles and extracellular senile plaques. The formation of initial nucleus triggers conformational changes in Tau and leads to its deposition. Hence, there is a need to eliminate these toxic proteins for proper functioning of neuronal cells. In this aspect, we screened the effect of basic limonoids such as gedunin, epoxyazadiradione, azadirone and azadiradione on inhibiting Tau aggregation as well as disintegration of induced Tau aggregates. It was observed that these basic limonoids effectively prevented aggregates formation by Tau and also exhibited the property of destabilizing matured Tau aggregates. The molecular docking analysis suggests that the basic limonoids interact with hexapeptide regions of aggregated Tau. Although these limonoids caused the conformational changes in Tau to beta-sheet structure, the cytological studies indicate that basic limonoids rescued cell death. The dual role of limonoids in Tau aggregation inhibition and disintegration of matured aggregates suggests them to be potent molecules in overcoming Tau pathology. Further, their origin from a medicinally important plant neem, which known to possess remarkable biological activities was also found to play protective role in HEK293T cells. Basic limonoids were non-toxic to HEK293T cells and also aided in activation of HSF1 by inducing its accumulation in nucleus. Western blotting and immunofluorescence studies showed that HSF1 in downstream increased the transcription of Hsp70 thus, aggravating cytosolic Hsp70 levels that can channel clearance of aberrant Tau. All these results mark basic limonoids as potential therapeutic natural products.

}, issn = {2045-2322}, doi = {10.1038/s41598-020-60773-1}, author = {Gorantla, Nalini Vijay and Das, Rashmi and Chidambaram, Hariharakrishnan and Dubey, Tushar and Mulani, Fayaj A. and Thulasiram, V. Hirekodathakallu and Chinnathambi, Subashchandrabose} } @article {46768, title = {EGCG impedes human Tau aggregation and interacts with Tau}, journal = {Scientific Reports}, volume = {10}, year = {2020}, month = {JUL}, pages = {12579}, type = {Article}, abstract = {

Tau aggregation and accumulation is a key event in the pathogenesis of Alzheimer{\textquoteright}s disease. Inhibition of Tau aggregation is therefore a potential therapeutic strategy to ameliorate the disease. Phytochemicals are being highlighted as potential aggregation inhibitors. Epigallocatechin-3-gallate (EGCG) is an active phytochemical of green tea that has shown its potency against various diseases including aggregation inhibition of repeat Tau. The potency of EGCG in altering the PHF assembly of full-length human Tau has not been fully explored. By various biophysical and biochemical analyses like ThS fluorescence assay, MALDI-TOF analysis and Isothermal Titration Calorimetry, we demonstrate dual effect of EGCG on aggregation inhibition and disassembly of full-length Tau and their binding affinity. The IC50 for Tau aggregation by EGCG was found to be 64.2 mu M.

}, issn = {2045-2322}, doi = {10.1038/s41598-020-69429-6}, author = {Sonawane, Shweta Kishor and Chidambaram, Hariharakrishnan and Boral, Debjyoti and Gorantla, Nalini Vijay and Balmik, Abhishek Ankur and Dangi, Abha and Ramasamy, Sureshkumar and Marelli, Udaya Kiran and Chinnathambi, Subashchandrabose} } @article {46807, title = {G-protein coupled receptors and tau-different roles in alzheimer{\textquoteright}s disease}, journal = {Neuroscience}, volume = {438}, year = {2020}, month = {JUL }, pages = {198-214}, type = {Article}, abstract = {

Post-translational modification of Tau, a microtubule-associated protein in the neuronal cell, plays a major role in Alzheimer{\textquoteright}s disease. Tau is an axonal protein expressed in mature neurons that promote the self-assembly of tubulin into microtubules and its stabilization in neurons. Phosphorylation of Tau makes it prone to aggregation at the intra-neuronal region leading to impaired neurotransmission and dementia. Tau aggregates undergo trans-cellular propagation by the release of fibrillar species into the extra-cellular environment from damaged and infected neurons that can be internalized by neighbouring neuronal and glia cells and promotes aggregation in healthy cells. G-protein coupled receptors, the largest group of seven transmembrane receptors, are involved in neuronal signal transduction in response to various signals such as hormones and neurotransmitters. In Alzheimer{\textquoteright}s disease, GPCRs are involved in phosphorylation of Tau through various downstream kinases such as GSK-3b, CDK-5 and ERKs signalling cascade. Several neuronal GPCRs that are involved in Tau phosphorylation are elaborated in this review. The astrocytic GPCR, Tau phosphorylation mediated by CaS receptors and its propagation by exosomes are also elaborated. In the microglia, the extra-cellular Tau binding to a chemokine GPCR, CX3CR1 triggers its internalization, whereas Tau phosphorylation at specific sites decreases its binding affinity to this receptor. Here we highlight the role of GPCRs in Tau phosphorylation and Tau interaction in different cells of the nervous system. Hence, the role of GPCRs are attaining more attention in the therapeutic field of Alzheimer{\textquoteright}s disease. Specific agonists/antagonists and allosteric modulators could be the potential target for therapy against GPCR-mediated Tau phosphorylation in Alzheimer{\textquoteright}s disease. (C) 2020 IBRO. Published by Elsevier Ltd. All rights reserved.

}, keywords = {Alzheimer{\textquoteright}s disease, GPCRs, microglia, Tau internalization, Tau phosphorylation, Tau propagation}, issn = {0306-4522}, doi = {10.1016/j.neuroscience.2020.04.019}, author = {Chidambaram, Hariharakrishnan and Chinnathambi, Subashchandrabose} } @article {46605, title = {HDAC6 ZnF UBP as the modifier of tau structure and function}, journal = {Biochemistry}, volume = {59}, year = {2020}, month = {DEC }, pages = {4546-4562}, type = {Article}, abstract = {

Histone deacetylase 6 is a class H histone deacetylase primarily present in the cytoplasm and involved in the regulation of various cellular functions. It consists of two catalytic deacetylase domains and a unique zinc finger ubiquitin binding protein domain, which sets it apart from other HDACs. HDAC6 is known to regulate cellular activities by modifying the function of microtubules, HSP90, and cortactin through deacetylation. Apart from the catalytic activity of HDAC6, it interacts with other proteins through either the SE14 domain or the ZnF UBP domain to modulate their functions. Here, we have studied the role of the HDAC6 ZnF UBP domain as a modifier of Tau aggregation by its direct interaction with the polyproline region/repeat region of Tau. Interaction of HDAC6 ZnF UBP with Tau was found to reduce the propensity of Tau to self-aggregate and to disaggregate preformed aggregates in a concentration-dependent manner and also bring about the conformational changes in Tau protein. The interaction of HDAC6 ZnF UBP with Tau results in its degradation, suggesting either proteolytic activity of HDAC6 ZnF UBP or its role in enhancing autoproteolysis of Tau.

}, issn = {0006-2960}, doi = {10.1021/acs.biochem.0c00585}, author = {Balmik, Abhishek Ankur and Chidambaram, Hariharakrishnan and Dangi, Abha and Marelli, Udaya Kiran 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 {46847, title = {Role of microglia in regulating cholesterol and tau pathology in alzheimer{\textquoteright}s disease}, journal = {Cellular and Molecular Neurobiology}, year = {2020}, month = {MAY}, type = {Review; Early Access 2020}, abstract = {

Cholesterol, a principal constituent of the cell membrane, plays a crucial role in the brain by regulating the synaptic transmission, neuronal signaling, as well as neurodegenerative diseases. Defects in the cholesterol trafficking are associated with enhanced generation of hyperphosphorylated Tau and Amyloid-beta protein. Tau, a major microtubule-associated protein in the brain, is the key regulator of the mature neuron. Abnormally hyperphosphorylated Tau hampers the major functions related to microtubule assembly by promoting neurofibrillary tangles of paired helical filaments, twisted ribbons, and straight filaments. The observed pathological changes due to impaired cholesterol and Tau protein accumulation cause Alzheimer{\textquoteright}s disease. Thus, in order to regulate the pathogenesis of Alzheimer{\textquoteright}s disease, regulation of cholesterol metabolism, as well as Tau phosphorylation, is essential. The current review provides an overview of (1) cholesterol synthesis in the brain, neurons, astrocytes, and microglia; (2) the mechanism involved in modulating cholesterol concentration between the astrocytes and brain; (3) major mechanisms involved in the hyperphosphorylation of Tau and amyloid-beta protein; and (4) microglial involvement in its regulation. Thus, the answering key questions will provide an in-depth information on microglia involvement in managing the pathogenesis of cholesterol-modulated hyperphosphorylated Tau protein.

}, keywords = {Alzheimer{\textquoteright}s disease, Amyloid-beta protein, Cholesterol, microglia, Tau hyperphosphorylation}, issn = {0272-4340}, doi = {10.1007/s10571-020-00883-6}, author = {Nanjundaiah, Shwetha and Chidambaram, Hariharakrishnan and Chandrashekar, Madhura and Chinnathambi, Subashchandrabose} } @article {47803, title = {G-protein coupled purinergic P2Y12 receptor interacts and internalizes TauRD-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 (TauRD) with the microglial P2Y12 receptor and the corresponding residues for interaction have been analysed by various in-silico approaches. In the cellular studies, TauRD was found to interact with microglial P2Y12R and induces its cellular expression confirmed by co-immunoprecipitation and western blot analysis. Furthermore, the P2Y12R-mediated TauRD internalization has demonstrated activation of microglia with an increase in the Iba1 level, and TauRD becomes accumulated at the peri-nuclear region for the degradation. Similarly, immunofluorescence microscopic studies emphasized that TauRD 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 TauRD by lysosomal pathway. Altogether, microglial P2Y12R interacts with TauRD and mediates directed migration and activation for its internalization and degradation.}, keywords = {Alzheimer{\textquoteright}s disease, Internalization, microglia, P2Y12R, Phagocytosis, Tau}, issn = {0171-9335}, doi = {https://doi.org/10.1016/j.ejcb.2022.151201}, url = {https://www.sciencedirect.com/science/article/pii/S0171933522000048}, author = {Chidambaram, Hariharakrishnan and Das, Rashmi 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} } @article {46609, title = {Role of cysteines in accelerating Tau filament formation}, journal = {Journal of Biomolecular Structure \& Dynamics}, volume = {40}, year = {2022}, month = {JUN}, pages = {4366-4375}, type = {Article}, abstract = {

Alzheimer{\textquoteright}s disease is majorly associated with intracellular accumulation of Tau into paired helical filaments and tangles. The self-aggregated dimeric and oligomeric species of Tau formed are more toxic to neuronal cells and acts as seeds for filament formation. The two cysteine residues and the two hexapeptide regions of full-length Tau play a key role in initialization and filament formation during Tau aggregation. The role of cysteine residues in Tau aggregation has been studied by in-vitro aggregation assay that was measured by Thioflavin S fluorescence to observe the kinetics of aggregation. In this study, we have performed in-vitro aggregation assay with recombinant full-length Tau and the cysteine mutants to understand the mechanism of cysteine independent Tau aggregation. Here, we report that cysteine mutant full-length Tau can aggregate to form filaments under in-vitro conditions. To visualize the polymorphisms of Tau and cysteine mutants under different aggregation conditions anionic cofactor, heparin was employed. Wild-type Tau showed rapid aggregation to form oligomers and filaments. On the other hand, the cysteine mutant delayed the initial Tau aggregation. This indicates the importance of cysteine residues in accelerating initial Tau nucleation for its aggregation. The filament morphology of wild-type and cysteine mutant Tau has been characterized using transmission electron microscopy and high-resolution transmission electron microscopy. Communicated by Ramaswamy H. Sarma

}, keywords = {Heparin-induced aggregation, Paired helical filaments, Tau Aggregation, Tau Oligomers, tau protein}, issn = {0739-1102}, doi = {10.1080/07391102.2020.1856720}, author = {Chidambaram, Hariharakrishnan and Chinnathambi, Subashchandrabose} } @article {49442, title = {Dual modification of tau by pseudophosphorylation and glycation does not enhance amorphous aggregation}, journal = {Cellular Physiology and Biochemistry}, year = {2024}, month = {APR}, type = {Article}, abstract = {

Background/Aims:

\ The neurofibrillary tangles consisting of Tau protein are an important pathology in Alzheimer{\textquoteright}s disease. The paired helical filaments of Tau form most of the NFTs. These PHFs of Tau are found to carry numerous post-translational modifications, which stabilize them and aid in aggregation. The mechanistic function of Tau is to bind and stabilize the axonal microtubules. Hyperphosphorylation of Tau causes it to compromise its physiological function and accumulate in the neurons in the form of aggregates. Such residue-specific phosphorylation has been studied by employing Tau pseudophosphorylation mutants. But in addition to phosphorylation, several other modifications also aid in stabilizing the Tau PHF. Glycation is one such non-enzymatic PTM caused by sugars and their reactive intermediates. In this study, we employed the pseudophosphorylated Tau double mutants (262/404D, 262/396D, and 231/262) for studying their modification by methyl glyoxal, a reactive intermediate of glucose metabolism.\ 

Methods:

\ We studied various biophysical properties like aggregation propensity, Advanced glycation end-product formation, and global conformation of the Tau with dual modifications. Our study includes the use of\ in vitro\ techniques e.g., ThS fluorescence assay, electron microscopy, CD spectroscopy, SDS-PAGE.\ 

Results:

\ The overall result of the study suggest that the MG-induced Tau aggregation is influenced by the residue-specific Tau phosphorylation.\ 

Conclusion:

\ In conclusion, the combinatorial effect of discreet PTMs on Tau function could lead to a better understanding of Tauopathy.

}, doi = {10.33594/000000693}, author = {Chinnathambi, Subashchandrabose and Sonawane, Shweta Kishor and Chandrashekar, Madhura and Chidambaram, Hariharakrishnan and Thulasiram, Shrivatsa and Kulkarni, Mahesh J.} }