Biology subjects

Ghetti, B.

Publications and source records attributed to Ghetti, B..

25 records · Page 2Linked to original sources

bioRxiv2021

Structure-based Classification of Tauopathies

Ordered assembly of the tau protein into filaments characterizes multiple neurodegenerative diseases, which are called tauopathies. We previously reported that by electron cryo-microscopy (cryo-EM), tau filament structures from Alzheimers disease (1,2), chronic traumatic encephalopathy (CTE) (3), Picks disease (4) and corticobasal degeneration (CBD) (5) are distinct. Here we show that the structures of tau filaments from typical and atypical progressive supranuclear palsy (PSP), the most common tauopathy after Alzheimers disease, define a previously unknown, three-layered fold. Moreover, the tau filament structures from globular glial tauopathy (GGT, Types I and II) are similar to those from PSP. The tau filament fold of argyrophilic grain disease (AGD) differs from the above and resembles the four-layered CBD fold. The majority of tau filaments from aging-related tau astrogliopathy (ARTAG) also have the AGD fold. Surprisingly, tau protofilament structures from inherited cases with mutations +3/+16 in intron 10 of MAPT, the microtubule-associated protein tau gene, are identical to those from AGD, suggesting that a relative overproduction of four-repeat tau can give rise to the AGD fold. Finally, tau filament structures from cases of familial British dementia (FBD) and familial Danish dementia (FDD) are the same as those from Alzheimers disease and primary age-related tauopathy (PART). These structures provide the basis for a classification of tauopathies that also allows identification of new entities, as we show here for a case diagnosed as PSP, but with abundant spherical 4R tau inclusions in limbic and other brain areas. The structures of the tau fold of this new disease (Limbic-predominant Neuronal inclusion body 4R Tauopathy, LNT) were intermediate between those of GGT and PSP.

neuroscience↗

bioRxiv2021

Spontaneous Isomerization of Asp387 in Tau is Diagnostic for Alzheimer's Disease: An Endogenous Indicator of Reduced Autophagic Flux

Amino acid isomerization is a spontaneous chemical modification potentially related to the underlying causes of Alzheimers disease (AD). We demonstrate that data-independent acquisition mass spectrometry can be used to characterize isomerization in complex protein mixtures. Examination of a large cohort of brain tissue samples revealed a striking relationship between isomerization of tau and AD status. Surprisingly, isomerization was found to be more abundant in both autosomal dominant and sporadic AD samples relative to controls. We hypothesize that lower autophagic flux in AD brains accounts for these results. Additional data, including quantitative analysis of proteins related to autophagy, strongly support this hypothesis. For example, isomerization of tau is positively correlated with levels of p62, a recognized indicator of autophagic inhibition. In sum, the data suggest strong ties between isomerization and autophagic flux, which may therefore represent a promising target for future investigations into the therapy and prevention of AD.

neuroscience↗

bioRxiv2021

Microglia become hypofunctional and release metalloproteases and tau seeds after phagocytosing live neurons with P301S tau aggregates

The microtubule-associated protein tau aggregates in multiple neurodegenerative diseases, causing inflammation and changing the inflammatory signature of microglia by unknown mechanisms. We have shown that microglia phagocytose live neurons containing tau aggregates cultured from P301S tau transgenic mice due to neuronal tau aggregate-induced exposure of the eat me signal phosphatidylserine. Here we show that after phagocytosis, microglia become hypophagocytic while releasing seed-competent insoluble tau aggregates. These microglia activate acidic {beta}-galactosidase, and release senescence-associated cytokines and matrix remodeling enzymes alongside tau, indicating a senescent phenotype. In particular, the marked NF{kappa}B-induced activation of matrix metalloprotease 3 (MMP3/stromelysinl) was replicated in the brains of P301S mutant tau transgenic mice, and in human brains from tauopathy patients. These data show that microglia that have been activated to ingest live neurons with tau aggregates behave hormetically, becoming hypofunctional while acting as vectors of tau aggregate spreading.

neuroscience↗

bioRxiv2020

Structures of α-synuclein filaments from multiple system atrophy

Synucleinopathies are human neurodegenerative diseases that include multiple system atrophy (MSA), Parkinsons disease, Parkinsons disease dementia (PDD) and dementia with Lewy bodies (DLB) (1). Existing treatments are at best symptomatic. These diseases are characterised by the presence in brain cells of filamentous inclusions of -synuclein, the formation of which is believed to cause disease (2, 3). However, the structures of -synuclein filaments from human brain are not known. Here we show, using electron cryo-microscopy, that -synuclein inclusions from MSA are made of two types of filaments, each of which consists of two different protofilaments. Non-proteinaceous molecules are present at the protofilament interfaces. By two-dimensional class averaging, we show that -synuclein filaments from the brains of patients with MSA and DLB are different, suggesting that distinct conformers (or strains) characterise synucleinopathies. As was the case of tau assemblies (4-9), the structures of -synuclein filaments extracted from the brains of individuals with MSA differ from those formed in vitro using recombinant proteins, with implications for understanding the mechanisms of aggregate propagation and neurodegeneration in human brain. These findings have diagnostic and potential therapeutic relevance, especially in view of the unmet clinical need to be able to image filamentous -synuclein inclusions in human brain.

neuroscience↗

bioRxiv2019

Novel tau filament fold in corticobasal degeneration, a four-repeat tauopathy

Corticobasal degeneration (CBD) is a neurodegenerative tauopathy that is characterised by motor and cognitive disturbances (1-3). A higher frequency of the H1 haplotype of MAPT, the tau gene, is present in cases of CBD than in controls (4, 5) and genome-wide association studies have identified additional risk factors (6). By histology, astrocytic plaques are diagnostic of CBD (7, 8), as are detergent-insoluble tau fragments of 37 kDa by SDS-PAGE (9). Like progressive supranuclear palsy (PSP), globular glial tauopathy (GGT) and argyrophilic grain disease (AGD) (10), CBD is characterised by abundant filamentous tau inclusions that are made of isoforms with four microtubule-binding repeats (4R) (11-15). This distinguishes 4R tauopathies from Picks disease, filaments of which are made of three-repeat (3R) tau isoforms, and from Alzheimers disease and chronic traumatic encephalopathy (CTE), where both 3R and 4R tau isoforms are found in the filaments (16). Here we report the structures of tau filaments extracted from the brains of three individuals with CBD using electron cryo-microscopy (cryo-EM). They were identical between cases, but distinct from those of Alzheimers disease, Picks disease and CTE (17-19). The core of CBD filaments comprises residues K274-E380 of tau, spanning the last residue of R1, the whole of R2, R3 and R4, as well as 12 amino acids after R4. It adopts a novel four-layered fold, which encloses a large non-proteinaceous density. The latter is surrounded by the side chains of lysine residues 290 and 294 from R2 and 370 from the sequence after R4. CBD is the first 4R tauopathy with filaments of known structure.

neuroscience↗

bioRxiv2018

Tau filaments from multiple cases of sporadic and inherited Alzheimer’s disease adopt a common fold

The ordered assembly of tau protein into abnormal filaments is a defining characteristic of Alzheimers disease (AD) and other neurodegenerative disorders. It is not known if the structures of tau filaments vary within, or between, the brains of individuals with AD. We used a combination of electron cryo-microscopy (cryo-EM) and immuno-gold negative-stain electron microscopy (immuno-EM) to determine the structures of paired helical filaments (PHFs) and straight filaments (SFs) from the frontal cortex of 17 cases of typical AD (15 sporadic and 2 inherited) and 2 cases of atypical AD (posterior cortical atrophy). The high-resolution structures of PHFs and SFs from the frontal cortex of 3 cases of typical AD, 2 sporadic and 1 inherited, were determined by cryo-EM. We also used immuno-EM to study the PHFs and SFs from a number of cortical and subcortical brain regions. PHFs outnumbered SFs in all AD cases. By cryo-EM, PHFs and SFs were made of two C-shaped protofilaments with a combined cross-{beta}/{beta}-helix structure, as described previously for a case of AD. The higher resolution structures obtained here showed two additional amino acids at each end of the protofilament structure. The immuno-EM findings, which established the presence of repeats 3 and 4, but not repeats 1 and 2, of tau in the filament cores of all AD cases and brain regions thereof, were consistent with the cryo-EM results. These findings show that there is no significant variation in tau filament structures between individuals with AD. This knowledge will be crucial for understanding the mechanisms that underlie tau filament formation and for developing novel diagnostics and therapies.

neuroscience↗

bioRxiv2018

Structures of filaments from Pick’s disease reveal a novel tau protein fold

The ordered assembly of tau protein into abnormal filamentous inclusions underlies many human neurodegenerative diseases1. Tau assemblies appear to spread through specific neural networks in each disease2, with short filaments having the greatest seeding activity3. The abundance of tau inclusions strongly correlates with disease symptoms4. Six tau isoforms are expressed in normal adult human brain - three isoforms with four microtubule-binding repeats each (4R tau) and three isoforms lacking the second repeat (3R tau)1. In various diseases, tau filaments can be composed of either 3R tau or 4R tau, or of both 3R and 4R tau. They have distinct cellular and neuroanatomical distributions5, with morphological and biochemical differences suggesting that they may be able to adopt disease-specific molecular conformations6,7. Such conformers may give rise to different neuropathological phenotypes8,9, reminiscent of prion strains10. However, the underlying structures are not known. Using electron cryo-microscopy (cryo-EM), we recently reported the structures of tau filaments from Alzheimers disease, which contain both 3R and 4R tau11. Here we have determined the structures of tau filaments from Picks disease, a neurodegenerative disorder characterised by frontotemporal dementia. They consist of residues K254-F378 of 3R tau, which are folded differently when compared to tau in Alzheimers disease filaments, establishing the existence of conformers of assembled tau. The Pick fold explains the selective incorporation of 3R tau in Pick bodies and the differences in phosphorylation relative to the tau filaments of Alzheimers disease. Our findings show how tau can adopt distinct folds in human brain in different diseases, an essential step for understanding the formation and propagation of molecular conformers.

biophysics↗