Biology subjects

Bras, I. C.

Publications and source records attributed to Bras, I. C..

4 recordsLinked to original sources

bioRxiv2026

Loss of interruption in the HTT CAG repeat is associated with increased somatic expansion and loss of medium spiny neurons in HD

Synonymous loss of interruption variants in the expanded CAG repeat sequence of Huntingtin (HTT) accelerate the clinical onset and progression of Huntington disease (HD). Medium spiny neurons (MSNs) are gradually lost in HD and undergo selective somatic CAG expansion, but it is unclear how CAG expansion in MSNs relates to HD pathology. Here, we show that MSNs with large (111-150 CAG) and very large (>150 CAG) somatic expansions are rare in early manifest HD, but accumulate in proportion with duration of disease and inherited CAG repeat length. In patients with the deleterious CAG-CCG loss-of-interruption (CAG-CCG LOI) modifier, the proportion of MSNs with large and very large expansions is increased [~]5-fold despite reduced small somatic expansions in blood, and direct caudate MSN counts are reduced. Our findings suggest that increased somatic CAG expansion contributes to accelerated striatal MSN pathology and hastened onset of HD, but that MSNs with very large genomic CAG expansions can persist among surviving neurons of the HD brain.

neuroscience↗

bioRxiv2025

Neuron-derived extracellular vesicles in plasma present a potential non-invasive biomarker for Huntingtin protein and RNA assessment in Huntington disease

Huntington disease (HD) is a neurodegenerative disease caused by a trinucleotide repeat expansion in the HTT gene encoding an elongated polyglutamine tract in the huntingtin (HTT) protein. The use of biomarkers has become a major component in preclinical studies focusing on HTT lowering strategies. Quantification of soluble mutant HTT (mHTT) in cerebrospinal fluid (CSF) has served as a pharmacodynamic readout and as potential disease progression biomarker. However, development of future assays for HTT measurement from other biofluids, such as blood, will facilitate the access to human samples since CSF collection is an invasive outpatient procedure. Brain cells, in particular neurons, secrete extracellular vesicles (EVs) that cross the blood-brain barrier and circulate in blood. Importantly, EVs have been identified to be involved in HTT export from cells to the extracellular space. However, it is unknow which vesicle subtype correlates better with HD progression. Our work investigates the potential of EVs as non-invasive sources of clinical biomarkers in liquid biopsies. We developed an optimized ultracentrifugation protocol for the purification of ectosomes and exosomes from human samples and plasma of humanized HD mouse models. Ectosomes are larger vesicles that bud from the plasma membrane of cells, whereas exosomes originate from multivesicular bodies and are afterwards released to the extracellular space. Consistent with previous published data in other model systems, ectosomes isolated from plasma of the Hu97/18 mouse model contain both wild-type (wt) and mHTT in higher levels than in exosomes. Similar results were observed in media from HD induced pluripotent stem cells (iPSCs)-differentiated neurons and in Hu97/18 primary neuronal cultures. Interestingly, we also found higher levels of HTT transcripts in this EV subtype. We further demonstrate that initial storage of the samples using a slow freezing protocol preserves HTT and EV protein marker levels, highlighting the importance of sample preparation for EV isolation and analysis. Our results also show that plasma contains vesicles originated from neuronal cells that can be isolated using neuron-specific markers, such as ATPase Na+/K+ transporting subunit alpha 3 (ATP1A3), allowing the evaluation of HTT levels in the brain through vesicles circulating in the blood. Overall, our results demonstrate that HTT protein measurement from EVs isolated from blood can be a potential less-invasive disease biomarker. We also demonstrate that EVs subtypes contain different HTT protein and RNA levels, important for the development of consistent and reliable biomarkers. Further characterization of neuron-specific EVs content from patient-derived biofluids will lead to the development of novel clinical biomarkers and for evaluation of therapeutic strategies.

neuroscience↗

bioRxiv2021

Common molecular mechanisms underlie the transfer of alpha-synuclein, Tau and huntingtin and modulate spontaneous activity in neuronal cells

The misfolding and accumulation of disease-related proteins are common hallmarks among several neurodegenerative diseases. Alpha-synuclein (aSyn), Tau and huntingtin (wild-type and mutant, 25QHtt and 103QHtt, respectively) were recently shown to be transferred from cell-to-cell through different cellular pathways, thereby contributing to disease progression and neurodegeneration. However, the relative contribution of each of these mechanisms towards the spreading of these different proteins and the overall effect on neuronal function is still unclear. To address this, we exploited different cell-based systems to conduct a systematic comparison of the mechanisms of release of aSyn, Tau and Htt, and evaluated the effects of each protein upon internalization in microglial, astrocytic, and neuronal cells. In the models used, we demonstrate that 25QHtt, aSyn and Tau are released to the extracellular space at higher levels than 103QHtt, and their release can be further augmented with the co-expression of USP19. Furthermore, cortical neurons treated with recombinant monomeric 43QHtt exhibited alterations in neuronal activity that correlated with the toxicity of the polyglutamine expansion. Tau internalization resulted in an increase in neuronal activity, in contrast to slight effects observed with aSyn. Interestingly, all these disease-associated proteins were present at higher levels in ectosomes than in exosomes. The internalization of both types of extracellular vesicles (EVs) by microglial or astrocytic cells elicited the production of pro-inflammatory cytokines and promoted an increase in autophagy markers. Additionally, the uptake of the EVs modulated neuronal activity in cortical neurons. Overall, our systematic study demonstrates the release of neurodegenerative disease-associated proteins through similar cellular pathways. Furthermore, it emphasizes that protein release, both in a free form or in EVs, might contribute to a variety of detrimental effects in receiving cells and to progression of pathology, suggesting they may be exploited as valid targets for therapeutic intervention in different neurodegenerative diseases. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=153 SRC="FIGDIR/small/452825v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@1400e8org.highwire.dtl.DTLVardef@1478fccorg.highwire.dtl.DTLVardef@1319abcorg.highwire.dtl.DTLVardef@1a5ad40_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Ectosomes and exosomes are distinct proteomic entities that modulate spontaneous activity in neuronal cells

Extracellular vesicles (EVs) are important mediators in intercellular communication. However, understanding the biological origin and functional effects of EVs subtypes has been challenging due to the moderate differences in their physical properties and absence of reliable markers. Here, we characterize the proteomes of ectosomes and exosomes using an improved differential ultracentrifugation protocol and quantitative proteomics. Cytoskeleton and glycolytic proteins are distinctively present in ectosomes, while endosomal sorting complexes proteins and tetraspanins are enriched in exosomes. Furthermore, annexin-A2 was identified as a specific marker for ectosomes derived from cell media and human cerebrospinal fluid. Expression of EGFP as a cytosolic reporter leads to its incorporation in EVs and enables their imaging with higher resolution. Importantly, ectosomes and exosomes internalization in neuronal cells results in the modulation of neuronal spontaneous activity. Our findings suggest that EVs cargoes reflect core intracellular processes, and their functional properties might regulate basic biological and pathological processes.

neuroscience↗