Biology subjects

Barrasa, M. I.

Publications and source records attributed to Barrasa, M. I..

4 recordsLinked to original sources

bioRxiv2026

tRNA-derived fragments elevated in Alzheimer's disease facilitate Tau aggregation

Tauopathies, including Alzheimers disease (AD), are driven by pathological Tau aggregation, a process that requires co-factors. Small RNAs (sRNA) have been proposed as such co-factors, yet little is known about endogenous transcripts that promote Tau pathology. We identify stress-induced tRNA-derived RNAs or fragments (tDRs/tRFs) as the most dysregulated sRNA class in human AD brains, PS19 mice overexpressing mutant human Tau, and human neuronal tauopathy models. Notably, the highly accumulating 5GluCTC and 5GlyGCC tRFs directly bind Tau and induce its phosphorylation, oligomerization, fibril formation, and impact neurite growth. 5GluCTC is enriched in pathological Tau precipitates and co-localizes with oligomeric Tau in PS19 mouse brains. Inhibiting 5GluCTC mitigates Tau pathology. Furthermore, these tRFs are highly secreted by neurons and can be taken up by recipient cells, contributing to Tau pathology. Our findings establish 5GluCTC as a key regulator of Tau aggregation and suggest its inhibition as a promising therapeutic strategy for tauopathies. HighlightsO_LISpecific stress-induced 5tRFs strongly accumulate in Alzheimers disease brains C_LIO_LI5GluCTC binds and co-localizes with pathologic Tau in neurons and in the brain C_LIO_LI5GluCTC promotes pathologic Tau species while its inhibition reverses these effects C_LIO_LISpecific 5tRFs are horizontally transferred between neurons C_LI

neuroscience↗

bioRxiv2023

Rett Syndrome astrocytes disrupt neuronal activity and cerebral organoid development through transfer of dysfunctional mitochondria

Studies on the function of Methyl CpG binding protein 2 (MECP2) and the consequence of MECP2 deficiency and duplication have largely focused on neurons. The function of MECP2 in human glia, along with the comprehensive understanding of glial function in neurodevelopmental disorders, is much less understood. Using female and male human embryonic stem cell (hESC) lines to model MECP2 loss-of-function (LOF) in Rett Syndrome (RTT) in the developing brain, we investigated the molecular underpinnings of astrocyte (AST) development and dysfunction, and the mechanisms by which AST contribute to neuronal activity. Here we show that hESC-derived RTT ASTs have fewer mitochondria yet similar levels of reactive oxygen species compared to isogenic controls (CTR). We identified significantly diminished mitochondrial respiration that was compensated by increased glycolysis, and that the molecular mechanism behind mitochondrial dysfunction were reduced key proteins around the tricarboxylic acid (TCA) cycle and electron transport chain (ETC). We found an increased abundance of cytosolic amino acids in RTT ASTs under basal conditions that was readily depleted when energy demands were increased. We determined that RTT AST can donate their mitochondria to hESC-derived cortical neurons, and that isolated mitochondria from RTT ASTs are sufficient to cause significant changes to neuronal activity, increasing local field potentials to a hyperexcitable state. To examine mitochondrial health in the developing brain, we derived cerebral organoids. Ultrastructural analysis indicated that mitochondria from RTT hESC-derived organoids were significantly smaller compared to mitochondria from CTR organoids, indicating decreased connectivity and function, and this phenotype was stronger in glia compared to neurons. Using a multiomics epigenetics approach, we found hallmarks of RTT developmental delay and glial specific gene expression changes that corroborate altered energy metabolism and mitochondrial dysfunction. Based on these results, we propose that release of dysfunctional mitochondria from RTT ASTs to neurons furthers pathophysiology of the syndrome.

neuroscience↗

bioRxiv2023

LINE1-mediated reverse transcription and genomic integration of SARS-CoV-2 mRNA detected in virus-infected but not in viral mRNA-transfected cells

SARS-CoV-2 sequences can be reverse-transcribed and integrated into the genomes of virus-infected cells by a LINE1-mediated retrotransposition mechanism. Whole genome sequencing (WGS) methods detected retrotransposed SARS-CoV-2 subgenomic sequences in virus-infected cells overexpressing LINE1, while an enrichment method (TagMap) identified retrotranspositions in cells that did not overexpress LINE1. LINE1 overexpression increased retrotranspositions about 1,000-fold as compared to non-overexpressing cells. Nanopore WGS can directly recover retrotransposed viral and flanking host sequences but its sensitivity depends on the depth of sequencing (a typical 20-fold sequencing depth would only examine 10 diploid cell equivalents). In contrast, TagMap enriches for the host-virus junctions and can interrogate up to 20,000 cells and is able to detect rare viral retrotranspositions in LINE1 non-overexpressing cells. Although Nanopore WGS is 10 - 20-fold more sensitive per tested cell, TagMap can interrogate 1,000 - 2,000-fold more cells and therefore can identify infrequent retrotranspositions. When comparing SARS-CoV-2 infection and viral nucleocapsid mRNA transfection by TagMap, retrotransposed SARS-CoV-2 sequences were only detected in infected but not in transfected cells. Retrotransposition in virus-infected in contrast to transfected cells may be facilitated because virus infection in contrast to viral RNA transfection results in significantly higher viral RNA levels and stimulates LINE1-expression which causes cellular stress.

molecular biology↗

bioRxiv2022

Development of a physiological insulin resistance model in human stem cell-derived adipocytes

Adipocytes are key regulatory cells of human metabolism, and their dysfunction in insulin signaling is central to metabolic diseases such as type II diabetes mellitus (T2D). However, the progression of insulin resistance that leads to T2D is still poorly understood. This limited understanding is due, in part, to the dearth of suitable models of insulin signaling in human adipocytes. Traditionally, in vitro adipocyte models fail to recapitulate in vivo insulin signaling, possibly due to exposure to supraphysiological nutrient and hormone conditions. Here, we have developed a sensitization protocol for human pluripotent stem cell-derived adipocytes that uses physiologically relevant nutrient conditions to produce a potent signaling response comparable to in vivo adipocytes. After systematically optimizing conditions, this protocol allows for robust insulin-stimulated glucose uptake and transcriptional insulin response. Furthermore, exposure of these sensitized adipocytes to physiologically relevant hyperinsulinemic conditions dampens insulin-stimulated glucose uptake and dysregulates transcription of insulin-responsive genes. Overall, this sensitization methodology provides a novel platform for the mechanistic study of insulin signaling and resistance using human pluripotent stem cell-derived adipocytes. TeaserA new protocol to generate hPSC-adipocytes that respond to physiological insulin levels and can model diabetes.

cell biology↗