Biology subjects

Viana, R.

Publications and source records attributed to Viana, R..

4 recordsLinked to original sources

bioRxiv2025

Reconstruction and exploitation of a dedicated Genome-Scale Metabolic Model of the human pathogen C. neoformans

C. neoformans is notorious for causing severe pulmonary and central nervous system infections, particularly in immunocompromised patients. High mortality rates, associated with its tropism and adaptation to the brain microenvironment and its drug resistance profile, makes this pathogen a public health threat and a World Health Organization (WHO) priority. In this study, we reconstructed GSMM iRV890 for C. neoformans var. grubii, providing a promising platform for the comprehensive understanding of the unique metabolic features of C. neoformans, and subsequently shedding light on its complex tropism for the brain microenvironment and potentially informing the discovery of new drug targets. The GSMM iRV890 model is openly available in the SBML format, and underwent validation using experimental data for nitrogen and carbon assimilation, as well as specific growth and glucose consumption rates. Based on the comparison with GSMMs available for other pathogenic yeasts, unique metabolic features were predicted for C. neoformans, including key pathways shaping the dynamics between C. neoformans and the human host, and underlying its adaptation to the brain environment. Finally, predicted essential genes from the validated model are explored herein as potential novel antifungal drug targets.

bioinformatics↗

bioRxiv2024

Glial alterations in the glutamatergic and GABAergic signaling pathways in a mouse model of Lafora disease, a severe form of progressive myoclonus epilepsy

Lafora disease (LD; OMIM#254780) is a rare form of progressive myoclonus epilepsy characterized by the accumulation of insoluble deposits of aberrant glycogen (polyglucosans), named Lafora bodies (LBs), in the brain but also in peripheral tissues. It is assumed that the accumulation of LBs is related to the appearance of the characteristic pathological features of the disease. In mouse models of LD, we and others have reported an increase in the levels of reactive astrocytes and activated microglia, which triggers the expression of the different pro-inflammatory mediators. Recently, we have demonstrated that the TNF and IL-6 inflammatory signaling pathways are the main mediators of the neuroinflammatory phenotype associated with the disease. In this work, we present evidence that the activation of these pathways produces a dysregulation in the levels of different subunits of the excitatory ionotropic glutamatergic receptors (phopho-GluN2B, phospho-GluA2, GluK2) and also an increase in the levels of the GABA transporter GAT1 in the hippocampus of the Epm2b-/- mice. In addition, we present evidence of the presence of activated forms of the Src and Lyn protein kinases in this area. These effects may increase the excitatory glutamatergic signaling and decrease the inhibitory GABAergic tone, leading to hyper-excitability. More importantly, the enhanced production of these subunits occurs in non-neuronal cells such as activated microglia and reactive astrocytes, pointing out a key role of glia in the pathophysiology of LD.

neuroscience↗

bioRxiv2022

SARS-CoV-2 accessory proteins ORF3a and ORF7a modulate autophagic flux and Ca2+ homeostasis in yeast

Virus infection involves the manipulation of key host cell functions by specialized virulence proteins. The SARS-CoV-2 small accessory proteins ORF3a and ORF7a have been implicated in favoring virus replication and spreading by inhibiting the autophagic flux within the host cell. Here, we apply yeast models to gain insights into the physiological functions of both SARS-CoV-2 small ORFs. ORF3a and ORF7a can be stably overexpressed in yeast cells, producing a decrease in cellular fitness. Both proteins show a distinguishable intracellular localization. ORF3a specifically localizes to the vacuolar membrane, whereas ORF7a targets the endoplasmic reticulum. Overexpression of ORF3a and ORF7a leads to the accumulation of Atg8 specific autophagosomes. However, the underlying mechanism is different for each viral protein as assessed by the quantification of the autophagic degradation of Atg8-GFP fusion proteins, which is inhibited by ORF3a and stimulated by ORF7a. Overexpression of both SARS-CoV-2 ORFs decreases cellular fitness upon starvation conditions, where autophagic processes become essential. These data are in agreement with a model where both small ORFs have synergistic functions in stimulating intracellular autophagosome accumulation, ORF3a by inhibiting autophagosome processing at the vacuole and ORF7a by promoting autophagosome formation at the ER. ORF3a has an additional function in Ca2+ homeostasis. The overexpression of ORF3a confers calcineurin-dependent Ca2+ tolerance and activates a Ca2+ sensitive FKS2-luciferase reporter, suggesting a possible ORF3a-mediated Ca2+ efflux from the vacuole. Taken together, we show that viral accessory proteins can be functionally investigated in yeast cells and that SARS-CoV-2 ORF3a and ORF7a proteins interfere with autophagosome formation and processing as well as with Ca2+ homeostasis from distinct cellular targets.

microbiology↗

bioRxiv2021

An empirical pipeline for personalized diagnosis of Lafora disease mutations

Lafora disease (LD) is a fatal, insidious metabolic disorder characterized by progressive myoclonic epilepsy manifesting in the teenage years, rapid neurological decline, and death typically within ten years of onset. Mutations in either EPM2A, encoding the glycogen phosphatase laforin, or EPM2B, encoding the E3 ligase malin, cause LD. Whole exome sequencing has revealed many EPM2A variants associated with late-onset or slower disease progression. We established an empirical pipeline for characterizing laforin missense mutations in vitro using complimentary biochemical approaches. Analysis of 26 mutations revealed distinct functional classes associated with different outcomes supported by multiple clinical cases. For example, F321C and G279C mutations have attenuated functional defects and are associated with slow progression. This pipeline allows rapid characterization and classification of novel EPM2A mutations, enabling clinicians and researchers to rapidly utilize genetic information to guide treatment of LD patients.

biochemistry↗