Recent publications

MiR‐9‐5p protects from kidney fibrosis by metabolic reprogramming
Marta Fierro‐Fernández, Verónica Miguel, Laura Márquez‐Expósito, Cristina Nuevo‐Tapioles, J. Ignacio Herrero, Eva Blanco‐Ruiz, Jessica Tituaña, Carolina Castillo, Pablo Cannata, María Monsalve, Marta Ruiz‐Ortega, Ricardo Ramos, Santiago Lamas

MicroRNAs (miRNAs) regulate gene expression posttranscriptionally and control biological processes (BPs), including fibrogenesis. Kidney fibrosis remains a clinical challenge and miRNAs may represent a valid therapeutic avenue. We show that miR‐9‐5p protected from renal fibrosis in the mouse model of unilateral ureteral obstruction (UUO). This was reflected in reduced expression of pro‐fibrotic markers, decreased number of infiltrating monocytes/macrophages, and diminished tubular epithelial cell injury and transforming growth factor‐beta 1 (TGF‐β1)‐dependent de‐differentiation in human kidney proximal tubular (HKC‐8) cells. RNA‐sequencing (RNA‐Seq) studies in the UUO model revealed that treatment with miR‐9‐5p prevented the downregulation of genes related to key metabolic pathways, including mitochondrial function, oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), and glycolysis. Studies in human tubular epithelial cells demonstrated that miR‐9‐5p impeded TGF‐β1‐induced bioenergetics derangement. The expression of the FAO‐related axis peroxisome proliferator‐activated receptor gamma coactivator 1 alpha (PGC‐1α)‐peroxisome proliferator‐activated receptor alpha (PPARα) was reduced by UUO, although preserved by the administration of miR‐9‐5p. We found that in mice null for the mitochondrial master regulator PGC‐1α, miR‐9‐5p was unable to promote a protective effect in the UUO model. We propose that miR‐9‐5p elicits a protective response to chronic kidney injury and renal fibrosis by inducing reprogramming of the metabolic derangement and mitochondrial dysfunction affecting tubular epithelial cells.

Epigenetic Priming in Immunodeficiencies
Jorge Martínez-Cano, Elena Campos-Sánchez and César Cobaleda

Immunodeficiencies (IDs) are disorders of the immune system that increase susceptibility to infections and cancer, and are therefore associated with elevated morbidity and mortality. IDs can be primary (not caused by other condition or exposure) or secondary due to the exposure to different agents (infections, chemicals, aging, etc.). Most primary immunodeficiencies (PIDs) are of genetic origin, caused by mutations affecting genes with key roles in the development or function of the cells of the immune system. A large percentage of PIDs are associated with a defective development and/or function of lymphocytes and, especially, B cells, the ones in charge of generating the different types of antibodies. B-cell development is a tightly regulated process in which many different factors participate. Among the regulators of B-cell differentiation, a correct epigenetic control of cellular identity is essential for normal cell function. With the advent of next-generation sequencing (NGS) techniques, more and more alterations in different types of epigenetic regulators are being described at the root of PIDs, both in humans and in animal models. At the same time, it is becoming increasingly clear that epigenetic alterations triggered by the exposure to environmental agents have a key role in the development of secondary immunodeficiencies (SIDs). Due to their largely reversible nature, epigenetic modifications are quickly becoming key therapeutic targets in other diseases where their contribution has been known for more time, like cancer. Here, we establish a parallelism between IDs and the nowadays accepted role of epigenetics in cancer initiation and progression, and propose that epigenetics forms a “third axis” (together with genetics and external agents) to be considered in the etiology of IDs, and linking PIDs and SIDs at the molecular level. We therefore postulate that IDs arise due to a variable contribution of (i) genetic, (ii) environmental, and (iii) epigenetic causes, which in fact form a continuum landscape of all possible combinations of these factors. Additionally, this implies the possibility of a fully epigenetically triggered mechanism for some IDs. This concept would have important prophylactic and translational implications, and would also imply a more blurred frontier between primary and secondary immunodeficiencies.

Synergistic Lethal Mutagenesis of Hepatitis C Virus
Isabel Gallego, María Eugenia Soria, Josep Gregori, Ana I. de Ávila, Carlos García-Crespo, Elena Moreno, Ignacio Gadea, Jaime Esteban, Ricardo Fernández-Roblas, Juan Ignacio Esteban, Jordi Gómez, Josep Quer, Esteban Domingo, Celia Perales

Lethal mutagenesis is an antiviral approach that consists of extinguishing a virus by an excess of mutations acquired during replication in the presence of a mutagenic agent, often a nucleotide analogue. One of its advantages is its broad-spectrum nature, which renders the strategy potentially effective against emergent RNA viral infections. Here we describe the synergistic lethal mutagenesis of hepatitis C virus (HCV) by a combination of favipiravir (T-705) and ribavirin. Synergy has been documented over a broad range of analogue concentrations using the Chou-Talalay method implemented in CompuSyn graphics software, with the average dose reduction index (DRI) being above 1 (68.02 ± 101.6 for favipiravir and 5.83 ± 6.07 for ribavirin) and the average combination indices (CI) being below 1 (0.52 ± 0.28). Furthermore, analogue concentrations that individually did not extinguish high-fitness HCV in 10 serial infections extinguished high-fitness HCV in 1 to 2 passages when used in combination. Although both analogues displayed a preference for G → A and C → U transitions, deep sequencing analysis of mutant spectra indicated a different preference of the two analogues for the mutation sites, thus unveiling a new possible synergy mechanism in lethal mutagenesis. The prospects for synergy among mutagenic nucleotides as a strategy to confront emerging viral infections are discussed.

MEPSAnd: minimum energy path surface analysis over n-dimensional surfaces
Iñigo Marcos-Alcalde, Eduardo López-Viñas, Paulino Gómez-Puertas

n-dimensional energy surfaces are becoming computationally accessible, yet interpreting their information is not straightforward. We present minimum energy path surface analysis over n-dimensional surfaces (MEPSAnd), an open source GUI-based program that natively calculates minimum energy paths across energy surfaces of any number of dimensions. Among other features, MEPSAnd can compute the path through lowest barriers and automatically provide a set of alternative paths. MEPSAnd offers distinct plotting solutions as well as direct python scripting.

Viral quasispecies
Esteban Domingo, Celia Perales

Viral quasispecies refers to a population structure that consists of extremely large numbers of variant genomes, termed mutant spectra, mutant swarms or mutant clouds. Fueled by high mutation rates, mutants arise continually, and they change in relative frequency as viral replication proceeds. The term quasispecies was adopted from a theory of the origin of life in which primitive replicons) consisted of mutant distributions, as found experimentally with present day RNA viruses. The theory provided a new definition of wild type, and a conceptual framework for the interpretation of the adaptive potential of RNA viruses that contrasted with classical studies based on consensus sequences. Standard clonal analyses and deep sequencing methodologies have confirmed the presence of myriads of mutant genomes in viral populations, and their participation in adaptive processes. The quasispecies concept applies to any biological entity, but its impact is more evident when the genome size is limited and the mutation rate is high. This is the case of the RNA viruses, ubiquitous in our biosphere, and that comprise many important pathogens. In virology, quasispecies are defined as complex distributions of closely related variant genomes subjected to genetic variation, competition and selection, and that may act as a unit of selection. Despite being an integral part of their replication, high mutation rates have an upper limit compatible with inheritable information. Crossing such a limit leads to RNA virus extinction, a transition that is the basis of an antiviral design termed lethal mutagenesis.

Genetic deficiency or pharmacological inhibition of miR-33 protects from kidney fibrosis
Nathan L. Price, Verónica Miguel, Wen Ding, Abhishek K. Singh, Shipra Malik, Noemi Rotllan, Anna Moshnikova, Jakub Toczek, Caroline Zeiss, Mehran M. Sadeghi, Noemi Arias, Ángel Baldán, Oleg A. Andreev, Diego Rodríguez-Puyol, Raman Bahal, Yana K. Reshetnyak, Yajaira Suárez, Carlos Fernández-Hernando, and Santiago Lamas

Previous work has reported the important links between cellular bioenergetics and the development of chronic kidney disease, highlighting the potential for targeting metabolic functions to regulate disease progression. More recently, it has been shown that alterations in fatty acid oxidation (FAO) can have an important impact on the progression of kidney disease. In this work, we demonstrate that loss of miR-33, an important regulator of lipid metabolism, can partially prevent the repression of FAO in fibrotic kidneys and reduce lipid accumulation. These changes were associated with a dramatic reduction in the extent of fibrosis induced in 2 mouse models of kidney disease. These effects were not related to changes in circulating leukocytes because bone marrow transplants from miR-33–deficient animals did not have a similar impact on disease progression. Most important, targeted delivery of miR-33 peptide nucleic acid inhibitors to the kidney and other acidic microenvironments was accomplished using pH low insertion peptides as a carrier. This was effective at both increasing the expression of factors involved in FAO and reducing the development of fibrosis. Together, these findings suggest that miR-33 may be an attractive therapeutic target for the treatment of chronic kidney disease.

Extracellular vesicles: Vehicles of en bloc viral transmission
Nihal Altan-Bonnet, Celia Perales, Esteban Domingo

En Bloc transmission of viruses allow multiple genomes to collectivelly penetrate and initiate infection in the same cell, often resulting in enhanced infectivity. Given the quasispecies (mutant cloud) nature of RNA viruses and many DNA viruses, en bloc transmission of multiple genomes provides different starting points in sequence space to initiate adaptive walks, and has implications for modulation of viral fitness and for the response of viral populations to lethal mutagenesis. Mechanisms that can enable multiple viral genomes to be transported en bloc among hosts has only recently been gaining attention. A growing body of research suggests that extracellular vesicles (EV) are highly prevalent and robust vehicles for en bloc delivery of viral particles and naked infectious genomes among organisms. Both RNA and DNA viruses appear to exploit these vesicles to increase their multiplicity of infection and enhance virulence.

The archaeology of coding RNA
Ascensión Ariza‐Mateos, Carlos Briones, Celia Perales, Esteban Domingo, Jordi Gómez

Different theories concerning the origin of RNA (and, in particular, mRNA) point to the concatenation and expansion of proto‐tRNA−like structures. Different biochemical and biophysical tools have been used to search for ancient‐like RNA elements with a specific structure in genomic viral RNAs, including that of the hepatitis C virus, as well as in cellular mRNA populations, in particular those of human hepatocytes. We define this method as “archaeological,” and it has been designed to discover evolutionary patterns through a nonphylogenetic and nonrepresentational strategy. tRNA‐like elements were found in structurally or functionally relevant positions both in viral RNA and in one of the liver mRNAs examined, the antagonist interferon‐alpha subtype 5 (IFNA5) mRNA. Additionally, tRNA‐like elements are highly represented within the hepatic mRNA population, which suggests that they could have participated in the formation of coding RNAs in the distant past. Expanding on this finding, we have observed a recurring dsRNA‐like motif next to the tRNA‐like elements in both viral RNAs and IFNA5 mRNA. This suggested that the concatenation of these RNA motifs was an activity present in the RNA pools that might have been relevant in the RNA world. The extensive alteration of sequences that likely triggered the transition from the predecessors of coding RNAs to the first fully functional mRNAs (which was not the case in the stepwise construction of noncoding rRNAs) hinders the phylogeny‐based identification of RNA elements (both sequences and structures) that might have been active before the advent of protein synthesis. Therefore, our RNA archaeological method is presented as a way to better understand the structural/functional versatility of a variety of RNA elements, which might represent “the losers” in the process of RNA evolution as they had to adapt to the selective pressures favoring the coding capacity of the progressively longer mRNAs.

Lethal Mutagenesis of Rift Valley Fever Virus Induced by Favipiravir
Belén Borrego, Ana I. de Ávila, Esteban Domingo, Alejandro Brun

Rift Valley fever virus (RVFV) is an emerging, mosquito-borne, zoonotic pathogen with recurrent outbreaks taking a considerable toll in human deaths in many African countries, for which no effective treatment is available. In cell culture studies and with laboratory animal models, the nucleoside analogue favipiravir (T-705) has demonstrated great potential for the treatment of several seasonal, chronic, and emerging RNA virus infections in humans, suggesting applicability to control some viral outbreaks. Treatment with favipiravir was shown to reduce the infectivity of Rift Valley fever virus both in cell cultures and in experimental animal models, but the mechanism of this protective effect is not understood. In this work, we show that favipiravir at concentrations well below the toxicity threshold estimated for cells is able to extinguish RVFV from infected cell cultures. Nucleotide sequence analysis has documented RVFV mutagenesis associated with virus extinction, with a significant increase in G to A and C to U transition frequencies and a decrease of specific infectivity, hallmarks of lethal mutagenesis.

Viral fitness: history and relevance for viral pathogenesis and antiviral interventions
Esteban Domingo, Ana I de Ávila, Isabel Gallego, Julie Sheldon, Celia Perales

The quasispecies dynamics of viral populations (continuous generation of variant genomes and competition among them) has as one of its frequent consequences variations in overall multiplication capacity, a major component of viral fitness. This parameter has multiple implications for viral pathogenesis and viral disease control, some of them unveiled thanks to deep sequencing of viral populations. Darwinian fitness is an old concept whose quantification dates back to the early developments of population genetics. It was later applied to viruses (mainly to RNA viruses) to quantify relative multiplication capacities of individual mutant clones or complex populations. The present article reviews the fitness concept and its relevance for the understanding of the adaptive dynamics of viruses in constant and changing environments. Many studies have addressed the fitness cost of escape mutations (to antibodies, cytotoxic T cells or inhibitors) as an influence on the efficacy of antiviral interventions. Here, we summarize the evidence that the basal fitness level can be a determinant of inhibitor resistance.

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