Biology subjects

Vargas, G.

Publications and source records attributed to Vargas, G..

6 recordsLinked to original sources

bioRxiv2025

Proteasome Inhibition Reduces NBR1 Protein Levels in mATG8-Deficient Cells Independently of Lysosomal Degradation and RAB27A

Autophagy is a lysosome-dependent degradation process that involves autophagosome formation, typically mediated by mammalian ATG8 proteins (mATG8s). Autophagosomes can still form in their absence, suggesting alternative mechanisms. NBR1, a selective autophagy receptor, has been shown to compensate for autophagy defects. Here, we examined NBR1 regulation under proteotoxic stress in mATG8s-deficient HeLa cells. NBR1 levels were elevated in mATG8s knockout (KO) cells under basal conditions but decreased significantly after treatment with the proteasome inhibitor MG132. This reduction was not prevented by lysosomal inhibition with BafA1, indicating a non-lysosomal mechanism. Silencing of RAB27A reduced basal NBR1 levels, and the effects of MG132 were no longer observed, likely due to already diminished NBR1. Remaining NBR1 localized to puncta positive for ubiquitin and the ESCRT-0 component HRS, suggesting involvement of a ubiquitin-dependent endosomal pathway. Overall, our results suggest that under proteotoxic stress and impaired autophagy, cells activae alternative routes, potentially involving unconventional secretion, to regulate NBR1 levels. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/664987v2_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@10568bcorg.highwire.dtl.DTLVardef@1f3d53org.highwire.dtl.DTLVardef@f33508org.highwire.dtl.DTLVardef@11ec28e_HPS_FORMAT_FIGEXP M_FIG C_FIG Created with BioRender https://BioRender.com/geoh3sz In the absence of mATG8s, NBR1 may be recruited to multivesicular bodies (MVBs) via HRS, for later degradation in lysosomes (left panel). Under proteasomal inhibition (right panel), NBR1 associated with MVBs (with ubiquitinated cargos) is downregulated, independent of lysosomes. Possibly, this downregulation is due to a secretion process, through a RAB27A-independent mechanism.

cell biology↗

bioRxiv2025

The gut microbiome of the Passalid beetle has high cellulolytic potential and constitutes an unrecognized system for production of greenhouse gasses in neotropical forests

Herbivores, and their associated microbiomes, play a major role in the global carbon cycle. Recalcitrant cellulose molecules are broken down by microorganisms that colonize the herbivore gut, releasing greenhouse gasses in the process. Passalid beetles are tropical herbivores that feed only on decaying wood and present subsocial behavior that may lead to the acquisition and sharing of microbial symbionts for efficient biomass and energy production. We collected five groups of Veturius sp. Passalid beetles from different logs in the Costa Rican rainforest and analyzed the microbial communities of larval and adult guts, as well as the substrate material in which they resided (partially chewed wood material mixed with feces that covers their tunnels). Adults, larvae, and substrate harbor different microbial communities, with substrate showing the highest diversity and richness, and larvae gut comprising a high abundance of methanogenic archaea. Reconstructed metagenome assembled genomes (MAGs) revealed that larvae and adults are enriched in genomes encoding a myriad of glycosyl hydrolases. Methanogenic taxa were enriched within the larval MAGs and bins, suggesting that larval microbiota participate in the final steps of cellulose decomposition in the system. Finally, we assessed methane production rates by Passalid beetles and compared them with termites. Our results show that Passalid larvae and adults produce methane at rates comparable to termites. Passalid and other beetle larvae are potentially underappreciated contributors to the carbon cycle and the biotic production of the greenhouse gas methane.

microbiology↗

bioRxiv2021

Negative modulation of macroautophagy by HERPUD1 is counteracted by an increased ER-lysosomal network with impact in drug-induced stress cell survival

Macroautophagy and the ubiquitin proteasome system work as an interconnected network in the maintenance of cellular homeostasis. Indeed, efficient activation of macroautophagy upon nutritional deprivation is sustained by degradation of preexisting proteins by the proteasome. However, the specific substrates that are degraded by the proteasome in order to activate macroautophagy are currently unknown. By quantitative proteomic analysis we identified several proteins downregulated in response to starvation but independently of ATG5 expression. Among them, the most significant was HERPUD1, an ER protein of short-half life and a well-known substrate of the proteasome. We found that increased HERPUD1 stability by deletion of its ubiquitin-like domain (UBL) plays a negative role on basal and induced macroautophagy. Moreover, we found it triggers ER expansion by reordering the ER in crystalloid structures, but in the absence of unfolded protein response activation. Surprisingly, we found ER expansion led to an increase in the number and function of lysosomes establishing a tight network with the presence of membrane-contact sites. Importantly, a phosphomimetic S59D mutation within the UBL mimics UBL deletion on its stability and the ER-lysosomal network expansion revealing an increase of cell survival under stress conditions. Altogether, we propose stabilized HERPUD1 downregulates macroautophagy favoring instead a closed interplay between the ER and lysosomes with consequences in drug-cell stress survival. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=198 SRC="FIGDIR/small/447273v2_ufig1.gif" ALT="Figure 1"> View larger version (45K): org.highwire.dtl.DTLVardef@1136b35org.highwire.dtl.DTLVardef@1e39b7eorg.highwire.dtl.DTLVardef@1f59211org.highwire.dtl.DTLVardef@148b2b0_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2021

Loss of lamin-B1 and defective nuclear morphology are hallmarks of astrocyte senescence in vitro and in the aging human hippocampus

The increase in senescent cells in tissues, including the brain, is a general feature of normal aging and age-related pathologies. Senescent cells exhibit a specific phenotype, which includes an altered nuclear morphology and transcriptomic changes. Astrocytes undergo senescence in vitro and in age-associated neurodegenerative diseases, but little is known about whether this process also occurs in physiological aging. Here, we investigated astrocyte senescence in vitro, in old mouse brains and in post-mortem human brain tissue of elderly. We identified a significant loss of lamin-B1, a major component of the nuclear lamina, as a hallmark of senescent astrocytes. We showed a severe reduction of lamin-B1 in the dentate gyrus of aged mice, including in hippocampal astrocytes, and in the granular cell layer of the hippocampus of post-mortem human tissue from non-demented elderly. Interestingly, the lamin-B1 reduction was associated with nuclear deformations, represented by an increased incidence of invaginated nuclei and loss of nuclear circularity in senescent astrocytes in vitro and in the aging human hippocampus. In conclusion, our findings show that reduction of lamin-B1 is a conserved hallmark of astrocyte aging, as well as shed light on significant defects in nuclear lamina structure, which may impact astrocyte function during human aging.

neuroscience↗

bioRxiv2021

Hexavalent Sperm-Binding IgG Antibody Released from Self-Dissolving Vaginal Film Enables Potent, On-Demand Non-Hormonal Female Contraception

Non-hormonal products for on-demand contraception are a global health technology gap, motivating us to pursue the use of sperm-binding monoclonal antibodies as a strategy to enable safe, effective, desirable, on-demand contraception. Here, using cGMP-compliant Nicotiana-expression system, we produce an ultra-potent sperm-binding IgG antibody possessing 6 Fab arms per molecule that bind a well-established contraceptive antigen target, CD52g. We term this hexavalent antibody "Fab-IgG-Fab" (FIF) to reflect its molecular orientation. The Nicotiana-produced FIF exhibits at least 10-fold greater sperm agglutination potency and kinetics than the parent IgG, while preserving Fc-mediated trapping of individual spermatozoa in mucus. We formulate the Nicotiana-produced FIF into a polyvinyl alcohol-based water-soluble contraceptive film, and evaluate its potency in reducing progressively motile sperm in the sheep vagina. Two minutes after vaginal instillation of human semen, no progressively motile sperm are recovered from the vaginas of sheep receiving FIF-Film. In contrast, high numbers of progressively motile sperm are recovered from sheep receiving a placebo film control. Our work supports the potential of highly multivalent contraceptive antibodies to provide safe, effective, on-demand non-hormonal contraception.

bioengineering↗

bioRxiv2021

Extracellular vesicles regulate yeast growth, biofilm formation, and yeast-to-hypha differentiation in Candida albicans

The ability to undergo morphological changes during adaptation to distinct environments is exploited by Candida albicans and has a direct impact on virulence. In this study, we investigated the influence of fungal extracellular vesicles (EVs) during yeast growth, biofilm formation, and morphogenesis in C. albicans. Addition of C. albicans EVs (Ca EVs) to the culture medium positively affected yeast growth. Using crystal violet staining and scanning electron microscopy (SEM), we demonstrated that Ca EVs inhibited biofilm formation by C. albicans in vitro. By time-lapse microscopy and SEM, we showed that Ca EV-treatment stops filamentation promoting pseudohyphae formation with multiple sites for yeast budding. The ability of Ca EVs to regulate dimorphism was further compared to EVs isolated from different C. albicans strains, Saccharomyces cerevisiae, and Histoplasma capsulatum. Ca EVs from distinct strains robustly inhibited yeast-to-hyphae differentiation with morphological changes occurring in less than 4 hours. A minor inhibitory effect was promoted by EVs from S. cerevisiae and H. capsulatum only after 24 hours of incubation. The inhibitory effect of Ca EVs was promoted by a combination of lipid compounds identified by gas chromatography-tandem mass spectrometry analysis as sesquiterpenes, diterpenes, and fatty acids. Remarkably, Ca EVs were also able to reverse filamentation, transforming hyphal growth to yeast forms. Transcriptomic analysis demonstrated that treatment with Ca EVs modified the expression of more than 300 genes. The most effectively upregulated pathways were related to DNA metabolism. The downregulated genes were mostly associated with extracellular and adhesion proteins. Finally, yeast cells treated with Ca EVs for 24 hours lost their agar invasive ability and were avirulent when inoculated in Galleria mellonella larvae. In summary, our results indicate that fungal EVs can profoundly modify C. albicans growth and regulate yeast-to-hypha differentiation inhibiting biofilm formation and virulence.

microbiology↗