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Megalobrama amblycephala (Wuchang bream) is a widely farmed native species with the lowest hypoxic tolerance among the major aquaculture species in China. It is often threatened by hypoxic environments in aquaculture due to high culture densities and weather changes. Identification of the key genes and elucidation of the mechanisms involved in hypoxic tolerance provide the basis for genetic breeding of hypoxia-tolerant Megalobrama amblycephala strains. Here, we report that fih is evolutionarily conserved across species. CRISPR/Cas9-generated fih heterozygotes in Megalobrama amblycephala facilitate hypoxic tolerance and exhibit increased expression of hypoxia-responsive genes, including pdh3, glut1 and vegfa. Mechanistically, coimmunoprecipitation experiments indicated that overexpressed Megalobrama amblycephala fih (Ma-fih) interacts with the transcription factor hypoxia inducible factor (Ma-hif-α). Dual-luciferase assay showed that overexpression of Ma-fih inhibited the transcriptional activity of Ma-hif-α. In addition, we found that overexpression of Ma-fih suppressed hypoxia-induced glucose uptake in EPC cells. This study not only highlights the critical function of Ma-fih in regulating the hypoxia signaling pathway, but also provides a candidate gene for breeding hypoxia-tolerant Megalobrama amblycephala strains.

Abstract Oxygen is essential for aerobic organisms, but little is known about its role in antiviral immunity. Here, we report that during responses to viral infection, hypoxic conditions repress antiviral-responsive genes independently of HIF signaling. EGLN1 is identified as a key mediator of the oxygen enhancement of antiviral innate immune responses. Under sufficient oxygen conditions, EGLN1 retains its prolyl hydroxylase activity to catalyze the hydroxylation of IRF3 at proline 10. This modification enhances IRF3 phosphorylation, dimerization and nuclear translocation, leading to subsequent IRF3 activation. Furthermore, mice and zebrafish with Egln1 deletion, treatment with the EGLN inhibitor FG4592, or mice carrying an Irf3 P10A mutation are more susceptible to viral infections. These findings not only reveal a direct link between oxygen and antiviral responses, but also provide insight into the mechanisms by which oxygen regulates innate immunity.

The hypoxia-inducible factor (HIF)-mediated hypoxia signaling pathway influences oxygen homeostasis in aerobic organisms. This pathway is regulated by several other pathways. Elucidation of its regulation and the underlying mechanisms may provide insights into the strategies of adaptation and tolerance of organisms to hypoxia. In this study, we found that loss of ubiquitin-specific protease 3 (usp3) in zebrafish promotes hypoxia tolerance. Zebrafish usp3 specifically binds to hif-1αa and induces its proteasomal degradation, which is dependent on its deubiquitinase activity. This process leads to the suppression of hypoxia signaling under hypoxia. In addition, usp3 catalyzes the deubiquitination of K63-polyubiquitinated hif-1αa. Endogenous evidence indicated that mammalian USP3 behaves like zebrafish usp3 in regulating the activity of HIF-1α. These findings revealed a novel role for usp3 in influencing hypoxia signaling and showed that usp3-mediated HIF-1α degradation impairs hypoxia signaling, leading to a decrease in hypoxia tolerance.

To effectively protect the host from viral infection while avoiding excessive immunopathology, the innate immune response must be tightly controlled. However, the precise regulation of antiviral innate immunity and the underlying mechanisms remain unclear. Here, we find that sirtuin3 (SIRT3) interacts with mitochondrial antiviral signaling protein (MAVS) to catalyze MAVS deacetylation at lysine residue 7 (K7), which promotes MAVS aggregation, as well as TANK-binding kinase I and IRF3 phosphorylation, resulting in increased MAVS activation and enhanced type I interferon signaling. Consistent with these findings, loss of Sirt3 in mice and zebrafish renders them more susceptible to viral infection compared to their wild-type (WT) siblings. However, Sirt3 and Sirt5 double-deficient mice exhibit the same viral susceptibility as their WT littermates, suggesting that loss of Sirt5 in Sirt3-deficient mice may counteract the increased viral susceptibility displayed in Sirt3-deficient mice. Thus, we not only demonstrate that SIRT3 positively regulates antiviral immunity in vitro and in vivo, likely via MAVS, but also uncover a previously unrecognized mechanism by which SIRT3 acts as an accelerator and SIRT5 as a brake to orchestrate antiviral innate immunity. [ABSTRACT FROM AUTHOR]

HIF1α is one of the master regulators of the hypoxia signaling pathway and its activation is regulated by multiple post-translational modifications (PTMs). Deubiquitination mediated by deubiquitylating enzymes (DUBs) is an essential PTM that mainly modulates the stability of target proteins. USP38 belongs to the ubiquitin-specific proteases (USPs). However, whether USP38 can affect hypoxia signaling is still unknown. In this study, we used quantitative real-time PCR assays to identify USPs that can influence hypoxia-responsive gene expression. We found that overexpression of USP38 increased hypoxia-responsive gene expression, but knockout of USP38 suppressed hypoxia-responsive gene expression under hypoxia. Mechanistically, USP38 interacts with HIF1α to deubiquitinate K11-linked polyubiquitination of HIF1α at Lys769, resulting in stabilization and subsequent activation of HIF1α. In addition, we show that USP38 attenuates cellular ROS and suppresses cell apoptosis under hypoxia. Thus, we reveal a novel role for USP38 in the regulation of hypoxia signaling. [ABSTRACT FROM AUTHOR]