Hypoxia triggers the outbreak of infectious spleen and kidney necrosis virus disease through viral hypoxia response elements

Hypoxia frequently occurs in aquatic environments, especially in aquaculture areas. However, research on the relationship between hypoxic aquatic environments with viral diseases outbreak is limited, and its underlying mechanisms remain elusive. Herein, we demonstrated that hypoxia directly triggers the outbreak of infectious spleen and kidney necrosis virus (ISKNV) disease. Hypoxia or activated hypoxia-inducible factor (HIF) pathway could remarkably increase the levels of viral genomic DNA, titers, and gene expression, indicating that ISKNV can response to hypoxia and HIF pathway. To reveal the mechanism of ISKNV respond to HIF pathway, we identified the viral hypoxia response elements (HREs) in ISKNV genome. Fifteen viral HREs were identified, and four related viral genes responded to the HIF pathway, in which the <i>hre-orf077r</i> promoter remarkably responded to the HIF pathway. The level of <i>orf077r</i> mRNA dramatically increased after the infected cells were treated with dimethyloxalylglycine (DMOG) or the infected cells/fish subjected to hypoxic conditions, and overexpressed <i>orf077r</i> could remarkably increase the ISKNV replication. These finding shows that hypoxic aquatic environments induce the expression of viral genes through the viral HREs to promote ISKNV replication, indicating that viral HREs might be important biomarkers for the evaluation of the sensitivity of aquatic animal viral response to hypoxia stress. Furthermore, the frequencies of viral HREs in 43 species aquatic viral genomes from 16 families were predicted and the results indicate that some aquatic animal viruses, such as <i>Picornavirdea, Dicistronviridae</i>, and <i>Herpesviridae</i>, may have a high risk to outbreak when the aquatic environment encounters hypoxic stress.

水生环境中频繁出现低氧现象，尤以水产养殖区域为甚。然而，目前针对低氧水生环境与病毒性疾病暴发之间关联的研究较为匮乏，其潜在作用机制仍未阐明。在此项研究中，我们证实低氧可直接诱发传染性脾肾坏死病毒（ISKNV）病的暴发。低氧处理或激活缺氧诱导因子（HIF）通路，均可显著提升病毒基因组DNA水平、病毒滴度及基因表达量，表明ISKNV可对低氧及HIF通路产生应答。为揭示ISKNV应答HIF通路的机制，我们在ISKNV基因组中鉴定出病毒低氧应答元件（HREs）。共鉴定得到15个病毒HREs，其中4个相关病毒基因可对HIF通路产生应答，且hre-orf077r基因的启动子对HIF通路的应答效果最为显著。当感染细胞经二甲基乙二酰基甘氨酸（DMOG）处理，或感染细胞、宿主鱼暴露于低氧环境后，orf077r基因的mRNA水平会显著升高；而过表达orf077r可显著提升ISKNV的复制水平。上述研究结果表明，低氧水生环境可通过病毒HREs诱导病毒基因表达，进而促进ISKNV的复制，提示病毒HREs或可作为评估水生动物病毒对低氧胁迫应答敏感性的重要生物标志物。此外，我们预测了隶属于16个科的43种水生病毒基因组中病毒HREs的分布频率，结果显示部分水生动物病毒——如小核糖核酸病毒科（Picornaviridae）、双顺反子病毒科（Dicistronviridae）及疱疹病毒科（Herpesviridae）——在水生环境遭遇低氧胁迫时，具有较高的疾病暴发风险。