Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center at Houston, Houston TX, United States of America.
MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston TX, United States of America.
PLoS Genet. 2019 Jan 29;15(1):e1007944. doi: 10.1371/journal.pgen.1007944. eCollection 2019 Jan.
Heme-containing peroxidases are important components of innate immunity. Many of them functionally associate with NADPH oxidase (NOX)/dual oxidase (DUOX) enzymes by using the hydrogen peroxide they generate in downstream reactions. Caenorhabditis elegans encodes for several heme peroxidases, and in a previous study we identified the ShkT-containing peroxidase, SKPO-1, as necessary for pathogen resistance. Here, we demonstrated that another peroxidase, HPX-2 (Heme-PeroXidase 2), is required for resistance against some, but not all pathogens. Tissue specific RNA interference (RNAi) revealed that HPX-2 functionally localizes to the hypodermis of the worm. In congruence with this observation, hpx-2 mutant animals possessed a weaker cuticle structure, indicated by higher permeability to a DNA dye, but exhibited no obvious morphological defects. In addition, fluorescent labeling of HPX-2 revealed its expression in the pharynx, an organ in which BLI-3 is also present. Interestingly, loss of HPX-2 increased intestinal colonization of E. faecalis, suggesting its role in the pharynx may limit intestinal colonization. Moreover, disruption of a catalytic residue in the peroxidase domain of HPX-2 resulted in decreased survival on E. faecalis, indicating its peroxidase activity is required for pathogen resistance. Finally, RNA-seq analysis of an hpx-2 mutant revealed changes in genes encoding for cuticle structural components under the non-pathogenic conditions. Under pathogenic conditions, genes involved in infection response were differentially regulated to a greater degree, likely due to increased microbial burden. In conclusion, the characterization of the heme-peroxidase, HPX-2, revealed that it contributes to C. elegans pathogen resistance through a role in generating cuticle material in the hypodermis and pharynx.
含血红素的过氧化物酶是先天免疫的重要组成部分。它们中的许多通过利用下游反应中产生的过氧化氢与 NADPH 氧化酶 (NOX)/双氧化酶 (DUOX) 酶功能性结合。秀丽隐杆线虫编码了几种血红素过氧化物酶，在之前的一项研究中，我们发现含有 ShkT 的过氧化物酶 SKPO-1 对于病原体抗性是必需的。在这里，我们证明了另一种过氧化物酶 HPX-2（血红素过氧化物酶 2）对于抵抗某些但不是所有病原体是必需的。组织特异性 RNA 干扰 (RNAi) 表明 HPX-2 功能定位于线虫的表皮下组织。与这一观察结果一致，hpx-2 突变体动物的表皮结构较弱，这表现为对 DNA 染料的通透性更高，但没有明显的形态缺陷。此外，HPX-2 的荧光标记显示其在咽部表达，BLI-3 也存在于该器官中。有趣的是，HPX-2 的缺失增加了 E. faecalis 的肠道定植，表明其在咽部的作用可能限制了肠道定植。此外，破坏 HPX-2 过氧化物酶结构域中的催化残基导致在 E. faecalis 上的生存能力下降，表明其过氧化物酶活性对于病原体抗性是必需的。最后，hpx-2 突变体的 RNA-seq 分析显示，在非致病性条件下，编码表皮结构成分的基因发生了变化。在致病性条件下，参与感染反应的基因被更程度地差异调控，这可能是由于微生物负担增加所致。总之，血红素过氧化物酶 HPX-2 的特性表明，它通过在表皮下组织和咽部生成表皮材料的作用，有助于线虫抵抗病原体。
