Hypercapnia and Suppression of Antiviral Host Defense

高碳酸血症，血液和组织中二氧化碳分压升高，通常发生在严重的急性和 慢性肺部疾病。高碳酸血症是COPD、社区获得性肺炎、 囊性纤维化和腺病毒肺部感染。我们已经证明，高碳酸血症抑制了核因子-κB的转录。 在人、鼠和果蝇细胞中，受调节的先天免疫和宿主防御基因，与pH无关， 它还增加了小鼠和果蝇的细菌感染死亡率。我们也报道过， 高碳酸血症抑制肺泡巨噬细胞I型干扰素途径抗病毒基因表达 增加感染甲型流感病毒(IAV)小鼠的病毒复制、肺损伤和死亡率。 基于我们之前的研究，我们鉴定了锌指同源盒转录因子zfh2是一种 作为二氧化碳诱导果蝇免疫抑制的介体，我们培育了一只缺失哺乳动物Zfhx3的小鼠 Zfh2的直系同源基因，在髓系中。我们最近的研究表明，髓系Zfhx3缺乏症可以预防 高二氧化碳诱导巨噬细胞中抗病毒基因的抑制和IAV的生长，并且它 降低高碳酸血症引起的小鼠IAV感染死亡率的增加。我们还表明，高碳酸血症 增加和Zfhx3缺乏减少AM中多个基因的甲基化，包括宿主基因 对IAV复制至关重要。 我们实验室最近的研究证实，单核细胞来源的AM(MoAM)招募到 肺泡腔对各种侮辱的反应，包括IAV感染，是促炎和驱动肺的。 受伤。这与组织驻留AM(TRAM)不同，组织驻留AM(TRAM)对IAV诱导的损伤具有保护作用。因此， 我们假设，高碳酸血症通过抑制抗病毒基因和抗病毒基因而恶化IAV感染的结局。 TRAM和MoAM中炎症/损伤相关基因的表达增加，这是由于 高碳酸血症导致这些基因调节区甲基化的改变。我们进一步假设 巨噬细胞中Zfhx3的遗传缺陷减轻了高碳酸血症引起的DNA甲基化变化，并且 这保留了抗病毒基因的表达，并减少了高碳酸血症时IAV引起的肺损伤。 为了验证这些假设，我们将确定高碳酸血症是否通过以下方式恶化IAV感染的结局 抗病毒基因表达降低，炎症/损伤相关基因表达增加 TRAM和MoAM在小鼠中的表达；高碳酸血症是否导致DNA甲基化的变化 抗病毒和炎症/损伤相关基因的表达；以及高碳酸血症是否与类似 重症病毒性肺炎患者AM中DNA甲基化和基因表达的变化 这项研究将确定二氧化碳水平升高抑制抗病毒宿主的新机制 防御，这是以前未被认识到的高碳酸血症的不良后果，并将为未来奠定基础 旨在预防晚期肺部疾病患者高碳酸血症引起的免疫抑制的研究。

Hypercapnia, elevated PCO2 in blood and tissue, commonly develops in patients with severe acute and chronic pulmonary disease. Hypercapnia is a risk factor for mortality in COPD, community-acquired pneumonia, cystic fibrosis and adenoviral lung infection. We have shown that hypercapnia inhibits transcription of NF-κB- regulated innate immune and host defense genes, independent of pH, in human, mouse and Drosophila cells, and that it increases the mortality of bacterial infections in mice and Drosophila. We have also reported that hypercapnia inhibits type I interferon (IFN) pathway antiviral gene expression in alveolar macrophages (AM) and increases viral replication, lung injury and mortality in mice infected with influenza A virus (IAV). Based on previous studies in which we identified the zinc finger homeobox transcription factor zfh2 as a mediator of CO2-induced immune suppression in Drosophila, we bred a mouse lacking Zfhx3, a mammalian ortholog of zfh2, in the myeloid lineage. Our recent studies show that myeloid Zfhx3 deficiency protects against hypercapnia-induced suppression of antiviral genes and increased IAV growth in macrophages, and that it reduces the hypercapnia-induced increase in mortality of IAV infection in mice. We also show that hypercapnia increases and Zfhx3 deficiency decreases methylation of multiple genes in AM, including host genes that are essential for IAV replication. Recent studies from our laboratories have established that monocyte-derived AM (MoAM) recruited to the alveolar space in response to diverse insults, including IAV infection, are pro-inflammatory and drive lung injury. This is in contrast to tissue resident AM (TRAM), which are protective against IAV-induced injury. Thus, we hypothesize that hypercapnia worsens outcomes of IAV infection by suppressing antiviral genes and increasing expression of inflammation/injury-associated genes in TRAM and MoAM, and that this results from hypercapnia-induced alterations in methylation of regulatory regions of these genes. We further hypothesize that genetic deficiency of Zfhx3 in macrophages mitigates hypercapnia-induced changes in DNA methylation, and that this preserves antiviral gene expression and reduces lung injury caused by IAV in the setting of hypercapnia. To test these hypotheses, we will determine whether hypercapnia worsens outcomes of IAV infection by decreasing expression of antiviral genes and increasing expression of inflammation/injury-associated genes in TRAM and MoAM in mice; whether hypercapnia-induced changes in DNA methylation cause these changes in antiviral and inflammation/injury-associated gene expression; and whether hypercapnia is associated with similar changes in DNA methylation and gene expression in AM from humans with severe viral pneumonia. This investigation will define novel mechanisms by which elevated levels of CO2 suppress antiviral host defense, a previously-unrecognized adverse consequence of hypercapnia, and will lay the basis for future studies aimed at preventing hypercapnia-induced immunosuppression in patients with advanced lung disease.