Hypercapnia and Suppression of Anti-viral Host Defense

高碳酸血症，即血液和组织中PCO 2的升高，通常发生在晚期COPD和急性阻塞性肺疾病中。 呼吸衰竭COPD患者经常发生细菌和病毒性肺部感染，包括流感， 并且高碳酸血症是这些个体死亡的危险因素。我们已经证明高碳酸血症抑制了 多种NF-κ B调节的宿主防御所需的先天免疫基因的转录， 吞噬作用和自噬介导的巨噬细胞（MCAs）的细菌杀伤。此外，我们发现， 在小鼠和果蝇中，高碳酸血症增加由于细菌感染引起的死亡率。这些发现强烈 表明高碳酸血症不仅仅是晚期肺病的标志，而且在穷人中起着因果作用。 通过抑制免疫功能和增加对感染的易感性来实现临床结果。 高碳酸血症在果蝇和哺乳动物系统中的作用相似，表明CO2浓度升高 通过保守途径抑制先天免疫基因表达。因此，我们进行了全基因组RNAi， 在果蝇中筛选并鉴定了锌指同源盒转录因子zfh 2作为候选介质 二氧化碳的免疫抑制作用。值得注意的是，zfh 2缺陷的突变果蝇可以保护其免受 CO2诱导的细菌感染死亡率增加。接下来，我们发现ZFHX 3（哺乳动物zfh 2） 直向同源物，表达于Mc; ZFHX 3以CO2敏感的方式与多种高碳酸血症调节的 ZFHX 3的siRNA敲低阻断了高碳酸血症免疫基因抑制。 在当前应用的初步实验中，我们观察到高碳酸血症抑制LPS和流感病毒。 一种病毒（IAV）诱导的I型干扰素（IFN）途径抗病毒基因在人类和小鼠MØs中的表达。 值得注意的是，ZFHX 3结合IFN调节因子（IRF）和NF-κB基因，并且这种结合是CO2敏感的， 提示ZFHX 3通过阻断IRF-和NF-κB-介导高碳酸血症对抗病毒基因表达的影响。 激活IFN-α和IFN-β的转录。我们还发现高碳酸血症抑制了IAV诱导的自噬， 另一种抗病毒途径，这是继高碳酸血症诱导的表达增加，负 自噬调节因子Bcl-2和Bcl-xL以及Akt的激活。最后，至关重要的是，接触高浓度的 CO2可增强IAV在MIBs和其他细胞中的复制，并增加IAV感染小鼠的死亡率。 拟议的研究将检验高碳酸血症抑制IFN途径抗病毒药物表达的假设。 基因通过ZFHX 3介导的CO2依赖性转录变化;高碳酸血症抑制流感- 通过增加Bcl-2和Bcl-xL的表达和Akt的激活诱导自噬; 缺乏或阻断高碳酸血症对自噬的抑制将降低IAV相关的肺损伤和死亡率 对小鼠这项研究将确定CO2水平升高抑制抗病毒宿主的新机制 防御，以前未被认识到的高碳酸血症的不良后果，并将奠定基础，为未来 旨在预防晚期肺病患者中高碳酸血症诱导的免疫抑制的研究。

Hypercapnia, the elevation of PCO2 in blood and tissue, commonly occurs in advanced COPD and in acute respiratory failure. Patients with COPD frequently develop bacterial and viral lung infections, including influenza, and hypercapnia is a risk factor for mortality in such individuals. We have shown that hypercapnia suppresses transcription of multiple NF-κB-regulated innate immune genes required for host defense and inhibits phagocytosis and autophagy-mediated bacterial killing by macrophages (MØs). Moreover, we found that hypercapnia increases mortality due to bacterial infections in both mice and Drosophila. These findings strongly suggest that hypercapnia is not simply a marker of advanced lung disease, but that it plays a causal role in poor clinical outcomes by suppressing immune function and increasing susceptibility to infection. The similarity of hypercapnia's effects in Drosophila and mammalian systems suggested that elevated CO2 inhibits innate immune gene expression by conserved pathway(s). Thus, we conducted a genome-wide RNAi screen in Drosophila and identified the zinc finger homeobox transcription factor, zfh2, as a candidate mediator of CO2's immunosuppressive effects. Notably, mutant Drosophila deficient in zfh2 were protected against the CO2-induced increase in mortality from bacterial infection. Next, we found that ZFHX3, a mammalian zfh2 ortholog, is expressed in MØs; that ZFHX3 binds in a CO2-sensitive manner to multiple hypercapnia-regulated MØ genes; and that siRNA knockdown of ZFHX3 blocked hypercapnic immune gene suppression. In preliminary experiments for the current application, we observed that hypercapnia inhibited LPS- and influenza A virus (IAV)-induced expression of type I interferon (IFN) pathway antiviral genes in human and mouse MØs. Notably, ZFHX3 bound IFN regulatory factors (IRFs) and NF-κB genes, and this binding was CO2-sensitive, suggesting that ZFHX3 mediates hypercapnia's effect on antiviral gene expression by blocking IRF- and NF-κB- activated transcription of IFN-α and IFN-β. We also found that hypercapnia suppressed IAV-induced autophagy, another antiviral pathway, and that this followed hypercapnia-induced increases in expression of the negative autophagy regulators, Bcl-2 and Bcl-xL, and activation of Akt. Finally, of critical importance, exposure to elevated CO2 enhanced IAV replication in MØs and other cells and increased the mortality of IAV infection in mice. The proposed studies will test the hypothesis that hypercapnia inhibits expression of IFN pathway antiviral genes via CO2-dependent changes in transcription mediated by ZFHX3; that hypercapnia inhibits influenza- induced autophagy via increased expression of Bcl-2 and Bcl-xL and activation of Akt; and that myeloid ZFHX3 deficiency or blocking hypercapnic inhibition of autophagy will decrease IAV-associated lung injury and mortality in mice. 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.