W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA.
W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
J Virol. 2015 Jan;89(1):48-60. doi: 10.1128/JVI.02394-14. Epub 2014 Oct 15.
Susceptibility to alphavirus infection is age dependent, and host maturation is associated with decreased virus replication and less severe encephalitis. To identify factors associated with maturation-dependent restriction of virus replication, we studied AP-7 rat olfactory bulb neuronal cells, which can differentiate in vitro. Differentiation was associated with a 150- to 1,000-fold decrease in replication of the alphaviruses Sindbis virus and Venezuelan equine encephalitis virus, as well as La Crosse bunyavirus. Differentiation delayed synthesis of SINV RNA and protein but did not alter the susceptibility of neurons to infection or virion maturation. Additionally, differentiation slowed virus-induced translation arrest and death of infected cells. Differentiation of uninfected AP-7 neurons was associated with changes in expression of antiviral genes. Expression of key transcription factors was increased, including interferon regulatory factor 3 and 7 (IRF-3 and IRF-7) and STAT-1, suggesting that neuronal maturation may enhance the capacity for antiviral signaling upon infection. IRF-7 produced by undifferentiated AP-7 neurons was exclusively the short dominant negative γ-isoform, while that produced by differentiated neurons was the full-length α-isoform. A similar switch in IRF-7 isoforms also occurred in the brains of maturing C57BL/6J mice. Silencing of IRF expression did not improve virus multiplication in differentiated neurons. Therefore, neuronal differentiation is associated with upregulation of transcription factors that activate antiviral signaling, but this alone does not account for maturation-dependent restriction of virus replication.
Viral encephalomyelitis is an important cause of age-dependent morbidity and mortality. Because mature neurons are not readily regenerated, recovery from encephalitis suggests that mature neurons utilize unique antiviral mechanisms to block infection and/or clear virus. To identify maturational changes in neurons that may improve outcome, we compared immature and mature cultured neurons for susceptibility to three encephalitic arboviruses and found that replication of Old World and New World alphaviruses and a bunyavirus was reduced in mature compared to immature neurons. Neuronal maturation was associated with increased baseline expression of interferon regulatory factor 3 and 7 mRNAs and production of distinct isoforms of interferon regulatory factor 7 protein. Overall, our studies identified maturational changes in neurons that likely contribute to assembly of immunoregulatory factors prior to infection, a more rapid antiviral response, increased resistance to virus infection, and improved survival.
虫媒病毒感染易感性与年龄有关，宿主成熟与病毒复制减少和脑炎减轻有关。为了确定与病毒复制受宿主成熟限制相关的因素，我们研究了 AP-7 大鼠嗅球神经元细胞，其可在体外分化。分化与辛德毕斯病毒和委内瑞拉马脑炎病毒以及拉科罗塞病毒的复制降低 150 至 1000 倍有关。分化延迟了 SINV RNA 和蛋白的合成，但并不改变神经元对感染或病毒成熟的易感性。此外，分化减缓了病毒诱导的翻译阻断和感染细胞的死亡。未感染的 AP-7 神经元的分化与抗病毒基因表达的变化有关。关键转录因子的表达增加，包括干扰素调节因子 3 和 7（IRF-3 和 IRF-7）和 STAT-1，表明神经元成熟可能增强感染后抗病毒信号的能力。由未分化的 AP-7 神经元产生的 IRF-7 仅为短的显性负 γ-同种型，而由分化神经元产生的 IRF-7 为全长 α-同种型。IRF-7 同种型的类似转换也发生在成熟 C57BL/6J 小鼠的大脑中。IRF 表达的沉默并没有改善分化神经元中的病毒增殖。因此，神经元分化与激活抗病毒信号的转录因子上调有关，但这本身并不能解释病毒复制受宿主成熟限制的原因。
病毒性脑脊髓炎是年龄相关发病率和死亡率的重要原因。由于成熟神经元不易再生，从脑炎中恢复表明成熟神经元利用独特的抗病毒机制来阻止感染和/或清除病毒。为了确定可能改善结果的神经元成熟变化，我们比较了三种脑炎性虫媒病毒对幼稚和成熟培养神经元的易感性，发现与幼稚神经元相比，旧世界和新世界甲病毒和布尼亚病毒的复制减少。神经元成熟与干扰素调节因子 3 和 7 mRNA 的基础表达增加以及干扰素调节因子 7 蛋白的不同同种型的产生有关。总的来说，我们的研究确定了神经元成熟变化，这些变化可能有助于在感染前组装免疫调节因子，更快的抗病毒反应，增加对病毒感染的抵抗力和提高存活率。
