Epigenetic modifications of gene promoters in the liver of Balb/c mice protected by vaccination against blood-stage malaria of Plasmodium chabaudi

Protective vaccination induces survival of more than 80% of female Balb/c mice otherwise succumbing to blood-stage malaria of Plasmodium chabaudi. This study investigates the effect of protective vaccination and P. chabaudi infections on DNA methylation of gene promoters in the liver of Balb/c mice. Using DNA methylation microarrays, protective vaccination is shown to affect per se the constitutive DNA methylation status of numerous gene promoters in the liver: Promoters of 256 genes are hyper(=up)- and 345 genes are hypo (=down)-methylated at a significance of p<0.05. Gene enrichment analysis reveals that genes with down-methylated promoters are most statistically significant enriched (p<0.01) with functions related to negative regulation of transcription, whereas genes with up-methylated promoters are related to positive regulation of transcription and immune system. Infections with P. chabaudi also induce changes in promoter DNA methylation. In vaccinated mice, these changes are observable already on day 1 p.i. and, in particular, at peak parasitemia on day 8 p.i., when 571 and 1013 gene promoters have become up- and down-methylated, respectively, in relation to constitutive DNA methylation at a signicance level of p<0.05. The corresponding gene promoters in non-vaccinated mice are also responsive to infection, but by far not as pronounced as in vaccinated mice. Our data demonstrate that vaccination modifies DNA methylation of gene promoters in the liver and augments promoter responsiveness to infection-induced DNA methylation alterations, which ultimately control expression of those genes in the liver required for survival of otherwise lethal blood-stage malaria of P. chabaudi. 18 samples were analyzed; Nd0, Non-vaccinated day 0, 3 replicates Vd0, Vaccinated day 0, 3 replicates Nd1, Non-vaccinated day 1, 3 replicates Vd1, Vaccinated day 1, 3 replicates Nd8, Non-vaccinated day 8, 3 replicates Vd8, Vaccinated day 8, 3 replicates

保护性疫苗接种（protective vaccination）可使原本会死于查氏疟原虫（Plasmodium chabaudi）红内期疟疾的80%以上雌性BALB/c小鼠（Balb/c mice）存活。本研究旨在探究保护性疫苗接种与查氏疟原虫感染对BALB/c小鼠肝脏中基因启动子（gene promoters）DNA甲基化（DNA methylation）的影响。通过DNA甲基化芯片（DNA methylation microarrays）分析，研究发现保护性疫苗接种自身即可改变肝脏内众多基因启动子的组成型DNA甲基化状态：在p<0.05的显著性水平下，256个基因的启动子呈高甲基化（上调）、345个基因的启动子呈低甲基化（下调）。基因富集分析（gene enrichment analysis）结果显示，启动子低甲基化的基因在转录负调控相关功能上富集最为显著（p<0.01），而启动子高甲基化的基因则与转录正调控及免疫系统功能相关。查氏疟原虫感染同样可诱导启动子DNA甲基化发生改变。在免疫小鼠体内，此类改变在感染后第1天即可观测到，尤其在感染后第8天的虫血症（parasitemia）峰值期更为明显：此时相较于组成型DNA甲基化状态，分别有571个和1013个基因启动子出现高甲基化与低甲基化变化，显著性水平为p<0.05。未免疫小鼠体内的对应基因启动子同样会对感染产生响应，但其响应程度远不及免疫小鼠。本研究数据表明，疫苗接种可改变肝脏内基因启动子的DNA甲基化水平，并增强启动子对感染诱导的DNA甲基化改变的响应能力，最终调控那些可使小鼠免于死于查氏疟原虫红内期致死性疟疾的肝脏基因表达。本研究共分析18份样本：未免疫第0天（Non-vaccinated day 0, Nd0）3个生物学重复、免疫第0天（Vaccinated day 0, Vd0）3个生物学重复、未免疫第1天（Non-vaccinated day 1, Nd1）3个生物学重复、免疫第1天（Vaccinated day 1, Vd1）3个生物学重复、未免疫第8天（Non-vaccinated day 8, Nd8）3个生物学重复、免疫第8天（Vaccinated day 8, Vd8）3个生物学重复。