Genome Wide Transcriptome Analysis of Dendritic Cells Identifies Genes with Altered Expression in Psoriasis

Activation of dendritic cells by different pathogens induces the secretion of proinflammatory mediators resulting in local inflammation. Importantly, innate immunity must be properly controlled, as its continuous activation leads to the development of chronic inflammatory diseases such as psoriasis. Lipopolysaccharide (LPS) or peptidoglycan (PGN) induced tolerance, a phenomenon of transient unresponsiveness of cells to repeated or prolonged stimulation, proved valuable model for the study of chronic inflammation. Thus, the aim of this study was the identification of the transcriptional diversity of primary human immature dendritic cells (iDCs) upon PGN induced tolerance. Using SAGE-Seq approach, a tag-based transcriptome sequencing method, we investigated gene expression changes of primary human iDCs upon stimulation or restimulation with Staphylococcus aureus derived PGN, a widely used TLR2 ligand. Based on the expression pattern of the altered genes, we identified non-tolerizeable and tolerizeable genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (Kegg) analysis showed marked enrichment of immune-, cell cycle- and apoptosis related genes. In parallel to the marked induction of proinflammatory mediators, negative feedback regulators of innate immunity, such as TNFAIP3, TNFAIP8, Tyro3 and Mer are markedly downregulated in tolerant cells. We also demonstrate, that the expression pattern of TNFAIP3 and TNFAIP8 is altered in both lesional, and non-lesional skin of psoriatic patients. Finally, we show that pretreatment of immature dendritic cells with anti-TNF-α inhibits the expression of IL-6 and CCL1 in tolerant iDCs and partially releases the suppression of TNFAIP8. Our findings suggest that after PGN stimulation/restimulation the host cell utilizes different mechanisms in order to maintain critical balance between inflammation and tolerance. Importantly, the transcriptome sequencing of stimulated/restimulated iDCs identified numerous genes with altered expression to date not associated with role in chronic inflammation, underlying the relevance of our in vitro model for further characterization of IFN-primed iDCs.

不同病原体激活树突状细胞（dendritic cells）后，可诱导促炎介质（proinflammatory mediators）分泌，进而引发局部炎症反应。至关重要的是，先天免疫（innate immunity）必须受到严格调控，因其持续激活会诱发银屑病（psoriasis）等慢性炎症性疾病。脂多糖（Lipopolysaccharide, LPS）或肽聚糖（peptidoglycan, PGN）诱导的耐受现象——即细胞对反复或长期刺激产生暂时性无应答的状态——已被证实是研究慢性炎症的理想模型。因此，本研究旨在探究原代人未成熟树突状细胞（primary human immature dendritic cells, iDCs）经PGN诱导耐受后的转录多样性（transcriptional diversity）。本研究采用基于标签的转录组测序方法SAGE-Seq，对经金黄色葡萄球菌（Staphylococcus aureus）来源PGN（一种广泛使用的Toll样受体2（TLR2）配体）刺激或再次刺激的原代人iDCs的基因表达变化进行了系统分析。基于差异基因的表达模式，我们鉴定出了非耐受型基因与耐受型基因两类群体。基因本体（Gene Ontology, GO）与京都基因与基因组百科全书（Kyoto Encyclopedia of Genes and Genomes, KEGG）富集分析结果显示，免疫相关、细胞周期相关及凋亡相关基因存在显著富集。在促炎介质显著诱导的同时，先天免疫的负反馈调控因子（如TNFAIP3、TNFAIP8、Tyro3及Mer）在耐受细胞中呈现显著下调趋势。本研究还证实，银屑病患者的皮损皮肤与非皮损皮肤中，TNFAIP3与TNFAIP8的表达模式均发生显著改变。最后，我们发现，对未成熟树突状细胞进行抗TNF-α预处理，可抑制耐受型iDCs中白细胞介素6（IL-6）与趋化因子配体1（CCL1）的表达，并部分逆转TNFAIP8的表达抑制。本研究结果表明，在PGN刺激/再次刺激后，宿主细胞会调动多种调控机制以维持炎症与耐受间的关键平衡。值得注意的是，对刺激或再次刺激的iDCs进行转录组测序，发现了大量此前未被证实与慢性炎症相关的差异表达基因，这凸显了本体外模型在进一步表征干扰素预处理的未成熟树突状细胞（IFN-primed iDCs）方面的重要研究价值。