Retinoic acid exerts disease stage-dependent effects on pristane-induced lupus

We previously showed that all-trans-retinoic acid (tRA), an active metabolite of vitamin A, exacerbated pre-existing autoimmunity in lupus; however, its effects before the development of autoimmunity are unknown. Here, using a pristane-induced model, we show that tRA exerts differential effects when given at the initiation vs. continuation phase of lupus. Unlike tRA treatment during active disease, pre-pristane treatment with tRA aggravated glomerulonephritis through increasing renal expression of pro-fibrotic protein laminin ß1, activating bone marrow conventional dendritic cells (cDCs), and upregulating the interaction of ICAM-1 and LFA-1 in the spleen indicating an active process of leukocyte activation and trafficking. Transcriptomic analysis revealed that prior to lupus induction, tRA significantly upregulated the expression of genes associated with cDC activation and migration. Post-pristane tRA treatment, on the other hand, did not significantly alter the severity of glomerulonephritis; rather, it exerted immunosuppressive functions of decreasing circulatory and renal deposition of autoantibodies as well as suppressing the renal expression of proinflammatory cytokines and chemokines. Together, these findings suggest that tRA differentially modulate lupus-associated kidney inflammation depending on the time of administration. Interestingly, both pre- and post-pristane treatments with tRA reversed pristane-induced leaky gut and modulated the gut microbiota in a similar fashion, suggesting a gut microbiota-independent mechanism by which tRA affects the initiation vs. continuation phase of lupus. Overall design: RNAseq performed on total splenocytes harvested at 3 months of age following daily oral dosing of tRA compared to control samples

我们此前的研究证实，全反式维甲酸（all-trans-retinoic acid, tRA）——维生素A的活性代谢产物——会加重狼疮已存在的自身免疫反应，但在自身免疫发生前其发挥的作用仍不明确。
本研究借助姥鲛烷（pristane）诱导的狼疮模型，发现tRA在狼疮造模起始阶段与疾病持续阶段给药时，可产生截然不同的调控效应。与疾病活动期给予tRA的干预方案不同，造模前予以tRA处理会通过上调肾脏促纤维化蛋白层粘连蛋白β1（laminin ß1）的表达、活化骨髓常规树突状细胞（conventional dendritic cells, cDCs），以及增强脾脏内细胞间黏附分子1（intercellular adhesion molecule 1, ICAM-1）与淋巴细胞功能相关抗原1（lymphocyte function-associated antigen 1, LFA-1）的相互作用，从而加重肾小球肾炎，该过程提示白细胞活化与迁移处于活跃状态。
转录组学分析显示，在狼疮造模前，tRA可显著上调与cDC活化及迁移相关的基因表达。与之相反，造模后给予tRA干预则不会显著改变肾小球肾炎的严重程度；反而发挥免疫抑制功能：降低循环与肾脏中的自身抗体沉积量，并抑制肾脏促炎细胞因子与趋化因子的表达。
综上，上述结果表明tRA可根据给药时机的不同，对狼疮相关的肾脏炎症产生差异化调控。
值得注意的是，造模前与造模后给予tRA均可通过相似的方式逆转姥鲛烷诱导的肠道屏障损伤，并调控肠道菌群，这提示tRA对狼疮造模起始与疾病持续阶段的影响存在不依赖于肠道菌群的作用机制。
整体实验设计：对每日口服给予tRA的实验动物，在其3月龄时采集全脾细胞进行RNA测序（RNA-seq），并以同期对照组样本作为对照。