Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, The Second Hospital of Tianjin Medical University, Tianjin, China.
Department of Cardiology, Tianjin Hospital, Tianjin, China.
FASEB J. 2021 Oct;35(10):e21936. doi: 10.1096/fj.202100726RR.
Lipopolysaccharide (LPS)-stimulated macrophages express an aconitate decarboxylase (IRG1, also called ACOD1), leading to accumulation of the endogenous metabolite itaconate. However, the precise mechanisms by which elevated itaconate levels alter macrophage function are not clear. Our hypothesis is itaconate affects macrophage function through some uncertain mechanism. Based on this, we established a transcriptional and proteomic signature of macrophages stimulated by itaconate and identified the pathways of IL-1β secretion and altered iron metabolism. Consistently, the effect of IRG1 deficiency on IL-1β secretion and iron metabolism was confirmed in IRG1 knockout THP-1 cell lines. Several common inhibitors and other compounds were used to examine the molecular mechanisms involved. Only cysteine and antioxidants (catechin hydrate) could inhibit caspase-1 activation and IL-1β secretion in itaconate-stimulated macrophages. We further found that aconitase activity was decreased by itaconate stimulation. Our results demonstrate the counteracting effects of overexpression of mitochondrial aconitase (ACO2, a tricarboxylic acid cycle enzyme) or cytosolic aconitase (ACO1, an iron regulatory protein) on IL-1β secretion and altered iron metabolism. Both enzyme activities were inhibited by itaconate because of iron-sulfur (Fe-S) cluster destruction. Our findings indicate that the immunoregulatory functions of IRG1 and itaconate in macrophages are stressful Fe-S cluster of aconitases disrupting and iron metabolism rebalancing.
脂多糖 (LPS) 刺激的巨噬细胞表达一种 aconitate decarboxylase（IRG1，也称为 ACOD1），导致内源性代谢物 itaconate 的积累。然而，升高的 itaconate 水平改变巨噬细胞功能的确切机制尚不清楚。我们的假设是 itaconate 通过某种不确定的机制影响巨噬细胞功能。基于此，我们建立了受 itaconate 刺激的巨噬细胞的转录组和蛋白质组特征，并确定了 IL-1β 分泌和改变的铁代谢途径。一致地，IRG1 缺失对 THP-1 细胞系中 IL-1β 分泌和铁代谢的影响得到了 IRG1 敲除的证实。使用几种常见的抑制剂和其他化合物来研究所涉及的分子机制。只有半胱氨酸和抗氧化剂（儿茶素）才能抑制 itaconate 刺激的巨噬细胞中 caspase-1 的激活和 IL-1β 的分泌。我们进一步发现，aconitase 活性被 itaconate 刺激所降低。我们的结果表明，过表达线粒体 aconitase（三羧酸循环酶 ACO2）或胞质 aconitase（铁调节蛋白 ACO1）对 IL-1β 分泌和改变的铁代谢具有拮抗作用。由于铁硫 (Fe-S) 簇的破坏，两种酶的活性都被 itaconate 抑制。我们的研究结果表明，IRG1 和 itaconate 在巨噬细胞中的免疫调节功能是应激的 aconitases 的 Fe-S 簇破坏和铁代谢再平衡。
