BTRC x MAP3K7

Protocatechuic acid (PCA), a natural compound found in a variety of Chinese herbal medicines and plant foods, has been documented to inhibit atherosclerosis partially by reducing inflammation burden in arterial endothelial cells. Interestingly, in vitro studies showed that PCA at physiologically reachable concentrations does not affect inflammation burden in TNF-α-stimulated aortic endothelial cells, whereas it increases the content of exosomal miR-10b secreted by macrophages that have engulfed apoptotic cells (efferocytic macrophages).

This study was aimed at investigating whether the in vivo anti-inflammatory effect of PCA in arterial endothelial cells was due to the uptake of efferocytic macrophage exosomal miR-10b.

A transwell co-culture system of aortic endothelial cells with efferocytic macrophages was used to evaluate the effect of PCA on NF-κB-mediated inflammation in aortic endothelial cells. An inhibitor of exosome secretion, GW4869, was applied to confirm the role of exosomes played in the anti-inflammatory effect of PCA. The aortic endothelial cells were administrated with exosomes isolated from PCA-treated efferocytic macrophages or miR-10b mimic or antagomir to ascertain the role of miR-10b in downregulating inflammation effect of PCA. Bioinformatics analyses, loss-of- and gain-of-function assays and luciferase reporter gene assays were performed to identify targeting relationship between miR-10b and mitogen-activated protein kinase kinase kinase 7 (MAP3K7)/β-transducin repeat-containing protein (β-TrCP). Besides, Apoe^-/- mice with advanced atherosclerotic plaques were subjected to intragastric administration of PCA and intraperitoneal injection of GW4869. The miR-10b/MAP3K7/β-TrCP/NF-κB signaling pathways and inflammation indicators were determined in vivo.

PCA at physiologically reachable concentrations inhibited NF-κB-mediated inflammation in TNF-α-stimulated aortic endothelial cells co-cultured with efferocytic macrophages, in which treatment of GW4869 reversed this effect. Exosomes isolated from PCA-treated efferocytic macrophages inhibited inflammation and increased miR-10b levels in aortic endothelial cells. Mechanistically, exosomal miR-10b post-transcriptionally repressed MAP3K7 and β-TrCP, both of which promote NF-κB activation. Knockdown of Map3k7 and Btrc with siRNA in aortic endothelial cells abolished the inhibitory effects of exosomes isolated from PCA-treated efferocytic macrophages on NF-κB-mediated inflammation. Consistently, oral administration of PCA increased miR-10b level and inhibited Map3k7 and Btrc mRNA expression as well as inflammation in aortic endothelial cells in Apoe^-/- mice, all of which were abrogated by GW4869 co-treatment.

Our current findings suggest that PCA could transfer exosomal miR-10b from efferocytic macrophages to endothelial cells and thus inhibit NF-κB-mediated inflammation in arterial endothelial cells through repressing MAP3K7 and β-TrCP, two new targets of miR-10b.