miR-146a deficiency in hematopoietic cells is not involved in the development of atherosclerosis

Abstract

BackgroundAtherosclerosis involves activation of the IRAK1/TRAF6/NF-κB inflammatory cascade, which is negatively regulated by miR146a. Previous studies showed that the TT genotype of rs2431697, located near the miR-146a gene, drives lower miR-146a transcription and predicts adverse cardiovascular events in anticoagulated atrial fibrillation patients. Moreover, systemic miR-146a administration protects mice from atherosclerosis. Here we evaluated the ability of miR-146a expression in the hematopoietic component to regulate atherosclerosis in low-density lipoprotein receptor-null mice (Ldlr-/-).Methods and resultsLethally-irradiated Ldlr-/- mice transplanted with bone marrow from wild-type or miR-146a-null mice were fed an atherogenic diet for 8 and 20 weeks. Irak1, Traf6 and MIR146A expression were quantified in thoracic aorta by qRT-PCR and Western blot. Aortic plaque size and composition were characterized by Oil-Red staining and immunohistochemistry and leukocyte recruitment by intravital microscopy. Blood cell counts were similar in fat-fed Ldlr-/-mice with or without hematopoietic miR-146a expression. However, plasma cholesterol decreased in fat-fed Ldlr-/-mice transplanted with bone marrow deficient for miR-146a. Finally, aortic atherosclerosis burden and recruitment of leukocytes into the vessel wall were undistinguishable between the two groups, despite higher levels of Irak1 and Traf6 mRNA and protein in the aorta of fat-fed mice lacking hematopoietic miR-146a expression.ConclusionsmiR-146a deficiency exclusively in hematopoietic cells modulates cholesterol levels in plasma and the expression of its targets in the artery wall of fat-fed Ldlr-/- mice, but does not accelerate atherosclerosis. Atheroprotection upon systemic miR-146a administration may therefore be caused by specific effects on vascular cells.

miR-146a is a pivotal regulator of neutrophil extracellular trap formation promoting thrombosis

“…Briefly, Ldlr -/mice were transplanted with BM from miR-146a -/or from WT animals and fed with HFD for 8 weeks ( Figure 1A). As reported, transplant efficiency, body weight, circulating blood cell counts, plasma lipid profile, and atherosclerotic burden (atheroma, lesion, and necrotic core areas) were similar between the experimental groups 26 . No differences were found in cfDNA and NE plasma levels between the two mice groups before HFD (data not shown).…”

“…First, we demonstrated that sterile inflammation in a model of miR-146a deficiency in the hematopoietic lineage had higher NET formation. However, we previously showed that miR-146a deficiency in the hematopoietic lineage had no effect on atherogenesis after an 8-week HFD treatment 26 . Here, our results suggest that miR-146a deficiency may participate in thrombosis rather than in atherogenesis, through NETosis.…”

“…Thus, we aimed to extrapolate this finding to different in vivo models. We first utilized an atherosclerosis mouse model previously generated by our group 26 . Briefly, Ldlr -/mice were transplanted with BM from miR-146a -/or from WT animals and fed with HFD for 8 weeks ( Figure 1A).…”

Non-coding RNAs in cardiovascular cell biology and atherosclerosis

“…However, it should be noted that the pro-atherogenic effects of monocyte/macrophagerestricted miR-146a were only observed with prolonged hypercholesterolemia and within the aortic arch as opposed to short-term feeding and other vascular beds including the aortic root 165 . A similar study also demonstrated miR-146a deficiency exclusively in hematopoietic cells regulates circulating cholesterol levels in Ldlr-deficient mice, but does not affect atherogenesis after either short-or long-term high-fat feeding 166 . Paradoxically, an athero-protective effect for miR-146a has been proposed as systemic delivery of a miR-146 mimic to Apoe/Ldlr double-deficient mice or Ldlr-deficient suppressed atherogenesis within the aortic root, which was associated with decreased intra-plaque macrophage content but without affecting plasma cholesterol levels 167 .…”

Circulating miRNAs as molecular markers of occupational grain dust exposure

“…MiR-146a-5p has the ability to negatively regulate several pro-inflammatory factors that promote progression of diseases such as COPD and atherosclerosis, including toll-like receptor (TLR4), IL-1 receptor-associated kinase 1 (IRAK1) and TNF-receptor associated protein factor 6 (TRAF6) 39 . MiR-146a-5p is involved in epithelial-fibroblast communication in the lungs, and the pro-inflammatory phenotype of COPD fibroblasts that have been shown to result from dysregulation of epithelial-fibroblast interaction, partly due to the reduced ability of COPD-derived fibroblasts to upregulate miR-146a-5p to counter-regulate pro-inflammatory activity 40 .…”