Rationale Activated nuclear factor (NF)-κB signaling in the vascular endothelium promotes the initiation and progression of atherosclerosis. Targeting endothelial NF-κB may provide a novel strategy to limit chronic inflammation. Objective To examine the role of microRNA-181b (miR-181b) in endothelial NF-κB signaling and effects on atherosclerosis. Methods and Results MiR-181b expression was reduced in the aortic intima and plasma in apolipoprotein E–deficient mice fed a high-fat diet. Correspondingly, circulating miR-181b in the plasma was markedly reduced in human subjects with coronary artery disease. Systemic delivery of miR-181b resulted in a 2.3-fold overexpression of miR-181b in the aortic intima of apolipoprotein E–deficient mice and suppressed NF-κB signaling revealed by bioluminescence imaging and reduced target gene expression in the aortic arch in apolipoprotein E–deficient/NF-κB-luciferase transgenic mice. MiR-181b significantly inhibited atherosclerotic lesion formation, proinflammatory gene expression and the influx of lesional macrophages and CD4+ T cells in the vessel wall. Mechanistically, miR-181b inhibited the expression of the target gene importin-α3, an effect that reduced NF-κB nuclear translocation specifically in the vascular endothelium of lesions, whereas surprisingly leukocyte NF-κB signaling was unaffected despite a 7-fold overexpression of miR-181b. Our findings uncover that NF-κB nuclear translocation in leukocytes does not involve importin-α3, but rather importin-α5, which miR-181b does not target, highlighting that inhibition of NF-κB signaling in the endothelium is sufficient to mediate miR-181b's protective effects. Conclusions Systemic delivery of miR-181b inhibits the activation of NF-κB and atherosclerosis through cell-specific mechanisms in the vascular endothelium. These findings support the rationale that delivery of miR-181b may provide a novel therapeutic approach to treat chronic inflammatory diseases such as atherosclerosis.

Rationale The pathogenesis of insulin resistance involves dysregulated gene expression and function in multiple cell types including endothelial cells (ECs). Posttranscriptional mechanisms such as microRNA-mediated regulation of gene expression could affect insulin action by modulating EC function. Objective To determine whether microRNA-181b (miR-181b) affects the pathogenesis of insulin resistance by regulating EC function in white adipose tissue during obesity. Methods and Results MiR-181b expression was reduced in adipose tissue ECs of obese mice, and rescue of miR-181b expression improved glucose homeostasis and insulin sensitivity. Systemic intravenous delivery of miR-181b robustly accumulated in adipose tissue ECs, enhanced insulin-mediated Akt phosphorylation at Ser473, and reduced endothelial dysfunction, an effect that shifted macrophage polarization towards an M2 anti-inflammatory phenotype in epididymal white adipose tissue (eWAT). These effects were associated with increased eNOS and FoxO1 phosphorylation as well as nitric oxide activity in eWAT. In contrast, miR-181b did not affect insulin-stimulated Akt phosphorylation in liver and skeletal muscle. Bioinformatics and gene profiling approaches revealed that PHLPP2, a phosphatase that dephosphorylates Akt at Ser473, is a novel target of miR-181b. Knockdown of PHLPP2 increased Akt phosphorylation at Ser473 in ECs, and ‘phenocopied’ miR-181b’s effects on glucose homeostasis, insulin sensitivity, and inflammation of eWAT in vivo. Finally, ECs from diabetic subjects exhibited increased PHLPP2 expression. Conclusions Our data underscore the importance of adipose tissue EC function in controlling the development of insulin resistance. Delivery of miR-181b or PHLPP2 inhibitors may represent a new therapeutic approach to ameliorate insulin resistance by improving adipose tissue endothelial Akt-eNOS-NO signaling.