Background Upregulated by atheroprotective flow, the transcription factor Krüppel-like factor 2 (KLF2) is crucial for maintaining endothelial function. MicroRNAs (miRNAs) are non-coding small RNAs that regulate gene expression at the post-transcriptional level. We examined the role of miRNAs, particularly miR-92a, in the atheroprotective flow-regulated KLF2. Methods and Results Dicer knockdown increased the level of KLF2 mRNA in human umbilical vein endothelial cells (HUVECs), suggesting that KLF2 is regulated by miRNA. In silico analysis predicted that miR-92a could bind to the 3’ untranslated region (3’UTR) of KLF2 mRNA. Overexpression of miR-92a precursor (pre-92a) decreased the expression of KLF2 and the KLF2-regulated endothelial nitric oxide synthase (eNOS) and thrombomodulin (TM) at mRNA and protein levels. A complementary finding is that miR-92a inhibitor (anti-92a) increased the mRNA and protein expression of KLF2, eNOS, and TM. Subsequent studies revealed that atheroprotective laminar flow downregulated the level of miR-92a to induce KLF2 and the level of this flow-induced KLF2 was reduced by pre-92a. Furthermore, miR-92a level was lower in HUVECs exposed to the atheroprotective pulsatile shear flow (PS) than under atheroprone oscillatory shear flow. Anti-Ago1/2 immunopreciptation coupled with RT-PCR revealed that PS decreased the functional targeting of miR-92a/KLF2 mRNA in HUVECs. Consistent with these findings, mouse carotid arteries receiving pre-92a exhibited impaired vasodilatory response to flow. Conclusions Atheroprotective flow patterns decrease the level of miR-92a, which in turn increases KLF2 expression to maintain endothelial homeostasis.

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AimsThe formyl peptide receptor (FPR) subtype FPR2/ALX transduces pro-inflammatory responses and participates in the resolution of inflammation depending on activation. The aim of the present study was to unravel the role of FPR2/ALX signalling in atherosclerosis.Methods and resultsExpression of FPR2/ALX was analysed in 127 human carotid atherosclerotic lesions and revealed that this receptor was expressed on macrophages, smooth muscle cells (SMCs), and endothelial cells. Furthermore, FPR2/ALX mRNA levels were significantly up-regulated in atherosclerotic lesions compared with healthy vessels. In multiple regression, age, creatinine, and clinical signs of increased cerebral ischaemia were independent predictors of FPR2/ALX expression. To provide mechanistic insights into these observations, we generated Ldlr−/−xFpr2−/− mice, which exhibited delayed atherosclerosis development and less macrophage infiltration compared with Ldlr−/−xFpr2+/+ mice. These findings were reproduced by transplantation of Fpr2−/− bone marrow into Ldlr−/− mice and further extended by in vitro experiments, demonstrating a lower inflammatory state in Fpr2−/− macrophages. FPR2/ALX expression correlated with chemo- and cytokines in human atherosclerotic lesions and leucocytes. Finally, atherosclerotic lesions in Ldlr−/−xFpr2−/− mice exhibited decreased collagen content, and Fpr2−/− SMCs exhibited a profile of increased collagenase and decreased collagen production pathways.ConclusionFPR2/ALX is proatherogenic due to effects on bone marrow-derived cells, but promoted a more stable plaque phenotype through effects on SMCs. Taken together, these results suggest a dual role of FPR2/ALX signalling in atherosclerosis by way of promoting disease progression and but increasing plaque stability.