Yuanyuan Wei

MicroRNA-155 promotes atherosclerosis by repressing Bcl6 in macrophages

Macrophages in atherosclerotic plaques drive inflammatory responses, degrade lipoproteins, and phagocytose dead cells. MicroRNAs (miRs) control the differentiation and activity of macrophages by regulating the signaling of key transcription factors. However, the functional role of macrophage-related miRs in the immune response during atherogenesis is unknown. Here, we report that miR-155 is specifically expressed in atherosclerotic plaques and proinflammatory macrophages, where it was induced by treatment with mildly oxidized LDL (moxLDL) and IFN-γ. Leukocyte-specific Mir155 deficiency reduced plaque size and number of lesional macrophages after partial carotid ligation in atherosclerotic (Apoe-/-) mice. In macrophages stimulated with moxLDL/IFN-γ in vitro, and in lesional macrophages, loss of Mir155 reduced the expression of the chemokine CCL2, which promotes the recruitment of monocytes to atherosclerotic plaques. Additionally, we found that miR-155 directly repressed expression of BCL6, a transcription factor that attenuates proinflammatory NF-κB signaling. Silencing of Bcl6 in mice harboring Mir155-/- macrophages enhanced plaque formation and CCL2 expression. Taken together, these data demonstrated that miR-155 plays a key role in atherogenic programming of macrophages to sustain and enhance vascular inflammation.

MicroRNA-126-5p promotes endothelial proliferation and limits atherosclerosis by suppressing Dlk1

Atherosclerosis, a hyperlipidemia-induced chronic inflammatory process of the arterial wall, develops preferentially at sites where disturbed laminar flow compromises endothelial cell (EC) function. Here we show that endothelial miR-126-5p maintains a proliferative reserve in ECs through suppression of the Notch1 inhibitor delta-like 1 homolog (Dlk1) and thereby prevents atherosclerotic lesion formation. Endothelial recovery after denudation was impaired in Mir126−/− mice because lack of miR-126-5p, but not miR-126-3p, reduced EC proliferation by derepressing Dlk1. At nonpredilection sites, high miR-126-5p levels in endothelial cells confer a proliferative reserve that compensates for the antiproliferative effects of hyperlipidemia, such that atherosclerosis was exacerbated in Mir126−/− mice. In contrast, downregulation of miR-126-5p by disturbed flow abrogated EC proliferation at predilection sites in response to hyperlipidemic stress through upregulation of Dlk1 expression. Administration of miR-126-5p rescued EC proliferation at predilection sites and limited atherosclerosis, introducing a potential therapeutic approach.

MicroRNA-126, -145, and -155: A Therapeutic Triad in Atherosclerosis?

Atherosclerosis is a condition caused by lipid-induced inflammation of the vessel wall orchestrated by a complex interplay of various cell types, such as endothelial cells, smooth muscle cells, and macrophages. MicroRNAs (miRNAs) have emerged as key regulators of gene expression typically by repressing the target mRNA, which determines cell fate and function under homeostatic and disease conditions. Here, we outline the effects of miRNA-145, -126, and -155 in atherosclerosis in vivo. Downregulation of miR-145, which controls differentiation of smooth muscle cells, promotes lesion formation, whereas the endothelial cell-specific miRNA-126 signals the need for endothelial repair through its transfer from apoptotic endothelial cells in microvesicles. Elevated miR-155 levels are characteristic of proinflammatory macrophages and atherosclerotic lesions. However, the effects of miR-155 seem to be different in early and advanced atherosclerosis. The discovery of the role of these miRNAs in atherosclerosis sheds light on the current concepts of atherogenesis and may provide novel treatment options for cardiovascular diseases.

The microRNA-342-5p Fosters Inflammatory Macrophage Activation Through an Akt1- and microRNA-155–Dependent Pathway During Atherosclerosis

Background— Atherosclerosis is a chronic inflammatory vascular disease driven by the subendothelial accumulation of macrophages. The mechanism regulating the inflammatory response in macrophages during atherogenesis remains unclear. Because microRNAs (miRNAs) play a crucial role in cellular signaling by posttranscriptional regulation of gene expression, we studied the miRNA expression profiles during the progression of atherosclerosis. Methods and Results— Using an miRNA real-time polymerase chain reaction array, we found that macrophage-derived miR-342-5p and miR-155 are selectively upregulated in early atherosclerotic lesions in Apoe−/− mice. miR-342-5p directly targets Akt1 through its 3′-untranslated region. Akt1 suppression by miR-342-5p induces proinflammatory mediators such as Nos2 and II6 in macrophages via the upregulation of miR-155. The local application of an miR-342-5p antagomir inhibits the development of atherosclerosis in partially ligated carotid arteries. In atherosclerotic lesions, the miR-342-5p antagomir upregulated Akt1 expression and suppressed the expression of miR-155 and Nos2. This reduced Nos2 expression was associated with a diminished generation of nitrotyrosine in the plaques. Furthermore, systemic treatment with an inhibitor of miR-342-5p reduced the progression of atherosclerosis in the aorta of Apoe−/− mice. Conclusions— Macrophage-derived miR-342-5p promotes atherosclerosis and enhances the inflammatory stimulation of macrophages by suppressing the Akt1-mediated inhibition of miR-155 expression. Therefore, targeting miR-342-5p may offer a promising strategy to treat atherosclerotic vascular disease.

Pathogenic arterial remodeling: the good and bad of microRNAs

A number of cardiovascular diseases, such as restenosis, aneurysm, and atherosclerosis, lead to vascular remodeling associated with complex adaptive reactions of different cell populations. These reactions include growth of smooth muscle cells, proliferation of endothelial cells, and the inflammatory response of macrophages. MicroRNAs (miRNAs), a class of short RNAs, play key roles in various biological processes and in the development of human disease by post-transcriptional regulation of gene expression. Here, we review the molecular mechanisms of a subset of miRNAs involved in vascular remodeling, including miR-143/145, miR-221/222, miR-126, miR-21, and miR-155. Some of these miRNAs, such as miR-143/145 and miR-126, have been shown to be protective during vascular remodeling, whereas others, such as miR-21, may promote the cellular response that leads to neointima formation. The increasing knowledge regarding the roles of miRNAs in vascular remodeling opens novel avenues for the treatment of various cardiovascular diseases. However, more in vivo studies on the functional roles of these miRNAs are required in the future.

The role of microRNAs in arterial remodelling

Adaptive alterations of the vessel wall architecture, called vascular remodelling, can be found in arterial hypertension, during the formation of aneurysms, in restenosis after vascular interventions, and in atherosclerosis. MicroRNAs (miR) critically affect the main cellular players in arterial remodelling and may either promote or inhibit the structural changes in the vessel wall. They regulate the phenotype of smooth muscle cells (SMCs) and control the inflammatory response in endothelial cells and macrophages. In SMCs, different sets of miRs induce either a synthetic or contractile phenotype, respectively. The conversion into a synthetic SMC phenotype is a crucial event in arterial remodelling. Therefore, reprogramming of the SMC phenotype by miR targeting can modulate the remodelling process. Furthermore, the effects of stimuli that induce remodelling, such as shear stress, angiotensin II, oxidised low-density lipoprotein, or apoptosis, on endothelial cells are mediated by miRs. The endothelial cell-specific miR-126, for example, is transferred in microvesicles from apoptotic endothelial cells and plays a protective role in atherogenesis. The inflammatory response of the innate immune system, especially through macrophages, promotes arterial remodelling. miR-155 induces the expression of inflammatory cytokines, whereas miR-146a and miR-147 are involved in the resolution phase of inflammation. However, in vivo data on the role of miRs in vascular remodelling are still scarce, which are required to test the therapeutic potential of the available, highly effective miR inhibitors.

Regulation of Csf1r and Bcl6 in Macrophages Mediates the Stage-Specific Effects of MicroRNA-155 on Atherosclerosis

Objective— The function of microRNAs is highly context and cell type dependent because of their highly dynamic expression pattern and the regulation of multiple mRNA targets. MicroRNA-155 (miR-155) plays an important role in the innate immune response by regulating macrophage function; however, the effects of miR-155 in macrophages on atherosclerosis are controversial. We hypothesized that the stage-dependent target selection of miR-155 in macrophages determines its effects on atherosclerosis. Approach and Results— The expression of miR-155 increased in lesional macrophages of apolipoprotein E–deficient mice between 12 and 24 weeks of a high-cholesterol diet. Mir155 knockout in apolipoprotein E–deficient mice enhanced lesion formation, increased the lesional macrophage content, and promoted macrophage proliferation after 12 weeks of the high-cholesterol diet. In vitro, miR-155 inhibited macrophage proliferation by suppressing colony-stimulating factor-1 receptor, which was upregulated in lesional macrophages of Mir155 –/– apolipoprotein E–deficient mice. By contrast, Mir155 deficiency reduced necrotic core formation and the deposition of apoptotic cell debris, thereby preventing the progression of atherosclerosis between 12 and 24 weeks of the high-cholesterol diet. miR-155 inhibited efferocytosis in vitro by targeting B-cell leukemia/lymphoma 6 and thus activating RhoA (ras homolog gene family, member A). Accordingly, B-cell leukemia/lymphoma 6 was upregulated in lesional macrophages of Mir155 –/– apolipoprotein E–deficient mice after 24 weeks, but not after 12 weeks of the high-cholesterol diet. Conclusions— Our findings demonstrate a stage-specific role of miR-155 in lesion formation. miR-155 suppressed macrophage proliferation by targeting colony-stimulating factor-1 receptor in early and impaired efferocytosis by downregulating B-cell leukemia/lymphoma 6 in advanced atherosclerosis. Therefore, targeting the interaction between miR-155 and B-cell leukemia/lymphoma 6 may be a promising approach to inhibit the progression of atherosclerosis.

Endothelial Dicer promotes atherosclerosis and vascular inflammation by miRNA-103-mediated suppression of KLF4

MicroRNAs regulate the maladaptation of endothelial cells (ECs) to naturally occurring disturbed blood flow at arterial bifurcations resulting in arterial inflammation and atherosclerosis in response to hyperlipidemic stress. Here, we show that reduced endothelial expression of the RNAse Dicer, which generates almost all mature miRNAs, decreases monocyte adhesion, endothelial C–X–C motif chemokine 1 (CXCL1) expression, atherosclerosis and the lesional macrophage content in apolipoprotein E knockout mice (Apoe−/−) after exposure to a high-fat diet. Endothelial Dicer deficiency reduces the expression of unstable miRNAs, such as miR-103, and promotes Krüppel-like factor 4 (KLF4)-dependent gene expression in murine atherosclerotic arteries. MiR-103 mediated suppression of KLF4 increases monocyte adhesion to ECs by enhancing nuclear factor-κB-dependent CXCL1 expression. Inhibiting the interaction between miR-103 and KLF4 reduces atherosclerosis, lesional macrophage accumulation and endothelial CXCL1 expression. Overall, our study suggests that Dicer promotes endothelial maladaptation and atherosclerosis in part by miR-103-mediated suppression of KLF4.

MicroRNA regulation of macrophages in human pathologies

Macrophages play a crucial role in the innate immune system and contribute to a broad spectrum of pathologies, like in the defence against infectious agents, in inflammation resolution, and wound repair. In the past several years, microRNAs (miRNAs) have been demonstrated to play important roles in immune diseases by regulating macrophage functions. In this review, we will summarize the role of miRNAs in the differentiation of monocytes into macrophages, in the classical and alternative activation of macrophages, and in the regulation of phagocytosis and apoptosis. Notably, miRNAs preferentially target genes related to the cellular cholesterol metabolism, which is of key importance for the inflammatory activation and phagocytic activity of macrophages. miRNAs functionally link various mechanisms involved in macrophage activation and contribute to initiation and resolution of inflammation. miRNAs represent promising diagnostic and therapeutic targets in different conditions, such as infectious diseases, atherosclerosis, and cancer.

Hyperlipidemia-Induced MicroRNA-155-5p Improves β-Cell Function by Targeting Mafb

A high-fat diet increases bacterial lipopolysaccharide (LPS) in the circulation and thereby stimulates glucagon-like peptide 1 (GLP-1)–mediated insulin secretion by upregulating interleukin-6 (IL-6). Although microRNA-155-5p (miR-155-5p), which increases IL-6 expression, is upregulated by LPS and hyperlipidemia and patients with familial hypercholesterolemia less frequently develop diabetes, the role of miR-155-5p in the islet stress response to hyperlipidemia is unclear. In this study, we demonstrate that hyperlipidemia-associated endotoxemia upregulates miR-155-5p in murine pancreatic β-cells, which improved glucose metabolism and the adaptation of β-cells to obesity-induced insulin resistance. This effect of miR-155-5p is because of suppression of v-maf musculoaponeurotic fibrosarcoma oncogene family, protein B, which promotes β-cell function through IL-6–induced GLP-1 production in α-cells. Moreover, reduced GLP-1 levels are associated with increased obesity progression, dyslipidemia, and atherosclerosis in hyperlipidemic Mir155 knockout mice. Hence, induction of miR-155-5p expression in β-cells by hyperlipidemia-associated endotoxemia improves the adaptation of β-cells to insulin resistance and represents a protective mechanism in the islet stress response.