Many attempts to modulate leukocyte-endothelial interaction to prevent or reduce excessive inflammatory reactions were made in the past. However, the basic regulatory principles of the endothelial inflammatory process remain unclear. It seems that the inhibition of individual components of the inflammatory cascade, for example, by a single antibody against an adhesion molecule, may not be enough to achieve a sustained effect on vascular inflammation.In the past years, microRNAs have been identified as important regulators of gene expression in a wide range of Molecular Medicine© 2017 American Heart Association, Inc. Rationale:The interaction of circulating cells within the vascular wall is a critical event in chronic inflammatory processes, such as atherosclerosis, but the control of the vascular inflammatory state is still largely unclear.Objective: This study was undertaken to characterize the function of the endothelial-enriched microRNA miR-100 during vascular inflammation and atherogenesis. Methods and Results:Based on a transcriptome analysis of endothelial cells after miR-100 overexpression, we identified miR-100 as a potent suppressor of endothelial adhesion molecule expression, resulting in attenuated leukocyte-endothelial interaction in vitro and in vivo as shown by flow cytometry and intravital imaging. Mechanistically, miR-100 directly repressed several components of mammalian target of rapamycin complex 1-signaling, including mammalian target of rapamycin and raptor, which resulted in a stimulation of endothelial autophagy and attenuated nuclear factor κB signaling in vitro and in vivo. In a low-density lipoprotein receptordeficient atherosclerotic mouse model, pharmacological inhibition of miR-100 resulted in enhanced plaque lesion formation and a higher macrophage content of the plaque, whereas a systemic miR-100 replacement therapy had protective effects and attenuated atherogenesis, resulting in a decrease of plaque area by 45%. Finally, analysis of miR-100 expression in >70 samples obtained during carotid endarterectomy revealed that local miR-100 expression was inversely correlated with inflammatory cell content in patients. Conclusions: In summary, we describe an anti-inflammatory function of miR-100 in the vascular response to injury and inflammation and identify an important novel modulator of mammalian target of rapamycin signaling and autophagy

During the course of atherosclerotic vascular disease, the adaptive growth of blood vessels is a naturally occurring process that can partly compensate for the decrease in blood flow after the narrowing or occlusion of a major artery. It includes both the sprouting of new endothelial capillaries (angiogenesis) and the enlargement of pre-existing arteriolar and arterial anastomoses to functional collateral arteries (arteriogenesis).1 During angiogenesis, a drop in tissue oxygen tension results in increased expression of hypoxiainducible transcription factors and cytokines, stimulating endothelial proliferation and sprouting in the ischemic tissue, improving distribution and use of the remaining blood flow. On the other hand, arteriogenesis is characterized by a well-orchestrated inflammatory response that is not restricted to the endothelial cell (EC) layer but facilitated by the perivascular infiltration of bone marrow-derived cell populations, mediating the proliferation of both endothelial and vascular smooth muscle cells. During the past decade, monocytes and macrophages were especially demonstrated to exert an important stimulatory function in the regulation of collateral artery growth.2 Although our knowledge about these contributing cell populations in the different forms of vascular growth steadily increases, our understanding of the basic regulatory principles controlling these processes is still limited. Other than canonical mediators of blood vessel growth, such as growth factors and their receptors, an additional functional group of regulators has recently emerged: microRNAs (miRNAs). These short (17-24 nucleotides), single-stranded regulatory RNA sequences are transcribed as precursor hairpin structures from intergenic or intronic regions of the genome that undergo several nuclear and cytoplasmatic processing steps to the mature miRNA.3 Together with Argonaute proteins, they form the RNA-induced silencing complex and recognize specific sequences mostly located in the 3′ untranslated region of their target mRNA, resulting either in inhibition of translation or degradation of Background-Adaptive neovascularization after arterial occlusion is an important compensatory mechanism in cardiovascular disease and includes both the remodeling of pre-existing vessels to collateral arteries (arteriogenesis) and angiogenic capillary growth. We now aimed to identify regulatory microRNAs involved in the modulation of neovascularization after femoral artery occlusion in mice. Methods and Results-Using microRNA-transcriptome analysis, we identified miR-155 as a downregulated microRNA during hindlimb ischemia. Correspondingly, inhibition of miR-155 in endothelial cells had a stimulatory effect on proliferation and angiogenic tube formation via derepression of its direct target gene angiotensin II type 1 receptor. Surprisingly, miR-155-deficient mice showed an unexpected phenotype in vivo, with a strong reduction of blood flow recovery after femoral artery ligation (arteriogenesis) dependent on the attenuation of leuko...

The inflammatory sequelae of ischemia-reperfusion injury (IRI) are a major causal factor of tissue injury in various clinical settings. MicroRNAs (miRs) are short, non-coding RNAs, which regulate protein expression. Here, we investigated the role of miR-155 in IR-related tissue injury. Quantifying microRNA-expression levels in a human muscle tissue after IRI, we found miR-155 expression to be significantly increased and to correlate with the increased expression of TNF-α, IL-1β, CD105, and Caspase3 as well as with leukocyte infiltration. The direct miR-155 target gene SOCS-1 was downregulated. In a mouse model of myocardial infarction, temporary LAD ligation and reperfusion injury resulted in a smaller area of necrosis in miR-155-/- animals compared to wildtype animals. To investigate the underlying mechanisms, we evaluated the effect of miR-155 on inflammatory cell recruitment by intravital microscopy and on the generation of reactive oxygen species (ROS) of macrophages. Our intravital imaging results demonstrated a decreased recruitment of inflammatory cells in miR-155-/- animals during IRI. The generation of ROS in leukocytic cells of miR-155-/- animals was also reduced. RNA silencing of the direct miR-155 target gene SOCS-1 abrogated this effect. In conclusion, miR-155 aggravates the inflammatory response, leukocyte infiltration and tissue damage in IRI via modulation of SOCS-1-dependent generation of ROS. MiR-155 is thus a potential target for the treatment or prevention of IRI.

miR-155 deficiency alleviates AAI by diminishing Th2 priming capacity and ATP-/P2R-induced activation of DCs in mice, suggesting this miRNA as a potential therapeutic target of AAI.