Lanosterol Modulates TLR4-Mediated Innate Immune Responses in Macrophages

Macrophages perform critical functions in both innate immunity and cholesterol metabolism. Here, we report that activation of Toll-like receptor 4 (TLR4) in macrophages causes lanosterol, the first sterol intermediate in the cholesterol biosynthetic pathway, to accumulate. This effect is due to type I interferon (IFN)-dependent histone deacetylase 1 (HDAC1) transcriptional repression of lanosterol-14 alpha-demethylase, the gene product of Cyp51A1. Lanosterol accumulation in macrophages, because of either treatment with ketoconazole or induced conditional disruption of Cyp51A1 in mouse macrophages in vitro, decreases IFN beta-mediated signal transducer and activator of transcription (STAT)-1-STAT2 activation and IFN beta-stimulated gene expression. These effects translate into increased survival to endotoxemic shock by reducing cytokine secretion. In addition, lanosterol accumulation increases membrane fluidity and ROS production, thus potentiating phagocytosis and the ability to kill bacteria. This improves resistance of mice to Listeria monocytogenes infection by increasing bacterial clearance in the spleen and liver. Overall, our data indicate that lanosterol is an endogenous selective regulator of macrophage immunity

Macrophage deficiency of miR-21 promotes apoptosis, plaque necrosis, and vascular inflammation during atherogenesis

Atherosclerosis, the major cause of cardiovascular disease, is a chronic inflammatory disease characterized by the accumulation of lipids and inflammatory cells in the artery wall. Aberrant expression of microRNAs has been implicated in the pathophysiological processes underlying the progression of atherosclerosis. Here, we define the contribution of miR-21 in hematopoietic cells during atherogenesis. Interestingly, we found that miR-21 is the most abundant miRNA in macrophages and its absence results in accelerated atherosclerosis, plaque necrosis, and vascular inflammation. miR-21 expression influences foam cell formation, sensitivity to ER-stress-induced apoptosis, and phagocytic clearance capacity. Mechanistically, we discovered that the absence of miR-21 in macrophages increases the expression of the miR-21 target gene, MKK3, promoting the induction of p38-CHOP and JNK signaling. Both pathways enhance macrophage apoptosis and promote the post-translational degradation of ABCG1, a transporter that regulates cholesterol efflux in macrophages. Altogether, these findings reveal a major role for hematopoietic miR-21 in atherogenesis

miR-27b inhibits LDLR and ABCA1 expression but does not influence plasma and hepatic lipid levels in mice

Rationale: Recently, there has been significant interest in the therapeutic administration of miRNA mimics and inhibitors to treat cardiovascular disease. In particular, miR-27b has emerged as a regulatory hub in cholesterol and lipid metabolism and potential therapeutic target for treating atherosclerosis. Despite this, the impact of miR-27b on lipid levels in vivo remains to be determined. As such, here we set out to further characterize the role of miR-27b in regulating cholesterol metabolism in vitro and to determine the effect of miR-27b overexpression and inhibition on circulating and hepatic lipids in mice. Methods and results: Our results identify miR-27b as an important regulator of LDLR activity in human and mouse hepatic cells through direct targeting of LDLR and LDLRAP1. In addition, we report that modulation of miR-27b expression affects ABCA1 protein levels and cellular cholesterol efflux to ApoA1 in human hepatic Huh7 cells. Overexpression of pre-miR-27b in the livers of wild-type mice using AAV8 vectors increased pre-miR-27b levels 50efold and reduced hepatic ABCA1 and LDLR expression by 50% and 20%, respectively, without changing circulating and hepatic cholesterol and triglycerides. To determine the effect of endogenous miR-27b on circulating lipids, wild-type mice were fed a Western diet for one month and injected with 5 mg/kg of LNA control or LNA anti-miR-27b oligonucleotides. Following two weeks of treatment, the expression of ABCA1 and LDLR were increased by 10-20% in the liver, demonstrating effective inhibition of miR-27b function. Intriguingly, no differences in circulating and hepatic lipids were observed between treatment groups. Conclusions: The results presented here provide evidence that short-term modulation of miR-27b expression in wild-type mice regulates hepatic LDLR and ABCA1 expression but does not influence plasma and hepatic lipid levels. (C) 2015 Elsevier Ireland Ltd. All rights reserved

MicroRNA-148a regulates LDL receptor and ABCA1 expression to control circulating lipoprotein levels

The hepatic low-density lipoprotein receptor (LDLR) pathway is essential for clearing circulating LDL cholesterol (LDL-C). Whereas the transcriptional regulation of LDLR is well characterized, the post-transcriptional mechanisms that govern LDLR expression are just beginning to emerge. Here we develop a high-throughput genome-wide screening assay to systematically identify microRNAs (miRNAs) that regulate LDLR activity in human hepatic cells. From this screen we identified and characterized miR-148a as a negative regulator of LDLR expression and activity and defined a sterol regulatory element binding protein 1 (SREBP1)-mediated pathway through which miR-148a regulates LDL-C uptake. In mice, inhibition of miR-148a increased hepatic LDLR expression and decreased plasma LDL-C. Moreover, we found that miR-148a regulates hepatic expression of ATP-binding cassette, subfamily A, member 1 (ABCA1) and circulating high-density lipoprotein cholesterol (HDL-C) levels in vivo. These studies uncover a role for miR-148a as a key regulator of hepatic LDL-C clearance through direct modulation of LDLR expression and demonstrate the therapeutic potential of inhibiting miR-148a to ameliorate an elevated LDL-C/HDL-C ratio, a prominent risk factor for cardiovascular disease

Genetic Ablation of miR-33 Increases Food Intake, Enhances Adipose Tissue Expansion, and Promotes Obesity and Insulin Resistance

While therapeutic modulation of miRNAs provides a promising approach for numerous diseases, the promiscuous nature of miRNAs raises concern over detrimental off-target effects. miR-33 has emerged as a likely target for treatment of cardiovascular diseases. However, the deleterious effects of long-term anti-miR-33 therapies and predisposition of miR-33(-/-) mice to obesity and metabolic dysfunction exemplify the possible pitfalls of miRNA-based therapies. Our work provides an in-depth characterization of miR-33(-/-) mice and explores the mechanisms by which loss of miR-33 promotes insulin resistance in key metabolic tissues. Contrary to previous reports, our data do not support a direct role for SREBP-1-mediated lipid synthesis in promoting these effects. Alternatively, in adipose tissue of miR-33(-/-) mice, we observe increased pre-adipocyte proliferation, enhanced lipid uptake, and impaired lipolysis. Moreover, we demonstrate that the driving force behind these abnormalities is increased food intake, which can be prevented by pair feeding with wild-type animals

Endothelial TGF-β signalling drives vascular inflammation and atherosclerosis

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Atherosclerosis is a progressive vascular disease triggered by interplay between abnormal shear stress and endothelial lipid retention. A combination of these and, potentially, other factors leads to a chronic inflammatory response in the vessel wall, which is thought to be responsible for disease progression characterized by a buildup of atherosclerotic plaques. Yet molecular events responsible for maintenance of plaque inflammation and plaque growth have not been fully defined. Here we show that endothelial transforming growh factor β (TGF-β) signalling is one of the primary drivers of atherosclerosis-associated vascular inflammation. Inhibition of endothelial TGF-β signalling in hyperlipidemic mice reduces vessel wall inflammation and vascular permeability and leads to arrest of disease progression and regression of established lesions. These proinflammatory effects of endothelial TGF-β signalling are in stark contrast with its effects in other cell types and identify it as an important driver of atherosclerotic plaque growth and show the potential of cell-type-specific therapeutic intervention aimed at control of this disease

Endothelial TGF-β signalling drives vascular inflammation and atherosclerosis

Atherosclerosis is a progressive vascular disease triggered by interplay between abnormal shear stress and endothelial lipid retention. A combination of these and, potentially, other factors leads to a chronic inflammatory response in the vessel wall, which is thought to be responsible for disease progression characterized by a buildup of atherosclerotic plaques. Yet molecular events responsible for maintenance of plaque inflammation and plaque growth have not been fully defined. Here we show that endothelial transforming growh factor β (TGF-β) signalling is one of the primary drivers of atherosclerosis-associated vascular inflammation. Inhibition of endothelial TGF-β signalling in hyperlipidemic mice reduces vessel wall inflammation and vascular permeability and leads to arrest of disease progression and regression of established lesions. These proinflammatory effects of endothelial TGF-β signalling are in stark contrast with its effects in other cell types and identify it as an important driver of atherosclerotic plaque growth and show the potential of cell-type-specific therapeutic intervention aimed at control of this disease