miR-467b regulates the cholesterol ester formation via targeting ACAT1 gene in RAW 264.7 macrophages

The emerging crosstalk between atherosclerosis-related microRNAs and Bermuda triangle of foam cells: Cholesterol influx, trafficking, and efflux

In atherosclerosis, the gradual buildup of lipid particles into the sub-endothelium of damaged arteries leads to numerous lipid alterations. The absorption of these modified lipids by monocyte-derived macrophages in the arterial wall leads to cholesterol accumulation and increases the likelihood of foam cell formation and fatty streak, which is an early characteristic of atherosclerosis. Foam cell formation is related to an imbalance in cholesterol influx, trafficking, and efflux. The formation of foam cells is heavily regulated by various mechanisms, among them, the role of epigenetic factors like microRNA alteration in the formation of foam cells has been well studied. Recent studies have focused on the potential interplay between microRNAs and foam cell formation in the pathogenesis of atherosclerosis; nevertheless, there is significant space to progress in this attractive field. This review has focused to examine the underlying processes of foam cell formation and microRNA crosstalk to provide a deep insight into therapeutic implications in atherosclerosis.

Regulation of cholesterol homeostasis in health and diseases: from mechanisms to targeted therapeutics

Disturbed cholesterol homeostasis plays critical roles in the development of multiple diseases, such as cardiovascular diseases (CVD), neurodegenerative diseases and cancers, particularly the CVD in which the accumulation of lipids (mainly the cholesteryl esters) within macrophage/foam cells underneath the endothelial layer drives the formation of atherosclerotic lesions eventually. More and more studies have shown that lowering cholesterol level, especially low-density lipoprotein cholesterol level, protects cardiovascular system and prevents cardiovascular events effectively. Maintaining cholesterol homeostasis is determined by cholesterol biosynthesis, uptake, efflux, transport, storage, utilization, and/or excretion. All the processes should be precisely controlled by the multiple regulatory pathways. Based on the regulation of cholesterol homeostasis, many interventions have been developed to lower cholesterol by inhibiting cholesterol biosynthesis and uptake or enhancing cholesterol utilization and excretion. Herein, we summarize the historical review and research events, the current understandings of the molecular pathways playing key roles in regulating cholesterol homeostasis, and the cholesterol-lowering interventions in clinics or in preclinical studies as well as new cholesterol-lowering targets and their clinical advances. More importantly, we review and discuss the benefits of those interventions for the treatment of multiple diseases including atherosclerotic cardiovascular diseases, obesity, diabetes, nonalcoholic fatty liver disease, cancer, neurodegenerative diseases, osteoporosis and virus infection.

MiR-467b alleviates lipopolysaccharide-induced inflammation through targeting STAT1 in chondrogenic ATDC5 cells

Osteoarthritis (OA) is one of the most common degenerative joint diseases worldwide. Chondrocytes are activated in OA patients, accompanied by excessive chondrogenic proliferation and production of inflammatory cytokines. MiR-467b is implicated in the regulation of artherosclerosis and pro-inflammatory cytokine secretion. However, the precise role of miR-467b in OA remains unclear. In the present study, we induced inflammation in chondrogenic ATDC5 cells using lipopolysaccharide (LPS). LPS treatment significantly elevated the production of interleukin-6 (IL-6), IL-1β and tumour necrosis factor-α (TNF-α) in ATDC5 cells, accompanied by decreased miR-467 level. Then, we over-expressed miR-467b using its specific mimics in ATDC5 cells, and LPS-induced inflammation was significantly inhibited as evidenced by decreased IL-6, IL-1β and TNF-α levels. MiR-467b agomir also alleviated inflammation in rat knee osteoarthritis (KOA) model. In addition, we validated that signal transducer and activator of transcription 1 (STAT1) was a downstream target of miR-467b. LPS treatment significantly increased the STAT1 expression while miR-467b mimic transfection partially reversed this effect. Moreover, STAT1 knockout reversed the increased contents of IL-6, IL-1β and TNF-α. Furthermore, miR-467b over-expression significantly decreased the production of IL-6, IL-1β and TNF-α induced by LPS treatment, which was partially reversed by further STAT1 over-expression. In summary, our findings demonstrated that miR-467b alleviated LPS-induced inflammation through targeting STAT1, and this miR-467b/STAT1 regulation axis may provide a new therapeutic target for OA clinical management.

Grape seed proanthocyanidins suppressed macrophage foam cell formation by miRNA-9 via targeting ACAT1 in THP-1 cells

Abnormal lipid metabolism in macrophages leads to atherosclerosis (AS). Excessive LDL cholesterol uptake by macrophages in the aortic endothelium leads to formation of foam cells. Previous studies suggested that proanthocyanidins effectively suppress this process, while the in-depth mechanism has not been elucidated. In mononuclear THP-1 cells, we found that the oligomeric fraction of proanthocyanidins was more effective in suppressing foam cell formation and 25 μg ml-1 for 48 h were the optimum conditions. Under these model conditions, we investigated gene expression and for the first time reported expression of regulatory microRNA (miRNA). It was found that the proanthocyanidins restrained macrophage foaming mainly by lowering the expression levels of cholesterol influx-related receptors CD36 and SR-A, and promoting the expression of cholesterol efflux-related receptor ABCA1. Further, it was latest revealed that proanthocyanidins could notably inhibit the expression of ACAT1, a key gene for intracellular cholesterol esterification. Further investigation was performed on the expression of regulatory miRNAs (miR-134 for CD36, miR-134, miR-155 for SR-A, miR-155, let-7g for LOX-1, miR-9 for ACAT1, miR-27a, miR-19b, miR-10b and miR-33a for ABCA1). The relative expression of miR-9, a miRNA targeting ACAT1, was decreased after the treatment of proanthocyanidins. It was most likely that proanthocyanidins suppressed the expression of ACAT1 via up-regulating the expression of miR-9, thus lessening the intracellular lipid accumulation and eventually inhibiting macrophage foam cell formation. This assumption was further verified by use of miR-9 mimic and its inhibitor.

Sterol-O acyltransferase 1 is inhibited by gga-miR-181a-5p and gga-miR-429-3p through the TGFβ pathway in endodermal epithelial cells of Japanese quail

Nutrients are utilized and re-constructed by endodermal epithelial cells (EECs) of yolk sac membrane (YSM) in avian species during embryonic development. Sterol O-acyltransferase 1 (SOAT1) is the key enzyme to convert cholesterol to cholesteryl ester for delivery to growing embryos. During embryonic development, yolk absorption is concomitant with significant changes of SOAT1 mRNA concentration and enzyme activity in YSM. Presence of microRNAs (miRNAs) are observed in the embryonic liver and muscle during avian embryogenesis. However, the expression of miRNAs in YSM during embryogenesis and the involvement of miRNAs in lipid utilization are not known. Using a miRNA sequencing technique, we found several miRNA candidates and confirmed their expression patterns individually by real time PCR. MiRNA candidates were selected based on the expression pattern and their possible roles in inhibiting transforming growth factor beta receptor type 1 (TGFBR1) that would regulate the function of SOAT1. Similar to SOAT1 mRNA, the gga-miR-181a-5p expression was gradually elevated during embryonic development. However, the expression of gga-miR-429-3p in YSM was gradually decreased during embryonic development. The inhibitory effects of gga-miR-181a-5p or gga-miR-429-3p on the potential targets (SOAT1 and TGFBR1) were demonstrated by transient miRNA transfections in EECs. We also found that mutated TGFBR1 3'UTR prevented the direct pairings of gga-miR-181a-5p and gga-miR-429-3p. Treatment of TGFBR1 inhibitor, LY364947, further decreased SOAT1 transcription. Similar results were also observed by the miRNA transfection studies. The results showed the vital participations of gga-miR-181a-5p and gga-miR-429-3p in regulating TGFβ pathway, and affecting downstream SOAT1 expression and function in the YSM. This is indicative of possible regulation of avian yolk lipid utilization by changing YSM miRNA expressions.

Targeting Foam Cell Formation in Atherosclerosis: Therapeutic Potential of Natural Products

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of atherosclerotic lesions. Targeting foam cell formation in the atherosclerotic lesions can be a promising approach to treat and prevent atherosclerosis. The formation of foam cells is determined by the balanced effects of three major interrelated biologic processes, including lipid uptake, cholesterol esterification, and cholesterol efflux. Natural products are a promising source for new lead structures. Multiple natural products and pharmaceutical agents can inhibit foam cell formation and thus exhibit antiatherosclerotic capacity by suppressing lipid uptake, cholesterol esterification, and/or promoting cholesterol ester hydrolysis and cholesterol efflux. This review summarizes recent findings on these three biologic processes and natural products with demonstrated potential to target such processes. Discussed also are potential future directions for studying the mechanisms of foam cell formation and the development of foam cell-targeted therapeutic strategies.

Cholesterol transport system: An integrated cholesterol transport model involved in atherosclerosis

Atherosclerosis, the pathological basis of most cardiovascular disease (CVD), is closely associated with cholesterol accumulation in the arterial intima. Excessive cholesterol is removed by the reverse cholesterol transport (RCT) pathway, representing a major antiatherogenic mechanism. In addition to the RCT, other pathways are required for maintaining the whole-body cholesterol homeostasis. Thus, we propose a working model of integrated cholesterol transport, termed the cholesterol transport system (CTS), to describe body cholesterol metabolism. The novel model not only involves the classical view of RCT but also contains other steps, such as cholesterol absorption in the small intestine, low-density lipoprotein uptake by the liver, and transintestinal cholesterol excretion. Extensive studies have shown that dysfunctional CTS is one of the major causes for hypercholesterolemia and atherosclerosis. Currently, several drugs are available to improve the CTS efficiently. There are also several therapeutic approaches that have entered into clinical trials and shown considerable promise for decreasing the risk of CVD. In recent years, a variety of novel findings reveal the molecular mechanisms for the CTS and its role in the development of atherosclerosis, thereby providing novel insights into the understanding of whole-body cholesterol transport and metabolism. In this review, we summarize the latest advances in this area with an emphasis on the therapeutic potential of targeting the CTS in CVD patients.

Dietary compounds have potential in controlling atherosclerosis by modulating macrophage cholesterol metabolism and inflammation via miRNA

Atherosclerosis (AS) is a typical example of a widespread fatal cardiovascular disease. Accumulation of cholesterol-laden macrophages in the artery wall forms the starting point of AS. Increased influx of oxidized low-density lipoprotein to macrophages and decreased efflux of free cholesterol out of macrophages constitute major factors promoting the development of AS. Inflammation further aggravates the development of AS along or via interaction with the cholesterol metabolism. Many microRNAs (miRNAs) are related to the regulation of macrophage in AS in aspects of cholesterol metabolism and inflammation signaling. Dietary compounds perform AS inhibitory effects via miRNAs in the cholesterol metabolism (miR-19b, miR-378, miR-10b, miR-33a, and miR-33b) and two miRNAs in the inflammation signaling (miR-155 and miR-146a). The targeted miRNAs in the cholesterol metabolism vary greatly among different food compounds; however, in inflammation signaling, most food compounds target miR-155. Many receptors are involved in macrophages via miRNAs, including ABCA1 and ABCG1 as major receptors in the cholesterol metabolism, while nuclear factor-κB (NF-κB) and Nrf2 signaling and PI3K/AKT signaling pathways are targeted during inflammation. This article reviews current literature to investigate possible AS therapy with dietary compounds via targeting miRNAs. Currently existing problems were also discussed to guide further studies.