A big role for small RNAs in HDL homeostasis

Evaluation of high-density lipoprotein-bound long non-coding RNAs in subjects with familial hypercholesterolaemia

BACKGROUND

Long non-coding RNAs (lncRNAs) could be attractive circulating biomarkers for cardiovascular risk stratification in subjects at high atherosclerotic cardiovascular disease risk such as familial hypercholesterolaemia (FH). Our aim was to investigate the presence of lncRNAs carried by high-density lipoprotein (HDL) in FH subjects and to evaluate the associations of HDL-lncRNAs with lipoproteins and mechanical vascular impairment assessed by pulse wave velocity (PWV).

METHODS

This was a retrospective observational study involving 94 FH subjects on statin treatment. Biochemical assays, HDL purification, lncRNA and PWV analyses were performed in all subjects.

RESULTS

LncRNA HIF1A-AS2, LASER and LEXIS were transported by HDL; moreover, HDL-lncRNA LEXIS was associated with Lp(a) plasma levels (p < .01). In a secondary analysis, the study population was stratified into two groups based on the Lp(a) median value. The high-Lp(a) group exhibited a significant increase of PWV compared to the low-Lp(a) group (9.23 ± .61 vs. 7.67 ± .56, p < .01). While HDL-lncRNA HIF1A-AS2 and LASER were similar in the two groups, the high-Lp(a) group exhibited a significant downregulation of HDL-lncRNA LEXIS compared to the low-Lp(a) group (fold change -4.4, p < .0001). Finally, Lp(a) and HDL-lncRNA LEXIS were associated with PWV (for Lp(a) p < .01; for HDL-lncRNA LEXIS p < .05).

CONCLUSIONS

LncRNA HIF1A-AS2, LASER and LEXIS were transported by HDL; moreover, significant relationships of HDL-lncRNA LEXIS with Lp(a) levels and PWV were found. Our study suggests that HDL-lncRNA LEXIS may be useful to better identify FH subjects with more pronounced vascular damage.

Gene network based analysis identifies a coexpression module involved in regulating plasma lipids with high-fat diet response

Plasma lipids are modulated by gene variants and many environmental factors, including diet-associated weight gain. However, understanding how these factors jointly interact to influence molecular networks that regulate plasma lipid levels is limited. Here, we took advantage of the BXD recombinant inbred family of mice to query weight gain as an environmental stressor on plasma lipids. Coexpression networks were examined in both nonobese and obese livers, and a network was identified that specifically responded to the obesogenic diet. This obesity-associated module was significantly associated with plasma lipid levels and enriched with genes known to have functions related to inflammation and lipid homeostasis. We identified key drivers of the module, including Cidec, Cidea, Pparg, Cd36, and Apoa4. The Pparg emerged as a potential master regulator of the module as it can directly target 19 of the top 30 hub genes. Importantly, activation of this module is causally linked to lipid metabolism in humans, as illustrated by correlation analysis and inverse-variance weighed Mendelian randomization. Our findings provide novel insights into gene-by-environment interactions for plasma lipid metabolism that may ultimately contribute to new biomarkers, better diagnostics, and improved approaches to prevent or treat dyslipidemia in patients.

HDL and Reverse Cholesterol Transport

Cardiovascular disease, with atherosclerosis as the major underlying factor, remains the leading cause of death worldwide. It is well established that cholesterol ester-enriched foam cells are the hallmark of atherosclerotic plaques. Multiple lines of evidence support that enhancing foam cell cholesterol efflux by HDL (high-density lipoprotein) particles, the first step of reverse cholesterol transport (RCT), is a promising antiatherogenic strategy. Yet, excitement towards the therapeutic potential of manipulating RCT for the treatment of cardiovascular disease has faded because of the lack of the association between cardiovascular disease risk and what was typically measured in intervention trials, namely HDL cholesterol, which has an inconsistent relationship to HDL function and RCT. In this review, we will summarize some of the potential reasons for this inconsistency, update the mechanisms of RCT, and highlight conditions in which impaired HDL function or RCT contributes to vascular disease. On balance, the evidence still argues for further research to better understand how HDL functionality contributes to RCT to develop prevention and treatment strategies to reduce the risk of cardiovascular disease.

Intraindividual variation of microRNA expression levels in plasma and peripheral blood mononuclear cells and the associations of these levels with the pathogenesis of autoimmune thyroid diseases

Background:

microRNAs (miRNAs) circulate in the blood and negatively regulate the expression of mRNAs. Some miRNAs are associated with the development of autoimmune thyroid diseases (AITD); however, there are few reports on the association between miRNA expression and the pathogenesis of AITD or the physiological variations of circulating miRNAs, which are important to examine as biomarkers.

Methods:

We examined the circadian and day-to-day variations in the expression levels of 5 miRNAs (miR-125a, miR-146a, miR-155, let-7e and miR-106a) in plasma and peripheral blood mononuclear cells (PBMC). We also analysed the expression levels of two of these miRNAs (miR-146a and miR-155) in 20 healthy controls, 60 Graves’ disease (GD) patients and 50 Hashimoto’s disease (HD) patients.

Results:

For each miRNA, we observed wide intraindividual variation [coefficient of variation value (CV): 70%–100%] compared to measurement error (CV: 20%–40%). In patients with AITD, HD, GD in remission and mild HD, the expression levels of miR-146a in PBMC were increased 296%, 328%, 348% and 464% above the levels in healthy controls, respectively (p=0.0443 and p=0.0273, p=0.0267 and p=0.0052, respectively). In severe HD, the expression level of miR-155 in plasma was increased to 347% of that in healthy controls (p=0.0256).

Conclusions:

The expression levels of miRNAs in plasma and PBMC showed wide intraindividual variation. In addition, miR-146a may be associated with the development of AITD.

DNA damage response (DDR) and senescence: shuttled inflamma-miRNAs on the stage of inflamm-aging

A major issue in aging research is how cellular phenomena affect aging at the systemic level. Emerging evidence suggests that DNA damage response (DDR) signaling is a key mechanism linking DNA damage accumulation, cell senescence, and organism aging. DDR activation in senescent cells promotes acquisition of a proinflammatory secretory phenotype (SASP), which in turn elicits DDR and SASP activation in neighboring cells, thereby creating a proinflammatory environment extending at the local and eventually the systemic level. DDR activation is triggered by genomic lesions as well as emerging bacterial and viral metagenomes. Therefore, the buildup of cells with an activated DDR probably fuels inflamm-aging and predisposes to the development of the major age-related diseases (ARDs). Micro (mi)-RNAs - non-coding RNAs involved in gene expression modulation - are released locally and systemically by a variety of shuttles (exosomes, lipoproteins, proteins) that likely affect the efficiency of their biological effects. Here we suggest that some miRNAs, previously found to be associated with inflammation and senescence - miR-146, miR-155, and miR-21 - play a central role in the interplay among DDR, cell senescence and inflamm-aging. The identification of the functions of shuttled senescence-associated miRNAs is expected to shed light on the aging process and on how to delay ARD development.

Prostasomes as a source of diagnostic biomarkers for prostate cancer

New biomarkers are needed to improve the diagnosis of prostate cancer. Similarly to healthy cells, prostate epithelial cancer cells produce extracellular vesicles (prostasomes) that can be isolated from seminal fluid, urine, and blood. Prostasomes contain ubiquitously expressed and prostate-specific membrane and cytosolic proteins, as well as RNA. Both quantitative and qualitative changes in protein, mRNA, long noncoding RNA, and microRNA composition of extracellular vesicles isolated from prostate cancer patients have been reported. In general, however, the identified extracellular vesicle-associated single-marker molecules or combinations of marker molecules require confirmation in large cohorts of patients to validate their specificity and sensitivity as prostate cancer markers. Complications include variable factors such as prostate manipulation and urine flux, as well as masking by ubiquitously expressed free molecules and extracellular vesicles from tissues other than the prostate. Herein, we propose that the most promising methods include comprehensive combinational screening for (mutant) RNA in prostasomes that are immunoisolated with antibodies targeting prostate-specific epitopes.

miRNA Targeting of Oxysterol-Binding Protein-Like 6 Regulates Cholesterol Trafficking and Efflux

OBJECTIVE

Cholesterol homeostasis is fundamental to human health and is, thus, tightly regulated. MicroRNAs exert potent effects on biological pathways, including cholesterol metabolism, by repressing genes with related functions. We reasoned that this mode of pathway regulation could be exploited to identify novel genes involved in cholesterol homeostasis.

APPROACH AND RESULTS

Here, we identify oxysterol-binding protein-like 6 (OSBPL6) as a novel target of 2 miRNA hubs regulating cholesterol homeostasis: miR-33 and miR-27b. Characterization of OSBPL6 revealed that it is transcriptionally regulated in macrophages and hepatocytes by liver X receptor and in response to cholesterol loading and in mice and nonhuman primates by Western diet feeding. OSBPL6 encodes the OSBPL-related protein 6 (ORP6), which contains dual membrane- and endoplasmic reticulum-targeting motifs. Subcellular localization studies showed that ORP6 is associated with the endolysosomal network and endoplasmic reticulum, suggesting a role for ORP6 in cholesterol trafficking between these compartments. Accordingly, knockdown of OSBPL6 results in aberrant clustering of endosomes and promotes the accumulation of free cholesterol in these structures, resulting in reduced cholesterol esterification at the endoplasmic reticulum. Conversely, ORP6 overexpression enhances cholesterol trafficking and efflux in macrophages and hepatocytes. Moreover, we show that hepatic expression of OSBPL6 is positively correlated with plasma levels of high-density lipoprotein cholesterol in a cohort of 200 healthy individuals, whereas its expression is reduced in human atherosclerotic plaques.

CONCLUSIONS

These studies identify ORP6 as a novel regulator of cholesterol trafficking that is part of the miR-33 and miR-27b target gene networks that contribute to the maintenance of cholesterol homeostasis.

Macrophage miRNAs in atherosclerosis

The discovery of endogenous microRNAs (miRNAs) in the early 1990s has been followed by the identification of hundreds of miRNAs and their roles in regulating various biological processes, including proliferation, apoptosis, lipid metabolism, glucose homeostasis and viral infection Esteller (2011), Ameres and Zamore (2013) [1,2]. miRNAs are small (~22 nucleotides) non-coding RNAs that function as "rheostats" to simultaneously tweak the expression of multiple genes within a genetic network, resulting in dramatic functional modulation of biological processes. Although the last decade has brought the identification of miRNAs, their targets and function(s) in health and disease, there remains much to be deciphered from the human genome and its complexities in mechanistic regulation of entire genetic networks. These discoveries have opened the door to new and exciting avenues for therapeutic interventions to treat various pathological diseases, including cardiometabolic diseases such as atherosclerosis, diabetes and obesity. In a complex multi-factorial disease like atherosclerosis, many miRNAs have been shown to contribute to disease progression and may offer novel targets for future therapy. This article is part of a Special Issue entitled: MicroRNAs and lipid/energy metabolism and related diseases edited by Carlos Fernández-Hernando and Yajaira Suárez.

Integration of lipidomics and transcriptomics unravels aberrant lipid metabolism and defines cholesteryl oleate as potential biomarker of prostate cancer

In-depth delineation of lipid metabolism in prostate cancer (PCa) is significant to open new insights into prostate tumorigenesis and progression, and provide potential biomarkers with greater accuracy for improved diagnosis. Here, we performed lipidomics and transcriptomics in paired prostate cancer tumor (PCT) and adjacent nontumor (ANT) tissues, followed by external validation of biomarker candidates. We identified major dysregulated pathways involving lipogenesis, lipid uptake and phospholipids remodeling, correlated with widespread lipid accumulation and lipid compositional reprogramming in PCa. Specifically, cholesteryl esters (CEs) were most prominently accumulated in PCa, and significantly associated with cancer progression and metastasis. We showed that overexpressed scavenger receptor class B type I (SR-BI) may contribute to CEs accumulation. In discovery set, CEs robustly differentiated PCa from nontumor (area under curve (AUC) of receiver operating characteristics (ROC), 0.90–0.94). In validation set, CEs potently distinguished PCa and non-malignance (AUC, 0.84–0.91), and discriminated PCa and benign prostatic hyperplasia (BPH) (AUC, 0.90–0.96), superior to serum prostate-specific antigen (PSA) (AUC = 0.83). Cholesteryl oleate showed highest AUCs in distinguishing PCa from non-malignance or BPH (AUC = 0.91 and 0.96). Collectively, our results unravel the major lipid metabolic aberrations in PCa and imply the potential role of CEs, particularly, cholesteryl oleate, as molecular biomarker for PCa detection.

Non-coding RNAs and lipid metabolism

A high percentage of the mammalian genome consists of non-coding RNAs (ncRNAs). Among ncRNAs two main subgroups have been identified: long ncRNAs (lncRNAs) and micro RNAs (miRNAs). ncRNAs have been demonstrated to play a role in a vast variety of diseases, since they regulate gene transcription and are involved in post-transcriptional regulation. They have the potential to function as molecular signals or as guides for transcription factors and to regulate epigenetic modifiers. In this literature review we have summarized data on miRNAs and lncRNAs and their involvement in dyslipidaemia, atherosclerosis, insulin resistance and adipogenesis. Outlining certain ncRNAs as disease biomarkers and/or therapeutic targets, and testing them in vivo, will be the next steps in future research.

MicroRNAs as novel biomarkers for pancreatic cancer diagnosis: a meta-analysis based on 18 articles

Dysregulated microRNAs (miRNAs) have been reported to be associated with pancreatic cancer (PaC), suggesting that they may serve as useful novel diagnostic biomarkers for PaC. Various studies have been performed to investigate the diagnostic value of miRNAs for PaC but have obtained conflicting results. Therefore, this meta-analysis aims to comprehensively and quantitatively evaluate the potential diagnostic value of miRNAs for PaC. We systematically searched PubMed, Embase, Google Scholar, Cochrane Library, and Chinese National Knowledge Infrastructure for publications concerning the diagnostic value of miRNAs for PaC without language restriction. The quality of each study was scored using the revised Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2). The summary receiver operator characteristic curve and other parameters were applied to check the overall test performance. Heterogeneity was tested with the I (2) test and publication bias was tested with the Deek's funnel plot asymmetry test. This meta-analysis included 18 articles with a total of 2,036 patients and 1,444 controls. The pooled sensitivity was 82 % (95 % CI, 78-86 %); the specificity was 77 % (95 % CI, 73-81 %); the PLR was 3.6 (95 % CI, 3.0-4.4); the NLR was 0.23 (95 % CI, 0.18-0.29); the DOR was 16 (95 % CI, 10-24); and the AUC was 0.86 (95 % CI, 0.83-0.89). Subgroups analyses were also performed and revealed that there were significant differences between some subgroups: the multiple-miRNAs profiling-based assays, non-blood-based assays, and healthy control-based studies all showed higher accuracies in diagnosing PaC than that of their counterparts. This meta-analysis suggests that the use of miRNAs has potential diagnostic value with a relatively high sensitivity and specificity for PaC, particularly the use of multiple miRNAs for discriminating PaC patients from healthy individuals. More prospective studies on the diagnostic value of miRNAs for PaC are needed in the future.