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

The microbiota-derived bile acid taurodeoxycholic acid improves hepatic cholesterol levels in mice with cancer cachexia

Alterations in bile acid profile and pathways contribute to hepatic inflammation in cancer cachexia, a syndrome worsening the prognosis of cancer patients. As the gut microbiota impinges on host metabolism through bile acids, the current study aimed to explore the functional contribution of gut microbial dysbiosis to bile acid dysmetabolism and associated disorders in cancer cachexia. Using three mouse models of cancer cachexia (the C26, MC38 and HCT116 models), we evidenced a reduction in the hepatic levels of several secondary bile acids, mainly taurodeoxycholic (TDCA). This reduction in hepatic TDCA occurred before the appearance of cachexia. Longitudinal analysis of the gut microbiota pinpointed an ASV, identified as Xylanibacter rodentium, as a bacterium potentially involved in the reduced production of TDCA. Coherently, stable isotope-based experiments highlighted a robust decrease in the microbial 7α-dehydroxylation (7α-DH) activity with no changes in the bile salt hydrolase (BSH) activity in cachectic mice. This approach also highlighted a reduced microbial 7α-hydroxysteroid dehydrogenase (7α-HSDH) and 12α-hydroxysteroid dehydrogenase (12α-HSDH) activities in these mice. The contribution of the lower production of TDCA to cancer cachexia was explored in vitro and in vivo. In vitro, TDCA prevented myotube atrophy, whereas in vivo hepatic whole transcriptome analysis revealed that TDCA administration to cachectic mice improved the unfolded protein response and cholesterol homeostasis pathways. Coherently, TDCA administration reversed hepatic cholesterol accumulation in these mice. Altogether, this work highlights the contribution of the gut microbiota to bile acid dysmetabolism and the therapeutic interest of the secondary bile acid TDCA for hepatic cholesterol homeostasis in the context of cancer cachexia. Such discovery may prove instrumental in the understanding of other metabolic diseases characterized by microbial dysbiosis. More broadly, our work demonstrates the interest and relevance of microbial activity measurements using stable isotopes, an approach currently underused in the microbiome field.

The use of transcriptomics to explore the mechanism of silver nanoparticle in inducing the dysregulation of cholesterol metabolism in human neural progenitor cells

Owing to their exceptional antibacterial properties, silver nanoparticles (SNPs) are the most widely used nanoparticles in commercial products. However, this prevalence also heightens the risk of human exposure and raises concerns regarding their adverse environmental effects and potential toxicity to organs, especially the brain. Thus, the aim of this study was to explore the effects and underlying mechanisms of noncytotoxic and cytotoxic SNPs on cholesterol metabolism in a human neural progenitor cell (hNPC) model. The SNPs were synthesized via the sodium borohydride reduction of silver nitrate, and the MTT assay and live/dead cell viability assay were used to compare the effects of different concentrations of SNPs on cell proliferation and death rate. Subsequently, RNA sequencing was performed to analyze the impact of noncytotoxic (5 μM) and cytotoxic (100/200 μM) SNPs on gene expression profiles in hNPCs after 24 hours of exposure, with differentially expressed genes identified and subjected to bioinformatic analysis. The results revealed that both noncytotoxic and cytotoxic SNPs affect cellular lipid homeostasis, with fewer cholesterol metabolism-related hub genes identified in the 5 μM SNP group than in the 100/200 μM SNP groups. Validation experiments indicated that SNPs significantly increase total cholesterol content and trigger negative feedback mechanisms to maintain cholesterol homeostasis. The greater impact of cytotoxic SNPs than noncytotoxic SNPs on cholesterol metabolism might be related to the differential expression of hub genes.

Potential prognostic biomarker of OSBPL10 in pan-cancer associated with immune infiltration

Oxysterol binding protein-related protein 10 (OSBPL10) is a crucial sterol transporter that plays a significant role in regulating metabolic homeostasis. Previous studies have indicated that OSBPL10 promotes the development of several tumors. However, an integrative bioinformatics and immune infiltration analysis of OSBPL10 across various cancers has yet to be conducted. In this study, we comprehensively analyzed the expression patterns, prognostic value, genetic variations, protein modifications, immune infiltration characteristics, and biological functions of OSBPL10 in 33 human cancers using bioinformatics methods and publicly available databases, including TCGA, GEPIA2, GTEx, UCSC, UALCAN, HPA and TISCH2.0. The function of OSBPL10 and its associated mechanisms were confirmed in the pancreatic cancer cell lines Panc-1 and Mia PaCa-2. Our results revealed that OSBPL10 mRNA expression was significantly upregulated in 12 types of tumor tissues and downregulated in 3 cancers, which was notably associated with poor prognosis, pathological stage, and subtype in 10 tumors. Additionally, the level of promoter methylation exhibited a significant negative correlation with OSBPL10 mRNA expression. OSBPL10 expression was found to be dramatically associated with the levels of chemokines, chemokine receptors, immune checkpoints, and immune cell infiltration across various tumors by activating cancer pathways related to the extracellular matrix (ECM) and TSC/mTOR while downregulating tumor cell stemness. Furthermore, elevated OSBPL10 expression was negatively correlated with most drug sensitivities. In vitro experiments showed that OSBPL10 promoted the proliferation and migration of pancreatic cancer cells through the VEGF/AKT signaling pathway. In conclusion, our pan-cancer analysis suggests that OSBPL10 may serve as a critical biomarker for improving prognosis through OSBPL10-targeted therapies, immunotherapies, and chemotherapeutic combinations in cancer patients.

Single-Nuclei Transcriptome Profiling Reveals Intra-Tumoral Heterogeneity and Characterizes Tumor Microenvironment Architecture in a Murine Melanoma Model

Malignant melanoma is an aggressive cancer, with a high risk of metastasis and mortality rates, characterized by cancer cell heterogeneity and complex tumor microenvironment (TME). Single cell biology is an ideal and powerful tool to address these features at a molecular level. However, this approach requires enzymatic cell dissociation that can influence cellular coverage. By contrast, single nucleus RNA sequencing (snRNA-seq) has substantial advantages including compatibility with frozen samples and the elimination of a dissociation-induced, transcriptional stress response. To better profile and understand the functional diversity of different cellular components in melanoma progression, we performed snRNA-seq of 16,839 nuclei obtained from tumor samples along the growth of murine syngeneic melanoma model carrying a BRAFV600E mutation and collected 9 days or 23 days after subcutaneous cell injection. We defined 11 different subtypes of functional cell clusters among malignant cells and 5 different subsets of myeloid cells that display distinct global transcriptional program and different enrichment in early or advanced stage of tumor growth, confirming that this approach was useful to accurately identify intratumor heterogeneity and dynamics during tumor evolution. The current study offers a deep insight into the biology of melanoma highlighting TME reprogramming through tumor initiation and progression, underlying further discovery of new TME biomarkers which may be potentially druggable.

Immunometabolism and immune response regulate macrophage function in atherosclerosis

Macrophages are crucial in the progression of atherosclerotic cardiovascular disease (ASCVD). In the atherosclerotic lesions, macrophages play a central role in maintaining inflammatory response, promoting plaque development, and facilitating thrombosis. Increasing studies indicate that metabolic reprogramming and immune response mediate macrophage functional changes in all stages of atherosclerosis. In this review article, we explain how metabolic changes in glycolysis, oxidative phosphorylation, the tricarboxylic acid cycle, fatty acid synthesis, fatty acid oxidation, and cholesterol metabolism regulate macrophage function in atherosclerosis. We discuss how immune response to oxidized lipids regulate macrophage function in atherosclerosis. Additionally, we explore how abnormal metabolism leads to macrophage mitochondrial dysfunction in atherosclerosis.

Effects of miR-33 Deficiency on Metabolic and Cardiovascular Diseases: Implications for Therapeutic Intervention

MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally inhibit gene expression. These small molecules are involved in several biological conditions such as inflammation, cell growth and proliferation, and regulation of energy metabolism. In the context of metabolic and cardiovascular diseases, miR-33 is of particular interest as it has been implicated in the regulation of lipid and glucose metabolism. This miRNA is located in introns harboured in the genes encoding sterol regulatory element-binding protein (SREBP)-1 and SREBP-2, which are key transcription factors involved in lipid biosynthesis and cholesterol efflux. This review outlines the role of miR-33 in a range of metabolic and cardiovascular pathologies, such as dyslipidaemia, nonalcoholic fatty liver disease (NAFLD), obesity, diabetes, atherosclerosis, and abdominal aortic aneurysm (AAA), and it provides discussion about the effectiveness of miR-33 deficiency as a possible therapeutic strategy to prevent the development of these diseases.

ARMH3-mediated recruitment of PI4KB directs Golgi-to-endosome trafficking and activation of the antiviral effector STING

The cGAS-STING pathway mediates cytoplasmic DNA-triggered innate immunity. STING activation is initiated by cyclic-GMP-AMP (cGAMP)-induced translocation from the endoplasmic reticulum and sulfated glycosaminoglycans-induced polymerization at the Golgi. Here, we examine the mechanisms underlying STING transport and activation beyond the Golgi. A genome-wide CRISPR-Cas9 screen identified Armadillo-like helical domain-containing protein 3 (ARMH3) as critical for STING activation. Upon cGAMP-triggered translocation, ARMH3 interacted with STING at the Golgi and recruited phosphatidylinositol 4-kinase beta (PI4KB) to synthesize PI4P, which directed STING Golgi-to-endosome trafficking via PI4P-binding proteins AP-1 and GGA2. Disrupting PI4P-dependent lipid transport through RNAi of other PI4P-binding proteins impaired STING activation. Consistently, disturbed lipid composition inhibited STING activation, whereas aberrantly elevated cellular PI4P led to cGAS-independent STING activation. Armh3^fl/fllLyz^Cre/Cre mice were susceptible to DNA virus challenge in vivo. Thus, ARMH3 bridges STING and PIK4B to generate PI4P for STING transportation and activation, an interaction conserved in all eukaryotes.

Roles of Phosphatidylinositol 4-Phosphorylation in Non-vesicular Cholesterol Trafficking

Cholesterol (Chol) is an essential component of all eukaryotic cell membranes that affects the function of numerous peripheral as well as integral membrane proteins. Chol is synthesized in the ER, but it is selectively enriched within the plasma membrane (PM) and other endomembranes, which requires Chol to cross the aqueous phase of the cytoplasm. In addition to the classical vesicular trafficking pathways that are known to facilitate the bulk transport of membrane intermediates, Chol is also transported via non-vesicular lipid transfer proteins that work primarily within specialized membrane contact sites. Some of these transport pathways work against established concentration gradients and hence require energy. Recent studies highlight the unique role of phosphoinositides (PPIns), and phosphatidylinositol 4-phosphate (PI4P) in particular, for the control of non-vesicular Chol transport. In this chapter, we will review the emerging connection between Chol, PPIns, and lipid transfer proteins that include the important family of oxysterol-binding protein related proteins, or ORPs.

Structure, function and small molecule modulation of intracellular sterol transport proteins

Intracellular sterol transport proteins (STPs) are crucial for maintaining cellular lipid homeostasis by regulating local sterol pools. Despite structural similarities in their sterol binding domains, STPs have different substrate specificities, intracellular localisation and biological functions. In this review, we highlight recent advances in the determination of STP structures and how this regulates their lipid specificities. Furthermore, we cover the important discoveries relating to the intracellular localisation of STPs, and the organelles between which lipid transport is carried out, giving rise to specific functions in health and disease. Finally, serendipitous and targeted efforts to identify small molecule modulators of STPs, as well as their ability to act as tool compounds and potential therapeutics, will be discussed.

The involvement of oxysterol-binding protein related protein (ORP) 6 in the counter-transport of phosphatidylinositol-4-phosphate (PI4P) and phosphatidylserine (PS) in neurons

Oxysterol-binding protein (OSBP)-related protein (ORP) 6, a member of subfamily III in the ORP family, localizes to membrane contact sites between the endoplasmic reticulum (ER) and other organelles and functions in non-vesicular exchange of lipids including phosphatidylinositol-4-phosphate (PI4P) in neurons. In this study, we searched for the lipid counter-transported in exchange for PI4P by using molecular cell biology techniques. Deconvolution microscopy revealed that knockdown of ORP6 partially shifted localization of a phosphatidylserine (PS) marker but not filipin in primary cultured cerebellar neurons. Overexpression of ORP6 constructs lacking the OSBP-related ligand binding domain (ORD) resulted in the same shift of the PS marker. A PI4KⅢα inhibitor specifically inhibiting the synthesis and plasma membrane (PM) localization of PI4P, suppressed the localization of ORP6 and the PS marker at the PM. Overexpression of mutant PS synthase 1 (PSS1) inhibited transport of the PS marker to the PM and relocated the PI4P marker to the PM in Neuro-2A cells. Introduction of ORP6 but not the dominant negative ORP6 constructs, shifted the localization of PS back to the PM. These data collectively suggest the involvement of ORP6 in the counter-transport of PI4P and PS.

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Knockdown of ORP6 changed localization of PS marker.

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Localization of PS marker and ORP6 at the PM was suppressed by PI4K inhibitor.

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ORP6 restored PS from the ER to PM when mutant PSS1 is expressed.

The miR-23-27-24 cluster: an emerging target in NAFLD pathogenesis

The incidence of non-alcoholic fatty liver disease (NAFLD) is increasing globally, being the most widespread form of chronic liver disease in the west. NAFLD includes a variety of disease states, the mildest being non-alcoholic fatty liver that gradually progresses to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Small non-coding single-stranded microRNAs (miRNAs) regulate gene expression at the miRNA or translational level. Numerous miRNAs have been shown to promote NAFLD pathogenesis and progression through increasing lipid accumulation, oxidative stress, mitochondrial damage, and inflammation. The miR-23-27-24 clusters, composed of miR-23a-27a-24-2 and miR-23b-27b-24-1, have been implicated in various biological processes as well as many diseases. Herein, we review the current knowledge on miR-27, miR-24, and miR-23 in NAFLD pathogenesis and discuss their potential significance in NAFLD diagnosis and therapy.

LncRNAs and Cardiovascular Disease

A novel class of RNA molecule emerged from human transcriptome sequencing studies termed long non-coding RNAs. These RNA molecules differ from other classes of non-coding RNAs such as microRNAs in their sizes, sequence motifs and structures. Studies have demonstrated that long non-coding RNAs play a prominent role in the development and progression of cardiovascular disease. They provide the cell with tiered levels of gene regulation interacting with DNA, other RNA molecules or proteins acting in various capacities to control a variety of cellular mechanisms. Cell specificity is a hallmark of lncRNA studies and they have been identified in macrophages, smooth muscle cells, endothelial cells and hepatocytes. Recent lncRNA studies have uncovered functional micropeptides encoded within lncRNA genes that can have a different function to the lncRNA. Disease associated mutations in the genome tend to occur in non-coding regions signifying the importance of non-coding genes in disease associations. There is a great deal of work to be done in the non-coding RNA field and tremendous therapeutic potential due to their cell type specificity. A better understanding of the functions and interactions of lncRNAs will inevitably have clinical implications.

Cholesterol transport in the late endocytic pathway: Roles of ORP family proteins

Oxysterol-binding protein (OSBP) homologues, designated ORP or OSBPL proteins, constitute one of the largest families of intracellular lipid-binding/transfer proteins (LTP). This review summarizes the mounting evidence that several members of this family participate in the machinery facilitating cholesterol trafficking in the late endocytic pathway. There are indications that OSBP, besides acting as a cholesterol/phosphatidylinositol 4-phosphate (PI4P) exchanger at the endoplasmic reticulum (ER)-trans-Golgi network (TGN) membrane contact sites (MCS), also exchanges these lipids at ER-lysosome (Lys) contacts, increasing Lys cholesterol content. The long isoform of ORP1 (ORP1L), which also targets ER-late endosome (LE)/Lys MCS, has the capacity to mediate cholesterol transport either from ER to LE or in the opposite direction. Moreover, it regulates the motility, positioning and fusion of LE as well as autophagic flux. ORP2, the closest relative of ORP1, is mainly cytosolic, but also targets PI(4,5)P₂-rich endosomal compartments. Our latest data suggest that ORP2 transfers cholesterol from LE to recycling endosomes (RE) in exchange for PI(4,5)P₂, thus stimulating the recruitment of focal adhesion kinase (FAK) on the RE and cell adhesion. FAK activates phosphoinositide kinase on the RE to enhance PI(4,5)P₂ synthesis. ORP2 in turn transfers PI(4,5)P₂ from RE to LE, thus regulating LE tubule formation and transport activity.

Coordination of inter-organelle communication and lipid fluxes by OSBP-related proteins

Oxysterol-binding protein (OSBP) and OSBP-related proteins (ORPs) constitute one of the largest families of lipid-binding/transfer proteins (LTPs) in eukaryotes. The current view is that many of them mediate inter-organelle lipid transfer over membrane contact sites (MCS). The transfer occurs in several cases in a 'counter-current' fashion: A lipid such as cholesterol or phosphatidylserine (PS) is transferred against its concentration gradient driven by transport of a phosphoinositide in the opposite direction. In this way ORPs are envisioned to maintain the distinct organelle lipid compositions, with impacts on multiple organelle functions. However, the functions of ORPs extend beyond lipid homeostasis to regulation of processes such as cell survival, proliferation and migration. Important expanding areas of mammalian ORP research include their roles in viral and bacterial infections, cancers, and neuronal function. The yeast OSBP homologue (Osh) proteins execute multifaceted functions in sterol and glycerophospholipid homeostasis, post-Golgi vesicle transport, phosphatidylinositol-4-phosphate, sphingolipid and target of rapamycin (TOR) signalling, and cell cycle control. These observations identify ORPs as lipid transporters and coordinators of signals with an unforeseen variety of cellular processes. Understanding their activities not only enlightens the biology of the living cell but also allows their employment as targets of new therapeutic approaches for disease.

Detection of Atherosclerosis by Small RNA-Sequencing Analysis of Extracellular Vesicle Enriched Serum Samples

Atherosclerosis can occur throughout the arterial vascular system and lead to various diseases. Early diagnosis of atherosclerotic processes and of individual disease patterns would be more likely to be successful if targeted therapies were available. For this, it is important to find reliable biomarkers that are easily accessible and with little inconvenience for patients. There are many cell culture, animal model or tissue studies that found biomarkers at the microRNA (miRNA) and mRNA level describing atherosclerotic processes. However, little is known about their potential as circulating and liquid biopsy markers in patients. In this study, we examined serum-derived miRNA - profiles from 129 patients and 28 volunteers to identify potential biomarkers. The patients had four different atherosclerotic manifestations: abdominal aneurysm (n = 35), coronary heart disease (n = 34), carotid artery stenosis (n = 24) and peripheral arterial disease (n = 36). The samples were processed with an extracellular vesicle enrichment protocol, total-RNA extraction and small RNA-sequencing were performed. A differential expression analysis was performed bioinformatically to find potentially regulated miRNA biomarkers. Resulting miRNA candidates served as a starting point for an overrepresentation analysis in which relevant target mRNAs were identified. The Gene Ontology database revealed relevant biological functions in relation to atherosclerotic processes. In patients, expression of specific miRNAs changed significantly compared to healthy volunteers; 27 differentially expressed miRNAs were identified. We were able to detect a group-specific miRNA fingerprint: miR-122-5p, miR-2110 and miR-483-5p for abdominal aortic aneurysm, miR-370-3p and miR-409-3p for coronary heart disease, miR-335-3p, miR-381-3p, miR493-5p and miR654-3p for carotid artery stenosis, miR-199a-5p, miR-215-5p, miR-3168, miR-582-3p and miR-769-5p for peripheral arterial disease. The results of the study show that some of the identified miRNAs have already been associated with atherosclerosis in previous studies. Overrepresentation analysis on this data detected biological processes that are clearly relevant for atherosclerosis, its development and progression showing the potential of these miRNAs as biomarker candidates. In a next step, the relevance of these findings on the mRNA level is to be investigated and substantiated.

Intertwined and Finely Balanced: Endoplasmic Reticulum Morphology, Dynamics, Function, and Diseases

The endoplasmic reticulum (ER) is an organelle that is responsible for many essential subcellular processes. Interconnected narrow tubules at the periphery and thicker sheet-like regions in the perinuclear region are linked to the nuclear envelope. It is becoming apparent that the complex morphology and dynamics of the ER are linked to its function. Mutations in the proteins involved in regulating ER structure and movement are implicated in many diseases including neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and amyotrophic lateral sclerosis (ALS). The ER is also hijacked by pathogens to promote their replication. Bacteria such as Legionella pneumophila and Chlamydia trachomatis, as well as the Zika virus, bind to ER morphology and dynamics-regulating proteins to exploit the functions of the ER to their advantage. This review covers our understanding of ER morphology, including the functional subdomains and membrane contact sites that the organelle forms. We also focus on ER dynamics and the current efforts to quantify ER motion and discuss the diseases related to ER morphology and dynamics.

RalA and PLD1 promote lipid droplet growth in response to nutrient withdrawal

Lipid droplets (LDs) are dynamic organelles that undergo dynamic changes in response to changing cellular conditions. During nutrient depletion, LD numbers increase to protect cells against toxic fatty acids generated through autophagy and provide fuel for beta-oxidation. However, the precise mechanisms through which these changes are regulated have remained unclear. Here, we show that the small GTPase RalA acts downstream of autophagy to directly facilitate LD growth during nutrient depletion. Mechanistically, RalA performs this function through phospholipase D1 (PLD1), an enzyme that converts phosphatidylcholine (PC) to phosphatidic acid (PA) and that is recruited to lysosomes during nutrient stress in a RalA-dependent fashion. RalA inhibition prevents recruitment of the LD-associated protein perilipin 3, which is required for LD growth. Our data support a model in which RalA recruits PLD1 to lysosomes during nutrient deprivation to promote the localized production of PA and the recruitment of perilipin 3 to expanding LDs.

MicroRNAs and Circular RNAs in Lipoprotein Metabolism

PURPOSE OF REVIEW

Non-coding RNAs (ncRNAs) including microRNAs (miRNAs) and circular RNAs (circRNAs) are pivotal regulators of mRNA and protein expression that critically contribute to cardiovascular pathophysiology. Although little is known about the origin and function of such ncRNAs, they have been suggested as promising biomarkers with powerful therapeutic value in cardiovascular disease (CVD). In this review, we summarize the most recent findings on ncRNAs biology and their implication on cholesterol homeostasis and lipoprotein metabolism that highlight novel therapeutic avenues for treating dyslipidemia and atherosclerosis.

RECENT FINDINGS

Clinical and experimental studies have elucidated the underlying effects that specific miRNAs impose both directly and indirectly regulating circulating high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL) metabolism and cardiovascular risk. Some of these relevant miRNAs include miR-148a, miR-128-1, miR-483, miR-520d, miR-224, miR-30c, miR-122, miR-33, miR-144, and miR-34. circRNAs are known to participate in a variety of physiological and pathological processes due to their abundance in tissues and their stage-specific expression activation. Recent studies have proven that circRNAs may be considered targets of CVD as well. Some of these cirRNAs are circ-0092317, circ_0003546, circ_0028198, and cirFASN that have been suggested to be strongly involved in lipoprotein metabolism; however, their relevance in CVD is still unknown. MicroRNA and cirRNAs have been proposed as powerful therapeutic targets for treating cardiometabolic disorders including atherosclerosis. Here, we discuss the recent findings in the field of lipid and lipoprotein metabolism underscoring the novel mechanisms by which some of these ncRNAs influence lipoprotein metabolism and CVD.

miR-33 in cardiometabolic diseases: lessons learned from novel animal models and approaches

miRNAs have emerged as critical regulators of nearly all biologic processes and important therapeutic targets for numerous diseases. However, despite the tremendous progress that has been made in this field, many misconceptions remain among much of the broader scientific community about the manner in which miRNAs function. In this review, we focus on miR‐33, one of the most extensively studied miRNAs, as an example, to highlight many of the advances that have been made in the miRNA field and the hurdles that must be cleared to promote the development of miRNA‐based therapies. We discuss how the generation of novel animal models and newly developed experimental techniques helped to elucidate the specialized roles of miR‐33 within different tissues and begin to define the specific mechanisms by which miR‐33 contributes to cardiometabolic diseases including obesity and atherosclerosis. This review will summarize what is known about miR‐33 and highlight common obstacles in the miRNA field and then describe recent advances and approaches that have allowed researchers to provide a more complete picture of the specific functions of this miRNA.

miR-33 Silencing Reprograms the Immune Cell Landscape in Atherosclerotic Plaques

[Figure: see text].

MicroRNA-33 Inhibits Adaptive Thermogenesis and Adipose Tissue Beiging

[Figure: see text].

The emerging roles of OSBP-related proteins in cancer: Impacts through phosphoinositide metabolism and protein-protein interactions

Oxysterol-binding protein -related proteins (ORPs) form a large family of intracellular lipid binding/transfer proteins. A number of ORPs are implicated in inter-organelle lipid transfer over membrane contacts sites, their mode of action involving in several cases the transfer of two lipids in opposite directions, termed countercurrent lipid transfer. A unifying feature appears to be the capacity to bind phosphatidylinositol polyphosphates (PIPs). These lipids are in some cases transported by ORPs from one organelle to another to drive the transfer of another lipid against its concentration gradient, while they in other cases may act as allosteric regulators of ORPs, or an ORP may introduce a PIP to an enzyme for catalysis. Dysregulation of several ORP family members is implicated in cancers, ORP3, -4, -5 and -8 being thus far the most studied examples. The most likely mechanisms underlying their associations with malignant growth are (i) impacts on PIP-mediated signaling events resulting in altered Ca²⁺ homeostasis, bioenergetics, cell survival, proliferation, and migration, (ii) protein-protein interactions affecting the activity of signaling factors, and (iii) modification of cellular lipid transport in a way that facilitates the proliferation of malignant cells. In this review I discuss the existing functional evidence for the involvement of ORPs in cancerous growth, discuss the findings in the light of the putative mechanisms outlined above and the possibility of employing ORPs as targets of anti-cancer therapy.

MicroRNA regulation of cholesterol metabolism

MicroRNAs are small noncoding RNAs that regulate gene expression at the posttranscriptional level. Since many microRNAs have multiple mRNA targets, they are uniquely positioned to regulate the expression of several molecules and pathways simultaneously. For example, the multiple stages of cholesterol metabolism are heavily influenced by microRNA activity. Understanding the scope of microRNAs that control this pathway is highly relevant to diseases of perturbed cholesterol metabolism, most notably cardiovascular disease (CVD). Atherosclerosis is a common cause of CVD that involves inflammation and the accumulation of cholesterol-laden cells in the arterial wall. However, several different cell types participate in atherosclerosis, and perturbations in cholesterol homeostasis may have unique effects on the specialized functions of these various cell types. Therefore, our review discusses the current knowledge of microRNA-mediated control of cholesterol homeostasis, followed by speculation as to how these microRNA-mRNA target interactions might have distinctive effects on different cell types that participate in atherosclerosis.

Bis(monoacylglycero)phosphate, an important actor in the host endocytic machinery hijacked by SARS-CoV-2 and related viruses

Viruses, including the novel coronavirus SARS-CoV-2, redirect infected cell metabolism to their own purposes. After binding to its receptor angiotensin-converting enzyme 2 (ACE2) on the cell surface, the SARS-CoV-2 is taken up by receptor-mediated endocytosis ending in the acidic endolysosomal compartment. The virus hijacks the endosomal machinery leading to fusion of viral and endosomal membranes and release of the viral RNA into the cytosol. This mini-review specifically highlights the membrane lipid organization of the endosomal system focusing on the unconventional and late endosome/lysosome-specific phospholipid, bis(monoacylglycero)phosphate (BMP). BMP is enriched in alveolar macrophages of lung, one of the target tissue of SARS-CoV-2. This review details the BMP structure, its unsaturated fatty acid composition and fusogenic properties that are essential for the highly dynamic formation of the intraluminal vesicles inside the endosomes. Interestingly, BMP is necessary for infection and replication of enveloped RNA virus such as SARS-CoV-1 and Dengue virus. We also emphasize the role of BMP in lipid sorting and degradation, especially cholesterol transport in cooperation with Niemann Pick type C proteins (NPC 1 and 2) and with some oxysterol-binding protein (OSBP)-related proteins (ORPs) as well as in sphingolipid degradation. Interestingly, numerous virus infection required NPC1 as well as ORPs along the endocytic pathway. Furthermore, BMP content is increased during pathological endosomal lipid accumulation in various lysosomal storage disorders. This is particularly important knowing the high percentage of patients with metabolic disorders among the SARS-CoV-2 infected patients presenting severe forms of COVID-19.

Immunometabolic function of cholesterol in cardiovascular disease and beyond

Inflammation represents the driving feature of many diseases, including atherosclerosis, cancer, autoimmunity and infections. It is now established that metabolic processes shape a proper immune response and within this context the alteration in cellular cholesterol homeostasis has emerged as a culprit of many metabolic abnormalities observed in chronic inflammatory diseases. Cholesterol accumulation supports the inflammatory response of myeloid cells (i.e. augmentation of toll-like receptor signalling, inflammasome activation, and production of monocytes and neutrophils) which is beneficial in the response to infections, but worsens diseases associated with chronic metabolic inflammation including atherosclerosis. In addition to the innate immune system, cells of adaptive immunity, upon activation, have also been shown to undergo a reprogramming of cellular cholesterol metabolism, which results in the amplification of inflammatory responses. Aim of this review is to discuss (i) the molecular mechanisms linking cellular cholesterol metabolism to specific immune functions; (ii) how cellular cholesterol accumulation sustains chronic inflammatory diseases such as atherosclerosis; (iii) the immunometabolic profile of patients with defects of genes affecting cholesterol metabolism including familial hypercholesterolaemia, cholesteryl ester storage disease, Niemann-Pick type C, and immunoglobulin D syndrome/mevalonate kinase deficiency. Available data indicate that cholesterol immunometabolism plays a key role in directing immune cells function and set the stage for investigating the repurposing of existing 'metabolic' drugs to modulate the immune response.

Cholesterol Handling in Lysosomes and Beyond

Lysosomes are of major importance for the regulation of cellular cholesterol homeostasis. Food-derived cholesterol and cholesterol esters contained within lipoproteins are delivered to lysosomes by endocytosis. From the lysosomal lumen, cholesterol is transported to the inner surface of the lysosomal membrane through the glycocalyx; this shuttling requires Niemann-Pick C (NPC) 1 and NPC2 proteins. The lysosomal membrane proteins lysosomal-associated membrane protein (LAMP)-2 and lysosomal integral membrane protein (LIMP)-2/SCARB2 also bind cholesterol. LAMP-2 may serve as a cholesterol reservoir, whereas LIMP-2, like NPC1, is able to transport cholesterol through a transglycocalyx tunnel. Contact sites and fusion events between lysosomes and other organelles mediate the distribution of cholesterol. Lysosomal cholesterol content is sensed thereby regulating mammalian target of rapamycin complex (mTORC)-dependent signaling. This review summarizes our understanding of the major steps in cholesterol handling from the moment it enters the lysosome until it leaves this compartment.

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.

Oxysterol-binding protein-related protein 1 variants have opposing cholesterol transport activities from the endolysosomes

OSBPL1 encodes the full-length oxysterol-binding protein-related protein ORP1L, which transports LDL-derived cholesterol at membrane contacts between the late endosomes/lysosomes (LEL) and the endoplasmic reticulum (ER). OSBPL1 also encodes the truncated variant ORP1S that contains only the C-terminal lipid binding domain. HeLa cells in which both variants were knocked out (ORP1-null) were used to determine the functional relationship between ORP1L and ORP1S with respect to cellular cholesterol localization and regulation. ORP1-null cells accumulated cholesterol in LEL and had reduced plasma membrane (PM) cholesterol. PM cholesterol was restored by expression of wild-type ORP1S or a phosphatidylinositol phosphate-binding mutant but not by a sterol-binding mutant. Expression of ORP2, another truncated variant, also restored PM cholesterol in ORP1-null cells. Consistent with a LEL-to-PM cholesterol transport activity, a small fraction of ORP1S was detected on the PM. As a consequence of reduced delivery of cholesterol to the PM in ORP1-null cells, cholesterol was diverted to the ER resulting in normalization of de novo cholesterol synthesis. The deficiency in PM cholesterol also reduced ABCA1-dependent cholesterol efflux and LDL receptor activity in ORP1-null cells. We conclude that ORP1S, which lacks discrete membrane-targeting motifs, transports cholesterol from LEL to the PM.

MicroRNA-144 Silencing Protects Against Atherosclerosis in Male, but Not Female Mice

OBJECTIVE

Atherosclerosis is a leading cause of death in developed countries. MicroRNAs act as fine-tuners of gene expression and have been shown to have important roles in the pathophysiology and progression of atherosclerosis. We, and others, previously demonstrated that microRNA-144 (miR-144) functions to post-transcriptionally regulate ABCA1 (ATP binding cassette transporter A1) and plasma HDL (high-density lipoprotein) cholesterol levels. Here, we explore how miR-144 inhibition may protect against atherosclerosis. Approach and Results: We demonstrate that miR-144 silencing reduced atherosclerosis in male, but not female low-density lipoprotein receptor null (Ldlr-/-) mice. MiR-144 antagonism increased circulating HDL cholesterol levels, remodeled the HDL particle, and enhanced reverse cholesterol transport. Notably, the effects on HDL and reverse cholesterol transport were more pronounced in male mice suggesting sex-specific differences may contribute to the effects of silencing miR-144 on atherosclerosis. As a molecular mechanism, we identify the oxysterol metabolizing enzyme CYP7B1 (cytochrome P450 enzyme 7B1) as a miR-144 regulated gene in male, but not female mice. Consistent with miR-144-dependent changes in CYP7B1 activity, we show decreased levels of 27-hydroxycholesterol, a known proatherogenic sterol and the endogenous substrate for CYP7B1 in male, but not female mice.

CONCLUSIONS

Our data demonstrate silencing miR-144 has sex-specific effects and that treatment with antisense oligonucleotides to target miR-144 might result in enhancements in reverse cholesterol transport and oxysterol metabolism in patients with cardiovascular disease.

Transcriptome Sequencing Analysis of Peripheral Blood of Type 2 Diabetes Mellitus Patients With Thirst and Fatigue

Purpose: The purpose of this study is to explore the differences in transcriptome expression profiles between healthy subjects and type 2 diabetes mellitus patients with thirst and fatigue (D-T2DM) and, in addition, to investigate the possible role of noncoding ribonucleic acids (RNAs) in the pathogenesis of D-T2DM. Methods: We constructed the expression profiles of RNAs by RNA sequencing in the peripheral blood of D-T2DM patients and healthy subjects and analyzed differentially expressed RNAs. Results: Compared with healthy subjects, a total of 469 mRNAs, 776 long non-coding RNAs (lncRNAs), and 21 circular RNAs (circRNAs) were differentially expressed in D-T2DM patients. Furthermore, several genes associated with insulin resistance, inflammation, and mitochondrial dysfunction were identified within the differentially expressed mRNAs. Differentially expressed lncRNAs were primarily involved in biological processes associated with immune responses. In addition, differentially expressed circRNAs may target miRNAs associated with glucose metabolism and mitochondrial function. Conclusions: Our results may bring a new perspective on differential RNA expression involved in the pathogenesis of D-T2DM and promote the development of novel treatments for this disease.

Delivery of MicroRNAs by Chitosan Nanoparticles to Functionally Alter Macrophage Cholesterol Efflux in Vitro and in Vivo

The prevention and treatment of cardiovascular diseases (CVD) has largely focused on lowering circulating LDL cholesterol, yet a significant burden of atherosclerotic disease remains even when LDL is low. Recently, microRNAs (miRNAs) have emerged as exciting therapeutic targets for cardiovascular disease. miRNAs are small noncoding RNAs that post-transcriptionally regulate gene expression by degradation or translational inhibition of target mRNAs. A number of miRNAs have been found to modulate all stages of atherosclerosis, particularly those that promote the efflux of excess cholesterol from lipid-laden macrophages in the vessel wall to the liver. However, one of the major challenges of miRNA-based therapy is to achieve tissue-specific, efficient, and safe delivery of miRNAs in vivo. We sought to develop chitosan nanoparticles (chNPs) that can deliver functional miRNA mimics to macrophages and to determine if these nanoparticles can alter cholesterol efflux and reverse cholesterol transport in vivo. We developed chNPs with a size range of 150-200 nm via the ionic gelation method using tripolyphosphate (TPP) as a cross-linker. In this method, negatively charged miRNAs were encapsulated in the nanoparticles by ionic interactions with polymeric components. We then optimized the efficiency of intracellular delivery of different formulations of chitosan/TPP/miRNA to mouse macrophages. Using a well-defined miRNA with roles in macrophage cholesterol metabolism, we tested whether chNPs could deliver functional miRNAs to macrophages. We find chNPs can transfer exogenous miR-33 to naïve macrophages and reduce the expression of ABCA1, a potent miR-33 target gene, both in vitro and in vivo, confirming that miRNAs delivered via nanoparticles can escape the endosomal system and function in the RISC complex. Because miR-33 and ABCA1 play a key role in regulating the efflux of cholesterol from macrophages, we also confirmed that macrophages treated with miR-33-loaded chNPs exhibited reduced cholesterol efflux to apolipoprotein A1, further confirming functional delivery of the miRNA. In vivo, mice treated with miR33-chNPs showed decreased reverse cholesterol transport (RCT) to the plasma, liver, and feces. In contrast, when efflux-promoting miRNAs were delivered via chNPs, ABCA1 expression and cholesterol efflux into the RCT pathway were improved. Over all, miRNAs can be efficiently delivered to macrophages via nanoparticles, where they can function to regulate ABCA1 expression and cholesterol efflux, suggesting that these miRNA nanoparticles can be used in vivo to target atherosclerotic lesions.

Integrative roles of microRNAs in lipid metabolism and dyslipidemia

PURPOSE OF REVIEW

The purpose of the review is to discuss recent advances in microRNA (miRNA) regulation of lipid metabolism and highlight the importance of miRNA-mediated gene regulation in dyslipidemia and fatty liver disease. This article reviews examples of miRNAs that bridge disparate metabolic pathways in the liver. For example, we highlight miRNAs that are regulated by the sterol-sensing pathway in the liver that in turn regulate cellular or systemic cholesterol, fatty acid, and glucose levels.

RECENT FINDINGS

The most widely studied of these miRNAs are miR-33a/b; however, we recently reported that miRNAs in the miR-183/96/182 cluster are also likely regulated by hepatic cholesterol content and mediate the observed glucose-lowering effects of the bile acid sequestrant colesevelam through the sterol-sensing pathway. In addition, several other hepatic and adipose miRNAs have been recently demonstrated to be key regulators of cellular lipid synthesis, storage, and catabolism, as well as systemic lipid metabolism. Moreover, many of these miRNAs are altered in fatty liver disease and dyslipidemia.

SUMMARY

miRNAs are not just fine-tuners of lipid metabolism, but critical regulatory factors in lipid homeostasis and health. Loss of these miRNA regulatory modules very likely contributes to the underlying metabolic defects observed in lipid disorders.

Vesicular and non-vesicular lipid export from the ER to the secretory pathway

The endoplasmic reticulum is the site of synthesis of most glycerophospholipids, neutral lipids and the initial steps of sphingolipid biosynthesis of the secretory pathway. After synthesis, these lipids are distributed within the cells to create and maintain the specific compositions of the other secretory organelles. This represents a formidable challenge, particularly while there is a simultaneous and quantitatively important flux of membrane components stemming from the vesicular traffic of proteins through the pathway, which can also vary depending on the cell type and status. To meet this challenge cells have developed an intricate system of interorganellar contacts and lipid transport proteins, functioning in non-vesicular lipid transport, which are able to ensure membrane lipid homeostasis even in the absence of membrane trafficking. Nevertheless, under normal conditions, lipids are transported in cells by both vesicular and non-vesicular mechanisms. In this review we will discuss the mechanism and roles of vesicular and non-vesicular transport of lipids from the ER to other organelles of the secretory pathway.

Multi-population GWAS and enrichment analyses reveal novel genomic regions and promising candidate genes underlying bovine milk fatty acid composition

Background

The power of genome-wide association studies (GWAS) is often limited by the sample size available for the analysis. Milk fatty acid (FA) traits are scarcely recorded due to expensive and time-consuming analytical techniques. Combining multi-population datasets can enhance the power of GWAS enabling detection of genomic region explaining medium to low proportions of the genetic variation. GWAS often detect broader genomic regions containing several positional candidate genes making it difficult to untangle the causative candidates. Post-GWAS analyses with data on pathways, ontology and tissue-specific gene expression status might allow prioritization among positional candidate genes.

Results

Multi-population GWAS for 16 FA traits quantified using gas chromatography (GC) in sample populations of the Chinese, Danish and Dutch Holstein with high-density (HD) genotypes detects 56 genomic regions significantly associated to at least one of the studied FAs; some of which have not been previously reported. Pathways and gene ontology (GO) analyses suggest promising candidate genes on the novel regions including OSBPL6 and AGPS on Bos taurus autosome (BTA) 2, PRLH on BTA 3, SLC51B on BTA 10, ABCG5/8 on BTA 11 and ALG5 on BTA 12. Novel genes in previously known regions, such as FABP4 on BTA 14, APOA1/5/7 on BTA 15 and MGST2 on BTA 17, are also linked to important FA metabolic processes.

Conclusion

Integration of multi-population GWAS and enrichment analyses enabled detection of several novel genomic regions, explaining relatively smaller fractions of the genetic variation, and revealed highly likely candidate genes underlying the effects. Detection of such regions and candidate genes will be crucial in understanding the complex genetic control of FA metabolism. The findings can also be used to augment genomic prediction models with regions collectively capturing most of the genetic variation in the milk FA traits.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5573-9) contains supplementary material, which is available to authorized users.

Transient Compound Treatment Induces a Multigenerational Reduction of Oxysterol-Binding Protein (OSBP) Levels and Prophylactic Antiviral Activity

Oxysterol-binding protein (OSBP) is a lipid transport and regulatory protein required for the replication of Enterovirus genus viruses, which includes many significant human pathogens. Short-term exposure (i.e., 1–6 h) to a low dose (i.e., 1 nM) of the natural product compound OSW-1 induces a reduction of cellular OSBP levels by ∼90% in multiple different cell lines with no measurable cytotoxicity, defect in cellular proliferation, or global proteome reduction. Interestingly, the reduction of OSBP levels persists multiple days after the low-dose, transient OSW-1 compound treatment is ended and the intracellular OSW-1 compound levels drop to undetectable levels. The reduction in OSBP levels is inherited in multiple generations of cells that are propagated after the OSW-1 compound treatment is stopped. The enduring multiday, multigenerational reduction of OSBP levels triggered by the OSW-1 compound is not due to proteasome degradation of OSBP or due to a reduction in OSBP mRNA levels. OSW-1 compound treatment induces transient autophagy in cells, but blocking autophagy does not rescue OSBP levels. Although the specific cellular mechanism of long-term OSBP repression is not yet identified, these results clearly show the existence of an OSBP specific cellular regulation process that is triggered upon treatment with an OSBP-binding compound. The stable reduction of OSBP levels upon short-term, transient OSW-1 compound treatment will be a powerful tool to understand OSBP regulation and cellular function. Additionally, the persistent reduction in OSBP levels triggered by the transient OSW-1 compound treatment substantially reduces viral replication in treated cells. Therefore, the long-term, compound-induced reduction of OSBP in cells presents a new route to broad spectrum anti-Enterovirus activity, including as a novel route to antiviral prophylactic treatment through small molecule targeting a human host protein.

The long noncoding RNA CHROME regulates cholesterol homeostasis in primate

The human genome encodes thousands of long non-coding RNAs (lncRNAs), the majority of which are poorly conserved and uncharacterized. Here we identify a primate-specific lncRNA (CHROME), elevated in the plasma and atherosclerotic plaques of individuals with coronary artery disease, that regulates cellular and systemic cholesterol homeostasis. LncRNA CHROME expression is influenced by dietary and cellular cholesterol via the sterol-activated liver X receptor transcription factors, which control genes mediating responses to cholesterol overload. Using gain- and loss-of-function approaches, we show that CHROME promotes cholesterol efflux and HDL biogenesis by curbing the actions of a set of functionally related microRNAs that repress genes in those pathways. CHROME knockdown in human hepatocytes and macrophages increases levels of miR-27b, miR-33a, miR-33b and miR-128, thereby reducing expression of their overlapping target gene networks and associated biologic functions. In particular, cells lacking CHROME show reduced expression of ABCA1, which regulates cholesterol efflux and nascent HDL particle formation. Collectively, our findings identify CHROME as a central component of the non-coding RNA circuitry controlling cholesterol homeostasis in humans.

The Adrenal Clock Prevents Aberrant Light-Induced Alterations in Circadian Glucocorticoid Rhythms

The glucocorticoid (GC) rhythm is entrained to light-dark (LD) cycles via a molecular clock in the suprachiasmatic nucleus (SCN) and is maintained by an adrenal clock synchronized by SCN-dependent signals. Targeted deletion of the core clock gene Bmal1 can disrupt adrenal clock function. The requirement of the adrenal clock to stabilize the circadian GC rhythm during exposure to aberrant LD cycles was determined using novel aldosterone synthase (AS)Cre/+::Bmal1Fl/Fl mice in which Bmal1 deletion occurred during postnatal adrenal transdifferentiation. To examine whether adrenal Bmal1 deletion results in loss of the adrenal clock, mice were crossed with mPER2::Luciferase (mPER2Luc/+) mice. Adrenals from ASCre/+::Bmal1+/+::PER2Luc/+ [control (CTRL)] mice show mPER2Luc rhythms ex vivo, whereas slices from ASCre/+::Bmal1Fl/Fl::PER2Luc/+ [knockout (KO)] mice show dampened rhythms. To monitor corticosterone rhythmicity, mice were implanted with subcutaneous microdialysis probes and sampled at 60-minute intervals for up to 3 days under 12:12-hour [τ (T) 24] LD or 3.5:3.5-hour (T7) LD cycles. Corticosterone rhythms were entrained to T24 LD in CTRL and KO mice. Under T7 LD, circadian corticosterone rhythms persisted in most CTRL mice but not KO mice. Hyperadrenocorticism also was observed in KO mice under T7 LD, reflected by increased corticosterone peak amplitude, total daily corticosterone, and responses to ACTH. Analysis of dysregulated adrenal genes in KO mice exposed to aberrant light identified candidates involved in cholesterol metabolism and trafficking, including steroidogenic acute regulatory protein, which could increase steroidogenesis. Our results show that the adrenal clock functions to buffer steroidogenic responses to aberrant light and stabilize circadian GC rhythmicity.

Nonhuman Primates and Translational Research-Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States. Human epidemiological studies provide challenges for understanding mechanisms that regulate initiation and progression of CVD due to variation in lifestyle, diet, and other environmental factors. Studies describing metabolic and physiologic aspects of CVD, and those investigating genetic and epigenetic mechanisms influencing CVD initiation and progression, have been conducted in multiple Old World nonhuman primate (NHP) species. Major advantages of NHPs as models for understanding CVD are their genetic, metabolic, and physiologic similarities with humans, and the ability to control diet, environment, and breeding. These NHP species are also genetically and phenotypically heterogeneous, providing opportunities to study gene by environment interactions that are not feasible in inbred animal models. Each Old World NHP species included in this review brings unique strengths as models to better understand human CVD. All develop CVD without genetic manipulation providing multiple models to discover genetic variants that influence CVD risk. In addition, as each of these NHP species age, their age-related comorbidities such as dyslipidemia and diabetes are accelerated proportionally 3 to 4 times faster than in humans.In this review, we discuss current CVD-related research in NHPs focusing on selected aspects of CVD for which nonprimate model organism studies have left gaps in our understanding of human disease. We include studies on current knowledge of genetics, epigenetics, calorie restriction, maternal calorie restriction and offspring health, maternal obesity and offspring health, nonalcoholic steatohepatitis and steatosis, Chagas disease, microbiome, stem cells, and prevention of CVD.

Bridging the molecular and biological functions of the oxysterol-binding protein family

Oxysterol-binding protein (OSBP) and OSBP-related proteins (ORPs) constitute a large eukaryotic gene family that transports and regulates the metabolism of sterols and phospholipids. The original classification of the family based on oxysterol-binding activity belies the complex dual lipid-binding specificity of the conserved OSBP homology domain (OHD). Additional protein- and membrane-interacting modules mediate the targeting of select OSBP/ORPs to membrane contact sites between organelles, thus positioning the OHD between opposing membranes for lipid transfer and metabolic regulation. This unique subcellular location, coupled with diverse ligand preferences and tissue distribution, has identified OSBP/ORPs as key arbiters of membrane composition and function. Here, we will review how molecular models of OSBP/ORP-mediated intracellular lipid transport and regulation at membrane contact sites relate to their emerging roles in cellular and organismal functions.

Intracellular and Plasma Membrane Events in Cholesterol Transport and Homeostasis

Cholesterol transport between intracellular compartments proceeds by both energy- and non-energy-dependent processes. Energy-dependent vesicular traffic partly contributes to cholesterol flux between endoplasmic reticulum, plasma membrane, and endocytic vesicles. Membrane contact sites and lipid transfer proteins are involved in nonvesicular lipid traffic. Only “active" cholesterol molecules outside of cholesterol-rich regions and partially exposed in water phase are able to fast transfer. The dissociation of partially exposed cholesterol molecules in water determines the rate of passive aqueous diffusion of cholesterol out of plasma membrane. ATP hydrolysis with concomitant conformational transition is required to cholesterol efflux by ABCA1 and ABCG1 transporters. Besides, scavenger receptor SR-B1 is involved also in cholesterol efflux by facilitated diffusion via hydrophobic tunnel within the molecule. Direct interaction of ABCA1 with apolipoprotein A-I (apoA-I) or apoA-I binding to high capacity binding sites in plasma membrane is important in cholesterol escape to free apoA-I. ABCG1-mediated efflux to fully lipidated apoA-I within high density lipoprotein particle proceeds more likely through the increase of “active” cholesterol level. Putative cholesterol-binding linear motifs within the structure of all three proteins ABCA1, ABCG1, and SR-B1 are suggested to contribute to the binding and transfer of cholesterol molecules from cytoplasmic to outer leaflets of lipid bilayer. Together, plasma membrane events and intracellular cholesterol metabolism and traffic determine the capacity of the cell for cholesterol efflux.

Oxysterol-binding protein-related protein (ORP) 6 localizes to the ER and ER-plasma membrane contact sites and is involved in the turnover of PI4P in cerebellar granule neurons

Oxysterol-binding protein (OSBP)-related proteins (ORPs) are conserved lipid binding proteins found in organisms ranging from yeast to mammals. Recent findings have indicated that these proteins mainly localize to contact sites of 2 different membranous organelles. ORP6, a member of the ORP subfamily III, is one of the least studied ORPs. Using approaches in molecular cell biology, we attempted to study the characteristics of ORP6 and found that ORP6 is abundantly expressed in mouse cultured neurons. Deconvolution microscopy of cultured cerebellar granular cells revealed that ORP6 is localized to the endoplasmic reticulum (ER) and ER-plasma membrane (PM) contact sites, where it co-localized with extended synaptotagmin2 (E-Syt2), a well-known ER-PM contact site marker. E-Syt2 also co-localized with ORP3, another subfamily III member, and ORP5, a subfamily IV member. However, ORP5 does not distribute to the same ER-PM contact sites as subfamily III members. Also, the co-expression of ORP3 but not ORP5 altered the distribution of ORP6 into the processes of cerebellar neurons. Immunoprecipitation demonstrated binding between the intermediate region of ORP6 and ORP3 or ORP6 itself. Additionally, the localization of ORP6 in the PM decreased when co-expressed with the intermediate region of ORP6, in which the pleckstrin homology (PH) domain and OSBP-related ligand binding domain (ORD) are deleted. Over-expression of this intermediate region shifted the location of a phophtidylinositol-4-phosphate (PI4P) marker from the Golgi to the PM. Knockdown of ORP6 resulted in the same shift of the PI4P marker. Collectively, our data suggests that the recruitment of ORP6 to ER-PM contact sites is involved in the turnover of PI4P in cerebellar granular neurons.

Non-coding RNAs in lipid metabolism

Cardiovascular disease (CVD), the leading cause of death and morbidity in the Western world, begins with lipid accumulation in the arterial wall, which is the initial step in atherogenesis. Alterations in lipid metabolism result in increased risk of cardiometabolic disorders, and treatment of lipid disorders remains the most common strategy aimed at reducing the incidence of CVD. Work done over the past decade has identified numerous classes of non-coding RNA molecules including microRNAs (miRNAs) and long-non-coding RNAs (lncRNAs) as critical regulators of gene expression involved in lipid metabolism and CVD, mostly acting at post-transcriptional level. A number of miRNAs, including miR-33, miR-122 and miR-148a, have been demonstrated to play important role in controlling the risk of CVD through regulation of cholesterol homeostasis and lipoprotein metabolism. lncRNAs are recently emerging as important regulators of lipid and lipoprotein metabolism. However, much additional work will be required to fully understand the impact of lncRNAs on CVD and lipid metabolism, due to the high abundance of lncRNAs and the poor-genetic conservation between species. This article reviews the role of miRNAs and lncRNAs in lipid and lipoprotein metabolism and their potential implications for the treatment of CVD.

Cholesterol transfer at endosomal-organelle membrane contact sites

PURPOSE OF REVIEW

Cholesterol is delivered to the limiting membrane of late endosomes by Niemann-Pick Type C1 and C2 proteins. This review summarizes recent evidence that cholesterol transfer from endosomes to the endoplasmic reticulum and other organelles is mediated by lipid-binding proteins that localize to membrane contact sites (MCS).

RECENT FINDINGS

LDL-cholesterol in the late endosomal/lysosomes is exported to the plasma membrane, where most cholesterol resides, and the endoplasmic reticulum, which harbors the regulatory complexes and enzymes that control the synthesis and esterification of cholesterol. A major advance in dissecting these cholesterol transport pathways was identification of frequent and dynamic MCS between endosomes and the endoplasmic reticulum, peroxisomes and plasma membrane. Positioned at these MCS are members of the oxysterol-binding protein (OSBP) and steroidogenic acute regulatory protein-related lipid-transfer family of lipid transfer proteins that bridge the opposing membranes and directly or indirectly mediate cholesterol transfer. OSBP-related protein 1L (ORP1L), ORP5 and ORP6 mediate cholesterol transfer to the endoplasmic reticulum that regulates cholesterol homeostasis. ORP1L and STARD3 also move cholesterol from the endoplasmic reticulum-to-late endosomal/lysosomes under low-cholesterol conditions to facilitate intraluminal vesicle formation. Cholesterol transport also occurs at MCS with peroxisomes and possibly the plasma membrane.

SUMMARY

Frequent contacts between organelles and the endo-lysosomal vesicles are sites for bidirectional transfer of cholesterol.

Regulation of macrophage immunometabolism in atherosclerosis

After activation, cells of the myeloid lineage undergo robust metabolic transitions, as well as discrete epigenetic changes, that can dictate both ongoing and future inflammatory responses. In atherosclerosis, in which macrophages play central roles in the initiation, growth, and ultimately rupture of arterial plaques, altered metabolism is a key feature that dictates macrophage function and subsequent disease progression. This Review explores how factors central to the plaque microenvironment (for example, altered cholesterol metabolism, oxidative stress, hypoxia, apoptotic and necrotic cells, and hyperglycemia) shape the metabolic rewiring of macrophages in atherosclerosis as well as how these metabolic shifts in turn alter macrophage immune-effector and tissue-reparative functions. Finally, this overview offers insight into the challenges and opportunities of harnessing metabolism to modulate aberrant macrophage responses in disease.