Interferon-mediated reprogramming of membrane cholesterol to evade bacterial toxins.

Plasma membranes of animal cells are enriched for cholesterol. Cholesterol-dependent cytolysins (CDCs) are pore-forming toxins secreted by bacteria that target membrane cholesterol for their effector function. Phagocytes are essential for clearance of CDC-producing bacteria; however, the mechanisms by which these cells evade the deleterious effects of CDCs are largely unknown. Here, we report that interferon (IFN) signals convey resistance to CDC-induced pores on macrophages and neutrophils. We traced IFN-mediated resistance to CDCs to the rapid modulation of a specific pool of cholesterol in the plasma membrane of macrophages without changes to total cholesterol levels. Resistance to CDC-induced pore formation requires the production of the oxysterol 25-hydroxycholesterol (25HC), inhibition of cholesterol synthesis and redistribution of cholesterol to an esterified cholesterol pool. Accordingly, blocking the ability of IFN to reprogram cholesterol metabolism abrogates cellular protection and renders mice more susceptible to CDC-induced tissue damage. These studies illuminate targeted regulation of membrane cholesterol content as a host defense strategy.

Limiting Cholesterol Biosynthetic Flux Spontaneously Engages Type I IFN Signaling.

Cellular lipid requirements are achieved through a combination of biosynthesis and import programs. Using isotope tracer analysis, we show that type I interferon (IFN) signaling shifts the balance of these programs by decreasing synthesis and increasing import of cholesterol and long chain fatty acids. Genetically enforcing this metabolic shift in macrophages is sufficient to render mice resistant to viral challenge, demonstrating the importance of reprogramming the balance of these two metabolic pathways in vivo. Unexpectedly, mechanistic studies reveal that limiting flux through the cholesterol biosynthetic pathway spontaneously engages a type I IFN response in a STING-dependent manner. The upregulation of type I IFNs was traced to a decrease in the pool size of synthesized cholesterol and could be inhibited by replenishing cells with free cholesterol. Taken together, these studies delineate a metabolic-inflammatory circuit that links perturbations in cholesterol biosynthesis with activation of innate immunity.

RNF130 Regulates LDLR Availability and Plasma LDL Cholesterol Levels.

BACKGROUND: Removal of circulating plasma low-density lipoprotein cholesterol (LDL-C) by the liver relies on efficient endocytosis and intracellular vesicle trafficking. Increasing the availability of hepatic LDL receptors (LDLRs) remains a major clinical target for reducing LDL-C levels. Here, we describe a novel role for RNF130 (ring finger containing protein 130) in regulating plasma membrane availability of LDLR. METHODS: We performed a combination of gain-of-function and loss-of-function experiments to determine the effect of RNF130 on LDL-C and LDLR recycling. We overexpressed RNF130 and a nonfunctional mutant RNF130 in vivo and measured plasma LDL-C and hepatic LDLR protein levels. We performed in vitro ubiquitination assays and immunohistochemical staining to measure levels and cellular distribution of LDLR. We supplement these experiments with 3 separate in vivo models of RNF130 loss-of-function where we disrupted Rnf130 using either ASO (antisense oligonucleotides), germline deletion, or AAV CRISPR (adeno-associated virus clustered regularly interspaced short palindromic repeats) and measured hepatic LDLR and plasma LDL-C. RESULTS: We demonstrate that RNF130 is an E3 ubiquitin ligase that ubiquitinates LDLR resulting in redistribution of the receptor away from the plasma membrane. Overexpression of RNF130 decreases hepatic LDLR and increases plasma LDL-C levels. Further, in vitro ubiquitination assays demonstrate RNF130-dependent regulation of LDLR abundance at the plasma membrane. Finally, in vivo disruption of Rnf130 using ASO, germline deletion, or AAV CRISPR results in increased hepatic LDLR abundance and availability and decreased plasma LDL-C levels. CONCLUSIONS: Our studies identify RNF130 as a novel posttranslational regulator of LDL-C levels via modulation of LDLR availability, thus providing important insight into the complex regulation of hepatic LDLR protein levels.

An integrative systems genetic analysis of mammalian lipid metabolism.

Dysregulation of lipid homeostasis is a precipitating event in the pathogenesis and progression of hepatosteatosis and metabolic syndrome. These conditions are highly prevalent in developed societies and currently have limited options for diagnostic and therapeutic intervention. Here, using a proteomic and lipidomic-wide systems genetic approach, we interrogated lipid regulatory networks in 107 genetically distinct mouse strains to reveal key insights into the control and network structure of mammalian lipid metabolism. These include the identification of plasma lipid signatures that predict pathological lipid abundance in the liver of mice and humans, defining subcellular localization and functionality of lipid-related proteins, and revealing functional protein and genetic variants that are predicted to modulate lipid abundance. Trans-omic analyses using these datasets facilitated the identification and validation of PSMD9 as a previously unknown lipid regulatory protein. Collectively, our study serves as a rich resource for probing mammalian lipid metabolism and provides opportunities for the discovery of therapeutic agents and biomarkers in the setting of hepatic lipotoxicity.

Re-Examining the Role of Pulmonary Lipids in the Pathogenesis of Pulmonary Fibrosis.

Pulmonary fibrosis (PF) can be idiopathic or driven by a specific insult or disease process. Inflammation plays a role in the pathophysiology, the extent of which remains a longstanding topic of debate. More recently there has been increasing interest in a potential inciting role for aberrant lipid metabolism. Lipids are essential for the structure and function of all cell membranes but specifically in the lung for surfactant composition, intra and intercellular lipid mediators and lipofibroblasts. Clinically, there is evidence of increased lipid deposition in the subpleural space, and at a whole lung tissue level in PF. There is evidence of increased parenchymal lipid deposition and abnormal mediastinal fat shape on chest CT. A protective role for cholesterol lowering drugs including statins and ezetimibe has been described in PF. At a cellular level, fatty acid (FA), phospholipid (PL) and glucose metabolism are disordered, as is the production of lipid mediators. In this perspectives piece we put forward the argument that there is substantive clinical and biological evidence to support a role for aberrant lipid metabolism and lipid mediators in the pathogenesis of PF.

Alveolar macrophage lipid burden correlates with clinical improvement in patients with pulmonary alveolar proteinosis.

Pulmonary alveolar proteinosis (PAP) is a life-threatening, rare lung syndrome for which there is no cure and no approved therapies. PAP is a disease of lipid accumulation characterized by alveolar macrophage foam cell formation. While much is known about the clinical presentation, there is a paucity of information regarding temporal changes in lipids throughout the course of disease. Our objectives were to define the detailed lipid composition of alveolar macrophages in PAP patients at the time of diagnosis and during treatment. We performed comprehensive mass spectrometry to profile the lipid signature of alveolar macrophages obtained from three independent mouse models of PAP and from PAP and non-PAP patients. Additionally, we quantified changes in macrophage-associated lipids during clinical treatment of PAP patients. We found remarkable variations in lipid composition in PAP patients, which were consistent with data from three independent mouse models. Detailed lipidomic analysis revealed that the overall alveolar macrophage lipid burden inversely correlated with clinical improvement and response to therapy in PAP patients. Specifically, as PAP patients experienced clinical improvement, there was a notable decrease in the total lipid content of alveolar macrophages. This crucial observation suggests that the levels of these macrophage-associated lipids can be utilized to assess the efficacy of treatment. These findings provide valuable insights into the dysregulated lipid metabolism associated with PAP, offering the potential for lipid profiling to serve as a means of monitoring therapeutic interventions in PAP patients.

Analysis of tissue lipidomics and computed tomography pulmonary fat attenuation volume (CTPFAV ) in idiopathic pulmonary fibrosis.

BACKGROUND AND OBJECTIVE: There is increasing interest in the role of lipids in processes that modulate lung fibrosis with evidence of lipid deposition in idiopathic pulmonary fibrosis (IPF) histological specimens. The aim of this study was to identify measurable markers of pulmonary lipid that may have utility as IPF biomarkers. STUDY DESIGN AND METHODS: IPF and control lung biopsy specimens were analysed using a unbiased lipidomic approach. Pulmonary fat attenuation volume (PFAV) was assessed on chest CT images (CTPFAV ) with 3D semi-automated lung density software. Aerated lung was semi-automatically segmented and CTPFAV calculated using a Hounsfield-unit (-40 to -200HU) threshold range expressed as a percentage of total lung volume. CTPFAV was compared to pulmonary function, serum lipids and qualitative CT fibrosis scores. RESULTS: There was a significant increase in total lipid content on histological analysis of IPF lung tissue (23.16 nmol/mg) compared to controls (18.66 mol/mg, p = 0.0317). The median CTPFAV in IPF was higher than controls (1.34% vs. 0.72%, p < 0.001) and CTPFAV correlated significantly with DLCO% predicted (R2 = 0.356, p < 0.0001) and FVC% predicted (R2 = 0.407, p < 0.0001) in patients with IPF. CTPFAV correlated with CT features of fibrosis; higher CTPFAV was associated with >10% reticulation (1.6% vs. 0.94%, p = 0.0017) and >10% honeycombing (1.87% vs. 1.12%, p = 0.0003). CTPFAV showed no correlation with serum lipids. CONCLUSION: CTPFAV is an easily quantifiable non-invasive measure of pulmonary lipids. In this pilot study, CTPFAV correlates with pulmonary function and radiological features of IPF and could function as a potential biomarker for IPF disease severity assessment.

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.

ABCG1 regulates pulmonary surfactant metabolism in mice and men.

Idiopathic pulmonary alveolar proteinosis (PAP) is a rare lung disease characterized by accumulation of surfactant. Surfactant synthesis and secretion are restricted to epithelial type 2 (T2) pneumocytes (also called T2 cells). Clearance of surfactant is dependent upon T2 cells and macrophages. ABCG1 is highly expressed in both T2 cells and macrophages. ABCG1-deficient mice accumulate surfactant, lamellar body-loaded T2 cells, lipid-loaded macrophages, B-1 lymphocytes, and immunoglobulins, clearly demonstrating that ABCG1 has a critical role in pulmonary homeostasis. We identify a variant in the ABCG1 promoter in patients with PAP that results in impaired activation of ABCG1 by the liver X receptor α, suggesting that ABCG1 basal expression and/or induction in response to sterol/lipid loading is essential for normal lung function. We generated mice lacking ABCG1 specifically in either T2 cells or macrophages to determine the relative contribution of these cell types on surfactant lipid homeostasis. These results establish a critical role for T2 cell ABCG1 in controlling surfactant and overall lipid homeostasis in the lung and in the pathogenesis of human lung disease.

Intracellular Localization of Endogenous Mouse ABCG1 Is Mimicked by Both ABCG1-L550 and ABCG1-P550-Brief Report.

OBJECTIVE: In a recent article in Arteriosclerosis, Thrombosis, and Vascular Biology, it was reported that ATP-binding cassette transporter G1 (ABCG1) containing leucine at position 550 (ABCG1-L550) was localized to the plasma membrane, whereas ABCG1-P550 (proline at position 550) was intracellular. Because the published data on the subcellular localization of ABCG1 are controversial, we performed additional experiments to determine the importance of leucine or proline at amino acid 550. APPROACH AND RESULTS: We transfected multiple cell lines (CHO-K1, Cos-7, and HEK293 [human embryonic kidney]) with untagged or FLAG-tagged ABCG1 containing either leucine or proline at position 550. Immunofluorescence studies demonstrated that in all cases, ABCG1 localized to intracellular endosomal vesicles. We also show that both ABCG1-L550 and ABCG1-P550 are equally active in both promoting the efflux of cellular cholesterol to exogenous high-density lipoprotein and in inducing the activity of sterol regulatory element-binding protein-2, presumably as a result of redistributing intracellular sterols away from the endoplasmic reticulum. Importantly, we treated nontransfected primary peritoneal macrophages with a liver X receptor agonist and demonstrate, using immunofluorescence, that although endogenous ABCG1 localizes to intracellular endosomes, none was detectable at the cell surface/plasma membrane. CONCLUSIONS: ABCG1, irrespective of either a leucine or proline at position 550, is an intracellular protein that localizes to vesicles of the endosomal pathway where it functions to mobilize sterols away from the endoplasmic reticulum and out of the cell.

The nuclear receptor FXR uncouples the actions of miR-33 from SREBP-2.

OBJECTIVE: To determine whether activation of farnesoid X receptor (FXR) alters cellular and plasma cholesterol homeostasis as a result of regulation of Srebp-2 and miR-33. APPROACH AND RESULTS: Chromatin immunoprecipitation sequencing data identified an FXR response element within intron 10 of the Srebp-2 gene. Consistent with this observation, treatment of mice with FXR-specific agonists (GSK2324 or GW4064) rapidly increased hepatic levels of Srebp-2 mRNA, precursor sterol response element binding protein 2 (pSREBP-2) protein, and miR-33. Furthermore, miR-33 targets, that include ABCA1 (ATP binding cassette transporter A1), NSF (N-ethylmaleimide-sensitive factor), and CPT1 (carnitine palmitoyltransferase 1), were all reduced in GSK2324-treated mice. In contrast, neither nuclear SREBP-2 protein (nSREBP-2) nor SREBP-2 target genes were induced after FXR activation. The inability to process pSREBP-2 to nSREBP-2 is likely a consequence of the induction of insulin INSIG-2A (induced gene 2A) by FXR agonists. Finally, we show that FXR-dependent induction of both Srebp-2 and miR-33 is ablated in Scap(-/-) mice that lack nuclear SREBP-2. CONCLUSIONS: We demonstrate that the activation of FXR uncouples the expression of nuclear SREBP-2 and miR-33, and the regulation of their respective target genes. Further, we conclude that the FXR agonist-dependent increase in miR-33 requires transcription of the Srebp-2 gene.

ABCG1 is required for pulmonary B-1 B cell and natural antibody homeostasis.

Many metabolic diseases, including atherosclerosis, type 2 diabetes, pulmonary alveolar proteinosis, and obesity, have a chronic inflammatory component involving both innate and adaptive immunity. Mice lacking the ATP-binding cassette transporter G1 (ABCG1) develop chronic inflammation in the lungs, which is associated with the lipid accumulation (cholesterol, cholesterol ester, and phospholipid) and cholesterol crystal deposition that are characteristic of atherosclerotic lesions and pulmonary alveolar proteinosis. In this article, we demonstrate that specific lipids, likely oxidized phospholipids and/or sterols, elicit a lung-specific immune response in Abcg1(-/-) mice. Loss of ABCG1 results in increased levels of specific oxysterols, phosphatidylcholines, and oxidized phospholipids, including 1-palmitoyl-2-(5'-oxovaleroyl)-sn-glycero-3-phosphocholine, in the lungs. Further, we identify a niche-specific increase in natural Ab (NAb)-secreting B-1 B cells in response to this lipid accumulation that is paralleled by increased titers of IgM, IgA, and IgG against oxidation-specific epitopes, such as those on oxidized low-density lipoprotein and malondialdehyde-modified low-density lipoprotein. Finally, we identify a cytokine/chemokine signature that is reflective of increased B cell activation, Ab secretion, and homing. Collectively, these data demonstrate that the accumulation of lipids in Abcg1(-/-) mice induces the specific expansion and localization of B-1 B cells, which secrete NAbs that may help to protect against the development of atherosclerosis. Indeed, despite chronic lipid accumulation and inflammation, hyperlipidemic mice lacking ABCG1 develop smaller atherosclerotic lesions compared with controls. These data also suggest that Abcg1(-/-) mice may represent a new model in which to study the protective functions of B-1 B cells/NAbs and suggest novel targets for pharmacologic intervention and treatment of disease.

ABCG1 regulates mouse adipose tissue macrophage cholesterol levels and ratio of M1 to M2 cells in obesity and caloric restriction.

In addition to triacylglycerols, adipocytes contain a large reserve of unesterified cholesterol. During adipocyte lipolysis and cell death seen during severe obesity and weight loss, free fatty acids and cholesterol become available for uptake and processing by adipose tissue macrophages (ATMs). We hypothesize that ATMs become cholesterol enriched and participate in cholesterol clearance from adipose tissue. We previously showed that ABCG1 is robustly upregulated in ATMs taken from obese mice and further enhanced by caloric restriction. Here, we found that ATMs taken from obese and calorie-restricted mice derived from transplantation of WT or Abcg1-deficient bone marrow are cholesterol enriched. ABCG1 levels regulate the ratio of classically activated (M1) to alternatively activated (M2) ATMs and their cellular cholesterol content. Using WT and Abcg1(-/-) cultured macrophages, we found that Abcg1 is most highly expressed by M2 macrophages and that ABCG1 deficiency is sufficient to retard macrophage chemotaxis. However, changes in myeloid expression of Abcg1 did not protect mice from obesity or impaired glucose homeostasis. Overall, ABCG1 modulates ATM cholesterol content in obesity and weight loss regimes leading to an alteration in M1 to M2 ratio that we suggest is due to the extent of macrophage egress from adipose tissue.

MicroRNA-144 regulates hepatic ATP binding cassette transporter A1 and plasma high-density lipoprotein after activation of the nuclear receptor farnesoid X receptor.

RATIONALE: The bile acid receptor farnesoid X receptor (FXR) regulates many aspects of lipid metabolism by variouscomplex and incompletely understood molecular mechanisms. We set out to investigate the molecular mechanisms for FXR-dependent regulation of lipid and lipoprotein metabolism. OBJECTIVE: To identify FXR-regulated microRNAs that were subsequently involved in regulating lipid metabolism. METHODS AND RESULTS: ATP binding cassette transporter A1 (ABCA1) is a major determinant of plasma high-density lipoprotein (HDL)-cholesterol levels. Here, we show that activation of the nuclear receptor FXR in vivo increases hepatic levels of miR-144, which in turn lowers hepatic ABCA1 and plasma HDL levels. We identified 2 complementary sequences to miR-144 in the 3' untranslated region of ABCA1 mRNA that are necessary for miR-144-dependent regulation. Overexpression of miR-144 in vitro decreased both cellular ABCA1 protein and cholesterol efflux to lipid-poor apolipoprotein A-I protein, whereas overexpression in vivo reduced hepatic ABCA1 protein and plasma HDL-cholesterol. Conversely, silencing miR-144 in mice increased hepatic ABCA1 protein and HDL-cholesterol. In addition, we used tissue-specific FXR-deficient mice to show that induction of miR-144 and FXR-dependent hypolipidemia requires hepatic, but not intestinal, FXR. Finally, we identified functional FXR response elements upstream of the miR-144 locus, consistent with direct FXR regulation. CONCLUSIONS: We have identified a novel pathway involving FXR, miR-144, and ABCA1 that together regulate plasma HDL-cholesterol.

ABCC6 localizes to the mitochondria-associated membrane.

RATIONALE: Mutations of the orphan transporter ABCC6 (ATP-binding cassette, subfamily C, member 6) cause the connective tissue disorder pseudoxanthoma elasticum. ABCC6 was thought to be located on the plasma membrane of liver and kidney cells. OBJECTIVE: Mouse systems genetics and bioinformatics suggested that ABCC6 deficiency affects mitochondrial gene expression. We therefore tested whether ABCC6 associates with mitochondria. METHODS AND RESULTS: We found ABCC6 in crude mitochondrial fractions and subsequently pinpointed its localization to the purified mitochondria-associated membrane fraction. Cell-surface biotinylation in hepatocytes confirmed that ABCC6 is intracellular. Abcc6-knockout mice demonstrated mitochondrial abnormalities and decreased respiration reserve capacity. CONCLUSIONS: Our finding that ABCC6 localizes to the mitochondria-associated membrane has implications for its mechanism of action in normal and diseased states.

ATP binding cassette transporter G1 (ABCG1) is an intracellular sterol transporter.

Four members of the mammalian ATP binding cassette (ABC) transporter G subfamily are thought to be involved in transmembrane (TM) transport of sterols. The residues responsible for this transport are unknown. The mechanism of action of ABCG1 is controversial and it has been proposed to act at the plasma membrane to facilitate the efflux of cellular sterols to exogenous high-density lipoprotein (HDL). Here we show that ABCG1 function is dependent on localization to intracellular endosomes. Importantly, localization to the endosome pathway distinguishes ABCG1 and/or ABCG4 from all other mammalian members of this superfamily, including other sterol transporters. We have identified critical residues within the TM domains of ABCG1 that are both essential for sterol transport and conserved in some other members of the ABCG subfamily and/or the insulin-induced gene 2 (INSIG-2). Our conclusions are based on studies in which (i) biotinylation of peritoneal macrophages showed that endogenous ABCG1 is intracellular and undetectable at the cell surface, (ii) a chimeric protein containing the TM of ABCG1 and the cytoplasmic domains of the nonsterol transporter ABCG2 is both targeted to endosomes and functional, and (iii) ABCG1 colocalizes with multiple proteins that mark late endosomes and recycling endosomes. Mutagenesis studies identify critical residues in the TM domains that are important for ABCG1 to alter sterol efflux, induce sterol regulatory element binding protein-2 (SREBP-2) processing, and selectively attenuate the oxysterol-mediated repression of SREBP-2 processing. Our data demonstrate that ABCG1 is an intracellular sterol transporter that localizes to endocytic vesicles to facilitate the redistribution of specific intracellular sterols away from the endoplasmic reticulum (ER).

Expanding roles of ABCG1 and sterol transport.

PURPOSE OF REVIEW: To offer a comprehensive review on the role of ABCG1 in cellular sterol homeostasis. RECENT FINDINGS: Early studies with Abcg1 mice indicated that ABCG1 was crucial for tissue lipid homeostasis, especially in the lung. More recent studies have demonstrated that loss of ABCG1 has wide-ranging consequences and impacts lymphocyte and stem cell proliferation, endothelial cell function, macrophage foam cell formation, as well as insulin secretion from pancreatic ß cells. Recent studies have also demonstrated that ABCG1 functions as an intracellular lipid transporter, localizes to intracellular vesicles/endosomes, and that the transmembrane domains are sufficient for localization and transport function. SUMMARY: ABCG1 plays a crucial role in maintaining intracellular sterol and lipid homeostasis. Loss of this transporter has significant, cell-type-specific consequences ranging from effects on cellular proliferation, to surfactant production and/or insulin secretion. Elucidation of the mechanisms by which ABCG1 affects intracellular sterol flux/movement should provide important information that may link ABCG1 to diseases of dysregulated tissue lipid homeostasis.

Mechanosensitive membrane domains regulate calcium entry in arterial endothelial cells to protect against inflammation.

Endothelial cells (ECs) in the descending aorta are exposed to high laminar shear stress, and this supports an antiinflammatory phenotype. High laminar shear stress also induces flow-aligned cell elongation and front-rear polarity, but whether these are required for the antiinflammatory phenotype is unclear. Here, we showed that caveolin-1-rich microdomains polarize to the downstream end of ECs that are exposed to continuous high laminar flow. These microdomains were characterized by high membrane rigidity, filamentous actin (F-actin), and raft-associated lipids. Transient receptor potential vanilloid (TRPV4) ion channels were ubiquitously expressed on the plasma membrane but mediated localized Ca2+ entry only at these microdomains where they physically interacted with clustered caveolin-1. These focal Ca2+ bursts activated endothelial nitric oxide synthase within the confines of these domains. Importantly, we found that signaling at these domains required both cell body elongation and sustained flow. Finally, TRPV4 signaling at these domains was necessary and sufficient to suppress inflammatory gene expression and exogenous activation of TRPV4 channels ameliorated the inflammatory response to stimuli both in vitro and in vivo. Our work revealed a polarized mechanosensitive signaling hub in arterial ECs that dampened inflammatory gene expression and promoted cell resilience.

Dancing with the sterols: critical roles for ABCG1, ABCA1, miRNAs, and nuclear and cell surface receptors in controlling cellular sterol homeostasis.

ATP binding cassette (ABC) transporters represent a large and diverse family of proteins that transport specific substrates across a membrane. The importance of these transporters is illustrated by the finding that inactivating mutations within 17 different family members are known to lead to specific human diseases. Clinical data from humans and/or studies with mice lacking functional transporters indicate that ABCA1, ABCG1, ABCG4, ABCG5 and ABCG8 are involved in cholesterol and/or phospholipid transport. This review discusses the multiple mechanisms that control cellular sterol homeostasis, including the roles of microRNAs, nuclear and cell surface receptors and ABC transporters, with particular emphasis on recent findings that have provided insights into the role(s) of ABCG1. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).