Jaspreet Sandhu

Feedback modulation of cholesterol metabolism by the lipid-responsive non-coding RNA LeXis

The liver X receptors (LXRs) are transcriptional regulators of cellular and systemic cholesterol homeostasis. In the setting of cholesterol excess, LXR activation induces the expression of a battery of genes involved in cholesterol efflux 1, facilities cholesterol esterification by promoting fatty acid synthesis 2, and inhibits cholesterol uptake by the low-density lipoprotein receptor (LDLR)3. The fact that sterol content is maintained in a narrow range in most cell types and in the organism as a whole suggests that extensive crosstalk between regulatory pathways must exist. However, the molecular mechanisms that integrate LXRs with other lipid metabolic pathways, are incompletely understood. Here we show that ligand activation of LXRs in liver not only promotes cholesterol efflux, but also simultaneously inhibits cholesterol biosynthesis. We further identify the long non-coding RNA LeXis as one mediator of this effect. Hepatic LeXis expression is robustly induced in response to western diet feeding or pharmacologic LXR activation. Raising or lowering the levels of LeXis in liver affects the expression of cholesterol biosynthetic genes, and the levels of cholesterol in the liver and plasma. LeXis interacts with and affects the DNA interactions of Raly, a heterogeneous ribonucleoprotein that is required for the maximal expression of cholesterologenic genes in mouse liver. These studies outline a regulatory role for a non-coding RNA in lipid metabolism and advance our understanding of the mechanisms orchestrating sterol homeostasis.

Transcriptional regulation of macrophage cholesterol efflux and atherogenesis by a long noncoding RNA

Nuclear receptors regulate gene expression in response to environmental cues, but the molecular events governing the cell type specificity of nuclear receptors remain poorly understood. Here we outline a role for a long noncoding RNA (lncRNA) in modulating the cell type–specific actions of liver X receptors (LXRs), sterol-activated nuclear receptors that regulate the expression of genes involved in cholesterol homeostasis and that have been causally linked to the pathogenesis of atherosclerosis. We identify the lncRNA MeXis as an amplifier of LXR-dependent transcription of the gene Abca1, which is critical for regulation of cholesterol efflux. Mice lacking the MeXis gene show reduced Abca1 expression in a tissue-selective manner. Furthermore, loss of MeXis in mouse bone marrow cells alters chromosome architecture at the Abca1 locus, impairs cellular responses to cholesterol overload, and accelerates the development of atherosclerosis. Mechanistic studies reveal that MeXis interacts with and guides promoter binding of the transcriptional coactivator DDX17. The identification of MeXis as a lncRNA modulator of LXR-dependent gene expression expands understanding of the mechanisms underlying cell type–selective actions of nuclear receptors in physiology and disease.

Long Noncoding RNA Discovery in Cardiovascular Disease: Decoding Form to Function

Despite significant improvements during the past 3 decades, cardiovascular disease remains a leading worldwide health epidemic. The recent identification of a fascinating group of mediators known as long noncoding RNAs (lncRNAs) has provided a wealth of new biology to explore for cardiovascular risk mitigation. lncRNAs are expressed in a highly context-specific fashion, and multiple lines of evidence implicated them in diverse biological processes. Indeed, abnormalities of lncRNAs have been directly linked with human ailments, including cardiovascular biology and disease. Of particular interest to the cardiovascular research community, dysregulation in lncRNA regulatory circuits have been associated with cardiac pathological hypertrophy, vascular disease, cell fate programming and development, atherosclerosis, dyslipidemia, and metabolic syndrome. Although techniques in interrogating noncoding RNAs are rapidly evolving, a major challenge in studying lncRNAs remains navigating through multiple technical constraints. In this review, we provide a road map for lncRNA discovery and interrogation in biological systems relevant to cardiovascular disease and highlight approaches to decipher their modes of action.

IL-10 Signaling Remodels Adipose Chromatin Architecture to Limit Thermogenesis and Energy Expenditure

Signaling pathways that promote adipose tissue thermogenesis are well characterized, but the limiters of energy expenditure are largely unknown. Here, we show that ablation of the anti-inflammatory cytokine IL-10 improves insulin sensitivity, protects against diet-induced obesity, and elicits the browning of white adipose tissue. Mechanistic studies define bone marrow cells as the source of the IL-10 signal and adipocytes as the target cell type mediating these effects. IL-10 receptor alpha is highly enriched in mature adipocytes and is induced in response to differentiation, obesity, and aging. Assay for transposase-accessible chromatin sequencing (ATAC-seq), ChIP-seq, and RNA-seq reveal that IL-10 represses the transcription of thermogenic genes in adipocytes by altering chromatin accessibility and inhibiting ATF and C/EBPβ recruitment to key enhancer regions. These findings expand our understanding of the relationship between inflammatory signaling pathways and adipose tissue function and provide insight into the physiological control of thermogenesis that could inform future therapy.

Inhibition of cholesterol biosynthesis through RNF145-dependent ubiquitination of SCAP

Cholesterol homeostasis is maintained through concerted action of the SREBPs and LXRs. Here, we report that RNF145, a previously uncharacterized ER membrane ubiquitin ligase, participates in crosstalk between these critical signaling pathways. RNF145 expression is induced in response to LXR activation and high-cholesterol diet feeding. Transduction of RNF145 into mouse liver inhibits the expression of genes involved in cholesterol biosynthesis and reduces plasma cholesterol levels. Conversely, acute suppression of RNF145 via shRNA-mediated knockdown, or chronic inactivation of RNF145 by genetic deletion, potentiates the expression of cholesterol biosynthetic genes and increases cholesterol levels both in liver and plasma. Mechanistic studies show that RNF145 triggers ubiquitination of SCAP on lysine residues within a cytoplasmic loop essential for COPII binding, potentially inhibiting its transport to Golgi and subsequent processing of SREBP-2. These findings define an additional mechanism linking hepatic sterol levels to the reciprocal actions of the SREBP-2 and LXR pathways.

Critical Roles of the Histone Methyltransferase MLL4/KMT2D in Murine Hepatic Steatosis Directed by ABL1 and PPARγ2

The pathophysiologic continuum of non-alcoholic fatty liver disease begins with steatosis. Despite recent advances in our understanding of the gene regulatory program directing steatosis, how it is orchestrated at the chromatin level is unclear. PPARγ2 is a hepatic steatotic transcription factor induced by overnutrition. Here, we report that the histone H3 lysine 4 methyltransferase MLL4/KMT2D directs overnutrition-induced murine steatosis via its coactivator function for PPARγ2. We demonstrate that overnutrition facilitates the recruitment of MLL4 to steatotic target genes of PPARγ2 and their transactivation via H3 lysine 4 methylation because PPARγ2 phosphorylated by overnutrition-activated ABL1 kinase shows enhanced interaction with MLL4. We further show that Pparg2 (encoding PPARγ2) is also a hepatic target gene of ABL1-PPARγ2-MLL4. Consistently, inhibition of ABL1 improves the fatty liver condition of mice with overnutrition by suppressing the pro-steatotic action of MLL4. Our results uncover a murine hepatic steatosis regulatory axis consisting of ABL1-PPARγ2-MLL4, which may serve as a target of anti-steatosis drug development.

CMF22 Is a Broadly Conserved Axonemal Protein and Is Required for Propulsive Motility in Trypanosoma brucei

ABSTRACT The eukaryotic flagellum (or cilium) is a broadly conserved organelle that provides motility for many pathogenic protozoa and is critical for normal development and physiology in humans. Therefore, defining core components of motile axonemes enhances understanding of eukaryotic biology and provides insight into mechanisms of inherited and infectious diseases in humans. In this study, we show that component of motile flagella 22 (CMF22) is tightly associated with the flagellar axoneme and is likely to have been present in the last eukaryotic common ancestor. The CMF22 amino acid sequence contains predicted IQ and ATPase associated with a variety of cellular activities (AAA) motifs that are conserved among CMF22 orthologues in diverse organisms, hinting at the importance of these domains in CMF22 function. Knockdown by RNA interference (RNAi) and rescue with an RNAi-immune mRNA demonstrated that CMF22 is required for propulsive cell motility in Trypanosoma brucei. Loss of propulsive motility in CMF22-knockdown cells was due to altered flagellar beating patterns, rather than flagellar paralysis, indicating that CMF22 is essential for motility regulation and likely functions as a fundamental regulatory component of motile axonemes. CMF22 association with the axoneme is weakened in mutants that disrupt the nexin-dynein regulatory complex, suggesting potential interaction with this complex. Our results provide insight into the core machinery required for motility of eukaryotic flagella.

Macrophages release plasma membrane-derived particles rich in accessible cholesterol

Significance Earlier studies suggested that particles are released from the macrophage plasma membrane, but the mechanism has been unclear. We found that filopodia of macrophages release large numbers of vesicular particles. Nanoscale secondary ion mass spectrometry revealed that these particles are enriched in cholesterol, including the “accessible” pool of cholesterol detectable by the cholesterol-binding protein. The cholesterol content of macrophage particles increased when the cells were loaded with cholesterol and could be depleted by incubating the cells with high-density lipoproteins. Our studies suggest that the release of particles by macrophages could be one mechanism for cholesterol efflux and that particles could be an intermediate in the movement of cholesterol to high-density lipoproteins. Macrophages are generally assumed to unload surplus cholesterol through direct interactions between ABC transporters on the plasma membrane and HDLs, but they have also been reported to release cholesterol-containing particles. How macrophage-derived particles are formed and released has not been clear. To understand the genesis of macrophage-derived particles, we imaged mouse macrophages by EM and nanoscale secondary ion mass spectrometry (nanoSIMS). By scanning EM, we found that large numbers of 20- to 120-nm particles are released from the fingerlike projections (filopodia) of macrophages. These particles attach to the substrate, forming a “lawn” of particles surrounding macrophages. By nanoSIMS imaging we showed that these particles are enriched in the mobile and metabolically active accessible pool of cholesterol (detectable by ALO-D4, a modified version of a cholesterol-binding cytolysin). The cholesterol content of macrophage-derived particles was increased by loading the cells with cholesterol or by adding LXR and RXR agonists to the cell-culture medium. Incubating macrophages with HDL reduced the cholesterol content of macrophage-derived particles. We propose that release of accessible cholesterol-rich particles from the macrophage plasma membrane could assist in disposing of surplus cholesterol and increase the efficiency of cholesterol movement to HDL.

Aster Proteins Facilitate Nonvesicular Plasma Membrane to ER Cholesterol Transport in Mammalian Cells.

The mechanisms underlying sterol transport in mammalian cells are poorly understood. In particular, how cholesterol internalized from HDL is made available to the cell for storage or modification is unknown. Here, we describe three ER-resident proteins (Aster-A, -B, -C) that bind cholesterol and facilitate its removal from the plasma membrane. The crystal structure of the central domain of Aster-A broadly resembles the sterol-binding fold of mammalian StARD proteins, but sequence differences in the Aster pocket result in a distinct mode of ligand binding. The Aster N-terminal GRAM domain binds phosphatidylserine and mediates Aster recruitment to plasma membrane-ER contact sites in response to cholesterol accumulation in the plasma membrane. Mice lacking Aster-Bxa0are deficient in adrenal cholesterol ester storage and steroidogenesis because of an inability to transport cholesterol from SR-BI to the ER. These findings identify a nonvesicular pathway for plasma membrane to ER sterol trafficking in mammals.

PD39-06 DE NOVO URINARY STORAGE SYMPTOMS ARE COMMON AFTER RADICAL PROSTATECTOMY: INCIDENCE, NATURAL HISTORY AND PREDICTORS

demographics, bladder diaries, subjective response rates, ICIQ-OAB and PGI-I scores were recorded. Success was defined as greater than 50% symptom improvement in urgency, urge incontinence, and a greater than 50% improvement in voided volume or reduction of postvoid residual volumes. RESULTS: Twenty patients underwent stage 1 trial of SNM. Average age was 68.5 years, IQR (54.25 -76.25). 13 (65%) patients were female. 13/20 (65%) of patients had a response to the detrusor overactivity component. 10/20 (50%) of patients showed an improvement in the voiding component. 9/20 (45%) of patients showed responses to both components. 6/20 (30%) patients had no response whatsoever. Overall, 12/20 (60%) patients proceeded to insertion of an IPG. At follow up of 17 months, IQR (1.5 e 35), 11/12 (91.7%) of patients were still using the SNM device, median PGI score was 2, IQR (2 e 4). In addition, SNM resulted in statistically significant improvement in voided volume (p1⁄40.016), PVR (p1⁄40.0296), ICIQ-OAB score (p<0.0001) and ICIQ-OAB bother score (p1⁄40.016). CONCLUSIONS: SNM is a potential treatment option for DHIC with an acceptable success rate, treating both the detrusor hyperactivity, and impaired contractility components of this condition.