Faculty Bibliography
Searched for:
person:fishee01
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469
Opposing roles of cell death-inducing DFF45-like effector B and perilipin 2 in controlling hepatic VLDL lipidation
Regulation of hepatic very low density lipoprotein (VLDL) assembly and maturation is crucial in controlling lipid homeostasis and in the development of metabolic disorders, including obesity, hepatic steatosis, and insulin resistance. Cideb, a member of cell death-inducing DFF45-like effector (CIDE) protein family, has been previously shown to promote VLDL lipidation and maturation. However, the precise subcellular location of Cideb-mediated VLDL lipidation and the factors modulating its activity remain elusive. In addition to its localization to endoplasmic reticulum (ER) and lipid droplets (LD), we observed that Cideb was also localized to the Golgi apparatus. Mature and lipid-rich VLDL particles did not accumulate in the Golgi apparatus in Cideb(-/-) livers. Interestingly, we observed that hepatic perilipin 2/adipose differentiation-related protein (ADRP) levels were markedly increased in Cideb(-/-) mice. Liver-specific knockdown of perilipin 2 in Cideb(-/-) mice resulted in the reduced accumulation of hepatic triglycerides (TAG), increased VLDL-TAG secretion, and the accumulation of mature TAG-rich VLDL in the Golgi apparatus. These data reveal that Cideb and perilipin 2 play opposing roles in controlling VLDL lipidation and hepatic lipid homeostasis.
PMCID:3413228
PMID: 22661308
ISSN: 0022-2275
CID: 178175
Rationale for cholesteryl ester transfer protein inhibition
PURPOSE OF REVIEW: Raising HDL cholesterol (HDL-C) has become an attractive therapeutic target to lower cardiovascular risk in addition to statins. Inhibition of the cholesteryl ester transfer protein (CETP), which mediates the transfer of cholesteryl esters from HDL to apolipoprotein B-containing particles, leads to a substantial increase in HDL-C levels. Various CETP inhibitors are currently being evaluated in phase II and phase III clinical trials. However, the beneficial effect of CETP inhibition on cardiovascular outcome remains to be established. RECENT FINDINGS: Torcetrapib, the first CETP inhibitor tested in a phase III clinical trial (ILLUMINATE), failed in 2006 because of an increase in all-cause mortality and cardiovascular events that subsequently were attributed to nonclass-related off-target effects (particularly increased blood pressure and low serum potassium) related to the stimulation of aldosterone production. Anacetrapib, another potent CETP inhibitor, raises HDL-C levels by approximately 138% and decreases LDL cholesterol (LDL-C) levels by approximately 40%, without the adverse off-targets effects of torcetrapib (DEFINE study). The CETP modulator dalcetrapib raises HDL-C levels by approximately 30% (with only minimal effect on LDL-C levels) and proved safety in the dal-VESSEL and dal-PLAQUE trials involving a total of nearly 600 patients. Evacetrapib, a relatively new CETP inhibitor, exhibited favorable changes in the lipid profile in a phase II study. SUMMARY: The two ongoing outcome trials, dal-OUTCOMES (dalcetrapib) and REVEAL (anacetrapib), will provide more conclusive answers for the concept of reducing cardiovascular risk by raising HDL-C with CETP inhibition.
PMCID:3924318
PMID: 22517614
ISSN: 0957-9672
CID: 173016
Hepatic sortilin regulates both apolipoprotein B secretion and LDL catabolism
Genome-wide association studies (GWAS) have identified a genetic variant at a locus on chromosome 1p13 that is associated with reduced risk of myocardial infarction, reduced plasma levels of LDL cholesterol (LDL-C), and markedly increased expression of the gene sortilin-1 (SORT1) in liver. Sortilin is a lysosomal sorting protein that binds ligands both in the Golgi apparatus and at the plasma membrane and traffics them to the lysosome. We previously reported that increased hepatic sortilin expression in mice reduced plasma LDL-C levels. Here we show that increased hepatic sortilin not only reduced hepatic apolipoprotein B (APOB) secretion, but also increased LDL catabolism, and that both effects were dependent on intact lysosomal targeting. Loss-of-function studies demonstrated that sortilin serves as a bona fide receptor for LDL in vivo in mice. Our data are consistent with a model in which increased hepatic sortilin binds intracellular APOB-containing particles in the Golgi apparatus as well as extracellular LDL at the plasma membrane and traffics them to the lysosome for degradation. We thus provide functional evidence that genetically increased hepatic sortilin expression both reduces hepatic APOB secretion and increases LDL catabolism, providing dual mechanisms for the very strong association between increased hepatic sortilin expression and reduced plasma LDL-C levels in humans.
PMCID:3408750
PMID: 22751103
ISSN: 0021-9738
CID: 174572
Regression of Inflammation in Atherosclerosis by the LXR Agonist R211945: A Noninvasive Assessment and Comparison With Atorvastatin
OBJECTIVES: The aim of this study was to noninvasively detect the anti-inflammatory properties of the novel liver X receptor agonist R211945. BACKGROUND: R211945 induces reversal cholesterol transport and modulates inflammation in atherosclerotic plaques. We aimed to characterize with (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) and dynamic contrast-enhanced cardiac magnetic resonance (DCE-CMR) inflammation and neovascularization, respectively, in atherosclerotic plaques with R211945 treatment compared with atorvastatin treatment and a control. METHODS: Twenty-one atherosclerotic New Zealand white rabbits were divided into 3 groups (control, R211945 [3 mg/kg orally], and atorvastatin [3 mg/kg orally] groups). All groups underwent (18)F-FDG-PET/CT and DCE-CMR at baseline and at 1 and 3 months after treatment initiation. Concomitantly, serum metabolic parameters and histology were assessed. For statistical analysis, continuous DCE-CMR and PET/CT outcomes were modeled as linear functions of time by using a linear mixed model, whereas the histological data, animal characteristics data, and nonlinear regression imaging data were analyzed with a 2-tailed Student t test. RESULTS: (18)F-FDG-PET/CT detected a decrease in mean and maximum standard uptake values (SUV) over time in the R211945 group (both p = 0.001), indicating inflammation regression. The atorvastatin group displayed no significant change (p = 0.371 and p = 0.600, respectively), indicating no progression or regression. The control group demonstrated an increase in SUV (p = 0.01 and p = 0.04, respectively), indicating progression. There was a significant interaction between time and group for mean and maximum SUV (p = 0.0003 and p = 0.0016, respectively) . DCE-CMR detected a trend toward difference (p = 0.06) in the area under the curve in the atorvastatin group, suggesting a decrease in neovascularization. There was no significant interaction between time and group (p = 0.6350 and p = 0.8011, respectively). Macrophage and apolipoprotein B immunoreactivity decreased in the R211945 and atorvastatin groups (p < 0.0001 and p = 0.0004, respectively), and R211945 decreased oxidized phospholipid immunoreactivity (p = 0.02). CONCLUSIONS: Noninvasive imaging with (18)F-FDG-PET/CT and DCE-CMR and histological analysis demonstrated significant anti-inflammatory effects of the LXR agonist R211945 compared with atorvastatin. The results suggest a possible role for LXR agonists in the treatment of atherosclerosis.
PMCID:3600612
PMID: 22897996
ISSN: 1876-7591
CID: 177096
The double-edged sword of fibronectin in atherosclerosis
PMCID:3407944
PMID: 22649036
ISSN: 1757-4676
CID: 171126
Summing up
PMID: 22592118
ISSN: 1079-5642
CID: 166833
The degradation of apolipoprotein B100: Multiple opportunities to regulate VLDL triglyceride production by different proteolytic pathways
Very low density lipoproteins (VLDL) are a major secretory product of the liver. They serve to transport endogenously synthesized lipids, mainly triglycerides (but also some cholesterol and cholesteryl esters) to peripheral tissues. VLDL is also the precursor of LDL. ApoB100 is absolutely required for VLDL assembly and secretion. The amount of VLDL triglycerides secreted by the liver depends on the amount loaded onto each lipoprotein particle, as well as the number of particles. Each VLDL has one apoB100 molecule, making apoB100 availability a key determinant of the number of VLDL particles, and hence, triglycerides, that can be secreted by hepatic cells. Surprisingly, the pool of apoB100 in the liver is typically regulated not by its level of synthesis, which is relatively constant, but by its level of degradation. It is now recognized that there are multiple opportunities for the hepatic cell to intercept apoB100 molecules and to direct them to distinct degradative processes. This mini-review will summarize progress in understanding these processes, with an emphasis on autophagy, the most recently described pathway of apoB100 degradation, and the one with possibly the most physiologic relevance to common metabolic perturbations affecting VLDL production. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.
PMCID:3593638
PMID: 22342675
ISSN: 0006-3002
CID: 166878
Guidelines for the use and interpretation of assays for monitoring autophagy [Guideline]
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
PMCID:3404883
PMID: 22966490
ISSN: 1554-8627
CID: 181862
Apoprotein B: quality control early and late in the secretory pathway for this atherogenic protein [Meeting Abstract]
Apoprotein B (apoB100) is required for the formation of VLDL, the precursor of LDL, the plasma level of which is a strong risk factor for atherosclerosis and coronary artery disease (CAD). It is an exceptionally large (>4000 aa) and hydrophobic protein. As the nascent polypeptide is translocating across the ER, if lipids are not transferred to stabilize its conformation, we and others have shown that like other abnormally folded proteins in the ER, its quality control is governed by ER-associated ub-proteasome degradation (ERAD). Using a combination of systems from yeast to genetically modified mice, we and our collaborators have shown apoB100 ERAD to involve chaperone and chaperone-like molecules, such as Hsp70, 90, 110, and p58. The full assembly of VLDL does not occur until the Golgi. We have discovered that nascent particles ("pre-VLDL") that do not complete this maturation process (e.g., under the influence of certain dietary fatty acids), are subject to a late stage quality control process mediated by autophagy. In summary, the production of apoB100-lipoproteins, whose plasma levels correlate with the risk of CAD, is determined in part by quality control processes that recognize features of the protein specific to its stage of assembly and that are separated between the ER and Golgi compartments
EMBASE:70852949
ISSN: 0892-6638
CID: 178107
Preclinical mouse models and methods for the discovery of the causes and treatments of atherosclerosis
Introduction: Atherosclerosis is the leading cause of death in the Western world. Despite huge advances in understanding its pathophysiological mechanisms, current treatment is mostly based on 'traditional' risk factors. The introduction of statins more than 20 years ago reduced morbidity and mortality of atherosclerosis by 30%, leaving a residual cardiovascular risk. Therefore, efforts continue toward the development of novel therapies that can be added to established treatments. Besides targeting dyslipidemia, recent focus has been put on preventing or resolving inflammatory processes involved in atherosclerosis. Areas covered: The article discusses therapeutic and diagnostic targets in atherosclerosis and how they can be discovered and studied in preclinical animal models. The roles of immune cells, specifically macrophages and monocytes, in plaque inflammation are discussed. The article also describes current preclinical models of atherosclerosis, specifically the mouse, study designs (for progression and regression studies), basic and advanced methods of analysis of atherosclerotic lesions, and discusses the challenges of translating the findings to humans. Expert opinion: Advances in genomics, proteomics, lipidomics and the development of high-throughput screening techniques help to improve our understanding of atherosclerosis disease mechanisms immensely and facilitate the discovery of new diagnostic and therapeutic targets. Preclinical studies in animals are still indispensable to uncover pathways involved in atherosclerotic disease and to evaluate novel drug targets. The translation of these targets, however, from animal studies to humans remains challenging. There is a strong need for novel biomarkers that can be used to prove the concept of a new target in humans.
PMCID:3612348
PMID: 22468952
ISSN: 1746-0441
CID: 163580
