Publications by authors named "Nancy R Webb"

62 Publications

High-Density Lipoproteins and Serum Amyloid A (SAA).

Authors:
Nancy R Webb

Curr Atheroscler Rep 2021 Jan 15;23(2). Epub 2021 Jan 15.

Department of Pharmacology and Nutritional Sciences, Saha Cardiovascular Research Center, and Barnstable Brown Diabetes Center, University of Kentucky, 553 Wethington Building, 900 South Limestone, Lexington, KY, 40536-0200, USA.

Purpose Of Review: Serum amyloid A (SAA) is a highly sensitive acute phase reactant that has been linked to a number of chronic inflammatory diseases. During a systemic inflammatory response, liver-derived SAA is primarily found on high-density lipoprotein (HDL). The purpose of this review is to discuss recent literature addressing the pathophysiological functions of SAA and the significance of its association with HDL.

Recent Findings: Studies in gene-targeted mice establish that SAA contributes to atherosclerosis and some metastatic cancers. Accumulating evidence indicates that the lipidation state of SAA profoundly affects its bioactivities, with lipid-poor, but not HDL-associated, SAA capable of inducing inflammatory responses in vitro and in vivo. Factors that modulate the equilibrium between lipid-free and HDL-associated SAA have been identified. HDL may serve to limit SAA's bioactivities in vivo. Understanding the factors leading to the release of systemic SAA from HDL may provide insights into chronic disease mechanisms.
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http://dx.doi.org/10.1007/s11883-020-00901-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7808882PMC
January 2021

Aortic Aneurysms and Dissections Series: Part II: Dynamic Signaling Responses in Aortic Aneurysms and Dissections.

Arterioscler Thromb Vasc Biol 2020 04 25;40(4):e78-e86. Epub 2020 Mar 25.

Department of Physiology and Saha Cardiovascular Research Center (A.D., H.S.L.), University of Kentucky, Lexington.

Aortic structure and function are controlled by the coordinated actions of different aortic cells and the extracellular matrix. Several pathways have been identified that control the aortic wall in a cell-type-specific manner and play diverse roles in various phases of aortic injury, repair, and remodeling. This complexity of signaling in the aortic wall poses challenges to the development of therapeutic strategies for treating aortic aneurysms and dissections. Here, in part II of this Recent Highlights series on aortic aneurysms and dissections, we will summarize recent studies published in that have contributed to our knowledge of the signaling pathway-related mechanisms of aortic aneurysms and dissections.
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http://dx.doi.org/10.1161/ATVBAHA.120.313804DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7122036PMC
April 2020

Aortic Aneurysms and Dissections Series.

Arterioscler Thromb Vasc Biol 2020 03 26;40(3):e37-e46. Epub 2020 Feb 26.

Department of Physiology and Saha Cardiovascular Research Center (A.D., H.S.L.), University of Kentucky, Lexington.

The aortic wall is composed of highly dynamic cell populations and extracellular matrix. In response to changes in the biomechanical environment, aortic cells and extracellular matrix modulate their structure and functions to increase aortic wall strength and meet the hemodynamic demand. Compromise in the structural and functional integrity of aortic components leads to aortic degeneration, biomechanical failure, and the development of aortic aneurysms and dissections (AAD). A better understanding of the molecular pathogenesis of AAD will facilitate the development of effective medications to treat these conditions. Here, we summarize recent findings on AAD published in . In this issue, we focus on the dynamics of aortic cells and extracellular matrix in AAD; in the next issue, we will focus on the role of signaling pathways in AAD.
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http://dx.doi.org/10.1161/ATVBAHA.120.313991DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7233726PMC
March 2020

Serum amyloid A is not incorporated into HDL during HDL biogenesis.

J Lipid Res 2020 03 8;61(3):328-337. Epub 2020 Jan 8.

Saha Cardiovascular Research Center, University of Kentucky, Lexington, KY

Liver-derived serum amyloid A (SAA) is present in plasma where it is mainly associated with HDL and from which it is cleared more rapidly than are the other major HDL-associated apolipoproteins. Although evidence suggests that lipid-free and HDL-associated forms of SAA have different activities, the pathways by which SAA associates and disassociates with HDL are poorly understood. In this study, we investigated SAA lipidation by hepatocytes and how this lipidation relates to the formation of nascent HDL particles. We also examined hepatocyte-mediated clearance of lipid-free and HDL-associated SAA. We prepared hepatocytes from mice injected with lipopolysaccharide or an SAA-expressing adenoviral vector. Alternatively, we incubated primary hepatocytes from SAA-deficient mice with purified SAA. We analyzed conditioned media to determine the lipidation status of endogenously produced and exogenously added SAA. Examining the migration of lipidated species, we found that SAA is lipidated and forms nascent particles that are distinct from apoA-I-containing particles and that apoA-I lipidation is unaltered when SAA is overexpressed or added to the cells, indicating that SAA is not incorporated into apoA-I-containing HDL during HDL biogenesis. Like apoA-I formation, generation of SAA-containing particles was dependent on ABCA1, but not on scavenger receptor class B type I. Hepatocytes degraded significantly more SAA than apoA-I. Taken together, our results indicate that SAA's lipidation and metabolism by the liver is independent of apoA-I and that SAA is not incorporated into HDL during HDL biogenesis.
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http://dx.doi.org/10.1194/jlr.RA119000329DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7053844PMC
March 2020

Hepatocytes direct the formation of a pro-metastatic niche in the liver.

Nature 2019 03 6;567(7747):249-252. Epub 2019 Mar 6.

Abramson Cancer Center, University of Pennsylvania, Philadelphia, PA, USA.

The liver is the most common site of metastatic disease. Although this metastatic tropism may reflect the mechanical trapping of circulating tumour cells, liver metastasis is also dependent, at least in part, on the formation of a 'pro-metastatic' niche that supports the spread of tumour cells to the liver. The mechanisms that direct the formation of this niche are poorly understood. Here we show that hepatocytes coordinate myeloid cell accumulation and fibrosis within the liver and, in doing so, increase the susceptibility of the liver to metastatic seeding and outgrowth. During early pancreatic tumorigenesis in mice, hepatocytes show activation of signal transducer and activator of transcription 3 (STAT3) signalling and increased production of serum amyloid A1 and A2 (referred to collectively as SAA). Overexpression of SAA by hepatocytes also occurs in patients with pancreatic and colorectal cancers that have metastasized to the liver, and many patients with locally advanced and metastatic disease show increases in circulating SAA. Activation of STAT3 in hepatocytes and the subsequent production of SAA depend on the release of interleukin 6 (IL-6) into the circulation by non-malignant cells. Genetic ablation or blockade of components of IL-6-STAT3-SAA signalling prevents the establishment of a pro-metastatic niche and inhibits liver metastasis. Our data identify an intercellular network underpinned by hepatocytes that forms the basis of a pro-metastatic niche in the liver, and identify new therapeutic targets.
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http://dx.doi.org/10.1038/s41586-019-1004-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6430113PMC
March 2019

Serum Amyloid A Is an Exchangeable Apolipoprotein.

Arterioscler Thromb Vasc Biol 2018 08;38(8):1890-1900

From the Department of Veterans Affairs, Lexington, KY (P.G.W., J.C.T., N.R.W., L.R.T.).

Objective- SAA (serum amyloid A) is a family of acute-phase reactants that have proinflammatory and proatherogenic activities. SAA is more lipophilic than apoA-I (apolipoprotein A-I), and during an acute-phase response, <10% of plasma SAA is found lipid-free. In most reports, SAA is found exclusively associated with high-density lipoprotein; however, we and others have reported SAA on apoB (apolipoprotein B)-containing lipoproteins in both mice and humans. The goal of this study was to determine whether SAA is an exchangeable apolipoprotein. Approach and Results- Delipidated human SAA was incubated with SAA-free human lipoproteins; then, samples were reisolated by fast protein liquid chromatography, and SAA analyzed by ELISA and immunoblot. Both in vitro and in vivo, we show that SAA associates with any lipoprotein and does not remain in a lipid-free form. Although SAA is preferentially found on high-density lipoprotein, it can exchange between lipoproteins. In the presence of CETP (cholesterol ester transfer protein), there is greater exchange of SAA between lipoproteins. Subjects with diabetes mellitus, but not those with metabolic syndrome, showed altered SAA lipoprotein distribution postprandially. Proteoglycan-mediated lipoprotein retention is thought to be an underlying mechanism for atherosclerosis development. SAA has a proteoglycan-binding domain. Lipoproteins containing SAA had increased proteoglycan binding compared with SAA-free lipoproteins. Conclusions- Thus, SAA is an exchangeable apolipoprotein and increases apoB-containing lipoproteins' proteoglycan binding. We and others have previously reported the presence of SAA on low-density lipoprotein in individuals with obesity, diabetes mellitus, and metabolic syndrome. We propose that the presence of SAA on apoB-containing lipoproteins may contribute to cardiovascular disease development in these populations.
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http://dx.doi.org/10.1161/ATVBAHA.118.310979DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6202200PMC
August 2018

High-density lipoprotein inhibits serum amyloid A-mediated reactive oxygen species generation and NLRP3 inflammasome activation.

J Biol Chem 2018 08 5;293(34):13257-13269. Epub 2018 Jul 5.

Barnstable Brown Diabetes Center, University of Kentucky, Lexington, Kentucky 40536.

Serum amyloid A (SAA) is a high-density apolipoprotein whose plasma levels can increase more than 1000-fold during a severe acute-phase inflammatory response and are more modestly elevated in chronic inflammation. SAA is thought to play important roles in innate immunity, but its biological activities have not been completely delineated. We previously reported that SAA deficiency protects mice from developing abdominal aortic aneurysms (AAAs) induced by chronic angiotensin II (AngII) infusion. Here, we report that SAA is required for AngII-induced increases in interleukin-1β (IL-1β), a potent proinflammatory cytokine that is tightly controlled by the Nod-like receptor protein 3 (NLRP3) inflammasome and caspase-1 and has been implicated in both human and mouse AAAs. We determined that purified SAA stimulates IL-1β secretion in murine J774 and bone marrow-derived macrophages through a mechanism that depends on NLRP3 expression and caspase-1 activity, but is independent of P2X7 nucleotide receptor (P2X7R) activation. Inhibiting reactive oxygen species (ROS) by -acetyl-l-cysteine or mito-TEMPO and inhibiting activation of cathepsin B by CA-074 blocked SAA-mediated inflammasome activation and IL-1β secretion. Moreover, inhibiting cellular potassium efflux with glyburide or increasing extracellular potassium also significantly reduced SAA-mediated IL-1β secretion. Of note, incorporating SAA into high-density lipoprotein (HDL) prior to its use in cell treatments completely abolished its ability to stimulate ROS generation and inflammasome activation. These results provide detailed insights into SAA-mediated IL-1β production and highlight HDL's role in regulating SAA's proinflammatory effects.
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http://dx.doi.org/10.1074/jbc.RA118.002428DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6109913PMC
August 2018

Serum amyloid A3 is a high density lipoprotein-associated acute-phase protein.

J Lipid Res 2018 02 15;59(2):339-347. Epub 2017 Dec 15.

Saha Cardiovascular Research Center, University of Kentucky, Lexington, KY

Serum amyloid A (SAA) is a family of acute-phase reactants. Plasma levels of human SAA1/SAA2 (mouse SAA1.1/2.1) can increase ≥1,000-fold during an acute-phase response. Mice, but not humans, express a third relatively understudied SAA isoform, SAA3. We investigated whether mouse SAA3 is an HDL-associated acute-phase SAA. Quantitative RT-PCR with isoform-specific primers indicated that SAA3 and SAA1.1/2.1 are induced similarly in livers (∼2,500-fold vs. ∼6,000-fold, respectively) and fat (∼400-fold vs. ∼100-fold, respectively) of lipopolysaccharide (LPS)-injected mice. In situ hybridization demonstrated that all three SAAs are produced by hepatocytes. All three SAA isoforms were detected in plasma of LPS-injected mice, although SAA3 levels were ∼20% of SAA1.1/2.1 levels. Fast protein LC analyses indicated that virtually all of SAA1.1/2.1 eluted with HDL, whereas ∼15% of SAA3 was lipid poor/free. After density gradient ultracentrifugation, isoelectric focusing demonstrated that ∼100% of plasma SAA1.1 was recovered in HDL compared with only ∼50% of SAA2.1 and ∼10% of SAA3. Thus, SAA3 appears to be more loosely associated with HDL, resulting in lipid-poor/free SAA3. We conclude that SAA3 is a major hepatic acute-phase SAA in mice that may produce systemic effects during inflammation.
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http://dx.doi.org/10.1194/jlr.M080887DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794427PMC
February 2018

Serum amyloid A3 is pro-atherogenic.

Atherosclerosis 2018 01 17;268:32-35. Epub 2017 Nov 17.

Department of Veterans Affairs, Lexington, KY 40502, USA; Department of Internal Medicine, University of Kentucky, Lexington, KY, 40536, USA; Barnstable Brown Diabetes Center, University of Kentucky, Lexington, KY, 40536, USA; Saha Cardiovascular Research Center, University of Kentucky, Lexington, KY, 40536, USA. Electronic address:

Background And Aims: Serum amyloid A (SAA) predicts cardiovascular events. Overexpression of SAA increases atherosclerosis development; however, deficiency of two of the murine acute phase isoforms, SAA1.1 and SAA2.1, has no effect on atherosclerosis. SAA3 is a pseudogene in humans, but is an expressed acute phase isoform in mice. The goal of this study was to determine if SAA3 affects atherosclerosis in mice.

Methods: ApoE mice were used as the model for all studies. SAA3 was overexpressed by an adeno-associated virus or suppressed using an anti-sense oligonucleotide approach.

Results: Over-expression of SAA3 led to a 4-fold increase in atherosclerosis lesion area compared to control mice (p = 0.01). Suppression of SAA3 decreased atherosclerosis in mice genetically deficient in SAA1.1 and SAA2.1 (p < 0.0001).

Conclusions: SAA3 augments atherosclerosis in mice. Our results resolve a previous paradox in the literature and support extensive epidemiological data that SAA is pro-atherogenic.
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http://dx.doi.org/10.1016/j.atherosclerosis.2017.11.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5839639PMC
January 2018

The dual role of group V secretory phospholipase A in pancreatic β-cells.

Endocrine 2017 Oct 19;58(1):47-58. Epub 2017 Aug 19.

Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY, 40536, USA.

Purpose: Group X (GX) and group V (GV) secretory phospholipase A (sPLA) potently release arachidonic acid (AA) from the plasma membrane of intact cells. We previously demonstrated that GX sPLA negatively regulates glucose-stimulated insulin secretion (GSIS) by a prostaglandin E2 (PGE2)-dependent mechanism. In this study we investigated whether GV sPLA similarly regulates GSIS.

Methods: GSIS and pancreatic islet-size were assessed in wild-type (WT) and GV sPLA-knock out (GV KO) mice. GSIS was also assessed ex vivo in isolated islets and in vitro using MIN6 pancreatic beta cell lines with or without GV sPLA overexpression or silencing.

Results: GSIS was significantly decreased in islets isolated from GV KO mice compared to WT mice and in MIN6 cells with siRNA-mediated GV sPLA suppression. MIN6 cells overexpressing GV sPLA (MIN6-GV) showed a significant increase in GSIS compared to control cells. Though the amount of AA released into the media by MIN6-GV cells was significantly higher, PGE2 production was not enhanced or cAMP content decreased compared to control MIN6 cells. Surprisingly, GV KO mice exhibited a significant increase in plasma insulin levels following i.p. injection of glucose compared to WT mice. This increase in GSIS in GV KO mice was associated with a significant increase in pancreatic islet size and number of proliferating cells in β-islets compared to WT mice.

Conclusions: Deficiency of GV sPLA results in diminished GSIS in isolated pancreatic beta-cells. However, the reduced GSIS in islets lacking GV sPLA appears to be compensated by increased islet mass in GV KO mice.
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http://dx.doi.org/10.1007/s12020-017-1379-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693688PMC
October 2017

Secreted Phospholipases A2 Are Intestinal Stem Cell Niche Factors with Distinct Roles in Homeostasis, Inflammation, and Cancer.

Cell Stem Cell 2016 07 9;19(1):38-51. Epub 2016 Jun 9.

Department of Pathology, Erasmus MC Cancer Institute, Rotterdam 3000CA, The Netherlands. Electronic address:

The intestinal stem cell niche provides cues that actively maintain gut homeostasis. Dysregulation of these cues may compromise intestinal regeneration upon tissue insult and/or promote tumor growth. Here, we identify secreted phospholipases A2 (sPLA2s) as stem cell niche factors with context-dependent functions in the digestive tract. We show that group IIA sPLA2, a known genetic modifier of mouse intestinal tumorigenesis, is expressed by Paneth cells in the small intestine, while group X sPLA2 is expressed by Paneth/goblet-like cells in the colon. During homeostasis, group IIA/X sPLA2s inhibit Wnt signaling through intracellular activation of Yap1. However, upon inflammation they are secreted into the intestinal lumen, where they promote prostaglandin synthesis and Wnt signaling. Genetic ablation of both sPLA2s improves recovery from inflammation but increases colon cancer susceptibility due to release of their homeostatic Wnt-inhibitory role. This "trade-off" effect suggests sPLA2s have important functions as genetic modifiers of inflammation and colon cancer.
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http://dx.doi.org/10.1016/j.stem.2016.05.023DOI Listing
July 2016

Impact of individual acute phase serum amyloid A isoforms on HDL metabolism in mice.

J Lipid Res 2016 06 27;57(6):969-79. Epub 2016 Mar 27.

Departments of Internal Medicine, University of Kentucky Medical Center, Lexington, KY 40536 Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY 40536 Molecular and Cellular Biochemistry, University of Kentucky Medical Center, Lexington, KY 40536

The acute phase (AP) reactant serum amyloid A (SAA), an HDL apolipoprotein, exhibits pro-inflammatory activities, but its physiological function(s) are poorly understood. Functional differences between SAA1.1 and SAA2.1, the two major SAA isoforms, are unclear. Mice deficient in either isoform were used to investigate plasma isoform effects on HDL structure, composition, and apolipoprotein catabolism. Lack of either isoform did not affect the size of HDL, normally enlarged in the AP, and did not significantly change HDL composition. Plasma clearance rates of HDL apolipoproteins were determined using native HDL particles. The fractional clearance rates (FCRs) of apoA-I, apoA-II, and SAA were distinct, indicating that HDL is not cleared as intact particles. The FCRs of SAA1.1 and SAA2.1 in AP mice were similar, suggesting that the selective deposition of SAA1.1 in amyloid plaques is not associated with a difference in the rates of plasma clearance of the isoforms. Although the clearance rate of SAA was reduced in the absence of the HDL receptor, scavenger receptor class B type I (SR-BI), it remained significantly faster compared with that of apoA-I and apoA-II, indicating a relatively minor role of SR-BI in SAA's rapid clearance. These studies enhance our understanding of SAA metabolism and SAA's effects on AP-HDL composition and catabolism.
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http://dx.doi.org/10.1194/jlr.M062174DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4878182PMC
June 2016

Dysfunctional HDL and atherosclerotic cardiovascular disease.

Nat Rev Cardiol 2016 Jan 1;13(1):48-60. Epub 2015 Sep 1.

Pharmacology &Nutritional Sciences and Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, KY, USA.

High-density lipoproteins (HDLs) protect against atherosclerosis by removing excess cholesterol from macrophages through the ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette transporter G1 (ABCG1) pathways involved in reverse cholesterol transport. Factors that impair the availability of functional apolipoproteins or the activities of ABCA1 and ABCG1 could, therefore, strongly influence atherogenesis. HDL also inhibits lipid oxidation, restores endothelial function, exerts anti-inflammatory and antiapoptotic actions, and exerts anti-inflammatory actions in animal models. Such properties could contribute considerably to the capacity of HDL to inhibit atherosclerosis. Systemic and vascular inflammation has been proposed to convert HDL to a dysfunctional form that has impaired antiatherogenic effects. A loss of anti-inflammatory and antioxidative proteins, perhaps in combination with a gain of proinflammatory proteins, might be another important component in rendering HDL dysfunctional. The proinflammatory enzyme myeloperoxidase induces both oxidative modification and nitrosylation of specific residues on plasma and arterial apolipoprotein A-I to render HDL dysfunctional, which results in impaired ABCA1 macrophage transport, the activation of inflammatory pathways, and an increased risk of coronary artery disease. Understanding the features of dysfunctional HDL or apolipoprotein A-I in clinical practice might lead to new diagnostic and therapeutic approaches to atherosclerosis.
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http://dx.doi.org/10.1038/nrcardio.2015.124DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6245940PMC
January 2016

Deficiency of Endogenous Acute-Phase Serum Amyloid A Protects apoE-/- Mice From Angiotensin II-Induced Abdominal Aortic Aneurysm Formation.

Arterioscler Thromb Vasc Biol 2015 May 5;35(5):1156-65. Epub 2015 Mar 5.

From the Departments of Pharmacology Division of Nutritional Sciences (N.R.W.), Physiology (M.C.D.B.) and Internal Medicine (J.M.W., A.J., W.B., P.S., V.P.N., D.A.H., A.B., D.L.R., A.D., F.C.D.B.), and Saha Cardiovascular Research Center (N.R.W., M.C.D.B., J.M.W., A.J., P.S., V.P.N., D.A.H., A.B., D.L.R., A.D., F.C.D.B.), and Departments of Statistics and Biostatistics (R.J.C.), University of Kentucky, Lexington; and Foundation Gastroenterology, Nashua, NH (J.W.).

Objective: Rupture of abdominal aortic aneurysm (AAA), a major cause of death in the aged population, is characterized by vascular inflammation and matrix degradation. Serum amyloid A (SAA), an acute-phase reactant linked to inflammation and matrix metalloproteinase induction, correlates with aortic dimensions before aneurysm formation in humans. We investigated whether SAA deficiency in mice affects AAA formation during angiotensin II (Ang II) infusion.

Approach And Results: Plasma SAA increased ≈60-fold in apoE(-/-) mice 24 hours after intraperitoneal Ang II injection (100 μg/kg; n=4) and ≈15-fold after chronic 28-day Ang II infusion (1000 ng/kg per minute; n=9). AAA incidence and severity after 28-day Ang II infusion was significantly reduced in apoE(-/-) mice lacking both acute-phase SAA isoforms (SAAKO; n=20) compared with apoE(-/-) mice (SAAWT; n=20) as assessed by in vivo ultrasound and ex vivo morphometric analyses, despite a significant increase in systolic blood pressure in SAAKO mice compared with SAAWT mice after Ang II infusion. Atherosclerotic lesion area of the aortic arch was similar in SAAKO and SAAWT mice after 28-day Ang II infusion. Immunostaining detected SAA in AAA tissues of Ang II-infused SAAWT mice that colocalized with macrophages, elastin breaks, and enhanced matrix metalloproteinase activity. Matrix metalloproteinase-2 activity was significantly lower in aortas of SAAKO mice compared with SAAWT mice after 10-day Ang II infusion.

Conclusions: Lack of endogenous acute-phase SAA protects against experimental AAA through a mechanism that may involve reduced matrix metalloproteinase-2 activity.
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http://dx.doi.org/10.1161/ATVBAHA.114.304776DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4823018PMC
May 2015

Ectopically expressed pro-group X secretory phospholipase A2 is proteolytically activated in mouse adrenal cells by furin-like proprotein convertases: implications for the regulation of adrenal steroidogenesis.

J Biol Chem 2015 Mar 26;290(12):7851-60. Epub 2015 Jan 26.

the Department of Internal Medicine, University of Kentucky Medical Center, Lexington, Kentucky 40536

Group X secretory phospholipase A2 (GX sPLA2) hydrolyzes mammalian cell membranes, liberating free fatty acids and lysophospholipids. GX sPLA2 is produced as a pro-enzyme (pro-GX sPLA2) that contains an N-terminal 11-amino acid propeptide ending in a dibasic motif, suggesting cleavage by a furin-like proprotein convertase (PC). Although propeptide cleavage is clearly required for enzymatic activity, the protease(s) responsible for pro-GX sPLA2 activation have not been identified. We previously reported that GX sPLA2 negatively regulates adrenal glucocorticoid production, likely by suppressing liver X receptor-mediated activation of steroidogenic acute regulatory protein expression. In this study, using a FLAG epitope-tagged pro-GX sPLA2 expression construct (FLAG-pro-GX sPLA2), we determined that adrenocorticotropic hormone (ACTH) enhanced FLAG-pro-GX sPLA2 processing and phospholipase activity secreted by Y1 adrenal cells. ACTH increased the expression of furin and PCSK6, but not other members of the PC family, in Y1 cells. Overexpression of furin and PCSK6 in HEK 293 cells significantly enhanced FLAG-pro-GX sPLA2 processing, whereas siRNA-mediated knockdown of both PCs almost completely abolished FLAG-pro-GX sPLA2 processing in Y1 cells. Expression of either furin or PCSK6 enhanced the ability of GX sPLA2 to suppress liver X receptor reporter activity. The PC inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone significantly suppressed FLAG-pro-GX sPLA2 processing and sPLA2 activity in Y1 cells, and it significantly attenuated GX sPLA2-dependent inhibition of steroidogenic acute regulatory protein expression and progesterone production. These findings provide strong evidence that pro-GX sPLA2 is a substrate for furin and PCSK6 proteolytic processing and define a novel mechanism for regulating corticosteroid production in adrenal cells.
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http://dx.doi.org/10.1074/jbc.M114.634667DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367284PMC
March 2015

Group X secretory phospholipase A2 regulates insulin secretion through a cyclooxygenase-2-dependent mechanism.

J Biol Chem 2014 Oct 13;289(40):27410-7. Epub 2014 Aug 13.

From Saha Cardiovascular Research Center and Pharmacology and Nutritional Sciences, Division of Nutritional Sciences, University of Kentucky Medical Center, Lexington Kentucky 40536.

Group X secretory phospholipase A2 (GX sPLA2) potently hydrolyzes membrane phospholipids to release arachidonic acid (AA). While AA is an activator of glucose-stimulated insulin secretion (GSIS), its metabolite prostaglandin E2 (PGE2) is a known inhibitor. In this study, we determined that GX sPLA2 is expressed in insulin-producing cells of mouse pancreatic islets and investigated its role in beta cell function. GSIS was measured in vivo in wild-type (WT) and GX sPLA2-deficient (GX KO) mice and ex vivo using pancreatic islets isolated from WT and GX KO mice. GSIS was also assessed in vitro using mouse MIN6 pancreatic beta cells with or without GX sPLA2 overexpression or exogenous addition. GSIS was significantly higher in islets isolated from GX KO mice compared with islets from WT mice. Conversely, GSIS was lower in MIN6 cells overexpressing GX sPLA2 (MIN6-GX) compared with control (MIN6-C) cells. PGE2 production was significantly higher in MIN6-GX cells compared with MIN6-C cells and this was associated with significantly reduced cellular cAMP. The effect of GX sPLA2 on GSIS was abolished when cells were treated with NS398 (a COX-2 inhibitor) or L-798,106 (a PGE2-EP3 receptor antagonist). Consistent with enhanced beta cell function, GX KO mice showed significantly increased plasma insulin levels following glucose challenge and were protected from age-related reductions in GSIS and glucose tolerance compared with WT mice. We conclude that GX sPLA2 plays a previously unrecognized role in negatively regulating pancreatic insulin secretion by augmenting COX-2-dependent PGE2 production.
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http://dx.doi.org/10.1074/jbc.M114.591735DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4183781PMC
October 2014

Impact of phospholipid transfer protein on nascent high-density lipoprotein formation and remodeling.

Arterioscler Thromb Vasc Biol 2014 Sep 24;34(9):1910-6. Epub 2014 Jul 24.

From the Department of Internal Medicine (A.J., J.M.W., D.R.v.d.W.), Department of Pharmacology and Nutritional Sciences (A.J., J.M.W., N.R.W., D.R.v.d.W.), Department of Molecular and Cellular Biochemistry (D.R.v.d.W.), and Saha Cardiovascular Research Center (A.J., J.M.W., N.R.W., D.R.v.d.W.), University of Kentucky, Lexington; and Department of Veterans Affairs Medical Center (N.R.W., D.R.v.d.W.), Lexington, KY.

Objective: Phospholipid transfer protein (PLTP), which binds phospholipids and facilitates their transfer between lipoproteins in plasma, plays a key role in lipoprotein remodeling, but its influence on nascent high-density lipoprotein (HDL) formation is not known. The effect of PLTP overexpression on apolipoprotein A-I (apoA-I) lipidation by primary mouse hepatocytes was investigated.

Approach And Results: Overexpression of PLTP through an adenoviral vector markedly affected the amount and size of lipidated apoA-I species that were produced in hepatocytes in a dose-dependent manner, ultimately generating particles that were <7.1 nm but larger than lipid-free apoA-I. These <7.1-nm small particles generated in the presence of overexpressed PLTP were incorporated into mature HDL particles more rapidly than apoA-I both in vivo and in vitro and were less rapidly cleared from mouse plasma than lipid-free apoA-I. The <7.1-nm particles promoted both cellular cholesterol and phospholipid efflux in an ATP-binding cassette transporter A1-dependent manner, similar to apoA-I in the presence of PLTP. Lipid-free apoA-I had a greater efflux capacity in the presence of PLTP than in the absence of PLTP, suggesting that PLTP may promote ATP-binding cassette transporter A1-mediated cholesterol and phospholipid efflux. These results indicate that PLTP alters nascent HDL formation by modulating the lipidated species and by promoting the initial process of apoA-I lipidation.

Conclusions: Our findings suggest that PLTP exerts significant effects on apoA-I lipidation and nascent HDL biogenesis in hepatocytes by promoting ATP-binding cassette transporter A1-mediated lipid efflux and the remodeling of nascent HDL particles.
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http://dx.doi.org/10.1161/ATVBAHA.114.303533DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4141034PMC
September 2014

Deficiency of endogenous acute phase serum amyloid A does not affect atherosclerotic lesions in apolipoprotein E-deficient mice.

Arterioscler Thromb Vasc Biol 2014 Feb 21;34(2):255-61. Epub 2013 Nov 21.

From the Graduate Center for Nutritional Science (M.C.D.B., J.M.W., V.P.N., A.J., P.S., J.C.T., D.R.v.d.W., L.R.T., N.R.W., F.C.D.B.), Saha Cardiovascular Research Center (M.C.D.B., J.M.W., V.P.N., D.L.R., D.A.H., A.B., A.J., P.S., J.C.T., D.R.v.d.W., L.R.T., A.D., N.R.W., F.C.D.B.), and the Departments of Physiology (M.C.D.B.) and Internal Medicine (J.M.W., V.P.N., D.L.R., D.A.H., A.B., A.J., P.S., J.C.T., D.R.v.d.W., L.R.T., A.D., N.R.W., F.C.D.B.), University of Kentucky Medical Center, Lexington, KY; and Department of Veterans Affairs Medical Center, Lexington, KY (D.R.v.d.W., L.R.T.).

Objective: Although elevated plasma concentrations of serum amyloid A (SAA) are associated strongly with increased risk for atherosclerotic cardiovascular disease in humans, the role of SAA in the pathogenesis of lesion formation remains obscure. Our goal was to determine the impact of SAA deficiency on atherosclerosis in hypercholesterolemic mice.

Approach And Results: Apolipoprotein E-deficient (apoE(-/-)) mice, either wild type or deficient in both major acute phase SAA isoforms, SAA1.1 and SAA2.1, were fed a normal rodent diet for 50 weeks. Female mice, but not male apoE-/- mice deficient in SAA1.1 and SAA2.1, had a modest increase (22%; P≤0.05) in plasma cholesterol concentrations and a 53% increase in adipose mass compared with apoE-/- mice expressing SAA1.1 and SAA2.1 that did not affect the plasma cytokine levels or the expression of adipose tissue inflammatory markers. SAA deficiency did not affect lipoprotein cholesterol distributions or plasma triglyceride concentrations in either male or female mice. Atherosclerotic lesion areas measured on the intimal surfaces of the arch, thoracic, and abdominal regions were not significantly different between apoE-/- mice deficient in SAA1.1 and SAA2.1 and apoE-/- mice expressing SAA1.1 and SAA2.1 in either sex. To accelerate lesion formation, mice were fed a Western diet for 12 weeks. SAA deficiency had effect neither on diet-induced alterations in plasma cholesterol, triglyceride, or cytokine concentrations nor on aortic atherosclerotic lesion areas in either male or female mice. In addition, SAA deficiency in male mice had no effect on lesion areas or macrophage accumulation in the aortic roots.

Conclusions: The absence of endogenous SAA1.1 and 2.1 does not affect atherosclerotic lipid deposition in apolipoprotein E-deficient mice fed either normal or Western diets.
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http://dx.doi.org/10.1161/ATVBAHA.113.302247DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3951741PMC
February 2014

Translation of high-density lipoprotein function into clinical practice: current prospects and future challenges.

Circulation 2013 Sep;128(11):1256-67

Cardiovascular Institute, Icahn School of Medicine at Mount Sinai, New York, NY (R.S.R.); Cardiovascular Research Institute, MedStar Research Institute, Washington Hospital Center, Washington, DC (H.B.B.); Atherosclerosis Research Unit, Division of Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA (B.A.); Centre for Vascular Research at the University of New South Wales, Sydney, Australia (P.B.); Dyslipidemia, Atherosclerosis and Inflammation Research Unit 939, National Institute for Health and Medical Research, University of Pierre and Marie Curie - Paris 6, Pitie-Salpetriere Hospital, Paris, France (M.J.C., A.K.) Division of Metabolism, Endocrinology, and Nutrition, University of Washington, Seattle (J.W.H.); Department of Medicine, Columbia University, New York, NY (A.R.T.); and Internal Medicine and Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington (N.R.W.).

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http://dx.doi.org/10.1161/CIRCULATIONAHA.113.000962DOI Listing
September 2013

The Impairment of Macrophage-to-Feces Reverse Cholesterol Transport during Inflammation Does Not Depend on Serum Amyloid A.

J Lipids 2013 30;2013:283486. Epub 2013 Jan 30.

Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY 40536, USA ; Department of Physiology, University of Kentucky Medical Center, Lexington, KY 40536, USA.

Studies suggest that inflammation impairs reverse cholesterol transport (RCT). We investigated whether serum amyloid A (SAA) contributes to this impairment using an established macrophage-to-feces RCT model. Wild-type (WT) mice and mice deficient in SAA1.1 and SAA2.1 (SAAKO) were injected intraperitoneally with (3)H-cholesterol-labeled J774 macrophages 4 hr after administration of LPS or buffered saline. (3)H-cholesterol in plasma 4 hr after macrophage injection was significantly reduced in both WT and SAAKO mice injected with LPS, but this was not associated with a reduced capacity of serum from LPS-injected mice to promote macrophage cholesterol efflux in vitro. Hepatic accumulation of (3)H-cholesterol was unaltered in either WT or SAAKO mice by LPS treatment. Radioactivity present in bile and feces of LPS-injected WT mice 24 hr after macrophage injection was reduced by 36% (P < 0.05) and 80% (P < 0.001), respectively. In contrast, in SAAKO mice, LPS did not significantly reduce macrophage-derived (3)H-cholesterol in bile, and fecal excretion was reduced by only 45% (P < 0.05). Injection of cholesterol-loaded allogeneic J774 cells, but not syngeneic bone-marrow-derived macrophages, transiently induced SAA in C57BL/6 mice. Our study confirms reports that acute inflammation impairs steps in the RCT pathway and establishes that SAA plays only a minor role in this impairment.
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http://dx.doi.org/10.1155/2013/283486DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3572687PMC
February 2013

SAA does not induce cytokine production in physiological conditions.

Cytokine 2013 Feb 17;61(2):506-12. Epub 2012 Nov 17.

Department of Internal Medicine, University of Kentucky Medical Center, Lexington, KY 40536, USA.

SAA has been shown to have potential proinflammatory properties in inflammatory diseases such as atherosclerosis. These include induction of tumor necrosis factor α, interleukin-6, and monocyte chemoattractant protein 1 in vitro. However, concern has been raised that these effects might be due to use of recombinant SAA with low level of endotoxin contaminants or its non-native forms. Therefore, physiological relevance has not been fully elucidated. In this study, we investigated the role of SAA in the production of inflammatory cytokines. Stimulation of mouse monocyte J774 cells with lipid-poor recombinant human SAA and purified SAA derived from cardiac surgery patients, but not ApoA-I and ApoA-II, elicited pro-inflammatory cytokines like granulocyte colony stimulating factor (G-CSF). However, HDL-associated SAA failed to stimulate production of these cytokines. Using neutralizing antibodies against toll like receptor (TLR) 2 and 4, we could evaluate that TLR 2 is responsible for G-CSF production by lipid-poor SAA. To confirm these data in vivo, we expressed mouse SAA in SAA deficient C57BL/6 mice using an adenoviral vector. G-CSF was identically expressed in SAA-Adenoviral infected mice as well as in control null-Adenoviral mice at the early time points (4-8h) and could not be detected in plasma 24h after infection when plasma SAA levels were maximally elevated, indicating that adenoviral vector rather than SAA affected G-CSF levels. Taken together, our findings suggest that lipid-poor SAA, but not HDL-associated SAA, stimulates G-CSF production and this stimulation is mediated through TLR 2 in J774 cells. However, its physiological role in vivo remains ambiguous.
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http://dx.doi.org/10.1016/j.cyto.2012.10.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3616876PMC
February 2013

Group V secretory phospholipase A2 enhances the progression of angiotensin II-induced abdominal aortic aneurysms but confers protection against angiotensin II-induced cardiac fibrosis in apoE-deficient mice.

Am J Pathol 2012 Sep 17;181(3):1088-98. Epub 2012 Jul 17.

Endocrinology Division, the Department of Internal Medicine, University of Kentucky, Lexington, USA.

Abdominal aortic aneurysms (AAAs) and heart failure are complex life-threatening diseases whose etiology is not completely understood. In this study, we investigated whether deficiency of group V secretory phospholipase A(2) (GV sPLA(2)) protects from experimental AAA. The impact of GV sPLA(2) deficiency on angiotensin (Ang) II-induced cardiac fibrosis was also investigated. Apolipoprotein E (apoE)(-/-) mice and apoE(-/-) mice lacking GV sPLA(2) (GV DKO) were infused with 1000 ng/kg per minute Ang II for up to 28 days. Increases in systolic blood pressure, plasma aldosterone level, and urinary and heart prostanoids were similar in apoE(-/-) and GV DKO mice after Ang II infusion. The incidence of aortic rupture in Ang II-infused GV DKO mice (10%) was significantly reduced compared with apoE(-/-) mice (29.4%). Although the incidence of AAA in GV DKO mice (81.3%) and apoE(-/-) mice (100%) was similar, the mean percentage increase in maximal luminal diameter of abdominal aortas was significantly smaller in GV DKO mice (68.5% ± 7.7%) compared with apoE(-/-) mice (92.6% ± 8.3%). Deficiency of GV sPLA(2) resulted in increased Ang II-induced cardiac fibrosis that was most pronounced in perivascular regions. Perivascular collagen, visualized by picrosirius red staining, was associated with increased TUNEL staining and increased immunopositivity for macrophages and myofibroblasts and nicotinamide adenine dinucleotide phosphate oxidase (NOX)-2 and NOX-4, respectively. Our findings indicate that GV sPLA(2) modulates pathological responses to Ang II, with different outcomes for AAA and cardiac fibrosis.
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http://dx.doi.org/10.1016/j.ajpath.2012.05.037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3432434PMC
September 2012

Nascent HDL formation in hepatocytes and role of ABCA1, ABCG1, and SR-BI.

J Lipid Res 2012 Mar 20;53(3):446-55. Epub 2011 Dec 20.

Department of Veterans Affairs Medical Center, Lexington, KY, USA.

To study the mechanisms of hepatic HDL formation, we investigated the roles of ABCA1, ABCG1, and SR-BI in nascent HDL formation in primary hepatocytes isolated from mice deficient in ABCA1, ABCG1, or SR-BI and from wild-type (WT) mice. Under basal conditions, in WT hepatocytes, cholesterol efflux to exogenous apoA-I was accompanied by conversion of apoA-I to HDL-sized particles. LXR activation by T0901317 markedly enhanced the formation of larger HDL-sized particles as well as cellular cholesterol efflux to apoA-I. Glyburide treatment completely abolished the formation of 7.4 nm diameter and greater particles but led to the formation of novel 7.2 nm-sized particles. However, cells lacking ABCA1 failed to form such particles. ABCG1-deficient cells showed similar capacity to efflux cholesterol to apoA-I and to form nascent HDL particles compared with WT cells. Cholesterol efflux to apoA-I and nascent HDL formation were slightly but significantly enhanced in SR-BI-deficient cells compared with WT cells under basal but not LXR activated conditions. As in WT but not in ABCA1-deficient hepatocytes, 7.2 nm-sized particles generated by glyburide treatment were also detected in ABCG1-deficient and SR-BI-deficient hepatocytes. Our data indicate that hepatic nascent HDL formation is highly dependent on ABCA1 but not on ABCG1 or SR-BI.
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http://dx.doi.org/10.1194/jlr.M017079DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276468PMC
March 2012

Nascent HDL formation by hepatocytes is reduced by the concerted action of serum amyloid A and endothelial lipase.

J Lipid Res 2011 Dec 27;52(12):2255-61. Epub 2011 Sep 27.

Department of Internal Medicine, Endocrinology Division and Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY 40536, USA.

Inflammation is associated with significant decreases in plasma HDL-cholesterol (HDL-C) and apoA-I levels. Endothelial lipase (EL) is known to be an important determinant of HDL-C in mice and in humans and is upregulated during inflammation. In this study, we investigated whether serum amyloid A (SAA), an HDL apolipoprotein highly induced during inflammation, alters the ability of EL to metabolize HDL. We determined that EL hydrolyzes SAA-enriched HDL in vitro without liberating lipid-free apoA-I. Coexpression of SAA and EL in mice by adenoviral vector produced a significantly greater reduction in HDL-C and apoA-I than a corresponding level of expression of either SAA or EL alone. The loss of HDL occurred without any evidence of HDL remodeling to smaller particles that would be expected to have more rapid turnover. Studies with primary hepatocytes demonstrated that coexpression of SAA and EL markedly impeded ABCA1-mediated lipidation of apoA-I to form nascent HDL. Our findings suggest that a reduction in nascent HDL formation may be partly responsible for reduced HDL-C during inflammation when both EL and SAA are known to be upregulated.
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http://dx.doi.org/10.1194/jlr.M017681DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3220292PMC
December 2011

Group X secretory phospholipase A2 enhances TLR4 signaling in macrophages.

J Immunol 2011 Jul 27;187(1):482-9. Epub 2011 May 27.

University of Kentucky Medical Center, Lexington, KY 40536, USA.

Secretory phospholipase A(2)s (sPLA(2)) hydrolyze glycerophospholipids to liberate lysophospholipids and free fatty acids. Although group X (GX) sPLA(2) is recognized as the most potent mammalian sPLA(2) in vitro, its precise physiological function(s) remains unclear. We recently reported that GX sPLA(2) suppresses activation of the liver X receptor in macrophages, resulting in reduced expression of liver X receptor-responsive genes including ATP-binding cassette transporters A1 (ABCA1) and G1 (ABCG1), and a consequent decrease in cellular cholesterol efflux and increase in cellular cholesterol content (Shridas et al. 2010. Arterioscler. Thromb. Vasc. Biol. 30: 2014-2021). In this study, we provide evidence that GX sPLA(2) modulates macrophage inflammatory responses by altering cellular cholesterol homeostasis. Transgenic expression or exogenous addition of GX sPLA(2) resulted in a significantly higher induction of TNF-α, IL-6, and cyclooxygenase-2 in J774 macrophage-like cells in response to LPS. This effect required GX sPLA(2) catalytic activity, and was abolished in macrophages that lack either TLR4 or MyD88. The hypersensitivity to LPS in cells overexpressing GX sPLA(2) was reversed when cellular free cholesterol was normalized using cyclodextrin. Consistent with results from gain-of-function studies, peritoneal macrophages from GX sPLA(2)-deficient mice exhibited a significantly dampened response to LPS. Plasma concentrations of inflammatory cytokines were significantly lower in GX sPLA(2)-deficient mice compared with wild-type mice after LPS administration. Thus, GX sPLA(2) amplifies signaling through TLR4 by a mechanism that is dependent on its catalytic activity. Our data indicate this effect is mediated through alterations in plasma membrane free cholesterol and lipid raft content.
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http://dx.doi.org/10.4049/jimmunol.1003552DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3119755PMC
July 2011

Scavenger receptor SR-BI in macrophage lipid metabolism.

Atherosclerosis 2011 Jul 9;217(1):106-12. Epub 2011 Apr 9.

Department of Internal Medicine, University of Kentucky, Lexington, KY 40536, USA.

Objective: To investigate the mechanisms by which macrophage scavenger receptor BI (SR-BI) regulates macrophage cholesterol homeostasis and protects against atherosclerosis.

Methods And Results: The expression and function of SR-BI was investigated in cultured mouse bone marrow-derived macrophages (BMM). SR-BI, the other scavenger receptors SRA and CD36 and the ATP-binding cassette transporters ABCA1 and ABCG1 were each distinctly regulated during BMM differentiation. SR-BI levels increased transiently to significant levels during culture. SR-BI expression in BMM was reversibly down-regulated by lipid loading with modified LDL; SR-BI was shown to be present both on the cell surface as well as intracellularly. BMM exhibited selective HDL CE uptake, however, this was not dependent on SR-BI or another potential candidate glycosylphosphatidylinositol anchored high density lipoprotein binding protein 1 (GPIHBP1). SR-BI played a significant role in facilitating bidirectional cholesterol flux in non lipid-loaded cells. SR-BI expression enhanced both cell cholesterol efflux and cholesterol influx from HDL, but did not lead to altered cellular cholesterol mass. SR-BI-dependent efflux occurred to larger HDL particles but not to smaller HDL(3). Following cholesterol loading, ABCA1 and ABCG1 were up-regulated and served as the major contributors to cholesterol efflux, while SR-BI expression was down-regulated.

Conclusion: Our results suggest that SR-BI plays a significant role in macrophage cholesterol flux that may partly account for its effects on atherogenesis.
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http://dx.doi.org/10.1016/j.atherosclerosis.2011.03.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3139003PMC
July 2011

ATP binding cassette G1-dependent cholesterol efflux during inflammation.

J Lipid Res 2011 Feb 7;52(2):345-53. Epub 2010 Dec 7.

Departments of Physiology, University of Kentucky Medical Center, Lexington, KY, USA.

ATP binding cassette transporter G1 (ABCG1) mediates the transport of cellular cholesterol to HDL, and it plays a key role in maintaining macrophage cholesterol homeostasis. During inflammation, HDL undergoes substantial remodeling, acquiring lipid changes and serum amyloid A (SAA) as a major apolipoprotein. In the current study, we investigated whether remodeling of HDL that occurs during acute inflammation impacts ABCG1-dependent efflux. Our data indicate that lipid free SAA acts similarly to apolipoprotein A-I (apoA-I) in mediating sequential efflux from ABCA1 and ABCG1. Compared with normal mouse HDL, acute phase (AP) mouse HDL containing SAA exhibited a modest but significant 17% increase in ABCG1-dependent efflux. Interestingly, AP HDL isolated from mice lacking SAA (SAAKO mice) was even more effective in promoting ABCG1 efflux. Hydrolysis with Group IIA secretory phospholipase A(2) (sPLA(2)-IIA) significantly reduced the ability of AP HDL from SAAKO mice to serve as a substrate for ABCG1-mediated cholesterol transfer, indicating that phospholipid (PL) enrichment, and not the presence of SAA, is responsible for alterations in efflux. AP human HDL, which is not PL-enriched, was somewhat less effective in mediating ABCG1-dependent efflux compared with normal human HDL. Our data indicate that inflammatory remodeling of HDL impacts ABCG1-dependent efflux independent of SAA.
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http://dx.doi.org/10.1194/jlr.M012328DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3023555PMC
February 2011

Group X secretory phospholipase A2 negatively regulates ABCA1 and ABCG1 expression and cholesterol efflux in macrophages.

Arterioscler Thromb Vasc Biol 2010 Oct;30(10):2014-21

Graduate Center for Nutritional Sciences, Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington 40536-0200, USA.

Objective: GX sPLA(2) potently hydrolyzes plasma membranes to generate lysophospholipids and free fatty acids; it has been implicated in inflammatory diseases, including atherosclerosis. To identify a novel role for group X (GX) secretory phospholipase A(2) (sPLA(2)) in modulating ATP binding casette transporter A1 (ABCA1) and ATP binding casette transporter G1 (ABCG1) expression and, therefore, macrophage cholesterol efflux.

Methods And Results: The overexpression or exogenous addition of GX sPLA(2) significantly reduced ABCA1 and ABCG1 expression in J774 macrophage-like cells, whereas GX sPLA(2) deficiency in mouse peritoneal macrophages was associated with enhanced expression. Altered ABC transporter expression led to reduced cholesterol efflux in GX sPLA(2)-overexpressing J774 cells and increased efflux in GX sPLA(2)-deficient mouse peritoneal macrophages. Gene regulation was dependent on GX sPLA(2) catalytic activity, mimicked by arachidonic acid and abrogated when liver X receptor (LXR)α/β expression was suppressed, and partially reversed by the LXR agonist T0901317. Reporter assays indicated that GX sPLA(2) suppresses the ability of LXR to transactivate its promoters through a mechanism involving the C-terminal portion of LXR spanning the ligand-binding domain.

Conclusions: GX sPLA(2) modulates gene expression in macrophages by generating lipolytic products that suppress LXR activation. GX sPLA(2) may play a previously unrecognized role in atherosclerotic lipid accumulation by negatively regulating the genes critical for cellular cholesterol efflux.
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http://dx.doi.org/10.1161/ATVBAHA.110.210237DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2958102PMC
October 2010

Group X secretory phospholipase A(2) augments angiotensin II-induced inflammatory responses and abdominal aortic aneurysm formation in apoE-deficient mice.

Atherosclerosis 2011 Jan 19;214(1):58-64. Epub 2010 Aug 19.

Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, KY 40536-0200, USA.

Objective: Abdominal aortic aneurysm (AAA) is a complex vascular disease characterized by matrix degradation and inflammation and is a major cause of mortality in older men. Specific interventions that prevent AAA progression remain to be identified. In this study, we tested the hypothesis that Group X secretory phospholipase A(2) (GX sPLA(2)), an enzyme implicated in inflammatory processes, mediates AAA.

Methods And Results: GX sPLA(2) was detected by immunostaining in human aneurysmal tissue and in angiotensin II (Ang II)-induced AAAs in apolipoprotein E-deficient (apoE(-/-)) mice. GX sPLA(2) mRNA was increased significantly (11-fold) in abdominal aortas of apoE(-/-) mice in response to Ang II infusion. To define the role of GX sPLA(2) in experimental AAAs, apoE(-/-) and apoE(-/-) x GX sPLA(2)(-/-) (GX DKO) mice were infused with Ang II for either 10 (n=7) or 28 (n=24-26) days. Deficiency of GX sPLA(2) significantly reduced the incidence and severity of AAAs, as assessed by ultrasound measurements in vivo of aortic lumens and by computer-assisted morphometric analyses ex vivo of external diameter. Results from gene expression profiling indicated that the expression of specific matrix metalloproteinases and inflammatory mediators was blunted in aortas from GX DKO mice compared to apoE(-/-) mice after 10-day Ang II infusion. Ang II induction of cyclooxygenase-2, interleukin-6, matrix metalloproteinase (MMP)-2, MMP-13 and MMP-14 was reduced significantly in GX DKO mice compared to apoE(-/-) mice.

Conclusion: GX sPLA(2) promotes Ang II-induced pathological responses leading to AAA formation.
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http://dx.doi.org/10.1016/j.atherosclerosis.2010.08.054DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3005558PMC
January 2011