lesterol transport during the acute phase response but not group IIA secretory phospholipase A 2 . J. Lipid Res . 2010. 51: 743-754. Supplementary key words feces • infl ammation • sepsis • atherosclerosis • miceEpidemiological studies established a strong inverse association between plasma HDL cholesterol levels and the risk of atherosclerotic cardiovascular disease (CVD) ( 1, 2 ). A major anti-atherogenic activity of HDL is regarded to be reverse cholesterol transport (RCT), a process comprising removal of excess cholesterol from peripheral cells, most importantly macrophage foam cells in atherosclerotic lesions, and transport back to the liver for subsequent excretion into bile and feces ( 2, 3 ). Understanding the pathophysiological factors regulating RCT is therefore of prime importance.Infl ammation is strongly linked to atherosclerosis ( 4-6 ). The atherosclerotic plaque itself is increasingly considered a site of chronic infl ammation within the vessel wall ( 5, 7 ). In addition, markers of infl ammation are elevated in plasma of patients with established atherosclerotic CVD, and circulating levels of several acute phase proteins Abstract Atherosclerosis is linked to infl ammation. HDL protects against atherosclerotic cardiovascular disease, mainly by mediating cholesterol effl ux and reverse cholesterol transport (RCT). The present study aimed to test the impact of acute infl ammation as well as selected acute phase proteins on RCT with a macrophage-to-feces in vivo RCT assay using intraperitoneal administration of [ 3 H]cholesterol-labeled macrophage foam cells. In patients with acute sepsis, cholesterol effl ux toward plasma and HDL were signifi cantly decreased ( P < 0.001). In mice, acute infl ammation (75 µg/mouse lipopolysaccharide) decreased [ 3 H] cholesterol appearance in plasma ( P < 0.05) and tracer excretion into feces both within bile acids ( ؊ 84%) and neutral sterols ( ؊ 79%, each P < 0.001). In the absence of systemic infl ammation, overexpression of serum amyloid A (SAA, adenovirus) reduced overall RCT ( P < 0.05), whereas secretory phospholipase A 2 (sPLA 2 , transgenic mice) had no effect. Myeloperoxidase injection reduced tracer appearance in plasma ( P < 0.05) as well as RCT ( ؊ 36%, P < 0.05). Hepatic expression of bile acid synthesis genes ( P < 0.01) and transporters mediating biliary sterol excretion ( P < 0.01) was decreased by infl ammation. In conclusion, our data demonstrate that acute infl ammation impairs cholesterol effl ux in patients and macrophage-to-feces RCT in vivo in mice. Myeloperoxidase and SAA contribute to a certain extent to reduced RCT during infl ammation but not sPLA 2 . However, reduced bile acid formation and decreased biliary sterol excretion might represent major contributing factors to decreased RCT in infl ammation. -Annema, W., N. Nijstad, M. Tölle, J. F. de Boer, R. V. C. Buijs, P. Heeringa, M. van der Giet, and U. J. F. Tietge. Myeloperoxidase and serum amyloid A contribute to impaired in vivo reverse cho-

A major atheroprotective functionality of high-density lipoproteins (HDLs) is to promote ''reverse cholesterol transport'' (RCT). In this process, HDLs mediate the efflux and transport of cholesterol from peripheral cells and its subsequent transport to the liver for further metabolism and biliary excretion. We have previously demonstrated in cultured hepatocytes that P2Y 13 (purinergic receptor P2Y, G protein-coupled, 13) activation is essential for HDL uptake but the potential of P2Y 13 as a target to promote RCT has not been documented. Here, we show that P2Y 13 -deficient mice exhibited a decrease in hepatic HDL cholesterol uptake, hepatic cholesterol content, and biliary cholesterol output, although their plasma HDL and other lipid levels were normal. These changes translated into a substantial decrease in the rate of macrophage-to-feces RCT. Therefore, hallmark features of RCT are impaired in P2Y 13 -deficient mice. Furthermore, cangrelor, a partial agonist of P2Y 13 , stimulated hepatic HDL uptake and biliary lipid secretions in normal mice and in mice with a targeted deletion of scavenger receptor class B type I (SR-BI) in liver (hypomSR-BIknockout liver ) but had no effect in P2Y 13 knockout mice, which indicate that P2Y 13 -mediated HDL uptake pathway is independent of SR-BI-mediated HDL selective cholesteryl ester uptake. Conclusion: These results establish P2Y 13 as an attractive novel target for modulating RCT and support the emerging view that steady-state plasma HDL levels do not necessarily reflect the capacity of HDL to promote RCT.

Scavenger receptor class B type I (SR-BI) mediates selective uptake of cholesterol from highdensity lipoprotein (HDL) particles by the liver and influences biliary cholesterol secretion. However, it is not clear, if this effect is direct or indirect. The aim of this study was to determine the impact of SR-BI on biliary cholesterol secretion, especially in a functional context with ATP-binding cassette transporter g5 (Abcg5)/Abcg8 and Abcb4. SR-BI was overexpressed by means of adenovirus (AdSR-BI) in livers of wild-type, liver X receptor-null (Lxr ؊/؊ ), Abcg5 ؊/؊ , and Abcb4 ؊/؊ mice. Consistent with previous reports, AdSR-BI decreased plasma HDL cholesterol levels in all models (P < 0.001). Hepatic cholesterol content increased (at least P < 0.05), whereas expression of sterol regulatory element binding protein 2 target genes was decreased (at least P < 0.05,) and established Lxr target genes were unaltered. Biliary cholesterol secretion was increased by AdSR-BI in wild-type as well as in Lxr ؊/؊ and Abcg5 ؊/؊ mice, and considerably less in Abcb4 ؊/؊ mice (each P < 0.001), independent of bile acid and phospholipid secretion. T he scavenger receptor class B type I (SR-BI) has been characterized as a receptor that mediates cholesterol transport across membranes. 1,2 In nonpolarized cells, namely macrophages and the hepatoma cell line Fu5AH, SR-BI expression either results in selective uptake of cholesterol, mainly from high-density lipoprotein (HDL), or in cholesterol efflux toward suitable acceptors. [3][4][5][6] In hepatocytes, which is a highly polarized cell type, SR-BI is the main receptor responsible for selective uptake of cholesterol from plasma HDL. 7 Consequently, hepatic overexpression of SR-BI results in decreased plasma HDL cholesterol levels, 8-10 whereas SR-BI knockout mice have increased plasma HDL cholesterol. 11,12 Interestingly, hepatocyte SR-BI appears to accelerate reverse cholesterol transport in vivo in the face of decreased plasma HDL cholesterol levels, 13 which is in line with studies demonstrating that hepatic SR-BI expression protects against atherosclerosis development in mouse models. 14,15 Hepatic SR-BI expression is also linked to biliary cholesterol

Microsomal triglyceride transfer protein (MTP) facilitates the transport of dietary and endogenous fat by the intestine and liver by assisting in the assembly and secretion of triglyceride-rich apolipoprotein B-containing lipoproteins. Higher concentrations of apolipoprotein B lipoproteins predispose individuals to various cardiovascular and metabolic diseases such as atherosclerosis, diabetes, obesity and the metabolic syndrome. These can potentially be avoided by reducing MTP activity. In this article, we discuss regulation of MTP during development, cellular differentiation and diurnal variation. Furthermore, we focus on the regulation of MTP that occurs at transcriptional, post-transcriptional and post-translational levels. Transcriptional regulation of MTP depends on a few highly conserved cis-elements in the promoter. Several transcription factors that bind to these elements and either increase or decrease MTP expression have been identified. Additionally, MTP is regulated by macronutrients, hormones and other factors. This article will address the many ways in which MTP is regulated and advance the idea that reducing MTP levels, rather than its inhibition, might be an option to lower plasma lipids.

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The ATPase SecA provides the driving force for the transport of secretory proteins across the cytoplasmic membrane of Escherichia coli. SecA exists as a dimer in solution, but the exact oligomeric state of SecA during membrane binding and preprotein translocation is a topic of debate. To study the requirements of oligomeric changes in SecA during protein translocation, a non-dissociable SecA dimer was formed by oxidation of the carboxyl-terminal cysteines. The cross-linked SecA dimer interacts with the SecYEG complex with a similar stoichiometry as non-cross-linked SecA. Cross-linking reversibly disrupts the SecB binding site on SecA. However, in the absence of SecB, the activity of the disulfide-bonded SecA dimer is indistinguishable from wild-type SecA. Moreover, SecYEG binding stabilizes a cold sodium dodecylsulfate-resistant dimeric state of SecA. The results demonstrate that dissociation of the SecA dimer is not an essential feature of the protein translocation reaction.Translocase mediates the translocation of precursor proteins (preproteins) across the cytoplasmic membrane of Escherichia coli and other bacteria. The ATPase SecA (1) is the peripheral motor domain of the translocase. The SecYEG complex constitutes a membrane-embedded protein-conducting channel (reviewed in Ref. 2) and a high affinity binding site for SecA (3). When bound to SecYEG, SecA functions as a high affinity membrane receptor for the molecular chaperone SecB with associated preproteins (3). The movement of the preprotein through the protein-conducting channel is driven by multiple cycles of ATP binding and hydrolysis at SecA (4) and the proton motive force.In solution, SecA exist as a homodimer (5) that equilibrates with its monomeric form in a temperature-, salt-and protein concentration-dependent manner (6). Under physiological conditions, the dissociation constant (K D ) for the monomer-dimer equilibrium is ϳ0

Endothelial lipase (EL) is a negative regulator of high density lipoprotein (HDL) cholesterol plasma levels, and scavenger receptor BI (SR-BI) is involved in remodeling of HDL. The present study investigates the requirement of SR-BI for the effects of EL-mediated phospholipid hydrolysis on HDL metabolism in vivo. In vitro, selective uptake from EL-modified HDL was 129% higher than selective uptake from control HDL in SR-BI-overexpressing cells (p ‫؍‬ 0.01). In vivo overexpression of human EL by means of recombinant adenovirus decreased HDL plasma levels significantly (p < 0.01). Fast protein liquid chromatography analysis and agarose gel electrophoresis revealed that EL expression resulted in the generation of small pre-␤ HDL particles in wild-type mice, whereas in SR-BI ؊/؊ mice small HDL were preferentially removed. In kinetic experiments the fractional catabolic rate (FCR) of HDL cholesteryl ester increased by 110% (p < 0.001), and the FCR of HDL apolipoproteins increased by 64% (p < 0.001) in response to EL overexpression in wild-type mice. In SR-BI ؊/؊ mice a similar increase in the HDL apolipoprotein FCR occurred (p < 0.001); however, there was no further increase in HDL cholesteryl ester catabolism. The apparent whole body selective uptake was increased 3-fold by EL in wild-type mice (p < 0.001), whereas there was no selective uptake in SR-BI knock-out mice. EL overexpression increased hepatic selective uptake as well as holoparticle uptake (each p < 0.01) in wild-type mice, whereas in SR-BI knock-out mice only holoparticle uptake increased (p < 0.01). Our results indicate that SR-BI-mediated selective uptake of HDL cholesteryl ester is essential for the remodeling of large ␣-migrating HDL particles by EL. Plasma levels of high density lipoprotein (HDL)3 cholesterol and its major apolipoprotein apoA-I are inversely correlated with the risk of atherosclerotic cardiovascular disease, a major cause of mortality in developed countries (1, 2). The factors responsible for the considerable variation in HDL cholesterol plasma levels are still incompletely understood. However, metabolic studies of HDL and apoA-I in humans have established that the substantial variation in their levels is primarily due to variation in the rate of apoA-I catabolism (3).Among the factors impacting on the remodeling and catabolism of HDL particles within the plasma compartment, the recently discovered endothelial lipase (EL) is of prime importance (4). EL is expressed in endothelial cells and macrophages, as well as in hepatocytes (5). EL has merely phospholipase and very little apparent triglyceridase activity (6), and HDL phospholipids represent a preferred substrate for the enzyme in in vitro assays (6, 7). The physiological relevance of EL-mediated hydrolysis of HDL particles for determining the plasma levels of HDL cholesterol has been established in experimental animals using both overexpression (5, 8) as well as loss-of-function models (9 -11). Overexpression of EL resulted in significantly decreased HDL cholesterol plasma leve...

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