Axel Ring - Academia.edu (original) (raw)

Papers by Axel Ring

Research paper thumbnail of Group B Streptococcal b-Hemolysin Induces Nitric Oxide Production

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. To examine the role of the GBS b-hemolysin in NO production, the murine macrophage line RAW 264.7 was exposed to a wild-type (WT) GBS isolate and to hyperhemolytic (HH) and nonhemolytic (NH) transposon mutants derived from that isolate. After activation of macrophages by the WT strain, the HH mutant, or cell-free extracts of b-hemolysin, nitrite release into the su-pernatant increased 110-fold and inducible NO synthase (iNOS) levels in cell lysates increased up to 10-fold compared with treatment with the NH mutant or extracts from that mutant. Hemolysin-induced NO production was dependent on protein tyrosine kinases and NF-kB, but not on extracellular signal-related kinase-1/2±mitogen-activated kinases or protein kinase A. These results indicate that GBS b-hemolysin induces murine macrophage iNOS via intra-cellular pathway...

[Research paper thumbnail of Group B streptococcal b-hemolysin induces NO synthase in macrophages in vitro and multiorgan injury and death in vivo [abstract 26](https://attachments.academia-assets.com/86424109/thumbnails/1.jpg)

New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) sero... more New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) serotype III strain (COH1) and its isogenic nonhemolytic (NH) and hyperhemolytic (HH) mutants. Mortality differed significantly between rabbits infected with the HH mutant IN40 (67%), compared with rabbits infected with the wt COH1 strain (27%) and the NH strains COH1-20 and COH1:cyl EDcat (13 % and 0%, respectively; P,:05). Histopathologically, dissemi-nated septic microabscesses surrounded by necrotic foci were found exclusively in the livers of HH mutant IN40–infected animals. Serum transaminase levels were 20-fold higher in the HH-in-fected group, compared with rabbits infected with the other strains. Positive TUNEL (in situ terminal deoxynucleotide transferase–mediated dUTP nick end labeling) staining and activation of caspase-3 in hepatocytes were more frequent in HH-infected than in wt-infected animals and absent in the NH mutant COH1-20–infected group, indicating that GBS b-hemolysin...

Research paper thumbnail of Therapie des metastasierten Kolonkarzinoms bei terminaler Niereninsuffizienz mit 5-FU, Folinsäure und Bevacizumab

Zeitschrift für Gastroenterologie, 2006

Research paper thumbnail of Group B Streptococcal �-Hemolysin Induces Nitric Oxide Production in Murine Macrophages

J Infec Dis, 2000

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. To examine the role of the GBS b-hemolysin in NO production, the murine macrophage line RAW 264.7 was exposed to a wild-type (WT) GBS isolate and to hyperhemolytic (HH) and nonhemolytic (NH) transposon mutants derived from that isolate. After activation of macrophages by the WT strain, the HH mutant, or cell-free extracts of b-hemolysin, nitrite release into the supernatant increased 110-fold and inducible NO synthase (iNOS) levels in cell lysates increased up to 10-fold compared with treatment with the NH mutant or extracts from that mutant. Hemolysin-induced NO production was dependent on protein tyrosine kinases and NF-kB, but not on extracellular signal-related kinase-1/2-mitogen-activated kinases or protein kinase A. These results indicate that GBS b-hemolysin induces murine macrophage iNOS via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Group B streptococcus (GBS; Streptococcus agalactiae) is the leading cause of pneumonia, meningitis, and septic shock in newborns, particularly those born prematurely [1]. All clinical isolates are encapsulated, and 98%-99% are b-hemolytic [2]. The GBS capsular polysaccharide contributes to virulence by virtue of its antiphagocytic property [3]. The GBS b-hemolysin, a potent membrane cytotoxin that injures lung epithelial [4] and endothelial [5] and brain endothelial [6] cells, may contribute to the pathogenesis of neonatal pneumonia and meningitis. Crude b-hemolysin preparations from GBS cultures induce cardiotoxicity and hypotension after intravenous administration to rabbits or rats, suggesting a role in septic shock [7]; however, the molecular mechanisms by which the GBS b-hemolysin may contribute to the pathogenesis of septic shock have not been delineated. The hypotension of septic shock is thought to be due in part to an excess production of nitric oxide (NO), as elevated NO levels are found in septic patients [8, 9]. Three isoforms of NO synthases (NOS) are present in mammals: the high-output in

Research paper thumbnail of Antibiotic prophylaxis after variceal hemorrhage reduces incidence of early rebleeding

Hepato-gastroenterology

This study aims to evaluate the role of new onset infection in the initiation of early rebleeding... more This study aims to evaluate the role of new onset infection in the initiation of early rebleeding after variceal hemorrhage in patients with liver cirrhosis and the effect of prophylactic antibiotic treatment. Two hundred and twenty-one consecutive admissions for variceal bleeding with no signs of infection at the time of admission were evaluated retrospectively. Systemic antibiotic prophylaxis was administered in 126 cases and significantly reduced the overall incidence of new onset infections (19.8% vs. 34.71%; p<0.01) and of early rebleeding (17.5% vs. 32.6%; p<0.01). Multivariate analysis showed strong correlation of rebleeding with new onset infection (p<0.001) and lack of prophylactic antibiotic treatment (p<0.05). Child-Pugh C cirrhosis, ventilatory assistance, and balloon tamponade were independent predictors of new onset infection (p<0.001, respectively). In the subgroup of patients with at least one predictor prophylactic treatment nearly halved the incidenc...

Research paper thumbnail of The Hepatic Microvascular Responses to Sepsis

Seminars in Thrombosis and Hemostasis, 2000

The liver is believed to play a major role in the initiation of multiorgan failure, the most leth... more The liver is believed to play a major role in the initiation of multiorgan failure, the most lethal complication in the clinical course of sepsis. Microbes and their virulence factors enter the hepatic circulation where they first activate sinusoidal endothelial cells and Kupffer cells to produce proinflammatory mediators, including TNF-alpha, IL-1, IL-6, reactive oxygen metabolites, and eicosanoids. These mediators cause not only microbial killing, but also structural and functional liver damage concerning mainly the parenchymal cells. Leukocytes are targeted to the liver sinusoids by chemoattractants and, like platelets, tether to the sinusoidal endothelial cells, which are in a procoagulant state of inflammatory activation. Clogging of the sinusoids by these cells leads to a decrease of blood flow through the sinusoids, which is further aggravated by endothelin-1 effectuating the constriction of hepatic stellate cells in the sinusoids. In contrast, both nitric oxide (NO) and carbon monoxide (CO) act as antagonists of endothelin-1 by mediating relaxation of sinusoidal vessels. By maintaining an adequate sinusoidal perfusion, both NO and CO are hepatoprotective during the early, hyperdynamic phase of sepsis characterized by an increased cardiac output and moderate peripheral vasodilation. However, during the late, hypodynamic phase of sepsis, massive overproduction of NO by the inducible NO synthase leads to circulatory collapse, which inevitably includes breakdown of the liver circulation.

Research paper thumbnail of New concepts of cellular fatty acid uptake: role of fatty acid transport proteins and of caveolae

Proceedings of the Nutrition Society, 2004

Efficient uptake and channelling of long-chain fatty acids (LCFA) are critical cell functions. Ev... more Efficient uptake and channelling of long-chain fatty acids (LCFA) are critical cell functions. Evidence is emerging that proteins are important mediators of LCFA-trafficking into cells and various proteins have been suggested to be involved in this process. Amongst these proteins is a family of membrane-associated proteins termed fatty acid transport proteins (FATP). So far six members of this family, designated FATP 1–6, have been characterized. FATP 1, 2 and 6 show a highly-conserved AMP-binding region that participates in the activation of very-long-chain fatty acids (VLCFA) to form their acyl-CoA derivatives. The mechanisms by which FATP mediate LCFA uptake are not well understood, but several studies provide evidence that uptake of LCFA across cellular membranes is closely linked to acyl-CoA synthetase activity. It is proposed that FATP indirectly enhance LCFA uptake by activating VLCFA to their CoA esters, which are required to maintain the typical structure of lipid rafts in ...

Research paper thumbnail of FAT/CD36-mediated Long-Chain Fatty Acid Uptake in Adipocytes Requires Plasma Membrane Rafts

Molecular Biology of the Cell, 2004

We previously reported that lipid rafts are involved in long-chain fatty acid (LCFA) uptake in 3T... more We previously reported that lipid rafts are involved in long-chain fatty acid (LCFA) uptake in 3T3-L1 adipocytes. The present data show that LCFA uptake does not depend on caveolae endocytosis because expression of a dominant negative mutant of dynamin had no effect on uptake of [3H]oleic acid, whereas it effectively prevented endocytosis of cholera toxin. Isolation of detergent-resistant membranes (DRMs) from 3T3-L1 cell homogenates revealed that FAT/CD36 was expressed in both DRMs and detergent-soluble membranes (DSMs), whereas FATP1 and FATP4 were present only in DSMs but not DRMs. Disruption of lipid rafts by cyclodextrin and specific inhibition of FAT/CD36 by sulfo-N-succinimidyl oleate (SSO) significantly decreased uptake of [3H]oleic acid, but simultaneous treatment had no additional or synergistic effects, suggesting that both treatments target the same mechanism. Indeed, subcellular fractionation demonstrated that plasma membrane fatty acid translocase (FAT/CD36) is exclusi...

Research paper thumbnail of Translocation of long chain fatty acids across the plasma membrane – lipid rafts and fatty acid transport proteins

Molecular and Cellular Biochemistry, 2006

Translocation of long chain fatty acids across the plasma membrane is achieved by a concert of co... more Translocation of long chain fatty acids across the plasma membrane is achieved by a concert of co-existing mechanisms. These lipids can passively diffuse, but transport can also be accelerated by certain membrane proteins as well as lipid rafts. Lipid rafts are dynamic assemblies of proteins and lipids, that float freely within the two dimensional matrix of the membrane bilayer. They are receiving increasing attention as devices that regulate membrane function in vivo and play an important role in membrane trafficking and signal transduction. In this review we will discuss how lipid rafts might be involved in the uptake process and how the candidate proteins for fatty acid uptake FAT/CD36 and the FATP proteins interact with these domains. We will also discuss the functional role of FATPs in general. To our understanding FATPs are indirectly involved in the translocation process across the plasma membrane by providing long chain fatty acid synthetase activity.

Research paper thumbnail of A new concept of cellular uptake and intracellular trafficking of long-chain fatty acids

Lipids, 2001

Fatty acids are the main structural and energy sources of the human body. Within the organism, th... more Fatty acids are the main structural and energy sources of the human body. Within the organism, they are presented to cells as fatty acid:albumin complexes. Dissociation from albumin represents the first step of the cellular uptake process, involving membrane proteins with high affinity for fatty acids, e.g., fatty acid translocase (FAT/CD 36) or the membrane fatty acid-binding protein (FABP pm). According to the thus created transmembrane concentration gradient, uncharged fatty acids can flip-flop from the outer leaflet across the phospholipid bilayer. At the cytosolic surface of the plasma membrane, fatty acids can associate with the cytosolic FABP (FABP c) or with caveolin-1. Caveolins are constituents of caveolae, which are proposed to serve as lipid delivery vehicles for subcellular organelles. It is not known whether protein (FABP c)-and lipid (caveolae)-mediated intracellular trafficking of fatty acids operates in conjunction or in parallel. Channeling fatty acids to the different metabolic pathways requires activation to acyl-CoA. For this process, the family of fatty acid transport proteins (FATP 1-5/6) might be relevant because they have been shown to possess acyl-CoA synthetase activity. Their variable Nterminal signaling sequences suggest that they might be targeted to specific organelles by anchoring in the phospholipid bilayer of the different subcellular membranes. At the highly conserved cytosolic AMP-binding site of FATP, fatty acids are activated to acyl-CoA for subsequent metabolic disposition by specific organelles. Overall, fatty acid uptake represents a continuous flow involving the following: dissociation from albumin by membrane proteins with high affinity for fatty acids; passive flip-flop across the phospholipid bilayer; binding to FABP c and caveolin-1 at the cytosolic plasma membrane; and intracellular trafficking via FABP c and/or caveolae to sites of metabolic disposition. The uptake process is terminated after activation to acyl-CoA by the members of the FATP family targeted intracellularly to different organelles.

Research paper thumbnail of Group B Streptococcal β‐Hemolysin Induces Nitric Oxide Production in Murine Macrophages

The Journal of Infectious Diseases, 2000

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. To examine the role of the GBS b-hemolysin in NO production, the murine macrophage line RAW 264.7 was exposed to a wild-type (WT) GBS isolate and to hyperhemolytic (HH) and nonhemolytic (NH) transposon mutants derived from that isolate. After activation of macrophages by the WT strain, the HH mutant, or cell-free extracts of b-hemolysin, nitrite release into the supernatant increased 110-fold and inducible NO synthase (iNOS) levels in cell lysates increased up to 10-fold compared with treatment with the NH mutant or extracts from that mutant. Hemolysin-induced NO production was dependent on protein tyrosine kinases and NF-kB, but not on extracellular signal-related kinase-1/2-mitogen-activated kinases or protein kinase A. These results indicate that GBS b-hemolysin induces murine macrophage iNOS via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Group B streptococcus (GBS; Streptococcus agalactiae) is the leading cause of pneumonia, meningitis, and septic shock in newborns, particularly those born prematurely [1]. All clinical isolates are encapsulated, and 98%-99% are b-hemolytic [2]. The GBS capsular polysaccharide contributes to virulence by virtue of its antiphagocytic property [3]. The GBS b-hemolysin, a potent membrane cytotoxin that injures lung epithelial [4] and endothelial [5] and brain endothelial [6] cells, may contribute to the pathogenesis of neonatal pneumonia and meningitis. Crude b-hemolysin preparations from GBS cultures induce cardiotoxicity and hypotension after intravenous administration to rabbits or rats, suggesting a role in septic shock [7]; however, the molecular mechanisms by which the GBS b-hemolysin may contribute to the pathogenesis of septic shock have not been delineated. The hypotension of septic shock is thought to be due in part to an excess production of nitric oxide (NO), as elevated NO levels are found in septic patients [8, 9]. Three isoforms of NO synthases (NOS) are present in mammals: the high-output in

Research paper thumbnail of Group B Streptococcal β‐Hemolysin Induces Mortality and Liver Injury in Experimental Sepsis

The Journal of Infectious Diseases, 2002

New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) sero... more New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) serotype III strain (COH1) and its isogenic nonhemolytic (NH) and hyperhemolytic (HH) mutants. Mortality differed significantly between rabbits infected with the HH mutant IN40 (67%), compared with rabbits infected with the wt COH1 strain (27%) and the NH strains COH1-20 and COH1:cyl EDcat (13% and 0%, respectively; P , :05). Histopathologically, disseminated septic microabscesses surrounded by necrotic foci were found exclusively in the livers of HH mutant IN40-infected animals. Serum transaminase levels were 20-fold higher in the HH-infected group, compared with rabbits infected with the other strains. Positive TUNEL (in situ terminal deoxynucleotide transferase-mediated dUTP nick end labeling) staining and activation of caspase-3 in hepatocytes were more frequent in HH-infected than in wt-infected animals and absent in the NH mutant COH1-20-infected group, indicating that GBS b-hemolysin triggers apoptotic pathways in hepatocytes. This work provides the first evidence that GBS b-hemolysin plays a crucial role in the pathophysiology of GBS sepsis by inducing liver failure and high mortality.

Research paper thumbnail of Synergistic Action of Nitric Oxide Release from Murine Macrophages Caused by Group B Streptococcal Cell Wall and β‐Hemolysin/Cytolysin

The Journal of Infectious Diseases, 2002

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. It has been shown that GBS b-hemolysin/cytolysin (b-h/c) stimulates the transcription of inducible NO synthase (iNOS) in murine macrophages via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Here, it is demonstrated that the GBS cell wall and b-h/c act synergistically to induce iNOS in interferon (IFN)-a-primed RAW 264.7 murine macrophages. In nonprimed macrophages, combined activation by the GBS cell wall plus bh/c is necessary to induce an NO response, which indicates that both virulence factors cooperate to substitute for the priming signal typically provided by IFN-a. Group B streptococcus (GBS) is the leading cause of pneumonia, meningitis, and septic shock in newborns, particularly those born prematurely. All clinical isolates are encapsulated, and 98%-99% are b-hemolytic [1]. GBS b-hemolytic activity is mediated by a pore-forming cytotoxin, the genetic basis of which has recently been elucidated [2]. In vitro, the GBS b-hemolysin/cytolysin (b-h/c) is associated with injury to lung epithelial, lung endothelial, and brain endothelial cells and is thus speculated to contribute to GBS penetration of host cellular barriers. Very recently, we reported that b-h/c is responsible for high mortality and liver injury in a rabbit model of GBS septic shock [3]. The hypotension of septic shock is thought to be due, in part, to an excess production of nitric oxide (NO), because elevated NO levels are found in patients with sepsis. Three isoforms of NO synthases (NOS) are present in mammals, the high-output inducible NOS (iNOS) and 2 constitutive isoforms, one originally identified in neurons and the other in endothelial cells. Activated macrophages constitute a major source of NO production. The inflammatory activation of macrophages is thought to involve 2 sequential steps, priming and triggering [4]. Priming is initiated by binding of interferon (IFN)-a to its specific receptor, which results in a number of biochemical and functional alterations that render the macrophages sensitive to triggering agents such as proinflammatory cytokines, lipopolysaccharide (LPS) [4],

Research paper thumbnail of Uptake of long-chain fatty acids in HEPG2 cells involves caveolin-1

Journal of Hepatology, 2001

We investigated the role of caveolae in uptake and intracellular trafficking of long chain fatty ... more We investigated the role of caveolae in uptake and intracellular trafficking of long chain fatty acids (LCFA) in HepG2 human hepatoma cells. The uptake of [(3)H]oleic acid and [(3)H]stearic acid into HepG2 cells was measured by radioactive assays and internalization of the non-metabolizable fluorescent fatty acid 12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino] (12-NBD) stearate into single HepG2 cells was semi-quantitatively assessed by laser scanning microscopy. The initial rate of [(3)H]oleic acid uptake (V(0)) in HepG2 cells exhibited saturable transport kinetics with increasing concentrations of free oleic acid (V(max) 854 +/- 46 pmol mg protein(-1) min(-1), K(m) 100 +/- 14 nmol/l). While inhibition of clathrin coated pits did not influence LCFA uptake in HepG2, inhibition of caveolae formation by filipin III, cyclodextrin, and caveolin-1 antisense oligonucleotides resulted in reduction of [(3)H]oleic acid uptake by 54%, 45%, and 23%, respectively. Furthermore, filipin III inhibited the uptake of [(3)H]stearic acid and its fluorescent derivative 12-NBD stearate by 44% and 50%, respectively. Transfection studies with alpha-caveolin-1/cyanofluorescent protein chimeras showed significant colocalization of caveolae and internalized 12-NBD stearate. In conclusion, these data suggest a significant role for caveolae mediated uptake and intracellular trafficking of LCFA in HepG2 cells.

Research paper thumbnail of The role of dominant stenoses in bacterial infections of bile ducts in primary sclerosing cholangitis

European Journal of Gastroenterology & Hepatology, 2006

Objective Primary sclerosing cholangitis (PSC) is characterized by progressive fibrotic inflammat... more Objective Primary sclerosing cholangitis (PSC) is characterized by progressive fibrotic inflammation and strictures of the biliary system. We studied the role of dominant stenoses in bacterial biliary infections and the effect of routine antibiotic administration with cholangiography. Design A prospective clinical trial without blinding or randomization. Setting The endoscopy unit in a university hospital. Participants Fifty patients with PSC entered and finished the study.

Research paper thumbnail of Long-Chain Fatty Acid Uptake into Adipocytes Depends on Lipid Raft Function

Biochemistry, 2004

This study investigates the role of lipid rafts and caveolae, a subclass of lipid raft microdomai... more This study investigates the role of lipid rafts and caveolae, a subclass of lipid raft microdomains, in the binding and uptake of long-chain fatty acids (LCFA) by 3T3-L1 cells during differentiation. Disruption of lipid rafts by beta-cyclodextrin (betaCD) or selective inhibition of caveolae by overexpression of a dominant-negative mutant of caveolin-3 (Cav(DGV)) resulted in disassembly of caveolae structures at the cell surface, as assessed by electron microscopy. While in 3T3-L1 fibroblasts, which express few caveolae, Cav(DGV) or betaCD had no effect on LCFA uptake, in 3T3-L1 adipocytes the same treatments decreased the level of [(3)H]oleic acid uptake by up to 55 +/- 8 and 49 +/- 7%, respectively. In contrast, cholesterol loading of 3T3-L1 adipocytes resulted in a 4-fold increase in the extent of caveolin-1 expression and a 1.7-fold increase in the level of LCFA uptake. Both the inhibitory and enhancing effects of these treatments were constantly increasing with the [(3)H]oleic acid incubation time up to 5 min. Incubation of 3T3-L1 adipocytes with [(3)H]stearate followed by isolation of a caveolin-1 positive detergent-resistant membrane (DRM) fraction revealed that [(3)H]stearate binds to caveolae. Fatty acid translocase (FAT/CD36) was found to be present in this DRM fraction as well. Our data thus strongly indicate a critical involvement of lipid rafts in the binding and uptake of LCFA into 3T3-L1 adipocytes. Furthermore, our findings suggest that caveolae play a pivotal role in lipid raft-dependent LCFA uptake. This transport mechanism is induced in conjunction with cell differentiation and might be mediated by FAT/CD36.

Research paper thumbnail of Caveolin-1 is required for fatty acid translocase (FAT/CD36) localization and function at the plasma membrane of mouse embryonic fibroblasts

Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2006

Several lines of evidence suggest that lipid rafts are involved in cellular fatty acid uptake and... more Several lines of evidence suggest that lipid rafts are involved in cellular fatty acid uptake and influence fatty acid translocase (FAT/CD36) function. However, it remains unknown whether caveolae, a specialized raft type, are required for this mechanism. Here, we show that wild-type (WT) mouse embryonic fibroblasts (MEFs) and caveolin-1 knockout (KO) MEFs, which are devoid of caveolae, have comparable overall expression of FAT/CD36 protein but altered subcellular FAT/CD36 localization and function. In WT MEFs, FAT/CD36 was isolated with both lipid raft enriched detergent-resistant membranes (DRMs) and detergent-soluble membranes (DSMs), whereas in cav-1 KO cells it was exclusively associated with DSMs. Subcellular fractionation demonstrated that FAT/CD36 in WT MEFs was localized intracellularly and at the plasma membrane level while in cav-1 KO MEFs it was absent from the plasma membrane. This mistargeting of FAT/CD36 in cav-1 KO cells resulted in reduced fatty acid uptake compared to WT controls. Adenoviral expression of caveolin-1 in KO MEFs induced caveolae formation, redirection of FAT/CD36 to the plasma membrane and rescue of fatty acid uptake. In conclusion, our data provide evidence that caveolin-1 is necessary to target FAT/CD36 to the plasma membrane. Caveolin-1 may influence fatty acid uptake by regulating surface availability of FAT/CD36.

Research paper thumbnail of Role of FATP in parenchymal cell fatty acid uptake

Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2004

Long-chain fatty acids (LCFAs) represent key metabolites for energy generation and storage. Trans... more Long-chain fatty acids (LCFAs) represent key metabolites for energy generation and storage. Transport and metabolism of LCFA are believed to be regulated by membrane-associated proteins that bind and transport LCFA. Identifying the postulated fatty acid transporters is of considerable interest since altered fatty acid uptake has been implicated in disease such as insulin resistance and obesity. Recently, a family of membrane associated proteins, termed fatty acid transport proteins (FATPs), have been described that enhance uptake of LCFAs. Until today, six members of this family, designated FATP1-6, have been characterized. This review will focus on FATP structure, expression patterns, regulation, mechanism of transport and clinical implications.

Research paper thumbnail of Group B Streptococcal b-Hemolysin Induces Nitric Oxide Production

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. To examine the role of the GBS b-hemolysin in NO production, the murine macrophage line RAW 264.7 was exposed to a wild-type (WT) GBS isolate and to hyperhemolytic (HH) and nonhemolytic (NH) transposon mutants derived from that isolate. After activation of macrophages by the WT strain, the HH mutant, or cell-free extracts of b-hemolysin, nitrite release into the su-pernatant increased 110-fold and inducible NO synthase (iNOS) levels in cell lysates increased up to 10-fold compared with treatment with the NH mutant or extracts from that mutant. Hemolysin-induced NO production was dependent on protein tyrosine kinases and NF-kB, but not on extracellular signal-related kinase-1/2±mitogen-activated kinases or protein kinase A. These results indicate that GBS b-hemolysin induces murine macrophage iNOS via intra-cellular pathway...

[Research paper thumbnail of Group B streptococcal b-hemolysin induces NO synthase in macrophages in vitro and multiorgan injury and death in vivo [abstract 26](https://attachments.academia-assets.com/86424109/thumbnails/1.jpg)

New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) sero... more New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) serotype III strain (COH1) and its isogenic nonhemolytic (NH) and hyperhemolytic (HH) mutants. Mortality differed significantly between rabbits infected with the HH mutant IN40 (67%), compared with rabbits infected with the wt COH1 strain (27%) and the NH strains COH1-20 and COH1:cyl EDcat (13 % and 0%, respectively; P,:05). Histopathologically, dissemi-nated septic microabscesses surrounded by necrotic foci were found exclusively in the livers of HH mutant IN40–infected animals. Serum transaminase levels were 20-fold higher in the HH-in-fected group, compared with rabbits infected with the other strains. Positive TUNEL (in situ terminal deoxynucleotide transferase–mediated dUTP nick end labeling) staining and activation of caspase-3 in hepatocytes were more frequent in HH-infected than in wt-infected animals and absent in the NH mutant COH1-20–infected group, indicating that GBS b-hemolysin...

Research paper thumbnail of Therapie des metastasierten Kolonkarzinoms bei terminaler Niereninsuffizienz mit 5-FU, Folinsäure und Bevacizumab

Zeitschrift für Gastroenterologie, 2006

Research paper thumbnail of Group B Streptococcal �-Hemolysin Induces Nitric Oxide Production in Murine Macrophages

J Infec Dis, 2000

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. To examine the role of the GBS b-hemolysin in NO production, the murine macrophage line RAW 264.7 was exposed to a wild-type (WT) GBS isolate and to hyperhemolytic (HH) and nonhemolytic (NH) transposon mutants derived from that isolate. After activation of macrophages by the WT strain, the HH mutant, or cell-free extracts of b-hemolysin, nitrite release into the supernatant increased 110-fold and inducible NO synthase (iNOS) levels in cell lysates increased up to 10-fold compared with treatment with the NH mutant or extracts from that mutant. Hemolysin-induced NO production was dependent on protein tyrosine kinases and NF-kB, but not on extracellular signal-related kinase-1/2-mitogen-activated kinases or protein kinase A. These results indicate that GBS b-hemolysin induces murine macrophage iNOS via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Group B streptococcus (GBS; Streptococcus agalactiae) is the leading cause of pneumonia, meningitis, and septic shock in newborns, particularly those born prematurely [1]. All clinical isolates are encapsulated, and 98%-99% are b-hemolytic [2]. The GBS capsular polysaccharide contributes to virulence by virtue of its antiphagocytic property [3]. The GBS b-hemolysin, a potent membrane cytotoxin that injures lung epithelial [4] and endothelial [5] and brain endothelial [6] cells, may contribute to the pathogenesis of neonatal pneumonia and meningitis. Crude b-hemolysin preparations from GBS cultures induce cardiotoxicity and hypotension after intravenous administration to rabbits or rats, suggesting a role in septic shock [7]; however, the molecular mechanisms by which the GBS b-hemolysin may contribute to the pathogenesis of septic shock have not been delineated. The hypotension of septic shock is thought to be due in part to an excess production of nitric oxide (NO), as elevated NO levels are found in septic patients [8, 9]. Three isoforms of NO synthases (NOS) are present in mammals: the high-output in

Research paper thumbnail of Antibiotic prophylaxis after variceal hemorrhage reduces incidence of early rebleeding

Hepato-gastroenterology

This study aims to evaluate the role of new onset infection in the initiation of early rebleeding... more This study aims to evaluate the role of new onset infection in the initiation of early rebleeding after variceal hemorrhage in patients with liver cirrhosis and the effect of prophylactic antibiotic treatment. Two hundred and twenty-one consecutive admissions for variceal bleeding with no signs of infection at the time of admission were evaluated retrospectively. Systemic antibiotic prophylaxis was administered in 126 cases and significantly reduced the overall incidence of new onset infections (19.8% vs. 34.71%; p<0.01) and of early rebleeding (17.5% vs. 32.6%; p<0.01). Multivariate analysis showed strong correlation of rebleeding with new onset infection (p<0.001) and lack of prophylactic antibiotic treatment (p<0.05). Child-Pugh C cirrhosis, ventilatory assistance, and balloon tamponade were independent predictors of new onset infection (p<0.001, respectively). In the subgroup of patients with at least one predictor prophylactic treatment nearly halved the incidenc...

Research paper thumbnail of The Hepatic Microvascular Responses to Sepsis

Seminars in Thrombosis and Hemostasis, 2000

The liver is believed to play a major role in the initiation of multiorgan failure, the most leth... more The liver is believed to play a major role in the initiation of multiorgan failure, the most lethal complication in the clinical course of sepsis. Microbes and their virulence factors enter the hepatic circulation where they first activate sinusoidal endothelial cells and Kupffer cells to produce proinflammatory mediators, including TNF-alpha, IL-1, IL-6, reactive oxygen metabolites, and eicosanoids. These mediators cause not only microbial killing, but also structural and functional liver damage concerning mainly the parenchymal cells. Leukocytes are targeted to the liver sinusoids by chemoattractants and, like platelets, tether to the sinusoidal endothelial cells, which are in a procoagulant state of inflammatory activation. Clogging of the sinusoids by these cells leads to a decrease of blood flow through the sinusoids, which is further aggravated by endothelin-1 effectuating the constriction of hepatic stellate cells in the sinusoids. In contrast, both nitric oxide (NO) and carbon monoxide (CO) act as antagonists of endothelin-1 by mediating relaxation of sinusoidal vessels. By maintaining an adequate sinusoidal perfusion, both NO and CO are hepatoprotective during the early, hyperdynamic phase of sepsis characterized by an increased cardiac output and moderate peripheral vasodilation. However, during the late, hypodynamic phase of sepsis, massive overproduction of NO by the inducible NO synthase leads to circulatory collapse, which inevitably includes breakdown of the liver circulation.

Research paper thumbnail of New concepts of cellular fatty acid uptake: role of fatty acid transport proteins and of caveolae

Proceedings of the Nutrition Society, 2004

Efficient uptake and channelling of long-chain fatty acids (LCFA) are critical cell functions. Ev... more Efficient uptake and channelling of long-chain fatty acids (LCFA) are critical cell functions. Evidence is emerging that proteins are important mediators of LCFA-trafficking into cells and various proteins have been suggested to be involved in this process. Amongst these proteins is a family of membrane-associated proteins termed fatty acid transport proteins (FATP). So far six members of this family, designated FATP 1–6, have been characterized. FATP 1, 2 and 6 show a highly-conserved AMP-binding region that participates in the activation of very-long-chain fatty acids (VLCFA) to form their acyl-CoA derivatives. The mechanisms by which FATP mediate LCFA uptake are not well understood, but several studies provide evidence that uptake of LCFA across cellular membranes is closely linked to acyl-CoA synthetase activity. It is proposed that FATP indirectly enhance LCFA uptake by activating VLCFA to their CoA esters, which are required to maintain the typical structure of lipid rafts in ...

Research paper thumbnail of FAT/CD36-mediated Long-Chain Fatty Acid Uptake in Adipocytes Requires Plasma Membrane Rafts

Molecular Biology of the Cell, 2004

We previously reported that lipid rafts are involved in long-chain fatty acid (LCFA) uptake in 3T... more We previously reported that lipid rafts are involved in long-chain fatty acid (LCFA) uptake in 3T3-L1 adipocytes. The present data show that LCFA uptake does not depend on caveolae endocytosis because expression of a dominant negative mutant of dynamin had no effect on uptake of [3H]oleic acid, whereas it effectively prevented endocytosis of cholera toxin. Isolation of detergent-resistant membranes (DRMs) from 3T3-L1 cell homogenates revealed that FAT/CD36 was expressed in both DRMs and detergent-soluble membranes (DSMs), whereas FATP1 and FATP4 were present only in DSMs but not DRMs. Disruption of lipid rafts by cyclodextrin and specific inhibition of FAT/CD36 by sulfo-N-succinimidyl oleate (SSO) significantly decreased uptake of [3H]oleic acid, but simultaneous treatment had no additional or synergistic effects, suggesting that both treatments target the same mechanism. Indeed, subcellular fractionation demonstrated that plasma membrane fatty acid translocase (FAT/CD36) is exclusi...

Research paper thumbnail of Translocation of long chain fatty acids across the plasma membrane – lipid rafts and fatty acid transport proteins

Molecular and Cellular Biochemistry, 2006

Translocation of long chain fatty acids across the plasma membrane is achieved by a concert of co... more Translocation of long chain fatty acids across the plasma membrane is achieved by a concert of co-existing mechanisms. These lipids can passively diffuse, but transport can also be accelerated by certain membrane proteins as well as lipid rafts. Lipid rafts are dynamic assemblies of proteins and lipids, that float freely within the two dimensional matrix of the membrane bilayer. They are receiving increasing attention as devices that regulate membrane function in vivo and play an important role in membrane trafficking and signal transduction. In this review we will discuss how lipid rafts might be involved in the uptake process and how the candidate proteins for fatty acid uptake FAT/CD36 and the FATP proteins interact with these domains. We will also discuss the functional role of FATPs in general. To our understanding FATPs are indirectly involved in the translocation process across the plasma membrane by providing long chain fatty acid synthetase activity.

Research paper thumbnail of A new concept of cellular uptake and intracellular trafficking of long-chain fatty acids

Lipids, 2001

Fatty acids are the main structural and energy sources of the human body. Within the organism, th... more Fatty acids are the main structural and energy sources of the human body. Within the organism, they are presented to cells as fatty acid:albumin complexes. Dissociation from albumin represents the first step of the cellular uptake process, involving membrane proteins with high affinity for fatty acids, e.g., fatty acid translocase (FAT/CD 36) or the membrane fatty acid-binding protein (FABP pm). According to the thus created transmembrane concentration gradient, uncharged fatty acids can flip-flop from the outer leaflet across the phospholipid bilayer. At the cytosolic surface of the plasma membrane, fatty acids can associate with the cytosolic FABP (FABP c) or with caveolin-1. Caveolins are constituents of caveolae, which are proposed to serve as lipid delivery vehicles for subcellular organelles. It is not known whether protein (FABP c)-and lipid (caveolae)-mediated intracellular trafficking of fatty acids operates in conjunction or in parallel. Channeling fatty acids to the different metabolic pathways requires activation to acyl-CoA. For this process, the family of fatty acid transport proteins (FATP 1-5/6) might be relevant because they have been shown to possess acyl-CoA synthetase activity. Their variable Nterminal signaling sequences suggest that they might be targeted to specific organelles by anchoring in the phospholipid bilayer of the different subcellular membranes. At the highly conserved cytosolic AMP-binding site of FATP, fatty acids are activated to acyl-CoA for subsequent metabolic disposition by specific organelles. Overall, fatty acid uptake represents a continuous flow involving the following: dissociation from albumin by membrane proteins with high affinity for fatty acids; passive flip-flop across the phospholipid bilayer; binding to FABP c and caveolin-1 at the cytosolic plasma membrane; and intracellular trafficking via FABP c and/or caveolae to sites of metabolic disposition. The uptake process is terminated after activation to acyl-CoA by the members of the FATP family targeted intracellularly to different organelles.

Research paper thumbnail of Group B Streptococcal β‐Hemolysin Induces Nitric Oxide Production in Murine Macrophages

The Journal of Infectious Diseases, 2000

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. To examine the role of the GBS b-hemolysin in NO production, the murine macrophage line RAW 264.7 was exposed to a wild-type (WT) GBS isolate and to hyperhemolytic (HH) and nonhemolytic (NH) transposon mutants derived from that isolate. After activation of macrophages by the WT strain, the HH mutant, or cell-free extracts of b-hemolysin, nitrite release into the supernatant increased 110-fold and inducible NO synthase (iNOS) levels in cell lysates increased up to 10-fold compared with treatment with the NH mutant or extracts from that mutant. Hemolysin-induced NO production was dependent on protein tyrosine kinases and NF-kB, but not on extracellular signal-related kinase-1/2-mitogen-activated kinases or protein kinase A. These results indicate that GBS b-hemolysin induces murine macrophage iNOS via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Group B streptococcus (GBS; Streptococcus agalactiae) is the leading cause of pneumonia, meningitis, and septic shock in newborns, particularly those born prematurely [1]. All clinical isolates are encapsulated, and 98%-99% are b-hemolytic [2]. The GBS capsular polysaccharide contributes to virulence by virtue of its antiphagocytic property [3]. The GBS b-hemolysin, a potent membrane cytotoxin that injures lung epithelial [4] and endothelial [5] and brain endothelial [6] cells, may contribute to the pathogenesis of neonatal pneumonia and meningitis. Crude b-hemolysin preparations from GBS cultures induce cardiotoxicity and hypotension after intravenous administration to rabbits or rats, suggesting a role in septic shock [7]; however, the molecular mechanisms by which the GBS b-hemolysin may contribute to the pathogenesis of septic shock have not been delineated. The hypotension of septic shock is thought to be due in part to an excess production of nitric oxide (NO), as elevated NO levels are found in septic patients [8, 9]. Three isoforms of NO synthases (NOS) are present in mammals: the high-output in

Research paper thumbnail of Group B Streptococcal β‐Hemolysin Induces Mortality and Liver Injury in Experimental Sepsis

The Journal of Infectious Diseases, 2002

New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) sero... more New Zealand White rabbits were challenged with the wild-type (wt) group B streptococci (GBS) serotype III strain (COH1) and its isogenic nonhemolytic (NH) and hyperhemolytic (HH) mutants. Mortality differed significantly between rabbits infected with the HH mutant IN40 (67%), compared with rabbits infected with the wt COH1 strain (27%) and the NH strains COH1-20 and COH1:cyl EDcat (13% and 0%, respectively; P , :05). Histopathologically, disseminated septic microabscesses surrounded by necrotic foci were found exclusively in the livers of HH mutant IN40-infected animals. Serum transaminase levels were 20-fold higher in the HH-infected group, compared with rabbits infected with the other strains. Positive TUNEL (in situ terminal deoxynucleotide transferase-mediated dUTP nick end labeling) staining and activation of caspase-3 in hepatocytes were more frequent in HH-infected than in wt-infected animals and absent in the NH mutant COH1-20-infected group, indicating that GBS b-hemolysin triggers apoptotic pathways in hepatocytes. This work provides the first evidence that GBS b-hemolysin plays a crucial role in the pathophysiology of GBS sepsis by inducing liver failure and high mortality.

Research paper thumbnail of Synergistic Action of Nitric Oxide Release from Murine Macrophages Caused by Group B Streptococcal Cell Wall and β‐Hemolysin/Cytolysin

The Journal of Infectious Diseases, 2002

Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release... more Group B streptococcus (GBS) is the leading cause of sepsis in neonates. Nitric oxide (NO) release plays a role in the hypotension that characterizes septic shock. It has been shown that GBS b-hemolysin/cytolysin (b-h/c) stimulates the transcription of inducible NO synthase (iNOS) in murine macrophages via intracellular pathways similar to those that mediate lipopolysaccharide-induced iNOS activation. Here, it is demonstrated that the GBS cell wall and b-h/c act synergistically to induce iNOS in interferon (IFN)-a-primed RAW 264.7 murine macrophages. In nonprimed macrophages, combined activation by the GBS cell wall plus bh/c is necessary to induce an NO response, which indicates that both virulence factors cooperate to substitute for the priming signal typically provided by IFN-a. Group B streptococcus (GBS) is the leading cause of pneumonia, meningitis, and septic shock in newborns, particularly those born prematurely. All clinical isolates are encapsulated, and 98%-99% are b-hemolytic [1]. GBS b-hemolytic activity is mediated by a pore-forming cytotoxin, the genetic basis of which has recently been elucidated [2]. In vitro, the GBS b-hemolysin/cytolysin (b-h/c) is associated with injury to lung epithelial, lung endothelial, and brain endothelial cells and is thus speculated to contribute to GBS penetration of host cellular barriers. Very recently, we reported that b-h/c is responsible for high mortality and liver injury in a rabbit model of GBS septic shock [3]. The hypotension of septic shock is thought to be due, in part, to an excess production of nitric oxide (NO), because elevated NO levels are found in patients with sepsis. Three isoforms of NO synthases (NOS) are present in mammals, the high-output inducible NOS (iNOS) and 2 constitutive isoforms, one originally identified in neurons and the other in endothelial cells. Activated macrophages constitute a major source of NO production. The inflammatory activation of macrophages is thought to involve 2 sequential steps, priming and triggering [4]. Priming is initiated by binding of interferon (IFN)-a to its specific receptor, which results in a number of biochemical and functional alterations that render the macrophages sensitive to triggering agents such as proinflammatory cytokines, lipopolysaccharide (LPS) [4],

Research paper thumbnail of Uptake of long-chain fatty acids in HEPG2 cells involves caveolin-1

Journal of Hepatology, 2001

We investigated the role of caveolae in uptake and intracellular trafficking of long chain fatty ... more We investigated the role of caveolae in uptake and intracellular trafficking of long chain fatty acids (LCFA) in HepG2 human hepatoma cells. The uptake of [(3)H]oleic acid and [(3)H]stearic acid into HepG2 cells was measured by radioactive assays and internalization of the non-metabolizable fluorescent fatty acid 12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino] (12-NBD) stearate into single HepG2 cells was semi-quantitatively assessed by laser scanning microscopy. The initial rate of [(3)H]oleic acid uptake (V(0)) in HepG2 cells exhibited saturable transport kinetics with increasing concentrations of free oleic acid (V(max) 854 +/- 46 pmol mg protein(-1) min(-1), K(m) 100 +/- 14 nmol/l). While inhibition of clathrin coated pits did not influence LCFA uptake in HepG2, inhibition of caveolae formation by filipin III, cyclodextrin, and caveolin-1 antisense oligonucleotides resulted in reduction of [(3)H]oleic acid uptake by 54%, 45%, and 23%, respectively. Furthermore, filipin III inhibited the uptake of [(3)H]stearic acid and its fluorescent derivative 12-NBD stearate by 44% and 50%, respectively. Transfection studies with alpha-caveolin-1/cyanofluorescent protein chimeras showed significant colocalization of caveolae and internalized 12-NBD stearate. In conclusion, these data suggest a significant role for caveolae mediated uptake and intracellular trafficking of LCFA in HepG2 cells.

Research paper thumbnail of The role of dominant stenoses in bacterial infections of bile ducts in primary sclerosing cholangitis

European Journal of Gastroenterology & Hepatology, 2006

Objective Primary sclerosing cholangitis (PSC) is characterized by progressive fibrotic inflammat... more Objective Primary sclerosing cholangitis (PSC) is characterized by progressive fibrotic inflammation and strictures of the biliary system. We studied the role of dominant stenoses in bacterial biliary infections and the effect of routine antibiotic administration with cholangiography. Design A prospective clinical trial without blinding or randomization. Setting The endoscopy unit in a university hospital. Participants Fifty patients with PSC entered and finished the study.

Research paper thumbnail of Long-Chain Fatty Acid Uptake into Adipocytes Depends on Lipid Raft Function

Biochemistry, 2004

This study investigates the role of lipid rafts and caveolae, a subclass of lipid raft microdomai... more This study investigates the role of lipid rafts and caveolae, a subclass of lipid raft microdomains, in the binding and uptake of long-chain fatty acids (LCFA) by 3T3-L1 cells during differentiation. Disruption of lipid rafts by beta-cyclodextrin (betaCD) or selective inhibition of caveolae by overexpression of a dominant-negative mutant of caveolin-3 (Cav(DGV)) resulted in disassembly of caveolae structures at the cell surface, as assessed by electron microscopy. While in 3T3-L1 fibroblasts, which express few caveolae, Cav(DGV) or betaCD had no effect on LCFA uptake, in 3T3-L1 adipocytes the same treatments decreased the level of [(3)H]oleic acid uptake by up to 55 +/- 8 and 49 +/- 7%, respectively. In contrast, cholesterol loading of 3T3-L1 adipocytes resulted in a 4-fold increase in the extent of caveolin-1 expression and a 1.7-fold increase in the level of LCFA uptake. Both the inhibitory and enhancing effects of these treatments were constantly increasing with the [(3)H]oleic acid incubation time up to 5 min. Incubation of 3T3-L1 adipocytes with [(3)H]stearate followed by isolation of a caveolin-1 positive detergent-resistant membrane (DRM) fraction revealed that [(3)H]stearate binds to caveolae. Fatty acid translocase (FAT/CD36) was found to be present in this DRM fraction as well. Our data thus strongly indicate a critical involvement of lipid rafts in the binding and uptake of LCFA into 3T3-L1 adipocytes. Furthermore, our findings suggest that caveolae play a pivotal role in lipid raft-dependent LCFA uptake. This transport mechanism is induced in conjunction with cell differentiation and might be mediated by FAT/CD36.

Research paper thumbnail of Caveolin-1 is required for fatty acid translocase (FAT/CD36) localization and function at the plasma membrane of mouse embryonic fibroblasts

Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2006

Several lines of evidence suggest that lipid rafts are involved in cellular fatty acid uptake and... more Several lines of evidence suggest that lipid rafts are involved in cellular fatty acid uptake and influence fatty acid translocase (FAT/CD36) function. However, it remains unknown whether caveolae, a specialized raft type, are required for this mechanism. Here, we show that wild-type (WT) mouse embryonic fibroblasts (MEFs) and caveolin-1 knockout (KO) MEFs, which are devoid of caveolae, have comparable overall expression of FAT/CD36 protein but altered subcellular FAT/CD36 localization and function. In WT MEFs, FAT/CD36 was isolated with both lipid raft enriched detergent-resistant membranes (DRMs) and detergent-soluble membranes (DSMs), whereas in cav-1 KO cells it was exclusively associated with DSMs. Subcellular fractionation demonstrated that FAT/CD36 in WT MEFs was localized intracellularly and at the plasma membrane level while in cav-1 KO MEFs it was absent from the plasma membrane. This mistargeting of FAT/CD36 in cav-1 KO cells resulted in reduced fatty acid uptake compared to WT controls. Adenoviral expression of caveolin-1 in KO MEFs induced caveolae formation, redirection of FAT/CD36 to the plasma membrane and rescue of fatty acid uptake. In conclusion, our data provide evidence that caveolin-1 is necessary to target FAT/CD36 to the plasma membrane. Caveolin-1 may influence fatty acid uptake by regulating surface availability of FAT/CD36.

Research paper thumbnail of Role of FATP in parenchymal cell fatty acid uptake

Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2004

Long-chain fatty acids (LCFAs) represent key metabolites for energy generation and storage. Trans... more Long-chain fatty acids (LCFAs) represent key metabolites for energy generation and storage. Transport and metabolism of LCFA are believed to be regulated by membrane-associated proteins that bind and transport LCFA. Identifying the postulated fatty acid transporters is of considerable interest since altered fatty acid uptake has been implicated in disease such as insulin resistance and obesity. Recently, a family of membrane associated proteins, termed fatty acid transport proteins (FATPs), have been described that enhance uptake of LCFAs. Until today, six members of this family, designated FATP1-6, have been characterized. This review will focus on FATP structure, expression patterns, regulation, mechanism of transport and clinical implications.