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Biomedical subjects

Ruth McPherson

Publications and source records attributed to Ruth McPherson.

30 records · Page 2Linked to original sources
PubMed2004

Severe hypoalphalipoproteinemia in mice expressing human hepatic lipase deficient in binding to heparan sulfate proteoglycan.

Unlike human hepatic lipase (hHL) that is mainly cell surface-anchored via binding to heparan sulfate proteoglycans (HSPG), mouse HL (mHL) has a low affinity to HSPG and thus is largely blood-borne. The reduced HSPG binding of mHL is attributable to the C-terminal amino acids. To determine the functions of HSPG binding of hHL in vivo, we created adenovirus vectors encoding hHL or a chimeric protein (designated hHLmt) in which the C-terminal HSPG-binding sequences were replaced with the corresponding mouse sequences. Injecting hHLmt-expressing virus into C57BL/6J mice (1.8 x 10(10) virus particles/mouse) resulted in a 3-fold increase in pre-heparin HL activity, whereas infection with an identical dose of hHL virus did not change pre-heparin HL activity. In hHLmt-expressing mice, the concentration of total cholesterol and phospholipids was inversely related to the hHL activity in pre-heparin plasma in a dose- and time-dependent manner, and the decrease was mainly attributable to high density lipoproteins (HDL) cholesterol and HDL phospholipids. The expression of hHL exhibited no change in plasma total cholesterol or phospholipid levels as compared with control mice infected with luciferase or injected with saline. The reduced HDL lipids in the hHLmt-expressing mice were accompanied by markedly decreased plasma and hepatic apolipoprotein (apo) A-I. In primary hepatocytes isolated from hHLmt-expressing mice, the concentration of cell-associated and secreted apoA-I was decreased by 2-3-fold as compared with hepatocytes isolated from control mice, whereas the levels of apoB and apoE were unaltered. Infection of primary hepatocytes with hHLmt virus ex vivo also resulted in reduced apoA-I secretion but had no effect on cell-associated apoA-I. These results suggest that expression of HSPG binding-deficient hHL has a profound HDL-lowering effect.

Adenoviridae↗
PubMed2004

Role of cholesteryl ester transfer protein in selective uptake of high density lipoprotein cholesteryl esters by adipocytes.

Previous reports attributed cholesteryl ester transfer protein (CETP)-mediated HDL cholesteryl ester (CE) selective uptake to the CETP-mediated transfer of CE from HDL to newly secreted apolipoprotein B-containing lipoproteins, which are then internalized by the LDL receptor (LDL-R). CETP has also been implicated in the remodeling of HDL, which renders it a better substrate for selective uptake by scavenger receptor class B type I (SR-BI). However, CETP-mediated selective uptake of HDL3-derived CE was not diminished in LDL-R null adipocytes, SR-BI null adipocytes, or in the presence of the receptor-associated protein. We found that monensin treatment or energy depletion of the SW872 liposarcoma cells with 2-deoxyglucose and NaN3 had no effect on CETP-mediated selective uptake, demonstrating that endocytosis is not required. This is supported by data indicating that CETP transfers CE into a compartment from which it can be extracted by unlabeled HDL. CETP could also mediate the selective uptake of HDL3-derived triacylglycerol (TG) and phospholipid (PL). The CETP-specific kinetics for TG and CE uptake were similar, and both reached saturation at approximately 5 microg/ml HDL. In contrast, CETP-specific PL uptake did not attain saturation at 5 microg/ml HDL and was approximately 6-fold greater than the uptake of CE. We propose two possible mechanisms to account for the role of CETP in selective uptake.

Adipocytes↗
PubMed2004

A novel efflux-recapture process underlies the mechanism of high-density lipoprotein cholesteryl ester-selective uptake mediated by the low-density lipoprotein receptor-related protein.

OBJECTIVE: To determine the mechanism of low-density lipoprotein (LDL) receptor-related protein (LRP)-mediated selective uptake of high-density lipoprotein (HDL)-derived cholesteryl esters (CE). METHODS AND RESULTS: Apolipoprotein E (apoE) and heparin sulfate proteoglycans are required for LRP-mediated selective uptake in adipocytes. Furthermore, 2-deoxyglucose and NaN(3) abolish this process, indicating that cellular energy is required. LRP-mediated selective uptake is also abolished by monensin or when clathrin-mediated internalization is inhibited (using hypotonic, K(+)-free medium or hyperosmolar sucrose), clearly implicating receptor endocytosis. The receptor-associated protein (RAP), an inhibitor of ligand binding to LRP, reduced the transport of CE into an intracellular compartment but not into the plasma membrane. Remarkably, the CE that is ultimately transported by LRP first enters the plasma membrane then undergoes apoE-mediated CE efflux before being recaptured and internalized by LRP. CONCLUSIONS: According to this "efflux-recapture" model, LRP contributes to selective uptake because it recovers CE that would normally be lost by efflux mediated by apoE. In adipocytes, the LDL receptor-related protein contributes to selective uptake when it recaptures and internalizes HDL-derived cholesteryl esters that are otherwise lost by apoE-mediated efflux. This novel "efflux-recapture" process explains some conflicting observations of selective uptake and underscores the bi-directional nature of efflux.

Adipocytes↗
PubMed2004

Molecular regulation of SREBP function: the Insig-SCAP connection and isoform-specific modulation of lipid synthesis.

Sterol regulatory element binding proteins (SREBPs) are a family of membrane-bound transcription factors that play a unique and fundamental role in both cholesterol and fatty acid metabolism, relevant to human disease. There are three SREBPs that regulate the expression of over 30 genes. SREBPs are subject to regulation at three levels: proteolytic cleavage, rapid degradation by the ubiquitin-proteasome pathway, and sumoylation. Recently, there have been exciting advances in our understanding of the molecular mechanism of SREBP trafficking and processing with new information on the role of insulin-induced genes and the differential role and regulation of SREBP-1c and -2, which may ultimately lead to novel strategies for the treatment of dyslipidemia and insulin resistance.

Animals↗
PubMed2003

Secretory vesicular transport from the Golgi is altered during ATP-binding cassette protein A1 (ABCA1)-mediated cholesterol efflux.

Apolipoprotein AI (apoAI)-mediated cholesterol efflux is a process by which cells export excess cellular cholesterol to apoAI to form high density lipoprotein. ATP-binding cassette protein A1 (ABCA1) has recently been identified as the key regulator of this process. The pathways of intracellular cholesterol transport during efflux are largely unknown nor is the molecular mechanism by which ABCA1 governs cholesterol efflux well understood. Here, we report that, in both macrophages and fibroblasts, the secretory vesicular transport changes in response to apoAI-mediated cholesterol efflux. Vesicular transport from the Golgi to the plasma membrane increased 2-fold during efflux. This increase in vesicular transport during efflux was observed in both raft-poor and raft-rich vesicle populations originated from the Golgi. Importantly, enhanced vesicular transport in response to apoAI is absent in Tangier fibroblasts, a cell type with deficient cholesterol efflux due to functional ABCA1 mutations. These findings are consistent with an efflux model whereby cholesterol is transported from the storage site to the plasma membrane via the Golgi. ABCA1 may influence cholesterol efflux in part by enhancing vesicular trafficking from the Golgi to the plasma membrane.

ATP Binding Cassette Transporter 1↗
PubMed2003

Adipocyte low density lipoprotein receptor-related protein gene expression and function is regulated by peroxisome proliferator-activated receptor gamma.

The alpha(2)-macroglobulin receptor/low density lipoprotein receptor-related protein (LRP) is a large multifunctional receptor that interacts with a variety of molecules. It is implicated in biologically important processes such as lipoprotein metabolism, neurological function, tissue remodeling, protease complex clearance, and cell signal transduction. However, the regulation of LRP gene expression remains largely unknown. In this study, we have analyzed 2 kb of the 5'-flanking region of the LRP gene and identified a predicted peroxisome proliferator response element (PPRE) from -1185 to -1173. Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands such as fatty acids and rosiglitazone increased functional cell surface LRP by 1.5-2.0-fold in primary human adipocytes and in the SW872 human liposarcoma cell line as assessed by activated alpha(2)-macroglobulin binding and degradation. These agents were found to increase LRP transcription. Gel shift analysis of the putative PPRE demonstrated direct binding of PPARgamma/retinoid X receptor alpha heterodimers to the PPRE in the LRP gene. Furthermore, these heterodimers could no longer interact with a mutated PPRE probe. The isolated promoter was functional in SW872 cells, and its activity was increased by 1.5-fold with the addition of rosiglitazone. Furthermore, the isolated response element was similarly responsive to rosiglitazone when placed upstream of an ideal promoter. Mutagenesis of the predicted PPRE abolished the ability of this construct to respond to rosiglitazone. These data demonstrate that fatty acids and rosiglitazone directly stimulate transcription of the LRP gene through activation of PPARgamma and increase functional LRP expression.

Adipocytes↗
PubMed2003

Comparative effects of rosuvastatin and atorvastatin across their dose ranges in patients with hypercholesterolemia and without active arterial disease.

The lipid-lowering effects of rosuvastatin and atorvastatin were determined across their dose ranges in a 6-week, randomized, double-blind trial. Three hundred seventy-four hypercholesterolemic patients with fasting low-density lipoprotein (LDL) cholesterol > or =160 but <250 mg/dl (> or =4.14 but <6.47 mmol/L) and fasting triglycerides <400 mg/dl (<4.52 mmol/L) and without active arterial disease within 3 months of entry received once-daily rosuvastatin (5, 10, 20, 40, or 80 mg [n = 209]) or atorvastatin (10, 20, 40, or 80 mg [n = 165]). The percentage decrease in plasma LDL cholesterol versus dose was log-linear for each drug, ranging from -46.6% to -61.9% for rosuvastatin 10 and 80 mg, compared with -38.2% to -53.5% for atorvastatin 10 and 80 mg. The dose curve for rosuvastatin yielded an 8.4% greater decrease in LDL cholesterol compared with atorvastatin at any given dose (p <0.001). Similarly greater decreases were observed for rosuvastatin across the dose range in total cholesterol (-4.9%), non-high-density lipoprotein (non-HDL) cholesterol (-7.0%), apolipoprotein B (-6.3%), and related ratios versus atorvastatin (all p <0.001). Because dose responses for HDL cholesterol, triglycerides, and apolipoprotein A-I were non-log-linear and nonparallel between the 2 drugs, percentage changes from baseline were compared at each dose. Significantly greater increases for rosuvastatin compared with atorvastatin were observed for HDL cholesterol at 40 and 80 mg, and for apolipoprotein A-I at 80 mg. Significantly greater triglyceride decreases were seen at 80 mg with atorvastatin over rosuvastatin. Both rosuvastatin and atorvastatin were well tolerated over 6 weeks.

Anticholesteremic Agents↗
PubMed2003

Statin therapy and the management of acute coronary syndromes.

The pathophysiology of acute coronary syndromes is related to erosion or rupture of vulnerable plaque leading to intracoronary thrombosis as a result of activation of the coagulation cascade and platelet aggregation. Potential benefit of hypolipidemic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition may be related to the pleiotropic effects such as endothelial function improvement, stabilization of the plaque in relation to reduced macrophage activity and smooth muscle cell proliferation, as well as other anti-inflammatory effects that have been demonstrated in animal models. With the publication of the Myocardial Ischemia Reduction with Aggressive Cholesterol Lowering (MIRACL) study, early initiation of statin therapy within 24 to 96 h has been recognized as an important addition to the therapeutic armamentarium in the management of patients with acute coronary syndromes.

Acute Disease↗
PubMed2002

Decreased mitochondrial proton leak and reduced expression of uncoupling protein 3 in skeletal muscle of obese diet-resistant women.

Weight loss in response to caloric restriction is variable. Because skeletal muscle mitochondrial proton leak may account for a large proportion of resting metabolic rate, we compared proton leak in diet-resistant and diet-responsive overweight women and compared the expression and gene characteristics of uncoupling protein (UCP)2 and UCP3. Of 1,129 overweight women who completed the University of Ottawa Weight Management Clinic program, 353 met compliance criteria and were free of medical conditions that could affect weight loss. Subjects were ranked according to percent body weight loss during the first 6 weeks of a 900-kcal meal replacement protocol. The highest and lowest quintiles of weight loss were defined as diet responsive and diet resistant, respectively. After body weight had been stable for at least 10 weeks, 12 of 70 subjects from each group consented to muscle biopsy and blood sampling for determinations of proton leak, UCP mRNA expression, and genetic studies. Despite similar baseline weight and age, weight loss was 43% greater, mitochondrial proton leak-dependent (state 4) respiration was 51% higher (P = 0.0062), and expression of UCP3 mRNA abundance was 25% greater (P < 0.001) in diet-responsive than in diet-resistant subjects. There were no differences in UCP2 mRNA abundance. None of the known polymorphisms in UCP3 or its 5' flanking sequence were associated with weight loss or UCP3 mRNA abundance. Thus, proton leak and the expression of UCP3 correlate with weight loss success and may be candidates for pharmacological regulation of fat oxidation in obese diet-resistant subjects.

Body Weight↗