Expression of human lecithin:cholesterol acyltransferase in transgenic mice: effects on cholesterol efflux, esterification, and transport

161

Tissue arachidonic acid (AA) pools originate from the diet, and from hepatic and extrahepatic desaturationelongation of dietary linoleic acid (LA). This review summarizes the roles of absorption, transport, and formation of AA in the buildup of tissue AA pools. In humans who ingest 0.2-0.3 g of AA and 10-20 g of LA per day on a Western diet, the formation of AA from LA exceeds the dietary supply of AA. A number of factors favor the partitioning of AA to tissue phospholipids rather than adipose tissue and plasma triglycerides. The characteristics of AA transport with lipoproteins are discussed with focus on the role of lipoprotein lipase, lecithin:cholesterol acyltransferase, hepatic lipase, and the scavenger receptor BI and LDL receptors in tissue uptake of AA. Liver-derived 2-acyl-lysophosphatidylcholine and plasma free AA are two important sources of AA for extrahepatic tissues which exhibit a low rate of uptake of lipoprotein AA. Desaturation-elongation of LA to produce AA occurs both in liver and in extrahepatic tissues, plasma free LA being an important substrate particularly during fasting. The AA preference of the reacylation and transacylation reactions is crucial for the selective retention of AA in phospholipids. -Zhou, L., and Å. Nilsson. Sources of eicosanoid precursor fatty acid pools in tissues.

Section: Transport By Liver-derived Lipoproteinsmentioning

confidence: 99%

Sources of eicosanoid precursor fatty acid pools in tissues

Zhou

Nilsson

2001

161

“…To isolate lipoproteins from plasma, 400 l of pooled plasma containing 1.5 m m 5,5 Ј -dithio-bis(2-nitrobenzoic acid) (DTNB) from HuAITg, HuAICETPTg, HuAILCATTg, and HuAILCAT-CETPTg mice on a chow diet was fractionated using two tandem Superose 6 columns (Pharmacia, LKB Biotechnology, Piscataway, NJ) as previously described (5). Cholesterol was determined enzymatically as described above while human apoA-I was determined by ELISA.…”

Section: Plasma Lipids and Lipoprotein Analysismentioning

confidence: 99%

“…Plasma levels of apoA-I and CETP levels were determined by enzyme-linked immunosorbent assays as described previously (5,22).…”

Section: Plasma Lipids and Lipoprotein Analysismentioning

confidence: 99%

“…Mice normally lack CETP activity in plasma and when a human CETP transgene is introduced there is a lowering of plasma HDL levels, associated with increased catabolism of HDL CE due to enhanced clearance by the liver (4). Conversely, overexpression of the human LCAT transgene leads to an increase in HDL CE (5) and a decrease in the fractional clearance of HDL CE by the liver (6). Effects of human LCAT and human CETP transgenes on HDL CE are much greater on a background of human apoA-I transgene expression (4,7).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Remodeling of HDL by CETP in vivo and by CETP and hepatic lipase in vitro results in enhanced uptake of HDL CE by cells expressing scavenger receptor B-I

Collet

Tall

Serajuddin

et al. 1999

114

The transport of HDL cholesteryl esters (CE) from plasma to the liver involves a direct uptake pathway, mediated by hepatic scavenger receptor B-I (SR-BI), and an indirect pathway, involving the exchange of HDL CE for triglycerides (TG) of TG-rich lipoproteins by cholesteryl ester transfer protein (CETP). We carried out HDL CE turnover studies in mice expressing human CETP and/or human lecithin:cholesterol acyltransferase (LCAT) transgenes on a background of human apoA-I expression. The fractional clearance of HDL CE by the liver was delayed by LCAT transgene, while the CETP transgene increased it. However, there was no incremental transfer of HDL CE radioactivity to the TG-rich lipoprotein fraction in mice expressing CETP, suggesting increased direct removal of HDL CE in the liver. To evaluate the possibility that this might be mediated by SR-BI, HDL isolated from plasma of the different groups of transgenic mice was incubated with SR-BI transfected or control CHO cells. HDL isolated from mice expressing CETP showed a 2-to 4-fold increase in SR-BImediated HDL CE uptake, compared to HDL from mice lacking CETP. The addition of pure CETP to HDL in cell culture did not lead to increased selective uptake of HDL CE by cells. However, when human HDL was enriched with TG by incubation with TG-rich lipoproteins in the presence of CETP, then treated with hepatic lipase, there was a significant enhancement of HDL CE uptake. Thus, the remodeling of human HDL by CETP, involving CE-TG interchange, followed by the action of hepatic lipase (HL), leads to the enhanced uptake of HDL CE by cellular SR-BI. These observations suggest that in animals such as humans in which both the selective uptake and CETP pathways are active, the two pathways could operate in a synergistic fashion to enhance reverse cholesterol transport. -Collet, X., A. R. Tall, H. Serajuddin, K. Guendouzi, L. Royer, H. Oliveira, R. Barbaras, X-c. Jiang, and O. L. Francone. Remodeling of HDL by CETP in vivo and by CETP and hepatic lipase in vitro results in enhanced uptake of HDL CE by cells expressing scavenger receptor B-I.

“…The physiological consequences of the esterification of cholesterol by LCAT are profound and illustrated by the biochemical and clinical characteristics of patients with either partial or total deficiency in LCAT (5). In addition, the expression of human LCAT in transgenic animals has provided further evidence for its role in plasma cholesterol homeostasis (6)(7)(8), reverse cholesterol transport (9), and atherosclerosis (10).…”

mentioning

confidence: 99%

Binding and functional effects of transcription factors Sp1 and Sp3 on the proximal human lecithin:cholesterol acyltransferase promoter

Hoppe

Francone

1998

Human lecithin:cholesterol acyltransferase (LCAT) circulates in plasma bound to high density lipoproteins (HDL) and modulates the rate by which cholesteryl ester is transported to the liver. So far, little is known about the regulation of the expression of the LCAT gene. In this study we have defined the cis -elements, identified the trans -acting factors and demonstrated their functional effects and significance in determining transcriptional activity of the proximal LCAT promoter. Using deletion mutants having 5 variable ends (from nucleotides ؊ 72 to ؊ 27), we have identified the presence of two non-consensus GC-rich regions that stimulate transcription in HepG2 and HeLa cells. These regions designated sites A ( ؊ 29 to ؊ 47) and B ( ؊ 49 to ؊ 65) contain the CCTCC core sequence which in electromobility shift analysis is critical for the formation of two DNA-protein complexes designated I and II. Site-directed mutagenesis suggests that both sites are equally important in promoter activity, and that cooperative interactions between both sites are not required for activity. Electromobility shift and supershift experiments using oligonucleotides spanning sites A and B identified Sp1 and Sp3 as the transcription factors interacting at these sites. To determine the significance and functional effects that Sp1 and Sp3 have in regulating LCAT promoter activity, we performed transfection experiments in Drosophila SL-2 cells as they lack endogenous Sp1 and Sp3. Sp1 but not Sp3 activates the human LCAT promoter and when Sp1 is co-transfected along with Sp3, Sp3 functions as a dose-dependent repressor of Sp1mediated activation. These findings indicate that Sp1 is capable of trans -activating a reporter gene linked to the LCAT promoter containing Sp binding sites and suggests that the levels of Sp3 or the nuclear Sp1/Sp3 ratio may play an important role in determining the transcriptional activity of the LCAT promoter in vivo.-Hoppe, K. L., and O. L. Francone. Binding and functional effects of transcription factors Sp1 and Sp3 on the proximal human lecithin: cholesterol acyltransferase promoter.