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At least 307 records · Page 17Linked to original sources
PubMed1995

Lipopolysaccharide regulation of lipoprotein lipase expression in murine macrophages.

The enzyme lipoprotein lipase is expressed in a number of cell types and plays a central role in lipid metabolism. Multiple factors regulate its expression in a tissue-specific manner. In murine macrophages, lipopolysaccharide inhibits lipoprotein lipase enzyme activity. The current work examines this process in the established J774 macrophage line and primary peritoneal macrophages from endotoxin-sensitive (C3HeB/Fej) and endotoxin-resistant (C3H/Hej) murine strains. Lipopolysaccharide inhibition of macrophage lipoprotein lipase occurred at the enzyme and mRNA levels in a time- and concentration-dependent manner. Cells from endotoxin-resistant animals maintained their expression of lipoprotein lipase following treatment with lipopolysaccharide. Results of gel retention assays showed that lipopolysaccharide treatment of the J774 macrophages altered the level of nuclear proteins recognizing and binding the lipoprotein lipase promoter DNA. Nuclear extracts from resting J774 cells contained proteins which bound specifically to the octamer motif and to the CAAT box within the lipoprotein lipase promoter. Exposure of the J774 cells to lipopolysaccharide for 16 h increased the level of protein-octamer DNA complexes. Similar responses were obtained in endotoxin-sensitive, but not endotoxin-resistant, primary macrophages following in vitro treatment with lipopolysaccharide. This finding suggests that transcriptional events may contribute to the lipopolysaccharide regulation of macrophage lipoprotein lipase expression.

Animals↗
PubMed1992

Regulation of expression of the lipoprotein lipase gene in brown adipose tissue.

The regulation of lipoprotein lipase gene expression in brown adipose tissue was studied. Rats were preacclimated to 21 degrees C. Exposure to cold (4 degrees C) resulted in a rapid increase in the level of lipoprotein lipase mRNA in the tissue. The level peaked (expressed per microgram total RNA) after approximately 8 h and then slowly declined. The increased lipoprotein lipase mRNA level was not due to an increased stability of the mRNA, but, in a transition event from a high to a low expression of the lipoprotein lipase gene, a transcription-dependent process was recruited that accelerated the breakdown of lipoprotein lipase mRNA. Norepinephrine injections increased lipoprotein lipase mRNA levels in the tissue; this effect was mediated via a beta-adrenergic receptor. The effect of cold could be mimicked by norepinephrine injections, and these two effects were not additive, indicating that the cold effect was mediated by norepinephrine. The lipoprotein lipase mRNA level was also increased by insulin injections (into fasted animals); thus an increase in lipoprotein lipase gene expression in brown adipose tissue may be induced via two different stimuli, which, intracellularly, would be mediated via different signaling systems. In all investigated conditions, the changes in lipoprotein lipase mRNA levels observed here were parallelled by alterations in lipoprotein lipase activity reported earlier from this laboratory. It was therefore concluded that, under the conditions studied, lipoprotein lipase activity in brown adipose tissue was primarily regulated at the transcriptional level.

Adipose Tissue, Brown↗
PubMed1982

Purification and properties of lipoprotein lipase in guinea pig milk.

Lipoprotein lipase was purified from guinea pig milk by chromatography on heparin-Sepharose followed by chromatography on an immobilized preparation of heparin that had been N-desulphated and then acetylated. This second step was necessary to separate a plasma protein, presumably antithrombin, from the lipase. The guinea pig enzyme turned out to be quite similar to lipoprotein lipase from bovine milk with respect to composition and molecular size. Furthermore, the specific activities and the dose-response relations for activation by apolipoprotein C-II were quite similar for the two enzymes. Antibodies raised against the guinea pig milk enzyme inhibited not only this enzyme but also the lipoprotein lipase activity in post-heparin plasma and in homogenates from adipose tissue and heart.

Amino Acids↗
PubMed1981

Heparin-releasable and nonreleasable lipoprotein lipase in the perfused rat heart.

Lipoprotein lipase released from the rat heart during a 30-s perfusion with heparin was compared to the lipase remaining in the heart tissue. The perfusate, containing the heparin-releasable enzyme, as well as the heart tissue extract ("residue"), was purified on heparin-Sepharose affinity columns. Both purified fractions showed pronounced inhibition by 1 M NaCl and by antiserum to heart lipoprotein lipase, thus displaying mainly lipoprotein lipase activities. However, their apparent Km values for triglyceride differed significantly (perfusate, 0.4 mM; residue, 4.0 mM). Also, the pattern of the immunotitration curves for the two fractions differed, the perfusate being more susceptible to antibody inhibition than the residue. Addition of heparin (0.5 unit/ml) inhibited the perfusate activity up to 60%, whereas the residual activity was actually stimulated by 15%. Based on these findings, we propose that the heart tissue contains a less active, low affinity enzyme form, possibly representing the precursor of the high affinity, functional, endothelial-bound lipoprotein lipase.

Animals↗
PubMed1992

Adipose cell size and distribution in familial lipoprotein lipase deficiency.

To determine the effect of lipoprotein lipase deficiency on the size distribution of fat cell populations in human adipose tissues, abdominal and femoral subcutaneous fat tissue biopsies were obtained from seven patients affected by familial hyperchylomicronaemia. These patients were characterized by massive accumulation of chylomicrons in the fasting state due to defective catabolism of plasma triglyceride-rich lipoproteins. They had no post-heparin plasma lipoprotein lipase activity and their fat tissues were deficient in lipoprotein lipase activity. The size distribution of adipocytes examined by scanning electron microscopy were similar to distributions observed in control subjects. Patient fat cell diameters were not statistically different from control fat cells obtained from subjects of similar body mass index. Mature fat cells contributed to 99% of the total fat tissue mass in lipoprotein lipase deficiency. Normal adiposity in lipoprotein lipase deficiency can thus be attributed to mature adipocytes and not to hyperplastic growth of immature fat cells. It is concluded that normal adipose tissue homeostasis is maintained in these patients in spite of the deficiency in lipoprotein lipase activity.

Adipose Tissue↗
PubMed1981

Combined deficiency of apolipoprotein C-II and lipoprotein lipase in familial hyperchylomicronemia.

The underlying pathophysiological defect was studied in four siblings with familial hyperchylomicronemia. Deficiency of apolipoprotein C-II and E-3 was identified. In addition, these subjects had markedly decreased LPL activity in postheparin plasma. Addition of normal plasma to the assay as source for apoC-II enhanced LPL activity only to a limited extent. In contrast with previously reported patients with apoC-II deficiency, a far less pronounced effect of intravenous infusion of normal plasma was seen in one of the siblings, probably due to the combined deficiency of apoC-II and LPL. Plasma VLDL-TG turnover rate was not decreased in one of the siblings with apoC-II and LPL deficiency, suggesting different metabolic pathways for chylomicrons and VLDL. Family study confirmed an autosomal recessive mode of inheritance both for apoC-II and for apoE-3 deficiency. The mode of inheritance for LPL deficiency could not be established exactly.

Adult↗