Cell-free translation of avian adipose tissue lipoprotein lipase messenger RNA

Gene expression and protein content in relation to intramuscular fat content in Muscovy and Pekin ducks

Independent of their nutritional condition, Pekin ducks always exhibit higher i.m. fat content than Muscovy ducks. To understand this difference between species, the expression level of genes involved in lipid metabolism was analyzed in the pectoralis major muscle of Pekin and Muscovy ducks ad libitum-fed or overfed. The lipoprotein lipase (LPL) gene expression was not different between species and not influenced by overfeeding. The protein content for LPL was higher in Pekin ducks than in Muscovy ducks when birds were ad libitum-fed, whereas in overfed ducks, we found no difference between species. Adipocyte fatty acid-binding protein (A-FABP) gene expression and protein content were higher in Pekin ducks than in Muscovy ducks for each nutritional condition (suggesting a higher intracellular transport within i.m. adipocytes of fatty acids mainly provided by liver for this species). Overfeeding did not affect the expression of genes involved in oxidation [carnitine palmitoyl transferase 1A (CPT1A), cytochrome-c oxidase 4 (COX4), succinyl-coenzyme A:3-ketoacid coenzyme A transferase (SCOT)] but increased the expression of fatty acid synthase (FAS) involved in lipogenesis. For all nutritional conditions, Pekin duck exhibited higher expression levels of CPT1A, COX4, SCOT, and FAS than Muscovy ducks. Results for mRNA SCOT suggested that the muscles of Pekin ducks use ketone bodies as an energy source. In conclusion, i.m. lipogenesis could contribute to the i.m. fat, particularly in Pekin ducks.

A micromethod for the isolation of total RNA from adipose tissue

We have developed a simple and rapid procedure for the isolation of total RNA from small amounts of adipose tissue. Using this method, it is possible to obtain quantitative recovery of RNA from less than 300 mg of adipose tissue, with an average yield of 70 micrograms of RNA per gram of adipose tissue. Northern blot analysis of rat epididymal adipose tissue RNA samples was performed using a beta-actin probe and demonstrated that intact total RNA had been isolated. The procedure has been adapted for use in 1.5-ml microcentrifuge Eppendorf tubes, providing a convenient and inexpensive method for the reproducible recovery of intact RNA from sparse samples of adipose tissue.

Two different mechanisms are involved in nutritional regulation of lipoprotein lipase in guinea-pig adipose tissue

Lipoprotein lipase activity in adipose tissue responds rapidly to changes in the physiological state. To study what mechanisms are involved in the regulation, guinea pigs were fasted and the decrease in adipose-tissue lipoprotein lipase activity was compared with the decreases in mRNA and lipase synthesis. The mRNA pattern (three species) did not change. There was a close parallelism between the abundance of lipase mRNA and relative lipase synthesis (immunoprecipitable 35S-labelled lipoprotein lipase as fraction of total [35S]protein after pulse-labelling with [35S]methionine). Total protein synthesis decreased on fasting, compounding the decrease in relative lipase synthesis. Lipoprotein lipase mRNA changed similarly in fat-pads and in isolated adipocytes, whereas lipase activity changed more in the pads, indicating disproportionally large changes in extracellularly located lipase. In old guinea pigs the decreases in lipoprotein lipase activity and lipase synthesis were comparable, but in young animals the change in lipase activity was substantially larger than the change in lipase synthesis. Refeeding of fasted young guinea pigs with glucose resulted in a rapid increase in lipoprotein lipase activity, but there was only a small change in lipase mRNA. Old animals responded slowly to refeeding. The results indicate that in older animals the major mechanism for regulation of adipose lipoprotein lipase activity is a relatively slow change in lipase mRNA, whereas in younger animals an additional, more rapid, regulation is exerted on the transport and turnover of the enzyme.

The role of the endothelium in myocardial lipoprotein dynamics

This overview is presented, in the main, to summarize the following areas of myocardial lipoprotein metabolism: 1. The nature and extent of the cardiac endothelium. 2. The interactions between the endothelium and chylomicrons, very low, low and high density lipoproteins in the presence and absence of lipoprotein lipase. 3. The importance of the endothelial lipoprotein lipase and the mechanisms involved in the enzymes' sequestration at that site. 4. The physiological role of lipoprotein lipase in the provision of oxidizable fuel for the heart.

Avian adipose lipoprotein lipase: cDNA sequence and reciprocal regulation of mRNA levels in adipose and heart

cDNA clones for chicken adipose lipoprotein lipase were isolated from an expression library in lambda gt11 by antibody screening and characterized by hybridization selection and nucleotide sequencing. Based on the cDNA sequence and on N-terminal sequence analysis of the purified enzyme, chicken adipose lipoprotein lipase is a mature protein of 465 amino acids with a signal peptide of 19 or 25 amino acids, depending on which of two methionine residues is used for translation initiation. The predicted amino-acid sequence was found to be 73-77% identical to the four known mammalian adipose lipoprotein lipase sequences, with conservation of position of cysteine residues and putative functional domains, and number of potential N-glycosylation sites. Chicken lipoprotein lipase differs from mammalian lipoprotein lipases with respect to the position of one N-glycosylation site and the presence of an additional 15-17 C-terminal amino acids. 32P-labeled cDNA clones hybridized to mRNA species of 3.7 and 4.0 kb in Northern blots of heart and adipose, but not of liver RNA. In chickens that were fasted for 48 h and then refed, lipoprotein lipase mRNA levels in adipose increased to a maximal level of 350% that of controls at 10 h, whereas heart lipoprotein lipase mRNA levels fell to 40% of controls at 14 h. Concomitantly, no changes in total RNA were observed. Thus, avian lipoprotein lipase is subject to reciprocal pretranslational regulation in adipose and heart.

Tissue-specific regulation of guinea pig lipoprotein lipase; effects of nutritional state and of tumor necrosis factor on mRNA levels in adipose tissue, heart and liver

Levels of mRNA for lipoprotein lipase (LPL) in guinea pig epididymal adipose tissue, heart and liver were determined by dot blot analysis of total RNA using a cDNA probe complementary to the coding region, and compared to the LPL activity. For adipose tissue we also measured the incorporation of radioactivity into immunoprecipitable LPL after pulse-labeling with [35S]methionine. LPL activity was 93%, LPL mRNA 82% and LPL synthesis 85% lower in epididymal fat pads from animals fasted for 48 h compared to rigorously fed animals. In contrast, neither LPL activity nor LPL mRNA levels differed in heart. A single dose of tumor necrosis factor (TNF) decreased LPL activity and LPL mRNA in fat pads with no effects in heart. In the liver, TNF caused a marked increase in LPL mRNA levels, which are normally very low. Northern-blot analysis confirmed a previous observation that the patterns of mRNA species differ between heart, in which a 3.8-kb mRNA dominates, and adipose tissue, in which the LPL mRNAs of 3.3 and 2.1 kb occur in similar abundance as the 3.8-kb species.