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- Ruge, Toralph, et al.
(author)
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Lipoprotein lipase in the kidney : activity varies widely among animal species.
- 2004
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In: American Journal of Physiology - Renal Physiology. - : American Physiological Society. - 0363-6127 .- 1522-1466 .- 1931-857X. ; 287:6, s. F1131-1139
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Journal article (peer-reviewed)abstract
- Much evidence points to a relationship among kidney disease, lipoprotein metabolism, and the enzyme lipoprotein lipase (LPL), but there is little information on LPL in the kidney. The range of LPL activity in the kidney in five species differed by >500-fold. The highest activity was in mink, followed by mice, Chinese hamsters, and rats, whereas the activity was low in guinea pigs. In contrast, the ranges for LPL activities in heart and adipose tissue were less than six- and fourfold, respectively. The activity in the kidney (in mice) decreased by >50% on food deprivation for 6 h without corresponding changes in mRNA or mass. This decrease in LPL activity did not occur when transcription was blocked with actinomycin D. Immunostaining for kidney LPL in mice and mink indicated that the enzyme is produced in tubular epithelial cells. To explore the previously suggested possibility that the negatively charged glomerular filter picks up LPL from the blood, bovine LPL was injected into rats and mice. This resulted in decoration of the glomerular capillary network with LPL. This study shows that in some species LPL is produced in the kidney and is subject to nutritional regulation by a posttranscriptional mechanism. In addition, LPL can be picked up from blood in the glomerulus.
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- Ruge, Toralph, et al.
(author)
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Nutritional regulation of lipoprotein lipase in mice
- 2004
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In: International Journal of Biochemistry and Cell Biology. - 1357-2725 .- 1878-5875. ; 36:2, s. 320-329
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Journal article (peer-reviewed)abstract
- Tissue-specific regulation of lipoprotein lipase (LPL) has been extensively studied in rats. The mouse is now the most used animal in lipoprotein research, and we have therefore explored the regulation of LPL in this species. In C57 black mice, fed ad libitum adipose tissue LPL activity changed about three-fold with the time of day, indicating a circadian rhythm. The highest activity was at midnight and the lowest activity was at noon. Withdrawal of food did not markedly accelerate the drop of activity that occurred from midnight until noon, but prevented the return of activity that occurred during the evening and early night. When food was returned to mice that had been fasted for 24h, adipose tissue LPL activity rose rapidly and returned to the fed level in 2h. LPL mass in adipose tissue changed less than LPL activity, indicating that regulation is mainly post-translational as previously demonstrated for rats. When transcription was blocked in fasted mice, adipose tissue LPL activity increased, as previously observed in rats. LPL activity in heart was highest early in the light period at 9:00h and lowest at 21:00h. The change was, however, only about 30%. Heparin-releasable LPL activity in heart was 1.8-fold higher in mice fasted for 6h compared to fed controls. We conclude that LPL activity responds to the nutritional state in the same direction and by the same mechanisms in mice as in rats, but the magnitude of the changes are less in mice.
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- Wu, Gengshu, 1963-
(author)
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Lipoprotein lipase : mechanism for adaptation of activity to the nutritional state
- 2004
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Doctoral thesis (other academic/artistic)abstract
- Lipoprotein lipase (LPL) is an enzyme to hydrolyze triglycerides in lipoproteins and thereby make the fatty acids available for cellular metabolic reactions. Short-term fasting down-regulates LPL activity in adipose tissue. This regulation is through post-translational mechanism. The objective of this work was to investigate (1) The molecular mechansim for regulation of LPL activity in adipose tissue; (2) The basis for the tissue-specific regulation of LPL in adipose tissue, heart and skeletal muscle. LPL in adipose tissue can be found both inside (intracellular) and outside adipocytes (extracellular). Within adipocytes, neither LPL mass nor the distribution of LPL between active and inactive forms changed on fasting. Extracellular LPL mass also did not change significantly, but shifted from predominantly active to predominantly inactive. Activie, extracellular LPL was distributed in a similar way in the two nutritional states. The down-regulation during fasting is due to a decline of extracellular LPL activity. The up-regulation of LPL activity induced by re-feeding did not need new mRNA. The down-regulation of LPL activity induced by fasting did not occur when mRNA synthesis was inhibited. LPL activity in adipose tissue from fasted rats was fully restored by actinomycin. So fasting switches on a gene, whose product suppresses LPL activity. Similar results were also obtained in experiments on mice. When food was removed from young rats in the early morning, adipose tissue TNF-α activity increased and LPL activity decreased within six hours. There was a negative correlation between TNF-α and LPL activities. Pentoxifylline, that inhibits biosynthesis of TNF-α, almost abolished the rise of TNF-α and the decrease of LPL activity. Actinomycin D virtually abolished the response of LPL activity to fasting or exogenous TNF-α. This study suggests that fasting signals via TNF-α to a gene whose product causes a rapid shift of newly-synthesized LPL molecules towards an inactive form.
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