Regulation of lipoprotein lipase by dibutyryl cAMP, cholera toxin, Hepes and heparin in F1 heart-cell cultures

Cilostazol, a selective type III phosphodiesterase inhibitor, decreases triglyceride and increases HDL cholesterol levels by increasing lipoprotein lipase activity in rats

Cilostazol, a selective type III phosphodiesterase inhibitor, has antiplatelet and vasodilating effects. In this study, the effects of cilostazol on lipid metabolism and lipoprotein lipase (LPL) activity were studied in rats. Cilostazol was administered orally at doses of 30 or 100 mg/kg twice a day for 1-2 weeks to rats. Cilostazol decreased the serum triglyceride level in normolipidemic rats. The serum triglyceride level was reduced and HDL cholesterol level was increased by cilostazol in streptozotocin (STZ)-induced diabetic rats. The disappearance of exogenous triglyceride was accelerated by cilostazol in normolipidemic rats. Cilostazol increased post-heparin plasma LPL activity but had no effect on hepatic triglyceride lipase activity in STZ-induced diabetic rats. Cilostazol also increased LPL activity in the heart in STZ-induced diabetic rats. These findings suggest that an increase in LPL activity is responsible for the serum triglyceride lowering and HDL cholesterol elevating effects of cilostazol in rats.

Adrenergic stimulation of lipoprotein lipase gene expression in rat brown adipocytes differentiated in culture: mediation via beta3- and alpha1-adrenergic receptors

In order to investigate whether the positive effect of adrenergic stimulation on lipoprotein lipase (LPL) gene expression in brown adipose tissue is a direct effect on the brown adipocytes themselves, the expression of the LPL gene was investigated by measuring LPL mRNA levels in brown adipocytes, isolated as precursors from the brown adipose tissue of rats and grown in culture in a fully defined medium before experimentation. Addition of noradrenaline led to an enhancement of LPL gene expression; the mRNA levels increased as a linear function of time for at least 5 h and were finally approx. 3 times higher than in control cells, an increase commensurate with that seen in vivo in both LPL mRNA levels and LPL activity during physiological stimulation. The increase was dependent on transcription. The effect of noradrenaline showed simple Michaelis-Menten kinetics with an EC50 of approx. 11 nM. beta3-Agonists (BRL-37344 and CGP-12177) could mimic the effect of noradrenaline; the beta1-agonist dobutamine and the beta2-agonist salbutamol could not; the alpha1-agonist cirazoline had only a weak effect. The effect of noradrenaline was fully inhibited by the beta-antagonist propranolol and was halved by the alpha1-antagonist prazosin; the alpha2-antagonist yohimbine was without effect. An increase in LPL mRNA level similar to (but not significantly exceeding) that caused by noradrenaline could also be induced by the cAMP-elevating agents forskolin and cholera toxin, and 8-Br-cAMP also increased LPL mRNA levels. The increase in LPL gene expression was not mediated via an increase in the level of an intermediary proteinaceous factor. It is concluded that the physiologically induced increase in LPL gene expression is a direct effect of noradrenaline on the brown adipocytes themselves, mediated via a dominant beta3-adrenergic pathway and an auxiliary alpha1-adrenergic pathway which converge at a regulatory point in transcriptional control.

Expression and regulation of the lipoprotein lipase gene in human adrenal cortex

Lipoprotein lipase (LPL), an enzyme which hydrolyzes triglycerides and participates in the catabolism of remnant lipoproteins, plays a crucial role in energy and lipid metabolism. The goal of this study was to analyze the expression and regulation of the LPL gene in human adrenals. Reverse transcriptase-polymerase chain reaction amplification and sequence analysis demonstrated the presence of LPL mRNA in fetal and adult human adrenal cortex. Furthermore, the human adrenocortical carcinoma cell line, NCI-H295, expresses LPL mRNA and protein, which is localized to the outer cellular membrane as demonstrated by immunofluorescence confocal microscopy and can be released in the medium by heparin addition. To asses whether the LPL gene is regulated by agents regulating adrenal steroidogenesis, NCI-H295 cells were treated with activators of second messenger systems. Whereas the calcium-ionophore A23187 did not affect LPL gene expression, treatment with phorbol 12-myristate 13-acetate decreased LPL mRNA levels in a time- and dose-dependent manner. This decrease after phorbol 12-myristate 13-acetate was associated with diminished heparin-releasable LPL mass and activity in the culture medium. Addition of the cAMP analog 8-Br-cAMP to NCI-H295 cells resulted in a rapid, but transient dose-dependent induction of LPL mRNA. Treatment with the protein synthesis inhibitor cycloheximide gradually induced, whereas simultaneous addition of cAMP and cycloheximide superinduced LPL mRNA levels. Nuclear run-on analysis indicated that the effects of cAMP and cycloheximide occurred at the transcriptional and post-transcriptional level, respectively. Transient co-transfection assays demonstrated that the first 230 base pairs of the proximal LPL promoter contain a cAMP-responsive element activated by protein kinase A and transcription factors belonging to the CREB/CREM family. These data indicate that LPL is expressed in human adrenal cortex and regulated in NCI-H295 adrenocortical carcinoma cells by activators of the protein kinase A and protein kinase C second messenger pathways in a manner comparable to P450scc, which catalyzes the first step in adrenal steroidogenesis. These observations suggest a role for LPL in adrenal energy and/or lipid metabolism and possibly in steroidogenesis.

Effect of transforming growth factor-beta on lipoprotein lipase in rat mesenchymal heart cell cultures

The effect of recombinant transforming growth factor-beta 2 (rTGF-beta 2) on lipoprotein lipase (LPL) synthesis was studied in mesenchymal rat heart cell cultures. Addition of rTGF-beta 2 to culture medium containing 20% serum resulted in a time-dependent decrease in LPL activity. With 10 ng/ml a 30% fall occurred after 12 h and only 20% of enzyme activity remained after 24 h with 5 or 10 ng/ml. The minimal effective dose of rTGF-beta 2 was 0.1 ng/ml and a 20% decrease occurred after exposure for 24 h. Antibodies specific to TGF-beta 2 blocked this effect. The decrease in enzymic activity was accompanied by a decrease in enzyme mass and LPL mRNA. Addition of rTGF-beta 2 was effective only during the first week in culture, when enzyme activity was increasing but not after 12 days when the cultures were overconfluent, and the enzyme activity was high.

Lipoprotein lipase is produced by cardiac myocytes rather than interstitial cells in human myocardium

Lipoprotein lipase (LPL) may play an important role in myocardial metabolism by releasing free fatty acids from triglycerides for oxidation by myocytes. However, studies in species other than humans have differed in their conclusions as to whether LPL is produced by cardiac myocytes or interstitial cells. The location and source of LPL in human myocardium were determined on formalin-fixed samples from 25 cardiomyopathy patients and seven control patients. LPL protein was detected immunohistochemically on cardiac myocytes, adipocytes, and endothelial cells, as well as on interstitial cells consisting of both vascular pericytes and smooth muscle cells. In all 32 patients, in situ hybridization localized LPL mRNA to cardiac myocytes and adipocytes, but LPL mRNA was not detected in interstitial cells. Quantitative in situ hybridization failed to reveal correlations between LPL mRNA levels and New York Heart Association functional class, left ventricular ejection fraction, or beta-adrenergic agonist therapy. Also, quantitative in situ hybridization demonstrated apparently linear loss of detectable myocardial mRNA after onset of ischemia, with a disappearance half-time of approximately 26 hours. In summary, LPL is produced primarily by cardiac myocytes rather than by interstitial cells in human myocardium. Furthermore, LPL protein is present on cells with and without detectable LPL mRNA, suggesting that LPL is translocated from sites of synthesis to sites of utilization.