Adrenergic stimulation of lipoprotein lipase gene expression in rat brown adipocytes differentiated in culture: mediation via β3- and α1-adrenergic receptors

Abstract

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.

Combining β-adrenergic and peroxisome proliferator–activated receptor γ stimulation improves lipoprotein composition in healthy moderately obese subjects

“…However, this reduction in apoC-III is probably not a direct effect on apoC-III synthesis because the total plasma apoC-III was not reduced. It appears that the apoC-III was simply transferred to HDL, probably because of an increase in LPL activity, as previously described for both of these therapies [5][6][7][8]. Consistent with this interpretation, the apoC-III/apoB ratio in VLDL, which represents the number of apoC-III molecules per particle, was not reduced by therapy.…”

“…The ABCA1 transporter activity, which is responsible for cholesterol efflux from most tissues, including vascular foam cells, has been shown to be stimulated by both cAMP [1,2] and PPARc [3,4]. Similarly, LPL is also stimulated by both cAMP [5,6] and PPARc [7,8]. Laplante et al [8] demonstrated that PPARc activated LPL only in subcutaneous fat, not visceral fat.…”

Adipocyte transdifferentiation and its molecular targets

“…Lipase hastens the liberation of free fatty acid from triglyceride which acts both as fuel for thermogenesis and as an activator of UCP1 (Kuusela et al, 1997). Apart from cold exposure, nonshivering thermogenesis can also be induced by using β3-AR agonists such as BRL-35135 and CL-316243 (Klaus et al, 2001;Shih and Taberner, 1995).…”

α1-Adrenergic Stimulation Potentiates the Thermogenic Action of β3-Adrenoreceptor-generated cAMP in Brown Fat Cells

“…For regulation of the expression of the uncoupling protein UCP1 (53,54) and lipoprotein lipase (55), an ␣ 1 -adrenergic component has been identified, and a synergistic interaction between ␣ 1 -and ␤-receptors and signaling pathways has been demonstrated for both thyroxine deiodinase (40) and c-fos (22) expression. Here, unexpectedly, we demonstrate that even for a process that has been accepted to be essentially ␤-adrenergically stimulated and cAMP-mediated, a strong ␣ 1 /␤-receptor synergism can be observed.…”