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

SUBMITTER: Kuusela P

PROVIDER: S-EPMC1218133 | biostudies-other | 1997 Feb

REPOSITORIES: biostudies-other

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Project description:In brown adipocytes, fundamental cellular processes (cell proliferation, differentiation and apoptosis) are regulated by adrenergic stimulation, notably through beta-adrenergic receptors. The presence of all three beta-receptor subtypes has been demonstrated in brown adipose tissue. Due to the significance of the action of these receptors and indications that the subtypes govern different processes, the adrenergic regulation of the expression of the beta(1)-(,) beta(2)- and beta(3)-adrenoceptor genes was examined in murine brown-fat primary cell cultures. Moderate levels of beta(1)-receptor mRNA, absence of beta(2)-receptor mRNA and high levels of beta(3)-receptor mRNA were observed in mature brown adipocytes (day 6 in culture). Noradrenaline (norepinephrine) addition led to diametrically opposite effects on beta(1)- (markedly enhanced expression) and beta(3)-gene expression (full cessation of expression, as previously shown). beta(2)-Gene expression was induced by noradrenaline, but only transiently (<1 h). The apparent affinities (EC(50)) of noradrenaline were clearly different (7 nM for the beta(1)-gene and</=1 nM for the beta(3)-gene), as were the mediation pathways (solely via beta(3)-receptors and cAMP for the beta(1)-gene and via beta(3)-receptors and cAMP, as well as via alpha(1)-receptors and protein kinase C, for the beta(3)-gene). The half-lives of the corresponding mRNA species were very short but different (17 min for beta(1)-mRNA and 27 min for beta(3)-mRNA), and these degradation rates were not affected by noradrenaline, implying that the mRNA levels were controlled by transcription. Inhibition of protein synthesis also led to diametrically opposite effects on beta(1)- and beta(3)-gene expression, but - notably - these effects were congruent with the noradrenaline effects, implying that a common factor regulating beta(1)-gene expression negatively and beta(3)-gene expression positively could be envisaged. In conclusion, very divergent effects of adrenergic stimulation on the expression of the different beta-receptor genes were found within one cell type, and no unifying concept of adrenergic control of beta-receptor gene expression can be formulated, either concerning different cell types, or concerning the different beta-receptor subtype genes.

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

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