β3-Adrenergic receptor regulates hepatic apolipoprotein A-I gene expression

BACKGROUND

β₃-adrenergic receptor (β₃-AR) was shown to upregulate hepatic apolipoprotein A-I (apoA-I) expression and reverse atherosclerotic plaques in vivo experiments. However, the effect of β₃-AR on apoA-I expression in vitro is unknown. The specific mechanism underlying β₃-AR prevention of atherosclerosis is unclear.

OBJECTIVE

The present study was designed to investigate the molecular mechanism of β₃-AR-mediated regulation of hepatic apoA-I gene expression.

METHODS

HepG2 cells were preincubated with/without a selective protein kinase A inhibitor (H-89) and then treated with a selective β₃-AR agonist (BRL37344) or antagonist (SR59230A). The hepatic apoA-I expression was detected by reverse transcription real-time quantitative polymerase chain reaction and Western blot analysis. Enzyme-linked immunosorbent assay was used to evaluate the secretion of apoA-I. A recombinant plasmid containing the apoA-I promoter was constructed and transiently transfected into HepG2 cells, and dual-luciferase reporter assays were used to examine the activity of the apoA-I promoter. A chromatin immunoprecipitation polymerase chain reaction assay was used to evaluate binding activities of hepatocyte nuclear factor-4 (HNF-4), HNF-3, and early growth response protein-1.

RESULTS

β₃-AR activation significantly upregulated apoA-I expression, promoted apoA-I secretion, and enhanced the activities of the apoA-I promoter, HNF-4, and HNF-3 in hepatocytes, whereas early growth response protein-1 was not affected. Moreover, protein kinase A inhibition partially suppressed the activation of the apoA-I promoter, HNF-4, and HNF-3 and almost completely blocked the upregulation of apoA-I expression induced by β₃-AR.

CONCLUSION

β₃-AR activation increased the activities of the apoA-I promoter, HNF-4, and HNF-3, which might account for the mechanism of β₃-AR-mediated upregulation of hepatic apoA-I expression. β₃-AR might exert an anti-atherosclerotic effect by upregulating hepatic apoA-I expression and promoting the cholesterol reverse transport process.

Effects of carvedilol on ventricular remodeling and the expression of β3-adrenergic receptor in a diabetic rat model subjected myocardial infarction

BACKGROUND

This study was to assess effects of carvedilol on ventricular remodeling and expression of β3-adrenergic receptor (β3-AR) and Gi protein in a rat model of diabetes subjected to myocardial infarction (MI).

METHODS

Rat model of type II diabetes was established by injection of streptozotion. MI was then induced by ligating the left anterior descending coronary artery. Rats were then randomly divided into two groups treated with either placebo (PL) or carvedilol (CA - 10mg·kg(-1)·d(-)(1)). Additional controls consisted of sham-operated rats with diabetes (DS) and rats fed a normal diet subjected to myocardial infarction (NM). Echocardiographic and hemodynamic studies were performed to assess the structural and functional changes. β3-AR and Gi mRNA in the myocardium distal from the infarction region were measured, and β3-AR and Gi protein were measured with western blot.

RESULTS

There were no significant differences in MI size among the three MI groups. In the PL group, LVEDd, LVWI, E/A and CVF were significantly increased, while LVEF and PW% significantly decreased as compared with the DS and NM groups. Compared with the DS group, the expression of β3-AR and Gi mRNA and protein in the PL group was significantly increased, however, in the CA group, β3-AR and Gi mRNA and protein were decreased.

CONCLUSIONS

The expression of β3-AR and Gi mRNA and protein was increased in diabetic rats subjected to MI as compared with rats subject to either condition alone. Carvedilol treatment prevented many of these deleterious effects.