Effect of the (C825T) Gβ3 Polymorphism on Adrenoceptor-Mediated Lipolysis in Human Fat Cells

Abstract

A common G␤ 3 gene polymorphism (C825T) influences G protein receptor-mediated signal transduction. We investigated whether this polymorphism influences lipolysis in isolated subcutaneous fat cells from 114 healthy obese subjects. The G␤ 3 protein content was markedly decreased in adipocytes of TT carriers, but the alternatively spliced short form of G␤ 3 previously shown in platelets of 825T carriers was not detected. Fat cells of TT carriers showed a significant 10-fold decrease in the half-maximum effective concentration of agonists selective for lipolytic ␤ 1 -and ␤ 2 -adrenoceptors as well as for the antilipolytic ␣ 2 A-adrenoceptor. In TT carriers, maximum ␤-adrenoceptor agonist-stimulated lipolysis was decreased, but the maximum antilipolytic effect of ␣ 2 -adrenoceptors was less marked. Norepinephrine induced adipocyte lipolysis and circulating fasting levels of free fatty acids and glycerol were reduced by half in TT carriers. The polymorphism did not influence the adipocyte content of ␣ 2 A-adrenoceptors, ␤ 2 -adrenoceptors, G␣ i , or G␣ s . In conclusion, the C825T variant of G␤ 3 influences lipolysis. Adipocytes of TT carriers have a lower G␤ 3 protein content and a decreased function of native G s -as well as G i -coupled adrenoceptors, which reduces the lipolytic effect of catecholamines. These data differ from those obtained in other cell systems that have shown increased expression of an alternative spliced G␤ 3 variant and enhanced G protein signaling in 825T carriers, indicating that the polymorphism has cell type؊specific effects that may be of importance for type 2 diabetes and other insulinresistant conditions.

Association of a beta-2 adrenoceptor (ADRB2) gene variant with a blunted in vivo lipolysis and fat oxidation

“…38 The observed genotype frequency for the polymorphism in the GNB3 gene was similar to that previously reported in other Caucasian populations. 26,31 Rydén et al 35 showed that the T variant of this polymorphism was associated with a blunted in vitro responsiveness for the non-selective ISO in abdominal subcutaneous adipocytes of male and female overweight subjects. In contrast with Ryden et al 35 we found a tendency toward a reduced lipolysis aney in male overweight subjects.…”

“…26,31 Rydén et al 35 showed that the T variant of this polymorphism was associated with a blunted in vitro responsiveness for the non-selective ISO in abdominal subcutaneous adipocytes of male and female overweight subjects. In contrast with Ryden et al 35 we found a tendency toward a reduced lipolysis aney in male overweight subjects. It should be mentioned that our sample has no adequate power to provide a conclusive result about a genotype effect for the C825T polymorphism in the GNB3 gene.…”

“…Amplification of the relevant segments of the ADRB2 and GNB3 genes was performed by polymerase chain reaction (PCR) as previously described. 16,35 PCR products were digested at 371C for 1 h using BsrDI, ItaI, MnlI or BseDI. The digested fragments were visualized using ethidium bromide staining and UV-transmitted light.…”

“…[27][28][29][30][31][32][33][34] In vitro studies indicated that the 825T variant of Gb 3 in its homozygous form was associated with a decreased amount of Gb 3 in fat cells, thereby inhibiting signaling through b 1 -, b 2 -and a 2 -adrenoceptors, resulting in decreased catecholamine action and blunted lipolysis in isolated subcutaneous adipocytes of male and female obese subjects. 35 Thus, there are indications that polymorphisms in the ADRB2 gene and the GNB3 gene may be related to an impaired in vitro lipolytic response. So far, however, few in vivo lipolysis studies on these polymorphisms have been performed.…”

Human adipose triglyceride lipase (PNPLA2) is not regulated by obesity and exhibits low in vitro triglyceride hydrolase activity

“…One portion of adipose tissue (∼1 g) from obese subjects (cohort 1) was immediately subjected to collagenase treatment and isolated fat cells were incubated in duplicate exactly as described [13]. In brief, diluted cells were incubated in an albumin-containing buffer (pH 7.4) for 2 h at 37°C with air as gas phase without (basal) or with increasing concentrations of either the natural catecholamine noradrenaline, the selective beta-1 adrenergic receptor agonist dobutamine or the selective beta-2 adrenergic receptor agonist terbutaline.…”