Levels of G-proteins in liver and brain of lean and obese (ob/ob) mice

Abstract

G-protein levels were assessed in liver and brain membranes of lean and obese mice. ADP-ribosylation and immunodetection studies revealed a decrease in the abundance of G8 and G, a-subunits in the liver membranes of obese mice compared with lean mice. In contrast, in brain membranes, the abundance of these proteins was not significantly different between lean and obese mice. Studies at the mRNA level in both liver and brain revealed no difference in gene expression between lean and obese mice. Protein and mRNA studies both showed that G., Gial, Gia2, Goa and G,? subunits are present in brain membranes, and Gia3 is barely detectable. In liver, G,a, Gia2 and G/J subunits are the major constituents, whereas Gial, G1a3 and Goa are barely detectable. It is possible that the differences observed at the protein level are due to different rates of translation of the mRNA. Different rates of release of the a-subunits from the membrane and/or different rates of degradation would also explain these results.

Comparison of the subcellular distribution of G-proteins in hepatocytes in situ and in primary cultures

“…In previous studies using Northern and Western blotting we found that Gia2, Gp3, Gsa, and GP subunits were the major peptides present in the liver [McFarlane-Anderson et al, 1992;Begin-Heick, 19941.…”

Up-regulation of CB1 cannabinoid receptors located at glutamatergic terminals in the medial prefrontal cortex of the obese Zucker rat

“…In this sense, our results show for the first time that the Gα i 2 subunit is down-regulated in the mPCx of obese rats. However, the situation bears comparison with previously published results in membranes of hepatocytes and adipocytes of obese Zucker rats ( Bushfield et al, 1990 ; Strassheim et al, 1991 ), hepatocytes from obese (ob/ob) mice ( McFarlane-Anderson et al, 1992 ) and fat cells obtained from obese human subjects ( Ohisalo and Milligan, 1989 ). The results indicate a lower expression and function of Gα i/o subunits in obese individuals leading to a reduction of the potency of p[NH]ppG, a non-hydrolyzable GTP analog, to inhibit forskolin-stimulated adenylate cyclase activity.…”

“…Moreover, Bushfield et al (1990) concluded that their results may be explained by an increased protein kinase C activity in hepatocytes of obese Zucker rats leading to phosphorylation-induced inactivation of Gα i 2 proteins. The possibility that this phenomenon could be present in the brains of obese animals only has been evaluated in whole brain homogenates of obese (ob/ob) mice with negative results ( McFarlane-Anderson et al, 1992 ). However, as in our present study, it is possible that a separate analysis of discrete areas of the brain could find differences between the obese and lean phenotypes.…”

The Functional State of Hormone-Sensitive Adenylyl Cyclase Signaling System in Diabetes Mellitus

“…In the liver membranes isolated from ob/ob mice with hyperglycemia, hyperinsulinemia, and obesity typical of T2DM, the number of β 2 -AR binding sites was increased threefold, and the response of AC to catecholamines was significantly enhanced as compared to both control animals and db/db mice, the other animal model of T2DM [146]. The content of G i and G s proteins, especially their G α i2 subunits, was reduced in the liver of ob/ob and db/db mice [146–148]. In the hepatic membranes of db/db mice, the levels of expression of G α i2 , G α i3 , and G β subunits were reduced by 75%, 63%, and 73%, respectively, and the maximal inhibitory effect of GppNHp on forskolin-stimulated AC activity was reduced to 60%, as compared to lean animals, which indicates the abolition of G i proteins activity in the liver in T2DM [149].…”