Abstract
Abstract ID 94591
Poster Board 551
The Gnb5 gene encodes a unique G protein b subunit. Unlike other Gb subunits, Gb5 dimerizes with regulators of G protein signaling (RGS) proteins of the R7 family, instead of the expected Gg subunit. This interaction between R7 and Gb5 is obligatory and is essential for the stability of these complexes, and the knockout of Gnb5 causes proteosome degradation of the entire Gb5-R7 family. Our lab has previously reported that the global Gnb5 knockout (Gnb5 -/-) mice were lean and were resistant to a high-fat diet throughout their lifetime. Surprisingly, the Gnb5 heterozygous (Gnb5 -/+) mice had an opposite phenotype: they were heavier than their Gnb5 +/+ age- and sex-matched littermates and had increased adiposity, insulin resistance, and liver steatosis. Here, we tested our hypothesis that the creation of a local knockout of Gnb5 in the hypothalamus using Cre-lox technology may result in an increased BMI. We used two approaches to deliver the Cre recombinase to “floxed” mice, in which the first exon of their Gnb5 gene is flanked by lox P sites. The first approach used direct hypothalamic injections of Cre-carrying AAV into either wild-type or floxed Gnb5 mice. The second approach used cross breeding between mice carrying Cre under a hypothalamus-specific promoter, Nkx2.1. Both sets of Gnb5 conditional knockouts were subjected to a high-fat diet and measured body weight over 8 weeks. Our data from the AAV-injected cohort aligned with our hypothesis; these animals did have increased body weight and adiposity. The Nkx2.1-Cre mice did not follow the same trend, showing no increase in adiposity. However, we made an unexpected observation. Both sets of mice with hypothalamus-specific Gnb5 KO had an increase in brain mass. The magnitude of the increase depended on the sex of the animal and the method of Cre-application. For example, females that were cross bred with the Nkx2.1-Cre exhibiting the largest (38.2%) increase over their wild-type counterparts. Currently we are focused on characterizing the cause and implications of this increase in brain mass. We thus far conclude that the selective reduction of the level of Gb5-R7 expression in the hypothalamus is sufficient to perturb animal metabolism and organ morphology. These findings may contribute to understanding the earlier observations of genetic linkage between R7 family mutations and obesity in humans.