Obesity is a major co-morbidity factor in diabetes, cancer, cardiovascular, neurological and other diseases. Recently, a new group of human genes was linked to obesity, the genes encoding the R7 family of regulator of G protein signaling proteins (RGS6, 7, 9 and 11) and Gnb5, which encodes the atypical G protein beta subunit Gb5. This proposal studies how a deficiency in the Gnb5 and R7 genes can lead to obesity and other abnormalities in control of body weight. The ultimate goal is to discover effective treatments of disorders associated with neuroendocrine pathways regulated by these genes. The proposed research plan builds upon earlier discoveries that together constitute a strong premise for this study. Gb5 and R7 proteins form obligatory dimers, so that the Gnb5 knockout causes complete degradation of the entire Gb5-R7 complex. Ablation of one Gnb5 allele leads to obesity and metabolic syndrome in mice; this finding was later confirmed by human genetics. Subsequent mechanistic investigations in this lab identified a novel role for the Gb5-R7 complex in pancreatic beta cells where Gb5- R7 strongly promoted secretion of insulin. Brain is the main organ regulating body weight, and the expression level of Gb5-R7 is much higher in the CNS than in the pancreas or any other peripheral tissues. These considerations lead us to the hypothesis that Gb5-RGS7 regulates body weight via its function in the neurons, where, similarly to the insulin-secreting beta cells, it controls secretion of neurotransmitters and hormones. In support of this hypothesis, recent studies in the lab demonstrated that local knockout of Gnb5 in the adult mouse hypothalamus dramatically increased body and adiposity. The proposed experiments will develop this discovery through a series of experiments performed at the organismal, tissue and cellular levels.
Specific Aim 1 will use the Cre-loxP approach to inactivate Gnb5 in specific hypothalamic nuclei and types of neurons and examine the effect of the knockout on body weight and metabolism. Overexpression of Gnb5 using viral gene transfer will be performed to rescue the changes caused by the knockout.
Aim 2 will study co-expression of Gnb5 with GPCRs and gene encoding hypothalamic hormones and tissue slices will be examined ex vivo for signal-stimulated secretion of specific hormones.
Specific Aim 3 will study Gb5-R7 its knockout (CRISPR/Cas9), knockdown and overexpression in cell lines that endogenously express Gb5-R7. Experiments will utilize pharmacological agents and structure-function analysis to interrogate molecular events in signaling and secretory pathways. The proposed investigation of the Gb5-R7 complex will elucidate the novel mechanism regulating secretion of hypothalamic hormones and significantly advance our understanding of G protein signaling, etiology of obesity and other metabolic and neuroendocrine disorders.
Many pathologic conditions are associated with genetic or acquired abnormalities in the levels of hormones secreted by the central nervous system. This project studies Gbeta5-R7, a protein complex highly expressed in the brain, and the new finding is it is responsible for maintaining normal body weight in mice. Mutations in the human genes that encode Gbeta5-R7 are genetically linked in with obesity, and this research will develop a new avenue for understanding, diagnosing and treating obesity and other metabolic disorders.