The Obesity-Linked Gene Nudt3 Drosophila Homolog Aps Is Associated With Insulin Signaling

Abstract

Several genome-wide association studies have linked the Nudix hydrolase family member nucleoside diphosphate-linked moiety X motif 3 (NUDT3) to obesity. However, the manner of NUDT3 involvement in obesity is unknown, and NUDT3 expression, regulation, and signaling in the central nervous system has not been studied. We performed an extensive expression analysis in mice, as well as knocked down the Drosophila NUDT3 homolog Aps in the nervous system, to determine its effect on metabolism. Detailed in situ hybridization studies in the mouse brain revealed abundant Nudt3 mRNA and protein expression throughout the brain, including reward- and feeding-related regions of the hypothalamus and amygdala, whereas Nudt3 mRNA expression was significantly up-regulated in the hypothalamus and brainstem of food-deprived mice. Knocking down Aps in the Drosophila central nervous system, or a subset of median neurosecretory cells, known as the insulin-producing cells (IPCs), induces hyperinsulinemia-like phenotypes, including a decrease in circulating trehalose levels as well as significantly decreasing all carbohydrate levels under starvation conditions. Moreover, lowering Aps IPC expression leads to a decreased ability to recruit these lipids during starvation. Also, loss of neuronal Aps expression caused a starvation susceptibility phenotype while inducing hyperphagia. Finally, the loss of IPC Aps lowered the expression of Akh, Ilp6, and Ilp3, genes known to be inhibited by insulin signaling. These results point toward a role for this gene in the regulation of insulin signaling, which could explain the robust association with obesity in humans.

High Fat Diet Feeding and High Throughput Triacylglyceride Assay in <em>Drosophila Melanogaster</em>

“…The rapid induction of fat accumulation mediated by conserved cellular and molecular processes controlling lipid and glucose metabolism is advantageous for many obesity-related studies, such as diabetic or lipotoxic cardiomyopathy 10,12,13,14,15,16 . Key findings in the consequences of metabolic imbalances and related cardiac dysfunctions will likely allow comparative translational studies in humans.…”

“…This TAG protocol is based on PBS, a non-toxic buffer that allows easy handling and experimentation without a fume hood, in contrast to previously used organic solvents (methanol/chloroform or diethyl ether) in lipid extraction and quantification 15,29,30 . Another advantage of this buffer is that it can normalize the TAG levels to protein content based on the same initial homogenate, making the fat determination in small tissue samples easily achievable and offering new opportunities to study organ cross-talk in organismal metabolic homeostasis.…”

“…Also, characteristic processes carried out by adipose tissue, the gut and pancreas are represented in the fly and mediate regulatory functions in glucose and lipid metabolism, for example, that are similar to humans 9,10,11 . Moreover, the basic molecular pathways involved in the control of obesity, insulin resistance and diabetes in humans are functionally conserved in Drosophila melanogaster 12,13,14,15,16 . Like higher organisms, Drosophila has a beating heart that is formed during development by similar processes to that of the mammalian heart 3,17 .…”

Drosophilaas a model to study obesity and metabolic disease

“…Conditional ablation of IPCs during adulthood elicits modest increases in stored and circulating TAGs (Haselton et al, 2010). The IPC-expressed gene nudt3 is a human obesity susceptibility gene that is required in IPCs for lipolysis of stored fat during starvation (Williams et al, 2015). Similarly, the serotonin receptor 5-HT1A is required in IPCs for the catabolism of stored fat to supply energy during starvation .…”

Nudt3 is an mRNA decapping enzyme that modulates cell migration

“…Nudt3 is ubiquitously expressed in mouse tissue (Williams et al 2015). Polymorphism of NUDT3, among more than 50 genetic variants, was implicated by genome-wide association to increase BMI and obesity (Hofker and Wijmenga 2009) possibly through its phosphatase activity against polyphosphate substrates (Shears 2009).…”