The dietary regulation of LEAP2 depends on meal composition in mice.

Ghrelin represents a key hormone regulating energy balance. Upon activation of the growth hormone secretagogue receptor (GHSR), ghrelin increases blood glucose levels, food intake, and promotes weight gain. The liver-expressed antimicrobial peptide 2 (LEAP2) acts as an endogenous antagonist of the GHSR. While the regulation of LEAP2 and its effect on the GHSR likely occur in an opposite pattern to that of ghrelin, the dietary regulation of LEAP2 remains to be described. We, therefore, examined the regulation of LEAP2 by different acute meal challenges (glucose, mixed meal, olive, lard, and fish oil) and diets (chow vs. high-fat) in C57BL/6 male mice. In addition, the effect of specific fatty acids (oleic, docosahexaenoic, and linoleic acid) on LEAP2 was assessed in murine intestinal organoids. While only mixed meal increased liver Leap2 expression, all meal challenges except fish oil increased jejunal Leap2 expression compared to water. Leap2 expression correlated with levels of hepatic glycogen and jejunal lipids. Lipid versus water dosing increased LEAP2 levels in the systemic circulation and portal vein where fish oil was associated with the smallest increase. In line with this, oleic acid, but not docosahexaenoic acid increased Leap2 expression in intestinal organoids. Feeding mice with high-fat versus chow diet not only increased plasma LEAP2 levels, but also the increment in plasma LEAP2 upon dosing with olive oil versus water. Taken together, these results show that LEAP2 is regulated by meal ingestion in both the small intestine and the liver according to the meal/diet of interest and local energy stores.

Pharmacological inhibition of FTO.

In 2007, a genome wide association study identified a SNP in intron one of the gene encoding human FTO that was associated with increased body mass index. Homozygous risk allele carriers are on average three kg heavier than those homozygous for the protective allele. FTO is a DNA/RNA demethylase, however, how this function affects body weight, if at all, is unknown. Here we aimed to pharmacologically inhibit FTO to examine the effect of its demethylase function in vitro and in vivo as a first step in evaluating the therapeutic potential of FTO. We showed that IOX3, a known inhibitor of the HIF prolyl hydroxylases, decreased protein expression of FTO (in C2C12 cells) and reduced maximal respiration rate in vitro. However, FTO protein levels were not significantly altered by treatment of mice with IOX3 at 60 mg/kg every two days. This treatment did not affect body weight, or RER, but did significantly reduce bone mineral density and content and alter adipose tissue distribution. Future compounds designed to selectively inhibit FTO's demethylase activity could be therapeutically useful for the treatment of obesity.

FTO influences adipogenesis by regulating mitotic clonal expansion.

The fat mass and obesity-associated (FTO) gene plays a pivotal role in regulating body weight and fat mass; however, the underlying mechanisms are poorly understood. Here we show that primary adipocytes and mouse embryonic fibroblasts (MEFs) derived from FTO overexpression (FTO-4) mice exhibit increased potential for adipogenic differentiation, while MEFs derived from FTO knockout (FTO-KO) mice show reduced adipogenesis. As predicted from these findings, fat pads from FTO-4 mice fed a high-fat diet show more numerous adipocytes. FTO influences adipogenesis by regulating events early in adipogenesis, during the process of mitotic clonal expansion. The effect of FTO on adipogenesis appears to be mediated via enhanced expression of the pro-adipogenic short isoform of RUNX1T1, which enhanced adipocyte proliferation, and is increased in FTO-4 MEFs and reduced in FTO-KO MEFs. Our findings provide novel mechanistic insight into how upregulation of FTO leads to obesity.

Role of FTO in Adipocyte Development and Function: Recent Insights.

In 2007, FTO was identified as the first genome-wide association study (GWAS) gene associated with obesity in humans. Since then, various animal models have served to establish the mechanistic basis behind this association. Many earlier studies focussed on FTO's effects on food intake via central mechanisms. Emerging evidence, however, implicates adipose tissue development and function in the causal relationship between perturbations in FTO expression and obesity. The purpose of this mini review is to shed light on these new studies of FTO function in adipose tissue and present a clearer picture of its impact on obesity susceptibility.

Fetal programming of adipose tissue function: an evolutionary perspective.

Obesity is an escalating threat of pandemic proportions and has risen to such unrivaled prominence in such a short period of time that it has come to define a whole generation in many countries around the globe. The burden of obesity, however, is not equally shared among the population, with certain ethnicities being more prone to obesity than others, while some appear to be resistant to obesity altogether. The reasons behind this ethnic basis for obesity resistance and susceptibility, however, have remained largely elusive. In recent years, much evidence has shown that the level of brown adipose tissue thermogenesis, which augments energy expenditure and is negatively associated with obesity in both rodents and humans, varies greatly between ethnicities. Interestingly, the incidence of low birth weight, which is associated with an increased propensity for obesity and cardiovascular disease in later life, has also been shown to vary by ethnic background. This review serves to reconcile ethnic variations in BAT development and function with ethnic differences in birth weight outcomes to argue that the variation in obesity susceptibility between ethnic groups may have its origins in the in utero programming of BAT development and function as a result of evolutionary adaptation to cold environments.

Changes in gene expression associated with FTO overexpression in mice.

Single nucleotide polymorphisms in the first intron of the fat-mass-and-obesity-related gene FTO are associated with increased body weight and adiposity. Increased expression of FTO is likely underlying this obesity phenotype, as mice with two additional copies of Fto (FTO-4 mice) exhibit increased adiposity and are hyperphagic. FTO is a demethylase of single stranded DNA and RNA, and one of its targets is the m6A modification in RNA, which might play a role in the regulation of gene expression. In this study, we aimed to examine the changes in gene expression that occur in FTO-4 mice in order to gain more insight into the underlying mechanisms by which FTO influences body weight and adiposity. Our results indicate an upregulation of anabolic pathways and a downregulation of catabolic pathways in FTO-4 mice. Interestingly, although genes involved in methylation were differentially regulated in skeletal muscle of FTO-4 mice, no effect of FTO overexpression on m6A methylation of total mRNA was detected.

Role of ghrelin in the pathophysiology of eating disorders: implications for pharmacotherapy.

Ghrelin is the only known circulating orexigenic hormone. It increases food intake by interacting with hypothalamic and brainstem circuits involved in energy balance, as well as reward-related brain areas. A heightened gut-brain ghrelin axis is an emerging feature of certain eating disorders such as anorexia nervosa and Prader-Willi syndrome. In common obesity, ghrelin levels are lowered, whereas post-meal ghrelin levels remain higher than in lean individuals. Agents that interfere with ghrelin signalling have therapeutic potential for eating disorders, including obesity. However, most of these drugs are only in the preclinical phase of development. Data obtained so far suggest that ghrelin agonists may have potential in the treatment of anorexia nervosa, while ghrelin antagonists seem promising for other eating disorders such as obesity and Prader-Willi syndrome. However, large clinical trials are needed to evaluate the efficacy and safety of these drugs.

Ghrelin mediates anticipation to a palatable meal in rats.

Food anticipatory activity (FAA) is displayed in rats when access to food is restricted to a specific time frame of their circadian phase, a behavior thought to reflect both hunger and the motivation to eat. Rats also display FAA in a feeding schedule with ad libitum access to normal chow, but limited availability of a palatable meal, which is thought to involve mainly motivational aspects. The orexigenic hormone ghrelin has been implicated in FAA in rodents with restricted access to chow. Because ghrelin plays an important role not only in the control of food intake, but also in reward, we sought to determine the role of ghrelin in anticipation to a palatable meal. Plasma ghrelin levels of non-restricted rats that anticipated chocolate correlated positively with FAA and were increased compared with chow-fed control rats. Furthermore, centrally injected ghrelin increased, whereas an antagonist of the ghrelin receptor decreased, the anticipation to chocolate. Therefore, we hypothesize that central ghrelin signaling is able to mediate the motivational drive to eat.

Multimeric alpha-MSH has increased efficacy to activate the melanocortin MC4 receptor.

alpha-Melanocyte stimulating hormone (alpha-MSH) has a relatively low affinity for the melanocortin MC4 receptor. Constructs of multimeric alpha-MSH varying from one to eight subunits were synthesized to test whether they displayed an improved ability to bind to and activate the human melanocortin MC4 receptor. alpha-MSH subunits were coupled by a flexible linker and placed in front of an IRES-eGFP sequence. Efficacy for activation of the melanocortin MC4 receptor increased with every extra subunit, resulting in a 100 fold lower EC50 value of alpha-MSH8 when compared with alpha-MSH1. Furthermore, supernatant of cells transfected with alpha-MSH8 proved to have an increased affinity to the melanocortin MC4 receptor when compared to cells transfected with the other multimers. Together, these data show that multimeric alpha-MSH has improved ability to activate the human melanocortin MC4 receptor in vitro.