The partial inhibition of hypothalamic IRX3 exacerbates obesity

Fat mass and obesity associated gene and homeobox transcription factor iriquois-3 mRNA profiles in the metabolic tissues of zebrafish are modulated by feeding and food deprivation

Fat mass and obesity associated gene (FTO) has been strongly associated with obesity, and it is functionally linked to the homeobox transcription factor iriquois-3 (IRX3). In mammals, FTO and IRX3 are involved in the regulation of food intake and metabolism. This study aimed to determine whether FTO and IRX3are affected by feeding and food unavailability. FTO and IRX3 mRNA and protein were found widely distributed in all tissues examined, including the brain, muscle, gut, and liver. Postprandial increase in the abundance of FTO and IRX3 mRNAs was observed in metabolic tissues of both male and female zebrafish at 1 h post-feeding. Meanwhile, their expression in the brain and gut decreased at 3 h post-feeding, reaching preprandial levels. Additionally, FTO and IRX3 mRNA abundance in examined tissues increased after 7 days of food deprivation, but substantially decreased after refeeding for 24 h. In summary, we report that both FTO and IRX3 are meal-sensitive genes in zebrafish. The fasting-induced increase suggests a possible appetite regulatory role for FTO and IRX3 in zebrafish. These findings highlight the importance of FTO and IRX3 in appetite and metabolic regulation in zebrafish.

Risk of Fat Mass- and Obesity-Associated Gene-Dependent Obesogenic Programming by Formula Feeding Compared to Breastfeeding

It is the purpose of this review to compare differences in postnatal epigenetic programming at the level of DNA and RNA methylation and later obesity risk between infants receiving artificial formula feeding (FF) in contrast to natural breastfeeding (BF). FF bears the risk of aberrant epigenetic programming at the level of DNA methylation and enhances the expression of the RNA demethylase fat mass- and obesity-associated gene (FTO), pointing to further deviations in the RNA methylome. Based on a literature search through Web of Science, Google Scholar, and PubMed databases concerning the dietary and epigenetic factors influencing FTO gene and FTO protein expression and FTO activity, FTO's impact on postnatal adipogenic programming was investigated. Accumulated translational evidence underscores that total protein intake as well as tryptophan, kynurenine, branched-chain amino acids, milk exosomal miRNAs, NADP, and NADPH are crucial regulators modifying FTO gene expression and FTO activity. Increased FTO-mTORC1-S6K1 signaling may epigenetically suppress the WNT/β-catenin pathway, enhancing adipocyte precursor cell proliferation and adipogenesis. Formula-induced FTO-dependent alterations of the N6-methyladenosine (m6A) RNA methylome may represent novel unfavorable molecular events in the postnatal development of adipogenesis and obesity, necessitating further investigations. BF provides physiological epigenetic DNA and RNA regulation, a compelling reason to rely on BF.

Maternal choline supplementation mitigates premature foetal weight gain induced by an obesogenic diet, potentially linked to increased amniotic fluid leptin levels in rats

Placental leptin may impact foetal development. Maternal overnutrition has been linked to increased plasma leptin levels and adverse effects on offspring, whereas choline, an essential nutrient for foetal development, has shown promise in mitigating some negative impacts of maternal obesity. Here, we investigate whether a maternal obesogenic diet alters foetal growth and leptin levels in the foetal stomach, amniotic fluid (AF), and placenta in late gestation and explore the potential modulating effects of maternal choline supplementation. Female rats were fed a control (CD) or a western diet (WD) four weeks before mating and during gestation, half of them supplemented with choline (pregnancy days 11-17). Leptin levels (in foetal stomach, AF, and placenta) and leptin gene expression (in placenta) were assessed on gestation days 20 and 21. At day 20, maternal WD feeding resulted in greater leptin levels in foetal stomach, placenta, and AF. The increased AF leptin levels were associated with a premature increase in foetal weight in both sexes. Maternal choline supplementation partially prevented these alterations, but effects differed in CD dams, causing increased AF leptin levels and greater weight in male foetuses at day 20. Maternal choline supplementation effectively mitigates premature foetal overgrowth induced by an obesogenic diet, potentially linked to increased AF leptin levels. Further research is needed to explore the sex-specific effects.

Determinants of obesity in Latin America

Obesity rates are increasing almost everywhere in the world, although the pace and timing for this increase differ when populations from developed and developing countries are compared. The sharp and more recent increase in obesity rates in many Latin American countries is an example of that and results from regional characteristics that emerge from interactions between multiple factors. Aware of the complexity of enumerating these factors, we highlight eight main determinants (the physical environment, food exposure, economic and political interest, social inequity, limited access to scientific knowledge, culture, contextual behaviour and genetics) and discuss how they impact obesity rates in Latin American countries. We propose that initiatives aimed at understanding obesity and hampering obesity growth in Latin America should involve multidisciplinary, global approaches that consider these determinants to build more effective public policy and strategies, accounting for regional differences and disease complexity at the individual and systemic levels.

RNA methylations in depression, from pathological mechanism to therapeutic potential

Depression is caused by a variety of factors such as genetic factors, biological factors, and psychosocial factors, and the pathogenesis is complex. RNA methylations and related downstream signaling pathways influence a variety of biological mechanisms, including cell differentiation, tumorigenesis, sex determination, and stress response. In this work, we searched the PubMed, Web of Science, National Library of Science and Technology (NSTL), and ScienceDirect Online (SDOL) databases to summarize the biological roles of RNA methylations and their impact on the pathological mechanisms of depression. RNA methylations play a key role in the development of many diseases, and current research shows that RNA methylations are also closely linked to depression. RNA methylations in depression mainly involve "writers" (mediating the methylation modification process of RNAs), "erasers" (mediating the demethylation modification process of RNA methylation). Fat Mass and Obesity Associated (FTO) influences the development of depression by increasing body mass index (BMI), decreases the dopamine level, inhibits the adrenoceptor beta 2 (ADRB2)-c-Myc-sirt1 pathway, results in the m6A/m6Am dysregulation in brain, and may be involved in the pathogenesis of depression. The study of RNA methylations in depression has further deepened our understanding of the pathogenesis and development process of depression, provides new perspectives for the study of the pathological mechanism of depression, and provides new targets for the prevention and treatment of this disease.

The metabolic effects of resumption of a high fat diet after weight loss are sex dependent in mice

Dietary restriction is a frequent strategy for weight loss, but adherence is difficult and returning to poor dietary habits can result in more weight gain than that previously lost. How weight loss due to unrestricted intake of a healthy diet affects the response to resumption of poor dietary habits is less studied. Moreover, whether this response differs between the sexes and if the insulin-like growth factor (IGF) system, sex dependent and involved in metabolic control, participates is unknown. Mice received rodent chow (6% Kcal from fat) or a high-fat diet (HFD, 62% Kcal from fat) for 4 months, chow for 3 months plus 1 month of HFD, or HFD for 2 months, chow for 1 month then HFD for 1 month. Males and females gained weight on HFD and lost weight when returned to chow at different rates (p < 0.001), but weight gain after resumption of HFD intake was not affected by previous weight loss in either sex. Glucose metabolism was more affected by HFD, as well as the re-exposure to HFD after weight loss, in males. This was associated with increases in hypothalamic mRNA levels of IGF2 (p < 0.01) and IGF binding protein (IGFBP) 2 (p < 0.05), factors involved in glucose metabolism, again only in males. Likewise, IGF2 increased IGFBP2 mRNA levels only in hypothalamic astrocytes from males (p < 0.05). In conclusion, the metabolic responses to dietary changes were less severe and more delayed in females and the IGF system might be involved in some of the sex specific observations.

Technologies, strategies, and cautions when deconvoluting genome-wide association signals: FTO in focus

Genome-wide association studies have revealed a plethora of genetic variants that correlate with polygenic conditions. However, causal molecular mechanisms have proven challenging to fully define. Without such information, the associations are not physiologically useful or clinically actionable. By reviewing studies of the FTO locus in the genetic etiology of obesity, we wish to highlight advances in the field fueled by the evolution of technical and analytic strategies in assessing the molecular bases for genetic associations. Particular attention is drawn to extrapolating experimental findings from animal models and cell types to humans, as well as technical aspects used to identify long-range DNA interactions and their biological relevance with regard to the associated trait. A unifying model is proposed by which independent obesogenic pathways regulated by multiple FTO variants and genes are integrated at the primary cilium, a cellular antenna where signaling molecules that control energy balance convene.

Investigating neural differentiation of mouse P19 embryonic stem cells in a time-dependent manner by bioinformatic, microscopic and transcriptional analyses

BACKGROUND

As an available cell line, mouse pluripotent P19 has been widely employed for neuronal differentiation studies. In this research, by applying the in vitro differentiation of this cell line into neuron-like cells through retinoic acid (RA) treatment, the roles of some genes including DNMT3B, ICAM1, IRX3, JAK2, LHX1, SOX9, TBX3 and THY1 in neural differentiation was investigated.

METHODS AND RESULTS

Bioinformatics, microscopic, and transcriptional studies were conducted in a time-dependent manner after RA-induced neural differentiation. According to bioinformatics studies, we determined the engagement of the metabolic and developmental super-pathways and pathways in neural cell differentiation, particularly focusing on the considered genes. According to our qRT-PCR analyses, JAK2, SOX9, TBX3, LHX1 and IRX3 genes were found to be significantly overexpressed in a time-dependent manner (p < 0.05). In addition, the significant downregulation of THY1, DNMT3B and ICAM1 genes was observed during the experiment (p < 0.05). The optical microscopic investigation showed that the specialized extensions of the neuron-like cells were revealed on day 8 after RA treatment.

CONCLUSION

Accordingly, the neural differentiation of P19 cell line and the role of the considered genes during the differentiation were proved. However, our results warrant further in vivo studies.

The orphan G protein-coupled receptor, GPR139, is expressed in the hypothalamus and is involved in the regulation of body mass, blood glucose, and insulin

GPR139 is an orphan G-protein-coupled receptor that is expressed in restricted areas of the nervous system, including the hypothalamus. In this study, we hypothesized that GPR139 could be involved in the regulation of energy balance and metabolism. In the first part of the study, we confirmed that GPR139 is expressed in the hypothalamus and particularly in proopiomelanocortin and agouti-related peptide neurons of the mediobasal hypothalamus. Using a lentivirus with a short-hairpin RNA, we inhibited the expression of GPR139 bilaterally in the mediobasal hypothalamus of mice. The intervention promoted a 40% reduction in the hypothalamic expression of GPR139, which was accompanied by an increase in body mass, a reduction in fasting blood glucose levels, and an increase in insulin levels. In the hypothalamus, inhibition of GPR139 was accompanied by a reduction in the expression of orexin. As previous studies using a pharmacological antagonist of orexin showed a beneficial impact on type 2 diabetes and glucose metabolism, we propose that the inhibition of hypothalamic GPR139 could be acting indirectly through the orexin system to control systemic glucose and insulin. In conclusion, this study advances the characterization of GPR139 in the hypothalamus, demonstrating its involvement in the regulation of body mass, blood insulin, and glycemia.

Possible role of transcription factors (BSX, NKX2.1, IRX3 and SIRT1) in the regulation of appetite in goldfish (Carassius auratus)

The homeobox genes play important roles in the embryonic development of animals. Recent evidence suggests they might also regulate feeding and act as transcription factors of appetite regulators. Examples of these genes are a brain-specific homeobox transcription factor (BSX), NK2 homeobox 1 (NKX2.1) and the Iroquois homeobox 3 (IRX3). Sirtuin1 (SIRT1) acts as a transcription factor for nutrient (e.g. lipid, glucose) homeostasis and responds to stress and nutrient availability, and has been shown to interact with appetite regulators. Very little is known about the role of these genes in the regulation of feeding and nutrient homeostasis in fish. In this study, we assessed the roles of BSX, NKX2.1, IRX3 and SIRT1 in the central regulation of feeding in goldfish by examining their mRNA brain distribution, assessing the effects of fasting on their brain expression and assessing the effects of peripheral injections of cholecystokinin (CCK, a brain-gut peptide), on their brain expression. All genes showed a widespread distribution in the brain, with high levels in the hypothalamus. In both hypothalamus and telencephalon, fasting induced increases in BSX, IRX3 and NKX2.1 expressions but had no effect on SIRT1 expression levels. CCK injections increased hypothalamic expression levels of IRX3 and SIRT1, and telencephalic expression levels of NKX2.1 and SIRT1, with no effect on either hypothalamic BSX or NKX2.1 expression levels or telencephalon BSX or IRX3 expression levels. Our results suggest that, in goldfish as in mammals, central BSX, NKX2.1, IRX3 and SIRT1 are present in regions of the brain regulating feeding, are sensitive to nutrient status and interact with appetite-regulating peptides.

Critical roles of FTO-mediated mRNA m6A demethylation in regulating adipogenesis and lipid metabolism: Implications in lipid metabolic disorders

The goal this review is to clarify the effects of the fat mass and obesity-associated protein (FTO) in lipid metabolism regulation and related underlying mechanisms through the FTO-mediated demethylation of m⁶A modification. FTO catalyzes the demethylation of m⁶A to alter the processing, maturation and translation of the mRNAs of lipid-related genes. FTO overexpression in the liver promotes lipogenesis and lipid droplet (LD) enlargement and suppresses CPT-1–mediated fatty acid oxidation via the SREBP1c pathway, promoting excessive lipid storage and nonalcoholic fatty liver diseases (NAFLD). FTO enhances preadipocyte differentiation through the C/EBPβ pathway, and facilitates adipogenesis and fat deposition by altering the alternative splicing of RUNX1T1, the expression of PPARγ and ANGPTL4, and the phosphorylation of PLIN1, whereas it inhibits lipolysis by inhibiting IRX3 expression and the leptin pathway, causing the occurrence and development of obesity. Suppression of the PPARβ/δ and AMPK pathways by FTO-mediated m⁶A demethylation damages lipid utilization in skeletal muscles, leading to the occurrence of diabetic hyperlipidemia. m⁶A demethylation by FTO inhibits macrophage lipid influx by downregulating PPARγ protein expression and accelerates cholesterol efflux by phosphorylating AMPK, thereby impeding foam cell formation and atherosclerosis development. In summary, FTO-mediated m⁶A demethylation modulates the expression of lipid-related genes to regulate lipid metabolism and lipid disorder diseases.

IRX3 plays an important role in the pathogenesis of metabolic-associated fatty liver disease by regulating hepatic lipid metabolism

Metabolic-associated fatty liver disease (MAFLD) affects approximately a quarter of the global population. Identification of the key genes and pathways involved in hepatic lipid metabolism is of the utmost importance for the diagnosis, treatment, and prevention of MAFLD. In this study, differentially expressed genes were identified through whole-genome transcriptional analysis of liver tissue from MAFLD patients and healthy controls, and a series of lipid metabolism-related molecules and pathways were obtained through pathway analysis. Subsequently, we focused on Iroquois homeobox protein 3 (IRX3), one of 13 transcription factors that were screened from the 331 differentially expressed genes. The transcription factor IRX3 was significantly decreased in the liver tissue of patients with MAFLD when compared with healthy controls. Pearson's correlation analysis showed that the expression levels of IRX3 in liver tissue were negatively correlated with serum total cholesterol, triglycerides, low-density lipoprotein cholesterol, and uric acid levels. The overexpression and interference of IRX3 induced the increased and decreased lipid droplet accumulation in vitro, respectively. Moreover, interference of IRX3 expression increased mitochondrial fragmentation and reduced the activity of the mitochondrial respiratory chain complex IV. In summary, the study demonstrated that IRX3 regulated hepatic lipid metabolism of MAFLD, and also revealed the effect of IRX3 on mitochondria might be an important mechanism by which IRX3 regulated hepatic lipid metabolism of MAFLD.

Irx3 and Irx5 - Novel Regulatory Factors of Postnatal Hypothalamic Neurogenesis

The hypothalamus is a brain region that exhibits highly conserved anatomy across vertebrate species and functions as a central regulatory hub for many physiological processes such as energy homeostasis and circadian rhythm. Neurons in the arcuate nucleus of the hypothalamus are largely responsible for sensing of peripheral signals such as leptin and insulin, and are critical for the regulation of food intake and energy expenditure. While these neurons are mainly born during embryogenesis, accumulating evidence have demonstrated that neurogenesis also occurs in postnatal-adult mouse hypothalamus, particularly in the first two postnatal weeks. This second wave of active neurogenesis contributes to the remodeling of hypothalamic neuronal populations and regulation of energy homeostasis including hypothalamic leptin sensing. Radial glia cell types, such as tanycytes, are known to act as neuronal progenitors in the postnatal mouse hypothalamus. Our recent study unveiled a previously unreported radial glia-like neural stem cell (RGL-NSC) population that actively contributes to neurogenesis in the postnatal mouse hypothalamus. We also identified Irx3 and Irx5, which encode Iroquois homeodomain-containing transcription factors, as genetic determinants regulating the neurogenic property of these RGL-NSCs. These findings are significant as IRX3 and IRX5 have been implicated in FTO-associated obesity in humans, illustrating the importance of postnatal hypothalamic neurogenesis in energy homeostasis and obesity. In this review, we summarize current knowledge regarding postnatal-adult hypothalamic neurogenesis and highlight recent findings on the radial glia-like cells that contribute to the remodeling of postnatal mouse hypothalamus. We will discuss characteristics of the RGL-NSCs and potential actions of Irx3 and Irx5 in the regulation of neural stem cells in the postnatal-adult mouse brain. Understanding the behavior and regulation of neural stem cells in the postnatal-adult hypothalamus will provide novel mechanistic insights in the control of hypothalamic remodeling and energy homeostasis.

Macrophage IRX3 promotes diet-induced obesity and metabolic inflammation

Metabolic inflammation is closely linked to obesity, and is implicated in the pathogenesis of metabolic diseases. FTO harbors the strongest genetic association with polygenic obesity, and IRX3 mediates the effects of FTO on body weight. However, in what cells and how IRX3 carries out this control are poorly understood. Here we report that macrophage IRX3 promotes metabolic inflammation to accelerate the development of obesity and type 2 diabetes. Mice with myeloid-specific deletion of Irx3 were protected against diet-induced obesity and metabolic diseases via increasing adaptive thermogenesis. Mechanistically, macrophage IRX3 promoted proinflammatory cytokine transcription and thus repressed adipocyte adrenergic signaling, thereby inhibiting lipolysis and thermogenesis. JNK1/2 phosphorylated IRX3, leading to its dimerization and nuclear translocation for transcription. Further, lipopolysaccharide stimulation stabilized IRX3 by inhibiting its ubiquitination, which amplified the transcriptional capacity of IRX3. Together, our findings identify a new player, macrophage IRX3, in the control of body weight and metabolic inflammation, implicating IRX3 as a therapeutic target.

Irx3 and Irx5 in Ins2-Cre+ cells regulate hypothalamic postnatal neurogenesis and leptin response

Obesity is mainly due to excessive food intake. IRX3 and IRX5 have been suggested as determinants of obesity in connection with the intronic variants of FTO, but how these genes contribute to obesity via changes in food intake remains unclear. Here, we show that mice doubly heterozygous for Irx3 and Irx5 mutations exhibit lower food intake with enhanced hypothalamic leptin response. By lineage tracing and single-cell RNA sequencing using the Ins2-Cre system, we identify a previously unreported radial glia-like neural stem cell population with high Irx3 and Irx5 expression in early postnatal hypothalamus and demonstrate that reduced dosage of Irx3 and Irx5 promotes neurogenesis in postnatal hypothalamus leading to elevated numbers of leptin-sensing arcuate neurons. Furthermore, we find that mice with deletion of Irx3 in these cells also exhibit a similar food intake and hypothalamic phenotype. Our results illustrate that Irx3 and Irx5 play a regulatory role in hypothalamic postnatal neurogenesis and leptin response.

Variable expression quantitative trait loci analysis of breast cancer risk variants

Genome wide association studies (GWAS) have identified more than 180 variants associated with breast cancer risk, however the underlying functional mechanisms and biological pathways which confer disease susceptibility remain largely unknown. As gene expression traits are under genetic regulation we hypothesise that differences in gene expression variability may identify causal breast cancer susceptibility genes. We performed variable expression quantitative trait loci (veQTL) analysis using tissue-specific expression data from the Genotype-Tissue Expression (GTEx) Common Fund Project. veQTL analysis identified 70 associations (p < 5 × 10^–8) consisting of 60 genes and 27 breast cancer risk variants, including 55 veQTL that were observed in breast tissue only. Pathway analysis of genes associated with breast-specific veQTL revealed an enrichment of four genes (CYP11B1, CYP17A1 HSD3B2 and STAR) involved in the C21-steroidal biosynthesis pathway that converts cholesterol to breast-related hormones (e.g. oestrogen). Each of these four genes were significantly more variable in individuals homozygous for rs11075995 (A/A) breast cancer risk allele located in the FTO gene, which encodes an RNA demethylase. The A/A allele was also found associated with reduced expression of FTO, suggesting an epi-transcriptomic mechanism may underlie the dysregulation of genes involved in hormonal biosynthesis leading to an increased risk of breast cancer. These findings provide evidence that genetic variants govern high levels of expression variance in breast tissue, thus building a more comprehensive insight into the underlying biology of breast cancer risk loci.

Short Dietary Intervention with Olive Oil Increases Brown Adipose Tissue Activity in Lean but not Overweight Subjects

BACKGROUND

The brown adipose tissue (BAT) is a potential target for the treatment of obesity and metabolic disorders. Its activation by cold exposure or adrenergic drugs can increase systemic insulin sensitivity and improve lipid metabolism; however, little is known about the effects of specific dietary components on BAT activity.

OBJECTIVES

We asked if a short-term (4 weeks) dietary intervention with olive oil could modify BAT activity in lean and overweight/obese volunteers.

DESIGN

This was a 4-week open clinical trial in which all participants underwent a dietary intervention with extra-virgin olive oil supplementation. As the initial intake of olive oil was controlled all the participants were controls of themselves.

RESULTS

The intervention resulted in significant increase in blood monounsaturated fatty acid levels, which was accompanied by increased BAT activity in lean but not in overweight/obese volunteers. In the lean group, an increase in leptin was detected after the intervention, and low leptin values at the beginning of the study were predictive of greater BAT activity after intervention. In addition, increase in leptin concentration was associated with increased BAT activity. Three known endogenous mediators of BAT activity, secretin, fibroblast growth factor 21 (FGF21), and 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME) were increased by intervention in lean, whereas only secretin and FGF21 were increased in subjects with excessive weight.

CONCLUSION

This study provides clinical evidence for the impact of monounsaturated fatty acids on BAT activity and an advance in the understanding of the beneficial health effects of olive oil.

IRX3 Overexpression Enhances Ucp1 Expression In Vivo

OBJECTIVE

The Iroquois homeobox 3 (IRX3) gene was recently reported to be a functional downstream target of a common polymorphism in the FTO gene, which encodes an obesity-associated protein; however, the role of IRX3 in energy expenditure remains unclear. Studies have revealed that the overexpression of a dominant-negative form of IRX3 in the mouse hypothalamus and adipose tissue promoted energy expenditure by enhancing brown/browning activities. Meanwhile, we and others recently demonstrated that IRX3 knockdown impaired the browning program of primary preadipocytes in vitro. In this study, we aimed to further clarify the effects of overexpressing human IRX3 (hIRX3) on brown/beige adipose tissues in vivo.

METHODS

Brown/beige adipocyte-specific hIRX3-overexpressing mice were generated and the browning program of white adipose tissues was induced by both chronic cold stimulation and CL316,243 injection. Body weight, fat mass, lean mass, and energy expenditure were measured, while morphological changes and the expression of thermogenesis-related genes in adipose tissue were analyzed. Moreover, the browning capacity of primary preadipocytes derived from hIRX3-overexpressing mice was assessed. RNA sequencing was also employed to investigate the effect of hIRX3 on the expression of thermogenesis-related genes.

RESULTS

hIRX3 overexpression in embryonic brown/beige adipose tissues (Rosa26^hIRX3 ;Ucp1-Cre) led to increased energy expenditure, decreased fat mass, and a lean body phenotype. After acute cold exposure or CL316,243 stimulation, brown/beige tissue hIRX3-overexpressing mice showed an increase in Ucp1 expression. Consistent with this, induced hIRX3 overexpression in adult mice (Rosa26^hIRX3 ;Ucp1-Cre^ERT2) also promoted a moderate increase in Ucp1 expression. Ex vitro experiments further revealed that hIRX3 overexpression induced by Ucp1-driven Cre recombinase activity upregulated brown/beige adipocytes Ucp1 expression and oxygen consumption rate (OCR). RNA sequencing analyses indicated that hIRX3 overexpression in brown adipocytes enhanced brown fat cell differentiation, glycolysis, and gluconeogenesis.

CONCLUSION

Consistent with the in vitro findings, brown/beige adipocyte-specific overexpression of hIRX3 promoted Ucp1 expression and thermogenesis, while reducing fat mass.

Tumor Necrosis Factor α and Interleukin-1β Acutely Inhibit AgRP Neurons in the Arcuate Nucleus of the Hypothalamus

Obesity-associated low-grade inflammation favors weight gain, whereas systemic infection frequently leads to anorexia. Thus, inflammatory signals can either induce positive or negative energy balance. In this study, we used whole-cell patch-clamp to investigate the acute effects of three important proinflammatory cytokines, tumor necrosis factor α (TNF-α), interleukin-6, and interleukin-1β (IL-1β) on the membrane excitability of agouti-related peptide (AgRP)- or proopiomelanocortin (POMC)-producing neurons. We found that both TNF-α and IL-1β acutely inhibited the activity of 35-42% of AgRP-producing neurons, whereas very few POMC neurons were depolarized by TNF-α. Interleukin-6 induced no acute changes in the activity of AgRP or POMC neurons. Our findings indicate that the effect of TNF-α and IL-1β, especially on the activity of AgRP-producing neurons, may contribute to inflammation-induced anorexia observed during acute inflammatory conditions.

Impact of Long-Term HFD Intake on the Peripheral and Central IGF System in Male and Female Mice

The insulin-like growth factor (IGF) system is responsible for growth, but also affects metabolism and brain function throughout life. New IGF family members (i.e., pappalysins and stanniocalcins) control the availability/activity of IGFs and are implicated in growth. However, how diet and obesity modify this system has been poorly studied. We explored how intake of a high-fat diet (HFD) or commercial control diet (CCD) affects the IGF system in the circulation, visceral adipose tissue (VAT) and hypothalamus. Male and female C57/BL6J mice received HFD (60% fat, 5.1 kcal/g), CCD (10% fat, 3.7 kcal/g) or chow (3.1 % fat, 3.4 kcal/g) for 8 weeks. After 7 weeks of HFD intake, males had decreased glucose tolerance (p < 0.01) and at sacrifice increased plasma insulin (p < 0.05) and leptin (p < 0.01). Circulating free IGF1 (p < 0.001), total IGF1 (p < 0.001), IGF2 (p < 0.05) and IGFBP3 (p < 0.01) were higher after HFD in both sexes, with CCD increasing IGFBP2 in males (p < 0.001). In VAT, HFD reduced mRNA levels of IGF2 (p < 0.05), PAPP-A (p < 0.001) and stanniocalcin (STC)-1 (p < 0.001) in males. HFD increased hypothalamic IGF1 (p < 0.01), IGF2 (p < 0.05) and IGFBP5 (p < 0.01) mRNA levels, with these changes more apparent in females. Our results show that diet-induced changes in the IGF system are tissue-, sex- and diet-dependent.

Acute effects of fatty acids on autophagy in NPY neurones

High-fat diet (HFD) feeding is deleterious to hypothalamic tissue, leading to inflammation and lipotoxicity, as well as contributing to central insulin resistance. Autophagy is a process that restores cellular homeostasis by degrading malfunctioning organelles and proteins. Chronic HFD-feeding down-regulates hypothalamic autophagy. However, the effects of short-term HFD-feeding and the saturated fatty acid palmitate (PA) on hypothalamic autophagy and in neurones that express neuropeptide Y (NPY) and agouti-related peptide remains unknown. Therefore, we assessed hypothalamic autophagy after 1 and 3 days of HFD-feeding. We also injected PA i.c.v and analysed the modulation of autophagy in hypothalamic tissue. Both interventions resulted in changes in autophagy-related gene profiles without significant differences in protein content of p62 and LC3B-II, markers of the autophagy pathway. When we assessed native NPY neurones in brain slices from PA-treated animals, we observed increased levels of Atg7 and LC3B protein in response to PA treatment, indicating the induction of autophagy. We then tested the direct effects of fatty acids using the immortalised hypothalamic NPY-expressing neuronal cell model mHypoE-46. We found that PA, but not palmitoleate (PO) (a monounsaturated fatty acid), was able to induce autophagy. Co-treatment with PA and PO was able to block the PA-mediated induction of autophagy, as assessed by flow cytometry. When the de novo ceramide synthesis pathway was blocked with myriocin pre-treatment, we observed a decrease in PA-mediated induction of autophagy, although there was no change with the toll-like receptor 4 inhibitor, TAK-242. Taken together, these findings provide evidence that saturated and unsaturated fatty acids can differentially regulate hypothalamic autophagy and that ceramide synthesis may be an important mediator of those effects. Understanding the mechanisms by which dietary fats affect autophagy in neurones involved in the control of energy homeostasis will provide potential new pathways for targeting and containing the obesity epidemic.

Hunger and BMI modulate neural responses to sweet stimuli: fMRI meta-analysis

OBJECTIVE

Consuming sweet foods, even when sated, can lead to unwanted weight gain. Contextual factors, such as longer time fasting, subjective hunger, and body mass index (BMI), may increase the likelihood of overeating. Nevertheless, the neural mechanisms underlying these moderating influences on energy intake are poorly understood.

METHODS

We conducted both categorical meta-analysis and meta-regression of factors modulating neural responses to sweet stimuli, using data from 30 functional magnetic resonance imaging (fMRI) articles incorporating 39 experiments (N = 995) carried out between 2006 and 2019.

RESULTS

Responses to sweet stimuli were associated with increased activity in regions associated with taste, sensory integration, and reward processing. These taste-evoked responses were modulated by context. Longer fasts were associated with higher posterior cerebellar, thalamic, and striatal activity. Greater self-reported hunger was associated with higher medial orbitofrontal cortex (OFC), dorsal striatum, and amygdala activity and lower posterior cerebellar activity. Higher BMI was associated with higher posterior cerebellar and insular activity.

CONCLUSIONS

Variations in fasting time, self-reported hunger, and BMI are contexts associated with differential sweet stimulus responses in regions associated with reward processing and homeostatic regulation. These results are broadly consistent with a hierarchical model of taste processing. Hunger, but not fasting or BMI, was associated with sweet stimulus-related OFC activity. Our findings extend existing models of taste processing to include posterior cerebellar regions that are associated with moderating effects of both state (fast length and self-reported hunger) and trait (BMI) variables.

Differential Responses of Liver and Hypothalamus to the Nutritional Condition During Lactation and Adult Life

It was previously reported that liver glucose metabolism in rats under caloric restriction differs from that of freely-fed rats. This study hypothesized that these changes (1) were related to the expression of hypothalamic neuropeptides involved in metabolic control, and (2) were not a residual effect of litter size. To those purposes, liver glucose metabolism and hypothalamic expression of the orexigenic neuropeptides NPY (neuropeptide Y) and AgRP (agouti gene-related peptide); and of the anorexigenic neuropeptides POMC (pro-opiomelanocortin) and CART (cocaine- and amphetamine-related transcripts) were investigated. Male Wistar rats from two different litter sizes (G6 and G12, with 6 or 12 pups, respectively) were subjected to free feeding (GL, ad libitum), 50% caloric restriction (GR) or caloric restriction+ad libitum refeeding (GRL) until the age of 90 days. Biometric values were lower in GR than in GL, while in GRL they were totally or partially recovered. Blood glucose variation during the pyruvate tolerance test (PTT) was small in GR. During in situ liver perfusion, total, basal, and adrenaline-stimulated liver glucose outputs were high in GR, but additional glucose output in the presence of alanine was negligible. Refeeding (GRL) yielded values close to those of GL. Litter size did not consistently influence any of these variables. The expression of transcripts of the hypothalamic neuropeptides was responsive to feeding regimen, litter size and/or their interaction and differed from G6 to G12, while the metabolic changes of the liver were qualitatively equal in both GR. Therefore, the changes in glucose metabolism in the liver of rats under caloric restriction were not determined by either litter size or hypothalamic neuropeptide expression and were linked only to the prevailing feeding regimen of the adult animal.

Hypothalamic IRX3: A New Player in the Development of Obesity

Genome-wide association studies (GWASs) have identified SNPs of the fat mass and obesity (FTO) gene as the most important risk alleles for obesity. However, how the presence of risk alleles affect phenotype is still a matter of intense investigation. In 2014, a study revealed that long-range enhancers from the intronic regions of the FTO gene regulate iroquois-class homeobox protein (IRX)3 expression. IRX3 is expressed in hypothalamic pro-opiomelanocortin (POMC) neurons and changes in its expression levels affect body adiposity by modifying food intake and energy expenditure. These findings have placed IRX3 as a potential target for the treatment of obesity. Here, we review studies that evaluated the roles of IRX3 in development, neurogenesis, and body energy homeostasis.

The homeobox factor Irx3 maintains adipogenic identity

BACKGROUND

Inhibition of Irx3 and Irx5 has been shown to reduce body weight and white adipose tissue (WAT) mass through cell-autonomous and sympathetic-induced increases in adipocyte beiging and thermogenesis in mice and humans. However, the underlying mechanisms of the Irx control over beiging are still largely unknown, as illustrated by recent reports showing divergent effects of Irx3 on adipocyte metabolism and function. Here, we investigated the role of Irx3 in controlling beige preadipocyte function and differentiation.

METHODS

Stable knock out of Irx3 in ME3 mouse preadipocytes capable of beiging was performed using a CRISPR-Cas9 system, and the effect on cell differentiation was assessed by qPCR, RNA-seq, Oil-red-O lipid staining and Alcian Blue staining of proteoglycans. Changes in cell identities were validated using cell type enrichment analysis from RNA-seq data. Proliferation and cell cycle progression in undifferentiated cells were measured by WST-1 and flow cytometry, reactive oxygen species (ROS) generation was determined by fluorescence spectrometry and mitochondrial respiration was investigated by Seahorse assay.

RESULTS

Irx3 was found to be essential for the identity, function and adipogenic differentiation of beige adipocyte precursors. Irx3-KO impaired proliferation, ROS generation and mitochondrial respiration in the preadipocytes. We further observed profound changes in numerous genes during both early and late stages of adipogenic differentiation, including genes important for adipocyte differentiation, cell cycle progression, oxidative phosphorylation (OXPHOS) and morphogenesis. Irx3-KO cells failed to accumulate lipids following adipogenic stimuli, and cell enrichment analysis revealed a loss of preadipocyte identity and a gain of chondrocyte-like identity in Irx3-KO cells during early differentiation. Finally, unlike the control cells, the Irx3-KO cells readily responded to chondrogenic stimuli.

CONCLUSIONS

Irx3 is required for preadipocyte identity and differentiation capacity. Our findings suggest that, while inhibition of Irx3 may be beneficial during later developmental stages to modulate adipogenesis in the beige direction, constitutive and complete absence of Irx3 in the embryonic fibroblast stage leads to detrimental loss of adipogenic differentiation capacity.

Association between impulsivity traits and body mass index at the observational and genetic epidemiology level

We investigated the association between impulsivity related traits and BMI at the observational and genetic epidemiology level in a cross-sectional population of healthy young American-European adults. We studied 998 students and university staff of European ancestry recruited from Chicago (Illinois) and Athens (Georgia). We measured 14 impulsivity variables using three broad categories: impulsive choice, action and personality. Weight and height of participants were measured by research assistants. The single-nucleotide polymorphism (SNP) rs3751812 in the fat mass and obesity-associated (FTO) gene was genotyped using the Illumina PsychArray BeadChip platform. Within the three broad domains of impulsivity, 4 parameters (delay discounting of rewards area under the curve and average of k indexes, Conner's continuous performance test, and negative urgency) were associated with BMI. The FTO rs3751812 minor allele T was associated with higher BMI. Of the 14 impulsivity variables, rs3751812 T was associated with more premeditation and perseverance, before and after adjusting for BMI. The association between FTO rs3751812 and BMI adjusted for premeditation remained significant, but disappeared after adjusting for perseverance and for both perseverance and premeditation traits. Our observational and genetic data indicate a complex pattern of association between impulsive behaviors and BMI in healthy young American-European adults.

The FTO genetic variants are associated with dietary intake and body mass index amongst Emirati population

BACKGROUND

The risk of obesity is determined by complex interactions between genetic and environmental factors. Little research to date has investigated the interaction between gene and food intake. The aim of the current study is to explore the potential effect of fat mass and obesity-associated protein gene (FTO) rs9939609 and rs9930506 single nucleotide polymorphism (SNP) on the pattern of food intake in the Emirati population.

METHODS

Adult healthy Emirati subjects with Body mass index (BMI) of 16-40 kg/m2 were included in the study. Genotyping for FTO rs9939609(A>T) and rs9930506(A>G) was performed using DNA from saliva samples. Subjects were categorized according to the WHO classification by calculating the BMI to compare different classes. Dietary intake was assessed by a sixty-one-item FFQ that estimated food and beverage intakes over the past year. The daily energy, macronutrient, and micronutrient consumption were computed.

RESULTS

We included 169 subjects in the final analysis (mean age 30.49± 9.1years, 57.4% females). The mean BMI of the study population was 26.19 kg/m2. Both SNPs were in Hardy Weinberg Equilibrium. The rs9939609 AA genotype was significantly associated with higher BMI (p = 0.004); the effect was significant in females (p = 0.028), but not in males (p = 0.184). Carbohydrate intake was significantly higher in AA subjects with a trend of lower fat intake compared to other genotypes. The odds ratio for the AA was 3.78 in the fourth quartile and 2.67 for the A/T in the second quartile of total carbohydrate intake, considering the first quartile as a reference (95% CI = 1.017-14.1 and 1.03-6.88, respectively). Fat intake was significantly lower in the FTO rs9930506 GG subjects. The presence of FTO rs9930506 GG genotype decreased the fat intake in subjects with FTO rs9939609 AA (p = 0.037).

CONCLUSIONS

The results of this study highlight the interaction of the FTO risk alleles on the food intake in Emirati subjects. The FTO rs9939609 AA subjects had higher carbohydrate and lower fat intake. The latter was accentuated in presence of rs9930506 GG genotype.

C3orf70 Is Involved in Neural and Neurobehavioral Development

Neurogenesis is the process by which undifferentiated progenitor cells develop into mature and functional neurons. Defects in neurogenesis are associated with neurodevelopmental and neuropsychiatric disorders; therefore, elucidating the molecular mechanisms underlying neurogenesis can advance our understanding of the pathophysiology of these disorders and facilitate the discovery of novel therapeutic targets. In this study, we performed a comparative transcriptomic analysis to identify common targets of the proneural transcription factors Neurog1/2 and Ascl1 during neurogenesis of human and mouse stem cells. We successfully identified C3orf70 as a novel common target gene of Neurog1/2 and Ascl1 during neurogenesis. Using in situ hybridization, we demonstrated that c3orf70a and c3orf70b, two orthologs of C3orf70, were expressed in the midbrain and hindbrain of zebrafish larvae. We generated c3orf70 knockout zebrafish using CRISPR/Cas9 technology and demonstrated that loss of c3orf70 resulted in significantly decreased expression of the mature neuron markers elavl3 and eno2. We also found that expression of irx3b, a zebrafish ortholog of IRX3 and a midbrain/hindbrain marker, was significantly reduced in c3orf70 knockout zebrafish. Finally, we demonstrated that neurobehaviors related to circadian rhythm and altered light–dark conditions were significantly impaired in c3orf70 knockout zebrafish. These results suggest that C3orf70 is involved in neural and neurobehavioral development and that defects in C3orf70 may be associated with midbrain/hindbrain-related neurodevelopmental and neuropsychiatric disorders.

Changes in FTO and IRX3 gene expression in obese and overweight male adolescents undergoing an intensive lifestyle intervention and the role of FTO genotype in this interaction

Background

Lifestyle intervention may have a critical effect on the association between genetics and obesity. This study aimed to investigate changes in FTO and IRX3 gene expression in obese and overweight male adolescents undergoing a lifestyle intervention and the role of FTO genotype in this interaction.

Methods

This study was a field trial of 62 adolescents from boys’ high schools in Tehran, Iran. Two schools were randomly allocated as the intervention (n = 30) and control (n = 32) schools. The rs9930506 SNP in FTO was genotyped at baseline and the level of FTO and IRX3 expression in peripheral blood mononuclear cells (PBMCs). Anthropometric measurements were assessed at baseline and after 18 weeks of intensive lifestyle intervention.

Results

Our results showed that IRX3 expression in the intervention group was significantly up-regulated compared to baseline (P = 0.007) and compared to the control group (P = 0.011).The intervention group had significantly up-regulated transcripts of IRX3 only in rs9930506 risk allele carriers of the intervention group compared to risk allele carriers of the control group (P = 0.017). Moreover, our data showed that the FTO expression was up-regulated in AA genotype carriers and down-regulated in AG/GG genotype carriers (P = 0.017).

Conclusion

Lifestyle modification may exert its effects on obesity through changes in the expression level of the FTO and IRX3 genes. However, FTO genotype plays a role in the extent of the effect of lifestyle changes on gene expression. Further studies are crucial to have a better understanding of the interaction between lifestyle, genetics and anthropometric measurements.

Trial registration This paper reports a comprehensive intervention study (Interactions of Genetics, Lifestyle and Anthropometrics study or IGLA study), which is retrospectively registered in the Iranian Registry of Clinical Trials as IRCT2016020925699N2. Date registered: April 24, 2016. (https://www.irct.ir/searchresult.php?id=25699&number=2)

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1921-4) contains supplementary material, which is available to authorized users.

Obesity an overview: Genetic conditions and recent developments in therapeutic interventions

Obesity is a complex disorder that is linked to many coexisting disorders. Recent epidemiological data have suggested that the prevalence of obesity is at an all-time high, growing to be one of the world's biggest problems. There are several mechanisms on how individuals develop obesity which includes genetic and environmental factors. Not only does obesity contribute to other health issues but it also greatly affects the quality of life, physical ability, mental strength and imposes a huge burden in terms of healthcare costs. Along with that, obesity is associated with the risk of mortality and has been shown to reduce the median survival rate. Obesity is basically when the body is not able to balance energy intake and output. When energy intake exceeds energy expenditure, excess calories will be stored as fat leading to weight gain and eventually obesity. The therapeutic market for treating obesity is composed of many different interventions from lifestyle intervention, surgical procedures to pharmacotherapeutic approaches. All of these interventions have their respective benefits and disadvantages and are specifically prescribed to a patient based on the severity of their obesity as well as the existence of other health conditions. This review discusses the genetic and environmental causes of obesity along with the recent developments in anti-obesity therapies.

Ciliary gene RPGRIP1L is required for hypothalamic arcuate neuron development

Intronic polymorphisms in the α-ketoglutarate-dependent dioxygenase gene (FTO) that are highly associated with increased body weight have been implicated in the transcriptional control of a nearby ciliary gene, retinitis pigmentosa GTPase regulator-interacting protein-1 like (RPGRIP1L). Previous studies have shown that congenital Rpgrip1l hypomorphism in murine proopiomelanocortin (Pomc) neurons causes obesity by increasing food intake. Here, we show by congenital and adult-onset Rpgrip1l deletion in Pomc-expressing neurons that the hyperphagia and obesity are likely due to neurodevelopmental effects that are characterized by a reduction in the Pomc/Neuropeptide Y (Npy) neuronal number ratio and marked increases in arcuate hypothalamic-paraventricular hypothalamic (ARH-PVH) axonal projections. Biallelic RPGRIP1L mutations result in fewer cilia-positive human induced pluripotent stem cell-derived (iPSC-derived) neurons and blunted responses to Sonic Hedgehog (SHH). Isogenic human ARH-like embryonic stem cell-derived (ESc-derived) neurons homozygous for the obesity-risk alleles at rs8050136 or rs1421085 have decreased RPGRIP1L expression and have lower numbers of POMC neurons. RPGRIP1L overexpression increases POMC cell number. These findings suggest that apparently functional intronic polymorphisms affect hypothalamic RPGRIP1L expression and impact development of POMC neurons and their derivatives, leading to hyperphagia and increased adiposity.