Hypothalamic IRX3: A New Player in the Development of 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.

High-intensity interval training improves hypothalamic inflammation by suppressing HIF-1α signaling in microglia of male C57BL/6J mice

Repeated bouts of high-intensity interval training (HIIT) induce an improvement in metabolism via plasticity of melanocortin circuits and attenuated hypothalamic inflammation. HIF-1α, which plays a vital role in hypothalamus-mediated regulation of peripheral metabolism, is enhanced in the hypothalamus by HIIT. This study aimed to investigate the effects of HIIT on hypothalamic HIF-1α expression and peripheral metabolism in obese mice and the underlying molecular mechanisms. By using a high-fat diet (HFD)-induced obesity mouse model, we determined the effect of HIIT on energy balance and the expression of the hypothalamic appetite-regulating neuropeptides, POMC and NPY. Moreover, hypothalamic HIF-1α signaling and its downstream glycolytic enzymes were explored after HIIT intervention. The state of microglia and microglial NF-κB signaling in the hypothalamus were also examined in vivo. In vitro by using an adenovirus carrying shRNA-HIF1β, we explored the impact of HIF-1 signaling on glycolysis and NF-κB inflammatory signaling in BV2 cells. Food intake was suppressed and whole-body metabolism was improved in exercised DIO mice, accompanied by changes in the expression of POMC and NPY. Moreover, total and microglial HIF-1α signaling were obviously attenuated in the hypothalamus, consistent with the decreased levels of glycolytic enzymes. Both HFD-induced microglial activation and hypothalamic NF-κB signaling were significantly suppressed following HIIT in vivo. In BV2 cells, after HIF-1 complex knockdown, glycolysis and NF-κB inflammatory signaling were significantly attenuated. The data indicate that HIIT improves peripheral metabolism probably via attenuated HFD-induced microglial activation and microglial NF-κB signaling in the hypothalamus, which could be mediated by suppressed microglial HIF-1α signaling.

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.

The Iroquois (Iro/Irx) homeobox genes are conserved Hox targets involved in motor neuron development

The Iroquois (Iro/Irx) homeobox genes encode transcription factors with fundamental roles in animal development. Despite their link to various congenital conditions in humans, our understanding of Iro/Irx gene expression, function, and regulation remains incomplete. Here, we conducted a systematic expression analysis of all six mouse Irx genes in the embryonic spinal cord. We found five Irx genes (Irx1, Irx2, Irx3, Irx5, and Irx6) to be confined mostly to ventral spinal domains, offering new molecular markers for specific groups of post-mitotic motor neurons (MNs). Further, we engineered Irx2, Irx5, and Irx6 mouse mutants and uncovered essential but distinct roles for Irx2 and Irx6 in MN development. Last, we found that the highly conserved regulators of MN development across species, the HOX proteins, directly control Irx gene expression both in mouse and C. elegans MNs, critically expanding the repertoire of HOX target genes in the developing nervous system. Altogether, our study provides important insights into Iro/Irx expression and function in the developing spinal cord, and uncovers an ancient gene regulatory relationship between HOX and Iro/Irx genes.

1,2-bis(2,4,6-tribromophenoxy) ethane, a novel brominated flame retardant, disrupts intestinal barrier function via the IRX3/NOS2 axis in rat small intestine

Novel brominated flame retardants are widely used in electronics, textiles, furniture, and other products; they can enter the human body through ingestion and respiration and cause harm to the human body, and have been proven to have potential biological toxicity and accumulation effects. 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE) is a widely used novel brominated flame retardant; however, there is a lack of research on its mechanism of toxicity, particularly that of intestinal toxicity. Currently, studies on the functionality of iroquois homeobox 3 (IRX3) are extremely limited. In our study, BTBPE was administered to Sprague-Dawley (SD) rats and rat small intestinal crypt epithelial cells (IEC6 cells) in vivo and in vitro, respectively, and hematoxylin and eosin (HE), immunohistochemical, Alcian blue-periodic acid-Schiff (AB-PAS), CCK8, acridine orange/ethidium bromide (AO/EB), fluorescent probes, qPCR, western blotting, and immunofluorescence analyses were performed. To explore the damage mechanism of BTBPE, we used siRNA to silence IRX3 and iNOs-IN-1 (yeast extract-peptone-wheat; YPW) to inhibit nitric oxide synthase 2 (NOS2). The results showed that BTBPE exposure caused inflammation and necroptosis in the jejunum and ileum, as well as destruction of the tight junctions and mucus layer. Moreover, BTBPE activated the IRX3/NOS2 axis both in vivo and in vitro. Silencing IRX3 or inhibiting NOS2 inhibits necroptosis and restores tight junctions in IEC6 cells. In conclusion, our study found that in the jejunum, ileum, and IEC6 cells, BTBPE exposure caused necroptosis and tight junction destruction by activating the IRX3/NOS2 axis. Blocking the IRX3/NOS2 axis can effectively inhibit necroptosis and restore tight junction. In addition, BTBPE exposure caused inflammation and loss of the mucous layer in the jejunum and ileum. Our study is the first to explore the mechanism of intestinal damage caused by BTBPE exposure and to discover new biological functions regulated by the IRX3/NOS2 axis, providing new research directions for necroptosis and tight junctions.

Characterization of metabolic phenotypes and distinctive genes in mice with low-weight gain

Being overweight exacerbates various metabolic diseases, necessitating the identification of target molecules for obesity control. In the current study, we investigated common physiological features related to metabolism in mice with low weight gain: (1) G protein-coupled receptor, family C, group 5, member B-knockout; (2) gastric inhibitory polypeptide receptor-knockout; and (3) Iroquois-related homeobox 3-knockout. Moreover, we explored genes involved in metabolism by analyzing differentially expressed genes (DEGs) between low-weight gain mice and the respective wild-type control mice. The common characteristics of the low-weight gain mice were low inguinal white adipose tissue (iWAT) and liver weight despite similar food intake along with lower blood leptin levels and high energy expenditure. The DEGs of iWAT, epididymal (gonadal) WAT, brown adipose tissue, muscle, liver, hypothalamus, and hippocampus common to these low-weight gain mice were designated as candidate genes associated with metabolism. One such gene tetraspanin 7 (Tspan7) from the iWAT was validated using knockout and overexpressing mouse models. Mice with low Tspan7 expression gained more weight, while those with high Tspan7 expression gained less weight, confirming the involvement of the Tspan7 gene in weight regulation. Collectively, these findings suggest that the candidate gene list generated in this study contains potential target molecules for obesity regulation. Further validation and additional data from low-weight gain mice will aid in understanding the molecular mechanisms associated with obesity.

Exogenous succinate impacts mouse brown adipose tissue mitochondrial proteome and potentiates body mass reduction induced by liraglutide

Obesity is one of the leading noncommunicable diseases in the world. Despite intense efforts to develop strategies to prevent and treat obesity, its prevalence continues to rise worldwide. A recent study has shown that the tricarboxylic acid intermediate succinate increases body energy expenditure by promoting brown adipose tissue thermogenesis through the activation of uncoupling protein-1; this has generated interest surrounding its potential usefulness as an approach to treat obesity. It is currently unknown how succinate impacts brown adipose tissue protein expression, and how exogenous succinate impacts body mass reduction promoted by a drug approved to treat human obesity, the glucagon-like-1 receptor agonist, liraglutide. In the first part of this study, we used bottom-up shotgun proteomics to determine the acute impact of exogenous succinate on the brown adipose tissue. We show that succinate rapidly affects the expression of 177 brown adipose tissue proteins, which are mostly associated with mitochondrial structure and function. In the second part of this study, we performed a short-term preclinical pharmacological intervention, treating diet-induced obese mice with a combination of exogenous succinate and liraglutide. We show that the combination was more efficient than liraglutide alone in promoting body mass reduction, food energy efficiency reduction, food intake reduction, and an increase in body temperature. Using serum metabolomics analysis, we showed that succinate, but not liraglutide, promoted a significant increase in the blood levels of several medium and long-chain fatty acids. In conclusion, exogenous succinate promotes rapid changes in brown adipose tissue mitochondrial proteins, and when used in association with liraglutide, increases body mass reduction.NEW & NOTEWORTHY Exogenous succinate induces major changes in brown adipose tissue protein expression affecting particularly mitochondrial respiration and structural proteins. When given exogenously in drinking water, succinate mitigates body mass gain in a rodent model of diet-induced obesity; in addition, when given in association with the glucagon-like peptide-1 receptor agonist, liraglutide, succinate increases body mass reduction promoted by liraglutide alone.

Epitranscriptomics in metabolic disease

While epigenetic modifications of DNA and histones play main roles in gene transcription regulation, recently discovered post-transcriptional RNA modifications, known as epitranscriptomic modifications, have been found to have a profound impact on gene expression by regulating RNA stability, localization and decoding efficiency. Importantly, genetic variations or environmental perturbations of epitranscriptome modifiers (that is, writers, erasers and readers) are associated with obesity and metabolic diseases, such as type 2 diabetes. The epitranscriptome is closely coupled to epigenetic signalling, adding complexity to our understanding of gene expression in both health and disease. Moreover, the epitranscriptome in the parental generation can affect organismal phenotypes in the next generation. In this Review, we discuss the relationship between epitranscriptomic modifications and metabolic diseases, their relationship with the epigenome and possible therapeutic strategies.

Cardiac copper content and its relationship with heart physiology: Insights based on quantitative genetic and functional analyses using BXD family mice

Background

Copper (Cu) is essential for the functioning of various enzymes involved in important cellular and physiological processes. Although critical for normal cardiac function, excessive accumulation, or deficiency of Cu in the myocardium is detrimental to the heart. Fluctuations in cardiac Cu content have been shown to cause cardiac pathologies and imbalance in systemic Cu metabolism. However, the genetic basis underlying cardiac Cu levels and their effects on heart traits remain to be understood. Representing the largest murine genetic reference population, BXD strains have been widely used to explore genotype-phenotype associations and identify quantitative trait loci (QTL) and candidate genes.

Methods

Cardiac Cu concentration and heart function in BXD strains were measured, followed by QTL mapping. The candidate genes modulating Cu homeostasis in mice hearts were identified using a multi-criteria scoring/filtering approach.

Results

Significant correlations were identified between cardiac Cu concentration and left ventricular (LV) internal diameter and volumes at end-diastole and end-systole, demonstrating that the BXDs with higher cardiac Cu levels have larger LV chamber. Conversely, cardiac Cu levels negatively correlated with LV posterior wall thickness, suggesting that lower Cu concentration in the heart is associated with LV hypertrophy. Genetic mapping identified six QTLs containing a total of 217 genes, which were further narrowed down to 21 genes that showed a significant association with cardiac Cu content in mice. Among those, Prex1 and Irx3 are the strongest candidates involved in cardiac Cu modulation.

Conclusion

Cardiac Cu level is significantly correlated with heart chamber size and hypertrophy phenotypes in BXD mice, while being regulated by multiple genes in several QTLs. Prex1 and Irx3 may be involved in modulating Cu metabolism and its downstream effects and warrant further experimental and functional validations.

The Mechanism and Role of N6-Methyladenosine (m6A) Modification in Atherosclerosis and Atherosclerotic Diseases

N6-methyladenosine (m6A) modification is a newly discovered regulatory mechanism in eukaryotes. As one of the most common epigenetic mechanisms, m6A's role in the development of atherosclerosis (AS) and atherosclerotic diseases (AD) has also received increasing attention. Herein, we elucidate the effect of m6A on major risk factors for AS, including lipid metabolism disorders, hypertension, and hyperglycemia. We also describe how m6A methylation contributes to endothelial cell injury, macrophage response, inflammation, and smooth muscle cell response in AS and AD. Subsequently, we illustrate the m6A-mediated aberrant biological role in the pathogenesis of AS and AD, and analyze the levels of m6A methylation in peripheral blood or local tissues of AS and AD, which helps to further discuss the diagnostic and therapeutic potential of m6A regulation for AS and AD. In summary, studies on m6A methylation provide new insights into the pathophysiologic mechanisms of AS and AD, and m6A methylation could be a novel diagnostic biomarker and therapeutic target for AS and AD.

Angiotensin-(3–4) normalizes the elevated arterial blood pressure and abnormal Na+/energy handling associated with chronic undernutrition by counteracting the effects mediated by type 1 angiotensin II receptors

We investigated the mechanisms by which chronic administration of a multideficient diet after weaning alters bodily Na⁺ handling, and culminates in high systolic blood pressure (SBP) at a juvenile age. From 28 to 92 days of age, weaned male Wistar rats were given a diet with low content and poor-quality protein, and low lipid, without vitamin supplementation, which mimics the diets consumed in impoverished regions worldwide. We measured food, energy and Na⁺ ingestion, together with urinary Na⁺ excretion, Na⁺ density (Na⁺ intake/energy intake), plasma Na⁺ concentration, SBP, and renal proximal tubule Na⁺-transporting ATPases. Undernourished rats aged 92 days had only one-third of the control body mass, lower plasma albumin, higher SBP, higher energy intake, and higher positive Na⁺ balance accompanied by decreased plasma Na⁺ concentration. Losartan or Ang-(3–4) normalized SBP, and the combination of the 2 substances induced an accentuated negative Na⁺ balance as a result of strong inhibition of Na⁺ ingestion. Na⁺ density in undernourished rats was higher than in control, irrespective of the treatment, and they had downregulated (Na⁺+K⁺)ATPase and upregulated Na⁺-ATPase in proximal tubule cells, which returned to control levels after Losartan or Ang-(3–4). We conclude that Na⁺ density, not only Na⁺ ingestion, plays a central role in the pathophysiology of elevated SBP in chronically undernourished rats. The observations that Losartan and Ang-(3–4) normalized SBP together with negative Na⁺ balance give support to the proposal that Ang II⇒AT₁R and Ang II⇒AT₂R axes have opposite roles within the renin-angiotensin-aldosterone system of undernourished juvenile rats.

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.

Genetic variation in satiety signaling and hypothalamic inflammation: merging fields for the study of obesity

Although obesity has been a longstanding health crisis, the genetic architecture of the disease remains poorly understood. Genome-wide association studies have identified many genomic loci associated with obesity, with genes being enriched in the brain, particularly in the hypothalamus. This points to the role of the central nervous system (CNS) in predisposition to obesity, and we emphasize here several key genes along the satiety signaling pathway involved in genetic susceptibility. Interest has also risen regarding the chronic, low-grade obesity-associated inflammation, with a growing concern toward inflammation in the hypothalamus as a precursor to obesity. Recent studies have found that genetic variation in inflammatory genes play a role in obesity susceptibility, and we highlight here several key genes. Despite the interest in the genetic variants of these pathways individually, there is a lack of research that investigates the relationship between the two. Understanding the interplay between genetic variation in obesity genes enriched in the CNS and inflammation genes will advance our understanding of obesity etiology and heterogeneity, improve genetic risk prediction analyses, and highlight new drug targets for the treatment of obesity. Additionally, this increased knowledge will assist in physician's ability to develop personalized nutrition and medication strategies for combating the obesity epidemic. Though it often seems to present universally, obesity is a highly individual disease, and there remains a need in the field to develop methods to treat at the individual level.

Positive Selection and Enhancer Evolution Shaped Lifespan and Body Mass in Great Apes

Within primates, the great apes are outliers both in terms of body size and lifespan, since they include the largest and longest-lived species in the order. Yet, the molecular bases underlying such features are poorly understood. Here, we leveraged an integrated approach to investigate multiple sources of molecular variation across primates, focusing on over 10,000 genes, including approximately 1,500 previously associated with lifespan, and additional approximately 9,000 for which an association with longevity has never been suggested. We analyzed dN/dS rates, positive selection, gene expression (RNA-seq), and gene regulation (ChIP-seq). By analyzing the correlation between dN/dS, maximum lifespan, and body mass, we identified 276 genes whose rate of evolution positively correlates with maximum lifespan in primates. Further, we identified five genes, important for tumor suppression, adaptive immunity, metastasis, and inflammation, under positive selection exclusively in the great ape lineage. RNA-seq data, generated from the liver of six species representing all the primate lineages, revealed that 8% of approximately 1,500 genes previously associated with longevity are differentially expressed in apes relative to other primates. Importantly, by integrating RNA-seq with ChIP-seq for H3K27ac (which marks active enhancers), we show that the differentially expressed longevity genes are significantly more likely than expected to be located near a novel "ape-specific" enhancer. Moreover, these particular ape-specific enhancers are enriched for young transposable elements, and specifically SINE-Vntr-Alus. In summary, we demonstrate that multiple evolutionary forces have contributed to the evolution of lifespan and body size in primates.

N6-methyladenosine and Neurological Diseases

N6-methyladenosine (m6A) is a dynamic reversible methylation modification of the adenosine N6 position and is the most common chemical epigenetic modification among mRNA post-transcriptional modifications, including methylation, demethylation, and recognition. Post-transcriptional modification involves multiple protein molecules, including METTL3, METTL14, WTAP, KIAA1429, ALKBH5, YTHDF1/2/3, and YTHDC1/2. m6A-related proteins are expressed in almost all cells. However, the abnormal expression of m6A-related proteins may occur in the nervous system, thereby affecting neuritogenesis, brain volume, learning and memory, memory formation and consolidation, etc., and is implicated in the development of diseases, such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, depression, epilepsy, and brain tumors. This review focuses on the functions of m6A in the development of central nervous system diseases, thus contributing to a deeper understanding of disease pathogenesis and providing potential clinical therapeutic targets for neurological diseases.

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.

The role of RNA m6A methylation in lipid metabolism

The m6A methylation is the most numerous modification of mRNA in mammals, coordinated by RNA m6A methyltransferases, RNA m6A demethylases, and RNA m6A binding proteins. They change the RNA m6A methylation level in their specific manner. RNA m6A modification has a significant impact on lipid metabolic regulation. The "writer" METTL3/METTL14 and the "eraser" FTO can promote the accumulation of lipids in various cells by affecting the decomposition and synthesis of lipids. The "reader" YTHDF recognizes m6A methylation sites of RNA and regulates the target genes' translation. Due to this function that regulates lipid metabolism, RNA m6A methylation plays a pivotal role in metabolic diseases and makes it a great potential target for therapy.

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.

The FTO rs17817449 Polymorphism is Not Associated With Sedentary Time, Physical Activity, or Cardiorespiratory Fitness: Findings From the GENADIO Cross-Sectional Study

BACKGROUND

Genetic variants within the FTO gene have been associated with increased adiposity and metabolic markers; however, there is limited evidence regarding the association of FTO gene variants with physical activity-related variables. The authors aimed to investigate the association of the rs17817449 single-nucleotide polymorphism of FTO with physical activity, sedentary time, and cardiorespiratory fitness in Chilean adults.

METHODS

A total of 409 participants from the GENADIO study were included and genotyped for the rs17817449 single-nucleotide polymorphism of FTO in this cross-sectional study. Physical activity and sedentary time were measured with ActiGraph accelerometers. Cardiorespiratory fitness was assessed using the Chester step test. The associations were assessed by using multivariate regression analyses.

RESULTS

No associations were found for FTO variant with physical activity levels and cardiorespiratory fitness. The risk allele (G) of the FTO was found to be associated with sedentary time in the minimally adjusted model (β = 19.7 min/d; 95% confidence interval, 4.0 to 35.5, per each copy of the risk allele; P = .006), but the association was no longer significant when body mass index was included as a confounder (P = .211).

CONCLUSION

The rs17817449 single-nucleotide polymorphism of the FTO gene was not associated with the level of physical activity, cardiorespiratory fitness, and sedentary behaviors in Chilean adults.

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.

Interleukin-6 actions in the hypothalamus protects against obesity and is involved in the regulation of neurogenesis

Background

Interleukin-6 (IL6) produced in the context of exercise acts in the hypothalamus reducing obesity-associated inflammation and restoring the control of food intake and energy expenditure. In the hippocampus, some of the beneficial actions of IL6 are attributed to its neurogenesis-inducing properties. However, in the hypothalamus, the putative neurogenic actions of IL6 have never been explored, and its potential to balance energy intake can be an approach to prevent or attenuate obesity.

Methods

Wild-type (WT) and IL6 knockout (KO) mice were employed to study the capacity of IL6 to induce neurogenesis. We used cell labeling with Bromodeoxyuridine (BrdU), immunofluorescence, and real-time PCR to determine the expression of markers of neurogenesis and neurotransmitters. We prepared hypothalamic neuroprogenitor cells from KO that were treated with IL6 in order to provide an ex vivo model to further characterizing the neurogenic actions of IL6 through differentiation assays. In addition, we analyzed single-cell RNA sequencing data and determined the expression of IL6 and IL6 receptor in specific cell types of the murine hypothalamus.

Results

IL6 expression in the hypothalamus is low and restricted to microglia and tanycytes, whereas IL6 receptor is expressed in microglia, ependymocytes, endothelial cells, and astrocytes. Exogenous IL6 reduces diet-induced obesity. In outbred mice, obesity-resistance is accompanied by increased expression of IL6 in the hypothalamus. IL6 induces neurogenesis-related gene expression in the hypothalamus and in neuroprogenitor cells, both from WT as well as from KO mice.

Conclusion

IL6 induces neurogenesis-related gene expression in the hypothalamus of WT mice. In KO mice, the neurogenic actions of IL6 are preserved; however, the appearance of new fully differentiated proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons is either delayed or disturbed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02242-8.

Association of serum 25-OH-vitamin D level with FTO and IRX3 genes expression in obese and overweight boys with different FTO rs9930506 genotypes

Background

The roles of FTO gene and the level of serum 25-OH-vitamin D in obesity are frequently reported. This study aimed to investigate the interactions of serum 25-OH-vitamin D level, FTO and IRX3 genes expression, and FTO genotype in obese and overweight boys.

Methods

This study was carried out on the 120 male adolescents with overweight in Tehran, Iran. Blood samples were collected from the participants in order to evaluate the serum level of 25-OH-vitamin D, the expression level of FTO and IRX3 genes, and FTO genotype for rs9930506 at baseline and after 18 weeks of the study.

Results

In general, no significant association was found between serum 25-OH-vitamin D level and IRX3 and FTO genes expression. The results of linear regression on the relationship between 25-OH-vitamin D serum level and FTO and IRX3 genes expression based on FTO genotypes for rs9930506 indicated that in AA/AG genotype carriers, serum 25-OH-vitamin D level was positively associated with FTO gene expression (B = 0.07, p = 0.02) and inversely associated with IRX3 gene expression (B = − 0.07, p = 0.03). In GG carriers, serum 25-OH-vitamin D level was not associated with expression of IRX3 and FTO genes.

Conclusion

There are significant interactions between 25-OH-vitamin D and the expression of FTO and IRX3 genes in the subset of obese patients with specific genotypes for FTO rs9930506. There was no association between serum 25-OH-vitamin D levels and the expression of FTO and IRX genes in individuals with a homozygous genotype for the risk allele of the FTO gene polymorphism.

Caveolin-1, a novel player in cognitive decline

Cognitive decline (CD), which related to vascular dementia, Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and diabetes mellitus, is a growing health concern that has a great impact on the patients' quality of life. Although extensive efforts, the mechanisms of CD are still far from being clarified, not to mention the effective treatment and prevention strategies. Caveolin-1 (Cav-1), a trans-membrane protein, is a major component of the caveolae structure and scaffolding proteins. Recently, ample evidence depicts a strong correlation between Cav-1 and CD, however, the specific role of Cav-1 in CD has not been clearly examined and how they might be connected have yet to be identified. This review seeks to provide a comprehensive overview about how Cav-1 modulates pathogeneses of CD-associated diseases. In summary, Cav-1 can promote structural and functional plasticity of neurons, improve neurogenesis, relieve mitochondrial dysfunction, inhibit inflammation and suppress oxidative stress, which have shed light on the idea that Cav-1 may be an efficacious therapeutic target to treat CD.

Homeobox A5 and C10 genes modulate adaptation of brown adipose tissue during exercise training in juvenile rats

NEW FINDINGS

What is the central question of this study? Exercise can stimulate brown adipose tissue (BAT) with subsequent increase in uncoupling protein 1 expression and mitochondrial biogenesis. In that case, do BAT-specific Hox genes modify BAT functioning and cause uncoupling protein expression changes due to exercise? What is the main finding and its importance? Exercise enhanced brown adipocyte markers, with significant upregulation of HoxA5 and downregulation of HoxC10 mRNA expression in rat BAT. HoxA5 and HoxC10 are thus likely to play distinct roles in exercise-induced changes in BAT markers during the early postnatal period. These findings provide new insight into the mechanisms underlying exercise-induced changes in BAT function.

ABSTRACT

Brown adipose tissue (BAT) recruitment is involved in increased energy expenditure associated with cold exposure and exercise training. We explored whether exercise training induced changes in expression levels of brown adipocyte-selective factors and Homeobox (Hox) genes during the post-weaning growth period of male Wistar rats. Relative to total body weight, BAT weights alone were lower in exercise-trained (EX) rats compared to sedentary control (SED) rats. mRNA expression of HoxA5 was higher and that of HoxC10 was lower in EX rats than in SED rats, accompanied by both higher citrate synthase activity and protein expression levels for uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor (PPAR) α, and PPARγ-coactivator (PGC)-1α. HoxA5 knockdown with siRNA reduced the expression of PR-domain containing 16 (Prdm16), cell death-inducing DNA fragmentation factor-α-like effector A (Cidea) gene, type 2 deiodinase mRNA, and PRDM16 protein. Comparatively, HoxC10 knockdown with siRNA enhanced mRNA expression of Prdm16, Pparα and Pgc1α and protein expression of UCP1, PPARα and PGC1α in brown adipocytes. The stimulation of brown adipocytes with isoproterenol, a β-adrenoceptor agonist, caused a phenomenon similar to the effect of exercise training on the genes tested: upregulation of HoxA5 mRNA, downregulation of HoxC10 mRNA, and increased protein expression for UCP1 and PGC1α. Collectively, HoxA5 and HoxC10 may have unique functions that contribute to modulating the expression of BAT-selective markers in BAT of juvenile rats during exercise training. The study findings regarding activation and recruitment of BAT during exercise training have implications for anti-obesity management.

Intracellular and tissue specific expression of FTO protein in pig: changes with age, energy intake and metabolic status

Genome-wide association studies in the FTO gene have identified SNPs correlating with obesity and type 2 diabetes. In mice, lack of Fto function leads to intrauterine growth retardation and lean phenotype, whereas in human it is lethal. The aim of this study in a pig model was to determine the localization of the FTO protein in different tissues and cell compartments, in order to investigate potential targets of FTO action. To better understand physiological role of FTO protein, its expression was studied in pigs of different age, metabolic status and nutrition, using both microscopic methods and Western blot analysis. For the first time, FTO protein was found in vivo in the cytoplasm, of not all, but specific tissues and cells e.g. in the pancreatic β-cells. Abundant FTO protein expression was found in the cerebellum, salivary gland and kidney of adult pigs. No FTO protein expression was detected in blood, saliva, and bile, excluding its role in cell-to-cell communication. In the pancreas, FTO protein expression was positively associated with energy intake, whereas in the muscles it was strictly age-related. In IUGR piglets, FTO protein expression was much higher in the cerebellum and kidneys, as compared to normal birth body weight littermates. In conclusion, our data suggest that FTO protein may play a number of distinct, yet unknown intracellular functions due to its localization. Moreover, it may play a role in animal growth/development and metabolic state, although additional studies are necessary to clarify the detailed mechanism(s) of action.