Role of Ucp1 enhancer methylation and chromatin remodelling in the control of Ucp1 expression in murine adipose tissue

Dnmt3b deficiency in adipocyte progenitor cells ameliorates obesity in female mice

Obesity arises from chronic energy imbalance where energy intake exceeds energy expenditure. Emerging evidence supports a key role of DNA methylation in the regulation of adipose tissue development and metabolism. We recently discovered a key role of DNA methylation, catalyzed by DNA methyltransferase 1 or 3a (Dnmt1 or 3a), in the regulation of adipocyte differentiation and metabolism. Here, we aimed to investigate the role of adipocyte progenitor cell Dnmt3b, an enzyme mediating de novo DNA methylation, in energy metabolism and obesity. We generated a genetic model with Dnmt3b knockout in adipocyte progenitor cells (PD3bKO) by crossing Dnmt3b -floxed mice with platelet-derived growth factor receptor alpha (Pdgfrα)-Cre mice. Dnmt3b gene deletion in adipocyte progenitors enhanced thermogenic gene expression in brown adipose tissue, increased overall energy expenditure, and mitigated high-fat diet (HFD)-induced obesity in female mice. PD3bKO mice also displayed a lower respiratory exchange ratio (RER), indicative of a metabolic shift favoring fat utilization as an energy source. Furthermore, female PD3bKO mice exhibited improved insulin sensitivity alongside their lean phenotype. In contrast, male PD3bKO mice showed no changes in body weight but demonstrated decreased insulin sensitivity, revealing a sexually dimorphic metabolic response to Dnmt3b deletion in adipocyte progenitor cells. These findings underscore the critical role of Dnmt3b in regulating energy homeostasis, body weight, and metabolic health, with significant implications for understanding sex-specific mechanisms of obesity and metabolism.

Identification of a distal enhancer of Ucp1 essential for thermogenesis and mitochondrial function in brown fat

Uncoupling protein 1 (UCP1) is a crucial protein located in the mitochondrial inner membrane that mediates nonshivering thermogenesis. However, the molecular mechanisms by which enhancer-promoter chromatin interactions control Ucp1 transcriptional regulation in brown adipose tissue (BAT) are unclear. Here, we employed circularized chromosome conformation capture coupled with next-generation sequencing (4C-seq) to generate high-resolution chromatin interaction profiles of Ucp1 in interscapular brown adipose tissue (iBAT) and epididymal white adipose tissue (eWAT) and revealed marked changes in Ucp1 chromatin interaction between iBAT and eWAT. Next, we identified four iBAT-specific active enhancers of Ucp1, and three of them were activated by cold stimulation. Transcriptional repression of the Ucp1-En4 or Ucp1-En6 region significantly downregulated Ucp1 and impaired mitochondrial function in brown adipocytes. Furthermore, depletion of the cohesin subunit RAD21 decreased the interaction intensity between Ucp1-En4 and the Ucp1 promoter and downregulated Ucp1. EBF2 cooperated with the acetyltransferase CBP to regulate Ucp1-En4 activity and increase Ucp1 transcriptional activity. In vivo, lentivirus-mediated repression of Ucp1-En4 was injected into iBAT, resulting in impacted iBAT thermogenic capacity and impaired iBAT mitochondrial function under cold acclimation conditions. Studying the functional enhancers regulating Ucp1 expression in iBAT will provide important insights into the regulatory mechanisms of BAT activity.

Perivascular adipose tissue: a central player in the triad of diabetes, obesity, and cardiovascular health

Perivascular adipose tissue (PVAT) is a dynamic tissue that affects vascular function and cardiovascular health. The connection between PVAT, the immune system, obesity, and vascular disease is complex and plays a pivotal role in the pathogenesis of vascular diseases such as atherosclerosis, hypertension, and vascular inflammation. In cardiometabolic diseases, PVAT becomes a significant source of proflammatory adipokines, leading to increased infiltration of immune cells, in cardiometabolic diseases, PVAT becomes a significant source of proinflammatory adipokines, leading to increased infiltration of immune cells, promoting vascular smooth muscle cell proliferation and migrationpromoting vascular smooth muscle cell proliferation and migration. This exacerbates vascular dysfunction by impairing endothelial cell function and promoting endothelial activation. Dysregulated PVAT also contributes to hemodynamic alterations and hypertension through enhanced sympathetic nervous system activity and impaired vasodilatory capacity of PVAT-derived factors. Therapeutic interventions targeting key components of this interaction, such as modulating PVAT inflammation, restoring adipokine balance, and attenuating immune cell activation, hold promise for mitigating obesity-related vascular complications. Lifestyle interventions, pharmacological agents targeting inflammatory pathways, and surgical approaches aimed at reducing PVAT mass or improving adipose tissue function are potential therapeutic avenues for managing vascular diseases associated with obesity and PVAT dysfunction.

Adipose tissue senescence: Biological changes, hallmarks and therapeutic approaches

Adipose tissue (AT), the largest energy storage reservoir and endocrine organ, plays a crucial role in regulating systemic energy metabolism. As one of the most vulnerable tissues during aging, the plasticity of AT is impaired. With age, AT undergoes redistribution, characterized by expansion of visceral adipose tissue (VAT) and reduction of peripheral subcutaneous adipose tissue (SAT). Additionally, age-related changes in AT include reduced adipogenesis of white adipocytes, decreased proliferation and differentiation capacity of mesenchymal stromal/stem cells (MSCs), diminished thermogenic capacity in brown/beige adipocytes, and dysregulation of immune cells. Specific and sensitive hallmarks enable the monitoring and evaluation of the biological changes associated with aging. In this study, we have innovatively proposed seven characteristic hallmarks of AT senescence, including telomere attrition, epigenetic alterations, genomic instability, mitochondrial dysfunction, disabled macroautophagy, cellular senescence, and chronic inflammation, which are intricately interconnected and mutually regulated. Finally, we discussed anti-aging strategies targeting AT, offering insights into mitigating or delaying metabolic disturbances caused by AT senescence.

Early Life Programming of Adipose Tissue Remodeling and Browning Capacity by Micronutrients and Bioactive Compounds as a Potential Anti-Obesity Strategy

The early stages of life, especially the period from conception to two years, are crucial for shaping metabolic health and the risk of obesity in adulthood. Adipose tissue (AT) plays a crucial role in regulating energy homeostasis and metabolism, and brown AT (BAT) and the browning of white AT (WAT) are promising targets for combating weight gain. Nutritional factors during prenatal and early postnatal stages can influence the development of AT, affecting the likelihood of obesity later on. This narrative review focuses on the nutritional programming of AT features. Research conducted across various animal models with diverse interventions has provided insights into the effects of specific compounds on AT development and function, influencing the development of crucial structures and neuroendocrine circuits responsible for energy balance. The hormone leptin has been identified as an essential nutrient during lactation for healthy metabolic programming against obesity development in adults. Studies have also highlighted that maternal supplementation with polyunsaturated fatty acids (PUFAs), vitamin A, nicotinamide riboside, and polyphenols during pregnancy and lactation, as well as offspring supplementation with myo-inositol, vitamin A, nicotinamide riboside, and resveratrol during the suckling period, can impact AT features and long-term health outcomes and help understand predisposition to obesity later in life.

Anthocyanins and their metabolites promote white adipose tissue beiging by regulating mitochondria thermogenesis and dynamics

High-fat diet (HFD) consumption and excess nutrient availability can cause alterations in mitochondrial function and dynamics. We previously showed that anthocyanins (AC) decreased HFD-induced body weight gain and fat deposition. This study investigated: i) the capacity of AC to mitigate HFD-induced alterations in mitochondrial dynamics, biogenesis, and thermogenesis in mouse subcutaneous white adipose tissue (sWAT), and ii) the underlying mechanisms of action of cyanidin-3-O-glucoside (C3G), delphinidin-3-O-glucoside (D3G), and their gut metabolites on mitochondria function/dynamics in 3T3-L1 adipocytes treated with palmitate. Mice were fed control or HFD diets, added or not with 40 mg AC/kg body weight (BW). Compared to control and AC-supplemented mice, HFD-fed mice had fewer sWAT mitochondria that presented alterations of their architecture. AC supplementation prevented HFD-induced decrease of proteins involved in mitochondria biogenesis (PPARγ, PRDM16 and PGC-1α), and thermogenesis (UCP-1), and decreased AMPK phosphorylation. AC supplementation also restored the alterations in sWAT mitochondrial dynamics (Drp-1, OPA1, MNF-2, and Fis-1) and mitophagy (BNIP3L/NIX) caused by HFD consumption. In mature 3T3-L1, C3G, D3G, and their metabolites protocatechuic acid (PCA), 4-hydroxybenzaldehyde (HB), and gallic acid (GA) differentially affected palmitate-mediated decreased cAMP, PKA, AMPK, and SIRT-1 signaling pathways. C3G, D3G, and metabolites also prevented palmitate-mediated decreased expression of PPARγ, PRDM16, PGC-1α, and UCP1. Results suggest that consumption of select AC, i.e. cyanidin and delphinidin, could promote sWAT mitochondriogenesis and improve mitochondria dynamics in the context of HFD/obesity-induced dysmetabolism in part by regulating PKA, AMPK, and SIRT-1 signaling pathways.

A recognition of exosomes as regulators of epigenetic mechanisms in central nervous system diseases

Exosomes, vesicular structures originating from cells, participate in the conveyance of proteins and nucleic acids. Presently, the centrality of epigenetic modifications in neurological disorders is widely acknowledged. Exosomes exert influence over various epigenetic phenomena, thereby modulating post-transcriptional regulatory processes contingent upon their constituent makeup. Consequently, the heightened attention directed toward exosomes as instigators of epigenetic alterations has burgeoned in recent years. Notably, exosomes serve as vehicles for delivering methyltransferases to recipient cells. More significantly, non-coding RNAs, particularly microRNAs (miRNAs), represent pivotal contents within exosomes, wielding the capacity to influence the expression of diverse factors within the cerebral milieu. The transfer of these exosomal contents amidst brain cells, encompassing neuronal cells and microglia, assumes a critical role in the genesis and progression of neurological disorders, also, this role is not limited to neurological disorders, it may deal with any human disease, such as cancer, and cardiovascular diseases. This review will concentrate on elucidating the regulation of exosome-induced epigenetic events and its subsequent ramifications for neurological diseases. A more profound comprehension of the involvement of exosome-mediated epigenetic regulation in neurological disorders contributes to a heightened awareness of the etiology and advancement of cerebral afflictions.

Perivascular adipose tissue: Fine-tuner of vascular redox status and inflammation

Perivascular adipose tissue (PVAT) refers to the aggregate of adipose tissue surrounding the vasculature, exhibiting the phenotypes of white, beige and brown adipocytes. PVAT has emerged as an active modulator of vascular homeostasis and pathogenesis of cardiovascular diseases in addition to its structural role to provide mechanical support to blood vessels. More specifically, PVAT is closely involved in the regulation of reactive oxygen species (ROS) homeostasis and inflammation along the vascular tree, through the tight interaction between PVAT and cellular components of the vascular wall. Furthermore, the phenotype-genotype of PVAT at different regions of vasculature varies corresponding to different cardiovascular risks. During ageing and obesity, the cellular proportions and signaling pathways of PVAT vary in favor of cardiovascular pathogenesis by promoting ROS generation and inflammation. Physiological means and drugs that alter PVAT mass, components and signaling may provide new therapeutic insights in the treatment of cardiovascular diseases. In this review, we aim to provide an updated understanding towards PVAT in the context of redox regulation, and to highlight the therapeutic potential of targeting PVAT against cardiovascular complications.

Molecular Crosstalk between Chromatin Remodeling and Tumor Microenvironment in Multiple Myeloma

Multiple myeloma (MM) is a complex disease driven by numerous genetic and epigenetic alterations that are acquired over time. Despite recent progress in the understanding of MM pathobiology and the availability of innovative drugs, which have pronounced clinical outcome, this malignancy eventually progresses to a drug-resistant lethal stage and, thus, novel therapeutic drugs/models always play an important role in effective management of MM. Modulation of tumor microenvironment is one of the hallmarks of cancer biology, including MM, which affects the myeloma genomic architecture and disease progression subtly through chromatin modifications. The bone marrow niche has a prime role in progression, survival, and drug resistance of multiple myeloma cells. Therefore, it is important to develop means for targeting the ecosystem between multiple myeloma bone marrow microenvironment and chromatin remodeling. Extensive gene expression profile analysis has indeed provided the framework for new risk stratification of MM patients and identifying novel molecular targets and therapeutics. However, key tumor microenvironment factors/immune cells and their interactions with chromatin remodeling complex proteins that drive MM cell growth and progression remain grossly undefined.

5-Aza-2'-Deoxycytidine Regulates White Adipocyte Browning by Modulating miRNA-133a/Prdm16

The conversion of white adipocytes into brown adipocytes improves their thermogenesis and promotes energy consumption. Epigenetic modifications affect related genes and interfere with energy metabolism, and these are the basis of new ideas for obesity treatment. Neonatal mice show high levels of DNA hypermethylation in white adipose tissue early in life and low levels in brown adipose tissue. Thus, we considered that the regulation of DNA methylation may play a role in the conversion of white adipose to brown. We observed growth indicators, lipid droplets of adipocytes, brown fat specific protein, and miRNA-133a after treatment with 5-Aza-2'-deoxycytidine. The expression of Prdm16 and Ucp-1 in adipocytes was detected after inhibiting miRNA-133a. The results showed a decrease in total lipid droplet formation and an increased expression of the brown fat specific proteins Prdm16 and Ucp-1. This study indicated that 5-Aza-2'-deoxycytidine promotes white adipocyte browning following DNA demethylation, possibly via the modulation of miR-133a and Prdm16.

Evidence of selection in the uncoupling protein 1 gene region suggests local adaptation to solar irradiance in savannah monkeys (Chlorocebus spp.)

In the last 300 thousand years, the genus Chlorocebus expanded from equatorial Africa into the southernmost latitudes of the continent, where colder climate was a probable driver of natural selection. We investigated population-level genetic variation in the mitochondrial uncoupling protein 1 (UCP1) gene region-implicated in non-shivering thermogenesis (NST)-in 73 wild savannah monkeys from three taxa representing this southern expansion (Chlorocebus pygerythrus hilgerti, Chlorocebus cynosuros and Chlorocebus pygerythrus pygerythrus) ranging from Kenya to South Africa. We found 17 single nucleotide polymorphisms with extended haplotype homozygosity consistent with positive selective sweeps, 10 of which show no significant linkage disequilibrium with each other. Phylogenetic generalized least-squares modelling with ecological covariates suggest that most derived allele frequencies are significantly associated with solar irradiance and winter precipitation, rather than overall low temperatures. This selection and association with irradiance is demonstrated by a relatively isolated population in the southern coastal belt of South Africa. We suggest that sunbathing behaviours common to savannah monkeys, in combination with the strength of solar irradiance, may mediate adaptations to thermal stress via NST among savannah monkeys. The variants we discovered all lie in non-coding regions, some with previously documented regulatory functions, calling for further validation and research.

Browning of the white adipose tissue regulation: new insights into nutritional and metabolic relevance in health and diseases

Adipose tissues are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. Although white adipose tissue and brown adipose tissue are currently considered key endocrine organs, they differ functionally and morphologically. The existence of the beige or brite adipocytes, cells displaying intermediary characteristics between white and brown adipocytes, illustrates the plastic nature of the adipose tissue. These cells are generated through white adipose tissue browning, a process associated with augmented non-shivering thermogenesis and metabolic capacity. This process involves the upregulation of the uncoupling protein 1, a molecule that uncouples the respiratory chain from Adenosine triphosphate synthesis, producing heat. β-3 adrenergic receptor system is one important mediator of white adipose tissue browning, during cold exposure. Surprisingly, hyperthermia may also induce beige activation and white adipose tissue beiging. Physical exercising copes with increased levels of specific molecules, including Beta-Aminoisobutyric acid, irisin, and Fibroblast growth factor 21 (FGF21), which induce adipose tissue browning. FGF21 is a stress-responsive hormone that interacts with beta-klotho. The central roles played by hormones in the browning process highlight the relevance of the individual lifestyle, including circadian rhythm and diet. Circadian rhythm involves the sleep-wake cycle and is regulated by melatonin, a hormone associated with UCP1 level upregulation. In contrast to the pro-inflammatory and adipose tissue disrupting effects of the western diet, specific food items, including capsaicin and n-3 polyunsaturated fatty acids, and dietary interventions such as calorie restriction and intermittent fasting, favor white adipose tissue browning and metabolic efficiency. The intestinal microbiome has also been pictured as a key factor in regulating white tissue browning, as it modulates bile acid levels, important molecules for the thermogenic program activation. During embryogenesis, in which adipose tissue formation is affected by Bone morphogenetic proteins that regulate gene expression, the stimuli herein discussed influence an orchestra of gene expression regulators, including a plethora of transcription factors, and chromatin remodeling enzymes, and non-coding RNAs. Considering the detrimental effects of adipose tissue browning and the disparities between adipose tissue characteristics in mice and humans, further efforts will benefit a better understanding of adipose tissue plasticity biology and its applicability to managing the overwhelming burden of several chronic diseases.

The pathobiology of perivascular adipose tissue (PVAT), the fourth layer of the blood vessel wall

The perivascular adipose tissue (PVAT) is an adipose tissue depot which surrounds most human blood vessels. It is metabolically active and has both a protective and a pathogenic role in vascular biology and pathobiology. It regulates vascular homeostasis and promotes vascular dysfunction. The purpose of this review is to consider the origin, structure, function, and dysfunction of this unique adipose depot consisting of white (WAT), brown (BAT) and beige adipose tissue, to support the concept that PVAT may be considered the fourth layer of the normal arterial wall (tunica adiposa), in which dysfunction creates a microenvironment that regulates, in part, the initiation and growth of the fibro-inflammatory lipid atherosclerotic plaque. Experimental in-vivo and in-vitro studies and human investigations show that the adipocytes, extracellular matrix, nerve fibers and vasa vasorum found in PVAT form a functional adipose tissue unit adjacent to, but not anatomically separated from, the adventitia. PVAT maintains and regulates the structure and function of the normal arterial wall through autocrine and paracrine mechanisms, that include modulation of medial smooth muscle cell contractility and secretion of anti-inflammatory molecules. PVAT shows regional phenotypic heterogeneity which may be important in its effect on the wall of specific sections of the aorta and its muscular branches during perturbations and various injuries including obesity and diabetes. In atherosclerosis, a pan-vascular microenvironment is created that functionally links the intima-medial atherosclerotic plaque to the adventitia and PVAT beneath the plaque, highlighting the local impact of PVAT on atherogenesis. PVAT adipocytes have inflammatory effects which in response to injury show activation and phenotypic changes, some of which are considered to have direct and indirect effects on the intima and media during the initiation, growth, and development of complicated atherosclerotic plaques. Thus, it is important to maintain the integrity of the full vascular microenvironment so that design of experimental and human studies include investigation of PVAT. The era of discarding PVAT tissue in both experimental and human research and clinical vascular studies should end.

DNA Methylation Modulates Aging Process in Adipocytes

Aging has been recognized to be a highly complex biological health problem with a high risk of chronic diseases, including type 2 diabetes, atherosclerosis, chronic bronchitis or emphysema, cancer and Alzheimer's disease. Particularly, age-related turnover in adipose tissue is a major contributor to metabolic syndromes and shortened lifespan. Adipocytes undergo senescence in early stage, which results in adipose tissue metabolic dysfunction, redistribution, and inflammation. The well-established association between DNA methylation (DNAm) and aging has been observed in the past few decades. Indeed, age-related alteration in DNAm is highly tissue-specific. This review intends to summarize the advancements how DNAm changes coupled with aging process in adipose tissue, by which DNAm regulates cellular senescence, metabolic function, adipokine secretion and beiging process in adipocytes. Elucidation of the effect of DNAm on adipose aging would have great potential to the development of epigenetic therapeutic strategies against aging-related diseases in clinical settings.

Brown Fat Dnmt3b Deficiency Ameliorates Obesity in Female Mice

Obesity results from a chronic energy imbalance due to energy intake exceeding energy expenditure. Activation of brown fat thermogenesis has been shown to combat obesity. Epigenetic regulation, including DNA methylation, has emerged as a key regulator of brown fat thermogenic function. Here we aimed to study the role of Dnmt3b, a DNA methyltransferase involved in de novo DNA methylation, in the regulation of brown fat thermogenesis and obesity. We found that the specific deletion of Dnmt3b in brown fat promotes the thermogenic and mitochondrial program in brown fat, enhances energy expenditure, and decreases adiposity in female mice fed a regular chow diet. With a lean phenotype, the female knockout mice also exhibit increased insulin sensitivity. In addition, Dnmt3b deficiency in brown fat also prevents diet-induced obesity and insulin resistance in female mice. Interestingly, our RNA-seq analysis revealed an upregulation of the PI3K-Akt pathway in the brown fat of female Dnmt3b knockout mice. However, male Dnmt3b knockout mice have no change in their body weight, suggesting the existence of sexual dimorphism in the brown fat Dnmt3b knockout model. Our data demonstrate that Dnmt3b plays an important role in the regulation of brown fat function, energy metabolism and obesity in female mice.

The interplay between diet, gut microbes, and host epigenetics in health and disease

The mechanisms linking the function of microbes to host health are becoming better defined but are not yet fully understood. One recently explored mechanism involves microbe-mediated alterations in the host epigenome. Consumption of specific dietary components such as fiber, glucosinolates, polyphenols, and dietary fat has a significant impact on gut microbiota composition and function. Microbial metabolism of these dietary components regulates important epigenetic functions that ultimately influences host health. Diet-mediated alterations in the gut microbiome regulate the substrates available for epigenetic modifications like DNA methylation or histone methylation and/or acetylation. In addition, generation of microbial metabolites such as butyrate inhibits the activity of core epigenetic enzymes like histone deacetylases (HDACs). Reciprocally, the host epigenome also influences gut microbial composition. Thus, complex interactions exist between these three factors. This review comprehensively examines the interplay between diet, gut microbes, and host epigenetics in modulating host health. Specifically, the dietary impact on gut microbiota structure and function that in-turn regulates host epigenetics is evaluated in terms of promoting protection from disease development.

Dnmt3b Deficiency in Myf5+-Brown Fat Precursor Cells Promotes Obesity in Female Mice

Increasing energy expenditure through activation of brown fat thermogenesis is a promising therapeutic strategy for the treatment of obesity. Epigenetic regulation has emerged as a key player in regulating brown fat development and thermogenic program. Here, we aimed to study the role of DNA methyltransferase 3b (Dnmt3b), a DNA methyltransferase involved in de novo DNA methylation, in the regulation of brown fat function and energy homeostasis. We generated a genetic model with Dnmt3b deletion in brown fat-skeletal lineage precursor cells (3bKO mice) by crossing Dnmt3b-floxed (fl/fl) mice with Myf5-Cre mice. Female 3bKO mice are prone to diet-induced obesity, which is associated with decreased energy expenditure. Dnmt3b deficiency also impairs cold-induced thermogenic program in brown fat. Surprisingly, further RNA-seq analysis reveals a profound up-regulation of myogenic markers in brown fat of 3bKO mice, suggesting a myocyte-like remodeling in brown fat. Further motif enrichment and pyrosequencing analysis suggests myocyte enhancer factor 2C (Mef2c) as a mediator for the myogenic alteration in Dnmt3b-deficient brown fat, as indicated by decreased methylation at its promoter. Our data demonstrate that brown fat Dnmt3b is a key regulator of brown fat development, energy metabolism and obesity in female mice.

Exosome-Derived MicroRNAs of Human Milk and Their Effects on Infant Health and Development

Multiple biologically active components of human milk support infant growth, health and development. Milk provides a wide spectrum of mammary epithelial cell-derived extracellular vesicles (MEVs) for the infant. Although the whole spectrum of MEVs appears to be of functional importance for the growing infant, the majority of recent studies report on the MEV subfraction of milk exosomes (MEX) and their miRNA cargo, which are in the focus of this review. MEX and the dominant miRNA-148a play a key role in intestinal maturation, barrier function and suppression of nuclear factor-κB (NF-κB) signaling and may thus be helpful for the prevention and treatment of necrotizing enterocolitis. MEX and their miRNAs reach the systemic circulation and may impact epigenetic programming of various organs including the liver, thymus, brain, pancreatic islets, beige, brown and white adipose tissue as well as bones. Translational evidence indicates that MEX and their miRNAs control the expression of global cellular regulators such as DNA methyltransferase 1-which is important for the up-regulation of developmental genes including insulin, insulin-like growth factor-1, α-synuclein and forkhead box P3-and receptor-interacting protein 140, which is important for the regulation of multiple nuclear receptors. MEX-derived miRNA-148a and miRNA-30b may stimulate the expression of uncoupling protein 1, the key inducer of thermogenesis converting white into beige/brown adipose tissue. MEX have to be considered as signalosomes derived from the maternal lactation genome emitted to promote growth, maturation, immunological and metabolic programming of the offspring. Deeper insights into milk's molecular biology allow the conclusion that infants are both "breast-fed" and "breast-programmed". In this regard, MEX miRNA-deficient artificial formula is not an adequate substitute for breastfeeding, the birthright of all mammals.

Epigenetic Regulators of White Adipocyte Browning

Adipocytes play an essential role in maintaining energy homeostasis in mammals. The primary function of white adipose tissue (WAT) is to store energy; for brown adipose tissue (BAT), primary function is to release fats in the form of heat. Dysfunctional or excess WAT can induce metabolic disorders such as dyslipidemia, obesity, and diabetes. Preadipocytes or adipocytes from WAT possess sufficient plasticity as they can transdifferentiate into brown-like beige adipocytes. Studies in both humans and rodents showed that brown and beige adipocytes could improve metabolic health and protect from metabolic disorders. Brown fat requires activation via exposure to cold or β-adrenergic receptor (β-AR) agonists to protect from hypothermia. Considering the fact that the usage of β-AR agonists is still in question with their associated side effects, selective induction of WAT browning is therapeutically important instead of activating of BAT. Hence, a better understanding of the molecular mechanisms governing white adipocyte browning is vital. At the same time, it is also essential to understand the factors that define white adipocyte identity and inhibit white adipocyte browning. This literature review is a comprehensive and focused update on the epigenetic regulators crucial for differentiation and browning of white adipocytes.

Maternal High-Fat Diet Disturbs the DNA Methylation Profile in the Brown Adipose Tissue of Offspring Mice

The prevalence of obesity has become a threatening global public health issue. The consequence of obesity is abnormal energy metabolism. Unlike white adipose tissue (WAT), brown adipose tissue (BAT) has a unique role in nonshivering thermogenesis. Lipids and glucose are consumed to maintain energy and metabolic homeostasis in BAT. Recently, accumulating evidence has indicated that exposure to excess maternal energy intake affects energy metabolism in offspring throughout their life. However, whether excess intrauterine energy intake influences BAT metabolism in adulthood is not clear. In this study, mouse dams were exposed to excess energy intake by feeding a high-fat diet (HFD) before and during pregnancy and lactation. The histology of BAT was assessed by hematoxylin and eosin staining. The genome-wide methylation profile of BAT was determined by a DNA methylation array, and specific site DNA methylation was quantitatively analyzed by methylated DNA immunoprecipitation (MeDIP) qPCR. We found that intrauterine exposure to a high-energy diet resulted in blood lipid panel disorders and impaired the BAT structure. Higher methylation levels of genes involved in thermogenesis and fatty acid oxidation (FAO) in BAT, such as Acaa2, Acsl1, and Cox7a1, were found in 16-week-old offspring from mothers fed with HFD. Furthermore, the expression of Acaa2, Acsl1, and Cox7a1 was down-regulated by intrauterine exposure to excess energy intake. In summary, our results reveal that excess maternal energy leads to a long-term disorder of BAT in offspring that involves the activation of DNA methylation of BAT-specific genes involved in fatty acid oxidation and thermogenesis.

Perivascular adipose tissue in age-related vascular disease

Perivascular adipose tissue (PVAT), a crucial regulator of vascular homeostasis, is actively involved in vascular dysfunction during aging. PVAT releases various adipocytokines, chemokines and growth factors. In an endocrine and paracrine manner PVAT-derived factors regulate vascular signalling and inflammation modulating functions of adjacent layers of the vasculature. Pathophysiological conditions such as obesity, type 2 diabetes, vascular injury and aging can cause PVAT dysfunction, leading to vascular endothelial and smooth muscle cell dysfunctions. We and others have suggested that PVAT is involved in the inflammatory response of the vascular wall in diet induced obesity animal models leading to vascular dysfunction due to disappearance of the physiological anticontractile effect. Previous studies confirm a crucial role for pinpointed PVAT inflammation in promoting vascular oxidative stress and inflammation in aging, enhancing the risk for development of cardiovascular disease. In this review, we discuss several studies and mechanisms linking PVAT to age-related vascular diseases. An overview of the suggested roles played by PVAT in different disorders associated with the vasculature such as endothelial dysfunction, neointimal formation, aneurysm, vascular contractility and stiffness will be performed. PVAT may be considered a potential target for therapeutic intervention in age-related vascular disease.

Alternative Polyadenylation and Differential Regulation of Ucp1: Implications for Brown Adipose Tissue Thermogenesis Across Species

Brown adipose tissue (BAT) is a thermogenic organ owing to its unique expression of uncoupling protein 1 (UCP1), which is a proton channel in the inner mitochondrial membrane used to dissipate the proton gradient and uncouple the electron transport chain to generate heat instead of adenosine triphosphate. The discovery of metabolically active BAT in human adults, especially in lean people after cold exposure, has provoked the "thermogenic anti-obesity" idea to battle weight gain. Because BAT can expend energy through UCP1-mediated thermogenesis, the molecular mechanisms regulating UCP1 expression have been extensively investigated at both transcriptional and posttranscriptional levels. Of note, the 3'-untranslated region (3'-UTR) of Ucp1 mRNA is differentially processed between mice and humans that quantitatively affects UCP1 synthesis and thermogenesis. Here, we summarize the regulatory mechanisms underlying UCP1 expression, report the number of poly(A) signals identified or predicted in Ucp1 genes across species, and discuss the potential and caution in targeting UCP1 for enhancing thermogenesis and metabolic fitness.

Dietary alpha-ketoglutarate promotes beige adipogenesis and prevents obesity in middle-aged mice

Aging usually involves the progressive development of certain illnesses, including diabetes and obesity. Due to incapacity to form new white adipocytes, adipose expansion in aged mice primarily depends on adipocyte hypertrophy, which induces metabolic dysfunction. On the other hand, brown adipose tissue burns fatty acids, preventing ectopic lipid accumulation and metabolic diseases. However, the capacity of brown/beige adipogenesis declines inevitably during the aging process. Previously, we reported that DNA demethylation in the Prdm16 promoter is required for beige adipogenesis. DNA methylation is mediated by ten–eleven family proteins (TET) using alpha‐ketoglutarate (AKG) as a cofactor. Here, we demonstrated that the circulatory AKG concentration was reduced in middle‐aged mice (10‐month‐old) compared with young mice (2‐month‐old). Through AKG administration replenishing the AKG pool, aged mice were associated with the lower body weight gain and fat mass, and improved glucose tolerance after challenged with high‐fat diet (HFD). These metabolic changes are accompanied by increased expression of brown adipose genes and proteins in inguinal adipose tissue. Cold‐induced brown/beige adipogenesis was impeded in HFD mice, whereas AKG rescued the impairment of beige adipocyte functionality in middle‐aged mice. Besides, AKG administration up‐regulated Prdm16 expression, which was correlated with an increase of DNA demethylation in the Prdm16 promoter. In summary, AKG supplementation promotes beige adipogenesis and alleviates HFD‐induced obesity in middle‐aged mice, which is associated with enhanced DNA demethylation of the Prdm16 gene.

Metabolic Benefits of MicroRNA-22 Inhibition

Diabesity is a growing pandemic with substantial health and financial consequences. We are developing microRNA (miRNA)-based drug candidates that transform fat storing adipocytes into fat burning adipocytes (browning effect) to treat metabolic diseases characterized by lipotoxicity. Through phenotypic screening in primary cultures of human subcutaneous adipocytes, we discovered that inhibition of miRNA-22-3p by several complementary antagomirs resulted in increased lipid oxidation, mitochondrial activity, and energy expenditure (EE). These effects may be mediated through activation of target genes like KDM3A, KDM6B, PPARA, PPARGC1B, and SIRT1 involved in lipid catabolism, thermogenesis, and glucose homeostasis. In the model of Diet-Induced Obesity in mice of various ages, weekly subcutaneous injections of various miRNA-22-3p antagomirs produced a significant fat mass reduction, but no change of appetite or body temperature. Insulin sensitivity, as well as circulating glucose and cholesterol levels, was also improved. These original findings suggest that miRNA-22-3p inhibition could become a potent treatment of human obesity and type 2 diabetes mellitus, the so-called diabesity characterized by lipotoxicity and insulin resistance.

DNA methylation of the PLIN1 promoter downregulates expression in chicken lines

Evidence suggests that Perilipin-1 (PLIN1) is subject to functional regulation by epigenetic modifications in women with obesity. However, whether chicken PLIN1 expression is regulated by DNA methylation is unknown. Here, Sequenom MassARRAY and real-time polymerase chain reaction (PCR) were conducted to analyze the promoter methylation status and expression of the PLIN1 gene in Northeast Agricultural University broiler lines divergently selected for abdominal fat content. We found that chicken PLIN1 expression was significantly higher in adipose tissue of fat-line broilers than in lean lines at 1-7 weeks of age, and was significantly positively correlated with abdominal fat percentage (AFP) in chicken adipose development (Pearson's r = 0.627 , P < 0.001 ). The region analyzed for DNA methylation was from - 12 to - 520  bp upstream of the translation start codon ATG, and had five CpG sites, where only the DNA methylation levels of CpG5 located at position - 490  bp were significantly higher in lean compared to fat chickens at 5 and 6 weeks ( P < 0.05 ) and were significantly negatively correlated with PLIN1 mRNA levels and AFP ( P < 0.05 ). These results shed new light on the regulation of hypertrophic growth in chicken adipose development.

The Beige Adipocyte as a Therapy for Metabolic Diseases

Adipose tissue is traditionally categorized into white and brown relating to their function and morphology. The classical white adipose tissue builds up energy in the form of triglycerides and is useful for preventing fatigue during periods of low caloric intake and the brown adipose tissue more energetically active, with a greater number of mitochondria and energy production in the form of heat. Since adult humans possess significant amounts of active brown fat depots and its mass inversely correlates with adiposity, brown fat might play an important role in human obesity and energy homeostasis. New evidence suggests two types of thermogenic adipocytes with distinct developmental and anatomical features: classical brown adipocytes and beige adipocytes. Beige adipocyte has recently attracted special interest because of its ability to dissipate energy and the possible ability to differentiate themselves from white adipocytes. The presence of brown and beige adipocyte in human adults has acquired attention as a possible therapeutic intervention for metabolic diseases. Importantly, adult human brown appears to be mainly composed of beige-like adipocytes, making this cell type an attractive therapeutic target for obesity and obesity-related diseases, such as atherosclerosis, arterial hypertension and diabetes mellitus type 2. Because many epigenetics changes can affect beige adipocyte differentiation from adipose progenitor cells, the knowledge of the circumstances that affect the development of beige adipocyte cells may be important to new pathways in the treatment of metabolic diseases. New molecules have emerged as possible therapeutic targets, which through the impulse to develop beige adipocytes can be useful for clinical studies. In this review will discuss some recent observations arising from the unique physiological capacity of these cells and their possible role as ways to treat obesity and diabetes mellitus type 2.

Gestational oxidative stress protects against adult obesity and insulin resistance

Pregnancy complications such as preeclampsia cause increased fetal oxidative stress and fetal growth restriction, and associate with a higher incidence of adult metabolic syndrome. However, the pathophysiological contribution of oxidative stress per se is experimentally difficult to discern and has not been investigated. This study determined, if increased intrauterine oxidative stress (IUOx) affects adiposity, glucose and cholesterol metabolism in adult Ldlr−/−xSod2+/+ offspring from crossing male Ldlr−/−xSod2+/+ mice with Ldlr−/−xSod2 +/- dams (IUOx) or Ldlr−/−xSod2 +/- males with Ldlr−/−xSod2+/+ dams (control). At 12 weeks of age mice received Western diet for an additional 12 weeks. Adult male IUOx offspring displayed lower body weight and reduced adiposity associated with improved glucose tolerance compared to controls. Reduced weight gain in IUOx was conceivably due to increased energy dissipation in white adipose tissue conveyed by higher expression of Ucp1 and an accompanying decrease in DNA methylation in the Ucp1 enhancer region. Female offspring did not show comparable phenotypes. These results demonstrate that fetal oxidative stress protects against the obesogenic effects of Western diet in adulthood by programming energy dissipation in white adipose tissue at the level of Ucp1.

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Intrauterine oxidative stress (IUOx) in absence of growth restriction was induced.

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IUOx results in less obesity and improved glucose tolerance in adult male mice.

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Reduced adiposity in adult males is due to browning of white adipose tissue (WAT).

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Increased UCP-1 expression in WAT of IUOx mice is explained by lower methylation.

Programming mediated by fatty acids affects uncoupling protein 1 (UCP-1) in brown adipose tissue

Brown adipose tissue (BAT) has recently been given more attention for the part it plays in obesity. BAT can generate great amounts of heat through thermogenesis by the activation of uncoupling protein 1 (UCP-1), which can be regulated by many environmental factors such as diet. Moreover, the build-up of BAT relates to maternal nutritional changes during pregnancy and lactation. However, at present, there is a limited number of studies looking at maternal nutrition and BAT development, and it seems that the research trend in this field has been considerably declining since the 1980s. There is much to discover yet about the role of different fatty acids on the development of BAT and the activation of UCP-1 during the fetal and the postnatal periods of life. A better understanding of the impact of nutritional intervention on the epigenetic regulation of BAT could lead to new preventive care for metabolic diseases such as obesity. It is important to know in which circumstances lipids could programme BAT during pregnancy and lactation. The modification of maternal dietary fatty acids, amount and composition, during pregnancy and lactation might be a promising strategy for the prevention of obesity in the offspring and future generations.

The role of DNA methylation in thermogenic adipose biology

The two types of thermogenic fat cells, beige and brown adipocytes, play a significant role in regulating energy homeostasis. Their development and thermogenesis are tightly regulated by dynamic epigenetic mechanisms, which could potentially be targeted to treat metabolic disorders such as obesity. However, we are just beginning to catalog and understand these dynamic changes. In this review, we will discuss the current understanding of the role of DNA (de)methylation events in beige and brown adipose biology in order to highlight the holes in our knowledge and to point the way forward for future studies.

Functional Implications of DNA Methylation in Adipose Biology

The twin epidemics of obesity and type 2 diabetes (T2D) are a serious health, social, and economic issue. The dysregulation of adipose tissue biology is central to the development of these two metabolic disorders, as adipose tissue plays a pivotal role in regulating whole-body metabolism and energy homeostasis (1). Accumulating evidence indicates that multiple aspects of adipose biology are regulated, in part, by epigenetic mechanisms. The precise and comprehensive understanding of the epigenetic control of adipose tissue biology is crucial to identifying novel therapeutic interventions that target epigenetic issues. Here, we review the recent findings on DNA methylation events and machinery in regulating the developmental processes and metabolic function of adipocytes. We highlight the following points: 1) DNA methylation is a key epigenetic regulator of adipose development and gene regulation, 2) emerging evidence suggests that DNA methylation is involved in the transgenerational passage of obesity and other metabolic disorders, 3) DNA methylation is involved in regulating the altered transcriptional landscape of dysfunctional adipose tissue, 4) genome-wide studies reveal specific DNA methylation events that associate with obesity and T2D, and 5) the enzymatic effectors of DNA methylation have physiological functions in adipose development and metabolic function.

Promoter Methylation Regulates ApoA-I Gene Transcription in Chicken Abdominal Adipose Tissue

As a central constituent of HDL (high-density lipoprotein), apolipoprotein A-I (ApoA-I) has a vital function in lipid metabolism. Our previous studies confirmed that ApoA-I was differentially expressed in the adipose tissue of the abdomen of lean and fat broilers. The aim of the current work was to evaluate whether the transcription of ApoA-I in chicken abdominal adipose tissue was regulated by DNA methylation. The methylation status of ApoA-I promoter CpG island (PCGI) and promoter non-CpG island (PNCGI) as well as the ApoA-I expression level in adipose tissue of lean and fat broilers were determined using Sequenom MassARRAY and real-time PCR. The correlation analysis results showed that the methylation level of PCGI and the ApoA-I mRNA expression level were negatively correlated. Bisulfite sequencing PCR was used to assess the methylation level of ApoA-I promoter in the ICP1 cells treated with 5-aza-2'-deoxycytidine (5-Aza-CdR: an inhibitor of DNA methyltransferase). The result showed that 5-Aza-CdR caused a reduction in the methylation level of the ApoA-I promoter, thereby causing an increase in expression of the ApoA-I mRNA. Meanwhile, luciferase reporter assays indicated that in vitro methylation of the ApoA-I promoter containing CpG island with CpG methyltransferase led to transcriptional repression. Furthermore, the noticeable activation of NRF1 on ApoA-I transcription was largely enhanced  by the demethylation of the ApoA-I PCGI region. These observations indicated that the differential expression of ApoA-I gene in the adipose tissue of broilers could be mediated by transcription regulation, at least in part by DNA methylation in its PCGI region.

Effects of Cyclocarya paliurus polysaccharide on lipid metabolism-related genes DNA methylation in rats

The present study was conducted to evaluate the effect of CPP on the DNA methylation and expressions of lipid metabolism-related genes (leptin and MTTP) in hyperlipidemic rats. After 8 weeks intervention of CPP, the abdominal wall fat index, liver weight, the serum concentrations of TC, TG and LDL-C were significantly decreased, while HDL was increased. In addition, DNA methylation was analyzed by bisulfite sequencing method, and the mRNA expression levels of leptin and MTTP were detected by Q-PCR. The results showed that CPP could considerably decrease DNA methylation levels of leptin (regions from -694 ~ -370 bp contains 14 CpGs and -324 ~ -29 bp contains 18 CpGs) and MTTP (region from -350 ~ -1 bp contains 11 CpGs) promoters in the liver with the maximum decrease rate of 43.2%, 40.2% and 7.7%, respectively. In parallel, the mRNA contents of leptin and MTTP were dramatically down-regulated. In conclusion, the present findings demonstrated that CPP can regulate the level of mRNA by controlling DNA methylation levels in the liver, thereby reducing blood lipids.

Class I and II Histone Deacetylase Inhibitors Differentially Regulate Thermogenic Gene Expression in Brown Adipocytes

Class I histone deacetylase inhibitors (HDACis) enhance whole body energy expenditure and attenuate high fat diet-induced insulin resistance. However, it is not clear whether this is exerted directly through activating brown fat thermogenesis. Here, we find that pan-HDACi TSA exerts paradoxical effects on brown fat gene expression, as it inhibits the expression of Ucp1, Pparγ and Prdm16 in brown adipocytes, while promoting the expression of other brown fat-specific genes such as Pgc1α, Pgc1β, Acox1 and Cidea. Further studies indicate that class I HDACi MS-275 significantly increases; whereas class II HDACi MC-1568 markedly reduces, the expression of Ucp1 and other brown fat-specific genes in treated brown adipocytes. ChIP assay reveals an enhanced H3 acetylation at the Pgc1α promoter in MS-275-treated brown adipocytes; whereas the effect of MC-1568 is associated with up-regulation of retinoblastoma protein (Rb) and an enhanced acetylation of H3K27 at the Rb promoter. Loss of function studies indicate that Pgc1α up-regulation largely mediates the stimulatory effect of class I HDACis on the thermogenic program, whereas up-regulation of Rb may be responsible for the inhibitory effect of class II HDACis. Thus, our data suggest that class I and II HDACis have differential effects on brown fat thermogenic gene expression.

Identification of a G-quadruplex forming sequence in the promoter of UCP1

G-quadruplexes are higher-order nucleic acid structures formed in G-rich sequences in DNA or RNA. G-quadruplexes are distributed in many locations in the human genome, including promoter regions, and are viewed as promising therapeutic targets. Uncoupling protein-1 (UCP1) is a mitochondrial thermogenic gene critical for energy expenditure in the form of heat in the brown adipose tissue. UCP1 is only expressed during brown fat cell differentiation and is a candidate target for treating obesity. However, the regulation of UCP1 expression is not clear. We reported here that a G-quadruplex forming sequence exists in the promoter of UCP1. The 5,10,15,20-tetra(N-methyl-4-pyridyl) porphyrin (TMPyP4) enhanced cellular expression of UCP1 and destabilized the G-quadruplex formed by the sequence from the promoter of UCP1. Mutations in the G-quadruplex regulated the cellular activity of UCP1 promoter as evidenced by a UCP1-promoter luciferase assay. These results suggest that G-quadruplex structure is a potential target to regulate the expression of UCP1.

Epigenomic Control of Thermogenic Adipocyte Differentiation and Function

Obesity and its associated metabolic disorders are spreading at a fast pace throughout the world; thus, effective therapeutic approaches are necessary to combat this epidemic. Obesity develops when there is a greater caloric intake than energy expenditure. Promoting energy expenditure has recently attracted much attention as a promising approach for the management of body weight. Thermogenic adipocytes are capable of burning fat to dissipate chemical energy into heat, thereby enhancing energy expenditure. After the recent re-discovery of thermogenic adipocytes in adult humans, much effort has focused on understanding the molecular mechanisms, especially the epigenetic mechanisms, which regulate thermogenic adipocyte development and function. A number of chromatin signatures, such as histone modifications, DNA methylation, chromatin accessibilities, and interactions, have been profiled at the genome level and analyzed in various murine and human thermogenic fat cell systems. Moreover, writers and erasers, as well as readers of the epigenome are also investigated using genomic tools in thermogenic adipocytes. In this review, we summarize and discuss the recent advance in these studies and highlight the insights gained into the epigenomic regulation of thermogenic program as well as the pathogenesis of human metabolic diseases.

Evolution of UCP1 Transcriptional Regulatory Elements Across the Mammalian Phylogeny

Uncoupling protein 1 (UCP1) permits non-shivering thermogenesis (NST) when highly expressed in brown adipose tissue (BAT) mitochondria. Exclusive to placental mammals, BAT has commonly been regarded to be advantageous for thermoregulation in hibernators, small-bodied species, and the neonates of larger species. While numerous regulatory control motifs associated with UCP1 transcription have been proposed for murid rodents, it remains unclear whether these are conserved across the eutherian mammal phylogeny and hence essential for UCP1 expression. To address this shortcoming, we conducted a broad comparative survey of putative UCP1 transcriptional regulatory elements in 139 mammals (135 eutherians). We find no evidence for presence of a UCP1 enhancer in monotremes and marsupials, supporting the hypothesis that this control region evolved in a stem eutherian ancestor. We additionally reveal that several putative promoter elements (e.g., CRE-4, CCAAT) identified in murid rodents are not conserved among BAT-expressing eutherians, and together with the putative regulatory region (PRR) and CpG island do not appear to be crucial for UCP1 expression. The specificity and importance of the upTRE, dnTRE, URE1, CRE-2, RARE-2, NBRE, BRE-1, and BRE-2 enhancer elements first described from rats and mice are moreover uncertain as these motifs differ substantially—but generally remain highly conserved—in other BAT-expressing eutherians. Other UCP1 enhancer motifs (CRE-3, PPRE, and RARE-3) as well as the TATA box are also highly conserved in nearly all eutherian lineages with an intact UCP1. While these transcriptional regulatory motifs are generally also maintained in species where this gene is pseudogenized, the loss or degeneration of key basal promoter (e.g., TATA box) and enhancer elements in other UCP1-lacking lineages make it unlikely that the enhancer region is pleiotropic (i.e., co-regulates additional genes). Importantly, differential losses of (or mutations within) putative regulatory elements among the eutherian lineages with an intact UCP1 suggests that the transcriptional control of gene expression is not highly conserved in this mammalian clade.

Brown adipose tissue (BAT) specific vaspin expression is increased after obesogenic diets and cold exposure and linked to acute changes in DNA-methylation

OBJECTIVE

Several studies have demonstrated anti-diabetic and anti-obesogenic properties of visceral adipose tissue-derived serine protease inhibitor (vaspin) and so evoked its potential use for treatment of obesity-related diseases. The aim of the study was to unravel physiological regulators of vaspin expression and secretion with a particular focus on its role in brown adipose tissue (BAT) biology.

METHODS

We analyzed the effects of obesogenic diets and cold exposure on vaspin expression in liver and white and brown adipose tissue (AT) and plasma levels. Vaspin expression was analyzed in isolated white and brown adipocytes during adipogenesis and in response to adrenergic stimuli. DNA-methylation within the vaspin promoter was analyzed to investigate acute epigenetic changes after cold-exposure in BAT.

RESULTS

Our results demonstrate a strong induction of vaspin mRNA and protein expression specifically in BAT of both cold-exposed and high-fat (HF) or high-sugar (HS) fed mice. While obesogenic diets also upregulated hepatic vaspin mRNA levels, cold exposure tended to increase vaspin gene expression of inguinal white adipose tissue (iWAT) depots. Concomitantly, vaspin plasma levels were decreased upon obesogenic or thermogenic triggers. Vaspin expression was increased during adipogenesis but unaffected by sympathetic activation in brown adipocytes. Analysis of vaspin promoter methylation in AT revealed lowest methylation levels in BAT, which were acutely reduced after cold exposure.

CONCLUSIONS

Our data demonstrate a novel BAT-specific regulation of vaspin gene expression upon physiological stimuli in vivo with acute epigenetic changes that may contribute to cold-induced expression in BAT. We conclude that these findings indicate functional relevance and potentially beneficial effects of vaspin in BAT function.

Mitochondria and Epigenetics - Crosstalk in Homeostasis and Stress

Through epigenetic mechanisms cells integrate environmental stimuli to fine-tune gene expression levels. Mitochondrial function is essential to provide the intermediate metabolites necessary to generate and modify epigenetic marks in the nucleus, which in turn can regulate the expression of mitochondrial proteins. In this review we summarize the function of mitochondria in the regulation of epigenetic mechanisms as a new aspect of mitonuclear communication. We focus in particular on the most common epigenetic modifications - histone acetylation and histone and DNA methylation. We also discuss the emerging field of mitochondrial DNA (mtDNA) methylation, whose physiological role remains unknown. Finally, we describe the essential role of some histone modifications in regulating the mitochondrial unfolded protein response (UPR^mt) and the mitochondrial stress-dependent lifespan extension.

Epigenetic Regulation of the Thermogenic Adipose Program

In contrast to white adipose tissue (WAT), which stores energy in the form of triglycerides, brown adipose tissue (BAT) dissipates energy by producing heat to maintain body temperature by burning glucose and fatty acids in a process called adaptive thermogenesis. The presence of an inducible thermogenic adipose tissue, and its beneficial effects for maintaining body weight and glucose and lipid homeostasis, has raised intense interest in understanding the regulation of thermogenesis. Elucidating the regulatory mechanisms underlying the thermogenic adipose program may provide excellent targets for therapeutics against obesity and diabetes. Here we review recent research on the role of epigenetics in the thermogenic gene program, focusing on DNA methylation and histone modifications.

Epigenetic regulation of macrophage polarization and inflammation by DNA methylation in obesity

Obesity is associated with increased classically activated M1 adipose tissue macrophages (ATMs) and decreased alternatively activated M2 ATMs, both of which contribute to obesity-induced inflammation and insulin resistance. However, the underlying mechanism remains unclear. We find that inhibiting DNA methylation pharmacologically using 5-aza-2'-deoxycytidine or genetically by DNA methyltransferase 1 (DNMT1) deletion promotes alternative activation and suppresses inflammation in macrophages. Consistently, mice with myeloid DNMT1 deficiency exhibit enhanced macrophage alternative activation, suppressed macrophage inflammation, and are protected from obesity-induced inflammation and insulin resistance. The promoter and 5'-untranslated region of peroxisome proliferator-activated receptor γ1 (PPARγ1) are enriched with CpGs and are epigenetically regulated. The saturated fatty acids stearate and palmitate and the inflammatory cytokine TNF-α significantly increase, whereas the TH2 cytokine IL-4 significantly decreases PPARγ1 promoter DNA methylation. Accordingly, inhibiting PPARγ1 promoter DNA methylation pharmacologically using 5-aza-2'-deoxycytidine or genetically by DNMT1 deletion promotes macrophage alternative activation. Our data therefore establish DNA hypermethylation at the PPARγ1 promoter induced by obesity-related factors as a critical determinant of ATM proinflammatory activation and inflammation, which contributes to insulin resistance in obesity.

Transcriptional regulation of the uncoupling protein-1 gene

Regulated transcription of the uncoupling protein-1 (UCP1) gene, and subsequent UCP1 protein synthesis, is a hallmark of the acquisition of the differentiated, thermogenically competent status of brown and beige/brite adipocytes, as well as of the responsiveness of brown and beige/brite adipocytes to adaptive regulation of thermogenic activity. The 5' non-coding region of the UCP1 gene contains regulatory elements that confer tissue specificity, differentiation dependence, and neuro-hormonal regulation to UCP1 gene transcription. Two main regions-a distal enhancer and a proximal promoter region-mediate transcriptional regulation through interactions with a plethora of transcription factors, including nuclear hormone receptors and cAMP-responsive transcription factors. Co-regulators, such as PGC-1α, play a pivotal role in the concerted regulation of UCP1 gene transcription. Multiple interactions of transcription factors and co-regulators at the promoter region of the UCP1 gene result in local chromatin remodeling, leading to activation and increased accessibility of RNA polymerase II and subsequent gene transcription. Moreover, a commonly occurring A-to-G polymorphism in close proximity to the UCP1 gene enhancer influences the extent of UCP1 gene transcription. Notably, it has been reported that specific aspects of obesity and associated metabolic diseases are associated with human population variability at this site. On another front, the unique properties of the UCP1 promoter region have been exploited to develop brown adipose tissue-specific gene delivery tools for experimental purposes.

Histone Deacetylase 1 (HDAC1) Negatively Regulates Thermogenic Program in Brown Adipocytes via Coordinated Regulation of Histone H3 Lysine 27 (H3K27) Deacetylation and Methylation

Inhibiting class I histone deacetylases (HDACs) increases energy expenditure, reduces adiposity, and improves insulin sensitivity in obese mice. However, the precise mechanism is poorly understood. Here, we demonstrate that HDAC1 is a negative regulator of the brown adipocyte thermogenic program. The Hdac1 level is lower in mouse brown fat (BAT) than white fat, is suppressed in mouse BAT during cold exposure or β3-adrenergic stimulation, and is down-regulated during brown adipocyte differentiation. Remarkably, overexpressing Hdac1 profoundly blocks, whereas deleting Hdac1 significantly enhances, β-adrenergic activation-induced BAT-specific gene expression in brown adipocytes. β-Adrenergic activation in brown adipocytes results in a dissociation of HDAC1 from promoters of BAT-specific genes, including uncoupling protein 1 (Ucp1) and peroxisome proliferator-activated receptor γ co-activator 1α (Pgc1α), leading to increased acetylation of histone H3 lysine 27 (H3K27), an epigenetic mark of gene activation. This is followed by dissociation of the polycomb repressive complexes, including the H3K27 methyltransferase enhancer of zeste homologue (EZH2), suppressor of zeste 12 (SUZ12), and ring finger protein 2 (RNF2) from (and concomitant recruitment of H3K27 demethylase ubiquitously transcribed tetratricopeptide repeat on chromosome X (UTX) to) Ucp1 and Pgc1α promoters, leading to decreased H3K27 trimethylation, a histone transcriptional repression mark. Thus, HDAC1 negatively regulates the brown adipocyte thermogenic program, and inhibiting Hdac1 promotes BAT-specific gene expression through a coordinated control of increased acetylation and decreased methylation of H3K27, thereby switching the transcriptional repressive state to the active state at the promoters of Ucp1 and Pgc1α. Targeting HDAC1 may be beneficial in prevention and treatment of obesity by enhancing BAT thermogenesis.

The Histone Demethylase UTX Promotes Brown Adipocyte Thermogenic Program Via Coordinated Regulation of H3K27 Demethylation and Acetylation

Brown adipocytes function to dissipate energy as heat through adaptive thermogenesis. Understanding the molecular mechanisms underlying the brown fat thermogenic program may provide insights for the development of therapeutic approaches in the treatment of obesity. Most studies investigating the mechanisms underlying brown fat development focus on genetic mechanisms; little is known about the epigenetic mechanisms in this process. We have discovered that ubiquitously transcribed tetratricopeptide repeat on chromosome X (UTX), a histone demethylase for di- or tri-methylated histone 3 lysine 27 (H3K27me2/3), plays a potential role in regulating brown adipocyte thermogenic program. We found that UTX is up-regulated during brown adipocyte differentiation and by cold exposure in both brown adipose tissue (BAT) and white adipose tissue (WAT) of mice, suggesting a potential role in thermogenesis. Inactivation of UTX down-regulates brown fat specific gene expression, while overexpression of UTX does the opposite. Notably, activation of β adrenergic signaling recruits UTX to the UCP1 and PGC1α promoters, leading to decreased H3K27me3, a histone transcriptional repressive mark. UTX demethylates H3K27me3 and subsequently interacts with the histone acetyltransferase (HAT) protein CBP, resulting in increased H3K27 acetylation (H3K27ac), a histone transcriptional active mark. UTX positively regulate brown adipocyte thermogenic program through coordinated control of demethylating H3K27me3 and acetylating H3K27, switching the transcriptional repressive state to the transcriptional active state at the promoters of UCP1 and PGC1α. We conclude that UTX may play a potential role in regulation of brown adipocyte gene expression and may mediate β adrenergic activation of brown fat function.

Genome-wide DNA methylation analysis in precursor B-cells

DNA methylation is responsible for regulating gene expression and cellular differentiation and for maintaining genomic stability during normal human development. Furthermore, it plays a significant role in the regulation of hematopoiesis. In order to elucidate the influence of DNA methylation during B-cell development, genome-wide DNA methylation status of pro-B, pre-BI, pre-BII, and naïve-B-cells isolated from human umbilical cord blood was determined using the methylated CpG island recovery assay followed by next generation sequencing. On average, 182–200 million sequences were generated for each precursor B-cell subset in 10 biological replicates. An overall decrease in methylation was observed during the transition from pro-B to pre-BI, whereas no differential methylation was observed in the pre-BI to pre-BII transition or in the pre-BII to naïve B-cell transition. Most of the methylated regions were located within intergenic and intronic regions not present in a CpG island context. Putative novel enhancers were identified in these regions that were differentially methylated between pro-B and pre-BI cells. The genome-wide methylation profiles are publically available and may be used to gain a better understanding of the involvement of atypical DNA methylation in the pathogenesis of malignancies associated with precursor B-cells.

Energizing Genetics and Epi-genetics: Role in the Regulation of Mitochondrial Function

Energy metabolism and mitochondrial function hold a core position in cellular homeostasis. Oxidative metabolism is regulated at multiple levels, ranging from gene transcription to allosteric modulation. To accomplish the fine tuning of these multiple regulatory circuits, the nuclear and mitochondrial compartments are tightly and reciprocally controlled. The fact that nuclear encoded factors, PPARγ coactivator 1α and mitochondrial transcription factor A, play pivotal roles in the regulation of oxidative metabolism and mitochondrial biogenesis is paradigmatic of this crosstalk. Here we provide an updated survey of the genetic and epigenetic mechanisms involved in the control of energy metabolism and mitochondrial function. Chromatin dynamics highly depends on post-translational modifications occurring at specific amino acids in histone proteins and other factors associated to nuclear DNA. In addition to the well characterized enzymes responsible for histone methylation/demethylation and acetylation/deacetylation, other factors have gone on the "metabolic stage". This is the case of the new class of α-ketoglutarate-regulated demethylases (Jumonji C domain containing demethylases) and of the NAD+-dependent deacetylases, also known as sirtuins. Moreover, unexpected features of the machineries involved in mitochondrial DNA (mtDNA) replication and transcription, mitochondrial RNA processing and maturation have recently emerged. Mutations or defects of any component of these machineries profoundly affect mitochondrial activity and oxidative metabolism. Finally, recent evidences support the importance of mtDNA packaging in replication and transcription. These observations, along with the discovery that non-classical CpG islands present in mtDNA undergo methylation, indicate that epigenetics also plays a role in the regulation of the mitochondrial genome function.

Inhibiting DNA Methylation by 5-Aza-2'-deoxycytidine ameliorates atherosclerosis through suppressing macrophage inflammation

Inflammation marks all stages of atherogenesis. DNA hypermethylation in the whole genome or specific genes is associated with inflammation and cardiovascular diseases. Therefore, we aimed to study whether inhibiting DNA methylation by DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) ameliorates atherosclerosis in low-density lipoprotein receptor knockout (Ldlr(-/-)) mice. Ldlr(-/-) mice were fed an atherogenic diet and adminisered saline or 5-aza-dC (0.25 mg/kg) for up to 30 weeks. 5-aza-dC treatment markedly decreased atherosclerosis development in Ldlr(-/-) mice without changes in body weight, plasma lipid profile, macrophage cholesterol levels and plaque lipid content. Instead, this effect was associated with decreased macrophage inflammation. Macrophages with 5-aza-dC treatment had downregulated expression of genes involved in inflammation (TNF-α, IL-6, IL-1β, and inducible nitric oxidase) and chemotaxis (CD62/L-selectin, chemokine [C-C motif] ligand 2/MCP-1 [CCL2/MCP-1], CCL5, CCL9, and CCL2 receptor CCR2). This resulted in attenuated macrophage migration and adhesion to endothelial cells and reduced macrophage infiltration into atherosclerotic plaques. 5-aza-dC also suppressed macrophage endoplasmic reticulum stress, a key upstream signal that activates macrophage inflammation and apoptotic pathways. Finally, 5-aza-dC demethylated liver X receptor α (LXRα) and peroxisome proliferator-activated receptor γ1 (PPARγ1) promoters, which are both enriched with CpG sites. This led to overexpression of LXRα and PPARγ, which may be responsible for 5-aza-dC's anti-inflammatory and atheroprotective effect. Our findings provide strong evidence that DNA methylation may play a significant role in cardiovascular diseases and serve as a therapeutic target for prevention and treatment of atherosclerosis.

White, brite, and brown adipocytes: the evolution and function of a heater organ in mammals

Brown fat is a specialized heater organ in eutherian mammals. In contrast to the energy storage function of white adipocytes, brown adipocytes dissipate nutrient energy by uncoupling of mitochondrial oxidative phosphorylation, which depends on uncoupling protein 1 (UCP1). UCP1, as well as UCP2 and UCP3, belong to the family of mitochondrial carriers inserted into the inner mitochondrial membrane for metabolite trafficking between the matrix and the intermembrane space. UCP1 transports protons into the mitochondrial matrix when activated by a rise in free fatty acid levels in the cell. This UCP1-dependant proton leak drives high oxygen consumption rates in the absence of ATP synthesis and dissipates proton motive force as heat. The enormous heating capacity of brown fat is supported by dense vascularization, high rates of tissue perfusion, and high mitochondrial density in brown adipocytes.

It has been known for more than 50 years that nonshivering thermogenesis in brown fat serves to maintain body temperature of neonates and small mammals in cold environments, and is used by hibernators for arousal from torpor. It has been speculated that the development of brown fat as a new source for nonshivering thermogenesis provided mammals with a unique advantage for survival in the cold. Indeed brown fat and UCP1 is found in ancient groups of mammals, like the afrotherians and marsupials. In the latter, however, the thermogenic function of UCP1 and brown fat has not been demonstrated as of yet. Notably, orthologs of all three mammalian UCP genes are also present in the genomes of bony fishes and in amphibians. Molecular phylogeny reveals a striking increase in the substitution rate of UCP1 between marsupial and eutherian lineages. At present, it seems that UCP1 only gained thermogenic function in brown adipocytes of eutherian mammals, whereas the function of UCP1 and that of the other UCPs in ectotherms remains to be identified.

Evolution of thermogenic function required expression of UCP1 in a brown-adipocyte-like cell equipped with high mitochondrial density embedded in a well-vascularized tissue. Brown-adipocyte-like cells in white adipose tissue, called “brite” (brown-in-white) or “beige” adipocytes, emerge during adipogenesis and in response to cold exposure in anatomically distinct adipose tissue depots of juvenile and adult rodents. These brite adipocytes may resemble the archetypical brown adipocyte in vertebrate evolution. It is therefore of interest to elucidate the molecular mechanisms of brite adipocyte differentiation, study the bioenergetic properties of these cells, and search for the presence of related brown-adipocyte-like cells in nonmammalian vertebrates.

Developmental programming by high fructose decreases phosphorylation efficiency in aging offspring brain mitochondria, correlating with enhanced UCP5 expression

Fructose has recently been observed to affect brain metabolism and cognitive function in adults. Yet, possible late-onset effects by gestational fructose exposure have not been examined. We evaluated mitochondrial function in the brain of aging (15 months) male offspring of Fischer F344 rat dams fed a high-fructose diet (50% energy from fructose) during gestation and lactation. Maternal fructose exposure caused a significantly lower body weight of the offspring throughout life after weaning, while birth weight, litter size, and body fat percentage were unaffected. Isolated brain mitochondria displayed a significantly increased state 3 respiration of 8%, with the substrate combinations malate/pyruvate, malate/pyruvate/succinate, and malate/pyruvate/succinate/rotenone, as well as a significant decrease in the P/O₂ ratio, compared with the control. Uncoupling protein 5 (UCP5) protein levels increased in the fructose group compared with the control (P=0.03) and both UCP5 mRNA and protein levels were inversely correlated with the P/O₂ ratio (P=0.008 and 0.03, respectively), suggesting that UCP5 may have a role in the observed decreased phosphorylation efficiency. In conclusion, maternal high-fructose diet during gestation and lactation has long-term effects (fetal programming) on brain mitochondrial function in aging rats, which appears to be linked to an increase in UCP5 protein levels.