Uncoupling protein gene: quantification of expression levels in adipose tissues of obese and non-obese humans

Lipedema: The Use of Cultured Adipocytes for Identification of Diagnostic Markers

BACKGROUND

Lipedema, diagnosed most often in women, is a progressive disease characterized by the disproportionate and symmetrical distribution of adipose tissue, primarily in the extremities. Although numerous results from in vitro and in vivo studies have been published, many questions regarding the pathology and genetic background of lipedema remain unanswered.

METHODS

In this study, adipose tissue-derived stromal/stem cells were isolated from lipoaspirates derived from nonobese and obese donors with or without lipedema. Growth and morphology, metabolic activity, differentiation potential, and gene expression were evaluated using quantification of lipid accumulation, metabolic activity assay, live-cell imaging, reverse transcription polymerase chain reaction, quantitative polymerase chain reaction, and immunocytochemical staining.

RESULTS

The adipogenic potential of lipedema and nonlipedema adipose tissue-derived stromal/stem cells did not rise in parallel with the donors' body mass index and did not differ significantly between groups. However, in vitro differentiated adipocytes from nonobese lipedema donors showed significant upregulation of adipogenic gene expression compared with nonobese controls. All other genes tested were expressed equally in lipedema and nonlipedema adipocytes. The adiponectin/leptin ratio was significantly reduced in adipocytes from obese lipedema donors compared with their nonobese lipedema counterparts. Increased stress fiber-integrated smooth muscle actin was visible in lipedema adipocytes compared with nonlipedema controls and appeared enhanced in adipocytes from obese lipedema donors.

CONCLUSIONS

Not only lipedema per se but also body mass index of donors affect adipogenic gene expression substantially in vitro. The significantly reduced adiponectin/leptin ratio and the increased occurrence of myofibroblast-like cells in obese lipedema adipocyte cultures underscores the importance of attention to the co-occurrence of lipedema and obesity. These are important findings toward accurate diagnosis of lipedema.

CLINICAL RELEVANCE STATEMENT

Our study highlights not only the difficulty in lipedema diagnostics but also the tremendous need for further studies on lipedema tissue. Although lipedema might seem to be an underestimated field in plastic and reconstructive surgery, the power it holds to provide better treatment to future patients can not be promoted enough.

Adipose tissue plasticity in pheochromocytoma patients suggests a role of the splicing machinery in human adipose browning

Adipose tissue from pheochromocytoma patients acquires brown fat features, making it a valuable model for studying the mechanisms that control thermogenic adipose plasticity in humans. Transcriptomic analyses revealed a massive downregulation of splicing machinery components and splicing regulatory factors in browned adipose tissue from patients, with upregulation of a few genes encoding RNA-binding proteins potentially involved in splicing regulation. These changes were also observed in cell culture models of human brown adipocyte differentiation, confirming a potential involvement of splicing in the cell-autonomous control of adipose browning. The coordinated changes in splicing are associated with a profound modification in the expression levels of splicing-driven transcript isoforms for genes involved in the specialized metabolism of brown adipocytes and those encoding master transcriptional regulators of adipose browning. Splicing control appears to be a relevant component of the coordinated gene expression changes that allow human adipose tissue to acquire a brown phenotype.

Uncoupling Protein 2 Expression Modulates Obesity in Chronic Kidney Disease Patients

Background

Obesity is a multifactorial metabolic disease resulting from behavioral and genetic factors. Obesity is linked to diabetes mellitus and hypertension, which are considered as major risk factors for chronic kidney disease (CKD); moreover, it has a direct effect on developing CKD and end stage renal disease (ESRD). Here was aimed to examine the association between uncoupling protein 2 (UCP2) gene expression and obesity in CKD patients.

Methods

UCP2 gene expression was analyzed by real time polymerase chain reaction (RT-PCR) in 93 participants divided into three groups. The groups included 31 non-obese CKD patients, 31 obese CKD patients, and 31 healthy, age-matched, unrelated volunteers as a control group.

Results

UCP2 gene expression was significantly relevant when comparing the non-obese CKD and obese CKD groups to the control group (p< 0.001). No significant association was found when the groups were compared by gender; Chi-square (X2) was 2.38 and p= 0.304. A significant negative correlation was found between UCP2 gene expression and BMI in CKD (p< 0.05).

Conclusion

These results indicate that UCP2 gene expression plays a significant role as a risk factor for obesity in CKD patients.

Developmental programming of offspring adipose tissue biology and obesity risk

Obesity is reaching epidemic proportions and imposes major negative health crises and an economic burden in both high and low income countries. The multifaceted nature of obesity represents a major health challenge, with obesity affecting a variety of different organs and increases the risk of many other noncommunicable diseases, such as type 2 diabetes, fatty liver disease, dementia, cardiovascular diseases, and even cancer. The defining organ of obesity is the adipose tissue, highlighting the need to more comprehensively understand the development and biology of this tissue to understand the pathogenesis of obesity. Adipose tissue is a miscellaneous and highly plastic endocrine organ. It comes in many different sizes and shades and is distributed throughout many different locations in the body. Though its development begins prenatally, quite uniquely, it has the capacity for unlimited growth throughout adulthood. Adipose tissue is also a highly sexually dimorphic tissue, patterning men and women in different ways, which means the risks associated with obesity are also sexually dimorphic. Recent studies show that environmental factors during prenatal and early stages of postnatal development have the capacity to programme the structure and function of adipose tissue, with implications for the development of obesity. This review summarizes the evidence for a role for early environmental factors, such as maternal malnutrition, hypoxia, and exposure to excess hormones and endocrine disruptors during gestation in the programming of adipose tissue and obesity in the offspring. We will also discuss the complexity of studying adipose tissue biology and the importance of appreciating nuances in adipose tissue, such as sexual dimorphism and divergent responses to metabolic and endocrine stimuli. Given the rising levels of obesity worldwide, understanding how environmental conditions in early life affects adipose tissue phenotype and the subsequent development of obesity is of absolute importance.

Interleukin-10 Attenuates Liver Fibrosis Exacerbated by Thermoneutrality

Background: Crosstalk between brown adipose tissue (BAT) and the liver is receiving increasing attention. This study investigated the effect of BAT dysfunction by thermoneutral (TN) housing on liver fibrosis in mice and examined the effect of secreted factors from brown adipocytes on the activation of hepatic stellate cells (HSCs).

Methods: The carbon tetrachloride (CCl₄)-induced liver fibrosis mouse model was used to evaluate fibrotic changes in the livers of mice housed under standard and TN conditions. The effect of BAT on the activation of HSCs was examined using cultured cells treated with conditioned media from brown adipocytes.

Results: Under TN conditions, mice with CCl₄-induced liver fibrosis exhibited increased liver injury, collagen deposition, and alpha smooth muscle actin (α-SMA) expression in the liver compared with mice maintained at room temperature. The numbers of liver-infiltrating immune cells and T cells producing IL-17A and IFN-γ were also significantly increased in the livers of mice housed under TN conditions. Treatment of HSCs with conditioned media from brown adipocytes markedly attenuated HSC activation, as shown by down-regulated α-SMA expression at day 4, day 7 and day 10 of culture. At thermoneutrality, with CCl₄ administration, IL-10-deficient mice exhibited more severe liver fibrosis than wild-type mice. Interestingly, conditioned media from IL-10-deficient brown adipocytes could up-regulate the expression of α-SMA and induce HSCs activation.

Conclusions: BAT inactivation by thermoneutrality contributes to the activation of pro-inflammatory and pro-fibrotic pathways in mice with CCl₄-induced liver fibrosis. Normal brown adipocytes secreted factors that impair the activation of HSCs, while this protective effect was lost in IL-10-deficient brown adipocytes. Thus, the BAT–liver axis may serve as a potential therapeutic target for liver fibrosis, and IL-10 may be a key factor regulating the activation of HSCs by BAT.

Brown and beige adipose tissue regulate systemic metabolism through a metabolite interorgan signaling axis

Brown and beige adipose tissue are emerging as distinct endocrine organs. These tissues are functionally associated with skeletal muscle, adipose tissue metabolism and systemic energy expenditure, suggesting an interorgan signaling network. Using metabolomics, we identify 3-methyl-2-oxovaleric acid, 5-oxoproline, and β-hydroxyisobutyric acid as small molecule metabokines synthesized in browning adipocytes and secreted via monocarboxylate transporters. 3-methyl-2-oxovaleric acid, 5-oxoproline and β-hydroxyisobutyric acid induce a brown adipocyte-specific phenotype in white adipocytes and mitochondrial oxidative energy metabolism in skeletal myocytes both in vitro and in vivo. 3-methyl-2-oxovaleric acid and 5-oxoproline signal through cAMP-PKA-p38 MAPK and β-hydroxyisobutyric acid via mTOR. In humans, plasma and adipose tissue 3-methyl-2-oxovaleric acid, 5-oxoproline and β-hydroxyisobutyric acid concentrations correlate with markers of adipose browning and inversely associate with body mass index. These metabolites reduce adiposity, increase energy expenditure and improve glucose and insulin homeostasis in mouse models of obesity and diabetes. Our findings identify beige adipose-brown adipose-muscle physiological metabokine crosstalk.

The roles of triiodothyronine and irisin in improving the lipid profile and directing the browning of human adipose subcutaneous cells

Triiodothyronine (T3) and irisin (I) can modulate metabolic status, increase heat production, and promote differentiation of white adipose tissue (WAT) into brown adipose tissue (BAT). Herein, human subcutaneous white adipocytes were treated with 10 nM T3 or 20 nM I for 24 h to evaluate intracellular lipid accumulation, triglyceride, and glycerol levels, oxidative stress, DNA damage, and protein levels of uncoupling protein 1 (UCP1), adiponectin, leptin, peroxisome proliferator-activated receptor gamma (PPARγ), and fibronectin type III domain-containing protein 5 (FNDC5). T3 and irisin improved UCP1 production, lipid profile, oxidative stress, and DNA damage. T3 elevated adiponectin and leptin levels with a concomitant decrease in PPARy and FNDC5 levels. However, irisin did not alter adipokine, PPARy, and FNDC5 levels. The results indicate that T3 may be used to increase leptin and adiponectin levels to improve insulin sensitivity, and irisin may be used to prevent obesity or maintain weight due to its impact on the lipid profile without altering adipokine levels.

-866G/A and Ins/Del polymorphisms in the UCP2 gene and diabetic kidney disease: case-control study and meta-analysis

Uncoupling protein 2 (UCP2) decreases reactive oxygen species (ROS). ROS overproduction is a key contributor to the pathogenesis of diabetic kidney disease (DKD). Thus, UCP2 polymorphisms are candidate risk factors for DKD; however, their associations with this complication are still inconclusive. Here, we describe a case-control study and a meta-analysis conducted to investigate the association between UCP2 -866G/A and Ins/Del polymorphisms and DKD. The case-control study comprised 385 patients with type 1 diabetes mellitus (T1DM): 223 patients without DKD and 162 with DKD. UCP2 -866G/A (rs659366) and Ins/Del polymorphisms were genotyped by real-time PCR and conventional PCR, respectively. For the meta-analysis, a literature search was conducted to identify all studies that investigated associations between UCP2 polymorphisms and DKD in patients with T1DM or type 2 diabetes mellitus. Pooled odds ratios were calculated for different inheritance models. Allele and genotype frequencies of -866G/A and Ins/Del polymorphisms did not differ between T1DM case and control groups. Haplotype frequencies were also similar between groups. Four studies plus the present one were eligible for inclusion in the meta-analysis. In agreement with case-control data, the meta-analysis results showed that the -866G/A and Ins/Del polymorphisms were not associated with DKD. In conclusion, our case-control and meta-analysis studies did not indicate an association between the analyzed UCP2 polymorphisms and DKD.

Reactive oxygen, nitrogen, and sulfur species in human male fertility. A crossroad of cellular signaling and pathology

Infertility is a significant global health problem that currently affects one of six couples in reproductive age. The quality of male reproductive cells dramatically decreased over the last years and almost every aspect of modern life additionally worsen sperm functional parameters that consequently markedly increase male infertility. This clearly points out the importance of finding a new approach to treat male infertility. Redox signaling mediated by reactive oxygen, nitrogen and sulfur species (ROS, RNS, and RSS respectively), has appeared important for sperm reproductive function. Present review summarizes the current knowledge of ROS, RNS, and RSS in male reproductive biology and identifies potential targets for development of novel pharmacological and therapeutic approaches for male infertility by targeted therapeutic modulation of redox signaling.

Adrenomedullin has a role in angiogenic effects of resveratrol in adipose tissues of obese female rats

Obesity is a complex, chronic disease that arises according to the interaction between genetic and environmental factors. The expansion and growth of white adipose tissue (WAT) could be related to angiogenesis. Resveratrol and adrenomedullin (AdM) were used for the inhibition of angiogenesis in metabolically passive WAT for inhibiting the expansion of this tissue, and the activation of angiogenesis in metabolically active brown adipose tissue (BAT) for increasing daily energy consumption as a way of reducing obesity. Rats were divided into eight groups. Four obese groups were fed with a high-fat diet containing 60% fat as energy for three months. After obtaining obesity, 2.5 nmol/kg AdM and 10 mg/kg resveratrol were treated to experiment groups intraperitoneally (i.p.) every other day for four weeks. AdM and vascular endothelial growth factor A (VEGF-A) mRNA levels were detected with semi-quantitative PCR; protein levels were detected with Western Blotting. AdM and resveratrol are multifactorial molecules, thus, this study has revealed a few novel evidence. The results were distinct in the group and treatment levels. The results showed that resveratrol has a role in angiogenesis in obesity and contributed to AdM production. It is observed that AdM has regulated its expression and increased the effect of resveratrol in WAT. AdM and VEGF-A gene expressions could not be detected in BAT; however, it is suggested that resveratrol may have a pro-angiogenic effect in BAT of obese rats according to the protein levels. AdM also has regulated VEGF-A level according to the metabolic situation of the organism.

Dietary sn-2 palmitic triacylglycerols reduced faecal lipids, calcium contents and altered lipid metabolism in Sprague-Dawley rats

In this study, the impact of dietary sn-2 palmitic triacylglycerol (sn-2 PTAG) on faecal lipids, calcium excretion and lipid metabolic alternation was investigated in Sprague-Dawley (SD) rats fed with high-fat diet containing either palm olein (PO, sn-2 palmitic acid (PA) of 14.8%), sn-2 PTAG50 (sn-2 PA of 56.4%) or sn-2 PTAG70 (sn-2 PA of 72.4%), respectively. After 4-week feeding period, SD rats fed with sn-2 PTAGs showed reduced faecal soap fatty acids, neutral lipid and calcium excretion compared to those of PO-fed rats, whereas a significant difference was only observed for the sn-2 PTAG70-fed rats (p < .05). Moreover, dietary sn-2 PTAG70 also showed a significant effect on decreasing serum triacylglycerol (TAG) level, reducing perirenal adipocyte size and regulating lipid metabolism in small intestine and perirenal adipose tissue of SD rats. Significantly increased mRNA levels of genes involved in intestinal lipid anabolism as well as lipid catabolism were both observed in the sn-2 PTAG70-fed rats (p < .05). Meanwhile, dietary sn-2 PTAG70 also significantly up-regulated lipolysis, mitochondrial fatty acid oxidation and thermogenesis-related gene and protein levels in perirenal adipose tissue, which might be correlated with the reduced perirenal adipocyte size. Taken together, our findings indicated that sn-2 PTAG70 may have some beneficial effects on intestinal lipid utilisation and lipid metabolic activity for energy supply in visceral adipose tissue.

Activation of Human Brown Adipose Tissue (BAT): Focus on Nutrition and Eating

Brown adipose tissue activation occurs most effectively by cold exposure. In the modern world, we do not spend long periods in cold environment, and eating and meals may be other activators of brown fat function. Short-term regulation of brown fat functional activity by eating involves most importantly insulin. Insulin is capable to increase glucose uptake in human brown adipose tissue fivefold to fasting conditions. Oxidative metabolism in brown fat is doubled both by cold and by a meal. Human brown adipose tissue is an insulin-sensitive tissue type, and insulin resistance impairs the function, as is found in obesity. Body weight reduction improves cold-induced activation of human brown adipose tissue.

MiR-27b-3p Regulation in Browning of Human Visceral Adipose Related to Central Obesity

OBJECTIVE

Given the rising prevalence of central obesity and the discovery that beige cells appear within white adipose tissue, strategies to enhance these energy-expending adipocytes or "browning" within white adipose depots have become of therapeutic interest to combat obesity and its associated disorders. This study focused on, the role of microRNA (miRNA)-27b-3p in human visceral adipose tissue (VAT) browning.

METHODS

Expression of miR-27b-3p and UCP1 in VAT and serum of humans was measured. MiR-27b-3p was overexpressed or suppressed in human visceral stromal fraction cells to analyze the potential role of miR-27b-3p.

RESULTS

UCP1 expression in human VAT decreased with elevated BMI and waist-hip ratio, whereas expression of miR-27b-3p was found to correlate positively with BMI and waist-hip ratio. High expression of miR-27b-3p was associated with reduced browning ability of human visceral adipocytes. Antagonism of miR-27b-3p led to the enhancement of browning ability in human visceral adipocytes.

CONCLUSIONS

These findings highlight the decreased browning ability of VAT from humans with obesity and the role of miR-27b-3p in regulating browning of human visceral adipocytes. They suggest that miR-27b-3p should be further explored as a potential target for the treatment of central obesity.

Human brown adipose tissue as a target for obesity management; beyond cold-induced thermogenesis

Elevating energy expenditure via adaptive thermogenesis in brown adipose tissue (BAT) is a potential strategy to reverse obesity. Much early enthusiasm for this approach, based on rodent studies, was tempered by the belief that BAT was relatively inconsequential in healthy adult humans. Interest was reinvigorated a decade ago when a series of studies re-identified BAT, primarily in upper thoracic regions, in adults. Despite the ensuing explosion of pre-clinical investigations and identification of an extensive list of potential target molecules for BAT recruitment, our understanding of human BAT physiology remains limited, particularly regarding interventions which might hold therapeutic promise. Cold-induced BAT thermogenesis (CIT) has been well studied, although is not readily translatable as an anti-obesity approach, whereas little is known regarding the role of BAT in human diet-induced thermogenesis (DIT). Furthermore, human studies dedicated to translating known pharmacological mechanisms of adipose browning from animal models are sparse. Several lines of recent evidence suggest that molecular regulation and physiology of human BAT differ to that of laboratory rodents, which form the majority of our knowledge base. This review will summarize knowledge on CIT and expand upon the current understanding and evidence gaps related to human adaptive thermogenesis via mechanisms other than cold.

Apolipoprotein A5 regulates intracellular triglyceride metabolism in adipocytes

It has previously been demonstrated that apolipoprotein A5 (apoA5) can be internalized by human adipocytes and significantly decreases intracellular triglyceride content. In the present study, endocytosis of apoA5 by adipocytes under different conditions, and the underlying mechanism by which apoA5 regulates cellular triglyceride storage, was investigated. The results revealed that the apoA5 protein was detected in human subcutaneous abdominal adipose tissues. In addition, the uptake of apoA5 was attenuated in human obese adipose tissues and in cultured adipocytes with hypertrophy or insulin resistance. Low-density lipoprotein receptor protein 1 (LRP1) knockdown in adipocytes resulted in a decrease in internalized apoA5 content, suggesting that LRP1 serves a role in apoA5 uptake. Treatment of adipocytes with apoA5 decreased the expression of the lipid droplet-associated proteins such as cidec and perilipin. ApoA5-treated adipocytes demonstrated an increase in lipolysis activity and expression of uncoupling protein 1, which is the molecular effector of thermogenesis in brown adipocytes. These results suggested that decreased triglyceride accumulation in adipocytes induced by apoA5 may be associated with enhanced lipolysis and energy expenditure, which may result from reduced expression of cidec and perilipin. In conclusion, the present study demonstrated a novel role of apoA5 in regulating the intracellular triglyceride metabolism of adipocytes. The results of the present study suggested that apoA5 may serve as a potential therapeutic target for the treatment of obesity and its related disorders.

Features of omental adipose tissue in endometrial cancer patients with 'standard' or 'metabolically healthy' obesity: associations with tumor process characteristics

Purpose

Adipose tissue products may contribute to endometrial cancer (EC) initiation and further growth that encourages the analysis of this issue in patients with different obesity phenotypes.

Methods/patients

Omental fat depot characteristics were studied in EC patients (n = 57) with “standard” (SO) or “metabolically healthy” (MHO) obesity. Collected omental samples were evaluated by immunohistochemistry /IHC/ for brown fat marker UCP1, CYP19 (aromatase) and macrophage infiltration markers (CD68, CD163, crown-like structures/CLS) expression. Total RNA extracted from the same samples was investigated for UCP1, CYP19, PTEN and adipokine omentin mRNA.

Results

Immunohistochemistry data revealed a statistically significant increase in aromatase and CD68 expression and tendency to increase of UCP1 expression in SO patients’ omental fat compared to samples obtained from MHO patients. Additionally, positive correlation of EC clinical stage with UCP1 protein and its mRNA content in omental fat was pronounced in MHO as well as SO group, while with omentin mRNA it was discovered only in patients with SO. An inclination to the correlation with better tumor differentiation was seen for UCP1 and CD68 protein expression in patients with MHO and with worse (high grade) differentiation—for CD68 expression in the group with SO.

Conclusions

In aggregate, this suggests that obesity phenotype has significant impact on omental fat tissue characteristics which is related to the clinical course of EC and may have practical consequences.

FoxO1 interacts with transcription factor EB and differentially regulates mitochondrial uncoupling proteins via autophagy in adipocytes

Mitochondrial uncoupling proteins (UCPs) are inducible and play an important role in metabolic and redox homeostasis. Recent studies have suggested that FoxO1 controls mitochondrial biogenesis and morphology, but it remains largely unknown how FoxO1 may regulate mitochondrial UCPs. Here we show that FoxO1 interacted with transcription factor EB (Tfeb), a key regulator of autophagosome and lysosome, and mediated the expression of UCP1, UCP2 and UCP3 differentially via autophagy in adipocytes. UCP1 was down-regulated but UCP2 and UCP3 were upregulated during adipocyte differentiation, which was associated with increased Tfeb and autophagy activity. However, inhibition of FoxO1 suppressed Tfeb and autophagy, attenuating UCP2 and UCP3 but increasing UCP1 expression. Pharmacological blockade of autophagy recapitulated the effects of FoxO1 inhibition on UCPs. Chromatin immunoprecipitation assay demonstrated that FoxO1 interacted with Tfeb by directly binding to its promoter, and silencing FoxO1 led to drastic decrease in Tfeb transcript and protein levels. These data provide the first line of evidence that FoxO1 interacts with Tfeb to regulate autophagy and UCP expression in adipocytes. Dysregulation of FoxO1→autophagy→UCP pathway may account for metabolic changes in obesity.

Can thermogenic adipocytes protect from obesity?

The role of brown adipocytes and adipocytes of a new beige type in the energy metabolism of a healthy person and in the pathogenesis of obesity has extensively been discussed in recent years. The interest to these cells has been stimulated owing to the application of new noninvasive methods for studying the metabolic activity of tissues. Using these methods, the presence of thermogenically active adipocytes in adults and their reactivity to cold stimuli have been proved. These data, together with the results of animal experiments support the idea of thermogenic fat being a direct regulator of the energy balance of man. However, for several reasons there are some objections to this viewpoint. The main objection is that the total activity of the human thermogenic adipocytes is about 100 kJ/day, i.e., it is negligible. In addition, the burn of excessive nutrients is biologically inappropriate for an organism. Therefore, the idea that obesity is caused by the decreased activity of thermogenic adipocytes is erroneous. The statement that the causes of obesity are associated with the increased efficiency of energy-dependent processes seems more reasonable. The consequence is a reduction in energy expenditure to perform a unit of biological work. This results in excess of nutrients deposited in the form of fat.

Does inorganic nitrate say NO to obesity by browning white adipose tissue?

The dietary constituent inorganic nitrate, found in large concentrations in green leafy vegetables, has beneficial effects on cardiometabolic health. Contemporary studies employing nitrate have demonstrated that the anion has anti-obesity and anti-diabetic properties; however the nitrate-mediated mechanisms for improving metabolic health remain unclear. Recently, we employed a combined histological, metabolomics, and transcriptional and protein analysis approach to establish that nitrate promoted the "browning" of white adipose tissue via the xanthine oxidoreductase catalyzed reductive nitrate-nitrite-nitric oxide pathway. Interestingly, it was observed that nitrate-stimulated brown adipose-associated gene expression in white adipose tissue was augmented in hypoxia. These findings not only suggest that protection from metabolic disease offered by vegetable consumption may, in part, be mediated through the effects of nitrate on white adipose tissue, but also, since hypoxia is a serious co-morbidity affecting adipose tissue in obese individuals, that nitrate may be effective in promoting the browning of adipose tissue to improve metabolic fitness.

Polymorphisms of the UCP2 Gene Are Associated with Glomerular Filtration Rate in Type 2 Diabetic Patients and with Decreased UCP2 Gene Expression in Human Kidney

INTRODUCTION

Uncoupling protein 2 (UCP2) reduces production of reactive oxygen species (ROS) by mitochondria. ROS overproduction is one of the major contributors to the pathogenesis of chronic diabetic complications, such as diabetic kidney disease (DKD). Thus, deleterious polymorphisms in the UCP2 gene are candidate risk factors for DKD. In this study, we investigated whether UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms were associated with DKD in patients with type 2 diabetes mellitus (T2DM), and whether they had an effect on UCP2 gene expression in human kidney tissue biopsies.

MATERIALS AND METHODS

In a case-control study, frequencies of the UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms as well as frequencies of the haplotypes constituted by them were analyzed in 287 T2DM patients with DKD and 281 T2DM patients without this complication. In a cross-sectional study, UCP2 gene expression was evaluated in 42 kidney biopsy samples stratified according to the presence of the UCP2 mutated -866A/55Val/Ins haplotype.

RESULTS

In the T2DM group, multivariate logistic regression analysis showed that the -866A/55Val/Ins haplotype was an independent risk factor for DKD (OR = 2.136, 95% CI 1.036-4.404), although neither genotype nor allele frequencies of the individual polymorphisms differed between case and control groups. Interestingly, T2DM patients carrying the mutated haplotype showed decreased estimated glomerular filtration rate (eGFR) when compared to subjects with the reference haplotype (adjusted P= 0.035). In kidney biopsy samples, UCP2 expression was significantly decreased in UCP2 mutated haplotype carriers when compared to kidneys from patients with the reference haplotype (0.32 ± 1.20 vs. 1.85 ± 1.16 n fold change; adjusted P< 0.000001).

DISCUSSION

Data reported here suggest that the UCP2 -866A/55Val/Ins haplotype is associated with an increased risk for DKD and with a lower eGFR in T2DM patients. Furthermore, this mutated haplotype was associated with decreased UCP2 gene expression in human kidneys.

Thermogenic brown and beige/brite adipogenesis in humans

Evidence from rodents established an important role of brown adipose tissue (BAT) in energy expenditure. Moreover, to sustain thermogenesis, BAT has been shown to be a powerful sink for draining and oxidation of glucose and triglycerides from blood. The potential of BAT activity in protection against obesity and metabolic syndrome is recognized. Recently, an unexpected presence and activity of BAT has been found in adult humans. Here we review the most recent research in this field and, specifically, how new findings apply to humans. Moreover, we seek to clarify the underlying biological processes occurring beyond the burst of new nomenclature in the field. The cell type responsible for thermogenesis, the brown adipocyte, arises from complex developmental processes. In addition to 'classical' brown adipocytes, present in developmentally programmed BAT depots, there are brown adipocytes, named 'brite' (from 'brown-in-white') or 'beige', which appear in response to thermogenic stimuli in white fat due to the so-called 'browning' process. Beige/brite cells appear to be important components of BAT depots in adult humans. In addition to the known control of BAT activity by the sympathetic nervous system, metabolic and hormonal signals originating in muscle or liver (e.g. irisin, FGF21) are recognized as activators of BAT and beige/brite adipocytes.

Inorganic nitrate promotes the browning of white adipose tissue through the nitrate-nitrite-nitric oxide pathway

Inorganic nitrate was once considered an oxidation end product of nitric oxide metabolism with little biological activity. However, recent studies have demonstrated that dietary nitrate can modulate mitochondrial function in man and is effective in reversing features of the metabolic syndrome in mice. Using a combined histological, metabolomics, and transcriptional and protein analysis approach, we mechanistically defined that nitrate not only increases the expression of thermogenic genes in brown adipose tissue but also induces the expression of brown adipocyte-specific genes and proteins in white adipose tissue, substantially increasing oxygen consumption and fatty acid β-oxidation in adipocytes. Nitrate induces these phenotypic changes through a mechanism distinct from known physiological small molecule activators of browning, the recently identified nitrate-nitrite-nitric oxide pathway. The nitrate-induced browning effect was enhanced in hypoxia, a serious comorbidity affecting white adipose tissue in obese individuals, and corrected impaired brown adipocyte-specific gene expression in white adipose tissue in a murine model of obesity. Because resulting beige/brite cells exhibit antiobesity and antidiabetic effects, nitrate may be an effective means of inducing the browning response in adipose tissue to treat the metabolic syndrome.

The effect of neuropeptide Y on brown-like adipocyte's differentiation and activation

Despite its wide distribution in the central nervous system, the presence of Neuropeptide Y (NPY) in peripheral tissues has been detected. White adipose tissue (WAT) is a new site of NPY synthesis and secretion. The development of brown-like adipocytes in WAT is controlled by hypothalamic NPY neurons through interaction with sympathetic nervous system (SNS). However, whether peripheral NPY has a direct effect on induction of the Uncoupling protein1 (UCP1)-positive adipocytes is unknown. We have used adipocytes derived from C3H10T1/2 stem cells as a model of brown-like adipocyte, and investigated the role of NPY in their differentiation and activation. In general, NPY had no effect on brown adipogenesis of C3H10T1/2 stem cell, but suppressed db-cAMP activation of brown-like adipocytes, which was due to blunting brown fat-relevant gene expression and mitochondrial function. NPY showed suppression in a receptor-dependent manner, inhibition of endogenous cAMP production and cAMP-PKA-dependent pathways p38 MAPK and CREB phosphorylation were involved in the downstream mechanisms. A novel role of NPY in the peripheral is presented, which may help decrease energy expenditure in WAT of obese subjects.

White, brown and pink adipocytes: the extraordinary plasticity of the adipose organ

In mammals, adipocytes are lipid-laden cells making up the parenchyma of the multi-depot adipose organ. White adipocytes store lipids for release as free fatty acids during fasting periods; brown adipocytes burn glucose and lipids to maintain thermal homeostasis. A third type of adipocyte, the pink adipocyte, has recently been characterised in mouse subcutaneous fat depots during pregnancy and lactation. Pink adipocytes are mammary gland alveolar epithelial cells whose role is to produce and secrete milk. Emerging evidence suggests that they derive from the transdifferentiation of subcutaneous white adipocytes. The functional response of the adipose organ to a range of metabolic and environmental challenges highlights its extraordinary plasticity. Cold exposure induces an increase in the 'brown' component of the organ to meet the increased thermal demand; in states of positive energy balance, the 'white' component expands to store excess nutrients; finally, the 'pink' component develops in subcutaneous depots during pregnancy to ensure litter feeding. At the cell level, plasticity is provided not only by stem cell proliferation and differentiation but also, distinctively, by direct transdifferentiation of fully differentiated adipocytes by the stimuli that induce genetic expression reprogramming and through it a change in phenotype and, consequently function. A greater understanding of adipocyte transdifferentiation mechanisms would have the potential to shed light on their biology as well as inspire novel therapeutic strategies against metabolic syndrome (browning) and breast cancer (pinking).

Reduced UCP-1 content in in vitro differentiated beige/brite adipocytes derived from preadipocytes of human subcutaneous white adipose tissues in obesity

Introduction

Brown adipose tissue (BAT) is a potential therapeutic target to reverse obesity. The purpose of this study was to determine whether primary precursor cells isolated from human adult subcutaneous white adipose tissue (WAT) can be induced to differentiate in-vitro into adipocytes that express key markers of brown or beige adipose, and whether the expression level of such markers differs between lean and obese young adult males.

Methods

Adipogenic precursor cells were isolated from lean and obese individuals from subcutaneous abdominal WAT biopsies. Cells were grown to confluence, differentiated for 2.5 weeks then harvested for measurement of gene expression and UCP1 protein.

Results

There was no difference between groups with respect to differentiation into adipocytes, as indicated by oil red-O staining, rates of lipolysis, and expression of adipogenic genes (FABP4, PPARG). WAT genes (HOXC9, RB1) were expressed equally in the two groups. Post differentiation, the beige adipose specific genes CITED1 and CD137 were significantly increased in both groups, but classic BAT markers ZIC1 and LHX8 decreased significantly. Cell lines from both groups also equally increased post-differentiation expression of the thermogenic-responsive gene PPARGC1A (PGC-1α). UCP1 gene expression was undetectable prior to differentiation, however after differentiation both gene expression and protein content were increased in both groups and were significantly greater in cultures from lean compared with obese individuals (p<0.05).

Conclusion

Human subcutaneous WAT cells can be induced to attain BAT characteristics, but this capacity is reduced in WAT cells from obese individuals.

The formation of brown adipose tissue induced by transgenic over-expression of PPARγ2

Brown adipose tissue (BAT) is specialized to dissipate energy as heat, therefore reducing fat deposition and counteracting obesity. Brown adipocytes arise from myoblastic progenitors during embryonic development by the action of transcription regulator PRDM16 binding to PPARγ, which promotes BAT-like phenotype in white adipose tissue. To investigate the capability of converting white adipose tissue to BAT or browning by PPARγ in vivo, we generated transgenic mice with over-expressed PPARγ2. The transgenic mice showed strong brown fat features in subcutaneous fat in morphology and histology. To provide molecular evidences on browning characteristics of the adipose tissue, we employed quantitative real-time PCR to determine BAT-specific gene expressions. The transgenic mice had remarkably elevated mRNA level of UCP1, Elovl3, PGC1α and Cebpα in subcutaneous fat. Compared with wild-type mice, UCP1 protein levels were increased significantly in transgenic mice. ATP concentration was slightly decreased in the subcutaneous fat of transgenic mice. Western blotting analysis also confirmed that phosphorylated AMPK and ACC proteins were significantly (P<0.01) increased in the transgenic mice. Therefore, this study demonstrated that over-expression of PPARγ2 in skeletal muscle can promote conversion of subcutaneous fat to brown fat formation, which can have beneficial effects on increasing energy metabolisms and combating obesity.

Oleoylethanolamide enhances β-adrenergic-mediated thermogenesis and white-to-brown adipocyte phenotype in epididymal white adipose tissue in rat

β-adrenergic receptor activation promotes brown adipose tissue (BAT) β-oxidation and thermogenesis by burning fatty acids during uncoupling respiration. Oleoylethanolamide (OEA) can inhibit feeding and stimulate lipolysis by activating peroxisome proliferator-activating receptor-α (PPARα) in white adipose tissue (WAT). Here we explore whether PPARα activation potentiates the effect of β3-adrenergic stimulation on energy balance mediated by the respective agonists OEA and CL316243. The effect of this pharmacological association on feeding, thermogenesis, β-oxidation, and lipid and cholesterol metabolism in epididymal (e)WAT was monitored. CL316243 (1 mg/kg) and OEA (5 mg/kg) co-administration over 6 days enhanced the reduction of both food intake and body weight gain, increased the energy expenditure and reduced the respiratory quotient (VCO₂/VO₂). This negative energy balance agreed with decreased fat mass and increased BAT weight and temperature, as well as with lowered plasma levels of triglycerides, cholesterol, nonessential fatty acids (NEFAs), and the adipokines leptin and TNF-α. Regarding eWAT, CL316243 and OEA treatment elevated levels of the thermogenic factors PPARα and UCP1, reduced p38-MAPK phosphorylation, and promoted brown-like features in the white adipocytes: the mitochondrial (Cox4i1, Cox4i2) and BAT (Fgf21, Prdm16) genes were overexpressed in eWAT. The enhancement of the fatty-acid β-oxidation factors Cpt1b and Acox1 in eWAT was accompanied by an upregulation of de novo lipogenesis and reduced expression of the unsaturated-fatty-acid-synthesis enzyme gene, Scd1. We propose that the combination of β-adrenergic and PPARα receptor agonists promotes therapeutic adipocyte remodelling in eWAT, and therefore has a potential clinical utility in the treatment of obesity.

The presence of at least three alleles of the ADRB3 Trp64Arg (C/T) and UCP1 -3826A/G polymorphisms is associated with protection to overweight/obesity and with higher high-density lipoprotein cholesterol levels in Caucasian-Brazilian patients with type 2 diabetes

BACKGROUND

We investigated whether the -3826A/G polymorphism (rs1800592) of the uncoupling protein 1 gene (UCP1) and the Trp64Arg polymorphism (rs4994) of the β3-adrenergic receptor gene (ADRB3) are associated with type 2 diabetes mellitus (T2DM) and features of metabolic syndrome in a Brazilian-Caucasian population.

METHODS

Both polymorphisms were genotyped in 1015 T2DM patients and 561 nondiabetic subjects. The combined effect of both polymorphisms on T2DM and metabolic syndrome-related parameters was analyzed according to a triallelic inheritance pattern, by which at least three minor alleles from two loci are necessary for trait manifestation.

RESULTS

UCP1 -3826A/G and ADRB3 Trp64Arg polymorphisms were not associated with T2DM (P>0.05). Patients carrying the ADRB3 64Arg allele had higher fasting plasma glucose and high-density lipoprotein cholesterol (HDL-C) than patients with the Trp64Trp genotype (P=0.0001 and P=0.015, respectively). The 64Arg allele was also associated with protection against overweight/obesity (body mass index ≥ 25 kg/m(2); odds ratio [OR]=0.598; P=0.014). Interestingly, prevalence of overweight/obesity was lower among carriers of at least three minor alleles of the -3826A/G and ADRB3 Trp64Arg polymorphisms than among patients with fewer than three minor alleles (54.5% vs. 79.1%; OR=0.288; P=0.007, respectively). Subjects with at least three minor alleles also had higher HDL-C levels (P=0.018).

CONCLUSIONS

UCP1 -3826A/G and ADRB3 Trp64Arg polymorphisms may have a combined effect in the modulation of overweight/obesity and HDL-C levels in type 2 diabetes mellitus (T2DM) Caucasian-Brazilian patients.

Retinoic acid has different effects on UCP1 expression in mouse and human adipocytes

Background

Increased adipose thermogenesis is being considered as a strategy aimed at preventing or reversing obesity. Thus, regulation of the uncoupling protein 1 (UCP1) gene in human adipocytes is of significant interest. Retinoic acid (RA), the carboxylic acid form of vitamin A, displays agonist activity toward several nuclear hormone receptors, including RA receptors (RARs) and peroxisome proliferator-activated receptor δ (PPARδ). Moreover, RA is a potent positive regulator of UCP1 expression in mouse adipocytes.

Results

The effects of all-trans RA (ATRA) on UCP1 gene expression in models of mouse and human adipocyte differentiation were investigated. ATRA induced UCP1 expression in all mouse white and brown adipocytes, but inhibited or had no effect on UCP1 expression in human adipocyte cell lines and primary human white adipocytes. Experiments with various RAR agonists and a RAR antagonist in mouse cells demonstrated that the stimulatory effect of ATRA on UCP1 gene expression was indeed mediated by RARs. Consistently, a PPARδ agonist was without effect. Moreover, the ATRA-mediated induction of UCP1 expression in mouse adipocytes was independent of PPARγ coactivator-1α.

Conclusions

UCP1 expression is differently affected by ATRA in mouse and human adipocytes. ATRA induces UCP1 expression in mouse adipocytes through activation of RARs, whereas expression of UCP1 in human adipocytes is not increased by exposure to ATRA.

Brown adipose tissue in humans: therapeutic potential to combat obesity

Harnessing the considerable capacity of brown adipose tissue (BAT) to consume energy was first proposed as a potential target to control obesity nearly 40years ago. The plausibility of this approach was, however, questioned due to the prevailing view that BAT was either not present or not functional in adult humans. Recent definitive identification of functional BAT in adult humans as well as a number of important advances in the understanding of BAT biology has reignited interest in BAT as an anti-obesity target. Proof-of-concept evidence demonstrating drug-induced BAT activation provides an important foundation for development of targeted pharmacological approaches with clinical application. This review considers evidence from both human and relevant animal studies to determine whether harnessing BAT for the treatment of obesity via pharmacological intervention is a realistic goal.

Diet-induced changes in Ucp1 expression in bovine adipose tissues

Brown adipocytes, which regulate non-shivering thermogenesis, have been believed to exist in a limited number of mammalian species, and only under limited physiological conditions. Recent discoveries indicate that adult humans possess a significant number of functional brown adipocytes. This study explores the regulatory emergence of brown adipocytes in white adipose tissue (WAT) depots of fattening cattle. RT-PCR analyses indicated significant expression of Ucp1, a brown adipocyte-specific gene, in the WAT of 31-month-old Japanese Black steers. Immunohistochemical analysis revealed that Ucp1-positive small adipocytes were dispersed in the subcutaneous WAT. Next, we examined expression level of Ucp1 and other brown adipocyte-selective genes such as Pgc1α, Cidea, Dio2, Cox1, Cox7a1 and Cox8b in WAT of 30-month-old steers fed either diet with low protein/energy content (roughage diet) or that with high protein/energy content (concentrate diet) for 20months. Ucp1 expression in the subcutaneous WAT was significantly higher in the concentrate diet group than in the roughage diet group. Furthermore, the higher Ucp1 expression levels were limited to the subcutaneous WAT, and no differences between groups were detected in the mesenteric, perirenal, intermuscular or intramuscular WAT. Expression of Dio2, Cox1 and Cox8b was higher in the subcutaneous WAT but not in the mesenteric WAT of the concentrate diet group. Furthermore, expression of Prdm16, a positive regulator of differentiation toward brown adipocyte-lineage cells, and expression of leptin, a molecule that enhances activity of brown adipocytes, were significantly higher in the subcutaneous WAT of the concentrate diet group. This study demonstrates the presence of brown adipocytes in WAT depots of fattening cattle, and suggests the diet-related modulation of expression of genes predominantly expressed in brown adipocytes.

The adipose organ at a glance

The main parenchymal cells of the adipose organ are adipocytes. White adipocytes store energy, whereas brown adipocytes dissipate energy for thermogenesis. These two cell types with opposing functions can both originate from endothelial cells, and co-exist in the multiple fat depots of the adipose organ - a feature that I propose is crucial for this organ's plasticity. This poster review provides an overview of the adipose organ, describing its anatomy, cytology, physiological function and histopathology in obesity. It also highlights the remarkable plasticity of the adipose organ, explaining theories of adipocyte transdifferentiation during chronic cold exposure, physical exercise or lactation, as well as in obesity. White-to-brown adipocyte transdifferentiation is of particular medical relevance, because animal data indicate that higher amounts of brown adipose tissue are positively associated with resistance to obesity and its co-morbidities, and that 'browning' of the adipose organ curbs these disorders.

Mechanism of body weight reducing effect of oral boric Acid intake

Objective. The effect of oral boric acid intake on reducing body weight has been previously demonstrated although the mechanism has been unclear. This research study reveals the mechanism. Subjects. Twelve mice were used, in groups of six each in the control and study groups. For five days, control group mice drank standard tap water while during the same time period the study group mice drank tap water which contains 0.28 mg/250 mL boric acid. After a 5-day period, gene expression levels for uncoupling proteins (UCPs) in the white adipose tissue (WAT), brown adipose tissue (BAT), and skeletal muscle tissue (SMT) and total body weight changes were analyzed. Results. Real time PCR analysis revealed no significant change in UCP3 expressions, but UCP2 in WAT (P: 0.0317), BAT (P: 0.014), and SMT (P: 0.0159) and UCP1 in BAT (P: 0.026) were overexpressed in the boric acid group. In addition, mice in the boric acid group lost body weight (mean 28.1%) while mice in the control group experienced no weight loss but a slight weight gain (mean 0.09%, P < 0.001). Conclusion. Oral boric acid intake causes overexpression of thermogenic proteins in the adipose and skeletal muscle tissues. Increasing thermogenesis through UCP protein pathway results in the accelerated lipolysis and body weight loss.

Brown adipose tissue functions in humans

Human adults have functionally active BAT. The metabolic function can be reliably measured in vivo using modern imaging modalities (namely PET/CT). Cold seems to be one of the most potent stimulators of BAT metabolic activity but other stimulators (for example insulin) are actively studied. Obesity is related to lower metabolic activity of BAT but it may be reversed after successful weight reduction such as after bariatric surgery. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.

Targeting adipose tissue

Two different types of adipose tissues can be found in humans enabling them to respond to starvation and cold: white adipose tissue (WAT) is generally known and stores excess energy in the form of triacylglycerol (TG), insulates against cold, and serves as a mechanical cushion. Brown adipose tissue (BAT) helps newborns to cope with cold. BAT has the capacity to uncouple the mitochondrial respiratory chain, thereby generating heat rather than adenosine triphosphate (ATP). The previously widely held view was that BAT disappears rapidly after birth and is no longer present in adult humans. Using positron emission tomography (PET), however, it was recently shown that metabolically active BAT occurs in defined regions and scattered in WAT of the adult and possibly has an influence on whole-body energy homeostasis. In obese individuals adipose tissue is at the center of metabolic syndrome. Targeting of WAT by thiazolidinediones (TZDs), activators of peroxisome proliferator-activated receptor γ (PPARγ) a 'master' regulator of fat cell biology, is a current therapy for the treatment of type 2 diabetes. Since its unique capacity to increase energy consumption of the body and to dissipate surplus energy as heat, BAT offers new perspectives as a therapeutic target for the treatment of obesity and associated diseases such as type 2 diabetes and metabolic syndrome. Recent discoveries of new signaling pathways of BAT development give rise to new therapeutic possibilities in order to influence BAT content and activity.

Association of the UCP-1 single nucleotide polymorphism A-3826G with the dampness-phlegm pattern among Korean stroke patients

Background

Patients with stroke have various syndromes and symptoms. Through pattern identification (PI), traditional Korean medicine (TKM) classifies the several syndromes and symptoms of stroke patients into five categories: Fire-heat (FH), Dampness-phlegm (DP), Yin-deficiency (YD), Qi-deficiency (QD) and Blood-stasis (BS). DP has been associated with obesity and hyperlipidemia. Uncoupling protein-1 (UCP-1), which plays a major role in thermogenesis and energy expenditure can increase the risk of obesity and can be related metabolic disorders. In this study, we elucidated the association of three polymorphisms located in the UCP-1 promoter and coding region with DP among Korean stroke patients.

Methods

1,593 patients with cerebral infarction (583/DP, 1,010/non-DP) and 587 normal subjects were enrolled. The genotypes A-3826G, G-1766A and Ala64Thr (G+1068A) for each subject were determined by polymerase chain reaction with TaqMan probes and five percent of subjects were re-genotyped by sequencing method to confirm the accuracy of genotyping. The results were analyzed using a multiple logistic regression model to evaluate the genetic associations: the UCP-1polymorphisms of normal versus those of DP subjects and those of normal versus those of non-DP subjects.

Results

A significantly higher percentage of subjects in the DP group possessed the A-3826G G allele than the A allele (OR=1.508, p=0.006). Furthermore, the number of subjects with the GG type of A-1766G was significantly lower in the non-DP group than the normal group in the recessive model (OR=0.606, p=0.042). In addition, an analysis of the relationship among 2 SNPs of UCP-1 and lipid serum concentration showed that the serum level of HDL cholesterol was significantly higher in subjects with the A-3826G G allele in the normal group (p=0.032). Serum triglyceride and HDL cholesterol were also associated with the A-1766G variant in the recessive model (p=0.002, p=0.046).

Conclusions

These results suggest that that the A-3826G and A-1766G UCP-1 polymorphisms, which are related to obesity, might be candidate genetic markers for the DP pattern in the TKM diagnosis system.

Molecular and histological evidence of brown adipose tissue in adult cats

Brown adipose tissue (BAT) can influence glucose, lipid, and energy metabolism in rodents. Active BAT is now known to be present in adult humans, and interventions targeting BAT are being investigated for the treatment of human obesity and disorders of glucose and lipid metabolism. Domestic cats, like humans, are at increasing risk for obesity and diabetes but little is known about the presence and role of BAT in adult cats. The purpose of this study was to determine if brown adipocytes, identifiable by histological features and molecular markers, were present in the fat depots of adult cats. Adipose tissue samples from intrascapular, perirenal, and subcutaneous depots of eleven 8-12 year old cats (6 lean, 5 obese), were analyzed by real-time PCR for brown adipocyte markers uncoupling protein 1 (UCP1) and Type II iodothyronine 5'deiodinase (D2), by histological examination and by immunohistochemistry for UCP1. UCP1 mRNA was detectable in interscapular and subcutaneous depots in all cats, and in the perirenal depot in 10/11 cats. D2 mRNA was detectable in all depots from all cats. Multilocular adipocytes were identified in the interscapular depots of 4/11 cats and these were positive for UCP1 immunoreactivity. The results demonstrate that UCP1-expressing brown adipocytes are present in multiple depots of adult lean and long-term obese cats, even at 8-12 years of age. It is possible that dietary components or pharmacological agents that influence brown fat activity could exert a relevant biological effect in cats.

Rare adipose disorders (RADs) masquerading as obesity

Rare adipose disorders (RADs) including multiple symmetric lipomatosis (MSL), lipedema and Dercum's disease (DD) may be misdiagnosed as obesity. Lifestyle changes, such as reduced caloric intake and increased physical activity are standard care for obesity. Although lifestyle changes and bariatric surgery work effectively for the obesity component of RADs, these treatments do not routinely reduce the abnormal subcutaneous adipose tissue (SAT) of RADs. RAD SAT likely results from the growth of a brown stem cell population with secondary lymphatic dysfunction in MSL, or by primary vascular and lymphatic dysfunction in lipedema and DD. People with RADs do not lose SAT from caloric limitation and increased energy expenditure alone. In order to improve recognition of RADs apart from obesity, the diagnostic criteria, histology and pathophysiology of RADs are presented and contrasted to familial partial lipodystrophies, acquired partial lipodystrophies and obesity with which they may be confused. Treatment recommendations focus on evidence-based data and include lymphatic decongestive therapy, medications and supplements that support loss of RAD SAT. Associated RAD conditions including depression, anxiety and pain will improve as healthcare providers learn to identify and adopt alternative treatment regimens for the abnormal SAT component of RADs. Effective dietary and exercise regimens are needed in RAD populations to improve quality of life and construct advanced treatment regimens for future generations.

A new era for brown adipose tissue: New insights into brown adipocyte function and differentiation

Until quite recently, brown adipose tissue was considered of metabolic significance only in small mammals and human newborns, since it was thought to disappear rapidly after birth in humans. However, nowadays this tissue is known to play a role in the regulation of energy balance not only in rodents, but also in humans. In this review we highlight new features regarding brown adipose tissue origin and function and revise old paradigms about brown adipocyte differentiation.

Brown fat and obesity: the next big thing?

Brown adipose tissue (BAT) is well recognised to have an important role in the maintenance of body temperature in animals and human neonates, its thermogenic action affected by a tissue-specific uncoupling protein; fatty acid oxidation within the numerous brown adipocyte mitochondria is rendered inefficient leading to heat, rather than adenosine triphosphate (ATP), production. BAT was believed to show rapid involution in early childhood, leaving only vestigial amounts in adults. However, recent evidence suggests that its expression in adults is far more common than previously appreciated, with a higher likelihood of detection in women and leaner individuals. It is conceivable that BAT activity might reduce the risk of developing obesity since fat stores are used for thermogenesis, and a directed enhancement of adipocyte metabolism might have value in weight reduction. However, it is as yet unclear how such manipulation of BAT might be achieved; even in animal models, the control of thermogenic activity is incompletely understood. Even so, there is still much to interest the endocrinologist in BAT, with a range of hormones affecting adipocyte activity. This may either contribute to normal physiological function, or the phenotypical presentation of states of pathological hormone excess or deficiency. Thus, the gender differences in BAT distribution may be attributable to the differential effects of male and female sex hormones, whilst BAT expansion may drive the weight loss associated with catecholamine-producing phaeochromocytomas. These observations support an important influence of the endocrine system on BAT activity and offer new potential targets in the treatment of obesity.

Novel genes and cellular pathways related to infection with adenovirus-36 as an obesity agent in human mesenchymal stem cells

OBJECTIVE

The objective of this study was to investigate the molecular mechanisms underlying adenovirus-36 (Ad-36)-induced obesity by the identification of novel genes and cellular pathways.

DESIGN

Viral growth, intracellular lipid accumulation and gene expression profiles were determined in human mesenchymal stem cells (hMSCs) infected with Ad-36 or Ad-2. A microarray assay and gene set enrichment analysis (GSEA) were performed to assess alterations in global gene expression profiles.

RESULTS

Ad-36, but not Ad-2, induced lipid accumulation and upregulated adipogenesis-related genes. There was no difference in viral growth between Ad-36 infection and Ad-2 infection in hMSCs. GSEA revealed that Ad-36 infection was more frequently associated with activation of novel pathways, including the PPAR-gamma signaling pathway, and inflammation compared with Ad-2 infection, raising the possibility that these pathways may be key regulators of Ad-36-induced adipogenesis.

CONCLUSION

This study may help foster a better understanding of the roles of several cellular factors in Ad-36-induced obesity.

Implications of nonshivering thermogenesis for energy balance regulation in humans

The incidence of the metabolic syndrome has reached epidemic levels in the Western world. With respect to the energy balance, most attention has been given to reducing energy (food) intake. Increasing energy expenditure is an important alternative strategy. Facultative thermogenesis, which is the increase in energy expenditure in response to cold or diet, may be an effective way to affect the energy balance. The recent identification of functional brown adipose tissue (BAT) in adult humans promoted a renewed interest in nonshivering thermogenesis (NST). The purpose of this review is to highlight the recent insight in NST, general aspects of its regulation, the major tissues involved, and its metabolic consequences. Sustainable NST in adult humans amounts to 15% of the average daily energy expenditure. Calculations based on the limited available literature show that BAT thermogenesis can amount to 5% of the basal metabolic rate. It is likely that at least a substantial part of NST can be attributed to BAT, but it is possible that other tissues contribute to NST. Several studies on mitochondrial uncoupling indicate that skeletal muscle is another potential contributor to facultative thermogenesis in humans. The general and synergistic role of the sympathetic nervous system and the thyroid axis in relation to NST is discussed. Finally, perspectives on BAT and skeletal muscle NST are given.

Brown adipose tissue in morbidly obese subjects

Background

Cold-stimulated adaptive thermogenesis in brown adipose tissue (BAT) to increase energy expenditure is suggested as a possible therapeutic target for the treatment of obesity. We have recently shown high prevalence of BAT in adult humans, which was inversely related to body mass index (BMI) and body fat percentage (BF%), suggesting that obesity is associated with lower BAT activity. Here, we examined BAT activity in morbidly obese subjects and its role in cold-induced thermogenesis (CIT) after applying a personalized cooling protocol. We hypothesize that morbidly obese subjects show reduced BAT activity upon cold exposure.

Methods and Findings

After applying a personalized cooling protocol for maximal non-shivering conditions, BAT activity was determined using positron-emission tomography and computed tomography (PET-CT). Cold-induced BAT activity was detected in three out of 15 morbidly obese subjects. Combined with results from lean to morbidly obese subjects (n = 39) from previous study, the collective data show a highly significant correlation between BAT activity and body composition (P<0.001), respectively explaining 64% and 60% of the variance in BMI (r = 0.8; P<0.001) and BF% (r = 0.75; P<0.001). Obese individuals demonstrate a blunted CIT combined with low BAT activity. Only in BAT-positive subjects (n = 26) mean energy expenditure was increased significantly upon cold exposure (51.5±6.7 J/s versus 44.0±5.1 J/s, P = 0.001), and the increase was significantly higher compared to BAT-negative subjects (+15.5±8.9% versus +3.6±8.9%, P = 0.001), indicating a role for BAT in CIT in humans.

Conclusions

This study shows that in an extremely large range of body compositions, BAT activity is highly correlated with BMI and BF%. BAT-positive subjects showed higher CIT, indicating that BAT is also in humans involved in adaptive thermogenesis. Increasing BAT activity could be a therapeutic target in (morbid) obesity.

[Physiological mechanisms in the development of adiposity]

The phenomenon of the so-called "obesity pandemic" having arisen over the last decades has to be, in large part, attributed to changes of lifestyle and the associated changes in dietary habits and physical activity observed world-wide. The resulting interference in energy homeostasis plays a central role in the development of obesity in a large proportion of the population worldwide. In this article, current knowledge about central biological mechanisms of energy intake, energy storage, and energy expenditure is summarized. This includes, for example, the feeling of hunger/satiety, lipid turnover with the two components of lipolysis and lipogenesis, adipogenesis, as well as energy-consuming processes like (adaptive) thermogenesis, resting metabolic rate, and physical activity energy expenditure. Based on examples, the possible influence of genetic polymorphisms contributing to the development of adiposity are illustrated.