Two key temporally distinguishable molecular and cellular components of white adipose tissue browning during cold acclimation

Exercise training and cold exposure trigger distinct molecular adaptations to inguinal white adipose tissue

Exercise training and cold exposure both improve systemic metabolism, but the mechanisms are not well established. Here, we tested the hypothesis that inguinal white adipose tissue (iWAT) adaptations are critical for these beneficial effects and determined the impact of exercise-trained and cold-exposed iWAT on systemic glucose metabolism and the iWAT proteome and secretome. Transplanting trained iWAT into sedentary mice improves glucose tolerance, while cold-exposed iWAT transplantation shows no such benefit. Compared to training, cold leads to more pronounced alterations in the iWAT proteome and secretome, downregulating >2,000 proteins but also boosting the thermogenic capacity of iWAT. In contrast, only training increases extracellular space and vesicle transport proteins, and only training upregulates proteins that correlate with favorable fasting glucose, suggesting fundamental changes in trained iWAT that mediate tissue-to-tissue communication. This study defines the unique exercise training- and cold exposure-induced iWAT proteomes, revealing distinct mechanisms for the beneficial effects of these interventions on metabolic health.

Adipose tissue browning and thermogenesis under physiologically energetic challenges: a remodelled thermogenic system

Metabolic diseases such as obesity and diabetes are often thought to be caused by reduced energy expenditure, which poses a serious threat to human health. Cold exposure, exercise and caloric restriction have been shown to promote adipose tissue browning and thermogenesis. These physiological interventions increase energy expenditure and thus have emerged as promising strategies for mitigating metabolic disorders. However, that increased adipose tissue browning and thermogenesis elevate thermogenic consumption is not a reasonable explanation when humans and animals confront energetic challenges imposed by these interventions. In this review, we collected numerous results on adipose tissue browning and whitening and evaluated this bi-directional conversion of adipocytes from the perspective of energy homeostasis. Here, we propose a new interpretation of the role of adipose tissue browning under energetic challenges: increased adipose tissue browning and thermogenesis under energy challenge is not to enhance energy expenditure, but to reestablish a more economical thermogenic pattern to maintain the core body temperature. This can be achieved by enhancing the contribution of non-shivering thermogenesis (adipose tissue browning and thermogenesis) and lowering shivering thermogenesis and high intensity shivering. Consequently, the proportion of heat production in fat increases and that in skeletal muscle decreases, enabling skeletal muscle to devote more energy reserves to overcoming environmental stress.

Redox and metabolic reprogramming in breast cancer and cancer-associated adipose tissue

Redox and metabolic processes are tightly coupled in both physiological and pathological conditions. In cancer, their integration occurs at multiple levels and is characterized by synchronized reprogramming both in the tumor tissue and its specific but heterogeneous microenvironment. In breast cancer, the principal microenvironment is the cancer-associated adipose tissue (CAAT). Understanding how the redox-metabolic reprogramming becomes coordinated in human breast cancer is imperative both for cancer prevention and for the establishment of new therapeutic approaches. This review aims to provide an overview of the current knowledge of the redox profiles and regulation of intermediary metabolism in breast cancer while considering the tumor and CAAT of breast cancer as a unique Warburg's pseudo-organ. As cancer is now recognized as a systemic metabolic disease, we have paid particular attention to the cell-specific redox-metabolic reprogramming and the roles of estrogen receptors and circadian rhythms, as well as their crosstalk in the development, growth, progression, and prognosis of breast cancer.

Exercise Training and Cold Exposure Trigger Distinct Molecular Adaptations to Inguinal White Adipose Tissue

Exercise training and cold exposure both improve systemic metabolism, but the mechanisms are not well-established. We tested the hypothesis that adaptations to inguinal white adipose tissue (iWAT) are critical for these beneficial effects by determining the impact of exercise-trained and cold-exposed iWAT on systemic glucose metabolism and the iWAT proteome and secretome. Transplanting trained iWAT into sedentary mice improved glucose tolerance, while cold-exposed iWAT transplantation showed no such benefit. Compared to training, cold led to more pronounced alterations in the iWAT proteome and secretome, downregulating >2,000 proteins but also boosting iWAT's thermogenic capacity. In contrast, only training increased extracellular space and vesicle transport proteins, and only training upregulated proteins that correlate with favorable fasting glucose, suggesting fundamental changes in trained iWAT that mediate tissue-to-tissue communication. This study defines the unique exercise training- and cold exposure-induced iWAT proteomes, revealing distinct mechanisms for the beneficial effects of these interventions on metabolic health.

Redox-metabolic reprogramming of skin in mice lacking functional Nrf2 under basal conditions and cold acclimation

Adaptive responses to environmental and physiological challenges, including exposure to low environmental temperature, require extensive structural, redox, and metabolic reprogramming. Detailed molecular mechanisms of such processes in the skin are lacking, especially the role of nuclear factor erythroid 2-related factor 2 (Nrf2) and other closely related redox-sensitive transcription factors Nrf1, Nrf3, and nuclear respiratory factor (NRF1). To investigate the role of Nrf2, we examined redox and metabolic responses in the skin of wild-type (WT) mice and mice lacking functional Nrf2 (Nrf2 KO) at room (RT, 24 ± 1°C) and cold (4 ± 1°C) temperature. Our results demonstrate distinct expression profiles of major enzymes involved in antioxidant defense and key metabolic and mitochondrial pathways in the skin, depending on the functional Nrf2 and/or cold stimulus. Nrf2 KO mice at RT displayed profound alterations in redox, mitochondrial and metabolic responses, generally akin to cold-induced skin responses in WT mice. Immunohistochemical analyses of skin cell compartments (keratinocytes, fibroblasts, hair follicle, and sebaceous gland) and spatial locations (nucleus and cytoplasm) revealed synergistic interactions between members of the Nrf transcription factor family as part of redox-metabolic reprogramming in WT mice upon cold acclimation. In contrast, Nrf2 KO mice at RT showed loss of NRF1 expression and a compensatory activation of Nrf1/Nrf3, which was abolished upon cold, concomitant with blunted redox-metabolic responses. These data show for the first time a novel role for Nrf2 in skin physiology in response to low environmental temperature, with important implications in human connective tissue diseases with altered thermogenic responses.

Health effects of voluntary exposure to cold water - a continuing subject of debate

This review is based on a multiple database survey on published literature to determine the effects on health following voluntary exposure to cold-water immersion (CWI) in humans. After a filtering process 104 studies were regarded relevant. Many studies demonstrated significant effects of CWI on various physiological and biochemical parameters. Although some studies were based on established winter swimmers, many were performed on subjects with no previous winter swimming experience or in subjects not involving cold-water swimming, for example, CWI as a post-exercise treatment. Clear conclusions from most studies were hampered by the fact that they were carried out in small groups, often of one gender and with differences in exposure temperature and salt composition of the water. CWI seems to reduce and/or transform body adipose tissue, as well as reduce insulin resistance and improve insulin sensitivity. This may have a protective effect against cardiovascular, obesity and other metabolic diseases and could have prophylactic health effects. Whether winter swimmers as a group are naturally healthier is unclear. Some of the studies indicate that voluntary exposure to cold water has some beneficial health effects. However, without further conclusive studies, the topic will continue to be a subject of debate.

Induction of beige-like adipocyte markers and functions in 3T3-L1 cells by Clk1 and PKCβII inhibitory molecules

Excessive dietary intake of fat results in its storage in white adipose tissue (WAT). Energy expenditure through lipid oxidation occurs in brown adipose tissue (BAT). Certain WAT depots can undergo a change termed beiging where markers that BAT express are induced. Little is known about signalling pathways inducing beiging. Here, inhibition of a signalling pathway regulating alternative pre‐mRNA splicing is involved in adipocyte beiging. Clk1/2/4 kinases regulate splicing by phosphorylating factors that process pre‐mRNA. Clk1 inhibition by TG003 results in beige‐like adipocytes highly expressing PGC1α and UCP1. SiRNA for Clk1, 2 and 4, demonstrated that Clk1 depletion increased UCP1 and PGC1α expression, whereas Clk2/4 siRNA did not. TG003‐treated adipocytes contained fewer lipid droplets, are smaller, and contain more mitochondria, resulting in proton leak increases. Additionally, inhibition of PKCβII activity, a splice variant regulated by Clk1, increased beiging. PGC1α is a substrate for both Clk1 and PKCβII kinases, and we surmised that inhibition of PGC1α phosphorylation resulted in beiging of adipocytes. We show that TG003 binds Clk1 more than Clk2/4 through direct binding, and PGC1α binds to Clk1 at a site close to TG003. Furthermore, we show that TG003 is highly specific for Clk1 across hundreds of kinases in our activity screen. Hence, Clk1 inhibition becomes a target for induction of beige adipocytes.

l-Arginine Induces White Adipose Tissue Browning-A New Pharmaceutical Alternative to Cold

The beneficial effects of l-arginine supplementation in obesity and type II diabetes involve white adipose tissue (WAT) reduction and increased substrate oxidation. We aimed to test the potential of l-arginine to induce WAT browning. Therefore, the molecular basis of browning was investigated in retroperitoneal WAT (rpWAT) of rats exposed to cold or treated with 2.25% l-arginine for 1, 3, and 7 days. Compared to untreated control, levels of inducible nitric oxide (NO) synthase protein expression and NO signaling increased in both cold-exposed and l-arginine-treated groups. These increases coincided with the appearance of multilocular adipocytes and increased expression levels of uncoupling protein 1 (UCP1), thermogenic and beige adipocyte-specific genes (Cidea, Cd137, and Tmem26), mitochondriogenesis markers (peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α, mitochondrial DNA copy number), nuclear respiratory factor 1, PPARα and their respective downstream lipid oxidation enzymes after l-arginine treatment. Such browning phenotype in the l-arginine-treated group was concordant with end-course decreases in leptinaemia, rpWAT mass, and body weight. In conclusion, l-arginine mimics cold-mediated increases in NO signaling in rpWAT and induces molecular and structural fingerprints of rpWAT browning. The results endorse l-arginine as a pharmaceutical alternative to cold exposure, which could be of great interest in obesity and associated metabolic diseases.

Baicalin promotes the activation of brown and white adipose tissue through AMPK/PGC1α pathway

Obesity occurs when energy intake overtops energy expenditure. Promoting activation of brown adipose tissue (BAT) and white adipose tissue (WAT) has been proven a promising therapeutic strategy for obesity. Baicalin (BAI) has been shown to be protective for various animal models of cardiovascular diseases, such as pulmonary hypertension, atherosclerosis and myocardial hypertrophy. However, whether BAI could stimulate activation of BAT or browning of WAT remains unknown. Here we show that BAI limits weight gaining, ameliorates glucose tolerance, improves cold tolerance and promotes brown-like tissue formation in diet induced obesity mice model. BAI increases the mitochondrial copy number as judged by mtDNA detection. BAI also increases the expression of UCP1 and other classical browning-specific genes in BAT and WAT and cultured C3H10T1/2 adipocytes through a mechanism involving AMPK/PGC1α pathway. Collectively, our study established a role for BAI in regulating energy metabolism, which will provide new idea and theoretical basis for the treatment of obesity.

Inhibitory effect of androgens on white adipose tissue thermogenic capacity

White adipose tissue (WAT) browning has gained interest due to its impact in obesity. Here, we evaluated the effect of androgens on the Ucp1-dependent thermogenic process from inguinal (IAT) and retroperitoneal (RPAT) WAT. Surgically androgens depleted rats (ODX) showed basal thermogenic activation (room temperature) in both WAT depots, which expressed higher levels of Ucp1, Prdm16 and Pgc1a. WAT pads from ODX cold-exposed rats (ODX-C) expressed increased levels of Ucp1 and Pgc1a and showed high UCP1 protein content. In primary beige adipocyte cultures, testosterone decreased the mitochondrial marker Cox8b and mitochondrial content. Finally, testosterone and dihydrotestosterone (DHT) decreased the expression of Ucp1, Pcg1a and Prdm16 in forskolin-stimulated beige adipocytes, an effect that was prevented by the antiandrogen flutamide. In conclusion, androgen deficient rats developed WAT depots with enhanced basal and cold-stimulated thermogenic activity. Additionally, in vitro androgen treatments inhibited the thermogenic program, effect which was mediated by the androgen receptor pathway.

Maternal high fructose diet exacerbates white adipose tissue thermogenic process in offspring upon exposure to cold temperature

AIM

An adverse endogenous environment during early life predisposes to metabolic disorder development. We previously reported adverse metabolic and adipose tissue effects in adult male rats born to dams fed with a fructose-rich diet (FRD). The aim of this work was to determine the effect of a FRD consumed by the pregnant mother on the white adipose tissue (WAT) browning capacity of male offspring at adulthood.

MAIN METHODS

Adult SD male offspring from control (C) and FRD-fed mothers were exposed during one week to a cold stimulus. WAT browning capacity was studied through in vivo and in vitro approaches.

KEY FINDINGS

After cold exposure, WAT browning was higher in fructose-programmed animals as evidenced by an increase in ucp-1 gene expression, protein levels, and higher UCP-1 positive foci. Moreover, pgc1-α gene expression was increased. In vitro studies showed a lower adipogenic capacity in cells of prenatally fructose-exposed animals differentiated with a white differentiation cocktail, while a higher ucp-1 expression was noted when their cells were treated with a pro-beige differentiation cocktail.

SIGNIFICANCE

For the first time we demonstrate that pre-natal fructose exposure predisposes programmed male rats to a higher WAT browning-induced response, under stimulated conditions, despite an apparent lower basal thermogenic capacity. These results should be considered in future studies to generate new therapeutic approaches to deal with adverse programming malnutrition effects.

Adipose tissue expression of UCP1 and PRDM16 genes and their association with postprandial triglyceride metabolism and glucose intolerance

AIMS

UCP1 and PRDM16 genes, primarily involved in browning of adipose tissue that can affect lipid metabolism are also associated with diabetes risk. Therefore, we planned to study the adipose tissue expression of UCP1 and PRDM 16 genes in subjects with glucose intolerance to find out its association with postprandial triglyceride (PPTg) measures and T2DM.

METHODS

A total of 30 subjects were recruited in three groups i.e., NGT, prediabetes and T2DM (NDDM + known T2DM) who were matched for age, sex and BMI. An 8-hour standardized fat challenge test was performed to study lipemic responses. UCP1 and PRDM16 genes quantification in adipose tissue was performed by real-time PCR followed by SDS PAGE.

RESULTS

UCP1 gene expression in SAT was significantly lower in T2DM and prediabetes as compared to NGT group while PRDM16 gene expression was significantly lower in T2DM group as compared to NGT group. UCP1 gene expression correlated with PPTg measures as well as with glycaemic measures while PRDM16 gene expression correlated with glycaemic measures only.

CONCLUSION

This study found downregulation of PRDM16 and UCP1 gene expression in SAT in subjects with glucose intolerance. The association of UCP1 gene expression with PPTg dysmetabolism may contribute to greater predisposition to T2DM.

Brown and beige adipose tissue: a novel therapeutic strategy for obesity and type 2 diabetes mellitus

Mammalian adipose tissue can be divided into two major types, namely, white adipose tissue (WAT) and brown adipose tissue (BAT). According to classical view, the main function of WAT is to store excess energy in the form of triglycerides, while BAT is a thermogenic tissue that acts a pivotal part in maintaining the core body temperature. White adipocytes display high plasticity and can transdifferentiate into beige adipocytes which have many similar morphological and functional properties with brown adipocytes under the stimulations of exercise, cold exposure and other factors. This phenomenon is also known as 'browning of WAT'. In addition to transdifferentiation, beige adipocytes can also come from de novo differentiation from tissue-resident progenitors. Activating BAT and inducing browning of WAT can accelerate the intake of glycolipids and reduce the insulin secretion requirement, which may be a new strategy to improve glycolipids metabolism and insulin resistance of obese and type 2 diabetes mellitus (T2DM) patients. This review mainly discusses the significance of brown and beige adipose tissues in the treatment of obesity and T2DM, and focuses on the effect of the browning agent on obesity and T2DM, which provides a brand-new theoretical reference for the prevention and treatment of obesity and T2DM.

Predictive Value of Abdominal Fat Distribution on Coronary Artery Disease Severity Stratified by Computed Tomography-Derived SYNTAX Score

This study aimed to evaluate the association between abdominal fat distribution (AFD) and coronary artery disease (CAD) complexities using the computed tomography (CT)-derived SYNTAX score (CT-SXscore). Coronary computed tomographic angiography (CCTA) was performed in patients with suspected CAD. Plain abdominal CT was performed to measure visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) areas. To assess AFD, VAT/SAT (V/S) ratios were calculated. The CT-SXscore was calculated in patients with significant stenoses assessed by CCTA. Of 942 enrolled patients, 310 (32.9%) had 1 or more significant stenoses. The CT-SXscore showed a positive correlation with the V/S ratio (r = 0.33, p < 0.001). In the multivariate regression analysis, the V/S ratio was the only independent predictor for CAD severity based on the CT-SXscore (β = 0.25; t = 4.14; p < 0.001), even though the absolute SAT and VAT areas showed no relationship to the CT-SXscore. Regarding the 4 CAD-patient groups divided according to their median VAT and SAT areas, the CT-SXscore was significantly higher for the high VAT/low SAT group than for any other group (19.6 ± 11.5 vs 13.3 ± 9.6 in the low VAT/low SAT, 10.1 ± 8.5 in the low VAT/high SAT, and 12.2 ± 8.7 in the high VAT/high SAT groups; p < 0.001 for all). In conclusion, it was found that the V/S ratio is a useful index for predicting CAD severity and that AFD may be a more important risk factor for CAD than the absolute amount of each abdominal fat.

Atrial Natriuretic Peptide Orchestrates a Coordinated Physiological Response to Fuel Non-shivering Thermogenesis

Atrial natriuretic peptide (ANP) is a cardiac hormone controlling blood volume and pressure in mammals. It is still unclear whether ANP controls cold-induced thermogenesis in vivo. Here, we show that acute cold exposure induces cardiac ANP secretion in mice and humans. Genetic inactivation of ANP promotes cold intolerance and suppresses half of cold-induced brown adipose tissue (BAT) activation in mice. While white adipocytes are resistant to ANP-mediated lipolysis at thermoneutral temperature in mice, cold exposure renders white adipocytes fully responsive to ANP to activate lipolysis and a thermogenic program, a physiological response that is dramatically suppressed in ANP null mice. ANP deficiency also blunts liver triglycerides and glycogen metabolism, thus impairing fuel availability for BAT thermogenesis. ANP directly increases mitochondrial uncoupling and thermogenic gene expression in human white and brown adipocytes. Together, these results indicate that ANP is a major physiological trigger of BAT thermogenesis upon cold exposure in mammals.

Transcriptional Factors of Thermogenic Adipocyte Development and Generation of Brown and Beige Adipocytes From Stem Cells

Brown and beige adipocytes have been widely known for their potential to dissipate excessive energy into heat form, resulting in an alleviation of obesity and other overweight-related conditions. This review highlights the origins, characteristics, and functions of the various kinds of adipocytes, as well as their anatomic distribution inside the human body. This review mainly focuses on various essential transcriptional factors such as PRDM16, FGF21, PPARα, PPARγ and PGC-1α, which exert their effects on the development and activation of thermogenic adipocytes via important pathways such as JAK-STAT, cAMP-PKA and PI3K-AKT signaling pathways. Additionally, this review will underline promising strategies to generate an unexhausted source of thermogenic adipocytes differentiated from human stem cells. These exogenous thermogenic adipocytes offer therapeutic potential for improvement of metabolic disorders via application as single cell or whole tissue transplantation. Graphical abstract Caption is required. Please provide.

Tissue-Specific Warburg Effect in Breast Cancer and Cancer-Associated Adipose Tissue-Relationship between AMPK and Glycolysis

Simple Summary

Specific metabolic phenotypes of breast cancer result from local interactions such as cancer-adipocyte cross-talk and systemic metabolic influences such as obesity. Here we examined key regulatory enzymes involved in glucose metabolism in breast cancer tissue and cancer-associated adipose tissue of normal-weight and overweight/obese premenopausal women in comparison to benign breast tumor tissue and adipose tissue of weight-matched women. We show a simultaneous increase in 5′-AMP-activated protein kinase (AMPK) protein expression with glucose utilization favoring glycolysis and pentose phosphate pathway in breast cancer tissue. In parallel, we show an increased AMPK protein expression with glucose utilization favoring the pentose phosphate pathway in cancer-associated adipose tissue. Moreover, specific features of cancer tissue glycolysis and glycogen metabolism differ between normal-weight and overweight/obese women. The results suggest context-dependent induction of tissue-specific Warburg effect in breast cancer and cancer-associated adipose tissue.

Abstract

Typical features of the breast malignant phenotype rely on metabolic reprogramming of cancer cells and their interaction with surrounding adipocytes. Obesity is strongly associated with breast cancer mortality, yet the effects of obesity on metabolic reprogramming of cancer and cancer-associated adipose tissue remain largely unknown. Paired biopsies of breast tumor tissue and adipose tissue from premenopausal women were divided according to pathohistological analyses and body mass index on normal-weight and overweight/obese with benign or malignant tumors. We investigated the protein expression of key regulatory enzymes of glycolysis, pentose phosphate pathway (PPP), and glycogen synthesis. Breast cancer tissue showed a simultaneous increase in 5′-AMP-activated protein kinase (AMPK) protein expression with typical features of the Warburg effect, including hexokinase 2 (HK 2) overexpression and its association with mitochondrial voltage-dependent anion-selective channel protein 1, associated with an overexpression of rate-limiting enzymes of glycolysis (phosphofructokinase 1—PFK-1) and pentose phosphate pathway (glucose-6-phosphate dehydrogenase—G6PDH). In parallel, cancer-associated adipose tissue showed increased AMPK protein expression with overexpression of HK 2 and G6PDH in line with increased PPP activity. Moreover, important obesity-associated differences in glucose metabolism were observed in breast cancer tissue showing prominent glycogen deposition and higher glycogen synthase kinase-3 protein expression in normal-weight women and higher PFK-1 and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) protein expression in overweight/obese women. In conclusion, metabolic reprogramming of glycolysis contributes to tissue-specific Warburg effect in breast cancer and cancer-associated adipose tissue.

Redox profile of breast tumor and associated adipose tissue in premenopausal women - Interplay between obesity and malignancy

One of the underlying mechanisms that could link breast cancer and obesity is shifted redox homeostasis in the tumor microenvironment. To reveal the relationship between the malignant phenotype and obesity, we compared redox profiles of breast tumor and tumor-associated adipose tissue from premenopausal women: normal-weight with benign tumors, overweight/obese with benign tumors, normal-weight with malignant tumors, and overweight/obese with malignant tumors. Namely, we examined the protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2), protein expression and activity of main antioxidant defense (AD) enzymes: copper, zinc- and manganese superoxide dismutase, catalase, and glutathione peroxidase, as well as the level of 4-hydroxy-2-nonenal (4-HNE) modified proteins. Higher protein expression and activity of AD enzymes were found in malignant tumor tissue than benign tumor tissue, irrespective of obesity. Nevertheless, malignant tumor tissue of overweight/obese women was characterized by higher protein expression of Nrf2 and weaker immunopositivity for 4-HNE modified proteins. In malignant tumor-associated adipose tissue, the redox profile was clearly related to obesity. Higher Nrf2 protein expression and higher AD enzyme levels were observed in normal-weight women, while stronger immunopositivity for 4-HNE modified proteins was found in overweight/obese women. The results suggest that the complex interplay between obesity and malignancy involves redox-sensitive pathways in breast tumor and tumor-associated adipose tissue.

•

In malignant breast tumor tissue, antioxidant defense enzyme levels are not related to obesity.

•

In malignant tumor-associated adipose tissue, redox profile is related to obesity.

•

Nrf2 contributes to the “activated” phenotype of adipose tissue in malignancy.

Lactate Metabolism in Breast Cancer Microenvironment: Contribution Focused on Associated Adipose Tissue and Obesity

Metabolic reprogramming that favors high glycolytic flux with lactate production in normoxia is among cancer hallmarks. Lactate is an essential oncometabolite regulating cellular redox homeostasis, energy substrate partitioning, and intracellular signaling. Moreover, malignant phenotype's chief characteristics are dependent on the interaction between cancer cells and their microenvironment. In breast cancer, mammary adipocytes represent an essential cellular component of the tumor milieu. We analyzed lactate concentration, lactate dehydrogenase (LDH) activity, and isozyme pattern, and LDHA/LDHB protein expression and tissue localization in paired biopsies of breast cancer tissue and cancer-associated adipose tissue in normal-weight and overweight/obese premenopausal women, compared to benign breast tumor tissue and adipose tissue in normal-weight and overweight/obese premenopausal women. We show that higher lactate concentration in cancer tissue is concomitant with a shift in isozyme pattern towards the "muscle-type" LDH and corresponding LDHA and LDHB protein expression changes. In contrast, significantly higher LDH activity in cancer-associated adipose tissue seems to be directed towards lactate oxidation. Moreover, localization patterns of LDH isoforms varied substantially across different areas of breast cancer tissue. Invasive front of the tumor showed cell-specific protein localization of LDHA in breast cancer cells and LDHB in cancer-associated adipocytes. The results suggest a specific, lactate-centric relationship between cancer tissue and cancer-associated adipose tissue and indicate how cancer-adipose tissue cross-talk may be influenced by obesity in premenopausal women.

Emerging Role of Adipocyte Dysfunction in Inducing Heart Failure Among Obese Patients With Prediabetes and Known Diabetes Mellitus

Adipose tissue dysfunction is a predictor for cardiovascular (CV) events and heart failure (HF) in patient population with obesity, metabolic syndrome, and known type 2 diabetes mellitus. Previous preclinical and clinical studies have yielded controversial findings regarding the role of accumulation of adipose tissue various types in CV risk and HF-related clinical outcomes in obese patients. There is evidence for direct impact of infiltration of epicardial adipocytes into the underlying myocardium to induce adverse cardiac remodeling and mediate HF development and atrial fibrillation. Additionally, perivascular adipocytes accumulation is responsible for release of proinflammatory adipocytokines (adiponectin, leptin, resistin), stimulation of oxidative stress, macrophage phenotype switching, and worsening vascular reparation, which all lead to microvascular inflammation, endothelial dysfunction, atherosclerosis acceleration, and finally to increase in CV mortality. However, systemic effects of white and brown adipose tissue can be different, and adipogenesis including browning of adipose tissue and deficiency of anti-inflammatory adipocytokines (visfatin, omentin, zinc-α2-glycoprotein, glypican-4) was frequently associated with adipose triglyceride lipase augmentation, altered glucose homeostasis, resistance to insulin of skeletal muscles, increased cardiomyocyte apoptosis, lowered survival, and weak function of progenitor endothelial cells, which could significantly influence on HF development, as well as end-organ fibrosis and multiple comorbidities. The exact underlying mechanisms for these effects are not fully understood, while they are essential to help develop improved treatment strategies. The aim of the review is to summarize the evidence showing that adipocyte dysfunction may induce the onset of HF and support advance of HF through different biological mechanisms involving inflammation, pericardial, and perivascular adipose tissue accumulation, adverse and electrical cardiac remodeling, and skeletal muscle dysfunction. The unbalancing effects of natriuretic peptides, neprilysin, and components of renin–angiotensin system, as exacerbating cause of altered adipocytokine signaling on myocardium and vasculature, in obesity patients at high risk of HF are disputed. The profile of proinflammatory and anti-inflammatory adipocytokines as promising biomarker for HF risk stratification is discussed in the review.

Adipose-derived exosomal miR-210/92a cluster inhibits adipose browning via the FGFR-1 signaling pathway in high-altitude hypoxia

Cold and hypoxia are critical drivers of adaptation to high altitudes. Organisms at high altitudes have adapted to maximize the efficiency of oxygen utilization and are less prone to obesity and diabetes than those at low altitudes. Brown adipose tissue (BAT) dissipates energy in the form of heat in both humans and rodents; it also serves to regulate metabolism to curb obesity. However, the role of BAT in high-altitude populations is poorly understood. Serum exosomes can be easily obtained, enabling the study of BAT functions and identification of biomarkers in serum exosomes, both of which contribute to understanding the role of BAT in high-altitude populations. ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography integrated with computed tomography (PET/CT) is the gold standard for studying BAT in human adults. Here, we studied BAT in healthy high-altitude populations via PET/CT and serum exosomal microRNAs (miRNAs). The observations were validated in mouse tissues and demonstrated that high-altitude hypoxia activated BAT through attenuated white adipose tissue (WAT) secreted exosomal miR-210/92a, which enhanced the FGFR-1 expression in BAT.

Investigation of 3T3-L1 Cell Differentiation to Adipocyte, Affected by Aqueous Seed Extract of Phoenix Dactylifera L

Background

Obesity, often associated with insulin resistance and type 2 diabetes, is a metabolic disease that can result in dyslipidemia and hyperglycemia. Many reports describe the hypoglycemic and hypolipidemic properties of the Phoenix dactylifera L. seed extract in STZ-induced diabetic rat models, however, its anti-diabetic effects in other diabetic models are less characterized in the literature. This study set out to determine the possible effects of the Phoenix dactylifera L. seed extract on adipogenesis and glucose homeostasis.

Methods

3T3-L1 cells were cultured in adipocyte differentiation media with or without varying doses of Phoenix dactylifera L. extract (0.312-1 mg/ml). Assays were performed on days 5, 8, and 12 after induced differentiation.

Results

Our results demonstrate that the triglyceride content in treated groups was significantly lower compared to controls. Further, treating 3T3-L1 cells with Phoenix dactylifera L. seed extract reduced adipogenesis through the downregulation of PPAR-γ and CEBP-α, and adipocyte-specific genes involved in fatty acid metabolism including ap2, ACACA, and FAS.

Conclusion

Phoenix dactylifera L. seeds have the potential to inhibit adipogenesis and obesity. Overall, this study explored the inhibitory effects of Phoenix dactylifera L. seed extract on adipogenesis in 3T3-L1 cells on the molecular level.

Safflower yellow improves insulin sensitivity in high-fat diet-induced obese mice by promoting peroxisome proliferator-activated receptor-γ2 expression in subcutaneous adipose tissue

Aims/Introduction

Safflower yellow (SY) and its main component, hydroxysafflor yellow A, have been demonstrated to show anti‐obesity effects. Peroxisome proliferator‐activated receptor‐γ2 (PPARγ2) is a critical transcription factor in adipose tissue metabolism. The aim of the present study was to explore the effects of SY in high‐fat diet‐induced obese mice, and further investigate the mechanism involving PPARγ2.

Methods

High‐fat diet‐induced obese mice were given 120 mg/kg/day SY for 8 weeks. Glucose and insulin tolerance tests were carried out. Fat mass and serum levels of glucose and insulin were measured. The expression of insulin signaling pathway‐related genes and PPARγ2 in the adipose tissue was measured. In vitro, the effects of SY (0–500 mg/L) and hydroxysafflor yellow A (0–100 mg/L) on PPARγ2 promoter activities and PPARγ2 messenger ribonucleic acid (mRNA) levels in 3T3‐L1 preadipocytes or adipocytes were also detected.

Results

Safflower yellow reduced fat mass, decreased glucose levels and improved insulin sensitivity in obese mice. SY also increased the mRNA levels of insulin signaling pathway‐related genes, and increased PPARγ2 mRNA levels by 39.1% in subcutaneous adipose tissue (P < 0.05). In vitro, SY and hydroxysafflor yellow A significantly enhanced PPARγ2 promoter activities by 1.3–2.1‐fold, and increased PPARγ2 mRNA levels by 1.2–1.6‐fold in 3T3‐L1 preadipocytes or adipocytes (P < 0.05).

Conclusions

SY could reduce fat mass, decrease glucose levels and improve insulin sensitivity in high‐fat diet‐induced obese mice. The probable mechanism is to increase PPARγ2 expression by stimulating PPARγ2 promoter activities, further increasing the expression of insulin signaling pathway‐related genes in subcutaneous adipose tissue.

TL1A regulates adipose-resident innate lymphoid immune responses and enables diet-induced obesity in mice

BACKGROUND/OBJECTIVES

TL1A is a pro-inflammatory cytokine that is homologous to TNFα and connected with the development of several chronic inflammatory disorders. The preliminary results of this study indicated reduced fat accumulation in 9-month-old TL1A-deficient mice at steady state. Thus, the objective was to investigate whether TL1A-deficient mice are resistant to the development of high-fat (HF) diet-induced obesity and to investigate the impact on lymphocyte infiltration in adipose tissue.

METHODS

TL1A-deficient and TL1A-sufficient male BALB/cJ littermate mice were fed a 60% HF diet or a 10% low-fat control diet for 22 weeks. Mouse body composition and weight were monitored, and tissues were processed and evaluated by flow cytometry, qPCR, and histology.

RESULTS

In this study, the TL1A-deficient HF-diet-fed mice had reduced whole-body weight gain, which was directly explained by a corresponding fat mass reduction (average 37.2%), compared with that of their TL1A-sufficient littermates. Despite previous data showing marked changes in the gut microbial community, TL1A-deficient GF mice also displayed reduced adiposity. Furthermore, the TL1A-deficient mice were resistant to hepatic steatosis and were shown to have improved glucose tolerance, as determined by oral glucose tolerance test (OGTT), and greater insulin sensitivity. In the epididymal white adipose tissue (eWAT), TL1A deficiency in HF-diet-fed mice resulted in a reduced abundance of IL-18Ra⁺ type-1 ILCs and γδT cells as well as markedly reduced expression of the mitochondria-regulating genes Ucp1, Ucp2, Ucp3, and Prdm16. Finally, to investigate the link of TL1A to obesity in humans, we identified a noncoding polymorphism (rs4979453) close to the TL1A locus that is associated with waist circumference in men (p = 0.00096, n = 60586).

CONCLUSIONS

These findings indicate that TL1A plays an important role in regulating adipose tissue mass and that this role is independent of the gut microbiota. Furthermore, we show that TL1A regulates adipose-resident innate lymphocytes and mitochondria-mediated oxidative stress in eWAT.

Nanotechnology advances towards development of targeted-treatment for obesity

Obesity through its association with type 2 diabetes (T2D), cancer and cardiovascular diseases (CVDs), poses a serious health threat, as these diseases contribute to high mortality rates. Pharmacotherapy alone or in combination with either lifestyle modification or surgery, is reliable in maintaining a healthy body weight, and preventing progression to obesity-induced diseases. However, the anti-obesity drugs are limited by non-specificity and unsustainable weight loss effects. As such, novel and improved approaches for treatment of obesity are urgently needed. Nanotechnology-based therapies are investigated as an alternative strategy that can treat obesity and be able to overcome the drawbacks associated with conventional therapies. The review presents three nanotechnology-based anti-obesity strategies that target the white adipose tissues (WATs) and its vasculature for the reversal of obesity. These include inhibition of angiogenesis in the WATs, transformation of WATs to brown adipose tissues (BATs), and photothermal lipolysis of WATs. Compared to conventional therapy, the targeted-nanosystems have high tolerability, reduced side effects, and enhanced efficacy. These effects are reproducible using various nanocarriers (liposomes, polymeric and gold nanoparticles), thus providing a proof of concept that targeted nanotherapy can be a feasible strategy that can combat obesity and prevent its comorbidities.

Adipogenesis: A Necessary but Harmful Strategy

Obesity is considered to significantly increase the risk of the development of a vast range of metabolic diseases. However, adipogenesis is a complex physiological process, necessary to sequester lipids effectively to avoid lipotoxicity in other tissues, like the liver, heart, muscle, essential for maintaining metabolic homeostasis and has a crucial role as a component of the innate immune system, far beyond than only being an inert mass of energy storage. In pathophysiological conditions, adipogenesis promotes a pro-inflammatory state, angiogenesis and the release of adipokines, which become dangerous to health. It results in a hypoxic state, causing oxidative stress and the synthesis and release of harmful free fatty acids. In this review, we try to explain the mechanisms occurring at the breaking point, at which adipogenesis leads to an uncontrolled lipotoxicity. This review highlights the types of adipose tissue and their functions, their way of storing lipids until a critical point, which is associated with hypoxia, inflammation, insulin resistance as well as lipodystrophy and adipogenesis modulation by Krüppel-like factors and miRNAs.

Interaction between the amount of dietary protein and the environmental temperature on the expression of browning markers in adipose tissue of rats

Background

A low-protein diet increases the expression and circulating concentration of FGF21. FGF21 stimulates the browning process of WAT by enhancing the expression of UCP1 coupled with an increase in PGC1α. Interestingly, the consumption of a low-protein diet could stimulate WAT differentiation into beige/brite cells by increasing FGF21 expression and Ucp1 mRNA abundance. However, whether the stimulus of a low-protein diet on WAT browning can synergistically interact with another browning stimulus, such as cold exposure, remains elusive.

Results

In the present study, rats were fed 6% (low), 20% (adequate), or 50% (high) dietary protein for 10 days and subsequently exposed to 4 °C for 72 h. Body weight, food intake, and energy expenditure were measured, as well as WAT browning and BAT thermogenesis markers and FGF21 circulating levels. The results showed that during cold exposure, the consumption of a high-protein diet reduced UCP1, TBX1, Cidea, Cd137, and Prdm16 in WAT when compared with the consumption of a low-protein diet. In contrast, at room temperature, a low-protein diet increased the expression of UCP1, Cidea, and Prdm16 associated with an increase in FGF21 expression and circulating levels when compared with a consumption of a high-protein diet. Consequently, the consumption of a low-protein diet increased energy expenditure.

Conclusions

These results indicate that in addition to the environmental temperature, WAT browning is nutritionally modulated by dietary protein, affecting whole-body energy expenditure.

Graphical abstract

3,5 Diiodo-l-Thyronine (T₂) Promotes the Browning of White Adipose Tissue in High-Fat Diet-Induced Overweight Male Rats Housed at Thermoneutrality

The conversion of white adipose cells into beige adipose cells is known as browning, a process affecting energy metabolism. It has been shown that 3,5 diiodo-l-thyronine (T₂), an endogenous metabolite of thyroid hormones, stimulates energy expenditure and a reduction in fat mass. In light of the above, the purpose of this study was to test whether in an animal model of fat accumulation, T₂ has the potential to activate a browning process and to explore the underlying mechanism. Three groups of rats were used: (i) receiving a standard diet for 14 weeks; (ii) receiving a high-fat diet (HFD) for 14 weeks; and (iii) receiving a high fat diet for 10 weeks and being subsequently treated for four weeks with an HFD together with the administration of T₂. We showed that T₂ was able to induce a browning in the white adipose tissue of T₂-treated rats. We also showed that some miRNA (miR133a and miR196a) and MAP kinase 6 were involved in this process. These results indicate that, among others, the browning may be another cellular/molecular mechanism by which T₂ exerts its beneficial effects of contrast to overweight and of reduction of fat mass in rats subjected to HFD.

Relation of Redox and Structural Alterations of Rat Skin in the Function of Chronological Aging

Accumulation of oxidative insults on molecular and supramolecular levels could compromise renewal potency and architecture in the aging skin. To examine and compare morphological and ultrastructural changes with redox alterations during chronological skin aging, activities of antioxidant defense (AD) enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), thioredoxin reductase (TR), and methionine sulfoxide reductase A (MsrA), and the markers of oxidative damage of biomolecules-4-hydroxynonenal (HNE) and 8-oxoguanine (8-oxoG)-were examined in the rat skin during life (from 3 days to 21 months). As compared to adult 3-month-old skin, higher activities of CAT, GSH-Px, and GR and a decline in expression of MsrA are found in 21-month-old skin. These changes correspond to degenerative changes at structural and ultrastructural levels in epidermal and dermal compartments, low proliferation capacity, and higher levels of HNE-modified protein aldehydes (particularly in basal lamina) and 8-oxoG positivity in nuclei and mitochondria in the sebaceous glands and root sheath. In 3-day-old skin, higher activities of AD enzymes (SOD, CAT, GR, and TR) and MsrA expression correspond to intensive postnatal development and proliferation. In contrast to 21-month-old skin, a high level of HNE in young skin is not accompanied by 8-oxoG positivity or any morphological disturbances. Observed results indicate that increased activity of AD enzymes in elderly rat skin represents the compensatory response to accumulated oxidative damage of DNA and proteins, accompanied by attenuated repair and proliferative capacity, but in young rats the redox changes are necessary and inherent with processes which occur during postnatal skin development. Мorphological and ultrastructurаl changes are in line with the redox profile in the skin of young and old rats.

Interleukin-6 is important for regulation of core body temperature during long-term cold exposure in mice

Interleukin-6 (IL6) is a cytokine important for inducing the fever response during infection and has been reported to uphold core body temperature during acute cold exposure. Recently it has also been indicated that IL6 in serum increases in cold-exposed mice. The aim of the present study was to investigate if IL6 is important for core body temperature regulation following a long-term cold exposure in mice. Experiments were performed with global IL6 deficient (-/-) mice, mice with conditional IL6 receptor α (IL6Rα) knockdown in the central nervous system (CNS; IL6Rα^NesCre) and appropriate wild-type (Wt) controls. All mice were placed in a cold environment (4°C) for 6 days. Core body temperature and oxygen consumption were measured by telemetry probes and indirect calorimetry at room temperature (20°C), and during the first and last day of cold exposure. Brain stem, hypothalamus and white and brown adipose tissues from the cold-exposed mice were subjected to gene expression analysis. After 6 days in 4°C, the IL6-/- mice exhibited significantly lower body temperature and oxygen consumption compared with Wt mice (P<0.05). The IL6Rα^NesCre mice also exhibited lower body temperature compared with Wt^NesCre controls during the last day of cold exposure (P<0.05). Furthermore, an increase in the mRNA level of brain-derived neurotrophic factor (Bdnf) was detected in the brain stem of both IL6-/- and IL6Rα^NesCre mice compared with the Wt groups (P<0.05). The finding that body temperature was decreased in IL6-/- and IL6Rα^NesCre mice indicates a decrease in thermogenesis in these animals. Bdnf has previously been indicated to increase body temperature and could in the present study be a mechanistic factor involved in counteracting the low body temperature in IL6-/- and IL6Rα^NesCre mice. These results suggest that IL6 is not only involved in body temperature regulation during infection, but also during long-term cold exposure, probably through mechanisms in the CNS.

Adipose and skeletal muscle thermogenesis: studies from large animals

The balance between energy intake and energy expenditure establishes and preserves a 'set-point' body weight. The latter is comprised of three major components including metabolic rate, physical activity and thermogenesis. Thermogenesis is defined as the cellular dissipation of energy via heat production. This process has been extensively characterised in brown adipose tissue (BAT), wherein uncoupling protein 1 (UCP1) creates a proton leak across the inner mitochondrial membrane, diverting protons away from ATP synthesis and resulting in heat dissipation. In beige adipocytes and skeletal muscle, thermogenesis can occur independent of UCP1. Beige adipocytes have been shown to produce heat via UCP1 as well as via both futile creatine and calcium cycling pathways. On the other hand, the UCP1 homologue UCP3 is abundant in skeletal muscle and post-prandial thermogenesis has been associated with UCP3 and the futile calcium cycling. This review will focus on the differential contributions of adipose tissue and skeletal muscle in determining total thermogenic output and energy expenditure in large mammals. Sheep and pigs do not have a circumscribed brown fat depot but rather possess white fat depots that contain brown and beige adipocytes interspersed amongst white adipose tissue. This is representative of humans, where brown, beige and white adipocytes have been identified in the neck and supraclavicular regions. This review will describe the mechanisms of thermogenesis in pigs and sheep and the relative roles of skeletal muscle and adipose tissue thermogenesis in controlling body weight in larger mammals.

Short-term thermoneutral housing alters glucose metabolism and markers of adipose tissue browning in response to a high-fat diet in lean mice

Systemic insulin resistance and glucose intolerance occur with as little as 3 days of a high-fat diet (HFD) in mice and humans; the mechanisms that initiate acute insulin resistance are unknown. Most laboratories house mice at 22°C, which is below their thermoneutral temperature (~30°C). Cold stress has been shown to increase white adipose tissue (WAT) browning, alter lipid trafficking, and impair immune function, whereas energy intake and expenditure decrease with increasing ambient temperature; importantly, dysregulation of these parameters has been strongly linked to obesity-induced insulin resistance. Therefore, we compared acute changes in glucose metabolism and the metabolic phenotype in lean mice in response to a control diet or HFD housed at standard vivarium (22°C) and thermoneutral (30°C) temperatures. Glucose intolerance occurred following 1 or 5 days of HFD and was independent of housing temperature or adiposity; however, the reduction in tissue-specific glucose clearance with HFD diverged by temperature with reduced brown adipose tissue (BAT) glucose uptake at 22°C but reduced soleus glucose uptake at 30°C. Fasting glucose, food intake, and energy expenditure were significantly lower at 30°C, independent of diet. Additionally, markers of browning in both BAT and inguinal subcutaneous WAT, but not perigonadal epididymal WAT, decreased at 30°C. Together, we find housing temperature has a significant impact on the cellular pathways that regulate glucose tolerance in response to an acute HFD exposure. Thus, even short-term changes in housing temperature should be highly considered in interpretation of metabolic studies in mice.

Grape pomace extract induced beige cells in white adipose tissue from rats and in 3T3-L1 adipocytes

This study investigated the effects of a grape pomace extract (GPE) rich in phenolic compounds on brown-like adipocyte induction and adiposity in spontaneously hypertensive (SHR) and control normotensive Wistar-Kyoto (WKY) rats fed a high-fat diet (HFD). HFD consumption for 10 weeks significantly increased epididymal white adipose tissue (eWAT) in WKY but not in SHR rats. Supplementation with GPE (300 mg/kg body weight/day) reduced adipocyte diameter and increased levels of proteins that participate in adipogenesis and angiogenesis, i.e., peroxisome-proliferator activated receptor gamma (PPARγ), vascular endothelial grow factor-A (VEGF-A) and its receptor 2 (VEGF-R2), and partially increased the uncoupling protein 1 (UCP-1) in WKY. In both strains, GPE attenuated adipose inflammation. In eWAT from SHR, GPE increased the expression of proteins involved in adipose tissue "browning," i.e., PPARγ-coactivator-1α (PGC-1α), PPARγ, PR domain containing 16 (PRDM16) and UCP-1. In primary cultures of SHR adipocytes, GPE-induced UCP-1 up-regulation was dependent on p38 and ERK activation. Accordingly, in 3T3-L1 adipocytes treated with palmitate, the addition of GPE (30 μM) activated the β-adrenergic signaling cascade (PKA, AMPK, p38, ERK). This led to the associated up-regulation of proteins involved in mitochondrial biogenesis (PGC-1α, PPARγ, PRDM16 and UCP-1) and fatty acid oxidation (ATGL). These effects were similar to those exerted by (-)-epicatechin and quercetin, major phenolic compounds in GPE. Overall, in HFD-fed rats, supplementation with GPE promoted brown-like cell formation in eWAT and diminished adipose dysfunction. Thus, winemaking residues, rich in bioactive compounds, could be useful to mitigate the adverse effects of HFD-induced adipose dysfunction.

The Peroxisome Proliferator-Activated Receptor α is dispensable for cold-induced adipose tissue browning in mice

Objective

Chronic cold exposure causes white adipose tissue (WAT) to adopt features of brown adipose tissue (BAT), a process known as browning. Previous studies have hinted at a possible role for the transcription factor Peroxisome Proliferator-Activated Receptor alpha (PPARα) in cold-induced browning. Here we aimed to investigate the importance of PPARα in driving transcriptional changes during cold-induced browning in mice.

Methods

Male wildtype and PPARα−/− mice were housed at thermoneutrality (28 °C) or cold (5 °C) for 10 days. Whole genome expression analysis was performed on inguinal WAT. In addition, other analyses were carried out. Whole genome expression data of livers of wildtype and PPARα−/− mice fasted for 24 h served as positive control for PPARα-dependent gene regulation.

Results

Cold exposure increased food intake and decreased weight of BAT and WAT to a similar extent in wildtype and PPARα−/− mice. Except for plasma non-esterified fatty acids, none of the cold-induced changes in plasma metabolites were dependent on PPARα genotype. Histological analysis of inguinal WAT showed clear browning upon cold exposure but did not reveal any morphological differences between wildtype and PPARα−/− mice. Transcriptomics analysis of inguinal WAT showed a marked effect of cold on overall gene expression, as revealed by principle component analysis and hierarchical clustering. However, wildtype and PPARα−/− mice clustered together, even after cold exposure, indicating a similar overall gene expression profile in the two genotypes. Pathway analysis revealed that cold upregulated pathways involved in energy usage, oxidative phosphorylation, and fatty acid β-oxidation to a similar extent in wildtype and PPARα−/− mice. Furthermore, cold-mediated induction of genes related to thermogenesis such as Ucp1, Elovl3, Cox7a1, Cox8, and Cidea, as well as many PPAR target genes, was similar in wildtype and PPARα−/− mice. Finally, pharmacological PPARα activation had a minimal effect on expression of cold-induced genes in murine WAT.

Conclusion

Cold-induced changes in gene expression in inguinal WAT are unaltered in mice lacking PPARα, indicating that PPARα is dispensable for cold-induced browning.

•

Chronic cold markedly induces PPARα expression in inguinal fat.

•

Cold exposure causes transient hypothermia in PPARα−/− mice.

•

Chronic cold-induced changes in gene expression in inguinal fat are unaltered in PPARα−/− mice.

•

Chronic cold does not lead to PPARα activation in liver.

Visceral Fat Dysfunctions in the Rat Social Isolation Model of Psychosis

Medication with neuroleptics has been associated with adipose tissue dysfunctions and, in particular, with increased visceral fat amount. However, several studies suggested that antipsychotic treatment might not be the main responsible of fat mass accumulation, as this has been also described in not treated psychotic patients. One of the most used “drug-free” rodent models of psychosis is the social isolation rearing of young adult rats, which provides a non-pharmacologic method of inducing long-term alterations reminiscent of symptoms seen in psychotic patients. Recent data highlighted a crucial role of redox imbalance in adipose tissue dysfunctions, in terms of decreased antioxidant defense and increased reactive oxygen species (ROS). Here, we investigated possible oxidative stress-related biomolecular alterations associated with visceral fat increase in 7 week isolated rats. To this purpose, we quantified total and visceral fat amount by using dual-energy X-ray (DEXA) absorptiometry. On visceral fat, we analyzed the expression of specific ROS-producer genes (Nox1, Nox4, Hmox-1), antioxidant enzymes (Prdx1 and Ucp-1) and oxidative stress-induced damage markers (Cidea, Slc2a4, and Acacb). The impact of oxidative stress on beta3-adrenergic receptors (Adrb3), at both mRNA and protein level, was also assessed. We found that 7 weeks of social isolation induced an increase in total and visceral fat, associated with a decrease in Prdx1 (mRNA and protein) as well as Ucp-1 mRNA levels and an enhanced expression of Nox1 (mRNA and protein) and Hmox-1 mRNA. No differences were detected in Nox4 mRNA levels between grouped and isolated animals. Elevations in Cidea, Slc2a4, and Acacb expression in visceral fat of isolated animals accounted for oxidative stress-related damage in this tissue, further associated with a significant increase in Adrb3 mRNA and protein. Our results provide a novel understanding of the pathological link existing among psychosocial stress-induced psychosis, adipose tissue dysfunctions and redox imbalance, opening new therapeutic perspectives for the treatment of alterations in peripheral tissues associated with this mental disorder.

Physiological regulation and metabolic role of browning in white adipose tissue

Great progress has been made in our understanding of the browning process in white adipose tissue (WAT) in rodents. The recognition that i) adult humans have physiologically inducible brown adipose tissue (BAT) that may facilitate resistance to obesity and ii) that adult human BAT molecularly and functionally resembles beige adipose tissue in rodents, reignited optimism that obesity and obesity-related diabetes type 2 can be battled by controlling the browning of WAT. In this review the main cellular mechanisms and molecular mediators of browning of WAT in different physiological states are summarized. The relevance of browning of WAT in metabolic health is considered primarily through a modulation of biological role of fat tissue in overall metabolic homeostasis.

Critical review of beige adipocyte thermogenic activation and contribution to whole-body energy expenditure

Beige (or brite, "brown in white") adipocytes are uncoupling protein 1 (UCP1)-positive cells residing in white adipose depots that, depending on the conditions, behave either as classic white adipocytes, storing energy as lipids, or as brown adipocytes, dissipating energy from oxidative metabolism as heat through non-shivering thermogenesis. Because of their thermogenic potential and, therefore, possible usage to treat metabolic diseases such as obesity and type 2 diabetes, beige cells have attracted the attention of many scientists worldwide aiming to develop strategies to safely recruit and activate their thermogenic activity. Indeed, in recent years, a large variety of conditions, molecules (including nutrients) and signaling pathways were reported to promote the recruitment of beige adipocytes. Despite of those advances, the true contribution of beige adipocyte thermogenesis to whole-body energy expenditure is still not completely defined. Herein, we discuss some important aspects that should be considered when studying beige adipocyte biology and the contribution to energy balance and whole-body metabolism.

Targeting the NO/superoxide ratio in adipose tissue: relevance to obesity and diabetes management

Insulin sensitivity and metabolic homeostasis depend on the capacity of adipose tissue to take up and utilize excess glucose and fatty acids. The key aspects that determine the fuel-buffering capacity of adipose tissue depend on the physiological levels of the small redox molecule, nitric oxide (NO). In addition to impairment of NO synthesis, excessive formation of the superoxide anion (О2•- ) in adipose tissue may be an important interfering factor diverting the signalling of NO and other reactive oxygen and nitrogen species in obesity, resulting in metabolic dysfunction of adipose tissue over time. Besides its role in relief from superoxide burst, enhanced NO signalling may be responsible for the therapeutic benefits of different superoxide dismutase mimetics, in obesity and experimental diabetes models. This review summarizes the role of NO in adipose tissue and highlights the effects of NO/О2•- ratio 'teetering' as a promising pharmacological target in the metabolic syndrome.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Now UCP(rotein), Now You Don't: UCP1 Is Not Mandatory for Thermogenesis

Adipocyte-targeted therapies could potentially combat obesity and metabolic disorders; however, our understanding of adipogenesis and the characterization of the various adipose tissues are incomplete. In this issue, Bertholet et al. (2017) report the existence of two types of heat-producing beige-like adipocytes, those with and those without the mitochondrial uncoupling protein 1 (UCP1).

The Role of Adipocytes in Tissue Regeneration and Stem Cell Niches

Classically, white adipose tissue (WAT) was considered an inert component of connective tissue but is now appreciated as a major regulator of metabolic physiology and endocrine homeostasis. Recent work defining how WAT develops and expands in vivo emphasizes the importance of specific locations of WAT or depots in metabolic regulation. Interestingly, mature white adipocytes are integrated into several tissues. A new perspective regarding the in vivo regulation and function of WAT in these tissues has highlighted an essential role of adipocytes in tissue homeostasis and regeneration. Finally, there has been significant progress in understanding how mature adipocytes regulate the pathology of several diseases. In this review, we discuss these novel roles of WAT in the homeostasis and regeneration of epithelial, muscle, and immune tissues and how they contribute to the pathology of several disorders.

Chronic l-menthol-induced browning of white adipose tissue hypothesis: A putative therapeutic regime for combating obesity and improving metabolic health

INTRODUCTION

Obesity constitutes a serious global health concern reaching pandemic prevalence rates. The existence of functional brown adipose tissue (BAT) in adult humans has provoked intense research interest in the role of this metabolically active tissue in whole-body energy balance and body weight regulation. A number of environmental, physiological, pathological, and pharmacological stimuli have been proposed to induce BAT-mediated thermogenesis and functional thermogenic BAT-like activity in white adipose tissue (WAT), opening new avenues for therapeutic strategies based on enhancing the number of beige adipocytes in WAT.

HYPOTHESIS

Recent evidence support a role of l-menthol cooling, mediated by TRPM8 receptor, on UCP1-dependent thermogenesis and BAT-like activity in classical WAT depots along with the recruitment of BAT at specific anatomical sites. l-Menthol-induced BAT thermogenesis has been suggested to occur by a β-adrenergic-independent mechanism, avoiding potential side-effects due to extensive β-adrenergic stimulation mediated by available beta receptor agonists. l-Menthol has been also linked to the activation of the cold-gated ion channel TRPA1. However, its role in l-menthol-induced UCP1-dependent thermogenic activity in BAT and WAT remains undetermined. White adipose tissue plasticity has important clinical implications for obesity prevention and/or treatment because higher levels of UCP1-dependent thermogenesis can lead to enhanced energy expenditure at a considerable extent. We hypothesize that chronic dietary l-menthol treatment could induce TRPM8- and TRPA1-dependent WAT adaptations, resembling BAT-like activity, and overall improve whole-body metabolic health in obese and overweight individuals.

CONCLUSIONS

The putative impact of chronic l-menthol dietary treatment on the stimulation of BAT-like activity in classical WAT depots in humans remains unknown. A detailed experimental design has been proposed to investigate the hypothesized l-menthol-induced browning of WAT. If our hypothesis was to be confirmed, TRPM8/TRPA1-induced metabolic adaptations of WAT to BAT-like activity could provide a promising novel therapeutic approach for increasing energy expenditure, regulating body weight, and preventing obesity and its related co-morbidities in humans.

Ginsenoside Rb1 promotes browning through regulation of PPARγ in 3T3-L1 adipocytes

Browning of white adipocyte tissue (WAT) has received considerable attention due to its potential implication in preventing obesity and related comorbidities. Ginsenoside Rb1 is reported to improve glycolipid metabolism and reduce body weight in obese animals. However whether the body reducing effect mediates by browning effect remains unclear. For this purpose, 3T3-L1 adipocytes were used to study the effect of ginsenoside Rb1 on browning adipocytes specific genes and oxygen consumptions. The results demonstrate that 10 μM of ginsenoside Rb1 increases basal glucose uptake and promoted browning evidenced by significant increases in mRNA expressions of UCP-1, PGC-1α and PRDM16 in 3T3-L1 mature adipocytes. Further, ginsenoside Rb1 also increases PPARγ activity. And the browning effect is abrogated by GW9692, a PPARγ antagonist. In addition, ginsenoside Rb1 increases basal respiration rate, ATP production and uncoupling capacity in 3T3-L1 adipocytes. Those effects are also blunted by GW9692. The results suggest that ginsenoside Rb1 promote browning of 3T3-L1 adipocytes through induction of PPARγ. Our finding offer a new source to discover browning agonists and also useful to understand and extend the applications of ginseng and its constituents.

Redox implications in adipose tissue (dys)function--A new look at old acquaintances

Obesity is an energy balance disorder associated with dyslipidemia, insulin resistance and diabetes type 2, also summarized with the term metabolic syndrome or syndrome X. Increasing evidence points to “adipocyte dysfunction”, rather than fat mass accretion per se, as the key pathophysiological factor for metabolic complications in obesity. The dysfunctional fat tissue in obesity characterizes a failure to safely store metabolic substrates into existing hypertrophied adipocytes and/or into new preadipocytes recruited for differentiation. In this review we briefly summarize the potential of redox imbalance in fat tissue as an instigator of adipocyte dysfunction in obesity. We reveal the challenge of the adipose redox changes, insights in the regulation of healthy expansion of adipose tissue and its reduction, leading to glucose and lipids overflow.

•

Adipose tissue (AT) buffers nutrient excess determining overall metabolic health.

•

Redox insight in lipid storage and adipogenesis of AT is reviewed.

•

Redox modulation of AT as therapeutic target in obesity/syndrome X is considered.