Pink adipose tissue: A paradigm of adipose tissue plasticity.

Adipose tissue is highly plastic, as illustrated mainly by the transdifferentiation of white adipocytes into beige adipocytes, depending on environmental conditions. However, during gestation and lactation in rodent, there is an amazing phenomenon of transformation of subcutaneous adipose tissue into mammary glandular tissue, known as pink adipose tissue, capable of synthesizing and secreting milk. Recent work using transgenic lineage-tracing experiments, mainly carried out in Saverio Cinti's team, has demonstrated very convincingly that this process does indeed correspond to a transdifferentiation of white adipocytes into mammary alveolar cells (pink adipocytes) during gestation and lactation. This phenomenon is reversible, since during the post-lactation phase, pink adipocytes revert to the white adipocyte phenotype. The molecular mechanisms underlying this reversible transdifferentiation remain poorly understood.

CXCL5 inhibits excessive oxidative stress by regulating white adipocyte differentiation.

Chemokines have been well-documented as a major factor in immune cell migration and the regulation of immune responses. However, recent studies have reported that chemokines have diverse roles, both in immune cells and other cell types, including adipocytes. This study investigated the molecular functions of C-X-C motif chemokine ligand 5 (CXCL5) in white adipose cells using Cxcl5 knock-out (KO) mice fed a high-fat diet (HFD). The expression of Cxcl5 decreased by 90% during adipocyte differentiation and remained at a low level in mature adipocytes. Moreover, adipogenesis was enhanced when adipocytes were differentiated from the stromal vascular fraction (SFV) of Cxcl5 KO mice. Feeding an HFD increased the generation of reactive oxygen species (ROS) and promoted abnormal adipogenesis in Cxcl5 KO mice. Oxidative stress and insulin resistance occurred in Cxcl5 KO mice due to decreased antioxidant enzymes and failure to remove ROS. These results indicate the principal roles of CXCL5 in adipogenesis and ROS regulation in adipose tissue, further suggesting that CXCL5 is a valuable chemokine for metabolic disease research.

Engineering and Characterization of a Biomimetic Microchip for Differentiating Mouse Adipocytes in a 3D Microenvironment.

Although two-dimensional (2D) cell cultures are the standard in cell research, one pivotal disadvantage is the lack of cell-cell and cell-extracellular matrix (ECM) signaling in the culture milieu. However, such signals occur in three-dimensional (3D) in vivo environments and are essential for cell differentiation, proliferation, and a range of cellular functions. In this study, we developed a microfluidic device to proliferate and differentiate functional adipose tissue and adipocytes by utilizing 3D cell culture technology. This device was used to generate a tissue-specific 3D microenvironment to differentiate 3T3-L1 preadipocytes into either visceral white adipocytes using visceral adipose tissue (VAT) or subcutaneous white adipose tissue (SAT). The microchip has been tested and validated by functional assessments including cell morphology, inflammatory response to a lipopolysaccharide (LPS) challenge, GLUT4 tracking, and gene expression analyses. The biomimetic microfluidic chip is expected to mimic functional adipose tissues that can replace 2D cell cultures and allow for more accurate analysis of adipose tissue physiology.

Tangeretin prevents obesity by modulating systemic inflammation, fat browning, and gut microbiota in high-fat diet-induced obese C57BL/6 mice.

Obesity and associated comorbidities are closely linked to gut microbiota dysbiosis, energy balance, and chronic inflammation. Tangeretin, a key citrus polymethoxylated flavone (PMF), is abundant in citrus fruits and has preventative and therapeutic effects for numerous diseases. The current study investigated the effects and possible mechanisms of tangeretin supplementation in preventing obesity in high-fat diet (HFD)-fed mice. Treatment of HFD-fed mice with tangeretin potently ameliorated HFD-induced body weight, liver steatosis, glucose intolerance, and insulin resistance. Tangeretin mitigated systemic chronic inflammation by reducing metabolic endotoxemia and inflammation-related gene expression in HFD-fed mice. An increased number of small brown adipocytes possessing multilocular and cytoplasmic lipid droplets and upregulation of thermogenic gene expression were observed after tangeretin treatment. 16S rRNA amplicon sequencing indicated that tangeretin markedly altered the gut microbiota composition (richness and diversity) and reversed 16 operational taxonomic units (OTUs) back to levels seen in mice consuming a normal chow diet (NCD). Notably, tangeretin decreased the ratio of Firmicutes-to-Bacteroidetes and greatly enriched Bacteroides and Lactobacillus. Overall, our results suggest that long-term supplementation with citrus tangeretin ameliorates the phenotype of obesity by improving adipose thermogenesis and reducing systemic inflammation and gut microbiota dysbiosis, which provides a good basis for studying the mechanism of tangeretin's beneficial effects.

Theobromine enhances the conversion of white adipocytes into beige adipocytes in a PPARγ activation-dependent manner.

The adipocytes play an important role in driving the obese-state-white adipose tissue (WAT) stores the excess energy as fat, wherein brown adipose tissue (BAT) is responsible for energy expenditure via the thermoregulatory function of uncoupling protein 1 (UCP1)-the imbalance between these two onsets obesity. Moreover, the anti-obesity effects of brown-like-adipocytes (beige) in WAT are well documented. Browning, the process of transformation of energy-storing into energy-dissipating adipocytes, is a potential preventive strategy against obesity and its related diseases. In the present study, to explore an alternative source of natural products in the regulation of adipocyte transformation, we assessed the potential of theobromine (TB), a bitter alkaloid of the cacao plant, inducing browning in mice (in vivo) and primary adipocytes (in vitro). Dietary supplementation of TB significantly increased skin temperature of the inguinal region in mice and induced the expression of UCP1 protein. It also increased the expression levels of mitochondrial marker proteins in subcutaneous adipose tissues but not in visceral adipose tissues. The microarray analysis showed that TB supplementation upregulated multiple thermogenic and beige adipocyte marker genes in subcutaneous adipose tissue. Furthermore, in mouse-derived primary adipocytes, TB upregulated the expression of the UCP1 protein and mitochondrial mass in a PPARγ ligand-dependent manner. It also increased the phosphorylation levels of PPARγ coactivator 1α without affecting its protein expression. These results indicate that dietary supplementation of TB induces browning in subcutaneous WAT and enhances PPARγ-induced UCP1 expression in vitro, suggesting its potential to treat obesity.

Caloric restriction and Roux-en-Y Gastric Bypass promote white adipose tissue browning in mice.

PURPOSE: Caloric restriction (CR) and Roux-en-Y Gastric Bypass (RYGB) are considered effective means of body weight control, but the mechanism by which CR and RYGB protect against high-fat diet (HFD)-induced obesity remains elusive. The browning of white adipose tissue (WAT) is a potential approach to combat obesity. Here we assess whether browning of WAT is involved in CR- and RYGB-treatment. METHODS: The average size of adipocytes was determined by histological analysis. Expression of thermogenic genes in both human subjects and mice were measured by quantitative real-time PCR and immunohistochemical staining. RESULTS: The average size of adipocytes was bigger, while the expression of thermogenic genes such as uncoupling protein 1 (UCP1), nuclear factor erythroid-2 like 1 (NRF1) and PPARγ coactivator-1 α (PGC1α) were lower in the WAT of obese subjects when compared to lean controls. Both CR and RYGB promoted weight and fat loss. Increment of the average adipocytes size and down-regulation of thermogenic genes were significantly reversed by both CR and RYGB in the WAT of obese mice. CONCLUSIONS: Our findings showed that CR and RYGB significantly improved high-fat diet-induced lipid accumulation by promoting the browning of WAT.

Partial Deficiency of Zfp217 Resists High-Fat Diet-Induced Obesity by Increasing Energy Metabolism in Mice.

Obesity-induced adipose tissue dysfunction and disorders of glycolipid metabolism have become a worldwide research priority. Zfp217 plays a crucial role in adipogenesis of 3T3-L1 preadipocytes, but about its functions in animal models are not yet clear. To explore the role of Zfp217 in high-fat diet (HFD)-induced obese mice, global Zfp217 heterozygous knockout (Zfp217+/-) mice were constructed. Zfp217+/- mice and Zfp217+/+ mice fed a normal chow diet (NC) did not differ significantly in weight gain, percent body fat mass, glucose tolerance, or insulin sensitivity. When challenged with HFD, Zfp217+/- mice had less weight gain than Zfp217+/+ mice. Histological observations revealed that Zfp217+/- mice fed a high-fat diet had much smaller white adipocytes in inguinal white adipose tissue (iWAT). Zfp217+/- mice had improved metabolic profiles, including improved glucose tolerance, enhanced insulin sensitivity, and increased energy expenditure compared to the Zfp217+/+ mice under HFD. We found that adipogenesis-related genes were increased and metabolic thermogenesis-related genes were decreased in the iWAT of HFD-fed Zfp217+/+ mice compared to Zfp217+/- mice. In addition, adipogenesis was markedly reduced in mouse embryonic fibroblasts (MEFs) from Zfp217-deleted mice. Together, these data indicate that Zfp217 is a regulator of energy metabolism and it is likely to provide novel insight into treatment for obesity.

The molecular and metabolic program by which white adipocytes adapt to cool physiologic temperatures.

Although visceral adipocytes located within the body's central core are maintained at approximately 37°C, adipocytes within bone marrow, subcutaneous, and dermal depots are found primarily within the peripheral shell and generally exist at cooler temperatures. Responses of brown and beige/brite adipocytes to cold stress are well studied; however, comparatively little is known about mechanisms by which white adipocytes adapt to temperatures below 37°C. Here, we report that adaptation of cultured adipocytes to 31°C, the temperature at which distal marrow adipose tissues and subcutaneous adipose tissues often reside, increases anabolic and catabolic lipid metabolism, and elevates oxygen consumption. Cool adipocytes rely less on glucose and more on pyruvate, glutamine, and, especially, fatty acids as energy sources. Exposure of cultured adipocytes and gluteal white adipose tissue (WAT) to cool temperatures activates a shared program of gene expression. Cool temperatures induce stearoyl-CoA desaturase-1 (SCD1) expression and monounsaturated lipid levels in cultured adipocytes and distal bone marrow adipose tissues (BMATs), and SCD1 activity is required for acquisition of maximal oxygen consumption at 31°C.

Defining the lineage of thermogenic perivascular adipose tissue.

Brown adipose tissue can expend large amounts of energy, and therefore increasing its size or activity is a promising therapeutic approach to combat metabolic disease. In humans, major deposits of brown fat cells are found intimately associated with large blood vessels, corresponding to perivascular adipose tissue (PVAT). However, the cellular origins of PVAT are poorly understood. Here, we determine the identity of perivascular adipocyte progenitors in mice and humans. In mice, thoracic PVAT develops from a fibroblastic lineage, consisting of progenitor cells (Pdgfra+, Ly6a+ and Pparg-) and preadipocytes (Pdgfra+, Ly6a+ and Pparg+), which share transcriptional similarity with analogous cell types in white adipose tissue. Interestingly, the aortic adventitia of adult animals contains a population of adipogenic smooth muscle cells (Myh11+, Pdgfra- and Pparg+) that contribute to perivascular adipocyte formation. Similarly, human PVAT contains presumptive fibroblastic and smooth muscle-like adipocyte progenitor cells, as revealed by single-nucleus RNA sequencing. Together, these studies define distinct populations of progenitor cells for thermogenic PVAT, providing a foundation for developing strategies to augment brown fat activity.

Genome-wide discovery of genetic loci that uncouple excess adiposity from its comorbidities.

Obesity is a major risk factor for cardiometabolic diseases. Nevertheless, a substantial proportion of individuals with obesity do not suffer cardiometabolic comorbidities. The mechanisms that uncouple adiposity from its cardiometabolic complications are not fully understood. Here, we identify 62 loci of which the same allele is significantly associated with both higher adiposity and lower cardiometabolic risk. Functional analyses show that the 62 loci are enriched for genes expressed in adipose tissue, and for regulatory variants that influence nearby genes that affect adipocyte differentiation. Genes prioritized in each locus support a key role of fat distribution (FAM13A, IRS1 and PPARG) and adipocyte function (ALDH2, CCDC92, DNAH10, ESR1, FAM13A, MTOR, PIK3R1 and VEGFB). Several additional mechanisms are involved as well, such as insulin-glucose signalling (ADCY5, ARAP1, CREBBP, FAM13A, MTOR, PEPD, RAC1 and SH2B3), energy expenditure and fatty acid oxidation (IGF2BP2), browning of white adipose tissue (CSK, VEGFA, VEGFB and SLC22A3) and inflammation (SH2B3, DAGLB and ADCY9). Some of these genes may represent therapeutic targets to reduce cardiometabolic risk linked to excess adiposity.

Huang-Qi San ameliorates hyperlipidemia with obesity rats via activating brown adipocytes and converting white adipocytes into brown-like adipocytes.

BACKGROUND: Brown adipose tissue (BAT) activation is a promising therapeutic target to treat hyperlipidemia with obesity. Huang-Qi San (HQS), an traditional Chinese medicine, can ameliorate hyperlipidemia with obesity, but its mechanism of action (MOA) is not understood. PURPOSE: To articulate the MOA for HQS with animal models. METHODS: The main chemical constituents of HQS were identified by high-performance liquid chromatography (HPLC) based assay. Hyperlipidemia with obesity rat models induced by high-fat diet were employed in the study. The levels of the fasting plasma glucose (FPG), triglyceride (TG), total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C) and high-density lipoprotein-cholesterol (HDL-C) were measured to evaluate the ability of HQS to ameliorate hyperlipidemia with obesity. Pathological analyses of organs were conducted with Oil Red O staining, hematoxylin-eosin (H&E) staining and transmission electron microscopy. The expression of mRNAs related to thermogenic genes, fatty acid oxidation-related genes and mitochondria biogenic genes were examined by quantitative real-time PCR. The protein expressions of uncoupling protein 1 (UCP1) were investigated by immunohistochemistry and western blot. Simultaneously, the protein expression of PR domain containing 16 (PRDM16), ATP synthase F1 subunit alpha (ATP5A) was detected by western blot. RESULTS: HQS ameliorates metabolic disorder, lipid ectopic deposition, obesity and maintained glucose homeostasis in hyperlipidemia with obesity rats. HQS can significantly increase the number of mitochondria and reduced the size of the intracellular lipid droplets in BAT, and increase the expression of BAT activation-related genes (UCP1, PGC1α, PGC1ß, Prdm16, CD137, TBX1, CPT1a, PPARα, Tfam, NRF1 and NRF2) in vivo. Furthermore, UCP1, PRDM16 and ATP5A proteins of BAT were increased. CONCLUSION: HQS can activate BAT and browning of S-WAT (subcutaneous white adipose tissue) through activating the PRDM16/PGC1α/UCP1 pathway, augmenting mitochondrial biogenesis and fatty acid oxidation to increase thermogenesis and energy expenditure, resulting in a significant amelioration of hyperlipidemia with obesity. Therefore, HQS is an effective therapeutic medicine for the treatment of hyperlipidemia with obesity.

miR17-92 cluster drives white adipose tissue browning.

White adipose tissue (WAT) browning may have beneficial effects for treating metabolic syndrome. miRNA are important regulators of the differentiation, development, and function of brown and beige adipocytes. Here, we found that the cold-inducible miRNA17-92 cluster is enriched in brown adipose tissue (BAT) compared with WAT. Overexpression of the miR17-92 cluster in C3H10T1/2 cells, a mouse mesenchymal stem cell line, enhanced the thermogenic capacity of adipocytes. Furthermore, we observed a significant reduction in adiposity in adipose tissue-specific miR17-92 cluster transgenic (TG) mice. This finding is partly explained by dramatic increases in white fat browning and energy expenditure. Interestingly, the miR17-92 cluster stimulated WAT browning without altering BAT activity in mice. In addition, when we removed the intrascapular BAT (iBAT), the TG mice could maintain their body temperature well under cold exposure. At the molecular level, we found that the miR17-92 cluster targets Rb1, a beige cell repressor in WAT. The present study reveals a critical role for the miR17-92 cluster in regulating WAT browning. These results may be helpful for better understanding the function of beige fat, which could compensate for the lack of BAT in humans, and may open new avenues for combatting metabolic syndrome.

Browning of the subcutaneous adipocytes in diet-induced obese mouse submitted to intermittent fasting.

PURPOSE: We studied subcutaneous white adipose tissue (sWAT) of obese mice submitted to intermittent fasting (IF). METHODS: Twelve-week-old C57BL/6 male mice received the diets Control (C) or high-fat (HF) for eight weeks (n = 20/each). Then, part of each group performed IF (24 h feeding/24 h fasting) for four weeks: C, C-IF, HF, and HF-IF (n = 10/each). RESULTS: Food intake did not show a difference in feeding and fasting days, but HF groups had a high energy intake. IF led to multilocular adipocytes in sWAT (browning), and improved respiratory quotient on the fed day. IF decreased gene expression of Leptin, but increased Adiponectin, ß3ar (beta3 adrenoreceptor), and Ucp1 (uncoupling protein). IF enhanced immunostaining of Caspase 3, Pcna (proliferating cell nuclear antigen), and UCP1 in sWAT. IF attenuated pro-inflammatory markers and pro-apoptotic markers in sWAT. CONCLUSIONS: IF in obese mice led to browning in sWAT adipocytes, enhanced thermogenesis, an improved adipose tissue pro-inflammatory profile.

Sustained mitochondrial biogenesis is essential to maintain caloric restriction-induced beige adipocytes.

BACKGROUND: Caloric restriction (CR) delays the onset of metabolic and age-related disorders. Recent studies have demonstrated that formation of beige adipocytes induced by CR is strongly associated with extracellular remodeling in adipose tissue, decrease in adipose tissue inflammation, and improved systemic metabolic homeostasis. However, beige adipocytes rapidly transition to white upon CR withdrawal through unclear mechanisms. MATERIALS AND METHODS: Six-week old C57BL6 mice were fed with 40% CR chow diet for 6 weeks. Subsequently, one group of mice was switched back to ad libitum chow diet, which was continued for additional 2 weeks. Adipose tissues were assessed histologically and biochemically for beige adipocytes. RESULTS: Beige adipocytes induced by CR rapidly transition to white adipocytes when CR is withdrawn independent of parkin-mediated mitophagy. We demonstrate that the involution of mitochondria during CR withdrawal is strongly linked with a decrease in mitochondrial biogenesis. We further demonstrate that beige-to-white fat transition upon ß3-AR agonist-withdrawal could be attenuated by CR, partly via maintenance of mitochondrial biogenesis. CONCLUSION: In the model of CR, our study highlights the dominant role of mitochondrial biogenesis in the maintenance of beige adipocytes. We propose that loss of beige adipocytes upon ß3-AR agonist withdrawal could be attenuated by CR.

Chia oil induces browning of white adipose tissue in high-fat diet-induced obese mice.

Previous research suggests that omega-3 fatty acids from animal origin may promote the browning of subcutaneous white adipose tissue. We evaluated if supplementation with a plant oil (chia, Salvia hispanica L.) rich in alpha-linolenic fatty acid (C18:3; ω-3) would promote browning and improve glucose metabolism in animals subjected to an obesogenic diet. Swiss male mice (n = 28) were divided into 4 groups: C: control diet; H: high-fat diet; HC: animals in the H group supplemented with chia oil after reaching obesity; HCW: animals fed since weaning on a high-fat diet supplemented with chia oil. Glucose tolerance, inflammatory markers, and expression of genes and proteins involved in the browning process were examined. When supplemented since weaning, chia oil improved glucose metabolism and promoted the browning process and a healthier phenotype. Results of this study suggested that chia oil has potential to protect against the development of obesity-related diseases.

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.

Secreted protein acidic and rich in cysteine (SPARC) regulates thermogenesis in white and brown adipocytes.

SPARC, also known as osteonectin, is well known for its physiological roles in bone formation and tissue remodeling, as well as in cancer pathology; however, evidence regarding its function in adipocytes is lacking. The present study explored the physiological role of SPARC in cultured 3T3-L1 white and HIB1B brown adipocytes of murine cell lines. Treatment of recombinant SPARC upregulated the fat browning marker proteins and genes in white adipocytes and activated brown adipocytes. Conversely, knockdown of Sparc markedly reduced these genes and proteins in both cell lines. In addition, recombinant SPARC inhibited expression of adipogenic and lipogenic proteins but elevated lipolytic and fatty acid oxidation proteins. Furthermore, in silico analysis revealed that SPARC directly interacted and regulated VEGF in adipocytes. In conclusion, SPARC acts as a regulatory protein in both white and brown adipocytes by controlling thermogenesis and is thus regarded as a possible therapeutic target for treatment of obesity.

Elucidating the Regulatory Role of Melatonin in Brown, White, and Beige Adipocytes.

The high prevalence of obesity and its associated metabolic diseases has heightened the importance of understanding control of adipose tissue development and energy metabolism. In mammals, 3 types of adipocytes with different characteristics and origins have been identified: white, brown, and beige. Beige and brown adipocytes contain numerous mitochondria and have the capability to burn energy and counteract obesity, while white adipocytes store energy and are closely associated with metabolic disorders and obesity. Thus, regulation of the development and function of different adipocytes is important for controlling energy balance and combating obesity and related metabolic disorders. Melatonin is a neurohormone, which plays multiple roles in regulating inflammation, blood pressure, insulin actions, and energy metabolism. This article summarizes and discusses the role of melatonin in white, beige, and brown adipocytes, especially in affecting adipogenesis, inducing beige formation or white adipose tissue browning, enhancing brown adipose tissue mass and activities, improving anti-inflammatory and antioxidative effects, regulating adipokine secretion, and preventing body weight gain. Based on the current findings, melatonin is a potential therapeutic agent to control energy metabolism, adipogenesis, fat deposition, adiposity, and related metabolic diseases.