Differentiating SGBS adipocytes respond to PPARγ stimulation, irisin and BMP7 by functional browning and beige characteristics

Establishment of the Myeloid TBX-Code Reveals Aberrant Expression of T-Box Gene TBX1 in Chronic Myeloid Leukemia

T-box genes encode transcription factors, which control developmental processes and promote cancer if deregulated. Recently, we described the lymphoid TBX-code, which collates T-box gene activities in normal lymphopoiesis, enabling identification of members deregulated in lymphoid malignancies. Here, we have extended this analysis to cover myelopoiesis, compiling the myeloid TBX-code and, thus, highlighting which of these genes might be deregulated in myeloid tumor types. We analyzed public T-box gene expression datasets bioinformatically for normal and malignant cells. Candidate T-box-gene-expressing model cell lines were identified and examined by RQ-PCR, Western Blotting, genomic profiling, and siRNA-mediated knockdown combined with RNA-seq analysis and live-cell imaging. The established myeloid TBX-code comprised 10 T-box genes, including progenitor-cell-restricted TBX1. Accordingly, we detected aberrant expression of TBX1 in 10% of stem/progenitor-cell-derived chronic myeloid leukemia (CML) patients. The classic CML cell line K-562 expressed TBX1 at high levels and served as a model to identify TBX1 activators, including transcription factor GATA1 and genomic amplification of the TBX1 locus at 22q11; inhibitors, including BCR::ABL1 fusion and downregulated GNAI2, as well as BMP, FGF2, and WNT signaling; and the target genes CDKN1A, MIR17HG, NAV1, and TMEM38A. The establishment of the myeloid TBX-code permitted identification of aberrant TBX1 expression in subsets of CML patients and cell lines. TBX1 forms an integral part of an oncogenic regulatory network impacting proliferation, survival, and differentiation. Thus, the data spotlight novel diagnostic markers and potential therapeutic targets for this malignancy.

Extracellular thiamine concentration influences thermogenic competency of differentiating neck area-derived human adipocytes

Introduction

Brown adipose tissue (BAT) dissipates energy in the form of heat majorly via the mitochondrial uncoupling protein 1 (UCP1). The activation of BAT, which is enriched in the neck area and contains brown and beige adipocytes in humans, was considered as a potential therapeutic target to treat obesity. Therefore, finding novel agents that can stimulate the differentiation and recruitment of brown or beige thermogenic adipocytes are important subjects for investigation. The current study investigated how the availability of extracellular thiamine (vitamin B1), an essential cofactor of mitochondrial enzyme complexes that catalyze key steps in the catabolism of nutrients, affects the expression of thermogenic marker genes and proteins and subsequent functional parameters during ex vivo adipocyte differentiation.

Methods

We differentiated primary human adipogenic progenitors that were cultivated from subcutaneous (SC) or deep neck (DN) adipose tissues in the presence of gradually increasing thiamine concentrations during their 14-day differentiation program. mRNA and protein expression of thermogenic genes were analyzed by RT-qPCR and western blot, respectively. Cellular respiration including stimulated maximal and proton-leak respiration was measured by Seahorse analysis.

Results

Higher thiamine levels resulted in increased expression of thiamine transporter 1 and 2 both at mRNA and protein levels in human neck area-derived adipocytes. Gradually increasing concentrations of thiamine led to increased basal, cAMP-stimulated, and proton-leak respiration along with elevated mitochondrial biogenesis of the differentiated adipocytes. The extracellular thiamine availability during adipogenesis determined the expression levels of UCP1, PGC1a, CKMT2, and other browning-related genes and proteins in primary SC and DN-derived adipocytes in a concentration-dependent manner. Providing abundant amounts of thiamine further increased the thermogenic competency of the adipocytes.

Discussion

Case studies in humans reported that thiamine deficiency was found in patients with type 2 diabetes and obesity. Our study raises the possibility of a novel strategy with long-term thiamine supplementation, which can enhance the thermogenic competency of differentiating neck area-derived adipocytes for preventing or combating obesity.

Human abdominal subcutaneous-derived active beige adipocytes carrying FTO rs1421085 obesity-risk alleles exert lower thermogenic capacity

Introduction: White adipocytes store lipids, have a large lipid droplet and few mitochondria. Brown and beige adipocytes, which produce heat, are characterized by high expression of uncoupling protein (UCP) 1, multilocular lipid droplets, and large amounts of mitochondria. The rs1421085 T-to-C single-nucleotide polymorphism (SNP) of the human FTO gene interrupts a conserved motif for ARID5B repressor, resulting in adipocyte type shift from beige to white. Methods: We obtained abdominal subcutaneous adipose tissue from donors carrying FTO rs1421085 TT (risk-free) or CC (obesity-risk) genotypes, isolated and differentiated their preadipocytes into beige adipocytes (driven by the PPARγ agonist rosiglitazone for 14 days), and activated them with dibutyryl-cAMP for 4 hours. Then, either the same culture conditions were applied for additional 14 days (active beige adipocytes) or it was replaced by a white differentiation medium (inactive beige adipocytes). White adipocytes were differentiated by their medium for 28 days. Results and Discussion: RNA-sequencing was performed to investigate the gene expression pattern of adipocytes carrying different FTO alleles and found that active beige adipocytes had higher brown adipocyte content and browning capacity compared to white or inactive beige ones when the cells were obtained from risk-free TT but not from obesity-risk CC genotype carriers. Active beige adipocytes carrying FTO CC had lower thermogenic gene (e.g., UCP1, PM20D1, CIDEA) expression and thermogenesis measured by proton leak respiration as compared to TT carriers. In addition, active beige adipocytes with CC alleles exerted lower expression of ASC-1 neutral amino acid transporter (encoded by SLC7A10) and less consumption of Ala, Ser, Cys, and Gly as compared to risk-free carriers. We did not observe any influence of the FTO rs1421085 SNP on white and inactive beige adipocytes highlighting its exclusive and critical effect when adipocytes were activated for thermogenesis.

Availability of abundant thiamine determines efficiency of thermogenic activation in human neck area derived adipocytes

Brown/beige adipocytes express uncoupling protein-1 (UCP1) that enables them to dissipate energy as heat. Systematic activation of this process can alleviate obesity. Human brown adipose tissues are interspersed in distinct anatomical regions including deep neck. We found that UCP1 enriched adipocytes differentiated from precursors of this depot highly expressed ThTr2 transporter of thiamine and consumed thiamine during thermogenic activation of these adipocytes by cAMP which mimics adrenergic stimulation. Inhibition of ThTr2 led to lower thiamine consumption with decreased proton leak respiration reflecting reduced uncoupling. In the absence of thiamine, cAMP-induced uncoupling was diminished but restored by thiamine addition reaching the highest levels at thiamine concentrations larger than present in human blood plasma. Thiamine is converted to thiamine pyrophosphate (TPP) in cells; the addition of TPP to permeabilized adipocytes increased uncoupling fueled by TPP-dependent pyruvate dehydrogenase. ThTr2 inhibition also hampered cAMP-dependent induction of UCP1, PGC1a, and other browning marker genes, and thermogenic induction of these genes was potentiated by thiamine in a concentration dependent manner. Our study reveals the importance of amply supplied thiamine during thermogenic activation in human adipocytes which provides TPP for TPP-dependent enzymes not fully saturated with this cofactor and by potentiating the induction of thermogenic genes.

D-Chiro-Inositol and Myo-Inositol Induce WAT/BAT Trans-Differentiation in Two Different Human Adipocyte Models (SGBS and LiSa-2)

White adipose tissue/brown adipose tissue trans-differentiation is one of the main study targets for therapies against obesity and metabolic diseases. In recent years, numerous molecules able to induce such trans-differentiation have been identified; however, their effect in obesity therapies has not been as expected. In the present study, we investigated whether myo-inositol and its stereoisomer D-chiro-inositol could be involved in the browning of white adipose tissue. Our preliminary results clearly indicate that both, at 60 μM concentration, induce the upregulation of uncoupling protein 1 mRNA expression, the main brown adipose tissue marker, and increase mitochondrial copy number as well as oxygen consumption ratio. These changes demonstrate an activation of cell metabolism. Therefore, our results show that human differentiated adipocytes (SGBS and LiSa-2), assume the features typical of brown adipose tissue after both treatments. Furthermore, in the cell lines examined, we proved that D-chiro-inositol and myo-Inositol induce an increase in the expression of estrogen receptor mRNAs, suggesting a possible modulation by these isomers. We also found an increase in the mRNA of peroxisome proliferator-activated receptor gamma, a very important target in lipid metabolism and metabolic diseases. Our results open new opportunities for the use of inositols in therapeutic strategies to counteract obesity and its metabolic complications.

Meteorin-like levels are associated with active brown adipose tissue in early infancy

INTRODUCTION

Meteorin-like (METRNL) is a hormonal factor released by several tissues, including thermogenically active brown and beige adipose tissues. It exerts multiple beneficial effects on metabolic and cardiovascular systems in experimental models. However, the potential role of METRNL as brown adipokine in humans has not been investigated previously, particularly in relation to the metabolic adaptations taking place in early life, when brown adipose tissue (BAT) is particularly abundant.

METHODS AND MATERIALS

METRNL levels, as well as body composition (DXA) and circulating endocrine-metabolic variables, were assessed longitudinally in a cohort of infants at birth, and at ages 4 and 12 months. BAT activity was measured by infrared thermography at age 12 months. METRNL levels were also determined cross-sectionally in adults; METRNL gene expression (qRT-PCR) was assessed in BAT and liver samples from neonates, and in adipose tissue and liver samples form adults. Simpson-Golabi-Behmel Syndrome (SGBS) adipose cells were thermogenically activated using cAMP, and METRNL gene expression and METRNL protein released were analysed.

RESULTS

Serum METRNL levels were high at birth and declined across the first year of life albeit remaining higher than in adulthood. At age 4 and 12 months, METRNL levels correlated positively with circulating C-X-C motif chemokine ligand 14 (CXCL14), a chemokine released by thermogenically active BAT, but not with parameters of adiposity or metabolic status. METRNL levels also correlated positively with infrared thermography-estimated posterior-cervical BAT activity in girls aged 12 months. Gene expression analysis indicated high levels of METRNL mRNA in neonatal BAT. Thermogenic stimulus of brown/beige adipocytes led to a significant increase of METRNL gene expression and METRN protein release to the cell culture medium.

CONCLUSION

Circulating METRNL levels are high in the first year of life and correlate with indices of BAT activity and with levels of an established brown adipokine such as CXCL14. These data, in addition with the high expression of METRNL in neonatal BAT and in thermogenically-stimulated brown/beige adipocytes, suggest that METRNL is actively secreted by BAT and may be a circulating biomarker of BAT activity in early life.

Effects of allicin on human Simpson-Golabi-Behmel syndrome cells in mediating browning phenotype

INTRODUCTION

Obesity is a major health problem because it is associated with increased risk of cardiovascular disease, diabetes, hypertension, and some cancers. Strategies to prevent or reduce obesity focus mainly on the possible effects of natural compounds that can induce a phenotype of browning adipocytes capable of releasing energy in the form of heat. Allicin, a bioactive component of garlic with numerous pharmacological functions, is known to stimulate energy metabolism.

METHODS

In the present study, the effects of allicin on human Simpson-Golabi-Behmel Syndrome (SGBS) cells were investigated by quantifying the dynamics of lipid droplets (LDs) and mitochondria, as well as transcriptomic changes after six days of differentiation.

RESULTS

Allicin significantly promoted the reduction in the surface area and size of LDs, leading to the formation of multilocular adipocytes, which was confirmed by the upregulation of genes related to lipolysis. The increase in the number and decrease in the mean aspect ratio of mitochondria in allicin-treated cells indicate a shift in mitochondrial dynamics toward fission. The structural results are confirmed by transcriptomic analysis showing a significant arrangement of gene expression associated with beige adipocytes, in particular increased expression of T-box transcription factor 1 (TBX1), uncoupling protein 1 (UCP1), PPARG coactivator 1 alpha (PPARGC1A), peroxisome proliferator-activated receptor alpha (PPARA), and OXPHOS-related genes. The most promising targets are nuclear genes such as retinoid X receptor alpha (RXRA), retinoid X receptor gamma (RXRG), nuclear receptor subfamily 1 group H member 3 (NR1H3), nuclear receptor subfamily 1 group H member 4 (NR1H4), PPARA, and oestrogen receptor 1 (ESR1).

DISCUSSION

Transcriptomic data and the network pharmacology-based approach revealed that genes and potential targets of allicin are involved in ligand-activated transcription factor activity, intracellular receptor signalling, regulation of cold-induced thermogenesis, and positive regulation of lipid metabolism. The present study highlights the potential role of allicin in triggering browning in human SGBS cells by affecting the LD dynamics, mitochondrial morphology, and expression of brown marker genes. Understanding the potential targets through which allicin promotes this effect may reveal the underlying signalling pathways and support these findings.

Adipose microtissue-on-chip: a 3D cell culture platform for differentiation, stimulation, and proteomic analysis of human adipocytes

Human fat tissue has evolved to serve as a major energy reserve. An imbalance between energy intake and expenditure leads to an expansion of adipose tissue. Maintenance of this energy imbalance over long periods leads to obesity and metabolic disorders such as type 2 diabetes, for which a clinical cure is not yet available. In this study, we developed a microfluidic large-scale integration chip platform to automate the formation, long-term culture, and retrieval of 3D adipose microtissues to enable longitudinal studies of adipose tissue in vitro. The chip was produced from soft-lithography molds generated by 3D-printing, which allowed scaling of pneumatic membrane valves for parallel fluid routing and thus incorporated microchannels with variable dimensions to handle 3D cell cultures with diameters of several hundred micrometers. In 32 individual fluidically accessible cell culture chambers, designed to enable the self-aggregation process of three microtissues, human adipose stem cells differentiated into mature adipocytes over a period of two weeks. Coupling mass spectrometry to the cell culture platform, we determined the minimum cell numbers required to obtain robust and complex proteomes with over 1800 identified proteins. The adipose microtissues on the chip platform were then used to periodically simulate food intake by alternating the glucose level in the cell-feeding media every 6 h over the course of one week. The proteomes of adipocytes under low/high glucose conditions exhibited unique protein profiles, confirming the technical functionality and applicability of the chip platform. Thus, our adipose tissue-on-chip in vitro model may prove useful for elucidating the molecular and functional mechanisms of adipose tissue in normal and pathological conditions, such as obesity.

Jinlida Granules Reduce Obesity in db/db Mice by Activating Beige Adipocytes

Recent studies indicate existence of beige adipocytes in adults. Upon activation, beige adipocytes burn energy for thermogenesis and contribute to regulation of energy balance. In this study, we have analyzed whether Jinlida granules (JLD) could activate beige adipocytes. JLD suspended in 0.5% carboxymethyl cellulose (CMC) was gavage fed to db/db mice at a daily dose of 3.8 g/kg. After 10 weeks, body weight, biochemical, and histological analyses were performed. In situ hybridization, immunofluorescence, and western blotting were conducted to test beige adipocyte activation in mice. X9 cells were induced with induction medium and maintenance medium containing 400 μg/mL of JLD. After completion of induction, cells were analyzed by Nile red staining, time polymerase chain reaction (PCR), western blotting, and immunofluorescence to understand the effect of JLD on the activation of beige adipocytes. A molecular docking method was used to preliminarily identify compounds in JLD, which hold the potential activation effect on uncoupling protein 1 (UCP1). JLD treatment significantly improved obesity in db/db mice. Biochemical results showed that JLD reduced blood glucose (GLU), triglyceride (TG), and low-density lipoprotein cholesterol (LDL) levels as well as liver aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in mice. Hematoxylin and eosin staining (H&E) showed that JLD reduced hepatocyte ballooning changes in the liver. Immunofluorescence showed that JLD increased the expression of the thermogenic protein, UCP1, in the beige adipose tissue of mice. JLD also increased the expression of UCP1 and inhibited the expression of miR-27a in X9 cells. Molecular docking results showed that epmedin B, epmedin C, icariin, puerarin, and salvianolic acid B had potential activation effects on UCP1. The results suggest that JLD may activate beige adipocytes by inhibiting miR-27a expression, thereby promoting thermogenesis in beige adipocytes. This study provides a new pharmacological basis for the clinical use of JLD.

Targeting ERK3/MK5 complex for treatment of obesity and diabetes

Kinases represent one of the largest druggable families of proteins. Importantly, many kinases are aberrantly activated/de-activated in multiple organs during obesity, which contributes to the development of diabetes and associated diseases. Previous results indicate that the complex between Extracellular-regulated kinase 3 (ERK3) and Mitogen-Activated Protein Kinase (MAPK)-activated protein kinase 5 (MK5) suppresses energy dissipation and promotes fatty acids (FAs) output in adipose tissue and, therefore promotes obesity and diabetes. However, the therapeutic potential of targeting this complex at the systemic level has not been fully explored. Here we applied a translational approach to target the ERK3/MK5 complex in mice. Importantly, deletion of ERK3 in the whole body or administration of MK5-specific inhibitor protects against obesity and promotes insulin sensitivity. Finally, we show that the expression of ERK3 and MK5 correlates with the degree of obesity and that ERK3/MK5 complex regulates energy dissipation in human adipocytes. Altogether, we demonstrate that ERK3/MK5 complex can be targeted in vivo to preserve metabolic health and combat obesity and diabetes.

Mitophagy Mediates the Beige to White Transition of Human Primary Subcutaneous Adipocytes Ex Vivo

Brown and beige adipocytes have multilocular lipid droplets, express uncoupling protein (UCP) 1, and promote energy expenditure. In rodents, when the stimulus of browning subsides, parkin-dependent mitophagy is activated and dormant beige adipocytes persist. In humans, however, the molecular events during the beige to white transition have not been studied in detail. In this study, human primary subcutaneous abdominal preadipocytes were differentiated to beige for 14 days, then either the beige culture conditions were applied for an additional 14 days or it was replaced by a white medium. Control white adipocytes were differentiated by their specific cocktail for 28 days. Peroxisome proliferator-activated receptor γ-driven beige differentiation resulted in increased mitochondrial biogenesis, UCP1 expression, fragmentation, and respiration as compared to white. Morphology, UCP1 content, mitochondrial fragmentation, and basal respiration of the adipocytes that underwent transition, along with the induction of mitophagy, were similar to control white adipocytes. However, white converted beige adipocytes had a stronger responsiveness to dibutyril-cAMP, which mimics adrenergic stimulus, than the control white ones. Gene expression patterns showed that the removal of mitochondria in transitioning adipocytes may involve both parkin-dependent and -independent pathways. Preventing the entry of beige adipocytes into white transition can be a feasible way to maintain elevated thermogenesis and energy expenditure.

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.

Irisin Stimulates the Release of CXCL1 From Differentiating Human Subcutaneous and Deep-Neck Derived Adipocytes via Upregulation of NFκB Pathway

Thermogenic brown and beige adipocytes might open up new strategies in combating obesity. Recent studies in rodents and humans have indicated that these adipocytes release cytokines, termed "batokines". Irisin was discovered as a polypeptide regulator of beige adipocytes released by myocytes, primarily during exercise. We performed global RNA sequencing on adipocytes derived from human subcutaneous and deep-neck precursors, which were differentiated in the presence or absence of irisin. Irisin did not exert an effect on the expression of characteristic thermogenic genes, while upregulated genes belonging to various cytokine signaling pathways. Out of the several upregulated cytokines, CXCL1, the highest upregulated, was released throughout the entire differentiation period, and predominantly by differentiated adipocytes. Deep-neck area tissue biopsies also showed a significant release of CXCL1 during 24 h irisin treatment. Gene expression data indicated upregulation of the NFκB pathway upon irisin treatment, which was validated by an increase of p50 and decrease of IκBα protein level, respectively. Continuous blocking of the NFκB pathway, using a cell permeable inhibitor of NFκB nuclear translocation, significantly reduced CXCL1 release. The released CXCL1 exerted a positive effect on the adhesion of endothelial cells. Together, our findings demonstrate that irisin stimulates the release of a novel adipokine, CXCL1, via upregulation of NFκB pathway in neck area derived adipocytes, which might play an important role in improving tissue vascularization.

BMP7 Increases UCP1-Dependent and Independent Thermogenesis with a Unique Gene Expression Program in Human Neck Area Derived Adipocytes

White adipocytes contribute to energy storage, accumulating lipid droplets, whereas brown and beige adipocytes mainly function in dissipating energy as heat primarily via the action of uncoupling protein 1 (UCP1). Bone morphogenic protein 7 (BMP7) was shown to drive brown adipocyte differentiation in murine interscapular adipose tissue. Here, we performed global RNA-sequencing and functional assays on adipocytes obtained from subcutaneous (SC) and deep-neck (DN) depots of human neck and differentiated with or without BMP7. We found that BMP7 did not influence differentiation but upregulated browning markers, including UCP1 mRNA and protein in SC and DN derived adipocytes. BMP7 also enhanced mitochondrial DNA content, levels of oxidative phosphorylation complex subunits, along with PGC1α and p-CREB upregulation, and fragmentation of mitochondria. Furthermore, both UCP1-dependent proton leak and UCP1-independent, creatine-driven substrate cycle coupled thermogenesis were augmented upon BMP7 addition. The gene expression analysis also shed light on the possible role of genes unrelated to thermogenesis thus far, including ACAN, CRYAB, and ID1, which were among the highest upregulated ones by BMP7 treatment in both types of adipocytes. Together, our study shows that BMP7 strongly upregulates thermogenesis in human neck area derived adipocytes, along with genes, which might have a supporting role in energy expenditure.

ASC-1 transporter-dependent amino acid uptake is required for the efficient thermogenic response of human adipocytes to adrenergic stimulation

Brown and beige adipocytes dissipate energy by uncoupling protein 1 (UCP1)-dependent and UCP1-independent thermogenesis, which may be utilized to develop treatments against obesity. We have found that mRNA and protein expression of the alanine/serine/cysteine transporter-1 (ASC-1) was induced during adipocyte differentiation of human brown-prone deep neck and beige-competent subcutaneous neck progenitors, and SGBS preadipocytes. cAMP stimulation of differentiated adipocytes led to elevated uptake of serine, cysteine, and glycine, in parallel with increased oxygen consumption, augmented UCP1-dependent proton leak, increased creatine-driven substrate cycle-coupled respiration, and upregulation of thermogenesis marker genes and several respiratory complex subunits; these outcomes were impeded in the presence of the specific ASC-1 inhibitor, BMS-466442. Our data suggest that ASC-1-dependent consumption of serine, cysteine, and glycine is required for efficient thermogenic stimulation of human adipocytes.

Irisin induces white adipose tissue browning in mice as assessed by magnetic resonance imaging

This study aimed to track and evaluate the effect of low-dose irisin on the browning of white adipose tissue (WAT) in mice using magnetic resonance imaging (MRI) noninvasively in vivo. Mature white adipocytes extracted from mice were cultured, induced and characterized before being treated by irisin. The volume and fat fraction of WAT were quantified using MRI in normal chow diet and high fat mice after injection of irisin. The browning of cultured white adipocytes and WAT in mice were validated by immunohistochemistry and western blotting for uncoupling protein 1 (UCP1) and deiodinase type II (DIO2). The serum indexes were examined with high fat diet after irisin intervention. UCP1 and DIO2 in adipocytes showed increases responding to the irisin treatment. The size of white adipocytes in mice receiving irisin intervention was reduced. MRI measured volumes and fat fraction of WAT were significantly lower after Irisin treatment. Blood glucose and cholesterol levels were reduced in high fat diet mice after irisin treatment. Irisin intervention exerted browning of WAT, resulting reduction of volume and fat fraction of WAT as measured by MRI. Furthermore, it improved the condition of mice with diet-induced obesity and related metabolic disorders.

Natural Extracts to Augment Energy Expenditure as a Complementary Approach to Tackle Obesity and Associated Metabolic Alterations

Obesity is the epidemic of the 21st century. In developing countries, the prevalence of obesity continues to rise, and obesity is occurring at younger ages. Obesity and associated metabolic stress disrupt the whole-body physiology. Adipocytes are critical components of the systemic metabolic control, functioning as an endocrine organ. The enlarged adipocytes during obesity recruit macrophages promoting chronic inflammation and insulin resistance. Together with the genetic susceptibility (single nucleotide polymorphisms, SNP) and metabolic alterations at the molecular level, it has been highlighted that key modifiable risk factors, such as those related to lifestyle, contribute to the development of obesity. In this scenario, urgent therapeutic options are needed, including not only pharmacotherapy but also nutrients, bioactive compounds, and natural extracts to reverse the metabolic alterations associated with obesity. Herein, we first summarize the main targetable processes to tackle obesity, including activation of thermogenesis in brown adipose tissue (BAT) and in white adipose tissue (WAT-browning), and the promotion of energy expenditure and/or fatty acid oxidation (FAO) in muscles. Then, we perform a screening of 20 natural extracts (EFSA approved) to determine their potential in the activation of FAO and/or thermogenesis, as well as the increase in respiratory capacity. By means of innovative technologies, such as the study of their effects on cell bioenergetics (Seahorse bioanalyzer), we end up with the selection of four extracts with potential application to ameliorate the deleterious effects of obesity and the chronic associated inflammation.

In vitro and ex vivo models of adipocytes

Adipocytes are specialized cells with pleiotropic roles in physiology and pathology. Several types of fat cells with distinct metabolic properties coexist in various anatomically defined fat depots in mammals. White, beige, and brown adipocytes differ in their handling of lipids and thermogenic capacity, promoting differences in size and morphology. Moreover, adipocytes release lipids and proteins with paracrine and endocrine functions. The intrinsic properties of adipocytes pose specific challenges in culture. Mature adipocytes float in suspension culture due to high triacylglycerol content and are fragile. Moreover, a fully differentiated state, notably acquirement of the unilocular lipid droplet of white adipocyte, has so far not been reached in two-dimensional culture. Cultures of mouse and human-differentiated preadipocyte cell lines and primary cells have been established to mimic white, beige, and brown adipocytes. Here, we survey various models of differentiated preadipocyte cells and primary mature adipocyte survival describing main characteristics, culture conditions, advantages, and limitations. An important development is the advent of three-dimensional culture, notably of adipose spheroids that recapitulate in vivo adipocyte function and morphology in fat depots. Challenges for the future include isolation and culture of adipose-derived stem cells from different anatomic location in animal models and humans differing in sex, age, fat mass, and pathophysiological conditions. Further understanding of fat cell physiology and dysfunction will be achieved through genetic manipulation, notably CRISPR-mediated gene editing. Capturing adipocyte heterogeneity at the single-cell level within a single fat depot will be key to understanding diversities in cardiometabolic parameters among lean and obese individuals.

D-Chiro-Inositol Regulates Insulin Signaling in Human Adipocytes

D-Chiro-Inositol (D-Chiro-Ins) is a secondary messenger in the insulin signaling pathway. D-Chiro-Ins modulates insulin secretion, the mitochondrial respiratory chain, and glycogen storage. Due to these actions D-Chiro-Ins has been proposed to correct defective insulin function in a variety of conditions characterized by metabolic dysfunction, such as polycystic ovary syndrome (PCOS), obesity, gestational diabetes and fat accumulation at menopause. Since it is unclear whether D-Chiro-Ins directly acts on adipocytes, we aimed to study D-Chiro-Ins's actions on adipocyte viability, proliferation, differentiation, and insulin-related protein expression using a human adipocyte cell line derived from Simpson-Golabi-Behmel Syndrome (SGBS) which fully differentiates to mature adipocytes. Throughout differentiation, cells were treated with D-Chiro-Ins, 17β-estradiol (E2) or Insulin. Cell viability and proliferation were not affected by D-Chiro-Ins, then D-Chiro-Ins promoted cell differentiation only during the final days of the process, while E2 enhanced it from the first phases. D-Chiro-Ins stimulated lipid storage and the production of big lipid droplets, thus reducing the content of free fatty acids. We also found that D-Chiro-Ins, either alone or in combination with insulin and E2 increased the expression and activation of insulin receptor substrate-1 (IRS1) and glucose transporter type 4 (GLUT4). In conclusion, this work shows that D-Chiro-Ins plays a direct role in the differentiation and in the function of human adipocytes, where it synergizes with insulin and estrogen through the recruitment of signal transduction pathways involved in lipid and glucose storage. These findings give clear insights to better understand the actions of D-Chiro-Ins on fat metabolism in women in physiology and in a variety of diseases.

Potential Functions of the BMP Family in Bone, Obesity, and Glucose Metabolism

Characteristic bone metabolism was observed in obesity and diabetes with controversial conclusions. Type 2 diabetes (T2DM) and obesity may manifest increased bone mineral density. Also, obesity is more easily to occur in T2DM. Therefore, we infer that some factors may be linked to bone and obesity as well as glucose metabolism, which regulate all of them. Bone morphogenetic proteins (BMPs), belonging to the transforming growth factor- (TGF-) beta superfamily, regulate a diverse array of cellular functions during development and in the adult. More and more studies revealed that there exists a relationship between bone metabolism and obesity as well as glucose metabolism. BMP2, BMP4, BMP6, BMP7, and BMP9 have been shown to affect the pathophysiological process of obesity and glucose metabolism beyond bone metabolism. They may exert functions in adipogenesis and differentiation as well as insulin resistance. In the review, we summarize the literature on these BMPs and their association with metabolic diseases including obesity and diabetes.

Modeling Adipogenesis: Current and Future Perspective

Adipose tissue is contemplated as a dynamic organ that plays key roles in the human body. Adipogenesis is the process by which adipocytes develop from adipose-derived stem cells to form the adipose tissue. Adipose-derived stem cells’ differentiation serves well beyond the simple goal of producing new adipocytes. Indeed, with the current immense biotechnological advances, the most critical role of adipose-derived stem cells remains their tremendous potential in the field of regenerative medicine. This review focuses on examining the physiological importance of adipogenesis, the current approaches that are employed to model this tightly controlled phenomenon, and the crucial role of adipogenesis in elucidating the pathophysiology and potential treatment modalities of human diseases. The future of adipogenesis is centered around its crucial role in regenerative and personalized medicine.

Irisin modulates genes associated with severe coronavirus disease (COVID-19) outcome in human subcutaneous adipocytes cell culture

Obesity patients are more susceptible to develop COVID-19 severe outcome due to the role of angiotensin-converting enzyme 2 (ACE2) in the viral infection. ACE2 is regulated in the human cells by different genes associated with increased (TLR3, HAT1, HDAC2, KDM5B, SIRT1, RAB1A, FURIN and ADAM10) or decreased (TRIB3) virus replication. RNA-seq data revealed 14857 genes expressed in human subcutaneous adipocytes, including genes mentioned above. Irisin treatment increased by 3-fold the levels of TRIB3 transcript and decreased the levels of other genes. The decrease in FURIN and ADAM10 expression enriched diverse biological processes, including extracellular structure organization. Our results, in human subcutaneous adipocytes cell culture, indicate a positive effect of irisin on the expression of multiple genes related to viral infection by SARS-CoV-2; furthermore, translatable for other tissues and organs targeted by the novel coronavirus and present, thus, promising approaches for the treatment of COVID-19 infection as therapeutic strategy to decrease ACE2 regulatory genes.

Thermogenic Activation Downregulates High Mitophagy Rate in Human Masked and Mature Beige Adipocytes

Thermogenic brown and beige adipocytes oxidize metabolic substrates producing heat, mainly by the mitochondrial uncoupling protein UCP1, and can thus counteract obesity. Masked beige adipocytes possess white adipocyte-like morphology, but can be made thermogenic by adrenergic stimuli. We investigated the regulation of mitophagy upon thermogenic activation of human masked and mature beige adipocytes. Human primary abdominal subcutaneous adipose-derived stromal cells (hASCs) and Simpson-Golabi-Behmel syndrome (SGBS) preadipocytes were differentiated to white and beige adipocytes, then their cAMP-induced thermogenic potential was assessed by detecting increased expressions of UCP1, mitochondrial DNA content and respiratory chain complex subunits. cAMP increased the thermogenic potential of white adipocytes similarly to beige ones, indicating the presence of a masked beige population. In unstimulated conditions, a high autophagic flux and mitophagy rates (demonstrated by LC3 punctae and TOM20 co-immunostaining) were observed in white adipocytes, while these were lower in beige adipocytes. Silencing and gene expression experiments showed that the ongoing mitophagy was Parkin-independent. cAMP treatment led to the downregulation of mitophagy through PKA in both types of adipocytes, resulting in more fragmented mitochondria and increased UCP1 levels. Our data indicates that mitophagy is repressed upon encountering a short-term adrenergic stimulus, as a fast regulatory mechanism to provide high mitochondrial content for thermogenesis.

The colorful versatility of adipocytes: white-to-brown transdifferentiation and its therapeutic potential in humans

Brown and brite adipocytes contribute to energy expenditure through nonshivering thermogenesis. Though these cell types are thought to arise primarily from the de novo differentiation of precursor cells, their abundance is also controlled through the transdifferentiation of mature white adipocytes. Here, we review recent advances in our understanding of the regulation of white-to-brown transdifferentiation, as well as the conversion of brown and brite adipocytes to dormant, white-like fat cells. Converting mature white adipocytes into brite cells or reactivating dormant brown and brite adipocytes has emerged as a strategy to ameliorate human metabolic disorders. We analyze the evidence of learning from mice and how they translate to humans to ultimately scrutinize the relevance of this concept. Moreover, we estimate that converting a small percentage of existing white fat mass in obese subjects into active brite adipocytes could be sufficient to achieve meaningful benefits in metabolism. In conclusion, novel browning agents have to be identified before adipocyte transdifferentiation can be realized as a safe and efficacious therapy.

Lipidomic Phenotyping Reveals Extensive Lipid Remodeling during Adipogenesis in Human Adipocytes

Differentiation of preadipocytes into mature adipocytes is a highly complex cellular process. At lipidome level, the adipogenesis remains poorly characterized. To investigate the lipidomic changes during human adipogenesis, we used the Lipidyzer^TM assay, which quantified 743 lipid species from 11 classes. The undifferentiated human SGBS cell strain showed a heterogeneous lipid class composition with the most abundant classes, phosphatidylethanolamines (PE), phosphatidylcholines (PC), and sphingomyelins (SM). The differentiation process was accompanied by increased ceramide concentrations. After completion of differentiation around day 4, massive lipid remodeling occurred during maturation, characterized by substantial synthesis of diacylglycerols (DAG), lysophosphatidylethanolamines (LPE), PC, PE, SM, and triacylglycerols (TAG). Lipid species composition became more homogeneous during differentiation to highly concentrated saturated and monounsaturated long-chain fatty acids (LCFA), with the four most abundant being C16:0, C16:1, C18:0, and C18:1. Simultaneously, the amount of polyunsaturated and very long-chain fatty acids (VLCFA) markedly decreased. High negative correlation coefficients between PE and PC species containing VLCFA and TAG species as well as between ceramides and SM imply that PE, PC, and ceramides might have served as additional sources for TAG and SM synthesis, respectively. These results highlight the enormous remodeling at the lipid level over several lipid classes during adipogenesis.

FTO Intronic SNP Strongly Influences Human Neck Adipocyte Browning Determined by Tissue and PPARγ Specific Regulation: A Transcriptome Analysis

Brown adipocytes, abundant in deep-neck (DN) area in humans, are thermogenic with anti-obesity potential. FTO pro-obesity rs1421085 T-to-C single-nucleotide polymorphism (SNP) shifts differentiation program towards white adipocytes in subcutaneous fat. Human adipose-derived stromal cells were obtained from subcutaneous neck (SC) and DN fat of nine donors, of which 3-3 carried risk-free (T/T), heterozygous or obesity-risk (C/C) FTO genotypes. They were differentiated to white and brown (long-term Peroxisome proliferator-activated receptor gamma (PPARγ) stimulation) adipocytes; then, global RNA sequencing was performed and differentially expressed genes (DEGs) were compared. DN and SC progenitors had similar adipocyte differentiation potential but differed in DEGs. DN adipocytes displayed higher browning features according to ProFAT or BATLAS scores and characteristic DEG patterns revealing associated pathways which were highly expressed (thermogenesis, interferon, cytokine, and retinoic acid, with UCP1 and BMP4 as prominent network stabilizers) or downregulated (particularly extracellular matrix remodeling) compared to SC ones. Part of DEGs in either DN or SC browning was PPARγ-dependent. Presence of the FTO obesity-risk allele suppressed the expression of mitochondrial and thermogenesis genes with a striking resemblance between affected pathways and those appearing in ProFAT and BATLAS, underlining the importance of metabolic and mitochondrial pathways in thermogenesis. Among overlapping regulatory influences that determine browning and thermogenic potential of neck adipocytes, FTO genetic background has a thus far not recognized prominence.