Differentiation-induced gene expression in 3T3-L1 preadipocytes: CCAAT/enhancer binding protein interacts with and activates the promoters of two adipocyte-specific genes

Molecular targets for management of diabetes: Remodelling of white adipose to brown adipose tissue

Diabetes mellitus is a disorder characterised metabolic dysfunction that results in elevated glucose level in the bloodstream. Diabetes is of two types, type1 and type 2 diabetes. Obesity is considered as one of the major reasons intended for incidence of diabetes hence it turns out to be essential to study about the adipose tissue which is responsible for fat storage in body. Adipose tissues play significant role in maintaining the balance between energy stabilization and homeostasis. The three forms of adipose tissue are - White adipose tissue (WAT), Brown adipose tissue (BAT) and Beige adipose tissue (intermediate form). The amount of BAT gets reduced, and WAT starts to increase with the age. WAT when exposed to certain stimuli gets converted to BAT by the help of certain transcriptional regulators. The browning of WAT has been a matter of study to treat the metabolic disorders and to initiate the expenditure of energy. The three main regulators responsible for the browning of WAT are PRDM16, PPARγ and PGC-1α via various cellular and molecular mechanism. Presented review article includes the detailed elaborative aspect of genes and proteins involved in conversion of WAT to BAT.

An intronic enhancer of Cebpa regulates adipocyte differentiation and adipose tissue development via long-range loop formation

Cebpa is a master transcription factor gene for adipogenesis. However, the mechanisms of enhancer-promoter chromatin interactions controlling Cebpa transcriptional regulation during adipogenic differentiation remain largely unknown. To reveal how the three-dimensional structure of Cebpa changes during adipogenesis, we generated high-resolution chromatin interactions of Cebpa in 3T3-L1 preadipocytes and 3T3-L1 adipocytes using circularized chromosome conformation capture sequencing (4C-seq). We revealed dramatic changes in chromatin interactions and chromatin status at interaction sites during adipogenic differentiation. Based on this, we identified five active enhancers of Cebpa in 3T3-L1 adipocytes through epigenomic data and luciferase reporter assays. Next, epigenetic repression of Cebpa-L1-AD-En2 or -En3 by the dCas9-KRAB system significantly down-regulated Cebpa expression and inhibited adipocyte differentiation. Furthermore, experimental depletion of cohesin decreased the interaction intensity between Cebpa-L1-AD-En2 and the Cebpa promoter and down-regulated Cebpa expression, indicating that long-range chromatin loop formation was mediated by cohesin. Two transcription factors, RXRA and PPARG, synergistically regulate the activity of Cebpa-L1-AD-En2. To test whether Cebpa-L1-AD-En2 plays a role in adipose tissue development, we injected dCas9-KRAB-En2 lentivirus into the inguinal white adipose tissue (iWAT) of mice to suppress the activity of Cebpa-L1-AD-En2. Repression of Cebpa-L1-AD-En2 significantly decreased Cebpa expression and adipocyte size, altered iWAT transcriptome, and affected iWAT development. We identified functional enhancers regulating Cebpa expression and clarified the crucial roles of Cebpa-L1-AD-En2 and Cebpa promoter interaction in adipocyte differentiation and adipose tissue development.

Structural basis for specific DNA sequence recognition by the transcription factor NFIL3

The CCAAT/enhancer-binding proteins (C/EBPs) constitute a family of pivotal transcription factors involved in tissue development, cellular function, proliferation, and differentiation. NFIL3, as one of them, plays an important role in regulating immune cell differentiation, circadian clock system, and neural regeneration, yet its specific DNA recognition mechanism remains enigmatic. In this study, we showed by the ITC binding experiments that NFIL3 prefers to bind to the TTACGTAA DNA motif. Our structural studies revealed that the α-helical NFIL3 bZIP domain dimerizes through its leucine zipper region, and binds to DNA via its basic region. The two basic regions of the NFIL3 bZIP dimer were pushed apart upon binding to DNA, facilitating the snug accommodation of the two basic regions within the major grooves of the DNA. Remarkably, our binding and structural data also revealed that both NFIL3 and C/EBPα/β demonstrate a shared preference for the TTACGTAA sequence. Furthermore, our study revealed that disease-associated mutations within the NFIL3 bZIP domain result in either reduction or complete disruption of its DNA binding ability. These discoveries not only provide valuable insights into the DNA binding mechanisms of NFIL3 but also elucidate the causal role of NFIL3 mutations in disease pathogenesis.

TET2 is recruited by CREB to promote Cebpb, Cebpa, and Pparg transcription by facilitating hydroxymethylation during adipocyte differentiation

Ten-eleven translocation proteins (TETs) are dioxygenases that convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), an important epigenetic mark that regulates gene expression during development and differentiation. Here, we found that the TET2 expression was positively associated with adipogenesis. Further, in vitro and in vivo experiments showed that TET2 deficiency blocked adipogenesis by inhibiting the expression of the key transcription factors CCAAT/enhancer-binding protein beta (C/EBPβ), C/EBPα and peroxisome proliferator-activated receptor gamma (PPARγ). In addition, TET2 promoted 5hmC on the CpG islands (CGIs) of Cebpb, Cebpa and Pparg at the initial time point of their transcription, which requires the cAMP-responsive element-binding protein (CREB). At last, specific knockout of Tet2 in preadipocytes enabled mice to resist obesity and attenuated the obesity-associated insulin resistance. Together, TET2 is recruited by CREB to promote the expression of Cebpb, Cebpa and Pparg via 5hmC during adipogenesis and may be a potential therapeutic target for obesity and insulin resistance.

C/EBPα Confers Dependence to Fatty Acid Anabolic Pathways and Vulnerability to Lipid Oxidative Stress-Induced Ferroptosis in FLT3-Mutant Leukemia

Although transcription factor CCAAT-enhancer binding protein α (C/EBPα) is critical for normal and leukemic differentiation, its role in cell and metabolic homeostasis is largely unknown in cancer. Here, multiomics analyses uncovered a coordinated activation of C/EBPα and Fms-like tyrosine kinase 3 (FLT3) that increased lipid anabolism in vivo and in patients with FLT3-mutant acute myeloid leukemia (AML). Mechanistically, C/EBPα regulated the fatty acid synthase (FASN)-stearoyl-CoA desaturase (SCD) axis to promote fatty acid (FA) biosynthesis and desaturation. We further demonstrated that FLT3 or C/EBPα inactivation decreased monounsaturated FA incorporation to membrane phospholipids through SCD downregulation. Consequently, SCD inhibition enhanced susceptibility to lipid redox stress that was exploited by combining FLT3 and glutathione peroxidase 4 inhibition to trigger lipid oxidative stress, enhancing ferroptotic death of FLT3-mutant AML cells. Altogether, our study reveals a C/EBPα function in lipid homeostasis and adaptation to redox stress, and a previously unreported vulnerability of FLT3-mutant AML to ferroptosis with promising therapeutic application.

SIGNIFICANCE

FLT3 mutations are found in 30% of AML cases and are actionable by tyrosine kinase inhibitors. Here, we discovered that C/EBPα regulates FA biosynthesis and protection from lipid redox stress downstream mutant-FLT3 signaling, which confers a vulnerability to ferroptosis upon FLT3 inhibition with therapeutic potential in AML. This article is highlighted in the In This Issue feature, p. 1501.

Single-cell transcriptome dataset of human and mouse in vitro adipogenesis models

Adipogenesis is a process in which fat-specific progenitor cells (preadipocytes) differentiate into adipocytes that carry out the key metabolic functions of the adipose tissue, including glucose uptake, energy storage, and adipokine secretion. Several cell lines are routinely used to study the molecular regulation of adipogenesis, in particular the immortalized mouse 3T3-L1 line and the primary human Simpson-Golabi-Behmel syndrome (SGBS) line. However, the cell-to-cell variability of transcriptional changes prior to and during adipogenesis in these models is not well understood. Here, we present a single-cell RNA-Sequencing (scRNA-Seq) dataset collected before and during adipogenic differentiation of 3T3-L1 and SGBS cells. To minimize the effects of experimental variation, we mixed 3T3-L1 and SGBS cells and used computational analysis to demultiplex transcriptomes of mouse and human cells. In both models, adipogenesis results in the appearance of three cell clusters, corresponding to preadipocytes, early and mature adipocytes. These data provide a groundwork for comparative studies on these widely used in vitro models of human and mouse adipogenesis, and on cell-to-cell variability during this process.

Single-cell transcriptome dataset of human and mouse in vitro adipogenesis models

Adipogenesis is a process in which fat-specific progenitor cells (preadipocytes) differentiate into adipocytes that carry out the key metabolic functions of the adipose tissue, including glucose uptake, energy storage, and adipokine secretion. Several cell lines are routinely used to study the molecular regulation of adipogenesis, in particular the immortalized mouse 3T3-L1 line and the primary human Simpson-Golabi-Behmel syndrome (SGBS) line. However, the cell-to-cell variability of transcriptional changes prior to and during adipogenesis in these models is not well understood. Here, we present a single-cell RNA-Sequencing (scRNA-Seq) dataset collected before and during adipogenic differentiation of 3T3-L1 and SGBS cells. To minimize the effects of experimental variation, we mixed 3T3-L1 and SGBS cells and used computational analysis to demultiplex transcriptomes of mouse and human cells. In both models, adipogenesis results in the appearance of three cell clusters, corresponding to preadipocytes, early and mature adipocytes. These data provide a groundwork for comparative studies on human and mouse adipogenesis, as well as on cell-to-cell variability in gene expression during this process.

A Wrong Fate Decision in Adipose Stem Cells upon Obesity

Progress has been made in identifying stem cell aging as a pathological manifestation of a variety of diseases, including obesity. Adipose stem cells (ASCs) play a core role in adipocyte turnover, which maintains tissue homeostasis. Given aberrant lineage determination as a feature of stem cell aging, failure in adipogenesis is a culprit of adipose hypertrophy, resulting in adiposopathy and related complications. In this review, we elucidate how ASC fails in entering adipogenic lineage, with a specific focus on extracellular signaling pathways, epigenetic drift, metabolic reprogramming, and mechanical stretch. Nonetheless, such detrimental alternations can be reversed by guiding ASCs towards adipogenesis. Considering the pathological role of ASC aging in obesity, targeting adipogenesis as an anti-obesity treatment will be a key area of future research, and a strategy to rejuvenate tissue stem cell will be capable of alleviating metabolic syndrome.

Identification of DDX5 as an indispensable activator of the glucocorticoid receptor in adipocyte differentiation

The expression of CCAAT/enhancer-binding protein (C/EBP) family members and peroxisome proliferator-activated receptor γ (PPAR γ) is essential for the differentiation of pre-adipocyte 3T3-L1 cells into mature adipocytes induced by a combined stimulation with dexamethasone, 3-isobutyl-1-methylxanthine and insulin (DMI). We herein demonstrated that the RNA helicase DDX5, the expression of which was induced by DMI, played an important role in the adipocyte differentiation of 3T3-L1 cells. The DMI-induced accumulation of lipid droplets and expression of adipocyte markers in 3T3-L1 cells were significantly inhibited by the knockdown of DDX5. The knockdown of DDX5 interfered with the expressional induction of C/EBPδ, which was the first to be induced in the transcription factor cascade, and inhibited the subsequent expression of the other transcription factors, C/EBPβ, PPARγ and C/EBPα. DDX5 interacted with the glucocorticoid receptor (GR), which induced the expression of C/EBPδ. The knockdown of DDX5 failed to induce the nuclear translocation of GR, suggesting the essential role of DDX5 in the early stage of adipocyte differentiation. Furthermore, the reconstitution of DDX5, but not the DDX5 mutant (K144N) lacking RNA helicase activity, restored DMI-induced GR activation and adipocyte differentiation in 3T3-L1 cells in which DDX5 was knocked down, confirming that the RNA helicase activity of DDX5 is essential for adipogenesis. Collectively, these results revealed for the first time that DDX5 is necessary for GR activation and plays an essential role in early adipocyte differentiation.

Early enforcement of cell identity by a functional component of the terminally differentiated state

How progenitor cells can attain a distinct differentiated cell identity is a challenging problem given the fluctuating signaling environment in which cells exist and that critical transcription factors are often not unique to a differentiation process. Here, we test the hypothesis that a unique differentiated cell identity can result from a core component of the differentiated state doubling up as a signaling protein that also drives differentiation. Using live single-cell imaging in the adipocyte differentiation system, we show that progenitor fat cells (preadipocytes) can only commit to terminally differentiate after up-regulating FABP4, a lipid buffer that is highly enriched in mature adipocytes. Upon induction of adipogenesis in mouse preadipocyte cells, we show that after a long delay, cells first abruptly start to engage a positive feedback between CEBPA and PPARG before then engaging, after a second delay, a positive feedback between FABP4 and PPARG. These sequential positive feedbacks both need to engage in order to drive PPARG levels past the threshold for irreversible differentiation. In the last step before commitment, PPARG transcriptionally increases FABP4 expression while fatty acid-loaded FABP4 increases PPARG activity. Together, our study suggests a control principle for robust cell identity whereby a core component of the differentiated state also promotes differentiation from its own progenitor state.

The anti-obesity effect of mulberry leaf (Mori Folium) extracts was increased by bioconversion with Pectinex

Mulberry leaf (Mori Folium) extract (MLE) is known to have anti-obesity effects. In this study, the enhanced effects of MLE after bioconversion treatment using Pectinex (BMLE) on obesity were explored, and the underlying mechanisms were investigated using the active components, neochlorogenic acid (5-CQA) and cryptochlorogenic acid (4-CQA), whose amounts were increased by bioconversion of MLE. Both MLE and BMLE inhibited lipid accumulation in 3T3-L1 adipocytes without cytotoxicity and suppressed the expression of CCAAT/enhancer-binding protein alpha (C/EBPα). In addition, MLE and BMLE decreased high-fat diet-induced adipose tissue mass expansion. Notably, BMLE significantly increased antiadipogenic and anti-obesity effects compared to MLE in vitro and in vivo. The active ingredients increased by bioconversion, 5-CQA and 4-CQA, inhibited the protein levels of C/EBPα and the mRNA levels of stearoyl-CoA desaturase 1 (Scd1). These findings provide new insights into the therapeutic possibility of using bioconversion of MLE, by which upregulation of 5-CQA and 4-CQA potently inhibits adipogenesis.

Exosome-mediated delivery of SCD-1 siRNA promoted the death of anaplastic thyroid carcinoma cells via regulating ROS level

PURPOSE

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive cancers in the world. Stearoyl-CoA desaturase-1 (SCD-1) is one of major enzymes in the de novo synthesis of fatty acids and is related to cancer aggressiveness and poor patient prognosis. The study aimed to construct exosomes loaded SCD-1 interference, investigate its effects and mechanisms on the cell proliferation and apoptosis of ATC cells.

METHODS

The expressions of SCD-1 in normal thyroid cell line and ATC cell lines were determined by qRT-PCR and western blotting, respectively. Exosomes were prepared and purification then loaded with SCD-1 siRNA by electroporation and observed by transmission electron microscopy. Higher SCD-1 mRNA and protein levels were found in ATC cell lines compared than normal thyroid cell line (P < 0.05), and both Hth-7 and FRO cells could uptake PKH67-labeled exosomes. The effects of exosomes loaded SCD-1 siRNA on ATC cells were measured by CCK8 assay and apoptosis detection kit.

RESULTS

When compared with control group, the cell viability significantly decreased in both two ATC cell lines taken up exosomes loaded SCD-1 siRNA (P < 0.001), and apoptotic and necrotic cells obviously increased (P < 0.05). In order to explore the mechanism of exosomes loaded SCD-1 on ATC, the ROS level was detected by fluorescence reagent. It was found that exosomes loaded SCD-1 siRNA significantly increased intracellular ROS level of ATC cells (P < 0.05).

CONCLUSIONS

Exosomes loaded SCD-1 siRNA inhibited ATC cellular proliferation and promoted cellular apoptosis, and the mechanisms involved maybe the regulation of fatty acids metabolism and ROS level. Our study provides a promising therapeutic strategy for ATC.

Unveiling the Role of the Fatty Acid Binding Protein 4 in the Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD), the main cause of chronic liver disease worldwide, is a progressive disease ranging from fatty liver to steatohepatitis (metabolic-associated steatohepatitis; MASH). Nevertheless, it remains underdiagnosed due to the lack of effective non-invasive methods for its diagnosis and staging. Although MAFLD has been found in lean individuals, it is closely associated with obesity-related conditions. Adipose tissue is the main source of liver triglycerides and adipocytes act as endocrine organs releasing a large number of adipokines and pro-inflammatory mediators involved in MAFLD progression into bloodstream. Among the adipocyte-derived molecules, fatty acid binding protein 4 (FABP4) has been recently associated with fatty liver and additional features of advanced stages of MAFLD. Additionally, emerging data from preclinical studies propose FABP4 as a causal actor involved in the disease progression, rather than a mere biomarker for the disease. Therefore, the FABP4 regulation could be considered as a potential therapeutic strategy to MAFLD. Here, we review the current knowledge of FABP4 in MAFLD, as well as its potential role as a therapeutic target for this disease.

Adipocyte Biology from the Perspective of In Vivo Research: Review of Key Transcription Factors

Obesity and type 2 diabetes are both significant contributors to the contemporary pandemic of non-communicable diseases. Both disorders are interconnected and associated with the disruption of normal homeostasis in adipose tissue. Consequently, exploring adipose tissue differentiation and homeostasis is important for the treatment and prevention of metabolic disorders. The aim of this work is to review the consecutive steps in the postnatal development of adipocytes, with a special emphasis on in vivo studies. We gave particular attention to well-known transcription factors that had been thoroughly described in vitro, and showed that the in vivo research of adipogenic differentiation can lead to surprising findings.

Adipocyte-specific tribbles pseudokinase 1 regulates plasma adiponectin and plasma lipids in mice

OBJECTIVE

Multiple genome-wide association studies (GWAS) have identified SNPs in the 8q24 locus near TRIB1 that are significantly associated with plasma lipids and other markers of cardiometabolic health, and prior studies have revealed the roles of hepatic and myeloid Trib1 in plasma lipid regulation and atherosclerosis. The same 8q24 SNPs are additionally associated with plasma adiponectin levels in humans, implicating TRIB1 in adipocyte biology. Here, we hypothesize that TRIB1 in adipose tissue regulates plasma adiponectin, lipids, and metabolic health.

METHODS

We investigate the metabolic phenotype of adipocyte-specific Trib1 knockout mice (Trib1_ASKO) fed on chow and high-fat diet (HFD). Through secretomics of adipose tissue explants and RNA-seq of adipocytes and livers from these mice, we further investigate the mechanism of TRIB1 in adipose tissue.

RESULTS

Trib1_ASKO mice have an improved metabolic phenotype with increased plasma adiponectin levels, improved glucose tolerance, and decreased plasma lipids. Trib1_ASKO adipocytes have increased adiponectin production and secretion independent of the known TRIB1 function of regulating proteasomal degradation. RNA-seq analysis of adipocytes and livers from Trib1_ASKO mice indicates that alterations in adipocyte function underlie the observed plasma lipid changes. Adipose tissue explant secretomics further reveals that Trib1_ASKO adipose tissue has decreased ANGPTL4 production, and we demonstrate an accompanying increase in the lipoprotein lipase (LPL) activity that likely underlies the triglyceride phenotype.

CONCLUSIONS

This study shows that adipocyte Trib1 regulates multiple aspects of metabolic health, confirming previously observed genetic associations in humans and shedding light on the further mechanisms by which TRIB1 regulates plasma lipids and metabolic health.

Astragalin mediates the pharmacological effects of Lysimachia candida Lindl on adipogenesis via downregulating PPARG and FKBP51 signaling cascade

Metabolic disturbances in different tissue cells and obesity are caused by excessive calorie intake, and medicinal plants are potential sources of phytochemicals for combating these health problems. This study investigated the role of methanolic extract of the folklore medicinal plant Lysimachia candida (LCM) and its phytochemical, astragalin, in managing obesity in vivo and in vitro. Administration of LCM (200 mg/kg/body weight) daily for 140 days significantly decreased both the body weight gain (15.66%) and blood triglyceride and free fatty acid levels in high-fat-diet-fed male Wistar rats but caused no substantial change in leptin and adiponectin levels. The protein expression of adipogenic transcription factors in visceral adipose tissue was significantly reduced. Further, the 3T3-L1 cell-based assay revealed that the butanol fraction of LCM and its isolated compound, astragalin, exhibited antiadipogenic activity through downregulating adipogenic transcription factors and regulatory proteins. Molecular docking studies were performed to depict the possible binding patterns of astragalin to adipogenesis proteins. Overall, we show the potential antiobesity effects of L. candida and its bioactive compound, astragalin, and suggest clinical studies with LCM and astragalin.

MicroRNA-126b-5p Exacerbates Development of Adipose Tissue and Diet-Induced Obesity

Obesity has become a worldwide epidemic, caused by many factors such as genetic regulatory elements, unhealthy diet, and lack of exercise. MicroRNAs (miRNAs) are non-coding single-stranded RNA classes, which are about 22 nucleotides in length and highly conserved among species. In the last decade, a series of miRNAs were identified as therapeutic targets for obesity. In the present study, we found that miR-126b-5p was associated with adipogenesis. miR-126b-5p overexpression promoted the proliferation of 3T3-L1 preadipocytes by upregulating the expression of proliferation-related genes and downregulating the expression of apoptosis-related genes; the inhibition of miR-126b-5p gave rise to opposite results. Similarly, miR-126b-5p overexpression could promote the differentiation of 3T3-L1 preadipocytes by increasing the expression of lipid deposition genes and triglyceride (TG) and total cholesterol (TC) levels. Moreover, luciferase reporter assay demonstrated that adiponectin receptor 2 (Adipor2) and acyl-CoA dehydrogenase, long chain (ACADL) were the direct target genes of miR-126b-5p. Moreover, overexpression of miR-126b-5p could exacerbate the clinical symptoms of obesity when mice were induced by a high-fat diet, including increased adipose tissue weight, adipocyte volume, and insulin resistance. Interestingly, overexpression of miR-126b-5p in preadipocytes and mice could significantly increase total fatty acid content and change the fatty acid composition of adipose tissue. Taken together, the present study showed that miR-126b-5p promotes lipid deposition in vivo and in vitro, indicating that miR-126b-5p is a potential target for treating obesity.

A novel approach towards obesity: The use of a bacterial product, gassericin A, in 3T3-L1 cells

BACKGROUND AND OBJECTIVE

The problem of obesity and its related complications are adversely affecting human society. We studied the effects of gassericin A, a bacteriocin produced by the intestinal bacteria, on adipocyte differentiation and development.

DESIGN

Gassericin A was purified from Lactobacillus gasseri LA39 and was added to the culture medium of 3T3-L1 cells in two phases: Phase 1, 3T3-L1 cells were incubated with gassericin A while being induced to adipocytes (days 1-7); phase 2, the cells were incubated with the bacteriocin after being induced to adipocytes (days 8-12). The resultant changes in the pattern of expression of some of the important genes involved in adipogenesis were evaluated by RT-qPCR. The viability of cells and their numbers were also studied.

RESULTS

In phase 1 of the study, the levels of transcripts for stearoyl CoA desaturase (SCD-1), zinc finger protein 423 (zfp-423), and glucose transporter 4 (GLUT4) genes were significantly reduced, while that of 422ap2 gene showed a significant increment (p < 0.05). In phase 2, the zfp-423 gene showed a reduction of expression and the 422ap2 gene showed an increase in expression (p < 0.05). The other genes including UCP-1 and TNF-α did not show any significant changes in neither of the groups. Gassericin A did not affect the morphology or viability of the cells, however, the numbers of cells had nearly doubled in the treatment groups.

CONCLUSION

It seems that gassericin A could significantly alter the properties of adipocytes while they are in the process of development and after they have developed.

Correction to: An in vitro mechanistic approach towards understanding the distinct pathways regulating insulin resistance and adipogenesis by apocynin

In the 2021 issue of the Journal of Biosciences in the article titled ''An in vitro mechanistic approach towards understanding the distinct pathways regulating insulin resistance and adipogenesis by apocynin'' by Sai Bharadwaja, Praveen Kumar Issac, Jocelyn Cleta, Rakesh Jeganathan, Sri Snehaa Chandrakumar and Sujatha Sundaresan (https://doi.org/10.1007/s12038-020-00134-2; Vol. 46, Article No. 008), the author Rakesh Jeganaathan's name was incorrectly mentioned as ''Rakesh Jeganathan''. The correct name should read as ''Rakesh Jeganaathan''.

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.

Progesterone receptor membrane associated component 1 enhances obesity progression in mice by facilitating lipid accumulation in adipocytes

Progesterone receptor membrane associated component 1 (PGRMC1) exhibits haem-dependent dimerization on cell membrane and binds to EGF receptor and cytochromes P450 to regulate cancer proliferation and chemoresistance. However, its physiological functions remain unknown. Herein, we demonstrate that PGRMC1 is required for adipogenesis, and its expression is significantly enhanced by insulin or thiazolidine, an agonist for PPARγ. The haem-dimerized PGRMC1 interacts with low-density lipoprotein receptors (VLDL-R and LDL-R) or GLUT4 to regulate their translocation to the plasma membrane, facilitating lipid uptake and accumulation, and de-novo fatty acid synthesis in adipocytes. These events are cancelled by CO through interfering with PGRMC1 dimerization. PGRMC1 expression in mouse adipose tissues is enhanced during obesity induced by a high fat diet. Furthermore, adipose tissue-specific PGRMC1 knockout in mice dramatically suppressed high-fat-diet induced adipocyte hypertrophy. Our results indicate a pivotal role of PGRMC1 in developing obesity through its metabolic regulation of lipids and carbohydrates in adipocytes.

Human Adipose Tissue Derivatives as a Potent Native Biomaterial for Tissue Regenerative Therapies

BACKGROUND

Human adipose tissue is a great source of translatable biomaterials owing to its ease of availability and simple processing. Reusing discardable adipose tissue for tissue regeneration helps in mimicking the exact native microenvironment of tissue. Over the past 10 years, extraction, processing, tuning and fabrication of adipose tissue have grabbed the attention owing to their native therapeutic and regenerative potential. The present work gives the overview of next generation biomaterials derived from human adipose tissue and their development with clinical relevance.

METHODS

Around 300 articles have been reviewed to widen the knowledge on the isolation, characterization techniques and medical applications of human adipose tissue and its derivatives from bench to bedside. The prospective applications of adipose tissue derivatives like autologous fat graft, stromal vascular fraction, stem cells, preadipocyte, adipokines and extracellular matrix, their behavioural mechanism, rational property of providing native bioenvironment, circumventing their translational abilities, recent advances in featuring them clinically have been reviewed extensively to reveal the dormant side of human adipose tissue.

RESULTS

Basic understanding about the molecular and structural aspect of human adipose tissue is necessary to employ it constructively. This review has nailed the productive usage of human adipose tissue, in a stepwise manner from exploring the methods of extracting derivatives, concerns during processing and its formulations to turning them into functional biomaterials. Their performance as functional biomaterials for skin regeneration, wound healing, soft tissue defects, stem cell and other regenerative therapies under in vitro and in vivo conditions emphasizes the translational efficiency of adipose tissue derivatives.

CONCLUSION

In the recent years, research interest has inclination towards constructive tissue engineering and regenerative therapies. Unravelling the maximum utilization of human adipose tissue derivatives paves a way for improving existing tissue regeneration and cellular based therapies and other biomedical applications.

Induction of DEAD Box helicase 5 in early adipogenesis is regulated by Ten-eleven translocation 2

Dead box helicase 5 (DDX5) is an RNA helicase that is has cellular function on RNA splicing and transcriptional regulation. It has been reported to be involved in cell differentiation including adipogenesis. However, it is not clear how DDX5 is regulated during adipogenesis. Our previous report demonstrated that the Ten-eleven translocation methyl-cytosine dioxygenase 2 (TET2) is required for adipogenesis. This study was aimed to investigate DDX5 as a direct target of TET2 upon adipogenic induction of 3T3-L1 preadipocyte. Microarray-based screening of differentially expressed genes upon TET2 knockdown identified genes involved in cell cycle, DNA replication, and ribosome biology as major targets of TET2 in the initial step of adipogenic induction. The Ddx5 gene was identified and validated as the target. TET2-mediated epigenetic regulation of the Ddx5 gene was measured by two independent methods including immunoprecipitation against 5-hydroxymethylcytosine (5hmC) and 5-methylcytosine (5mC) as well as EpiMark 5hmC and 5mC analysis. Ddx5 expression was downregulated upon TET2 knockdown, coincided with a significant decrease of 5hmC at the Ddx5 locus. DDX5 knockdown significantly suppressed adipogenesis, while DDX5 overexpression promoted it. Importantly, DDX5 overexpression, when co-transfected, rescued the process of adipogenesis, which was hindered by TET2 siRNA treatment. The findings suggest TET2-mediated regulation of the Ddx5 gene is required for an initial step of adipogenesis.

Role of the COP1 protein in cancer development and therapy

COP1, an E3 ubiquitin ligase, has been demonstrated to play a vital role in the regulation of cell proliferation, apoptosis and DNA repair. Accumulated evidence has revealed that COP1 is involved in carcinogenesis via targeting its substrates, including p53, c-Jun, ETS, β-catenin, STAT3, MTA1, p27, 14-3-3σ, and C/EBPα, for ubiquitination and degradation. COP1 can play tumor suppressive and oncogenic roles in human malignancies, urging us to summarize the functions of COP1 in tumorigenesis. In this review, we describe the structure of COP1 and its known substrates. Moreover, we dissect the function of COP1 by physiological (mouse models), pathological (human tumor specimens) and biochemical (ubiquitin substrates) Evidence. Furthermore, we discuss COP1 as a potential therapeutic target for cancer therapy.

25-Hydroxycholesterol Inhibits Adipogenic Differentiation of C3H10T1/2 Pluripotent Stromal Cells

Understanding of adipogenesis is important to find remedies for obesity and related disorders. In addition, it is also critical in bone disorders because there is a reciprocal relationship between adipogenesis and osteogenesis in bone micro-environment. Oxysterols are pro-osteogenic and anti-adipogenic molecules via hedgehog activation in pluripotent bone marrow stomal cells. However, no study has evaluated the role of specific oxysterols in C3H10T1/2 cells, which are a good cell model for studying osteogenesis and adipogenesis in bone-marrows. Thus, we investigated the effects of specific oxysterols on adipogenesis and expression of adipogenic transcripts in C3H10T1/2 cells. Treatment of cells with DMITro significantly induced mRNA expression of Pparγ. This induction was significantly inhibited by 25-HC. The expression of C/cepα, Fabp4 and Lpl was also inhibited by 25-HC. To determine the mechanism by which 25-HC inhibits adipogenesis, the effects of the hedgehog signalling pathway inhibitor, cyclopamine and CUR61414, were evaluated. Treatment of C3H10T1/2 cells with DMITro + cyclopamine or DMITro + CUR61414 for 96h did not modulate adipocyte differentiation; cyclopamine and CUR61414 did not reverse the inhibitory effects of 25-HC, suggesting that the canonical hedgehog signalling may not play a role in the anti-adipogenic effects of 25-HC in C3H10T1/2 cells. In addition, LXR agonist did not inhibit adipogenesis, but 25-HC strongly inhibits adipogenesis of C3H10T1/2 cells. Our observations showed that 25-HC was the most potent oxysterol in inhibiting adipogenesis and the expression of key adipogenic transcripts in C3H10T1/2 cells among the tested oxysterols, suggesting its potential application in providing an intervention in osteoporosis and obesity. We also report that the inhibitory effects of 25-HC on adipogenic differentiation in C3H10T1/2 cells are not mediated by hedgehog signaling and LXR.

Type I collagen inhibits adipogenic differentiation via YAP activation in vitro

Extracellular matrix (ECM) has a marked influence on adipose tissue development. Adipose tissue formation is initiated with proliferation of preadipocytes and migration before undergoing further differentiation into mature adipocytes. Previous studies showed that collagen I (col I) provides a good substratum for 3T3-L1 preadipocytes to grow and migrate. However, it remains unclear whether and how col I regulates adipogenic differentiation of preadipocytes. This study reports that lipid accumulation, representing in vitro adipogenesis of the 3T3-L1 preadipocytes or the mouse primary adipocyte precursor cells derived from subcutaneous adipose tissue in the inguinal region is inhibited by the culture on col I, owing to downregulation of adipogenic factors. Previous study shows that col I enhances 3T3-L1 cell migration via stimulating the nuclear translocation of yes-associated protein (YAP). In this study, we report that downregulation of YAP is associated with in vitro adipogenesis of preadipocytes as well as with in vivo adipose tissue of high-fat diet fed mice. Increased expression of YAP in the cells cultured on col I-coated dishes is correlated with repression of adipogenic differentiation processes. The inactivation of YAP using YAP inhibitor, verteporfin, or YAP small-interfering RNA enhanced adipogenic differentiation and reversed the inhibitory effect of col I. Activation of YAP either by the transfection of YAP plasmid or the silence of large tumor suppressor 1 (LATS1), an inhibitory kinase of YAP, inhibited adipogenic differentiation. The results indicate that col I inhibits adipogenic differentiation via YAP activation in vitro.

Fatty Acid-Binding Protein 4 in Cardiovascular and Metabolic Diseases

Fatty acid-binding proteins (FABPs), a family of lipid chaperones, contribute to systemic metabolic regulation via several lipid signaling pathways. Fatty acid-binding protein 4 (FABP4), known as adipocyte FABP (A-FABP) or aP2, is mainly expressed in adipocytes and macrophages and plays important roles in the development of insulin resistance and atherosclerosis in relation to metabolically driven low-grade and chronic inflammation, referred to as ‘metaflammation’. FABP4 is secreted from adipocytes in a non-classical pathway associated with lipolysis and acts as an adipokine for the development of insulin resistance and atherosclerosis. Circulating FABP4 levels are associated with several aspects of metabolic syndrome and cardiovascular disease. Ectopic expression and function of FABP4 in cells and tissues are also related to the pathogenesis of several diseases. Pharmacological modification of FABP4 function by specific inhibitors, neutralizing antibodies or antagonists of unidentified receptors would be novel therapeutic strategies for several diseases, including obesity, diabetes mellitus, atherosclerosis and cardiovascular disease. Significant roles of FABP4 as a lipid chaperone in physiological and pathophysiological conditions and the possibility of FABP4 being a therapeutic target for metabolic and cardiovascular diseases are discussed in this review.

Anti-Obesity Activities of Chikusetsusaponin IVa and Dolichos lablab L. Seeds

Obesity, a condition where excess body fat accumulates to the extent, causes a negative effect on health. Previously, we reported the extract of Dolichos lablab L. (DLL-Ex) inhibited high-fat diet (HFD)-induced increases in body weight and body fat mass and ameliorated increases in body weight. In the present work, we studyed the molecular mechanism for the inhibitory effect of DLL-Ex or Chikusetsusaponin IVa (CS-IVa), as isolated from Dolichos lablab L. (DLL) seeds extract, on adipocyte differentiation. We evaluated the effect of DLL-Ex, an anti-obesity agent, and CS-IVa, an active component of DLL-Ex, on 3T3-L1 cell differentiation via Oil red O assay and Q-PCR, along with their effects on CCAAT element binding protein alpha (C/EBPα), peroxisome proliferator-activated receptor gamma (PPARγ), fatty acid synthase (FAS), and fatty acid-binding protein 4 (FABP4) mRNA transcriptions. FAS and FABP4 protein expression levels after exposure to CS-IVa were also tested. The results showed that DLL-Ex and CS-IVa have potent inhibitory activity on adipocyte differentiation. Therefore, DLL and CS-IVa may be developed as a functional food material to treat obesity.

1,3,6,7-Tetrahydroxy-8-prenylxanthone ameliorates inflammatory responses resulting from the paracrine interaction of adipocytes and macrophages

BACKGROUND AND PURPOSE

Chronic inflammation in adipose tissue is critical in the onset and development of insulin resistance and type 2 diabetes. Macrophage infiltration into adipose tissue and pro-inflammatory polarization play key roles in adipose tissue inflammation. The fruit hull of mangosteen (Garcinia mangostana) is used in traditional medicine to treat various inflammatory diseases. However, its role in regulating adipose tissue inflammation is unexplored. This study was designed to identify xanthones from G. mangostana, which could ameliorate adipose tissue inflammation.

EXPERIMENTAL APPROACH

Expressions of inducible NOS, cytokines, chemokines and components of the NF-κB and MAPKs pathways were evaluated using Western blotting, immunofluorescence, quantitative real-time PCR or ELISA. The migration of macrophages towards adipocytes was tested using Transwell experiments in vitro. A murine model of LPS-induced acute inflammation was used to examine effects of 1,3,6,7-tetrahydroxy-8-prenylxanthone (TPX) on inflammatory responses in adipose tissue in vivo.

KEY RESULTS

From a series of xanthones isolated from G. mangostana, TPX was identified as a potent inhibitor of LPS-induced NO production and IL-6 secretion in RAW264.7 macrophages. TPX ameliorated LPS-induced inflammatory responses in RAW264.7 macrophages, and TNF-α-mediated inflammation in 3T3-L1 adipocytes, through inhibiting MAPKs and NF-κB activation and promoting sirtuin 3 expression. TPX also blocked RAW264.7 macrophages migration towards 3T3-L1 adipocytes in co-cultures. Furthermore, TPX alleviated LPS-induced adipose tissue inflammation in vivo by reducing pro-inflammatory cytokines and preventing the pro-inflammatory polarization of macrophages.

CONCLUSIONS AND IMPLICATIONS

Taken together, our results indicate that TPX disrupts the inflammatory responses between macrophages and adipocytes, and attenuates adipose tissue inflammation.

AZD1208, a pan-Pim kinase inhibitor, inhibits adipogenesis and induces lipolysis in 3T3-L1 adipocytes

The proviral integration moloney murine leukaemia virus (Pim) kinases, consisting of Pim-1, Pim-2 and Pim-3, are involved in the control of cell growth, metabolism and differentiation. Pim kinases are emerging as important mediators of adipocyte differentiation. AZD1208 is a pan-Pim kinase inhibitor and is known for its anti-cancer activity. In this study, we investigated the effect of AZD1208 on adipogenesis and lipolysis in 3T3-L1 cells, a murine preadipocyte cell line. AZD1208 markedly suppressed lipid accumulation and reduced triglyceride contents in differentiating 3T3-L1 cells, suggesting the drug's anti-adipogenic effect. On mechanistic levels, AZD1208 reduced not only the expressions of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC) and perilipin A but also the phosphorylation of signal transducer and activator of transcription-3 (STAT-3) in differentiating 3T3-L1 cells. Remarkably, AZD1208 increased cAMP-activated protein kinase (AMPK) and LKB-1 phosphorylation while decreased intracellular ATP contents in differentiating 3T3-L1 cells. Furthermore, in differentiated 3T3-L1 adipocytes, AZD1208 also partially promoted lipolysis and enhanced the phosphorylation of hormone-sensitive lipase (HSL), a key lipolytic enzyme, indicating the drug's HSL-dependent lipolysis. In summary, the findings show that AZD1208 has anti-adipogenic and lipolytic effects on 3T3-L1 adipocytes. These effects are mediated by the expression and/or phosphorylation levels of C/EBP-α, PPAR-γ, FAS, ACC, perilipin A, STAT-3, AMPK and HSL.

Transdifferentiation of adipocytes to osteoblasts: potential for orthopaedic treatment

OBJECTIVES

As both adipocytes and osteoblasts originate from the same pool of mesenchymal stem cells, increasing clinical evidence has emerged of the plasticity between the two lineages. For instance, the downregulation of osteoblast differentiation and upregulation of adipogenesis are common features of conditions such as multiple myeloma, obesity and drug-induced bone loss in diabetes mellitus. However, despite in-vitro and in-vivo observations of adipocyte transdifferentiation into osteoblasts, little is known of the underlying mechanisms.

KEY FINDINGS

This review summarises the current knowledge of this particular transdifferentiation process whereby the Wnt/β-catenin signalling pathway and Runx2 overexpression have been postulated to play a critical role.

SUMMARY

Furthermore, due to the possibility of a novel therapy in the treatment of bone conditions, a number of agents with the potential to induce adipo-to-osteoblast transdifferentiation have been investigated such as all-trans retinoic acid, bone morphogenetic protein-9 and vascular endothelial growth factor.

Fatty acid-binding protein 4 regulates fatty infiltration after rotator cuff tear by hypoxia-inducible factor 1 in mice

BACKGROUND

Fatty infiltration in skeletal muscle is directly linked to loss of muscle strength and is associated with various adverse physical outcomes such as muscle atrophy, inflammation, insulin resistance, mobility impairments, and even mortality in the elderly. Aging, mechanical unloading, muscle injury, and hormonal imbalance are main causes of muscle fat accumulation, and the fat cells are derived from muscle stem cells via adipogenic differentiation. However, the pathogenesis and molecular mechanisms of fatty infiltration in muscles are still not fully defined. Fatty acid-binding protein 4 (FABP4) is a carrier protein for fatty acids and is involved in fatty acid uptake, transport, and lipid metabolism. Rotator cuff tear (RCT) usually occurs in the elderly and is closely related with fatty infiltration in injured muscle. To investigate potential mechanisms for fatty infiltration other than adipogenic differentiation of muscle stem cells, we examined the role of FABP4 in muscle fatty infiltration in an RCT mouse model.

METHODS

In the RCT model, we evaluated the expression of FABP4 by qRT-PCR, western blotting, and immunohistochemical analyses. Histological changes such as inflammation and fat accumulation in the injured muscles were examined immunohistochemically. To evaluate whether hypoxia induces FABP4 expression, the levels of FABP4 mRNA and protein in C3H10T1/2 cells after hypoxia were examined. Using a transient transfection assay in 293T cells, we assessed the promoter activity of FABP4 by hypoxia-inducible factors (HIFs). Additionally, we evaluated the reduction in FABP4 expression and fat accumulation using specific inhibitors for HIF1 and FABP4, respectively.

RESULTS

FABP4 expression was significantly increased after RCT in mice, and its expression was localized in the intramuscular fatty region. Rotator cuff tear-induced FABP4 expression was up-regulated by hypoxia. HIF1α, which is activated by hypoxia, augmented the promoter activity of FABP4, together with HIF1β. Hypoxia-induced FABP4 expression was significantly decreased by HIF1 inhibitor treatment. Furthermore, in RCT model mice, fat accumulation was remarkably reduced by FABP4 inhibitor treatment.

CONCLUSIONS

This study shows that RCT induces FABP4 expression, leading to fat accumulation in injured muscle. FABP4 transcription is regulated by the direct binding of HIF1 to the FABP4 promoter in the hypoxic condition induced by RCT. Fat accumulation in injured muscle was reduced by the inhibition of FABP4. Ultimately, in the RCT model, we identified a novel mechanism for fatty infiltration by FABP4, which differs from adipogenic differentiation of muscle stem cells, and we found that fatty infiltration might be regulated by inhibition of HIF1 or FABP4.

Anti-Adipogenic Effects on 3T3-L1 Cells and Zebrafish by Tanshinone IIA

Tanshinone IIA is a diterpene quinone isolated from the roots of Salviamiltiorrhiza bunge that has traditionally been used in China for the treatment of cardiovascular and cerebrovascular disorders. Although there is recent evidence showing that tanshinone IIA has an anti-obesity effect, its underlying mechanism of anti-obesity effect is poorly understood. Here, we investigated the effect of tanshinone IIA on lipid accumulation in 3T3-L1 preadipocytes and zebrafish. Notably, tanshinone IIA at 10 μM concentration greatly reduced lipid accumulation and triglyceride (TG) contents during 3T3-L1 preadipocyte differentiation, suggesting its anti-adipogenic effect. On mechanistic levels, tanshinone IIA reduced the expression levels of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), and perilipin A but also the phosphorylation levels of signal transducer and activator of transcription-3/5 (STAT-3/5) in differentiating 3T3-L1 cells. In addition, tanshinone IIA strongly inhibited leptin and resistin mRNA expression in differentiating 3T3-L1 cells. Importantly, the tanshinone IIA's lipid-reducing effect was also seen in zebrafish. In sum, these findings demonstrate that tanshinone IIA has anti-adipogenic effects on 3T3-L1 cells and zebrafish, and its anti-adipogenic effect on 3T3-L1 cells is largely attributable to the reduced expression and/or phosphorylation levels of C/EBP-α, PPAR-γ, FAS, perilipin A, and STAT-3/5.

CD38 deficiency suppresses adipogenesis and lipogenesis in adipose tissues through activating Sirt1/PPARγ signaling pathway

It has been recently reported that CD38 was highly expressed in adipose tissues from obese people and CD38-deficient mice were resistant to high-fat diet (HFD)-induced obesity. However, the role of CD38 in the regulation of adipogenesis and lipogenesis is unknown. In this study, to explore the roles of CD38 in adipogenesis and lipogenesis in vivo and in vitro, obesity models were generated with male CD38^-/- and WT mice fed with HFD. The adipocyte differentiations were induced with MEFs from WT and CD38^-/- mice, 3T3-L1 and C3H10T1/2 cells in vitro. The lipid accumulations and the alternations of CD38 and the genes involved in adipogenesis and lipogenesis were determined with the adipose tissues from the HFD-fed mice or the MEFs, 3T3-L1 and C3H10T1/2 cells during induction of adipocyte differentiation. The results showed that CD38^-/- male mice were significantly resistant to HFD-induced obesity. CD38 expressions in adipocytes were significantly increased in WT mice fed with HFD, and the similar results were obtained from WT MEFs, 3T3-L1 and C3H10T1/2 during induction of adipocyte differentiation. The expressions of PPARγ, AP2 and C/EBPα were markedly attenuated in adipocytes from HFD-fed CD38^-/- mice and CD38^-/- MEFs at late stage of adipocyte differentiation. Moreover, the expressions of SREBP1 and FASN were also significantly decreased in CD38^-/- MEFs. Finally, the CD38 deficiency-mediated activations of Sirt1 signalling were up-regulated or down-regulated by resveratrol and nicotinamide, respectively. These results suggest that CD38 deficiency impairs adipogenesis and lipogenesis through activating Sirt1/PPARγ-FASN signalling pathway during the development of obesity.

Role of the fatty acid-binding protein 4 in heart failure and cardiovascular disease

Obesity and ectopic fat accumulation in non-adipose tissues are major contributors to heart failure (HF) and cardiovascular disease (CVD). Adipocytes act as endocrine organs by releasing a large number of bioactive molecules into the bloodstream, which participate in a communication network between white adipose tissue and other organs, including the heart. Among these molecules, fatty acid-binding protein 4 (FABP4) has recently been shown to increase cardiometabolic risk. Both clinical and experimental evidence have identified FABP4 as a relevant player in atherosclerosis and coronary artery disease, and it has been directly related to cardiac alterations such as left ventricular hypertrophy (LVH) and both systolic and diastolic cardiac dysfunction. The available interventional studies preclude the establishment of a direct causal role of this molecule in CVD and HF and propose FABP4 as a biomarker rather than as an aetiological factor. However, several experimental reports have suggested that FABP4 may act as a direct contributor to cardiac metabolism and physiopathology, and the pharmacological targeting of FABP4 may restore some of the metabolic alterations that are conducive to CVD and HF. Here, we review the current knowledge regarding FABP4 in the context of HF and CVD as well as the molecular basis by which this protein participates in the regulation of cardiac function.

Coffee extract inhibits adipogenesis in 3T3-L1 preadipocyes by interrupting insulin signaling through the downregulation of IRS1

Although epidemiological data have indicated that a strong negative association exists between coffee consumption and the prevalence of obesity-associated diseases, the molecular mechanisms by which coffee intake prevents obesity-associated diseases has not yet been elucidated. In this study, we found that coffee intake significantly suppressed high-fat diet (HFD)-induced metabolic alternations such as increases in body weight and the accumulation of adipose tissue, and up-regulation of glucose, free fatty acid, total cholesterol and insulin levels in the blood. We also found that coffee extract significantly inhibited adipogenesis in 3T3-L1 preadipocytes. In the early phase of adipogenesis, 3T3-L1 cells treated with coffee extract displayed the retardation of cell cycle entry into the G2/M phase called as mitotic clonal expansion (MCE). Coffee extract also inhibited the activation of CCAAT/enhancer-binding protein β (C/EBPβ) by preventing its phosphorylation by ERK. Furthermore, the coffee extract suppressed the adipogenesis-related events such as MCE and C/EBPβ activation through the down-regulation of insulin receptor substrate 1 (IRS1). The stability of the IRS1 protein was markedly decreased by the treatment with coffee extract due to proteasomal degradation. These results have revealed an anti-adipogenic function for coffee intake and identified IRS1 as a novel target for coffee extract in adipogenesis.

TET-mediated hydroxymethylcytosine at the Pparγ locus is required for initiation of adipogenic differentiation

BACKGROUND/OBJECTIVES

Adipose tissue is one of the main organs regulating energy homeostasis via energy storage as well as endocrine function. The adipocyte cell number is largely determined by adipogenesis. While the molecular mechanism of adipogenesis has been extensively studied, its role in dynamic DNA methylation plasticity remains unclear. Recently, it has been shown that Tet methylcytosine dioxygenase (TET) is catalytically capable of oxidizing DNA 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine (5-hmC) toward a complete removal of the methylated cytosine. We investigate whether expression of the Tet genes and production of hydroxymethylcytosine are required for preadipocyte differentiation.

SUBJECTS/METHODS

Murine 3T3-L1 preadipocytes were used to evaluate the role of Tet1 and Tet2 genes during adipogenesis. Changes in adipogenic ability and in epigenetic status were analyzed, with and without interfering Tet1 and Tet2 expression using small interfering RNA (siRNA). The adipogenesis was evaluated by Oil-Red-O staining and induced expression of adipogenic genes using quantitative polymerase chain reaction (qPCR). Levels of 5-hmC and 5-mC were measured by MassARRAY, immunoprecipitation and GC mass spectrometry at specific loci as well as globally.

RESULTS

Both Tet1 and Tet2 genes were upregulated in a time-dependent manner, accompanied by increased expression of hallmark adipogenic genes such as Pparγ and Fabp4 (P<0.05). The TET upregulation led to reduced DNA methylation and elevated hydroxymethylcytosine, both globally and specifically at the Pparγ locus (P<0.05 and P<0.01, respectively). Knockdown of Tet1 and Tet2 blocked adipogenesis (P<0.01) by repression of Pparγ expression (P<0.05). In particular, Tet2 knockdown repressed conversion of 5-mC to 5-hmC at the Pparγ locus (P<0.01). Moreover, vitamin C treatment enhanced adipogenesis (P<0.05), while fumarate treatment inhibited it (P<0.01) by modulating TET activities.

CONCLUSIONS

TET proteins, particularly TET2, were required for adipogenesis by modulating DNA methylation at the Pparγ locus, subsequently by inducing Pparγ gene expression.

Deficiency of stearoyl-CoA desaturase-1 aggravates colitogenic potential of adoptively transferred effector T cells

Stearoyl-CoA desaturase-1 (SCD1) is a lipogenic enzyme involved in the de novo biosynthesis of oleate (C18:1, n9), a major fatty acid in the phospholipids of lipid bilayers of cell membranes. Accordingly, Scd1KO mice display substantially reduced oleate in cell membranes. An altered SCD1 level was observed during intestinal inflammation; however, its role in modulating inflammatory bowel disease remains elusive. Herein, we investigated the colitogenic capacity of Scd1KO effector T cells by employing the adoptive T-cell transfer colitis model. Splenic effector T cells (CD4⁺CD25^-) from age- and sex-matched wild-type (WT) and Scd1KO mice were isolated by FACS and intraperitoneally administered to Rag1KO mice, which were monitored for the development of colitis. At day 60 postcell transfer, Rag1KO mice that received Scd1KO CD4⁺CD25^- T cells displayed accelerated and exacerbated colitis than mice receiving WT CD4⁺CD25^- T cells. Intriguingly, Scd1KO CD4⁺CD25^- T cells display augmented inflammatory cytokine profile and cellular membrane fluidity with a concomitant increase in proinflammatory saturated fatty acids, which we postulate to potentially underlie their augmented colitogenic potential.

Expression of acute phase proteins by bone marrow stromal cells

The current work examines the expression of acute phase genes in a murine-derived bone marrow stromal cell model (BMS2) which exhibits adipocyte and osteoblast characteristics and supports lymphopoiesis in vitro. Each of these physiologic processes is responsive to inflammatory events such as endotoxemia. Exposure of BMS2 cells to pro-inflammatory cytokines induced the expression of the serum amyloid A and complement factor B. During adipocyte differentiation, expression of complement C3, complement factor D (adipsin), and angiotensinogen increased in a time dependent manner. The bone metabolic steroid, 1,25 dihydroxy vitamin D3, specifically induced complement C3 expression in a time- and dose-dependent manner. Based on gel retention analysis, BMS2 nuclear extract contained proteins recognizing specific response elements from the complement C3, angiotensinogen, and complement factor B promoters. These results suggest that the bone marrow's repertoire of acute phase proteins is dependent on the stromal cell's phenotype or activation state.

Stearoyl-CoA desaturase 1 expression is downregulated in liver and udder during E. coli mastitis through enhanced expression of repressive C/EBP factors and reduced expression of the inducer SREBP1A

Background

Stearoyl-CoA desaturase 1 (SCD1) desaturates long chain fatty acids and is therefore a key enzyme in fat catabolism. Its synthesis is downregulated in liver during illnesses caused by high levels of circulating lipopolysaccharide (LPS). SCD1 expression is known to be stimulated under adipogenic conditions through a variety of transcription factors, notably SREBP1 and C/EBPα and −β. However, mechanisms downregulating SCD1 expression during illness related reprograming of the metabolism were unknown. Escherichia coli elicited mastitis is an example of such a condition and was found to downregulates milk and milk fat synthesis. This is in part mediated through epigenetic mechanisms. We analyzed here mechanism controlling SCD1 expression in livers and udders from cows suffering from experimentally induced E. coli mastitis.

Results

We validated with RT-qPCR that SCD1 expression was reduced in these organs of the experimental cows. They also featured decreased levels of mRNAs encoding SREBP1a but increased levels for C/EBP α and −β. Chromatin accessibility PCR (CHART) revealed that downregulation of SCD1 expression in liver was not caused by tighter chromatin compaction of the SCD1 promoter. Reporter gene analyses showed in liver (HepG2) and mammary epithelial (MAC-T) model cells that overexpression of SREBP1a expectedly activated the promoter, while unexpectedly C/EBPα and −β strongly quenched the promoter activity. Abrogation of two from among of the three C/EBP DNA-binding motifs of the promoter revealed that C/EBPα acts in cis but C/EBPβ in trans. Overexpressing truncated C/EBPα or −β factors lacking their repressive domains confirmed in both model cells the direct action of C/EBPα, but not of C/EBPβ on the promoter.

Conclusions

We found no evidence that epigenetic mechanism remodeling the chromatin compaction of the SCD1 promoter would contribute to downregulate SCD1 expression during infection. Instead, our data show for the first time that C/EBP factors may repress SCD1 expression in liver and udder rather than stimulating as it was previously shown in adipocytes. This cell type specific dual and opposite function of C/EBP factors for regulating SCD1 expression was previously unknown. Infection related activation of their expression combined with downregulated expression of SREBP1a explains reduced SCD1 expression in liver and udder during acute mastitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12867-016-0069-5) contains supplementary material, which is available to authorized users.

MiR-25 suppresses 3T3-L1 adipogenesis by directly targeting KLF4 and C/EBPα

In the past decade, miRNA emerges as a vital player in orchestrating gene regulation and maintaining cellular homeostasis. It is well documented that miRNA influences a variety of biological events, including embryogenesis, cell fate decision, and cellular differentiation. Adipogenesis is an organized process of cellular differentiation by which pre-adipocytes differentiate towards mature adipocytes. It has been shown that adipogenesis is tightly modulated by a number of transcription factors such as PPARγ, KLF4, and C/EBPα. However, the molecular mechanisms underlying the missing link between miRNA and adipogenesis-related transcription factors remain elusive. In this study, we unveiled that miR-25, a member of miR-106b-25 cluster, was remarkably downregulated during 3T3-L1 adipogenesis. Restored expression of miR-25 significantly impaired 3T3-L1 adipogenesis and downregulated the expression of serial adipogenesis-related genes. Further experiments presented that ectopic expression of miR-25 did not affect cell proliferation and cell cycle progression. Finally, KLF4 and C/EBPα, two key regulators of adipocyte differentiation, were experimentally identified as bona fide targets for miR-25. These data indicate that miR-25 is a novel negative regulator of adipocyte differentiation and it suppressed 3T3-L1 adipogenesis by targeting KLF4 and C/EBPα, which provides novel insights into the molecular mechanism of miRNA-mediated cellular differentiation.

Arachidonic and oleic acid exert distinct effects on the DNA methylome

Abnormal fatty acid metabolism and availability are landmarks of metabolic diseases, which in turn are associated with aberrant DNA methylation profiles. To understand the role of fatty acids in disease epigenetics, we sought DNA methylation profiles specifically induced by arachidonic (AA) or oleic acid (OA) in cultured cells and compared those with published profiles of normal and diseased tissues. THP-1 monocytes were stimulated with AA or OA and analyzed using Infinium HumanMethylation450 BeadChip (Illumina) and Human Exon 1.0 ST array (Affymetrix). Data were corroborated in mouse embryonic fibroblasts. Comparisons with publicly available data were conducted by standard bioinformatics. AA and OA elicited a complex response marked by a general DNA hypermethylation and hypomethylation in the 1-200 μM range, respectively, with a maximal differential response at the 100 μM dose. The divergent response to AA and OA was prominent within the gene body of target genes, where it correlated positively with transcription. AA-induced DNA methylation profiles were similar to the corresponding profiles described for palmitic acid, atherosclerosis, diabetes, obesity, and autism, but relatively dissimilar from OA-induced profiles. Furthermore, human atherosclerosis grade-associated DNA methylation profiles were significantly enriched in AA-induced profiles. Biochemical evidence pointed to β-oxidation, PPAR-α, and sirtuin 1 as important mediators of AA-induced DNA methylation changes. In conclusion, AA and OA exert distinct effects on the DNA methylome. The observation that AA may contribute to shape the epigenome of important metabolic diseases, supports and expands current diet-based therapeutic and preventive efforts.

Silibinin Regulates Lipid Metabolism and Differentiation in Functional Human Adipocytes

Silibinin, a natural plant flavonolignan is the main active constituent found in milk thistle (Silybum marianum). It is known to have hepatoprotective, anti-neoplastic effect, and suppresses lipid accumulation in adipocytes. Objective of this study was to investigate the effect of silibinin on adipogenic differentiation and thermogenic capacity of human adipose tissue derived mesenchymal stem cells. Silibinin (10 μM) treatment, either at the beginning or at the end of adipogenic differentiation, resulted in an increase of SIRT-1, PPARα, Pgc-1α, and UCPs gene expression. Moreover, silibinin administration resulted in a decrease of PPARγ, FABP4, FAS, and MEST/PEG1 gene expression during the differentiation, confirming that this compound is able to reduce fatty acid accumulation and adipocyte size. Our data showed that silibinin regulated adipocyte lipid metabolism, inducing thermogenesis and promoting a brown remodeling in adipocyte. Taken together, our findings suggest that silibinin increases UCPs expression by stimulation of SIRT1, PPARα, and Pgc-1α, improved metabolic parameters, decreased lipid mass leading to the formation of functional adipocytes.

Molecular Regulation of Adipogenesis and Potential Anti-Adipogenic Bioactive Molecules

Adipogenesis is the process by which precursor stem cells differentiate into lipid laden adipocytes. Adipogenesis is regulated by a complex and highly orchestrated gene expression program. In mammalian cells, the peroxisome proliferator-activated receptor γ (PPARγ), and the CCAAT/enhancer binding proteins (C/EBPs) such as C/EBPα, β and δ are considered the key early regulators of adipogenesis, while fatty acid binding protein 4 (FABP4), adiponectin, and fatty acid synthase (FAS) are responsible for the formation of mature adipocytes. Excess accumulation of lipids in the adipose tissue leads to obesity, which is associated with cardiovascular diseases, type II diabetes and other pathologies. Thus, investigating adipose tissue development and the underlying molecular mechanisms is vital to develop therapeutic agents capable of curbing the increasing incidence of obesity and related pathologies. In this review, we address the process of adipogenic differentiation, key transcription factors and proteins involved, adipogenic regulators and potential anti-adipogenic bioactive molecules.

A proline-type fullerene derivative inhibits adipogenesis by preventing PPARγ activation

Obesity and its associated metabolic diseases represent some of the most rapidly expanding health issues worldwide, and, thus, the development of a novel chemical compound to suppress adipogenesis is strongly expected. We herein investigated the effects of water-soluble fullerene derivatives: a bis-malonic acid derivative and three types of proline-type fullerene derivatives, on adipogenesis using NIH-3T3 cells overexpressing PPARγ. One of the proline-type fullerene derivatives (P3) harboring three carboxy groups significantly inhibited lipid accumulation and the expression of adipocyte-specific genes, such as aP2, induced by the PPARγ agonist rosiglitazone. On the other hand, the bis-malonic acid derivative (M) and the 2 other proline-type fullerene derivatives (P1, P2), which have two carboxy groups, had no effect on PPARγ-mediated lipid accumulation or the expression of aP2. P3 fullerene also inhibited lipid accumulation induced by the combined stimulation with 3-isobutyl-1-methylxanthine (IBMX), dexamethasone, and insulin in 3T3-L1 preadipocytes. During the differentiation of 3T3-L1 cells into adipocytes, P3 fullerene did not affect the expression of C/EBPδ, C/EBPβ, or PPARγ, but markedly inhibited that of aP2 mRNA. These results suggest that P3 fullerene exhibits anti-obesity activity by preventing the activation of PPARγ.

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Fullerene derivative inhibits the rosiglitazone-induced adipogenesis.

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Fullerene derivative inhibits the rosiglitazone-induced expression of aP2 mRNA.

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Fullerene derivative inhibits adipogenesis of 3T3-L1 preadipocyte.

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Fullerene derivative inhibits the activation of PPARγ in 3T3-L1 preadipocyte.

The novel anti-adipogenic effect and mechanisms of action of SGI-1776, a Pim-specific inhibitor, in 3T3-L1 adipocytes

The proviral integration site for moloney murine leukemia virus (Pim) kinases, consisting of Pim-1, Pim-2 and Pim-3, belongs to a family of serine/threonine kinases that are involved in controlling cell growth and differentiation. Pim kinases are emerging as important mediators of adipocyte differentiation. SGI-1776, an inhibitor of Pim kinases, is widely used to assess the physiological roles of Pim kinases, particularly cell functions. In the present study, we examined the effects of SGI-1776 on adipogenesis. The anti‑adipogenic effect of SGI‑1776 was measured by Oil Red O staining and AdipoRed assays. The effect of SGI‑1776 on the growth of 3T3‑L1 adipocytes was determined by cell count analysis. The effects of SGI‑1776 on the protein and mRNA expression of adipogenesis-related proteins and adipokines in 3T3‑L1 adipocytes were also evaluated by western blot analysis and RT‑PCR, respectively. Notably, SGI-1776 markedly inhibited lipid accumulation during the differentiation of 3T3-L1 preadipocytes into adipocytes. On a mechanistic level, SGI-1776 inhibited not only the expression of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ) and fatty acid synthase (FAS), but also the phosphorylation of signal transducer and activator of transcription-3 (STAT-3). Moreover, SGI-1776 decreased the expression of adipokines, including the expression of leptin and regulated on activation, normal T cell expressed and secreted (RANTES) during adipocyte differentiation. These findings demonstrate that SGI-1776 inhibits adipogenesis by downregulating the expression and/or phosphorylation levels of C/EBP-α, PPAR-γ, FAS and STAT-3.

Dual Regulatory Role of Polyamines in Adipogenesis

Adipogenesis is a complex process, accompanied by a chain of interdependent events. Disruption of key events in this cascade may interfere with the correct formation of adipose tissue. Polyamines were demonstrated necessary for adipogenesis; however, the underlying mechanism by which they act has not been established. Here, we examined the effect of polyamine depletion on the differentiation of 3T3-L1 preadipocytes. Our results demonstrate that polyamines are required early in the adipogenic process. Polyamine depletion inhibited the second division of the mitotic clonal expansion (MCE), and inhibited the expression of PPARγ and C/EBPα, the master regulators of adipogenesis. However, it did not affect the expression of their transcriptional activator, C/EBPβ. Additionally, polyamine depletion resulted in elevation of mRNA and protein levels of the stress-induced C/EBP homologous protein (CHOP), whose dominant negative function is known to inhibit C/EBPβ DNA binding activity. Conditional knockdown of CHOP in polyamine-depleted preadipocytes restored PPARγ and C/EBPα expression, but failed to recover MCE and differentiation. Thus, our results suggest that the need for MCE in the adipogenic process is independent from the requirement for PPARγ and C/EBPα expression. We conclude that de novo synthesis of polyamines during adipogenesis is required for down-regulation of CHOP to allow C/EBPβ activation, and for promoting MCE.

Inhibition of dipeptidyl peptidase 8/9 impairs preadipocyte differentiation

Adipocytes are the primary cells in adipose tissue, and adipocyte dysfunction causes lipodystrophy, obesity and diabetes. The dipeptidyl peptidase (DPP) 4 family includes four enzymes, DPP4, DPP8, DPP9 and fibroblast activation protein (FAP). DPP4 family inhibitors have been used for the treatment of type 2 diabetes patients, but their role in adipocyte formation are poorly understood. Here we demonstrate that the DPP8/9 selective inhibitor 1G244 blocks adipogenesis in preadipocyte 3T3-L1 and 3T3-F422A, while DPP4 and FAP inhibitors have no effect. In addition, knockdown of DPP8 or DPP9 significantly impairs adipocyte differentiation in preadipocytes. We further uncovered that blocking the expression or activities of DPP8 and DPP9 attenuates PPARγ2 induction during preadipocyte differentiation. Addition of PPARγ agonist thiazolidinediones (TZDs), or ectopic expression of PPARγ2, is able to rescue the adipogenic defect caused by DPP8/9 inhibition in preadipocytes. These results indicate the importance of DPP8 and DPP9 on adipogenesis.

Expression analysis of human adipose-derived stem cells during in vitro differentiation to an adipocyte lineage

Background

Adipose tissue-derived stromal stem cells (ASCs) represent a promising regenerative resource for soft tissue reconstruction. Although autologous grafting of whole fat has long been practiced, a major clinical limitation of this technique is inconsistent long-term graft retention. To understand the changes in cell function during the transition of ASCs into fully mature fat cells, we compared the transcriptome profiles of cultured undifferentiated human primary ASCs under conditions leading to acquisition of a mature adipocyte phenotype.

Methods

Microarray analysis was performed on total RNA extracted from separate ACS isolates of six human adult females before and after 7 days (7 days: early stage) and 21 days (21 days: late stage) of adipocyte differentiation in vitro. Differential gene expression profiles were determined using Partek Genomics Suite Version 6.4 for analysis of variance (ANOVA) based on time in culture. We also performed unsupervised hierarchical clustering to test for gene expression patterns among the three cell populations. Ingenuity Pathway Analysis was used to determine biologically significant networks and canonical pathways relevant to adipogenesis.

Results

Cells at each stage showed remarkable intra-group consistency of expression profiles while abundant differences were detected across stages and groups. More than 14,000 transcripts were significantly altered during differentiation while ~6000 transcripts were affected between 7 days and 21 days cultures. Setting a cutoff of +/-two-fold change, 1350 transcripts were elevated while 2929 genes were significantly decreased by 7 days. Comparison of early and late stage cultures revealed increased expression of 1107 transcripts while 606 genes showed significantly reduced expression. In addition to confirming differential expression of known markers of adipogenesis (e.g., FABP4, ADIPOQ, PLIN4), multiple genes and signaling pathways not previously known to be involved in regulating adipogenesis were identified (e.g. POSTN, PPP1R1A, FGF11) as potential novel mediators of adipogenesis. Quantitative RT-PCR validated the microarray results.

Conclusions

ASC maturation into an adipocyte phenotype proceeds from a gene expression program that involves thousands of genes. This is the first study to compare mRNA expression profiles during early and late stage adipogenesis using cultured human primary ASCs from multiple patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-015-0119-8) contains supplementary material, which is available to authorized users.