An adenosine receptor-Krüppel-like factor 4 protein axis inhibits adipogenesis

Transcriptome profiling of longissimus dorsi during different prenatal stages to identify genes involved in intramuscular fat deposition in lean and obese pig breeds

BACKGROUND

There was significant difference in muscle development between fat-type and lean-type pig breeds.

METHODS AND RESULTS

In current study, transcriptome analysis and bioinformatics analysis were used to compare the difference in longissimus dorsi (LD) muscle at three time-points (38 days post coitus (dpc), 58 dpc, and 78 dpc ) between Huainan (HN) and Large white (LW) pig breeds. A total of 24500 transcripts were obtained in 18 samples, and 2319, 2799, and 3713 differently expressed genes (DEGs) were identified between these two breeds at 38 dpc, 58 dpc, and 78 dpc, respectively. And the number and foldchange of DEGs were increased, the alternative splice also increased. The cluster analysis of DEGs indicated the embryonic development progress of LD muscle between these two breeds was different. There were 539 shared DEGs between HN and LW at three stages, and the top-shared DEGs were associated with muscle development and lipid deposition, such as KLF4, NR4A1, HSP70, ZBTB16 and so on.

CONCLUSIONS

The results showed DEGs between Huainan (HN) and Large white (LW) pig breeds, and contributed to the understanding the muscle development difference between HN and LW, and provided basic materials for improvement of meat quality.

Purinergic Signaling and its Role in the Stem Cell Differentiation

Purinergic signaling is a mechanism in which extracellular purines and pyrimidines interact with specialized cell surface receptors known as purinergic receptors. These receptors are divided into two families of P1 and P2 receptors, each responding to different nucleosides and nucleotides. P1 receptors are activated by adenosine, while P2 receptors are activated by pyrimidine and purines. P2X receptors are ligand-gated ion channels, including seven subunits (P2X1-7). However, P2Y receptors are the G-protein coupled receptors comprising eight subtypes (P2Y1/2/4/6/11/12/13/14). The disorder in purinergic signaling leads to various health-related issues and diseases. In various aspects, it influences the activity of non-neuronal cells and neurons. The molecular mechanism of purinergic signaling provides insight into treating various human diseases. On the contrary, stem cells have been investigated for therapeutic applications. Purinergic signaling has shown promising effect in stem cell engraftment. The immune system promotes the autocrine and paracrine mechanisms and releases the significant factors essential for successful stem cell therapy. Each subtype of purinergic receptor exerts a beneficial effect on the damaged tissue. The most common effect caused by purinergic signaling is the proliferation and differentiation that treat different health-related conditions.

Eukaryotic initiation factor 5A hypusine as a negative regulator of adenosine 2B receptor (A2bAR) through interaction with stem loop sequences within the A2bAR 3'-untranslated region

PURPOSE

The aim of this study was to investigate whether eIF5A hypusine (eIF5A^Hyp) reduces adenosine 2b receptor (A2bAR) gene expression through interaction with highly structured stem-loop sequences within the A2bAR 3'UTR.

METHODS AND RESULTS

Based on real-time PCR and western blotting, expression of A2bAR mRNA was significantly decreased upon treatment with eIF5A^Hyp in mouse embryonic fibroblasts of eIF5A (eIF5A-MEF) and 3T3-L1 cells. Target Scan software and RNAfold web server predicted two different structures formed by stem-loop sequences with overlapping microRNA 27 seed sequences and mutations. The EMSA results showed significantly impaired formation of the wild type (WT) biotin-labeled A2bAR probe (27 base) containing stem loop sequences-eIF5A^Hyp complex by mutation of stem-loop sequences or by eIF5A non-hypusine (eIF5A^Lys). The luciferase reporter assay showed that GC7-induced eIF5A^Lys accumulation increased the activity of pMIR-A2bAR WT containing the same stem-loop sequence in 3T3-L1 cells, whereas the activity with pMIR-A2bAR Mut was increased compared to WT control without dependence on GC7. Oil Red O staining showed that suppression of A2bAR expression (A2bAR siRNA and eIF5A^Hyp) increased the amount of lipid droplet formation and the mRNA levels of lipid droplet-related genes (C/EBP-β, PPAR-γ, FABP4, SREBP-1, and Perilipin). In contrast, overexpression of A2bAR (A2bAR vector, eIF5A^Lys vector, and GC7) significantly decreased the expression of lipid droplet-associated genes and lipid droplet formation.

CONCLUSIONS

eIF5A^Hyp acts as a negative regulator of A2bAR gene expression through stem loop sequences in A2bAR 3'UTR, allowing differentiation of adipocytes.

Pathophysiology roles for adenosine 2A receptor in obesity and related diseases

Obesity, a burgeoning worldwide health system challenge, is associated with several comorbidities, including non-alcoholic fatty liver disease (NAFLD), diabetes, atherosclerosis, and osteoarthritis, leading to serious problems to people's health. Adenosine is a critical extracellular signaling molecule that has essential functions in regulating most organ systems by binding to four G-protein-coupled adenosine receptors, denoted A₁ , A_2A , A_2B , and A₃ . Among the receptors, a growing body evidence highlights the key roles of the adenosine 2A receptor (A_2A R) in obesity and related diseases. In the current review, we summarize the effects of A_2A R in obesity and obesity-associated non-alcoholic fatty liver disease, diabetes, atherosclerosis, and osteoarthritis, to clarify the complicated impacts of A_2A R on obesity and related diseases.

Novel positive allosteric modulators of A2B adenosine receptor acting as bone mineralisation promoters

Small-molecules acting as positive allosteric modulators (PAMs) of the A_2B adenosine receptor (A_2B AR) could potentially represent a novel therapeutic strategy for pathological conditions characterised by altered bone homeostasis, including osteoporosis. We investigated a library of compounds (4-13) exhibiting different degrees of chemical similarity with three indole derivatives (1-3), which have been recently identified by us as PAMs of the A_2B AR able to promote mesenchymal stem cell differentiation and bone formation. Evaluation of mineralisation activity of 4-13 in the presence and in the absence of the agonist BAY60-6583 allowed the identification of lead compounds with therapeutic potential as anti-osteoporosis agents. Further biological characterisation of one of the most performing compounds, the benzofurane derivative 9, confirmed that such a molecule behaves as PAM of the A_2B AR.

MYOD1 inhibits avian adipocyte differentiation via miRNA-206/KLF4 axis

BACKGROUND

A considerable number of muscle development-related genes were differentially expressed in the early stage of avian adipocyte differentiation. However, the functions of them in adipocyte differentiation remain largely known. In this study, the myoblast determination protein 1 (MYOD1) was selected as a representative of muscle development. We investigated its expression, function, and regulation in avian adipocyte differentiation.

RESULTS

The expression of MYOD1 decreased significantly in the early stage of avian adipocyte differentiation. CRISPR/Cas9-mediated deletion of MYOD1 induced adipocyte differentiation, whereas over-expression of MYOD1 inhibited adipogenesis. The mRNA-seq data showed that MYOD1 could perturb the lipid biosynthetic process during differentiation. Our results showed that MYOD1 directly up-regulates the miR-206 expression by binding the upstream 1200 bp region of miR-206. Then, over-expression of miR-206 can inhibit the adipogenesis. Furthermore, MYOD1 affected the expression of endogenous miR-206 and its target gene Kruppel-like factor 4 (KLF4), which is an important activator of adipogenesis. Accordingly, the inhibition of miR-206 or over-expression of KLF4 could counteract the inhibitory effect of MYOD1 on adipocyte differentiation.

CONCLUSIONS

Our results establish that MYOD1 inhibits adipocyte differentiation by up-regulating miR-206 to suppress the KLF4 expression. These findings identify a novel function of MYOD1 in adipocyte differentiation, suggesting a potential role in body-fat distribution regulation.

Impact of Adenosine A2 Receptor Ligands on BCL2 Expression in Skeletal Muscle Cells

Background: Adenosine plays the role of regulating cell differentiation, proliferation, and apoptosis in various kinds of cells through the B-cell lymphoma 2 (BCL2) pathway. Objectives: Since anti-apoptotic (BCL2) expression plays a role in controlling apoptosis in some cell lines, this study was designed to investigate whether adenosine analogue, NECA (non-selective adenosine receptors agonist), selective adenosine A2B receptor antagonist, PSB 603, and a selective adenosine A2A receptor agonist, CG21680, affect BCL2-gene expression in the skeletal muscle cells of rats. The purpose of this investigation was to test the hypothesis that CG21680 treatment would significantly intensify BCL2 gene expression in rat skeletal muscle. Methods: Flasks measuring 25 cm2 were employed in culturing the rat L6 skeletal muscle cells. After treating these differential cells, the relative mRNA expression level for the BCL2 gene, at varying conditions of treatment, was measured using quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Results: From the qRT-PCR analysis results, it was concluded that BCL2 expression was markedly amplified after selective adenosine A2A receptor agonist, CGS21680 (p < 0.01) treatment. More prospective validation for the adenosine receptors’ contribution in modulating apoptosis by NECA was delivered by the outcomes from the combined pre-treatment of the cells with NECA and PSB 603. These outcomes show that when starved skeletal muscle cells are treated with a combination of NECA and 100 nM PSB 603, there was a substantial decrease in comparison to either treatment used on its own. Conclusions: This study’s results showed, for the first time, an increase in BCL2 gene expression within skeletal muscle after CGS21680 treatment. Hence, the prospective escalation in BCL2 protein expression might have a protective role to play against apoptosis and avert damage to the skeletal muscle.

The adenosinergic pathway in mesenchymal stem cell fate and functions

Mesenchymal stem cells (MSCs) play an important role in tissue homeostasis and damage repair through their ability to differentiate into cells of different tissues, trophic support, and immunomodulation. These properties made them attractive for clinical applications in regenerative medicine, immune disorders, and cell transplantation. However, despite multiple preclinical and clinical studies demonstrating beneficial effects of MSCs, their native identity and mechanisms of action remain inconclusive. Since its discovery, the CD73/ecto-5'-nucleotidase is known as a classic marker for MSCs, but its role goes far beyond a phenotypic characterization antigen. CD73 contributes to adenosine production, therefore, is an essential component of purinergic signaling, a pathway composed of different nucleotides and nucleosides, which concentrations are finely regulated by the ectoenzymes and receptors. Thus, purinergic signaling controls pathophysiological functions such as proliferation, migration, cell fate, and immune responses. Despite the remarkable progress already achieved in considering adenosinergic pathway as a therapeutic target in different pathologies, its role is not fully explored in the context of the therapeutic functions of MSCs. Therefore, in this review, we provide an overview of the role of CD73 and adenosine-mediated signaling in the functions ascribed to MSCs, such as homing and proliferation, cell differentiation, and immunomodulation. Additionally, we will discuss the pathophysiological role of MSCs, via CD73 and adenosine, in different diseases, as well as in tumor development and progression. A better understanding of the adenosinergic pathway in the regulation of MSCs functions will help to provide improved therapeutic strategies applicable in regenerative medicine.

Regulatory roles of G-protein coupled receptors in adipose tissue metabolism and their therapeutic potential

The high incidence of obesity has increased the need to discover new therapeutic targets to combat obesity and obesity-related metabolic diseases. Obesity is defined as an abnormal accumulation of adipose tissue, which is one of the major metabolic organs that regulate energy homeostasis. However, there are currently no approved anti-obesity therapeutics that directly target adipose tissue metabolism. With recent advances in the understanding of adipose tissue biology, molecular mechanisms involved in brown adipose tissue expansion and metabolic activation have been investigated as potential therapeutic targets to increase energy expenditure. This review focuses on G-protein coupled receptors (GPCRs) as they are the most successful class of druggable targets in human diseases and have an important role in regulating adipose tissue metabolism. We summarize recent findings on the major GPCR classes that regulate thermogenesis and mitochondrial metabolism in adipose tissue. Improved understanding of GPCR signaling pathways that regulate these processes could facilitate the development of novel pharmacological approaches to treat obesity and related metabolic disorders.

MiR-25-3p regulates the differentiation of intramuscular preadipocytes in goat via targeting KLF4

Adipocyte differentiation, which plays an important role in fat deposition, involves a complex molecular mechanism. MicroRNAs (miRNAs) are essential in this progress. Here, we showed that miR-25-3p expression had increased during goat intramuscular preadipocyte differentiation, which peaked at day 3. Using liposome transfection and qRT-PCR techniques, we found that knocking down miR-25-3p reduced the accumulation of lipid droplets by downregulating or upregulating the expression of LPL, PPARγ, AP2, SREBP1, and C/EBPβ but upregulating the expression of KLF4. Overexpression of miR-25-3p results in the opposite. Furthermore, the dual luciferase assay showed that overexpression of miR-25-3p significantly inhibited luciferase activity of KLF4. These results showed that miR-25-3p has a binding site within the 3′-UTR of KLF4 mRNA. Together, these findings indicate that miR-25-3p is a positive regulator of intramuscular preadipocyte differentiation via targeting to KLF4 in goats.

New insights of Krüppel-like transcription factors in adipogenesis and the role of their regulatory neighbors

Obesity is a serious public health problem associated with predisposition to develop metabolic diseases. Over the past decade, several studies in vitro and in vivo have shown that the activity of Krüppel-like factors (KLFs) regulates adipogenesis, adipose tissue function and metabolism. Comprehension of both the origin and development of adipocytes and of adipose tissue could provide new insights into therapeutic strategies to contend against obesity and related metabolic diseases. This review focus on the transcriptional role that KLF family members play during adipocyte differentiation, describes their main interactions and the mechanisms involved in this fine-tuned developmental process. We also summarize new findings of the involvement of several effectors that modulate KLFs expression during adipogenesis, including growth factors, circadian clock proteins, interleukins, nuclear receptors, protein kinases and importantly, microRNAs. Thus, KLFs regulation by these factors and emerging molecules might constitute a potential therapeutic target for anti-obesity intervention.

Bone Marrow and Adipose Tissue Adenosine Receptors Effect on Osteogenesis and Adipogenesis

Adenosine is an extracellular signaling molecule that is particularly relevant in times of cellular stress, inflammation and metabolic disturbances when the levels of the purine increase. Adenosine acts on two G-protein-coupled stimulatory and on two G-protein-coupled inhibitory receptors, which have varying expression profiles in different tissues and conditions, and have different affinities for the endogenous ligand. Studies point to significant roles of adenosine and its receptors in metabolic disease and bone health, implicating the receptors as potential therapeutic targets. This review will highlight our current understanding of the dichotomous effects of adenosine and its receptors on adipogenesis versus osteogenesis within the bone marrow to maintain bone health, as well as its relationship to obesity. Therapeutic implications will also be reviewed.

Pitfalls and challenges of the purinergic signaling cascade in obesity

Obesity is a worldwide health problem which have reached pandemic proportions, now also including low and middle-income countries. Excessive or abnormal fat deposition in the abdomen especially in the visceral compartment is tightly associated with a high metabolic risk for arterial hypertension, type II diabetes, cardiovascular diseases, musculoskeletal disorders (especially articular degeneration) and some cancers. Contrariwise, accumulation of fat in the subcutaneous compartment has been associated with a neutral metabolic impact, favoring a lower risk of insulin resistance. Obesity results more often from an avoidable imbalance between food consumption and energy expenditure. There are several recommended strategies for dealing with obesity, including pharmacological therapies, but their success remains incomplete and may not compensate the associated adverse effects. Purinergic signaling operated by ATP and its metabolite, adenosine, has attracted increasing attention in obesity. The extracellular levels of purines often reflect the energy status of a given cell population. Adenine nucleotides and nucleosides fine tuning control adipogenesis and mature adipocytes function via the activation of P2 and P1 purinoceptors, respectively. These features make the purinergic signaling cascade a putative target for therapeutic intervention in obesity and related metabolic syndromes. There are, however, gaps in our knowledge regarding the role of purines in adipocyte precursors differentiation and mature adipocytes functions, as well as their impact among distinct adipose tissue deposits (e.g. white vs. brown, visceral vs. subcutaneous), which warrants further investigations before translation to clinical trials can be made.

Exploring adipogenic and myogenic circulatory biomarkers of recurrent pressure injury risk for persons with spinal cord injury

Purpose:

To investigate linkages between circulatory adipogenic and myogenic biomarkers, gluteal intramuscular adipose tissue (IMAT), and pressure injury (PrI) history following spinal cord injury (SCI).

Methods:

This is an observational repeated-measures study of 30 individuals with SCI. Whole blood was collected regularly over 2-3 years. Circulatory adipogenic and myogenic gene expression was determined. IMAT was defined as above/below 15% (IMATd) or percentage (IMAT%). PrI history was defined as recurrent PrI (RPrI) or PrI number (n PrI). Model development used R packages (version 3.5.1). Univariate analysis screened for discriminating genes for downstream multivariate and combined models of averaged and longitudinal data for binary (RPrI/IMATd) and finer scales (n PrI/IMAT%).

Results:

For adipogenesis, Krüppel-like factor 4 was the top RPrI predictor together with resistin and cyclin D1, and sirtuin 2 was the top IMAT predictor. For myogenesis, the top RPrI predictor was dysferlin 2B, and pyruvate dehydrogenase kinase-4 was the top IMAT predictor together with dystrophin.

Conclusion:

Circulatory adipogenic and myogenic biomarkers have statistically significant relationships with PrI history and IMAT for persons with SCI. Biomarkers of interest may act synergistically or additively. Variable importance rankings can reveal nonlinear correlations among the predictors. Biomarkers of interest may act synergistically or additively, thus multiple genes may need to be included for prediction with finer distinction.

Identification and characterization of adipose surface epitopes

Adipose tissue is a central regulator of metabolism and an important pharmacological target to treat the metabolic consequences of obesity, such as insulin resistance and dyslipidemia. Among the various cellular compartments, the adipocyte cell surface is especially appealing as a drug target as it contains various proteins that when activated or inhibited promote adipocyte health, change its endocrine function and eventually maintain or restore whole-body insulin sensitivity. In addition, cell surface proteins are readily accessible by various drug classes. However, targeting individual cell surface proteins in adipocytes has been difficult due to important functions of these proteins outside adipose tissue, raising various safety concerns. Thus, one of the biggest challenges is the lack of adipose selective surface proteins and/or targeting reagents. Here, we discuss several receptor families with an important function in adipogenesis and mature adipocytes to highlight the complexity at the cell surface and illustrate the problems with identifying adipose selective proteins. We then discuss that, while no unique adipocyte surface protein might exist, how splicing, posttranslational modifications as well as protein/protein interactions can create enormous diversity at the cell surface that vastly expands the space of potentially unique epitopes and how these selective epitopes can be identified and targeted.

Knockout and Knock-in Mouse Models to Study Purinergic Signaling

Purinergic signaling involves extracellular purines and pyrimidines acting upon specific cell surface purinoceptors classified into the P1, P2X, and P2Y families for nucleosides and nucleotides. This widespread signaling mechanism is active in all major tissues and influences a range of functions in health and disease. Orthologs to all but one of the human purinoceptors have been found in mouse, making this laboratory animal a useful model to study their function. Indeed, analyses of purinoceptors via knock-in or knockout approaches to produce gain or loss of function phenotypes have revealed several important therapeutic targets. None of the homozygous purinoceptor knockouts proved to be developmentally lethal, which suggest that either these receptors are not involved in key developmental processes or that the large number of receptors in each family allowed for functional compensation. Different models for the same purinoceptor often show compatible phenotypes but there have been examples of significant discrepancies. These revealed unexpected differences in the structure of human and mouse genes and emphasized the importance of the genetic background of different mouse strains. In this chapter, we provide an overview of the current knowledge and new trends in the modifications of purinoceptor genes in vivo. We discuss the resulting phenotypes, their applications and relative merits and limitations of mouse models available to study purinoceptor subtypes.

Role of microRNA in CB1 antagonist-mediated regulation of adipose tissue macrophage polarization and chemotaxis during diet-induced obesity

Although cannabinoid receptor 1 (CB1) antagonists have been shown to attenuate diet-induced obesity (DIO) and associated inflammation, the precise molecular mechanisms involved are not clear. In the current study, we investigated the role of microRNA (miR) in the regulation of adipose tissue macrophage (ATM) phenotype following treatment of DIO mice with the CB1 antagonist SR141716A. DIO mice were fed high-fat diet (HFD) for 12 weeks and then treated daily with SR141716A (10 mg/kg) for 4 weeks while continuing HFD. Treated mice experienced weight loss, persistent reduction in fat mass, improvements in metabolic profile, and decreased adipose inflammation. CB1 blockade resulted in down-regulation of several miRs in ATMs, including the miR-466 family and miR-762. Reduced expression of the miR-466 family led to induction of anti-inflammatory M2 transcription factors KLF4 and STAT6, whereas down-regulation of miR-762 promoted induction of AGAP-2, a negative regulator of the neuroimmune retention cues, Netrin-1 and its coreceptor UNC5B. Furthermore, treatment of primary macrophages with SR141716A up-regulated KLF4 and STAT6, reduced secretion of Netrin-1, and increased migration toward the lymph node chemoattractant CCL19. These studies demonstrate for the first time that CB1 receptor blockade attenuates DIO-associated inflammation through alterations in ATM miR expression that promote M2 ATM polarization and macrophage egress from adipose tissue. The current study also identifies additional novel therapeutic targets for diet-induced obesity and metabolic disorder.

The Krüppel-Like Factors and Control of Energy Homeostasis

Nutrient handling by higher organisms is a complex process that is regulated at the transcriptional level. Studies over the past 15 years have highlighted the critical importance of a family of transcriptional regulators termed the Krüppel-like factors (KLFs) in metabolism. Within an organ, distinct KLFs direct networks of metabolic gene targets to achieve specialized functions. This regulation is often orchestrated in concert with recruitment of tissue-specific transcriptional regulators, particularly members of the nuclear receptor family. Upon nutrient entry into the intestine, gut, and liver, KLFs control a range of functions from bile synthesis to intestinal stem cell maintenance to effect nutrient acquisition. Subsequently, coordinated KLF activity across multiple organs distributes nutrients to sites of storage or liberates them for use in response to changes in nutrient status. Finally, in energy-consuming organs like cardiac and skeletal muscle, KLFs tune local metabolic programs to precisely match substrate uptake, flux, and use, particularly via mitochondrial function, with energetic demand; this is achieved in part via circulating mediators, including glucocorticoids and insulin. Here, we summarize current understanding of KLFs in regulation of nutrient absorption, interorgan circulation, and tissue-specific use.

Role or Synergistic Interaction of Adenosine and Vitamin D3 Alongside High-Intensity Interval Training and Isocaloric Moderate Intensity Training on Metabolic Parameters: Protocol for an Experimental Study

Background

Obesity is known as one of the major causes of epidemiologic diseases worldwide; therefore, the introduction of treatment strategies by medical professionals, such as the use of various medicines and exercise programs to reduce fat or prevent obesity, is on the rise. Recently, researchers have shown special interest in assessing the effect of lipolytic adenosine and vitamin D deficiency, as well as the effect of exercise, on decreasing body fat percentage.

Objective

This study has been designed to examine the effect of adenosine and vitamin D3 injections, in conjunction with high-intensity interval training and isocaloric moderate-intensity training, on the metabolic parameters of obesity induced by a high-fat diet.

Methods

This is an experimental study using 92 Wistar rats. At 6 weeks of age, the rats' weights will be recorded, after which they will have 1 week to adapt to their new environment before being divided into 12 groups. The rats will participate in a 2-stage experimental intervention, including a 13-week fattening diet phase followed by a 12-week exercise training phase consisting of an exercise program and the injection of adenosine and vitamin D3. Groups 1 and 2 will have a normal diet, and the other groups will have a diet of 40% fat, with free access to food and water up to the second half of the second stage of the study (end of the sixth week of training). After termination of the interventions, tissue collection and molecular assessments (blood for biochemical, tissues for gene expression analyses, and anthropometrical indexes) will be performed.

Results

The project was initiated in April 2017 and completed in December 2017. Data analysis is under way, and the first results are expected to be submitted for publication in November 2018.

Conclusions

We hypothesize that weight loss–induced molecular changes and upregulation will be observed in line with an increase in lipolysis and beta oxidation in muscle and fat tissue as a result of performing isocaloric training in drug-receiving rats and groups on a high-fat diet.

International Registered Report Identifier (IRRID)

RR1-10.2196/10753

Role of adenosine receptors in the adipocyte-macrophage interaction during obesity

Lipoinflamation is the inflammation generated in the adipose tissue. It can contribute to the development of insulin resistance. The lipoinflammation-associated mechanisms are related to the function of adipocytes and macrophages present in the adipose tissue. In this regard, the level of nucleoside adenosine is increased in individuals with obesity. Causes or consequences of this increase are unknown. Although, adenosine activating its receptors (A₁, A_2A, A_2B and A₃) is able to differentially modulate the function of adipocytes and macrophages, in order to avoid the reduction of insulin sensitivity and generate an anti-inflammatory state in subject with obesity. In this review we propose that adenosine could be a key element in the development of new strategies for limit lipoinflammation and regulate metabolic homeostasis through modulation of adipocyte-macrophage dialogue.

Transcriptional Regulation of Adipogenesis

Adipocytes are the defining cell type of adipose tissue. Once considered a passive participant in energy storage, adipose tissue is now recognized as a dynamic organ that contributes to several important physiological processes, such as lipid metabolism, systemic energy homeostasis, and whole-body insulin sensitivity. Therefore, understanding the mechanisms involved in its development and function is of great importance. Adipocyte differentiation is a highly orchestrated process which can vary between different fat depots as well as between the sexes. While hormones, miRNAs, cytoskeletal proteins, and many other effectors can modulate adipocyte development, the best understood regulators of adipogenesis are the transcription factors that inhibit or promote this process. Ectopic expression and knockdown approaches in cultured cells have been widely used to understand the contribution of transcription factors to adipocyte development, providing a basis for more sophisticated in vivo strategies to examine adipogenesis. To date, over two dozen transcription factors have been shown to play important roles in adipocyte development. These transcription factors belong to several families with many different DNA-binding domains. While peroxisome proliferator-activated receptor gamma (PPARγ) is undoubtedly the most important transcriptional modulator of adipocyte development in all types of adipose tissue, members of the CCAAT/enhancer-binding protein, Krüppel-like transcription factor, signal transducer and activator of transcription, GATA, early B cell factor, and interferon-regulatory factor families also regulate adipogenesis. The importance of PPARγ activity is underscored by several covalent modifications that modulate its activity and its ability to modulate adipocyte development. This review will primarily focus on the transcriptional control of adipogenesis in white fat cells and on the mechanisms involved in this fine-tuned developmental process. © 2017 American Physiological Society. Compr Physiol 7:635-674, 2017.

Molecular implications of adenosine in obesity

Adenosine has broad activities in organisms due to the existence of multiple receptors, the differential adenosine concentrations necessary to activate these receptors and the presence of proteins able to synthetize, degrade or transport this nucleoside. All adenosine receptors have been reported to be involved in glucose homeostasis, inflammation, adipogenesis, insulin resistance, and thermogenesis, indicating that adenosine could participate in the process of obesity. Since adenosine seems to be associated with several effects, it is plausible that adenosine participates in the initiation and development of obesity or may function to prevent it. Thus, the purpose of this review was to explore the involvement of adenosine in adipogenesis, insulin resistance and thermogenesis, with the aim of understanding how adenosine could be used to avoid, treat or improve the metabolic state of obesity. Treatment with specific agonists and/or antagonists of adenosine receptors could reverse the obesity state, since adenosine receptors normalizes several mechanisms involved in obesity, such as lipolysis, insulin sensitivity and thermogenesis. Furthermore, obesity is a preventable state, and the specific activation of adenosine receptors could aid in the prevention of obesity. Nevertheless, for the treatment of obesity and its consequences, more studies and therapeutic strategies in addition to adenosine are necessary.

Potential Therapeutic Applications of Adipose-Derived Mesenchymal Stem Cells

Stem cells are subdivided into two main categories: embryonic and adult stem cells. In principle, pluripotent embryonic stem cells might differentiate in any cell types of the organism, whereas the potential of adult stem cells would be more restricted. Although adult stem cells from bone marrow have been initially the most extensively studied, those derived from human adipose tissue have been lately more widely investigated, because of several advantages. First, they can be easily obtained in large amounts from subcutaneous adipose tissue, with minimal pain and morbidity for the patients during harvesting. In addition, they feature low immunogenicity and can differentiate not only in cells of mesodermal lineage (adipocytes, osteoblasts, chondrocytes and muscle cells), but also in cells of other germ layers, such as neural or epithelial cells. As their multilineage differentiation capabilities are increasingly highlighted, their possible use in cell-based regenerative medicine is now broadly explored. In fact, starting from in vitro observations, many studies have already entered the preclinical and clinical phases. In this review, because of our main scientific interest, adipogenic, osteogenic, chondrogenic, and neurogenic differentiation abilities of adipose-derived mesenchymal stem cells, as well as their possible therapeutic applications, are chiefly focused. In addition, their ability to differentiate toward muscle, epithelial, pancreatic, and hepatic cells is briefly reported.

Correlation of A2bAR and KLF4/KLF15 with Obesity-Dyslipidemia Induced Inflammation in Uygur Population

In this paper, the researchers collected visceral adipose tissue from the Uygur population, which were divided into two groups: the normal control group (NC, n = 50, 18.0 kg/m(2) ≤ BMI ≤ 23.9 kg/m(2)) and the obese group (OB, n = 45, BMI ≥ 28 kg/m(2)), and then use real-time PCR to detect the mRNA expression level of key genes involved in inflammation signaling pathway. The findings suggest that, in obese status, the lower expression level of A2bAR, KLF4, and KLF15 of visceral adipose tissue may correlate with obese-dyslipidemia induced inflammation in Uygur population.

The Many Faces of the A2b Adenosine Receptor in Cardiovascular and Metabolic Diseases

Modulation of the low affinity adenosine receptor subtype, the A2b adenosine receptor (A2bAR), has gained interest as a therapeutic target in various pathologic areas associated with cardiovascular disease. The actions of the A2bAR are diverse and at times conflicting depending on cell and tissue type and the timing of activation or inhibition of the receptor. The A2bAR is a promising and exciting pharmacologic target, however, a thorough understanding of A2bAR action is necessary to reach the therapeutic potential of this receptor. This review will focus on the role of the A2bAR in various cardiovascular and metabolic pathologies in which the receptor is currently being studied. We will illustrate the complexities of A2bAR signaling and highlight areas of research with potential for therapeutic development.

Biomineralized matrices dominate soluble cues to direct osteogenic differentiation of human mesenchymal stem cells through adenosine signaling

Stem cell differentiation is determined by a repertoire of signals from its microenvironment, which includes the extracellular matrix (ECM) and soluble cues. The ability of mesenchymal stem cells (MSCs), a common precursor for the skeletal system, to differentiate into osteoblasts and adipocytes in response to their local cues plays an important role in skeletal tissue regeneration and homeostasis. In this study, we investigated whether a bone-specific calcium phosphate (CaP) mineral environment could induce osteogenic differentiation of human MSCs, while inhibiting their adipogenic differentiation, in the presence of adipogenic-inducing medium. We also examined the mechanism through which the mineralized matrix suppresses adipogenesis of hMSCs to promote their osteogenic differentiation. Our results show that hMSCs cultured on mineralized matrices underwent osteogenic differentiation despite being cultured in the presence of adipogenic medium, which indicates the dominance of matrix-based cues of the mineralized matrix in directing osteogenic commitment of stem cells. Furthermore, the mineralized matrix-driven attenuation of adipogenesis was reversed with the inhibition of A2b adenosine receptor (A2bR), implicating a role of adenosine signaling in mineralized environment-mediated inhibition of adipogenesis. Such synthetic matrices with an intrinsic ability to direct differentiation of multipotent adult stem cells toward a targeted phenotype while inhibiting their differentiation into other lineages not only will be a powerful tool in delineating the role of complex microenvironmental cues on stem cell commitment but also will contribute to functional tissue engineering and their translational applications.

The role of purinergic receptors in stem cell differentiation

A major challenge modern society has to face is the increasing need for tissue regeneration due to degenerative diseases or tumors, but also accidents or warlike conflicts. There is great hope that stem cell-based therapies might improve current treatments of cardiovascular diseases, osteochondral defects or nerve injury due to the unique properties of stem cells such as their self-renewal and differentiation potential. Since embryonic stem cells raise severe ethical concerns and are prone to teratoma formation, adult stem cells are still in the focus of research. Emphasis is placed on cellular signaling within these cells and in between them for a better understanding of the complex processes regulating stem cell fate. One of the oldest signaling systems is based on nucleotides as ligands for purinergic receptors playing an important role in a huge variety of cellular processes such as proliferation, migration and differentiation. Besides their natural ligands, several artificial agonists and antagonists have been identified for P1 and P2 receptors and are already used as drugs. This review outlines purinergic receptor expression and signaling in stem cells metabolism. We will briefly describe current findings in embryonic and induced pluripotent stem cells as well as in cancer-, hematopoietic-, and neural crest-derived stem cells. The major focus will be placed on recent findings of purinergic signaling in mesenchymal stem cells addressed in in vitro and in vivo studies, since stem cell fate might be manipulated by this system guiding differentiation towards the desired lineage in the future.