Global transcriptome profiling identifies KLF15 and SLC25A10 as modifiers of adipocytes insulin sensitivity in obese women

Identification and analysis of key genes in adipose tissue for human obesity based on bioinformatics

BACKGROUND

Obesity is a complex condition that is affected by a variety of factors, including the environment, behavior, and genetics. However, the genetic mechanisms underlying obesity remains poorly elucidated. Therefore, our study aimed at identifying key genes for human obesity using bioinformatics analysis.

METHODS

The microarray datasets of adipose tissue in humans were downloaded from the Gene Expression Omnibus (GEO) database. After the selection of differentially expressed genes (DEGs), we used Lasso regression and Support Vector Machine (SVM) algorithm to further identify the feature genes. Moreover, immune cell infiltration analysis, gene set variation analysis (GSVA), GeneCards database and transcriptional regulation analysis were conducted to study the potential mechanisms by which the feature genes may impact obesity. We utilized receiver operating characteristic (ROC) curve to analysis the diagnostic efficacy of feature genes. Finally, we verified the feature genes in cell experiments and animal experiments. The statistical analyses in validation experiments were conducted using SPSS version 28.0, and the graph were generated using GraphPad Prism 9.0 software. The bioinformatics analyses were conducted using R language (version 4.2.2), with a significance threshold of p < 0.05 used.

RESULTS

199 DEGs were selected using Limma package, and subsequently, 5 feature genes (EGR2, NPY1R, GREM1, BMP3 and COL8A1) were selected through Lasso regression and SVM algorithm. Through various bioinformatics analyses, we found some signaling pathways by which feature genes influence obesity and also revealed the crucial role of these genes in the immune microenvironment, as well as their strong correlations with obesity-related genes. Additionally, ROC curve showed that all the feature genes had good predictive and diagnostic efficiency in obesity. Finally, after validation through in vitro experiments, EGR2, NPY1R and GREM1 were identified as the key genes.

CONCLUSIONS

This study identified EGR2, GREM1 and NPY1R as the potential key genes and potential diagnostic biomarkers for obesity in humans. Moreover, EGR2 was discovered as a key gene for obesity in human adipose tissue for the first time, which may provide novel targets for diagnosing and treating obesity.

Integrated bioinformatics approach reveals methylation-regulated differentially expressed genes in obesity

Objective

To identify DNA methylation and gene expression profiles involved in obesity by implementing an integrated bioinformatics approach.

Materials and methods

Gene expression (GSE94752, GSE55200, and GSE48964) and DNA methylation (GSE67024 and GSE111632) datasets were obtained from the GEO database. Differentially expressed genes (DEGs) and differentially methylated genes (DMGs) in subcutaneous adipose tissue of patients with obesity were identified using GEO2R. Methylation-regulated DEGs (MeDEGs) were identified by overlapping DEGs and DMGs. The protein-protein interaction (PPI) network was constructed with the STRING database and analyzed using Cytoscape. Functional modules and hub-bottleneck genes were identified by using MCODE and CytoHubba plugins. Functional enrichment analyses were performed based on Gene Ontology terms and KEGG pathways. To prioritize and identify candidate genes for obesity, MeDEGs were compared with obesity-related genes available at the DisGeNET database.

Results

A total of 54 MeDEGs were identified after overlapping the lists of significant 274 DEGs and 11,556 DMGs. Of these, 25 were hypermethylated-low expression genes and 29 were hypomethylated-high expression genes. The PPI network showed three hub-bottleneck genes (PTGS2, TNFAIP3, and FBXL20) and one functional module. The 54 MeDEGs were mainly involved in the regulation of fibroblast growth factor production, the molecular function of arachidonic acid, and ubiquitin-protein transferase activity. Data collected from DisGeNET showed that 11 of the 54 MeDEGs were involved in obesity.

Conclusion

This study identifies new MeDEGs involved in obesity and assessed their related pathways and functions. These results data may provide a deeper understanding of methylation-mediated regulatory mechanisms of obesity.

Identification and Verification of Biomarkers and Immune Infiltration in Obesity-Related Atrial Fibrillation

Obesity is an independent risk factor for atrial fibrillation (AF). However, the mechanisms underlying this crosstalk are still being uncovered. Co-differentially expressed genes (co-DEGs) of AF and obesity microarrays were identified by bioinformatics analysis. Subsequently, functional enrichment, cell-type enrichment, and protein-protein interaction network analyses of co-DEGs were carried out. Then, we validated the hub genes by qRT-PCR of patients' blood samples. Finally, CIBERSORT was utilized to evaluate the AF microarray to determine immune infiltration and the correlation between validated hub genes and immune cells. A total of 23 co-up-regulated DEGs in AF and obesity microarrays were identified, and these genes were enriched in inflammation- and immune-related function. The enriched cells were whole blood, CD33+ myeloid, and CD14+ monocytes. The hub genes were identified as MNDA, CYBB, CD86, FCGR2C, NCF2, LCP2, TLR8, HLA-DRA, LCP1, and PTPN22. All hub genes were only elevated in blood samples of obese-AF patients. The CIBERSORT analysis revealed that the AF patients' left atrial appendage had increased infiltration of naïve B cells and decreased infiltration of memory B cells. The hub genes were related positively to naïve B cells and negatively to memory B cells. Ten hub genes may serve as biomarkers for obesity-related AF. These findings may also aid in comprehending pathophysiological mechanisms for obesity-related AF.

The Role of Molecular and Hormonal Factors in Obesity and the Effects of Physical Activity in Children

Obesity and overweight are defined as abnormal fat accumulations. Adipose tissue consists of more than merely adipocytes; each adipocyte is closely coupled with the extracellular matrix. Adipose tissue stores excess energy through expansion. Obesity is caused by the abnormal expansion of adipose tissue as a result of adipocyte hypertrophy and hyperplasia. The process of obesity is controlled by several molecules, such as integrins, kindlins, or matrix metalloproteinases. In children with obesity, metabolomics studies have provided insight into the existence of unique metabolic profiles. As a result of low-grade inflammation in the system, abnormalities were observed in several metabolites associated with lipid, carbohydrate, and amino acid pathways. In addition, obesity and related hormones, such as leptin, play an instrumental role in regulating food intake and contributing to childhood obesity. The World Health Organization states that physical activity benefits the heart, the body, and the mind. Several noncommunicable diseases, such as cardiovascular disease, cancer, and diabetes, can be prevented and managed through physical activity. In this work, we reviewed pediatric studies that examined the molecular and hormonal control of obesity and the influence of physical activity on children with obesity or overweight. The purpose of this review was to examine some orchestrators involved in this disease and how they are related to pediatric populations. A larger number of randomized clinical trials with larger sample sizes and long-term studies could lead to the discovery of new key molecules as well as the detection of significant factors in the coming years. In order to improve the health of the pediatric population, omics analyses and machine learning techniques can be combined in order to improve treatment decisions.

Adiposity associated DNA methylation signatures in adolescents are related to leptin and perinatal factors

Epigenetics links perinatal influences with later obesity. We identifed differentially methylated CpG (dmCpG) loci measured at 17 years associated with concurrent adiposity measures and examined whether these were associated with hsCRP, adipokines, and early life environmental factors. Genome-wide DNA methylation from 1192 Raine Study participants at 17 years, identified 29 dmCpGs (Bonferroni corrected p < 1.06E-07) associated with body mass index (BMI), 10 with waist circumference (WC) and 9 with subcutaneous fat thickness. DmCpGs within Ras Association (RalGDS/AF-6), Pleckstrin Homology Domains 1 (RAPH1), Musashi RNA-Binding Protein 2 (MSI2), and solute carrier family 25 member 10 (SLC25A10) are associated with both BMI and WC. Validation by pyrosequencing confirmed these associations and showed that MSI2 , SLC25A10 , and RAPH1 methylation was positively associated with serum leptin. These were  also associated with the early environment; MSI2 methylation (β = 0.81, p = 0.0004) was associated with pregnancy maternal smoking, SLC25A10 (CpG2 β = 0.12, p = 0.002) with pre- and early pregnancy BMI, and RAPH1 (β = -1.49, p = 0.036) with gestational weight gain. Adjusting for perinatal factors, methylation of the dmCpGs within MSI2, RAPH1, and SLC25A10 independently predicted BMI, accounting for 24% of variance. MSI2 methylation was additionally associated with BMI over time (17 years old β = 0.026, p = 0.0025; 20 years old β = 0.027, p = 0.0029) and between generations (mother β = 0.044, p = 7.5e-04). Overall findings suggest that DNA methylation in MSI2, RAPH1, and SLC25A10 in blood may be robust markers, mediating through early life factors.

Adipocyte lysoplasmalogenase TMEM86A regulates plasmalogen homeostasis and protein kinase A-dependent energy metabolism

Dysregulation of adipose tissue plasmalogen metabolism is associated with obesity-related metabolic diseases. We report that feeding mice a high-fat diet reduces adipose tissue lysoplasmalogen levels and increases transmembrane protein 86 A (TMEM86A), a putative lysoplasmalogenase. Untargeted lipidomic analysis demonstrates that adipocyte-specific TMEM86A-knockout (AKO) increases lysoplasmalogen content in adipose tissue, including plasmenyl lysophosphatidylethanolamine 18:0 (LPE P-18:0). Surprisingly, TMEM86A AKO increases protein kinase A signalling pathways owing to inhibition of phosphodiesterase 3B and elevation of cyclic adenosine monophosphate. TMEM86A AKO upregulates mitochondrial oxidative metabolism, elevates energy expenditure, and protects mice from metabolic dysfunction induced by high-fat feeding. Importantly, the effects of TMEM86A AKO are largely reproduced in vitro and in vivo by LPE P-18:0 supplementation. LPE P-18:0 levels are significantly lower in adipose tissue of human patients with obesity, suggesting that TMEM86A inhibition or lysoplasmalogen supplementation might be therapeutic approaches for preventing or treating obesity-related metabolic diseases.

Integrative analysis of miRNA and mRNA profiles reveals that gga-miR-106-5p inhibits adipogenesis by targeting the KLF15 gene in chickens

Background

Excessive abdominal fat deposition in commercial broilers presents an obstacle to profitable meat quality, feed utilization, and reproduction. Abdominal fat deposition depends on the proliferation of preadipocytes and their maturation into adipocytes, which involves a cascade of regulatory molecules. Accumulating evidence has shown that microRNAs (miRNAs) serve as post-transcriptional regulators of adipogenic differentiation in mammals. However, the miRNA-mediated molecular mechanisms underlying abdominal fat deposition in chickens are still poorly understood. This study aimed to investigate the biological functions and regulatory mechanism of miRNAs in chicken abdominal adipogenesis.

Results

We established a chicken model of abdominal adipocyte differentiation and analyzed miRNA and mRNA expression in abdominal adipocytes at different stages of differentiation (0, 12, 48, 72, and 120 h). A total of 217 differentially expressed miRNAs (DE-miRNAs) and 3520 differentially expressed genes were identified. Target prediction of DE-miRNAs and functional enrichment analysis revealed that the differentially expressed targets were significantly enriched in lipid metabolism-related signaling pathways, including the PPAR signaling and MAPK signaling pathways. A candidate miRNA, gga-miR-106-5p, exhibited decreased expression during the proliferation and differentiation of abdominal preadipocytes and was downregulated in the abdominal adipose tissues of fat chickens compared to that of lean chickens. gga-miR-106-5p was found to inhibit the proliferation and adipogenic differentiation of chicken abdominal preadipocytes. A dual-luciferase reporter assay suggested that the KLF15 gene, which encodes a transcriptional factor, is a direct target of gga-miR-106-5p. gga-miR-106-5p suppressed the post-transcriptional activity of KLF15, which is an activator of abdominal preadipocyte proliferation and differentiation, as determined with gain- and loss-of-function experiments.

Conclusions

gga-miR-106-5p functions as an inhibitor of abdominal adipogenesis by targeting the KLF15 gene in chickens. These findings not only improve our understanding of the specific functions of miRNAs in avian adipogenesis but also provide potential targets for the genetic improvement of excessive abdominal fat deposition in poultry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00727-x.

Mouse Embryonic Fibroblast Adipogenic Potential: A Comprehensive Transcriptome Analysis

Our understanding of adipose tissue has progressed from an inert tissue for energy storage to be one of the largest endocrine organs regulating metabolic homoeostasis through its ability to synthesize and release various adipokines that regulate a myriad of pathways. The field of adipose tissue biology is growing due to this association with various chronic metabolic diseases. An important process in the regulation of adipose tissue biology is adipogenesis, which is the formation of new adipocytes. Investigating adipogenesis in vitro is currently a focus for identifying factors that might be utilized in clinically. A powerful tool for such work is high-throughput sequencing which can rapidly identify changes at gene expression level. Various cell models exist for studying adipogenesis and has been used in high-throughput studies, yet little is known about transcriptome profile that underlies adipogenesis in mouse embryonic fibroblasts. This study utilizes RNA-sequencing and computational analysis with DESeq2, gene ontology, protein–protein networks, and robust rank analysis to understand adipogenesis in mouse embryonic fibroblasts in-depth. Our analyses confirmed the requirement of mitotic clonal expansion prior to adipogenesis in this cell model and highlight the role of Cebpa and Cebpb in regulating adipogenesis through interactions of large numbers of genes.

The mitochondrial dicarboxylate carrier prevents hepatic lipotoxicity by inhibiting white adipocyte lipolysis

BACKGROUND & AIMS

We have previously reported that the mitochondrial dicarboxylate carrier (mDIC [SLC25A10]) is predominantly expressed in the white adipose tissue (WAT) and subject to regulation by metabolic cues. However, the specific physiological functions of mDIC and the reasons for its abundant presence in adipocytes are poorly understood.

METHODS

To systemically investigate the impact of mDIC function in adipocytes in vivo, we generated loss- and gain-of-function mouse models, selectively eliminating or overexpressing mDIC in mature adipocytes, respectively.

RESULTS

In in vitro differentiated white adipocytes, mDIC is responsible for succinate transport from the mitochondrial matrix to the cytosol, from where succinate can act on the succinate receptor SUCNR1 and inhibit lipolysis by dampening the cAMP- phosphorylated hormone-sensitive lipase (pHSL) pathway. We eliminated mDIC expression in adipocytes in a doxycycline (dox)-inducible manner (mDIC^iKO) and demonstrated that such a deletion results in enhanced adipocyte lipolysis and promotes high-fat diet (HFD)-induced adipocyte dysfunction, liver lipotoxicity, and systemic insulin resistance. Conversely, in a mouse model with dox-inducible, adipocyte-specific overexpression of mDIC (mDIC^iOE), we observed suppression of adipocyte lipolysis both in vivo and ex vivo. mDIC^iOE mice are potently protected from liver lipotoxicity upon HFD feeding. Furthermore, they show resistance to HFD-induced weight gain and adipose tissue expansion with concomitant improvements in glucose tolerance and insulin sensitivity. Beyond our data in rodents, we found that human WAT SLC25A10 mRNA levels are positively correlated with insulin sensitivity and negatively correlated with intrahepatic triglyceride levels, suggesting a critical role of mDIC in regulating overall metabolic homeostasis in humans as well.

CONCLUSIONS

In summary, we highlight that mDIC plays an essential role in governing adipocyte lipolysis and preventing liver lipotoxicity in response to a HFD.

LAY SUMMARY

Dysfunctional fat tissue plays an important role in the development of fatty liver disease and liver injury. Our present study identifies a mitochondrial transporter, mDIC, which tightly controls the release of free fatty acids from adipocytes to the liver through the export of succinate from mitochondria. We believe this mDIC-succinate axis could be targeted for the treatment of fatty liver disease.

An RNAi Screening of Clinically Relevant Transcription Factors Regulating Human Adipogenesis and Adipocyte Metabolism

CONTEXT

Healthy hyperplasic (many but smaller fat cells) white adipose tissue (WAT) expansion is mediated by recruitment, proliferation and/or differentiation of new fat cells. This process (adipogenesis) is controlled by transcriptional programs that have been mostly identified in rodents.

OBJECTIVE

A systemic investigation of adipogenic human transcription factors (TFs) that are relevant for metabolic conditions has not been revealed previously.

METHODS

TFs regulated in WAT by obesity, adipose morphology, cancer cachexia, and insulin resistance were selected from microarrays. Their role in differentiation of human adipose tissue-derived stem cells (hASC) was investigated by RNA interference (RNAi) screen. Lipid accumulation, cell number, and lipolysis were measured for all screened factors (148 TFs). RNA (RNAseq), protein (Western blot) expression, insulin, and catecholamine responsiveness were examined in hASC following siRNA treatment of selected target TFs.

RESULTS

Analysis of TFs regulated by metabolic conditions in human WAT revealed that many of them belong to adipogenesis-regulating pathways. The RNAi screen identified 39 genes that affected fat cell differentiation in vitro, where 11 genes were novel. Of the latter JARID2 stood out as being necessary for formation of healthy fat cell metabolic phenotype by regulating expression of multiple fat cell phenotype-specific genes.

CONCLUSION

This comprehensive RNAi screening in hASC suggests that a large proportion of WAT TFs that are impacted by metabolic conditions might be important for hyperplastic adipose tissue expansion. The screen also identified JARID2 as a novel TF essential for the development of functional adipocytes.

The Vagus Nerve and Spleen: Influence on White Adipose Mass and Histology of Obese and Non-obese Rats

The vagus nerve (VN) and spleen represent a complex interface between neural and immunological functions, affecting both energy metabolism and white adipose tissue (WAT) content. Here, we evaluated whether vagal and splenic axis participates in WAT mass regulation in obese and non-obese male Wistar rats. High doses of monosodium glutamate (M; 4 g/Kg) were administered during the neonatal period to induce hypothalamic lesion and obesity (M-Obese rats). Non-obese or Control (CTL) rats received equimolar saline. At 60 days of life, M-Obese and CTL rats were randomly distributed into experimental subgroups according to the following surgical procedures: sham, subdiaphragmatic vagotomy (SV), splenectomy (SPL), and SV + SPL (n = 11 rats/group). At 150 days of life and after 12 h of fasting, rats were euthanized, blood was collected, and the plasma levels of glucose, triglycerides, cholesterol, insulin, and interleukin 10 (IL10) were analyzed. The visceral and subcutaneous WAT depots were excised, weighed, and histologically evaluated for number and size of adipocytes as well as IL10 protein expression. M-Obese rats showed higher adiposity, hyperinsulinemia, hypertriglyceridemia, and insulin resistance when compared with CTL groups (p < 0.05). In CTL and M-Obese rats, SV reduced body weight gain and triglycerides levels, diminishing adipocyte size without changes in IL10 expression in WAT (p< 0.05). The SV procedure resulted in high IL10 plasma levels in CTL rats, but not in the M-Obese group. The splenectomy prevented the SV anti-adiposity effects, as well as blocked the elevation of IL10 levels in plasma of CTL rats. In contrast, neither SV nor SPL surgeries modified the plasma levels of IL10 and IL10 protein expression in WAT from M-Obese rats. In conclusion, vagotomy promotes body weight and adiposity reduction, elevating IL10 plasma levels in non-obese animals, in a spleen-dependent manner. Under hypothalamic obesity conditions, VN ablation also reduces body weight gain and adiposity, improving insulin sensitivity without changes in IL10 protein expression in WAT or IL10 plasma levels, in a spleen-independent manner. Our findings indicate that the vagal-spleen axis influence the WAT mass in a health state, while this mechanism seems to be disturbed in hypothalamic obese animals.

Aquaporins in insulin resistance and diabetes: More than channels!

Aquaporins (AQPs) are part of the family of the integral membrane proteins. Their function is dedicated to the transport of water, glycerol, ammonia, urea, H₂O₂, and other small molecules across the biological membranes. Although for many years they were scarcely considered, AQPs have a relevant role in the development of many diseases. Recent discoveries suggest, that AQPs may play an important role in the process of fat accumulation and regulation of oxidative stress, two crucial aspects of insulin resistance and type-2 diabetes (T2D).

Insulin resistance (IR) and T2D are multi-faceted systemic diseases with multiple connections to obesity and other comorbidities such as hypertension, dyslipidemia and metabolic syndrome. Both IR and T2D transcends different tissues and organs, creating the maze of mutual relationships between adipose fat depots, skeletal muscle, liver and other insulin-sensitive organs. AQPs with their heterogenous properties, distinctive tissue distribution and documented involvement in both the lipid metabolism and regulation of the oxidative stress appear to be feasible candidates in the search for the explanation to this third-millennium plague. A lot of research has been assigned to adipose tissue AQP7 and liver tissue AQP9, clarifying their relationship and coordinated work in the induction of hepatic insulin resistance. Novel research points also to other aquaporins, such as AQP11 which may be associated with the induction of insulin resistance and T2D through its involvement in hydrogen peroxide transport.

In this review we collected recent discoveries in the field of AQP's involvement in the insulin resistance and T2D. Novel paths which connect AQPs with metabolic disorders can give new fuel to the research on obesity, insulin resistance and T2D - one of the most worrying problems of the modern society.

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Presentation of the current knowledge on the involvement of aquaporins in disease state.

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Overview on latest research regarding insulin resistance and AQPs.

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Conceptualisation of an AQPs network involved regulation of lipid-related metabolism.

Molecular pathways behind acquired obesity: Adipose tissue and skeletal muscle multiomics in monozygotic twin pairs discordant for BMI

Tissue-specific mechanisms prompting obesity-related development complications in humans remain unclear. We apply multiomics analyses of subcutaneous adipose tissue and skeletal muscle to examine the effects of acquired obesity among 49 BMI-discordant monozygotic twin pairs. Overall, adipose tissue appears to be more affected by excess body weight than skeletal muscle. In heavier co-twins, we observe a transcriptional pattern of downregulated mitochondrial pathways in both tissues and upregulated inflammatory pathways in adipose tissue. In adipose tissue, heavier co-twins exhibit lower creatine levels; in skeletal muscle, glycolysis- and redox stress-related protein and metabolite levels remain higher. Furthermore, metabolomics analyses in both tissues reveal that several proinflammatory lipids are higher and six of the same lipid derivatives are lower in acquired obesity. Finally, in adipose tissue, but not in skeletal muscle, mitochondrial downregulation and upregulated inflammation are associated with a fatty liver, insulin resistance, and dyslipidemia, suggesting that adipose tissue dominates in acquired obesity.

Multiomics analyses of adipose tissue and skeletal muscle in BMI-discordant twins

Excess body weight downregulates mitochondrial pathways in both tissues

Excess body weight upregulates proinflammatory pathways in both tissues

Adipose tissue alterations are associated with metabolic health in acquired obesity

Involvement of aquaglyceroporins in energy metabolism in health and disease

Aquaglyceroporins are a group of the aquaporin (AQP) family of transmembrane water channels. While AQPs facilitate the passage of water, small solutes, and gases across biological membranes, aquaglyceroporins allow passage of water, glycerol, urea and some other solutes. Thanks to their glycerol permeability, aquaglyceroporins are involved in energy homeostasis. This review provides an overview of what is currently known concerning the functional implication and control of aquaglyceroporins in tissues involved in energy metabolism, i.e. liver, adipose tissue and endocrine pancreas. The expression, role and (dys)regulation of aquaglyceroporins in disorders affecting energy metabolism, and the potential relevance of aquaglyceroporins as drug targets to treat the alterations of the energy balance is also addressed.

KibioR & Kibio: a new architecture for next-generation data querying and sharing in big biology

MOTIVATION

The growing production of massive heterogeneous biological data offers opportunities for new discoveries. However, performing multi-omics data analysis is challenging, and researchers are forced to handle the ever-increasing complexity of both data management and evolution of our biological understanding. Substantial efforts have been made to unify biological datasets into integrated systems. Unfortunately, they are not easily scalable, deployable and searchable, locally or globally.

RESULTS

This publication presents two tools with a simple structure that can help any data provider, organization or researcher, requiring a reliable data search and analysis base. The first tool is Kibio, a scalable and adaptable data storage based on Elasticsearch search engine. The second tool is KibioR, a R package to pull, push and search Kibio datasets or any accessible Elasticsearch-based databases. These tools apply a uniform data exchange model and minimize the burden of data management by organizing data into a decentralized, versatile, searchable and shareable structure. Several case studies are presented using multiple databases, from drug characterization to miRNAs and pathways identification, emphasizing the ease of use and versatility of the Kibio/KibioR framework.

AVAILABILITY

Both KibioR and Elasticsearch are open source. KibioR package source is available at https://github.com/regisoc/kibior and the library on CRAN at https://cran.r-project.org/package=kibior.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

SLC25A10 performs an oncogenic role in human osteosarcoma

Osteosarcoma is one of the most common primary malignant bone tumors in adolescents. It is associated with high risk of relapse and the outcomes of patients with high-grade osteosarcoma remain poor. Therefore, additional studies investigating the molecular mechanisms involved in tumor initiation, growth, migration and invasion of osteosarcoma are necessary. In the present study, the protein levels of solute carrier family 25 member 10 (SLC25A10) were increased in osteosarcoma tissue, compared with normal bone tissue. In patients with osteosarcoma, high expression levels of SLC25A10 were associated with poor clinicopathological parameters, including metastasis, clinical Enneking stage, relapse-free survival and overall survival rates. Short hairpin RNA knockdown of SLC25A10 significantly suppressed cell proliferation as determined by cell counting, MTT assay and cell colony formation assays. In addition, SLC25A10 knockdown caused an increase in apoptosis and a decrease in mitosis in osteosarcoma cells. Cyclin E1 (CCNE1) was positively regulated by SLC25A10, while P21 and P27 were negatively regulated by SLC25A10. Therefore, SLC25A10 may play an oncogenic role in human osteosarcoma, which could be mediated by CCNE1, P21 and P27.

Cell-autonomous light sensitivity via Opsin3 regulates fuel utilization in brown adipocytes

Opsin3 (Opn3) is a transmembrane heptahelical G protein–coupled receptor (GPCR) with the potential to produce a nonvisual photoreceptive effect. Interestingly, anatomical profiling of GPCRs reveals that Opn3 mRNA is highly expressed in adipose tissue. The photosensitive functions of Opn3 in mammals are poorly understood, and whether Opn3 has a role in fat is entirely unknown. In this study, we found that Opn3-knockout (Opn3-KO) mice were prone to diet-induced obesity and insulin resistance. At the cellular level, Opn3-KO brown adipocytes cultured in darkness had decreased glucose uptake and lower nutrient-induced mitochondrial respiration than wild-type (WT) cells. Light exposure promoted mitochondrial activity and glucose uptake in WT adipocytes but not in Opn3-KO cells. Brown adipocytes carrying a defective mutation in Opn3’s putative G protein–binding domain also exhibited a reduction in glucose uptake and mitochondrial respiration in darkness. Using RNA-sequencing, we identified several novel light-sensitive and Opn3-dependent molecular signatures in brown adipocytes. Importantly, direct exposure of brown adipose tissue (BAT) to light in living mice significantly enhanced thermogenic capacity of BAT, and this effect was diminished in Opn3-KO animals. These results uncover a previously unrecognized cell-autonomous, light-sensing mechanism in brown adipocytes via Opn3-GPCR signaling that can regulate fuel metabolism and mitochondrial respiration. Our work also provides a molecular basis for developing light-based treatments for obesity and its related metabolic disorders.

Brown adipose tissue plays a pivotal role in energy homeostasis and serves as a metabolic sink for glucose and fatty acid. This study demonstrates a novel light-sensing mechanism in mice via the photoreceptor Opsin3 that regulates fuel utilization and mitochondrial activity of brown adipocytes.

Impaired Peroxisomal Fitness in Obese Mice, a Vicious Cycle Exacerbating Adipocyte Dysfunction via Oxidative Stress

Aims: Peroxisome is a critical organelle for fatty acid oxidation (FAO) and metabolism of reactive oxygen species (ROS). Increased oxidative stress in adipose tissue contributes to the development of insulin resistance and metabolic syndrome in obesity. This study aimed to investigate the role of peroxisomal fitness in maintaining adipocyte function, which has been under-rated in the obesity research area. Results: Reduced peroxisomal gene expressions in white adipose tissue (WAT) of obese mice suggested a close correlation between peroxisomes and obesity. Peroxisomal biogenesis factor 5 siRNA increased cellular ROS and inflammatory mediators in 3T3-L1 adipocytes. On the contrary, hydrogen peroxide or tumor necrosis factor-α treatment significantly decreased biogenesis- and function-related peroxisomal proteins, suggesting a positive feedback loop of ROS/inflammation and peroxisomal dysfunction. Correspondingly, catalase (a major peroxisomal antioxidant)-knockout mice fed with high-fat diet (HFD) exhibited suppressed peroxisomal proteins along with increased oxidative stress and accelerated obesity. In response to fenofibrate (a peroxisomal proliferator) treatment, WAT of HFD-fed wild-type mice showed not only increases in peroxisomal biogenesis and FAO but also attenuated features of adipocyte dysfunction and obesity. However, these results were not observed in peroxisome proliferator-activated receptor-alpha null obese mice. Innovation: Impaired peroxisomal fitness enhanced oxidative stress and inflammation in adipocytes, which exacerbates obesity. Conclusion: Adipose tissue peroxisomal homeostasis plays an important role in attenuating the features of obesity, and it can be a potential therapeutic target of obesity.

Transcriptome Analysis Reveals the Effect of Long Intergenic Noncoding RNAs on Pig Muscle Growth and Fat Deposition

Muscle growth and fat deposition are the two important biological processes in the development of pigs which are closely related to the pig production performance. Long intergenic noncoding RNAs (lincRNAs), with lack of coding potential and the length of at least 200nt, have been extensively studied to play important roles in many biological processes. However, the importance and molecular regulation mechanism of lincRNAs in the process of muscle growth and fat deposition in pigs are still to be further studied comprehensively. In our study, we used the data, including liver, abdominal fat, and longissimus dorsi muscle of 240 days' age of two F2 full-sib female individuals from the white Duroc and Erhualian crossbreed, to identify 581 putative lincRNAs associated with pig muscle growth and fat deposition. The 581 putative lincRNAs shared many common features with other mammalian lincRNAs, such as fewer exons, lower expression levels, and shorter transcript lengths. Cross-tissue comparisons showed that many transcripts were tissue-specific and were involved in the important biological processes in their corresponding tissues. Gene ontology and pathway analysis revealed that many potential target genes (PTGs) of putative lincRNAs were involved in pig muscle growth and fat deposition-related processes, including muscle cell proliferation, lipid metabolism, and fatty acid degradation. In Quantitative Trait Locus (QTLs) analysis, some PTGs were screened from putative lincRNAs, MRPL12 is associated with muscle growth, GCGR and SLC25A10 were associated with fat deposition, and PPP3CA, DPYD, and FGGY were related not only to muscle growth but also to fat deposition. Therefore, it implied that these lincRNAs might participate in the biological processes related to muscle growth or fat deposition through homeostatic regulation of PTGs, but the detailed molecular regulatory mechanisms still needed to be further explored. This study lays the molecular foundation for the in-depth study of the role of lincRNAs in the pig muscle growth and fat deposition and further provides the new molecular markers for understanding the complex biological mechanisms of pig muscle growth and fat deposition.

Hyperinsulinemia-induced KLF5 mediates endothelial angiogenic dysfunction in diabetic endothelial cells

Reduced expression of endothelial nitric oxide synthase (eNOS) is a hallmark of endothelial dysfunction in diabetes, which predisposes diabetic patients to numerous cardiovascular complications including blunted angiogenesis. The Krüppel-like factor (KLF) five has been implicated as a central regulator of cardiovascular remodeling, but its role in endothelial cells (ECs) remains poorly understood. We show here that expression of endothelial KLF5 was significantly increased in the ECs from mouse diabetes mellitus type 2 (T2DM) model, when compared to non-diabetic or T1DM mouse. KLF5 up-regulation by insulin was dependent on activation of multiple pathways, including mammalian target of rapamycin, oxidative stress and Protein kinase C pathways. Hyperinsulinemia-induced KLF5 inhibited endothelial function and migration, and thereby compromised in vitro and in vivo angiogenesis. Mechanistically, KLF5 acted in concert with the MTA1 coregulator to negatively regulate NOS3 transcription, thereby leading to the diminished eNOS levels in ECs. Conversely, potentiation of cGMP content (the essential downstream effector of eNOS signaling) by pharmacological approaches successfully rescued the endothelial proliferation and in vitro tube formation, in the HUVECs overexpressing the exogenous KLF5. Collectively, the available data suggest that the augmentation of endothelial KLF5 expression by hyperinsulinemia may represent a novel mechanism for negatively regulating eNOS expression, and may thus help to explain for the T2DM-related endothelial dysfunction at the transcriptional level.

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.

Metformin downregulates the mitochondrial carrier SLC25A10 in a glucose dependent manner

Metformin, a commonly used agent in the treatment of type 2 diabetes, is also associated with reduced risk of cancer development and improvement in cancer survival. Although much is known about metformin, the mechanisms behind its anti-cancer properties are not fully understood. In this study we addressed the role of a mitochondrial transporter commonly upregulated in cancer cells, SLC25A10, for cell survival and metabolism in the presence of metformin. SLC25A10 is a carrier in the mitochondrial inner membrane that transports malate and succinate out of the mitochondria, in exchange of phosphate and sulfate. We show that metformin treatment results in decreased gene expression of the SLC25A10 carrier both in lung cancer A549 mock cells and A549 SLC25A10 knockdown (siSLC25A10) cells. The decrease was even more pronounced when cells were grown at low glucose concentrations. The expression levels of key enzymes in glucose metabolism showed slightly altered mean values for all genes tested in both control cells and siSLC25A10 cells upon metformin treatment. The gene expression of the metabolic regulator glutamic-oxaloacetic transaminase 1 decreased in wild type cells upon metformin treatment whereas there was a trend of increased expression in the siSLC25A10 cells upon metformin treatment. In addition, the gene expression of the cyclin-dependent kinase inhibitor 1A was markedly increased in the siSLC25A10 compared to control A549 cells, and with even larger increases in the presence of metformin and at low glucose concentration. Our data show that in siSLC25A10 cell lines, metformin significantly alters the SLC25A10 carrier at both mRNA and protein levels and can thereby affect the supply of nutrients and the metabolic state of cancer cells.

Aquaglyceroporins: Drug Targets for Metabolic Diseases?

Aquaporins (AQPs) are a family of transmembrane channel proteins facilitating the transport of water, small solutes, and gasses across biological membranes. AQPs are expressed in all tissues and ensure multiple roles under normal and pathophysiological conditions. Aquaglyceroporins are a subfamily of AQPs permeable to glycerol in addition to water and participate thereby to energy metabolism. This review focalizes on the present knowledge of the expression, regulation and physiological roles of AQPs in adipose tissue, liver and endocrine pancreas, that are involved in energy metabolism. In addition, the review aims at summarizing the involvement of AQPs in metabolic disorders, such as obesity, diabetes and liver diseases. Finally, challenges and recent advances related to pharmacological modulation of AQPs expression and function to control and treat metabolic diseases are discussed.

Cdkn2a deficiency promotes adipose tissue browning

Objectives

Genome-wide association studies have reported that DNA polymorphisms at the CDKN2A locus modulate fasting glucose in human and contribute to type 2 diabetes (T2D) risk. Yet the causal relationship between this gene and defective energy homeostasis remains elusive. Here we sought to understand the contribution of Cdkn2a to metabolic homeostasis.

Methods

We first analyzed glucose and energy homeostasis from Cdkn2a-deficient mice subjected to normal or high fat diets. Subsequently Cdkn2a-deficient primary adipose cells and human-induced pluripotent stem differentiated into adipocytes were further characterized for their capacity to promote browning of adipose tissue. Finally CDKN2A levels were studied in adipocytes from lean and obese patients.

Results

We report that Cdkn2a deficiency protects mice against high fat diet-induced obesity, increases energy expenditure and modulates adaptive thermogenesis, in addition to improving insulin sensitivity. Disruption of Cdkn2a associates with increased expression of brown-like/beige fat markers in inguinal adipose tissue and enhances respiration in primary adipose cells. Kinase activity profiling and RNA-sequencing analysis of primary adipose cells further demonstrate that Cdkn2a modulates gene networks involved in energy production and lipid metabolism, through the activation of the Protein Kinase A (PKA), PKG, PPARGC1A and PRDM16 signaling pathways, key regulators of adipocyte beiging. Importantly, CDKN2A expression is increased in adipocytes from obese compared to lean subjects. Moreover silencing CDKN2A expression during human-induced pluripotent stem cells adipogenic differentiation promoted UCP1 expression.

Conclusion

Our results offer novel insight into brown/beige adipocyte functions, which has recently emerged as an attractive therapeutic strategy for obesity and T2D. Modulating Cdkn2a-regulated signaling cascades may be of interest for the treatment of metabolic disorders.

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Cdkn2a deficiency protects mice against high fat diet-induced obesity.

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Cdkn2a modulates brown-like/beige fat gene networks involved in energy production and lipid metabolism.

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Increased CDKN2A expression in human obese adipocytes.

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Increased UCP1 levels in adipocytes differentiated from CDKN2A-silenced hiPS cells.