Dietary oleic acid drives obesogenic adipogenesis via modulation of LXRasignaling
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ABSTRACT: Dietary fat composition has changed substantially as the obesity epidemic has spread. Adipocyte hyperplasia is a major mechanism of fat mass expansion in obesity, but how dietary fats contribute to obesogenic adipocyte hyperplasia is unknown. Here we employed various dietary strategies, including an unbiased dietary screen, to determine the effect of dietary fat composition on adipocyte hyperplasia in mice. We identified oleic acid (OA) as the only dietary fatty acid that induces adipogenesis and obesogenic hyperplasia at physiologic levels. OA induced differentiation via AKT2 signaling, a hallmark of obesogenic hyperplasia. We also demonstrate that reduction of LXR signaling in APCs is necessary for OA-stimulated adipogenesis. Furthermore, blocking LXRaphosphorylation at S196 results in APC hyperproliferation upon HFD feeding, suggesting that LXRaphosphorylation inhibits HFD-stimulated proliferation. As OA is associated with numerous health effects, our findings that OA is a unique physiologic metabolic regulator underscores the importance of understanding the mechanisms by which OA effects metabolic health.
Project description:Dietary fat composition has changed substantially as the obesity epidemic has spread. Adipocyte hyperplasia is a major mechanism of fat mass expansion in obesity, but how dietary fats contribute to obesogenic adipocyte hyperplasia is unknown. Here we employed various dietary strategies, including an unbiased dietary screen, to determine the effect of dietary fat composition on adipocyte hyperplasia in mice. We identified oleic acid (OA) as the only dietary fatty acid that induces adipogenesis and obesogenic hyperplasia at physiologic levels. OA induced differentiation via AKT2 signaling, a hallmark of obesogenic hyperplasia. We also demonstrate that reduction of LXR signaling in APCs is necessary for OA-stimulated adipogenesis. Furthermore, blocking LXRa phosphorylation at S196 results in APC hyperproliferation upon HFD feeding, suggesting that LXRa phosphorylation inhibits HFD-stimulated proliferation. As OA is associated with numerous health effects, our findings that OA is a unique physiologic metabolic regulator underscores the importance of understanding the mechanisms by which OA effects metabolic health.
Project description:White adipose tissue (WAT) distribution is sex dependent. Adipocyte hyperplasia contributes to WAT distribution in mice driven by cues in the tissue microenvironment, with females displaying hyperplasia in subcutaneous and visceral WAT, while males and ovariectomized females have visceral WAT (VWAT)-specific hyperplasia. However, the mechanism underlying sex-specific hyperplasia remains elusive. Here, transcriptome analysis in female mice shows that high-fat diet (HFD) induces estrogen signaling in adipocyte precursor cells (APCs). Analysis of APCs throughout the estrous cycle demonstrates increased proliferation only when proestrus (high estrogen) coincides with the onset of HFD feeding. We further show that estrogen receptor α (ERα) is required for this proliferation and that estradiol treatment at the onset of HFD feeding is sufficient to drive it. This estrous influence on APC proliferation leads to increased obesity driven by adipocyte hyperplasia. These data indicate that estrogen drives ERα-dependent obesogenic adipocyte hyperplasia in females, exacerbating obesity and contributing to the differential fat distribution between the sexes.
Project description:Abstract Background In obesity, adipose tissue undergoes a remodeling process characterized by increased adipocyte size (hypertrophia) and number (hyperplasia). The individual ability to tip the balance toward the hyperplastic growth, with recruitment of new fat cells through adipogenesis, seems to be critical for a healthy adipose tissue expansion, as opposed to the development of inflammation and detrimental metabolic consequences. However, the molecular mechanisms underlying this fine-tuned regulation are far from being understood. Methods We analyzed by mass spectrometry-based proteomics visceral white adipose tissue (vWAT) samples collected from C57BL6 mice fed with a HFD for 8 weeks. A subset of these mice, called low responders (LowR HFD), showed a low susceptibility to the onset of adipose tissue inflammation, as opposed to their HFD counterpart. We identified the discriminants between LowR HFD and HFD vWAT samples and explored their function in Adipose Derived human Mesenchymal Stem Cells (AD-hMSCs) differentiated to adipocytes. Results We quantified 6051 proteins. Among the candidates that most differentiate LowR HFD from HFD vWAT, we found proteins involved in adipocyte function, including adiponectin and hormone sensitive lipase, suggesting that adipocyte differentiation is enhanced in LowR HFD, as compared to HFD. The chromatin modifier SET and MYND Domain Containing 3 (SMYD3), whose function in adipose tissue was totally unknown, was another top-scored hit. SMYD3 expression was significantly higher in LowR HFD vWAT, as confirmed by western blot analysis. In vitro, we found that SMYD3 mRNA and protein levels decrease rapidly along the differentiation process of AD-hMSCs. Moreover, SMYD3 knock-down at the beginning of adipocyte differentiation resulted in reduced cell proliferation and, at longer term, reduced lipid accumulation in adipocytes. Conclusions Our study describes for the first time the role of SMYD3 as a regulator of adipocyte proliferation during the early steps of adipogenesis.
Project description:The development of obesity is characterized by metabolic overload of tissues and sub-sequent organ inflammation. Health effects of krill oil (KrO) on obesity-associated inflammation remain largely elusive, because long-term treatments with KrO have not been performed so far. In this study, mice were fed an obesogenic diet (HFD) containing 3% (w/w) KrO for 28 weeks. KrO treatment increased the concentrations of EPA and DHA and associated oxylipins, including 18-HEPE, RvE2, 14-HDHA in white adipose tissue (WAT) and liver. Simultaneously, KrO decreased arachidonic acid (ARA) concentrations and ARA-derived oxylipins (e.g. HETEs, PGD2, PGE2, PGF2α, TXB2). In epididymal WAT (eWAT), KrO activated regulators of adipogenesis (e.g. PPARγ, CEBPα, KLF15, STAT5A), induced a shift towards smaller adipocytes and increased total adipocyte numbers indicative for hyperplasia. KrO reduced crown-like structures in eWAT, and suppressed HFD-stimulated inflammatory pathways including TNFα and CCL2/MCP-1 signaling. The ob-served changes in eWAT were accompanied by reduced leptin and increased adiponectin levels over time, and an improvement in insulin resistance (HOMA-IR). In liver, KrO suppressed in-flammatory signaling pathways including those controlled by IL-1β and M-CSF, without affecting liver histology. Furthermore, KrO deactivated hepatic REL-A/p65-NF-κB signaling, consistent with increased PPARα protein expression and a trend increase in IkBα. In conclusion, long-term KrO treatment increased several anti-inflammatory PUFAs and oxylipins in WAT and liver. These changes were accompanied by beneficial effects on general metabolism and inflammatory tone at tissue level. Stimulation of adipogenesis by KrO allows for safe fat storage and may, together with more direct PPAR-mediated anti-inflammatory mechanisms, attenuate inflammation.
Project description:Human antigen R (HuR) protein, a RNA binding protein (RBP), has been reported to regulate essential steps in RNA metabolism and immune response in a variety of cell types, but its function in metabolism remains unclear. This study identifies HuR as a major repressor during adipogenesis. Knockdown and overexpression of HuR in primary adipocyte culture enhances and inhibits adipogenesis in vitro, respectively. Fat-specific knockout of HuR significantly enhances adipogenic gene program in all three major adipose tissues including epidydimal, inguinal white and brown adipose tissue, accompanied with systemic glucose intolerance and insulin resistance. Conversely, transgenic overexpression of HuR in adipose tissue prevents the HFD induced obesity by repressing adipogenesis. Mechanistically, HuR may inhibit adipogenesis by recognizing and modulating the stability of hundreds of adipocyte transcripts, including the mRNA of Insig1, a negative regulator during adipogenesis. Taken together, our work establishes HuR as a novel posttranscriptional regulator of adipogenesis and provides a new insight into how RNA processing contributes to adipocyte development.
Project description:Human antigen R (HuR) protein, a RNA binding protein (RBP), has been reported to regulate essential steps in RNA metabolism and immune response in a variety of cell types, but its function in metabolism remains unclear. This study identifies HuR as a major repressor during adipogenesis. Knockdown and overexpression of HuR in primary adipocyte culture enhances and inhibits adipogenesis in vitro, respectively. Fat-specific knockout of HuR significantly enhances adipogenic gene program in all three major adipose tissues including epidydimal, inguinal white and brown adipose tissue, accompanied with systemic glucose intolerance and insulin resistance. Conversely, transgenic overexpression of HuR in adipose tissue prevents the HFD induced obesity by repressing adipogenesis. Mechanistically, HuR may inhibit adipogenesis by recognizing and modulating the stability of hundreds of adipocyte transcripts, including the mRNA of Insig1, a negative regulator during adipogenesis. Taken together, our work establishes HuR as a novel posttranscriptional regulator of adipogenesis and provides a new insight into how RNA processing contributes to adipocyte development.
Project description:Human antigen R (HuR) protein, a RNA binding protein (RBP), has been reported to regulate essential steps in RNA metabolism and immune response in a variety of cell types, but its function in metabolism remains unclear. This study identifies HuR as a major repressor during adipogenesis. Knockdown and overexpression of HuR in primary adipocyte culture enhances and inhibits adipogenesis in vitro, respectively. Fat-specific knockout of HuR significantly enhances adipogenic gene program in all three major adipose tissues including epidydimal, inguinal white and brown adipose tissue, accompanied with systemic glucose intolerance and insulin resistance. Conversely, transgenic overexpression of HuR in adipose tissue prevents the HFD induced obesity by repressing adipogenesis. Mechanistically, HuR may inhibit adipogenesis by recognizing and modulating the stability of hundreds of adipocyte transcripts, including the mRNA of Insig1, a negative regulator during adipogenesis. Taken together, our work establishes HuR as a novel posttranscriptional regulator of adipogenesis and provides a new insight into how RNA processing contributes to adipocyte development.
Project description:Obesity and insulin resistance are associated with oxidative stress, which may be implicated in their progression. The kinase JNK1 emerged as a promising drug target for the treatment of obesity and type-2 diabetes. However, JNK1 is a key mediator of the oxidative stress response, promoting either cell dead or survival depending on magnitude and context of its activation. Furthermore, JNK inactivation shortens lifespan in drosophila and c. elegans. To learn on the safety and efficacy of long-term JNK inhibition in vertebrates, we investigated mice lacking JNK1 (JNK1-/-) exposed over a long period to an obesogenic high-fat diet (HFD). JNK1-/- mice chronically fed an HFD developed more skin oxidative damage because of reduced catalase expression, but also showed sustained protection from obesity, adipose tissue inflammation, steatosis, and insulin resistance, paralleled by decreased oxidative damage in fat and liver. We conclude that JNK1 is a relatively safe drug target for obesity-related diseases. RNA was collected from liver, skin and epididymal fat tissues from JNK1 KO mice and WT mice fed in high fat diet. Each condition was run in quadruplicate
Project description:Obesogenic compounds are chemicals that might have an influence on obesity development through in utero or chronic lifetime exposure. Tributyltin (TBT) is one of the most studied obesogenic compounds, inducing adipogenesis in vitro and increasing body fat after in utero exposure of mice. This study was designed to unravel the molecular mechanisms of TBT, using microarray analysis, and to evaluate the use of toxicogenomics for obesogen screening. The murine 3T3-L1 cell line was used to study TBT induced adipogenesis. Lipid staining as well as gene expression measurements of an adipocyte specific marker gene were performed to select relevant concentrations (10 nM, 50 nM) and time points (day1, day10) for microarray analysis. Additionally, solvent control and positive control (MDI) treated 3T3-L1 cells were included in the analysis. The microarray results were analysed using GO enrichment and Pathway analysis tools, which revealed enrichment of several GO terms involved in energy and fat metabolism after 10 days of TBT exposure. Pathway analysis unveiled PPAR signalling pathway as the sole pathway significantly enriched after 1 day and the most significantly enriched pathway after 10 days of exposure. By examination of effects on both cell physiological and gene expression level we provide a detailed overview of TBT induced obesogenic mechanisms. To our knowledge, this is the first study delivering an in depth mechanistic outline of the mode of action of TBT as an obesogen. Furthermore, our results show that combining omics with 3T3-L1 cells is promising for screening of potential obesogenic compounds. A separate v+2 A-optimal hybridization design was used for each time-point. Using this design each exposure condition is represented by three biological replicates, with each biological replicate analysed in technical duplicate while applying the dye swap principle to correct for dye bias. Two concentrations of TBT (10 nM, 50 nM), DMSO and MDI (positive control, adipogenic hormone cocktail) were the conditions tested, at two time-points (day 1 and day10).
Project description:Despite wide efforts in the last decade, signaling aberrations associated with obesity remain enigmatic. Here, we carried out phosphoproteomic analysis of mouse white adipose tissues (WAT) upon low-fat diet (LFD) and high-fat diet (HFD) to dissect underlying molecular mechanisms of obesity. Of the 7696 phosphopeptides quantified, 191 proteins including various insulin-responsive proteins and metabolic enzymes functioning in lipid homeostasis, exhibited differential phosphorylation with high-fat feeding. Kinase predictions and integrated network analysis identified several deregulated kinase signaling pathways, and suggested possibilities of HFD-induced transcriptional rewiring. Further, functional validation of a novel HFD-responsive site on cytoplasmic acetyl-coA forming ACSS2 (S263) suggested that the phosphorylation is important in regulating insulin signaling and maintaining triglyceride levels. This study represents one of the first comprehensive phosphoproteome data in mouse obesity models, and describes a systems-level approach for identifying deregulated molecular events and potential therapeutic targets in the context of high-fat feeding and adipocyte perturbation.