Association of Lipidome Remodeling in the Adipocyte Membrane with Acquired Obesity in Humans

The authors describe a new approach to studying cellular lipid profiles and propose a compensatory mechanism that may help maintain the normal membrane function of adipocytes in the context of obesity

Pro-inflammatory cytokines induce lipocalin-2 expression in vivo and in vitro

Chronic inflammation in adipose tissue has been demonstrated to play an important role in the pathogenesis of insulin resistance. The infiltration of immune cells results in a significant increase of pro-inflammatory cytokines in adipose tissue that substantially affects adipocyte function. Lipocalin-2 (LCN2) is an adipocyte-secreted cytokine whose expression and secretion has been shown to be induced in obesity and insulin resistance in mouse and man. However, the underlying mechanisms have not been explored. Our studies indicate that interferon-gamma (IFNã) and tumor necrosis factor-alpha (TNFá), two primary pro-inflammatory cytokines secreted from immune cells, can induce LCN2 expression and secretion from adipocytes both in vivo and in vitro. Mechanistic studies reveal that IFNã modulates LCN2 expression via STAT1 and ERKs signaling pathways, while NF-êB and ERKs pathways mediate the actions of TNFá on LCN2 expression. Inhibition of ERKs activation attenuates the induction of LCN2 without significant effects on either the nuclear translocation or DNA binding activity of STAT1 and NF-êB. Further experiments show that pharmacological ERKs inhibition disrupts the serine phosphorylation of STAT1 and NF-êB p65 subunits, and reduces transactivation activity of both of these transcription factors. Moreover, we identified several STAT1 and NF-êB binding sites in both the murine and human LCN2 promoters. Overall, these studies enhance our knowledge regarding the requirements and mechanisms used by pro-inflammatory cytokines to induce LCN2 expression

The Role of Epicardial Adipose Tissue in the Development of Atrial Fibrillation, Coronary Artery Disease and Chronic Heart Failure in the Context of Obesity and Type 2 Diabetes Mellitus: A Narrative Review

Cardiovascular diseases (CVDs) are a significant burden globally and are especially prevalent in obese and/or diabetic populations. Epicardial adipose tissue (EAT) surrounding the heart has been implicated in the development of CVDs as EAT can shift from a protective to a maladaptive phenotype in diseased states. In diabetic and obese patients, an elevated EAT mass both secretes pro-fibrotic/pro-inflammatory adipokines and forms intramyocardial fibrofatty infiltrates. This narrative review considers the proposed pathophysiological roles of EAT in CVDs. Diabetes is associated with a disordered energy utilization in the heart, which promotes intramyocardial fat and structural remodeling. Fibrofatty infiltrates are associated with abnormal cardiomyocyte calcium handling and repolarization, increasing the probability of afterdepolarizations. The inflammatory phenotype also promotes lateralization of connexin (Cx) proteins, undermining unidirectional conduction. These changes are associated with conduction heterogeneity, together creating a substrate for atrial fibrillation (AF). EAT is also strongly implicated in coronary artery disease (CAD); inflammatory adipokines from peri-vascular fat can modulate intra-luminal homeostasis through an “outside-to-inside” mechanism. EAT is also a significant source of sympathetic neurotransmitters, which promote progressive diastolic dysfunction with eventual cardiac failure. Further investigations on the behavior of EAT in diabetic/obese patients with CVD could help elucidate the pathogenesis and uncover potential therapeutic targets

The Effects Of Bone Marrow Adipocytes On Metabolic Regulation In Metastatic Prostate Cancer

Bone is a preferential site of metastasis from prostate cancer (PCa). Although there have been many advances in therapeutic options for patients suffering from metastatic PCa, this disease remains incurable with an estimated five-year survival of 33%. To design effective therapeutic interventions for metastatic PCa, it is essential that we elucidate the molecular mechanisms responsible for tumor cell adaptation to and the ability to thrive within the bone metastatic niche. Age and obesity, conditions that increase adipocyte numbers in bone marrow, are risk factors for skeletal metastases from PCa; therefore, our laboratory is focused on the interactions between marrow adipocytes and PCa cells. We initially detailed the metabolic alterations that occur in prostate cancer cells in response to interactions with bone marrow adipocytes in multiple in vivo and in vitro models. The following conclusions were drawn as a result of these experiments: 1) Patients with metastatic disease have increased expression of glycolytic and hypoxic genes compared to primary PCa tumors; 2) tumors grown intratibially in vivo in diet induced models of high marrow adiposity have increased expression of glycolytic and hypoxic genes compared to mice with fewer marrow adipocytes; 3) paracrine interactions between tumor cells and adipocytes in vitro induce expression of glycolytic and hypoxic proteins in tumor cells; 4) PCa cells exposed to adipocytes with increased expression of glycolytic markers exhibit enhanced Warburg metabolism with increases in lactate production, decreases in oxidative phosphorylation, and decreases in ATP production without perturbation of mitochondrial integrity or cellular viability; 5) tumor cells stimulate lipolysis within adipocytes but the inhibition of lipolysis does not affect adipocyte-driven changes in PCa cell metabolism due to possible compensatory mechanisms; 6) metabolic effects are driven through the activation of HIF-1α in PCa cells as shown by increased expression of hypoxia-responsive genes and the reversal of adipocyte-induced metabolic changes upon knockdown of tumor cell HIF-1α. Additionally, we found novel signaling pathways are activated in tumor cells due to cross talk between tumor cells and adipocytes. We observed a regulation of COX-2 in adipocytes by tumor-secreted IL-1β that leads to increased PGE2 synthesis and release and this PGE2 signals through the EP receptors on the tumor cells to elicit downstream GSK3β/β-catenin signaling and subsequent HIF-1α activation. We also observed increased SPHK1 in adipocytes exposed to tumor cells as an effect of tumor-stimulated lipolysis within adipocytes, but that S1P was not sufficient to activate HIF-1α signaling in tumor cells or downstream metabolic alterations. In summary, we have discovered novel crosstalk between metastatic prostate tumor cells and bone marrow adipocytes that cause activation of many pathways involved in tumor survival and growth within the bone. We have revealed a functional contribution of bone marrow adipocytes to altered tumor metabolism and signaling in bone. The expected outcome of this research is the validation of the significance of adipocyte-derived lipids in growth and aggressiveness of metastatic PCa in bone. The ultimate goal is utilize findings from this study to explore whether adipocyte-driven metabolic adaptation contributes to chemoresistance of skeletal tumors and whether targeting tumor metabolism offers new options for improved therapy and/or prevention of aggressive disease

Macrophage-Dependent Interleukin-6-Production and Inhibition of I-K Contributes to Acquired QT Prolongation in Lipotoxic Guinea Pig Heart

[EN] In the heart, the delayed rectifier K current, I-K, composed of the rapid (I-Kr) and slow (I-Ks) components contributes prominently to normal cardiac repolarization. In lipotoxicity, chronic elevation of pro-inflammatory cytokines may remodel I-K, elevating the risk for ventricular arrythmias and sudden cardiac death. We investigated whether and how the pro-inflammatory interleukin-6 altered I-K in the heart, using electrophysiology to evaluate changes in I-K in adult guinea pig ventricular myocytes. We found that palmitic acid (a potent inducer of lipotoxicity), induced a rapid (~24 h) and significant increase in IL-6 in RAW264.7 cells. PA-diet fed guinea pigs displayed a severely prolonged QT interval when compared to low-fat diet fed controls. Exposure to isoproterenol induced torsade de pointes, and ventricular fibrillation in lipotoxic guinea pigs. Pre-exposure to IL-6 with the soluble IL-6 receptor produced a profound depression of I-Kr and I-Ks densities, prolonged action potential duration, and impaired mitochondrial ATP production. Only with the inhibition of I-Kr did a proarrhythmic phenotype of I-Ks depression emerge, manifested as a further prolongation of action potential duration and QT interval. Our data offer unique mechanistic insights with implications for pathological QT interval in patients and vulnerability to fatal arrhythmias.This study was supported by an AHA (13SDG16850065 to A.S.A), NIH (R01 HL147044 to A.S.A), and Programa Prometeu de la Conselleria d'innovacio, Universitats, Ciencia i Societat Digital de la Generalitat Valenciana (Award number prometeu/2020/043 to J.S).Chowdhury, MKH.; Martínez-Mateu, L.; Do, J.; Aromolaran, KA.; Saiz Rodríguez, FJ.; Aromolaran, A. (2021). Macrophage-Dependent Interleukin-6-Production and Inhibition of I-K Contributes to Acquired QT Prolongation in Lipotoxic Guinea Pig Heart. International Journal of Molecular Sciences. 22(20):1-15. https://doi.org/10.3390/ijms222011249S115222

Exploring the activation and function of PPARa and PPARß/d using genomics

For many tissues fatty acids represent the major source of fuel. In the past few decades it has become evident that in addition to their role as energy substrates, fatty acids also have an important signaling function by modulating transcription of genes. An important group of transcription factors involved in mediating the effects of dietary fatty acids on gene transcription are the Peroxisome Proliferator-Activated Receptors (PPARs). PPARs are members of the superfamily of nuclear hormone receptors and regulate genes involved in numerous important biological processes, ranging from lipid metabolism to inflammation and wound healing. In the liver the dominant PPAR isoform has been show to be PPARα, although PPARβ/δ and PPARγ are expressed in liver as well. The aim of this thesis was to further characterize the role of PPARα and PPARβ/δ in hepatic metabolism and study their activation by fatty acids. Even though PPARα as gene regulator in liver has been well described, a complete overview of its target genes has been lacking so far. By combining several nutrigenomics tools, we succeeded in creating a comprehensive list of PPARα-regulated genes involved in lipid metabolism in liver. Additionally, by using a unique design where mice were fed synthetic triglycerides consisting of one type of fatty acid, we could distinguish between different types of dietary unsaturated fatty acids in their ability to activate PPARα. Although it is well known that PPARα plays an important role in liver during fasting, no direct in vivo evidence exists that circulating free fatty acids are able to ligand activate hepatic PPARα. In our studies, we found that upregulation of gene expression by PPARβ/δ is sensitive to circulating plasma free fatty acids whereas this is not the case for PPARα. Not much is known about the function of PPARβ/δ in the liver. In order to better understand the role of this nuclear receptor, we compared the effects of PPARα and PPARβ/δ deletion on whole genome gene regulation and plasma and liver metabolites. Our results revealed that PPARβ/δ does not mediate an adaptive response to fasting, and pointed to a role for PPARβ/δ in hepatic glucose- and lipoprotein metabolism. In conclusion, this thesis contributes to the important work of mapping the molecular mechanisms dictating lipid metabolism in the liver. By using several nutrigenomics tools, we are able to show that PPARα is a key mediator of the effect of dietary fatty acids on hepatic gene expression. In addition, we better define the roles of PPARα and PPARβ/δ in hepatic metabolism and provide a new concept for functional differentiation between PPARs in liver. <br/

Interplay between genetic predisposition and diet in advancing obesity and type 2 Diabetes in the Tallyho mouse

Obesity is a global epidemic, affecting all ages. It is one of the leading causes of preventable death, as it increases the risk of type 2 diabetes (T2D), hypertension, cardiovascular disease, nonalcoholic fatty liver disease, and some cancers. Obesity is a complex disease that is caused by a combination of genetic and environmental factors such as diets high in fat and sedentary life style. Despite our increased knowledge of obesity development and progression, current obesity treatments have not stopped the rise in obesity rates. There are still many unknowns related to the underlying mechanisms of obesity that need to be investigated and understood, so that treatment of obesity can be more effective. To deal with the numerous variables involved with such studies, animal models are recommended. My dissertation centers around characterizing the TALLYHO/Jng (TH) mouse, a polygenic model for T2D and obesity, and identifying obesity gene(s) in this model. The first study focused on investigating the effect of diets high in fat and sucrose for the development of obesity and T2D in TH mice. Compared to normal C57BL/6J (B6) mice, TH mice responded more sensitively to the obesogenic diets in the development of obesity and type 2 diabetes, demonstrating that diets are important modulators of genetic susceptibility to the diseases in this model. The second study was conducted in an effort to identify obesity gene(s) in TH mice. We generated congenic mouse strains carrying obesity quantitative trait loci on chromosome 1 derived from TH mice on B6 background. Using these mouse strains, we determined that the distal segment of chromosome 1 from TH mice is necessary to cause diet induced obesity. In the last study, we demonstrated that increased pro-inflammatory cytokine interleukin-6 levels and decreased mitochondrial respiration may be in part a mechanism underlying the gene-diet interaction in advancing obesity and type 2 diabetes in TH mice

Role of resveratrol metabolites in adipose function

The rise in obesity rate has drastically increased over the last few decades and has quickly grown into a worldwide epidemic. Large increases in visceral adipose tissue accumulation increase risk for metabolic disorders including insulin resistance, type 2 diabetes, and cardiovascular diseases. Currently, increased levels of circulating non-esterified fatty acids (NEFA) have been suggested to be the mediator linking obesity and type 2 diabetes. Studies identifying ways to alleviate mobilization of NEFA in adipose tissue via dietary phytochemicals may useful as a therapeutic approach. Despite the established benefits of resveratrol in health and in the development of obesity, the role of resveratrol metabolites in lipid metabolism remains unknown.^ The objectives of this study were to determine the role of resveratrol metabolites in adipose function with a focus on the effect in lipolysis and lipogenesis. Resveratrol metabolite, piceatannol, previously demonstrated its role as an antilipolytic agent through the suppression of lipolysis via protein degradation of adipose triglyceride lipase (ATGL) and comparative gene identification-58 (CGI-58). We hypothesized other resveratrol metabolites exhibit similar effects in modulating the lipolysis process. In our study, we examined several resveratrol metabolites and identified trans-3, 4\u27, 5-trimethoxy resveratrol (TMR) having ability to suppress lipolysis in basal and stimulated conditions in mature murine adipocytes at non-cytotoxic levels. Upon further mechanistic studies, TMR at 50 µM reduces ATGL and CGI-58 protein expression with greatest efficacy in an acute, three hour treatment. mRNA expression analysis displayed that TMR may also play a role in transcriptionally regulating lipolytic genes. Additionally, we investigated the role of TMR in lipogenesis in maturing preadipocytes. Although TMR did not display significant reductions in lipid accumulation during lipogenesis, gene expression profiling indicates it may induce transcriptional remodeling of adipocyte function. Of interest, TMR upregulates expression of genes involved in mitochondria function suggesting increased catabolic processes, thermogenesis, and potential enhanced capacity for energy expenditure during development. Collectively, our study provides evidence that TMR, a resveratrol metabolite, might have a therapeutic potential in attenuating adiposity and its associated metabolic disorders