Identification of fatty acid binding protein 4 as an adipokine that regulates insulin secretion during obesity.

A critical feature of obesity is enhanced insulin secretion from pancreatic β-cells, enabling the majority of individuals to maintain glycaemic control despite adiposity and insulin resistance. Surprisingly, the factors coordinating this adaptive β-cell response with adiposity have not been delineated. Here we show that fatty acid binding protein 4 (FABP4/aP2) is an adipokine released from adipocytes under obesogenic conditions, such as hypoxia, to augment insulin secretion. The insulinotropic action of FABP4 was identified using an in vitro system that recapitulates adipocyte to β-cell endocrine signalling, with glucose-stimulated insulin secretion (GSIS) as a functional readout, coupled with quantitative proteomics. Exogenous FABP4 potentiated GSIS in vitro and in vivo, and circulating FABP4 levels correlated with GSIS in humans. Insulin inhibited FABP4 release from adipocytes in vitro, in mice and in humans, consistent with feedback regulation. These data suggest that FABP4 and insulin form an endocrine loop coordinating the β-cell response to obesity

FOXC2 Is a Winged Helix Gene that Counteracts Obesity, Hypertriglyceridemia, and Diet-Induced Insulin Resistance

AbstractObesity, hyperlipidemia, and insulin resistance are common forerunners of type 2 diabetes mellitus. We have identified the human winged helix/forkhead transcription factor gene FOXC2 as a key regulator of adipocyte metabolism. Increased FOXC2 expression, in adipocytes, has a pleiotropic effect on gene expression, which leads to a lean and insulin sensitive phenotype. FOXC2 affects adipocyte metabolism by increasing the sensitivity of the β-adrenergic-cAMP-protein kinase A (PKA) signaling pathway through alteration of adipocyte PKA holoenzyme composition. Increased FOXC2 levels, induced by high fat diet, seem to counteract most of the symptoms associated with obesity, including hypertriglyceridemia and diet-induced insulin resistance—a likely consequence hereof would be protection against type 2 diabetes

The role of aortic carboxypeptidase-like protein in adipose-derived mesenchymal stem cell adipogenesis and fibrosis

Thesis (M.A.)--Boston UniversityThe prevalence of obesity and obesity related diseases are increasing worldwide. Obesity is characterized by the pathological expansion of white adipose tissue. Previous studies on white adipose tissue of obese individuals have detected inflammation and fibrosis. These conditions may cause dysregulation of the tissue, leading to negative outcomes, including type II diabetes and metabolic syndrome. Aortic carboxypeptidase-like protein (ACLP) is a secreted extracellular matrix protein that is upregulated in fibrotic lung tissue. Importantly ACLP knockout mice are protected from experimentally induced lung fibrosis. ACLP is expressed in adipose tissue and is downregulated as stem cells undergo adipogenesis. Its overexpression increases α smooth muscle actin expression and impairs adipogenesis in preadipocyte lines; however, its role in white adipose tissue fibrosis has not been fully explored. The studies presented in this thesis aimed to investigate the hypothesis that ACLP overexpression in fibrotic white adipose tissue would promote a fibroblast to myofibroblast transition and repress adipogenesis. To determine if ACLP promotes a fibroblast to myofibroblast transition, we tested the capacity of ACLP to induce α smooth muscle actin and collagen I protein expression and increase contractility of primary stromal vascular cells. To assess the effects of ACLP on adipogenesis, we tested the ability of 10T1/2 fibroblasts and stromal vascular cells to undergo adipogenesis in collagen I gels under ACLP treatment. Results presented herein demonstrate ACLP is a potent inhibitor of adipogenesis and induces an upward trend in myofibroblast proteins and RNA expression. Significantly, these studies used murine adipose-derived cells to show the effects of ACLP, suggesting these results might be reflected in adipose tissue. These experiments support a model where ACLP potentiates adipose tissue fibrosis by inhibiting adipogenesis, resulting in fewer developing adipocytes, and stimulating myofibroblast differentiation, resulting in further collagen deposition and tissue compaction. This contribution to adipose tissue dysfunction also gives ACLP a possible role in the development of obesity related diseases, including diabetes and metabolic syndrome, identifying it as a possible target for therapeutics

Mice with targeted disruption of the fatty acid transport protein 4 (Fatp 4, Slc27a4) gene show features of lethal restrictive dermopathy

The fatty acid transport protein family is a group of evolutionarily conserved proteins that are involved in the cellular uptake and metabolism of long and very long chain fatty acids. However, little is known about their respective physiological roles. To analyze the functional significance of fatty acid transport protein 4 (Fatp4, Slc27a4), we generated mice with a targeted disruption of the Fatp4 gene. Fatp4-null mice displayed features of a neonatally lethal restrictive dermopathy. Their skin was characterized by hyperproliferative hyperkeratosis with a disturbed epidermal barrier, a flat dermal–epidermal junction, a reduced number of pilo-sebaceous structures, and a compact dermis. The rigid skin consistency resulted in an altered body shape with facial dysmorphia, generalized joint flexion contractures, and impaired movement including suckling and breathing deficiencies. Lipid analysis demonstrated a disturbed fatty acid composition of epidermal ceramides, in particular a decrease in the C26:0 and C26:0-OH fatty acid substitutes. These findings reveal a previously unknown, essential function of Fatp4 in the formation of the epidermal barrier

Towards Fish Lipid Nutrigenomics: Current State and Prospects for Fin-fish Aquaculture

Lipids are the predominant source of energy for fish. The mechanisms by which fish allocate energy from lipids, for metabolism, development, growth and reproduction are critical for understanding key life history strategies and transitions. Currently, the major lipid component in aquaculture diets is fish oil (FO), derived from wild capture fisheries that are exploited at their maximum sustainable limit. The increasing demand from aquaculture for FO will soon exceed supply and threaten the viability of aquaculture. Thus, it is essential to minimize FO use in aquaculture diets. This might be achieved by a greater understanding of lipid storage and muscle growth, or the identification of alternatives to FO in feeds. This review focuses on recent research applying molecular and genomic techniques to the study of fin-fish lipid metabolism from an aquaculture perspective. Accordingly, particular emphasis will be given to fatty acid metabolism and to highly unsaturated fatty acid (HUFA) biosynthesis, and to the transcriptional mechanisms and endocrine factors that regulate these processes in fish. Comparative studies of gene function and distribution are described which, when integrated with recent fish genome sequence information, provide insights into lipid homeostasis and the outcomes associated with the replacement of FO in fish diets

Lysosomal degradation of membrane lipids

AbstractThe constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide. Together with endosomal and lysosomal lipid-binding proteins, the Niemann–Pick disease, type C2-protein, the GM2-activator, and the saposins sap-A, -B, -C, and -D, a suitable membrane lipid composition is required for degradation of complex lipids by hydrolytic enzymes

Uptake of arachidonic acid and glucose into isolated human adipocytes

Both plasma glucose concentration and glucose uptake are deranged in insulin resistance. A high free fatty acid plasma level is a potential cause of insulin resistance, and therefore of type 2 diabetes mellitus animals and humans. The mechanism behind this is still unclear. The objectives of the present study were: (i) to research the effect of arachidonic acid (AA) as fatty acid representative, on glucose uptake into human isolated adipocytes, (ii) to investigate the uptake of AA into adipocyte membranes and nuclei, as a step to identify the mechanism whereby AA affects glucose uptake, and (iii) to verify the influence of insulin on AA uptake in adipocytes. The first objective was achieved by exposing adipocytes to AA and measuring the effect on deoxyglucose uptakt. To achieve the second objective, adipocytes were exposed to 14C-AA; radioactive uptake in membranes and nuclei was determined. The AA uptake into membranes was also determinate by membranes fatty acid profile using gas chromatography; the results of the two methods were compared. Finally, the third objective was achieved by exposing adipocytes to different concentrations of insulin and testing the effect by measuring arachidonic acid uptake by the entire cell. The results of this study shown that, acute (30 min) exposure of AA significantly stimulates glucose uptake by adipocytes (4.56 ± 0.6 nmole glucose /mg protein /min) compared to the control (3.12 ± 0.25 nmole glucose /mg protein /min). Secondly, 14C-AA was significantly taken up by the membranes between 20 and 30 minutes of exposure. The uptake into membranes was increased by 49.57 ± 29% and 123 ± 73% compared to the control 100% (1.77 ± 0.06 nmole AA /mg protein) respectively for 20 and 30 min exposure). AA significantly rose in the nuclei after 30 minutes (147 ± 19% increase) compared to the control 100% (2.25 ± 0.10 nmole AA /mg protein). The determination of AA uptake by gas chromatography analysis of the membrane fatty acid profile showed that the content of AA increased after 30 min exposure (0.57% AA of total membrane fatty acids) compared to the 10 min exposure (0.29% AA of total membrane fatty acid). Insulin was shown to stimulate 10 and 30 min AA uptake by adipocytes from a non-obese subject. The increases of AA uptake measured for 30 minutes were 20 ±8%, 21 ± 25% and 31 ± 4% compared to the control (0.58nmole AA / mg protein / min) respectively for the actions of 10nM, 20nM and 40 nM insulin. A similar tendency was observed when the AA uptake was measured for 10 min (81 ± 31% and 208 ± 36% respectively for the action of 10nM and 40nM insulin compared to the control 100% (0.06nmole AA/mg protein/min). In contrast to this finding, insulin depressed AA uptake by adipocytes from an obese subject (depression of 15 ± 5%, 14 ± 8% and 21 ± 5% respectively for 10nM, 20nM and 40nM insulin, compared to the control 100% (0.74 nmole AA/mg protein/min). In both situations the effect of insulin seemed dose dependent. The study demonstrated that AA acid positively modulates glucose uptake into adipocytes exposed for short periods (< 30 min). This was attributed to the probable this FA in the cell membrane, rather than its eventual effect on the DNA. The best method to measure membranes AA over short period of exposure when small amounts of adipocytes (2- 6 ml) are used was by radioactive means. It also suggested that insulin effect’s on AA acid uptake into adipocytes was dose dependent. This varies with the body mass index (BMI) of the patient, probably as a result of their cell’s insulin resistant state.Dissertation (MSc (Veterinary Science))--University of Pretoria, 2007.Anatomy and PhysiologyMScunrestricte

Heterologous transporter expression for improved fatty alcohol secretion in yeast

The yeast Saccharomyces cerevisiae is an attractive host for industrial scale production of biofuels including fatty alcohols due to its robustness and tolerance towards harsh fermentation conditions. Many metabolic engineering strategies have been applied to generate high fatty alcohol production strains. However, impaired growth caused by fatty alcohol accumulation and high cost of extraction are factors limiting large-scale production. Here, we demonstrate that the use of heterologous transporters is a promising strategy to increase fatty alcohol production. Among several plant and mammalian transporters tested, human FATP1 was shown to mediate fatty alcohol export in a high fatty alcohol production yeast strain. An approximately five-fold increase of fatty alcohol secretion was achieved. The results indicate that the overall cell fitness benefited from fatty alcohol secretion and that the acyl-CoA synthase activity of FATP1 contributed to increased cell growth as well. This is the first study that enabled an increased cell fitness for fatty alcohol production by heterologous transporter expression in yeast, and this investigation indicates a new potential function of FATP1, which has been known as a free fatty acid importer to date. We furthermore successfully identified the functional domain of FATP1 involved in fatty alcohol export through domain exchange between FATP1 and another transporter, FATP4. This study may facilitate a successful commercialization of fatty alcohol production in yeast and inspire the design of novel cell factories