Insulin Regulation of Lipoprotein Lipase Activity in 3T3-L1 Adipocytes is Mediated at Posttranscriptional and Posttranslational Levels

Deficiency of the lipid flippase ATP10A causes diet-induced dyslipidemia in female mice

Genetic association studies have linked ATP10A and closely related type IV P-type ATPases (P4-ATPases) to insulin resistance and vascular complications, such as atherosclerosis. ATP10A translocates phosphatidylcholine and glucosylceramide across cell membranes, and these lipids or their metabolites play important roles in signal transduction pathways regulating metabolism. However, the influence of ATP10A on lipid metabolism in mice has not been explored. Here, we generated gene-specific Atp10A knockout mice and show that Atp10A-/- mice fed a high-fat diet did not gain excess weight relative to wild-type littermates. However, Atp10A-/- mice displayed female-specific dyslipidemia characterized by elevated plasma triglycerides, free fatty acids and cholesterol, as well as altered VLDL and HDL properties. We also observed increased circulating levels of several sphingolipid species along with reduced levels of eicosanoids and bile acids. The Atp10A-/- mice also displayed hepatic insulin resistance without perturbations to whole-body glucose homeostasis. Thus, ATP10A has a sex-specific role in regulating plasma lipid composition and maintaining hepatic liver insulin sensitivity in mice.

Sex-specific responses in glucose-insulin homeostasis and lipoprotein-lipid components after high-dose supplementation with marine n-3 PUFAs in abdominal obesity: a randomized double-blind crossover study

Background

Clinical studies on effects of marine-derived omega-3 (n-3) polyunsaturated fatty acids (PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the plant-derived omega-6 (n-6) PUFA linoleic acid (LA) on lipoprotein-lipid components and glucose-insulin homeostasis have shown conflicting results, which may partly be explained by differential responses in females and males. However, we have lacked data on sexual dimorphism in the response of cardiometabolic risk markers following increased consumption of n-3 or n-6 PUFAs.

Objective

To explore sex-specific responses after n-3 (EPA + DHA) or n-6 (LA) PUFA supplementation on circulating lipoprotein subfractions, standard lipids, apolipoproteins, fatty acids in red blood cell membranes, and markers of glycemic control/insulin sensitivity among people with abdominal obesity.

Methods

This was a randomized double-blind crossover study with two 7-week intervention periods separated by a 9-week washout phase. Females (n = 16) were supplemented with 3 g/d of EPA + DHA (fish oil) or 15 g/d of LA (safflower oil), while males (n = 23) received a dose of 4 g/d of EPA + DHA or 20 g/d of LA. In fasting blood samples, we measured lipoprotein particle subclasses, standard lipids, apolipoproteins, fatty acid profiles, and markers of glycemic control/insulin sensitivity.

Results

The between-sex difference in relative change scores was significant after n-3 for total high-density lipoproteins (females/males: -11%*/-3.3%, p = 0.036; *: significant within-sex change), high-density lipoprotein particle size (+2.1%*/-0.1%, p = 0.045), and arachidonic acid (-8.3%*/-12%*, p = 0.012), and after n-6 for total (+37%*/+2.1%, p = 0.041) and small very-low-density lipoproteins (+97%*/+14%, p = 0.021), and lipoprotein (a) (-16%*/+0.1%, p = 0.028). Circulating markers of glucose-insulin homeostasis differed significantly after n-3 for glucose (females/males: -2.1%/+3.9%*, p = 0.029), insulin (-31%*/+16%, p < 0.001), insulin C-peptide (-12%*/+13%*, p = 0.001), homeostasis model assessment of insulin resistance index 2 (-12%*/+14%*, p = 0.001) and insulin sensitivity index 2 (+14%*/-12%*, p = 0.001), and quantitative insulin sensitivity check index (+4.9%*/-3.4%*, p < 0.001).

Conclusion

We found sex-specific responses after high-dose n-3 (but not n-6) supplementation in circulating markers of glycemic control/insulin sensitivity, which improved in females but worsened in males. This may partly be related to the sex differences we observed in several components of the lipoprotein-lipid profile following the n-3 intervention.

Clinical trial registration

https://clinicaltrials.gov/, identifier [NCT02647333].

Single-cell transcriptome dataset of human and mouse in vitro adipogenesis models

Adipogenesis is a process in which fat-specific progenitor cells (preadipocytes) differentiate into adipocytes that carry out the key metabolic functions of the adipose tissue, including glucose uptake, energy storage, and adipokine secretion. Several cell lines are routinely used to study the molecular regulation of adipogenesis, in particular the immortalized mouse 3T3-L1 line and the primary human Simpson-Golabi-Behmel syndrome (SGBS) line. However, the cell-to-cell variability of transcriptional changes prior to and during adipogenesis in these models is not well understood. Here, we present a single-cell RNA-Sequencing (scRNA-Seq) dataset collected before and during adipogenic differentiation of 3T3-L1 and SGBS cells. To minimize the effects of experimental variation, we mixed 3T3-L1 and SGBS cells and used computational analysis to demultiplex transcriptomes of mouse and human cells. In both models, adipogenesis results in the appearance of three cell clusters, corresponding to preadipocytes, early and mature adipocytes. These data provide a groundwork for comparative studies on these widely used in vitro models of human and mouse adipogenesis, and on cell-to-cell variability during this process.

Single-cell transcriptome dataset of human and mouse in vitro adipogenesis models

Adipogenesis is a process in which fat-specific progenitor cells (preadipocytes) differentiate into adipocytes that carry out the key metabolic functions of the adipose tissue, including glucose uptake, energy storage, and adipokine secretion. Several cell lines are routinely used to study the molecular regulation of adipogenesis, in particular the immortalized mouse 3T3-L1 line and the primary human Simpson-Golabi-Behmel syndrome (SGBS) line. However, the cell-to-cell variability of transcriptional changes prior to and during adipogenesis in these models is not well understood. Here, we present a single-cell RNA-Sequencing (scRNA-Seq) dataset collected before and during adipogenic differentiation of 3T3-L1 and SGBS cells. To minimize the effects of experimental variation, we mixed 3T3-L1 and SGBS cells and used computational analysis to demultiplex transcriptomes of mouse and human cells. In both models, adipogenesis results in the appearance of three cell clusters, corresponding to preadipocytes, early and mature adipocytes. These data provide a groundwork for comparative studies on human and mouse adipogenesis, as well as on cell-to-cell variability in gene expression during this process.

Is insulin resistance tissue-dependent and substrate-specific? The role of white adipose tissue and skeletal muscle

Insulin resistance (IR) refers to a reduction in the ability of insulin to exert its metabolic effects in organs such as adipose tissue (AT) and skeletal muscle (SM), leading to chronic diseases such as type 2 diabetes, hepatic steatosis, and cardiovascular diseases. Obesity is the main cause of IR, however not all subjects with obesity develop clinical insulin resistance, and not all clinically insulin-resistant people have obesity. Recent evidence implies that IR onset is tissue-dependent (AT or SM) and/or substrate-specific (glucometabolic or lipometabolic). Therefore, the aims of the present review are 1) to describe the glucometabolic and lipometabolic activities of insulin in AT and SM in the maintenance of whole-body metabolic homeostasis, 2) to discuss the pathophysiology of substrate-specific IR in AT and SM, and 3) to highlight novel validated tests to assess tissue and substrate-specific IR that are easy to perform in clinical practice. In AT, glucometabolic IR reduces glucose availability for glycerol and fatty acid synthesis, thus decreasing the esterification and synthesis of signaling bioactive lipids. Lipometabolic IR in AT impairs the antilipolytic effect of insulin and lipogenesis, leading to an increase in circulating FFAs and generating lipotoxicity in peripheral tissues. In SM, glucometabolic IR reduces glucose uptake, whereas lipometabolic IR impairs mitochondrial lipid oxidation, increasing oxidative stress and inflammation, all of which lead to metabolic inflexibility. Understanding tissue-dependent and substrate-specific IR is of paramount importance for early detection before clinical manifestations and for the development of more specific treatments or direct interventions to prevent chronic life-threatening diseases.

miR-222 exerts negative regulation on insulin signaling pathway in 3T3-L1 adipocytes

Increased miR-222 levels are associated with metabolic syndrome, insulin resistance, and diabetes. Moreover, rats fed an obesogenic diet during lactation have higher miR-222 content in breast milk and the offspring display greater body fat mass and impaired insulin sensitivity in adulthood. In order to investigate the molecular mechanisms involved and to dissect the specific effects of miR-222 on adipocytes, transfection with a mimic or an inhibitor of miR-222 has been conducted on 3T3-L1 preadipocytes. 3T3-L1 cells were transfected with either a mimic or an inhibitor of miR-222 and collected after 2 days (preadipocytes) or 8 days (mature adipocytes) for transcriptomic analysis. Results showed a relevant impact on pathways associated with insulin signaling, lipid metabolism and adipogenesis. Outcomes in key genes and proteins were further analyzed with quantitative reverse transcription polymerase chain reaction and Western Blotting, respectively, which displayed a general inhibition in important effectors of the identified routes under miR-222 mimic treatment in preadipocytes. Although to a lesser extent, this overall signature was maintained in differentiated adipocytes. Altogether, miR-222 exerts a direct effect in metabolic pathways of 3T3-L1 adipocytes that are relevant to adipocyte function, limiting adipogenesis and insulin signaling pathways, offering a mechanistic explanation for its reported association with metabolic diseases.

Metabolism of triglyceride-rich lipoproteins in health and dyslipidaemia

Accumulating evidence points to the causal role of triglyceride-rich lipoproteins and their cholesterol-enriched remnants in atherogenesis. Genetic studies in particular have not only revealed a relationship between plasma triglyceride levels and the risk of atherosclerotic cardiovascular disease, but have also identified key proteins responsible for the regulation of triglyceride transport. Kinetic studies in humans using stable isotope tracers have been especially useful in delineating the function of these proteins and revealing the hitherto unappreciated complexity of triglyceride-rich lipoprotein metabolism. Given that triglyceride is an essential energy source for mammals, triglyceride transport is regulated by numerous mechanisms that balance availability with the energy demands of the body. Ongoing investigations are focused on determining the consequences of dysregulation as a result of either dietary imprudence or genetic variation that increases the risk of atherosclerosis and pancreatitis. The identification of molecular control mechanisms involved in triglyceride metabolism has laid the groundwork for a 'precision-medicine' approach to therapy. Novel pharmacological agents under development have specific molecular targets within a regulatory framework, and their deployment heralds a new era in lipid-lowering-mediated prevention of disease. In this Review, we outline what is known about the dysregulation of triglyceride transport in human hypertriglyceridaemia.

Characterization of lipoprotein lipase storage vesicles in 3T3-L1 adipocytes

Lipoprotein lipase (LPL) is a secreted triglyceride lipase involved in the clearance of very-low-density lipoproteins and chylomicrons from circulation. LPL is expressed primarily in adipose and muscle tissues and transported to the capillary lumen. LPL secretion is regulated by insulin in adipose tissue; however, few studies have examined the regulatory and trafficking steps involved in secretion. Here, we describe the intracellular localization and insulin-dependent trafficking of LPL in 3T3-L1 adipocytes. We compared LPL trafficking to the better characterized trafficking pathways taken by leptin and GLUT4 (also known as SLC2A4). We show that the LPL trafficking pathway shares some characteristics of these other pathways, but that LPL subcellular localization and trafficking are distinct from those of GLUT4 and leptin. LPL secretion occurs slowly in response to insulin and rapidly in response to the Ca2+ ionophore ionomycin. This regulated trafficking is dependent on Golgi protein kinase D and the ADP-ribosylation factor GTPase ARF1. Together, these data give support to a new trafficking pathway for soluble cargo that is active in adipocytes.

Increased Fetal Cardiovascular Disease Risk: Potential Synergy Between Gestational Diabetes Mellitus and Maternal Hypercholesterolemia

Cardiovascular diseases (CVD) remain a major cause of death worldwide. Evidence suggests that the risk for CVD can increase at the fetal stages due to maternal metabolic diseases, such as gestational diabetes mellitus (GDM) and maternal supraphysiological hypercholesterolemia (MSPH). GDM is a hyperglycemic, inflammatory, and insulin-resistant state that increases plasma levels of free fatty acids and triglycerides, impairs endothelial vascular tone regulation, and due to the increased nutrient transport, exposes the fetus to the altered metabolic conditions of the mother. MSPH involves increased levels of cholesterol (mainly as low-density lipoprotein cholesterol) which also causes endothelial dysfunction and alters nutrient transport to the fetus. Despite that an association has already been established between MSPH and increased CVD risk, however, little is known about the cellular processes underlying this relationship. Our knowledge is further obscured when the simultaneous presentation of MSPH and GDM takes place. In this context, GDM and MSPH may substantially increase fetal CVD risk due to synergistic impairment of placental nutrient transport and endothelial dysfunction. More studies on the separate and/or cumulative role of both processes are warranted to suggest specific treatment options.

The Effect of FATP1 on Adipocyte Differentiation in Qinchuan Beef Cattle

Simple Summary

Previous research found that FATP1 plays an important role in the regulation of fatty acid metabolism and lipid accumulation in pig and chicken, but its function has not been explored in bovine adipocyte yet. In this study, we investigated the effect of FATP1 expression on preadipocyte differentiation in Qinchuan cattle using overexpression and interference assays. Our results reveal that FATP1 overexpression promoted preadipocyte differentiation, lipid droplet formation, and the expression of LPL and PPARγ, while FATP1 interference had the opposite effects on adipocyte differentiation and fat deposition. Following FATP1 overexpression and FATP1 interference in adipocytes, RNA-seq analysis identified that SLPI, STC1, SEMA6A, TNFRSF19, SLN, PTGS2, ADCYP1, FADS2, and SCD genes were differentially expressed. Pathway analysis revealed that the PPAR signaling pathway, AMPK signal pathway, and Insulin signaling pathway were enriched with differentially expressed genes. We propose that the FATP1 gene may affect the beef quality by involving adipocyte differentiation and lipid deposition, and may shed new light on the formation mechanisms of adipose tissues.

Abstract

FATP1 plays an important role in the regulation of fatty acid metabolism and lipid accumulation. In this study, we investigated the patterns of FATP1 expression in various tissues obtained from calf and adult Qinchuan cattle, and in differentiating adipocytes. Next, we investigated the effect of FATP1 expression on preadipocyte differentiation in Qinchuan cattle using overexpression and interference assays. We also identified the differentially expressed genes (DEGs) and pathways associated with FATP1 overexpression/interference. Our results reveal that FATP1 was broadly expressed in heart, kidney, muscle, small intestine, large intestine, and perirenal fat tissues. While FATP1 overexpression promoted preadipocyte differentiation, fat deposition, and the expression of several genes involved in fat metabolism, FATP1 interference had the opposite effects on adipocyte differentiation. Following FATP1 overexpression and FATP1 interference in adipocytes, RNA-seq analysis was performed to identify DEGs related to fat metabolism. The DEGs identified include SLPI, STC1, SEMA6A, TNFRSF19, SLN, PTGS2, ADCYP1, FADS2, and SCD. Pathway analysis revealed that the DEGs were enriched in the PPAR signaling pathway, AMPK signal pathway, and Insulin signaling pathway. Our results provide an in-depth understanding of the function and regulation mechanism of FAPT1 in fat metabolism.

Fasting, non-fasting and postprandial triglycerides for screening cardiometabolic risk

Fasting triacylglycerols have long been associated with cardiovascular disease (CVD) and other cardiometabolic conditions. Evidence suggests that non-fasting triglycerides (i.e. measured within 8 h of eating) better predict CVD than fasting triglycerides, which has led several organisations to recommend non-fasting lipid panels as the new clinical standard. However, unstandardised assessment protocols associated with non-fasting triglyceride measurement may lead to misclassification, with at-risk individuals being overlooked. A third type of triglyceride assessment, postprandial testing, is more controlled, yet historically has been difficult to implement due to the time and effort required to execute it. Here, we review differences in assessment, the underlying physiology and the pathophysiological relevance of elevated fasting, non-fasting and postprandial triglycerides. We also present data suggesting that there may be a distinct advantage of postprandial triglycerides, even over non-fasting triglycerides, for early detection of CVD risk and offer suggestions to make postprandial protocols more clinically feasible.

Progesterone eliminates 17β-estradiol-Mediated cardioprotection against diabetic cardiovascular dysfunction in ovariectomized rats

Background

Type2 Diabetes (T2D) remains one of the most important causes of cardiovascular diseases (CVD). Menopause leads to an increase in CVD and metabolic syndrome, which indicates the role of sex steroids as a protective factor. In the present study, we surveyed the effects of 17β-estradiol (E2) alone and in combination with progesterone (P4) on cardiovascular dysfunction in T2D.

Methods

Female ovariectomized (OVX) diabetic rats were divided into eight groups: Sham-Control, Diabetes (Dia), OVX + Dia, OVX + Dia + Vehicle, OVX + Dia + E2, OVX + Dia + P4, OVX + Dia + E2+P4, and OVX + Dia + E2+Vehicle. T2D was induced by a high-fat diet and streptozotocin. E2 and P4 were administrated every four days for four weeks. The heart cytokines and angiotensin II, lipid profile, insulin, water, and food intake and cardiovascular indices were measured.

Results

Results showed that single treatment with E2 decreased fasting blood glucose, water, and food intake, atherogenic and cardiac risk indices, and blood pressure. Also, P4 led to a decrease in atherogenic and cardiac risk indices. TNFα and IL-6 levels were increased and IL-10 was decreased in the Dia group, while E2 alone was able to inhibit these changes. The combined use of E2 and P4 eliminated the beneficial effects of E2 on these indices. Although diabetes results in an increment of cholesterol, LDL and triglyceride, hormone therapy with E2 was associated with improved dyslipidemia.

Conclusion

The use of E2 alone, and not the individual use of P4, and its combination with E2 improved cardiovascular function in OVX diabetic animals, possibly by reducing the amount of inflammatory cytokines and improving metabolic parameters.

Redox index of Cys-thiol residues of serum apolipoprotein E and its diagnostic potential

Background: The redox modulation of Cys-thiol participates in various pathophysiological processes. We explored the proper index for estimating the redox status of Cys-thiol of serum apolipoprotein E (apoE), named “redox-IDX-apoE,” which is necessary to understand the redox biology of age-related diseases.

Methods: The fractions of the reduced form (red-), reversible oxidized form (roxi-), and irreversibly oxidized form (oxi-) apoE in serum, obtained from the patients with no apparent disease (controls, n=192) and with atherosclerosis and type 2 diabetes (patients, n=16), were measured by a band-shift assay using a maleimide compound. Redox-IDX-apoE candidates were determined by calculating the values of these fractions and the total apoE concentration.

Results: Cys number of apoE significantly increased for the ratio of roxi-apoE to total-apoE (roxi/total) (E2/E3>E3/E3>E3/E4) but decreased for the ratios of red-apoE to roxi-apoE (red/roxi) and [red-apoE + oxi-apoE] to roxi-apoE ([red + oxi]/roxi) (E2/E3<E3/E3<E3/E4). Considering the subjects with apoE3/E3, these ratios were independent of age and sex. Roxi/total showed negative correlations with serum triglyceride (TG) and HbA1c levels, while both red/roxi and [red + oxi]/roxi showed significant positive correlations with them. However, red/roxi and [red + oxi]/roxi in patients were significantly lower than those in controls, although serum TG and HbA1c levels in the patients were significantly higher than those in controls.

Conclusion: The redox status of serum apoE-Cys-thiol is closely involved in the metabolism of TG-rich lipoproteins and glucose. The appropriate use of redox-IDX-apoE could be helpful in the diagnosis and prognosis of age-related diseases and in understanding the underlying mechanisms.

Individual and combined effects of GIP and xenin on differentiation, glucose uptake and lipolysis in 3T3-L1 adipocytes

The incretin hormone glucose-dependent insulinotropic polypeptide (GIP), released postprandially from K-cells, has established actions on adipocytes and lipid metabolism. In addition, xenin, a related peptide hormone also secreted from K-cells after a meal, has postulated effects on energy regulation and lipid turnover. The current study has probed direct individual and combined effects of GIP and xenin on adipocyte function in 3T3-L1 adipocytes, using enzyme-resistant peptide analogues, (d-Ala2)GIP and xenin-25-Gln, and knockdown (KD) of receptors for both peptides. (d-Ala2)GIP stimulated adipocyte differentiation and lipid accumulation in 3T3-L1 adipocytes over 96 h, with xenin-25-Gln evoking similar effects. Combined treatment significantly countered these individual adipogenic effects. Individual receptor KD impaired lipid accumulation and adipocyte differentiation, with combined receptor KD preventing differentiation. (d-Ala2)GIP and xenin-25-Gln increased glycerol release from 3T3-L1 adipocytes, but this lipolytic effect was significantly less apparent with combined treatment. Key adipogenic and lipolytic genes were upregulated by (d-Ala2)GIP or xenin-25-Gln, but not by dual peptide culture. Similarly, both (d-Ala2)GIP and xenin-25-Gln stimulated insulin-induced glucose uptake in 3T3-L1 adipocytes, but this effect was annulled by dual treatment. In conclusion, GIP and xenin possess direct, comparable, lipogenic and lipolytic actions in 3T3-L1 adipocytes. However, effects on lipid metabolism are significantly diminished by combined administration.

Exploring Therapeutic Targets to Reverse or Prevent the Transition from Metabolically Healthy to Unhealthy Obesity

The prevalence of obesity and obesity-related metabolic comorbidities are rapidly increasing worldwide, placing a huge economic burden on health systems. Excessive nutrient supply combined with reduced physical exercise results in positive energy balance that promotes adipose tissue expansion. However, the metabolic response and pattern of fat accumulation is variable, depending on the individual’s genetic and acquired susceptibility factors. Some develop metabolically healthy obesity (MHO) and are resistant to obesity-associated metabolic diseases for some time, whereas others readily develop metabolically unhealthy obesity (MUO). An unhealthy response to excess fat accumulation could be due to susceptibility intrinsic factors (e.g., increased likelihood of dedifferentiation and/or inflammation), or by pathogenic drivers extrinsic to the adipose tissue (e.g., hyperinsulinemia), or a combination of both. This review outlines the major transcriptional factors and genes associated with adipogenesis and regulation of adipose tissue homeostasis and describes which of these are disrupted in MUO compared to MHO individuals. It also examines the potential role of pathogenic insulin hypersecretion as an extrinsic factor capable of driving the changes in adipose tissue which cause transition from MHO to MUO. On this basis, therapeutic approaches currently available and emerging to prevent and reverse the transition from MHO to MUO transition are reviewed.

Fasting induces ANGPTL4 and reduces LPL activity in human adipose tissue

Objective

Studies in mice have shown that the decrease in lipoprotein lipase (LPL) activity in adipose tissue upon fasting is mediated by induction of the inhibitor ANGPTL4. Here, we aimed to validate this concept in humans by determining the effect of a prolonged fast on ANGPTL4 and LPL gene and protein expression in human subcutaneous adipose tissue.

Methods

Twenty-three volunteers ate a standardized meal at 18.00 h and fasted until 20.00 h the next day. Blood was drawn and periumbilical adipose tissue biopsies were collected 2 h and 26 h after the meal.

Results

Consistent with previous mouse data, LPL activity in human adipose tissue was significantly decreased by fasting (−60%), concurrent with increased ANGPTL4 mRNA (+90%) and decreased ANGPTL8 mRNA (−94%). ANGPTL4 protein levels in adipose tissue were also significantly increased by fasting (+46%), whereas LPL mRNA and protein levels remained unchanged. In agreement with the adipose tissue data, plasma ANGPTL4 levels increased upon fasting (+100%), whereas plasma ANGPTL8 decreased (−79%). Insulin, levels of which significantly decreased upon fasting, downregulated ANGPTL4 mRNA and protein in primary human adipocytes. By contrast, cortisol, levels of which significantly increased upon fasting, upregulated ANGPTL4 mRNA and protein in primary human adipocytes as did fatty acids.

Conclusion

ANGPTL4 levels in human adipose tissue are increased by fasting, likely via increased plasma cortisol and free fatty acids and decreased plasma insulin, resulting in decreased LPL activity.

This clinical trial was registered with identifier NCT03757767.

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24-h fast in humans reduces LPL activity in subcutaneous adipose tissue.

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24-h fast in humans increases adipose ANGPTL4 mRNA, protein, and plasma ANGPTL4 levels.

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Cortisol, fatty acids, and insulin regulate ANGPTL4 in vitro.

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ANGPTL4 mediates the reduction in adipose LPL activity during fasting.

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24-h fast in humans decreases adipose ANGPTL8 mRNA and plasma ANGPTL8 levels.

The structure of helical lipoprotein lipase reveals an unexpected twist in lipase storage

Lipases are enzymes necessary for the proper distribution and utilization of lipids in the human body. Lipoprotein lipase (LPL) is active in capillaries, where it plays a crucial role in preventing dyslipidemia by hydrolyzing triglycerides from packaged lipoproteins. Thirty years ago, the existence of a condensed and inactive LPL oligomer was proposed. Although recent work has shed light on the structure of the LPL monomer, the inactive oligomer remained opaque. Here we present a cryo-EM reconstruction of a helical LPL oligomer at 3.8-Å resolution. Helix formation is concentration-dependent, and helices are composed of inactive dihedral LPL dimers. Heparin binding stabilizes LPL helices, and the presence of substrate triggers helix disassembly. Superresolution fluorescent microscopy of endogenous LPL revealed that LPL adopts a filament-like distribution in vesicles. Mutation of one of the helical LPL interaction interfaces causes loss of the filament-like distribution. Taken together, this suggests that LPL is condensed into its inactive helical form for storage in intracellular vesicles.

Lipid Deposition and Mobilisation in Atlantic Salmon Adipocytes

The present study aimed to elucidate how Atlantic salmon adipocytes pre-enriched with palmitic (16:0, PA), oleic (18:1n−9, OA), or eicosapentaenoic (20:5n−3, EPA) acid respond to a fasting condition mimicked by nutrient deprivation and glucagon. All experimental groups were supplemented with radiolabeled PA to trace secreted lipids and distribution of radioactivity in different lipid classes. There was a higher content of intracellular lipid droplets in adipocytes pre-enriched with OA than in adipocytes pre-enriched with PA or EPA. In the EPA group, the radiolabeled PA was mainly esterified in phospholipids and triacylglycerols, whereas in the OA and PA groups, the radioactivity was mainly recovered in phospholipids and cholesterol-ester. By subjecting the experimental groups to nutrient-deprived media supplemented with glucagon, lipolysis occurred in all groups, although to a lower extent in the OA group. The lipids were mainly secreted as esterified lipids in triacylglycerols and phospholipids, indicating mobilization in lipoproteins. A significant proportion was secreted as free fatty acids and glycerol. Leptin secretion was reduced in all experimental groups in response to fasting, while the mitochondria area responded to changes in the energy supply and demand by increasing after 3 h of fasting. Overall, different lipid classes in adipocytes influenced their mobilization during fasting.

Effect of chronic exposure to monocrotophos on white adipose tissue in rats and its association with metabolic dyshomeostasis

Earlier, we demonstrated that chronic exposure to monocrotophos (MCP) elicits insulin resistance in rats along with increased white adipose tissue (WAT) weights. This study was carried out to delineate the biochemical and molecular changes in adipose tissues of rats subjected to chronic exposure to MCP (0.9 and 1.8 mg/kg bw/d for 180 days). Pesticide-treated rats exhibited increased fasting glucose and hyperinsulinemia as well as dyslipidemia. Tumor necrosis factor-alpha and leptin levels were elevated, while adiponectin level was suppressed in plasma of treated rats. MCP treatment caused discernable increase in the weights of perirenal and epididymal WAT. Acetyl coenzyme A carboxylase, fatty acid synthase, glyceraldehyde-3-phosphate dehydrogenase, lipin-1, and lipolytic activities were elevated in the WAT of MCP-treated rats. Corroborative changes were observed in the expression profile of proteins that are involved in lipogenesis and adipose tissue differentiation. Our results clearly demonstrate that long-term exposure to organophosphorus insecticides (OPIs) such as MCP has far-reaching consequences on metabolic health as evidenced by the association of adipogenic outcomes with insulin resistance, hyperinsulinemia, endocrine dysregulations, and dyslipidemia. Taken together, our results suggest that long-term exposure to OPI may be a risk factor for metabolic dysregulations.

Maternal Adipose Tissue Expansion, A Missing Link in the Prediction of Birth Weight Centile

CONTEXT

Maternal body mass index (BMI) is associated with increased birth weight but does not explain all the variance in fetal adiposity.

OBJECTIVE

To assess the contribution of maternal body fat distribution to offspring birth weight and adiposity.

DESIGN

Longitudinal study throughout gestation and at delivery.

SETTING

Women recruited at 12 weeks of gestation and followed up at 26 and 36 weeks. Cord blood was collected at delivery.

PATIENTS

Pregnant women (n = 45) with BMI 18.0 to 46.3 kg/m2 and healthy pregnancy outcome.

METHODS

Maternal first trimester abdominal subcutaneous and visceral adipose tissue thickness (SAT and VAT) was assessed by ultrasound.

MAIN OUTCOME MEASURES

Maternal body fat distribution, maternal and cord plasma glucose and lipid concentrations, placental weight, birth weight, and fetal adiposity assessed by cord blood leptin.

RESULTS

VAT was the only anthropometric measure independently associated with birth weight centile (r2 adjusted 15.8%, P = .002). BMI was associated with trimester 2 and trimesters 1 through 3 area under the curve (AUC) glucose and insulin resistance (Homeostatic Model Assessment). SAT alone predicted trimester 2 lipoprotein lipase (LPL) mass (a marker of adipocyte insulin sensitivity) (11.3%, P = .017). VAT was associated with fetal triglyceride (9.3%, P = .047). Placental weight was the only independent predictor of fetal adiposity (48%, P < .001). Maternal trimester 2 and AUC LPL were inversely associated with fetal adiposity (r = -0.69, P = .001 and r = -0.58, P = .006, respectively).

CONCLUSIONS

Maternal VAT provides additional information to BMI for prediction of birth weight. VAT may be a marker of reduced SAT expansion and increased availability of maternal fatty acids for placental transport.

Influence of glucose and insulin in human adipogenic differentiation models with adipose-derived stem cells

Autologous fat grafting represents an attractive source for tissue engineering applications in the field of reconstructive medicine. However, in adipogenic differentiation protocols for human adipose-derived stem cells, the concentration of glucose and insulin varies considerably. With the intent to gain maximum tissue augmentation, we focused on the late phase of adipogenesis. In this study, we modified the differentiation protocol for adipose-derived stem cells by prolongation of the induction period and the application highly concentrated glucose and insulin. Human adipose-derived stem cells were isolated from subcutaneous depots and differentiated in a standard induction medium for the first two weeks, followed by two weeks with varying glucose and insulin concentrations. Morphological changes assessed using Oil-Red-O staining were examined for corresponding alterations in the expression of the adipogenic markers peroxisome proliferator-activated receptor gamma (PPARγ) and lipoprotein lipase (LPL). Furthermore, glucose and lactate levels in conditioned media were monitored over the period of differentiation. We found high-glucose media increasing the level of lipid accumulation and the size of single droplets whereas insulin significantly showed a dose-dependent negative effect on fat storage. However, whereas high glucose stimulated PPARγ transcription, expression levels in insulin-treated cells remained constant. Results permit assumptions that a high-glucose medium intensifies the degree of differentiation in mature adipocytes providing conditions to promote graft volume while we have identified highly concentrated insulin treatment as an inhibitor of lipid storage in the late adipogenic differentiation.

Decreased GPIHBP1 protein levels in visceral adipose tissue partly underlie the hypertriglyceridemic phenotype in insulin resistance

GPIHBP1 is a protein localized at the endothelial cell surface that facilitates triglyceride (TG) lipolysis by binding lipoprotein lipase (LPL). Whether Glycosyl Phosphatidyl Inositol high density lipoprotein binding protein 1 (GPIHBP1) function is impaired and may underlie the hyperTG phenotype observed in type 2 diabetes is not yet established. To elucidate the mechanism underlying impaired TG homeostasis in insulin resistance state we studied the effect of insulin on GPIHBP1 protein expression in human microvascular endothelial cells (HMVEC) under flow conditions. Next, we assessed visceral adipose tissue GPIHBP1 protein expression in type 2 diabetes Lepr^db/db mouse model as well as in subjects with ranging levels of insulin resistance. We report that insulin reduces the expression of GPIHBP1 protein in HMVECs. Furthermore, GPIHBP1 protein expression in visceral adipose tissue in Lepr^db/db mice is significantly reduced as is the active monomeric form of GPIHBP1 as compared to Lepr^db/m mice. A similar decrease in GPIHBP1 protein was observed in subjects with increased body weight. GPIHBP1 protein expression was negatively associated with insulin and HOMA-IR.

In conclusion, our data suggest that decreased GPIHBP1 availability in insulin resistant state may hamper peripheral lipolysis capacity.

Implications of Lipids in Neonatal Body Weight and Fat Mass in Gestational Diabetic Mothers and Non-Diabetic Controls

PURPOSE OF REVIEW

Maternal lipid metabolism greatly changes during pregnancy and we review in this article how they influence fetal adiposity and growth under non-diabetic and gestational diabetic conditions.

RECENT FINDINGS

In pregnant women without diabetes (control), maternal glycemia correlates with neonatal glycemia, neonatal body weight and fat mass. In pregnant women with gestational diabetes mellitus (GDM), maternal glucose correlates with neither neonatal glycemia, neonatal birth weight nor fat mass, but maternal triacylglycerols (TAG), non-esterified fatty acids (NEFA) and glycerol do correlate with birth weight and neonatal adiposity. The proportions of maternal plasma arachidonic (AA) and docosahexaenoic (DHA) acids decrease from the first to the third trimester of pregnancy, and at term these long-chain polyunsaturated fatty acids are higher in cord blood plasma than in mothers, indicating efficient placental transfer. In control or pregnant women with GDM at term, the maternal concentration of individual fatty acids does not correlate with neonatal body weight or fat mass, but cord blood fatty acid levels correlate with birth weight and neonatal adiposity-positively in controls, but negatively in GDM. The proportion of AA and DHA in umbilical artery plasma in GDM is lower than in controls but not in umbilical vein plasma. Therefore, an increased utilization of those two fatty acids by fetal tissues, rather than impaired placental transfer, is responsible for their smaller proportion in plasma of GDM newborns. In control pregnant women, maternal glycemia controls neonatal body weight and fat mass, whereas in mothers with GDM-even with good glycemic control-maternal lipids and their greater utilization by the fetus play a critical role in neonatal body weight and fat mass. We propose that altered lipid metabolism rather than hyperglycemia constitutes a risk for macrosomia in GDM.

Reduced first-phase insulin secretion increases postprandial lipidemia in subjects with impaired glucose tolerance

OBJECTIVE

It is not clear which phase of insulin secretion is more important to regulate lipoprotein lipase (LPL) activity. After a meal, insulin is released and acts as a major regulator of LPL activity. Postprandial hyperlipidemia is a common comorbidity in subjects with insulin resistance (IR). Therefore this study aimed to evaluate the role of the first-phase insulin secretion (FPIS) on postprandial lipidemia in subjects with IR and impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS

This is a cross-sectional, observational and comparative study. We included male and female subjects between 40 and 60 years with a body mass index (BMI) between 23 and 30 kg/m². Then, patients were divided into three groups. Group 1 consisted of control subjects with normal glucose tolerance and preserved FPIS. Group 2 included patients with IGT and a reduced FPIS. Group 3 consisted of subjects with IGT but normal FPIS. Both groups were paired by age and BMI with subjects in the control group. Subjects underwent an intravenous glucose tolerance test to classify each case, and then a load with a mixed meal load to measure postprandial lipidemia.

RESULTS

A total of 32 subjects were evaluated: 10 were control subjects, 8 subjects with IGT with a reduced FPIS and 14 subjects with IGT and preserved FPIS. After administration of a standardized meal, group 2 showed a greater glucose area under the curve (AUC) at 30 and 120 min (p=0.001, for both). This group also showed a statistically significant increase (p<0.001) in triglyceride AUC.

CONCLUSIONS

A reduced FPIS is significantly and independently associated with a larger postprandial hyperlipidemia in subjects with IGT.

VY6, a β-lactoglobulin-derived peptide, altered metabolic lipid pathways in the zebra fish liver

Today enormous research efforts are being focused on alleviating the massive, adverse effects of obesity. Short peptides are key targets for research as they can be generated from natural proteins, like milk. Here we conducted trypsinogen digestion of beta-lactoglobulin (β-lg), the major mammalian milk protein, to release the hexamer VY6. It was assayed in vivo for its activities on lipid metabolism using zebra fish as a vertebrate model. Zebra fish juveniles were injected with two different doses of the peptide: 100 and 800 μg per g fish and left for 5 days before sacrificing. Lipid measurements showed significant reduction in liver triglycerides and free cholesterol, as well as increased liver HDL cholesterol. Dose-dependent increases of the mRNA levels of the genes coding for the enzymes acyl coenzyme A oxidase 1 (acox1) and lipoprotein lipase (lpl) were also found. The complete results suggest significant anti-obesity activity of the β-lg-derived VY6 peptide. Its use as a nutraceutical has been discussed.

Effects of Allium hookeri root water extracts on inhibition of adipogenesis and GLUT-4 expression in 3T3-L1 adipocytes

Anti-adipogenic and antidiabetic activities of Allium hookeri root water extracts (ARW) were assessed. Oil Red O staining showed that treatment with ARW caused a dose-dependent reduction in lipid accumulation. ARW was also involved in adipocyte lipolysis via LPL activity, and in the concentration of glycerol in a culture medium. On the basis of the concentration of adipokines following ARW treatment, ARW appeared to inhibit expression of PPAR-γ, to reduce concentrations of leptin and resistin, to increase the concentration of adiponectin, and to inhibit lipid accumulation. ARW modulated adipokine expression associated with insulin resistance and sensitivity. 3T3-L1 adipocytes treated with ARW showed increased GLUT-4 expression with increased glucose uptake into adipocytes. ARW showed effectiveness for improvement of diabetic conditions.

Effects of different amounts and types of dietary fatty acids on the body weight, fat accumulation, and lipid metabolism in hamsters

OBJECTIVES

The aim of this study was to explore the effects of different amounts of dietary fatty acids on body weight, fat accumulation, and lipid metabolism of hamsters.

METHODS

Sixty male golden Syrian hamsters were randomly divided into six groups. Three of the groups (the S groups) were fed experimental diets containing 5%, 15%, and 20% (w/w) fat of soybean oil (S5, S15, and S20, respectively), and the other three groups (the M groups) were fed the same proportions of an experimental oil mixture (M5, M15, and M20, respectively). The experimental oil mixture consisted of 60% monounsaturated fatty acids (MUFAs) and a polyunsaturated-to-saturated fatty acid ratio of 5 with a mixture of soybean and canola oils. Food consumption was measured daily, and body weights were measured weekly. Serum insulin and leptin concentrations were measured and hepatic fatty acid metabolic enzymes and adipose differentiation markers were determined using an enzyme activity analysis and quantitative polymerase chain reaction.

RESULTS

Results showed that the weight and weight gain of the S20 group were significantly greater than those of the other five groups. When the total fat consumption increased, the body weight, weight gain, and adipose tissue weight of the S groups significantly increased, but there were no significant differences in these parameters among the M groups. Serum low-density lipoprotein cholesterol concentrations were significantly lower in the M15 and S15 groups. The S20 group had significantly higher leptin and insulin concentrations and lipoprotein lipase was promoted, but the acetyl-coenzyme A oxidase and carnitine palmitoyltransferase-1, were significantly lower.

CONCLUSIONS

The study demonstrated that a special experimental oil mixture (with 60% MUFAs and a ratio of 5) with high fat can prevent body weight gain and body fat accumulation by lowering insulin concentrations and increasing hepatic lipolytic enzyme activities.

Ramie Leaf Extracts Suppresses Adipogenic Differentiation in 3T3-L1 Cells and Pig Preadipocytes

The present study was carried out to evaluate the anti-obesity effect of different concentrations of extracts of hot air-dried ramie leaf (HR) and freeze-dried ramie leaf (FR) in 3T3-L1 cells and pig preadipocytes. To analyze the effect on cell proliferation, cells were treated with 25 μg/mL or 100 μg/mL HR or FR extract for 2 days. Cell differentiation was evaluated by measuring glycerol-3-phosphate dehydrogenase and lipoprotein lipase (LPL) activities and intracellular triglyceride content. Treatment with either HR or FR extracts inhibited the proliferation of 3T3-L1 cells and pig preadipocytes in a dose-dependent manner. HR extract treatment inhibited the differentiation of both cell types more effectively than FR treatment. The extent of triglyceride accumulation decreased significantly in both cells following either HR or FR treatment. Furthermore, LPL activity significantly decreased after treatment with HR or FR extract. These results indicated that HR and FR extracts may inhibit proliferation and differentiation of 3T3-L1 cells and pig preadipocytes. Further studies are needed to explore the anti-obesity effect of HR and FR extracts.

Lipoprotein lipase: from gene to atherosclerosis

Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism and responsible for catalyzing lipolysis of triglycerides in lipoproteins. LPL is produced mainly in adipose tissue, skeletal and heart muscle, as well as in macrophage and other tissues. After synthesized, it is secreted and translocated to the vascular lumen. LPL expression and activity are regulated by a variety of factors, such as transcription factors, interactive proteins and nutritional state through complicated mechanisms. LPL with different distributions may exert distinct functions and have diverse roles in human health and disease with close association with atherosclerosis. It may pose a pro-atherogenic or an anti-atherogenic effect depending on its locations. In this review, we will discuss its gene, protein, synthesis, transportation and biological functions, and then focus on its regulation and relationship with atherosclerosis and potential underlying mechanisms. The goal of this review is to provide basic information and novel insight for further studies and therapeutic targets.

Adipogenic differentiation potential of adipose-derived mesenchymal stem cells from ovariectomized mice

OBJECTIVES

In human post-menopausal osteoporosis, enhanced adipogenesis in bone marrow and enhanced formation of adipose tissue in vivo are observed. These changes correlate with reduced trabecular bone volume and increased adipocyte cell size as well as cell number. However, cellular and molecular mechanisms underlying osteoporosis-related changes in adipocyte cell volume are not known. This study was designed to compare adipogenic potential of adipose tissue-derived stem cells (ADSCs) obtained from ovariectomized mice with that of control ADSCs, and to analyse pathological mechanisms from the point of functional changes of ADSCs.

MATERIALS AND METHODS

Healthy female C57BL/6J mice were randomly divided into ovariectomy and sham-surgery groups. Mouse ADSCs were isolated and cultured in vitro up to passage 3. After adipogenic induction, oil red O staining of lipid droplets was used to detect adipogenic ability of ADSCs; real-time PCR and immunofluorescence staining were used to detect expression of adipogenesis-related genes and proteins.

RESULTS

As indicated by increased expression of adipogenic and lipogenic genes and proteins, and lipid droplets accumulation shown by oil red-O staining, adipogenic differentiation of ADSCs was significantly enhanced in the ovariectomy group compared to the sham-surgery group (P < 0.05).

CONCLUSION

These findings suggest that enhanced adipogenic differentiation of ADSCs is likely to be the important cause for increased adipogenesis in vivo and subsequent obesity-like changes in body mass, in mice, after ovariectomy.

Lipid metabolism and hormonal interactions: impact on cardiovascular disease and healthy aging

Populations in developed nations are aging gradually; it is predicted that by 2050 almost a quarter of the world's population will be over 60 years old, more than twice the figure at the turn of the 20th century. Although we are living longer, this does not mean the extra years will be spent in good health. Cardiovascular diseases are the primary cause of ill health and their prevalence increases with age. Traditionally, lipid biomarkers have been utilized to stratify disease risk and predict the onset of cardiovascular events. However, recent evidence suggests that hormonal interplay with lipid metabolism could have a significant role to play in modulating cardiovascular disease risk. This review will explore recent findings which have investigated the role hormones have on the dynamics of lipid metabolism. The aim is to offer an insight into potential avenues for therapeutic intervention.

Physiological regulation of lipoprotein lipase

The enzyme lipoprotein lipase (LPL), originally identified as the clearing factor lipase, hydrolyzes triglycerides present in the triglyceride-rich lipoproteins VLDL and chylomicrons. LPL is primarily expressed in tissues that oxidize or store fatty acids in large quantities such as the heart, skeletal muscle, brown adipose tissue and white adipose tissue. Upon production by the underlying parenchymal cells, LPL is transported and attached to the capillary endothelium by the protein GPIHBP1. Because LPL is rate limiting for plasma triglyceride clearance and tissue uptake of fatty acids, the activity of LPL is carefully controlled to adjust fatty acid uptake to the requirements of the underlying tissue via multiple mechanisms at the transcriptional and post-translational level. Although various stimuli influence LPL gene transcription, it is now evident that most of the physiological variation in LPL activity, such as during fasting and exercise, appears to be driven via post-translational mechanisms by extracellular proteins. These proteins can be divided into two main groups: the liver-derived apolipoproteins APOC1, APOC2, APOC3, APOA5, and APOE, and the angiopoietin-like proteins ANGPTL3, ANGPTL4 and ANGPTL8, which have a broader expression profile. This review will summarize the available literature on the regulation of LPL activity in various tissues, with an emphasis on the response to diverse physiological stimuli.

Combinatorial regulation of lipoprotein lipase by microRNAs during mouse adipogenesis

MicroRNAs (miRNAs) regulate gene expression directly through base pairing to their targets or indirectly through participating in multi-scale regulatory networks. Often miRNAs take part in feed-forward motifs where a miRNA and a transcription factor act on shared targets to achieve accurate regulation of processes such as cell differentiation. Here we show that the expression levels of miR-27a and miR-29a inversely correlate with the mRNA levels of lipoprotein lipase (Lpl), their predicted combinatorial target, and its key transcriptional regulator peroxisome proliferator-activated receptor gamma (Pparg) during 3T3-L1 adipocyte differentiation. More importantly, we show that Lpl, a key lipogenic enzyme, can be negatively regulated by the two miRNA families in a combinatorial fashion on the mRNA and functional level in maturing adipocytes. This regulation is mediated through the Lpl 3'UTR as confirmed by reporter gene assays. In addition, a small mathematical model captures the dynamics of this feed-forward motif and predicts the changes in Lpl mRNA levels upon network perturbations. The obtained results might offer an explanation to the dysregulation of LPL in diabetic conditions and could be extended to quantitative modeling of regulation of other metabolic genes under similar regulatory network motifs.

Central Role of the PPARγ Gene Network in Coordinating Beef Cattle Intramuscular Adipogenesis in Response to Weaning Age and Nutrition

Adipogenic/lipogenic transcriptional networks regulating intramuscular fat deposition (IMF) in response to weaning age and dietary starch level were studied. The longissimus muscle (LM) of beef steers on an early weaning (141 days age) plus high-starch diet (EWS) or a normal weaning (NW, 222 days age) plus starch creep-feed diet (CFS) was biopsied at 0 (EW), 25, 50, 96 (NW), 167, and 222 (pre-slaughter) days. Expression patterns of 35 target genes were studied. From NW through slaughter, all steers received the same high-starch diet. In EWS steers the expression of PPARG, other adipogenic (CEBPA, ZFP423) and lipogenic (THRSP, SREBF1, INSIG1) activators, and several enzymes (FASN, SCD, ELOVL6, PCK1, DGAT2) that participate in the process of IMF increased gradually to a peak between 96 and 167 days on treatment. Steers in NW did not achieve similar expression levels even by 222 days on treatment, suggesting a blunted response even when fed a high-starch diet after weaning. High-starch feeding at an early age (EWS) triggers precocious and sustained adipogenesis, resulting in greater marbling.

Determinants of maternal triglycerides in women with gestational diabetes mellitus in the Metformin in Gestational Diabetes (MiG) study

OBJECTIVE

Factors associated with increasing maternal triglyceride concentrations in late pregnancy include gestational age, obesity, preeclampsia, and altered glucose metabolism. In a subgroup of women in the Metformin in Gestational Diabetes (MiG) trial, maternal plasma triglycerides increased more between enrollment (30 weeks) and 36 weeks in those treated with metformin compared with insulin. The aim of this study was to explain this finding by examining factors potentially related to triglycerides in these women.

RESEARCH DESIGN AND METHODS

Of the 733 women randomized to metformin or insulin in the MiG trial, 432 (219 metformin and 213 insulin) had fasting plasma triglycerides measured at enrollment and at 36 weeks. Factors associated with maternal triglycerides were assessed using general linear modeling.

RESULTS

Mean plasma triglyceride concentrations were 2.43 (95% CI 2.35-2.51) mmol/L at enrollment. Triglycerides were higher at 36 weeks in women randomized to metformin (2.94 [2.80-3.08] mmol/L; +23.13% [18.72-27.53%]) than insulin (2.65 [2.54-2.77] mmol/L, P = 0.002; +14.36% [10.91-17.82%], P = 0.002). At 36 weeks, triglycerides were associated with HbA1c (P = 0.03), ethnicity (P = 0.001), and treatment allocation (P = 0.005). In insulin-treated women, 36-week triglycerides were associated with 36-week HbA1c (P = 0.02), and in metformin-treated women, they were related to ethnicity.

CONCLUSIONS

At 36 weeks, maternal triglycerides were related to glucose control in women treated with insulin and ethnicity in women treated with metformin. Whether there are ethnicity-related dietary changes or differences in metformin response that alter the relationship between glucose control and triglycerides requires further study.

The role of estrogens in control of energy balance and glucose homeostasis

Estrogens play a fundamental role in the physiology of the reproductive, cardiovascular, skeletal, and central nervous systems. In this report, we review the literature in both rodents and humans on the role of estrogens and their receptors in the control of energy homeostasis and glucose metabolism in health and metabolic diseases. Estrogen actions in hypothalamic nuclei differentially control food intake, energy expenditure, and white adipose tissue distribution. Estrogen actions in skeletal muscle, liver, adipose tissue, and immune cells are involved in insulin sensitivity as well as prevention of lipid accumulation and inflammation. Estrogen actions in pancreatic islet β-cells also regulate insulin secretion, nutrient homeostasis, and survival. Estrogen deficiency promotes metabolic dysfunction predisposing to obesity, the metabolic syndrome, and type 2 diabetes. We also discuss the effect of selective estrogen receptor modulators on metabolic disorders.

High-fat diet-induced hyperinsulinemia and tissue-specific insulin resistance in Cry-deficient mice

Perturbation of circadian rhythmicity in mammals, either by environmental influences such as shiftwork or by genetic manipulation, has been associated with metabolic disturbance and the development of obesity and diabetes. Circadian clocks are based on transcriptional/translational feedback loops, comprising positive and negative components. Whereas the metabolic effects of deletion of the positive arm of the clock gene machinery, as in Clock- or Bmal1-deficient mice, have been well characterized, inactivation of Period genes (Per1-3) as components of the negative arm have more complex, sometimes contradictory effects on energy homeostasis. The CRYPTOCHROMEs are critical interaction partners of PERs, and simultaneous deletion of Cry1 and -2 results in behavioral and molecular circadian arrhythmicity. We show that, when challenged with a high-fat diet, Cry1/2(-/-) mice rapidly gain weight and surpass that of wild-type mice, despite displaying hypophagia. Transcript analysis of white adipose tissue reveals upregulated expression of lipogenic genes, many of which are insulin targets. High-fat diet-induced hyperinsulinemia, as a result of potentiated insulin secretion, coupled with selective insulin sensitivity in adipose tissue of Cry1/2(-/-) mice, correlates with increased lipid uptake. Collectively, these data indicate that Cry deficiency results in an increased vulnerability to high-fat diet-induced obesity that might be mediated by increased insulin secretion and lipid storage in adipose tissues.

Insulin signalling mechanisms for triacylglycerol storage

Insulin signalling is uniquely required for storing energy as fat in humans. While de novo synthesis of fatty acids and triacylglycerol occurs mostly in liver, adipose tissue is the primary site for triacylglycerol storage. Insulin signalling mechanisms in adipose tissue that stimulate hydrolysis of circulating triacylglycerol, uptake of the released fatty acids and their conversion to triacylglycerol are poorly understood. New findings include (1) activation of DNA-dependent protein kinase to stimulate upstream stimulatory factor (USF)1/USF2 heterodimers, enhancing the lipogenic transcription factor sterol regulatory element binding protein 1c (SREBP1c); (2) stimulation of fatty acid synthase through AMP kinase modulation; (3) mobilisation of lipid droplet proteins to promote retention of triacylglycerol; and (4) upregulation of a novel carbohydrate response element binding protein β isoform that potently stimulates transcription of lipogenic enzymes. Additionally, insulin signalling through mammalian target of rapamycin to activate transcription and processing of SREBP1c described in liver may apply to adipose tissue. Paradoxically, insulin resistance in obesity and type 2 diabetes is associated with increased triacylglycerol synthesis in liver, while it is decreased in adipose tissue. This and other mysteries about insulin signalling and insulin resistance in adipose tissue make this topic especially fertile for future research.

Rapid development of systemic insulin resistance with overeating is not accompanied by robust changes in skeletal muscle glucose and lipid metabolism

Prolonged overeating and the resultant weight gain are clearly linked with the development of insulin resistance and other cardiometabolic abnormalities, but adaptations that occur after relatively short periods of overeating are not completely understood. The purpose of this study was to characterize metabolic adaptations that may accompany the development of insulin resistance after 2 weeks of overeating. Healthy, nonobese subjects (n = 9) were admitted to the hospital for 2 weeks, during which time they ate ∼4000 kcals·day(-1) (70 kcal·kg(-1) fat free mass·day(-1)). Insulin sensitivity was estimated during a meal tolerance test, and a muscle biopsy was obtained to assess muscle lipid accumulation and protein markers associated with insulin resistance, inflammation, and the regulation of lipid metabolism. Whole-body insulin sensitivity declined markedly after 2 weeks of overeating (Matsuda composite index: 8.3 ± 1.3 vs. 4.6 ± 0.7, p < 0.05). However, muscle markers of insulin resistance and inflammation (i.e., phosphorylation of IRS-1-Ser(312), Akt-Ser(473), and c-Jun N-terminal kinase) were not altered by overeating. Intramyocellular lipids tended to increase after 2 weeks of overeating (triacylglyceride: 7.6 ± 1.6 vs. 10.0 ± 1.8 nmol·mg(-1) wet weight; diacylglyceride: 104 ± 10 vs. 142 ± 23 pmol·mg(-1) wet weight) but these changes did not reach statistical significance. Overeating induced a 2-fold increase in 24-h insulin response (area under the curve (AUC); p < 0.05), with a resultant ∼35% reduction in 24-h plasma fatty acid AUC (p < 0.05). This chronic reduction in circulating fatty acids may help explain the lack of a robust increase in muscle lipid accumulation. In summary, our findings suggest alterations in skeletal muscle metabolism may not contribute meaningfully to the marked whole-body insulin resistance observed after 2 weeks of overeating.

Effects of hyperinsulinemia on lipoprotein lipase, angiopoietin-like protein 4, and glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 in subjects with and without type 2 diabetes mellitus

Our aims were to compare the systemic effects of insulin on lipoprotein lipase (LPL) in tissues from subjects with different degrees of insulin sensitivity. The effects of insulin on LPL during a 4-hour hyperinsulinemic, euglycemic clamp were studied in skeletal muscle, adipose tissue, and postheparin plasma from young healthy subjects (YS), older subjects with type 2 diabetes mellitus (DS), and older control subjects (CS). In addition, we studied the effects of insulin on the expression of 2 recently recognized candidate genes for control of LPL activity: angiopoietin-like protein 4 (ANGPTL4) and glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1. As an effect of insulin, LPL activity decreased by 20% to 25% in postheparin plasma and increased by 20% to 30% in adipose tissue in all groups. In YS, the levels of ANGPTL4 messenger RNA in adipose tissue decreased 3-fold during the clamp. In contrast, there was no significant change in DS or CS. Regression analysis showed that the ability of insulin to reduce the expression of ANGPTL4 was positively correlated with M-values and inversely correlated with factors linked to the metabolic syndrome. Expression of glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 tended to be higher in YS than in DS or CS, but the expression was not affected by insulin in any of the groups. Our data imply that the insulin-mediated regulation of LPL is not directly linked to the control of glucose turnover by insulin or to ANGPTL4 expression in adipose tissue or plasma. Interestingly, the response of ANGPTL4 expression in adipose tissue to insulin was severely blunted in both DS and CS.

Lipoprotein lipase as a candidate target for cancer prevention/therapy

Epidemiological studies have shown that serum triglyceride (TG) levels are linked with risk of development of cancer, including colorectal and pancreatic cancers, and their precancerous lesions. Thus, it is assumed that serum TG plays an important role in carcinogenesis, and the key enzyme lipoprotein lipase (LPL), which catalyzes the hydrolysis of plasma TG, may therefore be involved. Dysregulation of LPL has been reported to contribute to many human diseases, such as atherosclerosis, chylomicronaemia, obesity, and type 2 diabetes. Recently, it has been reported that LPL gene deficiency, such as due to chromosome 8p22 loss, LPL gene polymorphism, and epigenetic changes in its promoter region gene, increases cancer risk, especially in the prostate. In animal experiments, high serum TG levels seem to promote sporadic/carcinogen-induced genesis of colorectal and pancreatic cancers. Interestingly, tumor suppressive effects of LPL inducers, such as PPAR ligands, NO-1886, and indomethacin, have been demonstrated in animal models. Moreover, recent evidence that LPL plays important roles in inflammation and obesity implies that it is an appropriate general target for chemopreventive and chemotherapeutic agents.

Regulation of lipoprotein lipase gene expression by insulin and troglitazone in rainbow trout (Oncorhynchus mykiss) adipocyte cells in culture

Adipose tissue plays a central role regulating the balance between deposition and mobilization of lipid reserves. Lipoprotein lipase (LPL) is a key enzyme controlling lipid accumulation in mammals and fish. In the present study, we have examined the expression of LPL in rainbow trout cultured adipocytes and we have investigated the effect of troglitazone, a member of thiazolidinediones (TZDs), and insulin on its expression. LPL gene expression increased from day 1 until day 12 of culture, and the level was maintained up to day 21. The addition of insulin at 10 nM and 1.7 μM increased significantly LPL gene expression in undifferentiated cells (days 7 to 12 maintained in growth medium). Nevertheless, treatment of day 7 cells incubated in growth medium with troglitazone (5 μM) or troglitazone plus insulin (1 μM each), tended to enhance LPL expression. In addition, LPL mRNA levels increased significantly in the presence of 1 μM and 5 μM of troglitazone (days 7 to 12) when the cells were induced to differentiate by addition of differentiation medium. Although troglitazone alone (1 μM) did not stimulate lipid accumulation in the cells neither in growth nor in differentiation medium, the simultaneous presence of troglitazone (1 μM) and insulin (1 μM) increased significantly the content of triglycerides in adipocyte cells maintained in growth medium (days 7 to 12). These results indicate that insulin and troglitazone regulate LPL gene expression during adipocyte differentiation and suggest that both factors may have combined effects in the modulation of adipogenesis.

Adipose tissue gene expression of factors related to lipid processing in obesity

Background

Adipose tissue lipid storage and processing capacity can be a key factor for obesity-related metabolic disorders such as insulin resistance and diabetes. Lipid uptake is the first step to adipose tissue lipid storage. The aim of this study was to analyze the gene expression of factors involved in lipid uptake and processing in subcutaneous (SAT) and visceral (VAT) adipose tissue according to body mass index (BMI) and the degree of insulin resistance (IR).

Methods and Principal Findings

VLDL receptor (VLDLR), lipoprotein lipase (LPL), acylation stimulating protein (ASP), LDL receptor-related protein 1 (LRP1) and fatty acid binding protein 4 (FABP4) gene expression was measured in VAT and SAT from 28 morbidly obese patients with Type 2 Diabetes Mellitus (T2DM) or high IR, 10 morbidly obese patients with low IR, 10 obese patients with low IR and 12 lean healthy controls. LPL, FABP4, LRP1 and ASP expression in VAT was higher in lean controls. In SAT, LPL and FABP4 expression were also higher in lean controls. BMI, plasma insulin levels and HOMA-IR correlated negatively with LPL expression in both VAT and SAT as well as with FABP4 expression in VAT. FABP4 gene expression in SAT correlated inversely with BMI and HOMA-IR. However, multiple regression analysis showed that BMI was the main variable contributing to LPL and FABP4 gene expression in both VAT and SAT.

Conclusions

Morbidly obese patients have a lower gene expression of factors related with lipid uptake and processing in comparison with healthy lean persons.

Skeletal muscle fatty acid handling in insulin resistant men

Disturbances in skeletal muscle lipid metabolism may precede or contribute to the development of whole body insulin resistance. In this study, we examined fasting and postprandial skeletal muscle fatty acid (FA) handling in insulin resistant (IR) men. Thirty men with the metabolic syndrome (MetS) (National Cholesterol Education Program-Adult Treatment Panel III) were included in this sub-study to the LIPGENE study, and divided in two groups (IR and control) based on the median of insulin sensitivity (S(I) = 2.06 (mU/l(-1))·min(-1)·10(-4)). Fasting and postprandial skeletal muscle FA handling were examined by combining the forearm balance technique with stable isotopes of palmitate. [(2)H(2)]-palmitate was infused intravenously to label endogenous triacylglycerol (TAG) and free FAs (FFAs) in the circulation and [U-(13)C]-palmitate was incorporated in a high-fat mixed meal (2.6 MJ, 61 E% fat) to label chylomicron-TAG. Muscle biopsies were taken to determine muscle TAG, diacylglycerol (DAG), FFA, and phospholipid (PL) content, their fractional synthetic rates (FSRs) and degree of saturation, as well as messenger RNA (mRNA) expression of genes involved in lipid metabolism. In the first 2 h after meal consumption, forearm muscle [(2)H(2)]-labeled TAG extraction was higher in IR vs. control (P = 0.05). Fasting percentage saturation of muscle DAG was higher in IR vs. control (P = 0.016). No differences were observed for intramuscular TAG, DAG, FFA, and PL content, FSR, and muscle mRNA expression. In conclusion, increased muscle (hepatically derived) TAG extraction during postprandial conditions and increased saturation of intramuscular DAG are associated with insulin resistance, suggesting that disturbances in skeletal muscle FA handling could play a role in the development of whole body insulin resistance and type 2 diabetes.

Dexamethasone-induced hepatic lipogenesis is insulin dependent in chickens (Gallus gallus domesticus)

Hepatic lipogenesis-induced de novo by glucocorticoids (GCs) is associated with the development of obesity and diabetes mellitus. The interaction of GCs and insulin in the regulation of hepatic lipogenesis remains unclear. The effect of exogenous GC administration on hepatic lipogenesis and fat deposition was studied in broiler chickens (Gallus gallus domesticus), and the role of insulin in the effect of GCs on hepatic lipogenesis was evaluated. Dexamethasone (DEX, 2 mg/kg body mass (BM)) administration for 3-d resulted in BM loss and increased liver and cervical adipose tissue mass compared to control and pair-fed counterparts. DEX treatment significantly (P < 0.05) increased plasma level of insulin in either the fed or fasting state, whereas plasma glucose level was only increased in the fed state. In fasted chickens, DEX treatment significantly (P < 0.01) upregulated the hepatic mRNA levels of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). In the fed state, the mRNA levels of ACC and FAS were not significantly influenced by DEX treatment, nor was FAS activity. In cultured primary hepatocytes, combined DEX and insulin significantly upregulated the transcription of the genes for FAS (1.34-fold) and malic enzyme (1.72-fold). By contrast, the expression of sterol response element-binding protein-1 (SREBP-1) was significantly upregulated by insulin (1.67-fold) regardless of DEX. In abdominal adipose tissue, DEX treatment had no significant (P>0.05) effect on the activities and transcription of FAS. The expressions of lipoprotein lipase and peroxisome proliferator-activated receptor-γ were not significantly (P>0.05) affected by DEX treatment in either the fasting or fed state. The results indicate that DEX increased hepatic de novo lipogenesis via the increased activity and expression of lipogenic enzymes. Insulin-activated gene expression for SREBP-1 is suggested to be involved in stress-augmented hepatic lipogenesis.

Effects of hyperinsulinemia on glucose and lipid transporter expression in insulin-sensitive horses

Plasma insulin concentrations are elevated (hyperinsulinemia) in horses with obesity-associated insulin resistance. In other species, insulin resistance is partly due to reduced levels of insulin receptor and the insulin-sensitive glucose transporter, and, in vitro, chronic hyperinsulinemic conditions reduce the expression of these proteins. Consumption of grain-based concentrate feeds results in postprandial hyperinsulinemia in horses, and adaptation to these diets is associated with insulin resistance. As such, it is possible that the repeated, chronic postprandial hyperinsulinemia associated with these diets could contribute to the development of insulin resistance. The purpose of the current study was to investigate the influence of a 6-h insulin infusion that increased plasma insulin concentrations to >1,000 mIU/L, on the expression of insulin receptor and glucose and lipid transporters in skeletal muscle and adipose tissue of lean, insulin-sensitive horses. Insulin infusion decreased transcript abundance of the glucose transporter 4 (P<0.05), glucose transporter 1 (GLUT1; P<0.09), and the insulin receptor (P<0.001) in adipose tissue, while increasing transcript abundance of GLUT1 (P<0.09) and decreasing protein abundance of the insulin receptor (P<0.09) in skeletal muscle. The acute, 6 hyperinsulinemic conditions achieved in this experiment resulted in alterations to mechanisms of glucose transport that could promote insulin resistance via reduced insulin-stimulated glucose disposal. Insulin infusion also reduced transcript abundance of the lipid transporters CD36 (P<0.001) and fatty acid transporter protein (FATP; P<0.05) in adipose tissue while increasing FATP (P<0.05) and lipoprotein lipase (P<0.01) in skeletal muscle. The reduction in adipose tissue lipid transporters could have been due to the decreased plasma lipid concentrations, whereas the increase in skeletal muscle may indicate that insulin stimulates lipid uptake into equine skeletal muscle. This report provides preliminary evidence that severe hyperinsulinemia alters glucose and lipid transporter expression that could promote an insulin-resistant state; these should be further investigated in horses consuming grain-based concentrates.