Uptake Of Triglyceride-derived Fatty Acids Research Articles

Triglyceride-derived fatty acids reduce autophagy in a model of retinal angiomatous proliferation.

Dyslipidemia and autophagy have been implicated in the pathogenesis of blinding neovascular age-related macular degeneration (NV-AMD). VLDL receptor (VLDLR), expressed in photoreceptors with a high metabolic rate, facilitates the uptake of triglyceride-derived fatty acids. Since fatty acid uptake is reduced in Vldlr–/– tissues, more remain in circulation, and the retina is fuel deficient, driving the formation in mice of neovascular lesions reminiscent of retinal angiomatous proliferation (RAP), a subtype of NV-AMD. Nutrient scarcity and energy failure are classically mitigated by increasing autophagy. We found that excess circulating lipids restrained retinal autophagy, which contributed to pathological angiogenesis in the Vldlr–/– RAP model. Triglyceride-derived fatty acid sensed by free fatty acid receptor 1 (FFAR1) restricted autophagy and oxidative metabolism in photoreceptors. FFAR1 suppressed transcription factor EB (TFEB), a master regulator of autophagy and lipid metabolism. Reduced TFEB, in turn, decreased sirtuin-3 expression and mitochondrial respiration. Metabolomic signatures of mouse RAP-like retinas were consistent with a role in promoting angiogenesis. This signature was also found in human NV-AMD vitreous. Restoring photoreceptor autophagy in Vldlr–/– retinas, either pharmacologically or by deleting Ffar1, enhanced metabolic efficiency and suppressed pathological angiogenesis. Dysregulated autophagy by circulating lipids might therefore contribute to the energy failure of photoreceptors driving neovascular eye diseases, and FFAR1 may be a target for intervention.

Regulation of fat partitioning by ANGPTL4

Altered triglyceride metabolism and changes in fatty acid partitioning are major contributors to metabolic diseases including metabolic syndrome, diabetes, and atherosclerosis. The triglycerides in plasma lipoproteins are hydrolyzed by lipoprotein lipase (LPL), and the levels of LPL activity in the capillary beds of peripheral tissues such as heart, skeletal muscle, and adipose serve as the primary determinant dietary fat delivery to those tissues. LPL activity is regulated by a variety of extracellular proteins including angiopoietin-like 4 (ANGPTL4). ANGPTL4 regulates plasma triglyceride metabolism by inactivating LPL. ANGPTL4 is most highly expressed in adipose tissue and liver, but it is also expressed at lower levels in muscle, heart, kidney, and intestine. It also circulates in plasma. Using whole-body and tissue-specific ANGPTL4 knockout mice we sought to determine where and when ANGPTL4 acts on LPL, and how the action of ANGPTL4 alters lipid partitioning. We found that ANGPTL4-deficiency specifically increases the uptake of triglyceride-derived fatty acids into adipose tissue, and that is effect is observed most prominently in the fasted state. Adipose-specific knockout of ANGPTL4 could wholly recapitulate the plasma triglyceride and fat partitioning phenotypes of whole-body ANGPTL4 knockouts, supporting the idea that adipose-derived ANGPTL4 is the primary driver of ANGPTL4’s effect on plasma triglycerides. Our data also suggest that ANGPTL4 expressed in adipose primarily acts locally to suppress LPL activity in the fasted state. Consistent with other reports, we also found that adipose-specific deletion of ANGPTL4 leads to short-term improvement in glucose tolerance in mice fed a high fat diet. However, we found that this improvement disappears with age. Moreover, we found that in wild-type mice LPL activity, ANGPTL4 expression, and lipid portioning are all altered with age. As age is also an important risk factor for metabolic disease, these finding suggest that age-induced changes in triglyceride metabolism may contribute to the increased risk of metabolic disease associated with aging.

Mild Exercise Does Not Prevent Atherosclerosis in APOE*3-Leiden.CETP Mice or Improve Lipoprotein Profile of Men with Obesity.

ObjectiveExercise has been shown to improve cardiometabolic health, yet neither the molecular connection nor the effects of exercise timing have been elucidated. The aim of this study was to investigate whether ad libitum or time‐restricted mild exercise reduces atherosclerosis development in atherosclerosis‐prone dyslipidemic APOE*3‐Leiden.CETP mice and whether mild exercise training in men with obesity affects lipoprotein levels.MethodsMice were group‐housed and subjected to ad libitum or time‐restricted (first or last 6 hours of the active phase) voluntary wheel running for 16 weeks while on a cholesterol‐rich diet, after which atherosclerosis development was assessed in the aortic root. Furthermore, nine men with obesity followed a 12‐week mild exercise training program. Lipoprotein levels were measured by nuclear magnetic resonance spectroscopy in plasma collected pre and post exercise training.ResultsWheel running did not affect plasma lipid levels, uptake of triglyceride‐derived fatty acids by tissues, and aortic atherosclerotic lesion size or severity. Markers of training status were unaltered. Exercise training in men with obesity did not alter lipoprotein levels.ConclusionsMild exercise training does not reduce dyslipidemia or atherosclerosis development in APOE*3‐Leiden.CETP mice or affect lipoprotein levels in humans. Future research on the effects of (time‐restricted) exercise on atherosclerosis or lipid metabolism should consider more vigorous exercise protocols.

A single day of high-fat diet feeding induces lipid accumulation and insulin resistance in brown adipose tissue in mice

Brown adipose tissue (BAT) catabolizes glucose and fatty acids to produce heat and thereby contributes to energy expenditure. Long-term high-fat diet (HFD) feeding results in so-called 'whitening' of BAT characterized by increased lipid deposition, mitochondrial dysfunction, and reduced fat oxidation. The aim of the current study was to unravel the rate and related mechanisms by which HFD induces BAT whitening and insulin resistance. Wild-type mice were fed a HFD for 0, 1, 3, or 7 days. Within 1 day of HFD, BAT weight and lipid content were increased. HFD also immediately reduced insulin-stimulated glucose uptake by BAT, indicating rapid induction of insulin resistance. This was accompanied by a tendency toward a reduced uptake of triglyceride-derived fatty acids by BAT. Mitochondrial mass and Ucp1 expression were unaltered, whereas after 3 days of HFD, markers of mitochondrial dynamics suggested induction of a more fused mitochondrial network. Additionally, HFD also increased macrophage markers in BAT after 3 days of HFD. Counterintuitively, the switch to HFD was accompanied by an acute rise in core body temperature. We showed that a single day of HFD feeding is sufficient to induce the first signs of whitening and insulin resistance in BAT, which reduces the uptake of glucose and triglyceride-derived fatty acids. BAT whitening and insulin resistance are likely sustained by reduced mitochondrial oxidation due to changes in mitochondrial dynamics and macrophage infiltration, respectively. Likely, the switch to HFD swiftly induces thermogenesis in other metabolic organs, which allows attenuation of BAT thermogenesis.

18F]BODIPY-triglyceride-containing chylomicron-like particles as an imaging agent for brown adipose tissue in vivo

Brown adipose tissue (BAT) is present in human adults and the current gold standard to visualize and quantify BAT is [18F]FDG PET-CT. However, this method fails to detect BAT under insulin-resistant conditions associated with ageing and weight gain, such as type 2 diabetes. The aim of this study was to develop a novel triglyceride-based tracer for BAT. For this purpose we designed a dual-modal fluorescent/PET fatty acid tracer based on commercially available BODIPY-FL-C16, which can be esterified to its correspondent triglyceride, radiolabeled and incorporated into pre-synthesized chylomicron-like particles. BODIPY-FL-C16 was coupled to 1,2-diolein with a subsequent radiolabeling step resulting in [18F]BODIPY-C16-triglyceride that was incorporated into chylomicron-like particles. Various quality control steps using fluorescent and radioactive methods were conducted before BAT visualization was tested in mice. Triglyceride synthesis, radiolabeling and subsequent incorporation into chylomicron-like particles was carried out in decent yields. This radiotracer appeared able to visualize BAT in vivo, and the uptake of the radiotracer was stimulated by cold exposure. The here reported method can be used to incorporate radiolabeled triglycerides into pre-synthesized chylomicron-like particles. Our approach is feasible to visualize and quantify the uptake of triglyceride-derived fatty acids by BAT.

Proteoglycan 4 deficiency protects against glucose intolerance and fatty liver disease in diet-induced obese mice

ObjectiveProteoglycan 4 (Prg4) has emerged from human association studies as a possible factor contributing to weight gain, dyslipidemia and insulin resistance. In the current study, we investigated the causal role of Prg4 in controlling lipid and glucose metabolism in mice. MethodsPrg4 knockout (KO) mice and wild-type (WT) littermates were challenged with an obesogenic high-fat diet (45% of total calories as fat) for 16 weeks. To further stimulate the development of metabolic alterations, 10% fructose water was provided starting from week 13. ResultsPrg4 deficiency only tended to reduce diet-induced body weight gain, but significantly improved glucose handling (AUC: −29%; p < 0.05), which was also reflected by a tendency towards a reduced HOMA-IR score (−49%; p = 0.06 as compared to WT mice). This coincided with lower hepatic expression of glycolysis (Gck: −30%; p < 0.05) and lipogenesis (Acc: −21%; p < 0.05 and Scd1: −38%; p < 0.001) genes, which translated in significantly lower hepatic triglyceride levels (−56%; p < 0.001) in Prg4 KO mice as compared to WT mice. Prg4 KO mice likely had lower glucose utilization by skeletal muscle as compared to WT mice, judged by a significant reduction in the genes Glut4 (−29%; p < 0.01), Pfkm (−21%; p < 0.05) and Hk2 (−39%; p < 0.001). Moreover, Prg4 KO mice showed a favorable white adipose tissue phenotype with lower uptake of triglyceride-derived fatty acids (−46%; p < 0.05) and lower gene expression of inflammatory markers Cd68, Mcp1 and Tnfα (−65%, −81% and −63%, respectively; p < 0.01) than WT mice. ConclusionPrg4 KO mice are protected from high-fat diet-induced glucose intolerance and fatty liver disease.

Prg4 KO Mice are Protected from High Fat Diet-induced Metabolic Disruptions

36 Proteoglycan 4 (Prg4) is highly expressed in metabolic tissues. The proteoglycan is a target gene for the nuclear receptor peroxisome proliferator receptor gamma which acts as metabolic switch. So, our aim was to investigate the function of Prg4 in metabolism. Male Prg4 knock-out (KO) mice and wild-type (WT) littermates were challenged with a obesogenic high fat diet (45% kcal lard fat) for 16 weeks. To stimulate the development of a diabetic phenotype, 10% fructose water was provided. Mice were subjected to an oral glucose tolerance test to investigate glucose handling. Flux studies with glycerol [3H]oleate-labeled VLDL-like particles were performed to determine the uptake of triglyceride-derived fatty acids in metabolically active organs. No significant difference in body weight was observed between both groups. However, both plasma triglyceride levels (-16%; p hepatic steatosis in Prg4 KO mice is most likely driven by decreased de novo lipogenesis , as judged by the significantly reduced expression of lipogenic genes ACC and SCD1 (-21% and -38%; p fatty acids . White adipose tissue of Prg4 KO mice showed decreased uptake of triglyceride-derived fatty acids (-46%; p CD68 and MCP1 was lower in Prg4 KO adipose tissue as compared to that of WT controls (2.9- and 5.1-fold decrease; p oral glucose tolerance test (AUC: -29%; p Prg4 KO and WT mice have a similar obesogenic potential, however Prg4 KO mice are protected from high fat diet-induced metabolic disruptions.

Chronic infusion of taurolithocholate into the brain increases fat oxidation in mice.

Bile acids can function in the postprandial state as circulating signaling molecules in the regulation of glucose and lipid metabolism via the transmembrane receptor TGR5 and nuclear receptor FXR. Both receptors are present in the central nervous system, but their function in the brain is unclear. Therefore, we investigated the effects of intracerebroventricular (i.c.v.) administration of taurolithocholate (tLCA), a strong TGR5 agonist, and GW4064, a synthetic FXR agonist, on energy metabolism. We determined the effects of chronic i.c.v. infusion of tLCA, GW4064, or vehicle on energy expenditure, body weight and composition as well as tissue specific fatty acid uptake in mice equipped with osmotic minipumps. We found that i.c.v. administration of tLCA (final concentration in cerebrospinal fluid: 1 μM) increased fat oxidation (tLCA group: 0.083 ± 0.006 vs control group: 0.036 ± 0.023 kcal/h, F = 5.46, P = 0.04) and decreased fat mass (after 9 days of tLCA infusion: 1.35 ± 0.13 vs controls: 1.96 ± 0.23 g, P = 0.03). These changes were associated with enhanced uptake of triglyceride-derived fatty acids by brown adipose tissue and with browning of subcutaneous white adipose tissue. I.c.v. administration of GW4064 (final concentration in cerebrospinal fluid: 10 μM) did not affect energy metabolism, body composition nor bile acid levels, negating a role of FXR in the central nervous system in metabolic control. In conclusion, bile acids such as tLCA may exert metabolic effects on fat metabolism via the brain.

Atorvastatin accelerates clearance of lipoprotein remnants generated by activated brown fat to further reduce hypercholesterolemia and atherosclerosis

Background and aimsActivation of brown adipose tissue (BAT) reduces both hyperlipidemia and atherosclerosis by increasing the uptake of triglyceride-derived fatty acids by BAT, accompanied by formation and clearance of lipoprotein remnants. We tested the hypothesis that the hepatic uptake of lipoprotein remnants generated by BAT activation would be accelerated by concomitant statin treatment, thereby further reducing hypercholesterolemia and atherosclerosis. MethodsAPOE*3-Leiden.CETP mice were fed a Western-type diet and treated without or with the selective β3-adrenergic receptor (AR) agonist CL316,243 that activates BAT, atorvastatin (statin) or both. Resultsβ3-AR agonism increased energy expenditure as a result of an increased fat oxidation by activated BAT, which was not further enhanced by statin addition. Accordingly, statin treatment neither influenced the increased uptake of triglyceride-derived fatty acids from triglyceride-rich lipoprotein-like particles by BAT nor further lowered plasma triglyceride levels induced by β3-AR agonism. Statin treatment increased the hepatic uptake of the formed cholesterol-enriched remnants generated by β3-AR agonism. Consequently, statin treatment further lowered plasma cholesterol levels. Importantly, statin, in addition to β3-AR agonism, also further reduced the atherosclerotic lesion size as compared to β3-AR agonism alone, without altering lesion severity and composition. ConclusionsStatin treatment accelerates the hepatic uptake of remnants generated by BAT activation, thereby increasing the lipid-lowering and anti-atherogenic effects of BAT activation in an additive fashion. We postulate that, in clinical practice, combining statin treatment with BAT activation is a promising new avenue to combat hyperlipidemia and cardiovascular disease.

Genetics and regulation of angiopoietin-like proteins 3 and 4

Lipoprotein lipase activity in a given tissue is the rate limiting step for the uptake of triglyceride-derived fatty acids. Imbalances in the partitioning of fatty acids have major metabolic consequences. Given the central role of lipoprotein lipase in energy metabolism, the discovery of new molecules that affect the activity of lipoprotein lipase holds great potential for novel therapeutic targets. Angiopoietin-like proteins 3 and 4 are two members of the angiopoietin-like family of proteins (Angptl). Unique within this family, Angptl3 and 4 inhibit lipoprotein metabolism via their ability to inhibit the activity of lipoprotein lipase. This review highlights recent studies on the biochemistry of Angptl3 and 4 as well as mouse models with selective overexpression of Angptl4 or global knockout of Angptl3, 4, or both. Both angiopoietins and angiopoietin-like proteins share similar domain structures. Angptl3 and 4 are the only two members of this superfamily that inhibit lipoprotein lipase activity. However, Angptl3 and 4 are differentially regulated at multiple levels, suggesting non-redundant functions in vivo. Angptl3 and 4 are proteolytically processed into two halves and are differentially regulated by nuclear receptors. Transgenic overexpression of Angptl4 as well as knockout of Angptl3 or 4 demonstrate that these two proteins play essential roles in lipoprotein metabolism: liver-derived Angptl3 inhibits lipoprotein lipase activity primarily in the fed state, while Angptl4 plays important roles in both fed and fasted states. In addition, Angptl4 regulates the tissue-specific delivery of lipoprotein-derived fatty acids. Angptl4 is thus an endocrine or autocrine/paracarine inhibitor of lipoprotein lipase depending on its sites of expression.

Apolipoprotein C3 Deficiency Results in Diet-Induced Obesity and Aggravated Insulin Resistance in Mice

Our aim was to study whether the absence of apolipoprotein (apo) C3, a strong inhibitor of lipoprotein lipase (LPL), accelerates the development of obesity and consequently insulin resistance. Apoc3(-/-) mice and wild-type littermates were fed a high-fat (46 energy %) diet for 20 weeks. After 20 weeks of high-fat feeding, apoc3(-/-) mice showed decreased plasma triglyceride levels (0.11 +/- 0.02 vs. 0.29 +/- 0.04 mmol, P < 0.05) and were more obese (42.8 +/- 3.2 vs. 35.2 +/- 3.3 g; P < 0.05) compared with wild-type littermates. This increase in body weight was entirely explained by increased body lipid mass (16.2 +/- 5.9 vs. 10.0 +/- 1.8 g; P < 0.05). LPL-dependent uptake of triglyceride-derived fatty acids by adipose tissue was significantly higher in apoc3(-/-) mice. LPL-independent uptake of albumin-bound fatty acids did not differ. It is interesting that whole-body insulin sensitivity using hyperinsulinemic-euglycemic clamps was decreased by 43% and that suppression of endogenous glucose production was decreased by 25% in apoc3(-/-) mice compared with control mice. Absence of apoC3, the natural LPL inhibitor, enhances fatty acid uptake from plasma triglycerides in adipose tissue, which leads to higher susceptibility to diet-induced obesity followed by more severe development of insulin resistance. Therefore, apoC3 is a potential target for treatment of obesity and insulin resistance.

PC65 LIPOPROTEIN LIPASE (LPL) mRNA EXPRESSION IN PLACENTAS FROM NORMAL AND IUGR (INTRAUTERINE GROWTH RESTRICTED) PREGNANCIES BY REAL-TIME PCR

Introduction: Adequate placental transfer is necessary for normal intrauterine growth and development of the fetus. Intra-uterine growth restriction (IUGR) is a condition associated with reduced nutritional placental supply. Recently, IUGR has been associated with changes in polyunsaturated fatty acid fetal-maternal relationships, mostly for the long chain polyunsaturated fatty acids, suggesting a role for these nutrients in the pathogenesis of IUGR. Lipoprotein lipase (LPL) plays a crucial role in lipoprotein and energy metabolism: it participates in the uptake of cholesterol-rich remnant particles, by acting as a ligand for VLDL receptor, LDL receptor, LDL-receptor related protein (LRP), and it is involved in the hydrolysis of triglycerides (TG) present in chylomicrons and very low-density lipoprotein (VLDL) to generate fatty acids, a source of energy for peripheral tissues. This suggests that the level of LPL expression in a given tissue is the rate limiting process for the uptake of triglyceride-derived fatty acids. LPL is expressed in human placenta, where it participates in the uptake of triglyceride-derived fatty acids. Methods: We compared the expression levels of LPL, at the mRNA level, in placentas from 11 AGA (appropriate for gestational age) and 30 IUGR pregnancies at the time of elective cesarean section. Relative Real-Time quantification of RNA extracted from placental villi was performed by the DeltaDeltaCt method, with Beta-actin as house-keeping, normaliser gene. Results: No significant relationship was observed between LPL expression levels and gestational age in either AGA or IUGR pregnancies. Average values of LPL mRNA were higher in IUGR (104.44 ± 77.68 a.u.) than in AGA (21.14 ± 10.09 a.u.) placentas, although not significantly. Moreover, a greater variability was observed in IUGR, with a sub-group of cases (40%) showing LPL mRNA expression over 60 a.u., a value never exceeded in normal cases. Conclusion: The increased levels of lipoprotein lipase expression observed in this sub-group of IUGR pregnancies could represent a compensatory mechanism to increase placental fatty acid availability.