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Session Webcast
Browning of white adipose tissue
Webcast
Whitening of brown adipose tissue - role of the mevalonate pathway
Webcast
Fibroblast growth factor 21: A powerful therapeutic for hypercholesterolemia and atherosclerosis
Abstract
Background and Aims
Fibroblast growth factor 21 (FGF21), a key regulator of energy metabolism, is currently evaluated in humans for treatment of cardiometabolic disease. However, its role in atherogenesis remains elusive. Therefore, the aim of this study is to investigate the therapeutic effects of FGF21 on atherosclerosis and the underlying mechanisms in APOE*3-Leiden.CETP mice, a well-established model for human-like lipoprotein metabolism.
Methods
Female APOE*3-Leiden.CETP mice were fed a cholesterol-rich Western-type diet for 3 weeks, and subcutaneously injected with either vehicle or FGF21 (1 mg/kg body weight) 3 times per week for 16 weeks. At the end of the study, kinetic studies were performed and atherosclerotic lesion area, severity and composition were assessed in the aortic root.
Results
FGF21 treatment reduced fat mass as explained by highly increased energy expenditure. Mechanistically, FGF21 promoted brown adipose tissue (BAT) activation and white adipose tissue (WAT) browning, thereby enhancing selective uptake of fatty acids from triglyceride-rich lipoproteins into BAT and into beige adipocytes in WAT, consequently accelerating the hepatic clearance of the cholesterol-enriched remnants as evidenced from kinetic studies with radiolabeled lipoprotein-like particles. Accordingly, FGF21 reduced plasma total cholesterol and non-HDL cholesterol levels resulting in largely decreased atherosclerotic lesion area and severity. Moreover, FGF21 increased atherosclerotic plaque stability as indicated by reduced macrophage content vs collagen and smooth muscle cell content.
Conclusions
FGF21 activates BAT and induces browning of WAT, thereby accelerating lipoprotein turnover, improving hypercholesterolemia and protecting against atherosclerosis. We have thus provided mechanistic evidence to support the clinical use of FGF21 in the treatment of atherosclerotic cardiovascular disease.
Webcast
Endothelial lysosomal acid lipase deficiency impairs white adipose tissue browning
Abstract
Background and Aims
Brown adipose tissue (BAT) is able to burn fatty acids and other substrates for heat production. Lipid uptake into BAT does not only involve lipoprotein lipase(LPL)-mediated hydrolysis of triglyceride-rich lipoproteins(TRL), but also includes whole particle uptake by endothelial cells. The relevance of endothelial TRL uptake and subsequent lysosomal processing for BAT function is still unknown. We investigated the impact of impaired lipoprotein handling in endothelial-specific lysosomal acid lipase(LAL)-deficient mice with regard to BAT biology and thermogenesis.
Methods
Tamoxifen-inducible endothelial-specific LAL knockout(Lipa-/-Cdh5cre) mice were fed Western-type diet(WTD) and exposed to cold. Cell type-specific analyses were performed using Magnetic-activated cell sorting (MACS). Gene and protein expression in WAT and BAT, indirect calorimetry and metabolic turnover studies were conducted to examine thermogenic adipose function.
Results
MACS confirmed the specific LAL knockout in endothelial cells. Lipid uptake studies using radiotracer revealed an accumulation of triolein and cholesterol in LAL-deficient endothelial cells indicating delayed lipid processing. In vivo, Lipa-/-Cdh5cre mice showed only minor differences in lipid uptake into BAT and beta3-adrenergic induced thermogenesis, which might be due to the compensatory induction of UCP1 and LPL. Cold exposure lead to impaired thermogenic capacity accompanied by diminished browning of white adipose tissue (WAT), in WTD, but not chow-fed mice. While BAT appearance is unaltered, LAL activity is essential for differentiation of beige adipocytes in WAT depots.
Conclusions
These data show the relevance of endothelial lipoprotein handling in thermogenic adipose tissues. Lysosomal lipoprotein processing is crucial for proper cold adaptation, since endothelial-specific deletion of LAL leads to impaired browning of WAT.
Webcast
The impact of ANGPTL3 deficiency on hepatic steatosis: observations from carriers of loss-of-function mutations
Abstract
Background and Aims
Loss-of-function (LOF) mutations in ANGPTL3 cause familial combined hypolipidemia (FHBL2) characterized by very low levels of all three major lipoprotein fractions (LDL-C, TGs and HDL-C). Targeting ANGPTL3 has emerged as a new therapeutic opportunity to lower two causal risk factors (LDL-C and TG) for coronary heart disease (CHD) with potentially favorable metabolic effects. It is unknown, however, if inhibiting ANGPTL3 will result in adverse consequences. The aim of this study was to evaluate if genetic loss of ANGPTL3 leads to hepatic fat accumulation.
Methods
We studied individuals carrying LOF mutations in ANGPTL3 resulting in complete (N=6) or partial (N=28) ANGPTL3 deficiency along with 76 wild-type controls. Magnetic resonance spectroscopy (MRS) and chemical shift magnetic resonance imaging (csMRI) were used to quantify hepatic triglyceride content in ANGPTL3 LOF carriers and non-carriers.
Results
The mean hepatic fat fraction (HFF) measured by MRS was not significantly different in ANGPTL3 LOF mutation carriers as compared with non-carrier controls [8.1%±13.3% (IQR 0.1%-9.2%) vs. 11.9%±16.3% (IQR 0.1%-21.6%), respectively, P=NS]. Similar results were found by csMRI [5.6%±3.8% (IQR 2.6%-7.1%) vs. 7.3%±6.2% (IQR 2.7%-9.7%), respectively, P=NS]. In a multivariate model including ANGPTL3 genotype, age, gender, triglycerides, BMI and HOMA-IR, we found that only BMI and HOMA-IR were independently associated with increased HFF.
Conclusions
Unlike other genetic causes of hypolipidemia, ANGPTL3 deficiency does not appear to cause hepatic fat accumulation. This suggests that pharmacological inhibition of ANGPTL3 may not be associated with an increased risk of fatty liver disease.
Webcast
Real-time imaging of vascular brown adipose tissue lipoprotein lipase activity
Abstract
Background and Aims
Lipoprotein lipase (LPL) liberates fatty acids and glycerol from the core of triglyceride-rich lipoproteins (TRLs). Delayed postprandial clearance of TRLs is associated with atherosclerosis. Measurement of the effective tissue LPL activity has proven difficult, as not only the intrinsic activity of the enzyme but also the intravascular localization is important for proper TRL processing. We developed an ultrafast confocal in vivo microscopy-based approach for visualizing LPL action in capillaries.
Methods
The method is based on increased fluorescence resulting from LPL-mediated liberation of resorufin from recombinant TRLs containing resorufin-oleate (R-TRL). R-TRL can be used for determining LPL activity in vitro, and for visualizing LPL action in vivo by intravital confocal microscopy.
Results
Enzymatic activity determined by the R-TRL method could be inhibited by the lipase inhibitor tetrahydrolipstatin. It was elevated in brown adipose tissue lysates of cold-exposed vs warm-housed mice, demonstrating specificity of the assay for LPL. To map the exact anatomical site of LPL activity in BAT, we injected R-TRL intravenously and performed intravital microscopy. The association of R-TRL with capillaries and the release of resorufin were profoundly increased in cold-exposed vs. control mice, and diminished in aLKO vs. WT mice. LPL action in cold-activated BAT was found to be a discontinuous process, showing pronounced fluctuation over time. The flucuations could be prevented by the vasodilator acepromazin.
Conclusions
We developed a novel specific method for determining LPL activity in vitro and visualizing LPL action in an ultrafast manner. Our data identify blood flow as a regulator of LPL substrate availability in cold-activated BAT.