| 1. |
- Dorfmeister, B, et al.
(författare)
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Effects of six APOA5 variants, identified in patients with severe hypertriglyceridemia, on in vitro lipoprotein lipase activity and receptor binding
- 2008
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Ingår i: Arteriosclerosis, Thrombosis and Vascular Biology. - 1079-5642 .- 1524-4636. ; 28:10, s. 1866-1871
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The purpose of this study was to identify rare APOA5 variants in 130 severe hypertriglyceridemic patients by sequencing, and to test their functionality, since no patient recall was possible. METHODS AND RESULTS: We studied the impact in vitro on LPL activity and receptor binding of 3 novel heterozygous variants, apoAV-E255G, -G271C, and -H321L, together with the previously reported -G185C, -Q139X, -Q148X, and a novel construct -Delta139 to 147. Using VLDL as a TG-source, compared to wild type, apoAV-G255, -L321 and -C185 showed reduced LPL activation (-25% [P=0.005], -36% [P<0.0001], and -23% [P=0.02]), respectively). ApoAV-C271, -X139, -X148, and Delta139 to 147 had little affect on LPL activity, but apoAV-X139, -X148, and -C271 showed no binding to LDL-family receptors, LR8 or LRP1. Although the G271C proband carried no LPL and APOC2 mutations, the H321L carrier was heterozygous for LPL P207L. The E255G carrier was homozygous for LPL W86G, yet only experienced severe hypertriglyceridemia when pregnant. CONCLUSIONS: The in vitro determined function of these apoAV variants only partly explains the high TG levels seen in carriers. Their occurrence in the homozygous state, coinheritance of LPL variants or common APOA5 TG-raising variant in trans, appears to be essential for their phenotypic expression.
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| 2. |
- Kovrov, Oleg, 1990-
(författare)
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Regulation of Lipoprotein Lipase Activity : an In-vitro Study of a Complex and Dynamic System
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The progress of human society outpaces our biological evolution, and this brings unexpected health problems. The industrial revolution brought up dramatic changes in nutrition and lifestyle – we are increasingly shifting towards a nutrient-rich Western-patterned diet and to a sedentary lifestyle. Unfortunately, our energy metabolism is not fully capable to adapt to these changes. The excess of nutrients has led to global epidemics in obesity, type 2 diabetes, and cardiovascular diseases. To battle this, medical research has focused on the metabolism of sugars and cholesterol, whereas the fate of triglycerides, the major dietary lipid, has received less attention. Recently it became clear that blood triglycerides are connected to the development of type 2 diabetes and cardiovascular diseases. As a result, triglyceride metabolism became a focus of attention in both basic and clinical research.Lipoprotein lipase (LPL) is the cornerstone of blood triglyceride metabolism. This means that LPL must be tightly regulated in response to the nutritional state of the body, and to the needs of particular tissues. LPL is produced and secreted by cells that store triglycerides or use them for generation of energy. After secretion, LPL stays attached to the capillary endothelium where it hydrolyses triglycerides from the triglyceride-rich lipoproteins. LPL is relatively unstable and the instability is a key property in its physiological regulation since transcriptional control of LPL does not respond to the metabolic changes fast enough. Instead, LPL is regulated by two groups of proteins – plasma apolipoproteins, which serve as activators or inhibitors of LPL, and angiopoietin-like (ANGPTL) proteins, which irreversibly inactivate LPL in the tissues which do not require triglycerides.One aim of my thesis was to study the effects of ANGPTL proteins on LPL structure and function. In papers I and II, using various biophysical and biochemical methods, we studied the effects of ANGPTL3, 4 and 8 on LPL structure and function. All data supported the concept that LPL is inactivated by dissociation of active dimers to monomers. Additionally, we describe the molecular basis for complex formation between ANGPTL3 and 8, as well as a novel complex between ANGPTL4 and 8 with unique properties. The other aim of my thesis was to perform an in-depth study of rate-limiting factors that control the activity of LPL in human plasma. In papers III and IV we study LPL activity using an isothermal titration calorimetry-based assay directly in plasma samples. We found that the normal variation in plasma levels of either ANGPTL proteins or apolipoproteins had no significant impact on LPL activity. Instead, the strongest determinant for LPL action was the size of the triglyceride-rich plasma lipoproteins.
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| 3. |
- Larsson, Mikael, et al.
(författare)
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Apolipoproteins C-I and C-III Inhibit Lipoprotein Lipase Activity by Displacement of the Enzyme from Lipid Droplets
- 2013
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 288:47, s. 33997-34008
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Tidskriftsartikel (refereegranskat)abstract
- Apolipoproteins (apo) C-I and C-III are known to inhibit lipoprotein lipase (LPL) activity, but the molecular mechanisms for this remain obscure. We present evidence that either apoC-I or apoC-III, when bound to triglyceride-rich lipoproteins, prevent binding of LPL to the lipid/water interface. This results in decreased lipolytic activity of the enzyme. Site-directed mutagenesis revealed that hydrophobic amino acid residues centrally located in the apoC-III molecule are critical for attachment to lipid emulsion particles and consequently inhibition of LPL activity. Triglyceride-rich lipoproteins stabilize LPL and protect the enzyme from inactivating factors such as angiopoietin-like protein 4 (angptl4). The addition of either apoC-I or apoC-III to triglyceride-rich particles severely diminished their protective effect on LPL and rendered the enzyme more susceptible to inactivation by angptl4. These observations were seen using chylomicrons as well as the synthetic lipid emulsion Intralipid. In the presence of the LPL activator protein apoC-II, more of apoC-I or apoC-III was needed for displacement of LPL from the lipid/water interface. In conclusion, we show that apoC-I and apoC-III inhibit lipolysis by displacing LPL from lipid emulsion particles. We also propose a role for these apolipoproteins in the irreversible inactivation of LPL by factors such as angptl4.
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| 4. |
- Larsson, Mikael, 1978-
(författare)
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Endogenous and exogenous factors affecting lipoprotein lipase activity
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Individuals with high levels of plasma triglycerides are at high risk to develop cardiovascular disease (CVD), currently one of the major causes of death worldwide. Recent epidemiological studies show that loss-of-function mutations in the APOC3 gene lower plasma triglyceride levels and reduce the incidence of coronary artery disease. The APOC3 gene encodes for apolipoprotein (APO) C3, known as an inhibitor of lipoprotein lipase (LPL) activity. Similarly, a common gain-of-function mutation in the LPL gene is associated with reduced risk for CVD.LPL is central for the metabolism of lipids in blood. The enzyme acts at the endothelial surface of the capillary bed where it hydrolyzes triglycerides in circulating triglyceride-rich lipoproteins (TRLs) and thereby allows uptake of fatty acids in adjacent tissues. LPL activity has to be rapidly modulated to adapt to the metabolic demands of different tissues. The current view is that LPL is constitutively expressed and that the rapid modulation of the enzymatic activity occurs by some different controller proteins. Angiopoietin-like protein 4 (ANGPTL4) is one of the main candidates for control of LPL activity. ANGPTL4 causes irreversible inactivation through dissociation of the active LPL dimer to inactive monomers. Other proteins that have effects on LPL activity are the APOCs which are surface components of the substrate TRLs. APOC2 is a well-known LPL co-factor, whereas APOC1 and APOC3 independently inhibit LPL activity.Given the important role of LPL for triglyceride homeostasis in blood, the aim of this thesis was to find small molecules that could increase LPL activity and serve as lead compounds in future drug discovery efforts. Another aim was to investigate the molecular mechanisms for how APOC1 and APOC3 inhibit LPL activity.Using a small molecule screening library we have identified small molecules that can protect LPL from inactivation by ANGPTL4 during incubations in vitro. Following a structure-activity relationship study we have synthesized lead compounds that more efficiently protect LPL from inactivation by ANGPTL4 in vitro and also have dramatic triglyceride-lowering properties in vivo. In a separate study we show that low concentrations of fatty acids possess the ability to prevent inactivation of LPL by ANGPTL4 under in vitro conditions.With regard to APOC1 and APOC3 we demonstrate that when bound to TRLs, these apolipoproteins prevent binding of LPL to the lipid/water interface. This results in decreased lipolysis and in an increased susceptibility of LPL to inactivation by ANGPTL4. We demonstrate that hydrophobic amino acid residues that are centrally located in the APOC3 molecule are critical for attachment of this protein to lipid emulsion particles and consequently for inhibition of LPL activity.In summary, this work has identified a lead compound that protects LPL from inactivation by ANGPTL4 in vitro and lowers triglycerides in vivo. In addition, we propose a molecular mechanism for inhibition of LPL activity by APOC1 and APOC3.
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| 5. |
- Larsson, Mikael, 1978-, et al.
(författare)
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Identification of a small molecule that stabilizes lipoprotein lipase in vitro and lowers triglycerides in vivo
- 2014
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier. - 0006-291X .- 1090-2104. ; 450:2, s. 1063-1069
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Tidskriftsartikel (refereegranskat)abstract
- Patients at increased cardiovascular risk commonly display high levels of plasma triglycerides (TGs) levels, elevated LDL cholesterol, small dense LDL particles and low levels of HDL-cholesterol. Many remain at high risk even after successful statin therapy, presumably because TG levels remain high. Lipoprotein lipase (LPL) maintains TG homeostasis in blood by hydrolysis of TG-rich lipoproteins. Efficient clearance of TGs is accompanied by increased levels of HDL-cholesterol and decreased levels of small dense LDL. Given the central role of LPL in lipid metabolism we sought to find small molecules that could increase LPL activity and serve as starting points for drug development efforts against cardiovascular disease. Using a small molecule screening approach we have identified small molecules that can protect LPL from inactivation by the controller protein angiopoietin-like protein 4 during incubations in vitro. One of the selected compounds, 50F10, was directly shown to preserve the active homodimer structure of LPL, as demonstrated by heparin-Sepharose chromatography. This compound tended to reduce fasting TG levels in normal rats. On injection to hypertriglyceridemic apolipoprotein A-V deficient mice the compound ameliorated the postprandial response after an olive oil gavage. This compound is a potential lead compound for the development of drugs that could reduce the residual risk associated with elevated TGs in dyslipidemia.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Mendoza-Barbera, Elena, et al.
(författare)
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Structural and functional analysis of APOA5 mutations identified in patients with severe hypertriglyceridemia
- 2013
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Ingår i: Journal of Lipid Research. - 0022-2275 .- 1539-7262. ; 54:3, s. 649-661
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Tidskriftsartikel (refereegranskat)abstract
- During the diagnosis of three unrelated patients with severe hypertriglyceridemia, three APOA5 mutations [p.(Ser232_Leu235)del,p.Leu253Pro,andp.Asp332ValfsX4] were found without evidence of concomitant LPL, APOC2, or GPIHBP1 mutations. The molecular mechanisms by which APOA5 mutations result in severe hypertriglyceridemia remain poorly understood, and the functional impairment/s induced by these specific mutations was not obvious. Therefore, we performed a thorough structural and functional analysis that included follow-up of patients and their closest relatives, measurement of apoA-V serum concentrations, and sequencing of the APOA5 gene in 200 nonhyperlipidemic controls. Further, we cloned, overexpressed, and purified both wild-type and mutant apoA-V variants and characterized their capacity to activate LPL. The interactions of recombinant wild-type and mutated apoA-V variants with liposomes of different composition, heparin, LRP1, sortilin, and SorLA/LR11 were also analyzed. Finally, to explore the possible structural consequences of these mutations, we developed a three-dimensional model of full-length, lipid-free human apoA-V. A complex, wide array of impairments was found in each of the three mutants, suggesting that the specific residues affected are critical structural determinants for apoA-V function in lipoprotein metabolism and, therefore, that these APOA5 mutations are a direct cause of hypertriglyceridemia.-Mendoza-Barbera, E., J. Julve, S. K. Nilsson, A. Lookene, J. M. Martin-Campos, R. Roig, A. M. Lechuga-Sancho, J. J. Sloan, P. Fuentes-Prior, and F. Blanco-Vaca. Structural and functional analysis of APOA5 mutations identified in patients with severe hypertriglyceridemia.
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| 10. |
- Nilsson, Emma C, 1979-, et al.
(författare)
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The GD1a glycan is a cellular receptor for adenoviruses causing epidemic keratoconjunctivitis (Letter)
- 2011
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Ingår i: Nature Medicine. - : Springer Science and Business Media LLC. - 1078-8956 .- 1546-170X. ; 17:1, s. 105-109
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Tidskriftsartikel (refereegranskat)abstract
- Adenovirus type 37 (Ad37) is a leading cause of epidemic keratoconjunctivitis (EKC), a severe and highly contagious ocular disease. Whereas most other adenoviruses infect cells by engaging CD46 or the coxsackie and adenovirus receptor (CAR), Ad37 binds previously unknown sialic acid-containing cell surface molecules. By glycan array screening, we show here that the receptor-recognizing knob domain of the Ad37 fiber protein specifically binds a branched hexasaccharide that is present in the GD1a ganglioside and that features two terminal sialic acids. Soluble GD1a glycan and GD1a-binding antibodies efficiently prevented Ad37 virions from binding and infecting corneal cells. Unexpectedly, the receptor is constituted by one or more glycoproteins containing the GD1a glycan motif rather than the ganglioside itself, as shown by binding, infection and flow cytometry experiments. Molecular modeling, nuclear magnetic resonance and X-ray crystallography reveal that the two terminal sialic acids dock into two of three previously established sialic acid-binding sites in the trimeric Ad37 knob. Surface plasmon resonance analysis shows that the knob-GD1a glycan interaction has high affinity. Our findings therefore form a basis for the design and development of sialic acid-containing antiviral drugs for topical treatment of EKC.
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