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Background: Many patients who are diagnosed with coronavirus disease 2019 (COVID-19) suffer from venous thromboembolic complications despite the use of stringent anticoagulant prophylaxis. Studies on the exact mechanism(s) underlying thrombosis in COVID-19 are limited as animal models commonly used to study venous thrombosis pathophysiology (i.e. rats and mice) are naturally not susceptible to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Ferrets are susceptible to SARS-CoV-2 infection, successfully used to study virus transmission, and have been previously used to study activation of coagulation and thrombosis during influenza virus infection. Objectives: This study aimed to explore the use of (heat-inactivated) plasma and lung material from SARS-CoV-2-inoculated ferrets studying COVID-19-associated changes in coagulation and thrombosis. Material and methods: Histology and longitudinal plasma profiling using mass spectrometry-based proteomics approach was performed. Results: Lungs of ferrets inoculated intranasally with SARS-CoV-2 demonstrated alveolar septa that were mildly expanded by macrophages, and diffuse interstitial histiocytic pneumonia. However, no macroscopical or microscopical evidence of vascular thrombosis in the lungs of SARS-CoV-2-inoculated ferrets was found. Longitudinal plasma profiling revealed minor differences in plasma protein profiles in SARS-CoV-2-inoculated ferrets up to 2 weeks post-infection. The majority of plasma coagulation factors were stable and demonstrated a low coefficient of variation. Conclusions: We conclude that while ferrets are an essential and well-suited animal model to study SARS-CoV-2 transmission, their use to study SARS-CoV-2-related changes relevant to thrombotic disease is limited.

Local coagulation activation has been shown to impact both primary tumor growth and metastasis in mice. It is well known that components of the blood clotting cascade such as tissue factor and thrombin play a role in tumor progression by activating cellular receptors and local formation of fibrin. However, whether venous thromboembolism (VTE) or a hypercoagulable state has a direct impact on cancer progression is unknown. Here we have combined an orthotopic murine breast cancer model, using female Nod-SCID mice, with siRNA-mediated silencing of antithrombin (siAT) leading to the induction of a systemic hypercoagulable state. We show that, compared to control siRNA-treated (not experiencing a hypercoagulable state) tumor-bearing mice, siAT treated tumor-bearing mice do not show enhanced tumor growth nor enhanced metastasis. We conclude that, in this murine model for hypercoagulability, induction of a hypercoagulable state does not contribute to breast cancer progression.

Background Treatment of the bleeding disorder von Willebrand disease (VWD) focuses on increasing von Willebrand factor (VWF) levels by administration of desmopressin or VWF‐containing concentrates. Both therapies leave the production of mutant VWF unhindered, which may have additional consequences, such as thrombocytopenia in patients with VWD type 2B, competition between mutant and normal VWF for platelet receptors, and the potential development of intestinal angiodysplasia. Most cases of VWD are caused by dominant‐negative mutations in VWF, and we hypothesize that diminishing expression of mutant VWF positively affects VWD phenotypes.ObjectivesTo investigate allele‐specific inhibition of VWF by applying small interfering RNAs (siRNAs) targeting common single‐nucleotide polymorphisms (SNPs) in VWF. This approach allows allele‐specific knockdown irrespective of the mutations causing VWD.MethodsFour SNPs with a high predicted heterozygosity within VWF were selected, and siRNAs were designed against both alleles of the four SNPs. siRNA efficiency, allele specificity and siRNA‐mediated phenotypic improvements were determined in VWF‐expressing HEK293 cells.ResultsTwelve siRNAs were able to efficiently inhibit single VWF alleles in HEK293 cells that stably produce VWF. Transient co-transfections of these siRNAs with two VWF alleles resulted in a clear preference for the targeted allele over the untargeted allele for 11 siRNAs. We also demonstrated siRNA‐mediated phenotypic improvement of the VWF multimerization pattern of the VWD type 2A mutation VWF p.Cys2773Ser.Conclusions Allele‐specific siRNAs are able to distinguish VWF alleles on the basis of one nucleotide variation, and are able to improve a severe multimerization defect caused by VWF p.Cys2773Ser. This holds promise for the therapeutic application of allele‐specific siRNAs in dominant‐negative VWD.

The cellular composition of atherosclerotic lesions is determined by many factors including cell infiltration, proliferation and cell death. Tumor suppressor gene p53 has been shown to regulate both cell proliferation and cell death in many cell types. In the present study, we investigated the role of macrophage p53 in the pathogenesis of early and advanced atherosclerosis. Using the Cre-loxP system we found that absence of macrophage p53 (p53del) strongly reduces apoptosis of macrophages both in early and advanced atherosclerotic lesions (-59% and -37%, respectively). Consequently, in advanced atherosclerosis, reduced apoptosis upon absence of macrophage p53, coincided with increased acellular necrotic core formation (+96%), increased macrophage content (+24%), and reduced cholesterol cleft accumulation (-41%). Proliferation was not affected by the absence of macrophage p53 in both early and advanced atherosclerosis. However, these significant changes in lesional cell death did not affect total lesion area in both early and advanced atherosclerosis, neither in the aortic root nor in the aortic arch and thoracic aorta in ApoE-deficient mice. Our data demonstrate that macrophage p53 is an important regulator of macrophage apoptosis, thereby preventing necrotic death of lesional macrophages. The regulation of this cell death balance directly affects lesion composition. © 2009 Elsevier Ireland Ltd. All rights reserved.

LPL activity plays an important role in preceding the VLDL remnant clearance via the three major apolipoprotein E (apoE)-recognizing receptors: the LDL receptor (LDLr), LDL receptor-related protein (LRP), and VLDL receptor (VLDLr). The aim of this study was to determine whether LPL activity is also important for VLDL remnant clearance irrespective of these receptors and to determine the mechanisms involved in the hepatic remnant uptake. Administration of an adenovirus expressing LPL (AdLPL) into lrp-ldlr-/-vldlr-/- mice reduced both VLDL-triglyceride (TG) and VLDL-total cholesterol (TC) levels. Conversely, inhibition of LPL by AdAPOC1 increased plasma VLDL-TG and VLDL-TC levels. Metabolic studies with radiolabeled VLDL-like emulsion particles showed that the clearance and hepatic association of their remnants positively correlated with LPL activity. This hepatic association was independent of the bridging function of LPL and HL, since heparin did not reduce the liver association. In vitro studies demonstrated that VLDL-like emulsion particles avidly bound to the cell surface of primary hepatocytes from lrp-ldlr-/-vldlr-/- mice, followed by slow internalization, and involved heparin-releaseable cell surface proteins as well as scavenger receptor class B type I (SR-BI). Collectively, we conclude that hepatic VLDL remnant uptake in the absence of the three classical apoE-recognizing receptors is regulated by LPL activity and involves heparan sulfate proteoglycans and SR-BI. Copyright © 2008 by the American Society for Biochemistry and Molecular Biology, Inc.

OBJECTIVE - In vitro studies implicate that the low-density lipoprotein receptor (LDLR)-related protein (LRP) in macrophages has a pro-atherogenic potential. In the present study, we investigated the in vivo role of macrophage specific LRP in atherogenesis independent of its role in the uptake of lipoproteins. METHODS AND RESULTS - We generated macrophage-specific LRP-deficient mice on an apoE/LDLR double-deficient background. Macrophage LRP deletion did not affect plasma cholesterol and triglyceride levels, lipoprotein distribution, and blood monocyte counts. Nevertheless, macrophage LRP deficiency resulted in a 1.8-fold increase in total atherosclerotic lesion area in the aortic root of 18-week-old mice. Moreover, LRP deficiency also resulted in a relatively higher number of advanced lesions. Whereas macrophage and smooth muscle cell content did not differ between LRP-deficient mice and control littermates, a 1.7-fold increase in collagen content and 2.3-fold decrease in relative number of CD3+ T cells were observed in lesions from macrophage specific LRP-deficient mice. CONCLUSIONS - Our data demonstrate that independent of its role in lipoprotein uptake, absence of LRP in macrophages resulted in more advanced atherosclerosis and in lesions that contained more collagen and less CD3+ T cells. In contrast to previous in vitro studies, we conclude that macrophage LRP has an atheroprotective potential and may modulate the extracellular matrix in the atherosclerotic lesions. © 2006 American Heart Association, Inc. Chemicals / CAS: cholesterol, 57-88-5; collagen, 9007-34-5; Apolipoproteins E; Collagen, 9007-34-5; LDL-Receptor Related Protein 1; Lipoproteins; Receptors, LDL

Here we describe a means to conditionally modify genes at a predefined and localized region of the vasculature using a perivascular drug delivery device (PDD). A 4-hydroxytamoxifen (4-OHT)-eluting PDD was applied around the carotid or femoral artery of a mouse strain carrying both the tamoxifen-inducible and smooth muscle cell (SMC)-specific Cre-recombinase (SM-Cre-ERT2) transgene and a stop-floxed β-galactosidase gene in the Rosa26 locus: the SM-CreERT2(ki)/rosa26 mouse. A dose and time curve of 0-10% (w/w) 4-OHT and 0-14 days application of the PDD in SM-CreERT2(ki)/rosa26 mice showed optimal gene recombination at 1% (w/w) 4-OHT loading at 7 days post application (carotid artery 2.4±1.8%; femoral artery 4.0±3.8% of SMCs). The unique 4-OHT-eluting PDD allowed us to achieve SMC-specific recombination in the same order of magnitude as compared to systemic tamoxifen administration. In addition, recombination was completely confined to the PDD-treated vessel wall segment. Thus, local application of a 4-OHT-eluting PDD results in vascular SMC-specific Cre-mediated recombination in SM-CreER T2(ki)/rosa26 mice without affecting additional SMCs. © Springer 2006. Chemicals / CAS: 4 hydroxytamoxifen, 65213-48-1, 68392-35-8; tamoxifen, 10540-29-1; 4-hydroxytamoxifen, 68392-35-8; Cre recombinase, 2.7.7.-; Integrases, 2.7.7.-; Tamoxifen, 10540-29-1

OBJECTIVE - We investigated whether the dual PPARα/γ agonist tesaglitazar has anti-atherogenic effects in ApoE*3Leiden mice with reduced insulin sensitivity. METHODS AND RESULTS - ApoE*3Leiden transgenic mice were fed a high-fat (HF) insulin-resistance-inducing diet. One group received a high-cholesterol (HC) supplement (1% wt/wt; HC group). A second group received the same HC supplement along with tesaglitazar (T) 0.5 μmol/kg diet (T group). A third (control) group received a low-cholesterol (LC) supplement (0.1% wt/wt; LC group). Tesaglitazar decreased plasma cholesterol by 20% compared with the HC group; cholesterol levels were similar in the T and LC groups. Compared with the HC group, tesaglitazar caused a 92% reduction in atherosclerosis, whereas a 56% reduction was seen in the cholesterol-matched LC group. Furthermore, tesaglitazar treatment significantly reduced lesion number beyond that expected from cholesterol lowering and induced a shift to less severe lesions. Concomitantly, tesaglitazar reduced macrophage-rich and collagen areas. In addition, tesaglitazar reduced inflammatory markers, including plasma SAA levels, the number of adhering monocytes, and nuclear factor κB-activity in the vessel wall. CONCLUSIONS - Tesaglitazar has anti-atherosclerotic effects in the mouse model that go beyond plasma cholesterol lowering, possibly caused by a combination of altered lipoprotein profiles and anti-inflammatory vascular effects. © 2006 American Heart Association, Inc. Chemicals / CAS: cholesterol, 57-88-5; collagen, 9007-34-5; tesaglitazar, 251565-85-2; lipid, 66455-18-3; peroxisome proliferator activated receptor alpha, 147258-70-6; 2-ethoxy-3-(4-((4-(methylsulfonyloxy)phenethyl)oxy)phenyl)propanoic acid; Alkanesulfonates; apolipoprotein E3 (Leidein); Apolipoprotein E3; Apolipoproteins E; Biological Markers; Cholesterol, 57-88-5; Cholesterol, Dietary; Collagen, 9007-34-5; Dietary Fats; Lipids; Lipoproteins; NF-kappa B; Phenylpropionates; PPAR alpha; PPAR gamma

The cellular composition of an atherosclerotic lesion is determined by cell infiltration, proliferation, and apoptosis. The tumor suppressor gene retinoblastoma (Rb) has been shown to regulate both cell proliferation and cell death in many cell types. To study the role of macrophage Rb in the development of atherosclerosis, we used apoE-deficient mice with a macrophage-restricted deletion of Rb (Rbdel mice) and control littermates (Rbfl mice). After 12 wk feeding a cholesterol-rich diet, the Rbdel mice showed a 51% increase in atherosclerotic lesion area with a 39% increase in the relative number of advanced lesions. Atherosclerotic lesions showed a 13% decrease in relative macrophage area and a 46% increase in relative smooth muscle cell area, reflecting the more advanced state of the lesions. The increase in atherosclerosis was independent of in vitro macrophage modified lipoprotein uptake or cytokine production. Whereas macrophage-restricted Rb deletion did not affect lesional macrophage apoptosis, a clear 2.6-fold increase in lesional macrophage proliferation was observed. These studies demonstrate that macrophage Rb is a suppressing factor in the progression of atherosclerosis by reducing macrophage proliferation. © FASEB.

Genetic factors appear to be important in the restenotic process after percutaneous coronary intervention (PCI), as well as in inflammation, a pivotal factor in restenosis. TNFα, a key regulator of inflammatory responses, may exert critical influence on the development of restenosis after PCI. The GENetic DEterminants of Restenosis (GENDER) project included 3104 patients who underwent a successful PCI. Systematic genotyping for six polymorphisms in the TNFα gene was performed. The role of TNFα in restenosis was also assessed in ApoE*3-Leiden mice, TNFα knockout mice, and by local delivery of a TNFα biosynthesis inhibitor, thalidomide. The -238G-1031T haplotype of the TNFα gene increased clinical and angiographic risk of restenosis (P=0.02 and P=0.002, respectively). In a mouse model of reactive stenosis, arterial TNFα mRNA was significantly time-dependently up-regulated. Mice lacking TNFα or treated locally with thalidomide showed a reduction in reactive stenosis (P=0.01 and P=0.005, respectively). Clinical and preclinical data indicate that TNFα plays an important role in restenosis. Therefore, TNFα genotype may be used as a risk marker for restenosis and may contribute to individual patient screening prior to PCI in clinical practice. Inhibition of TNFα may be an anti-restenotic target strategy. ©FASEB. Chemicals / CAS: thalidomide, 50-35-1; RNA, Messenger; Thalidomide, 50-35-1; Tumor Necrosis Factor-alpha

The very low density lipoprotein receptor (VLDLR), low density lipoprotein receptor (LDLR), and low density lipoprotein receptor-related protein (LRP) are the three main apolipoprotein E-recognizing endocytic receptors involved in the clearance of triglyceride (TG)-rich lipoproteins from plasma. Whereas LDLR deficiency in mice results in the accumulation of plasma LDL-sized lipoproteins, VLDLR or LRP deficiency alone only minimally affects plasma lipoproteins. To investigate the combined effect of the absence of these receptors on TG-rich lipoprotein levels, we have generated unique VLDLR, LDLR, and LRP triple-deficient mice. Compared with wild-type mice, these mice markedly accumulated plasma lipids and lipases. These mice did not show aggravated hyperlipidemia compared with LDLR and LRP double-deficient mice, but plasma TG was increased after highfat diet feeding. In addition, these mice showed a severely decreased postprandial TG clearance typical of VLDLR-deficient (VLDLR-/-) mice. Collectively, although VLDLR deficiency in LRP - and LDLR-/- mice does not aggravate hyperlipidemia, these triple-deficient mice represent a unique model of markedly delayed TG clearance on a hyperlipidemic background. Copyright © 2005 by the American Society for Biochemistry and Molecular Biology, Inc. Chemicals / CAS: lipid, 66455-18-3; triacylglycerol lipase, 9001-62-1; cholesterol, 57-88-5; Cholesterol, 57-88-5; DNA-Binding Proteins; Leucine-Responsive Regulatory Protein, 138791-20-5; Lipoproteins; Receptors, LDL; Transcription Factors; Triglycerides; VLDL receptor

Low-density lipoprotein receptor-related protein (LRP) contributes to factor VIII (FVIII) catabolism in vivo. Besides LRP, FVIII also interacts with very low-density lipoprotein receptor (VLDLR) in vitro. We investigated the physiological role of VLDLR in FVIII catabolism, using knockout mouse models for VLDLR and LRP, alone and in combination. VLDLR-/- mice displayed normal plasma FVIII, whereas VLDLR-/- LRP- double-knockout mice had slightly increased FVIII compared with LRP-deficient mice. Remarkably, VLDLR deficiency slightly accelerated FVIII clearance. Adenovirus-mediated overexpression of VLDLR did not lower plasma FVIII in LRP-deficient mice. We conclude that VLDLR does not act in concert with LRP in FVIII clearance in vivo. Chemicals / CAS: blood clotting factor 8, 9001-27-8; cholesterol, 57-88-5; Cre recombinase, EC 2.7.7.-; Factor VIII, 9001-27-8; Integrases, EC 2.7.7.-; LDL-Receptor Related Proteins; Receptors, LDL; VLDL receptor

The VLDL receptor (VLDLr) is involved in tissue delivery of VLDL-triglyceride (TG)-derived FFA by facilitating the expression of lipoprotein lipase (LPL). However, vldlr-/- mice do not show altered plasma lipoprotein levels, despite reduced LPL expression. Because LPL activity is crucial in postprandial lipid metabolism, we investigated whether the VLDLr plays a role in chylomicron clearance. Fed plasma TG levels of vldlr -/- mice were 2.5-fold increased compared with those of vldlr +/+ littermates (1.20 ± 0.37 mM vs. 0.47 ± 0.18 mM; P < 0.001). Strikingly, an intragastric fat load led to a 9-fold increased postprandial TG response in vldlr-/- compared with vldlr +/+ mice (226 ± 188 mM/h vs. 25 ± 11 mM/h; P < 0.05). Accordingly, the plasma clearance of [3H]TG-labeled protein-free chylomicron-mimicking emulsion particles was delayed in vldlr -/- compared with vldlr+/+ mice (half-life of 12.0 ± 2.6 min vs. 5.5 ± 0.9 min; P < 0.05), with a 60% decreased uptake of label into adipose tissue (P < 0.05). VLDLr deficiency did not affect the plasma half-life and adipose tissue uptake of albumin-complexed [14C]FFA, indicating that the VLDLr facilitates postprandial LPL-mediated TG hydrolysis rather than mediating FFA uptake. We conclude that the VLDLr plays a major role in the metabolism of postprandial lipoproteins by enhancing LPL-mediated TG hydrolysis. Chemicals / CAS: carbon 14, 14762-75-5; lipoprotein lipase, 83137-80-8, 9004-02-8; Albumins; Chylomicrons; Fatty Acids, Nonesterified; Lipoprotein Lipase, EC 3.1.1.34; Receptors, LDL; Triglycerides; VLDL receptor

The low-density lipoprotein (LDL) receptor-related protein (LRP) has a well-established role in the hepatic removal of atherogenic apolipoprotein E (APOE)-rich remnant lipoproteins from plasma. In addition, LRP recognizes multiple distinct pro- and antiatherogenic ligands in vitro. Here, we investigated the role of hepatic LRP in atherogenesis independent of its role in removal of APOE-rich remnant lipoproteins. Mice that allow inducible inactivation of hepatic LRP were combined with LDL receptor and APOE double-deficient mice (MX1Cre+LRPflox/floxLDLR -/-APOE-/- On an LDLR-/-APOE-/- background, hepatic LRP deficiency resulted in decreased plasma cholesterol and triglycerides (cholesterol: 17.1 ± 5.2 vs 23.4 ± 6.3 mM, P = . 025; triglycerides: 1.1 ± 0.5 vs 2.2 ± 0.8 mM, P = .002, for MX1Cre+LRPflox/flox-LDLR-/-APOE-/- and control LRPflox/flox-LDLR-/-APOE-/- mice, respectively). Lower plasma cholesterol in MX1Cre+LRP flox/flox-LDLR-/-APOE-/- mice coincided with increased plasma lipoprotein lipase (71.2 ± 7.5 vs 19.1 ± 2.4 ng/ml, P = .002), coagulation factor VIII (4.4 ± 1.1 vs 1.9 ± 0.5 U/mL, P = .001), von Willebrand factor (2.8 ± 0.6 vs 1.4 ± 0.3 U/mL, P = .001), and tissue-type plasminogen activator (1.7 ± 0.7 vs 0.9 ± 0.5 ng/ml, P = .008) compared with controls. Strikingly, MX1Cre +-LRPflox/floxLDLR-/-APOE-/- mice showed a 2-fold higher atherosclerotic lesion area compared with controls (408. 5 ± 115.1 vs 219.1 ± 86.0 103μm2, P = .003). Our data indicate that hepatic LRP plays a clear protective role in atherogenesis independent of plasma cholesterol, possibly due to maintaining low levels of its proatherogenic ligands. © 2004 by The American Society of Hematology. Chemicals/CAS: blood clotting factor 8, 9001-27-8; cholesterol, 57-88-5; lipoprotein lipase, 83137-80-8, 9004-02-8; tissue plasminogen activator, 105913-11-9; von Willebrand factor, 109319-16-6; Apolipoproteins E; Blood Coagulation Factors; Cholesterol, 57-88-5; LDL-Receptor Related Protein 1; Lipids; Receptors, LDL

Background - The presence of the tumor-suppressor gene p53 in advanced atherosclerotic plaques and the sensitivity to p53-induced cell death of smooth muscle cells isolated from these plaques have fueled speculation about the role of p53 in lesion destabilization and plaque rupture. In this study, we describe a strategy to promote (thrombotic) rupture of preexisting atherosclerotic lesions using p53-induced lesion remodeling. Methods and Results - Carotid atherogenesis was initiated in apolipoprotein E knockout mice by placement of a perivascular silastic collar. The resulting plaques were incubated transluminally with recombinant adenovirus carrying either a p53 or β-galactosidase (lacZ) transgene. p53 transfection was restricted to the smooth muscle cell-rich cap of the plaque and led to an increase in cap cell apoptosis 1 day after transfer. p53 overexpression resulted in a marked decrease in the cellular and extracellular content of the cap, reflected by a markedly reduced cap/intima ratio (0.21±0.04 versus 0.46±0.03, P

Transgenic technologies have provided a series of very useful mouse models to study hyperlipidemia and atherosclerosis. Normally, mice carry cholesterol mainly in the high density lipoprotein (HDL) sized lipoproteins, and have low density lipoprotein (LDL) and very low density lipoprotein (VLDL) cholesterol levels. These low LDL and VLDL levels are due to the very rapid metabolism of remnant clearance in mice, which hamper metabolic studies. In addition, due to the lack of atherogenic lipoproteins, mice will not readily develop atherosclerosis. This situation has changed completely, because to date, most known genes in lipoprotein metabolism have been used in transgenesis to obtain mice in which genes have been silenced or overexpressed. These experiments have yielded many mouse strains with high plasma lipid levels and a greater susceptibility for developing atherosclerosis. One of the most widely used strains are knock-out mice deficient for apoE, which is one of the central players in VLDL metabolism. Subsequently, a wide variety of other transgenic studies involving APOE have been performed elucidating the role of apoE and apoE mutants in lipolysis, remnant clearance, cellular cholesterol efflux and atherogenesis. In addition, the APOE mouse models are excellent tools for the development of gene therapy for hyperlipidemias.

Apolipoprotein (APO) E*3-Leiden mice with impaired chylomicron and VLDL (very low density lipoprotein) remnant metabolism display hyperlipidaemia and atherosclerosis. In the present study, these mice were used for testing the hypolipidaemic effect of two marketed agents, lovastatin (CAS 75330-75-5) and gemfibrozil (CAS 25812-30-0) as well as a novel compound, SB 204990 (the 5- ring lactone of ±(3R*,5S*) 3-carboxy-11-(2,4-dichlorophenyl)-3,5- dihydroxyundecanoic acid, CAS 154566-12-8), a potent inhibitor of cholesterol and fatty acid synthesis at the level of ATP-Citrate lyase. APOE*3-Leiden mice were fed a saturated fat and cholesterol-rich diet supplemented with either 0.05 or 0.1% w/w of lovastatin, 0.1 or 0.2% w/w of gemfibrozil or 0.1 or 0.2% w/w of SB 204990. Lovastatin showed a dose-related decrease in plasma cholesterol levels (up to -20%) due to a lowering of LDL and HDL (low density resp. high density lipoprotein)-cholesterol (-20 and -18%, respectively), while plasma triglyceride levels were unaffected. Gemfibrozil had no effect on plasma total cholesterol levels but gave significant dose-dependent decreases in plasma (VLDL) triglyceride levels (tip to -53%). SB 204990 resulted in a dose-dependent reduction of plasma cholesterol (up to -29%) by lowering VLDL, LDL and HDL-cholesterol (-50, -20 and -20%, respectively). In addition, a strong dose dependent reduction of plasma (VLDL) triglycerides up to -43% was observed with this compound. Although the effects of gemfibrozil and SB 204990 were not simply explained by changes in a single determinant of VLDL metabolism - no effects of these drugs were seen on post-heparin plasma lipoprotein lipase activity, in vivo rate of VLDL synthesis or hepatic apoC- III mRNA levels - APOE*3-Leiden mice were found to give robust hypolipidaemic responses to these test compounds. The responsiveness to hypolipidaemic therapy combined with a clear relationship between aortic lesion size and plasma cholesterol exposure, as demonstrated previously, makes this mouse an attractive model for the testing of anti-atherosclerotic properties of hypolipidaemic drugs.

Apolipoprotein E*2(Arg-155 → Cys) (APOE*2) transgenic mice were generated and compared to the previously generated apolipoprotein E*3- Leiden (APOE*3-Leiden) transgenic mice to study the variable expression of hyperlipoproteinemia associated with these two APOE variants. In the presence of the endogenous mouse Apoe gene, the expression of the APOE*3-Leiden gene resulted in slightly elevated levels of serum cholesterol as compared with control mice (2.7 ± 0.5 versus 2.1 ± 0.2 mmol/liter, respectively), whereas the expression of the APOE*2(Arg-158 → Cys) gene did not affect serum cholesterol levels, even after high/fat cholesterol feeding. The extreme cholesterol level usually found in apoE-deficient mice (Apoe(-/-) mice; 23.6 ± 5.0 mmol/liter) could be rescued by introducing the APOE*3-Leiden gene (APOE*3-Leiden·Apoe(-/-); 3.6 ± 1.5 mmol/liter), whereas the expression of the APOE*2(Arg-158 → Cys) gene in Apoe(-/-) mice minimally reduced serum cholesterol levels (APOE*2·Apoe(-/-); 16.6 ± 2.9 mmol/liter). In vivo very low density lipoprotein (VLDL) turnover studies revealed that APOE*2·Apoe(- /-) VLDL and APOE*3-Leiden·Apoe(-/-) VLDL display strongly reduced fractional catabolic rates as compared with control mouse VLDL (4.0 and 6.1 versus 22.1 pools/h). In vitro low density lipoprotein (LDL) receptor binding studies using HepG2 and J774 cells showed that APOE*2·Apoe(-/-) VLDL is completely defective in binding to the LDL receptor, whereas APOE*3- Leiden·Apoe(-/-) VLDL still displayed a considerable binding activity to the LDL receptor. After transfection of APOE*2·Apoe(-/-) and APOE*3- Leiden·Apoe(-/-) mice with adenovirus carrying the gene for the receptor- associated protein (AdCMV-RAP), serum lipid levels strongly increased (15.3 to 42.8 and 1.4 to 15.3 mmol/liter for cholesterol and 5.0 to 35.7 and 0.3 to 20.7 mmol/liter for triglycerides, respectively). This indicates that RAP- sensitive receptors, possibly the LDL receptor-related protein (LRP), mediate the plasma clearance of both APOE*2·Apoe(-/-) and APOE*3-Leiden·Apoe(-/- ) VLDL. We conclude that in vivo the APOE*2 variant is completely defective in LDL receptor binding but not in binding to LRP, whereas for the APOE*3- Leiden mutant both LRP and LDL receptor binding activity are only mildly affected. As a consequence of this difference, APOE*2·Apoe(-/-) develop more severe hypercholesterolemia than APOE*3-Leiden·Apoe(-/-) mice. Chemicals/CAS: Apolipoproteins E; Arginine, 74-79-3; Cysteine, 52-90-4; Heymann Nephritis Antigenic Complex; Lipoproteins, LDL; Lipoproteins, VLDL; Membrane Glycoproteins; Receptors, LDL

Veneuze trombose is een ziekte gekenmerkt door het ontstaan van een ongewenst bloedstolsel. Om inzichten te verkrijgen in de pathofysiologie van dit ziektebeeld zijn voorheen genoomstudies uitgevoerd. Deze studies hebben een nieuwe erfelijke factor voor veneuze trombose geïdentificeerd, namelijk het SLC44A2 gen. Dit was een opmerkelijke bevinding, aangezien SLC44A2 nooit eerder gekoppeld was aan de bloedstolling. Het onderzoek beschreven in dit proefschrift heeft als doel het mechanisme, onderliggend aan deze associatie, te ontrafelen. Er is hiervoor gebruik gemaakt van muizen die dit gen niet meer hebben, zogenaamde SLC44A2 knock-out muizen. Dierstudies maakten het mogelijk om de complexiteit van stromend bloed, de bloedvaatwand en het ontstaan van veneuze trombose nader te onderzoeken. We hebben aangetoond dat de afwezigheid van SLC44A2 de normale bloedstolling ongemoeid laat. De vorming van veneuze trombose in SLC44A2 knock-out muizen is echter afwijkend, met mogelijk betrokkenheid van neutrofielen en von Willebrand factor (VWF), een eiwit met een rol in veneuze trombose. Studies verricht aan SLC44A2 op de neutrofielen van mensen, met aandacht voor de twee verschillende vormen van SLC44A2 die bij mensen voorkomen, geven goede aanwijzingen dat SLC44A2 een rol speelt in de binding van neutrofielen aan VWF. Er werd ook geobserveerd dat de erfelijke variant van SLC44A2 op neutrofielen welke zwak bindt aan VWF, ook degene is die samengaat met een mindere kans op het krijgen van VT. Door deze studies begrijpen we beter hoe veneuze trombose ontstaat, met hopelijk in de nabije toekomst concrete aanknopingspunten voor alternatieve, betere en veiligere behandelingsstrategieën voor veneuze trombose.

The aim of this thesis is to identify emerging risk factors for VTE. To achieve this goal, we describe the supposedly causal role of statin and glucocorticoid use (i.e. two drugs that can influence inflammation) with changes in hemostasis and VTE risk. Systemic glucocorticoid use increases the relative risk of first VTE by more than three-fold and confers an 5% absolute risk of recurrent VTE per year. On the other hand, rosuvastatin use may reduce the risk of first VTE by 40%. Although the mechanisms behind this association are not fully elucidated, this thesis shows that rosuvastatin is capable of decreasing the thrombin generation potential by 10% in patients with a prior VTE. This thesis has shown that both statins and systemic glucocorticoids can affect the risk of VTE, improving the knowledge on the influence of these two commonly prescribed drugs on VTE pathophysiology. These findings have the potential to further refine the assessment of VTE risk since they highlight that the use of these drugs should be considered when evaluating the risk of VTE. Finally, this thesis provides insight into new therapeutic approaches since the results underscore that treatment strategies on VTE prevention in patients already taken statins, which may be sufficient for VTE prevention, are lacking. Treatment strategies to prevent glucocorticoid-associated VTE are also needed.

Von Willebrand disease (VWD) is the most common inherited bleeding disorder. Patients mainly develop mucocutaneous bleeding, like bruises, epistaxis and menorrhagia. The more severely affected patients may also develop joint bleeding, or bleeding from the gastrointestinal tract. Also, trauma, surgery or dental procedures may lead to critical bleeding events. VWD-related bleeding are caused by defects in von Willebrand factor (VWF), a large multimeric protein that is produced by endothelial cells and megakaryocytes. Most VWD patients develop the disease because of dominant-negative mutations in VWF. In this thesis we investigated whether inhibition of production of mutant VWF with limited inhibition of wildtype VWF positively affects the function of VWF and improves VWD phenotypes. We used small interfering RNAs (siRNAs) to selectively inhibit production of mutant VWF. These siRNAs were tested in several models for VWD. We indeed prove that siRNAs can distinguish a mutant and wildtype VWF allele in vitro in heterologous cell systems, ex vivo in patient-derived endothelial cells, and in vivo in a VWD mouse model. We also show in these disease models that we can improve several VWD phenotypes. These results are promising for further development of allele-specific siRNAs as a new treatment strategy for VWD.

Cardiovascular disease is the leading cause of death worldwide. The primary underlying pathology of cardiovascular disease is atherosclerosis. Atherosclerosis is a chronic, multifactorial disease in which lipid accumulates in the arterial wall, leading to a local inflammatory reaction and atherosclerotic plaque formation. Atherosclerotic disease develops largely asymptomatic over a lifetime. However, plaque rupture or erosion can cause the formation of a superimposed thrombus, blocking the flow of blood, and cause acute cardiovascular events such as myocardial infarction or ischemic stroke. Defects in cholesterol metabolism and hypercholesterolemia, which are major risk factors for atherosclerosis, have been shown to affect hematopoiesis, immune cell production and platelet counts and reactivity. Therefore, bone marrow cholesterol handling is an interesting target in the battle against cardiovascular disease, and acute cardiovascular events in particular. This thesis describes novel interactions between cholesterol metabolism and the production of immune cells and platelets, and its effects on atherosclerosis and atherothrombosis development.

During my research project we mainly focussed on studying the pathophysiology of venous and arterial thrombosis in mice. When we transiently lowered plasma protein levels of natural anticoagulants antithrombin and protein C using RNA interference, mice developed venous thrombosis in the head. In contrast to other mouse models for venous thrombosis where surgery is required for provoking the disease, mice injected with RNA interference against the mRNA of Serpinc1 and Proc (antithrombin and protein C, respectively) developed venous thrombosis without additional handlings. In this unique form of venous thrombosis, we studied the roles of platelets, neutrophils, and coagulation factor XII. These factors have been shown to be indispensable in experimental venous thrombosis in other mouse models, and they have been introduced as novel therapeutic targets. For the second part of my thesis we again used the RNA interference approach, to lower natural anticoagulation in atherosclerotic mice. When we lowered protein C in these mice, they developed atherothrombosis in the aortic root without any additional intervention. This unique form of atherothrombosis has been showed in multiple independent experiments, and we aimed to further characterize the process to learn more about prevention atherothrombosis in atherosclerotic mice and the role of protein C.

Thrombosis is considered to be a multifactorial disease in which both genetic and acquired risk factors are involved to cause disease. Over the past years epidemiological studies have revealed a number of acquired risk factors that increase the risk of venous thrombosis. Some acquired risk factors of venous thrombosis are associated with a hypercoagulable state, which may be to a certain extent dependent on the dysregulation of gene expression in the liver, as the liver is the major organ that produces coagulation factors. Coagulation gene transcription can be modulated at different levels through hepatic transcription factors, co-regulatory or intermediate proteins, however, the exact contribution of these modulators to coagulation gene transcription is largely unknown. We aimed to study the mechanisms by which hepatic coagulation gene transcription is regulated, in order to increase our understanding of how thrombotic risks conditions coincide with hypercoagulable state. RNA interference (via synthetic small interfering RNA; siRNA) was used as a tool to study genes involved in coagulation and coagulation control in mice. Studies described in this dissertation may contribute to a better understanding of which genes are involved in coagulation (control) and how thrombotic risk factors result in a hypercoagulable state

Over the years, a number of acquired risk factors for venous thrombosis have been identified in large epidemiological studies. We aimed to identify the biological mechanisms by which acquired risk factors like female hormones, thyroid hormone and obesity result in a hypercoagulable state and increased risk for venous thrombosis, since these are currently poorly understood. As these risk factors are all, to a certain extent, able to interfere with liver metabolism we hypothesized that they modulate hepatic transcription of coagulation genes, either directly via nuclear hormone receptors and hormone response elements in target genes (female hormones and thyroid hormone), or indirectly as a result of altered liver homeostasis (obesity). To study these hypotheses, we used an in vivo approach, which not only gives the opportunity to study the risk factor-mediated transcriptional modulation of coagulation genes, but also allowed us to study the relation between transcriptional changes on the one hand and plasma protein levels and a thrombotic tendency on the other. The data presented in this thesis clearly demonstrate that modulation of hepatic coagulation gene transcription is a key mechanism by which acquired risk factors for venous thrombosis impact the hemostatic balance.

In this thesis we aimed to expand our knowledge on the pathophysiological aspects of the metabolic syndrome in transgenic mice. The metabolic syndrome involves multiple aspects and has a major impact on cardiovascular diseases. In the first part of thesis the role of PAI-1 in the development of insulin resistance will addressed. This part will also focus on the mechanism of plasma PAI-1 clearance. In the second part of this thesis, the roles of LRP in atherosclerosis and LPL activity in lipid metabolism are addressed. In this thesis we showed the PAI-1 catabolism is facilitated by a RAP-sensitive mechanism other than LRP, LDLR and VLDLR. The increased plasma PAI-1 levels observed in insulin resistance and obesity is not explained by impaired clearance of PAI-1. The increased plasma PAI-1 levels might be an epiphenomenon of the chronic inflammatory state of insulin resistance or obesity. Furthermore, alternative pathways other than the traditional lipoprotein receptors are involved in the regulation of plasma cholesterol and triglyceride levels. The development of atherosclerosis is multi-factorial in which the balance between the antiand pro-inflammatory processes plays a central role. Macrophage LRP might be one of the features that control this balance. Inflammation not only promotes to the development of atherosclerosis, but might also be involved in the processes that restore the damaged vascular wall.

In this thesis we focus on atherosclerosis as the main cause of cardiovascular disease. Since inflammation and cell death are important processes in the onset and progression of atherosclerosis, we investigate the role of several genes involved in inflammation and cell death in the vessel wall and their effect on atherosclerosis. We use several ways to modulate gene expression. Examples from different chapters are whole body deletion of TNF (2), local gene targeting of Fas Ligand to the cap of the plaque (3), conditional gene targeting of mdm2, thereby upregulating p53 (4), and beta-galactosidase (5), and pharmacological targeting of PPARs (6). In this thesis we use various mouse models of atherosclerosis, such as the apoE deficient mouse, the "humanized" apoE3*Leiden mouse and accelerated atherosclerosis induced by collar placement.

The work described in this thesis was aimed at identifying the role of cell cycle and apoptosis genes in atherosclerosis. Atherosclerosis is the primary cause of cardiovascular disease, a disorder occurring in the large and medium-sized arteries of the body. Although in the beginning 90s promising lipid lowering therapies predicted a strong reduction in cardiovascular deaths, in westernized societies it is still the underlying cause of about 40% of all deaths, indicating that treatment of atherosclerosis goes beyond lipid lowering solely. In addition to lipids, continuous cell growth (cell cycle) and cell death (i.e. apoptosis and necrosis) processes play a central role in the development of atherosclerosis. To investigate the role of several cell cycle and apoptosis genes (i.e. p53, Rb and Mdm2) in atherosclerosis we generated and characterized several mouse models based on site-specific recombinase (SSR) technology. The studies described in this thesis show that next to therapies aiming at lifestyle interventions, lipid therapies and regulation of inflammation, targeting cell cycle and apoptosis genes on lesional or cellular level might prove the most effective way to reduce the burden of atherosclerosis.