Low Density Lipoprotein Catabolism Research Articles

Effect of Total SMS Activity on LDL Catabolism in Mice.

Sphingomyelin (SM) and cholesterol are 2 key lipid partners on cell membranes and on lipoproteins. Many studies have indicated the influence of cholesterol on SM metabolism. This study examined the influence of SM biosynthesis on cholesterol metabolism. Inducible global Sms1 KO (knockout)/global Sms2 KO mice were prepared to evaluate the effect of whole-body SM biosynthesis deficiency on lipoprotein metabolism. Tissue cholesterol, SM, ceramide, and glucosylceramide levels were measured. Triglyceride production rate and LDL (low-density lipoprotein) catabolism were measured. Lipid rafts were isolated and LDL receptor mass and function were evaluated. Also, the effects of exogenous sphingolipids on hepatocytes were investigated. We found that total SMS (SM synthase) depletion significantly reduced plasma SM levels. Also, the total deficiency significantly induced plasma cholesterol, apoB (apolipoprotein B), and apoE (apolipoprotein E) levels. Importantly, total SMS deficiency, but not SMS2 deficiency, dramatically decreased LDL receptors in the liver and attenuated LDL uptake through the receptor. Further, we found that total SMS deficiency greatly reduced LDL receptors in the lipid rafts, which contained significantly lower SM and significantly higher glucosylceramide, as well as cholesterol. Furthermore, we treated primary hepatocytes and Huh7 cells (a human hepatoma cell line) with SM, ceramide, or glucosylceramide, and we found that only SM could upregulate LDL receptor levels in a dose-dependent fashion. Whole-body SM biosynthesis plays an important role in LDL cholesterol catabolism. The total SMS deficiency, but not SMS2 deficiency, reduces LDL uptake and causes LDL cholesterol accumulation in the circulation. Given the fact that serum SM level is a risk factor for cardiovascular diseases, inhibiting SMS2 but not SMS1 should be the desirable approach.

Pathways of lipoprotein(a) catabolism

Lipoprotein(a) [Lp(a)] is a modified form of low-density lipoprotein (LDL) with an additional protein component, apolipoprotein(a). Elevated levels of Lp(a) (>50 mg/dL), which are present in 20% of the population, impart a risk of developing cardiovascular disease similar to LDL. A good understanding of LDL catabolism led to the development of therapies to effectively lower LDL, i.e., statins and the PCSK9 inhibitors which both upregulate the low-density-lipoprotein receptor (LDLR). The pathway for Lp(a) clearance is more complicated with multiple receptors operating via different forms of endocytosis being identified.

Liraglutide reduces plasma PCSK9 in patients with type 2 diabetes not treated with statins

AimDyslipidaemia in type 2 diabetes mellitus (T2DM), which increases cardiovascular risk, includes abnormal metabolism of low-density lipoproteins (LDL). Our group has recently shown that liraglutide increases LDL catabolism in patients with T2DM and that it reduces the expression of PCSK9 (a major inhibitor of LDL-receptor expression) in vitro and in mice. This prompted us to study the effect of liraglutide on plasma PCSK9 level in patients with T2DM. MethodsWe studied prospectively 82 patients with T2DM (51 without statins, 31 with statins). Plasma PCSK9 and plasma lipids were measured before and six months after the initiation of a treatment with liraglutide at a dose of 1.2 mg/day. ResultsPlasma PCSK9 was significantly reduced by liraglutide treatment (214.9 ± 56.4 vs 244.5 ± 99.2 ng/ml, P = 0.024) in patients not on statins, but not in patients treated with statins (301.1 ± 91.5 vs 281.2 ± 96.9 ng/ml, P = 0.41). In patients not on statins, a very significant 17% decrease in plasma PCSK9 was observed in patients with baseline haemoglobin A1c (HbA1c) < 10% (n = 33; mean = -45.0 ng/ml, P = 0.013), when it was not observed in patients with baseline HbA1c ≥ 10% (n = 18; mean = +5.2 ng/ml, P = 0.75). In multivariate analysis, baseline HbA1c was an independent factor associated with plasma PCSK9 reduction, in patients not on statins. ConclusionTreatment with liraglutide induces a significant reduction of plasma PCSK9 in patients with T2DM not on statins. This is in line with the acceleration of LDL catabolism that has been observed with liraglutide. However, this decrease in plasma PCSK9 is significantly influenced by glycaemic control and is not observed in patients with poorly controlled T2DM.

Clinical evaluation of dyslipidemia among type 2 diabetes and hypothyroidism patients

Aim: To evaluate the lipid profiles among type 2 diabetes and hypothyroid patients for establishing relation between dyslipidemia, diabetes and thyroid disorders. Background: Dyslipidaemia is the leading cause of death in cardiovascular disease (CVD) patients. Diabetes and hypothyroidism are the two main endocrine risk factors for dyslipidaemia. Diabetes is associated with altered metabolism of triglyceride (TG) levels and low-density lipoprotein (LDL) levels. Hypothyroidism leads to decreased clearance of TG and catabolism of LDL. Materials and Methods: This was a cross-sectional with 288 subjects that include normal population, diabetic and hypothyroid patients. The plasma lipid levels, thyroid profile and glucose levels were collected from the patients. The data were subjected to an unpaired t-test for statistical analysis. The P Results: The study included 288 patients out of which 104 were with type 2 diabetes, 81 were hypothyroid and 103 were controls. Dyslipidaemia cases found among them were 63, 26 and 32, respectively. The mean values of lipid levels in type 2 diabetes, hypothyroidism and control population were total cholesterol (TC) (211.4 ± 4.24, 190.5 ± 3.57 mg/dl and 187.3 ± 1.91 mg/dl), LDL (134.5 ± 3.01, 120.8 ± 2.035 and 115.8 ± 1.64 mg/dl), TG (188.6 ± 4.14, 169.9 ± 0.74 and 163.2 ± 2.42 mg/dl), high-density lipoprotein (HDL) (39.64 ± 0.45, 38.78 ± 0.49 and 38.64 ± 0.12 mg/dl) and non-HDL (171.75 ± 1.52, 151.75 ± 0.99 and 148.84 ± 1.99 mg/dl), respectively. Lipid levels of type 2 diabetes and hypothyroidism patients were found to be significantly more than the control population. The mean levels of TC, LDL, TG in type 2 diabetes and LDL, TG in hypothyroidism patients were found to be more than the normal range. Conclusion: There was a significant relationship between type 2 diabetes, hypothyroidism and dyslipidaemia. Routine lipid profile monitoring in patients with diabetes and hypothyroid disorders is advisable for the primary prevention of dyslipidaemia and CVD.

The α-defensins stimulate proteoglycan-dependent catabolism of low-density lipoprotein by vascular cells: a new class of inflammatory apolipoprotein and a possible contributor to atherogenesis

AbstractInflammation may contribute to the pathogenesis of atherosclerosis. On the basis of previous reports that human atherosclerotic lesions contain α-defensins, a class of cationic proteins released by activated neutrophils, the study was designed to ask whether defensins modulate the binding and catabolism of low-density lipoprotein (LDL) by human vascular cells. The results of the study demonstrated that defensin stimulated the binding of 125I-LDL to cultured human umbilical vein endothelial cells, smooth muscle cells, and fibroblasts approximately 5-fold in a dose-dependent and saturable manner. Defensin and LDL formed stable complexes in solution and on cell surfaces. Stimulation of LDL binding by defensin was not inhibited by antibodies against the LDL-receptor (LDL-R), or by recombinant receptor-associated protein, which blocks binding of ligands to the α2-macroglobulin receptor/LDL-R–related protein and other LDL-R family members. Furthermore, defensin stimulated the binding, endocytosis, and degradation of LDL by fibroblasts lacking LDL-R. Stimulation of LDL degradation by defensin was inhibited approximately 75% by low concentrations of heparin (0.2 units/mL) and was similarly reduced in CHO cells lacking heparan-sulfate–containing proteoglycans. The effect of defensin was substantially increased in cells overexpressing the core protein of the syndecan-1 heparan sulfate proteoglycan. The α-defensins released from activated neutrophils may provide a link between inflammation and atherosclerosis by changing the pattern of LDL catabolism from LDL-R to the less efficient LDL-R–independent, proteoglycan-dependent pathway.

Widening the spectrum of genetic testing in familial hypercholesterolaemia: Will it translate into better patient and population outcomes?

Familial hypercholesterolaemia (FH) is caused by pathogenic variants in LDLR, APOB or PCSK9. Impaired low-density lipoprotein (LDL) receptor function leads to decreased LDL catabolism and premature atherosclerotic cardiovascular disease (ASCVD). Thousands of LDLR variants are known, but assignation of pathogenicity requires accurate phenotyping, family studies and assessment of LDL receptor function. Precise, genetic diagnosis of FH using targeted next generation sequencing allows for optimal treatment, distinguishing FH from pathogenically distinct disorders requiring different treatment. Polygenic hypercholesterolaemia resulting from an accumulation of LDL cholesterol-raising single nucleotide polymorphisms (SNPs) could also be suspected by this approach. Similarly, ASCVD risk could be estimated by broader sequencing of cholesterol and non-cholesterol-related genes. Both of these areas require further research. The clinical management of FH, focusing on the primary or secondary prevention of ASCVD, has been boosted by PCSK9 inhibitor therapy. The efficacy of PCSK9 inhibitors in homozygous FH may be partly predicted by the LDLR variants. While expanded genetic testing in FH is clinically useful in providing an accurate diagnosis and enabling cost-effective testing of relatives, further research is needed to establish its value in improving clinical outcomes.

TLR4 (Toll-Like Receptor 4)-Dependent Signaling Drives Extracellular Catabolism of LDL (Low-Density Lipoprotein) Aggregates.

Aggregation and modification of LDLs (low-density lipoproteins) promote their retention and accumulation in the arteries. This is a critical initiating factor during atherosclerosis. Macrophage catabolism of agLDL (aggregated LDL) occurs using a specialized extracellular, hydrolytic compartment, the lysosomal synapse. Compartment formation by local actin polymerization and delivery of lysosomal contents by exocytosis promotes acidification of the compartment and degradation of agLDL. Internalization of metabolites, such as cholesterol, promotes foam cell formation, a process that drives atherogenesis. Furthermore, there is accumulating evidence for the involvement of TLR4 (Toll-like receptor 4) and its adaptor protein MyD88 (myeloid differentiation primary response 88) in atherosclerosis. Here, we investigated the role of TLR4 in catabolism of agLDL using the lysosomal synapse and foam cell formation. Approach and Results: Using bone marrow-derived macrophages from knockout mice, we find that TLR4 and MyD88 regulate compartment formation, lysosome exocytosis, acidification of the compartment, and foam cell formation. Using siRNA (small interfering RNA), pharmacological inhibition and knockout bone marrow-derived macrophages, we implicate SYK (spleen tyrosine kinase), PI3K (phosphoinositide 3-kinase), and Akt in agLDL catabolism using the lysosomal synapse. Using bone marrow transplantation of LDL receptor knockout mice with TLR4 knockout bone marrow, we show that deficiency of TLR4 protects macrophages from lipid accumulation during atherosclerosis. Finally, we demonstrate that macrophages in vivo form an extracellular compartment and exocytose lysosome contents similar to that observed in vitro for degradation of agLDL. We present a mechanism in which interaction of macrophages with agLDL initiates a TLR4 signaling pathway, resulting in formation of the lysosomal synapse, catabolism of agLDL, and lipid accumulation in vitro and in vivo.

Dynamic Actin Reorganization and Vav/Cdc42-Dependent Actin Polymerization Promote Macrophage Aggregated LDL (Low-Density Lipoprotein) Uptake and Catabolism.

Objective- During atherosclerosis, LDLs (low-density lipoproteins) accumulate in the arteries, where they become modified, aggregated, and retained. Such deposits of aggregated LDL (agLDL) can be recognized by macrophages, which attempt to digest and clear them. AgLDL catabolism promotes internalization of cholesterol and foam cell formation, which leads to the progression of atherosclerosis. Therapeutic blockade of this process may delay disease progression. When macrophages interact with agLDL in vitro, they form a novel extracellular, hydrolytic compartment-the lysosomal synapse (LS)-aided by local actin polymerization to digest agLDL. Here, we investigated the specific regulators involved in actin polymerization during the formation of the LS. Approach and Results- We demonstrate in vivo that atherosclerotic plaque macrophages contacting agLDL deposits polymerize actin and form a compartment strikingly similar to those made in vitro. Live cell imaging revealed that macrophage cortical F-actin depolymerization is required for actin polymerization to support the formation of the LS. This depolymerization is cofilin-1 dependent. Using siRNA-mediated silencing, pharmacological inhibition, genetic knockout, and stable overexpression, we elucidate key roles for Cdc42 Rho GTPase and GEF (guanine nucleotide exchange factor) Vav in promoting actin polymerization during the formation of the LS and exclude a role for Rac1. Conclusions- These results highlight critical roles for dynamic macrophage F-actin rearrangement and polymerization via cofilin-1, Vav, and Cdc42 in LS formation, catabolism of agLDL, and foam cell formation. These proteins might represent therapeutic targets to treat atherosclerotic disease.

Dynamic Actin Reorganization and Vav/Cdc42‐dependent Actin Polymerization Promote Macrophage Aggregated LDL Uptake and Catabolism

During atherosclerosis, low density lipoproteins (LDL) accumulate in the arteries, where they become modified, aggregated and retained. Such deposits of aggregated LDL (agLDL) can be recognized by macrophages, which attempt to digest and clear them. AgLDL catabolism promotes internalization of cholesterol and foam cell formation, which is an important component of atherosclerosis. Characterization and therapeutic blockade of this process will likely delay disease progression. When macrophages interact with agLDL in vitro, they form a novel extracellular, hydrolytic compartment, the lysosomal synapse, aided by local actin polymerization to digest agLDL. Here, we demonstrate in vivo that atherosclerotic plaque macrophages contacting cholesterol rich LDL deposits polymerize actin and form a strikingly similar compartment. Live cell imaging revealed macrophage cortical F‐actin depolymerization driven by PIP2 hydrolysis occurs in parallel to actin polymerization at the lysosomal synapse and is required for its formation. Using siRNA‐mediated silencing, pharmacological inhibition, genetic knockout and stable overexpression, we elucidate key roles for Cdc42 Rho GTPase and guanine nucleotide exchange factor Vav in promoting actin polymerization at the lysosomal synapse, and we rule out roles for Rac1 and Rac2. These data indicate that dynamic actin rearrangement and polymerization via Vav and Cdc42 aids compartment formation, catabolism of agLDL and promotes foam cell formation.Support or Funding InformationThe project described was supported by National Institutes of Health grants R37‐DK27083 and R01‐HL093324. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. R.K.S. is an American Heart Association Stanley Stahl Postdoctoral Fellow (ID: 15POST22990022).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 570: Macrophage Catabolism of Aggregated Lipoproteins Using a Novel Extracellular Compartment Regulates Lipid Accumulation During Atherosclerosis

Despite impressive advances in research, prevention, and treatment, atherosclerotic vascular disease remains the leading cause of death in the developed world. Mechanisms of cholesterol accumulation in the arteries have been studied intensively, but the in vivo contributions of different pathways leading to lipid accumulation and foam cell formation are not understood. In the arteries, low-density lipoprotein (LDL) is aggregated and bound to the extracellular matrix. When such aggregated LDL is presented to macrophages, they form a novel acidic, hydrolytic compartment that is topologically extracellular, to which lysosomal enzymes are secreted. Such compartments are observed in vivo in murine atherosclerotic plaque macrophages interacting with cholesterol rich deposits. Using state-of-the-art quantitative and high resolution microscopy techniques, characterization of compartment morphology reveals how macrophages use local actin polymerization to drive plasma membrane remodeling at the interface with aggregated LDL. This leads to sequestration of aggregated LDL into topologically convoluted structures that allow acidification, catabolism and internalization of LDL. We find that a TLR4/MyD88/Syk/PI3 kinase/Akt dependent signaling pathway in macrophages regulates the formation of such catabolic compartments. Consistent with this, deficiency of TLR4 in vivo can protect macrophages from lipid accumulation in murine atherosclerotic plaques. Herein, we provide compelling evidence for a novel form of catabolism that macrophages use to degrade aggregated LDL in vivo during atherosclerosis and this process leads to foam cell formation, cell death and promotes disease progression.

Mutations causative of familial hypercholesterolaemia: screening of 98 098 individuals from the Copenhagen General Population Study estimated a prevalence of 1 in 217.

Ideally, familial hypercholesterolaemia (FH) is diagnosed by testing for mutations that decrease the catabolism of low-density lipoprotein (LDL) cholesterol; however, genetic testing is not universally available. The aim of the present study was to assess the frequency and predictors of FH causing mutations in 98 098 participants from the general population, the Copenhagen General Population Study. We genotyped for LDLR[W23X;W66G;W556S] and APOB[R3500Q] accounting for 38.7% of pathogenic FH mutations in Copenhagen. Clinical FH assessment excluded mutation information. The prevalence of the four FH mutations was 0.18% (1:565), suggesting a total prevalence of FH mutations of 0.46% (1:217). Using the Dutch Lipid Clinic Network (DLCN) criteria, odds ratios for an FH mutation were 439 (95% CI: 170-1 138) for definite FH, 90 (53-152) for probable FH, and 18 (13-25) for possible FH vs. unlikely FH. Using the Simon Broome criteria, the odds ratio was 27 (20-36) for possible vs. unlikely FH, and using the Make Early Diagnosis to Prevent Early Death (MEDPED) criteria, 40 (28-58) for probable vs. unlikely FH. Odds ratios for an FH mutation were 17 (9-31) for LDL-cholesterol of 4-4.9 mmol/L, 69 (37-126) for LDL-cholesterol of 5-5.9 mmol/L, 132 (66-263) for LDL-cholesterol of 6-6.9 mmol/L, 264 (109-637) for LDL-cholesterol of 7-7.9 mmol/L, and 320 (129-798) for LDL-cholesterol above 7.9 mmol/L vs. LDL-cholesterol below 4 mmol/L. The most optimal threshold for LDL-cholesterol concentration to discriminate between mutation carriers and non-carriers was 4.4 mmol/L. Familial hypercholesterolaemia-causing mutations are estimated to occur in 1:217 in the general population and are best identified by a definite or probable phenotypic diagnosis of FH based on the DLCN criteria or an LDL-cholesterol above 4.4 mmol/L.

Abstract 18667: Lipoprotein(a) Catabolism and Apolipoprotein(a) Secretion is Regulated by Sortilin

Elevated levels of lipoprotein(a) (Lp(a)) in plasma have been identified as an independent, causal risk factor for coronary heart disease. Lp(a) consists of a low-density lipoprotein (LDL)-like particle whose apolipoproteinB-100 (apoB-100) moiety is covalently linked to the unique glycoprotein apolipoprotein(a) (apo(a)). Recently, Lp(a) internalization by the LDL-receptor (LDLr) in hepatic cells and primary human fibroblasts has been shown to be regulated by proprotein convertase subtilisin/kexin type 9 (PCSK9). However, Lp(a)/apo(a) internalization still occurs even with a defective LDLr or in the presence of PCSK9 (in fibroblasts and hepatic cells, respectively), indicating a role for receptors other than the LDLr in Lp(a) catabolism. Hepatic sortilin has been identified as a potential receptor mediating LDL catabolism as well as the regulation of apoB-100 secretion. Sortilin localizes to the Golgi apparatus where it mediates trafficking of specific bound ligands to the lysosome. Sortilin also localizes to clathrin-coated pits in the plasma membrane where it can act as an internalization receptor. We demonstrate in the current study that Lp(a), but not apo(a), internalization in hepatic cells is influenced by sortilin overexpression. In the presence of PCSK9, Lp(a) internalization greatly increases with sortilin overexpression compared to control. These results suggest that hepatic sortilin has the ability to act as a receptor for Lp(a) catabolism, through the LDL-like moiety, in a manner that is not dependent on the LDLr. Furthermore, Lp(a) internalization increases with sortilin overexpression in primary human fibroblasts with a defective LDLr, again emphasizing an LDLr-independent role for sortilin as a receptor for Lp(a). Interestingly, an increase in apo(a) secretion is observed with sortilin overexpression in hepatic cells. Removal of the carboxyl-terminal tail of sortilin results in an inability to promote the secretion of apo(a), indicating a direct role for the sorting motifs present in this region of sortilin for the regulation of apo(a) secretion. Taken together, these results indicate novel roles for sortilin in both Lp(a) catabolism and apo(a) secretion.

Circulating PCSK9 levels are positively correlated with NMR-assessed atherogenic dyslipidaemia in patients with high cardiovascular risk.

The proprotein convertase subtilisin/kexin type 9 (PCSK9) gene regulates cholesterol homoeostasis by accelerating low-density lipoprotein receptor (LDLR) degradation resulting in the decreased catabolism of low-density lipoprotein (LDL) leading to hypercholesterolaemia. PCSK9 has also been related to other metabolic risk factors such as triglycerides (TGs) and glucose levels and body mass index (BMI). Therefore, our aim was to study the relationship between the PCSK9 and the lipid and lipoprotein profile. We studied 267 diabetic and metabolic syndrome patients who were not receiving any lipid-lowering therapy. We measured circulating lipids, cholesterol in remnant lipoproteins (RLPc) and PCSK9 levels. A detailed lipoprotein profile was determined based on NMR. Plasma PCSK9 levels were significantly and positively correlated with TG (r=0.136, P=0.033), total cholesterol (r=0.219, P<0.001) and apoB (apolipoprotein B; r=0.226, P=0.006) circulating levels and with an atherogenic profile of lipoprotein subclasses. In further detail, circulating PCSK9 levels were positively correlated with large very-low density lipoprotein (VLDL) particles, (r=0.210, P=0.001) and with their remnants, the intermediate-density lipoprotein (IDL) particles (r=0.206, P=0.001); positively correlated with smaller LDL particles (for small LDL: r=0.224, P<0.001; for medium small LDL: r=0.235, P<0.001; and for very small LDL: r=0.220, P<0.001); and with high-density lipoprotein (HDL) particles (r=0.146, P<0.001), which is mainly explained by the PCSK9 correlation with the smallest HDL particles (r=0.130, P=0.037). In addition, circulating PCSK9 levels were positively correlated with the pro-atherogenic circulating RLPc levels (r=0.171, P=0.006). All of the correlations were adjusted by age, gender and BMI. PCSK9 levels are significantly and positively correlated with atherogenic lipoproteins such as large VLDL, IDL, the smallest LDL, the smallest HDL particles and RLPc levels.

Lipoprotein apheresis in the management of familial hypercholesterolaemia: historical perspective and recent advances.

At present, lipoprotein apheresis, combined with high-dose statin and ezetimibe therapy, is the best available means of treating patients with homozygous and statin-refractory heterozygous familial hypercholesterolaemia (FH). However, the extent of cholesterol-lowering achieved is often insufficient to meet the targets set by current guidelines. The recent advent of three new classes of lipid-lowering agents provides new hope that the latter objective may now be achievable. These compounds act either by reducing low-density lipoprotein (LDL) production by inhibiting apolipoprotein B synthesis with an antisense oligonucleotide (mipomersen) or by inhibiting microsomal triglyceride transfer protein (lomitapide), or by enhancing LDL catabolism via monoclonal antibody-mediated inhibition of the activity of proprotein convertase subtilisin/kexin 9 (PCSK9) (evolocumab). Depending on the outcome of current trials, it seems likely that these compounds, used alone or combined with lipoprotein apheresis, will markedly improve the management of refractory FH.

Increased Susceptibility to Amyloid-β-Induced Neurotoxicity in Mice Lacking the Low-Density Lipoprotein Receptor

Familial hypercholesterolemia is caused by inherited genetic abnormalities that directly or indirectly affect the function of the low-density lipoprotein (LDL) receptor. This condition is characterized by defective catabolism of LDL which results in increased plasma cholesterol concentrations and premature coronary artery disease. Nevertheless, there is increasing preclinical and clinical evidence indicating that familial hypercholesterolemia subjects show a particularly high incidence of mild cognitive impairment. Moreover, the LDL receptor (LDLr) has been implicated as the main central nervous system apolipoprotein E receptor that regulates amyloid deposition in distinct mouse models of β-amyloidosis. In this regard, herein we hypothesized that the lack of LDLr would enhance the susceptibility to amyloid-β-(Aβ)-induced neurotoxicity in mice. Using the acute intracerebroventricular injection of aggregated Aβ(1-40) peptide (400 pmol/mouse), a useful approach for the investigation of molecular mechanisms involved in Aβ toxicity, we observed oxidative stress, neuroinflammation, and neuronal membrane damage within the hippocampus of C57BL/6 wild-type mice, which were associated with spatial reference memory and working memory impairments. In addition, our data show that LDLr knockout (LDLr(-/-)) mice, regardless of Aβ treatment, displayed memory deficits and increased blood-brain barrier permeability. Nonetheless, LDLr(-/-) mice treated with Aβ(1-40) peptide presented increased acetylcholinesterase activity, astrogliosis, oxidative imbalance, and cell permeability within the hippocampus in comparison with Aβ(1-40)-treated C57BL/6 wild-type mice. Overall, the present study shows that the lack of LDLr increases the susceptibility to Aβ-induced neurotoxicity in mice providing new evidence about the crosslink between familial hypercholesterolemia and cognitive impairment.

Effect of Mediterranean Diet With and Without Weight Loss on Apolipoprotein B 100 Metabolism in Men With Metabolic Syndrome

To assess the effect of a Mediterranean diet (MedDiet) with and without weight loss (WL) on apolipoprotein B100 (apoB100) metabolism in men with metabolic syndrome. The diet of 19 men with metabolic syndrome (age, 24-62 years) was first standardized to a North American isoenergetic control diet for 5 weeks, followed by an isoenergetic MedDiet for an additional 5 weeks under full-feeding conditions (MedDiet-WL). Participants next underwent a 20-week supervised WL program under free-living conditions (-10.2 ± 2.9% body weight; P<0.01) and finally consumed the MedDiet (5 weeks) under weight-stabilizing feeding conditions (MedDiet+WL). In vivo kinetic of apoB100 was assessed in the fasted state at the end of the 3 controlled diets using a bolus of D3-leucine. Compared with the control diet, MedDiet-WL reduced low-density lipoprotein (LDL)-apoB100 pool size (-14.2%, P<0.01) primarily through an increase in LDL-apoB100 fractional catabolic rate (+30.4%, P=0.02) and increased LDL particle size (P<0.01) but had no effect on very-LDL (VLDL)-apoB100 pool size or triglyceride concentrations, despite a significant increase in VLDL-apoB100 fractional catabolic rate (+25.6%; P=0.03). MedDiet+WL had no further effect on LDL-apoB100 pool size and fractional catabolic rate but further increased LDL particle size and reduced VLDL-apoB100 pool size versus the control diet primarily through an increase in VLDL-apoB100 fractional catabolic rate (+30.7%; P<0.01). Consumption of MedDiet increases LDL size and reduces LDL-apoB100 concentrations primarily by increasing the catabolism of LDL even in the absence of WL in men with metabolic syndrome. MedDiet seems to have a trivial effect on VLDL concentrations and kinetics unless accompanied by significant WL. http://www.clinicaltrials.gov. Unique identifier: NCT00988650.

A combined LDL receptor/LDL receptor adaptor protein 1 mutation as the cause for severe familial hypercholesterolemia

Familial hypercholesterolemia (FH) results from impaired catabolism of plasma low density lipoproteins (LDL), thus leading to high cholesterol, atherosclerosis, and a high risk of premature myocardial infarction. FH is commonly caused by defects of the LDL receptor or its main ligand apoB, together mediating cellular uptake and clearance of plasma LDL. In some cases FH is inherited by mutations in the genes of PCSK9 and LDLRAP1 (ARH) in a dominant or recessive trait. The encoded proteins are required for LDL receptor stability and internalization within the LDLR pathway. To detect the underlying genetic defect in a family of Turkish descent showing unregular inheritance of severe FH, we screened the four candidate genes by denaturing gradient gel electrophoresis (DGGE) mutation analysis. We identified different combinatory mixtures of LDLR- and LDLRAP1-gene defects as the cause for severe familial hypercholesterolemia in this family. We also show for the first time that a heterozygous LDLR mutation combined with a homozygous LDLRAP1 mutation produces a more severe hypercholesterolemia phenotype in the same family than a homozygous LDLR mutation alone.

Description of a Large Family with Autosomal Dominant Hypercholesterolemia Associated with theAPOEp.Leu167del Mutation

Apolipoprotein (apo) E mutants are associated with type III hyperlipoproteinemia characterized by high cholesterol and triglycerides levels. Autosomal dominant hypercholesterolemia (ADH), due to the mutations in the LDLR, APOB, or PCSK9 genes, is characterized by an isolated elevation of cholesterol due to the high levels of low-density lipoproteins (LDLs). We now report an exceptionally large family including 14 members with ADH. Through genome-wide mapping, analysis of regional/functional candidate genes, and whole exome sequencing, we identified a mutation in the APOE gene, c.500_502delTCC/p.Leu167del, previously reported associated with sea-blue histiocytosis and familial combined hyperlipidemia. We confirmed the involvement of the APOE p.Leu167del in ADH, with (1) a predicted destabilization of an alpha-helix in the binding domain, (2) a decreased apo E level in LDLs, and (3) a decreased catabolism of LDLs. Our results show that mutations in the APOE gene can be associated with bona fide ADH.

Alteration of lipids and the transcription of lipid-related genes in myelodysplastic syndromes via a TP53-related pathway

Myelodysplastic syndromes (MDS) are clonal stem cell diseases of the bone marrow characterized by abnormalities in maturation of hematopoietic cells of all lineages. MDS patients frequently have lower lipids and high rates of apoptosis and p53 (TP53) expression. An association between the reduced lipids in MDS and the expression of lipid-related genes was sought. We further evaluated whether 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGcoAR) and low-density lipoprotein receptor (LDL-R) are regulated by TP53 invivo and invitro. Gene expression was measured using real-time reverse transcription polymerase chain reaction on RNA extracted from bone marrow and peripheral blood from eight newly diagnosed MDS patients and eight controls and from mice livers. Serum lipid profile was measured using colorimetric enzymatic procedures. Total- and LDL cholesterol were lower in MDS patients in comparison to controls (p = 0.04 and p = 0.01, respectively). HMGcoAR messenger RNA increased in peripheral blood and bone marrow of MDS patients compared to controls (p = 0.04 and p = 0.01, respectively). LDL-R messenger RNA was higher only in the peripheral blood of MDS patients (p = 0.05). Comparable results were obtained invivo. The transcription of these genes correlates with TP53 activation as documented by p21 messenger RNA elevation, a surrogate for TP53 activation and by using TP53 temperature-sensitive cells treated with adriamycin. To conclude, an association between reduced lipids in MDS and expression of HMGcoAR and LDL-R genes was documented. The transcription of these genes can be regulated by TP53.

Macrophages actively accumulate malonyldialdehyde-modified but not enzymatically oxidized low density lipoprotein

In this study, we show that low density lipoproteins (LDL) from human blood plasma which was oxidized by animal C-15 lipoxygenase is taken up by cultivated human macrophages with the same effectiveness as with non-oxidized (native) LDL. At the same time malonyldialdehyde-modified LDL is captured by cultivated macrophages very actively. Based on differences in catabolism of LDL with various levels of primary and secondary products of free-radical oxidation, it was offered to discriminate between the oxidized LDL itself (lipohydroperoxide-rich LDL) and the LDL that was chemically modified by free-radical oxidation secondary products of aldehyde nature. In this respect, aldehyde-modified but not oxidized (lipohydroperoxide-containing) LDL is atherogenic.