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Genetic lecithin:cholesterol acyltransferase (LCAT) deficiency is a rare, inherited, recessive disease, which manifests as two different syndromes: Familial LCAT deficiency (FLD) and Fish-eye disease (FED), characterized by low HDL-C and corneal opacity. FLD patients also develop anaemia and renal disease. There is currently no therapy for FLD, but novel therapeutics are at different stages of development. Here, we summarize the most recent advances and the opportunities for and barriers to the further development of such therapies.Recent publications highlight the heterogeneous phenotype of FLD and the uncertainty over the natural history of disease and the factors contributing to disease progression. Therapies that restore LCAT function (protein and gene replacement therapies and LCAT activators) showed promising effects on markers of LCAT activity. Although they do not restore LCAT function, HDL mimetics may slow renal disease progression.The further development of novel therapeutics requires the identification of efficacy endpoints, which include quantitative biomarkers of disease progression. Because of the heterogeneity of renal disease progression among FLD individuals, future treatments for FLD will have to be tailored based on the specific clinical characteristics of the patient. Extensive studies of the natural history and biomarkers of the disease will be required to achieve this goal.

Background: Hypertriglyceridemia (HTG) is the consequence of elevated triglyceride-rich lipoproteins (TGRLs) containing apolipoprotein B (apoB), such as VLDL and chylomicrons. Epidemiological and genetic studies indicate that triglycerides (TGs) and the cholesterol within TGRLs causally contribute to coronary heart disease risk (CHD). Evinacumab (EVIN), an angiopoietin-like 3 inhibitor, lowers TGs by derepressing lipoprotein lipase (LPL) and endothelial lipase activity. In a Phase 2 trial in patients (pts) with severe HTG (sHTG, fasting TGs ≥500 mg/dL), EVIN was previously shown to reduce TGs in patients (pts) without familial chylomicronemia syndrome (FCS) and to be generally well tolerated (NCT03452228). This post-hoc analysis reports further details on the efficacy of EVIN in reducing atherogenic lipids/lipoproteins. Methods: Pts (N=51) were treated and assigned to cohorts based on genotype: Cohort 1 (n=17), FCS pts with bi-allelic loss-of-function (LOF) LPL pathway mutations; Cohort 2 (n=15), multifactorial chylomicronemia syndrome (MCS) pts with heterozygous LOF LPL pathway mutations; Cohort 3 (n=19), MCS pts without LPL pathway mutations. Pts were randomized (2:1) to IV EVIN 15 mg/kg or placebo every 4 weeks over a 12-week double-blind treatment (tx) period (DBTP), followed by a 12-week single-blind tx period where all pts received EVIN. Results: Of 51 pts with sHTG treated in the DBTP, 70.6% were categorized as high cardiovascular risk, and 21.6% had a history of CHD. In non-FCS pts (Cohorts 2 and 3), in addition to reducing TGs, EVIN reduced atherogenic lipids and apolipoproteins at Week (W) 12 compared with baseline (Table), including non-HDL-C, remnant cholesterol, and apoB (including apoB100 and apoB48). Overall, reductions observed at W12 were maintained through W24. Conclusions: In this post-hoc analysis, EVIN reduced atherogenic lipids and apoB, indicating it may have the potential to reduce CHD risk in pts with sHTG without genetic FCS.

Plasma triglycerides (TGs) are an independent predictor of the risk for CAD, the leading cause of death worldwide. TGs are also positively associated with risk and severity of hyperTG-induced acute pancreatitis (HTG-AP). Current therapies are often insufficient in reducing extremely elevated TGs. We believe that apolipoprotein A-V (apoA-V, encoded by APOA5) can fill this unmet medical need. ApoA-V is a potent modulator of TG metabolism; it enhances lipoprotein lipase TG hydrolysis. We hypothesize that naturally occurring human APOA5 variants can inform ApoA-V function and identify novel ApoA-V based therapeutic axes. We used the Penn Medicine Biobank (PMBB) to identify and measure plasma TGs of carriers of APOA5 variants predicted to change ApoA-V structure-function. Then, we used hydrogen-deuterium exchange mass spectroscopy to determine the secondary structure of ApoA-V, thereby identifying putative functional domains onto which we mapped our variants of interest. Finally, we characterized the plasma lipid effects of these mutants using adeno-associated viral (AAV) vectors in apoa5 knockout (KO) mice. We identified APOA5 variants associated with changes in plasma TGs. These variants primarily fall near the central heparin binding domain or C-terminal lipid binding domain. We selected APOA5 Q275X, which removes the entire lipid binding domain, for further interrogation. Apoa5 KO mice that received APOA5 Q275X AAV had higher plasma TGs than mice treated with WT APOA5 AAV. While WT ApoA-V protein associated with VLDL and HDL particles, Q275X ApoA-V protein appeared in lipoprotein free fractions. We have identified APOA5 variants associated with plasma TG phenotypes in humans, and mapped them to an experimentally determined ApoA-V secondary structure to identify the functional domains likely impacted. We have identified APOA5 Q275X as a loss of function variant that fails to bind lipoprotein particles and is associated with elevated plasma TGs. Continued study of this and other interesting naturally occurring variants will provide insight into the function of ApoA-V in TG metabolism. These insights can help us to therapeutically enhance ApoA-V to rapidly reduce TG levels during acute HTG-AP and to help prevent recurrent HTG-AP.

Genetic variants near the TRIB1 gene are highly significantly associated with plasma lipid traits and coronary artery disease. While TRIB1 is likely causal of these associations, the molecular mechanisms are not well understood. Here we sought to investigate how TRIB1 influences low density lipoprotein cholesterol (LDL-C) levels in mice. Hepatocyte-specific deletion of Trib1 (Trib1(Δ)hep) in mice increased plasma cholesterol and apoB and slowed the catabolism of LDL-apoB due to decreased levels of LDL receptor (LDLR) mRNA and protein. Simultaneous deletion of the transcription factor CCAAT/enhancer-binding protein alpha (CEBPα) with TRIB1 eliminated the effects of TRIB1 on hepatic LDLR regulation and LDL catabolism. Using RNA-seq, we found that activating transcription factor 3 (Atf3) was highly upregulated in the livers of Trib1(Δ)hep but not Trib1(Δ)hep Cebpa(Δ)hep mice. ATF3 has been shown to directly bind to the CEBPα protein, and to repress the expression of LDLR by binding its promoter. Blunting the increase of ATF3 in Trib1(Δ)hep mice reduced the levels of plasma cholesterol and partially attenuated the effects on LDLR. Based on these data, we conclude that deletion of Trib1 leads to a posttranslational increase in CEBPα, which increases ATF3 levels, thereby contributing to the downregulation of LDLR and increased plasma LDL-C.

In humans, apolipoprotein C-III (apoC-III) plasma levels have been associated with increased risk of cardiovascular disease. This association is in part explained by the effects of apoC-III on triglyceride (TG) metabolism; apoC-III raises plasma TG by increasing very low density lipoprotein (VLDL) secretion, inhibiting lipoprotein lipase (LPL)-mediated TG lipolysis, and impairing the removal of triglyceride-rich lipoprotein (TRL) remnants from the circulation. In this study, we explored the structure-function relationship the interaction of apoC-III with plasma lipoproteins and its ultimate impact on LPL activity. The structural and functional properties of wild-type (WT) apoC-III were compared with two missense variants previously associated with lower (A23T) and higher (Q38K) plasma TG. ApoC-III in the lipid-free state is unstructured but its helix content and stability increases when bound to lipid. Lipid-bound apoC-III contains two alpha helices spanning residues amino acids 11 - 38 (helix 1) and 44 – 64 (helix 2). Investigation of the structural and functional consequences of the A23T and Q38K variants showed that these amino acid substitutions within helix 1 do not significantly alter the stability of the helical structure but affect its hydrophilic-lipophilic properties. The A23T substitution impairs lipoprotein binding capacity, reduces LPL inhibition, and ultimately leads to lower plasma TG levels. Conversely, the Q to K substitution at position 38 enhances the lipid affinity of helix 1, increases TRL binding capacity and LPL inhibition, and is associated with hypertriglyceridemia. This study indicates that structural modifications that perturb the hydrophilic/lipophilic properties of the alpha helices can modulate the hypertriglyceridemic effects of apoC-III.

Congenital disorders of glycosylation are a growing group of rare genetic disorders caused by deficient protein and lipid glycosylation. Here, we report the clinical, biochemical, and molecular features of seven patients from four families with GALNT2-congenital disorder of glycosylation (GALNT2-CDG), an O-linked glycosylation disorder. GALNT2 encodes the Golgi-localized polypeptide N-acetyl-d-galactosamine-transferase 2 isoenzyme. GALNT2 is widely expressed in most cell types and directs initiation of mucin-type protein O-glycosylation. All patients showed loss of O-glycosylation of apolipoprotein C-III, a non-redundant substrate for GALNT2. Patients with GALNT2-CDG generally exhibit a syndrome characterized by global developmental delay, intellectual disability with language deficit, autistic features, behavioural abnormalities, epilepsy, chronic insomnia, white matter changes on brain MRI, dysmorphic features, decreased stature, and decreased high density lipoprotein cholesterol levels. Rodent (mouse and rat) models of GALNT2-CDG recapitulated much of the human phenotype, including poor growth and neurodevelopmental abnormalities. In behavioural studies, GALNT2-CDG mice demonstrated cerebellar motor deficits, decreased sociability, and impaired sensory integration and processing. The multisystem nature of phenotypes in patients and rodent models of GALNT2-CDG suggest that there are multiple non-redundant protein substrates of GALNT2 in various tissues, including brain, which are critical to normal growth and development.

DHA (docosahexaenoic acid) is an essential fatty acid that is required for the normal development and function of the brain. Because of its inability to synthesize adequate amounts of DHA from the precursors, the brain has to acquire DHA from plasma through the blood brain barrier (BBB). Recent studies demonstrated the presence of a transporter at the BBB that specifically transports DHA into the brain in the form of lysophosphatidylcholine (LPC-DHA). However, the mechanism by which LPC-DHA is generated in the plasma is not known. Our previous studies showed that there are at least three different enzymes - lecithin cholesterol acyltransferase (LCAT), endothelial lipase (EL), and hepatic lipase (HL), which can generate LPC-DHA from sn-2 DHA phosphatidylcholine. Here we determined the relative contributions of these enzymes in the delivery of DHA to the brain by measuring the brain DHA levels in the mice deficient in each of these enzymes. The results show that the brain DHA levels of LCAT-deficient mice or EL-deficient mice were not significantly lower than those of their littermates. However, brain DHA was significantly decreased in HL deficient mice (13.5% of total fatty acids) compared to their littermates (17.1%) (p 0.002), and further decreased to 8.3% of total fatty acids in mice deficient in both HL and EL. These results suggest that HL activity may be the major source for the generation of LPC-DHA in the plasma necessary for transport into the brain, and EL might contribute to this process in the absence of HL.

Triglyceride-rich lipoproteins (TRLs) are circulating reservoirs of fatty acids used as vital energy sources for peripheral tissues. Lipoprotein lipase (LPL) is a predominant enzyme mediating triglyceride (TG) lipolysis and TRL clearance to provide fatty acids to tissues in animals. Physiological and human genetic evidence support a primary role for LPL in hydrolyzing TRL TGs. We hypothesized that endothelial lipase (EL), another extracellular lipase that primarily hydrolyzes lipoprotein phospholipids may also contribute to TRL metabolism. To explore this, we studied the impact of genetic EL loss-of-function on TRL metabolism in humans and mice. Humans carrying a loss-of-function missense variant in LIPG, p.Asn396Ser (rs77960347), demonstrated elevated plasma TGs and elevated phospholipids in TRLs, among other lipoprotein classes. Mice with germline EL deficiency challenged with excess dietary TG through refeeding or a high-fat diet exhibited elevated TGs, delayed dietary TRL clearance, and impaired TRL TG lipolysis in vivo that was rescued by EL reconstitution in the liver. Lipidomic analyses of postprandial plasma from high-fat fed Lipg-/- mice demonstrated accumulation of phospholipids and TGs harboring long-chain polyunsaturated fatty acids (PUFAs), known substrates for EL lipolysis. In vitro and in vivo, EL and LPL together promoted greater TG lipolysis than either extracellular lipase alone. Our data positions EL as a key collaborator of LPL to mediate efficient lipolysis of TRLs in humans and mice., Author summary Endothelial lipase (EL) plays a pivotal role in the breakdown of high-density lipoproteins (HDLs) by hydrolyzing phospholipids on HDL surfaces. Here we show through studies of humans and mice with genetic loss-of-function of EL activity that EL is also crucial in catabolizing triglyceride (TG)-rich lipoproteins, particularly in states of nutrient excess such as after refeeding or after feeding a high-fat diet. We demonstrate that EL collaborates with lipoprotein lipase (LPL), the predominant enzyme hydrolysing triglycerides, to promote the breakdown of triglycerides on lipoproteins. The mechanism for this may be due to an underappreciated ability of EL to hydrolyze TGs and cooperate with LPL to efficiently break down and clear these particles. Our data adds important insights into the mechanisms of circulating TG metabolism in mice and humans as informed by large-scale human genetics.

Lecithin:cholesterol acyltransferase (LCAT) is the only enzyme capable of esterifying cholesterol in plasma, thus determining the maturation of high-density lipoproteins. Because it maintains an unesterified cholesterol gradient between peripheral cells and extracellular acceptors, for a long time, LCAT has been considered as a key enzyme in reverse cholesterol transport. However, despite the fact that it has been more than 50 years since the identification of LCAT, the role of this enzyme in the pathogenesis of atherosclerosis is still debated. A number of studies have been conducted in different animal models, with contradictory results. Studies in humans, in particular in the general population, in subjects at high cardiovascular risk, and in carriers of genetic LCAT deficiency in an excellent model to evaluate the correlation between the reduction of LCAT activity and atherosclerosis also gave conflicting results. This review provides a comprehensive overview of the controversial findings obtained in animals and humans, strengthening the necessity of further investigation to establish how LCAT could be regulated in a promising therapeutic strategy to reduce cardiovascular risk.

Elevated high-density lipoprotein cholesterol levels in the blood (HDL-C) represent one of the strongest epidemiological surrogates for protection against coronary heart disease (CHD), but recent human genetic and pharmacological intervention studies have raised controversy about the causality of this relationship. Here, we review recent discoveries from human genome studies using new analytic tools as well as relevant animal studies that have both addressed, and in some cases, fueled this controversy. Methodologic developments in genotyping and sequencing, such as genome-wide association studies (GWAS), exome sequencing, and exome array genotyping, have been applied to the study of HDL-C and risk of CHD in large, multi-ethnic populations. Some of these efforts focused on population-wide variation in common variants have uncovered new polymorphisms at novel loci associated with HDL-C and, in some cases, CHD risk. Other efforts have discovered loss-of-function variants for the first time in genes previously implicated in HDL metabolism through common variant studies or animal models. These studies have allowed the genetic relationship between these pathways, HDL-C and CHD to be explored in humans for the first time through analysis tools such as Mendelian randomization. We explore these discoveries for selected key HDL-C genes CETP, LCAT, LIPG, SCARB1, and novel loci implicated from GWAS including GALNT2, KLF14, and TTC39B. Recent human genetics findings have identified new nodes regulating HDL metabolism while reshaping our current understanding of known candidate genes to HDL and CHD risk through the study of critical variants across model systems. Despite their effect on HDL-C, variants in many of the reviewed genes were found to lack any association with CHD. These data collectively indicate that HDL-C concentration, which represents a static picture of a very dynamic and heterogeneous metabolic milieu, is unlikely to be itself causally protective against CHD. In this context, human genetics represent an extremely valuable tool to further explore the biological mechanisms regulating HDL metabolism and investigate what role, if any, HDL plays in the pathogenesis of CHD.

Epidemiologic studies have shown that high density lipoprotein cholesterol (HDLc) levels are inversely associated with cardiovascular disease risk. This effect is believed to be mediated by several atheroprotective properties of HDL, including the ability to promote the reverse cholesterol transport and reduce vascular inflammation, oxidative stress and thrombosis. Thus, HDLc has been long considered a valid therapeutic target to reduce residual cardiovascular risk. Unfortunately, results obtained from large clinical trials with drugs increasing HDLc levels have been disappointing and have raised doubts on the effectiveness of this approach. With the recognition that HDLc levels may be a poor indicator of HDL atheroprotective potentials, recent strategies for drug development are focusing on enhancing HDL functions rather than HDLc levels per-se. In this chapter we will review established drugs able to raise HDLc levels as well as emerging HDL-targeting therapies currently undergoing preclinical and clinical research.

ATP-binding cassette transporter subfamily A member 1 (ABCA1) is a plasma membrane protein well known for its role in regulating cellular cholesterol efflux and high-density lipoprotein (HDL) formation.1 Carriers of loss-of-function mutations in ABCA1 are characterized by reduced HDL cholesterol levels, which are nearly absent in the rare homozygous state (Tangier disease), and accumulation of cholesterol in several tissues, especially those rich in macrophages and reticuloendothelial cells.2 Although patients with Tangier disease rarely manifest with premature coronary artery disease, carriers of functional mutations in ABCA1 are characterized by decreased cholesterol efflux from fibroblasts and increased carotid wall thickness when compared with control subjects.3,4 See accompanying article on page 1663 Cholesterol efflux from macrophages has been shown to be predictive of cardiovascular events and their incidence.5,6 ABCA1 is generally considered atheroprotective for its ability to meditate this first step of the reverse cholesterol transport pathway.7 Figure. Potential mechanisms underlying increased inflammatory status in ATP-binding cassette transporter subfamily A member 1 (ABCA1)–deficient subjects. A , ABCA1 plays a major role in nascent high-density lipoprotein (HDL) formation and cellular cholesterol homeostasis. Excess free cholesterol (FC) and phospholipid in peripheral tissues, including macrophages in the arterial wall, can be transported out of cells through active lipid efflux via transporters such as ABCA1 into HDL. Through this process ABCA1 can modulate the amount of FC present in the plasma membrane. ABCA1-mediated reduction in …

Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for cholesterol esterification in plasma. Mutations in the LCAT gene leads to two rare disorders, familial LCAT deficiency and fish-eye disease, both characterized by severe hypoalphalipoproteinemia associated with several lipoprotein abnormalities. No specific treatment is presently available for genetic LCAT deficiency. In the present study, recombinant human LCAT was expressed and tested for its ability to correct the lipoprotein profile in LCAT deficient plasma. The results show that rhLCAT efficiently reduces the amount of unesterified cholesterol (−30%) and promotes the production of plasma cholesteryl esters (+210%) in LCAT deficient plasma. rhLCAT induces a marked increase in HDL-C levels (+89%) and induces the maturation of small preβ-HDL into alpha-migrating particles. Moreover, the abnormal phospholipid-rich particles migrating in the LDL region were converted in normally sized LDL.

Epidemiological studies have clearly demonstrated that plasma concentrations of HDL cholesterol are strongly and inversely associated with cardiovascular risk. Besides playing a major role in reverse cholesterol transport, the process by which excess cholesterol in the arterial wall is removed by HDL and delivered to the liver for excretion, HDL have other atheroprotective functions. In particular, HDL can contribute to the maintenance of endothelial cell homeostasis by inhibiting cell adhesion molecule expression, by promoting the release of bioactive molecules such as nitric oxide and prostacyclin, and by regulating cell proliferation and migration. HDL inherited disorders represent a unique tool to understand the relationship between HDL concentration, HDL function and HDL-mediated atheroprotection.

The administration of thrombolytic drugs is of proven benefit in a variety of clinical conditions requiring acute revascularization, including acute myocardial infarction (AMI), ischemic stroke, pulmonary embolism, and venous thrombosis. Generated plasmin can degrade non-target proteins, including apolipoprotein A-I (apoA-I), the major protein constituent of high-density lipoproteins (HDL). Aim of the present study was to compare the extent of apoA-I proteolytic degradation in AMI patients treated with two thrombolytic drugs, alteplase and the genetically engineered t-PA variant tenecteplase. ApoA-I degradation was evaluated in sera from 38 AMI patients treated with alteplase or tenecteplase. In vitro, apoA-I degradation was tested by incubating control sera or purified HDL with alteplase or tenecteplase at different concentrations (5–100 μg/ml). Treatment with alteplase and tenecteplase results in apoA-I proteolysis; the extent of apoA-I degradation was more pronounced in alteplase-treated patients than in tenecteplase-treated patients. In vitro, the extent of apoA-I proteolysis was higher in alteplase-treated sera than in tenecteplase-treated sera, in the whole drug concentration range. No direct effect of the two thrombolytic agents on apoA-I degradation was observed. In addition to apoA-I, apoA-IV was also degraded by the two thrombolytic agents and again proteolytic degradation was higher with alteplase than tenecteplase. In conclusion, this study indicates that both alteplase and tenecteplase cause plasmin-mediated proteolysis of apoA-I, with alteplase resulting in a greater apoA-I degradation than tenecteplase, potentially causing a transient impairment of HDL atheroprotective functions.

Human genetics studies have implicated GALNT2, encoding GalNAc-T2, as a novel regulator of high-density lipoprotein cholesterol (HDL-C) metabolism, but the mechanisms relating GALNT2 to HDL-C remain unclear. We investigated the impact of homozygous GALNT2 deficiency on HDL-C in humans and mammalian models. We identified two humans homozygous for loss-of-function mutations in GALNT2 who demonstrated low HDL-C. We also found that GALNT2 loss-of-function in mice, rats, and nonhuman primates decreased HDL-C. O-glycoproteomics studies of a human GALNT2 deficient subject validated ANGPTL3 and ApoC-III as GalNAc-T2 targets. Additional glycoproteomics in rodents identified targets influencing HDL-C, including phospholipid transfer protein (PLTP). GALNT2 deficiency reduced plasma PLTP activity in humans and rodents, and in mice this was rescued by reconstitution of hepatic Galnt2. We also found that GALNT2 GWAS SNPs associated with reduced HDL-C also correlate with lower hepatic GALNT2 expression. These results posit GALNT2 as a direct modulator of HDL metabolism across mammals.

Cardiovascular diseases are currently the commonest cause of death worldwide. Different strategies for their primary prevention have been planned, taking into account the main known risk factors, which include an atherogenic lipid profile and visceral fat excess. The study was designed as a randomized, parallel, single-center study with a nutritional intervention duration of 12 weeks. Whole soy foods corresponding to 30 g/day soy protein were given in substitution of animal foods containing the same protein amount. Soy nutritional intervention resulted in a reduction in the number of MetS features in 13/26 subjects. Moreover, in the soy group we observed a significant improvement of median percentage changes for body weight (−1.5 %) and BMI (−1.5 %), as well as for atherogenic lipid markers, namely TC (−4.85 %), LDL-C (−5.25 %), non-HDL-C (−7.14 %) and apoB (−14.8 %). Since the majority of the studied variables were strongly correlated, three factors were identified which explained the majority (52 %) of the total variance in the whole data set. Among them, factor 1, which loaded lipid and adipose variables, explained the 22 % of total variance, showing a statistically significant difference between treatment arms (p = 0.002). The inclusion of whole soy foods (corresponding to 30 g/day protein) in a lipid-lowering diet significantly improved a relevant set of biomarkers associated with cardiovascular risk.

ATP-binding cassette transporter A1 (ABCA1) mediates formation of disc-shaped high-density lipoprotein (HDL) from cell lipid and lipid-free apolipoprotein A-I (apo A-I). Discoidal HDL particles are heterogeneous in physicochemical characteristics for reasons that are understood incompletely. Discoidal lipoprotein particles similar in characteristics and heterogeneity to cell-formed discoidal HDL can be reconstituted from purified lipids and apo A-I by cell-free, physicochemical methods. The heterogeneity of reconstituted HDL (rHDL) is sensitive to the lipid composition of the starting lipid/apo A-I mixture. To determine whether the heterogeneity of cell-formed HDL is similarly sensitive to changes in cell lipids, we investigated four compounds that have well-established effects on cell lipid metabolism and ABCA1-mediated cell cholesterol efflux. 2-Bromopalmitate, D609, monensin and U18666A decreased formation of the larger-sized, but dramatically increased formation of the smaller-sized HDL. 2-Bromopalmitate did not appear to affect ABCA1 activity, subcellular localization or oligomerization, but induced dissolution of the cholesterol-phospholipid complexes in the plasma membrane. Arachidonic and linoleic acids shifted HDL formation to the smaller-sized species. Tangier disease mutations and inhibitors of ABCA1 activity wheat germ agglutinin and AG 490 reduced formation of both larger-sized and smaller-sized HDL. The effect of probucol was similar to the effect of 2-bromopalmitate. Taking rHDL formation as a paradigm, we propose that ABCA1 mutations and activity inhibitors reduce the amount of cell lipid available for HDL formation, and the compounds in the 2-bromopalmitate group and the polyunsaturated fatty acids change cell lipid composition from one that favors formation of the larger-sized HDL particles to one that favors formation of the smaller-sized species.

Familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is characterized by low HDL, accumulation of an abnormal cholesterol-rich multilamellar particle called lipoprotein-X (LpX) in plasma, and renal disease. The aim of our study was to determine if LpX is nephrotoxic and to gain insight into the pathogenesis of FLD renal disease. We administered a synthetic LpX, nearly identical to endogenous LpX in its physical, and chemical properties, to wild-type and Lcat -/- mice. Our in vitro and in vivo studies demonstrated an apoA-I and LCAT-dependent pathway for LpX conversion to HDL-like particles, which likely mediates normal plasma clearance of LpX. Plasma clearance of exogenous LpX was markedly delayed in Lcat -/- mice, which have low HDL but only minimal amounts of endogenous LpX and do not spontaneously develop renal disease. Chronically administered exogenous LpX deposited in all renal glomerular cellular and matrical compartments of Lcat -/- mice, and induced proteinuria and nephrotoxic gene changes, as well as all of the hallmarks of FLD renal disease as assessed by histological, TEM, and SEM analyses. Extensive in vivo EM studies revealed LpX uptake by macropinocytosis into mouse glomerular endothelial cells, podocytes, and mesangial cells and delivery to lysosomes, where it was degraded. Endocytosed LpX appeared to be degraded by both human podocyte and mesangial cell lysosomal PLA 2 and induced podocyte secretion of pro-inflammatory IL-6 in vitro and renal Cxl10 expression in Lcat -/- mice. In conclusion, LpX is a nephrotoxic particle that in the absence of LCAT induces all of the histological and functional hallmarks of FLD and hence may serve as a biomarker for monitoring recombinant LCAT therapy. In addition, our studies suggest that LpX-induced loss of endothelial barrier function and release of cytokines by renal glomerular cells likely plays a role in the initiation and progression of FLD nephrosis.

Polyunsaturated fatty acids (PUFA) are essential constituents of the cell membrane. Brain PUFA content is critical for synaptic function and neuroinflammation and PUFA deficiency may underlie several neurological disorders. Prior work in murine models has showed that the predominant source of central nervous system (CNS) PUFAs is 2-acyl-lysophophatidylcholine (2-lysoPC), a class of phospholipids (PLs) circulating on blood lipoproteins that is formed from the enzymatic activity of phospholipases. Endothelial lipase (EL) is a phospholipase that is a critical determinant of HDL metabolism in humans and the predominant generator of 2-lysoPC on HDL particles. While the contribution of EL to circulating HDL metabolism is well-established, its contribution to CNS fatty acid availability and brain function has not been explored. In order to investigate the physiological contribution of EL to brain FA availability in vivo, we studied PL-derived PUFA uptake in mice with EL deficiency. We adopted a method for measuring EL activity using a fluorescent synthetic HDL particle containing sn2-TopFluor-PC, a fluorescent precursor of 2-lysoPC and demonstrated its utility in vitro. Next, we tested the clearance of this synthetic HDL-derived 2-lysoPC in C57BL/6 (WT) vs EL KO mice (n=12/group). Circulating plasma 2-lysoPC clearance was significantly impaired in in EL KO mice (-32%, p=0.024) and was accompanied by a slower remodeling of the HDL particles. Measurement of labeled PL content in tissues showed a significant reduction in hepatic uptake in KO mice (22% decrease, p=0.002). No significant differences were observed in total brain PL uptake, but the distribution of PL uptake differed between WT and KOs. Ongoing studies are evaluating the physiological consequences of reduced circulating 2-lysoPC clearance, reduced hepatic uptake, and altered distribution of brain PL uptake in EL KO mice. Collectively, our data demonstrate that EL is a key physiological regulator of systemic PL catabolism.

Humans with loss-of-function (LoF) variants in APOC3 , the gene encoding apolipoprotein C-III (apoC-III), have significantly reduced plasma triglycerides (TG) and protection from coronary disease. These findings suggest that apoC-III may be a viable therapeutic target for decreasing vascular risk through TG reduction, and that elucidation of the protective mechanism of APOC3 LoF variants would inform such strategies. We report here the protective mechanism of the APOC3 A43T missense variant, one of four recently identified CAD-protective variants. By genotyping >8,000 human participants with low TG, we identified 17 APOC3 A43T carriers and phenotyped 6 carriers and 54 matched controls. A43T heterozygotes demonstrate a significant reduction in apoC-III levels relative to non-carriers (50% reduction, P3-fold higher apoC-III clearance rate in vivo (Pin vivo . We are currently performing analogous studies of WT vs. A43T apoC-III turnover and VLDL clearance in human APOC3 A43T carriers. Collectively, our results support the rationale for therapeutic efforts to target circulating apoC-III through disruption of its binding to lipoproteins, mirroring the genetics-driven approaches for targeting PCSK9 that have recently yielded novel therapies.

Background We describe a kindred with high-density lipoprotein (HDL) deficiency due to APOA1 g ene mutation in which comorbidities affected the phenotypic expression of the disorder. Methods An overweight boy with hypertriglyceridemia (HTG) and HDL deficiency (HDL cholesterol 0.39 mmol/L, apoA-I 40 mg/dL) was investigated. We sequenced the candidate genes for HTG ( LPL, APOC2 , APOA5, GPIHBP1, LMF1 ) and HDL deficiency ( LCAT, ABCA1 and APOA1 ), analyzed HDL subpopulations, measured cholesterol efflux capacity (CEC) of sera and constructed a model of the mutant apoA-I. Results No mutations in HTG-related genes, ABCA1 and LCAT were found. APOA1 sequence showed that the proband, his mother and maternal grandfather were heterozygous of a novel frameshift mutation (c.546_547delGC), which generated a truncated protein (p.[L159Afs*20]) containing 177 amino acids with an abnormal C-terminal tail of 19 amino acids. Trace amounts of this protein were detectable in plasma. Mutation carriers had reduced levels of LpA-I, preβ-HDL and large HDL and no detectable HDL-2 in their plasma; their sera had a reduced CEC specifically the ABCA1-mediated CEC. Metabolic syndrome in the proband explains the extremely low HDL cholesterol level (0.31 mmol/L), which was half of that found in the other carriers. The proband's mother and grandfather, both presenting low plasma low-density lipoprotein cholesterol, were carriers of the β-thalassemic trait, a condition known to be associated with a reduced low-density lipoprotein cholesterol and a reduced prevalence of cardiovascular disease. This trait might have delayed the development of atherosclerosis related to HDL deficiency. Conclusions In these heterozygotes for apoA-I truncation, the metabolic syndrome has deleterious effect on HDL system, whereas β-thalassemia trait may delay the onset of cardiovascular disease.

Cholesterol is an essential component of both the peripheral nervous system and central nervous system (CNS) of mammals. Brain cholesterol is synthesized in situ by astrocytes and oligodendrocytes and is almost completely isolated from other pools of cholesterol in the body, but a small fraction can be taken up from the circulation as 27-hydroxycholesterol, or via the scavenger receptor class B type I. Glial cells synthesize native high-density lipoprotein (HDL)-like particles, which are remodelled by enzymes and lipid transfer proteins, presumably as it occurs in plasma. The major apolipoprotein constituent of HDL in the CNS is apolipoprotein E, which is produced by astrocytes and microglia. Apolipoprotein A-I, the major protein component of plasma HDL, is not synthesized in the CNS, but can enter and become a component of CNS lipoproteins. Low HDL-C levels have been shown to be associated with cognitive impairment and various neurodegenerative diseases. On the contrary, no clear association with brain disorders has been shown in genetic HDL defects, with the exception of Tangier disease. Mutations in a wide variety of lipid handling genes can result in human diseases, often with a neuronal phenotype caused by dysfunctional intracellular lipid trafficking.

Human familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is characterized by low HDL, accumulation of an abnormal cholesterol-rich multilamellar particle called lipoprotein-X (LpX) in plasma, and renal disease. The aim of our study was to determine if LpX is nephrotoxic and to gain insight into the pathogenesis of FLD renal disease. We administered a synthetic LpX, nearly identical to endogenous LpX in its physical, chemical and biologic characteristics, to wild-type and Lcat-/- mice. Our in vitro and in vivo studies demonstrated an apoA-I and LCAT-dependent pathway for LpX conversion to HDL-like particles, which likely mediates normal plasma clearance of LpX. Plasma clearance of exogenous LpX was markedly delayed in Lcat-/- mice, which have low HDL, but only minimal amounts of endogenous LpX and do not spontaneously develop renal disease. Chronically administered exogenous LpX deposited in all renal glomerular cellular and matrical compartments of Lcat-/- mice, and induced proteinuria and nephrotoxic gene changes, as well as all of the hallmarks of FLD renal disease as assessed by histological, TEM, and SEM analyses. Extensive in vivo EM studies revealed LpX uptake by macropinocytosis into mouse glomerular endothelial cells, podocytes, and mesangial cells and delivery to lysosomes where it was degraded. Endocytosed LpX appeared to be degraded by both human podocyte and mesangial cell lysosomal PLA2 and induced podocyte secretion of pro-inflammatory IL-6 in vitro and renal Cxl10 expression in Lcat-/- mice. In conclusion, LpX is a nephrotoxic particle that in the absence of Lcat induces all of the histological and functional hallmarks of FLD and hence may serve as a biomarker for monitoring recombinant LCAT therapy. In addition, our studies suggest that LpX-induced loss of endothelial barrier function and release of cytokines by renal glomerular cells likely plays a role in the initiation and progression of FLD nephrosis.