The carboxy-terminal region of apoA-I is required for the ABCA1-dependent formation of alpha-HDL but not prebeta-HDL particles in vivo

Deciphering structural aspects of reverse cholesterol transport: mapping the knowns and unknowns

Atherosclerosis is a major contributor to the onset and progression of cardiovascular disease (CVD). Cholesterol-loaded foam cells play a pivotal role in forming atherosclerotic plaques. Induction of cholesterol efflux from these cells may be a promising approach in treating CVD. The reverse cholesterol transport (RCT) pathway delivers cholesteryl ester (CE) packaged in high-density lipoproteins (HDL) from non-hepatic cells to the liver, thereby minimising cholesterol load of peripheral cells. RCT takes place via a well-organised interplay amongst apolipoprotein A1 (ApoA1), lecithin cholesterol acyltransferase (LCAT), ATP binding cassette transporter A1 (ABCA1), scavenger receptor-B1 (SR-B1), and the amount of free cholesterol. Unfortunately, modulation of RCT for treating atherosclerosis has failed in clinical trials owing to our lack of understanding of the relationship between HDL function and RCT. The fate of non-hepatic CEs in HDL is dependent on their access to proteins involved in remodelling and can be regulated at the structural level. An inadequate understanding of this inhibits the design of rational strategies for therapeutic interventions. Herein we extensively review the structure-function relationships that are essential for RCT. We also focus on genetic mutations that disturb the structural stability of proteins involved in RCT, rendering them partially or completely non-functional. Further studies are necessary for understanding the structural aspects of RCT pathway completely, and this review highlights alternative theories and unanswered questions.

Apolipoprotein A-I carboxy-terminal domain residues 187-243 are required for adiponectin-induced cholesterol efflux

Adiponectin exerts its atheroprotection by stimulating adenosine triphosphate binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux to apolipoprotein A-I (apoA-I). However, involvement of the apoA-I residues in this process have not been studied. In Tamm-Horsfall 1 (THP-1) macrophages and baby hamster kidney (BHK) cells we assessed adiponectin's potential to restore cholesterol efflux in the presence of apoA-I and ABCA1 mutants, respectively. Adiponectin was unable to restore efflux from THP-1 macrophages in the presence of apoA-I carboxy-terminal domain (CTD) successive mutants from residues 187-243 versus apoA-I mutants alone. Furthermore, adiponectin did not significantly influence cholesterol efflux to apoA-I from BHK-ABCA1 mutant cells. Adiponectin appears to require functional apoA-I CTD residues 187-243 and wild-type ABCA1 to mediate efficient cholesterol efflux from THP-1 macrophages and BHK cells, respectively. Therefore, adiponectin cannot rescue defective cholesterol efflux in apoA-I- or ABCA1-mutant conditions, but rather increases cholesterol efflux in wild-type apoA-I conditions compared to apoA-I exposure alone.

A novel apoA-I mimetic peptide suppresses atherosclerosis by promoting physiological HDL function in apoE-/- mice

BACKGROUND AND PURPOSE

Apolipoprotein A-I (apoA-I) mimetic peptides (AAMPs) are short peptides that can mimic the physiological effects of apoA-I, including the suppression of atherosclerosis by reversely transporting peripheral cholesterol to the liver. As the hydrophobicity of apoA-I is considered important for its lipid transport, novel AAMPs were designed and synthesized in this study by gradually increasing the hydrophobicity of the parent peptide, and their anti-atherosclerotic effects were tested.

EXPERIMENTAL APPROACH

Seventeen new AAMPs (P1-P17) with incrementally increased hydrophobicity were designed and synthesized by replacing the amino acids 221-240 of apoA-I (VLESFKVSFLSALEEYTKKL). Their effects on cholesterol efflux were evaluated. Their cytotoxicity and haemolytic activity were also measured. The in vitro mechanism of the action of the new peptides was explored. Adult apolipoprotein E^-/- mice were used to evaluate the anti-atherosclerotic activity of the best candidate, and the mechanistic basis of its anti-atherosclerotic effects was explored.

KEY RESULTS

Seventeen new AAMPs (P1-P17) were synthesized, and their cholesterol efflux activity and cytotoxicity were closely related to their hydrophobicity. P12 (FLEKLKELLEHLKELLTKLL) was the best candidate and most strongly promoted cholesterol efflux among the non-toxic peptides (P1-P12). With its phospholipid affinity, P12 facilitated cholesterol transport through the ATP-binding cassette transporter A1. In vivo, P12 exhibited prominent anti-atherosclerotic activity via coupling with HDL.

CONCLUSION AND IMPLICATIONS

P12 featured adequate hydrophobicity, which ensured its efficient binding with cytomembrane phospholipids, cholesterol and HDL, and provided a basis for its ability to reversely transport cholesterol and treat atherosclerosis.

Potential of Lipoprotein-Based Nanoparticulate Formulations for the Treatment of Eye Diseases

Lipoproteins are naturally occurring nanoparticles and their main physiological function is the promotion of lipid metabolism. They can be prepared in vitro for use as drug carriers, and these reconstituted lipoproteins show similar biological activity to their natural counterparts. Some lipoproteins can cross the blood-retinal barrier and are involved in intraocular lipid metabolism. Drug-loaded lipoproteins can be delivered to the retina for the treatment of posterior eye diseases. In this review, we have discussed the therapeutic applications of lipoproteins for eye diseases and introduced the emerging animal models used for the evaluation of their therapeutic effects.

Role of apolipoproteins, ABCA1 and LCAT in the biogenesis of normal and aberrant high density lipoproteins

In this review, we focus on the pathway of biogenesis of HDL, the essential role of apoA-I, ATP binding cassette transporter A1 (ABCA1), and lecithin: cholesterol acyltransferase (LCAT) in the formation of plasma HDL; the generation of aberrant forms of HDL containing mutant apoA-I forms and the role of apoA-IV and apoE in the formation of distinct HDL subpopulations. The biogenesis of HDL requires functional interactions of the ABCA1 with apoA-I (and to a lesser extent with apoE and apoA-IV) and subsequent interactions of the nascent HDL species thus formed with LCAT. Mutations in apoA-I, ABCA1 and LCAT either prevent or impair the formation of HDL and may also affect the functionality of the HDL species formed. Emphasis is placed on three categories of apoA-I mutations. The first category describes a unique bio-engineered apoA-I mutation that disrupts interactions between apoA-I and ABCA1 and generates aberrant preβ HDL subpopulations that cannot be converted efficiently to α subpopulations by LCAT. The second category describes natural and bio-engineered apoA-I mutations that generate preβ and small size α4 HDL subpopulations, and are associated with low plasma HDL levels. These phenotypes can be corrected by excess LCAT. The third category describes bio-engineered apoA-I mutations that induce hypertriglyceridemia that can be corrected by excess lipoprotein lipase and also have defective maturation of HDL. The HDL phenotypes described here may serve in the future for diagnosis, prognoses and potential treatment of abnormalities that affect the biogenesis and functionality of HDL.

Dysfunctional HDL in diabetes mellitus and its role in the pathogenesis of cardiovascular disease

Coronary artery disease, the leading cause of death in the developed and developing countries, is prevalent in diabetes mellitus with 68% cardiovascular disease (CVD)-related mortality. Epidemiological studies suggested inverse correlation between HDL and CVD occurrence. Therefore, low HDL concentration observed in diabetic patients compared to non-diabetic individuals was thought to be one of the primary causes of increased risks of CVD. Efforts to raise HDL level via CETP inhibitors, Torcetrapib and Dalcetrapib, turned out to be disappointing in outcome studies despite substantial increases in HDL-C, suggesting that factors beyond HDL concentration may be responsible for the increased risks of CVD. Therefore, recent studies have focused more on HDL function than on HDL levels. The metabolic environment in diabetes mellitus condition such as hyperglycemia-induced advanced glycation end products, oxidative stress, and inflammation promote HDL dysfunction leading to greater risks of CVD. This review discusses dysfunctional HDL as one of the mechanisms of increased CVD risks in diabetes mellitus through adversely affecting components that support HDL function in cholesterol efflux and LDL oxidation. The dampening of reverse cholesterol transport, a key process that removes cholesterol from lipid-laden macrophages in the arterial wall, leads to increased risks of CVD in diabetic patients. Therapeutic approaches to keep diabetes under control may benefit patients from developing CVD.

Cholesterol efflux and reverse cholesterol transport

Both alterations of lipid/lipoprotein metabolism and inflammatory events contribute to the formation of the atherosclerotic plaque, characterized by the accumulation of abnormal amounts of cholesterol and macrophages in the artery wall. Reverse cholesterol transport (RCT) may counteract the pathogenic events leading to the formation and development of atheroma, by promoting the high-density lipoprotein (HDL)-mediated removal of cholesterol from the artery wall. Recent in vivo studies established the inverse relationship between RCT efficiency and atherosclerotic cardiovascular diseases (CVD), thus suggesting that the promotion of this process may represent a novel strategy to reduce atherosclerotic plaque burden and subsequent cardiovascular events. HDL plays a primary role in all stages of RCT: (1) cholesterol efflux, where these lipoproteins remove excess cholesterol from cells; (2) lipoprotein remodeling, where HDL undergo structural modifications with possible impact on their function; and (3) hepatic lipid uptake, where HDL releases cholesterol to the liver, for the final excretion into bile and feces. Although the inverse association between HDL plasma levels and CVD risk has been postulated for years, recently this concept has been challenged by studies reporting that HDL antiatherogenic functions may be independent of their plasma levels. Therefore, assessment of HDL function, evaluated as the capacity to promote cell cholesterol efflux may offer a better prediction of CVD than HDL levels alone. Consistent with this idea, it has been recently demonstrated that the evaluation of serum cholesterol efflux capacity (CEC) is a predictor of atherosclerosis extent in humans.

HDL biogenesis, remodeling, and catabolism

In this chapter, we review how HDL is generated, remodeled, and catabolized in plasma. We describe key features of the proteins that participate in these processes, emphasizing how mutations in apolipoprotein A-I (apoA-I) and the other proteins affect HDL metabolism. The biogenesis of HDL initially requires functional interaction of apoA-I with the ATP-binding cassette transporter A1 (ABCA1) and subsequently interactions of the lipidated apoA-I forms with lecithin/cholesterol acyltransferase (LCAT). Mutations in these proteins either prevent or impair the formation and possibly the functionality of HDL. Remodeling and catabolism of HDL is the result of interactions of HDL with cell receptors and other membrane and plasma proteins including hepatic lipase (HL), endothelial lipase (EL), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP), apolipoprotein M (apoM), scavenger receptor class B type I (SR-BI), ATP-binding cassette transporter G1 (ABCG1), the F1 subunit of ATPase (Ecto F1-ATPase), and the cubulin/megalin receptor. Similarly to apoA-I, apolipoprotein E and apolipoprotein A-IV were shown to form discrete HDL particles containing these apolipoproteins which may have important but still unexplored functions. Furthermore, several plasma proteins were found associated with HDL and may modulate its biological functions. The effect of these proteins on the functionality of HDL is the topic of ongoing research.

Regulation of high-density lipoprotein metabolism

There is compelling evidence from human population studies that plasma levels of high-density lipoprotein (HDL) cholesterol correlate inversely with cardiovascular risk. Identification of this relationship has stimulated research designed to understand how HDL metabolism is regulated. The ultimate goal of these studies has been to develop HDL-raising therapies that have the potential to decrease the morbidity and mortality associated with atherosclerotic cardiovascular disease. However, the situation has turned out to be much more complex than originally envisaged. This is partly because the HDL fraction consists of multiple subpopulations of particles that vary in terms of shape, size, composition, and surface charge, as well as in their potential cardioprotective properties. This heterogeneity is a consequence of the continual remodeling and interconversion of HDL subpopulations by multiple plasma factors. Evidence that the remodeling of HDLs may impact on their cardioprotective properties is beginning to emerge. This serves to highlight the importance of understanding not only how the remodeling and interconversion of HDL subpopulations is regulated but also how these processes are affected by agents that increase HDL levels. This review provides an overview of what is currently understood about HDL metabolism and how the subpopulation distribution of these lipoproteins is regulated.

Significance of the hydrophobic residues 225-230 of apoA-I for the biogenesis of HDL

We studied the significance of four hydrophobic residues within the 225-230 region of apoA-I on its structure and functions and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of an apoA-I[F225A/V227A/F229A/L230A] mutant in apoA-I⁻/⁻ mice decreased plasma cholesterol, HDL cholesterol, and apoA-I levels. When expressed in apoA-I⁻/⁻ × apoE⁻/⁻ mice, approximately 40% of the mutant apoA-I as well as mouse apoA-IV and apoB-48 appeared in the VLDL/IDL/LDL. In both mouse models, the apoA-I mutant generated small spherical particles of pre-β- and α4-HDL mobility. Coexpression of the apoA-I mutant and LCAT increased and shifted the-HDL cholesterol peak toward lower densities, created normal αHDL subpopulations, and generated spherical-HDL particles. Biophysical analyses suggested that the apoA-I[225-230] mutations led to a more compact folding that may limit the conformational flexibility of the protein. The mutations also reduced the ability of apoA-I to promote ABCA1-mediated cholesterol efflux and to activate LCAT to 31% and 66%, respectively, of the WT control. Overall, the apoA-I[225-230] mutations inhibited the biogenesis of-HDL and led to the accumulation of immature pre-β- and α4-HDL particles, a phenotype that could be corrected by administration of LCAT.

Role of the hydrophobic and charged residues in the 218-226 region of apoA-I in the biogenesis of HDL

We investigated the significance of hydrophobic and charged residues 218-226 on the structure and functions of apoA-I and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of apoA-I[L218A/L219A/V221A/L222A] in apoA-I⁻/⁻ mice decreased plasma cholesterol and apoA-I levels to 15% of wild-type (WT) control mice and generated pre-β- and α4-HDL particles. In apoA-I⁻/⁻ × apoE⁻/⁻ mice, the same mutant formed few discoidal and pre-β-HDL particles that could not be converted to mature α-HDL particles by excess LCAT. Expression of the apoA-I[E223A/K226A] mutant in apoA-I⁻/⁻ mice caused lesser but discrete alterations in the HDL phenotype. The apoA-I[218-222] and apoA-I[E223A/K226A] mutants had 20% and normal capacity, respectively, to promote ABCA1-mediated cholesterol efflux. Both mutants had ∼65% of normal capacity to activate LCAT in vitro. Biophysical analyses suggested that both mutants affected in a distinct manner the structural integrity and plasticity of apoA-I that is necessary for normal functions. We conclude that the alteration of the hydrophobic 218-222 residues of apoA-I disrupts apoA-I/ABCA1 interactions and promotes the generation of defective pre-β particles that fail to mature into α-HDL subpopulations, thus resulting in low plasma apoA-I and HDL. Alterations of the charged 223, 226 residues caused milder but discrete changes in HDL phenotype.

Apolipoprotein A-I exerts bactericidal activity against Yersinia enterocolitica serotype O:3

Apolipoprotein A-I (apoA-I), the main protein component of high density lipoprotein (HDL), is well recognized for its antiatherogenic, antioxidant, and antiinflammatory properties. Here, we report a novel role for apoA-I as a host defense molecule that contributes to the complement-mediated killing of an important gastrointestinal pathogen, Gram-negative bacterium Yersinia enterocolitica. We specifically show that the C-terminal domain of apoA-I is the effector site providing the bactericidal activity. Although the presence of the lipopolysaccharide O-antigen on the bacterial surface is absolutely required for apoA-I to kill the bacteria, apoA-I does not interact with the bacteria directly. To the contrary, exposure of the bacteria by serum proteins triggers apoA-I deposition on the bacterial surface. As our data show that both purified lipid-free and HDL-associated apoA-I displays anti-bacterial potential, apoA-I mimetic peptides may be a promising therapeutic agent for the treatment of certain Gram-negative infections.

Domains of apoE4 required for the biogenesis of apoE-containing HDL

INTRODUCTION. We have studied the functions of truncated apoE4 forms in vitro and in vivo in order to identify the domains of apoE4 required for the biogenesis of apoE-containing high-density lipoprotein (HDL). RESULTS. We have found that apoE4-185, -202, -229, or -259 could promote ATP-binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux in vitro, although less efficiently than Full-length apoE4, and had diminished capacity to activate lecithin cholesterol acyltransferase (LCAT). Formation of HDL in vivo was assessed by various methods following gene transfer in apolipoprotein A-I(-/-) × apoE(-/-) mice. Fast protein liquid chromatography of plasma showed that the truncated apoE forms, except apoE4-185, generated an apoE-containing HDL peak. Two-dimensional gel electrophoresis of plasma and electron microscopy showed that truncated apoE forms generated distinct HDL subpopulations and formed discoidal HDL particles which could be converted to spherical by co-administration of truncated apoE4-202 and LCAT. CONCLUSION. Overall, the in-vivo and in-vitro data are consistent and indicate that apoE4-185 is the shortest truncated form that supports formation of discoidal apoE4-containing HDL particles.

Carboxyl terminus of apolipoprotein A-I (ApoA-I) is necessary for the transport of lipid-free ApoA-I but not prelipidated ApoA-I particles through aortic endothelial cells

High density lipoproteins (HDL) and apolipoprotein A-I (apoA-I) must leave the circulation and pass the endothelium to exert their atheroprotective actions in the arterial wall. We previously demonstrated that the transendothelial transport of apoA-I involves ATP-binding cassette transporter (ABC) A1 and re-secretion of lipidated particles. Transendothelial transport of HDL is modulated by ABCG1 and the scavenger receptor BI (SR-BI). We hypothesize that apoA-I transport is started by the ABCA1-mediated generation of a lipidated particle which is then transported by ABCA1-independent pathways. To test this hypothesis we analyzed the endothelial binding and transport properties of initially lipid-free as well as prelipidated apoA-I mutants. Lipid-free apoA-I mutants with a defective carboxyl-terminal domain showed an 80% decreased specific binding and 90% decreased specific transport by aortic endothelial cells. After prior cell-free lipidation of the mutants, the resulting HDL-like particles were transported through endothelial cells by an ABCG1- and SR-BI-dependent process. ApoA-I mutants with deletions of either the amino terminus or both the amino and carboxyl termini showed dramatic increases in nonspecific binding but no specific binding or transport. Prior cell-free lipidation did not rescue these anomalies. Our findings of stringent structure-function relationships underline the specificity of transendothelial apoA-I transport and suggest that lipidation of initially lipid-free apoA-I is necessary but not sufficient for specific transendothelial transport. Our data also support the model of a two-step process for the transendothelial transport of apoA-I in which apoA-I is initially lipidated by ABCA1 and then further processed by ABCA1-independent mechanisms.

Disruption of the C-terminal helix by single amino acid deletion is directly responsible for impaired cholesterol efflux ability of apolipoprotein A-I Nichinan

Apolipoprotein A-I (apoA-I) Nichinan, a naturally occurring variant with DeltaE235 in the C terminus, is associated with low plasma HDL levels. Here, we investigated the tertiary structure, lipid-binding properties, and ability to induce cellular cholesterol efflux of apoA-I Nichinan and its C-terminal peptide. Thermal and chemical denaturation experiments demonstrated that the DeltaE235 mutation decreased the protein stability compared with wild type (WT). ApoA-I Nichinan exhibited capabilities to bind to or solubilize lipid vesicles that are intermediate to that of WT and a L230P/L233P/Y236P variant in which the C-terminal alpha-helix folding is completely disrupted and forms relatively larger and unstable discoidal complexes, indicating that perturbation of the C-terminal alpha-helical structure by the DeltaE235 mutation leads to reduced lipid binding. Supporting this, apoA-I 209-241/DeltaE235 peptide showed significantly decreased ability to form alpha-helix both in the lipid-free and lipid-bound states, and reduced efficiency to solubilize vesicles. In addition, both apoA-I Nichinan and its C-terminal peptide exhibited reduced activity in ABCA1-mediated cellular cholesterol efflux. Thus, the disruption of the ability of the C-terminal region to form alpha-helix caused by the E235 deletion appears to be the important determinant of impaired lipid binding and cholesterol efflux ability and, consequently, the low plasma HDL levels of apoA-I Nichinan probands.

Transport of lipids by ABC proteins: interactions and implications for cellular toxicity, viability and function

Members of the ATP-binding cassette (ABC) family of membrane-bound transporters are involved in multiple aspects of transport and redistribution of various lipids and their conjugates. Most ABC transporters localize to the plasma membrane; some are associated with liquid-ordered cholesterol-/sphingolipid-rich microdomains, and to a lesser extent the membranes of the Golgi and endoplasmic reticulum. Hence, ABC transporters are well placed to regulate plasma membrane lipid composition and the efflux and redistribution of structural phospholipids and sphingolipids during periods of cellular stress and recovery. ABC transporters can also modulate cellular sensitivity to extrinsic pro-apoptotic signals through regulation of sphingomyelin-ceramide biosynthesis and metabolism. The functionality of ABC transporters is, in turn, modulated by the lipid content of the microdomains in which they reside. Cholesterol, a major membrane microdomain component, is not only a substrate of several ABC transporters, but also regulates ABC activity through its effects on microdomain structure. Several important bioactive lipid mediators and toxic lipid metabolites are also effluxed by ABC transporters. In this review, the complex interactions between ABC transporters and their lipid/sterol substrates will be discussed and analyzed in the context of their relevance to cellular function, toxicity and apoptosis.

Three-dimensional models of HDL apoA-I: implications for its assembly and function

The purpose of this review is to highlight recent advances toward the refinement of a three-dimensional structure for lipid-bound apolipoprotein A-I (apoA-I) on recombinant HDL. Recently, X-ray crystallography has yielded a new structure for full-length, lipid-free apoA-I. Although this approach has not yet been successful in solving the three-dimensional structure of lipid-bound apoA-I, analysis of the X-ray structures has been of immense help in the interpretation of structural data obtained from other methods that yield structural information. Recent studies emphasize the use of mass spectrometry to unambiguously identify cross-linked peptides or to quantify solvent accessibility using hydrogen-deuterium exchange. The combination of mass spectrometry, molecular modeling, molecular dynamic analysis, and small-angle X-ray diffraction has provided additional structural information on apoA-I folding that complements previous approaches.

Discrete roles of apoA-I and apoE in the biogenesis of HDL species: lessons learned from gene transfer studies in different mouse models

Using adenovirus-mediated gene transfer in apolipoprotein A-I (apoA-I)-deficient mice, we have established that apoA-I mutations inhibit discrete steps in a pathway that leads to the biogenesis and remodeling of high-density lipoprotein (HDL). To this point, five discrete categories of apoA-I mutants have been characterized that may affect the interactions of apoA-I with ATP-binding cassette superfamily A, member 1 (ABCA1) or lecithin:cholesterol acyl transferase (LCAT) or may influence the plasma phospholipid transfer protein activity or may cause various forms of dyslipidemia. Biogenesis of HDL is not a unique property of apoA-I. Using adenovirus-mediated gene transfer of apoE in apoA-I- or ABCA1-deficient mice, we have established that apolipoprotein E (apoE) also participates in a novel pathway of biogenesis of apoE-containing HDL particles. This process requires the functions of the ABCA1 lipid transporter and LCAT, and it is promoted by substitution of hydrophobic residues in the 261 to 269 region of apoE by Ala. The apoE-containing HDL particles formed in the circulation may have atheroprotective properties. ApoE-containing HDL may also have important biological functions in the brain that confer protection from Alzheimer's disease.

Naturally occurring and bioengineered apoA-I mutations that inhibit the conversion of discoidal to spherical HDL: the abnormal HDL phenotypes can be corrected by treatment with LCAT

In the present study we have used adenovirus-mediated gene transfer of apoA-I (apolipoprotein A-I) mutants in apoA-I-/- mice to investigate how structural mutations in apoA-I affect the biogenesis and the plasma levels of HDL (high-density lipoprotein). The natural mutants apoA-I(R151C)Paris, apoA-I(R160L)Oslo and the bioengineered mutant apoA-I(R149A) were secreted efficiently from cells in culture. Their capacity to activate LCAT (lecithin:cholesterol acyltransferase) in vitro was greatly reduced, and their ability to promote ABCA1 (ATP-binding cassette transporter A1)-mediated cholesterol efflux was similar to that of WT (wild-type) apoA-I. Gene transfer of the three mutants in apoA-I-/- mice generated aberrant HDL phenotypes. The total plasma cholesterol of mice expressing the apoA-I(R160L)Oslo, apoA-I(R149A) and apoA-I(R151C)Paris mutants was reduced by 78, 59 and 61% and the apoA-I levels were reduced by 68, 64 and 55% respectively, as compared with mice expressing the WT apoA-I. The CE (cholesteryl ester)/TC (total cholesterol) ratio of HDL was decreased and the apoA-I was distributed in the HDL3 region. apoA-I(R160L)Oslo and apoA-I(R149A) promoted the formation of prebeta1 and alpha4-HDL subpopulations and gave a mixture of discoidal and spherical particles. apoA-I(R151C)Paris generated subpopulations of different sizes that migrate between prebeta and alpha-HDL and formed mostly spherical and a few discoidal particles. Simultaneous treatment of mice with adenovirus expressing any of the three mutants and human LCAT normalized plasma apoA-I, HDL cholesterol levels and the CE/TC ratio. It also led to the formation of spherical HDL particles consisting mostly of alpha-HDL subpopulations of larger size. The correction of the aberrant HDL phenotypes by treatment with LCAT suggests a potential therapeutic intervention for HDL abnormalities that result from specific mutations in apoA-I.