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Jonathan D Smith

Publications and source records attributed to Jonathan D Smith.

At least 19 recordsLinked to original sources
PubMed2024

Membrane-bound O-acyltransferase 7 (MBOAT7) shapes lysosomal lipid homeostasis and function to control alcohol-associated liver injury.

Recent genome-wide association studies (GWAS) have identified a link between single-nucleotide polymorphisms (SNPs) near the MBOAT7 gene and advanced liver diseases. Specifically, the common MBOAT7 variant (rs641738) associated with reduced MBOAT7 expression is implicated in non-alcoholic fatty liver disease (NAFLD), alcohol-associated liver disease (ALD), and liver fibrosis. However, the precise mechanism underlying MBOAT7-driven liver disease progression remains elusive. Previously, we identified MBOAT7-driven acylation of lysophosphatidylinositol lipids as key mechanism suppressing the progression of NAFLD (Gwag et al., 2019). Here, we show that MBOAT7 loss of function promotes ALD via reorganization of lysosomal lipid homeostasis. Circulating levels of MBOAT7 metabolic products are significantly reduced in heavy drinkers compared to healthy controls. Hepatocyte- (Mboat7-HSKO), but not myeloid-specific (Mboat7-MSKO), deletion of Mboat7 exacerbates ethanol-induced liver injury. Lipidomic profiling reveals a reorganization of the hepatic lipidome in Mboat7-HSKO mice, characterized by increased endosomal/lysosomal lipids. Ethanol-exposed Mboat7-HSKO mice exhibit dysregulated autophagic flux and lysosomal biogenesis, associated with impaired transcription factor EB-mediated lysosomal biogenesis and autophagosome accumulation. This study provides mechanistic insights into how MBOAT7 influences ALD progression through dysregulation of lysosomal biogenesis and autophagic flux, highlighting hepatocyte-specific MBOAT7 loss as a key driver of ethanol-induced liver injury.

Animals↗
PubMed2006

Transcriptome profile of macrophages from atherosclerosis-sensitive and atherosclerosis-resistant mice.

We performed a strain intercross between two apoE-deficient mouse strains with a large difference in lesion susceptibility and measured aortic root lesion area in 98 female F(2) progeny. Total RNA was prepared from bone marrow-derived macrophages, and RNA from the five mice with the smallest and largest lesions were used for microarray gene expression profiling. Remarkably, approximately 5% of the 12,288 expressed transcripts were differentially expressed in the atherosclerosis-susceptible and atherosclerosis-resistant bone marrow-derived macrophages (unadjusted p < 0.05), thus defining the transcriptome of macrophages associated with atherosclerosis susceptibility. Using more stringent criteria of twofold or greater change and p < 0.01, 116 and 70 transcripts were overexpressed in lesion-prone and lesion-resistant bone marrow-derived macrophages, respectively. Transcription factor binding site analysis identified two promoter elements that were found more often in the genes overexpressed in the large-lesion group, and one promoter element that was found more often in the small-lesion group. The combination of this expression profiling data with the genetic method of quantitative trait locus mapping should give powerful insights into the genes that affect atherosclerosis susceptibility in mice.

Alternative Splicing↗
PubMed2006

Apolipoprotein A-I lysine modification: effects on helical content, lipid binding and cholesterol acceptor activity.

We examined the role of the positively charged lysine residues in apoAI by chemical modification. Lysine modification by reductive methylation did not alter apoAI's net charge, secondary or tertiary structure as observed by circular dichroism and trytophan fluorescence, respectively, or have much impact on lipid binding or ABCA1-dependent cholesterol acceptor activity. Acetylation of lysine residues lowered the isoelectric point of apoAI, altered its secondary and tertiary structure, and led to a 40% decrease in cholesterol acceptor activity, while maintaining 93% of its lipid binding activity. Exhaustive lysine acetoacetylation lowered apoAI's isoelectric point, profoundly disrupted its secondary and tertiary structure, and led to 90% and 82% reductions in cholesterol acceptor and lipid binding activities, respectively. The dose-dependent acetoacetylation of an increasing proportion of apoAI lysine residues demonstrated that cholesterol acceptor activity was more sensitive to this modification than lipid binding activity, suggesting that apoAI lysine positive charges play an important role in ABCA1 mediated lipid efflux beyond the role needed to maintain alpha-helical content and lipid binding activity.

Acetylation↗
PubMed2005

Identification of the cAMP-responsive enhancer of the murine ABCA1 gene: requirement for CREB1 and STAT3/4 elements.

OBJECTIVE: To determine the mechanism by which expression of the murine ABCA1 gene is highly induced by cAMP analogues. METHODS AND RESULTS: ABCA1 mRNA turnover cannot account for its induction by cAMP. Thus cAMP induction of ABCA1 mRNA occurs at a transcriptional level. Shotgun cloning DNA fragments from the murine ABCA1 locus identified a strong cAMP responsive enhancer located in the first intron, which led to 25- to 100-fold cAMP-mediated induction of reporter gene activity. Deletions and mutations of this enhancer led to the identification a cAMP-responsive element (CRE) that was essential for the cAMP induction. Furthermore, the capacity of this CRE site to mediate the cAMP induction required the presence of a STAT3/4 element located 81 bp away. A dominant-negative CREB expression vector inhibited the cAMP induction of ABCA1, demonstrating that CREB was required for cAMP induction of ABCA1 expression in RAW264.7 cells. CONCLUSIONS: Phospho-CREB1 controls the cAMP-mediated induction of murine ABCA1 gene expression through a CRE site acting in cooperation with a nearby STAT element. This CRE site is not conserved in the human ABCA1 gene, explaining why human ABCA1 is not strongly stimulated by cAMP analogs.

ATP Binding Cassette Transporter 1↗
PubMed2005

Atherosclerosis susceptibility loci identified from a strain intercross of apolipoprotein E-deficient mice via a high-density genome scan.

OBJECTIVE: Apolipoprotein (apo) E-deficient mice are hypercholesterolemic and develop atherosclerosis on low-fat chow diets; however, the genetic background strain has a large effect on atherosclerosis susceptibility. This study aimed to determine the genetic regions associated with strain effects on lesion area. METHODS AND RESULTS: We performed a strain intercross between atherosclerosis sensitive DBA/2 and atherosclerosis resistant AKR apoE-deficient mice. Aortic root lesion area, total cholesterol, body weights, and complete blood counts were ascertained for 114 male and 95 female F2 progeny. A high-density genome scan was performed using a mouse single nucleotide polymorphism chip yielding 1967 informative polymorphic markers. Quantitative trait locus (QTL) statistical analyses were performed. Novel loci associated with lesion or log lesion area were identified for the female and male F2 cohorts. The atherosclerosis QTLs in female mice reside on chromosomes 15, 5, 3, and 13, and in male mice on chromosomes 17, 18, and 2. QTL were also identified for body weight, total cholesterol, and blood count parameters. CONCLUSIONS: Loci were identified for atherosclerosis susceptibility in a strain intercross study. The identity of the responsible genes at these loci remains to be determined.

Animals↗
PubMed2005

A novel folding intermediate state for apolipoprotein A-I: role of the amino and carboxy termini.

Intramolecular interactions between the amino and carboxy termini of apolipoprotein A-I (apoAI) are believed to stabilize the helix bundle conformation of the protein. During lipid assembly the protein undergoes conformational changes that result in an exposure of the carboxy terminus and its insertion into the lipid phase. To determine the role of the two termini in the energetics of unfolding, we studied the guanidine-hydrochloride-induced unfolding and refolding of apoAI as well as its N-terminal deletion (del[1-43]), C-terminal deletion (del[186-243]), and the double deletion containing only the central residues 44-185. Thermodynamic analysis of the equilibrium unfolding measured by fluorescence spectroscopy revealed the presence of an intermediate unfolded state (I(equil)) in addition to the native (N) and unfolded states. Refolding kinetics of apoAI, measured by stopped-flow circular dichroism, revealed two kinetic intermediates, I(burst) and I(recovery). Computer modeling suggested that the first resembles the partially unfolded protein, whereas the second overlaps with the native state of the protein. The free energy changes for the N --> I(equil) transition of the N-terminal and double deletions were lower then that of the full-length form, whereas that for the C-terminal deletion was higher. Our findings suggest that the N-terminus of apoAI stabilizes the native state of the protein by increasing the Eyring energy barrier for the N --> I(equil) unfolding transition; whereas the carboxyl terminus destabilizes that state.

Apolipoprotein A-I↗
PubMed2005

Reevaluation of the role of the multidrug-resistant P-glycoprotein in cellular cholesterol homeostasis.

The multidrug resistance P-glycoprotein (P-gp) was recently proposed to redistribute cholesterol in the plasma membrane, suggesting that P-gp could modulate cholesterol efflux to cholesterol acceptors. To address this hypothesis and to reevaluate the role of P-gp in cholesterol homeostasis, we first analyzed the role of P-gp expression on cholesterol efflux in P-gp stably transfected drug-selected LLC-MDR1 cells. Cholesterol efflux to methyl-beta-cyclodextrin (CD) was 4-fold higher in LLC-MDR1 cells compared with control LLC-PK1 cells, indicating that the accessible pool of plasma membrane cholesterol was increased by P-gp expression. However, using the P-gp-inducible cells lines HeLa MDR-Tet and 77.1 MDR-Tet, cholesterol efflux to CD, apolipoprotein A-I, or HDL was not associated with P-gp expression. In addition, we did not observe any effect of P-gp expression on cellular free and esterified cholesterol content, cholesteryl ester uptake from LDL and HDL particles, or acyl-CoA:cholesterol acyltransferase activity. Therefore, we conclude that P-gp expression does not play a major role in cholesterol homeostasis in P-gp-inducible cells and that the effects of P-gp on cholesterol homeostasis previously described in drug-selected cells might result from non-P-gp pathways that were also induced by selection for drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Tyrosine modification is not required for myeloperoxidase-induced loss of apolipoprotein A-I functional activities.

Apolipoprotein A-I (apoAI), the major protein of high density lipoprotein, plays an important role in reverse cholesterol transport via its activity as an ABCA1-dependent acceptor of cellular cholesterol. We reported recently that myeloperoxidase (MPO) modification of apoAI inhibits its ABCA1-dependent cholesterol acceptor activity (Zheng, L., Nukuna, B., Brennan, M. L., Sun, M., Goormastic, M., Settle, M., Schmitt, D., Fu, X., Thomson, L., Fox, P. L., Ischiropoulos, H., Smith, J. D., Kinter, M., and Hazen, S. L. (2004) J. Clin. Invest. 114, 529-541). We also reported that MPO-mediated chlorination preferentially modifies two of the seven tyrosines in apoAI, and loss of parent peptides containing these residues dose-dependently correlates with loss in ABCA1-mediated cholesterol acceptor activity (Zheng, L., Settle, M., Brubaker, G., Schmitt, D., Hazen, S. L., Smith, J. D., and Kinter, M. (2005) J. Biol. Chem. 280, 38-47). To determine whether oxidative modification of apoA-I tyrosine residues was responsible for the MPO-mediated inactivation of cholesterol acceptor activity, we made recombinant apoAI with site-specific substitutions of all seven tyrosine residues to phenylalanine. ApoAI and the tyrosine-free apoAI were equally susceptible to dose-dependent MPO-mediated loss of ABCA1-dependent cholesterol acceptor activity, as well as lipid binding activity. MPO modification altered the migration of apoAI on SDS gels and decreased its alpha-helix content. MPO-induced modification also targeted apoAI tryptophan and lysine residues. Specifically, we detected apoAI tryptophan oxidation to mono- and dihydroxytryptophan and apoAI lysine modification to chlorolysine and 2-aminoadipic acid. Thus, tyrosine modification of apoAI is not required for its MPO-mediated inhibition of cholesterol acceptor activity.

ATP Binding Cassette Transporter 1↗
PubMed2005

Expression of the carrier protein apolipoprotein D in the mouse inner ear.

The cochlear portion of the inner ear converts movements produced by sound waves into electrical impulses. Transcripts enriched in the cochlea are likely to have an important role in hearing. In this paper, we report that microarray analyses of the Soares NMIE inner ear library revealed cochlear enriched expression of apolipoprotein D (apoD), a glycoprotein and member of the lipocalin family that transport small hydrophobic ligands. The cochlear enriched expression of Apod was validated by quantitative real time PCR analysis. To investigate the function of apoD in the inner ear the transcript and protein were localised in the cochlea. Apod messenger RNA (mRNA) expression was localised to the spiral ligament and spiral limbus, particularly in the suprastrial and supralimbral regions. The apoD protein was detected in the spiral ligament, spiral limbus and also in the outer hair cells of the organ of Corti. Investigation of cell lines exhibiting characteristics of hair and supporting cells revealed no Apod mRNA expression in these cells. This suggests transport of the protein within the cochlea, followed by internalisation into outer hair cells. The spiral limbus and ligament contain subpopulations of fibrocytes that are intimately involved in regulation of ion balance in the cochlear fluids and type I, II and III fibrocytes of the spiral ligament were all shown to be positive for apoD protein. On the basis of these results it was hypothesised that apoD could be involved in maintaining cochlear fluid homeostasis. To determine whether the apoD gene product was important for normal auditory function the hearing ability of an apoD knockout mouse was tested. The mouse was found to have a hearing threshold that was not significantly different to the control strain.

Animals↗
PubMed2005

Drug library screen to identify compounds that decrease secreted Abeta from a human cell line.

In order to discover compounds that may be useful in the prevention of Alzheimer disease, a drug library was screened for drugs that could decrease amyloid beta peptide (Abeta) accumulation secreted from a human CNS-derived cell line. Of the 2160 compounds subjected to a primary screen, 16, or 0.74%, reduced Abeta accumulation by at least 40%. Seven of these compounds were confirmed to be effective in a secondary screen using each compound at a dose of 5 microM. Three of these seven compounds were more effective than the others at reducing Abeta levels in a tertiary screen, and led to 68 to 85% reductions in total Abeta, at the 25 microM dosage. The effects of these three drugs on secreted Abeta40, Abeta42, and sAPPalpha were also determined. Thus, we have identified lead compounds that may be useful for subsequent studies to determine the mechanism of action of each drug, as well as for pre-clinical studies to determine whether each of these drugs is safe and effective in vivo.

Amyloid beta-Peptides↗
PubMed2004

Localization of nitration and chlorination sites on apolipoprotein A-I catalyzed by myeloperoxidase in human atheroma and associated oxidative impairment in ABCA1-dependent cholesterol efflux from macrophages.

We recently reported that apolipoprotein A-I (apoA-I), the major protein component of high density lipoprotein, is a selective target for myeloperoxidase (MPO)-catalyzed nitration and chlorination in both and serum of subjects with cardiovascular disease. We further showed that the extent of both apoA-I nitration and chlorination correlated with functional impairment in reverse cholesterol transport activity of the isolated lipoprotein. Herein we used tandem mass spectrometry to map the sites of MPO-mediated apoA-I nitration and chlorination in vitro and in vivo and to relate the degree of site-specific modifications to loss of apoA-I lipid binding and cholesterol efflux functions. Of the seven tyrosine residues in apoA-I, Tyr-192, Tyr-166, Tyr-236, and Tyr-29 were nitrated and chlorinated in MPO-mediated reactions. Site-specific liquid chromatography-mass spectrometry quantitative analyses demonstrated that the favored modification site following exposure to MPO-generated oxidants is Tyr-192. MPO-dependent nitration and chlorination both proceed with Tyr-166 as a secondary site and with Tyr-236 and Tyr-29 modified only minimally. Parallel functional studies demonstrated dose-dependent losses of ABCA1-dependent cholesterol acceptor and lipid binding activities with apoA-I modification by MPO. Finally tandem mass spectrometry analyses showed that apoA-I in human atherosclerotic tissue is nitrated at the MPO-preferred sites, Tyr-192 and Tyr-166. The present studies suggest that site-specific modifications of apoA-I by MPO are associated with impaired lipid binding and ABCA1-dependent cholesterol acceptor functions, providing a molecular mechanism that likely contributes to the clinical link between MPO levels and cardiovascular disease risk.

ATP Binding Cassette Transporter 1↗
PubMed2004

Cyclosporin A traps ABCA1 at the plasma membrane and inhibits ABCA1-mediated lipid efflux to apolipoprotein A-I.

OBJECTIVE: ABCA1 mediates cellular cholesterol and phospholipid efflux to apolipoprotein A-I and other apolipoprotein acceptors. In this study, we analyzed the effect of the immunosuppressant cyclosporin A on the ABCA1-mediated lipid effluxes reactions. METHODS AND RESULTS: Cyclosporin A acted as a potent inhibitor of ABCA1 activity in several cell lines. Using the RAW264.7 mouse macrophage cell line, in which ABCA1 and its associated cholesterol efflux activity are inducible by cAMP analogues, cyclosporin A inhibition of cholesterol efflux to apolipoprotein A-I was rapidly reversible after its removal from the culture media, implying that ABCA1 levels were not drastically reduced by cyclosporin A. In fact, cyclosporin A treatment decreased ABCA1 turnover and yielded a 2-fold increase in cell-surface ABCA1. Despite the increase in cell-surface ABCA1, cyclosporin A decreased apolipoprotein A-I uptake, resecretion, and degradation in RAW cells. Finally, consistent with the inhibition of ABCA1 in vitro, cyclosporin A treatment induced a 33% reduction of high-density lipoprotein (HDL) levels in mice. CONCLUSIONS: ABCA1 inhibition by cyclosporin A supports a role for ABCA1 endocytic trafficking in ABCA1-mediated lipid efflux and could explain in part the low HDL levels observed in some patients with transplants.

ATP Binding Cassette Transporter 1↗
PubMed2004

Similar promotion of Abeta1-42 fibrillogenesis by native apolipoprotein E epsilon3 and epsilon4 isoforms.

The apolipoprotein E epsilon4 allele contributes to the genetic susceptibility underlying a large proportion (~40-60%) of typical, sporadic Alzheimer disease. Apolipoprotein E deficient mice made transgenic for human apolipoprotein E epsilon4 accumulate excess cerebral amyloid when compared to similarly prepared mice expressing human apolipoprotein E epsilon3. Therefore, it is important to search for relevant interactions(s) between apolipoprotein E epsilon4 and Abeta in order to clarify the biological role for apolipoprotein E epsilon4 in Alzheimer disease. Using a thioflavine T (ThT)-based assay, we have investigated the effects of native human apolipoprotein E isoforms on the kinetics of Abeta fibrillogenesis. No obvious profibrillogenic activity was detected in Abeta1-40-based assays of any native apolipoprotein E isoform. However, when ThT assays were repeated using Abeta1-42, modest, but statistically significant, profibrillogenic activity was detected in both apolipoprotein E epsilon3- and apolipoprotein E epsilon4-containing media and was similar in magnitude for the two isoforms. These data demonstrate that native apolipoprotein E possesses "pathological chaperone"-type activity for Abeta: in other words, the data indicate that a chaperone-like misfolding reaction can occur between native apolipoprotein E and Abeta. However, the equipotent activities of the apolipoprotein E epsilon3 and epsilon4 isoforms suggests the possibility that either extended co-incubation of apolipoprotein E and Abeta, or, perhaps, the inclusion in the reaction of other fibrillogenesis-modulation co-factors (such as metal ions, or inflammatory mediators such as reactive oxygen species, alpha2-macroglobulin, apolipoprotein J, etc.) may be required for modeling in vitro the apolipoprotein E-isoform-specific-regulation of extracellular Abeta accumulation that occurs in vivo. Alternatively, other events, such as differential apolipoprotein E-isoform-mediated clearance of Abeta or of apolipoprotein E/Abeta complexes may underlie apolipoprotein E-isoform-dependent Abeta accumulation.

Journal Article↗
PubMed2004

Identification of a novel enhancer of brain expression near the apoE gene cluster by comparative genomics.

Comparative analysis of the human and mouse genomic sequences downstream of the apolipoprotein E gene (APOE) revealed a highly conserved element with previously undefined function. In reporter gene transfection studies, this element which is located approximately 42 kb distal to APOE was found to have silencer activity in a subset of cell lines examined. Analysis of transgenic mice containing a fusion construct linking this distal 631 bp conserved element to a reporter gene comprised of the human APOE gene with its proximal promoter resulted in robust brain expression of the transgenic human apoE mRNA in three independent transgenic lines, supporting the identification of a novel brain controlling region (BCR). Further studies using immunohistochemistry revealed widespread human apoE localization throughout the brains of the BCR-apoE transgenic mice with prominent expression in the cortex and diencephalon. In addition, double-label immunofluorescence performed on brain sections and cultures of primary cortical cells localized human apoE protein to cortical neurons and microglia. These studies demonstrate that comparative sequence analysis is a successful strategy to predict candidate regulatory regions in vivo, although they do not imply that this element controls apoE expression physiologically.

Animals↗
PubMed2004

ABCA1 mediates concurrent cholesterol and phospholipid efflux to apolipoprotein A-I.

Prior studies provide data supporting the notion that ATP binding cassette transporter A1 (ABCA1) promotes lipid efflux to extracellular acceptors in a two-step process: first, ABCA1 mediates phospholipid efflux to an apolipoprotein, and second, this apolipoprotein-phospholipid complex accepts free cholesterol in an ABCA1-independent manner. In the current study using RAW264.7 cells, ABCA1-mediated free cholesterol and phospholipid efflux to apolipoprotein A-I (apoA-I) were tightly coupled to each other both temporally and after treatment with ABCA1 inhibitors. The time course and temperature dependence of ABCA1-mediated lipid efflux to apoA-I support a role for endocytosis in this process. Cyclodextrin treatment of RAW264.7 cells partially inhibited 8Br-cAMP-induced efflux of free cholesterol and phospholipid to apoA-I. ABCA1-expressing cells are more sensitive to cell damage by high-dose cyclodextrin and vanadate, leading to increased lactate dehydrogenase leakage and phospholipid release even in the absence of the acceptor apoA-I. Finally, we could not reproduce a two-step effect on lipid efflux using conditioned medium from ABCA1-expressing cells pretreated with cyclodextrin.

ATP Binding Cassette Transporter 1↗
PubMed2004

Aging, gender and APOE isotype modulate metabolism of Alzheimer's Abeta peptides and F-isoprostanes in the absence of detectable amyloid deposits.

Aging and apolipoprotein E (APOE) isoform are among the most consistent risks for the development of Alzheimer's disease (AD). Metabolic factors that modulate risk have been elusive, though oxidative reactions and their by-products have been implicated in human AD and in transgenic mice with overt histological amyloidosis. We investigated the relationship between the levels of endogenous murine amyloid beta (Abeta) peptides and the levels of a marker of oxidation in mice that never develop histological amyloidosis [i.e. APOE knockout (KO) mice with or without transgenic human APOEepsilon3 or human APOEepsilon4 alleles]. Aging-, gender-, and APOE-genotype-dependent changes were observed for endogenous mouse brain Abeta40 and Abeta42 peptides. Levels of the oxidized lipid F2-isoprostane (F2-isoPs) in the brains of the same animals as those used for the Abeta analyses revealed aging- and gender-dependent changes in APOE KO and in human APOEepsilon4 transgenic KO mice. Human APOEepsilon3 transgenic KO mice did not exhibit aging- or gender-dependent increases in F2-isoPs. In general, the changes in the levels of brain F2-isoPs in mice according to age, gender, and APOE genotype mirrored the changes in brain Abeta levels, which, in turn, paralleled known trends in the risk for human AD. These data indicate that there exists an aging-dependent, APOE-genotype-sensitive rise in murine brain Abeta levels despite the apparent inability of the peptide to form histologically detectable amyloid. Human APOEepsilon3, but not human APOEepsilon4, can apparently prevent the aging-dependent rise in murine brain Abeta levels, consistent with the relative risk for AD associated with these genotypes. The fidelity of the brain Abeta/F2-isoP relationship across multiple relevant variables supports the hypothesis that oxidized lipids play a role in AD pathogenesis, as has been suggested by recent evidence that F2-isoPs can stimulate Abeta generation and aggregation.

Aging↗
PubMed2004

Apolipoprotein A-I is a selective target for myeloperoxidase-catalyzed oxidation and functional impairment in subjects with cardiovascular disease.

In recent studies we demonstrated that systemic levels of protein-bound nitrotyrosine (NO(2)Tyr) and myeloperoxidase (MPO), a protein that catalyzes generation of nitrating oxidants, serve as independent predictors of atherosclerotic risk, burden, and incident cardiac events. We now show both that apolipoprotein A-I (apoA-I), the primary protein constituent of HDL, is a selective target for MPO-catalyzed nitration and chlorination in vivo and that MPO-catalyzed oxidation of HDL and apoA-I results in selective inhibition in ABCA1-dependent cholesterol efflux from macrophages. Dramatic selective enrichment in NO(2)Tyr and chlorotyrosine (ClTyr) content within apoA-I recovered from serum and human atherosclerotic lesions is noted, and analysis of serum from sequential subjects demonstrates that the NO(2)Tyr and ClTyr contents of apoA-I are markedly higher in individuals with cardiovascular disease (CVD). Analysis of circulating HDL further reveals that higher NO(2)Tyr and ClTyr contents of the lipoprotein are each significantly associated with diminished ABCA1-dependent cholesterol efflux capacity of the lipoprotein. MPO as a likely mechanism for oxidative modification of apoA-I in vivo is apparently facilitated by MPO binding to apoA-I, as revealed by cross-immunoprecipitation studies in plasma, recovery of MPO within HDL-like particles isolated from human atheroma, and identification of a probable contact site between the apoA-I moiety of HDL and MPO. To our knowledge, the present results provide the first direct evidence for apoA-I as a selective target for MPO-catalyzed oxidative modification in human atheroma. They also suggest a potential mechanism for MPO-dependent generation of a proatherogenic dysfunctional form of HDL in vivo.

ATP Binding Cassette Transporter 1↗