CRISPR/Cas9-Mediated Gene Editing in Human iPSC-Derived Macrophage Reveals Lysosomal Acid Lipase Function in Human Macrophages-Brief Report.

OBJECTIVE: To gain mechanistic insights into the role of LIPA (lipase A), the gene encoding LAL (lysosomal acid lipase) protein, in human macrophages. APPROACH AND RESULTS: We used CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9) technology to knock out LIPA in human induced pluripotent stem cells and then differentiate to macrophage (human-induced pluripotent stem cells-derived macrophage [IPSDM]) to explore the human macrophage LIPA loss-of-function phenotypes. LIPA was abundantly expressed in monocyte-derived macrophages and was markedly induced on IPSDM differentiation to comparable levels as in human monocyte-derived macrophage. IPSDM with knockout of LIPA (LIPA-/-) had barely detectable LAL enzymatic activity. Control and LIPA-/- IPSDM were loaded with [3H]-cholesteryl oleate-labeled AcLDL (acetylated low-density lipoprotein) followed by efflux to apolipoprotein A-I. Efflux of liberated [3H]-cholesterol to apolipoprotein A-I was abolished in LIPA-/- IPSDM, indicating deficiency in LAL-mediated lysosomal cholesteryl ester hydrolysis. In cells loaded with [3H]-cholesterol-labeled AcLDL, [3H]-cholesterol efflux was, however, not different between control and LIPA-/- IPSDM. ABCA1 (ATP-binding cassette, subfamily A, member 1) expression was upregulated by AcLDL loading but to a similar extent between control and LIPA-/- IPSDM. In nonlipid loaded state, LIPA-/- IPSDM had high levels of cholesteryl ester mass compared with minute amounts in control IPSDM. Yet, with AcLDL loading, overall cholesteryl ester mass was increased to similar levels in both control and LIPA-/- IPSDM. LIPA-/- did not impact lysosomal apolipoprotein-B degradation or expression of IL1B, IL6, and CCL5. CONCLUSIONS: LIPA-/- IPSDM reveals macrophage-specific hallmarks of LIPA deficiency. CRISPR/Cas9 and IPSDM provide important tools to study human macrophage biology and more broadly for future studies of disease-associated LIPA genetic variation in human macrophages.

Overexpression and deletion of phospholipid transfer protein reduce HDL mass and cholesterol efflux capacity but not macrophage reverse cholesterol transport.

Phospholipid transfer protein (PLTP) may affect macrophage reverse cholesterol transport (mRCT) through its role in the metabolism of HDL. Ex vivo cholesterol efflux capacity and in vivo mRCT were assessed in PLTP deletion and PLTP overexpression mice. PLTP deletion mice had reduced HDL mass and cholesterol efflux capacity, but unchanged in vivo mRCT. To directly compare the effects of PLTP overexpression and deletion on mRCT, human PLTP was overexpressed in the liver of wild-type animals using an adeno-associated viral (AAV) vector, and control and PLTP deletion animals were injected with AAV-null. PLTP overexpression and deletion reduced plasma HDL mass and cholesterol efflux capacity. Both substantially decreased ABCA1-independent cholesterol efflux, whereas ABCA1-dependent cholesterol efflux remained the same or increased, even though preß HDL levels were lower. Neither PLTP overexpression nor deletion affected excretion of macrophage-derived radiocholesterol in the in vivo mRCT assay. The ex vivo and in vivo assays were modified to gauge the rate of cholesterol efflux from macrophages to plasma. PLTP activity did not affect this metric. Thus, deviations in PLTP activity from the wild-type level reduce HDL mass and ex vivo cholesterol efflux capacity, but not the rate of macrophage cholesterol efflux to plasma or in vivo mRCT.

Knockout of Adamts7, a novel coronary artery disease locus in humans, reduces atherosclerosis in mice.

BACKGROUND: Genome-wide association studies have established ADAMTS7 as a locus for coronary artery disease in humans. However, these studies fail to provide directionality for the association between ADAMTS7 and coronary artery disease. Previous reports have implicated ADAMTS7 in the regulation of vascular smooth muscle cell migration, but a role for and the direction of impact of this gene in atherogenesis have not been shown in relevant model systems. METHODS AND RESULTS: We bred an Adamts7 whole-body knockout mouse onto both the Ldlr and Apoe knockout hyperlipidemic mouse models. Adamts7(-/-)/Ldlr(-/-) and Adamts7(-/-)/Apoe(-/-) mice displayed significant reductions in lesion formation in aortas and aortic roots compared with controls. Adamts7 knockout mice also showed reduced neointimal formation after femoral wire injury. Adamts7 expression was induced in response to injury and hyperlipidemia but was absent at later time points, and primary Adamts7 knockout vascular smooth muscle cells showed reduced migration in the setting of tumor necrosis factor-α stimulation. ADAMTS7 localized to cells positive for smooth muscle cell markers in human coronary artery disease lesions, and subcellular localization studies in cultured vascular smooth muscle cells placed ADAMTS7 at the cytoplasm and cell membrane, where it colocalized with markers of podosomes. CONCLUSIONS: These data represent the first in vivo experimental validation of the association of Adamts7 with atherogenesis, likely through modulation of vascular cell migration and matrix in atherosclerotic lesions. These results demonstrate that Adamts7 is proatherogenic, lending directionality to the original genetic association and supporting the concept that pharmacological inhibition of ADAMTS7 should be atheroprotective in humans, making it an attractive target for novel therapeutic interventions.

Macrophage sortilin promotes LDL uptake, foam cell formation, and atherosclerosis.

RATIONALE: Noncoding gene variants at the SORT1 locus are strongly associated with low-density lipoprotein cholesterol (LDL-C) levels, as well as with coronary artery disease. SORT1 encodes a protein called sortilin, and hepatic sortilin modulates LDL metabolism by targeting apolipoprotein B-containing lipoproteins to the lysosome. Sortilin is also expressed in macrophages, but its role in macrophage uptake of LDL and in atherosclerosis independent of plasma LDL-C levels is unknown. OBJECTIVE: To determine the effect of macrophage sortilin expression on LDL uptake, foam cell formation, and atherosclerosis. METHODS AND RESULTS: We crossed Sort1(-/-) mice onto a humanized Apobec1(-/-); hAPOB transgenic background and determined that Sort1 deficiency on this background had no effect on plasma LDL-C levels but dramatically reduced atherosclerosis in the aorta and aortic root. To test whether this effect was a result of macrophage sortilin deficiency, we transplanted Sort1(-/-);LDLR(-/-) or Sort1(+/+);LDLR(-/-) bone marrow into Ldlr(-/-) mice and observed a similar reduction in atherosclerosis in mice lacking hematopoetic sortilin without an effect on plasma LDL-C levels. In an effort to determine the mechanism by which hematopoetic sortilin deficiency reduced atherosclerosis, we found no effect of sortilin deficiency on macrophage recruitment or lipopolysaccharide-induced cytokine release in vivo. In contrast, sortilin-deficient macrophages had significantly reduced uptake of native LDL ex vivo and reduced foam cell formation in vivo, whereas sortilin overexpression in macrophages resulted in increased LDL uptake and foam cell formation. CONCLUSIONS: Macrophage sortilin deficiency protects against atherosclerosis by reducing macrophage uptake of LDL. Sortilin-mediated uptake of native LDL into macrophages may be an important mechanism of foam cell formation and contributor to atherosclerosis development.

Peroxisome proliferator-activated receptor-α activation promotes macrophage reverse cholesterol transport through a liver X receptor-dependent pathway.

OBJECTIVE: Peroxisome proliferator-activated receptor-α (PPARα) activation has been shown in vitro to increase macrophage cholesterol efflux, the initial step in reverse cholesterol transport (RCT). However, it remains unclear whether PPARα activation promotes macrophage RCT in vivo. METHODS AND RESULTS: We demonstrated that a specific potent PPARα agonist GW7647 inhibited atherosclerosis and promoted macrophage RCT in hypercholesterolemic mice expressing the human apolipoprotein A-I (apoA-I) gene. We compared the effect of GW7647 on RCT in human apoA-I transgenic (hA-ITg) mice with wild-type mice and showed that the PPARα agonist promoted RCT in hA-ITg mice to a much greater extent than in wild-type mice, indicating that human apoA-I expression is important for PPARα-induced RCT. We further investigated the dependence of the macrophage PPARα-liver X receptor (LXR) pathway on the promotion of RCT by GW7647. Primary murine macrophages lacking PPARα or LXR abolished the ability of GW7647 to promote RCT in hA-ITg mice. In concert, the PPARα agonist promoted cholesterol efflux and ATP binding cassette transporter A1/G1 expression in primary macrophages, and this was also by the PPARα-LXR pathway. CONCLUSION: Our observations demonstrate that a potent PPARα agonist promotes macrophage RCT in vivo in a manner that is enhanced by human apoA-I expression and dependent on both macrophage PPARα and LXR expression.

Lecithin: cholesterol acyltransferase expression has minimal effects on macrophage reverse cholesterol transport in vivo.

BACKGROUND: Lecithin:cholesterol acyltransferase (LCAT) catalyzes the formation of plasma cholesteryl ester, plays a key role in high-density lipoprotein metabolism, and has been believed to be critical in the process of reverse cholesterol transport (RCT). METHODS AND RESULTS: The role of LCAT in RCT from macrophages was quantified with a validated assay involving intraperitoneal injection in mice of (3)H-cholesterol-labeled J774 macrophages and monitoring the appearance of tracer in plasma, liver, bile, and feces. Human LCAT overexpression in human apolipoprotein A-I transgenic mice substantially increased plasma high-density lipoprotein cholesterol levels but surprisingly did not increase macrophage RCT. Even in the setting of coexpression of scavenger receptor BI or cholesteryl ester transfer protein, both of which promoted the transfer of LCAT-derived high-density lipoprotein cholesterol ester to the liver, LCAT overexpression still had no effect on RCT. Serum from LCAT-overexpressing mice had reduced ability to promote cholesterol efflux from macrophages ex vivo via ABCA1. To determine the effect of LCAT deficiency on macrophage RCT, LCAT(-/-) and LCAT(+/-) mice were compared with wild-type mice. Despite extremely low plasma levels of high-density lipoprotein cholesterol, LCAT-deficient mice had only a 50% reduction in RCT. LCAT(+/-) mice had normal RCT despite a significant reduction in high-density lipoprotein cholesterol. Serum from LCAT-deficient mice had increased ability to promote ABCA1-mediated cholesterol efflux from macrophages ex vivo. CONCLUSIONS: These results demonstrate that LCAT overexpression does not promote an increased rate of macrophage RCT. Although LCAT activity does become rate limiting in the context of complete LCAT deficiency, RCT is reduced by only 50% even in the absence of LCAT. These data suggest that macrophage RCT may not be as dependent on LCAT activity as has previously been believed.

Effects of atorvastatin on nuclear magnetic resonance-defined lipoprotein subclasses and inflammatory markers in patients with hypercholesterolemia.

AIM: Information about the effects of HMG-CoA reductase inhibitor (statin) treatment on lipoprotein subclasses has been severely limited. Nuclear magnetic resonance (NMR) spectrometry has emerged as a new methodology to quantify lipoprotein subclass concentrations. In the present study, we attempted to evaluate the hypolipidemic effects of atorvastatin utilizing this method. METHODS: Twenty-six patients were administered with atorvastain 10 mg daily for 4 weeks. Lipoprotein subclasses were measured by nuclear magnetic resonance (NMR) spectroscopy. Inflammation markers, including C-reactive protein (CRP), interleukin-6 (IL-6), and monocyte chemotactic protein-1 (MCP-1), were also determined. RESULTS: Additional to a marked reduction of LDL-C (-43%), atorvastatin treatment significantly decreased TG, RLP-C, apoC-II, apoC-III, and apoE by 27%, 49%, 25%, 15%, and 28%, respectively. NMR analysis revealed marked reductions of all LDL subclasses, resulting in a significant reduction of LDL particle number as well as an increase in LDL particle size. Further, some VLDL were decreased and HDL particle size was increased by atorvastatin. Among inflammation markers, MDA-LDL and IL-6 were marginally to significantly decreased. CONCLUSION: In addition to a strong LDL-C lowering function, atorvastatin exerts beneficial effects on TG-rich lipoproteins and inflammation in hypercholesterolemic patients.

Effects of nevirapine and efavirenz on HDL cholesterol levels and reverse cholesterol transport in mice.

OBJECTIVE: The mechanism by which non-nucleoside reverse transcriptase inhibitors (NNRTIs) increase HDL cholesterol (HDL-C) in HIV+ patients and the benefits of this with respect to cardiovascular risk are not known. Studies were conducted to test the hypothesis that NNRTIs have a beneficial effect on HDL-C and reverse cholesterol transport (RCT). METHODS: LDLr-/- and hA-I transgenic mice were fed a Western diet containing either nevirapine (20mg/kg per day), efavirenz (10mg/kg per day), or diet alone. hA-I transgenic mice underwent a study to measure RCT (measured by excretion of macrophage [(3)H]-cholesterol into HDL and feces) at 8 weeks. RESULTS: LDLr-/- and hA-I transgenic mice treated with nevirapine and efavirenz had a significant increase in HDL-C level (up to 23% in hA-I transgenic) at 4 weeks. However, there was no difference in HDL levels beyond 4 weeks of treatment. At 4 weeks, the FPLC profile of hA-I transgenic mice showed an increase in large HDL. hApoA-I transgenic mice treated with efavirenz for 4 weeks had increased expression of human apoA-I in liver and an increased human apoA-I production rate. Incubation of plasma from hA-I transgenic mice treated for 4 weeks with [(3)H]-cholesterol-labeled macrophages revealed increased cholesterol efflux to plasma from mice treated with efavirenz and nevirapine. Following injection of hA-I transgenic mice treated for 8 weeks with [(3)H]-cholesterol-labeled macrophages, RCT was increased in the efavirenz (p=0.01) group and trended towards an increase in the nevirapine (p=0.15) group. CONCLUSION: Nevirapine and efavirenz transiently increased HDL-C in LDLr-/- and hA-I transgenic mice fed a Western diet that was associated with increased apoA-I production. An increase in RCT in hA-I transgenic mice at 8 weeks despite no difference in HDL levels indicates that these drugs affect additional factors in the RCT pathway that enhance cholesterol efflux from the macrophage and peripheral tissues to plasma and delivery to liver for excretion. These results suggest that treatment with NNRTIs has a beneficial effect on cholesterol efflux and RCT.

Expression of cholesteryl ester transfer protein in mice promotes macrophage reverse cholesterol transport.

BACKGROUND: Cholesteryl ester transfer protein (CETP) transfers cholesteryl esters from high-density lipoproteins to apolipoprotein (apo) B-containing lipoproteins and in humans plays an important role in lipoprotein metabolism. However, the role that CETP plays in mediation of reverse cholesterol transport (RCT) remains unclear. We used a validated in vivo assay of macrophage RCT to test the effect of CETP expression in mice (which naturally lack CETP) on macrophage RCT, including in mice that lack the low-density lipoprotein receptor or the scavenger receptor class B, type I. METHOD AND RESULTS: A vector based on adeno-associated virus serotype 8 (AAV8) with a liver-specific thyroglobulin promoter was used to stably express human CETP in livers of mice and was compared with an AAV8-lacZ control vector. The RCT assay was performed 4 weeks after vector injection and involved the intraperitoneal injection of acetylated low-density lipoprotein cholesterol-loaded and 3H-cholesterol-labeled J774 macrophages in mice with plasma sampling at several time points, liver and bile sampling at 48 hours, and continuous fecal collection to measure 3H-sterol as an integrated readout of macrophage RCT. In apobec-1-null mice, CETP expression reduced plasma high-density lipoprotein cholesterol levels but significantly increased fecal 3H-sterol excretion. In low-density lipoprotein receptor/apobec-1 double-null mice, CETP expression reduced high-density lipoprotein cholesterol levels and had no effect on fecal 3H-sterol excretion. Finally, in scavenger receptor class B, type I-null mice, CETP expression reduced high-density lipoprotein cholesterol levels and significantly increased fecal 3H-sterol excretion. CONCLUSION: The present results demonstrate that CETP expression promotes macrophage RCT in mice, that this effect is dependent on the low-density lipoprotein receptor, and that CETP expression restores to normal the impaired RCT in mice deficient in scavenger receptor class B, type I.

Increased remnant lipoprotein in patients with coronary artery disease--evaluation utilizing a newly developed remnant assay, remnant lipoproteins cholesterol homogenous assay (RemL-C).

AIM: Remnant lipoprotein is an emerging risk factor for coronary artery disease (CAD); however, the development of a specific remnant lipoprotein assay has struggled due to its heterogeneous nature. This study aimed to evaluate the clinical importance of a newly developed assay for remnant lipoprotein, RemL-C, in patients with CAD. METHODS: This assay utilizes surfactant and phospholipase-D to selectively degrade and solubilize remnant lipoprotein. One hundred and sixty consecutive CAD patients who underwent coronary catheterization were recruited. RESULTS: Remnant liporotein, RemL-C, was significantly higher in CAD patients (p< 0.001). Additionally, TG, hs-CRP, ICAM-1, VCAM-1, and homocysteine were significantly higher, but HDL-C and adiponectin were lower with LDL-C unchanged. Since RemL-C levels correlated with plasma TG levels, two subgroups, normotriglycedemic and normolipidemic CAD groups, were extracted. In both groups, RemL-C was still significantly higher than controls. HDL-C, but not RemL-C, was associated with the severity of CAD. RemL-C significantly correlated with TG-rich lipoproteins, in particular VLDL and IDL, when limited to normolipidemic CAD patients. CONCLUSION: Remnant lipoprotein, measured by RemL-C, was increased in CAD patients independent of TG levels, indicating impaired remnant lipoprotein metabolism in these patients. CAD severity was associated with HDL-C, but not with remnant lipoprotein, indicating differential roles of lipoproteins in the development of coronary atherosclerosis. This study therefore provides clinical significance to assess coronary risk by measuring RemL-C, particularly among patients with normal TG levels.

Effects of bezafibrate on lipoprotein subclasses and inflammatory markers in patients with hypertriglyceridemia--a nuclear magnetic resonance study.

BACKGROUND: Hypertriglyceridemia is often associated with elevated remnants, small dense LDL and decreased HDL-cholesterol (C). The objective of this study was to investigate the efficacy of bezafibrate on lipoprotein subfractions profile and inflammation markers in patients with hypertriglyceridemia. METHODS: Twenty-four hypertriglyceridemic subjects took bezafibrate, 400 mg daily, for 4 weeks. Lipoprotein subclasses were measured by nuclear magnetic resonance (NMR) spectroscopy. Inflammation markers including C-reactive protein (CRP), interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1) were also determined. RESULTS: Bezafibrate lowered triglyceride (TG) by 59% and increased HDL-C by 20%. NMR analysis revealed that bezafibrate lowered large TG-rich lipoproteins and IDL by 81% and 46%, respectively. Small LDL was selectively decreased by 53% with increase in large to intermediate LDL, thus altering the LDL distribution towards the larger particles (mean diameter 19.9 to 20.7 nm, p = 0.0001). Small (HDL1) and intermediate (HDL3) HDL significantly increased by 168% and 70%, whereby resulting in a significant reduction of the mean HDL particle size from 9.0 to 8.7 nm (p = 0.026). None of inflammation makers showed significant change by bezafibrate. CONCLUSIONS: Bezafibrate effectively ameliorates atherogenic dyslipidemia by reducing remnants and small LDL as well as by increasing HDL particles in hypertriglyceridemic subjects.

A novel two nucleotide deletion in the apolipoprotein A-I gene, apoA-I Shinbashi, associated with high density lipoprotein deficiency, corneal opacities, planar xanthomas, and premature coronary artery disease.

Familial HDL deficiency (FHD) is a rare autosomal dominant lipoprotein disorder. We describe a novel genetic variant of the apolipoprotein A-I (apoA-I) gene resulting in FHD. The proband is a 51-year-old woman who was hospitalized due to severe heart failure. Her plasma HDL-cholesterol (C) and apoA-I concentrations were 0.08mmol/l and 1mg/dl, respectively. She exhibited corneal opacities and planar xanthomas on eyelids and elbows. Coronary angiography demonstrated extensive obstructions in two major vessels. Genomic DNA sequencing of the patient's apoA-I gene revealed a homozygosity for a GC deletion between 5 GC repeats in exon 4, creating a frameshift and a stop codon at residue 178. We designated this mutation as apoA-I Shinbashi. The proband's father, son, and daughter were found to be heterozygous for this mutation and their HDL-C and apoA-I levels were about half of normal levels, demonstrating a gene dosage effect. The father underwent coronary bypass surgery at age of 70 years. Lecithin-cholesterol acyltransferase (LCAT) activity was decreased by 63% in the homozygote and 31% in heterozygotes, respectively. This new case of apoA-I deficiency, apoA-I Shinbashi, is the first case involving a single gene defect of the apoA-I gene to develop all the characteristics for apoA-I deficiency, including premature coronary heart disease.