Phospholipid transfer protein deficiency ameliorates diet-induced hypercholesterolemia and inflammation in mice

Phospholipid transfer protein (PLTP) facilitates the transfer of phospholipids from triglyceride-rich lipoproteins into HDL. PLTP has been shown to be an important factor in lipoprotein metabolism and atherogenesis. Here, we report that chronic high-fat, high-cholesterol diet feeding markedly increased plasma cholesterol levels in C57BL/6 mice. PLTP deficiency attenuated diet-induced hypercholesterolemia by dramatically reducing apolipoprotein E-rich lipoproteins (-88%) and, to a lesser extent, LDL (-40%) and HDL (-35%). Increased biliary cholesterol secretion, indicated by increased hepatic ABCG5/ABCG8 gene expression, and decreased intestinal cholesterol absorption may contribute to the lower plasma cholesterol in PLTP-deficient mice. The expression of proinflammatory genes (intercellular adhesion molecule-1 and vascular cell adhesion molecule-1) is reduced in aorta of PLTP knockout mice compared with wild-type mice fed either a chow or a high-cholesterol diet. Furthermore, plasma interleukin-6 levels are significantly lower in PLTP-deficient mice, indicating reduced systemic inflammation. These data suggest that PLTP appears to play a proatherogenic role in diet-induced hyperlipidemic mice.     

Reduction of HDL levels lowers plasma PLTP and affects its distribution among lipoproteins in mice

Phospholipid transfer protein (PLTP) is associated with HDL particles in plasma, where it transfers phospholipids between lipoproteins and remodels HDL particles. Tangier disease patients, with a mutated ABCA1 transporter, have extremely low plasma HDL concentration and reduced PLTP activity levels, a phenotype that is also observed in mice lacking ABCA1. We investigated whether low HDL levels and low PLTP activity are mechanistically related. Firstly, we studied PLTP expression and distribution among lipoproteins in mice lacking ABCA1 (ABCA1^−/−). Parallel to the strong reduction in PLTP activity in plasma of ABCA1^−/− mice, decreased PLTP protein levels were observed. Neither PLTP synthesis in liver or macrophages nor the ability of the macrophages to secrete PLTP were impaired in ABCA1^−/− mice. However, the PLTP activity level in the medium of cultured macrophages was determined by HDL levels in the medium. PLTP was associated with HDL particles in wild type mice, whereas in ABCA1^−/− mice, PLTP was associated with VLDL and LDL particles. Secondly, we treated different mouse models with varying plasma HDL and PLTP levels (wild type, ABCA1^−/−, apoE^−/− and PLTPtg mice, overexpressing human PLTP) with a synthetic LXR ligand, and investigated the relationship between LXR-mediated PLTP induction and HDL levels in plasma. Plasma PLTP activity in wild type mice was induced 5.6-fold after LXR activation, whereas in ABCA1^−/−, apoE^−/− and PLTPtg mice, all having reduced HDL levels, induction of PLTP activity was 2.4- , 3.2- and 2.0-fold, respectively. The less pronounced PLTP induction in these mice compared to wild type mice was not caused by a decreased PLTP gene expression in the liver or macrophages. Our findings indicate that the extent of LXR-mediated PLTP induction depends on plasma HDL levels. In conclusion, we demonstrate that ABCA1 deficiency in mice affects plasma PLTP level and distribution through an indirect effect on HDL metabolism. In addition, we show that the extent of LXR-mediated PLTP induction is HDL-dependent. These findings indicate that plasma HDL level is an important regulator of plasma PLTP and might play a role in the stabilization of PLTP in plasma.     

Degradation of phospholipid transfer protein (PLTP) and PLTP-generated pre-beta-high density lipoprotein by mast cell chymase impairs high affinity efflux of cholesterol from macrophage foam cells

Human atherosclerotic lesions contain mast cells filled with the neutral protease chymase. Here we studied the effect of human chymase on (i) phospholipid transfer protein (PLTP)-mediated phospholipid (PL) transfer activity, and (ii) the ability of PLTP to generate pre-beta-high density lipoprotein (HDL). Immunoblot analysis of PLTP after incubation with chymase for 6 h revealed, in addition to the original 80-kDa band, four specific proteolytic fragments of PLTP with approximate molecular masses of 70, 52, 48, and 31 kDa. This specific pattern of PLTP degradation remained stable for at least 24 h of incubation with chymase. Such proteolyzed PLTP had reduced ability (i) to transfer PL from liposome donor particles to acceptor HDL(3) particles, and (ii) to facilitate the formation of pre-beta-HDL. However, when PLTP was incubated with chymase in the presence of HDL(3), only one major cleavage product of PLTP (48 kDa) was generated, and PL transfer activity was almost fully preserved. Moreover, chymase effectively depleted the pre-beta-HDL particles generated from HDL(3) by PLTP and significantly inhibited the high affinity component of cholesterol efflux from macrophage foam cells. These results suggest that the mast cells in human atherosclerotic lesions, by secreting chymase, may prevent PLTP-dependent formation of pre-beta-HDL particles from HDL(3) and so impair the anti-atherogenic function of PLTP.     

Elevation of plasma phospholipid transfer protein in transgenic mice increases VLDL secretion

Two lipid transfer proteins are active in human plasma, cholesteryl ester transfer protein (CETP), and phospholipid transfer protein (PLTP). Mice by nature do not express CETP. Additional inactivation of the PLTP gene resulted in reduced secretion of VLDL and subsequently in decreased susceptibility to diet-induced atherosclerosis. The aim of this study is to assess possible effects of differences in PLTP expression on VLDL secretion in mice that are proficient in CETP and PLTP. We compared human CETP transgenic (huCETPtg) mice with mice expressing both human lipid transfer proteins (huCETPtg/huPLTPtg). Plasma cholesterol in huCETPtg mice was 1.5-fold higher compared with huCETPtg/huPLTPtg mice (P < 0.001). This difference was mostly due to a lower HDL level in the huCETPtg/huPLTPtg mice, which subsequently could lead to the somewhat decreased CETP activity and concentration that was found in huCETPtg/huPLTPtg mice (P < 0.05). PLTP activity was 2.8-fold increased in these animals (P < 0.001). The human PLTP concentration was 5 microg/ml. Moderate overexpression of PLTP resulted in a 1.5-fold higher VLDL secretion compared with huCETPtg mice (P < 0.05). The composition of nascent VLDL was similar in both strains. These results indicate that elevated PLTP activity in huCETPtg mice results in an increase in VLDL secretion. In addition, PLTP overexpression decreases plasma HDL cholesterol as well as CETP.     

Elevation of plasma phospholipid transfer protein increases the risk of atherosclerosis despite lower apolipoprotein B-containing lipoproteins

Plasma phospholipid transfer protein (PLTP) transfers phospholipids between lipoproteins and mediates HDL conversion. PLTP-overexpressing mice have increased atherosclerosis. However, mice do not express cholesteryl ester transfer protein (CETP), which is involved in the same metabolic pathways as PLTP. Therefore, we studied atherosclerosis in heterozygous LDL receptor-deficient (LDLR(+/-)) mice expressing both human CETP and human PLTP. We used two transgenic lines with moderately and highly elevated plasma PLTP activity. In LDLR(+/-)/huCETPtg mice, cholesterol is present in both LDL and HDL. Both are decreased in LDLR(+/-)/huCETPtg/huPLTPtg mice (>50%). An atherogenic diet resulted in high levels of VLDL+LDL cholesterol. PLTP expression caused a strong PLTP dose-dependent decrease in VLDL and LDL cholesterol (-26% and -69%) and a decrease in HDL cholesterol (-70%). Surprisingly, atherosclerosis was increased in the two transgenic lines with moderately and highly elevated plasma PLTP activity (1.9-fold and 4.4-fold, respectively), indicating that the adverse effect of the reduction in plasma HDL outweighs the beneficial effect of the reduction in apolipoprotein B (apoB)-containing lipoproteins. The activities of the antiatherogenic enzymes paraoxonase and platelet-activating factor acetyl hydrolase were both PLTP dose-dependently reduced ( approximately -33% and -65%, respectively). We conclude that expression of PLTP in this animal model results in increased atherosclerosis in spite of reduced apoB-containing lipoproteins, by reduction of HDL and of HDL-associated antioxidant enzyme activities.     

Hypolipidemic effect of young persimmon fruit in C57BL/6.KOR-ApoEshl mice

We investigated the hypolipidemic effects of young persimmon fruit (YP) on apolipoprotein E-deficient C57BL/6.KOR-ApoEshl mice. These mice exhibited higher plasma cholesterols, except for high-density lipoprotein (HDL), and lower plasma HDL cholesterol than C57BL/6.Cr mice that had the same genetic background as the C57BL/6.KOR-ApoEshl mice. Male C57BL/6.KOR-ApoEshl mice (n=5) were fed a diet supplemented with dry YP, Hachiya-kaki, at a concentration of 5% (w/w) for 10 weeks. YP treatment significantly lowered plasma chylomicron, very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) cholesterols, and triglyceride, and this response was accompanied by an elevation of fecal bile acid excretion. In the liver, sterol regulatory element binding protein-2 gene expression was significantly higher in mice fed YP, while the mRNA and protein levels of the LDL receptor did not change. These results indicate that acceleration of fecal bile acid excretion is a major mechanism of the hypolipidemic effect induced by YP in C57BL/6.KOR-ApoEshl mice.     

Synthetic low and high fat diets for the study of atherosclerosis in the mouse

Diets currently used to produce atherosclerotic lesions in mice are often undefined and cause accumulation of fat in the liver and gallstone formation. Therefore, synthetic low and high fat diets of known composition were formulated in this study. A synthetic diet containing 50% sucrose, 15% cocoa butter, 1% cholesterol, and 0.5% sodium cholate was found to produce a depression in high density lipoprotein cholesterol (HDL-C) and an elevation of very low density lipoprotein (VLDL) and low density lipoprotein cholesterol (LDL-C) in the atherosclerosis-susceptible strain, C57BL/6J. This diet was able to consistently produce aortic lesions and led to a decrease in liver damage and gallstone formation. The synthetic low fat diet did not produce HDL-C levels as high as those found in mice fed chow, but resulted in similar VLDL/LDL-C levels. Lipoprotein and apolipoprotein parameters were compared in C57BL/6J and the atherosclerosis-resistant strain, C3H/HeJ, consuming the synthetic low fat or high fat diets. As reported earlier, when consuming a high fat diet C57BL/6J mice have significantly lower HDL-C and apoA-I levels than C3H/HeJ mice. Further analysis shows that the molar ratio of plasma HDL-C to apoA-I is significantly lower in C57BL/6J mice, suggesting that HDL in the susceptible strain has a lower cholesterol-carrying capacity. This conclusion is consistent with the observation that the HDL particle size is smaller for C57BL/6J mice than for C3H/HeJ. Both strains increased their apoE levels when fed the synthetic high fat diet, but C3H/HeJ mice had higher levels of apoE on both diets. The major response to consumption of the high fat diet for both strains was an increase in apoB-48 from 5 micrograms/ml on a low fat diet to 54 and 109 micrograms/ml for C57BL/6J and C3H/HeJ, respectively. ApoB-100 showed minimal response to the high fat diet. The defined high fat diet can be used to study atherosclerosis in the mouse since it produces aortic lesions but reduces or eliminates other pathological changes such as gallstone formation and liver damage.     

PLTP deficiency improves the anti-inflammatory properties of HDL and reduces the ability of LDL to induce monocyte chemotactic activity

We reported that phospholipid transfer protein (PLTP) deficiency decreased atherosclerosis in mouse models. Because the decreased atherosclerosis was accompanied by a significant decrease in plasma HDL levels, we examined the properties of PLTP knockout (PLTP0) HDL and tested its ability to prevent LDL-induced monocyte chemotactic activity in human artery wall cell cocultures. We isolated HDL and LDL from LDL receptor knockout/PLTP knockout (LDLr0/PLTP0) mice and from apolipoprotein B transgenic (apoBTg)/PLTP0 mice as well as their controls. PLTP0 HDL was relatively rich in protein and depleted in phosphatidylcholine. Turnover studies revealed a 3.5- to 4.0-fold increase in the turnover of protein and cholesteryl ester in HDL from PLTP0 mice compared with control mice. The ability of HDL from LDLr0/PLTP0 and apoBTg/PLTP0 mice to prevent the induction of monocyte chemotactic activity in human artery wall cell cocultures exposed to human LDL was dramatically better than that in controls. Moreover, LDL from PLTP0 mice was markedly resistant to oxidation and induced significantly less monocyte chemotactic activity compared with that in controls. In vitro, PLTP0 HDL removed significantly more oxidized phospholipids from LDL than did control HDL. We conclude that PLTP deficiency improves the anti-inflammatory properties of HDL in mice and reduces the ability of LDL to induce monocyte chemotactic activity.     

Lack of adiponectin promotes formation of cholesterol gallstones in mice

Plasma adiponectin levels are reduced in obese people, and hypoadiponectinemia is recently reported to associate with cholesterol gallstone formation in human. The aim of this study was to examine the role of adiponectin in gallstone formation using adiponectin knockout mice. We analyzed male knockout and C57BL6J mice fed normal or lithogenic diet for 6 weeks. On lithogenic diet, the prevalence rate of gallstone was significantly greater in knockout mice than C57BL6J mice. The molar percentages of β and ω-muricholic acid were significantly higher and hepatic sterol 12α-hydroxylase expression (cyp8b1) was significantly lower in knockout mice than C57BL6J mice fed normal diet. The bile apolipoprotein A-I protein levels were decreased in knockout mice. Histological examination showed gallbladder wall thickening and accumulation of glycoprotein in the gallbladder of knockout mice. Gallbladder phospholipase A2-IVA expression was significantly higher in knockout mice than in C57BL6J mice fed lithogenic diet. Our results indicate that lack of adiponectin promotes gallstone formation in mice.     

Atherosclerotic lesion formation and triglyceride storage in obese apolipoprotein AI-deficient mice

Obese leptin-deficient (ob/ob) mice have increased levels of high-density lipoprotein (HDL) and a unique lipoprotein referred to as low-density lipoprotein (LDL)/HDL1. When crossed onto an apolipoprotein AI (apoAI)-deficient (-/-) background, ob/ob;apoAI-/- mice accumulate LDL/HDL1 in the absence of traditional HDL. To determine the role of LDL/HDL1 in atherosclerosis, C57BL/6, apoAI-/-, ob/ob and ob/ob;apoAI-/- mice were placed on butterfat diet. After 20 weeks, all four groups had a significant increase in total cholesterol levels. The cholesterol in C57BL/6 mice was carried on very low-density lipoprotein (VLDL) and LDL and, in ob/ob and ob/ob;apoAI-/- mice, on HDL and LDL/HDL1. Atherosclerotic lesion area was similar among C57BL/6, ob/ob and ob/ob;apoAI-/- groups despite their dissimilar lipoprotein profiles. Hepatic triglyceride production and VLDL clearance rates were similar among the four groups. The ob/ob;apoAI-/- group had a significant decrease in liver weight and an increase in white adipose tissue (WAT) weight compared to the ob/ob group. Hepatic scavenger receptor class B type I (SR-BI) levels were decreased in both liver and WAT in ob/ob;apoAI-/- compared to ob/ob mice. Conclusions regarding the atherogenicity of LDL/HDL1 were confounded by the differences in lipoprotein profiles among the four groups. However, our studies provide support for the concept that apoAI and SR-BI assist in the partitioning of lipid from adipose tissue to the liver.     

Fenofibrate reverses the decline in HDL cholesterol in mice overexpressing human phospholipid transfer protein

In humans, fibrates are used to treat dyslipidemia, because these drugs lower plasma triglycerides and raise HDL cholesterol. Treatment with fibrates lowers plasma phospholipid transfer protein (PLTP) activity in humans, but increases PLTP activity in mice, without a consistent effect on HDL-cholesterol concentration. Earlier, we found that PLTP overexpression in transgenic mice results in decreased plasma HDL levels and increased diet-induced atherosclerosis. So it seems that the interplay between fibrates, PLTP and HDL is different in mice and man, which may be important for atherosclerosis development. In the present study, we measured the effects of fibrates on PLTP expression in cultured human hepatocytes and effects of fibrate treatment on human PLTP expression, plasma PLTP activity and HDL levels in human PLTP transgenic mice. Fibrate treatment did not influence PLTP mRNA levels in human hepatocytes. Hepatic human PLTP mRNA levels and PLTP activity were both moderately elevated by fenofibrate treatment in human PLTP transgenic mice. In wild-type mice, however, feeding fenofibrate resulted in a strong induction of PLTP mRNA in the liver and a more than 4-fold increase of plasma PLTP activity. Plasma triglycerides were reduced in all mice by 48% or more by fenofibrate treatment. HDL-cholesterol concentrations were substantially increased by fenofibrate in PLTP overexpressing mice (+72%), but unaffected in wild-type mice. We conclude that fenofibrate treatment reverses the HDL-lowering effect of PLTP overexpression in human PLTP transgenic mice.     

Phospholipid Transfer Protein Is Expressed in Cerebrovascular Endothelial Cells and Involved in High Density Lipoprotein Biogenesis and Remodeling at the Blood-Brain Barrier

Phospholipid transfer protein (PLTP) is a key protein involved in biogenesis and remodeling of plasma HDL. Several neuroprotective properties have been ascribed to HDL. We reported earlier that liver X receptor (LXR) activation promotes cellular cholesterol efflux and formation of HDL-like particles in an established in vitro model of the blood-brain barrier (BBB) consisting of primary porcine brain capillary endothelial cells (pBCEC). Here, we report PLTP synthesis, regulation, and its key role in HDL metabolism at the BBB. We demonstrate that PLTP is highly expressed and secreted by pBCEC. In a polarized in vitro model mimicking the BBB, pBCEC secreted phospholipid-transfer active PLTP preferentially to the basolateral (“brain parenchymal”) compartment. PLTP expression levels and phospholipid transfer activity were enhanced (up to 2.5-fold) by LXR activation using 24(S)-hydroxycholesterol (a cerebral cholesterol metabolite) or TO901317 (a synthetic LXR agonist). TO901317 administration elevated PLTP activity in BCEC from C57/BL6 mice. Preincubation of HDL₃ with human plasma-derived active PLTP resulted in the formation of smaller and larger HDL particles and enhanced the capacity of the generated HDL particles to remove cholesterol from pBCEC by up to 3-fold. Pre-β-HDL, detected by two-dimensional crossed immunoelectrophoresis, was generated from HDL₃ in pBCEC-derived supernatants, and their generation was markedly enhanced (1.9-fold) upon LXR activation. Furthermore, RNA interference-mediated PLTP silencing (up to 75%) reduced both apoA-I-dependent (67%) and HDL₃-dependent (30%) cholesterol efflux from pBCEC. Based on these findings, we propose that PLTP is actively involved in lipid transfer, cholesterol efflux, HDL genesis, and remodeling at the BBB.     

Cholesteryl ester transfer protein and phospholipid transfer protein have nonoverlapping functions in vivo

Plasma phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) are homologous molecules that mediate neutral lipid and phospholipid exchange between plasma lipoproteins. Biochemical experiments suggest that only CETP can transfer neutral lipids but that there could be overlap in the ability of PLTP and CETP to transfer or exchange phospholipids. Recently developed PLTP gene knock-out (PLTP0) mice have complete deficiency of plasma phospholipid transfer activity and markedly reduced high density lipoprotein (HDL) levels. To see whether CETP can compensate for PLTP deficiency in vivo, we bred the CETP transgene (CETPTg) into the PLTP0 background. Using an in vivo assay to measure the transfer of [(3)H]PC from VLDL into HDL or an in vitro assay that determined [(3)H]PC transfer from vesicles into HDL, we could detect no phospholipid transfer activity in either PLTP0 or CETPTg/PLTP0 mice. On a chow diet, HDL-PL, HDL-CE, and HDL-apolipoprotein AI in CETPTg/PLTP0 mice were significantly lower than in PLTP0 mice (45 +/- 7 versus 79 +/- 9 mg/dl; 9 +/- 2 versus 16 +/- 5 mg/dl; and 51 +/- 6 versus 100 +/- 9, arbitrary units, respectively). Similar results were obtained on a high fat, high cholesterol diet. These results indicate 1) that there is no redundancy in function of PLTP and CETP in vivo and 2) that the combination of the CETP transgene with PLTP deficiency results in an additive lowering of HDL levels, suggesting that the phenotype of a human PLTP deficiency state would include reduced HDL levels.     

Elevated expression of phospholipid transfer protein in bone marrow derived cells causes atherosclerosis

Background

Phospholipid transfer protein (PLTP) is expressed by various cell types. In plasma, it is associated with high density lipoproteins (HDL). Elevated levels of PLTP in transgenic mice result in decreased HDL and increased atherosclerosis. PLTP is present in human atherosclerotic lesions, where it seems to be macrophage derived. The aim of the present study is to evaluate the atherogenic potential of macrophage derived PLTP.

Methods and Findings

Here we show that macrophages from human PLTP transgenic mice secrete active PLTP. Subsequently, we performed bone marrow transplantations using either wild type mice (PLTPwt/wt), hemizygous PLTP transgenic mice (huPLTPtg/wt) or homozygous PLTP transgenic mice (huPLTPtg/tg) as donors and low density lipoprotein receptor deficient mice (LDLR−/−) as acceptors, in order to establish the role of PLTP expressed by bone marrow derived cells in diet-induced atherogenesis. Atherosclerosis was increased in the huPLTPtg/wt→LDLR−/− mice (2.3-fold) and even further in the huPLTPtg/tg→LDLR−/− mice (4.5-fold) compared with the control PLTPwt/wt→LDLR−/− mice (both P<0.001). Plasma PLTP activity levels and non-HDL cholesterol were increased and HDL cholesterol decreased compared with controls (all P<0.01). PLTP was present in atherosclerotic plaques in the mice as demonstrated by immunohistochemistry and appears to co-localize with macrophages. Isolated macrophages from PLTP transgenic mice do not show differences in cholesterol efflux or in cytokine production. Lipopolysaccharide activation of macrophages results in increased production of PLTP. This effect was strongly amplified in PLTP transgenic macrophages.

Conclusions

We conclude that PLTP expression by bone marrow derived cells results in atherogenic effects on plasma lipids, increased PLTP activity, high local PLTP protein levels in the atherosclerotic lesions and increased atherosclerotic lesion size.     

Hyodeoxycholic acid efficiently suppresses atherosclerosis formation and plasma cholesterol levels in mice

We examined the effect of hyodeoxycholic acid (HDCA) on plasma cholesterol levels and atherosclerosis in mice. In wild-type C57BL/6 mice, feeding increasing amounts of HDCA resulted in i) progressive decrease in dietary cholesterol absorption, ii) increased concentrations of HDCA in the gallbladder bile, iii) decreased liver cholesterol content, iv) increased liver cholesterol synthesis, and v) increased plasma concentrations of HDCA. In C57BL/6 LDL-receptor knockouts (LDLR-KO) the addition of HDCA to chow and a 0.5% cholesterol diet decreased their total plasma cholesterol levels by 21% and 62%, respectively, because of a decrease in VLDL and LDL cholesterol. Turnover studies showed that HDCA has no effect on VLDL removal from plasma. Furthermore, the addition of HDCA to chow- and 0.5% cholesterol-fed LDLR-KO mice decreased the aortic root atherosclerosis lesion area by 50% and 80%, respectively. Finally, we tested the effect of HDCA on intestinal tumor formation. Feeding C57BL/6 ApcMin mice with HDCA did not affect the number of tumors but decreased the tumor volume in these animals. These results suggest that HDCA might have beneficial effects in the treatment of increased plasma cholesterol levels and atherosclerosis.     

Foxa2 activity increases plasma high density lipoprotein levels by regulating apolipoprotein M

Obesity, diabetes, insulin resistance, and hyperinsulinemia are frequently associated with a cluster of closely related lipid abnormalities such as low plasma levels of high density lipoprotein (HDL) and elevated levels of triglyceride, both known to increase the risk of developing atherosclerotic disease. The molecular mechanisms linking obesity, insulin resistance, and hyperinsulinemia to low HDL levels are incompletely understood. Here we demonstrate that insulin, through a Foxa2-mediated mechanism, inhibited the expression of apolipoprotein M (apoM), an important determinant of plasma pre-beta-HDL and alpha-HDL concentrations. Obese mice had decreased apoM expression and plasma pre-beta-HDL levels due to inactivation of Foxa2 in hyperinsulinemic states. Nuclear reexpression of Foxa2 with a phosphorylation-deficient mutant Foxa2T156A (Ad-T156A) activated apoM expression and increased plasma pre-beta-HDL and alpha-HDL levels. In contrast, haploinsufficient Foxa2(+/-) mice exhibited decreased hepatic apoM expression and plasma pre-beta-HDL and HDL levels. The increase in plasma HDL levels and pre-beta-HDL formation by Foxa2 was mediated exclusively by apoM, as constitutive active expression of Foxa2 in apoM(-/-) mice had no effect on plasma HDL levels. Our results identify a fundamental mechanism by which insulin regulates plasma HDL levels in physiological and insulin-resistant states and thus have important implications for novel therapeutic approaches to prevent atherosclerosis.     

Atherogenic, enlarged, and dysfunctional HDL in human PLTP/apoA-I double transgenic mice

In low density lipoprotein receptor (LDLR)-deficient mice, overexpression of human plasma phospholipid transfer protein (PLTP) results in increased atherosclerosis. PLTP strongly decreases HDL levels and might alter the antiatherogenic properties of HDL particles. To study the potential interaction between human PLTP and apolipoprotein A-I (apoA-I), double transgenic animals (hPLTPtg/hApoAItg) were compared with hApoAItg mice. PLTP activity was increased 4.5-fold. Plasma total cholesterol and phospholipid were decreased. Average HDL size (analyzed by gel filtration) increased strongly, hPLTPtg/hApoAItg mice having very large, LDL-sized, HDL particles. Also, after density gradient ultracentrifugation, a substantial part of the apoA-I-containing lipoproteins in hPLTPtg/hApoAItg mice was found in the LDL density range. In cholesterol efflux studies from macrophages, HDL isolated from hPLTPtg/hApoAItg mice was less efficient than HDL isolated from hApoAItg mice. Furthermore, it was found that the largest subfraction of the HDL particles present in hPLTPtg/hApoAItg mice was markedly inferior as a cholesterol acceptor, as no labeled cholesterol was transferred to this fraction. In an LDLR-deficient background, the human PLTP-expressing mouse line showed a 2.2-fold increased atherosclerotic lesion area. These data demonstrate that the action of human PLTP in the presence of human apoA-I results in the formation of a dysfunctional HDL subfraction, which is less efficient in the uptake of cholesterol from cholesterol-laden macrophages.     

NSD2 promotes ventricular remodelling mediated by the regulation of H3K36me2

Histone lysine methylation plays an important role in the regulation of ventricular remodelling. NSD2 is involved in many types of tumours through enhancing H3K36me2 expression. However, the role of NSD2 in the regulation of histone lysine methylation during ventricular remodelling remains unclear. In this study, we established cardiac hypertrophy model in C57BL/6 mice by transverse aortic constriction and found that histone lysine methylation participated in ventricular remodelling regulation via the up‐regulation of H3K27me2 and H3K36me2 expression. In addition, we constructed transgenic C57BL/6 mice with conditional knockout of NSD2 (NSD2^?/?) in the myocardium. NSD2^?/? C57BL/6 mice had milder ventricular remodelling and significantly improved cardiac function compared with wild‐type mice, and the expression of H3K36me2 but not H3K27me2 was down‐regulated. In conclusion, NSD2 promotes ventricular remodelling mediated by the regulation of H3K36me2.     

Plasma phospholipid transfer activity is essential for increased atherogenesis in PLTP transgenic mice: a mutation-inactivation study

Plasma phospholipid transfer protein (PLTP) interacts with HDL particles and facilitates the transfer of phospholipids from triglyceride (TG)-rich lipoproteins to HDL. Overexpressing human PLTP in mice increases the susceptibility to atherosclerosis. In human plasma, high-active and low-active forms of PLTP exist. To elucidate the contribution of phospholipid transfer activity to changes in lipoprotein metabolism and atherogenesis, we developed mice expressing mutant PLTP, still able to associate with HDL but lacking phospholipid transfer activity. In mice heterozygous for the LDL receptor, effects of the mutant and normal human PLTP transgene (mutPLTP tg and PLTP tg, respectively) were compared. In PLTP tg mice, plasma PLTP activity was increased 2.9-fold, resulting in markedly reduced HDL lipid levels. In contrast, in mutPLTP tg mice, lipid levels were not different from controls. Furthermore, hepatic VLDL-TG secretion was stimulated in PLTP tg mice, but not in mutPLTP tg mice. When mice were fed a cholesterol-enriched diet, atherosclerotic lesion size in PLTP tg mice was increased more than 2-fold compared with control mice, whereas in mutPLTP tg mice, there was no change. Our findings demonstrate that PLTP transfer activity is essential for the development of atherosclerosis in PLTP transgenic mice, identifying PLTP activity as a possible target to prevent atherogenesis, independent of plasma PLTP concentration.