Proliferative effect of lipoprotein lipase on human vascular smooth muscle cells

Artesunate inhibits macrophage-like phenotype switching of vascular smooth muscle cells and attenuates vascular inflammatory injury in atherosclerosis via NLRP3

Inflammation is one of the main pathogenic factors of atherosclerosis (AS), and the phenotypic transformation of macrophages in human vascular smooth muscle cells (HVSMCs) contributes to the inflammatory injury of blood vessels and the formation of atherosclerotic plaques. Artesunate reportedly exerts anti-inflammatory activity against AS. Herein, we aimed to explore the artesunate-mediated anti-inflammatory and HVSMC phenotypic switch effects against AS and elucidate potential underlying mechanisms. In vitro, artesunate decreased expression of NLRP3, caspase-1, and interleukin (IL)- 1β. Artesunate significantly inhibited low-density lipoprotein (LDL) expression in HVSMCs and macrophages. In vivo, artesunate reduced atherosclerotic plaque formation in high-fat diet (HFD)-fed ApoE-/- mice, as well as decreased NLRP3 and CD68 expression in atherosclerotic plaques. Artesunate decreased serum levels of triglycerides and increased high-density lipoprotein levels in HFD-med mice; however, serum levels of total cholesterol and LDL were unaltered. Treatment with artesunate substantially increased α-smooth muscle actin expression in aortic tissues while inhibiting expression levels of NLRP3, IL-1β, heparinase, matrix metalloproteinase 9, and Krüppel-like factor 4 (KLF4). Collectively, our findings suggest that artesunate-mediated effects may involve inhibition of the ERK1/2/NF-κB/IL-1β pathway in HVSMCs via the downregulation of NLRP3 expression. Thus, artesunate could serve as a novel strategy to treat AS by inhibiting AS plaque formation and suppressing macrophage-like phenotype switching of HVSMCs.

Plasma Lipoprotein Lipase Is Associated with Risk of Future Major Adverse Cardiovascular Events in Patients Following Carotid Endarterectomy

INTRODUCTION

Carotid plaque intraplaque haemorrhage (IPH) is associated with future cardiovascular events. It was hypothesised that plasma proteins associated with carotid plaque IPH are also likely to be associated with major adverse cardiovascular events (MACE) after carotid endarterectomy (CEA).

METHODS

In pre-operative blood samples from patients undergoing CEA within the Athero-Express biobank, proteins involved in cardiovascular disease were measured using three OLINK proteomics immunoassays. The association between proteins and IPH was analysed using logistic regression analyses. Subsequently, the association between the IPH associated plasma proteins and the three year post-operative risk of MACE (including stroke, myocardial infarction, or cardiovascular death) was analysed.

RESULTS

Within the three year follow up, 130 patients (18.9%) of 688 symptomatic and asymptomatic patients undergoing CEA developed MACE. Six of 276 plasma proteins were found to be significantly associated with IPH, from which only lipoprotein lipase (LPL) was associated with the post-operative risk of MACE undergoing CEA. Within the 30 day peri-operative period, high plasma LPL was independently associated with an increased risk of MACE (adjusted hazard ratio [HR] per standard deviation [SD] 1.60, 1.10 - 2.30), p = .014). From 30 days to three years, however, high LPL was associated with a lower risk of MACE (adjusted HR per SD 0.80, 0.65 - 0.99, p= .036).

CONCLUSION

High LPL concentrations were found to be associated with a higher risk of MACE in the first 30 post-operative days but with a lower risk MACE between 30 days and three years, meaning that LPL has different hazards at different time points.

Neutrophil elastase promotes neointimal hyperplasia by targeting toll-like receptor 4 (TLR4)-NF-κB signalling

BACKGROUND AND PURPOSE

Neointimal hyperplasia (NIH) is the fundamental cause for vascular diseases and vascular smooth muscle cell (VSMC) dysregulation has been widely implicated in NIH. Neutrophil elastase is a potential therapeutic target for multiple diseases. We investigated the role of neutrophil elastase in VSMC functions and injury-induced NIH and explored the therapeutic potential of targeting neutrophil elastase in NIH.

EXPERIMENTAL APPROACH

VSMCs were used to analyse the effects of neutrophil elastase. Proteomic analysis was used to identify potential neutrophil elastase targets. Artery injury model and neutrophil elastase inhibitor GW311616A were used to investigate the role of neutrophil elastase in NIH.

KEY RESULTS

TNF-α up-regulated neutrophil elastase in VSMCs through modulating GAPBα/Runx1/CEBPα/c-Myb signalling. Up-regulated neutrophil elastase promoted VSMC migration, proliferation and inflammation. Toll-like receptor 4 (TLR4) was identified as a target protein for neutrophil elastase in VSMCs and the TLR4/MyD88/IRAK1/TRAF6/NF-κB regulatory axis was shown to be the signalling pathway for neutrophil elastase in VSMC pathology. Importantly, TLR4 inhibition abolished neutrophil elastase-mediated VSMC dysregulation. Injury-induced NIH was significantly reduced in both neutrophil elastase-deficient mice and mice treated with GW311616A. The formation of neutrophil extracellular traps was impaired in injured arteries from neutrophil elastase-deficient mice. Finally, a similar role for neutrophil elastase in human VSMC pathology was confirmed and we observed higher expression levels of neutrophil elastase but lower expression levels of TLR4 in human atherosclerotic lesions.

CONCLUSION AND IMPLICATIONS

We provide new insight into the molecular mechanisms underlying NIH and identify neutrophil elastase as a potential therapeutic target for vascular disease.

ANGPTL8 Gene Polymorphism rs2278426 Is Related to Carotid Intima-Media Thickness in T2DM

AIM

ANGPTL8 is a cytokine expressed and secreted by liver and adipose tissue, and is involved in glucose, lipid, and energy metabolism. Although studies have shown that ANGPTL8 is elevated in type 2 diabetes mellitus (T2DM) and cardiovascular disease, few have examined the association between ANGPTL8 single-nucleotide polymorphisms and the risk of macrovascular complications in T2DM patients. This study aimed to explore the relationship between rs2278426 and carotid intima-media thickening (cIMT) in T2DM.

METHODS

A total of 217 T2DM patients and 201 healthy control subjects with normal glucose tolerance were recruited in the study. T2DM patients were divided into two groups: T2DM patients without cIM thickening (cIMT <1 mm, 109 cases) and T2DM patients with cIM thickening (cIMT ≥1 mm, 108 cases). rs2278426 genotypes in all 418 subjects were determined and the risk of T2DM and T2DM with cIM thickening analyzed.

RESULTS

CT+TT-genotype frequency in T2DM was higher than in controls with normal glucose tolerance, and the proportion of the CT+TT genotype in the group with cIMT was higher than in the group (P<0.05). In addition, T alleles were associated with waist:hip ratio, triglycerides, high density-lipoprotein cholesterol, plasma glucose at 2 hours' oral glucose tolerance, and homeostatic model assessment of insulin resistance (P<0.05).

CONCLUSION

Generally, carriers of the T allele at rs2278426 are more likely to develop T2DM, and the risk of cIM thickening is significantly increased for T-allele carriers with T2DM, which indicates an increased risk of macroangiopathy.

Differential proteomic analysis to identify proteins associated with beak deformity in chickens

The beak is the dominant avian facial feature, and beak deformity occurs in 0.5 to 2.5% of some indigenous chicken breeds, resulting in difficulties when eating, drinking, and performing natural behaviors. Previous studies on beak deformity focused largely on candidate molecules associated with skeletogenic development, providing insight into the molecular and genetic underpinnings of beak deformity. The present study was performed to identify candidate proteins related to this malformation in chickens. Three 12-day-old Beijing-You roosters with deformed beaks (D1, D2, and D3) and 3 with normal beaks (N1, N2, and N3) were used, and total beak proteins were isolated and subjected to standard iTRAQ labeling, strong cation-exchange chromatography, and liquid chromatography-tandem mass spectrometry. Mascot 2.3.02 was used to identify and quantitatively analyze proteins. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were used to identify functions and metabolic pathways of differentially expressed proteins, and key proteins were further validated using western blot. A total of 2,370, 2,401, and 2,378 proteins were reliably quantified in 3 biological replicates, among which, 2,345 were common to all, and 92 were differentially expressed between the 2 groups. These included 37 upregulated and 55 downregulated proteins in deformed beaks. Pentraxin-related protein 3, hemopexin, lipoprotein lipase, retinoid-binding protein 7, and biliverdin reductase A were downregulated in all 3 sets, while parvalbumin, peptidyl-prolyl cis-trans isomerase, and ubiquitin-fold modifier 1 were upregulated. Pathway analysis returned no enriched pathways, and western blot validated the iTRAQ results. Parvalbumin and lipoprotein lipase could be firstly selected as key proteins in view of their known functions in regulating the buffering of intracellular free Ca2+ in both cartilage and bone cells and bone mass, respectively. Their potential roles in beak deformity, however, deserve further studies. In summary, the onset of beak deformity could be very complex, and this study will be helpful for future investigation of mechanistic explanation for beak deformity.

Lipoprotein lipase in chronic lymphocytic leukemia: function and prognostic implications

Chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease characterized by the accumulation of a clonal population of B cells in peripheral blood, bone marrow, and lymphoid organs. More than 10 years ago, lipoprotein lipase (LPL) mRNA was identified as being strongly expressed in patients experiencing a more aggressive phenotype, while CLL patients with an indolent disease course lack expression of this marker. Since then, several reports confirmed the capability of LPL to predict CLL disease evolution at the moment of diagnosis. In contrast, data on the functional implications of LPL in CLL are scarce. LPL exerts a central role in overall lipid metabolism and transport, but plays additional, non-catalytic roles as well. Which of those is more important in the pathogenesis of CLL remains largely unclear. Here, we review the current knowledge on the prognostic and biological relevance of LPL in CLL.

Lipoprotein lipase: from gene to atherosclerosis

Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism and responsible for catalyzing lipolysis of triglycerides in lipoproteins. LPL is produced mainly in adipose tissue, skeletal and heart muscle, as well as in macrophage and other tissues. After synthesized, it is secreted and translocated to the vascular lumen. LPL expression and activity are regulated by a variety of factors, such as transcription factors, interactive proteins and nutritional state through complicated mechanisms. LPL with different distributions may exert distinct functions and have diverse roles in human health and disease with close association with atherosclerosis. It may pose a pro-atherogenic or an anti-atherogenic effect depending on its locations. In this review, we will discuss its gene, protein, synthesis, transportation and biological functions, and then focus on its regulation and relationship with atherosclerosis and potential underlying mechanisms. The goal of this review is to provide basic information and novel insight for further studies and therapeutic targets.

Combinatorial regulation of lipoprotein lipase by microRNAs during mouse adipogenesis

MicroRNAs (miRNAs) regulate gene expression directly through base pairing to their targets or indirectly through participating in multi-scale regulatory networks. Often miRNAs take part in feed-forward motifs where a miRNA and a transcription factor act on shared targets to achieve accurate regulation of processes such as cell differentiation. Here we show that the expression levels of miR-27a and miR-29a inversely correlate with the mRNA levels of lipoprotein lipase (Lpl), their predicted combinatorial target, and its key transcriptional regulator peroxisome proliferator-activated receptor gamma (Pparg) during 3T3-L1 adipocyte differentiation. More importantly, we show that Lpl, a key lipogenic enzyme, can be negatively regulated by the two miRNA families in a combinatorial fashion on the mRNA and functional level in maturing adipocytes. This regulation is mediated through the Lpl 3'UTR as confirmed by reporter gene assays. In addition, a small mathematical model captures the dynamics of this feed-forward motif and predicts the changes in Lpl mRNA levels upon network perturbations. The obtained results might offer an explanation to the dysregulation of LPL in diabetic conditions and could be extended to quantitative modeling of regulation of other metabolic genes under similar regulatory network motifs.

ω-6 lipids regulate PPAR turnover via reciprocal switch between PGC-1 alpha and ubiquitination

OBJECTIVE

Dietary ω-6 lipids such as linoleic acid and its oxidized forms (13-HPODE OxLA) interact with peroxisome proliferator-activated receptors (PPARs) and elicit pro and anti-atherogenic effects in vascular cells. Ligand-dependent PPAR protein turnover is promoted by ubiquitination, but attenuated by binding to its co-activator, peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1α). The objective of our study was to investigate if the dual atherogenic effects of ω-6 lipids are due to its regulation of PPAR turnover.

METHODS AND RESULTS

In rat aortic smooth muscle cells (RASMCs), oxidized linoleic acid (OxLA) at 10-50 μM induced and stabilized PPARα protein at earlier time points (0-4 h) but suppressed it at 12 h. Conversely, it activated PPARγ protein turnover at a later time point (12 h). Pre-treatment with the proteasome inhibitor (MG132) prevented OxLA mediated loss of PPAR stability and transactivity. Co-immunoprecipitation studies indicated a ligand mediated time-dependent reciprocal exchange of PPAR interaction between ubiquitination and PGC-1α. This ω-6 lipid mediated time-dependent switch between PPAR degradation versus stability helped modulate the pro and anti-atherogenic effects of these dietary lipids.

CONCLUSION

Our findings provide insights into the dual pro and anti-atherogenic effects of dietary ω-6 lipids on vascular cells by the regulation of PPAR turnover.

Investigation of the Interaction Between the Ser447Term Polymorphism of Lipoprotein Lipase and the Stroke-Related Risk Factors in Ischemic Stroke

The present study aimed to investigate the interaction between the Ser447Term polymorphism in the lipoprotein lipase (LPL) gene and some common risk factors for stroke. A total of 704 unrelated patients with ischemic stroke were recruited for genetic analysis; they were all of Han Chinese origin. These patients were classified into subgroups based on their exposure to stroke-related risk factors, including type 2 diabetes, hypertension, smoking, and hyperlipidemia. The Ser447Term polymorphism was genotyped by PCR-based restriction fragment length polymorphism analysis. The chi-square (χ (2)) test showed that the frequency of Ser447Term G allele was significantly higher in stroke patients with a history of diabetes than in those without a history of diabetes (χ (2) = 7.25, P = 0.007, OR = 1.78, 95%CI 1.18-2.68). Allelic association was not observed in patients exposed to the other three stroke-related risk factors. The combined effect of the LPL gene polymorphisms and diabetes may contribute to the development of a subgroup of ischemic stroke.

Therapeutic potential for protein kinase C inhibitor in vascular restenosis

Vascular restenosis, an overreaction of biological response to injury, is initialized by thrombosis and inflammation. This response is characterized by increased smooth muscle cell migration and proliferation. Available pharmacological treatments include anticoagulants, antiplatelet agents, immunosuppressants, and antiproliferation agents. Protein kinase C (PKC), a large family of serine/threonine kinases, has been shown to participate in various pathological stages of restenosis. Consequently, PKC inhibitors are expected to exert a wide range of pharmacological activities therapeutically beneficial for restenosis. In this review, the roles of PKC isozymes in platelets, leukocytes, endothelial cells, and smooth muscle cells are discussed, with emphasis given to smooth muscle cells. We will describe cellular and animal studies assessing prevention of restenosis with PKC inhibitors, particularly targeting -α, -β, -δ, and -ζ isozymes. The delivery strategy, efficacy, and safety of such PKC regulators will also be discussed.

The common biological basis for common complex diseases: evidence from lipoprotein lipase gene

The lipoprotein lipase (LPL) gene encodes a rate-limiting enzyme protein that has a key role in the hydrolysis of triglycerides. Hypertriglyceridemia, one widely prevalent syndrome of LPL deficiency and dysfunction, may be a risk factor in the development of dyslipidemia, type II diabetes (T2D), essential hypertension (EH), coronary heart disease (CHD) and Alzheimer's disease (AD). Findings from earlier studies indicate that LPL may have a role in the pathology of these diseases and therefore is a common or shared biological basis for these common complex diseases. To examine this hypothesis, we reviewed articles on the molecular structure, expression and function of the LPL gene, and its potential role in the etiology of diseases. Evidence from these studies indicate that LPL dysfunction is involved in dyslipidemia, T2D, EH, CHD and AD; and support the hypothesis that there is a common or shared biological basis for these common complex diseases.

n-3 fatty acids reduce arterial LDL-cholesterol delivery and arterial lipoprotein lipase levels and lipase distribution

OBJECTIVE

We previously reported that saturated fat (SAT)-enriched diets increase arterial cholesteryl ester (CE) deposition, especially from LDL-selective uptake (SU), and this was associated with increased arterial lipoprotein lipase (LpL). We now question how n-3 fatty acid rich diets influence arterial cholesterol delivery and arterial LpL levels.

METHODS AND RESULTS

C57BL/6 mice were fed chow or eucaloric high-fat diets enriched in SAT or fish oil (n-3) for 12 weeks, and then injected with double radiolabeled or fluorescent-labeled human LDL to separately trace LDL-CE and LDL-apoB uptake. SAT and n-3 diets increased plasma cholesterol levels similarly; n-3 diets lowered plasma triglyceride concentrations. SAT increased arterial LDL-SU with significantly higher CE infiltration into aortic media. In contrast, n-3 markedly reduced total LDL uptake and CE deposition and abolished SU with LDL localized only in aortic intima. Disparate patterns of CE deposition between diets were consistent with distribution of arterial LpL-SAT diets induced higher LpL levels throughout the aorta; n-3 diets decreased LpL levels and limited LpL expression to the aortic intima.

CONCLUSIONS

n-3 rich diets decrease arterial total LDL delivery and abrogate LDL-SU in parallel with changing arterial wall LpL expression and distribution.

Expression of lipoprotein lipase associated with lung adenocarcinoma tissues

Lipoprotein lipase (LPL) plays a key role in the lipid metabolism and transporting. It can catalyze the hydrolysis of chylomicron and very low-density lipoprotein triglyceride. Moreover, the abnormality of LPL associates with many pathophysiological conditions. Herein cDNA microarray and Northern blots analysis were used to study the expression of lipoprotein lipase in lung adenocarcinoma tissues. There were 113 genes of all tested blots in cDNA microarray expressed lowly. LPL gene is expressed lowly at the average ratio 0.26 (Cy5/Cy3) in lung adenocarcinoma tissues over controls. Northern blots confirmed those changes detected from the cDNA microarray and suggested that low expression of LPL may play an important role in the lung adenocarcinoma development.

Localized vessel expression of lipoprotein lipase in rabbits leads to rapid lipid deposition in the balloon-injured arterial wall

Recent studies on mice demonstrated that lipoprotein lipase (LPL) located in the arterial wall might play a pro-atherogenic role. There are major differences between humans and mice in lipoprotein metabolism and in susceptibility to atherosclerosis. We have therefore used rabbits fed normal chow diet as a model to assess such localized effects by adenovirus-mediated gene transfer of human catalytically active wild type LPL (hLPLwt) and an inactive mutant (hLPL194) to balloon-injured carotid arteries. By morphometric analysis on cryosections stained with Oil Red O (ORO) we found 7- and 4-fold increases, respectively, of lipid deposition in the arterial walls 7 days after infection with adenovirus expressing hLPLwt or hLPL194, when compared with a virus expressing human alkaline phosphatase (hAP) as control. Macrophages were detected in the arteries expressing both forms of LPL, but apoB was only found in arteries expressing hLPLwt. Expression of the LPL gene products was transient and was gone after 2 weeks, but the accumulated lipid deposits remained between the neointimal and the media layers even after 8 weeks. Our data demonstrate that expression of LPL in the arterial wall (with or without lipase activity) leads to lipid accumulation in balloon-injured rabbit arteries, and could result in enhanced formation of atherosclerotic lesions.

Haplotypes in the lipoprotein lipase gene influence high-density lipoprotein cholesterol response to statin therapy and progression of atherosclerosis in coronary artery bypass grafts

Lipoprotein lipase (LPL) hydrolyzes circulating triglycerides (TGs). We previously showed that 3'-end haplotypes in the LPL gene influence atherosclerosis and insulin resistance. This study asked whether these LPL haplotypes influence response to lipid-lowering therapy among 829 subjects from the Post-Coronary Artery Bypass Graft trial. Lipid profiles were obtained at baseline and 4-5 years after treatment with lovastatin. Haplotypes were based on 12 SNPs. The fourth most frequent haplotype, 12-4, was associated with a decreased increment in high-density lipoprotein-cholesterol (HDL-C) following treatment. Haplotypes 12-6, 12-7 and 12-8 were each associated with increased HDL-C response to therapy, and haplotype 12-2 with decreased TG response. The most common haplotype, 12-1, was protective against graft worsening or occlusion. Haplotype 12-4 reduced HDL-C response to lovastatin, possibly consistent with our prior observations of this haplotype as predisposing to coronary artery disease. LPL may influence atherosclerosis risk through pleiotropic effects on each aspect of the metabolic syndrome.

Advanced glycation end products potentiate the stimulatory effect of glucose on macrophage lipoprotein lipase expression

Lipoprotein lipase (LPL) secreted by macrophages in the arterial wall promotes atherosclerosis. We have shown that macrophages of patients with type 2 diabetes overproduce LPL and that metabolic factors, including glucose, stimulate macrophage LPL secretion. In this study, we determined the effect of advanced glycation end products (AGEs) on LPL expression by macrophages cultured in a high-glucose environment and the molecular mechanisms underlying this effect. Our results demonstrate that AGEs potentiate the stimulatory effect of high glucose on murine and human macrophage LPL gene expression and secretion. Induction of macrophage LPL mRNA levels by AGEs was identical to that elicited by physiologically relevant modified albumin and was inhibited by anti-AGE receptor as well as by antioxidants. Treatment of macrophages with AGEs resulted in protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) activation. Inhibition of these kinases abolished the effect of AGEs on LPL mRNA levels. Finally, exposure of macrophages to AGEs increased the binding of nuclear proteins to the activated protein-1 consensus sequence of the LPL promoter. This effect was inhibited by PKC and MAPK inhibitors. These results demonstrate for the first time that AGEs potentiate the stimulatory effect of high glucose on macrophage LPL expression. This effect appears to involve oxidative stress and PKC/MAPK activation.

Leptin increases lipoprotein lipase secretion by macrophages: involvement of oxidative stress and protein kinase C

Recent data suggest that plasma leptin may represent a cardiovascular risk factor in diabetic patients. To gain further insight into the role of leptin in atherogenesis associated with diabetes, we investigated in the present study the role of this hormone in the regulation of macrophage lipoprotein lipase (LPL), a proatherogenic cytokine overexpressed in patients with type 2 diabetes. Treatment of human macrophages with leptin (1-10 nmol/l) increased LPL expression, at both the mRNA and protein levels. Pretreatment of these cells with anti-leptin receptor (Ob-R) antibody, protein kinase C (PKC) inhibitors, calphostin C, and GF109203X, or the antioxidant N-acetylcysteine (NAC) blocked the effects of leptin. Similar results were observed in leptin-treated J774 macrophages. In these cells, leptin increased the membrane expression of conventional PKC isoforms and downregulation of endogenous PKC expression abolished the effects of leptin on macrophage LPL expression. In leptin-treated J774 cells, enhanced LPL synthetic rate and increased binding of nuclear proteins to the activated protein-1 (AP-1) consensus sequence of the LPL gene promoter were also observed. This latter effect was abrogated by GF109203X. Overall, these data demonstrate that binding of leptin at the macrophage cell surface increases, through oxidative stress- and PKC-dependent pathways, LPL expression. This effect appears to be exerted at the transcriptional level and to involve AP-1 activation.

Peroxisome proliferator-activated receptor alpha and gamma agonists upregulate human macrophage lipoprotein lipase expression

Peroxisome proliferator-activated receptors (PPARs) are transcriptional factors which mediate pleiotropic effects including regulation of genes involved in lipid metabolism and control of inflammation. In the present study, we measured the in vitro effects of PPAR alpha and gamma ligands on macrophage lipoprotein lipase (LPL) expression. Human monocyte-derived macrophages (MDM) were cultured for 1-3 days in the presence of PPAR alpha and gamma ligands. At the end of these incubation periods, extracellular LPL immunoreactive mass/activity and LPL mRNA levels were measured. Incubation of human MDM with PPAR alpha and gamma ligands stimulated, in a time- and dose-dependent manner, human MDM LPL mass and activity. These agents also significantly increased macrophage LPL mRNA expression. In THP-1 cells treated with PPAR alpha and gamma ligands, enhanced nuclear protein binding to the peroxisome proliferator responsive element (PPRE) of the human LPL promoter was observed. Furthermore, in these cells, a decreased rate of decay of LPL mRNA was documented. Overall, these results demonstrate that PPAR alpha and gamma activators increase macrophage LPL secretion. Given the proatherogenic effect of vascular wall LPL, better understanding of the role of PPARs in the regulation of macrophage LPL expression could lead to the development of new approaches in the prevention and treatment of atherosclerosis.

Homocysteine induces protein kinase C activation and stimulates c-Fos and lipoprotein lipase expression in macrophages

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease in human diabetes. Among the multiple factors that may account for the atherogenicity of homocysteine (Hcys) in patients with diabetes, macrophage (Mo) lipoprotein lipase (LPL) has unique features in that it is increased in human diabetes and acts as a proatherogenic factor in the arterial wall. In the present study, we determined the direct regulatory effect of Hcys on Mo LPL gene expression and secretion. Incubation of J774 Mo with Hcys increased, in a time- and dose-dependent manner, LPL mRNA expression and secretion. Induction of LPL gene expression was biphasic, peaking at 1 and 6 h. Whereas Hcys treatment increased protein kinase C (PKC) activity in Mo, pretreatment of Mo with PKC inhibitors totally suppressed Hcys-induced LPL mRNA expression. Hcys also increases the levels of c-fos mRNA in Mo and enhanced nuclear protein binding to the AP-1 sequence of the LPL gene promoter. Overall, these results demonstrate that Hcys stimulates Mo LPL at both the gene and protein levels and that Hcys-induced LPL mRNA expression requires PKC activation. They also suggest a possible role of c-fos in the stimulatory effect of Hcys on Mo LPL mRNA expression. These observations suggest a new mechanism by which Hcys may exert its proatherogenic effects in human diabetes.

A protective role for kidney apolipoprotein E. Regulation of mesangial cell proliferation and matrix expansion

Mesangial expansion is a key feature in the pathogenesis of numerous renal diseases involving the glomerulus. Studies indicate that mutations in apolipoprotein E (apoE) might independently contribute to kidney dysfunction. Although the role of apoE as an atheroprotective molecule is well established, its role in kidney is unclear. In this study, we sought to explore whether apoE has a protective function in kidney. Northern blotting and reverse transcriptase-polymerase chain reaction showed apoE expression in kidney, and mesangial cell is a major source of apoE in kidney. In the kidneys of 14-16-month-old apoE-null mice, hematoxylin-eosin (HE) staining revealed increased mesangial cell proliferation and matrix formation compared with wild type mice or apoB-overexpressing mice, which have elevated plasma cholesterol and triglycerides. These data suggest that lack of apoE, rather than hyperlipidemia, contributes to increased mesangial expansion. We isolated mesangial cells from mouse kidney and determined the effect of apoE on cell growth. ApoE (E3, 10 microg/ml) completely inhibited serum, platelet-derived growth factor (10 ng/ml), as well as low density lipoprotein-induced mesangial cell proliferation. Among the three isoforms, E3 was found to be most effective in inhibiting mesangial cell proliferation. ApoE did not show any cytotoxic effect, and moreover, inhibited mesangial cell apoptosis induced by oxidized low density lipoprotein. These data suggest that apoE regulates growth as well as survival of mesangial cells. We previously showed that apoE induces matrix heparan sulfate proteoglycan (HSPG) in vascular cells, which has an antiproliferative effect. Similarly, apoE induced the mesangial matrix HSPG. Perlecan is the major HSPG of mesangial matrix and subendothelial space, and consistent with this, blockade of perlecan reversed the antiproliferative effect of apoE. Immunohistochemistry revealed reduced staining of perlecan in kidney from apoE-null mice. Because the loss of anionic HSPG in the basement membrane and mesangial matrix is associated with disruption of filtration barrier, these data suggest a novel role for kidney apoE in preserving the filtration barrier. In summary, apoE has a protective function in kidney as an autocrine regulator of mesangial expansion and kidney function.