Involvement of reactive oxygen species and SP-1 in fibronectin production by oxidized LDL

Ablation of Galectin-12 Inhibits Atherosclerosis through Enhancement of M2 Macrophage Polarization

The formation of foam cells, which are macrophages that have engulfed oxidized low-density lipoprotein (OxLDL), constitutes the first stage in the development of atherosclerosis. Previously, we found that knocking down galectin-12, a negative regulator of lipolysis, leads to reduced secretion of monocyte chemoattractant protein-1 (MCP-1), a chemokine that plays an important role in atherosclerosis. This prompted us to study the role of galectin-12 in atherosclerosis. With that aim, we examined foam cell formation in Gal12^‒/‒ murine macrophages exposed to OxLDL and acetylated LDL (AcLDL). Then, we generated an LDL receptor and galectin-12 double knockout (DKO) mice and studied the effect of galectin-12 on macrophage function and atherosclerosis. Lastly, we evaluated the role of galectin-12 in human THP-1 macrophages using a doxycycline-inducible conditional knockdown system. Galectin-12 knockout significantly inhibited foam cell formation in murine macrophages through the downregulation of cluster of differentiation 36 (CD36), and the upregulation of ATP Binding Cassette Subfamily A Member 1 (ABCA1), ATP Binding Cassette Subfamily G Member 1 (ABCG1), and scavenger receptor class B type 1 (SRB1). Consistent with this, galectin-12 knockdown inhibited foam cell formation in human macrophages. In addition, the ablation of galectin-12 promoted M2 macrophage polarization in human and murine macrophages as evidenced by the upregulation of the M2 marker genes, CD206 and CD163, and downregulation of the M1 cytokines, tumor necrosis factor α (TNF- α), interleukin-6 (IL-6), and MCP-1. Moreover, the ablation of galectin-12 decreased atherosclerosis formation in DKO mice. Based on these results, we propose galectin-12 as a potential therapeutic target for atherosclerosis.

Serum Paraoxonase activity in relation to lipid profile in Age-related Macular Degeneration patients

Age-related Macular Degeneration (AMD) is a multifactorial disease causing visual impairment in old age. Oxidative stress is one of the main contributors for the disease progression. Paraoxonase (PON), a HDL-resident antioxidant enzyme which removes oxidized low density lipoprotein (oxLDL), which is not studied much in AMD. This study assesses the PON activities in relation to the lipid status and genetic variants in AMD patients. In this prospective case-control study, a total of 48 AMD patients and 30 unrelated healthy controls were recruited. The serum oxLDL and Plasma Homocysteine (Hcy) levels were estimated by ELISA. Plasma Homocysteine thiolactone (HCTL) was estimated by HPLC. Serum PON activities were estimated by spectrophotometry. PON gene expression was assessed by qPCR and protein expression by western blot, immunofluorescence and FACS analysis. Two known single nucleotide polymorphisms (SNPs) in the coding region of PON1, Q192R and L55M variants were checked in the AMD patients and controls and their association with PON activity and lipid levels were determined. Serum paraoxonase (PONase) and thiolactonase (PON-HCTLase) activities were significantly elevated in AMD patients than in controls apart from elevated serum levels of total cholesterol (TC), triglycerides (TG), oxLDL. While serum LDL levels in AMD patients correlate positively with PON HCTLase activity, the serum high density lipoprotein (HDL) correlates with both PONase and PON-HCTLase activities. However, multiple regression analysis showed that, amongst the parameters, only serum TG was a significant risk factor for AMD, after adjusting for demographic parameters as well as cataract. PON2 was significantly increased at the level of gene expression (p = 0.03) as seen in circulating peripheral blood mononuclear cells (PBMC) of AMD patients possibly mediated by the transcription factor SP1, that showed 2-fold increase. PON1 and 2 protein expressions also showed significant increase in the PBMC of AMD patients. At serum level, PON1 protein was significantly increased in AMD patients. Cholesterol transporters such as CD36, SR-B1 and ABCA1 gene expressions were also found to be higher (1.5, 1.9 and 2.4-fold respectively) in AMD, though not statistically significant. While the wet AMD (CNV) was found to be associated with increase in oxLDL and serum PONase activity, the dry AMD was associated with increased HDL and serum PON-HCTLase activity. The genotype and allele frequencies of Q192R & L55M were not significantly different between AMD patients and controls. However, altered lipid status and PON activities were associated with the genotype in AMD patients. A higher enzyme activity was observed for the RR genotype of Q192R in the cohort, irrespective of case and control. Thus the PON genotype and phenotype seem to play a role in the pathogenesis of AMD.

Reactive oxygen species: friend or foe?

It is a need to define the line between pathological and physiological functions of reactive oxygen species (ROS) in order to understand their beneficial role over their injurious consequences.

Mitochondria and reactive oxygen species: physiology and pathophysiology

The air that we breathe contains nearly 21% oxygen, most of which is utilized by mitochondria during respiration. While we cannot live without it, it was perceived as a bane to aerobic organisms due to the generation of reactive oxygen and nitrogen metabolites by mitochondria and other cellular compartments. However, this dogma was challenged when these species were demonstrated to modulate cellular responses through altering signaling pathways. In fact, since this discovery of a dichotomous role of reactive species in immune function and signal transduction, research in this field grew at an exponential pace and the pursuit for mechanisms involved began. Due to a significant number of review articles present on the reactive species mediated cell death, we have focused on emerging novel pathways such as autophagy, signaling and maintenance of the mitochondrial network. Despite its role in several processes, increased reactive species generation has been associated with the origin and pathogenesis of a plethora of diseases. While it is tempting to speculate that anti-oxidant therapy would protect against these disorders, growing evidence suggests that this may not be true. This further supports our belief that these reactive species play a fundamental role in maintenance of cellular and tissue homeostasis.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

CXCL16 and oxLDL are induced in the onset of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of end-stage renal failure worldwide. Oxidative stress has been reported to be a major culprit of the disease and increased oxidized low density lipoprotein (oxLDL) immune complexes were found in patients with DN. In this study we present evidence, that CXCL16 is the main receptor in human podocytes mediating the uptake of oxLDL. In contrast, in primary tubular cells CD36 was mainly involved in the uptake of oxLDL. We further demonstrate that oxLDL down-regulated alpha(3)-integrin expression and increased the production of fibronectin in human podocytes. In addition, oxLDL uptake induced the production of reactive oxygen species (ROS) in human podocytes. Inhibition of oxLDL uptake by CXCL16 blocking antibodies abrogated the fibronectin and ROS production and restored alpha(3) integrin expression in human podocytes. Furthermore we present evidence that hyperglycaemic conditions increased CXCL16 and reduced ADAM10 expression in podocytes. Importantly, in streptozotocin-induced diabetic mice an early induction of CXCL16 was accompanied by higher levels of oxLDL. Finally immunofluorescence analysis in biopsies of patients with DN revealed increased glomerular CXCL16 expression, which was paralleled by high levels of oxLDL. In summary, regulation of CXCL16, ADAM10 and oxLDL expression may be an early event in the onset of DN and therefore all three proteins may represent potential new targets for diagnosis and therapeutic intervention in DN.

Activation of transcription factors and gene expression by oxidized low-density lipoprotein

It is well recognized that oxidized LDL (OxLDL) plays a crucial role in the initiation and progression of atherosclerosis. Many biological effects of OxLDL are mediated through signaling pathways, especially via the activation of transcription factors, which in turn stimulate the expression of genes involved in the inflammatory and oxidative stress response or in cell cycle regulation. In this review, we will discuss the various transcription factors activated by OxLDL, the studied cell types, the active compounds of the OxLDL particle, and the downstream genes when identified. Identification of the transcription factors and some of the downstream genes regulated by OxLDL has helped us understand the molecular mechanism involved in generation of the atherosclerotic plaque.

Group IVA phospholipase A2-mediated production of fibronectin by oxidized LDL in mesangial cells

The deposition of atherogenic lipoproteins such as oxidized low-density lipoprotein (oxLDL) within the mesangium is involved in the overproduction of extracellular matrix proteins, a key event in the progression of glomerular diseases including glomerulosclerosis. To clarify the mechanisms underlying the oxLDL-induced production of extracellular matrix proteins, we examined the possible involvement of group IVA phospholipase A(2) (PLA(2)) using human mesangial cells and group IVA PLA(2)-deficient mouse mesangial cells. oxLDL accelerated the production of fibronectin and collagen (type IV), components of extracellular matrix proteins, with the preceding release of arachidonic acid. Methyl arachidonyl fluorophosphonate (MAFP), known as an inhibitor of group IVA PLA(2), markedly suppressed the oxLDL-induced production of fibronectin as well as the release of arachidonic acid, whereas it did not inhibit the production of collagen. The inhibitory effect of MAFP on the production of fibronectin was reversed by adding arachidonic acid and 12-hydroxyeicosatetraenoic acid. Furthermore, we found that in group IVA PLA(2)-deficient mouse mesangial cells, the production of fibronectin in response to oxLDL was weak as compared with that in wild-type cells. However, the production by oxLDL of collagen was not suppressed in the group IVA PLA(2)-deficient cells. These findings suggest that group IVA PLA(2) is involved in the production of fibronectin in oxLDL-stimulated mesangial cells.

Acceleration of matrix metalloproteinase-1 production and activation of platelet-derived growth factor receptor β in human coronary smooth muscle cells by oxidized LDL and 4-hydroxynonenal

Increases in matrix metalloproteinases (MMPs) at atherosclerotic lesions are involved in the migration of smooth muscle cells (SMCs) into the intima and to the rupture of plaques, being implicated in the progression of atherosclerosis. The present study examined the mechanisms underlying the production of MMP-1, interstitial collagenase-1, induced by oxidized low-density lipoprotein (oxLDL) and 4-hydroxynonenal (4-HNE), factors proposed to play a pivotal role in atherogenesis, in human coronary SMCs. oxLDL promoted the production of MMP-1 with the preceding phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. Immunoprecipitation of platelet-derived growth factor receptor beta (PDGFR-beta) revealed that oxLDL induced tyrosine phosphorylation of the receptor. Inhibition of the activation of PDGFR-beta and ERK1/2 resulted in a suppression of the production of MMP-1. Consistently, 4-HNE also elicited the production of MMP-1 with the preceding phosphorylation of PDGFR-beta and ERK1/2. The 4-HNE-induced production of MMP-1 was prevented when the activation of PDGFR-beta and ERK1/2 was inhibited. The present results suggest that the activation of PDGFR-beta and ERK1/2 is involved in the production of MMP-1 in oxLDL- and 4-HNE-stimulated human coronary SMCs.

Role of mitogen-activated protein kinase pathway in reactive oxygen species-mediated endothelin-1-induced beta-myosin heavy chain gene expression and cardiomyocyte hypertrophy

Endothelin-1 (ET-1) has been found to increase cardiac beta-myosin heavy chain (beta-MyHC) gene expression and induce hypertrophy in cardiomyocytes. ET-1 has been demonstrated to increase intracellular reactive oxygen species (ROS) in cardiomyocytes. The exact molecular mechanism by which ROS regulate ET-1-induced beta-MyHC gene expression and hypertrophy in cardiomyocytes, however, has not yet been fully described. We aim to elucidate the molecular regulatory mechanism of ROS on ET-1-induced beta-MyHC gene expression and hypertrophic signaling in neonatal rat cardiomyocytes. Following stimulation with ET-1, cultured neonatal rat cardiomyocytes were examined for 3H-leucine incorporation and beta-MyHC promoter activities. The effects of antioxidant pretreatment on ET-1-induced cardiac hypertrophy and mitogen-activated protein kinase (MAPKs) phosphorylation were studied to elucidate the redox-sensitive pathway in cardiomyocyte hypertrophy and beta-MyHC gene expression. ET-1 increased 3H-leucine incorporation and beta-MyHC promoter activities, which were blocked by the specific ET(A) receptor antagonist BQ-485. Antioxidants significantly reduced ET-1-induced 3H-leucine incorporation, beta-MyHC gene promoter activities and MAPK (extracellular signal-regulated kinase, p38, and c-Jun NH2 -terminal kinase) phosphorylation. Both PD98059 and SB203580 inhibited ET-1-increased 3H-leucine incorporation and beta-MyHC promoter activities. Co-transfection of the dominant negative mutant of Ras, Raf, and MEK1 decreased the ET-1-induced beta-MyHC promoter activities, suggesting that the Ras-Raf-MAPK pathway is required for ET-1 action. Truncation analysis of the beta-MyHC gene promoter showed that the activator protein-2 (AP-2)/specificity protein-1 (SP-1) binding site(s) were(was) important cis-element(s) in ET-1-induced beta-MyHC gene expression. Moreover, ET-1-induced AP-2 and SP-1 binding activities were also inhibited by antioxidant. These data demonstrate the involvement of ROS in ET-1-induced hypertrophic responses and beta-MyHC expression. ROS mediate ET-1-induced activation of MAPK pathways, which culminates in hypertrophic responses and beta-MyHC expression.

COX-2 inhibitors suppress integrin alpha5 expression in human lung carcinoma cells through activation of Erk: involvement of Sp1 and AP-1 sites

Tumor cell expression of COX-2 has been implicated in the progression of murine and human lung cancer. Inhibition of COX-2 by nonsteroidal antiinflammatory drugs reduces the risk of cancer development in humans and suppresses tumor growth in animal models. However, the underlying mechanisms for this beneficial effect are not fully understood. Here we explore the potential link between the anticancer effects of COX-2 inhibitors and the expression of the integrin alpha5beta1. Expression of this integrin in carcinoma cells is associated with invasiveness and malignant progression. This, together with our studies showing that fibronectin, the ligand of alpha5beta1, stimulates the growth of human lung carcinoma cells, and that this effect is mediated through alpha5beta1-dependent signals, has prompted us to examine the effects of COX-2 inhibitors on alpha5beta1 expression in human non small cell lung carcinoma (NSCLC) cells. We found that the selective COX-2 inhibitors NS398 and Nimesulide decreased mRNA expression and protein production of the integrin alpha5 subunit. This effect was associated with inhibition of NSCLC cell adhesion to fibronectin. The COX-2 inhibitors triggered the phosphorylation of extracellular signal-regulated kinase (Erk) in a time-dependent manner, and the inhibitor of Mek-1/Erk PD98095 prevented their inhibitory effects on integrin alpha5 expression. Transient transfection assays showed that the COX-2 inhibitors affected integrin alpha5 gene transcription by acting between -92 to -41 bp of the human integrin alpha5 gene promoter. Gel mobility shift assays showed that the COX-2 inhibitors increased Sp1 DNA binding, but decreased that of AP-1. These effects were accompanied by an increase in Sp1 protein and a decrease in c-Jun protein expression, as well as inhibition of SAPK/JNK phosphorylation. The Sp1 inhibitor, Mithramycin A, also blocked the inhibitory effect of the COX-2 inhibitors on alpha5 expression and promoter activity. Overall, these findings suggest that COX-2 inhibitors suppress alpha5beta1 integrin expression in NSCLC through effects on integrin alpha5 gene transcription mediated by Erk activation, increased Sp1, decreased AP-1 DNA binding and inactivation of SAPK/JNK signals. Our observations unveil a new mechanism of action against NSCLC for COX-2 inhibitors that relates to regulation of integrin alpha5 gene expression and, consequently, recognition of extracellular matrices (i.e., fibronectin) by tumor cells. (c) 2005 Wiley-Liss, Inc.

IGF-1 induces rat glomerular mesangial cells to accumulate triglyceride

Rat glomerular mesangial cells (MC) become lipid-laden foam cells when they are exposed to IGF-1. IGF-1 increased accumulation of triglyceride (TG) 2.5-fold in MC after 7 days. TG accumulation resulted from enhanced macropinocytosis and decreased efflux secondary to a 40-50% reduction in peroxisome proliferator-activated receptor (PPAR)-delta (PPARdelta). There was no evidence of primary or secondary changes in cholesterol or TG synthesis, increased uptake by LDL or scavenger receptors, or reduced efflux via ATP-binding cassette A-1. Although the lipid moiety taken up can be influenced by the concentration of cholesterol or TG in the medium, in standard medium MC preferentially accumulate TG. TG-rich MC foam cells fail to contract in response to angiotensin II (Berfield AK, Andress DL, and Abrass CK. Kidney Int 62: 1229-1237, 2002); however, their migratory response to IGF binding protein-5 is unaffected. This differs from cholesterol loading, which impairs both phagocytosis and migration. These findings have important implications for understanding the mechanisms that contribute to lipid accumulation in MC and the functional consequences of different forms of foam cells. These observations are relevant to understanding vascular disease and progressive renal diseases that are accelerated by abnormalities in lipid metabolism.

Oxidized LDL induces mitochondrially associated reactive oxygen/nitrogen species formation in endothelial cells

Exposure of cells to complex mixtures of oxidized lipids such as those found in oxidized low-density lipoprotein (oxLDL) induce reactive oxygen and nitrogen species (ROS/RNS) formation. The source of the ROS/RNS within cells is unknown; it is thought they may be involved in redox cell signaling. Although this possibility was initially overlooked, it is becoming clear that mitochondria, which are a source of superoxide and hydrogen peroxide, may play a critical role in the response of cells on exposure to oxidized lipids. In this study, we tested the possibility that mitochondria are a potential source of oxLDL-dependent formation of ROS/RNS in endothelial cells. Using confocal microscopy, we demonstrated that a significant proportion of oxLDL-dependent dichlorodihydrofluorescein (DCF) fluorescence is colocalized to mitochondria. In support of this concept, rho0 endothelial cells showed a substantial decrease in ROS/RNS formation stimulated by oxLDL. In contrast, mostly nonmitochondrial DCF fluorescence was detected in cells exposed to an extracellular source of hydrogen peroxide. The exposure of cells to a nitric oxide synthase inhibitor and urate resulted in a decrease in oxLDL-induced DCF fluorescence that was restored by addition of nitric oxide donors to the medium. Taken together, these results suggest that oxLDL-dependent DCF fluorescence is mitochondrially associated and may be due to the formation of peroxynitrite.

9HODE stimulates cell proliferation and extracellular matrix synthesis in human mesangial cells via PPARgamma

Plasma oxidized low-density lipoprotein (OX-LDL) levels are elevated in patients with renal diseases, including diabetic nephropathy. We examined effects of OX-LDL on cell proliferation and extracellular matrix (ECM) production by using normal human mesangial cells. Furthermore, we examined possible involvement of peroxisome proliferator-activated receptor gamma (PPARgamma). Mesangial cell proliferation with OX-LDL, 9-hydroxy-10,12-octadecadienoic acid (9HODE), and 13-hydroxy-9,11-octadecadienoic acid (13HODE), the major components of OX-LDL, were determined by 5-bromo-2'-deoxyuridine (BrdU) or 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) incorporation. The effect of OX-LDL on mesangial cell proliferation with PD98059 pretreatment was determined by BrdU incorporation. Type IV collagen, fibronectin, and PPARgamma expression with OX-LDL or 9HODE or 13HODE was determined by Western blotting. Type IV collagen expression with antisense oligonucleotide against PPARgamma pretreatment was also determined by Western blotting. The effect of PD98059 pretreatment on PPARgamma expression was determined by Western blotting. In mesangial cells exposed to isolated OX-LDL from human plasma, BrdU incorporation was increased, and this increase was deleted by PD98059. Type IV collagen expression was significantly increased by OX-LDL. 9HODE and 13HODE increased BrdU and MTT incorporation into mesangial cells and also increased expressions of Type IV collagen and fibronection, the major components of ECM. PPARgamma expression in mesangial cells was stimulated by 9HODE. The reduction of PPARgamma synthesis by pretreatment of antisense oligonucleotide against PPARgamma remarkably attenuated Type IV collagen synthesis induced by 9HODE. PPARgamma expression induced by 9HODE was also reduced by PD98059 pretreatment. These findings demonstrate that 9HODE, the major component of OX-LDL, stimulates cell proliferation and ECM production of human mesangial cells. In addition, the stimulatory effects are, at least in part, mediated by PPARgamma, which may exist in downstream of ERK1/2 pathway.

The leaf extract of Ginkgo Biloba L. suppresses oxidized LDL-stimulated fibronectin production through an antioxidant action in rat mesangial cells

1 The leaf extract of Ginkgo Biloba L. exhibits a variety of pharmacological effects through an antioxidant action. We examined the effects of the leaf extract (Ginkgolon-24) on the production of fibronectin induced by oxidized low-density lipoprotein (oxLDL) in rat mesangial cells. 2 Stimulation with oxLDL accelerated the production of fibronectin with the preceding generation of reactive oxygen species (ROS). Pretreatment with Ginkgolon-24 inhibited the oxLDL-induced fibronectin production as well as ROS generation. 3 oxLDL also elicited the activation of SP-1, nuclear factor-kappaB, and cAMP response element-binding protein, which are transcription factors involved in the fibronectin production. Among these activated transcription factors, Ginkgolon-24 inhibited the activation of SP-1 only. 4 Furthermore, 7-ketocholesterol, an oxidized lipid in oxLDL particles, induced the production of fibronectin and the activation of SP-1, which were also suppressed by Ginkgolon-24. 5 These results suggest that the leaf extract of Ginkgo Biloba L. inhibits the oxLDL-induced production of fibronectin probably through inhibitory effects on ROS generation and SP-1 activation in rat mesangial cells.