Oxidized LDL activates PAI-1 transcription through autocrine activation of TGF-beta signaling in mesangial cells

Probiotics, gut microbiome, and cardiovascular diseases: An update

Cardiovascular diseases (CVD) are one of the most challenging diseases and many factors have been demonstrated to affect their pathogenesis. One of the major factors that affect CVDs, especially atherosclerosis, is the gut microbiota (GM). Genetics play a key role in linking CVDs with GM, in addition to some environmental factors which can be either beneficial or harmful. The interplay between GM and CVDs is complex due to the numerous mechanisms through which microbial components and their metabolites can influence CVDs. Within this interplay, the immune system plays a major role, mainly based on the immunomodulatory effects of microbial dysbiosis and its resulting metabolites. The resulting modulation of chronic inflammatory processes was found to reduce the severity of CVDs and to maintain cardiovascular health. To better understand the specific roles of GM-related metabolites in this interplay, this review presents an updated perspective on gut metabolites related effects on the cardiovascular system, highlighting the possible benefits of probiotics in therapeutic strategies.

Role of platelet factor 4 in arteriovenous fistula maturation failure: What do we know so far?

The rate of arteriovenous fistula (AVF) maturation failure remains unacceptably high despite continuous efforts on technique improvement and careful pre-surgery planning. In fact, half of all newly created AVFs are unable to be used for hemodialysis (HD) without a salvage procedure. While vascular stenosis in the venous limb of the access is the culprit, the underlying factors leading to vascular narrowing and AVF maturation failure are yet to be determined. We have recently demonstrated that AVF non-maturation is associated with post-operative medial fibrosis and fibrotic stenosis, and post-operative intimal hyperplasia (IH) exacerbates the situation. Multiple pathological processes and signaling pathways are underlying the stenotic remodeling of the AVF. Our group has recently indicated that a pro-inflammatory cytokine platelet factor 4 (PF4/CXCL4) is upregulated in veins that fail to mature after AVF creation. Platelet factor 4 is a fibrosis marker and can be detected in vascular stenosis tissue, suggesting that it may contribute to AVF maturation failure through stimulation of fibrosis and development of fibrotic stenosis. Here, we present an overview of the how PF4-mediated fibrosis determines AVF maturation failure.

SB431542 alleviates lupus nephritis by regulating B cells and inhibiting the TLR9/TGFβ1/PDGFB signaling

Lupus nephritis (LN) is the most common cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Currently, immunosuppressive treatments for LN are suboptimal and can induce significant side effects. SB431542 is a selective and potent inhibitor of the TGFβ/Activin/NODAL pathway. Here, we study the effects of SB431542 treatment on LN and discuss the potential mechanisms. SB431542 ameliorated clinical outcomes with a consequent histological improvement in NZB/W mice. A comparative transcriptional profiling analysis revealed 586 differentially expressed genes (247 downregulated genes) in the SB431542 group compared to the control group. We found that the downregulated genes were mainly enriched in the biological processes of B cell activation, B cell proliferation, B cell differentiation, and B cell receptor signaling. Kyoto encyclopedia of genes and genomes pathway analysis revealed that the hematopoietic cell linage pathway was significantly downregulated in the SB431542 group. In addition, we observed that SB431542 reduced the splenic or renal levels of CD20 and the serum levels of anti-dsDNA antibody (IgG) in NZB/W mice. Furthermore, qRT-PCR and immunohistochemistry confirmed that SB431542 inhibits the production of TLR9, TGFβ1, and PDGFB. Thus, due to its immunomodulatory activities, SB431542 could be considered for clinical therapy development for LN.

Signaling pathways of chronic kidney diseases, implications for therapeutics

Chronic kidney disease (CKD) is a chronic renal dysfunction syndrome that is characterized by nephron loss, inflammation, myofibroblasts activation, and extracellular matrix (ECM) deposition. Lipotoxicity and oxidative stress are the driving force for the loss of nephron including tubules, glomerulus, and endothelium. NLRP3 inflammasome signaling, MAPK signaling, PI3K/Akt signaling, and RAAS signaling involves in lipotoxicity. The upregulated Nox expression and the decreased Nrf2 expression result in oxidative stress directly. The injured renal resident cells release proinflammatory cytokines and chemokines to recruit immune cells such as macrophages from bone marrow. NF-κB signaling, NLRP3 inflammasome signaling, JAK-STAT signaling, Toll-like receptor signaling, and cGAS-STING signaling are major signaling pathways that mediate inflammation in inflammatory cells including immune cells and injured renal resident cells. The inflammatory cells produce and secret a great number of profibrotic cytokines such as TGF-β1, Wnt ligands, and angiotensin II. TGF-β signaling, Wnt signaling, RAAS signaling, and Notch signaling evoke the activation of myofibroblasts and promote the generation of ECM. The potential therapies targeted to these signaling pathways are also introduced here. In this review, we update the key signaling pathways of lipotoxicity, oxidative stress, inflammation, and myofibroblasts activation in kidneys with chronic injury, and the targeted drugs based on the latest studies. Unifying these pathways and the targeted therapies will be instrumental to advance further basic and clinical investigation in CKD.

Obesity and the Development of Lung Fibrosis

Obesity is an epidemic worldwide and the obese people suffer from a range of respiratory complications including fibrotic changes in the lung. The influence of obesity on the lung is multi-factorial, which is related to both mechanical injury and various inflammatory mediators produced by excessive adipose tissues, and infiltrated immune cells. Adiposity causes increased production of inflammatory mediators, for example, cytokines, chemokines, and adipokines, both locally and in the systemic circulation, thereby rendering susceptibility to respiratory diseases, and altered responses. Lung fibrosis is closely related to chronic inflammation in the lung. Current data suggest a link between lung fibrosis and diet-induced obesity, although the mechanism remains incomplete understood. This review summarizes findings on the association of lung fibrosis with obesity, highlights the role of several critical inflammatory mediators (e.g., TNF-α, TGF-β, and MCP-1) in obesity related lung fibrosis and the implication of obesity in the outcomes of idiopathic pulmonary fibrosis patients.

Retinal vasodilatory responses are inversely associated with plasminogen activator inhibitor-1: The African-PREDICT study

AIMS

Plasminogen activator inhibitor-1 (PAI-1), traditionally associated with fibrinolysis, is increasingly implicated in impaired vascular function. However, studies on its association with microvascular function are limited to the cutaneous and coronary microvascular beds in older and diseased individuals. To better understand its potential involvement in the early stages of disease development, we investigated the associations of retinal vasodilatory responses to flicker light with PAI-1 activity (PAI-1_act) in young and healthy individuals.

METHODS

We included healthy Black and White women and men (n = 518; aged 20-30 years), and measured plasma PAI-1_act and retinal vasodilatory responses to flicker light provocation. We also collected demographic and lifestyle data, measured blood pressure, anthropometry, blood lipids, inflammatory and other biomarkers.

RESULTS

In multivariate regression analyses, maximal retinal venular dilation associated independently and inversely with PAI-1_act (adj. R² = 0.11; β = -0.15; p = 0.001) in the total group. In exploratory subgroup analyses, this association remained in White women (adj. R² = 0.07; β = -0.23; p = 0.005), and was more robust with younger age and lower blood pressure and in non-smokers, but also with greater central adiposity, higher low-density lipoprotein cholesterol and inflammation (all p < 0.05).

CONCLUSIONS

Our data suggest that in young individuals, PAI-1 may already be associated with subclinical microvascular dysfunction.

Antioxidants and Oxidative Stress in Children: Influence of Puberty and Metabolically Unhealthy Status

Oxidative stress could help explain the relationship between childhood obesity and a metabolically unhealthy (MU) status. Moreover, puberty could also influence this relationship, since it entails physiological cardiometabolic changes. We aimed to evaluate plasma antioxidants and oxidative stress biomarkers in MU and metabolically healthy (MH) prepubertal and pubertal children and their associations with pro-inflammatory and endothelial damage biomarkers, taking puberty into account. A total of 1444 Spanish children aged 3-17 years (48.9% males, 66% prepubertal, 47.1% with obesity) were recruited. Blood pressure, anthropometric and biochemical parameters were measured, and children were categorized as having a MU or MH status according to risk factors. Retinol, carotenes, tocopherols, total antioxidant capacity (TAC), oxidized low-density lipoprotein and selected pro-inflammatory and endothelial damage biomarkers were analyzed. General linear models adjusted for age, sex, recruitment center and body mass index, partial correlations and stepwise linear regressions were performed. Lower carotenes and tocopherols levels were found in MU than in MH children. Plasma TAC was lower in prepubertal and higher in pubertal children with obesity compared to normal-weight children. Antioxidants and oxidative stress biomarkers showed novel associations with several pro-inflammatory and endothelial damage biomarkers, with pubertal differences, supporting the importance of considering both the antioxidant and oxidative stress status and puberty in the prevention of metabolic diseases in childhood.

Aberrant DNA methylation of Tgfb1 in diabetic kidney mesangial cells

Epigenetic modulation may underlie the progression of diabetic nephropathy (DN). Involvement of TGFB1 in mesangial fibrosis of DN led us to hypothesize that Tgfb1 DNA demethylation contributes to progression of DN. In primary mesangial cells from diabetic (db/db) mouse kidneys, demethylation of Tgfb1 DNA and upregulation of Tgfb1 mRNA progressed simultaneously. USF1 binding site in Tgfb1 promoter region were demethylated, and binding of USF1 increased, with decreased binding of DNMT1 in db/db compared with control. Given downregulation of Tgfb1 expression by folic acid, antioxidant Tempol reversed DNA demethylation, with increased and decreased recruitment of DNMT1 and USF1 to the promoter, resulting in decreased Tgfb1 expression in db/db mice. Addition of H₂O₂ to mesangial cells induced DNA demethylation and upregulated Tgfb1 expression. Finally, Tempol attenuated mesangial fibrosis in db/db mice. We conclude that aberrant DNA methylation of Tgfb1 due to ROS overproduction play a key to mesangial fibrosis during DN progression.

Individual variations in cardiovascular-disease-related protein levels are driven by genetics and gut microbiome

Despite a growing body of evidence, the role of the gut microbiome in cardiovascular diseases (CVDs) is still unclear. Here we present a systems-genome-wide and metagenome-wide association study on plasma concentrations of 92 CVD-related proteins in the population cohort Lifelines-DEEP. We identified genetic components for 73 proteins and microbial associations for 41 proteins, of which 31 were associated to both. The genetic and microbial factors identified mostly exert additive effects and collectively explain up to 76.6% of inter-individual variation (17.5% on average). Genetics contributes most to concentrations of immune-related proteins, while the gut microbiome contributes most to proteins involved in metabolism and intestinal health. We found several host-microbe interactions that impact proteins involved in epithelial function, lipid metabolism and central nervous system function. This study reveals important evidence for a joint genetic and microbial effect in cardiovascular disease and provides directions for future applications in personalized medicine.

Synergistic in vitro antioxidant activity and observational clinical trial of F105, a phytochemical formulation including Citrus bergamia, in subjects with moderate cardiometabolic risk factors

We examined the clinical safety and efficacy of F105 in 11 subjects with moderate dyslipidemia. F105 is a combination of bergamot fruit extract (Citrus bergamia, BFE) and 9 phytoextracts selected for their ability to improve the antioxidant and anti-inflammatory activity of BFE. In vitro F105 exhibited a synergistic inhibition of oxygen radical absorbing capacity, peroxynitrite formation, and myeloperoxidase activity. Following 12 weeks of F105 daily, no treatment-related adverse events or changes in body mass were seen. Statistically significant changes were noted in total cholesterol (-7.3%), LDL-cholesterol (-10%), non-HDL cholesterol (-7.1%), cholesterol/HDL (-26%), and apolipoprotein B (-2.8%). A post hoc analysis of 8 subjects with HbA1c > 5.4 and HOMA-IR score > 2 or elevated triglycerides revealed additional statistically significant changes in addition to those previously observed in all subjects including triglycerides (-27%), oxLDL (-19%), LDL/HDL (-25%), triglycerides/HDL (-27%), oxLDL/HDL (-25%), and PAI-1 (-37%). A follow-up case report of a 70-year-old female patient, nonresponsive to statin therapy and placed on F105 daily, demonstrated improved cardiometabolic variables over 12 weeks similar to the subgroup. In summary, F105 was clinically well-tolerated and effective for ameliorating dyslipidemia in subjects with moderate cardiometabolic risk factors, particularly in the individuals with HbA1c > 5.4%.

TGRL Lipolysis Products Induce Stress Protein ATF3 via the TGF-β Receptor Pathway in Human Aortic Endothelial Cells

Studies have suggested a link between the transforming growth factor beta 1 (TGF-β1) signaling cascade and the stress-inducible activating transcription factor 3 (ATF3). We have demonstrated that triglyceride-rich lipoproteins (TGRL) lipolysis products activate MAP kinase stress associated JNK/c-Jun pathways resulting in up-regulation of ATF3, pro-inflammatory genes and induction of apoptosis in human aortic endothelial cells. Here we demonstrate increased release of active TGF-β at 15 min, phosphorylation of Smad2 and translocation of co-Smad4 from cytosol to nucleus after a 1.5 h treatment with lipolysis products. Activation and translocation of Smad2 and 4 was blocked by addition of SB431542 (10 μM), a specific inhibitor of TGF-β-activin receptor ALKs 4, 5, 7. Both ALK receptor inhibition and anti TGF-β1 antibody prevented lipolysis product induced up-regulation of ATF3 mRNA and protein. ALK inhibition prevented lipolysis product-induced nuclear accumulation of ATF3. ALKs 4, 5, 7 inhibition also prevented phosphorylation of c-Jun and TGRL lipolysis product-induced p53 and caspase-3 protein expression. These findings demonstrate that TGRL lipolysis products cause release of active TGF-β and lipolysis product-induced apoptosis is dependent on TGF-β signaling. Furthermore, signaling through the stress associated JNK/c-Jun pathway is dependent on TGF-β signaling suggesting that TGF-β signaling is necessary for nuclear accumulation of the ATF3/cJun transcription complex and induction of pro-inflammatory responses.

Effect and mechanism of the Ang-(1-7) on human mesangial cells injury induced by low density lipoprotein

Hyperlipidemia is an independent risk factor for renal disease, and lipid deposition is associated with glomerulosclerosis. The angiotensin converting enzyme 2-angiotensin-(1-7)-Mas axis (ACE2-Ang-(1-7)-Mas axis) has been reported to participate in lipid metabolic regulation but its mechanism remains unclear. We hypothesized Ang-(1-7) would reduce lipid uptake in human mesangial cells (HMCs) by regulating the low density lipoprotein receptor-sterol regulatory element binding proteins 2-SREBP cleavage activating protein (LDLr-SREBP2-SCAP) negative feedback system, and improve glomerulosclerosis by regulating the transforming growth factor-β1 (TGF-β1). In this study we found that ACE2 was undetected in HMCs. The administration of LDL caused normal LDLr-SREBPs-SCAP negative feedback effect. Exogenous Ang-(1-7) enhanced this negative feedback effect via down-regulating LDLr, SREBP2, and SCAP expression, and effectively inhibited LDL-induced lipid deposition and cholesterol increases. This enhanced inhibitory effect was reversed by the Mas receptor antagonist A-779. Meanwhile, Ang-(1-7) significantly decreased the high LDL-induced production of TGF-β1, an effect blocked by A-779. Interestingly, HMCs treated with Ang-(1-7) alone activated the TGF-β1 expression. Our results suggested that Ang-(1-7) inhibits LDL accumulation and decreases cholesterol levels via modulating the LDLr-SREBPs-SCAP negative feedback system through the Mas receptor. Moreover, Ang-(1-7) exhibits a dual regulatory effect on TGF-β1 in HMCs.

Integrin-linked kinase mediates the hydrogen peroxide-dependent transforming growth factor-β1 up-regulation

Transforming growth factor type-β1 (TGF-β1) has been recognized as a central mediator in many pathological events related to extracellular matrix (ECM) proteins accumulation, where their locally increased expression has been implicated in the fibrosis process of numerous organs, including glomerular fibrosis in the kidney. We and others have reported the TGF-β1 synthesis regulation by reactive oxygen species (ROS), and moreover we also described the implication of integrin-linked kinase (ILK) in the AP-1-dependent TGF-β1 up-regulation. Thus, we propose here that hydrogen peroxide (H2O2)-dependent TGF-β1 regulation may be mediated by ILK activation. First we confirmed the increase in TGF-β1 expression in human mesangial cells (HMC) after treatment with H2O2 or with an alternative H2O2-generating system such as the glucose-oxidase enzyme (GOX). By using immunoblotting, immunofluorescence, and ELISA techniques, we demonstrate that extracellular H2O2 up-regulates TGF-β1 transcription, as well as increases TGF-β1 promoter activity. Furthermore, catalase-decreased intracellular H2O2 abolished TGF-β1 up-regulation. The use of pharmacological inhibitors as well as knockdown of ILK with small interfering RNA (siRNA) demonstrated the implication of a PI3K/ILK/AKT/ERK MAPK signaling pathway axis in the H2O2-induced TGF-β1 overexpression. Finally, we explored the physiological relevance of these findings by treating HMC with angiotensin II, a known stimuli of H2O2 synthesis. Our results confirm the relevance of previous findings after a more physiological stimulus. In summary, our results provide evidence that ILK activity changes may act as a mechanism in response to different stimuli such as H2O2 in the induced TGF-β1 up-regulation in pathological or even physiological conditions.

Involvement of Kv1.5 protein in oxidative vascular endothelial cell injury

Endothelial injury related to oxidative stress is a key event in cardiovascular diseases, such as hypertension and atherosclerosis. The activation of the redox-sensitive Kv1.5 potassium channel mediates mitochondrial reactive oxygen species (ROS)-induced apoptosis in vascular smooth muscle cells and some cancer cells. Kv1.5 channel is therefore taken as a new potential therapeutic target for pulmonary hypertension and cancers. Although Kv1.5 is abundantly expressed in vascular endothelium, there is little knowledge of its role in endothelial injury related to oxidative stress. We found that DPO-1, a specific inhibitor of Kv1.5, attenuated H₂O₂-evoked endothelial cell apoptosis in an in vivo rat carotid arterial model. In human umbilical vein endothelial cells (HUVECs) and human pulmonary arterial endothelial cells (HPAECs), angiotensin II and oxLDL time- or concentration-dependently enhanced Kv1.5 protein expression in parallel with the production of intracellular ROS and endothelial cell injury. Moreover, siRNA-mediated knockdown of Kv1.5 attenuated, whereas adenovirus-mediated Kv1.5 cDNA overexpression enhanced oxLDL–induced cellular damage, NADPH oxidase and mitochondria-derived ROS production and restored the decrease in protein expression of mitochondria uncoupling protein 2 (UCP2). Collectively, these data suggest that Kv1.5 may play an important role in oxidative vascular endothelial injury.

PAI-1 in tissue fibrosis

Fibrosis is defined as a fibroproliferative or abnormal fibroblast activation-related disease. Deregulation of wound healing leads to hyperactivation of fibroblasts and excessive accumulation of extracellular matrix (ECM) proteins in the wound area, the pathological manifestation of fibrosis. The accumulation of excessive levels of collagen in the ECM depends on two factors: an increased rate of collagen synthesis and or decreased rate of collagen degradation by cellular proteolytic activities. The urokinase/tissue type plasminogen activator (uPA/tPA) and plasmin play significant roles in the cellular proteolytic degradation of ECM proteins and the maintenance of tissue homeostasis. The activities of uPA/tPA/plasmin and plasmin-dependent MMPs rely mostly on the activity of a potent inhibitor of uPA/tPA, plasminogen activator inhibitor-1 (PAI-1). Under normal physiologic conditions, PAI-1 controls the activities of uPA/tPA/plasmin/MMP proteolytic activities and thus maintains the tissue homeostasis. During wound healing, elevated levels of PAI-1 inhibit uPA/tPA/plasmin and plasmin-dependent MMP activities, and, thus, help expedite wound healing. In contrast to this scenario, under pathologic conditions, excessive PAI-1 contributes to excessive accumulation of collagen and other ECM protein in the wound area, and thus preserves scarring. While the level of PAI-1 is significantly elevated in fibrotic tissues, lack of PAI-1 protects different organs from fibrosis in response to injury-related profibrotic signals. Thus, PAI-1 is implicated in the pathology of fibrosis in different organs including the heart, lung, kidney, liver, and skin. Paradoxically, PAI-1 deficiency promotes spontaneous cardiac-selective fibrosis. In this review, we discuss the significance of PAI-1 in the pathogenesis of fibrosis in multiple organs.

Bariatric surgery and renal function

Obesity causes a significant healthcare burden and has been shown to be an important risk factor in the development of cardiovascular disease, type 2 diabetes, and increasingly chronic kidney disease. Bariatric surgery is the most effective treatment for obesity and has been shown to drastically improve both blood pressure and diabetic control. However, the interaction of bariatric surgery and renal function is less clear. This review focuses on the effect of bariatric surgery on renal function both in the acute situation, with respect to acute kidney injury, and also on changes in renal function parameters post-bariatric surgery weight loss. The interaction of obesity, bariatric surgery, and nephrolithiasis as a precipitant of acute kidney injury will also be considered. The role of bariatric surgery in pre- and post-renal transplant recipients is discussed as well as possible mechanisms underlying the improvement in renal function.

Association of macroalbuminuria with oxidized LDL and TGF-beta in type 2 diabetic patients: a case-control study

The pathogenesis of diabetic nephropathy, mainly characterized by macroalbuminuria, is still poorly understood, but it is reported that transforming growth factor-beta (TGF-beta) plays a key role. In vitro evidence suggests that administration of oxidized LDL (ox-LDL) can lead to upregulation of TGF-beta by human glomerular mesangial cells. This study aimed to evaluate the association between macroalbuminuria, ox-LDL, and TGF-beta in diabetic patients. A total of 77 type 2 diabetic patients with macroalbuminuria (albumin excretion rate: AER > or = 300 mg/24 h) and 66 patients with normoalbuminuria (AER < or = 30 mg/24 h) were recruited. Fasting blood samples were obtained and serum levels of ox-LDL and TGF-beta were determined. Ox-LDL and TGF-beta were significantly higher in patients with macroalbuminuria than in those with normoalbuminuria (98.93 + or - 3.99 vs. 72.45 + or - 2.48 U/l; P < 0.001 and 6.46 + or - 0.74 vs. 2.49 + or - 0.39 ng/ml; P < 0.001, respectively). In patients with macroalbuminuria, there was a significant correlation between Ox-LDL and TGF-beta (r = 0.376; P < 0.01). AER was significantly correlated to ox-LDL (r = 0.302; P < 0.05) and TGF-beta (r = 0.306; P < 0.05) in macroalbuminuric patients. This association remained significant after adjustment for potential confounders. Adjustment for TGF-beta (ox-LDL), attenuated the association of ox-LDL (TGF-beta) with AER. In conclusion, this study demonstrated the association of TGF-beta and ox-LDL with albuminuria in macroalbuminuric type 2 diabetic patients, and suggested that this relationship is highly mediated through the correlation between TGF-beta and ox-LDL.

Up-regulating PPAR-γ expression and NO concentration, and down-regulating PAI-1 concentration in a rabbit atherosclerotic model: the possible antiatherogenic and antithrombotic effects of atorvastatin

We investigated the effect of atorvastatin on the plasma concentration of plasminogen activator inhibitor-1 (PAI-1) and nitric oxide (NO) in a rabbit model, and the relationship between these effects and peroxisome proliferator-activated receptor γ (PPAR-γ). In our experiments, 24 male Japanese rabbits were divided into 3 groups: the high-cholesterol diet group (the high-C group), the high-cholesterol diet plus atorvastatin group (the atorvastatin group), and the normal diet group (the control group). All rabbits were killed after a 16-week feeding. The expression of PPAR-γ and the plasma concentrations of NO and PAI-1 were evaluated by an immunohistochemical assay while the level of the plasma lipid profile was measured using a commercially available kit. The atorvastatin not only reduces the plasma levels of the total cholesterol (TC) and the low-density lipoprotein cholesterol (LDL-C), but also increases the expression of PPAR-γ and the concentration of NO in comparison to the control group [16.11 ± 2.35% vs 7.68 ± 1.04%; 249.30 ± 27.90 vs 179.12 ± 28.51 (μml/L), p<0.05 respectively]. In addition, the concentration of PAI-1 in the atorvastatin group is lower than that in the control group (0.11 ± 0.01A vs 0.14 ± 0.02A, p<0.05). The changes of PAI-1 and NO in the atorvastatin group are in good accordance to that of PPAR-γ. Results show that atorvastatin significantly up-regulates the expression of nuclear transcription factor, namely PPAR-γ, and induces the changes of the other two factors, which might provide mechanisms for the antiatherosclerotic and antithrombotic effects of atorvastatin.

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.

Effects of different LDL particles on inflammatory molecules in human mesangial cells

AIMS/HYPOTHESIS

Inflammation is a mechanism of glomerular damage in chronic glomerulopathies. LDL may increase the production of inflammatory cytokines in renal tissues. However, the relative role of native, oxidised and glycated LDL in promoting this process has been only partially elucidated.

METHODS

We tested the inflammatory and proapoptotic effects of native, oxidised and glycated LDL in human mesangial cells (HMCs) by measuring levels of IL6, CD40 and macrophage migration inhibitory factor (MIF) genes, MIF protein, release of IL6, soluble CD40, fibronectin and laminin, early and late apoptosis, and extracellular regulated kinases (ERK) 1/2 and c-Jun N-terminal kinase (JNK) activation.

RESULTS

IL6 and CD40 mRNA were dose-dependently upregulated by all three species; this was closely paralleled by their increased release. MIF mRNA was potently stimulated by modified LDL, as confirmed by immunostaining. Fibronectin and laminin release was stimulated by both oxidised and glycated, but not native, LDL. All LDL species induced some increase in late, but not early, apoptosis, and similarly activated JNK2/3 phosphorylation; in contrast, ERK1/2 phosphorylation was more strongly upregulated by oxidised than either native or glycated LDL.

CONCLUSIONS

In HMCs, the production and release of IL6 and CD40 is stimulated by both native and modified LDL, while MIF is more strongly stimulated by oxidised LDL. Regarding the pattern of mesangial expansion, fibronectin and laminin are upregulated by oxidised and glycated LDL. Apoptosis, if modest, is induced by all species. Intracellular signalling of native and modified LDL involves JNK2/3 and, perhaps more specifically, ERK1/2. Tight control of the lipid profile may be useful in preserving kidney function in patients with metabolic alterations.

Lovastatin inhibits oxidized low-density lipoprotein-induced plasminogen activator inhibitor and transforming growth factor-beta1 expression via a decrease in Ras/extracellular signal-regulated kinase activity in mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) might be involved in the progression of renal disease. Ox-LDL stimulation of plasminogen activator inhibitor-1 (PAI-1) expression via transforming growth factor-beta (TGF-beta)/Smad signaling in mesangial cells required activation of extracellular signal-regulated kinase (ERK). Mevalonate depletion by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors, or statins, decreases the levels of farnesyl pyrophosphate (FPP) for isoprenylation of Ras. We postulate that statins may ameliorate the Ox-LDL-induced mesangial matrix accumulation by inhibiting Ras/ERK activation with subsequent downregulation of TGF-beta target genes. Quiescent mesangial cells were incubated for 18 h with and without the presence of lovastatin before 50 microg/mL of Ox-LDL treatment for 1 h. Lovastatin inhibited markedly the stimulatory effects of Ox-LDL on ERK1/2 activation, nuclear Smad3 expression, TGF-beta1 and PAI-1 mRNA and protein expression, and PAI-1 luciferase activity. These inhibitory effects of lovastatin were reversed almost completely by mevalonate or FPP. Similar to lovastatin, FTI-277, which is an inhibitor of Ras farnesylation, decreased the Ox-LDL-induced activation of ERK/Smad3 and induction of TGF-beta1/PAI-1. These results indicate that lovastatin prevents the Ox-LDL-induced Ras/ERK activation that results in inhibition of Smad3 activation in mesangial cells with subsequent downregulation of TGF-beta target genes. Thus, statins seem to have antifibrotic effects through their anti-TGF-beta response that are relevant in the treatment of chronic renal disease with dyslipidemia.

Blockade of cannabinoid CB1 receptors improves renal function, metabolic profile, and increased survival of obese Zucker rats

Obesity is a major risk factor in the development of chronic renal failure. Rimonabant, a cannabinoid CB1 receptor antagonist, improves body weight and metabolic disorders; however, its effect on mortality and chronic renal failure associated with obesity is unknown. Obese Zucker rats received either rimonabant or vehicle for 12 months and were compared to a pair-fed but untreated group of obese rats. Mortality in the obese rats was significantly reduced by rimonabant along with a sustained decrease in body weight, transient reduction in food intake, and an increase in plasma adiponectin. This was associated with significant reduction in plasma total cholesterol, low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio, triglycerides, glucose, norepinephrine, plasminogen activator inhibitor 1, and preservation of pancreatic weight and beta-cell mass index. The cannabinoid antagonist attenuated the increase in proteinuria, urinary N-acetylglucosaminidase excretion, plasma creatinine, and urea nitrogen levels while improving creatinine clearance. Renal hypertrophy along with glomerular and tubulointerstitial lesions were reduced by rimonabant. Although the drug did not modify hemodynamics, it normalized the pressor response to angiotensin II. Our study suggests that in a rat model of chronic renal failure due to obesity, rimonabant preserves renal function and increases survival.

Role of CAGA boxes in the plasminogen activator inhibitor-1 promoter in mediating oxidized low-density lipoprotein-induced transcriptional activation in mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) activates transforming growth factor-beta (TGF-beta)/Smad signaling to stimulate plasminogen activator inhibitor-1 (PAI-1) expression in mesangial cells. Smad-binding sequences, termed CAGA boxes, are present in the promoter of human PAI-1 gene, and they mediate TGF-beta transcriptional induction. However, the functional role of each CAGA box in the Ox-LDL-induced PAI-1 promoter activation is unknown. In this study, mutation of 1 of the 3 CAGA boxes located at -730, -580, and -280 of the PAI-1 promoter decreased the Ox-LDL-induced luciferase activity by 40 to 58%, whereas mutations in 2 sites reduced it over 75% or completely abolished it. Overexpression of Smad3 in N-terminal tagged Smad3-transfected cells increased the Ox-LDL-induced transcriptional activation of the PAI-1 promoter, whereas mutation of Smad3 abolished it. Electrophoretic mobility shift assay showed that the labeled -280, -580, and -730 CAGA box probes detected DNA/protein complexes induced by Ox-LDL, whereas mutant probes did not. When nuclear extracts were preincubated with a 100-fold of an unlabeled -280, -580, and -730 CAGA oligonucleotide, the formation of complexes was prevented but not with mutant CAGA box competitors. The addition of anti-Smad3 to the reaction with the labeled -280 or -580 CAGA box probe resulted in a supershift, but not with the -730 CAGA box probe. These results suggest that the 3 CAGA elements in the PAI-1 promoter mediate the Ox-LDL-induced PAI-1 transcription to a different degree, of which the -280 and -580 CAGA regions directly bind to Smad3.

Effects of long-term elevated glucose on collagen formation by mesangial cells

Glomerulosclerosis is one of the complications of diabetes that occurs after many years of uncontrolled hyperglycemia. Mesangial cells (MCs) exposed to high glucose (HG) for short periods have shown that transforming growth factor-beta (TGF-beta) and activated diacylglycerol-dependent protein kinase C (PKC) mediate increased collagen formation. Our study examined collagen formation by MCs exposed to HG for 8 weeks. Exposure to HG in overnight culture resulted in the activation of all PKC isoforms. In contrast, 8-week exposure to HG resulted in the persistent activation of PKC-delta, did not change PKC-alpha or -beta activity, and decreased PKC-epsilon activity while increasing collagen I and IV gene and protein expression. Collagen IV accumulation was reversed by specific PKC-delta inhibition. Collagen IV gene expression was completely normalized by TGF-beta neutralization; however, this was associated with plasminogen activator inhibitor-1 (PAI-1) overexpression and a modest reduction in collagen protein. Our studies suggest that prolonged exposure to HG results in PKC-delta-driven collagen accumulation by MCs mediated by PAI-1 but independent of TGF-beta.

Obesity and obesity-initiated metabolic syndrome: mechanistic links to chronic kidney disease

There is an epidemic of obesity and the metabolic syndrome in the United States and across the world. Both entities are associated with high mortality, mainly as a result of cardiovascular disease. The epidemic of obesity has been paralleled by an increase in the incidence of chronic kidney disease (CKD). Several recent epidemiologic studies have shown that obesity and the metabolic syndrome are independent predictors of CKD. In addition to diabetes and hypertension, several other mechanisms have been postulated to initiate and maintain kidney injury in patients with obesity and the metabolic syndrome. This article reviews the recent epidemiologic data linking obesity and the metabolic syndrome to CKD and summarizes the potential mechanisms of renal injury in this setting, with a focus on the role of inflammation, lipotoxicity, and hemodynamic factors. Potential preventive and therapeutic modalities based on the limited evidence available are discussed.

ERK contributes to the effects of Smad signaling on oxidized LDL-induced PAI-1 expression in human mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) stimulates plasminogen activator inhibitor-1 (PAI-1) expression in human mesangial cells mediated by transforming growth factor-beta (TGF-beta)/Smad signaling pathway. TGF-beta activates extracellular signal-regulated kinase (ERK) in mesangial cells, and ERK is involved in activation of Smad2/3. This study examines whether an interaction exists between Ox-LDL-induced TGF-beta/Smad signaling pathways and ERK activation leading to PAI-1 transcription in human mesangial cells. Ox-LDL (50 microg/mL) induced an acute increase in ERK activity within 15 min, which decreased to control value at 2 h. Incubation with anti-TGF-beta or SB-431542, an inhibitor of the TGF-beta type I receptor, along with Ox-LDL, inhibited the expected increase in ERK phosphorylation. Treatment with PD98059 or UO126, mitogen-activated ERK-activating kinase 1/2 inhibitors, significantly inhibited the Ox-LDL-induced increase in PAI-1 mRNA and nuclear Smad3 expression, DNA/protein complex formation, and PAI-1 promoter activity. These results suggest that phosphorylation of ERK is induced by Ox-LDL through the induction of the TGF-beta signaling pathway and that activated ERK, in turn, participates in the Ox-LDL-induced Smad3 activation and subsequent PAI-1 gene expression in mesangial cells.

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.

Glibenclamide prevents increased extracellular matrix formation induced by high glucose concentration in mesangial cells

Other than stimulation of cell contractility, little is known about the potential metabolic effects induced by sulfonylureas, independently of insulin action. Previous studies from our laboratory demonstrated complete abrogation of glomerulosclerosis in an experimental model of type 1 diabetes chronically (9 mo) treated with low-dose sulfonylureas (Biederman JI, Vera E, Pankhaniya R, Hassett C, Giannico G, Yee J, Cortes P. Kidney Int 67: 554-565, 2005). Therefore, the effects of glibenclamide (Glib) on net collagen I, collagen IV, and fibronectin medium net secretion and cell layer collagen I deposition were investigated in mesangial cells continuously exposed to 25 mM glucose for 8 wk and treated with predetermined increasing concentrations of Glib for the same period. Clinically relevant concentrations (0.01 microM) of Glib fully suppressed the high glucose-enhanced accumulation of collagen I, collagen IV, and fibronectin in the medium and inhibited collagen I deposition in the cell layer. These effects occurred while transforming growth factor (TGF)-beta1 medium concentration remained elevated and glucose uptake was increased to levels above those in 25 mM glucose-incubated cultures. The decreased collagen I accumulation occurred simultaneously with enhanced collagen I mRNA expression in concert with marked suppression of plasminogen inhibitor type-1 (PAI-1) mRNA and protein expression. This strongly suggests an accelerated matrix turnover favoring breakdown. Glib-induced effects demonstrated a biphasic pattern, being absent or reversed in cells treated with higher Glib concentrations (0.1 or 1 microM). Therefore, chronic Glib treatment at low concentrations markedly diminishes the high glucose-induced enhanced accumulation of extracellular matrix components by suppression of steady-state PAI-1 transcriptional activity. These results and those previously reported in vivo suggest that long-term Glib treatment may prevent glomerulosclerosis in insulin-deficient diabetes.

Acarbose improves fibrinolytic activity in patients with impaired glucose tolerance

Acarbose has been shown to ameliorate insulinemia, suggesting that it may exert favorable effects on the impaired fibrinolytic state in prediabetic patients. We therefore conducted a randomized controlled study to examine the effects of acarbose on fibrinolysis in patients with impaired glucose tolerance (IGT). The participants were randomized to receive (n = 20) or not (control, n = 20) 100 mg of acarbose before each meal (300 mg/d) for 3 months. A marked decrease in the plasma levels of plasminogen activator inhibitor 1 (by 42%) and fibrinogen (by 27%) was observed in the acarbose group at the end of the study, whereas no significant changes in the levels of these parameters were observed in the control group. We also conducted postprandial evaluation of insulin-related clinical markers and found ameliorated hyperinsulinemia in the subjects treated with acarbose. These results indicate that acarbose could improve fibrinolysis in patients with IGT, mainly by ameliorating insulinemia. Other favorable effects of acarbose, such as reduction in the plasma levels of oxidized low-density lipoprotein, glucose toxicity, and hyperglycemia, might also contribute, at least in part, to the beneficial effects of the drug on the fibrinolytic state in patients with IGT.