Oxidised LDL up-regulate CD36 expression by the Nrf2 pathway in 3T3-L1 preadipocytes

Krill oil inhibited adipogenic differentiation by inducing the nuclear Nrf2 expression and the AMPK activity

The current study investigated the antiadipogenic mechanism of krill oil from the 3T3-L1 adipocytes. The krill oil adhered to the criteria as a food standard by showing 50.8% of the total phospholipid, 5.27% myristic acid, and 1.63% linoleic acid. The lipid accumulation that was measured in the 3T3-L1 cells using oil red O staining was reduced up to 54% by the krill oil. The krill oil treatment reduced the adipogenic transcription factors by downregulating the sterol regulatory element binding protein 1 (SREBP1) and acetyl-CoA carboxylase (ACC), phospho-ACC, and AMP-activated protein kinase (AMPK) phosphorylation. The current study confirmed that the krill oil inhibited adipogenesis by downregulating SREBP1 and ACC via the upregulation of the AMPK and nuclear factors E2-related factor 2 (Nrf2) signaling pathway in the 3T3-L1 adipocytes. These findings suggest that krill oil is a good source of phospholipid and phosphatidylcholine, which could be a potential natural antiobesity ingredient by inhibiting adipogenesis.

The Protective Role of Nrf2 in Renal Tubular Cells in Oxidised Low-Density Lipoprotein-Induced Fibrosis

Background: CD36 is the receptor of oxidised low-density lipoprotein (OxLDL) in renal tubular epithelial cells. Nuclear factor erythroid 2-related factor 2 (Nrf2) is the key factor in the activation of the Nrf2 signalling pathway and the regulation of oxidative stress. Kelch-like ECH-associated protein 1 (Keap1) is known as an Nrf2 inhibitor. Methods: We used OxLDL and Nrf2 inhibitors at different concentrations and durations to treat renal tubular epithelial cells; the expression of CD36 and cytoplasmic and nucleic Nrf2 and E-cadherin in those cells were observed by Western blot and reverse-transcription polymerase chain reaction. Results: The protein levels of Nrf2 decreased in expression after 24 hours of OxLDL treatment. At the same time, the Nrf2 protein level in the cytoplasm did not change significantly compared with that of the control group, and the Nrf2 protein level expression in the nucleus increased. Both the messenger ribonucleic acid (mRNA) and protein expression of CD36 decreased following the treatment of cells with the Nrf2 inhibitor Keap1. Kelch-like ECH-associated protein 1 was overexpressed, and CD36 mRNA and protein expression were decreased in OxLDL-treated cells. Following the overexpression of Keap1, E-cadherin expression was reduced in NRK-52E cells. Conclusion: Nuclear factor erythroid 2-related factor 2 can be activated by OxLDL; however, it can only alleviate OxLDL-induced oxidative stress by transferring from the cytoplasm to the nucleus. Additionally, Nrf2 may play a protective role by upregulating CD36.

Lemongrass essential oil and its major constituent citral isomers modulate adipogenic gene expression in 3T3-L1 cells

Obesity is a predisposing factor to diseases such as diabetes mellitus, hypertension, and coronary artery disease. Lemongrass essential oil (LEO), from Cymbopogon flexuosus, possesses numerous therapeutic properties including modulation of obesity in vivo. This experiment investigated the effect of LEO and its major components citral (3,7-dimethyl-2,6-octadienal), citral dimethyl acetal (1,1-dimethoxy-3,7-dimethylocta-2,6-diene), and citral diethyl acetal (1,1-diethoxy-3,7-dimethylocta-2,6-diene) in modulation of adipogenesis and genetic expression in adipocytes. Adipogenesis was induced from murine 3T3-L1 preadipocytes procured from ATCC and maintained in Dulbecco's modified Eagle's medium (DMEM) enriched with calf serum. Differentiation was conducted using DMEM enriched with 10% fetal bovine serum, Dexamethasone 0.25 µM, 3-isobutyl-methylxanthine 0.5 mM, and insulin 10 mg/ml for 2 days, followed by 5 days of insulin 10 mg/ml alone. Samples were subjected to experimental treatments at a concentration of 2.5 × 10^-3 . Intracellular triglycerides were quantified and photomicrographs were obtained following Oil red O (ORO) staining procedure. Total ribonucleic acid was extracted and expression of genes effecting in lipid metabolism were quantitated using real-time polymerase chain reaction. ORO staining procedure and spectrophotometric analysis demonstrated decreased lipid accumulation following treatments. LEO and its major constituents significantly inhibited expression of sterol response binding protein 2, cluster of differentiation 36, fatty acid binding protein 4, and peripilin. These results indicate modulation of lipid accumulation through decreased lipid uptake, increased lipolysis, decreased differentiation, and downregulated lipid biosynthesis. This investigation suggests that LEO and its constituents exert effects on adipocyte metabolism and are important for understanding metabolic disease. Further investigation is required to elucidate the degree that each mechanism implicated contributes to the observed effect.

Tanshinone IIA attenuates atherosclerosis via inhibiting NLRP3 inflammasome activation

Tanshinone IIA (Tan IIA) possesses potent anti-atherogenic function, however, the underlying pharmacological mechanism remains incompletely understood. Previous studies suggest that oxidized LDL (oxLDL)-induced NLRP3 (NOD-like receptor (NLR) family, pyrin domain-containing protein 3) inflammasome activation in macrophages plays a vital role in atherogenesis. Whether the anti-atherogenic effect of Tan IIA relies on the inhibition of the NLRP3 inflammasome has not been investigated before. In this study, we found that Tan IIA treatment of high-fat diet fed ApoE-/- mice significantly attenuated NLRP3 inflammasome activation in vivo. Consistently, Tan IIA also potently inhibited oxLDL-induced NLRP3 inflammasome activation in mouse macrophages. Mechanically, Tan IIA inhibited NF-κB activation to downregulate pro-interleukin (IL) -1β and NLRP3 expression, and decreased oxLDL-induced expression of lectin-like oxidized LDL receptor-1 (LOX-1) and cluster of differentiation 36 (CD36), thereby attenuating oxLDL cellular uptake and subsequent induction of mitochondrial and lysosomal damage - events that promote the NLRP3 inflammasome assembly. Through regulating both the inflammasome 'priming' and 'activation' steps, Tan IIA potently inhibited oxLDL-induced NLRP3 inflammasome activation, thereby ameliorating atherogenesis.

SIRT3 deficiency exacerbates fatty liver by attenuating the HIF1α-LIPIN 1 pathway and increasing CD36 through Nrf2

Background

Deficiency of mitochondrial sirtuin 3 (SIRT3), a NAD⁺-dependent protein deacetylase that maintains redox status and lipid homeostasis, contributes to hepatic steatosis. In this study, we investigated additional mechanisms that might play a role in aggravating hepatic steatosis in Sirt3-deficient mice fed a high-fat diet (HFD).

Methods

Studies were conducted in wild-type (WT) and Sirt3^−/− mice fed a standard diet or a HFD and in SIRT3-knockdown human Huh-7 hepatoma cells.

Results

Sirt3^−/− mice fed a HFD presented exacerbated hepatic steatosis that was accompanied by decreased expression and DNA-binding activity of peroxisome proliferator-activated receptor (PPAR) α and of several of its target genes involved in fatty acid oxidation, compared to WT mice fed the HFD. Interestingly, Sirt3 deficiency in liver and its knockdown in Huh-7 cells resulted in upregulation of the nuclear levels of LIPIN1, a PPARα co-activator, and of the protein that controls its levels and localization, hypoxia-inducible factor 1α (HIF-1α). These changes were prevented by lipid exposure through a mechanism that might involve a decrease in succinate levels. Finally, Sirt3^−/− mice fed the HFD showed increased levels of some proteins involved in lipid uptake, such as CD36 and the VLDL receptor. The upregulation in CD36 was confirmed in Huh-7 cells treated with a SIRT3 inhibitor or transfected with SIRT3 siRNA and incubated with palmitate, an effect that was prevented by the Nrf2 inhibitor ML385.

Conclusion

These findings demonstrate new mechanisms by which Sirt3 deficiency contributes to hepatic steatosis.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Oxidized LDL Modify the Human Adipocyte Phenotype to an Insulin Resistant, Proinflamatory and Proapoptotic Profile

Little information exists in humans on the regulation that oxidized low-density lipoprotein (oxLDL) exerts on adipocyte metabolism, which is associated with obesity and type 2 diabetes. The aim was to analyze the oxLDL effects on adipocytokine secretion and scavenger receptors (SRs) and cell death markers in human visceral adipocytes. Human differentiated adipocytes from visceral adipose tissue from non-obese and morbidly obese subjects were incubated with increasing oxLDL concentrations. mRNA expression of SRs, markers of apoptosis and autophagy, secretion of adipocytokines, and glucose uptake were analyzed. In non-obese and in morbidly obese subjects, oxLDL produced a decrease in insulin-induced glucose uptake, a significant dose-dependent increase in tumor necrosis factor-α (TNF-α), IL-6, and adiponectin secretion, and a decrease in leptin secretion. OxLDL produced a significant increase of Lox-1 and a decrease in Cxcl16 and Cl-p1 expression. The expression of Bnip3 (marker of apoptosis, necrosis and autophagy) was significantly increased and Bcl2 (antiapoptotic marker) was decreased. OxLDL could sensitize adipocytes to a lower insulin-induced glucose uptake, a more proinflammatory phenotype, and could modify the gene expression involved in apoptosis, autophagy, necrosis, and mitophagy. OxLDL can upregulate Lox-1, and this could lead to a possible amplification of proinflammatory and proapoptotic effects of oxLDL.

CD36 signaling in vascular redox stress

Scavenger receptor CD36 is a multifunctional membrane protein that promotes thrombosis in conditions of oxidative stress such as metabolic disorders including dyslipidemia, diabetes mellitus, and chronic inflammation. In these conditions, specific reactive oxidant species are generated that are context and cell dependent. In the vasculature, CD36 signaling in smooth muscle cells and endothelial cells promotes generation of reactive oxygen species, genetic downregulation of antioxidant genes, and impaired smooth muscle and endothelial function. In hematopoietic cells, CD36 signaling enhances platelet dysfunction thus decreasing the threshold for platelet activation and accelerating arterial thrombosis, whereas in macrophages, CD36 promotes lipid-laden foam cell formation and atherosclerosis. These clinically significant processes are mediated through complex redox regulated signaling mechanisms that include Src-family kinases, MAP kinases and other downstream effectors. We provide an overview of CD36 signaling in vascular redox stress highlighting the role in oxidant generation in vascular and hematopoietic cells, but with special emphasis on platelets and dyslipidemia.

The Association of Polyunsaturated Fatty Acid δ-5-Desaturase Activity with Risk Factors for Type 2 Diabetes Is Dependent on Plasma ApoB-Lipoproteins in Overweight and Obese Adults

Background

δ-5 and δ-6 desaturases (D5D and D6D) catalyze the endogenous conversion of n-3 (ω-3) and n-6 (ω-6) polyunsaturated fatty acids (PUFAs). Their activities are negatively and positively associated with type 2 diabetes (T2D), respectively, by unclear mechanisms. Elevated plasma apoB-lipoproteins (measured as plasma apoB), which can be reduced by n-3 PUFA intake, promote T2D risk factors.

Objective

The aim of this study was to test the hypothesis that the association of D5D and D6D activities with T2D risk factors is dependent on plasma apoB.

Methods

This is a pooled analysis of 2 populations recruited for 2 different metabolic studies. It is a post hoc analysis of baseline data of these subjects [n = 98; 60% women (postmenopausal); mean ± SD body mass index (in kg/m2): 32.8 ± 4.7; mean ± SD age: 57.6 ± 6.3 y]. Glucose-induced insulin secretion (GIIS) and insulin sensitivity (IS) were measured using Botnia clamps. Plasma clearance of a high-fat meal (600 kcal/m2, 66% fat) and white adipose tissue (WAT) function (storage of 3H-triolein-labeled substrate) were assessed in a subpopulation (n = 47). Desaturase activities were estimated from plasma phospholipid fatty acids. Associations were examined using Pearson and partial correlations.

Results

While both desaturase activities were positively associated with percentage of eicosapentaenoic acid, only D5D was negatively associated with plasma apoB (r = -0.30, P = 0.003). Association of D5D activity with second-phase GIIS (r = -0.23, P = 0.029), IS (r = 0.33, P = 0.015, in women) and 6-h area-under-the-curve (AUC6h) of plasma chylomicrons (apoB48, r = -0.47, P = 0.020, in women) was independent of age and adiposity, but was eliminated after adjustment for plasma apoB. D6D activity was associated in the opposite direction with GIIS (r = 0.24, P = 0.049), IS (r = -0.36, P = 0.004) and AUC6h chylomicrons (r = 0.52, P = 0.004), independent of plasma apoB. Both desaturases were associated with plasma interleukin-1-receptor antagonist (D5D: r = -0.45, P < 0.001 in women; D6D: r = -0.33, P = 0.007) and WAT function (trend for D5D: r = 0.30, P = 0.05; D6D: r = 0.39, P = 0.027) independent of any adjustment.

Conclusions

Association of D5D activity with IS, lower GIIS, and plasma chylomicron clearance is dependent on plasma apoB in overweight and obese adults.

Cortisol regulates immune and metabolic processes in murine adipocytes and macrophages through HTR2c and HTR5a serotonin receptors

Epidemiological studies implicate stress as an important factor contributing to the increasing prevalence of metabolic disorders. Studies have correlated visceral obesity and atherosclerosis with hyper-cortisolemia, a sequela of chronic psychological stress in humans and animals. Although several hormonal markers of stress have been associated with various metabolic disorders, the mechanism by which these hormones alter metabolic functions have not been established. We used an in vitro model system, culturing 3T3-L1 pre-adipocytes and RAW 264.7 macrophages in the presence or absence of cortisol, to analyze cell signaling pathways mediating changes in metabolic functions. Our analysis revealed that cortisol up-regulated the expression and function of two serotonin (S) receptors, HTR2c and HTR5a. HTR2c and HTR5a were also directly involved in mediating cortisol enhanced adipogenesis when pre-adipocytes were cultured alone or in the presence of macrophages. Finally, cortisol treatment of pre-adipocytes co-cultured with macrophages enhanced adipogenesis in both macrophages and pre-adipocytes.

High plasma apolipoprotein B identifies obese subjects who best ameliorate white adipose tissue dysfunction and glucose-induced hyperinsulinemia after a hypocaloric diet

Background

To optimize the prevention of type 2 diabetes (T2D), high-risk obese subjects with the best metabolic recovery after a hypocaloric diet should be targeted. Apolipoprotein B lipoproteins (apoB lipoproteins) induce white adipose tissue (WAT) dysfunction, which in turn promotes postprandial hypertriglyceridemia, insulin resistance (IR), and hyperinsulinemia.

Objective

The aim of this study was to explore whether high plasma apoB, or number of plasma apoB lipoproteins, identifies subjects who best ameliorate WAT dysfunction and related risk factors after a hypocaloric diet.

Design

Fifty-nine men and postmenopausal women [mean ± SD age: 58 ± 6 y; body mass index (kg/m2): 32.6 ± 4.6] completed a prospective study with a 6-mo hypocaloric diet (-500 kcal/d). Glucose-induced insulin secretion (GIIS) and insulin sensitivity (IS) were measured by 1-h intravenous glucose-tolerance test (IVGTT) followed by a 3-h hyperinsulinemic-euglycemic clamp, respectively. Ex vivo gynoid WAT function (i.e., hydrolysis and storage of 3H-triolein-labeled triglyceride-rich lipoproteins) and 6-h postprandial plasma clearance of a 13C-triolein-labeled high-fat meal were measured in a subsample (n = 25).

Results

Postintervention first-phase GIISIVGTT and total C-peptide secretion decreased in both sexes, whereas second-phase and total GIISIVGTT and clamp IS were ameliorated in men (P < 0.05). Baseline plasma apoB was associated with a postintervention increase in WAT function (r = 0.61) and IS (glucose infusion rate divided by steady state insulin (M/Iclamp) r = 0.30) and a decrease in first-phase, second-phase, and total GIISIVGTT (r = -0.30 to -0.35) without sex differences. The association with postintervention amelioration in WAT function and GIISIVGTT was independent of plasma cholesterol (total, LDL, and HDL), sex, and changes in body composition. Subjects with high baseline plasma apoB (1.2 ± 0.2 g/L) showed a significant increase in WAT function (+105%; P = 0.012) and a decrease in total GIISIVGTT (-34%; P ≤ 0.001), whereas sex-matched subjects with low plasma apoB (0.7 ± 0.1 g/L) did not, despite equivalent changes in body composition and energy intake and expenditure.

Conclusions

High plasma apoB identifies obese subjects who best ameliorate WAT dysfunction and glucose-induced hyperinsulinemia, independent of changes in adiposity after consumption of a hypocaloric diet. We propose that subjects with high plasma apoB represent an optimal target group for the primary prevention of T2D by hypocaloric diets. This trial was registered at BioMed Central as ISRCTN14476404.

PPAR-gamma pathways attenuate pulmonary granuloma formation in a carbon nanotube induced murine model of sarcoidosis

Peroxisome proliferator activated receptor gamma (PPARγ), a ligand activated nuclear transcription factor, is constitutively expressed in alveolar macrophages of healthy individuals. PPARγ deficiencies have been noted in several lung diseases including the alveolar macrophages of pulmonary sarcoidosis patients. We have previously described a murine model of multiwall carbon nanotubes (MWCNT) induced pulmonary granulomatous inflammation which bears striking similarities to pulmonary sarcoidosis, including the deficiency of alveolar macrophage PPARγ. Further studies demonstrate alveolar macrophage PPARγ deficiency exacerbates MWCNT-induced pulmonary granulomas. Based on these observations we hypothesized that activation of PPARγ via administration of the PPARγ-specific ligand rosiglitazone would limit MWCNT-induced granuloma formation and promote PPARγ-dependent pathways. Results presented here show that rosiglitazone significantly limits the frequency and severity of MWCNT-induced pulmonary granulomas. Furthermore, rosiglitazone attenuates alveolar macrophage NF-κB activity and downregulates the expression of the pro-inflammatory mediators, CCL2 and osteopontin. PPARγ activation via rosiglitazone also prevents the MWCNT-induced deficiency of PPARγ-regulated ATP-binding cassette lipid transporter-G1 (ABCG1) expression. ABCG1 is crucial to pulmonary lipid homeostasis. ABCG1 deficiency results in lipid accumulation which promotes pro-inflammatory macrophage activation. Our results indicate that restoration of homeostatic ABCG1 levels by rosiglitazone correlates with both reduced pulmonary lipid accumulation, and decreased alveolar macrophage activation. These data confirm and further support our previous observations that PPARγ pathways are critical in regulating MWCNT-induced pulmonary granulomatous inflammation.

The Natural Compound Dansameum Reduces foam Cell Formation by Downregulating CD36 and Peroxisome Proliferator-activated Receptor-gamma; Expression

Background:

Atherosclerosis-induced vascular disorders are major causes of death in most western countries. During the development of atherosclerotic lesions, foam cell formation is essential and formed through the expression of CD36 and the peroxisome proliferator-activated receptor gamma (PPAR-γ).

Objective:

To investigate whether dansameum extract (DSE) could show anti-atherosclerotic effect through down-regulating cellular redox state including CD36 and PARP-γ expression in oxidative low-density lipoprotein (oxLDL)-treated RAW264.7 cells and on differentiated foam cells in ApoE Knockout (ApoE-/-) mice.

Materials and Methods:

The Korean polyherbal medicine DSE was prepared from three plants in the following proportions: 40 g of Salvia miltiorrhiza root, 4 g of Amomumxanthioides fruit, and 4 g of Santalum album lignum. The immunohistochemistry and reverse transcription-polymerase chain reaction was used for analysis of protein and mRNA involved in foam cell formation.

Results:

We first showed that effects of DSE on foam cell formation in both oxLDL-induced RAW264.7 cells and in blood vessels from apolipoprotein E deficientApoE-/- mice with high fat diet-fed. DSE treatment significantly reduced the expression of CD36 and PPAR-γ in oxLDL-stimulated RAW264.7 cells and ApoE-/-mice, in the latter case by regulating heme oxygenase-1. Furthermore, DSE treatment also reduced cellular lipid content in vitro and in vivo experiments.

Conclusion:

Our data suggest that DSE may have anti-atherosclerotic properties through regulating foam cell formation.

SUMMARY

Dansameum extract (DSE) Regulates the expression of CD36 and peroxisome proliferator-activated receptor gamma in oxidative low-density lipoprotein-stimulated RAW264.7 Cells and ApoE Knockout (ApoE Knockout [ApoE-/-]) mice

DSE Regulates Cholesterol Levels in the Serum of ApoE-deficient (ApoE-/-) mice

DSE Reduced the Formation of Foam Cells by Regulating heme oxygenase-1 in ApoE-/- mice with high fat diet-fed.

Abbreviations used: DSE: Dansameum extract, PPAR-γ: Peroxisome proliferator-activated receptor γ, HO-1: Heme oxygenase-1, CVD: Cardiovascular diseases

Effects of trigonelline inhibition of the Nrf2 transcription factor in vitro on Echinococcus granulosus

The aim of this study was to investigate the impact of trigonelline (TRG) on Echinococcus granulosus, and to explore the inhibition impact of nuclear factor erythroid-2-related factor 2 (Nrf2) signaling pathway on E. granulosus protoscoleces. Echinococcus granulosus protoscoleces were incubated with various concentrations of TRG, and then Nrf2 protein expression and its localization in protoscoleces were detected by western blot analysis and immunofluorescence assay, respectively. Reactive oxygen species (ROS) level in protoscoleces was measured using ROS detection kit. Caspase-3 activity was measured using a caspase-3 activity assay kit, and NAD(P)H quinone oxidoreductase (NQO)-1 and heme oxygenase (HO)-1 activities in protoscoleces were measured by ELISA. The effect of TRG on protoscoleces viability was investigated using 0.1% eosin staining, and ultrastructural alterations in protoscoleces were examined by scanning electron microscopy (SEM). Immunolocalization experiment clearly showed that Nrf2 protein was predominantly present in cells of protoscoleces. TRG treatment reduced NQO-1 and HO-1 activities in protoscoleces, but could increase ROS level at early time. Protoscoleces could not survive when treated with 250 μM TRG for 12 days. SEM results showed that TRG-treated protoscoleces presented damage in the protoscoleces region, including hook deformation, lesions, and digitiform protuberance. Nrf2 protein expression was significantly decreased and caspase-3 activity was clearly increased in protoscoleces treated with TRG for 24 and 48 h, respectively, when compared with that in controls (P < 0.05). Our results demonstrated that TRG had scolicidal activity against E. granulosus protoscoleces. Nrf2 protein was mainly expressed in the cells and TRG could efficiently inhibit the Nrf2 signaling pathway in E. granulosus.

Plasma IL-1Ra: linking hyperapoB to risk factors for type 2 diabetes independent of obesity in humans

Background/Objective:

Plasma apoB predicts the incidence of type 2 diabetes (T2D); however, the link between apoB-linpoproteins and risks for T2D remain unclear. Insulin resistance (IR) and compensatory hyperinsulinemia characterize prediabetes, and the involvement of an activated interleukin-1 (IL-1) family, mainly IL-1β and its receptor antagonist (IL-Ra), is well documented. ApoB-lipoproteins were reported to promote IL-1β secretion in immune cells; however, in vivo evidence is lacking. We hypothesized that obese subjects with hyperapoB have an activated IL-1 system that explains hyperinsulinemia and IR in these subjects.

Subjects/Methods:

We examined 81 well-characterized normoglycemic men and postmenopausal women (⩾27 kg m⁻², 45–74 years, non-smokers, sedentary, free of chronic disease). Insulin secretion and sensitivity were measured by the gold-standard Botnia clamp, which is a combination of a 1-h intravenous glucose tolerance test (IVGTT) followed by 3-h hyperinsulinemic euglycemic clamp.

Results:

Plasma IL-1β was near detection limit (0.071–0.216 pg ml⁻¹), while IL-1Ra accumulated at 1000-folds higher (77–1068 pg ml⁻¹). Plasma apoB (0.34–1.80 g l⁻¹) associated significantly with hypersinsulinemia (total_IVGTT: C-peptide r=0.27, insulin r=0.22), IR (M/I=−0.29) and plasma IL-1Ra (r=0.26) but not with IL-1β. Plasma IL-1Ra associated with plasma IL-1β (r=0.40), and more strongly with hyperinsulinemia and IR than apoB, while the association of plasma IL-1β was limited to second phase and total insulin secretion (r=0.23). Adjusting the association of plasma apoB to hyperinsulinemia and IR for IL-1Ra eliminated these associations. Furthermore, despite equivalent body composition, subjects with hyperapoB (⩾80th percentile, 1.14 g l⁻¹) had higher C-peptide secretion and lower insulin sensitivity than those with low plasma apoB (⩽20th percentile, 0.78 g l⁻¹). Adjustment for plasma IL-1 Ra eliminated all group differences.

Conclusion:

Plasma apoB is associated with hyperinsulinemia and IR in normoglycemic obese subjects, which is eliminated upon adjustment for plasma IL-1Ra. This may implicate the IL-1 family in elevated risks for T2D in obese subjects with hyperapoB.

High-density lipoprotein increases the uptake of oxidized low density lipoprotein via PPARγ/CD36 pathway in inflammatory adipocytes

Aim: Previous studies have demonstrated that the dysregulated-secretion of adipokines by adipocytes may contribute to obesity-associated atherosclerosis (As) and high density lipoprotein (HDL) may protect against atherogenesis through multiple pathways. This study was to explore the effect of HDL on the oxLDL uptake in inflammatory adipocytes stimulated by endotoxin lipopolysaccharide (LPS) and the possible mechanism.

Methods and Results: 3T3-L1 adipocytes were cultured and induced to differentiation and maturation. Acute inflammation in adipocytes was induced by LPS (100 ng/ml) for 6 hours. The adipocytes were pretreated with HDL in various concentrations (10, 50, 100 μg/ml) for 16 hours or with specific PPARγ antagonist (GW9662, 10 μM) or agonist (Rosiglitazone, 10 μM) for 30 min before administration of LPS. The results showed that LPS significantly increased the release of inflammation-related adipokines, such as monocyte chemoattractant protein-1 (MCP-1), plasminogen activator inhibitor 1 (PAI-1), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-8 and IL-6, while decreasing the release of leptin and adiponectin. Meanwhile, LPS reduced the uptake and degradation of ¹²⁵I-oxLDL, and down-regulated the expression of PPARγ and CD36. Pretreatment with HDL dose-dependently affected the release of IL-8 and IL-6 and the reduced uptake and degradation of oxLDL of adipocytes stimulated by LPS, accompanied with marked upregulation of PPARγ and CD36 expression. Pretreatment with GW9662 markedly inhibited the upregulation of CD36 expression mediated by HDL (100 μg/ml), while the effects of Rosiglitazone were opposite to GW9662.

Conclusions: HDL may increase oxLDL uptake of inflammatory adipocytes stimulated by LPS via upregulation of PPARγ/CD36 pathway, which may be a new mechanism of anti-atherosclerosis mediated by HDL.

CD36 upregulation mediated by intranasal LV-NRF2 treatment mitigates hypoxia-induced progression of Alzheimer's-like pathogenesis

AIMS

There is extensive evidence that oxidative stress induces cellular dysfunction in the brain and plays a critical role in Alzheimer's disease (AD) pathogenesis. Hypoxia increases factors involved in oxidative stress injury and contributes to the onset and progression of AD. Nuclear factor erythroid 2-related factor 2 (NRF2), a major component regulating antioxidant response, is attenuated in the AD brain. Importantly, NRF2 directly regulates the alternative first exons of CD36, an important participant in oxidative and inflammatory processes. To explore the effects of hypoxia-induced deterioration of AD-like pathogenesis and investigate the correlation between hypoxia-induced NRF2 signal alterations and CD36 expression, we examined the NRF2 signaling, CD36, and oxidative stress events in hypoxia-treated APPswe/PSEN1dE9 (APP/PS1) mice brain.

RESULTS

We observed that hypoxia treatment increased oxidative stress, exacerbated inflammation, and aggravated learning defects in aged APP/PS1 mice. Microglia from hypoxia-treated mice brain exhibited marked reduction in CD36 expression and inhibition of β-amyloid (Aβ) degradation. Accordingly, hypoxia treatment caused a decrease in transactivation of NRF2 target genes in the aging mouse brain. Intranasal administration with a lentiviral vector encoding human NRF2 increased CD36 expression, ameliorated the weak antioxidant response triggered by hypoxia, diminished Aβ deposition, and improved spatial memory defects.

INNOVATION

In this study, we demonstrated for the first time that NRF2 intranasal treatment-induced increases of CD36 could enhance Aβ clearance in AD transgenic mouse.

CONCLUSION

These results suggest that targeting NRF2-mediated CD36 expression might provide a beneficial intervention for cognitive impairment and oxidative stress in AD progression.

Compare the effect of eicosapentaenoic acid and oxidized low-density lipoprotein on the expression of CD36 and peroxisome proliferator-activated receptor gamma

BACKGROUND

There is evidence that CD36 promotes foam cell formation through internalizing oxidized LDL (ox-LDL) into macrophages; therefore, it plays a key role in pathogenesis of atherosclerosis. In addition, CD36 expression seems to be mediated by nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR-γ). The aim of the present study was to evaluate and compare the effect of PPAR-γ ligands, eicosapentaenoic acid (EPA) as an anti-atherogenic factor and ox-LDL as an atherogenic factor on CD36 expression. Mechanism of PPAR- γ action and its ligands in CD36 expression were also investigated.

METHODS

Raw 264.7 macrophage cell line was treated with ox-LDL (100 and 150 μg protein/LDL) and EPA (100 and 200 μM) for 24 and 48 hours in absence or presence of PPAR-γ inhibitor, T0070907. Quantitative real-time PCR and Western-blotting were used for analysis of gene and protein expression, respectively.

RESULTS

Raw 264.7 exposures to ox-LDL and EPA resulted in increased expression of CD36 mRNA and protein; however, mRNA and PPAR-γ protein were not up-regulated significantly. Pre-incubation of cells with T0070907 led to decreased expression of CD36 when treated with ox-LDL and EPA.

CONCLUSION

It was confirmed that both EPA and ox-LDL increased CD36 expression but not PPAR-γ, and also co-treatment with PPAR-γ inhibitor decreased CD36 expression. We concluded that up-regulation of CD36 depends on PPAR-γ activation and is not related to increased expression of PPAR-γ. Induction of CD36 by EPA showed that CD36 suppression is not the means by which ω-3 fatty acids (EPA) provide protection against formation of atherosclerotic plaque.

Are reactive oxygen species always detrimental to pathogens?

Reactive oxygen species (ROS) are deadly weapons used by phagocytes and other cell types, such as lung epithelial cells, against pathogens. ROS can kill pathogens directly by causing oxidative damage to biocompounds or indirectly by stimulating pathogen elimination by various nonoxidative mechanisms, including pattern recognition receptors signaling, autophagy, neutrophil extracellular trap formation, and T-lymphocyte responses. Thus, one should expect that the inhibition of ROS production promote infection. Increasing evidences support that in certain particular infections, antioxidants decrease and prooxidants increase pathogen burden. In this study, we review the classic infections that are controlled by ROS and the cases in which ROS appear as promoters of infection, challenging the paradigm. We discuss the possible mechanisms by which ROS could promote particular infections. These mechanisms are still not completely clear but include the metabolic effects of ROS on pathogen physiology, ROS-induced damage to the immune system, and ROS-induced activation of immune defense mechanisms that are subsequently hijacked by particular pathogens to act against more effective microbicidal mechanisms of the immune system. The effective use of antioxidants as therapeutic agents against certain infections is a realistic possibility that is beginning to be applied against viruses.

Curcumin inhibits oxLDL-induced CD36 expression and foam cell formation through the inhibition of p38 MAPK phosphorylation

The uptake of oxidized low density lipoprotein (oxLDL) via scavenger receptors transforms macrophages into foam cells, which are a hallmark of atherosclerosis. OxLDL markedly increases the expression of the CD36 scavenger receptor. Here, we investigated whether curcumin modulate CD36 expression in oxLDL-treated RAW 264.7 murine macrophages. Our results showed that curcumin dramatically inhibits CD36 expression and foam cell formation. Furthermore, oxLDL-induced expression and activity of peroxisome proliferator-activated receptor-gamma (PPAR-γ), which is involved in CD36 expression, is also blocked in curcumin-treated cells. OxLDL activates the mitogen-activated protein kinase (MAPK) signaling transduction pathway, and p38 MAPK is associated with oxLDL-induced CD36 and PPAR-γ expression. Overexpression of dominant negative p38 MAPK blocks oxLDL-induced CD36 and PPAR-γ expression. Furthermore, curcumin markedly inhibits p38 MAPK phosphorylation. Taken together, our results suggest that curcumin modulates oxLDL-induced CD36 expression and foam cell formation via the inhibition of p38 MAPK phosphorylation in RAW 264.7 murine macrophages.

Low density lipoprotein delays clearance of triglyceride-rich lipoprotein by human subcutaneous adipose tissue

Delayed clearance of triglyceride-rich lipoprotein (TRL) by white adipose tissue (WAT) promotes hypertriglyceridemia and elevated apoB-lipoproteins, which are primarily in the form of LDL. This study examines whether LDL promotes delayed clearance of TRL by WAT. Following the ingestion of a (13)C-triolein-labeled high-fat meal, obese women with high plasma apoB (> median 0.93 g/l, N = 11, > 98% as IDL/LDL) had delayed clearance of postprandial (13)C-triglyceride and (13)C-NEFA over 6 h compared with controls. AUC6 h of plasma (13)C-triglyceride and (13)C-NEFA correlated with plasma apoB but not with LDL diameter or adipocyte area. There was no group difference in (13)C-triolein oxidation rate, which suggests lower (13)C-NEFA storage in peripheral tissue in women with high apoB. Ex vivo/in vitro plasma apoB correlated negatively with WAT (3)H-lipid following a 4 h incubation of women's WAT with synthetic (3)H-triolein-TRL. LDL-differentiated 3T3-L1 adipocytes had lower (3)H-TRL hydrolysis and (3)H-NEFA storage. Treatment of women's WAT with their own LDL decreased (3)H-TRL hydrolysis and (3)H-NEFA uptake. Finally, LDL, although not an LPL substrate, reduced LPL-mediated (3)H-TRL hydrolysis as did VLDL and HDL. Exposure to LDL decreases TRL clearance by human WAT ex vivo. This may promote production of apoB-lipoproteins and hypertriglyceridemia through a positive-feedback mechanism in vivo.

Co-stimulation of PAFR and CD36 is required for oxLDL-induced human macrophages activation

The oxidative process of LDL particles generates molecules which are structurally similar to platelet-activating factor (PAF), and some effects of oxidized LDL (oxLDL) have been shown to be dependent on PAF receptor (PAFR) activation. In a previous study, we showed that PAFR is required for upregulation of CD36 and oxLDL uptake. In the present study we analyzed the molecular mechanisms activated by oxLDL in human macrophages and the contribution of PAFR to this response. Human adherent monocytes/macrophages were stimulated with oxLDL. Uptake of oxLDL and CD36 expression were determined by flow cytometry; MAP kinases and Akt phosphorylation by Western blot; IL-8 and MCP-1 concentration by ELISA and mRNA expression by real-time PCR. To investigate the participation of the PI3K/Akt pathway, Gαi-coupled protein or PAFR, macrophages were treated with LY294002, pertussis toxin or with the PAFR antagonists WEB2170 and CV3988, respectively before addition of oxLDL. It was found that the addition of oxLDL to human monocytes/macrophages activates the PI3K/Akt pathway which in turn activates the MAPK (p38 and JNK). Phosphorylation of Akt requires the engagement of PAFR and a Gαi-coupled protein. The upregulation of CD36 protein and the uptake of oxLDL as well as the IL-8 production are dependent on PI3K/Akt pathway activation. The increased CD36 protein expression is dependent on PAFR and Gαi-coupled protein. Transfection studies using HEK 293t cells showed that oxLDL uptake occurs with either PAFR or CD36, but IL-8 production requires the co-transfection of both PAFR and CD36. These findings show that PAFR has a pivotal role in macrophages response to oxLDL and suggest that pharmacological intervention at the level of PAFR activation might be beneficial in atherosclerosis.

PPARγ and Oxidative Stress: Con(β) Catenating NRF2 and FOXO

Peroxisome-proliferator activator receptor γ (PPARγ) is a nuclear receptor of central importance in energy homeostasis and inflammation. Recent experimental pieces of evidence demonstrate that PPARγ is implicated in the oxidative stress response, an imbalance between antithetic prooxidation and antioxidation forces that may lead the cell to apoptotic or necrotic death. In this delicate and intricate game of equilibrium, PPARγ stands out as a central player devoted to the quenching and containment of the damage and to foster cell survival. However, PPARγ does not act alone: indeed the nuclear receptor is at the point of interconnection of various pathways, such as the nuclear factor erythroid 2-related factor 2 (NRF2), Wnt/β-catenin, and forkhead box proteins O (FOXO) pathways. Here we reviewed the role of PPARγ in response to oxidative stress and its interaction with other signaling pathways implicated in this process, an interaction that emerged as a potential new therapeutic target for several oxidative-related diseases.

Nrf2, a PPARγ alternative pathway to promote CD36 expression on inflammatory macrophages: implication for malaria

CD36 is the major receptor mediating nonopsonic phagocytosis of Plasmodium falciparum-parasitized erythrocytes by macrophages. Its expression on macrophages is mainly controlled by the nuclear receptor PPARγ. Here, we demonstrate that inflammatory processes negatively regulate CD36 expression on human and murine macrophages, and hence decrease Plasmodium clearance directly favoring the worsening of malaria infection. This CD36 downregulation in inflammatory conditions is associated with a failure in the expression and activation of PPARγ. Interestingly, using siRNA mediating knock down of Nrf2 in macrophages or Nrf2- and PPARγ-deficient macrophages, we establish that in inflammatory conditions, the Nrf2 transcription factor controls CD36 expression independently of PPARγ. In these conditions, Nrf2 activators, but not PPARγ ligands, enhance CD36 expression and CD36-mediated Plasmodium phagocytosis. These results were confirmed in human macrophages and in vivo where only Nrf2 activators improve the outcome of severe malaria. Collectively, this report highlights that the Nrf2 transcription factor could be an alternative target to PPARγ in the control of severe malaria through parasite clearance.

Severe and fatal malaria is still increasing both in incidence and in its resistance to antimalarial agents. The improved understanding of immune mechanisms mediating Plasmodium elimination might therefore offer a complementary way to conventional therapeutic interventions. The main host innate immune defense mechanism against Plasmodium falciparum is the engulfment by macrophages through CD36, the macrophage receptor recognizing infected erythrocytes. The up-regulation of CD36 on macrophages therefore represents an alternative way to favor parasite clearance during infection. Severe malaria infection is associated with an excessive production of proinflammatory markers and an inability to control parasite proliferation. We demonstrate here that malaria-induced inflammation down regulates CD36 expression on macrophages and favors the worsening of malaria infection. The conventional way to promote CD36 expression through PPARγ nuclear receptor is inefficient under malaria inflammatory processes. Interestingly, we establish that the Nrf2 transcription factor may substitute PPARγ to promote CD36 expression and its associated functions in inflammatory conditions. As a consequence, only Nrf2 but not PPARγ activators improve the outcome of severe malaria in vivo. This paper which highlights a new area of application for Nrf2 activators in infectious diseases, heralds the emergence of a new therapeutic strategy against severe malaria.

Cyanidin-3-O-β-glucoside and protocatechuic acid exert insulin-like effects by upregulating PPARγ activity in human omental adipocytes

OBJECTIVE

Insulin resistance (IR) represents an independent risk factor for metabolic, cardiovascular, and neoplastic disorders. Preventing/attenuating IR is a major objective to be reached to preserve population health. Because many insulin-sensitizing drugs have shown unwanted side effects, active harmless compounds are sought after. Dietary anthocyanins have been demonstrated to ameliorate hyperglycemia and insulin sensitivity. This study aimed at investigating whether cyanidin-3-O-β-glucoside (C3G) and its metabolite protocatechuic acid (PCA) might have a role in glucose transport activation in human omental adipocytes and 3T3-L1 cells.

RESEARCH DESIGN AND METHODS

In cells treated with 50 µmol/L C3G and 100 µmol/L PCA, [(3)H]-2-deoxyglucose uptake, GLUT4 translocation by immunoblotting, adiponectin secretion, and peroxisome proliferator-activated receptor-γ (PPARγ) activation by enzyme-linked immunosorbent assay kits were evaluated. Parallel experiments were carried out in murine adipocyte 3T3-L1. To define the role of PPARγ in modulating polyphenol effects, small interfering RNA technique and PPARγ antagonist were used to inhibit transcription factor activity.

RESULTS

C3G and PCA increased adipocyte glucose uptake (P < 0.05) and GLUT4 membrane translocation (P < 0.01). Significant increases (P < 0.05) in nuclear PPARγ activity, as well as in adiponectin and GLUT4 expressions (P < 0.01), were also shown. It is interesting that PPARγ inhibition counteracted the polyphenol-induced adiponectin and GLUT4 upregulations, suggesting a direct involvement of PPARγ in this process.

CONCLUSIONS

Our study provides evidence that C3G and PCA might exert insulin-like activities by PPARγ activation, evidencing a causal relationship between this transcription factor and adiponectin and GLUT4 upregulation. Dietary polyphenols could be included in the preventive/therapeutic armory against pathological conditions associated with IR.

CCAAT/enhancer-binding protein-β participates in oxidized LDL-enhanced proliferation in 3T3-L1 cells

Increased circulating oxidized LDL (oxLDL) have been found in obese subjects. Obesity is characterized by an excess of fat mass resulting from an increase in adipocyte number and size. The generation of new adipocytes is a tightly controlled process where multiple factors acting in a signaling cascade follow a precise temporal expression pattern; oxLDL appear to have a role in the impairment of this process. The purpose of this study was to examine the effects of oxLDL on the mechanisms involved in the proliferative stage of the differentiation process in 3T3-L1 cells. After hormonal induction, 3T3-L1 cells undergo approximately two rounds of mitotic clonal expansion (MCE), a process required for adipogenesis. CCAAT/enhancer-binding protein β (C/EBPβ) is immediately expressed after induction, and plays a crucial role in MCE, but its expression must decrease to allow preadipocytes to mature into adipocytes. We found that, in the presence of stimuli to differentiate, oxLDL induced a higher proliferation rate in this cell line, associated with a sustained up-regulation of C/EBPβ, which remained activated inside the nucleus for several days. RNAi-mediated knockdown of C/EBPβ 24 h after oxLDL treatment counteracted the increase in proliferation rate. Both C/EBPβ expression and proliferation processes appear to be influenced by cAMP/protein kinase A (PKA) and extracellular signal-regulated kinases1/2 (ERK1/2) pathways. OxLDL treatment led to increased levels of cAMP, and to a strong, prolonged phosphorylation of ERK1/2 and C/EBPβ. The addition of cAMP and PKA inhibitors, SQ22536 and H-89, respectively, reduced proliferation only in oxLDL-treated cells, whereas the addition of ERK1/2 inhibitor U0126 blocked proliferation in both control and oxLDL-treated cells. C/EBPβ nuclear expression and DNA-binding activity were reduced by U0126, under all tested conditions. These findings show that the altered expression pattern of C/EBPβ is involved in the increase in the number of proliferating cells induced by oxLDL, in hormone-stimulated 3T3-L1 cells.

The plant-based immunomodulator curcumin as a potential candidate for the development of an adjunctive therapy for cerebral malaria

The clinical manifestations of cerebral malaria (CM) are well correlated with underlying major pathophysiological events occurring during an acute malaria infection, the most important of which, is the adherence of parasitized erythrocytes to endothelial cells ultimately leading to sequestration and obstruction of brain capillaries. The consequent reduction in blood flow, leads to cerebral hypoxia, localized inflammation and release of neurotoxic molecules and inflammatory cytokines by the endothelium. The pharmacological regulation of these immunopathological processes by immunomodulatory molecules may potentially benefit the management of this severe complication. Adjunctive therapy of CM patients with an appropriate immunomodulatory compound possessing even moderate anti-malarial activity with the capacity to down regulate excess production of proinflammatory cytokines and expression of adhesion molecules, could potentially reverse cytoadherence, improve survival and prevent neurological sequelae. Current major drug discovery programmes are mainly focused on novel parasite targets and mechanisms of action. However, the discovery of compounds targeting the host remains a largely unexplored but attractive area of drug discovery research for the treatment of CM. This review discusses the properties of the plant immune-modifier curcumin and its potential as an adjunctive therapy for the management of this complication.

The role of the antioxidant and longevity-promoting Nrf2 pathway in metabolic regulation

PURPOSE OF REVIEW

The vertebrate cap'n'collar family transcription factor Nrf2 and its invertebrate homologues SKN-1 (in worms) and CncC (in flies) function as master mediators of antioxidant and detoxification responses and regulators of the cellular redox state. Nrf2 controls gene expression programs that defend various tissues against diverse electrophilic stressors and oxidative insults, thus protecting the organism from disorders that are caused or exacerbated by such stresses. Moreover, studies on model organisms implicate the Nrf2 pathway in the prevention of aging-related diseases and suggest that SKN-1-regulated and CncC-regulated gene expression can promote longevity. These facets of Nrf2 signaling have been thoroughly reviewed. This article discusses another aspect of the Nrf2 pathway's function that has not yet received the same degree of attention, but emerges as a topic of increasing interest and potential clinical impact: its role in metabolic regulation and its interaction with central signaling systems that respond to nutritional inputs.

RECENT FINDINGS

Recent evidence identifies Nrf2 signaling as a mediator of the salutary effects of caloric restriction. Nrf2 signaling also crosstalks with metabolic signaling systems such as the insulin/Akt pathway as well as with the metabolism of lipids. Moreover, Nrf2 has a protective role in models of diabetic nephropathy.

SUMMARY

The emerging role of Nrf2 as an effector of metabolic and longevity signals offers new therapeutic perspectives. The potential impact of pharmacological manipulation of Nrf2 signaling as a strategy for the prevention and treatment of metabolic disease can be envisioned.

Transient glutathione depletion determines terminal differentiation in HL-60 cells

To better define the role of glutathione (GSH) in cell differentiation, the present study measured GSH concentrations during terminal HL-60 cell differentiation, in the presence and absence of differentiation-inducing agents, and in the presence and absence of GSH altering agents. Interestingly, there was a small transient increase in intracellular GSH levels during dimethyl sulfoxide (DMSO) or 1α,25-dihydroxyvitamin D3 (VD3) induced differentiation. This increase coincided with an increase in nitroblue tetrazolium (NBT) reduction capacity, a measure of superoxide anion production, but there was no apparent change in the GSH/glutathione disulfide (GSSG) ratio. Surprisingly, treatment of cells with low doses of 1-chloro-2,4-dinitrobenzene (CDNB; 5 µM) or diethylmaleate (DEM; 0.5 mM), which transiently deplete GSH levels to about 40% of control levels, resulted in enhanced differentiation of HL-60 cells exposed to VD3 or all-trans-retinoic acid (ATRA), as well as under un-induced conditions (i.e., spontaneous differentiation). Enhanced differentiation occurred when cells were treated with the GSH-depleting agents 4 hours after treatment with differentiation inducers. These findings indicate that intracellular GSH levels are regulated in a complex fashion during HL-60 cell differentiation, and that transient GSH depletion using low doses of CDNB and DEM enhances the differentiation process.

CD36 participates in a signaling pathway that regulates ROS formation in murine VSMCs

CD36 is a membrane glycoprotein expressed on platelets, monocytes, macrophages, and several other cell types that was recently demonstrated to be involved in platelet activation in response to oxidized phospholipids, including oxidized LDL. Although the role of CD36 in other vascular cells has not been well defined, previous studies have demonstrated that cd36-knockout (cd36-/-) mice have prolonged thrombosis times after vascular injury, which can be protective in the state of hyperlipidemia. Here, we found significantly less ROS in the vessel walls of cd36-/- mice compared with WT after chemically induced arterial injury, suggesting that CD36 may contribute to ROS generation in the VSMCs themselves. Gene expression analysis revealed that the antioxidant enzymes peroxiredoxin-2 (Prdx2) and heme oxygenase-1 were upregulated in cd36-/- VSMCs. Molecular dissection of the pathway in isolated mouse VSMCs revealed CD36 ligand-dependent induction of Fyn phosphorylation, with subsequent phosphorylation and degradation of the redox-sensitive transcription factor Nrf2. Chromatin immunoprecipitation experiments further showed that Nrf2 directly occupied the Prdx2 promoter. The importance of this pathway was evidenced by increased ROS generation in prdx2-/- mice and decreased thrombosis times in both prdx2-/- and nrf2-/- mice after vascular injury. These data suggest that CD36-mediated downregulation of antioxidant systems in VSMCs may contribute to its prothrombotic, proinflammatory, and atherogenic effects.

The rise of antioxidant signaling--the evolution and hormetic actions of Nrf2

Organisms have evolved sophisticated and redundant mechanisms to manage oxidative and electrophilic challenges that arise from internal metabolism or xenobiotic challenge for survival. NF-E2-related factor 2 (Nrf2) is a transcription factor that has evolved over millennia from primitive origins, with homologues traceable back to invertebrate Caenorhabditis and Drosophila species. The ancestry of Nrf2 clearly has deep-seated roots in hematopoiesis, yet has diversified into a transcription factor that can mediate a multitude of antioxidant signaling and detoxification genes. In higher organisms, a more sophisticated means of tightly regulating Nrf2 activity was introduced via the cysteine-rich kelch-like ECH-associated protein 1 (Keap1), thus suggesting a need to modulate Nrf2 activity. This is evidenced in Keap1(-/-) mice, which succumb to juvenile mortality due to hyperkeratosis of the gastrointestinal tract. Although Nrf2 activation protects against acute toxicity and prevents or attenuates several disease states, constitutive activation in some tumors leads to poor clinical outcomes, suggesting Nrf2 has evolved in response to a multitude of selective pressures. The purpose of this review is to examine the origins of Nrf2, while highlighting the versatility and protective abilities elicited upon activation. Various model systems in which Nrf2 is normally beneficial but in which exaggerated pharmacology exacerbates a physiological or pathological condition will be addressed. Although Darwinian principles have selected Nrf2 activity for maximal beneficial effect based on environmental and oxidative challenge, both sub- or super-physiological effects have been noted to be detrimental. The functions of Nrf2 thus suggest a hormetic factor that has evolved empirically over time.

Oxidized low-density lipoprotein-induced matrix metalloproteinase-9 expression via PKC-delta/p42/p44 MAPK/Elk-1 cascade in brain astrocytes

After ischemic injury to brain, disruption of the blood-brain barrier (BBB) raises the possibility of exposing the central nervous system (CNS) to oxidized low-density lipoprotein (oxLDL), a risk factor implicated in neurodegenerative diseases. Matrix metalloproteinases (MMPs), especially MMP-9, contribute to extracellular matrix (ECM) remodeling during the CNS diseases. However, the molecular mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes remained unclear. Here, we reported that oxLDL induced MMP-9 expression via a PKC-delta/p42/p44 MAPK-dependent Elk-1 activation in rat brain astrocyte (RBA)-1 cells, revealed by gelatin zymography, RT-PCR, and Western blotting analyses. These responses were attenuated by pretreatment with pharmacological inhibitors and transfection with dominant negative mutants. Moreover, Elk-1-mediated MMP-9 gene transcription was confirmed by transfection with an Elk-1 binding site-mutated MMP-9 promoter construct (mt-Ets-MMP9), which blocked oxLDL-stimulated MMP-9 luciferase activity. Understanding the regulatory mechanisms by which oxLDL induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain diseases.

Oxidized LDL impair adipocyte response to insulin by activating serine/threonine kinases

Oxidized LDL (oxLDL) increase in patients affected by type-2 diabetes, obesity, and metabolic syndrome. Likewise, insulin resistance, an impaired responsiveness of target tissues to insulin, is associated with those pathological conditions. To investigate a possible causal relationship between oxLDL and the onset of insulin resistance, we evaluated the response to insulin of 3T3-L1 adipocytes treated with oxLDL. We observed that oxLDL inhibited glucose uptake (-40%) through reduced glucose transporter 4 (GLUT4) recruitment to the plasma membrane (-70%), without affecting GLUT4 gene expression. These findings were associated to the impairment of insulin signaling. Specifically, in oxLDL-treated cells insulin receptor (IR) substrate-1 (IRS-1) was highly degraded likely because of the enhanced Ser(307)phosphorylation. This process was largely mediated by the activation of the inhibitor of kappaB-kinase beta (IKKbeta) and the c-Jun NH(2)-terminal kinase (JNK). Moreover, the activation of IKKbeta positively regulated the nuclear content of nuclear factor kappaB (NF-kappaB), by inactivating the inhibitor of NF-kappaB (IkappaBalpha). The activated NF-kappaB further impaired per se GLUT4 functionality. Specific inhibitors of IKKbeta, JNK, and NF-kappaB restored insulin sensitivity in adipocytes treated with oxLDL. These data provide the first evidence that oxLDL, by activating serine/threonine kinases, impaired adipocyte response to insulin affecting pathways involved in the recruitment of GLUT4 to plasma membranes (PM). This suggests that oxLDL might participate in the development of insulin resistance.