Modulation of CD36 protein expression by AGEs and insulin in aortic VSMCs from diabetic and non-diabetic rats

Cathepsin D inhibits AGEs-induced phenotypic transformation in vascular smooth muscle cells

This study investigates the role of Cathepsin D (CTSD) in diabetic vascular complications, particularly its impact on the phenotypic transformation of vascular smooth muscle cells (VSMCs) induced by advanced glycation end-products (AGEs), and explores its potential molecular mechanisms. CTSD was overexpressed in VSMCs using lentiviral vectors. Various methods, including CCK-8, immunofluorescence, SA-β-Gal staining, EdU assay, scratch assay, cell cycle analysis, and Western blotting, were employed to assess VSMC viability, proliferation, migration, senescence, and apoptosis. Additionally, transcriptomic and metabolomic analyses were conducted to investigate the molecular mechanisms underlying CTSD overexpression in VSMCs. AGEs treatment significantly inhibited CTSD expression in VSMCs, leading to reduced cell viability, enhanced proliferation and migration, increased senescence, and apoptosis. In contrast, overexpression of CTSD effectively inhibited AGEs-induced VSMCs proliferation, migration, senescence, and apoptosis. Combined transcriptomic and metabolomic analyses suggested that CTSD may affect VSMCs phenotypic transformation by inhibiting the glycolysis pathway. This study highlights the critical role of CTSD in the phenotypic transformation of VSMCs induced by AGEs and provides a new perspective for cardiovascular and cerebrovascular disease treatment. CTSD may emerge as a novel therapeutic target, though its specific molecular mechanisms and clinical application prospects in VSMCs phenotypic transformation require further investigation.

Metabolite Profiling of Antioxidant Rich Fractions of Punica granatum L. Mesocarp and CD36 Expression Regulation

OBJECTIVE

It was aimed at determining which polyphenolic compound(s) in pomegranate mesocarp extract (PME) is liable for the antioxidant, anti-glycation and anti-CD36 activities.

METHODS

The PME was fractionated using liquid-liquid extraction method. The fractions were tested for their polyphenolic content, antioxidant potency, anti-glycation activity and anti-CD36 potential. The metabolite compositions of PME and derived fractions were investigated in an untargeted manner using metabolomics in relation to its antioxidant and anti-glycation activities.

RESULTS

The ethyl acetate and n-butanol fractions of the pomegranate mesocarp demonstrated highest antioxidant and anti-glycation potencies. These fractions, represented by gallic and ellagic acids monomers, were enriched in tannins and phenolic acids. Orthogonal partial least squares discriminate analysis (OPLS-DA) modeling of ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) metabolite profiles from the different pomegranate mesocarp fractions indicated that gallic and ellagic acids were potential contributors to the antioxidant and anti-glycation effects of the pomegranate mesocarp. At cellular level, the polyphenolic-rich crude extract as well as the ethyl acetate, n-butanol and aqueous residual fractions suppressed the protein expression of CD36. The anti-CD36 activity of these extracts and fractions was attributed to the presence of punicalagin, the ellagitannins that occurred in equal amount in the different fractions.

CONCLUSION

This work demonstrated the protective effect of the non-edible part of the pomegranate fruit and showed that gallic and ellagic acids account for the antioxidant and anti-glycation activities while punicalagin is liable for the anti-CD36 activity of PME.

The RAGE/multiligand axis: a new actor in tumor biology

The receptor for advanced glycation end-products (RAGE) is a multiligand binding and single-pass transmembrane protein which actively participates in several chronic inflammation-related diseases. RAGE, in addition to AGEs, has a wide repertoire of ligands, including several damage-associated molecular pattern molecules or alarmins such as HMGB1 and members of the S100 family proteins. Over the last years, a large and compelling body of evidence has revealed the active participation of the RAGE axis in tumor biology based on its active involvement in several crucial mechanisms involved in tumor growth, immune evasion, dissemination, as well as by sculpturing of the tumor microenvironment as a tumor-supportive niche. In the present review, we will detail the consequences of the RAGE axis activation to fuel essential mechanisms to guarantee tumor growth and spreading.

Role of the Scavenger Receptor CD36 in Accelerated Diabetic Atherosclerosis

Diabetes mellitus entails increased atherosclerotic burden and medial arterial calcification, but the precise mechanisms are not fully elucidated. We aimed to investigate the implication of CD36 in inflammation and calcification processes orchestrated by vascular smooth muscle cells (VSMCs) under hyperglycemic and atherogenic conditions. We examined the expression of CD36, pro-inflammatory cytokines, endoplasmic reticulum (ER) stress markers, and mineralization-regulating enzymes by RT-PCR in human VSMCs, cultured in a medium containing normal (5 mM) or high glucose (22 mM) for 72 h with or without oxidized low-density lipoprotein (oxLDL) (24 h). The uptake of 1,1′-dioctadecyl-3,3,3′,3-tetramethylindocarbocyanine perchlorate-fluorescently (DiI) labeled oxLDL was quantified by flow cytometry and fluorimetry and calcification assays were performed in VSMC cultured in osteogenic medium and stained by alizarin red. We observed induction in the expression of CD36, cytokines, calcification markers, and ER stress markers under high glucose that was exacerbated by oxLDL. These results were confirmed in carotid plaques from subjects with diabetes versus non-diabetic subjects. Accordingly, the uptake of DiI-labeled oxLDL was increased after exposure to high glucose. The silencing of CD36 reduced the induction of CD36 and the expression of calcification enzymes and mineralization of VSMC. Our results indicate that CD36 signaling is partially involved in hyperglycemia and oxLDL-induced vascular calcification in diabetes.

CD36 Enhances Vascular Smooth Muscle Cell Proliferation and Development of Neointimal Hyperplasia

Objective- Dysregulated proliferation of vascular smooth muscle cells (VSMC) plays an essential role in neointimal hyperplasia. CD36 functions critically in atherogenesis and thrombosis. We hypothesize that CD36 regulates VSMC proliferation and contributes to the development of obstructive vascular diseases. Approach and Results- We found by immunofluorescent staining that CD36 was highly expressed in human vessels with obstructive diseases. Using guidewire-induced carotid artery injury and shear stress-induced intima thickening models, we compared neointimal hyperplasia in Apoe^-/-, Cd36^-/- /Apoe^-/-, and CD36 specifically deleted in VSMC (VSMC ^cd36-/-) mice. CD36 deficiency, either global or VSMC-specific, dramatically reduced injury-induced neointimal thickening. Correspondingly, carotid artery blood flow was significantly increased in Cd36^-/- /Apoe^-/- compared with Apoe^-/- mice. In cultured VSMCs from thoracic aorta of wild-type and Cd36^-/- mice, we found that loss of CD36 significantly decreased serum-stimulated proliferation and increased cell populations in S phase, suggesting that CD36 is necessary for VSMC S/G2-M-phase transition. Treatment of VSMCs with a TSR (thrombospondin type 1 repeat) peptide significantly increased wild-type, but not Cd36^-/- VSMC proliferation. TSR or serum treatment significantly increased cyclin A expression in wild-type, but not in Cd36^-/- VSMCs. STAT3 (signal transducer and activator of transcription), which reportedly enhances both VSMC differentiation and maturation, was higher in Cd36^-/- VSMCs. CD36 deficiency significantly decreased expression of Col1A1 (type 1 collagen A1 chain) and TGF-β1 (transforming growth factor beta 1), and increased expression of contractile proteins, including calponin 1 and smooth muscle α actin, and dramatically increased cell contraction. Conclusions- CD36 promotes VSMC proliferation via upregulation of cyclin A expression that contributes to the development of neointimal hyperplasia, collagen deposition, and obstructive vascular diseases.

A quick, simple method for detecting circulating fluorescent advanced glycation end-products: Correlation with in vitro and in vivo non-enzymatic glycation

OBJECTIVE

Advanced glycation end-products (AGEs) constitute a highly heterogeneous family of compounds, relevant in the pathogenesis of diabetic complications, which could represent efficient biomarkers of disease progression and drug response. Unfortunately, due to their chemical heterogeneity, no method has been validated to faithfully monitor their levels in the course of the disease. In this study, we refine a procedure to quantitatively analyze fluorescent AGEs (fAGEs), a subset considered remarkably representative of the entire AGE family, and measure them in in vitro glycated BSA (gBSA) and in plasma and vitreous of diabetic rats, for testing its use to possibly quantify circulating AGEs in patients, as markers of metabolic control.

METHODS

fAGE levels were evaluated by spectrofluorimetric analysis in in vitro and in vivo experimental models. BSA was glycated in vitro with increasing D-glucose concentrations for a fixed time or with a fixed D-glucose concentration for increasing time. In in vivo experiments, streptozotocin-induced diabetic rats were studied at 1, 3, 6 and 12weeks to analyze plasma and vitreous. To confirm the presence of AGEs in our models, non-diabetic rat retinal explants were exposed to high glucose (HG), to reproduce short-term effects, or in vitro gBSA, to reproduce long-term effects of elevated glucose concentrations. Rat retinal explants and diabetic retinal tissues were evaluated for the receptor for advanced glycation end-product (RAGE) by Western blot analysis.

RESULTS

In in vitro experiments, fluorescence emission showed glucose concentration- and time-dependent increase of fAGEs in gBSA (p≤0.05). In streptozotocin-induced diabetic rats, fAGE in plasma and vitrei showed an increase at 6 (p≤0.005) and 12 (p≤0.05) weeks of diabetes, with respect to control. RAGE was time-dependently upregulated in retinas incubated with gBSA, but not with HG, and in diabetic retinal tissue, substantiating exposure to AGEs.

CONCLUSIONS

Applying the proposed technique, we could show that fAGEs levels increase with glucose concentration and time of exposure in vitro. Furthermore, in diabetic rats, it showed that circulating fAGEs are similarly upregulated as those in vitreous, suggesting a correlation between circulating and tissue AGEs. These results support the use of this method as a simple and reliable test to measure circulating fAGEs and monitor diabetes progression.

FAM3B mediates high glucose-induced vascular smooth muscle cell proliferation and migration via inhibition of miR-322-5p

The proliferation and migration of vascular smooth muscle cells (VSMCs) play an essential role during the development of cardiovascular diseases (CVDs). While many factors potentially contribute to the abnormal activation of VSMCs, hyperglycemia is generally believed to be a major causative factor. On the other hand, FAM3B (named PANDER for its secretory form) is a uniquely structured protein strongly expressed within and secreted from the endocrine pancreas. FAM3B is co-secreted with insulin from the β-cell upon glucose stimulation and regulates glucose homeostasis. In the present study, we sought to determine the roles of FAM3B in the regulation of VSMC physiology, especially under the hyperglycemic condition. We found that FAM3B expression was induced by hyperglycemia both in vivo and in vitro. FAM3B knockdown inhibited, whereas FAM3B overexpression accelerated VSMC proliferation and migration. At the molecular level, FAM3B inhibited miR-322-5p expression, and enforced expression of miR-322-5p antagonized FAM3B-induced VSMC proliferation and migration, suggesting that FAM3B facilitated VSMC pathological activation via miR-322-5p. Taken together, FAM3B mediates high glucose-induced VSMC proliferation and migration via inhibition of miR-322-5p. Thus, FAM3B may therefore serve as a novel therapeutic target for diabetes-related CVDs.

Advanced Glycation End Products Impair Voltage-Gated K+ Channels-Mediated Coronary Vasodilation in Diabetic Rats

Background

We have previously reported that high glucose impairs coronary vasodilation by reducing voltage-gated K⁺ (K_v) channel activity. However, the underlying mechanisms remain unknown. Advanced glycation end products (AGEs) are potent factors that contribute to the development of diabetic vasculopathy. The aim of this study was to investigate the role of AGEs in high glucose-induced impairment of K_v channels-mediated coronary vasodilation.

Methods

Patch-clamp recording and molecular biological techniques were used to assess the function and expression of K_v channels. Vasodilation of isolated rat small coronary arteries was measured using a pressurized myograph. Treatment of isolated coronary vascular smooth muscle cells (VSMCs) and streptozotocin-induced diabetic rats with aminoguanidine, the chemical inhibitor of AGEs formation, was performed to determine the contribution of AGEs.

Results

Incubation of VSMCs with high glucose reduced K_v current density by 60.4 ± 4.8%, and decreased expression of K_v1.2 and K_v1.5 both at the gene and protein level, whereas inhibiting AGEs formation or blocking AGEs interacting with their receptors prevented high glucose-induced impairment of K_v channels. In addition, diabetic rats manifested reduced K_v channels-mediated coronary dilation (9.3 ± 1.4% vs. 36.9 ± 1.4%, P < 0.05), which was partly corrected by the treatment with aminoguanidine (24.4 ± 2.2% vs. 9.3 ± 1.4%, P < 0.05).

Conclusions

Excessive formation of AGEs impairs K_v channels in VSMCs, then leading to attenuation of K_v channels-mediated coronary vasodilation.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Apocynin decreases AGEs-induced stimulation of NF-κB protein expression in vascular smooth muscle cells from GK rats

CONTEXT

Elevated oxidative stress plays a key role in diabetes-associated vascular disease. Excessive production of reactive oxygen species via advanced glycation end products (AGEs) activates peroxisome proliferator-activated receptor gamma (PPARγ) and the transcription factor nuclear factor-kB (NF-κB) in aortic vascular smooth muscle cells (VSMCs). Apocynin, a drug with an antioxidant effect, has also been proposed as a therapeutic agent for atherosclerotic disease.

OBJECTIVES

This work investigates the effects of apocynin on the PPARγ and NF-κB protein expression evoked by AGEs in cultured VSMCs from Goto-Kakisaki (GK) rats, a non-obese insulin model of both insulin resistance and type 2 diabetes.

MATERIALS AND METHODS

VSMCs, isolated from aortas of GK and non-diabetic rats, were cultured. The expression of proteins was evaluated by Western blot. The blood glucose concentration was measured with a blood glucose test meter. The diabetes of GK rats was controlled by blood glucose and insulin determinations (non-fasting values). The serum insulin concentration was determined by radioimmunoassay.

RESULTS

In VSMCs from non-diabetic and GK rats, apocynin (1 and 10 µM) abolished the protein overexpression of NF-κB induced by glycated bovine serum albumin (AGEs-BSA) incubation. However, apocynin (1 and 10 µM) enhanced the expression of PPARγ protein in the presence of AGEs-BSA (100 μg/mL) in VSMCs from non-diabetic, but not from GK rats.

CONCLUSION

These findings suggest that apocynin decreases the incidence of alterations in VSMCs induced by AGEs through the reduction of NF-κB and may represent an attractive therapeutic approach to treat diabetes mellitus.

The emerging roles of fatty acid translocase/CD36 and the aryl hydrocarbon receptor in fatty liver disease

The fatty acid translocase (FAT)/CD36 belongs to the class B scavenger receptor family. In addition to the known functions of CD36 in the uptake of oxidized low-density lipoprotein by macrophages and uptake of fatty acids by adipose tissues, skeletal muscle and heart, emerging evidence has pointed to an equally important function of CD36 in the uptake of fatty acids in the liver and the pathogenesis of fatty liver disease. Recent reports have also suggested CD36 as a shared transcriptional target of several ligand-sensing and lipogenic transcriptional factors, such as the aryl hydrocarbon receptor, and several nuclear hormone receptors, such as pregnane X receptor, liver X receptor and peroxisome proliferator activated receptor γ. Non-alcoholic fatty liver disease is common and medically significant, because it is closely related to metabolic syndrome and has a potential to progress into the more harmful non-alcoholic steatohepatitis. It is hoped that CD36 and their transcriptional regulators can represent novel therapeutic targets for the prevention and management of fatty liver disease.

Effect of irreversibly glycated LDL in human vascular smooth muscle cells: lipid loading, oxidative and inflammatory stress

The major complication of diabetes is accelerated atherosclerosis, the progression of which entails complex interactions between the modified low-density lipoproteins (LDL) and the cells of the arterial wall. Advanced glycation end product-modified-LDL (AGE-LDL) that occurs at high rate in diabetes contributes to diabetic atherosclerosis, but the underlying mechanisms are not fully understood. The aim of this study was to assess the direct effect of AGE-LDL on human vascular smooth muscle cells (hSMC) dysfunction. Cultured hSMC incubated (24 hrs) with human AGE-LDL, native LDL (nLDL) or oxidized LDL (oxLDL) were subjected to: (i) quantification of the expression of the receptors for modified LDL and AGE proteins (LRP1, CD36, RAGE) and estimation of lipid loading, (ii) determination of NADPH oxidase activity and reactive oxygen species (ROS) production and (iii) evaluation of the expression of monocyte chemoattractant protein-1 (MCP-1). The results show that exposure of hSMC to AGE-LDL (compared to nLDL) induced: (a) increased NADPH oxidase activity (30%) and ROS production (28%) by up-regulation of NOX1, NOX4, p22phox and p67phox expression, (b) accumulation of intracellular cholesteryl esters, (c) enhanced gene expression of LRP1 (160%) and CD36 (35%), and protein expression of LRP1, CD36 and RAGE, (d) increased MCP-1 gene expression (160%) and protein secretion (300%) and (e) augmented cell proliferation (30%). In conclusion, AGE-LDL activates hSMC (increasing CD36, LRP1, RAGE), inducing a pro-oxidant state (activation of NADPHox), lipid accumulation and a pro-inflammatory state (expression of MCP-1). These results may partly explain the contribution of AGE-LDL and hSMC to the accelerated atherosclerosis in diabetes.

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.

Regulation of oxidative stress by glycaemic control: evidence for an independent inhibitory effect of insulin therapy

AIMS/HYPOTHESIS

We examined whether type of diabetes and/or insulin treatment can modulate the impact of sustained hyperglycaemia and glycaemic variability as activators of oxidative stress.

METHODS

This was an observational study in 139 patients with diabetes, 48 with type 1, 60 with type 2 treated by oral hypoglycaemic agents (OHAs) alone and 31 with type 2 treated with insulin plus OHAs. In addition, two groups of ten patients with type 2 diabetes were investigated either before and after introducing insulin treatment (add-on insulin group) or before and after add-on OHA therapy to metformin (add-on OHA group). Oxidative stress was estimated from 24 h urinary excretion rates of 8-isoprostaglandin F2alpha (8-iso-PGF2alpha). HbA(1c) was assessed and mean amplitude of glycaemic excursions (MAGE) was estimated by continuous monitoring.

RESULTS

The 24 h excretion rate of 8-iso-PGF2alpha (median [range] picomoles per millimole of creatinine) was much higher (p < 0.0001) in type 2 diabetes patients treated with OHAs alone (112 [26-329]) than in the type 1 diabetes group (65 [29-193]) and the type 2 diabetes group treated with insulin (69 [30-198]). It was associated with HbA(1c) (F = 12.9, p = 0.0008) and MAGE (F = 7.7, p = 0.008) in non-insulin-treated, but not in insulin-treated patients. A significant reduction in 24 h excretion rate of 8-iso-PGF2alpha from 126 (47-248) to 62 (35-111] pmol/mmol of creatinine was observed in the add-on insulin group (p = 0.005) but not in the add-on OHA group.

CONCLUSIONS/INTERPRETATION

In type 1 and type 2 diabetes, insulin exerts an inhibitory effect on oxidative stress, a metabolic disorder that is significantly activated by sustained hyperglycaemia and glucose variability in non-insulin-treated type 2 diabetes.

The receptor for advanced glycation endproducts (RAGE) and cardiovascular disease

Recent and compelling investigation has expanded our view of the biological settings in which the products of nonenzymatic glycation and oxidation of proteins and lipids - the advanced glycation endproducts (AGEs) - form and accumulate. Beyond diabetes, natural ageing and renal failure, AGEs form in inflammation, oxidative stress and in ischaemia-reperfusion. The chief signal transduction receptor for AGEs - the receptor for AGEs (RAGE) - is a multiligand-binding member of the immunoglobulin superfamily. In addition to AGEs, RAGE binds certain members of the S100/calgranulin family, high-mobility group box 1 (HMGB1), and beta-amyloid peptide and beta-sheet fibrils. Recent studies demonstrate beneficial effects of RAGE antagonism and genetic deletion in rodent models of atherosclerosis and ischaemia-reperfusion injury in the heart and great vessels. Experimental evidence is accruing that RAGE ligand generation and release during ischaemia-reperfusion may signal through RAGE, thus suggesting that antagonism of this receptor might provide a novel form of therapeutic intervention in heart disease. However, it is plausible that innate, tissue-regenerative roles for these RAGE ligands may also impact the failing heart - perhaps through RAGE and/or distinct receptors. In this review, we focus on RAGE and the consequences of its activation in the cardiovasculature.

Receptor of Advanced Glycation End Products (RAGE) Positively Regulates CD36 Expression and Reactive Oxygen Species Production in Human Monocytes in Diabetes

Introduction: Advanced glycation end products (AGEs) engagement of a monocyte surface receptor (RAGE) induces atherosclerosis. AGEs also act as CD36 ligands. We studied reactive oxygen species (ROS) and CD36 expression after siRNA inhibition of RAGE expression in human monocytes. Methods: We isolated monocytes from: a) 10 type 2 diabetics, and b) 5 age- and sex-matched healthy individuals. CD36 expression and ROS production were evaluated before and after RAGE knockdown. Results: After incubation of monocytes with AGE + bovine serum albumin (BSA), CD36 expression and intracellular ROS increased significantly in all groups. In RAGE-knockdown monocytes, AGE-induced CD36 expression and ROS generation were also significantly inhibited. Conclusions: Blocking RAGE expression using siRNA in human monocytes led to a significant inhibition of CD36 expression and ROS production, suggesting a positive interaction between RAGE, CD36 expression and ROS generation in monocytes.

CD36: implications in cardiovascular disease

CD36 is a broadly expressed membrane glycoprotein that acts as a facilitator of fatty acid uptake, a signaling molecule, and a receptor for a wide range of ligands, including apoptotic cells, modified forms of low density lipoprotein, thrombospondins, fibrillar beta-amyloid, components of Gram positive bacterial walls and malaria infected erythrocytes. CD36 expression on macrophages, dendritic and endothelial cells, and in tissues including muscle, heart, and fat, suggest diverse roles, and indeed, this is truly a multi-functional receptor involved in both homeostatic and pathological conditions. Despite an impressive increase in our knowledge of CD36 functions, in depth understanding of the mechanistic aspects of this protein remains elusive. This review focuses on CD36 in cardiovascular disease-what we know, and what we have yet to learn.