APE1/Ref-1 Inhibits Phosphate-Induced Calcification and Osteoblastic Phenotype Changes in Vascular Smooth Muscle Cells

Target analysis and identification of curcumin against vascular calcification

To investigate the mechanism of curcumin (CUR) on vascular calcification (VC), we screen for common targets of CUR and atherosclerosis and verify the targets genes in vivo and in vitro experiments. The common targets of CUR and AS were screened and obtained using different databases. These target genes were analyzed by GO and KEGG pathway enrichment analysis. PPI network analysis was performed and to analyze the key targets. A rat VC model was constructed and CUR was fed for three weeks. The changes of vascular structure and calcium salt deposition were observed in H&E and Von Kossa staining. Further, the expression of these target proteins was detected in the primary VSMCs of VC. The 31 common targets were obtained. GO functional enrichment analysis obtained 1284 terms and KEGG pathway enriched 66 pathways. The key genes were identified in the cytoHubba plugin. The molecular docking analysis showed that CUR bound strongly to EGFR, STAT3 and BCL2. The animal experiments showed the deposition calcium salt reduced by the CUR administration. These proteins BMP2, RUNX2, EGFR, STAT3 and BAX expression were upregulated in VC group and CUR attenuated the upregulated expression. The signal protein Akt and p65 expression increased in VC group and decreased in CUR group. We identified some common target genes of CUR and AS and identified these key genes. The anti-VC effect of CUR was associated with the inhibition of upregulation of EGFR, STAT3 and RUNX2 expression in VSMCs.

EVs-miR-17-5p attenuates the osteogenic differentiation of vascular smooth muscle cells potentially via inhibition of TGF-β signaling under high glucose conditions

Vascular calcification, which is a major complication of diabetes mellitus, is an independent risk factor for cardiovascular disease. Osteogenic differentiation of vascular smooth muscle cells (VSMCs) is one of the key mechanisms underlying vascular calcification. Emerging evidence suggests that macrophage-derived extracellular vesicles (EVs) may be involved in calcification within atherosclerotic plaques in patients with diabetes mellitus. However, the role of macrophage-derived EVs in the progression of vascular calcification is largely unknown. In this study, we investigated whether macrophage-derived EVs contribute to the osteogenic differentiation of VSMCs under high glucose conditions. We isolated EVs that were secreted by murine peritoneal macrophages under normal glucose (EVs-NG) or high glucose (EVs-HG) conditions. miRNA array analysis in EVs from murine macrophages showed that miR-17-5p was significantly increased in EVs-HG compared with EVs-NG. Prediction analysis with miRbase identified transforming growth factor β receptor type II (TGF-β RII) as a potential target of miR-17-5p. EVs-HG as well as miR-17-5p overexpression with lipid nanoparticles inhibited the gene expression of Runx2, and TGF-β RII. Furthermore, we demonstrated that VSMCs transfected with miR-17-5p mimic inhibited calcium deposition. Our findings reveal a novel role of macrophage-derived EVs in the negative regulation of osteogenic differentiation in VSMCs under high glucose conditions.

Relationship between arginine methylation and vascular calcification

In patients on maintenance hemodialysis (MHD), vascular calcification (VC) is an independent predictor of cardiovascular disease (CVD), which is the primary cause of death in chronic kidney disease (CKD). The main component of VC in CKD is the vascular smooth muscle cells (VSMCs). VC is an ordered, dynamic activity. Under the stresses of oxidative stress and calcium-‑phosphorus imbalance, VSMCs undergo osteogenic phenotypic transdifferentiation, which promotes the formation of VC. In addition to traditional epigenetics like RNA and DNA control, post-translational modifications have been discovered to be involved in the regulation of VC in recent years. It has been reported that the process of osteoblast differentiation is impacted by catalytic histone or non-histone arginine methylation. Its function in the osteogenic process is comparable to that of VC. Thus, we propose that arginine methylation regulates VC via many signaling pathways, including as NF-B, WNT, AKT/PI3K, TGF-/BMP/SMAD, and IL-6/STAT3. It might also regulate the VC-related calcification regulatory factors, oxidative stress, and endoplasmic reticulum stress. Consequently, we propose that arginine methylation regulates the calcification of the arteries and outline the regulatory mechanisms involved.

APE1/Ref-1 Inhibits Adipogenic Transcription Factors during Adipocyte Differentiation in 3T3-L1 Cells

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a multifunctional protein involved in DNA repair and redox regulation. The redox activity of APE1/Ref-1 is involved in inflammatory responses and regulation of DNA binding of transcription factors related to cell survival pathways. However, the effect of APE1/Ref-1 on adipogenic transcription factor regulation remains unknown. In this study, we investigated the effect of APE1/Ref-1 on the regulation of adipocyte differentiation in 3T3-L1 cells. During adipocyte differentiation, APE1/Ref-1 expression significantly decreased with the increased expression of adipogenic transcription factors such as CCAAT/enhancer binding protein (C/EBP)-α and peroxisome proliferator-activated receptor (PPAR)-γ, and the adipocyte differentiation marker adipocyte protein 2 (aP2) in a time-dependent manner. However, APE1/Ref-1 overexpression inhibited C/EBP-α, PPAR-γ, and aP2 expression, which was upregulated during adipocyte differentiation. In contrast, silencing APE1/Ref-1 or redox inhibition of APE1/Ref-1 using E3330 increased the mRNA and protein levels of C/EBP-α, PPAR-γ, and aP2 during adipocyte differentiation. These results suggest that APE1/Ref-1 inhibits adipocyte differentiation by regulating adipogenic transcription factors, suggesting that APE1/Ref-1 is a potential therapeutic target for regulating adipocyte differentiation.

NEDD4 attenuates oxidized low‑density lipoprotein‑induced inflammation and dysfunction in vascular endothelial cells via regulating APEX1 expression

Atherosclerosis chiefly results from inflammation as well as vascular endothelial cell dysfunction. Methylation levels of neuronally expressed developmentally downregulated 4 (NEDD4) were found to be fortified in atherosclerosis patients and NEDD4 deficiency enhanced vascular calcification. However, the exact function of NEDD4 in inflammation and vascular endothelial dysfunction remains to be elucidated. In the present study, CCK-8 assay was used to estimate cell viability. Reverse transcription-quantitative PCR was adopted to examine the expression of NEDD4, inflammation-associated enzymes and apurinic/apyrimidinic endodeoxyribonuclease 1 (APEX1). Western blotting was used to test NEDD4, endothelial nitric oxide synthase, inducible nitric oxide synthase and APEX1 protein levels. Cytotoxicity was detected by a lactate dehydrogenase (LDH) kit. Reactive oxygen species level was tested by a corresponding kit. Vascular cell adhesion molecule 1 and intercellular adhesion molecule 1 contents were examined with ELISA. Cell adhesion assays evaluated the adhesion of endothelial cells. Co-immunoprecipitation assay was used to test the relationship between NEDD4 and APEX1. The data revealed that NEDD4 expression rapidly declined in oxidized low density lipoprotein (ox-LDL)-induced human umbilical vein endothelial cells (HUVECs). Following NEDD4 overexpression, the active damage, inflammatory release and endothelial cell dysfunction in ox-LDL-induced HUVECs were attenuated. After co-transfection of APEX1 interference plasmids and NEDD4 overexpression plasmids, cell damage, inflammatory release and endothelial cell dysfunction in ox-LDL-induced HUVECs were improved again. Taken together, NEDD4 attenuated ox-LDL-induced inflammation and endothelial dysfunction by regulating APEX1 expression.

Phenotypic plasticity of vascular smooth muscle cells in vascular calcification: Role of mitochondria

Vascular calcification (VC) is an important hallmark of cardiovascular disease, the osteo-/chondrocyte phenotype differentiation of vascular smooth muscle cells (VSMCs) is the main cause of vascular calcification. Accumulating evidence shows that mitochondrial dysfunction may ultimately be more detrimental in the VSMCs calcification. Mitochondrial participate in essential cellular functions, including energy production, metabolism, redox homeostasis regulation, intracellular calcium homeostasis, apoptosis, and signal transduction. Mitochondrial dysfunction under pathological conditions results in mitochondrial reactive oxygen species (ROS) generation and metabolic disorders, which further lead to abnormal phenotypic differentiation of VSMCs. In this review, we summarize existing studies targeting mitochondria as a treatment for VC, and focus on VSMCs, highlighting recent progress in determining the roles of mitochondrial processes in regulating the phenotype transition of VSMCs, including mitochondrial biogenesis, mitochondrial dynamics, mitophagy, mitochondrial energy metabolism, and mitochondria/ER interactions. Along these lines, the impact of mitochondrial homeostasis on VC is discussed.

Mitochondria and vascular calcification in chronic kidney disease: Lessons learned from the past to improve future therapy

Chronic kidney disease-mineral and bone disorders (CKD-MBD) is a common complication of CKD Stages 3-5. Hyperphosphatemia is one of the major metabolic components of CKD-MBD, frequently resulting in vascular calcification (VC) in advanced-stage patients. Also, a long duration of renal replacement therapy can cause the worsening of VC, leading to increased cardiovascular morbidity and mortality. Vascular smooth muscle cells play an important role in the development of VC through osteochondrogenic transformation and the apoptotic process. It has been shown that mitochondrial dysfunction is involved with CKD progression, and excessive oxidative stress can aggravate osteoblastic transformation and VC. Currently, novel interventions targeting mitochondrial function and dynamics, in addition to mitochondrial antioxidants, have been studied with the aim of attenuating VC. This review aims to comprehensively summarize and discuss the experimental and clinical reports concerning mitochondrial studies, along with the purpose of interventions that can improve the outcomes of VC among CKD patients.

New Horizons for the Roles and Association of APE1/Ref-1 and ABCA1 in Atherosclerosis

Atherosclerosis is the leading cause of death worldwide. APE1/Ref-1 and ABCA1 play key roles in the progression of atherosclerosis. APE1/Ref-1 suppresses atherosclerosis via multiple mechanisms, including reducing the IL-6-, TNF-α-, and IL-1β-mediated proinflammatory responses, suppressing ROS-mediated oxidant activity and Bax/Bcl-2-mediated vascular calcification and apoptosis, and reducing LOX-1-mediated cholesterol uptake. However, APE1/Ref-1 also promotes atherosclerosis by increasing the activity of the NK-κB and S1PR1 pathways. APE1/Ref-1 localizes to the nucleus, cytoplasm, and mitochondria and can be secreted from the cell. APE1/Ref-1 localization is dynamically regulated by the disease state and may be responsible for its proatherogenic and antiatherogenic effects. ABCA1 promotes cholesterol efflux and anti-inflammatory responses by binding to apoA-I and regulates apoptotic cell clearance and HSPC proliferation to protect against inflammatory responses. Interestingly, in addition to mediating these functions, ABCA1 promotes the secretion of acetylated APE1/Ref-1 (AcAPE1/Ref-1), a therapeutic target, which protects against atherosclerosis development. The APE1/Ref-1 inhibitor APX3330 is being evaluated in a phase II clinical trial. The LXR agonist LXR-623 (WAY-252623) is an agonist of ABCA1 and the first LXR-targeting compound to be evaluated in clinical trials. In this article, we review the roles of ABCA1 and APE1/Ref-1 in atherosclerosis and focus on new insights into the ABCA1-APE1/Ref-1 axis and its potential as a novel therapeutic target in atherosclerosis.

Phenotypic and Functional Transformation in Smooth Muscle Cells Derived from a Superficial Thrombophlebitis-affected Vein Wall

BACKGROUND

Superficial thrombophlebitis (ST) is a frequent pathology, but its exact incidence remains to be determined. This study tested the hypothesis whether relationships exist among smooth muscle cells (SMCs) derived from ST, varicose great saphenous veins (VGSVs), and normal great saphenous veins (GSVs).

METHODS

Forty-one samples of ST, VGSVs, and GSVs were collected. SMCs were isolated and cultured. Proliferation, migration, adhesion, and senescence in SMCs from the three vein walls were compared by various methods. Bax, Bcl-2, caspase-3, matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and TIMP-2 messenger RNA (mRNA) and protein expressions were detected by fluorescence quantitative PCR and Western blot.

RESULTS

An obvious decrease in cytoskeletal filaments was observed in thrombophlebitic vascular smooth muscle cells (TVSMCs). The quantity of proliferation, migration, adhesion, and senescence in TVSMCs was significantly higher than in varicose vascular smooth muscle cells and normal vascular smooth muscle cells (NVSMCs) (all P < 0.05). Bax and caspase-3 mRNA and protein expression were decreased, while Bcl-2 mRNA and protein expression were increased in the TVSMCs compared with the varicose vascular smooth muscle cells and the NVSMCs (all P < 0.05). MMP-2, MMP-9, TIMP-1, and TIMP-2 mRNA and protein expression were significantly increased in the TVSMCs compared with the VVGSVs and the NVSMCs (all P < 0.05).

CONCLUSION

SMCs derived from ST are more dedifferentiated and demonstrate increased cell proliferation, migration, adhesion, and senescence, as well as obviously decreased cytoskeletal filaments. These results suggest that the phenotypic and functional differences could be related to the presence of atrophic and hypertrophic vein segments during the disease course among SMCs derived from ST, VGSVs, and GSVs.

Lactate accelerates vascular calcification through NR4A1-regulated mitochondrial fission and BNIP3-related mitophagy

Arterial media calcification is related to mitochondrial dysfunction. Protective mitophagy delays the progression of vascular calcification. We previously reported that lactate accelerates osteoblastic phenotype transition of VSMC through BNIP3-mediated mitophagy suppression. In this study, we investigated the specific links between lactate, mitochondrial homeostasis, and vascular calcification. Ex vivo, alizarin S red and von Kossa staining in addition to measurement of calcium content, RUNX2, and BMP-2 protein levels revealed that lactate accelerated arterial media calcification. We demonstrated that lactate induced mitochondrial fission and apoptosis in aortas, whereas mitophagy was suppressed. In VSMCs, lactate increased NR4A1 expression, leading to activation of DNA-PKcs and p53. Lactate induced Drp1 migration to the mitochondria and enhanced mitochondrial fission through NR4A1. Western blot analysis of LC3-II and p62 and mRFP-GFP-LC3 adenovirus detection showed that NR4A1 knockdown was involved in enhanced autophagy flux. Furthermore, NR4A1 inhibited BNIP3-related mitophagy, which was confirmed by TOMM20 and BNIP3 protein levels, and LC3-II co-localization with TOMM20. The excessive fission and deficient mitophagy damaged mitochondrial structure and impaired respiratory function, determined by mPTP opening rate, mitochondrial membrane potential, mitochondrial morphology under TEM, ATP production, and OCR, which was reversed by NR4A1 silencing. Mechanistically, lactate enhanced fission but halted mitophagy via activation of the NR4A1/DNA-PKcs/p53 pathway, evoking apoptosis, finally accelerating osteoblastic phenotype transition of VSMC and calcium deposition. This study suggests that the NR4A1/DNA-PKcs/p53 pathway is involved in the mechanism by which lactate accelerates vascular calcification, partly through excessive Drp-mediated mitochondrial fission and BNIP3-related mitophagy deficiency.

Overexpression of HOTAIR attenuates Pi-induced vascular calcification by inhibiting Wnt/β-catenin through regulating miR-126/Klotho/SIRT1 axis

Vascular calcification is one of the most common effects of macrovascular complications in patients in aging with chronic kidney disease and diabetes. Previous studies showed that HOTAIR attenuated vascular calcification via the Wnt/β-catenin-signaling pathway, yet the molecular mechanism has not been fully elucidated. This study aimed to identify the explicit molecular mechanism underlying HOTAIR regulated vascular calcification. In the phosphate (Pi)-induced calcification model of human aortic smooth muscle cells (HASMCs), we investigated whether HOTAIR was involved in the regulation of miR-126. The luciferase reporter was used to examine the effect of HOTAIR on miR-126 and miR-126 on Klotho 3'-UTR. Furthermore, we overexpressed Klotho to verify the regulation of Klotho on SIRT1, as well as their roles in mediating Pi-induced calcification in HASMCs via the Wnt/β-catenin signaling pathway. Finally, the results were verified in an in vivo mice calcification model. Overexpression of HOTAIR reduced the expression of miR-126 in Pi-induced HASMCs. Additionally, knockdown of miR-126 increased SIRT1 expression by regulating Klotho expression. An increased level of Klotho inhibited Wnt/β-catenin signaling pathway, which eventually attenuated Pi-induced HASMCs calcification. Luciferase reporter assay revealed that HOTAIR targeted miR-126 and miR-126 could directly target Klotho. Eventually, HOTAIR overexpression reversed Pi-induced calcium calcification in vivo mouse models. This study demonstrated that HOTAIR overexpression attenuated Pi-induced calcification by regulating the miR-126/Klotho/SIRT1 axis, thereby inhibiting the Wnt/β-catenin signaling pathway. It provides new potential target genes for the clinical treatment of vascular calcification.

Oxidative stress in vascular calcification

Vascular calcification (VC), which is closely associated with significant mortality in cardiovascular disease, chronic kidney disease (CKD), and/or diabetes mellitus, is characterized by abnormal deposits of hydroxyapatite minerals in the arterial wall. The impact of oxidative stress (OS) on the onset and progression of VC has not been well described. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, myeloperoxidase (MPO), nitric oxide synthases (NOSs), superoxide dismutase (SOD) and paraoxonases (PONs) are relevant factors that influence the production of reactive oxygen species (ROS). Furthermore, excess ROS-induced OS has emerged as a critical mediator promoting VC through several mechanisms, including phosphate balance, differentiation of vascular smooth muscle cells (VSMCs), inflammation, DNA damage, and extracellular matrix remodeling. Because OS is a significant regulator of VC, antioxidants may be considered as novel treatment options.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Vascular Calcification-New Insights Into Its Mechanism

Vascular calcification (VC), which is categorized by intimal and medial calcification, depending on the site(s) involved within the vessel, is closely related to cardiovascular disease. Specifically, medial calcification is prevalent in certain medical situations, including chronic kidney disease and diabetes. The past few decades have seen extensive research into VC, revealing that the mechanism of VC is not merely a consequence of a high-phosphorous and -calcium milieu, but also occurs via delicate and well-organized biologic processes, including an imbalance between osteochondrogenic signaling and anticalcific events. In addition to traditionally established osteogenic signaling, dysfunctional calcium homeostasis is prerequisite in the development of VC. Moreover, loss of defensive mechanisms, by microorganelle dysfunction, including hyper-fragmented mitochondria, mitochondrial oxidative stress, defective autophagy or mitophagy, and endoplasmic reticulum (ER) stress, may all contribute to VC. To facilitate the understanding of vascular calcification, across any number of bioscientific disciplines, we provide this review of a detailed updated molecular mechanism of VC. This encompasses a vascular smooth muscle phenotypic of osteogenic differentiation, and multiple signaling pathways of VC induction, including the roles of inflammation and cellular microorganelle genesis.

The Biological Role of Apurinic/Apyrimidinic Endonuclease1/Redox Factor-1 as a Therapeutic Target for Vascular Inflammation and as a Serologic Biomarker

Endothelial dysfunction promotes vascular inflammation by inducing the production of reactive oxygen species and adhesion molecules. Vascular inflammation plays a key role in the pathogenesis of vascular diseases and atherosclerotic disorders. However, whether there is an endogenous system that can participate in circulating immune surveillance or managing a balance in homeostasis is unclear. Apurinic/apyrimidinic endonuclease 1/redox factor-1 (henceforth referred to as APE1/Ref-1) is a multifunctional protein that can be secreted from cells. It functions as an apurinic/apyrimidinic endonuclease in the DNA base repair pathway and modulates redox status and several types of transcriptional factors, in addition to its anti-inflammatory activity. Recently, it was reported that the secretion of APE1/Ref-1 into the extracellular medium of cultured cells or its presence in the plasma can act as a serological biomarker for certain disorders. In this review, we summarize the possible biological functions of APE1/Ref-1 according to its subcellular localization or its extracellular secretions, as therapeutic targets for vascular inflammation and as a serologic biomarker.

Interleukin-1β-Induced Senescence Promotes Osteoblastic Transition of Vascular Smooth Muscle Cells

INTRODUCTION

Interleukin (IL)-1β, as a key biomarker and mediator of vascular calcification in patients with end-stage renal disease (ESRD), may be involved in the process of premature senescence of vascular smooth muscle cells (VSMCs). This work sought to investigate whether IL-1β-induced premature senescence contributes to the process of osteoblastic transition and vascular calcification in VSMCs.

METHODS

Eighty-eight patients with ESRD (aged 25-81 years), 11 healthy individuals, and 15 cases of lesion-free distal radial arteries from dialysis ESRD patients with angiostomy were collected in this study. Immunohistochemical analysis was performed to detect expression of IL-1β, p21, and bone morphogenetic protein-2 (BMP2) in the distal radial arteries. Primary human VSMCs from healthy neonatal umbilical cords were incubated with test agents for 1-3 days. Intracellular levels of reactive oxygen species (ROS) and senescence-associated-β-galactosidase (SA-β-gal) staining were used to detect senescent cells. Alizarin red staining and the calcium content of the cell layer were used to detect mineral deposition in VSMCs.

RESULTS

Coincident with positive staining of IL-1β, p21, and BMP2 in the lesion-free distal radial arteries, 66.67% patients showed mineral deposition. Serum IL-1β was 0.24 ± 0.57, 1.20 ± 2.95, and 9.41 ± 40.52 pg/mL in 11 healthy individuals, 20 patients without calcification, and 53 patients with calcification, respectively. Analysis of the cross-table chi-square test showed cardiovascular calcification is not correlated with levels of serum IL-1β in patients with ESRD (p = 0.533). In response to IL-1β, VSMCs showed a senescence-like phenotype, such as flat and enlarged morphology, increased expression of p21, an increased activity of SA-β-gal, and increased levels of ROS. IL-1β-induced senescence of VSMCs was required for the activation of IL-1β/NF-κB/p53/p21 signaling pathway. IL-1β-induced senescent VSMCs underwent calcification due to osteoblastic transition mainly depending upon the upregulation of BMP2. Resveratrol, an activator of sirtuin-1, postponed the IL-1β-induced senescence through blocking the NF-κB/p53/p21 pathway and attenuated the osteoblastic transition and calcification in VSMCs.

CONCLUSIONS

High levels of IL-1β in medial smooth muscles of arteries may play roles in inducing senescence-associated calcification. IL-1β-induced senescence depending on the activation of the NF-κB/p53/p21 signaling pathway and contributing to osteoblastic transition of VSMCs.

ATP Binding Cassette Transporter A1 is Involved in Extracellular Secretion of Acetylated APE1/Ref-1

Acetylation of nuclear apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE1/Ref-1) is associated with its extracellular secretion, despite the lack of an N-terminal protein secretion signal. In this study, we investigated plasma membrane targeting and translocation of APE1/Ref-1 in HEK293T cells with enhanced acetylation. While APE1/Ref-1 targeting was not affected by inhibition of the endoplasmic reticulum/Golgi-dependent secretion, its secretion was reduced by inhibitors of ATP-binding cassette (ABC) transporters, and siRNA-mediated down-regulation of ABC transporter A1. The association between APE1/Ref-1 and ABCA1 transporter was confirmed by proximal ligation assay and immunoprecipitation experiments. An APE1/Ref-1 construct with mutated acetylation sites (K6/K7R) showed reduced co-localization with ABC transporter A1. Exposure of trichostatin A (TSA) induced the acetylation of APE1/Ref-1, which translocated into membrane fraction. Taken together, acetylation of APE1/Ref-1 is considered to be necessary for its extracellular targeting via non-classical secretory pathway using the ABCA1 transporter.

Advanced glycation end products accelerate calcification in VSMCs through HIF-1α/PDK4 activation and suppress glucose metabolism

Arterial media calcification is associated with diabetes mellitus. Previous studies have shown that advanced glycation end products (AGEs) are responsible for vascular smooth muscle cell (VSMC) calcification, but the underlying mechanisms remain unclear. Hypoxia-inducible factor-1α (HIF-1α), one of the major factors during hypoxia, and pyruvate dehydrogenase kinase 4 (PDK4), an important mitochondrial matrix enzyme in cellular metabolism shift, have been reported in VSMC calcification. The potential link among HIF-1α, PDK4, and AGEs-induced vascular calcification was investigated in this study. We observed that AGEs elevated HIF-1α and PDK4 expression levels in a dose-dependent manner and that maximal stimulation was attained at 24 h. Two important HIF-1α-regulated genes, vascular endothelial growth factor A (VEGFA) and glucose transporter 1 (GLUT-1), were significantly increased after AGEs exposure. Stabilization or nuclear translocation of HIF-1α increased PDK4 expression. PDK4 inhibition attenuated AGEs-induced VSMC calcification, which was evaluated by measuring the calcium content, alkaline phosphatase (ALP) activity and runt-related transcription factor 2 (RUNX2) expression levels and by Alizarin red S staining. In addition, the glucose consumption, lactate production, key enzymes of glucose metabolism and oxygen consumption rate (OCR) were decreased during AGEs-induced VSMC calcification. In conclusion, this study suggests that AGEs accelerate vascular calcification partly through the HIF-1α/PDK4 pathway and suppress glucose metabolism.

Therapeutic Interference With Vascular Calcification-Lessons From Klotho-Hypomorphic Mice and Beyond

Medial vascular calcification, a major pathophysiological process associated with cardiovascular disease and mortality, involves osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). In chronic kidney disease (CKD), osteo-/chondrogenic transdifferentiation of VSMCs and, thus, vascular calcification is mainly driven by hyperphosphatemia, resulting from impaired elimination of phosphate by the diseased kidneys. Hyperphosphatemia with subsequent vascular calcification is a hallmark of klotho-hypomorphic mice, which are characterized by rapid development of multiple age-related disorders and early death. In those animals, hyperphosphatemia results from unrestrained formation of 1,25(OH)₂D₃ with subsequent retention of calcium and phosphate. Analysis of klotho-hypomorphic mice and mice with vitamin D₃ overload uncovered several pathophysiological mechanisms participating in the orchestration of vascular calcification and several therapeutic opportunities to delay or even halt vascular calcification. The present brief review addresses the beneficial effects of bicarbonate, carbonic anhydrase inhibition, magnesium supplementation, mineralocorticoid receptor (MR) blockage, and ammonium salts. The case is made that bicarbonate is mainly effective by decreasing intestinal phosphate absorption, and that carbonic anhydrase inhibition leads to metabolic acidosis, which counteracts calcium-phosphate precipitation and VSMC transdifferentiation. Magnesium supplementation, MR blockage and ammonium salts are mainly effective by interference with osteo-/chondrogenic signaling in VSMCs. It should be pointed out that the, by far, most efficient substances are ammonium salts, which may virtually prevent vascular calcification. Future research will probably uncover further therapeutic options and, most importantly, reveal whether these observations in mice can be translated into treatment of patients suffering from vascular calcification, such as patients with CKD.

Elevation of Serum APE1/Ref-1 in Experimental Murine Myocarditis

Myocarditis is an inflammatory disease of the myocardium that causes cardiogenic shock and death. However, endomyocardial biopsy that is, the gold standard for a diagnosis is limited. Apurinic/apyrimidinic endonuclease 1/redox effector factor-1 (APE1/Ref-1) is a multifunctional protein, which is involved in DNA-based excision repair pathway, and in redox signaling, its changes are observed in various cardiovascular diseases including hypertension and coronary artery disease. We analyzed serum APE1/Ref-1 in experimental murine myocarditis. To induce myocarditis, coxsackievirus B3 was injected intraperitoneally to BALB/c mice. The serum APE1/Ref-1, N-terminal pro-B-type natriuretic peptide (NT-proBNP) and troponin I were measured. The histology and virus titers measurements were performed. The troponin I and inflammation were significantly elevated at day 3, peaked to day 7 and decreased at day 10. The NT-proBNP and virus titers were significantly peaked at day 3, and dropped at day 7 and 10. The serum APE1/Ref-1 was gradually raised and its elevation is still maintained until a later time, namely day 10. Also, its level was positively correlated with myocardial inflammation, reflecting severity of myocardial injury. We suggest that serum APE1/Ref-1 can be used to assess for myocardial injury in viral myocarditis without endomyocardial biopsy.