Protective effects of PARP-1 knockout on dyslipidemia-induced autonomic and vascular dysfunction in ApoE mice: effects on eNOS and oxidative stress

ADP-ribosylation, a multifaceted modification: Functions and mechanisms in aging and aging-related diseases

Aging, a complex biological process, plays key roles the development of multiple disorders referred as aging-related diseases involving cardiovascular diseases, stroke, neurodegenerative diseases, cancers, lipid metabolism-related diseases. ADP-ribosylation is a reversible modification onto proteins and nucleic acids to alter their structures and/or functions. Growing evidence support the importance of ADP-ribosylation and ADP-ribosylation-associated enzymes in aging and age-related diseases. In this review, we summarized ADP-ribosylation-associated proteins including ADP-ribosyl transferases, the ADP-ribosyl hydrolyses and ADP-ribose binding domains. Furthermore, we outlined the latest knowledge about regulation of ADP-ribosylation in the pathogenesis and progression of main aging-related diseases, organism aging and cellular senescence, and we also speculated the underlying mechanisms to better disclose this novel molecular network. Moreover, we discussed current issues and provided an outlook for future research, aiming to revealing the unknown bio-properties of ADP-ribosylation, and establishing a novel therapeutic perspective in aging-related diseases and health aging via targeting ADP-ribosylation.

Sinomenine protects against atherosclerosis in apolipoprotein E-knockout mice by inhibiting of inflammatory pathway

Atherosclerosis, a multifaceted and persistent inflammatory condition, significantly contributes to the progression of cardiocerebrovascular disorders, such as myocardial infarctions and cerebrovascular accidents. It involves the accumulation of cholesterol, fatty deposits, calcium and cellular debris in the walls of arteries, leading to the formation of plaques. Our aim is to investigate the potential of sinomenine to counteract atherosclerosis in mice lacking Apolipoprotein E (ApoE-/-) Mice. We employed the high-fat diet-induced method to induce atherosclerosis in ApoE-/- mice, and the mice were treated with sinomenine (5, 10, and 15 mg/kg) and simvastatin (0.5 mg/kg) for 12 weeks. Body weight, water intake, and food intake were assessed. Lipid parameters, oxidative stress, inflammatory cytokines, and mRNA levels were estimated. Sinomenine treatment remarkably (P < 0.001) suppressed body weight, along with food and water intake. Sinomenine altered the levels of total cholesterol (TC), high-density lipoprotein (HDL), triglyceride (TG), low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL), which were modulated in the atherosclerosis group. Sinomenine treatment also altered the levels of oxidative stress parameters such as glutathione peroxidase (GPx), catalase (CAT), malonaldehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH). In addition, it modulated cardiac parameters like C-reactive protein (CRP), endothelin-1 (ET-1), thromboxane B2 (TXB2), nitric oxide (NO), cardiac troponin I (cTnI), lactate dehydrogenase (LDH), and creatinine kinase isoenzymes (CK-MB). Inflammatory cytokines interleukin (IL)-1α, IL-1β, TNF-α, IL-6, and IL-10 were also affected. Sinomenine further suppressed the mRNA expression of IL-6, IL-17, IL-10, tumor necrosis factor-α (TNF-α), Il-1β, monocyte chemoattractant protein-1 (MCP-1), MCP-2, MCP-3, transforming Growth Factor-1β (TGF-1β), vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1). The results suggest that sinomenine remarkably suppressed the development of atherosclerosis in the early stage.

Poly (ADP-ribose) polymerase: An Overview of Mechanistic Approaches and Therapeutic Opportunities in the Management of Stroke

Stroke is one of the leading causes of morbidity and mortality accompanied by blood supply loss to a particular brain area. Several mechanistic approaches such as inhibition of poly (ADP-ribose) polymerase, therapies against tissue thrombosis, and neutrophils lead to stroke's therapeutic intervention. Evidence obtained with the poly (ADP-ribose) polymerase (PARP) inhibition and animals having a deficiency of PARP enzymes; represented the role of PARP in cerebral stroke, ischemia/reperfusion, and neurotrauma. PARP is a nuclear enzyme superfamily with various isoforms, each with different structural domains and functions, and out of all, PARP-1 is the best-characterized member. It has been shown to perform multiple physiological as well as pathological processes, including its role in inflammation, oxidative stress, apoptosis, and mitochondrial dysfunction. The enzyme interacts with NF-κB, p53, and other transcriptional factors to regulate survival and cell death and modulates multiple downstream signaling pathways. Clinical trials have also been conducted using PARP inhibitors for numerous disorders and have shown positive results. However, additional information is yet to be established for the therapeutic intervention of PARP inhibitors in stroke. These agents' utilization appears to be challenging due to their unknown potential long-term side effects. PARP activity increased during ischemia, but its inhibition provided significant neuroprotection. Despite the increased interest in PARP as a pharmacological modulator for novel therapeutic therapies, the current review focused on stroke and poly ADP-ribosylation.

OUP accepted manuscript

Cardiovascular diseases (CVDs) arise from a complex interplay among genomic, proteomic, and metabolomic abnormalities. Emerging evidence has recently consolidated the presence of robust DNA damage in a variety of cardiovascular disorders. DNA damage triggers a series of cellular responses termed DNA damage response (DDR) including detection of DNA lesions, cell cycle arrest, DNA repair, cellular senescence, and apoptosis, in all organ systems including hearts and vasculature. Although transient DDR in response to temporary DNA damage can be beneficial for cardiovascular function, persistent activation of DDR promotes the onset and development of CVDs. Moreover, therapeutic interventions that target DNA damage and DDR have the potential to attenuate cardiovascular dysfunction and improve disease outcome. In this review, we will discuss molecular mechanisms of DNA damage and repair in the onset and development of CVDs, and explore how DDR in specific cardiac cell types contributes to CVDs. Moreover, we will highlight the latest advances regarding the potential therapeutic strategies targeting DNA damage signalling in CVDs.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

Heat-shock-induced tyrosinase gene ablation with CRISPR in zebrafish

Tyrosinase (TYR) converts L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA) and L-DOPA into L-dopaquinone, which can produce melanin pigment. The abrogation of the functional activity of TYR can result in albino skin and eye diseases because of a deficiency in melanin pigment production. In this study, we developed and characterized an inducible knockout TYR platform comprising the heat-inducible heat-shock-promoter-70-driving CRISPR/Cas9 system and a zU6-promoter-driving tyr single guide RNA (sgRNA) system to investigate the temporal expression of TYR genes. To overcome the difficulty of identifying zebrafish germline integrations and facilitate the observation of Cas9 expression, heart-specific cmlc2:enhanced green fluorescent protein (EGFP; used to confirm tyr sgRNA expression) and two selectable markers (P2A-mCherry and internal ribosomal entry site-EGFP) were applied in our system. Heat shock treatment administered to Cas9 transgenic embryos induced mCherry or EGFP fluorescence expression throughout the embryos' bodies, and Cas9 protein was detected 1 h after heat shock treatment. Mutations were created by direct injection and line crossing, which led to mosaic and complete depigmentation phenotypes in approximately 50% and 100% of the embryos, respectively. Using our system, conditional TYR knockout in zebrafish was achieved efficiently and simply.

The role of ADP-ribose metabolism in metabolic regulation, adipose tissue differentiation, and metabolism

In this review, Szanto et al. summarize the metabolic regulatory roles of PARP enzymes and their associated pathologies.

Poly(ADP-ribose) polymerases (PARPs or ARTDs), originally described as DNA repair factors, have metabolic regulatory roles. PARP1, PARP2, PARP7, PARP10, and PARP14 regulate central and peripheral carbohydrate and lipid metabolism and often channel pathological disruptive metabolic signals. PARP1 and PARP2 are crucial for adipocyte differentiation, including the commitment toward white, brown, or beige adipose tissue lineages, as well as the regulation of lipid accumulation. Through regulating adipocyte function and organismal energy balance, PARPs play a role in obesity and the consequences of obesity. These findings can be translated into humans, as evidenced by studies on identical twins and SNPs affecting PARP activity.

The impact of PARPs and ADP-ribosylation on inflammation and host-pathogen interactions

Poly-adenosine diphosphate-ribose polymerases (PARPs) promote ADP-ribosylation, a highly conserved, fundamental posttranslational modification (PTM). PARP catalytic domains transfer the ADP-ribose moiety from NAD⁺ to amino acid residues of target proteins, leading to mono- or poly-ADP-ribosylation (MARylation or PARylation). This PTM regulates various key biological and pathological processes. In this review, we focus on the roles of the PARP family members in inflammation and host-pathogen interactions. Here we give an overview the current understanding of the mechanisms by which PARPs promote or suppress proinflammatory activation of macrophages, and various roles PARPs play in virus infections. We also demonstrate how innovative technologies, such as proteomics and systems biology, help to advance this research field and describe unanswered questions.

The role of poly(ADP-ribose) polymerases in manganese exposed Caenorhabditis elegans

BACKGROUND AND AIM

When exceeding the homeostatic range, manganese (Mn) might cause neurotoxicity, characteristic of the pathophysiology of several neurological diseases. Although the underlying mechanism of its neurotoxicity remains unclear, Mn-induced oxidative stress contributes to disease etiology. DNA damage caused by oxidative stress may further trigger dysregulation of DNA-damage-induced poly(ADP-ribosyl)ation (PARylation), which is of central importance especially for neuronal homeostasis. Accordingly, this study was designed to assess in the genetically traceable in vivo model Caenorhabditis elegans the role of PARylation as well as the consequences of loss of pme-1 or pme-2 (orthologues of PARP1 and PARP2) in Mn-induced toxicity.

METHODS

A specific and sensitive isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to quantify PARylation in worms. Next to monitoring the PAR level, pme-1 and pme-2 gene expression as well as Mn-induced oxidative stress was studied in wildtype worms and the pme deletion mutants.

RESULTS AND CONCLUSION

While Mn failed to induce PARylation in wildtype worms, toxic doses of Mn led to PAR-induction in pme-1-deficient worms, due to an increased gene expression of pme-2 in the pme-1 deletion mutants. However, this effect could not be observed at sub-toxic Mn doses as well as upon longer incubation times. Regarding Mn-induced oxidative stress, the deletion mutants did not show hypersensitivity. Taken together, this study characterizes worms to model PAR inhibition and addresses the consequences for Mn-induced oxidative stress in genetically manipulated worms.

PARP-1 (Poly[ADP-Ribose] Polymerase 1) Inhibition Protects From Ang II (Angiotensin II)-Induced Abdominal Aortic Aneurysm in Mice

Abdominal aortic aneurysm (AAA) is a common vascular degenerative disease. PARP-1 (poly[ADP-ribose] polymerase 1) is a nuclear enzyme, which plays a critical role in vascular diseases. We hypothesized that PARP-1 inhibition might have protective effects on AAA. In vivo, Ang II (angiotensin II) was continuously infused by a micropump for 28 days to induce AAA in mice. In vitro, aortic endothelial cells and smooth muscle cells were stimulated by Ang II for 24 hours. Ang II infusion increased PARP-1 expression and activity and successfully induced AAA formation partly with a hemorrhage in ApoE^-/- mice. Genetic deletion of PARP-1 markedly reduced the AAA incidence, abdominal aortic diameter, macrophage infiltration, ICAM-1 (intercellular adhesion molecule 1) and VCAM-1 (vascular adhesion molecule 1) expression, and MMP (matrix metalloproteinase) expression, as well as MMP activity; but increased smooth muscle cells content and collagens expression in AAA. PARP-1 inhibition by PJ-34 also exerted a protective effect on AAA in mice. In aortic endothelial cells, Ang II-induced oxidative stress and DNA damage, resulting in increased PARP-1 expression and activity. Compared with the control, Ang II increased TNF-α (tumor necrosis factor α) and IL-6 (interleukin-6) secretions, ICAM-1 expression and THP-1 (human acute monocytic leukemia cell line) cells adhesion, while PARP-1 inhibition by siRNA reduced the inflammatory response probably through inhibition of the phosphorylation of ERK (extracellular signal-regulated kinase), NF-κB (nuclear factor-κB), and Akt signaling pathways. In smooth muscle cells, Ang II promoted cell migration, proliferation, and apoptosis, reduced collagens expression, but increased MMPs expression, while PARP-1 deletion alleviated these effects partly by reducing NF-κB-targeted MMP-9 expression. PARP-1 inhibition might be a feasible strategy for the treatment of AAA.

Poly(ADP-ribose) Polymerase (PARP) and PARP Inhibitors: Mechanisms of Action and Role in Cardiovascular Disorders

Poly(ADP-ribosyl)ation is an immediate cellular repair response to DNA damage and is catalyzed primarily by poly(ADP-ribose)polymerase-1 (PARP1), which is the most abundant of the 18 different PARP isoforms and accounts for more than 90% of the catalytic activity of PARP in the cell nucleus. Upon detection of a DNA strand break, PARP1 binds to the DNA, cleaves nicotinamide adenine dinucleotide between nicotinamide and ribose and then modifies the DNA nuclear acceptor proteins by formation of a bond between the protein and the ADP-ribose residue. This generates ribosyl-ribosyl linkages that act as a signal for other DNA-repairing enzymes and DNA base repair. Extensive DNA breakage in cells results in excessive activation of PARP with resultant depletion of the cellular stores of nicotinamide adenine dinucleotide (NAD+) which slows the rate of glycolysis, mitochondrial electron transport, and ultimately ATP formation in these cells. This paper focuses on PARP in DNA repair in atherosclerosis, acute myocardial infarction/reperfusion injury, and congestive heart failure and the role of PARP inhibitors in combating the effects of excessive PARP activation in these diseases. Free oxygen radicals and nitrogen radicals in arteries contribute to disruption of the vascular endothelial glycocalyx, which increase the permeability of the endothelium to inflammatory cells and also low-density lipoproteins and the accumulation of lipid in the vascular intima. Mild inflammation and DNA damage within vascular cells promote PARP1 activation and DNA repair. Moderate DNA damage induces caspase-dependent PARP cleavage and vascular cell apoptosis. Severe DNA damage due to vascular inflammation causes excessive activation of PARP1. This causes endothelial cell depletion of NAD+ and ATP, downregulation of atheroprotective SIRT1, necrotic cell death, and ultimately atherosclerotic plaque disruption. Inhibition of PARP decreases vascular endothelial cell adhesion P-selectin and ICAM-1 molecules, inflammatory cells, pro-death caspase-3, and c-Jun N-terminal kinase (JNK) activation and upregulates prosurvival extracellular signal-regulated kinases and AKT, which decrease vascular cell apoptosis and necrosis and limit atherosclerosis and plaque disruption. In myocardial infarction with coronary occlusion then reperfusion, which occurs with coronary angioplasty or thrombolytic therapy, reperfusion injury occurs in as many as 31% of patients and is caused by inflammatory cells, free oxygen and nitrogen radicals, the rapid transcriptional activation of inflammatory cytokines, and the activation of PARP1. Inhibition of PARP attenuates neutrophil infiltration and inflammatory cytokine expression in the reperfused myocardium and preserves myocardial NAD+ and ATP. In addition, PARP inhibition increases the activation of myocyte survival enzymes protein kinase B (Akt) and protein kinase C epsilon (PKCε), and decreases the activity of myocardial ventricular remodeling enzymes PKCα/β, PKCζ/λ, and PKCδ. As a consequence, cardiomyocyte and vascular endothelial cell necrosis is decreased and myocardial contractility is preserved. In heart failure and circulatory shock in animal models, PARP inhibition significantly attenuates decreases in left ventricular systolic pressure, ventricular contractility and relaxation, stroke volume, and increases survival by limiting or preventing upregulation of adhesion molecules, proinflammatory cytokines, myocardial mononuclear cell infiltration, and PKCα/β and PKC λ/ζ. In this manner, PARP inhibition partially restores the myocardial concentrations of NAD+, limits ventricular remodeling and fibrosis, and prevents significant decreases in myocardial contractility. Based primarily on investigations in preclinical models of atherosclerosis, myocardial infarction, and heart failure, PARP inhibition appears to be beneficial in limiting or inhibiting cardiovascular dysfunction. These studies indicate that investigations of acute and chronic PARP inhibition are warranted in patients with atherosclerotic coronary artery disease.

Poly (ADP-Ribose) Polymerase 1 Mediated Arginase II Activation Is Responsible for Oxidized LDL-Induced Endothelial Dysfunction

It is well known that arginase II leads to decreased synthesis of nitric oxide (NO) by competing with endothelial nitric oxide synthase (eNOS) for their same substrate L-arginine. However, the regulatory mechanisms of arginase II production remain unclear. In this study, we hypothesized that poly- (ADP-ribose) transferase/polymerase-1 (PARP-1) may be a critical factor responsible for ox-LDL (oxidized Low Density Lipoprotein)-enhanced arginase II activity. We used serial deletions within plasmid constructs and found that a core promoter region of arginase II was located at the element of -774 to -738 bp and PARP-1 was identified specifically binding to this region. Inhibition of PARP-1 markedly reduced the endogenous arginase II expression and enhanced eNOS and NO production. Similarly, ox-LDL-induced increase in arginase II production and eNOS and NO reduction was substantially abolished by PARP-1 inhibition both in vitro and in vivo. Significant decrease in arginase II expression and increase in eNOS expression and NO levels, as well as improved endothelial function were observed in PARP-1-/- mice. The underlying mechanisms of ox-LDL-induced changes of PARP-1 expression involved migration of phosphorylated ERK2 into nuclei and direct interaction with PARP-1 which dramatically enhanced PARP-1 production, followed by histone acetylation to activate arginase II transcription process. Our studies demonstrated for the first time that PARP-1 regulates basal transcription process and ox-LDL-induced up-regulation of arginase II. These results demonstrated that PARP-1 offers a promising therapeutic target for endothelial dysfunction and atherosclerosis.

Novel drug discovery strategies for atherosclerosis that target necrosis and necroptosis

INTRODUCTION

Formation and enlargement of a necrotic core play a pivotal role in atherogenesis. Since the discovery of necroptosis, which is a regulated form of necrosis, prevention of necrotic cell death has become an attractive therapeutic goal to reduce plaque formation. Areas covered: This review highlights the triggers and consequences of (unregulated) necrosis and necroptosis in atherosclerosis. The authors discuss different pharmacological strategies to inhibit necrotic cell death in advanced atherosclerotic plaques. Expert opinion: Addition of a necrosis or necroptosis inhibitor to standard statin therapy could be a promising strategy for primary prevention of cardiovascular disease. However, a necrosis inhibitor cannot block all necrosis stimuli in atherosclerotic plaques. A necroptosis inhibitor could be more effective, because necroptosis is mediated by specific proteins, termed receptor-interacting serine/threonine-protein kinases (RIPK) and mixed lineage kinase domain-like pseudokinase (MLKL). Currently, only RIPK1 inhibitors have been successfully used in atherosclerotic mouse models to inhibit necroptosis. However, because RIPK1 is involved in both necroptosis and apoptosis, and also RIPK1-independent necroptosis can occur, we feel that targeting RIPK3 and MLKL could be a more attractive therapeutic approach to inhibit necroptosis. Therefore, future challenges will consist of developing RIPK3 and MLKL inhibitors applicable in both preclinical and clinical settings.

PARP-1 Variant Rs1136410 Confers Protection against Coronary Artery Disease in a Chinese Han Population: A Two-Stage Case-Control Study Involving 5643 Subjects

Inhibition of poly(ADP-ribose) polymerase (PARP) may protect against coronary artery disease (CAD) in animal models, and rs1136410, a non-synonymous single nucleotide polymorphism (SNP) in PARP-1, has a potential impact on PARP activities in vitro. This two-stage case-control study, involving 2803 CAD patients and 2840 controls, aimed to investigate the associations of PARP-1 rs1136410 with CAD development, lipid levels, PARP activities, 8-hydroxy-2'-dexyguanosine (8-OHdG), and interleukin (IL)-6 levels in a Chinese Han population. Assuming a recessive model, the variant genotype GG of SNP rs1136410 showed a significantly inverse association with CAD risk (adjusted odds ratio (OR) = 0.73, P < 0.001), left main coronary artery (LMCA) lesions (P = 0.003), vessel scores (P = 0.003), and modified Gensini scores (P < 0.001). There were significant correlations of SNP rs1136410 with higher levels of total cholesterol (TC) and lower levels of high-density lipoprotein cholesterol (HDL-c). In gene-environment interaction analyses, participants with the variant genotype GG, but without smoking habit, type 2 diabetes mellitus, and hyperlipidemia, conferred an 84% (P < 0.001) decreased risk of CAD. The genotype-phenotype correlation analyses further supported the functional roles of SNP rs1136410 in decreasing PARP activities and 8-OHdG levels. Taken together, our data suggest that SNP rs1136410 may confer protection against CAD through modulation of PARP activities and gene-environment interactions in a Chinese Han population.

Poly(ADP-ribose) polymerase 1 deficiency increases nitric oxide production and attenuates aortic atherogenesis through downregulation of arginase II

Poly (ADP-ribose) polymerase (PARP) plays an important role in endothelial dysfunction, leading to atherogenesis and vascular-related diseases. However, whether PARP regulates nitric oxide (NO), a key regulator of endothelial function, is unclear so far. We investigated whether inhibition of PARP-1, the most abundant PARP isoform, prevents atherogenesis by regulating NO production and tried to elucidate the possible mechanisms involved in this phenomenon. In apolipoprotein E-deficient (apoE^-/- ) mice fed a high-cholesterol diet for 12 weeks, PARP-1 inhibition via treatment with 3,4-dihydro-54-(1-piperindinyl) butoxy-1(2H)-isoquinoline (DPQ) or PARP-1 gene knockout reduced aortic atherosclerotic plaque areas (49% and 46%, respectively). Both the groups showed restored NO production in mouse aortas with reduced arginase II (Arg II) expression compared to that in the controls. In mouse peritoneal macrophages and aortic endothelial cells (MAECs), PARP-1 knockout resulted in lowered Arg II expression. Moreover, phosphorylation of endothelial NO synthase (eNOS) was preserved in the aortas and MAECs when PARP-1 was inhibited. Reduced NO production in vitro due to PARP-1 deficiency could be restored by treating the MAECs with oxidized low-density lipoprotein treatment, but this effect could not be achieved with peritoneal macrophages, which was likely due to a reduction in the expression of induced NOS expression. Our findings indicate that PARP-1 inhibition may attenuate atherogenesis by restoring NO production in endothelial cells and thus by reducing Arg II expression and consequently arginase the activity.

Poly(ADP-ribose) Polymerase 1 Represses Liver X Receptor-mediated ABCA1 Expression and Cholesterol Efflux in Macrophages

Liver X receptors (LXR) are oxysterol-activated nuclear receptors that play a central role in reverse cholesterol transport through up-regulation of ATP-binding cassette transporters (ABCA1 and ABCG1) that mediate cellular cholesterol efflux. Mouse models of atherosclerosis exhibit reduced atherosclerosis and enhanced regression of established plaques upon LXR activation. However, the coregulatory factors that affect LXR-dependent gene activation in macrophages remain to be elucidated. To identify novel regulators of LXR that modulate its activity, we used affinity purification and mass spectrometry to analyze nuclear LXRα complexes and identified poly(ADP-ribose) polymerase-1 (PARP-1) as an LXR-associated factor. In fact, PARP-1 interacted with both LXRα and LXRβ. Both depletion of PARP-1 and inhibition of PARP-1 activity augmented LXR ligand-induced ABCA1 expression in the RAW 264.7 macrophage line and primary bone marrow-derived macrophages but did not affect LXR-dependent expression of other target genes, ABCG1 and SREBP-1c. Chromatin immunoprecipitation experiments confirmed PARP-1 recruitment at the LXR response element in the promoter of the ABCA1 gene. Further, we demonstrated that LXR is poly(ADP-ribosyl)ated by PARP-1, a potential mechanism by which PARP-1 influences LXR function. Importantly, the PARP inhibitor 3-aminobenzamide enhanced macrophage ABCA1-mediated cholesterol efflux to the lipid-poor apolipoprotein AI. These findings shed light on the important role of PARP-1 on LXR-regulated lipid homeostasis. Understanding the interplay between PARP-1 and LXR may provide insights into developing novel therapeutics for treating atherosclerosis.

Cardiovascular Protective Effect of Metformin and Telmisartan: Reduction of PARP1 Activity via the AMPK-PARP1 Cascade

Hyperglycemia and hypertension impair endothelial function in part through oxidative stress-activated poly (ADP-ribose) polymerase 1 (PARP1). Biguanides and angiotensin II receptor blockers (ARBs) such as metformin and telmisartan have a vascular protective effect. We used cultured vascular endothelial cells (ECs), diabetic and hypertensive rodent models, and AMPKα2-knockout mice to investigate whether metformin and telmisartan have a beneficial effect on the endothelium via AMP-activated protein kinase (AMPK) phosphorylation of PARP1 and thus inhibition of PARP1 activity. The results showed that metformin and telmisartan, but not glipizide and metoprolol, activated AMPK, which phosphorylated PARP1 Ser-177 in cultured ECs and the vascular wall of rodent models. Experiments using phosphorylated/de-phosphorylated PARP1 mutants show that AMPK phosphorylation of PARP1 leads to decreased PARP1 activity and attenuated protein poly(ADP-ribosyl)ation (PARylation), but increased endothelial nitric oxide synthase (eNOS) activity and silent mating type information regulation 2 homolog 1 (SIRT1) expression. Taken together, the data presented here suggest biguanides and ARBs have a beneficial effect on the vasculature by the cascade of AMPK phosphorylation of PARP1 to inhibit PARP1 activity and protein PARylation in ECs, thereby mitigating endothelial dysfunction.

Vagus Nerve Stimulation Improves Cardiac Function by Preventing Mitochondrial Dysfunction in Obese-Insulin Resistant Rats

Long-term high-fat diet (HFD) consumption leads to not only obese-insulin resistance, but also impaired left ventricular (LV) function. Vagus nerve stimulation (VNS) has been shown to exert cardioprotection. However, its effects on the heart and metabolic parameters under obese-insulin resistant condition is not known. We determined the effects of VNS on metabolic parameters, heart rate variability (HRV) and LV function in obese-insulin resistant rats. Male Wistar rats were fed with HFD for 12 weeks, and were randomly divided into sham and VNS groups. VNS was applied for the next 12 weeks. Echocardiography, blood pressure and HRV were examined. Blood samples were collected for metabolic parameters. At the end, the heart was removed for determination of apoptosis, inflammation, oxidative stress, and cardiac mitochondrial function. VNS for 12 weeks significantly decreased plasma insulin, HOMA index, total cholesterol, triglyceride, LDL and visceral fat. Serum adiponectin was significantly increased in the VNS group. VNS also significantly decreased blood pressure, improved HRV and LV function, decreased cardiac MDA, TNF-α and Bax levels, and improved cardiac mitochondrial function. VNS improves metabolic and hemodynamic parameters, and the LV function via its ability against apoptosis, inflammation and oxidative stress, and preserved cardiac mitochondrial function in obese-insulin resistant rats.

Deletion of PARP-2 induces hepatic cholesterol accumulation and decrease in HDL levels

Poly(ADP-ribose) polymerase-2 (PARP-2) is acknowledged as a DNA repair enzyme. However, recent investigations have attributed unique roles to PARP-2 in metabolic regulation in the liver. We assessed changes in hepatic lipid homeostasis upon the deletion of PARP-2 and found that cholesterol levels were higher in PARP-2(-/-) mice as compared to wild-type littermates. To uncover the molecular background, we analyzed changes in steady-state mRNA levels upon the knockdown of PARP-2 in HepG2 cells and in murine liver that revealed higher expression of sterol-regulatory element binding protein (SREBP)-1 dependent genes. We demonstrated that PARP-2 is a suppressor of the SREBP1 promoter, and the suppression of the SREBP1 gene depends on the enzymatic activation of PARP-2. Consequently, the knockdown of PARP-2 enhances SREBP1 expression that in turn induces the genes driven by SREBP1 culminating in higher hepatic cholesterol content. We did not detect hypercholesterolemia, higher fecal cholesterol content or increase in serum LDL, although serum HDL levels decreased in the PARP-2(-/-) mice. In cells and mice where PARP-2 was deleted we observed decreased ABCA1 mRNA and protein expression that is probably linked to lower HDL levels. In our current study we show that PARP-2 impacts on hepatic and systemic cholesterol homeostasis. Furthermore, the depletion of PARP-2 leads to lower HDL levels which represent a risk factor to cardiovascular diseases.

Regulation of SIRT1 by oxidative stress-responsive miRNAs and a systematic approach to identify its role in the endothelium

SIGNIFICANCE

Oxidative stress is a common denominator of various risk factors contributing to endothelial dysfunction and vascular diseases. Accumulated evidence suggests that sirtuin 1 (SIRT1) expression and/or activity is impaired by supraphysiological levels of oxidative stress, which in turn disrupts endothelial homeostasis.

RECENT ADVANCES

Several microRNAs (miRNAs) are induced by oxidative stress and termed as oxidative stress-responsive miRNAs. They may play a role linking the imbalanced redox state with dysregulated SIRT1.

CRITICAL ISSUES

This review summarizes recent findings on oxidative stress-responsive miRNAs and their involvement in SIRT1 regulation. Because of the unique characteristics of miRNAs, research in this new area requires an integrative approach that combines bioinformatics and experimental validation. Thus, a research strategy is discussed to identify the SIRT1-regulating miRNAs under oxidative stress and their functional outcomes in relation to endothelial dysfunction. Additionally, the miRNAs implicated in vascular diseases such as atherosclerosis and abdominal aortic aneurysms are discussed along with the translational potential and challenges of using miRNAs and its analogs as therapeutic agents.

FUTURE DIRECTIONS

Although at its infancy, research on oxidative stress-responsive miRNAs and their regulation of SIRT1 may provide new insights in understanding vascular disorders. Moreover, systematic approaches integrating in silico, in vitro, and in vivo observations can be useful tools in revealing the pathways modulating endothelial biology.

Poly(ADP-ribose) polymerase 1 (PARP1) in atherosclerosis: from molecular mechanisms to therapeutic implications

Poly(ADP-ribosyl)ation reactions, carried out by poly(ADP-ribose) polymerases (PARPs/ARTDs), are reversible posttranslational modifications impacting on numerous cellular processes (e.g., DNA repair, transcription, metabolism, or immune functions). PARP1 (EC 2.4.2.30), the founding member of PARPs, is particularly important for drug development for its role in DNA repair, cell death, and transcription of proinflammatory genes. Recent studies have established a novel concept that PARP1 is critically involved in the formation and destabilization of atherosclerotic plaques in experimental animal models and in humans. Reduction of PARP1 activity by pharmacological or molecular approaches attenuates atherosclerotic plaque development and enhances plaque stability as well as promotes the regression of pre-established atherosclerotic plaques. Mechanistically, PARP1 inhibition significantly reduces monocyte differentiation, macrophage recruitment, Sirtuin 1 (SIRT1) inactivation, endothelial dysfunction, neointima formation, foam cell death, and inflammatory responses within plaques, all of which are central to the pathogenesis of atherosclerosis. This article presents an overview of the multiple roles and underlying mechanisms of PARP1 activation (poly(ADP-ribose) accumulation) in atherosclerosis and emphasizes the therapeutic potential of PARP1 inhibition in preventing or reversing atherosclerosis and its cardiovascular clinical sequalae.

Endothelial dysfunction - a major mediator of diabetic vascular disease

The vascular endothelium is a multifunctional organ and is critically involved in modulating vascular tone and structure. Endothelial cells produce a wide range of factors that also regulate cellular adhesion, thromboresistance, smooth muscle cell proliferation, and vessel wall inflammation. Thus, endothelial function is important for the homeostasis of the body and its dysfunction is associated with several pathophysiological conditions, including atherosclerosis, hypertension and diabetes. Patients with diabetes invariably show an impairment of endothelium-dependent vasodilation. Therefore, understanding and treating endothelial dysfunction is a major focus in the prevention of vascular complications associated with all forms of diabetes mellitus. The mechanisms of endothelial dysfunction in diabetes may point to new management strategies for the prevention of cardiovascular disease in diabetes. This review will focus on the mechanisms and therapeutics that specifically target endothelial dysfunction in the context of a diabetic setting. Mechanisms including altered glucose metabolism, impaired insulin signaling, low-grade inflammatory state, and increased reactive oxygen species generation will be discussed. The importance of developing new pharmacological approaches that upregulate endothelium-derived nitric oxide synthesis and target key vascular ROS-producing enzymes will be highlighted and new strategies that might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated vascular complications.

Poly(ADP-ribose) polymerase inhibition improves erectile function by activation of nitric oxide/cyclic guanosine monophosphate pathway in diabetic rats

INTRODUCTION

Endothelial dysfunction-induced abnormalities of the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway in the corpus cavernosum are thought to be the main factors involved in the pathogenesis of diabetes-induced erectile dysfunction (ED). Recent studies have shown that the poly(adenosine diphosphate ribose) polymerase (PARP) pathway plays a critical role in diabetic endothelial dysfunction.

AIM

  The aim of this study is to determine whether activation of the PARP pathway is involved in diabetic cavernosal endothelial dysfunction and abnormalities of the NO/cGMP pathway.

METHODS

Male Sprague-Dawley rats were randomly divided into three groups: age-matched controls, diabetic controls (DM), and the 3-aminobenzamide (3-AB, a PARP inhibitor)-treated diabetic group (DM+3-AB). Diabetes was induced by intraperitoneal injection of streptozotocin. Eight weeks after inducing diabetes, the DM+3-AB group was treated with 3-AB for 4 weeks.

MAIN OUTCOME MEASURES

Erectile function was assessed at 12 weeks after inducing diabetes by stimulating the cavernous nerve. Expression of poly(ADP-ribose), protein kinase B (Akt), phospho-Akt, endothelial nitric oxide synthase (eNOS), phospho-eNOS, and neuronal nitric oxide synthase (nNOS) were evaluated by Western blot. Cavernous NO generation and cGMP levels were also determined.

RESULTS

The DM group showed impaired erectile function and significantly increased PARP activity. Expression of total eNOS and nNOS, phospho-Akt, and eNOS decreased significantly in the DM group compared with those in the control group. In addition, cavernous NO generation and cGMP levels decreased significantly in the DM group compared with those in the control group. Treatment with 3-AB restored erectile function and significantly reversed all molecular alterations except decreased nNOS expression.

CONCLUSION

Overactivation of the PARP pathway in the corpus cavernosum of diabetic rats was involved in cavernosal endothelial dysfunction and abnormalities of the NO/cGMP pathway resulting in ED. These findings may be applied to develop novel therapies for patients with diabetic ED.

Cardiac and vascular phenotypes in the apolipoprotein E-deficient mouse

Cardiovascular death is frequently associated with atherosclerosis, a chronic multifactorial disease and a leading cause of death worldwide. Genetically engineered mouse models have proven useful for the study of the mechanisms underlying cardiovascular diseases. The apolipoprotein E-deficient mouse has been the most widely used animal model of atherosclerosis because it rapidly develops severe hypercholesterolemia and spontaneous atherosclerotic lesions similar to those observed in humans. In this review, we provide an overview of the cardiac and vascular phenotypes and discuss the interplay among nitric oxide, reactive oxygen species, aging and diet in the impairment of cardiovascular function in this mouse model.

Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.

Chronic administration of BMS309403 improves endothelial function in apolipoprotein E-deficient mice and in cultured human endothelial cells

BACKGROUND AND PURPOSE

Adipocyte fatty acid-binding protein (A-FABP) is up-regulated in regenerated endothelial cells and modulates inflammatory responses in macrophages. Endothelial dysfunction accompanying regeneration is accelerated by hyperlipidaemia. Here, we investigate the contribution of A-FABP to the pathogenesis of endothelial dysfunction in the aorta of apolipoprotein E-deficient (ApoE(-/-) ) mice and in cultured human endothelial cells.

EXPERIMENTAL APPROACH

A-FABP was measured in aortae of ApoE(-/-) mice and human endothelial cells by RT-PCR, immunostaining and immunoblotting. Total and phosphorylated forms of endothelial nitric oxide synthase (eNOS) were measured by immunoblotting. Changes in isometric tension were measured in rings of mice aortae

KEY RESULTS

A-FABP was expressed in aortic endothelium of ApoE(-/-) mice aged 12 weeks and older, but not at 8 weeks or in C57 wild-type mice. Reduced endothelium-dependent relaxations to acetylcholine, UK14304 (selective α(2) -adrenoceptor agonist) and A23187 (calcium ionophore) and decreased protein presence of phosphorylated and total eNOS were observed in aortae of 18 week-old ApoE(-/-) mice compared with age-matched controls. A 6 week treatment with the A-FABP inhibitor, BMS309403, started in 12 week-old mice, improved endothelial function, phosphorylated and total eNOS and reduced plasma triglyceride levels but did not affect endothelium-independent relaxations. The beneficial effect of BMS309403 on UK14304-induced relaxations was attenuated by Pertussis toxin. In cultured human microvascular endothelial cells, lipid-induced A-FABP expression was associated with reduced phosphorylated eNOS and NO production and was reversed by BMS309403.

CONCLUSIONS AND IMPLICATIONS

Elevated expression of A-FABP in endothelial cells contributes to their dysfunction both in vivo and in vitro.

Cordycepin blocks lung injury-associated inflammation and promotes BRCA1-deficient breast cancer cell killing by effectively inhibiting PARP

Cordycepin has been shown to interfere with a myriad of molecular processes from RNA elongation to kinase activity, and prevents numerous inflammatory processes in animal models. Here we show in a mouse model of LPS-induced acute lung injury that cordycepin prevents airway neutrophilia via a robust blockade of expression of several inflammatory genes, including the adhesion molecule ICAM-1 and VCAM-1, the cytokine/chemokine MCP-1, MIP-1α, MIP-2 and KC, and the chemokine receptor CXCR2. Such a blockade appears to be related to a severe reduction in TNF-α expression. Interestingly, in an in vitro system of A549 epithelial cell inflammation, cordycepin effectively blocked LPS-induced, but not TNF-α-induced, VCAM-1 expression. Such effects correlated with a marked reduction in p65-NF-κB activation as assessed by its phosphorylation at serine-536 but without an apparent effect on its nuclear translocation. The effects of cordycepin on the expression of VCAM-1 and ICAM-1, and of NF-κB activation and nuclear translocation upon TNF-α stimulation resembled the effects achieved upon poly(ADP-ribose) polymerase (PARP) inhibition, suggesting that cordycepin may function as a PARP inhibitor. Indeed, cordycepin blocked H(2)O(2)-induced PARP activation in A549 cells. In a cell-free system, cordycepin inhibited PARP-1 activity at nanomolar concentrations. Similar to PARP inhibitors, cordycepin significantly induced killing of breast cancer susceptibility gene (BRCA1)-deficient MCF-7 cells, supporting its therapeutic use for the treatment of BRCA-deficient breast cancers. With added antiinflammatory characteristics, therapies that include cordycepin may prevent potential inflammation triggered by traditional chemotherapeutic drugs. Cordycepin, to the best of our knowledge, represents the first natural product possessing PARP inhibitory traits.

Poly(ADP-ribose) polymerase-1 is a determining factor in Crm1-mediated nuclear export and retention of p65 NF-kappa B upon TLR4 stimulation

The role of NF-kappaB in the expression of inflammatory genes and its participation in the overall inflammatory process of chronic diseases and acute tissue injury are well established. We and others have demonstrated a critical involvement of poly(ADP-ribose) polymerase (PARP)-1 during inflammation, in part, through its relationship with NF-kappaB. However, the mechanism by which PARP-1 affects NF-kappaB activation has been elusive. In this study, we show that PARP-1 inhibition by gene knockout, knockdown, or pharmacologic blockade prevented p65 NF-kappaB nuclear translocation in smooth muscle cells upon TLR4 stimulation, NF-kappaB DNA-binding activity, and subsequent inducible NO synthase and ICAM-1 expression. Such defects were reversed by reconstitution of PARP-1 expression. PARP-1 was dispensable for LPS-induced IkappaBalpha phosphorylation and subsequent degradation but was required for p65 NF-kappaB phosphorylation. A perinuclear p65 NF-kappaB localization in LPS-treated PARP-1(-/-) cells was associated with an export rather an import defect. Indeed, whereas PARP-1 deficiency did not alter expression of importin alpha3 and importin alpha4 and their cytosolic localization, the cytosolic levels of exportin (Crm)-1 were increased. Crm1 inhibition promoted p65 NF-kappaB nuclear accumulation as well as reversed LPS-induced p65 NF-kappaB phosphorylation and inducible NO synthase and ICAM-1 expression. Interestingly, p65 NF-kappaB poly(ADP-ribosyl)ation decreased its interaction with Crm1 in vitro. Pharmacologic inhibition of PARP-1 increased p65 NF-kappaB-Crm1 interaction in LPS-treated smooth muscle cells. These results suggest that p65 NF-kappaB poly(ADP-ribosyl)ation may be a critical determinant for the interaction with Crm1 and its nuclear retention upon TLR4 stimulation. These results provide novel insights into the mechanism by which PARP-1 promotes NF-kappaB nuclear retention, which ultimately can influence NF-kappaB-dependent gene regulation.

Requirement for inducible nitric oxide synthase in chronic allergen exposure-induced pulmonary fibrosis but not inflammation

The role of inducible NO synthase (iNOS) in allergic airway inflammation remains elusive. We tested the hypothesis that iNOS plays different roles during acute versus chronic airway inflammation. Acute and chronic mouse models of OVA-induced airway inflammation were used to conduct the study. We showed that iNOS deletion was associated with a reduction in eosinophilia, mucus hypersecretion, and IL-5 and IL-13 production upon the acute protocol. Such protection was completely abolished upon the chronic protocol. Interestingly, pulmonary fibrosis observed in wild-type mice under the chronic protocol was completely absent in iNOS(-/-) mice despite persistent IL-5 and IL-13 production, suggesting that these cytokines were insufficient for pulmonary fibrosis. Such protection was associated with reduced collagen synthesis and indirect but severe TGF-beta modulation as confirmed using primary lung smooth muscle cells. Although activation of matrix metalloproteinase-2/-9 exhibited little change, the large tissue inhibitor of metalloproteinase-2 (TIMP-2) increase detected in wild-type mice was absent in the iNOS(-/-) counterparts. The regulatory effect of iNOS on TIMP-2 may be mediated by peroxynitrite, as the latter reversed TIMP-2 expression in iNOS(-/-) lung smooth muscle cells and fibroblasts, suggesting that the iNOS-TIMP-2 link may explain the protective effect of iNOS-knockout against pulmonary fibrosis. Analysis of lung sections from chronically OVA-exposed iNOS(-/-) mice revealed evidence of residual but significant protein nitration, prevalent oxidative DNA damage, and poly(ADP-ribose) polymerase-1 activation. Such tissue damage, inflammatory cell recruitment, and mucus hypersecretion may be associated with substantial arginase expression and activity. The results in this study exemplify the complexity of the role of iNOS in asthma and the preservation of its potential as a therapeutic a target.

Opposing roles of PARP-1 in MMP-9 and TIMP-2 expression and mast cell degranulation in dyslipidemic dilated cardiomyopathy

INTRODUCTION

Previously, we demonstrated that inhibition of poly(ADP-ribose) polymerase (PARP) exerts protective effects against high-fat (HF) diet-induced atherogenesis in part by increasing tissue inhibitor of metalloproteinase (TIMP)-2 expression. Given that characteristics of dilated cardiomyopathy closely associate with atherosclerosis and are mediated by an imbalance between matrix metalloproteinases (MMPs) and TIMPs, we hypothesized that PARP-1 gene deletion may protect against HF-induced cardiac hypertrophy and dilatations by altering TIMP-2/MMPs balance in favor of a maintenance of tissue homeostasis.

METHODS AND RESULTS

Hemodynamic parameters determined by echocardiography were similar in ApoE(-/-) mice and PARP-1-deficient ApoE(-/-) mice (DKO) fed a regular diet (RD). However, histological analysis revealed that cardiomyocytes of ApoE(-/-) mice on RD were hypertrophied, displaying an enlarged cell body and nucleus, traits that were absent in DKO animals. HF diet-fed ApoE(-/-) mice exhibited increased interventricular septum, left ventricular (LV) internal dimension, LV volume, and LV mass in addition to a separation of myocardial fibers suggestive of dilated cardiomyopathy. PARP-1 gene deletion protected against these degenerative changes. MMP activity was dramatically increased in hearts of ApoE(-/-) mice on HF diet and was accompanied by increased collagen degradation, mast cell degranulation, and increased myocyte cell death. PARP-1 gene knockout was associated with increased TIMP-2 expression antagonizing, as a result, the damaging effects of active MMPs.

CONCLUSIONS

The present study demonstrates that PARP-1 gene deletion exerts protective effects against HF diet-induced dilated cardiomyopathy by maintaining increased expression of TIMP-2. With additional protective effects against cell death and inflammation, PARP-1 deficiency preserves cardiac tissue homeostasis.