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

ROS-triggered endothelial cell death mechanisms: Focus on pyroptosis, parthanatos, and ferroptosis

The endothelium is a single layer of epithelium covering the surface of the vascular system, and it represents a physical barrier between the blood and vessel wall that plays an important role in maintaining intravascular homeostasis. However, endothelial dysfunction or endothelial cell death can cause vascular barrier disruption, vasoconstriction and diastolic dysfunction, vascular smooth muscle cell proliferation and migration, inflammatory responses, and thrombosis, which are closely associated with the progression of several diseases, such as atherosclerosis, hypertension, coronary atherosclerotic heart disease, ischemic stroke, acute lung injury, acute kidney injury, diabetic retinopathy, and Alzheimer's disease. Oxidative stress caused by the overproduction of reactive oxygen species (ROS) is an important mechanism underlying endothelial cell death. Growing evidence suggests that ROS can trigger endothelial cell death in various ways, including pyroptosis, parthanatos, and ferroptosis. Therefore, this review will systematically illustrate the source of ROS in endothelial cells (ECs); reveal the molecular mechanism by which ROS trigger pyroptosis, parthanatos, and ferroptosis in ECs; and provide new ideas for the research and treatment of endothelial dysfunction-related diseases.

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.

Melatonin and regulation of autophagy: Mechanisms and therapeutic implications

Mitochondria are essential subcellular units that generate basic energy for the cell, as well as influence Ca²⁺ flux, apoptosis, and cell signaling. Mitophagy can selectively remove impaired mitochondria to preserve mitochondrial function, which is crucial for normal cellular maintenance. Mitochondrial dysfunction and mitophagy are widely reported to be linked to various pathogeneses. In addition, there is increasing evidence regarding the beneficial role of melatonin in the regulation and intervention of mitophagy progression. In this review, we focus on specific pathological conditions, including ischemia/reperfusion injury (IRI), cancer and neurodegenerative diseases, and elucidate the essential role of melatonin in the modulation of mitophagy in each of these distinct disorders.

Loss of PARP-1 attenuates diabetic arteriosclerotic calcification via Stat1/Runx2 axis

Accelerated atherosclerotic calcification is responsible for plaque burden, especially in diabetes. The regulatory mechanism for atherosclerotic calcification in diabetes is poorly characterized. Here we show that deletion of PARP-1, a main enzyme in diverse metabolic complications, attenuates diabetic atherosclerotic calcification and decreases vessel stiffening in mice through Runx2 suppression. Specifically, PARP-1 deficiency reduces diabetic arteriosclerotic calcification by regulating Stat1-mediated synthetic phenotype switching of vascular smooth muscle cells and macrophage polarization. Meanwhile, both vascular smooth muscle cells and macrophages manifested osteogenic differentiation in osteogenic media, which was attenuated by PARP-1/Stat1 inhibition. Notably, Stat1 acts as a positive transcription factor by directly binding to the promoter of Runx2 and promoting atherosclerotic calcification in diabetes. Our results identify a new function of PARP-1, in which metabolism disturbance-related stimuli activate the Runx2 expression mediated by Stat1 transcription to facilitate diabetic arteriosclerotic calcification. PARP-1 inhibition may therefore represent a useful therapy for this challenging complication.

Targeting mitochondria for cardiovascular disorders: therapeutic potential and obstacles

A large body of evidence indicates that mitochondrial dysfunction has a major role in the pathogenesis of multiple cardiovascular disorders. Over the past 2 decades, extraordinary efforts have been focused on the development of agents that specifically target mitochondria for the treatment of cardiovascular disease. Despite such an intensive wave of investigation, no drugs specifically conceived to modulate mitochondrial functions are currently available for the clinical management of cardiovascular disease. In this Review, we discuss the therapeutic potential of targeting mitochondria in patients with cardiovascular disease, examine the obstacles that have restrained the development of mitochondria-targeting agents thus far, and identify strategies that might empower the full clinical potential of this approach.

Poly (ADP-ribose) polymerase inhibition protects against myocardial ischaemia/reperfusion injury via suppressing mitophagy

Myocardial ischaemia/reperfusion (I/R) injury attenuates the beneficial effects of reperfusion therapy. Poly(ADP-ribose) polymerase (PARP) is overactivated during myocardial I/R injury. Mitophagy plays a critical role in the development of myocardial I/R injury. However, the effect of PARP activation on mitophagy in cardiomyocytes is unknown. In this study, we found that I/R induced PARP activation and mitophagy in mouse hearts. Poly(ADP-ribose) polymerase inhibition reduced the infarct size and suppressed mitophagy after myocardial I/R injury. In vitro, hypoxia/reoxygenation (H/R) activated PARP, promoted mitophagy and induced cell apoptosis in cardiomyocytes. Poly(ADP-ribose) polymerase inhibition suppressed H/R-induced mitophagy and cell apoptosis. Parkin knockdown with lentivirus vectors inhibited mitophagy and prevented cell apoptosis in H/R-treated cells. Poly(ADP-ribose) polymerase inhibition prevented the loss of the mitochondrial membrane potential (ΔΨm). Cyclosporin A maintained ΔΨm and suppressed mitophagy but FCCP reduced the effect of PARP inhibition on ΔΨm and promoted mitophagy, indicating the critical role of ΔΨm in H/R-induced mitophagy. Furthermore, reactive oxygen species (ROS) and poly(ADP-ribosylation) of CypD and TSPO might contribute to the regulation of ΔΨm by PARP. Our findings thus suggest that PARP inhibition protects against I/R-induced cell apoptosis by suppressing excessive mitophagy via the ΔΨm/Parkin pathway.

The Role of PARPs in Inflammation-and Metabolic-Related Diseases: Molecular Mechanisms and Beyond

Poly(ADP-ribosyl)ation (PARylation) is an essential post-translational modification catalyzed by poly(ADP-ribose) polymerase (PARP) enzymes. Poly(ADP-ribose) polymerase 1 (PARP1) is a well-characterized member of the PARP family. PARP1 plays a crucial role in multiple biological processes and PARP1 activation contributes to the development of various inflammatory and malignant disorders, including lung inflammatory disorders, cardiovascular disease, ovarian cancer, breast cancer, and diabetes. In this review, we will focus on the role and molecular mechanisms of PARPs enzymes in inflammation- and metabolic-related diseases. Specifically, we discuss the molecular mechanisms and signaling pathways that PARP1 is associated with in the regulation of pathogenesis. Recently, increasing evidence suggests that PARP inhibition is a promising strategy for intervention of some diseases. Thus, our in-depth understanding of the mechanism of how PARPs are activated and how their signaling downstream effecters can provide more potential therapeutic targets for the treatment of the related diseases in the future is crucial.

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.

Serum exosomes mediate delivery of arginase 1 as a novel mechanism for endothelial dysfunction in diabetes

Exosomes, abundant in blood, deliver various molecules to recipient cells. Endothelial cells are directly exposed to circulating substances. However, how endothelial cells respond to serum exosomes (SExos) and the implications in diabetes-associated vasculopathy have never been explored. In the present study, we showed that SExos from diabetic db/db mice (db/db SExos) were taken up by aortic endothelial cells, which severely impaired endothelial function in nondiabetic db/m⁺ mice. The exosomal proteins, rather than RNAs, mostly account for db/db SExos-induced endothelial dysfunction. Comparative proteomics analysis showed significant increase of arginase 1 in db/db SExos. Silence or overexpression of arginase 1 confirmed its essential role in db/db SExos-induced endothelial dysfunction. This study is a demonstration that SExos deliver arginase 1 protein to endothelial cells, representing a cellular mechanism during development of diabetic endothelial dysfunction. The results expand the scope of blood-borne substances that monitor vascular homeostasis.