Reactive Oxygen Species, SUMOylation, and Endothelial Inflammation. Int J Inflam. 2012;2012:678190. [PMID: 22991685 PMCID: PMC3443607 DOI: 10.1155/2012/678190]

Lipid Receptor G2A-Mediated Signal Pathway Plays a Critical Role in Inflammatory Response by Promoting Classical Macrophage Activation

Macrophage polarization is a dynamic and integral process in tissue inflammation and remodeling. In this study, we describe that lipoprotein-associated phospholipase A₂ (Lp-PLA₂) plays an important role in controlling inflammatory macrophage (M1) polarization in rodent experimental autoimmune encephalomyelitis (EAE) and in monocytes from multiple sclerosis (MS) patients. Specific inhibition of Lp-PLA₂ led to an ameliorated EAE via markedly decreased inflammatory and demyelinating property of M1. The effects of Lp-PLA₂ on M1 function were mediated by lysophosphatidylcholine, a bioactive product of oxidized lipids hydrolyzed by Lp-PLA₂ through JAK2-independent activation of STAT5 and upregulation of IRF5. This process was directed by the G2A receptor, which was only found in differentiated M1 or monocytes from MS patients. M1 polarization could be inhibited by a G2A neutralizing Ab, which led to an inhibited disease in rat EAE. In addition, G2A-deficient rats showed an ameliorated EAE and an inhibited autoimmune response. This study has revealed a mechanism by which lipid metabolites control macrophage activation and function, modification of which could lead to a new therapeutic approach for MS and other inflammatory disorders.

The Role of Posttranslational Modification and Mitochondrial Quality Control in Cardiovascular Diseases

Cardiovascular disease (CVD) is the leading cause of death in the world. The mechanism behind CVDs has been studied for decades; however, the pathogenesis is still controversial. Mitochondrial homeostasis plays an essential role in maintaining the normal function of the cardiovascular system. The alterations of any protein function in mitochondria may induce abnormal mitochondrial quality control and unexpected mitochondrial dysfunction, leading to CVDs. Posttranslational modifications (PTMs) affect protein function by reversibly changing their conformation. This review summarizes how common and novel PTMs influence the development of CVDs by regulating mitochondrial quality control. It provides not only ideas for future research on the mechanism of some types of CVDs but also ideas for CVD treatments with therapeutic potential.

Time-dependent replicative senescence vs. disturbed flow-induced pre-mature aging in atherosclerosis

Accumulation of senescent cells has a causative role in the pathology of age-related disorders including atherosclerosis (AS) and cardiovascular diseases (CVDs). However, the concept of senescence is now drastically changing, and the new concept of senescence-associated reprogramming/stemness has emerged, suggesting that senescence is not merely related to “cell cycle arrest” or halting various cellular functions. It is well known that disturbed flow (D-flow) accelerates pre-mature aging and plays a significant role in the development of AS. We will discuss in this review that pre-mature aging induced by D-flow is not comparable to time-dependent aging, particularly with a focus on the possible involvement of senescence-associated secretory phenotype (SASP) in senescence-associated reprogramming/stemness, or increasing cell numbers. We will also present our outlook of nicotinamide adenine dinucleotides (NAD)⁺ deficiency-induced mitochondrial reactive oxygen species (mtROS) in evoking SASP by activating DNA damage response (DDR). MtROS plays a key role in developing cross-talk between nuclear-mitochondria, SASP, and ultimately atherosclerosis formation. Although senescence induced by time and various stress factors is a classical concept, we wish that the readers will see the undergoing Copernican-like change in this concept, as well as to recognize the significant contrast between pre-mature aging induced by D-flow and time-dependent aging.

SUMO2 regulates vascular endothelial function and oxidative stress in mice

SUMOylation is a posttranslational modification of lysine residues. Modification of proteins by small ubiquitin-like modifiers (SUMO)1, -2, and -3 can achieve varied, and often unique, physiological and pathological effects. We looked for SUMO2-specific effects on vascular endothelial function. SUMO2 expression was upregulated in the aortic endothelium of hypercholesterolemic low-density lipoprotein receptor-deficient mice and was responsible for impairment of endothelium-dependent vasorelaxation in these mice. Moreover, overexpression of SUMO2 in aortas ex vivo, in cultured endothelial cells, and transgenically in the endothelium of mice increased vascular oxidative stress and impaired endothelium-dependent vasorelaxation. Conversely, inhibition of SUMO2 impaired physiological endothelium-dependent vasorelaxation in normocholesterolemic mice. These findings indicate that while endogenous SUMO2 is important in maintenance of normal endothelium-dependent vascular function, its upregulation impairs vascular homeostasis and contributes to hypercholesterolemia-induced endothelial dysfunction.

NEW & NOTEWORTHY Sumoylation is known to impair vascular function; however, the role of specific SUMOs in the regulation of vascular function is not known. Using multiple complementary approaches, we show that hyper-SUMO2ylation impairs vascular endothelial function and increases vascular oxidative stress, whereas endogenous SUMO2 is essential for maintenance of normal physiological function of the vascular endothelium.

The Role of Protein SUMOylation in the Pathogenesis of Atherosclerosis

Atherosclerosis is a progressive, inflammatory cardiovascular disorder characterized by the development of lipid-filled plaques within arteries. Endothelial cell dysfunction in the walls of blood vessels results in an increase in vascular permeability, alteration of the components of the extracellular matrix, and retention of LDL in the sub-endothelial space, thereby accelerating plaque formation. Epigenetic modification by SUMOylation can influence the surface interactions of target proteins and affect cellular functionality, thereby regulating multiple cellular processes. Small ubiquitin-like modifier (SUMO) can modulate NFκB and other proteins such as p53, KLF, and ERK5, which have critical roles in atherogenesis. Furthermore, SUMO regulates leukocyte recruitment and cytokine release and the expression of adherence molecules. In this review, we discuss the regulation by SUMO and SUMOylation modifications of proteins and pathways involved in atherosclerosis.

Low Serum Paraoxonase-1 Activity Associates with Incident Cardiovascular Disease Risk in Subjects with Concurrently High Levels of High-Density Lipoprotein Cholesterol and C-Reactive Protein

Paroxonase-1 (PON1) is a key enzyme that inhibits low-density lipoprotein oxidation and consequently atherogenesis. Here, we assessed whether low serum PON1 activity associates with incident cardiovascular disease (CVD) in subjects with high levels of high-density cholesterol (HDL-C) and C-reactive protein (CRP), a marker of low-grade systemic inflammation. Cox proportional-hazards modeling of incident CVD risk (11 years mean follow-up) adjusted for relevant clinical and biomarker covariates was performed on a population-based study (N = 7766) stratified into three groups: low CRP-(LR; event rate 4.9%); low HDL-C/high CRP-(HR1; event rate 14.4%); and high HDL-C/high CRP-(HR2; event rate 7.6%). Modeling results for PON1 activity in HR2 were significant and robust (hazard ratio/SD unit-0.68, 95% CI 0.55-0.83, p = 0.0003), but not so for LR and HR1. Analyses in HR2 of the interaction of PON1 with HDL-C, apoA-I, apoA-II, and apoE levels were significant only for PON1 with apoE (hazard ratio-1.77, 95% CI 1.29-2.41, p = 0.0003). Subsequent subgroup analysis revealed inverse risk dependence for apoE at low PON1 levels. In conclusion, in a population-based study of subjects with concurrently high HDL-C and CRP levels, low serum PON1 activity associates with incident CVD risk with risk accentuated at low apoE levels.

Inhibition of SENP3 by URB597 ameliorates neurovascular unit dysfunction in rats with chronic cerebral hypoperfusion

Disruption of the neurovascular unit (NVU), induced by chronic cerebral hypoperfusion (CCH), has been broadly found in various neurological disorders. SUMO-specific protease 3 (SENP3) is expressed in neurons, astrocytes, and microglia, and regulates a variety of cell events. However, whether SENP3 is involved in neurovascular injury under the condition of CCH is still elusive. To address this issue, we investigated the effect of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on NVU and the role of SENP3 in this process, as well as the underling mechanisms. The expression of SENP3 was detected by immunochemistry. The function and structure of the NVU was assessed by Western blot analysis and transmission electron microscopy. CCH caused the upregulation of SENP3, the disruption of cell and non-cell components at the protein level within the NVU, and ultrastructural deterioration. The NVU impairment as well as overexpression of SENP3 were reversed by treatment with URB597. These results reveal a novel neuroprotective role in URB597, which implicates URB597 in the amelioration of CCH-induced NVU impairment by inhibiting SENP3.

Aberrant post-translational protein modifications in the pathogenesis of alcohol-induced liver injury

It is likely that the majority of proteins will undergo post-translational modification, be it enzymatic or non-enzymatic. These modified protein(s) regulate activity, localization and interaction with other cellular molecules thereby maintaining cellular hemostasis. Alcohol exposure significantly alters several of these post-translational modifications leading to impairments of many essential physiological processes. Here, we present new insights into novel modifications following ethanol exposure and their role in the initiation and progression of liver injury. This critical review condenses the proceedings of a symposium at the European Society for the Biomedical Research on Alcoholism Meeting held September 12-15, 2015, in Valencia, Spain.

Protein Modifications as Manifestations of Hyperglycemic Glucotoxicity in Diabetes and Its Complications

Diabetes and its complications are hyperglycemic toxicity diseases. Many metabolic pathways in this array of diseases become aberrant, which is accompanied with a variety of posttranslational protein modifications that in turn reflect diabetic glucotoxicity. In this review, we summarize some of the most widely studied protein modifications in diabetes and its complications. These modifications include glycation, carbonylation, nitration, cysteine S-nitrosylation, acetylation, sumoylation, ADP-ribosylation, O-GlcNAcylation, and succination. All these posttranslational modifications can be significantly attributed to oxidative stress and/or carbon stress induced by diabetic redox imbalance that is driven by activation of pathways, such as the polyol pathway and the ADP-ribosylation pathway. Exploring the nature of these modifications should facilitate our understanding of the pathological mechanisms of diabetes and its associated complications.

Association study of C936T polymorphism of the VEGF gene and the C242T polymorphism of the p22phox gene with diabetes mellitus type 2 and distal diabetic polyneuropathy

Even with long‑term glycemic control, diabetes mellitus type 2 (DM2) remains the predominant cause of diabetic neuropathy. Single nucleotide polymorphism (SNP) C936T of the vascular endothelial growth factor (VEGF) gene and the SNP C242T of the p22phox (CYBA) gene have been investigated in relation to DM2 and its complications. The aim of the present study was to investigate the association between these two SNPs and DM2, and also between the SNPs and the signs and symptoms of diabetic distal polyneuropathy. The DM2 group consisted of 98 individuals and the control group consisted of 104 individuals. The results demonstrated that there was no association between the different genotypes or alleles and increased risk of the disease (P>0.05). With SNP C242T, a significant association with body mass index between the CTxTT genotypes (P=0.043) was identified; and the greatest body mass indexes were among individuals with the TT genotype. An association between the degree of neuropathic symptoms and genotypic/allelic distribution of these polymorphisms was not observed. In conclusion, the investigated polymorphisms are not correlated with the risk of developing DM2.

Posttranslational modifications of lysine and evolving role in heart pathologies-recent developments

The alteration in proteome composition induced by environmental changes and various pathologies is accompanied by the modifications of proteins by specific cotranslational and PTMs. The type and site stoichiometry of PTMs can affect protein functions, alter cell signaling, and can have acute and chronic effects. The particular interest is drawn to those amino acid residues that can undergo several different PTMs. We hypothesize that these selected amino acid residues are biologically rare and act within the cell as molecular switches. There are, at least, 12 various lysine modifications currently known, several of them have been shown to be competitive and they influence the ability of a particular lysine to be modified by a different PTM. In this review, we discuss the PTMs that occur on lysine, specifically neddylation and sumoylation, and the proteomic approaches that can be applied for the identification and quantification of these PTMs. Of interest are the emerging roles for these modifications in heart disease and what can be inferred from work in other cell types and organs.

Novel mechanisms of endothelial mechanotransduction

Atherosclerosis is a focal disease that develops preferentially where nonlaminar, disturbed blood flow occurs, such as branches, bifurcations, and curvatures of large arteries. Endothelial cells sense and respond differently to disturbed flow compared with steady laminar flow. Disturbed flow that occurs in so-called atheroprone areas activates proinflammatory and apoptotic signaling, and this results in endothelial dysfunction and leads to subsequent development of atherosclerosis. In contrast, steady laminar flow as atheroprotective flow promotes expression of many anti-inflammatory genes, such as Kruppel-like factor 2 and endothelial nitric oxide synthase and inhibits endothelial inflammation and athrogenesis. Here we will discuss that disturbed flow and steady laminar flow induce pro- and antiatherogenic events via flow type-specific mechanotransduction pathways. We will focus on 5 mechanosensitive pathways: mitogen-activated protein kinases/extracellular signal-regulated kinase 5/Kruppel-like factor 2 signaling, extracellular signal-regulated kinase/peroxisome proliferator-activated receptor signaling, and mechanosignaling pathways involving SUMOylation, protein kinase C-ζ, and p90 ribosomal S6 kinase. We think that clarifying regulation mechanisms between these 2 flow types will provide new insights into therapeutic approaches for the prevention and treatment of atherosclerosis.

Identification of activators of ERK5 transcriptional activity by high-throughput screening and the role of endothelial ERK5 in vasoprotective effects induced by statins and antimalarial agents

Because ERK5 inhibits endothelial inflammation and dysfunction, activating ERK5 might be a novel approach to protecting vascular endothelial cells (ECs) against various pathological conditions of the blood vessel. We have identified small molecules that protect ECs via ERK5 activation and determined their contribution to preventing cardiac allograft rejection. Using high-throughput screening, we identified certain statins and antimalarial agents including chloroquine, hydroxychloroquine, and quinacrine as strong ERK5 activators. Pitavastatin enhanced ERK5 transcriptional activity and Kruppel-like factor-2 expression in cultured human and bovine ECs, but these effects were abolished by the depletion of ERK5. Chloroquine and hydroxychloroquine upregulated ERK5 kinase activity and inhibited VCAM-1 expression in an ERK5-dependent but MAPK/ERK kinase 5- and Kruppel-like factor 2/4-independent manner. Leukocyte rolling and vascular reactivity were used to evaluate endothelial function in vivo, and we found that EC-specific ERK5 knockout (ERK5-EKO) mice exhibited increased leukocyte rolling and impaired vascular reactivity, which could not be corrected by pitavastatin. The role of endothelial ERK5 in acute cardiac allograft rejection was also examined by heterotopic grafting of the heart obtained from either wild-type or ERK5-EKO mice into allomismatched recipient mice. A robust increase in both inflammatory gene expression and CD45-positive cell infiltration into the graft was observed. These tissue rejection responses were inhibited by pitavastatin in wild-type but not ERK5-EKO hearts. Our study has identified statins and antimalarial drugs as strong ERK5 activators and shown that ERK5 activation is preventive of endothelial inflammation and dysfunction and acute allograft rejection.

Inhibition of cellular methyltransferases promotes endothelial cell activation by suppressing glutathione peroxidase 1 protein expression

S-adenosylhomocysteine (SAH) is a negative regulator of most methyltransferases and the precursor for the cardiovascular risk factor homocysteine. We have previously identified a link between the homocysteine-induced suppression of the selenoprotein glutathione peroxidase 1 (GPx-1) and endothelial dysfunction. Here we demonstrate a specific mechanism by which hypomethylation, promoted by the accumulation of the homocysteine precursor SAH, suppresses GPx-1 expression and leads to inflammatory activation of endothelial cells. The expression of GPx-1 and a subset of other selenoproteins is dependent on the methylation of the tRNA(Sec) to the Um34 form. The formation of methylated tRNA(Sec) facilitates translational incorporation of selenocysteine at a UGA codon. Our findings demonstrate that SAH accumulation in endothelial cells suppresses the expression of GPx-1 to promote oxidative stress. Hypomethylation stress, caused by SAH accumulation, inhibits the formation of the methylated isoform of the tRNA(Sec) and reduces GPx-1 expression. In contrast, under these conditions, the expression and activity of thioredoxin reductase 1, another selenoprotein, is increased. Furthermore, SAH-induced oxidative stress creates a proinflammatory activation of endothelial cells characterized by up-regulation of adhesion molecules and an augmented capacity to bind leukocytes. Taken together, these data suggest that SAH accumulation in endothelial cells can induce tRNA(Sec) hypomethylation, which alters the expression of selenoproteins such as GPx-1 to contribute to a proatherogenic endothelial phenotype.

Statins protect human endothelial cells from TNF-induced inflammation via ERK5 activation

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) exert pleiotropic effects on the cardiovascular system, in part through a decrease in reactive oxygen species (ROS) formation and reduction of vascular inflammation. To elucidate the molecular mechanisms involved in these effects, we investigated the effect of statins on TNF-α-induced ROS production, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) expression in human aortic endothelial cells (HAECs). Exposure of HAECs to TNF-α caused production of ROS via Rac-1 membrane translocation and activation. The Rac-1 activation and ROS liberation mediated TNF-stimulated NF-κB activation and the subsequent VCAM-1 and ICAM-1 expression. Extracellular-signal-regulated kinase 5 (ERK5) plays a central role in inhibiting endothelial inflammation. Immune complex kinase assay of protein extracts from HAECs treated with atorvastatin revealed increased ERK5 activity in a time- and dose-dependent manner. In addition, pretreatment with atorvastatin inhibited TNF-α-induced ROS production and VCAM-1 and ICAM-1 expression. Chemical or genetic inhibition of ERK5 ablated the statins inhibition of Rac-1 activation, ROS formation, NF-κB, VCAM-1 and ICAM-1 expression induced by TNF-α. Taken together, statins, via ERK5 activation, suppress TNF-stimulated Rac-1 activation, ROS generation, NF-κB activation and VCAM-1 and ICAM-1 expression in human ECs, which provides a novel explanation for the pleiotropic effects of statins that benefit the cardiovascular system.