Statin-mediated cytoprotection of human vascular endothelial cells: a role for Kruppel-like factor 2-dependent induction of heme oxygenase-1

Paradoxical effects of statins on endothelial and cancer cells: the impact of concentrations

In addition to their lipid-lowering functions, statins elicit additional pleiotropic effects on apoptosis, angiogenesis, inflammation, senescence, and oxidative stress. Many of these effects have been reported in cancerous and noncancerous cells like endothelial cells (ECs), endothelial progenitor cells (EPCs) and human umbilical vein cells (HUVCs). Not surprisingly, statins' effects appear to vary largely depending on the cell context, especially as pertains to modulation of cell cycle, senescence, and apoptotic processes. Perhaps the most critical reason for this discordance is the bias in selecting the applied doses in various cells. While lower (nanomolar) concentrations of statins impose anti-senescence, and antiapoptotic effects, higher concentrations (micromolar) appear to precipitate opposite effects. Indeed, most studies performed in cancer cells utilized high concentrations, where statin-induced cytotoxic and cytostatic effects were noted. Some studies report that even at low concentrations, statins induce senescence or cytostatic impacts but not cytotoxic effects. However, the literature appears to be relatively consistent that in cancer cells, statins, in both low or higher concentrations, induce apoptosis or cell cycle arrest, anti-proliferative effects, and cause senescence. However, statins' effects on ECs depend on the concentrations; at micromolar concentrations statins cause cell senescence and apoptosis, while at nonomolar concentrations statins act reversely.

The Effects of Statin Treatment on Serum Ferritin Levels: A Systematic Review and Meta-Analysis

Background: Statins are the most widely used drugs for decreasing elevated serum LDL-cholesterol (LDL-C) and thus for the prevention of atherosclerotic cardiovascular disease (ASCVD), but they have also some pleiotropic effects, including anti-inflammatory properties. Atherosclerosis is a low-grade inflammatory disease, and elevated ferritin is considered to be one of the markers of inflammation. Since the results of studies on the effects of statins on serum ferritin levels are conflicting, this meta-analysis was performed. Methods: A literature search was performed using major electronic databases (MEDLINE/PubMed, Scopus, Embase, and ISI Web of Science) from inception up to 5 March 2022 to find studies evaluating the effect of different statins on serum ferritin levels. The effect size was determined using weighted mean differences (WMDs) and the corresponding 95% confidence intervals (CIs). Results: The meta-analysis of nine studies (1611 patients) analyzing the effects of statins on serum ferritin levels that were included showed a significant decrease in circulating ferritin levels caused by statins. The results did not suggest any significant association between the changes in concentrations of serum ferritin and the duration of treatment with statins. Conclusions: Statin therapy decreases the circulating concentrations of ferritin, which might be beneficial for the prevention and/or progression of ASCVD. This effect might be explained by the anti-inflammatory effects and maybe some other pleiotropic effects of statins and not by their lipid-lowering effects.

N6-Methyladenosine Demethylase FTO (Fat Mass and Obesity-Associated Protein) as a Novel Mediator of Statin Effects in Human Endothelial Cells

BACKGROUND

N6-methyladenosine (m6A) plays a critical role in various biological processes. However, no study has addressed the role of m6A modification in the statin-induced protection of endothelial cells (ECs).

METHODS

Quantitative real-time polymerase chain reaction and Western blotting analyses were used to study the expression of m6A regulatory genes in atorvastatin-treated ECs. Gain- and loss-of-function assays, methylated RNA immunoprecipitation analysis, and dual-luciferase reporter assays were performed to clarify the function of FTO (fat mass and obesity-associated protein) in ECs.

RESULTS

Atorvastatin decreased FTO protein expression in ECs. The knockdown of FTO enhanced the mRNA and protein expression of KLF2 (Kruppel-like factor 2) and eNOS (endothelial NO synthase) but attenuated TNFα (tumor necrosis factor alpha)-induced VCAM-1 (vascular cell adhesion molecule 1) and ICAM-1 (intercellular adhesion molecule 1) expression, as well as the adhesion of monocytes to ECs. Conversely, FTO overexpression significantly upregulated the mRNA and protein levels of VCAM-1 and ICAM-1, downregulated those of KLF2 and eNOS, and strongly attenuated the atorvastatin-mediated induction of KLF2 and eNOS expression. Subsequent investigations demonstrated that KLF2 and eNOS are functionally critical targets of FTO. Mechanistically, FTO interacted with KLF2 and eNOS transcripts and regulated their expression in an m6A-dependent manner. After FTO silencing, KLF2 and eNOS transcripts with higher levels of m6A modification in their 3' untranslated regions were captured by YTHDF3 (YT521-B homology m6A RNA-binding protein 3), resulting in mRNA stabilization and the induction of KLF2 and eNOS protein expression.

CONCLUSIONS

FTO might serve as a novel molecular target to modulate endothelial function in vascular diseases.

Renoprotective Effect of KLF2 on Glomerular Endothelial Dysfunction in Hypertensive Nephropathy

Kruppel-like factor 2 (KLF2) regulates endothelial cell metabolism; endothelial dysfunction is associated with hypertension and is a predictor of atherosclerosis development and cardiovascular events. Here, we investigated the role of KLF2 in hypertensive nephropathy by regulating KLF2 expression in human primary glomerular endothelial cells (hPGECs) and evaluating this expression in the kidney tissues of a 5/6 nephrectomy mouse model as well as patients with hypertension. Hypertension-mimicking devices and KLF2 siRNA were used to downregulate KLF2 expression, while the expression of KLF2 was upregulated by administering simvastatin. After 4 mmHg of pressure was applied on hPGECs for 48 h, KLF2 mRNA expression decreased, while alpha-smooth muscle actin (αSMA) mRNA expression increased. Apoptosis and fibrosis rates were increased under pressure, and these phenomena were aggravated following KLF2 knockdown, but were alleviated after simvastatin treatment; additionally, these changes were observed in angiotensin II, angiotensin type-1 receptor (AT1R) mRNA, and interleukin-18 (IL-18), but not in angiotensin type-2 receptor mRNA. Reduced expression of KLF2 in glomerular endothelial cells due to hypertension was found in both 5/6 nephrectomy mice and patients with hypertensive nephropathy. Thus, our study demonstrates that the pressure-induced apoptosis and fibrosis of glomerular endothelial cells result from angiotensin II, AT1R activation, and KLF2 inhibition, and are associated with IL-18.

Indoxyl sulfate reduces Ito,f by activating ROS/MAPK and NF-κB signaling pathways

There is a high prevalence of ventricular arrhythmias related to sudden cardiac death in patients with chronic kidney disease (CKD). To explored the possible mechanism of CKD-related ventricular arrhythmias, a CKD rat model was created, and indoxyl sulfate (IS) was further used in vivo and in vitro. This project used the following methods: patch clamp, electrocardiogram, and some molecular biology experimental techniques. IS was found to be significantly elevated in the serum of CKD rats. Interestingly, the expression levels of the fast transient outward potassium current-related (Ito,f-related) proteins (Kv4.2, Kv4.3, and KChIP2) in the heart of CKD rats and rats treated with IS decreased. IS dose-dependently reduced Ito,f density, accompanied by the decreases in Kv4.2, Kv4.3, and KChIP2 proteins in vitro. IS also prolonged the action potential duration and QT interval, and paroxysmal ventricular tachycardia could be induced by IS. In-depth studies have shown that ROS/p38MAPK, ROS-p44/42 MAPK, and NF-κB signaling pathways play key roles in the reduction of Ito,f density and Ito,f-related proteins caused by IS. These data suggest that IS reduces Ito,f-related proteins and Ito,f density by activating ROS/MAPK and NF-κB signaling pathways, and the action potential duration and QT interval are subsequently prolonged, which contributes to increasing the susceptibility to arrhythmia in CKD.

Non-Transferrin-Bound Iron in the Spotlight: Novel Mechanistic Insights into the Vasculotoxic and Atherosclerotic Effect of Iron

Significance: While atherosclerosis is an almost inevitable consequence of aging, food preferences, lack of exercise, and other aspects of the lifestyle in many countries, the identification of new risk factors is of increasing importance to tackle a disease, which has become a major health burden for billions of people. Iron has long been suspected to promote the development of atherosclerosis, but data have been conflicting, and the contribution of iron is still debated controversially. Recent Advances: Several experimental and clinical studies have been recently published about this longstanding controversial problem, highlighting the critical need to unravel the complexity behind this topic. Critical Issues: The aim of the current review is to provide an overview of the current knowledge about the proatherosclerotic impact of iron, and discuss the emerging role of non-transferrin-bound iron (NTBI) as driver of vasculotoxicity and atherosclerosis. Finally, I will provide detailed mechanistic insights on the cellular processes and molecular pathways underlying iron-exacerbated atherosclerosis. Overall, this review highlights a complex framework where NTBI acts at multiple levels in atherosclerosis by altering the serum and vascular microenvironment in a proatherogenic and proinflammatory manner, affecting the functionality and survival of vascular cells, promoting foam cell formation and inducing angiogenesis, calcification, and plaque destabilization. Future Directions: The use of additional iron markers (e.g., NTBI) may help adequately predict predisposition to cardiovascular disease. Clinical studies are needed in the aging population to address the atherogenic role of iron fluctuations within physiological limits and the therapeutic value of iron restriction approaches. Antioxid. Redox Signal. 35, 387-414.

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.

Statins in patients with COVID-19: a retrospective cohort study in Iranian COVID-19 patients

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has profoundly affected the lives of millions of people. To date, there is no approved vaccine or specific drug to prevent or treat COVID-19, while the infection is globally spreading at an alarming rate. Because the development of effective vaccines or novel drugs could take several months (if not years), repurposing existing drugs is considered a more efficient strategy that could save lives now. Statins constitute a class of lipid-lowering drugs with proven safety profiles and various known beneficial pleiotropic effects. Our previous investigations showed that statins have antiviral effects and are involved in the process of wound healing in the lung. This triggered us to evaluate if statin use reduces mortality in COVID-19 patients.

RESULTS

After initial recruitment of 459 patients with COVID-19 (Shiraz province, Iran) and careful consideration of the exclusion criteria, a total of 150 patients, of which 75 received statins, were included in our retrospective study. Cox proportional-hazards regression models were used to estimate the association between statin use and rate of death. After propensity score matching, we found that statin use appeared to be associated with a lower risk of morbidity [HR = 0.85, 95% CI = (0.02, 3.93), P = 0.762] and lower risk of death [(HR = 0.76; 95% CI = (0.16, 3.72), P = 0.735)]; however, these associations did not reach statistical significance. Furthermore, statin use reduced the chance of being subjected to mechanical ventilation [OR = 0.96, 95% CI = (0.61-2.99), P = 0.942] and patients on statins showed a more normal computed tomography (CT) scan result [OR = 0.41, 95% CI = (0.07-2.33), P = 0.312].

CONCLUSIONS

Although we could not demonstrate a significant association between statin use and a reduction in mortality in patients with COVID19, we do feel that our results are promising and of clinical relevance and warrant the need for prospective randomized controlled trials and extensive retrospective studies to further evaluate and validate the potential beneficial effects of statin treatment on clinical symptoms and mortality rates associated with COVID-19.

HRD1 prevents atherosclerosis-mediated endothelial cell apoptosis by promoting LOX-1 degradation

The 3-hydroxy-3-methylglutaryl reductase degradation (HRD1) is an E3 ubiquitin ligase that can preserve heart structure and function, but its role in endothelial dysfunction and atherosclerosis (AS) is unclear. The aim of this study was to explore the role and biological function of HRD1 in AS. HRD1 expression was significantly decreased in atherosclerotic intima and ox-LDL led to a decrease of HRD1 level in endothelial cells (ECs). Forced expression of HRD1 inhibited the endothelial apoptosis induced by ox-LDL. The transcription factor KLF2 specifically bound to the HRD1 promoter and positively regulated HRD1 expression. KLF2 up-regulation could reverse the decrease of HRD1 level in ECs treated with ox-LDL. Further analysis showed that HRD1 interacted with LOX-1 and promoted ubiquitination and degradation of LOX-1 by the proteasome. Deletion of LOX-1 attenuated the ECs apoptosis induced by HRD1 downregulation. Pravastatin, which protected EC from damage via a KLF2-dependent mechanism, could dose-dependently enhanced HRD1 expression in EC exposed to ox-LDL. Interestingly, interference of HRD1 abolished the cytoprotective effect of pravastatin. Collectively, our data indicate that decreased HRD1 expression leads to apoptosis of ECs and restoration of HRD1 expression could represent a novel strategy for human AS therapy.

Chronic kidney disease in the pathogenesis of acute ischemic stroke

Chronic kidney disease has a graded and independent inverse impact on cerebrovascular health. Both thrombotic and hemorrhagic complications are highly prevalent in chronic kidney disease patients. Growing evidence suggests that in chronic kidney disease patients, ischemic strokes are more common than hemorrhagic strokes. Chronic kidney disease is asymptomatic until an advanced stage, but mild to moderate chronic kidney disease incites various pathogenic mechanisms such as inflammation, oxidative stress, neurohormonal imbalance, formation of uremic toxins and vascular calcification which damage the endothelium and blood vessels. Cognitive dysfunction, dementia, transient infarcts, and white matter lesions are widespread in mild to moderate chronic kidney disease patients. Uremic toxins produced after chronic kidney disease can pass through the blood-brain barrier and mediate cognitive dysfunction and neurodegeneration. Furthermore, chronic kidney disease precipitates vascular risk factors that can lead to atherosclerosis, hypertension, atrial fibrillation, and diabetes. Chronic kidney disease also exacerbates stroke pathogenesis, worsens recovery outcomes, and limits the eligibility of stroke patients to receive available stroke therapeutics. This review highlights the mechanisms involved in the advancement of chronic kidney disease and its possible association with stroke.

Oxidative stress in chronic kidney disease

Oxidative stress (OS), defined as disturbances in the pro-/antioxidant balance, is harmful to cells due to the excessive generation of highly reactive oxygen (ROS) and nitrogen (RNS) species. When the balance is not disturbed, OS has a role in physiological adaptations and signal transduction. However, an excessive amount of ROS and RNS results in the oxidation of biological molecules such as lipids, proteins, and DNA. Oxidative stress has been reported in kidney disease, due to both antioxidant depletions as well as increased ROS production. The kidney is a highly metabolic organ, rich in oxidation reactions in mitochondria, which makes it vulnerable to damage caused by OS, and several studies have shown that OS can accelerate kidney disease progression. Also, in patients at advanced stages of chronic kidney disease (CKD), increased OS is associated with complications such as hypertension, atherosclerosis, inflammation, and anemia. In this review, we aim to describe OS and its influence on CKD progression and its complications. We also discuss the potential role of various antioxidants and pharmacological agents, which may represent potential therapeutic targets to reduce OS in both pediatric and adult CKD patients.

ERK5/KLF2 activation is involved in the reducing effects of puerarin on monocyte adhesion to endothelial cells and atherosclerotic lesion in apolipoprotein E-deficient mice

Puerarin has properties of anti-oxidation and anti-inflammation, which has been demonstrated protective effects in atherosclerosis and other cardiovascular diseases. However, the detail molecular mechanism still remains unclear. Here, we determined whether the atheroprotective effect of puerarin was by reducing monocyte adhesion and explored the underlying mechanism. The results showed that puerarin dose- and time-dependently reduced oxLDL-induced monocyte THP-1 adhesion to HUVECs and the expression of adhesion-related genes such as VCAM-1, ICAM-1, MCP-1 and IL-8 in HUVECs. Puerarin activated ERK5 phosphorylation and up-regulated expressions of downstream KLF2 and its targeted genes endothelial nitric oxide synthase and thrombomodulin. However, the protective effects were reversed by ERK5/KLF2 pathway inhibitor XDM8-92, BIX02189 or KLF2 siRNA suggesting the pathway involved in the function. The ex vivo assay, in which THP-1 adhesion to endothelium isolated from apoE-/- mice received various treatments further confirmed the results from HUVECs. Finally, we found that the atherosclerotic lesions in both cross sections at aortic root and whole aorta were significantly reduced in high fat-diet (HFD) mice with puerarin treatment compared with the HFD-only mice, but were increased respectively by 76% and 71% in XMD8-92 group, and 82% and 73% in BIX02189 group. Altogether, the data revealed that puerarin inhibited the monocyte adhesion in vitro and in vivo and thus reduced atherosclerotic lesions in apoE-/- mice; the protective effects were mediated by activation of ERK5/KLF2 signaling pathway. Our findings advance the understanding of puerarin function in atherosclerosis and point out a way to prevent the disease.

Krüppel-Like Factors in Vascular Inflammation: Mechanistic Insights and Therapeutic Potential

The role of inflammation in vascular disease is well recognized, involving dysregulation of both circulating immune cells as well as the cells of the vessel wall itself. Unrestrained vascular inflammation leads to pathological remodeling that eventually contributes to atherothrombotic disease and its associated sequelae (e.g., myocardial/cerebral infarction, embolism, and critical limb ischemia). Signaling events during vascular inflammation orchestrate widespread transcriptional programs that affect the functions of vascular and circulating inflammatory cells. The Krüppel-like factors (KLFs) are a family of transcription factors central in regulating vascular biology in states of homeostasis and disease. Given their abundance and diversity of function in cells associated with vascular inflammation, understanding the transcriptional networks regulated by KLFs will further our understanding of the pathogenesis underlying several pervasive health concerns (e.g., atherosclerosis, stroke, etc.) and consequently inform the treatment of cardiovascular disease. Within this review, we will discuss the role of KLFs in coordinating protective and deleterious responses during vascular inflammation, while addressing the potential targeting of these critical transcription factors in future therapies.

The balance between induction and inhibition of mevalonate pathway regulates cancer suppression by statins: A review of molecular mechanisms

Statins are widely used drugs for their role in decreasing cholesterol in hypercholesterolemic patients. Statins through inhibition of Hydroxy Methyl Glutaryl-CoA Reductase (HMGCR), the main enzyme of the cholesterol biosynthesis pathway, inhibit mevalonate pathway that provides isoprenoids for prenylation of different proteins such as Ras superfamily which has an essential role in cancer developing. Inhibition of the mevalonate/isoprenoid pathway is the cause of the cholesterol independent effects of statins or pleotropic effects. Depending on their penetrance into the extra-hepatic cells, statins have different effects on mevalonate/isoprenoid pathway. Lipophilic statins diffuse into all cells and hydrophilic ones use a variety of membrane transporters to gain access to cells other than hepatocytes. It has been suggested that the lower accessibility of statins for extra-hepatic tissues may result in the compensatory induction of mevalonate/isoprenoid pathway and so cancer developing. However, most of the population-based studies have demonstrated that statins have no effect on cancer developing, even decrease the risk of different types of cancer. In this review we focus on the cancer developing "potentials" and the anti-cancer "activities" of statins regarding the effects of statins on mevalonate/isoprenoid pathway in the liver and extra-hepatic tissues.

Antioxidant properties of drugs used in Type 2 diabetes management: could they contribute to, confound or conceal effects of antioxidant therapy?

Objectives: This is a narrative review, investigating the antioxidant properties of drugs used in the management of diabetes, and discusses whether these antioxidant effects contribute to, confound, or conceal the effects of antioxidant therapy.

Methods: A systematic search for articles reporting trials, or observational studies on the antioxidant effect of drugs used in the treatment of diabetes in humans or animals was performed using Web of Science, PubMed, and Ovid. Data were extracted, including data on a number of subjects, type of treatment (and duration) received, and primary and secondary outcomes. The primary outcomes were reporting on changes in biomarkers of antioxidants concentrations and secondary outcomes were reporting on changes in biomarkers of oxidative stress.

Results: Diabetes Mellitus is a disease characterized by increased oxidative stress. It is often accompanied by a spectrum of other metabolic disturbances, including elevated plasma lipids, elevated uric acid, hypertension, endothelial dysfunction, and central obesity. This review shows evidence that some of the drugs in diabetes management have both in vivo and in vitro antioxidant properties through mechanisms such as scavenging free radicals and upregulating antioxidant gene expression.

Conclusion: Pharmaceutical agents used in the treatment of type 2 diabetes has been shown to exert an antioxidant effect..

Red Yeast Rice Protects Circulating Bone Marrow-Derived Proangiogenic Cells against High-Glucose-Induced Senescence and Oxidative Stress: The Role of Heme Oxygenase-1

The inflammation and oxidative stress of bone marrow-derived proangiogenic cells (PACs), also named endothelial progenitor cells, triggered by hyperglycemia contributes significantly to vascular dysfunction. There is supporting evidence that the consumption of red yeast rice (RYR; Monascus purpureus-fermented rice) reduces the vascular complications of diabetes; however, the underlying mechanism remains unclear. This study aimed to elucidate the effects of RYR extract in PACs, focusing particularly on the role of a potent antioxidative enzyme, heme oxygenase-1 (HO-1). We found that treatment with RYR extract induced nuclear factor erythroid-2-related factor nuclear translocation and HO-1 mRNA and protein levels in PACs. RYR extract inhibited high-glucose-induced (30 mM) PAC senescence and the development of reactive oxygen species (ROS) in a dose-dependent manner. The HO-1 inducer cobalt protoporphyrin IX also decreased high-glucose-induced cell senescence and oxidative stress, whereas the HO-1 enzyme inhibitor zinc protoporphyrin IX and HO-1 small interfering RNA significantly reversed RYR extract-caused inhibition of senescence and reduction of oxidative stress in high-glucose-treated PACs. These results suggest that RYR extract serves as alternative and complementary medicine in the treatment of these diseases, by inducing HO-1, thereby decreasing the vascular complications of diabetes.

Overexpression of angiotensinogen downregulates aquaporin 1 expression via modulation of Nrf2-HO-1 pathway in renal proximal tubular cells of transgenic mice

Introduction:

We aimed to examine the regulation of aquaporin 1 expression in an angiotensinogen transgenic mouse model, focusing on underlying mechanisms.

Methods:

Male transgenic mice overexpressing rat angiotensinogen in their renal proximal tubular cells (RPTCs) and rat immortalised RPTCs stably transfected with rat angiotensinogen cDNA were used.

Results:

Angiotensinogen-transgenic mice developed hypertension and nephropathy, changes that were either partially or completely attenuated by treatment with losartan or dual renin–angiotensin system blockade (losartan and perindopril), respectively, while hydralazine prevented hypertension but not nephropathy. Decreased expression of aquaporin 1 and heme oxygenase-1 and increased expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and sodium–hydrogen exchanger 3 were observed in RPTCs of angiotensinogen-transgenic mice and in angiotensinogen-transfected immortalised RPTCs. These parameters were normalised by dual renin–angiotensin system blockade. Both in vivo and in vitro studies identified a novel mechanism in which angiotensinogen overexpression in RPTCs enhances the cytosolic accumulation of Nrf2 via the phosphorylation of pGSK3β Y216. Consequently, lower intranuclear Nrf2 levels are less efficient to trigger heme oxygenase-1 expression as a defence mechanism, which subsequently diminishes aquaporin 1 expression in RPTCs.

Conclusions:

Angiotensinogen-mediated downregulation of aquaporin 1 and Nrf2 signalling may play an important role in intrarenal renin–angiotensin system-induced hypertension and kidney injury.

Cytoprotective pathways in the vascular endothelium. Do they represent a viable therapeutic target?

The vascular endothelium is a critical interface, which separates the organs from the blood and its contents. The endothelium has a wide variety of functions and maintenance of endothelial homeostasis is a multi-dimensional active process, disruption of which has potentially deleterious consequences if not reversed. Vascular injury predisposes to endothelial apoptosis, dysfunction and development of atherosclerosis. Endothelial dysfunction is an end-point, a central feature of which is increased ROS generation, a reduction in endothelial nitric oxide synthase and increased nitric oxide consumption. A dysfunctional endothelium is a common feature of diseases including rheumatoid arthritis, systemic lupus erythematosus, diabetes mellitus and chronic renal impairment. The endothelium is endowed with a variety of constitutive and inducible mechanisms that act to minimise injury and facilitate repair. Endothelial cytoprotection can be enhanced by exogenous factors such as vascular endothelial growth factor, prostacyclin and laminar shear stress. Target genes include endothelial nitric oxide synthase, heme oxygenase-1, A20 and anti-apoptotic members of the B cell lymphoma protein-2 family. In light of the importance of endothelial function, and the link between its disruption and the risk of atherothrombosis, interest has focused on therapeutic conditioning and reversal of endothelial dysfunction. A detailed understanding of cytoprotective signalling pathways, their regulation and target genes is now required to identify novel therapeutic targets. The ultimate aim is to add vasculoprotection to current therapeutic strategies for systemic inflammatory diseases, in an attempt to reduce vascular injury and prevent or retard atherogenesis.

Statins up-regulate SmgGDS through β1-integrin/Akt1 pathway in endothelial cells

AIMS

The pleiotropic effects of HMG-CoA reductase inhibitors (statins) independent of cholesterol-lowering effects have attracted much attention. We have recently demonstrated that the pleiotropic effects of statins are partly mediated through up-regulation of small GTP-binding protein dissociation stimulator (SmgGDS) with a resultant Rac1 degradation and reduced oxidative stress. However, it remains to be elucidated what molecular mechanisms are involved.

METHODS AND RESULTS

To first determine in what tissue statins up-regulate SmgGDS expression, we examined the effects of two statins (atorvastatin 10 mg/kg per day and pravastatin 50 mg/kg per day for 1 week) on SmgGDS expression in mice in vivo. The two statins increased SmgGDS expression especially in the aorta. Atorvastatin also increased SmgGDS expression in cultured human umbilical venous endothelial cells (HUVEC) and human aortic endothelial cells, but not in human aortic vascular smooth muscle cells. Furthermore, Akt phosphorylation was transiently enhanced only in HUVEC in response to atorvastatin. Then, to examine whether Akt is involved for up-regulation of SmgGDS by statins, we knocked out Akt1 by its siRNA in HUVEC, which abolished the effects by atorvastatin to up-regulate SmgGDS. Furthermore, when we knocked down β1-integrin to elucidate the upstream molecule of Akt1, the effect of atorvastatin to up-regulate SmgGDS was abolished. Finally, we confirmed that Akt activator, SC79, significantly up-regulate SmgGDS in HUVEC.

CONCLUSION

These results indicate that statins selectively up-regulate SmgGDS in endothelial cells, for which the β1-integrin/Akt1 pathway may be involved, demonstrating the novel aspects of the pleiotropic effects of statins.

Improved outcome after primary vitrectomy in diabetic patients treated with statins

PURPOSE

To evaluate the effect of preoperative statin treatment on the outcome of primary vitrectomy in type 1 and 2 diabetic patients.

METHODS

In this open, observational institutional study, a total of 192 eyes of 171 type 1 and 2 adult diabetic patients admitted for primary vitrectomy for management of sight-threatening forms of diabetic retinopathy were divided according to the use of lipid-lowering therapy: those with statin treatment (79 eyes of 73 patients) and those taking no statin medication (113 eyes of 98 patients). One-month best-corrected visual acuity (BCVA) gain and cumulative 12-month revitrectomy frequency were analyzed.

RESULTS

In multivariate linear regression, diabetic patients with statin treatment had a better 1-month BCVA improvement than did those without statin treatment (absolute difference 0.26, 95% confidence interval [CI] 0.02-0.50, p = 0.028). Subgroup analysis revealed that diabetic patients on statin had better postoperative BCVA improvement when preoperative status included partial or panretinal laser photocoagulation (p = 0.042 and p = 0.049) and anti-vascular endothelial growth factor therapy (p = 0.011). Moreover, diabetic patients with preoperative macular edema (p = 0.009), vitreous hemorrhage (p<0.001), proliferative retinopathy (p<0.001), or tractional retinal detachment (p = 0.010) had better BCVA recovery if receiving statin. In Cox proportional hazards regression model, revitrectomies in our 12-month follow-up were less frequent in diabetic patients on statin treatment (hazard ratio 0.28, 95% CI 0.08-0.93, p = 0.037).

CONCLUSIONS

These data provide novel insight into the potential clinical benefit for patients with sight-threatening diabetic retinopathy undergoing vitrectomy treated with statin.

The multifunctional role and therapeutic potential of HO-1 in the vascular endothelium

SIGNIFICANCE

Heme oxygenases (HO-1 and HO-2) catalyze the degradation of the pro-oxidant heme into carbon monoxide (CO), iron, and biliverdin, which is subsequently converted to bilirubin. In the vasculature, particular interest has focused on antioxidant and anti-inflammatory properties of the inducible HO-1 isoform in the vascular endothelium. This review will present evidence that illustrates the potential therapeutic significance of HO-1 and its products, with special emphasis placed on their beneficial effects on the endothelium in vascular diseases.

RECENT ADVANCES

The understanding of the molecular basis for the regulation and functions of HO-1 has led to the identification of a variety of drugs that increase HO-1 activity in the vascular endothelium. Moreover, therapeutic delivery of HO-1 products CO, biliverdin, and bilirubin has been shown to have favorable effects, notably on endothelial cells and in animal models of vascular disease.

CRITICAL ISSUES

To date, mechanistic data identifying the downstream target genes utilized by HO-1 and its products to exert their actions remain relatively sparse. Likewise, studies in man to investigate the efficacy of therapeutics known to induce HO-1 or the consequences of the tissue-specific delivery of CO or biliverdin/bilirubin are rarely performed.

FUTURE DIRECTIONS

Based on the promising in vivo data from animal models, clinical trials to explore the safety and efficacy of the therapeutic induction of HO-1 and the delivery of its products should now be pursued further, targeting, for example, patients with severe atherosclerotic disease, ischemic limbs, restenosis injury, or at high risk of organ rejection.

New insights into intracellular locations and functions of heme oxygenase-1

SIGNIFICANCE

Heme oxygenase-1 (HMOX1) plays a critical role in the protection of cells, and the inducible enzyme is implicated in a spectrum of human diseases. The increasing prevalence of cardiovascular and metabolic morbidities, for which current treatment approaches are not optimal, emphasizes the necessity to better understand key players such as HMOX1 that may be therapeutic targets.

RECENT ADVANCES

HMOX1 is a dynamic protein that can undergo post-translational and structural modifications which modulate HMOX1 function. Moreover, trafficking from the endoplasmic reticulum to other cellular compartments, including the nucleus, highlights that HMOX1 may play roles other than the catabolism of heme.

CRITICAL ISSUES

The ability of HMOX1 to be induced by a variety of stressors, in an equally wide variety of tissues and cell types, represents an obstacle for the therapeutic exploitation of the enzyme. Any capacity to modulate HMOX1 in cardiovascular and metabolic diseases should be tempered with an appreciation that HMOX1 may have an impact on cancer. Moreover, the potential for heme catabolism end products, such as carbon monoxide, to amplify the HMOX1 stress response should be considered.

FUTURE DIRECTIONS

A more complete understanding of HMOX1 modifications and the properties that they impart is necessary. Delineating these parameters will provide a clearer picture of the opportunities to modulate HMOX1 in human disease.

Cytoprotective signaling and gene expression in endothelial cells and macrophages-lessons for atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the medium and large arteries driven in large part by the accumulation of oxidized low-density lipoproteins and other debris at sites rendered susceptible because of the geometry of the arterial tree. As lesions develop, they acquire a pathologic microcirculation that perpetuates lesion progression, both by providing a means for further monocyte and T-lymphocyte recruitment into the arterial wall and by the physical and chemical stresses caused by micro-hemorrhage. This review summarizes work performed in our department investigating the roles of signaling pathways, alone and in combination, that lead to specific programs of gene expression in the atherosclerotic environment. Focusing particularly on cytoprotective responses that might be enhanced therapeutically, the work has encompassed the anti-inflammatory effects of arterial laminar shear stress, mechanisms of induction of membrane inhibitors that prevent complement-mediated injury, homeostatic macrophage responses to hemorrhage, and the transcriptional mechanisms that control the stability, survival, and quiescence of endothelial monolayers. Lastly, while the field has been dominated by investigation into the mechanisms of DNA transcription, we consider the importance of parallel post-transcriptional regulatory mechanisms for fine-tuning functional gene expression repertoires.

Venous endothelial injury in central nervous system diseases

The role of the venous system in the pathogenesis of inflammatory neurological/neurodegenerative diseases remains largely unknown and underinvestigated. Aside from cerebral venous infarcts, thromboembolic events, and cerebrovascular bleeding, several inflammatory central nervous system (CNS) diseases, such as multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), and optic neuritis, appear to be associated with venous vascular dysfunction, and the neuropathologic hallmark of these diseases is a perivenous, rather than arterial, lesion. Such findings raise fundamental questions about the nature of these diseases, such as the reasons why their pathognomonic lesions do not develop around the arteries and what exactly are the roles of cerebral venous inflammation in their pathogenesis. Apart from this inflammatory-based view, a new hypothesis with more focus on the hemodynamic features of the cerebral and extracerebral venous system suggests that MS pathophysiology might be associated with the venous system that drains the CNS. Such a hypothesis, if proven correct, opens new therapeutic windows in MS and other neuroinflammatory diseases. Here, we present a comprehensive review of the pathophysiology of MS, ADEM, pseudotumor cerebri, and optic neuritis, with an emphasis on the roles of venous vascular system programming and dysfunction in their pathogenesis. We consider the fundamental differences between arterial and venous endothelium, their dissimilar responses to inflammation, and the potential theoretical contributions of venous insufficiency in the pathogenesis of neurovascular diseases.

Donor simvastatin treatment prevents ischemia-reperfusion and acute kidney injury by preserving microvascular barrier function

Ischemia-reperfusion injury (IRI) after kidney transplantation may result in delayed graft function. We used rat renal artery clamping and transplantation models to investigate cholesterol-independent effects of clinically relevant single-dose peroral simvastatin treatment 2 h before renal ischemia on microvascular injury. The expression of HMG-CoA reductase was abundant in glomerular and peritubular microvasculature of normal kidneys. In renal artery clamping model with 30-min warm ischemia, simvastatin treatment prevented peritubular microvascular permeability and perfusion disturbances, glomerular barrier disruption, tubular dysfunction and acute kidney injury. In fully MHC-mismatched kidney allografts with 16-h cold and 1-h warm ischemia, donor simvastatin treatment increased the expression of flow-regulated transcription factor KLF2 and vasculoprotective eNOS and HO-1, and preserved glomerular and peritubular capillary barrier integrity during preservation. In vitro EC Weibel-Palade body exocytosis assays showed that simvastatin inhibited ischemia-induced release of vasoactive angiopoietin-2 and endothelin-1. After reperfusion, donor simvastatin treatment prevented microvascular permeability, danger-associated ligand hyaluronan induction, tubulointerstitial injury marker Kim-1 immunoreactivity and serum creatinine and NGAL levels, and activation of innate and adaptive immune responses. In conclusion, donor simvastatin treatment prevented renal microvascular dysfunction and IRI with beneficial effects on adaptive immune and early fibroproliferative responses. Further studies may determine potential benefits in clinical cadaveric kidney transplantation.

Glomerular mRNA expression of prothrombotic and antithrombotic factors in renal transplants with thrombotic microangiopathy

BACKGROUND

Thrombotic microangiopathy (TMA) in renal transplants (rTx-TMA) is a serious complication and is usually either recurrent TMA (RecTMA) due to humoral rejection (HR-TMA) or due to calcineurin inhibitor toxicity (CNI-TMA). Although the triggers are known, our knowledge about the thrombogenic transcriptome changes in the microvessels is rudimentary.

METHODS

We examined the expression of several prothrombotic and antithrombotic genes in 25 biopsies with rTx-TMA (6 RecTMA, 9 HR-TMA, and 10 CNI-TMA) and 8 controls. RNA from microdissected glomeruli of paraffin-embedded tissue was isolated and mRNA transcripts were quantified with real-time polymerase chain reaction after preamplification. Results were correlated with clinicopathologic parameters.

RESULTS

Glomerular mRNA expression of KLF2, KLF4, and tPA was lower and that of PAI-1 was higher in rTx-TMA than in the controls. Glomerular mRNA expression of KLF2 and KLF4 correlated with that of tPA and inversely with that of PAI-1 in rTx-TMA. The mRNA expression of complement regulators CD46 and CD59 were higher in rTx-TMA than in the controls. Only in HR-TMA were glomerular ADAMTS13 and CD55 down-regulated.

CONCLUSIONS

The glomerular capillary bed seems to contribute to all subtypes of rTx-TMA by down-regulation of the endothelial transcription factors KLF2 and KLF4, indicating dedifferentiation with subsequent up-regulation of PAI-1 and down-regulation of tPA, resulting in inhibition of local fibrinolysis. Decreased glomerular expression of ADAMTS13 and CD55 could be an additional pathway toward microthrombosis exclusively in HR-TMA.

Role of nitric oxide and CCAAT/enhancer-binding protein transcription factor in statin-dependent induction of heme oxygenase-1 in mouse macrophages

The effect of statins on heme oxygenase-1 (HO-1) was compared in 2 murine cell lines, RAW 264.7 and J774A.1 cell lines, and in primary peritoneal macrophages of BALB/c or C57BL/6 mice. The role of endogenous nitric oxide and the type of transcription factors involved were explored. Simvastatin and fluvastatin induced HO-1. Pretreatment of cells with l-NMMA or 1400 W, two different nitric oxide synthase inhibitors, partially blocked statin-dependent induction of HO-1 in RAW 264.7 and J774A.1 but not in primary peritoneal macrophages. Induction of HO-1 by statins was dependent on p-38 MAP kinase activation in all types of macrophages. In RAW 264.7 cells, both statins increased the activity of reporter genes linked to the proximal 1.3 kbp promoter of HO-1 (EC50 of 1.4±0.3 µM for simvastatin and 0.6±0.03 µM for fluvastatin). This effect was significantly blocked by 1400 W (80±5.2% inhibition, p<0.02) and mevalonate, the direct metabolite of HMGCoA reductase. Gel retardation experiments implicated C/EBPβ, AP-1 but not USF, for both RAW 264.7 and primary peritoneal macrophages of C57BL/6 mice. Collectively we showed a differential role of endogenous nitric oxide between macrophage cell lines and primary macrophages and an effect of statins in the protection against inflammation by increasing HO-1 expression.

The statin-iron nexus: anti-inflammatory intervention for arterial disease prevention

OBJECTIVES

We postulated the existence of a statin-iron nexus by which statins improve cardiovascular disease outcomes at least partially by countering proinflammatory effects of excess iron stores.

METHODS

Using data from a clinical trial of iron (ferritin) reduction in advanced peripheral arterial disease, the Iron and Atherosclerosis Study, we compared effects of ferritin levels versus high-density lipoprotein to low-density lipoprotein ratios (both were randomization variables) on clinical outcomes in participants receiving and not receiving statins.

RESULTS

Statins increased high-density lipoprotein to low-density lipoprotein ratios and reduced ferritin levels by noninteracting mechanisms. Improved clinical outcomes were associated with lower ferritin levels but not with improved lipid status.

CONCLUSIONS

There are commonalities between the clinical benefits of statins and the maintenance of physiologic iron levels. Iron reduction may be a safe and low-cost alternative to statins.

Might the beneficial effects of statin drugs be related to their action on iron metabolism?

Although the cholesterol-heart hypothesis is often regarded as a dogmatic belief, controversy continues to surround the aetiology and pathogenesis of atherosclerosis. In fact, lowering cholesterol with statin drugs has been shown to reduce cardiovascular risk. However, statins have pleiotropic effects independent of their capacity to lower cholesterol. We highlight that statin drugs exert an important action on iron metabolism, which in turn may prevent progression and destabilization of atherosclerotic plaque. If it is found that the effect of statins on iron metabolism is a mechanism of their beneficial action, this consequence of statin use can be clinically replicated by other methods, such as controlled reduction of body iron stores. This might allow the use of lower doses or even obviate the use of statins in primary cardiovascular prevention, and therefore avoid the side effects and expense of these drugs.

Cardiovascular events as a function of serum bilirubin levels in a large, statin-treated cohort

BACKGROUND

Serum bilirubin is an endogenous antioxidant that is routinely measured before a statin is prescribed primarily to assess liver function, but the association with cardiovascular disease (CVD) in this population has not been explored.

METHOD AND RESULTS

We identified patients from a United Kingdom primary care database (The Health Improvement Network) with measurements of serum total bilirubin levels recorded 3 months before the first statin treatment between January 1, 2000, and December 31, 2010, and no history of liver disease or CVD. In total, 130 052 patients met the inclusion criteria, and after a median follow-up of 43 months, there were 7850 CVD events. In men, the incidence of CVD in the lowest decile category of bilirubin (1-6 μmol/L [0.06-0.35 mg/dL]) was 215 per 10 000 person-years compared with 163 per 10 000 person-years in the highest decile (19-40 μmol/L [1.1-2.3 mg/dL]). Similar differences were seen for women. After conventional CVD risk factors were accounted for, the associations with bilirubin were nonlinear (L shaped), and the models predicted that, compared with patients with a bilirubin level of 10 μmol/L (0.6 mg/dL), those with a similar CVD risk profile but a bilirubin level of 5 μmol/L (0.3 mg/dL) had an 18% (95% confidence interval, 9-27) higher risk of any CVD event, a 34% (95% confidence interval, 13-56) higher risk of myocardial infarction, and a 33% (95% confidence interval, 21-46) higher risk of death resulting from any cause.

CONCLUSIONS

Serum bilirubin level measured before a statin prescription to assess liver function is an independent risk factor for CVD and death in both men and women.

Heme and haemoglobin direct macrophage Mhem phenotype and counter foam cell formation in areas of intraplaque haemorrhage

PURPOSE OF REVIEW

Several studies have recently shown that haemoglobin drives a novel macrophage subset that is protected from foam cell formation.

RECENT FINDINGS

In a previously overlooked area, two centres have independently shown that heme and haemoglobin drive an atheroprotective macrophage subset. We compare and contrast the approaches and findings of the laboratories and discuss some of the underlying biology and implications, concentrating on the aspects of lipidological relevance.

SUMMARY

Treatments based on direct heme-mimetics or other agonists of this pathway have enormous potential for linked antioxidant protection via heme oxygenase 1 and reduced foam cell formation via liver X receptor, a potent combination for treating atherosclerosis.

Angiogenesis within the duodenum of patients with cirrhosis is modulated by mechanosensitive Kruppel-like factor 2 and microRNA-126

BACKGROUND

The mechanism involved in neovascularization in splanchnic circulation and the main trigger that induces angiogenesis in patients with cirrhosis are not fully recognized.

AIMS

To explore the involvement of flow sensitive lung Kruppel-like factor (KLF2), microRNA-126 (miR-126), angiopoietin-2 (Ang-2) and heme oxygenase-1 (HO-1) in modulation of vascular endothelial growth factor (VEGF) signalling that have a critical effect on growth of new blood vessels.

METHODS

Duodenal biopsies from 22 patients with cirrhosis and 10 controls were obtained during routine endoscopy. The process of angiogenesis was evaluated by a measurement of CD31 concentration, immunodetection of CD34 protein and estimation of capillary densities. Messenger RNA (mRNA) and protein expressions were analysed by real-time PCR, Western blot or ELISA respectively.

RESULTS

Markers of angiogenesis (both, CD31 and CD34) were significantly enhanced in cirrhotic patients. In comparison to healthy controls, levels of Ang-2 and KLF-2 mRNAs as well as Ang-2, KLF-2, HO-1, VEGF protein expressions were considerably increased. Levels of sCD163, a surrogate marker of portal hypertension, correlated with levels of Ang-2, (P = 0.021) and VEGF (P = 0.009). The expression of miR-126, a KLF2-mediated regulator of the VEGF signalling was enhanced in cirrhotic patients.

CONCLUSIONS

Our results demonstrate, for the first time in humans, that neovascularization is induced in duodenal tissue of patients with cirrhosis and proangiogenic factors such as KLF-2, Ang-2, miR-126 and VEGF can contribute to the angiogenesis induced by hemodynamic forces. Thus, cirrhosis-induced blood flow and pressure within splanchnic vessels may be important hemodynamic triggers that initiate the angiogenic signalling cascade.

Statins as anti-inflammatory agents in atherogenesis: molecular mechanisms and lessons from the recent clinical trials

Ample evidence exists in support of the potent anti-inflammatory properties of statins. In cell studies and animal models statins exert beneficial cardiovascular effects. By inhibiting intracellular isoprenoids formation, statins suppress vascular and myocardial inflammation, favorably modulate vascular and myocardial redox state and improve nitric oxide bioavailability. Randomized clinical trials have demonstrated that further to their lipid lowering effects, statins are useful in the primary and secondary prevention of coronary heart disease (CHD) due to their anti-inflammatory potential. The landmark JUPITER trial suggested that in subjects without CHD, suppression of low-grade inflammation by statins improves clinical outcome. However, recent trials have failed to document any clinical benefit with statins in high risk groups, such in heart failure or chronic kidney disease patients. In this review, we aim to summarize the existing evidence on statins as an anti-inflammatory agent in atherogenesis. We describe the molecular mechanisms responsible for the anti-inflammatory effects of statins, as well as clinical data on the non lipid-lowering, anti-inflammatory effects of statins on cardiovascular outcomes. Lastly, the controversy of the recent large randomized clinical trials and the issue of statin withdrawal are also discussed.

Intimal hyperplasia: slow but deadly

Intimal hyperplasia is the leading cause of long-term failure in coronary artery bypass vein grafting, coronary artery stenting, angioplasty, arteriovenous fistula for dialysis, and allograft transplantation. Intimal hyperplasia is a product of vascular smooth muscle cell proliferation, migration through the internal elastic lamina, and deposition of extracellular matrix proteins driven by growth factors in the vasculature. This vascular pathology results in a progressive diminution of the vessel lumen and serves as a site for thrombosis and atherosclerotic lesions. A key cell type in the initiation of intimal hyperplasia is the vascular endothelial cell, which appears to have down-stream effects on the vascular smooth muscle proliferation and migration. Currently, the only means available for prevention of intimal hyperplasia is through inhibition of mammalian target of rapamycin (mTOR) with the immunosuppressant rapamycin. mTOR integrates up-stream signals from growth factors such as IL-2 and senses the cellular nutrient and energy levels and redox status. This presentation will discuss the potential means of preserving the vascular endothelial cell and, thereby, reducing the development of intimal hyperplasia in our open-heart surgical patients.

Myeloid-specific Krüppel-like factor 2 inactivation increases macrophage and neutrophil adhesion and promotes atherosclerosis

RATIONALE

Hemizygous deficiency of the transcription factor Krüppel-like factor 2 (KLF2) has been shown previously to augment atherosclerosis in hypercholesterolemic mice. However, the cell type responsible for the increased atherosclerosis due to KLF2 deficiency has not been identified. This study examined the consequence of myeloid cell-specific KLF2 inactivation in atherosclerosis.

METHODS AND RESULTS

Cell-specific knockout mice were generated by Cre/loxP recombination. Macrophages isolated from myeloid-specific Klf2 knockout (myeKlf2(-/-)) mice were similar to myeKlf2(+/+) macrophages in response to activation, polarization, and lipid accumulation. However, in comparison to myeKlf2(+/+) macrophages, myeKlf2(-/-) macrophages adhered more robustly to endothelial cells. Neutrophils from myeKlf2(-/-) mice also adhered more robustly to endothelial cells, and fewer myeKlf2(-/-) neutrophils survived in culture over a 24-hour period in comparison with myeKlf2(+/+) neutrophils. When myeKlf2(-/-) mice were mated to Ldlr(-/-) mice and then fed a high fat and high cholesterol diet, significant increase in atherosclerosis was observed in the myeKlf2(-/-)Ldlr(-/-) mice compared with myeKlf2(+/+)Ldlr(-/-) littermates. The increased atherosclerosis in myeKlf2(-/-)Ldlr(-/-) mice was associated with elevated presence of neutrophils and macrophages, with corresponding increase of myeloperoxidase as well as chlorinated and nitrosylated tyrosine epitopes in their lesion areas compared with myeKlf2(+/+)Ldlr(-/-) mice.

CONCLUSIONS

This study documents a role for myeloid KLF2 expression in modulating atherosclerosis. The increased neutrophil accumulation and atherosclerosis progression with myeloid-specific KLF2 deficiency also underscores the importance of neutrophils in promoting vascular oxidative stress and atherosclerosis. Collectively, these results suggest that elevating KLF2 expression may be a novel strategy for prevention and treatment of atherosclerosis.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.