Netrin-1 abrogates ischemia/reperfusion-induced cardiac mitochondrial dysfunction via nitric oxide-dependent attenuation of NOX4 activation and recoupling of NOS

Specific NOX4 Inhibition Preserves Mitochondrial Function and Dampens Kidney Dysfunction Following Ischemia-Reperfusion-Induced Kidney Injury

Background: Acute kidney injury (AKI) is a sudden episode of kidney failure which is frequently observed at intensive care units and related to high morbidity/mortality. Although AKI can have many different causes, ischemia-reperfusion (IR) injury is the main cause of AKI. Mechanistically, NADPH oxidases (NOXs) are involved in the pathophysiology contributing to oxidative stress following IR. Previous reports have indicated that knockout of NOX4 may offer protection in cardiac and brain IR, but there is currently less knowledge about how this could be exploited therapeutically and whether this could have significant protection in IR-induced AKI. Aim: To investigate the hypothesis that a novel and specific NOX4 inhibitor (GLX7013114) may have therapeutic potential on kidney and mitochondrial function in a mouse model of IR-induced AKI. Methods: Kidneys of male C57BL/6J mice were clamped for 20 min, and the NOX4 inhibitor (GLX7013114) was administered via osmotic minipump during reperfusion. Following 3 days of reperfusion, kidney function (i.e., glomerular filtration rate, GFR) was calculated from FITC-inulin clearance and mitochondrial function was assessed by high-resolution respirometry. Renal histopathological evaluations (i.e., hematoxylin-eosin) and TUNEL staining were performed for apoptotic evaluation. Results: NOX4 inhibition during reperfusion significantly improved kidney function, as evidenced by a better-maintained GFR (p < 0.05) and lower levels of blood urea nitrogen (p < 0.05) compared to untreated IR animals. Moreover, IR caused significant tubular injuries that were attenuated by simultaneous NOX4 inhibition (p < 0.01). In addition, the level of renal apoptosis was significantly reduced in IR animals with NOX4 inhibition (p < 0.05). These favorable effects of the NOX4 inhibitor were accompanied by enhanced Nrf2 Ser40 phosphorylation and conserved mitochondrial function, as evidenced by the better-preserved activity of all mitochondrial complexes. Conclusion: Specific NOX4 inhibition, at the time of reperfusion, significantly preserves mitochondrial and kidney function. These novel findings may have clinical implications for future treatments aimed at preventing AKI and related adverse events, especially in high-risk hospitalized patients.

Biomaterials-mediated targeted therapeutics of myocardial ischemia-reperfusion injury

Reperfusion therapy is widely used to treat acute myocardial infarction. However, its efficacy is limited by myocardial ischemia-reperfusion injury (MIRI), which occurs paradoxically due to the reperfusion therapy and contributes to the high mortality rate of acute myocardial infarction. Systemic administration of drugs, such as antioxidant and anti-inflammatory agents, to reduce MIRI is often ineffective due to the inadequate release at the pathological sites. Functional biomaterials are being developed to optimize the use of drugs by improving their targetability and bioavailability and reducing side effects, such as gastrointestinal irritation, thrombocytopenia, and liver damage. This review provides an overview of controlled drug delivery biomaterials for treating MIRI by triggering antioxidation, calcium ion overload inhibition, and/or inflammation regulation mechanisms and discusses the challenges and potential applications of these treatments clinically.

Robust therapeutic effects on COVID-19 of novel small molecules: Alleviation of SARS-CoV-2 S protein induction of ACE2/TMPRSS2, NOX2/ROS, and MCP-1

While new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) constantly emerge to prolong the pandemic of COVID-19, robust and safe therapeutics are in urgent need. During the previous and ongoing fight against the pandemic in China, Traditional Chinese Medicine (TCM) has proven to be markedly effective in treating COVID-19. Among active ingredients of TCM recipes, small molecules such as quercetin, glabridin, gallic acid, and chrysoeriol have been predicted to target viral receptor angiotensin-converting enzyme 2 (ACE2) via system pharmacology/molecular docking/visualization analyses. Of note, endothelial dysfunction induced by oxidative stress and inflammation represents a critical mediator of acute respiratory distress syndrome (ARDS) and multi-organ injuries in patients with COVID-19. Hence, in the present study, we examined whether quercetin, glabridin, gallic acide and chrysoeriol regulate viral receptors of ACE2 and transmembrane serine protease 2 (TMPRSS2), redox modulator NADPH oxidase isoform 2 (NOX2), and inflammatory protein of monocyte chemoattractant protein-1 (MCP-1) in endothelial cells to mediate therapeutic protection against COVID-19. Indeed, quercetin, glabridin, gallic acide and chrysoeriol completely attenuated SARS-CoV-2 spike protein (S protein)-induced upregulation in ACE2 protein expression in endothelial cells. In addition, these small molecules abolished S protein upregulation of cleaved/active form of TMPRSS2, while native TMPRSS2 was not significantly regulated. Moreover, these small molecules completely abrogated S protein-induced upregulation in NOX2 protein expression, which resulted in alleviated superoxide production, confirming their preventive efficacies against S protein-induced oxidative stress in endothelial cells. In addition, treatment with these small molecules abolished S protein induction of MCP-1 expression. Collectively, our findings for the first time demonstrate that these novel small molecules may be used as novel and robust therapeutic options for the treatment of patients with COVID-19, via effective attenuation of S protein induction of endothelial oxidative stress and inflammation.

Novel and robust treatment of pulmonary hypertension with netrin-1 and netrin-1-derived small peptides

Limited medical therapies have been implemented for the treatment of the devastating cardiorespiratory disease of pulmonary hypertension (PH) while none of which is sufficiently effective to stop or regress development of PH. We have previously shown that netrin-1, an axon-guiding protein during development, protects against ischemia reperfusion injury induced myocardial infarction via modest and stable production of nitric oxide (NO) and attenuation of oxidative stress. Since NO deficiency and oxidative stress-mediated vascular remodeling play important roles in the pathogenesis of PH, our present study investigated therapeutic effects on PH of netrin-1 and its derived small peptides. Infused into mice for 3 weeks during exposure to hypoxia, netrin-1 and netrin-1 derived small peptides V1, V2 or V3 substantially alleviated pathophysiological and molecular features of PH, as indicated by abrogated increases in mean pulmonary artery pressure (mPAP) and right ventricular systolic pressure (RVSP), attenuated right ventricular hypertrophy, diminished vascular remodeling of medial thickening and upregulation in smooth muscle alpha-actin (SMA) and proliferative cell nuclear antigen (PCNA), and alleviated perivascular and peribronchial fibrosis reflected by collagen deposition. NO bioavailability was substantially improved by treatment with netrin-1 and netrin-1 derived small peptides, while hypoxia induced increases in total superoxide production and eNOS uncoupling activity were all attenuated. These dual mechanisms of increasing NO bioavailability and decreasing oxidative stress at the same time, underlie robust protective effects on PH of netrin-1 and its derived small peptides, which are different from existing medications that primarily target NO signaling alone. Our data for the first time demonstrate intriguing findings that netrin-1 and netrin-1 derived small peptides can be used as novel and robust therapeutics for the treatment of PH.

Yin and Yang of NADPH Oxidases in Myocardial Ischemia-Reperfusion

Oxidative stress is critically involved in the pathophysiology of myocardial ischemic-reperfusion (I/R) injury. NADPH oxidase (Nox) 2 and 4, major sources of reactive oxygen species (ROS) in cardiomyocytes, are upregulated in response to I/R. Suppression of Nox-derived ROS prevents mitochondrial dysfunction and endoplasmic reticulum (ER) stress, leading to attenuation of myocardial I/R injury. However, minimal levels of ROS by either Nox2 or Nox4 are required for energy metabolism during I/R in the heart, preserving hypoxia-inducible factor-1α (HIF-1α) and peroxisome proliferator-activated receptor-α (PPARα) levels. Furthermore, extreme suppression of Nox activity induces reductive stress, leading to paradoxical increases in ROS levels. Nox4 has distinct roles in organelles such as mitochondria, ER, and ER-mitochondria contact sites (MAMs). Mitochondrial Nox4 exerts a detrimental effect, causing ROS-induced mitochondrial dysfunction during I/R, whereas Nox4 in the ER and MAMs is potentially protective against I/R injury through regulation of autophagy and MAM function, respectively. Although Nox isoforms are potential therapeutic targets for I/R injury, to maximize the effect of intervention, it is likely important to optimize the ROS level and selectively inhibit Nox4 in mitochondria. Here, we discuss the ‘Yin and Yang’ functions of Nox isoforms during myocardial I/R.

An Overview of the Molecular Mechanisms Associated with Myocardial Ischemic Injury: State of the Art and Translational Perspectives

Cardiovascular disease is the leading cause of death in western countries. Among cardiovascular diseases, myocardial infarction represents a life-threatening condition predisposing to the development of heart failure. In recent decades, much effort has been invested in studying the molecular mechanisms underlying the development and progression of ischemia/reperfusion (I/R) injury and post-ischemic cardiac remodeling. These mechanisms include metabolic alterations, ROS overproduction, inflammation, autophagy deregulation and mitochondrial dysfunction. This review article discusses the most recent evidence regarding the molecular basis of myocardial ischemic injury and the new potential therapeutic interventions for boosting cardioprotection and attenuating cardiac remodeling.

Upregulation of p67phox in response to ischemia/reperfusion is cardioprotective by increasing ZIP2 expression via STAT3

While the zinc transporter ZIP2 (Slc39a2) is upregulated via STAT3 as an adaptive response to protect the heart from ischemia/reperfusion (I/R) injury, the precise mechanism underlying its upregulation remains unclear. The purpose of this study was to investigate the role of NADPH oxidase (NOX) isoform NOX2-derived ROS in the regulation of ZIP2 expression, focusing on the role of the NOX2 cytosolic factor p67^phox. Mouse hearts or H9c2 cells were subjected to I/R. Protein expression was detected with Western blotting. Infarct size was measured with TTC staining. The cardiac-specific p67^phox conditional knockout mice (p67^phox cKO) were generated by adopting the CRISPR/Cas9 system. I/R-induced upregulation of STAT3 phosphorylation and ZIP2 expression was reversed by the ROS scavenger N-acetylcysteine (NAC) and the NOX inhibitor diphenyleneiodonium (DPI). p67^phox but not NOX2 expression was increased 30 min after the onset of reperfusion, and downregulation of p67^phox by siRNA or cKO invalidated I/R-induced upregulation of STAT3 phosphorylation and ZIP2 expression. Both NAC and DPI prevented upregulation of STAT3 phosphorylation and ZIP2 expression induced by overexpression of p67^phox, whereas the STAT3 inhibitor stattic abrogated upregulation ZIP2 expression, indicating that the increase of p67^phox at reperfusion is an upstream signaling event responsible for ZIP2 upregulation via STAT3. Experiments also showed that chelation of Zn²⁺ markedly enhanced p67^phox and ZIP2 expression as well as STAT3 phosphorylation, whereas supplementation of Zn²⁺ had the opposite effects, indicating that cardiac Zn²⁺ loss upon reperfusion triggers p67^phox upregulation. Furthermore, ischemic preconditioning (IPC) upregulated ZIP2 via p67^phox, and cKO of p67^phox aggravated cardiac injury after I/R, indicating that p67^phox upregulation is cardioprotective against I/R injury. In conclusion, an increase of p67^phox expression in response to Zn²⁺ is an intrinsic adaptive response to I/R and leads to cardioprotection against I/R by upregulating ZIP2 via STAT3.

Netrin-1: A Modulator of Macrophage Driven Acute and Chronic Inflammation

Netrins belong to the family of laminin-like secreted proteins, which guide axonal migration and neuronal growth in the developing central nervous system. Over the last 20 years, it has been established that netrin-1 acts as a chemoattractive or chemorepulsive cue in diverse biological processes far beyond neuronal development. Netrin-1 has been shown to play a central role in cell adhesion, cell migration, proliferation, and cell survival in neuronal and non-neuronal tissue. In this context, netrin-1 was found to orchestrate organogenesis, angiogenesis, tumorigenesis, and inflammation. In inflammation, as in neuronal development, netrin-1 plays a dichotomous role directing the migration of leukocytes, especially monocytes in the inflamed tissue. Monocyte-derived macrophages have long been known for a similar dual role in inflammation. In response to pathogen-induced acute injury, monocytes are rapidly recruited to damaged tissue as the first line of immune defense to phagocyte pathogens, present antigens to initiate the adaptive immune response, and promote wound healing in the resolution phase. On the other hand, dysregulated macrophages with impaired phagocytosis and egress capacity accumulate in chronic inflammation sites and foster the maintenance-and even the progression-of chronic inflammation. In this review article, we will highlight the dichotomous roles of netrin-1 and its impact on acute and chronic inflammation.

Nitric Oxide as a Central Molecule in Hypertension: Focus on the Vasorelaxant Activity of New Nitric Oxide Donors

Cardiovascular diseases include all types of disorders related to the heart or blood vessels. High blood pressure is an important risk factor for cardiac complications and pathological disorders. An increase in circulating angiotensin-II is a potent stimulus for the expression of reactive oxygen species and pro-inflammatory cytokines that activate oxidative stress, perpetuating a deleterious effect in hypertension. Studies demonstrate the capacity of NO to prevent platelet or leukocyte activation and adhesion and inhibition of proliferation, as well as to modulate inflammatory or anti-inflammatory reactions and migration of vascular smooth muscle cells. However, in conditions of low availability of NO, such as during hypertension, these processes are impaired. Currently, there is great interest in the development of compounds capable of releasing NO in a modulated and stable way. Accordingly, compounds containing metal ions coupled to NO are being investigated and are widely recognized as having great relevance in the treatment of different diseases. Therefore, the exogenous administration of NO is an attractive and pharmacological alternative in the study and treatment of hypertension. The present review summarizes the role of nitric oxide in hypertension, focusing on the role of new NO donors, particularly the metal-based drugs and their protagonist activity in vascular function.

Reactive oxygen species-based nanomaterials for the treatment of myocardial ischemia reperfusion injuries

Interventional coronary reperfusion strategies are widely adopted to treat acute myocardial infarction, but morbidity and mortality of acute myocardial infarction are still high. Reperfusion injuries are inevitable due to the generation of reactive oxygen species (ROS) and apoptosis of cardiac muscle cells. However, many antioxidant and anti-inflammatory drugs are largely limited by pharmacokinetics and route of administration, such as short half-life, low stability, low bioavailability, and side effects for treatment myocardial ischemia reperfusion injury. Therefore, it is necessary to develop effective drugs and technologies to address this issue. Fortunately, nanotherapies have demonstrated great opportunities for treating myocardial ischemia reperfusion injury. Compared with traditional drugs, nanodrugs can effectively increase the therapeutic effect and reduces side effects by improving pharmacokinetic and pharmacodynamic properties due to nanodrugs’ size, shape, and material characteristics. In this review, the biology of ROS and molecular mechanisms of myocardial ischemia reperfusion injury are discussed. Furthermore, we summarized the applications of ROS-based nanoparticles, highlighting the latest achievements of nanotechnology researches for the treatment of myocardial ischemia reperfusion injury.

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Cardiovascular diseases are the leading cause of death worldwide. Researches of the myocardial infarction pathology and development of new treatments have very important scientific significance in the biomedical field.

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Many nanomaterials have shown amazing therapeutic effects to reduce myocardial damage by eliminating ROS.

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Nanomaterials effectively reduced myocardial damage through eliminating ROS from NOXs, M-ETC, M-Ca²⁺, M-mPTP, and RIRR.

Toll-Like Receptor 2 (TLR2) Knockout Abrogates Diabetic and Obese Phenotypes While Restoring Endothelial Function via Inhibition of NOX1

We have previously demonstrated a novel role of bone morphogenic protein 4 (BMP4) in inducing NOX1-dependent endothelial nitric oxide synthase (eNOS) uncoupling, endothelial dysfunction, and inflammatory activation in type 2 diabetes mellitus (T2DM). However, how BMP4 activates NOX1 and whether targeting the new mechanistic pathway revealed is effective in preserving endothelial function in T2DM remains unclear. In this study, we observed that BMP4 induced a marked, time-dependent increase in physiological binding between TLR2 and NOX1 in aortic endothelial cells as well as increased binding of TLR2 to NOXO1. In TLR2 knockout (Tlr2 ^-/-) mice fed high-fat diet, body weight gain was significantly less compared with wild-type (WT) mice both in males and females. The high-fat diet-induced increases in fasting blood glucose levels, as well as in circulating insulin and leptin levels, were absent in Tlr2 ^-/- mice. High-fat feeding induced increases in overall fat mass, and in fat mass of different pockets were abrogated in Tlr2 ^-/- mice. Whereas energy intake was similar in high-fat-fed WT and Tlr2 ^-/- mice, TLR2 deficiency resulted in higher energy expenditure attributable to improved physical activity, which was accompanied by restored skeletal muscle mitochondrial function. In addition, TLR2 deficiency recoupled eNOS, reduced total superoxide production, improved H₄B and NO bioavailabilities in aortas, and restored endothelium-dependent vasorelaxation. Collectively, our data strongly indicate that TLR2 plays important roles in the development of metabolic features of T2DM and its related endothelial/vascular dysfunction. Therefore, targeting TLR2 may represent a novel therapeutic strategy for T2DM, obesity, and cardiovascular complications via specific inhibition of NOX1.

PMN-derived netrin-1 attenuates cardiac ischemia-reperfusion injury via myeloid ADORA2B signaling

Previous studies implicated the neuronal guidance molecule netrin-1 in attenuating myocardial ischemia-reperfusion injury. However, the tissue-specific sources and receptor signaling events remain elusive. Neutrophils are among the first cells responding to an ischemic insult and can be associated with tissue injury or rescue. We found netrin-1 levels were elevated in the blood of patients with myocardial infarction, as well as in mice exposed to myocardial ischemia-reperfusion. Selectively increased infarct sizes and troponin levels were found in Ntn1loxP/loxP Lyz2 Cre+ mice, but not in mice with conditional netrin-1 deletion in other tissue compartments. In vivo studies using neutrophil depletion identified neutrophils as the main source for elevated blood netrin-1 during myocardial injury. Finally, pharmacologic studies using treatment with recombinant netrin-1 revealed a functional role for purinergic signaling events through the myeloid adenosine A2b receptor in mediating netrin-1-elicited cardioprotection. These findings suggest an autocrine signaling loop with a functional role for neutrophil-derived netrin-1 in attenuating myocardial ischemia-reperfusion injury through myeloid adenosine A2b signaling.

Neuronal guidance proteins in cardiovascular inflammation

Cardiovascular pathologies are often induced by inflammation. The associated changes in the inflammatory response influence vascular endothelial biology; they complicate the extent of ischaemia and reperfusion injury, direct the migration of immune competent cells and activate platelets. The initiation and progression of inflammation is regulated by the classical paradigm through the system of cytokines and chemokines. Therapeutic approaches have previously used this knowledge to control the extent of cardiovascular changes with varying degrees of success. Neuronal guidance proteins (NGPs) have emerged in recent years and have been shown to be significantly involved in the control of tissue inflammation and the mechanisms of immune cell activation. Therefore, proteins of this class might be used in the future as targets to control the extent of inflammation in the cardiovascular system. In this review, we describe the role of NGPs during cardiovascular inflammation and highlight potential therapeutic options that could be explored in the future.

Targeting feed-forward signaling of TGFβ/NOX4/DHFR/eNOS uncoupling/TGFβ axis with anti-TGFβ and folic acid attenuates formation of aortic aneurysms: Novel mechanisms and therapeutics

In the present study we aimed to identify novel mechanisms and therapeutics for thoracic aortic aneurysm (TAA) in Fbn1^C1039G/+ Marfan Syndrome (MFS) mice. The expression of mature/active TGFβ and its downstream effector NOX4 were upregulated while tetrahydrobiopterin (H₄B) salvage enzyme dihydrofolate reductase (DHFR) was downregulated in Fbn1^C1039G/+ mice. In vivo treatment with anti-TGFβ completely attenuated NOX4 expression, restored DHFR protein abundance, reduced ROS production, recoupled eNOS and attenuated aneurysm formation. Intriguingly, oral administration with folic acid (FA) to recouple eNOS markedly alleviated expansion of aortic roots and abdominal aortas in Fbn1^C1039G/+ mice, which was attributed to substantially upregulated DHFR expression and activity in the endothelium to restore tissue and circulating levels of H₄B. Notably, circulating H₄B levels were accurately predictive of tissue H₄B bioavailability, and negatively associated with expansion of aortic roots, indicating a novel biomarker role of circulating H₄B for TAA. Furthermore, FA diet abrogated TGFβ and NOX4 expression, disrupting the feed-forward loop to inactivate TGFβ/NOX4/DHFR/eNOS uncoupling axis in vivo and in vitro, while PTIO, a NO scavenger, reversed this effect in cultured human aortic endothelial cells (HAECs). Besides, expression of the rate limiting H₄B synthetic enzyme GTP cyclohydrolase 1 (GTPCHI), was downregulated in Fbn1^C1039G/+ mice at baseline. In cultured HAECs, RNAi inhibition of fibrillin resulted in reduced GTPCHI expression, while this response was abrogated by anti-TGFβ, indicating TGFβ-dependent downregulation of GTPCHI in response to fibrillin deficiency. Taken together, our data for the first time reveal that uncoupled eNOS plays a central role in TAA formation, while anti-TGFβ and FA diet robustly abolish aneurysm formation via inactivation of a novel TGFβ/NOX4/DHFR/eNOS uncoupling/TGFβ feed-forward pathway. Correction of fibrillin deficiency is additionally beneficial via preservation of GTPCHI function.

Carnosic acid protects against pressure overload-induced cardiac remodelling by inhibiting the AKT/GSK3β/NOX4 signalling pathway

Oxidative stress and apoptosis serve an important role in the development of pressure overload-induced cardiac remodelling. Carnosic acid (CA) has been found to exert antioxidant and anti-apoptotic effects. The present study investigated the underlying mechanism of CA protection and whether this effect was exerted against pressure overload-induced cardiac remodelling. Aortic banding (AB) surgery was performed to induce cardiac remodelling. Mice were randomly divided into four groups (n=15/group): i) Sham + vehicle; ii) sham + CA; iii) AB + vehicle; and iv) AB + CA. After 2 days of AB, 50 mg kg CA was administered orally for 12 days. Echocardiography, histological analysis and molecular biochemistry techniques were performed to evaluate the roles of CA. CA treatment decreased cardiac hypertrophy, fibrosis, oxidative stress and apoptosis in mice challenged with pressure overload. CA also decreased the cross-sectional area of cardiomyocytes and the mRNA and protein expression levels of hypertrophic markers. Furthermore, CA treatment decreased collagen deposition, α-smooth muscle actin expression and the mRNA and protein expression of various fibrotic markers. Additionally, CA reversed the AB-mediated increase in NAPDH oxidase (NOX) 2, NOX4 and 4-hydroxynonenal levels. The number of apoptotic cells was decreased following CA treatment following under conditions of pressure overload. CA also suppressed the activation of AKT and glycogen synthase kinase 3 β (GSK3β) in mice challenged with AB. The present results suggested that CA could inhibit pressure overload-induced cardiac hypertrophy and fibrosis by suppressing the AKT/GSK3β/NOX4 signalling pathway. Therefore, CA may be a promising therapy for cardiac remodelling.

Arginine and Endothelial Function

Arginine (L-arginine), is an amino acid involved in a number of biological processes, including the biosynthesis of proteins, host immune response, urea cycle, and nitric oxide production. In this systematic review, we focus on the functional role of arginine in the regulation of endothelial function and vascular tone. Both clinical and preclinical studies are examined, analyzing the effects of arginine supplementation in hypertension, ischemic heart disease, aging, peripheral artery disease, and diabetes mellitus.

Suppression of Netrin-1 attenuates angiotension II-induced cardiac remodeling through the PKC/MAPK signaling pathway

BACKGROUND

Myocardial remodeling caused by angiotensin II (Ang II) is essential for the pathological process of heart failure. Netrin-1, which is an axonal guidance cue, has been shown to be involved in the inflammatory response, tumorigenesis, and angiogenesis in non-neuronal tissues. However, the role of Netrin-1 in cardiac remodeling has not been fully elucidated.

METHODS

The rat cardiomyocyte cell line H9c2 and primary neonatal rat cardiomyocytes were treated with Ang II. Cells were transfected with siRNA to silence Netrin-1 expression. Real-time polymerase chain reaction and Western blot analysis were used to detect the markers for fibrosis, apoptosis, and hypertrophy in cardiomyocytes. An Annexin V-EGFP/PI cell apoptosis detection kit was used to measure the level of apoptosis caused by angiotensin II.

RESULTS

We found that Netrin-1 expression was upregulated in the H9c2 cells and the neonatal rat cardiomyocytes stimulated by Ang II. The increased Netrin-1 expression was decreased by valsartan to block AT1R. Importantly, the application of Netrin-1 siRNA significantly alleviated the degrees of myocardial hypertrophy, fibrosis (reflected by Myhc, collagen I, and TGF-β) and apoptosis (reflected by the level of Caspase 3, Bax, and Bcl-2) induced by Ang II. In addition, the silencing of Netrin-1 substantially decreased the phosphorylation of PKCα, JNK, and P38. We treated H9c2 cells with LY317615, SP600125, and SB203580, inhibitors of PKCα, JNK, and P38, respectively, thereby resulting in a substantial decrease in hypertrophy, fibrosis, and apoptosis.

CONCLUSIONS

Ang II produces cardiac hypertrophy, fibrosis, and apoptosis through the upregulation of Netrin-1 and the activation of the AT1R/PKCα/MAPK (JNK, P38) pathway. Suppression of Netrin-1 can relieve Ang II-induced cardiac remodeling via inhibition of the PKCα/MAPK (JNK and P38) signaling pathway. Thus, Netrin-1 may be a novel therapeutic target for Ang II-mediated cardiac remodeling.

Targeting NOX4 alleviates sepsis-induced acute lung injury via attenuation of redox-sensitive activation of CaMKII/ERK1/2/MLCK and endothelial cell barrier dysfunction

Increased pulmonary vascular permeability due to endothelial cell (EC) barrier dysfunction is a major pathological feature of acute respiratory distress syndrome/acute lung injury (ARDS/ALI), which is a devastating critical illness with high incidence and excessive mortality. Activation of NADPH oxidase (NOX) induces EC dysfunction via production of reactive oxygen species (ROS). However, the role(s) of NOX isoform(s), and their downstream signaling events, in the development of ARDS/ALI have remained unclear. Cecal Ligation Puncture (CLP) was used to induce preclinical septic ALI in wild-type mice and mice deficient in NOX2 or p47phox, or mice transfected of control siRNA, NOX1 or NOX4 siRNA in vivo. The survival rate of the CLP group at 24 h (26.6%, control siRNA treated) was substantially improved by NOX4 knockdown (52.9%). Mice lacking NOX2 or p47phox, however, had worse outcomes after CLP (survival rates at 0% and 8.3% respectively), whereas NOX1-silenced mice had similar survival rate (30%). NOX4 knockdown attenuated lung ROS production in septic mice, whereas NOX1 knockdown, NOX2 knockout, or p47phox knockout in mice had no effects. In addition, NOX4 knockdown attenuated redox-sensitive activation of the CaMKII/ERK1/2/MLCK pathway, and restored expression of EC tight junction proteins ZO-1 and Occludin to maintain EC barrier integrity. Correspondingly, NOX4 knockdown in cultured human lung microvascular ECs also reduced LPS-induced ROS production, CaMKII/ERK1/2/MLCK activation and EC barrier dysfunction. Scavenging superoxide in vitro and in vivo with TEMPO, or inhibiting CaMKII activation with KN93, had similar effects as NOX4 knockdown in preserving EC barrier dysfunction. In summary, we have identified a novel, selective and causal role of NOX4 (versus other NOX isoforms) in inducing lung EC barrier dysfunction and injury/mortality in a preclinical CLP-induced septic model, which involves redox-sensitive activation of CaMKII/ERK1/2/MLCK pathway. Targeting NOX4 may therefore prove to an innovative therapeutic option that is markedly effective in treating ALI/ARDS.

The identification and function of a Netrin-1 mutation in a pedigree with premature atherosclerosis

BACKGROUND AND AIMS

Neuroimmune guidance cues have been shown to play a role in atherosclerosis, but their exact role in human pathophysiology is largely unknown. In the current study, we investigated the role of a c.1769G > T variant in Netrin-1 in (premature) atherosclerosis.

METHODS

To determine the effect of the genetic variation, purified Netrin-1, either wild type (wtNetrin-1) or the patient observed variation (mutNetrin-1), was used for migration, adhesion, endothelial barrier function and bindings assays. Expression of adhesion molecules and transcription proteins was analyzed by RT-PCR, Western blot or ELISA. To further delineate how mutNetrin-1 mediates its effect on cell migration, lenti-viral knockdown of UNC5B or DCC was used.

RESULTS

Bindings assays revealed a decreased binding capacity of mutNetrin-1 to the receptors UNC5B, DCC and β3-integrin and an increased binding capacity to neogenin, heparin and heparan sulfate compared to wtNetrin-1. Exposure of endothelial cells to mutNetrin-1 resulted in enhanced monocyte adhesion and expression of IL-6, CCL2 and ICAM-1 compared to wtNetrin-1. In addition, mutNetrin-1 lacks the inhibitory effect on the NF-κB pathway that is observed for wtNetrin-1. Moreover, the presence of mutNetrin-1 diminished migration of macrophages and smooth muscle cells. Importantly, UNC5B or DCC specific knockdown showed that mutNetrin-1 is unable to act through DCC resulting in enhanced inhibition of migration.

CONCLUSIONS

Our data demonstrates that mutNetrin-1 fails to exert anti-inflammatory effects on endothelial cells and more strongly blocks macrophage migration compared to wtNetrin-1, suggesting that the carriers of this genetic molecular variant may well be at risk for premature atherosclerosis.

NADPH oxidases and oxidase crosstalk in cardiovascular diseases: novel therapeutic targets

Reactive oxygen species (ROS)-dependent production of ROS underlies sustained oxidative stress, which has been implicated in the pathogenesis of cardiovascular diseases such as hypertension, aortic aneurysm, hypercholesterolaemia, atherosclerosis, diabetic vascular complications, cardiac ischaemia-reperfusion injury, myocardial infarction, heart failure and cardiac arrhythmias. Interactions between different oxidases or oxidase systems have been intensively investigated for their roles in inducing sustained oxidative stress. In this Review, we discuss the latest data on the pathobiology of each oxidase component, the complex crosstalk between different oxidase components and the consequences of this crosstalk in mediating cardiovascular disease processes, focusing on the central role of particular NADPH oxidase (NOX) isoforms that are activated in specific cardiovascular diseases. An improved understanding of these mechanisms might facilitate the development of novel therapeutic agents targeting these oxidase systems and their interactions, which could be effective in the prevention and treatment of cardiovascular disorders.

Knockout of dihydrofolate reductase in mice induces hypertension and abdominal aortic aneurysm via mitochondrial dysfunction

Hypertension and abdominal aortic aneurysm (AAA) are severe cardiovascular diseases with incompletely defined molecular mechanisms. In the current study we generated dihydrofolate reductase (DHFR) knockout mice for the first time to examine its potential contribution to the development of hypertension and AAA, as well as the underlying molecular mechanisms. Whereas the homozygote knockout mice were embryonically lethal, the heterozygote knockout mice had global reduction in DHFR protein expression and activity. Angiotensin II infusion into these animals resulted in substantially exaggerated elevation in blood pressure and development of AAA, which was accompanied by excessive eNOS uncoupling activity (featured by significantly impaired tetrahydrobiopterin and nitric oxide bioavailability), vascular remodeling (MMP2 activation, medial elastin breakdown and adventitial fibrosis) and inflammation (macrophage infiltration). Importantly, scavenging of mitochondrial reactive oxygen species with Mito-Tempo in vivo completely abrogated development of hypertension and AAA in DHFR knockout mice, indicating a novel role of mitochondria in mediating hypertension and AAA downstream of DHFR deficiency-dependent eNOS uncoupling. These data for the first time demonstrate that targeting DHFR-deficiency driven mitochondrial dysfunction may represent an innovative therapeutic option for the treatment of AAA and hypertension.

Netrin-1 prevents the attachment of monocytes to endothelial cells via an anti-inflammatory effect

Netrin-1 is best known for its function guiding axon growth and migration. Netrin-1 has been shown to be involved in regulating cardiovascular function. In this study, we aimed to understand the biological role of Netrin-1 and its receptor Unc5b in endothelial cells. Our results demonstrate that Unc5b was moderately expressed in human aortic endothelial cells (HAECs) and TNF-α had a dose-dependent inhibitory effect on Unc5b level. Netrin-1 potently suppressed TNF-α-induced vascular adhesion molecules VCAM-1, ICAM-1, E-selectin and blocked the adhesion of monocytes to endothelial cells. Netrin-1 also suppressed TNF-α-induced production of cytokines including MCP-1, IL-1β, and IL-6. Importantly, Netrin-1 suppressed toll like receptor 4 (TLR4) expression and prevented NF-κB activation. Mechanistically, Netrin-1 reduced TNF-α-induced IKK and IκBα activation and prevented degradation of IκBα. Netrin-1 reduced nuclear accumulation of p65 and strongly suppressed NF-κB promoter activation. Collectively, our data demonstrated that signaling of Netrin-1 and its receptor Unc5b had an anti-inflammatory effect in endothelial cells. Netrin-1 signaling could be imperative for normal endothelial function.

USP49 inhibits ischemia-reperfusion-induced cell viability suppression and apoptosis in human AC16 cardiomyocytes through DUSP1-JNK1/2 signaling

Dual-specificity protein phosphatases (DUSP) also known as mitogen-activated protein kinase (MAPK) phosphatases (MKPs) can dephosphorylate MAPKs, including extracellular signal-regulated kinase, c-Jun N-terminal kinase (JNK), and p38. DUSP1-mediated JNK dephosphorylation has been found to play an antiapoptotic role against cardiac ischemia-reperfusion (I/R) injury. However, the regulation of DUSP1-JNK pathway remains unclear. In the current study, ubiquitin-specific peptidase 49 (USP49) expression in human AC16 cardiomyocytes following I/R injury was measured by real-time polymerase chain reaction and western blot analysis. Cell viability, apoptosis, the Bax, Bcl-2, and DUSP1 expression, and the activity of MAPKs in AC16 cardiomyocytes following indicated treatment was measured by CCK-8, flow cytometry, and western blot analysis. The direct interaction between USP49 and DUSP1 was measured by coimmunoprecipitation and ubiquitination analysis. The effect of USP49 on apoptosis and JNK activity in rat cardiomyocytes following I/R injury was also measured by TUNEL and western blot analysis. Here, we found that USP49 expression was time-dependently increased in AC16 cardiomyocytes following I/R. I/R-induced cell apoptosis and JNK1/2 activation both in in vivo and in vitro reversed by USP49 overexpression in AC16 cardiomyocytes. Inhibiting JNK1/2 activation significantly inhibited USP49 knockdown-induced the cell viability inhibition, apoptosis and the JNK1/2 activation in AC16 cardiomyocytes. Moreover, USP49 positively regulated DUSP1 expression through deubiquitinating DUSP1. Overall, our findings establish USP49 as a novel regulator of DUSP1-JNK1/2 signaling pathway with a protective role in cardiac I/R injury.

Understanding netrins and semaphorins in mature endothelial cell biology

Netrins and semaphorins are known as neuronal guidance molecules that are important to the facilitate patterning of the nervous system in embryonic development. In recent years, their function has been broadened to guide development in other systems, including the vascular system, where netrins and semaphorins critically contribute to the development of the vascular system. Evidence is accumulating that these guidance cues are also of critical importance in the biology of the mature endothelium by regulating the maintenance of endothelial quiescence. Here we review our current insights into the roles of netrins and semaphorins in endothelial cell survival, self-renewing, barrier function, response to wall shear stress, and control of the vascular tone. We also provide suggestions for future research into the functions of netrins and semaphorins in mature endothelial cell biology.

New and revisited approaches to preserving the reperfused myocardium

Early coronary artery reperfusion improves outcomes for patients with ST-segment elevation myocardial infarction (STEMI), but morbidity and mortality after STEMI remain unacceptably high. The primary deficits seen in these patients include inadequate pump function, owing to rapid infarction of muscle in the first few hours of treatment, and adverse remodelling of the heart in the months that follow. Given that attempts to further reduce myocardial infarct size beyond early reperfusion in clinical trials have so far been disappointing, effective therapies are still needed to protect the reperfused myocardium. In this Review, we discuss several approaches to preserving the reperfused heart, such as therapies that target the mechanisms involved in mitochondrial bioenergetics, pyroptosis, and autophagy, as well as treatments that harness the cardioprotective properties of inhaled anaesthetic agents. We also discuss potential therapies focused on correcting the no-reflow phenomenon and its effect on healing and adverse left ventricular remodelling.

Netrin-1 is a novel regulator of vascular endothelial function in diabetes

BACKGROUND

Netrin-1, a secreted laminin-like protein identified as an axon guidance molecule, has been shown to be of critical importance in the cardiovascular system. Recent studies have revealed pro-angiogenic, anti-apoptotic and anti-inflammatory properties of netrin-1 as well as cardioprotective actions against myocardial injury in diabetic mice.

AIM

To examine the role of netrin-1 in diabetes-and high glucose (HG)-induced vascular endothelial dysfunction (VED) using netrin-1 transgenic mice (Tg3) and cultured bovine aortic endothelial cells (BAEC).

MAIN OUTCOME

Overexpression of netrin-1 prevented diabetes-induced VED in aorta from diabetic mice and netrin-1 treatment attenuated HG-induced impairment of nitric oxide synthase (NOS) function in BAECs.

METHODS AND RESULTS

Experiments were performed in Tg3 and littermate control (WT) mice rendered diabetic with streptozotocin (STZ) and in BAECs treated with HG (25 mmol/L). Levels of netrin-1 and its receptor DCC, markers of inflammation and apoptosis and vascular function were assessed in aortas from diabetic and non-diabetic Tg3 and WT mice. Vascular netrin-1 in WT mice was reduced under diabetic conditions. Aortas from non-diabetic Tg3 and WT mice showed similar maximum endothelium-dependent relaxation (MEDR) (83% and 87%, respectively). MEDR was markedly impaired in aorta from diabetic WT mice (51%). This effect was significantly blunted in Tg3 diabetic aortas (70%). Improved vascular relaxation in Tg3 diabetic mice was associated with increased levels of phospho-ERK1/2 and reduced levels of oxidant stress, NFκB, COX-2, p16INK4A, cleaved caspase-3 and p16 and p53 mRNA. Netrin-1 treatment prevented the HG-induced decrease in NO production and elevation of oxidative stress and apoptosis in BAECs.

CONCLUSIONS

Diabetes decreases aortic levels of netrin-1. However, overexpression of netrin-1 attenuates diabetes-induced VED and limits the reduction of NO levels, while increasing expression of p-ERK1/2, and suppressing oxidative stress and inflammatory and apoptotic processes. Enhancement of netrin-1 function may be a useful therapeutic means for preventing vascular dysfunction in diabetes.

Reperfusion therapy-What's with the obstructed, leaky and broken capillaries?

Microvascular dysfunction is well established as an early and rate-determining factor in the injury response of tissues to ischemia and reperfusion (I/R). Severe endothelial cell dysfunction, which can develop without obvious morphological cell injury, is a major underlying cause of the microvascular abnormalities that accompany I/R. While I/R-induced microvascular dysfunction is manifested in different ways, two responses that have received much attention in both the experimental and clinical setting are impaired capillary perfusion (no-reflow) and endothelial barrier failure with a transition to hemorrhage. These responses are emerging as potentially important determinants of the severity of the tissue injury response, and there is growing clinical evidence that they are predictive of clinical outcome following reperfusion therapy. This review provides a summary of animal studies that have focused on the mechanisms that may underlie the genesis of no-reflow and hemorrhage following reperfusion of ischemic tissues, and addresses the clinical evidence that implicates these vascular events in the responses of the ischemic brain (stroke) and heart (myocardial infarction) to reperfusion therapy. Inasmuch as reactive oxygen species (ROS) and matrix metalloproteinases (MMP) are frequently invoked as triggers of the microvascular dysfunction elicited by I/R, the potential roles and sources of these mediators are also discussed. The available evidence in the literature justifies the increased interest in the development of no-reflow and hemorrhage in heart and brain following reperfusion therapy, and suggests that these vascular events may be predictive of poor clinical outcome and warrant the development of targeted treatment strategies.

Dual character of flavonoids in attenuating and aggravating ischemia-reperfusion-induced myocardial injury

The concept that flavonoids exert cardioprotection against myocardial ischemia-reperfusion (I/R) injury has been acknowledged by a large body of evidence. However, recent studies reported cardiotoxic effects of certain flavonoids, while the underlying mechanisms have remained largely elusive. Flavonoids have been demonstrated to activate aryl hydrocarbon receptor (Ahr), which is implicated in an array of cell signaling processes. The present study examined the cardioprotective roles of quercetin (Qu) and β-naphthoflavone (β-NF) against I/R injury and explored whether the underlying mechanism proceeds via molecular signaling downstream of Ahr. An oxygen glucose deprivation/reoxygenation (OGD/R) model of I/R was established in myocardial H9c2 cells in the absence or presence of Qu or β-NF. Qu as well as β-NF reversed OGD/R-induced overproduction of reactive oxygen species by increasing the anti-oxidative capacity of the cells and protected them from lethal injury, as demonstrated by a decreased cell death rate, lactate hydrogenase leakage and caspase-3 activity as determined by flow cytometry, colorimetric assay and western blot analysis, respectively. Immunocytochemistry, co-immunoprecipitation and western blot assays collectively revealed that Qu and β-NF engendered the translocation of Ahr from the cytoplasm into the cell nucleus, where binding of Ahr with the Ahr nuclear translocator (ARNT) blocked its binding to hypoxia-inducible factor (HIF)-1α, which inhibited the cardioprotection of HIF-1α, including the induction of nitric oxide (NO) and inhibition of vascular endothelial growth factor (VEGF) production. Ahr knockdown recovered the binding of ARNT to HIF-1α and the generation of NO and VEGF. The results of the present study suggested a dual character of Qu and β-NF in the process of myocardial I/R.

Graphical review: The redox dark side of e-cigarettes; exposure to oxidants and public health concerns

Since the initial marketing in 2005, the use of e-cigarettes has increased exponentially. Nonetheless, accumulating evidence has demonstrated the ineffectiveness of e-cigarettes in leading to smoking cessation, and decreasing the adverse health impacts of cigarette smoking. The number of adolescents adapted to e-cigarettes has been increasing substantially each year, and this adaptation has promoted openness to tobacco smoking. The present review discusses controversies regarding the smoking cessation effects of e-cigarettes, recent governmental policies and regulations of e-cigarette use, toxic components and vaporization products of e-cigarettes, and the novel molecular mechanisms underlying the adverse health impacts of e-cigarettes leading to oxidative stress in target tissues, and consequent development of cardiopulmonary diseases (i.e. COPD), neurodegenerative disorders (i.e. Alzheimer's' disease), and cancer. Health warning signs on the packaging and professional consultation to avoid adaptation in risk groups might be helpful solutions to control negative impacts of e-cigarettes. It is also recommended to further expand basic and clinical investigations to reveal more detailed oxidative stress mechanisms of e-cigarette induced damages, which would ultimately result in more effective protective strategies.

Netrin-1 restores cell injury and impaired angiogenesis in vascular endothelial cells upon high glucose by PI3K/AKT-eNOS

Diabetic foot ulceration (DFU) represents a common vascular complication of diabetes mellitus (DM) with high morbidity and disability resulting from amputation. Netrin-1 level was decreased in type 2 DM patients and has been identified as a protective regulator against diabetes-triggered myocardial infarction and nephropathy. Unfortunately, its role and molecular mechanism in DFU remain poorly elucidated. Here, netrin-1 levels were reduced in DM and DFU patients relative to healthy controls, with netrin-1 levels being the lowest in DFU patients. Moreover, exposure to high glucose (HG) also suppressed netrin-1 expression in human umbilical vein endothelial cells (HUVECs). Elevated netrin-1 expression by infection with Ad-netrin-1 adenovirus vector protected against HUVEC injury in response to HG by ameliorating the inhibitory effects on cell viability, lactate dehydrogenase (LDH) and malondialdehyde (MDA) levels, cell apoptotic rate and caspase-3 activity. Importantly, HG-impaired angiogenesis was improved after netrin-1 overexpression by elevating cell migration, capillary-like tube formation and VEGF production. Mechanism assay substantiated that netrin-1 elevation increased the phosphorylation levels of AKT and eNOS, and NO production, which was notably suppressed by HG, indicating that netrin-1 overexpression restored HG-triggered impairment of the PI3K/AKT-eNOS pathway. More intriguingly, preconditioning with LY294002 (PI3K/AKT antagonist) or N^G-monomethyl-l-arginine (eNOS inhibitor) antagonized netrin-1-induced activation of the PI3K/AKT-eNOS pathway. Concomitantly, treatment with these antagonists also attenuated the protective role of netrin-1 in endothelial dysfunction upon HG stimulation. These results suggest that elevation of netrin-1 may restore HG-triggered impairment of HUVEC and angiogenesis by activating the PI3K/AKT-eNOS pathway, indicating a potential agent for wound healing in DFU patients.

NOX isoforms in the development of abdominal aortic aneurysm

Oxidative stress plays an important role in the formation of abdominal aortic aneurysm (AAA), and we have recently established a causal role of uncoupled eNOS in this severe human disease. We have also shown that activation of NADPH oxidase (NOX) lies upstream of uncoupled eNOS. Therefore, identification of the specific NOX isoforms that are required for eNOS uncoupling and AAA formation would ultimately lead to novel therapies for AAA. In the present study, we used the Ang II infused hph-1 mice to examine the roles of NOX isoforms in the development of AAA. We generated double mutants of hph-1-NOX1, hph-1-NOX2, hph-1-p47phox, and hph-1-NOX4. After two weeks of Ang II infusion, the incidence rate of AAA substantially dropped from 76.5% in Ang II infused hph-1 mice (n=34) to 11.1%, 15.0%, 9.5% and 0% in hph-1-NOX1 (n=27), hph-1-NOX2 (n=40), hph-1-p47phox (n=21), and hph-1-NOX4 (n=33) double mutant mice, respectively. The size of abdominal aortas of the four double mutant mice, determined by ultrasound analyses, was significantly smaller than the hph-1 mice. Aortic nitric oxide and H4B bioavailabilities were markedly improved in the double mutants, while superoxide production and eNOS uncoupling activity were substantially diminished. These effects seemed attributed to an endothelial specific restoration of dihydrofolate reductase expression and activity, deficiency of which has been shown to induce eNOS uncoupling and AAA formation in both Ang II-infused hph-1 and apoE null animals. In addition, over-expression of human NOX4 N129S or T555S mutant newly identified in aneurysm patients increased hydrogen peroxide production, further implicating a relationship between NOX and human aneurysm. Taken together, these data indicate that NOX isoforms 1, 2 or 4 lies upstream of dihydrofolate reductase deficiency and eNOS uncoupling to induce AAA formation. These findings may promote development of novel therapeutics for the treatment of the disease by inhibiting NOX signaling.

Ischemia/Reperfusion Injury following Acute Myocardial Infarction: A Critical Issue for Clinicians and Forensic Pathologists

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality. Reperfusion strategies are the current standard therapy for AMI. However, they may result in paradoxical cardiomyocyte dysfunction, known as ischemic reperfusion injury (IRI). Different forms of IRI are recognized, of which only the first two are reversible: reperfusion-induced arrhythmias, myocardial stunning, microvascular obstruction, and lethal myocardial reperfusion injury. Sudden death is the most common pattern for ischemia-induced lethal ventricular arrhythmias during AMI. The exact mechanisms of IRI are not fully known. Molecular, cellular, and tissue alterations such as cell death, inflammation, neurohumoral activation, and oxidative stress are considered to be of paramount importance in IRI. However, comprehension of the exact pathophysiological mechanisms remains a challenge for clinicians. Furthermore, myocardial IRI is a critical issue also for forensic pathologists since sudden death may occur despite timely reperfusion following AMI, that is one of the most frequently litigated areas of cardiology practice. In this paper we explore the literature regarding the pathophysiology of myocardial IRI, focusing on the possible role of the calpain system, oxidative-nitrosative stress, and matrix metalloproteinases and aiming to foster knowledge of IRI pathophysiology also in terms of medicolegal understanding of sudden deaths following AMI.

Prostaglandin E2 reduces swine myocardial ischemia reperfusion injury via increased endothelial nitric oxide synthase and vascular endothelial growth factor expression levels

Prostaglandin E2 (PGE₂) has been demonstrated to attenuate cardiac ischemia-reperfusion (I/R) injury. However, the underlying mechanism of PGE₂ in cardiac I/R injury remains unknown. Upregulated expression levels of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) were reported in acute myocardial infarction (AMI), and were demonstrated to diminish I/R injury. In the current study the involvement of VEGF and eNOS in the myocardial protective effect of PGE₂ were investigated in a catheter-based porcine model of AMI. Twenty-two Chinese miniature pigs were randomized into sham-surgery (n=6), control (n=8) and PGE₂ (n=8) groups. PGE₂ (1 µg/kg) was injected from 10 min prior to left anterior descending occlusion up to 1 h after reperfusion in the PGE₂ group. Subsequently, the hemodynamic parameters were evaluated. Thioflavin-S and Evans Blue double staining were performed to evaluate the extent of the myocardial reperfusion area (RA) and no-reflow area (NRA). Immunohistochemical and western blot analysis were used to evaluate protein expression levels of VEGF and eNOS. Left ventricular (LV) systolic pressure significantly improved and LV end-diastolic pressure significantly decreased in the PGE₂ group when compared with the control group 2 h after occlusion and 3 h after reperfusion (P<0.05, respectively). The RA and NRA were smaller in the PGE₂ group than in the control group (P<0.05, respectively). Furthermore, PGE₂ treatment increased the myocardial content of VEGF and eNOS when compared with the control group (P<0.05, respectively). Thus, the results of the present study demonstrate the cardio-protective mechanisms of PGE₂, which may protect the heart from I/R injury via enhancement of VEGF and eNOS expression levels.

Attenuation of neointimal formation with netrin-1 and netrin-1 preconditioned endothelial progenitor cells

Restenosis after angioplasty is a serious clinical problem that can result in re-occlusion of the coronary artery. Although current drug-eluting stents have proved to be more effective in reducing restenosis, they have drawbacks of inhibiting reendothelialization to promote thrombosis. New treatment options are in urgent need. We have shown that netrin-1, an axon-guiding protein, promotes angiogenesis and cardioprotection via production of nitric oxide (NO). The present study examined whether and how netrin-1 attenuates neointimal formation in a femoral wire injury model. Infusion of netrin-1 into C57BL/6 mice markedly attenuated neointimal formation following wire injury of femoral arteries, measured by intimal to media ratio (from 1.94 ± 0.55 to 0.45 ± 0.86 at 4 weeks). Proliferation of VSMC in situ was largely reduced. This protective effect was absent in DCC^+/- animals. NO production was increased by netrin-1 in both intact and injured femoral arteries, indicating netrin-1 stimulation of endogenous NO production from intact endothelium and remaining endothelial cells post-injury. VSMC migration was abrogated by netrin-1 via a NO/cGMP/p38 MAPK pathway, while timely EPC homing was induced. Injection of netrin-1 preconditioned wild-type EPCs, but not EPCs of DCC^+/- animals, substantially attenuated neointimal formation. EPC proliferation, NO production, and resistance to oxidative stress induced apoptosis were augmented by netrin-1 treatment. In conclusion, our data for the first time demonstrate that netrin-1 is highly effective in reducing neointimal formation following vascular endothelial injury, which is dependent on DCC, and attributed to inhibition of VSMC proliferation and migration, as well as improved EPC function. These data may support usage of netrin-1 and netrin-1 preconditioned EPCs as novel therapies for post angioplasty restenosis.

KEY MESSAGE

Netrin-1 attenuates neointimal formation following post endothelial injury via DCC and NO. Netrin-1 inhibits VSMC proliferation in situ following endothelial injury. Netrin-1 inhibits VSMC migration via a NO/cGMP/p38 MAPK pathway. Netrin-1 augments proliferation of endothelial progenitor cells (EPCs) and EPC eNOS/NO activation. Netrin-1 enhances resistance of EPCs to oxidative stress, improving re-endothelialization following injury.

Differential Roles of Protein Complexes NOX1-NOXO1 and NOX2-p47phox in Mediating Endothelial Redox Responses to Oscillatory and Unidirectional Laminar Shear Stress

The endothelium is exposed to various flow patterns such as vasoprotective unidirectional laminar shear stress (LSS) and atherogenic oscillatory shear stress (OSS). A software-controlled, valve-operated OsciFlow device with parallel chambers was used to apply LSS and OSS to endothelial cells. Although LSS inhibited superoxide over time, OSS time-dependently increased superoxide production from endothelial cells. Immunocytochemical staining revealed that, at resting state, p47phox colocalizes with NOX2, whereas NOXO1 colocalizes with NOX1. RNAi of p47phox had no effects on superoxide or NO production in response to OSS but significantly reduced NO production in LSS, implicating a p47phox-bound NADPH oxidase (NOX) in mediating basal NO production. Indeed, RNAi of p47phox inhibited endothelial nitric oxide synthase (eNOS) serine 1179 phosphorylation, whereas PEG-catalase scavenging of intracellular hydrogen peroxide or RNAi of NOX2 produced similar results, indicating a role of NOX2/p47phox-derived hydrogen peroxide in mediating the basal activity of NO production from eNOS. In contrast, RNAi of NOXO1 resulted in no significant changes in NO and superoxide levels in response to LSS but significantly reduced superoxide while increasing NO in response to OSS. Furthermore, we identified, for the first time, that OSS uncouples eNOS, which was corrected by RNAi of NOXO1. In summary, LSS activates the NOX2-p47phox complex to activate eNOS phosphorylation and NO production. OSS instead activates the NOX1-NOXO1 complex to uncouple eNOS. These results demonstrate differential roles of NOXs in modulating the redox state in response to different shear stresses, which may promote the development of novel therapeutic agents to mimic the protective effects of LSS while inhibiting the injurious effects of OSS.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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Netrin-1 as a novel therapeutic target in cardiovascular disease: to activate or inhibit?

Netrins are a family of laminin-like proteins, which were initially identified for their role in embryonic axonal guidance. Over recent years, it has become apparent that netrin-1 may additionally be involved in the underlying pathology of several multisystem diseases, making it an attractive potential therapeutic target. It is involved in postnatal angiogenesis, particularly in the context of an ischaemic insult, although there are conflicting reports as to whether netrin-1 acts in a pro- or anti-angiogenic capacity. In atherosclerosis, opposing effects have similarly been reported on plaque progression, due to the ability of netrin-1 to inhibit both macrophage egress from and monocyte ingress into lesions. Netrin-1 has also been shown to exert a cardioprotective action in the context of ischaemia-reperfusion injury following myocardial infarction. Moreover, urinary netrin-1 levels rise in response to acute kidney injury and at a faster rate than traditional markers of renal impairment, highlighting a potential clinical role for netrin-1 as a biomarker of renal function. The increased urinary excretion of netrin-1 during kidney disease is paralleled by a down-regulation of its plasma levels, with potential implications at a systemic level. In summary, the role of netrin-1 in cardiovascular disease is an emerging area of research requiring further in-depth study to elucidate its mechanism of action and potential as a therapeutic target, especially in view of its seemingly contradictory actions in certain physiological pathways which serve to highlight its manifold and often opposite effects in numerous physiological and pathophysiological processes.

Induction of cardioprotection by small netrin-1-derived peptides

We have shown that netrin-1 induces potent cardioprotection via extracellular signal-regulated kinases 1 and 2 (ERK1/2)-dependent endothelial nitric oxide synthase (eNOS)/NO activation. The present study investigated cardioprotective effects of small netrin-1-derived peptides. We synthesized three laminin (Lam) V peptides and found those time dependently increased phosphorylation of ERK1/2 and eNOSs1179 in endothelial cells at the same molar concentration used for netrin-1. Preperfusion with Lam V peptides induced a substantial reduction in infarct size (control 39.3 ± 0.2% vs. 14.6 ± 2.3%, 23.0 ± 2.8%, and 18.8 ± 0.8% for V1, V2, and V3, respectively). Furthermore, reperfusion with all three also induced potent cardioprotection (control 37.6 ± 1.3% vs. 17.6 ± 3.2%, 20.6 ± 1.7%, and 15.8 ± 2.0% for V1, V2, and V3, respectively), implicating that these peptides are consistently beneficial whenever they are delivered to the heart. Based on the sequence alignment, we found a region of high sequence homology and synthesized smaller peptides [V1-9 amino acid (aa), V2-10aa, and V3-11aa]. These smaller peptides markedly reduced infarct size during reperfusion (V1-9aa 16.8 ± 2.2%, V2-10aa 18.6 ± 1.7%, and V3-11aa 16.7 ± 3.0% vs. control 37.6 ± 1.3%). A negative control V3-16aa with no sequence homology failed to protect the heart. Of note, the core area has the characteristic sequence of: Cx(1-2)Cx(3-4)Tx(0-1)G. Furthermore, all three smaller peptides induced NO production in endothelial cells that could in turn diffuse to cardiomyocytes to promote survival. Combined applications of V1-9aa and V2-10aa synergistically induced more NO production. Taken together, these data strongly suggest that small netrin-1-derived peptides are highly effective in protecting the heart against myocardial ischemia-reperfusion injury and has the potential to be developed into peptide drugs directly applicable to the treatment of myocardial infarction.

Upstream regulators and downstream effectors of NADPH oxidases as novel therapeutic targets for diabetic kidney disease

Oxidative stress has been linked to the pathogenesis of diabetic nephropathy, the complication of diabetes in the kidney. NADPH oxidases of the Nox family, and in particular the homologue Nox4, are a major source of reactive oxygen species in the diabetic kidney and are critical mediators of redox signaling in glomerular and tubulointerstitial cells exposed to the diabetic milieu. Here, we present an overview of the current knowledge related to the understanding of the role of Nox enzymes in the processes that control mesangial cell, podocyte and tubulointerstitial cell injury induced by hyperglycemia and other predominant factors enhanced in the diabetic milieu, including the renin-angiotensin system and transforming growth factor-β. The nature of the upstream modulators of Nox enzymes as well as the downstream targets of the Nox NADPH oxidases implicated in the propagation of the redox processes that alter renal biology in diabetes will be highlighted.

Netrin-1 improves post-injury cardiac function in vivo via DCC/NO-dependent preservation of mitochondrial integrity, while attenuating autophagy

Reperfusion injury of the heart is a severe complication of angioplasty treatment of acute myocardial ischemia, for which no therapeutics are currently available. The present study aimed to identify whether and how a novel protein, netrin-1, induces cardioprotection in vivo during ischemia/reperfusion (I/R) injury. Wild type (WT) C57BL6/J mice were subjected to a 30 min coronary occlusion followed by a 24h reperfusion with vehicle (normal saline), netrin-1, UO126 (MEK1/2 inhibitor), PTIO (nitric oxide/NO scavenger), netrin-1/UO126 or netrin-1/PTIO intraventricularly. Some were injected of netrin-1 via tail vein. Netrin-1 at 5μg/kg induced a substantial reduction in infarct size (19.7 ± 5.0% from 41.3 ± 1.8% in the controls), and markedly improved cardiac function as measured by ejection fraction and fractional shortening from echocardiography. Experiments with mice deficient in netrin-1 receptor DCC (deleted in colorectal cancer, DCC+/-), or reperfusion with netrin-1/UO126 or netrin-1/PTIO, attenuated the protective effects of netrin-1, implicating intermediate roles of DCC, ERK1/2 and NO. Netrin-1 induced phosphorylation of ERK1/2 and eNOS was abolished in DCC+/-mice. Electron spin resonance (ESR) determination of NO production from isolated left ventricles demonstrated that netrin-1 improves NO bioavailability, which was attenuated by UO126 or in DCC+/-mice, suggesting upstream roles of DCC and ERK1/2 in NO production. Netrin-1 further reduced mitochondrial swelling and mitochondrial superoxide production, which was absent when co-treated with PTIO or UO126, or in DCC+/-mice, indicating critical roles of DCC, ERK1/2 and NO in preserving mitochondrial integrity. In a permanent coronary ligation model of myocardial infarction (MI) to assess post-MI remodeling, netrin-1 abolished the marked increase in autophagy. In summary, our data demonstrate robust cardioprotective effect of netrin-1 in vivo, as shown by reduced infarct size and improved cardiac function. Mechanistically, this protection is mediated by netrin-1 receptor DCC, and NO dependent preservation of mitochondria. This work clearly establishes a therapeutic potential of netrin-1 for acute treatment of MI, perhaps also for chronic post-MI remodeling. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Central role of SIAH inhibition in DCC-dependent cardioprotection provoked by netrin-1/NO

Deleted in colorectal cancer (DCC), a large transmembrane receptor of netrin-1, is critical for mediating netrin-1's cardioprotective function. In the present study we investigated novel mechanisms underlying netrin-1-induced, rapid, and feed-forward up-regulation of DCC, which is believed to sustain nitric oxide (NO) production to potentiate cardioprotection. Intriguingly, NO markedly reduced expression of the E3 ubiquitin ligase seven in absentia homolog (SIAH) that is specific for regulation of protesome-dependent DCC degradation, resulting in accumulation of DCC. The two SIAH isoforms compensate for each other when one is repressed; inhibition of both SIAH1 and SIAH2 using combined siRNAs significantly reduced infarct size while improving cardiac function after ischemia/reperfusion injury of the heart. This effect was absent in DCC-deficient mice. Moreover, in vivo RNAi inhibition of SIAH1/2 further augmented netrin-1's cardioprotective function. In summary, these data identify a novel therapeutic target of SIAH in facilitating NO/netrin-1-dependent cardioprotection, using the DCC receptor. Combination of netrin-1 and SIAH RNAi may prove to be a substantially effective therapy for myocardial infarction.

Solving mitochondrial mysteries

This is an exciting time in mitochondrial biology. The mitochondrion is finally beginning to reveal some of its long held secrets. The scientific community has started to identify at the molecular level some of the key channels and transporters that have been well studied biochemically, but which have escaped molecular identification. This special issue provides state-of-the art reviews and original articles on the mitochondrial permeability transition pore (mPTP), regulation of mitochondrial calcium homeostasis and regulation of mitochondrial dynamics.

The neuroimmune guidance cue netrin-1: a new therapeutic target in cardiovascular disease

Netrins are a family of proteins involved in cell migration and axon guidance during embryogenesis. The different functions and mechanisms of action of this family of proteins have been better characterized with the study of the netrin-1. They are chemotropic and act as a bifunctional regulator of neuron migration. Apart from its role in the central nervous system, researchers have proven that netrin-1 plays a role in the development and formation of non-neural tissue, thus netrin-1 is involved in regulation of cancers, cardiovascular diseases, kidney diseases and other diseases. Concerning the cardio-vascular realm, netrin-1 promotes angiogenesis and accelerates atherosclerosis, protects the heart against ischemia-reperfusion injury and reduces the infarct size. These findings make the neuroimmune guidance cue netrin-1 an important therapeutic target. This work seeks to review the subject based on studies that have been conducted over the past decade to identify the perspectives and extent of the research on this protein in the field of cardiology.