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

Arsenic aggravates the progression of diabetic nephropathy through miRNA-mRNA-autophagy axis

Environmental factors play an important role in the progression of diabetic nephropathy (DN), and previous study has shown that arsenic exposure can promote kidney damage in DN rats, however there is no relevant mechanism study so far. In this study, an arsenic-exposed (10 mg/L and 25 mg/L) DN mouse model was established through drinking water for 14 weeks. The results showed that 25 mg/L arsenic exposure increased the renal fibrosis in DN mice significantly, and urinary mAlb level increased with the increasing of arsenic exposure level. Transcriptome sequencing showed that autophagy-related pathways were significantly activated under the exposure dose of 25 mg/L, and levels of Beclin1 and p-ATG16L1/ATG16L1 were significantly higher in the 25 mg/L arsenic group compared to the control group. Silico analysis predicted the microRNAs those could regulate the hub genes of Mapk1, Rhoa and Cdc42, and dual-luciferase gene reporter assay was used to verify the targeted binding between these mRNAs and microRNAs. Our results suggested that high arsenic exposure could aggravate the progression of DN by altering autophagy, the miRNA-mRNA axles of let-7a-1-3p, let-7b-3p, let-7f-1-3p, miR-98-3p/Cdc42, Mapk1, Rhoa, could be considered promising targets to explore the mechanisms and therapeutic measures of DN after exposure to high levels of arsenic.

Reversal of Pulmonary Hypertension in a Human-Like Model: Therapeutic Targeting of Endothelial DHFR

BACKGROUND

Pulmonary hypertension (PH) is a progressive disorder characterized by remodeling of the pulmonary vasculature and elevated mean pulmonary arterial pressure, resulting in right heart failure.

METHODS

Here, we show that direct targeting of the endothelium to uncouple eNOS (endothelial nitric oxide synthase) with DAHP (2,4-diamino 6-hydroxypyrimidine; an inhibitor of GTP cyclohydrolase 1, the rate-limiting synthetic enzyme for the critical eNOS cofactor tetrahydrobiopterin) induces human-like, time-dependent progression of PH phenotypes in mice.

RESULTS

Critical phenotypic features include progressive elevation in mean pulmonary arterial pressure, right ventricular systolic blood pressure, and right ventricle (RV)/left ventricle plus septum (LV+S) weight ratio; extensive vascular remodeling of pulmonary arterioles with increased medial thickness/perivascular collagen deposition and increased expression of PCNA (proliferative cell nuclear antigen) and alpha-actin; markedly increased total and mitochondrial superoxide production, substantially reduced tetrahydrobiopterin and nitric oxide bioavailabilities; and formation of an array of human-like vascular lesions. Intriguingly, novel in-house generated endothelial-specific dihydrofolate reductase (DHFR) transgenic mice (tg-EC-DHFR) were completely protected from the pathophysiological and molecular features of PH upon DAHP treatment or hypoxia exposure. Furthermore, DHFR overexpression with a pCMV-DHFR plasmid transfection in mice after initiation of DAHP treatment completely reversed PH phenotypes. DHFR knockout mice spontaneously developed PH at baseline and had no additional deterioration in response to hypoxia, indicating an intrinsic role of DHFR deficiency in causing PH. RNA-sequencing experiments indicated great similarity in gene regulation profiles between the DAHP model and human patients with PH.

CONCLUSIONS

Taken together, these results establish a novel human-like murine model of PH that has long been lacking in the field, which can be broadly used for future mechanistic and translational studies. These data also indicate that targeting endothelial DHFR deficiency represents a novel and robust therapeutic strategy for the treatment of PH.

Macrophage neogenin deficiency exacerbates myocardial remodeling and inflammation after acute myocardial infarction through JAK1-STAT1 signaling

Immune response plays a crucial role in post-myocardial infarction (MI) myocardial remodeling. Neogenin (Neo1), a multifunctional transmembrane receptor, plays a critical role in the immune response; however, whether Neo1 participates in pathological myocardial remodeling after MI is unclear. Our study found that Neo1 expression changed significantly after MI in vivo and after LPS + IFN-γ stimulation in bone marrow-derived macrophages (BMDMs) in vitro. Neo1 functional deficiency (using a neutralizing antibody) and macrophage-specific Neo1 deficiency (induced by Neo1flox/flox;Cx3cr1cre mice) increased infarction size, enhanced cardiac fibrosis and cardiomyocyte apoptosis, and exacerbated left ventricular dysfunction post-MI in mice. Mechanistically, Neo1 deficiency promoted macrophage infiltration into the ischemic myocardium and transformation to a proinflammatory phenotype, subsequently exacerbating the inflammatory response and impairing inflammation resolution post-MI. Neo1 deficiency regulated macrophage phenotype and function, possibly through the JAK1-STAT1 pathway, as confirmed in BMDMs in vitro. Blocking the JAK1-STAT1 pathway with fludarabine phosphate abolished the impact of Neo1 on macrophage phenotype and function, inflammatory response, inflammation resolution, cardiomyocyte apoptosis, cardiac fibrosis, infarction size and cardiac function. In conclusion, Neo1 deficiency aggravates inflammation and left ventricular remodeling post-MI by modulating macrophage phenotypes and functions via the JAK1-STAT1 signaling pathway. These findings highlight the anti-inflammatory potential of Neo1, offering new perspectives for therapeutic targets in MI treatment. Neo1 deficiency aggravated inflammation and left ventricular remodeling after MI by modulating macrophage phenotypes and functions via the JAK1-STAT1 signaling pathway.

Regulation of autophagy of the heart in ischemia and reperfusion

Ischemia/reperfusion (I/R) of the heart leads to increased autophagic flux. Preconditioning stimulates autophagic flux by AMPK and PI3-kinase activation and mTOR inhibition. The cardioprotective effect of postconditioning is associated with activation of autophagy and increased activity of NO-synthase and AMPK. Oxidative stress stimulates autophagy in the heart during I/R. Superoxide radicals generated by NADPH-oxidase acts as a trigger for autophagy, possibly due to AMPK activation. There is reason to believe that AMPK, GSK-3β, PINK1, JNK, hexokinase II, MEK, PKCα, and ERK kinases stimulate autophagy, while mTOR, PKCδ, Akt, and PI3-kinase can inhibit autophagy in the heart during I/R. However, there is evidence that PI3-kinase could stimulate autophagy in ischemic preconditioning of the heart. It was found that transcription factors FoxO1, FoxO3, NF-κB, HIF-1α, TFEB, and Nrf-2 enhance autophagy in the heart in I/R. Transcriptional factors STAT1, STAT3, and p53 inhibit autophagy in I/R. MicroRNAs could stimulate and inhibit autophagy in the heart in I/R. Long noncoding RNAs regulate the viability and autophagy of cardiomyocytes in hypoxia/reoxygenation (H/R). Nitric oxide (NO) donors and endogenous NO could activate autophagy of cardiomyocytes. Activation of heme oxygenase-1 promotes cardiomyocyte tolerance to H/R and enhances autophagy. Hydrogen sulfide increases cardiac tolerance to I/R and inhibits apoptosis and autophagy via mTOR and PI3-kinase activation.

Antigen-specific downregulation of miR-150 in CD4 T cells promotes cell survival

MicroRNA-150 (miR-150) has been shown to play a general role in the immune system, but very little is known about its role on CD4+ T cell responses. During T cell responses against superantigen Staphylococcal Enterotoxin A, miR-150 expression was down-regulated in antigen-specific CD4+ T cells but up-regulated in CD8+ T cells. CD4+ and CD8+ T cell clonal expansion was greater in miR-150-KO mice than in WT mice, but miR-150 selectively repressed IL-2 production in CD4+ T cells. Transcriptome analysis of CD4+ T cells demonstrated that apoptosis and mTOR pathways were highly enriched in the absence of miR-150. Mechanistic studies confirmed that miR-150 promoted apoptosis specifically in antigen-specific CD4+ T cells, but not in bystander CD4+ nor in CD8+ T cells. Furthermore, inhibition of mTOR-linked mitochondrial superoxidedismutase-2 increased apoptosis in miR-150-/- antigen-specific CD4+ T. Thus, miR-150 impacts CD4+ T cell helper activity by attenuating IL-2 production along with clonal expansion, and suppresses superoxidedismutase to promote apoptosis.

The dual role of autophagy in periprosthetic osteolysis

Periprosthetic osteolysis (PPO) induced by wear particles is an important cause of aseptic loosening after artificial joint replacement, among which the imbalance of osteogenesis and osteoclastic processes occupies a central position. The cells involved in PPO mainly include osteoclasts (macrophages), osteoblasts, osteocytes, and fibroblasts. RANKL/RANK/OGP axis is a typical way for osteolysis. Autophagy, a mode of regulatory cell death and maintenance of cellular homeostasis, has a dual role in PPO. Although autophagy is activated in various periprosthetic cells and regulates the release of inflammatory cytokines, osteoclast activation, and osteoblast differentiation, its beneficial or detrimental role remains controversy. In particular, differences in the temporal control and intensity of autophagy may have different effects. This article focuses on the role of autophagy in PPO, and expects the regulation of autophagy to become a powerful target for clinical treatment of PPO.

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.

Netrin-1 in Post-stroke Neuroprotection: Beyond Axon Guidance Cue

BACKGROUND

Stroke, especially ischemic stroke, is a leading disease associated with death and long-term disability with limited therapeutic options. Neuronal death caused by vascular impairment, programmed cell death and neuroinflammation has been proven to be associated with increased stroke severity and poor stroke recovery. In light of this, a development of neuroprotective drugs targeting injured neurons is urgently needed for stroke treatment. Netrin-1, known as a bifunctional molecule, was originally described to mediate the repulsion or attraction of axonal growth by interacting with its different receptors. Importantly, accumulating evidence has shown that netrin-1 can manifest its beneficial functions to brain tissue repair and neural regeneration in different neurological disease models.

OBJECTIVE

In this review, we focus on the implications of netrin-1 and its possibly involved pathways on neuroprotection after ischemic stroke, through which a better understanding of the underlying mechanisms of netrin-1 may pave the way to novel treatments.

METHODS

Peer-reviewed literature was recruited by searching databases of PubMed, Scopus, Embase, and Web of Science till the year 2021.

CONCLUSION

There has been certain evidence to support the neuroprotective function of netrin-1 by regulating angiogenesis, autophagy, apoptosis and neuroinflammation after stroke. Netrin-1 may be a promising drug candidate in reducing stroke severity and improving outcomes.

Alternative adenosine Receptor activation: The netrin-Adora2b link

During hypoxia or inflammation, extracellular adenosine levels are elevated. Studies using pharmacologic approaches or genetic animal models pertinent to extracellular adenosine signaling implicate this pathway in attenuating hypoxia-associated inflammation. There are four distinct adenosine receptors. Of these, it is not surprising that the Adora2b adenosine receptor functions as an endogenous feedback loop to control hypoxia-associated inflammation. First, Adora2b activation requires higher adenosine concentrations compared to other adenosine receptors, similar to those achieved during hypoxic inflammation. Second, Adora2b is transcriptionally induced during hypoxia or inflammation by hypoxia-inducible transcription factor HIF1A. Studies seeking an alternative adenosine receptor activation mechanism have linked netrin-1 with Adora2b. Netrin-1 was originally discovered as a neuronal guidance molecule but also functions as an immune-modulatory signaling molecule. Similar to Adora2b, netrin-1 is induced by HIF1A, and has been shown to enhance Adora2b signaling. Studies of acute respiratory distress syndrome (ARDS), intestinal inflammation, myocardial or hepatic ischemia and reperfusion implicate the netrin-Adora2b link in tissue protection. In this review, we will discuss the potential molecular linkage between netrin-1 and Adora2b, and explore studies demonstrating interactions between netrin-1 and Adora2b in attenuating tissue inflammation.

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.

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.

Netrin-1 regulates ERK1/2 signaling pathway and autophagy activation in wear particle-induced osteoclastogenesis

Background

Artificial joint replacement surgery is often accompanied by osteolysis induced aseptic loosening around the prosthesis. Wear particles from joint replacement are thought to be one of the main factors leading to local inflammation and osteolysis at the prosthesis site. The aim of this study was to investigate the molecular mechanism of osteoclast formation and dissolution induced by wear particles and the potential roles of Netrin‐1, the ERK1/2 pathway and autophagy activation in this process.

Methods

The messenger RNA levels in cells and tissues were detected with real‐time quantitative PCR. The western blotting was used to detect the expression of proteins. A CCK‐8 kit was used to detect the viability of RAW 264.7 cells. Moreover, an air pouch model of bone resorption was established. Immunohistochemistry was used to detect the expression of TRAP and Netrin‐1 in rat bone tissue. Cell culture supernatants were collected in the rat air pouch model of bone resorption, and the levels of RANKL and OPG were detected with enzyme‐linked immunosorbent assay. The protein levels of TRAP and Netrin‐1 in bone tissue were examined by immunohistochemistry.

Results

Titanium wear particles induced osteoclast formation and autophagy activation. Moreover, blocking autophagy suppressed the osteoclastogenesis after exposure to wear particles in vitro. The activation of the ERK1/2 pathway and the overexpression of Netrin‐1 were both found to play important roles in osteoclastogenesis mediated by autophagy. Moreover, 3‐MA effectively decreased the secretion of proinflammatory cytokines mediated by wear particles.

Conclusion

Blockade of autophagy inhibits the osteoclastogenesis and inflammation induced by wear particles, thus potentially providing novel treatment strategies for abnormal osteoclastogenesis and aseptic prosthesis loosening induced by wear particles.

Macrophage-derived netrin-1 drives adrenergic nerve-associated lung fibrosis

Fibrosis is a macrophage-driven process of uncontrolled extracellular matrix accumulation. Neuronal guidance proteins such as netrin-1 promote inflammatory scarring. We found that macrophage-derived netrin-1 stimulates fibrosis through its neuronal guidance functions. In mice, fibrosis due to inhaled bleomycin engendered netrin-1-expressing macrophages and fibroblasts, remodeled adrenergic nerves, and augmented noradrenaline. Cell-specific knockout mice showed that collagen accumulation, fibrotic histology, and nerve-associated endpoints required netrin-1 of macrophage but not fibroblast origin. Adrenergic denervation; haploinsufficiency of netrin-1's receptor, deleted in colorectal carcinoma; and therapeutic α1 adrenoreceptor antagonism improved collagen content and histology. An idiopathic pulmonary fibrosis (IPF) lung microarray data set showed increased netrin-1 expression. IPF lung tissues were enriched for netrin-1+ macrophages and noradrenaline. A longitudinal IPF cohort showed improved survival in patients prescribed α1 adrenoreceptor blockade. This work showed that macrophages stimulate lung fibrosis via netrin-1-driven adrenergic processes and introduced α1 blockers as a potentially new fibrotic therapy.

High Serum Netrin-1 and IL-1β in Elderly Females with ACS: Worse Prognosis in 2-years Follow-up

Fundamento

Vários marcadores têm sido avaliados quanto a um potencial impacto nas decisões clínicas ou na predição de mortalidade na síndrome coronariana aguda (SCA), incluindo Netrina-1 e IL-1β.

Objetivo

Examinamos o valor prognóstico de Netrina-1 e IL-1β em pacientes com SCA (2 anos de acompanhamento).

Métodos

Avaliamos Netrina-1, IL-1β e outros fatores de risco em amostras de soro de 803 pacientes. Curvas de Kaplan-Meier e regressão de Cox foram usadas para análise de óbito por todas as causas, óbito por doenças cardiovasculares (DCV) e desfecho combinado de infarto agudo do miocárdio (IAM) fatal ou novo IAM não fatal, considerando p < 0,05.

Resultados

Houve 115 óbitos por todas as causas, 78 óbitos por DCV e 67 eventos no desfecho combinado. Níveis de Netrina-1 acima da mediana (> 44,8 pg/mL) foram associados a pior prognóstico (óbito por todas as causas e por DCV) em mulheres idosas, mesmo após o ajuste do modelo (HR: 2,08, p = 0,038 e HR: 2,68, p = 0,036). Níveis de IL-1β acima da mediana (> 13,4 pg/mL) em mulheres idosas foram associados a risco aumentado para todos os desfechos após o ajuste (todas as causas - HR: 2,03, p = 0,031; DCV - HR: 3,01, p = 0,013; desfecho combinado - HR: 3,05, p = 0,029). Para homens, não foram observadas associações entre Netrina-1 ou IL-1β e os desfechos.

Conclusão

Níveis séricos elevados de Netrina-1 e IL-1β mostraram associação significativa com pior prognóstico em idosas do sexo feminino. Eles podem ser úteis como indicadores prognósticos em SCA. (Arq Bras Cardiol. 2020; 114(3):507-514)

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.

Exogenous Netrin-1 Inhibits Autophagy of Ischemic Brain Tissues and Hypoxic Neurons via PI3K/mTOR Pathway in Ischemic Stroke

BACKGROUND AND OBJECTIVE

Ischemic stroke is a serious disease that endangers human health. How to reduce the damage of neurons in ischemic regions is an urgent problem to be explored. Autophagy is an important pathophysiological process in cerebral ischemia and Netrin-1 is an effective neuroprotective protein. This study aims to investigate the effect of Netrin-1 on autophagy of ischemic brain tissues and hypoxic neurons.

METHODS

We constructed rat persistent middle cerebral artery occlusion model in vivo and constructed the Oxygen Glucose-Deprivation model in vitro. Rats and cells were treated with or without Netrin-1. Western blot analysis was performed to detect autophagy related proteins LC3B, P62 and pathway related proteins PI3K, p-PI3K, mTOR, p-mTOR. CCK-8 assay was performed to detect the viability of hypoxic neurons. We also performed western-blot analysis and qRT-PCR test to detect levels of Netrin-1 protein and mRNA.

RESULTS

Autophagy enhanced both in ischemic brain tissues and hypoxic neurons. Netrin-1 inhibited autophagy through PI3K/mTOR pathway both in vivo and in vitro. At the same time, we found that exogenous Netrin-1 can promote the secretion of Netrin-1 protein by neurons themselves, which indicated that Netrin-1 can further amplify the neuroprotective effect through the positive feedback mechanism.

CONCLUSIONS

Exogenous Netrin-1 alleviates damage of ischemic brain tissues and enhances viability of hypoxic neurons by inhibiting autophagy via PI3K/mTOR pathway. This effect can be amplified by positive feedback mechanism.

Sevoflurane postconditioning protects against myocardial ischemia/reperfusion injury by restoring autophagic flux via an NO-dependent mechanism

Volatile anesthetics improve postischemic cardiac function and reduce infarction even when administered for only a brief time at the onset of reperfusion. A recent study showed that sevoflurane postconditioning (SPC) attenuated myocardial reperfusion injury, but the underlying mechanisms remain unclear. In this study, we examined the effects of sevoflurane on nitric oxide (NO) release and autophagic flux during the myocardial ischemia/reperfusion (I/R) injury in rats in vivo and ex vivo. Male rats were subjected to 30 min ischemia and 2 h reperfusion in the presence or absence of sevoflurane (1.0 minimum alveolar concentration) during the first 15 min of reperfusion. We found that SPC significantly improved hemodynamic performance after reperfusion, alleviated postischemic myocardial infarction, reduced nicotinamide adenine dinucleotide content loss, and cytochrome c release in heart tissues. Furthermore, SPC significantly increased the phosphorylation of endothelial nitric oxide synthase (NOS) and neuronal nitric oxide synthase, and elevated myocardial NOS activity and NO production. All these effects were abolished by treatment with an NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg, i.v.). We also observed myocardial I/R-induced accumulation of autophagosomes in heart tissues, as evidenced by increased ratios of microtubule-associated protein 1 light chain 3 II/I, up-regulation of Beclin 1 and P62, and reduced lysosome-associated membrane protein-2 expression. SPC significantly attenuated I/R-impaired autophagic flux, which were blocked by L-NAME. Moreover, pretreatment with the autophagic flux blocker chloroquine (10 mg/kg, i.p.) increased autophagosome accumulation in SPC-treated heart following I/R and blocked SPC-induced cardioprotection. The same results were also observed in a rat model of myocardial I/R injury ex vivo, suggesting that SPC protects rat hearts against myocardial reperfusion injury by restoring I/R-impaired autophagic flux via an NO-dependent mechanism.

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.

Netrin as a Novel Biomarker and Its Therapeutic Implications in Diabetes Mellitus and Diabetes-Associated Complications

Diabetes is a multifactorial metabolic syndrome and is one of the shared long-lasting illnesses globally. It is linked to long-term microvascular and macrovascular complications that contribute to disability, compromised quality of life, and reduction in lifespan, which eventually leads to death. This disease is not only incurring significant economic burden but also adversely affects the patients, caregivers, communities, and the society at large. The interruption of diabetes progress and its complications is a primary focus of scientific communities. In spite of various diagnostic modalities for diabetes, there is a limited marker to investigate the risk and progress of its complications. Netrin has recently received more attention as a biomarker of diabetes and a broader range of long-term complication. Therefore, the impetus of this review is to exhaustively discuss the role of Netrin as a potential biomarker and its therapeutic implication in diabetes and diverse sets of microvascular and macrovascular complications of diabetes. It also discourses the possible mechanisms of Netrin for the said pharmacological effect for a better understanding of the development and progression of diabetes and its complications in relation to this protein. It enables protective measures to be applied at the subclinical stage and the responses to preventive or therapeutic measures to be scrutinized. Besides, it might also facilitate the appraisal of novel therapeutic options for diabetes and various complications through modifying the endogenous Netrin and provide surrogate endpoints for intervention.

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.

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.

Organelle-Specific Initiation of Autophagy

Autophagy constitutes a prominent mechanism through which eukaryotic cells preserve homeostasis in baseline conditions and in response to perturbations of the intracellular or extracellular microenvironment. Autophagic responses can be relatively non-selective or target a specific subcellular compartment. At least in part, this depends on the balance between the availability of autophagic substrates ("offer") and the cellular need of autophagic products or functions for adaptation ("demand"). Irrespective of cargo specificity, adaptive autophagy relies on a panel of sensors that detect potentially dangerous cues and convert them into signals that are ultimately relayed to the autophagic machinery. Here, we summarize the molecular systems through which specific subcellular compartments-including the nucleus, mitochondria, plasma membrane, reticular apparatus, and cytosol-convert homeostatic perturbations into an increased offer of autophagic substrates or an accrued cellular demand for autophagic products or functions.

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.

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.

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

Despite an established role of mitochondrial dysfunction in cardiac ischemia/reperfusion (I/R) injury, the upstream activators have remained incompletely defined. We have recently identified an innovative role of exogenously applied netrin-1 in cardioprotection, which is mediated by increased nitric oxide (NO) bioavailability. Here, we tested the hypothesis that this "pharmacological" treatment of netrin-1 preserves mitochondrial function via novel mechanisms that are NO dependent. Freshly isolated C57BL6 mouse hearts were perfused using a Langendorff system, and subjected to a 20min global ischemia/60min reperfusion, in the presence or absence of netrin-1. I/R induced marked increases in infarct size, total superoxide and hydrogen peroxide production, activity and protein abundance of NADPH oxidase (NOX) isoform 4 (NOX4), as well as impaired mitochondrial integrity and function, all of which were attenuated by netrin-1. This protective effect of netrin-1 is attributed to cGMP, a downstream effector of NO. The protein levels of NOX1 and NOX2 were however unaffected, and infarct size from NOX1 and NOX2 knockouts was not different from wild type animals. Scavenging of NO with PTIO reversed inhibitory effects of netrin-1 on NOX4, while NO donor attenuated NOX4 protein abundance. In vivo NOX4 RNAi, or sepiapterin perfusion, resulted in recoupling of NOS, decreased infarct size, and blockade of dysfunctional mitochondrial swelling and mitochondrial superoxide production. These data demonstrate that netrin-1 induces cardioprotection through inhibition of NOX4 activity, which leads to recoupling of NOS, augmented NO bioavailability, reduction in oxidative stress, and ultimately preservation of mitochondrial function. The NO-dependent NOX4 inhibition connects with our previously established pathway of DCC/ERK1/2/eNOS/NO/DCC feed-forward mechanism, to maintain NOS in the coupling state to attenuate oxidative stress to preserve mitochondrial function. These findings may promote development of novel therapeutics for cardiac I/R injury. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".