Netrin-1 induces angiogenesis via a DCC-dependent ERK1/2-eNOS feed-forward mechanism

Netrin-1-engineered endothelial cell exosomes induce the formation of pre-regenerative niche to accelerate peripheral nerve repair

The formation of vascular niche is pivotal during the early stage of peripheral nerve regeneration. Nevertheless, the mechanisms of vascular niche in the regulation of peripheral nerve repair remain unclear. Netrin-1 (NTN1) was found up-regulated in nerve stump after peripheral nerve injury (PNI). Herein, we demonstrated that NTN1-high endothelial cells (NTN1+ECs) were the critical component of vascular niche, fostering angiogenesis, axon regeneration, and repair-related phenotypes. We also found that NTN1+EC-derived exosomes (NTN1 EC-EXO) were involved in the formation of vascular niche as a critical role. Multi-omics analysis further verified that NTN1 EC-EXO carried a low-level expression of let7a-5p and activated key pathways associated with niche formation including focal adhesion, axon guidance, phosphatidylinositol 3-kinase-AKT, and mammalian target of rapamycin signaling pathway. Together, our study suggested that the construction of a pre-regenerative niche induced by NTN1 EC-EXO could establish a beneficial microenvironment for nerve repair and facilitate functional recovery after PNI.

Role of Protein Phosphatases in Tumor Angiogenesis: Assessing PP1, PP2A, PP2B and PTPs Activity

Tumor angiogenesis, the formation of new blood vessels to support tumor growth and metastasis, is a complex process regulated by a multitude of signaling pathways. Dysregulation of signaling pathways involving protein kinases has been extensively studied, but the role of protein phosphatases in angiogenesis within the tumor microenvironment remains less explored. However, among angiogenic pathways, protein phosphatases play critical roles in modulating signaling cascades. This review provides a comprehensive overview of the involvement of protein phosphatases in tumor angiogenesis, highlighting their diverse functions and mechanisms of action. Protein phosphatases are key regulators of cellular signaling pathways by catalyzing the dephosphorylation of proteins, thereby modulating their activity and function. This review aims to assess the activity of the protein tyrosine phosphatases and serine/threonine phosphatases. These phosphatases exert their effects on angiogenic signaling pathways through various mechanisms, including direct dephosphorylation of angiogenic receptors and downstream signaling molecules. Moreover, protein phosphatases also crosstalk with other signaling pathways involved in angiogenesis, further emphasizing their significance in regulating tumor vascularization, including endothelial cell survival, sprouting, and vessel maturation. In conclusion, this review underscores the pivotal role of protein phosphatases in tumor angiogenesis and accentuate their potential as therapeutic targets for anti-angiogenic therapy in cancer.

Molecular Mechanisms of Ischemic Stroke: A Review Integrating Clinical Imaging and Therapeutic Perspectives

Ischemic stroke poses a significant global health challenge, necessitating ongoing exploration of its pathophysiology and treatment strategies. This comprehensive review integrates various aspects of ischemic stroke research, emphasizing crucial mechanisms, therapeutic approaches, and the role of clinical imaging in disease management. It discusses the multifaceted role of Netrin-1, highlighting its potential in promoting neurovascular repair and mitigating post-stroke neurological decline. It also examines the impact of blood-brain barrier permeability on stroke outcomes and explores alternative therapeutic targets such as statins and sphingosine-1-phosphate signaling. Neurocardiology investigations underscore the contribution of cardiac factors to post-stroke mortality, emphasizing the importance of understanding the brain-heart axis for targeted interventions. Additionally, the review advocates for early reperfusion and neuroprotective agents to counter-time-dependent excitotoxicity and inflammation, aiming to preserve tissue viability. Advanced imaging techniques, including DWI, PI, and MR angiography, are discussed for their role in evaluating ischemic penumbra evolution and guiding therapeutic decisions. By integrating molecular insights with imaging modalities, this interdisciplinary approach enhances our understanding of ischemic stroke and offers promising avenues for future research and clinical interventions to improve patient outcomes.

Insights from the neural guidance factor Netrin-1 into neurodegeneration and other diseases

Netrin-1 was initially discovered as a neuronal growth cue for axonal guidance, and its functions have later been identified in inflammation, tumorigenesis, neurodegeneration, and other disorders. We have recently found its alterations in the brains with Alzheimer's disease, which might provide important clues to the mechanisms of some unique pathologies. To provide better understanding of this promising molecule, we here summarize research progresses in genetics, pathology, biochemistry, cell biology and other studies of Netrin-1 about its mechanistic roles and biomarker potentials with an emphasis on clinical neurodegenerative disorders in order to expand understanding of this promising molecular player in human diseases.

Involvement of neuronal factors in tumor angiogenesis and the shaping of the cancer microenvironment

Emerging evidence suggests that nerves within the tumor microenvironment play a crucial role in regulating angiogenesis. Neurotransmitters and neuropeptides released by nerves can interact with nearby blood vessels and tumor cells, influencing their behavior and modulating the angiogenic response. Moreover, nerve-derived signals may activate signaling pathways that enhance the production of pro-angiogenic factors within the tumor microenvironment, further supporting blood vessel growth around tumors. The intricate network of communication between neural constituents and the vascular system accentuates the potential of therapeutically targeting neural-mediated pathways as an innovative strategy to modulate tumor angiogenesis and, consequently, neoplastic proliferation. Hereby, we review studies that evaluate the precise molecular interplay and the potential clinical ramifications of manipulating neural elements for the purpose of anti-angiogenic therapeutics within the scope of cancer treatment.

Intracellular delivery of nitric oxide enhances the therapeutic efficacy of mesenchymal stem cells for myocardial infarction

Cell therapy by autologous mesenchymal stem cells (MSCs) is a clinically acceptable strategy for treating various diseases. Unfortunately, the therapeutic efficacy is largely affected by the low quality of MSCs collected from patients. Here, we showed that the gene expression of MSCs from patients with diabetes was differentially regulated compared to that of MSCs from healthy controls. Then, MSCs were genetically engineered to catalyze an NO prodrug to release NO intracellularly. Compared to extracellular NO conversion, intracellular NO delivery effectively prolonged survival and enhanced the paracrine function of MSCs, as demonstrated by in vitro and in vivo assays. The enhanced therapeutic efficacy of engineered MSCs combined with intracellular NO delivery was further confirmed in mouse and rat models of myocardial infarction, and a clinically relevant cell administration paradigm through secondary thoracotomy has been attempted.

Substance P reversibly compromises the integrity and function of blood-brain barrier

BACKGROUND

Substance P (SP) plays a role in vasodilatation and tissue integrity through its receptor, neurokinin 1 (NK1R). However, its specific effect on blood-brain barrier (BBB) remains unknown.

METHODS

The impact of SP on the integrity/function of human BBB model in vitro, composed of brain microvascular endothelial cells (BMECs), astrocytes and pericytes, was assessed by measurements of transendothelial electrical resistance and paracellular flux of sodium fluorescein (NaF), respectively in the absence/presence of specific inhibitors targeting NK1R (CP96345), Rho-associated protein kinase (ROCK; Y27632) and nitric oxide synthase (NOS; N(G)-nitro-L-arginine methyl ester). Sodium nitroprusside (SNP), a NO donor, was employed as a positive control. The levels of tight junction proteins, zonula occludens-1, occludin and claudin-5 alongside RhoA/ROCK/myosin regulatory light chain-2 (MLC2) and extracellular signal‑regulated protein kinase (Erk1/2) proteins were detected by western analyses. Subcellular localisations of F-actin and tight junction proteins were visualized by immunocytochemistry. Flow cytometry was used to detect transient calcium release.

RESULTS

Exposure to SP increased RhoA, ROCK2 and phosphorylated serine-19 MLC2 protein levels and Erk1/2 phosphorylation in BMECs which were abolished by CP96345. These increases were independent of the changes in intracellular calcium availability. SP perturbed BBB in a time-dependent fashion through induction of stress fibres. Changes in tight junction protein dissolution or relocalisation were not involved in SP-mediated BBB breakdown. Inhibition of NOS, ROCK and NK1R mitigated the effect of SP on BBB characteristics and stress fibre formation.

CONCLUSION

SP promoted a reversible decline in BBB integrity independent of tight junction proteins expression or localisation.

Blueberries and their bioactives in the modulation of oxidative stress, inflammation and cardio/vascular function markers: a systematic review of human intervention studies

Blueberries represent a rich source of (poly)phenols and other bioactive compounds. Numerous in vitro and animal model studies documented the potential health-promoting properties of blueberries and blueberry-bioactives, while little is still known about their effects in humans. The objective of the present systematic review is to provide main evidence and the potential mechanisms of action of blueberry and its (poly)phenols in the regulation of markers related to oxidative stress, inflammation, vascular and cardiometabolic function in health and disease states. A total of 45 human intervention studies were included in this review. Overall, the evidence suggests that blueberries may play a role in the improvement of markers of vascular function. Their effects were observed following both post-prandial and long-term consumption, particularly in subjects with risk factors and/or disease conditions. Conversely, the conflicting results on inflammation, oxidative stress and cardiometabolic risk markers were most likely due to differences among studies in terms of study design, subject characteristics, duration of intervention, dosage, and type of biomarkers analyzed. For these reasons, high-quality, well-designed, human intervention studies are warranted to strengthen the current findings on vascular function and provide more evidence about the impact of blueberries on the different markers considered. In addition, studies focusing on the relationship between the structure and the function of (poly)phenols will be fundamental for a better comprehension of the mechanisms behind the health effects observed.

Combined Therapy with Simvastatin- and Coenzyme-Q10-Loaded Nanoparticles Upregulates the Akt-eNOS Pathway in Experimental Metabolic Syndrome

In addition to their LDL-cholesterol-lowering effect, statins have pleiotropic beneficial effects on the cardiovascular system. However, long-term treatment with statins may be associated with serious side effects. With the aim to make statin therapy more effective, we studied the effects of simvastatin- and coenzyme-Q10-loaded polymeric nanoparticles on the lipid profile and nitric oxide (NO)/reactive oxygen species (ROS) balance in the heart and aorta of adult male obese Zucker rats. The rats were divided into an untreated group, a group treated with empty nanoparticles, and groups treated with simvastatin-, coenzyme Q10 (CoQ10)-, or a combination of simvastatin- and CoQ10-loaded nanoparticles (SIMV+CoQ10). After 6 weeks, the lipid profile in the plasma and the concentration of conjugated dienes in the liver were determined. Nitric oxide synthase (NOS) activity, Akt, endothelial NOS (eNOS), phosphorylated eNOS (p-eNOS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and nuclear factor kappaB (NF-kappaB) protein expressions were measured in the heart and aorta. All simvastatin, CoQ10, and SIMV+CoQ10 treatments decreased plasma LDL levels, but only the combined SIMV+CoQ10 treatment increased NOS activity and the expression of Akt, eNOS, and p-eNOS in both the heart and the aorta. Interestingly, NADPH oxidase in the heart and NF-kappaB protein expression in the aorta were decreased by all treatments, including nanoparticles alone. In conclusion, only combined therapy with SIMV- and CoQ10-loaded nanoparticles increased NOS activity and upregulated the Akt-eNOS pathway in obese Zucker rats, which may represent a promising tool for the treatment of cardiometabolic diseases.

Diverse roles for axon guidance pathways in adult tissue architecture and function

Classical axon guidance ligands and their neuronal receptors were first identified due to their fundamental roles in regulating connectivity in the developing nervous system. Since their initial discovery, it has become clear that these signaling molecules play important roles in the development of a broad array of tissue and organ systems across phylogeny. In addition to these diverse developmental roles, there is a growing appreciation that guidance signaling pathways have important functions in adult organisms, including the regulation of tissue integrity and homeostasis. These roles in adult organisms include both tissue-intrinsic activities of guidance molecules, as well as systemic effects on tissue maintenance and function mediated by the nervous and vascular systems. While many of these adult functions depend on mechanisms that mirror developmental activities, such as regulating adhesion and cell motility, there are also examples of adult roles that may reflect signaling activities that are distinct from known developmental mechanisms, including the contributions of guidance signaling pathways to lineage commitment in the intestinal epithelium and bone remodeling in vertebrates. In this review, we highlight studies of guidance receptors and their ligands in adult tissues outside of the nervous system, focusing on in vivo experimental contexts. Together, these studies lay the groundwork for future investigation into the conserved and tissue-specific mechanisms of guidance receptor signaling in adult tissues.

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.

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.

Flavored and Nicotine-Containing E-Cigarettes Induce Impaired Angiogenesis and Diabetic Wound Healing via Increased Endothelial Oxidative Stress and Reduced NO Bioavailability

The prevalent use of electronic cigarettes (e-cigarettes) has increased exponentially in recent years, especially in youth who are attracted to flavored e-cigarettes. Indeed, e-cigarette or vaping product use-associated lung injury (EVALI) cases started to emerge in the United States in August 2019, resulting in 2807 hospitalized cases and 68 deaths as of 18 February 2020. In the present study, we investigated, for the first time, whether flavored and nicotine containing e-cigarettes induce endothelial dysfunction to result in impaired angiogenesis and wound healing particularly under diabetic condition. Nicotine containing e-cigarettes with various contents of nicotine (0, 1.2%, 2.4%), and flavored e-cigarettes of classic tobacco, mint, menthol, and vanilla or fruit from BLU (nicotine 2.4%) or JUUL (nicotine 3%), were used to treat endothelial cells in vitro and streptozotocin-induced diabetic mice in vivo. Endothelial cell superoxide production, determined by dihydroethidium (DHE) fluorescent imaging and electron spin resonance (ESR), was markedly increased by exposure to e-cigarette extract (e-CSE) in a nicotine-content dependent manner, while nitric oxide (NO) bioavailability detected by DAF-FM fluorescent imaging was substantially decreased. All of the different flavored e-cigarettes examined also showed significant effects in increasing superoxide production while diminishing NO bioavailability. Endothelial cell apoptosis evaluated by caspase 3 activity was markedly increased by exposure to e-CSE prepared from flavored and nicotine containing e-cigarettes. Endothelial monolayer wound assays revealed that nicotine-containing and flavored e-cigarettes induced impaired angiogenic wound repair of endothelial cell monolayers. Furthermore, vascular endothelial growth factor (VEGF) stimulated wound healing in diabetic mice was impaired by exposure to e-CSEs prepared from nicotine-containing and flavored e-cigarettes. Taken together, our data demonstrate for the first time that flavored and nicotine-containing e-cigarettes induce endothelial dysfunction through excessive ROS production, resulting in decreased NO bioavailability, increased endothelial cell apoptosis, and impairment in angiogenesis and wound healing, especially under diabetic condition. These responses of endothelial dysfunction likely underlie harmful effects of e-cigarettes in endothelial-rich organs, such as heart and lungs. These data also indicate that rigorous regulation on e-cigarette use should be enforced in diabetic and/or surgical patients to avoid severe consequences from impaired angiogenesis/wound healing.

PTPRD and DCC Are Novel BACE1 Substrates Differentially Expressed in Alzheimer's Disease: A Data Mining and Bioinformatics Study

The β-site Amyloid precursor protein Cleaving Enzyme 1 (BACE1) is an extensively studied therapeutic target for Alzheimer's disease (AD), owing to its role in the production of neurotoxic amyloid beta (Aβ) peptides. However, despite numerous BACE1 inhibitors entering clinical trials, none have successfully improved AD pathogenesis, despite effectively lowering Aβ concentrations. This can, in part, be attributed to an incomplete understanding of BACE1, including its physiological functions and substrate specificity. We propose that BACE1 has additional important physiological functions, mediated through substrates still to be identified. Thus, to address this, we computationally analysed a list of 533 BACE1 dependent proteins, identified from the literature, for potential BACE1 substrates, and compared them against proteins differentially expressed in AD. We identified 15 novel BACE1 substrates that were specifically altered in AD. To confirm our analysis, we validated Protein tyrosine phosphatase receptor type D (PTPRD) and Netrin receptor DCC (DCC) using Western blotting. These findings shed light on the BACE1 inhibitor failings and could enable the design of substrate-specific inhibitors to target alternative BACE1 substrates. Furthermore, it gives us a greater understanding of the roles of BACE1 and its dysfunction in AD.

CD146 mediates the anti-apoptotic role of Netrin-1 in endothelial progenitor cells under hypoxic conditions

Modulating the biological status of endothelial progenitor cells (EPCs), such as function and survival, is essential for therapeutic angiogenesis in ischemic vascular disease environments. This study aimed to explore the role and molecular mechanisms underlying Netrin-1 in the viability and angiogenic function of EPCs. EPCs were isolated from the bone barrow of adult C57/BL6 mice. The apoptosis and various functions of EPCs were analyzed in vitro by manipulating the expression of Netrin-1. The TUNEL assay was performed to detect apoptotic EPCs. Cell migration and tube formation assays were performed to detect EPC function. Trypan blue staining was performed to detect cell viability. Western blot analysis was performed to detect the protein expression levels of Netrin-1, CD146 and apoptotic factors. Quantitative PCR analysis was performed to detect the expression levels of Netrin-1 receptors. The results demonstrated that treatment with exogenous Netrin-1 promoted EPC migration and tube formation, whereas transfection with small interfering (si)RNA targeting Netrin-1 exhibited the opposite effects. Exogenous Netrin-1 protected EPCs from hypoxia-induced apoptosis, whereas the interruption of endogenous Netrin-1 enhancement under hypoxia by Netrin-1-siRNA exacerbated the apoptosis of EPCs. Furthermore, CD146, one of the immunoglobulin receptors activated by Netrin-1, was screened for in the present study. Results demonstrated that CD146 did not participate in Netrin-1-promoted EPC function, but mediated the anti-apoptotic effects of Netrin-1 in EPCs. In conclusion, Netrin-1 enhanced the angiogenic function of EPCs and alleviated hypoxia-induced apoptosis, which was mediated by CD146. This biological function of Netrin-1 may provide a potential therapeutic option to promote EPCs for the treatment of ischemic vascular diseases.

Serum Netrin-1 and Urinary KIM-1 levels as potential biomarkers for the diagnosis of early preeclampsia

The aim of this study was to evaluate whether the Serum Netrin-1 and Urinary KIM-1 (Kidney Injury Molecule-1) levels are associated with the detection of preeclampsia. A total of 90 patients, including 36 normal pregnant women, 29 patients with nonsevere preeclampsia and 25 patients with severe preeclampsia, were included in this study. Maternal serum Netrin-1 and Urinary KIM-1 levels were measured by using an enzyme-linked immunosorbent assay (ELISA). The results showed that the Levels of Netrin-1 and KIM-1 were statistically higher in women with preeclampsia as compared with normal pregnant women. Furthermore, the Netrin-1 level in women with severe preeclampsia was significantly higher than nonsevere preeclamptic women. inconclusion the current study showed that Maternal serum level of Netrin-1 and Urinary level of KIM-1 can be used as early biomarkers for the detection of preeclampsia.IMPACT STATEMENTWhat is already known on this subject? Preeclampsia is a disorder of widespread vascular endothelial malfunction and vasospasm that occurs after 20 weeks' gestation. Netrin-1 was found to promote angiogenesis. Alteration of placental angiogenesis in early pregnancy is a well-known reason for placental dysfunction such as preeclampsia. Kidney injury with proteinuria is a characteristic feature of preeclampsia. Urine KIM-1 is the most potential biomarker for renal injury in preeclampsia. Due to these facts, we aimed to investigate the role of maternal serum Netrin-1 and Urine KIM-1 levels in preeclampsia presence and severity.What the results of this study add? A significant relationship between Netrin-1 and KIM-1 levels with preeclampsia.What the implications are of these findings for clinical practice and/or further research? Based on these findings, we concluded that increased levels of Netrin-1 and KIM-1 are associated with severe preeclampsia.

Therapeutic application of estrogen for COVID-19: Attenuation of SARS-CoV-2 spike protein and IL-6 stimulated, ACE2-dependent NOX2 activation, ROS production and MCP-1 upregulation in endothelial cells

The outbreak of COVID-19 has remained uncontained with urgent need for robust therapeutics. We have previously reported sex difference of COVID-19 for the first time indicating male predisposition. Males are more susceptible than females, and more often to develop into severe cases with higher mortality. This predisposition is potentially linked to higher prevalence of cigarette smoking. Nonetheless, we found for the first time that cigarette smoking extract (CSE) had no effect on angiotensin converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) expression in endothelial cells. The otherwise observed worse outcomes in smokers is likely linked to baseline respiratory diseases associated with chronic smoking. Instead, we hypothesized that estrogen mediated protection might underlie lower morbidity, severity and mortality of COVID-19 in females. Of note, endothelial inflammation and barrier dysfunction are major mediators of disease progression, and development of acute respiratory distress syndrome (ARDS) and multi-organ failure in patients with COVID-19. Therefore, we investigated potential protective effects of estrogen on endothelial cells against oxidative stress induced by interleukin-6 (IL-6) and SARS-CoV-2 spike protein (S protein). Indeed, 17β-estradiol completely reversed S protein-induced selective activation of NADPH oxidase isoform 2 (NOX2) and reactive oxygen species (ROS) production that are ACE2-dependent, as well as ACE2 upregulation and induction of pro-inflammatory gene monocyte chemoattractant protein-1 (MCP-1) in endothelial cells to effectively attenuate endothelial dysfunction. Effects of IL-6 on activating NOX2-dependent ROS production and upregulation of MCP-1 were also completely attenuated by 17β-estradiol. Of note, co-treatment with CSE had no additional effects on S protein stimulated endothelial oxidative stress, confirming that current smoking status is likely unrelated to more severe disease in chronic smokers. These data indicate that estrogen can serve as a novel therapy for patients with COVID-19 via inhibition of initial viral responses and attenuation of cytokine storm induced endothelial dysfunction, to substantially alleviate morbidity, severity and mortality of the disease, especially in men and post-menopause women. Short-term administration of estrogen can therefore be readily applied to the clinical management of COVID-19 as a robust therapeutic option.

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.

The expression of Netrin-1 in the MIA-induced osteoarthritic temporomandibular joint in mice

Subchondral bone degeneration is the main pathological change during temporomandibular joint (TMJ) osteoarthritis (OA) development. Netrin-1, an axon-guiding factor, might play roles in OA development and pain. The purpose of this study was to investigate the expression of Netrin-1 in TMJ OA and its possible role in the progression of TMJ OA and pain. The synovial fluids of temporomandibular joint disorders (TMDs) patients were collected for Netrin-1 by enzyme linked immunosorbent assay (ELISA). TMJ OA model was built by MIA joint injection, and then the von Frey test, hematoxylin & eosin (H&E) staining, toluidine blue (TB) staining, immunohistochemical (IHC) staining and micro-CT were performed. After induction of osteoclast differentiation of raw264.7 cells, immunofluorescence (IF) was used to detect the Netrin-1 and its receptors on osteoclast membrane. The concentration of Netrin-1 increased in the synovial fluid of TMJ OA patients. After MIA injection to TMJ, the head withdrawal threshold (HWT) was significantly decreased. Microscopically, the structural disorder of subchondral bone was the most obvious at the 2nd week after MIA injection. In addition, Netrin-1 expression increased in the subchondral bone at the 2nd week after MIA injection. In vitro, the expressions of Netrin-1 and its receptor Unc5B were upregulated on the osteoclast membrane. Netrin-1 might be an important regulator during bone degeneration and pain in the process of TMJ OA.

Targeting MicroRNA-192-5p, a Downstream Effector of NOXs (NADPH Oxidases), Reverses Endothelial DHFR (Dihydrofolate Reductase) Deficiency to Attenuate Abdominal Aortic Aneurysm Formation

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Late Protective Effect of Netrin-1 in the Murine Acetaminophen Hepatotoxicity Model

Acetaminophen (APAP) overdose-induced acute liver failure is an important clinical problem in the United States and the current antidote N-acetylcysteine, has a short early therapeutic window. Since most patients present late to the clinic, there is need for novel late-acting therapeutic options. Though the neuronal guidance cue netrin-1, has been shown to promote hepatic repair and regeneration during liver ischemia/reperfusion injury, its effect in APAP-induced hepatotoxicity is unknown. In the quest for a late-acting therapeutic intervention in APAP-induced liver injury, we examined the role of netrin-1 in a mouse model of APAP overdose. Male C57BL/6J mice were cotreated with exogenous netrin-1 or vehicle control, along with 300 mg/kg APAP and euthanized at 6, 12, and 24 h. Significant elevations in alanine aminotransferase indicative of liver injury were seen in control mice at 6 h and this was not affected by netrin-1 administration. Also, netrin-1 treatment did not influence mitochondrial translocation of phospho-JNK, or peroxynitrite formation indicating that there was no interference with APAP-induced injury processes. Interestingly however, netrin-1 administration attenuated liver injury at 24 h, as seen by alanine aminotransferase levels and histology, at which time significant elevations in the netrin-1 receptor, adenosine A2B receptor (A2BAR) as well as macrophage infiltration was evident. Removal of resident macrophages with clodronate liposomes or treatment with the A2BAR antagonist PSB1115 blocked the protective effects of netrin-1. Thus, our data indicate a previously unrecognized role for netrin-1 in attenuation of APAP hepatotoxicity by enhancing recovery and regeneration, which is mediated through the A2BAR and involves resident liver macrophages.

Factors Affecting the Re-Endothelialization of Endothelial Progenitor Cell

The vascular endothelium, which plays an essential role in maintaining the normal shape and function of blood vessels, is a natural barrier between the circulating blood and the vascular wall tissue. The endothelial damage can cause vascular lesions, such as atherosclerosis and restenosis. After the vascular intima injury, the body starts the endothelial repair (re-endothelialization) to inhibit the neointimal hyperplasia. Endothelial progenitor cell is the precursor of endothelial cells and plays an important role in the vascular re-endothelialization. However, re-endothelialization is inevitably affected in vivo and in vitro by factors, which can be divided into two types, namely, promotion and inhibition, and act on different links of the vascular re-endothelialization. This article reviews these factors and related mechanisms.

Diagnostic efficacy of serum and urinary netrin-1 in the early detection of diabetic nephropathy

This study aimed to assess the diagnostic value of serum and urinary netrin-1 in patients with type 2 diabetes mellitus (T2DM) at different stages of diabetic nephropathy (DN) and to compare its efficacy of estimation in serum with that in the urine. This study was carried out on 135 patients with T2DM and 45 healthy subjects. The patients with diabetes were divided according to urinary albumin creatinine ratio (UACR) into: T2DM with normoalbuminuria, incipient DN with microalbuminuria, and overt DN with macroalbuminuria groups. Serum and urinary levels of netrin-1 were measured by ELISA. The mean levels of serum and urinary netrin-1 were significantly higher in the microalbuminuric and macroalbuminuric patients with DN than those in the normoalbuminuric patients with T2DM, with the highest values detected in macroalbuminuric patients with DN. Urinary netrin-1 level was significantly higher in the normoalbuminuric T2DM group than control group, whereas no significant difference existed regarding serum netrin-1 level. In T2DM groups, the urinary and serum netrin-1 correlated with each other and were independently related to fasting blood glucose, UACR, and estimated glomerular filtration rate. Receiver operating characteristic curve analysis showed that the area under the curve of urinary netrin-1 was 0.916 which is significantly higher than that of serum netrin-1 (0.812) for the detection of incipient DN and reached 0.938 on coestimation of both urinary and serum netrin-1. In conclusion, netrin-1 is a potential diagnostic marker for early detection of DN with its estimation in urine has higher accuracy than that of serum.

Functionalizing biomaterials to promote neurovascular regeneration following skeletal muscle injury

During embryogenesis, blood vessels and nerves develop with similar branching structure in response to shared signaling pathways guiding network growth. With both systems integral to physiological homeostasis, dual targeting of blood vessels and nerves to promote neurovascular regeneration following injury is an emerging therapeutic approach in biomedical engineering. A limitation to this strategy is that the nature of cross talk between emergent vessels and nerves during regeneration in an adult is poorly understood. Following peripheral nerve transection, intraneural vascular cells infiltrate the site of injury to provide a migratory pathway for mobilized Schwann cells of regenerating axons. As Schwann cells demyelinate, they secrete vascular endothelial growth factor, which promotes angiogenesis. Recent advances point to concomitant restoration of neurovascular architecture and function through simultaneous targeting of growth factors and guidance cues shared by both systems during regeneration. In the context of traumatic injury associated with volumetric muscle loss, we consider the nature of biomaterials used to engineer three-dimensional scaffolds, functionalization of scaffolds with molecular signals that guide and promote neurovascular growth, and seeding scaffolds with progenitor cells. Physiological success is defined by each tissue component of the bioconstruct (nerve, vessel, muscle) becoming integrated with that of the host. Advances in microfabrication, cell culture techniques, and progenitor cell biology hold great promise for engineering bioconstructs able to restore organ function after volumetric muscle loss.

Netrins: Evolutionarily Conserved Regulators of Epithelial Fusion and Closure in Development and Wound Healing

Epithelial remodelling plays a crucial role during development. The ability of epithelial sheets to temporarily lose their integrity as they fuse with other epithelial sheets underpins events such as the closure of the neural tube and palate. During fusion, epithelial cells undergo some degree of epithelial-mesenchymal transition (EMT), whereby cells from opposing sheets dissolve existing cell-cell junctions, degrade the basement membrane, extend motile processes to contact each other, and then re-establish cell-cell junctions as they fuse. Similar events occur when an epithelium is wounded. Cells at the edge of the wound undergo a partial EMT and migrate towards each other to close the gap. In this review, we highlight the emerging role of Netrins in these processes, and provide insights into the possible signalling pathways involved. Netrins are secreted, laminin-like proteins that are evolutionarily conserved throughout the animal kingdom. Although best known as axonal chemotropic guidance molecules, Netrins also regulate epithelial cells. For example, Netrins regulate branching morphogenesis of the lung and mammary gland, and promote EMT during Drosophila wing eversion. Netrins also control epithelial fusion during optic fissure closure and inner ear formation, and are strongly implicated in neural tube closure and secondary palate closure. Netrins are also upregulated in response to organ damage and epithelial wounding, and can protect against ischemia-reperfusion injury and speed wound healing in cornea and skin. Since Netrins also have immunomodulatory properties, and can promote angiogenesis and re-innervation, they hold great promise as potential factors in future wound healing therapies.

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.

Pharmacological postconditioning: a molecular aspect in ischemic injury

OBJECTIVE

Ischaemia/reperfusion (I/R) injury is defined as the damage to the tissue which is caused when blood supply returns to tissue after ischaemia. To protect the ischaemic tissue from irreversible injury, various protective agents have been studied but the benefits have not been clinically applicable due to monotargeting, low potency, late delivery or poor tolerability.

KEY FINDINGS

Strategies involving preconditioning or postconditioning can address the issues related to the failure of protective therapies. In principle, postconditioning (PoCo) is clinically more applicable in the conditions in which there is unannounced ischaemic event. Moreover, PoCo is an attractive beneficial strategy as it can be induced rapidly at the onset of reperfusion via series of brief I/R cycles following a major ischaemic event or it can be induced in a delayed manner. Various pharmacological postconditioning (pPoCo) mechanisms have been investigated systematically. Using different animal models, most of the studies on pPoCo have been carried out preclinically.

SUMMARY

However, there is a need for the optimization of the clinical protocols to quicken pPoCo clinical translation for future studies. This review summarizes the involvement of various receptors and signalling pathways in the protective mechanisms of pPoCo.

Role of Extracellular Matrix in Gastrointestinal Cancer-Associated Angiogenesis

Gastrointestinal tumors are responsible for more cancer-related fatalities than any other type of tumors, and colorectal and gastric malignancies account for a large part of these diseases. Thus, there is an urgent need to develop new therapeutic approaches to improve the patients' outcome and the tumor microenvironment is a promising arena for the development of such treatments. In fact, the nature of the microenvironment in the different gastrointestinal tracts may significantly influence not only tumor development but also the therapy response. In particular, an important microenvironmental component and a potential therapeutic target is the vasculature. In this context, the extracellular matrix is a key component exerting an active effect in all the hallmarks of cancer, including angiogenesis. Here, we summarized the current knowledge on the role of extracellular matrix in affecting endothelial cell function and intratumoral vascularization in the context of colorectal and gastric cancer. The extracellular matrix acts both directly on endothelial cells and indirectly through its remodeling and the consequent release of growth factors. We envision that a deeper understanding of the role of extracellular matrix and of its remodeling during cancer progression is of chief importance for the development of new, more efficacious, targeted therapies.

Effect of Serum Netrin-1 Levels on Diagnosis and Prognosis in Patients Admitted to the Emergency Service for Acute Coronary Syndrome

Background

Netrin-1 is a recently discovered diagnostic biomarker that indicates atherosclerosis, angiogenesis, and ischemia-reperfusion damage. There are no human studies about Netrin-1 in acute coronary syndrome (ACS). The purpose of the present study was to investigate Netrin-1 levels in the early diagnosis and successful reperfusion of ACS.

Method

The study was conducted with 188 patients diagnosed with ACS and 50 healthy subjects at the emergency unit in a prospective design. Blood samples were collected from the patient group at initial admission and after angiography. The control group consisted of healthy adult subjects without any disease. Netrin-1 levels were studied in both groups.

Results

The Netrin-1 levels of the patient group at the time of admission were found to be higher than of the control group (p<0.001). In the patient group, netrin-1 levels measured at initial admission (1.53±0.19) and after angiography (1.49±0.19) were determined to be statistically significant (p:0.049). In the patient group, where the Thrombolysis in Myocardial Infarction (TIMI) 3 flow was established after angiography, netrin-1 levels were detected to be low (p:0.039). Netrin-1 levels obtained at the time of admission were determined to be significantly different in the Global Registry of Acute Coronary Events (GRACE) moderate and high-risk groups in comparison to the low-risk group (p:0.017).

Conclusion

Netrin-1 was shown to increase in the early diagnosis of ACS and to decrease in patients for whom reperfusion was established after angiography. Therefore, Netrin-1 can be an important biomarker as an indicator of diagnosis and successful reperfusion in ACS.

Morinda citrifolia (Noni) fruit juice promotes vascular endothelium function in hypertension via glucagon-like peptide-1 receptor-CaMKKβ-AMPK-eNOS pathway

Morinda citrifolia (Noni) is extensively used in herbal remedies to prevent and treat various diseases, including hypertension. The purpose of this study was to investigate the vascular effects of noni fruit juice and characterize the upstream signaling pathways. We measured the systolic blood pressure, diastolic blood pressure, 24-hr urinary nitric oxide (NO) metabolite excretion, bodyweight (BW), and urine examination in SHR.Cg-Leprcp/NDmcr (SHR/cp) rats after 6 weeks noni juice (15 ml/kg) treatment. Noni juice significantly decreased blood pressure and 24-hr urinary NO metabolite without change of BW or urine volume. Furthermore, the noni juice extract (NJE) promoted endothelial vasorelaxation in rat aorta rings and NO product through an increase in phosphorylation of endothelial nitric oxide synthase (eNOS) in human umbilical vein endothelial cells (HUVECs). NJE might act on a glucagon like peptide-1 receptor (GLP-1R) via Ca²⁺ /calmodulin-dependent protein kinase kinase β (CaMKKβ)-AMPK signaling with pretreatment of their inhibitors or antagonist in HUVECs. Deacetylasperulosidic acid (DAA) was an active compound in noni juice to improve NO release through same pathway in HUVECs. These results suggested that noni is a novel dietary plant that probably regulates GLP-1R-induced CaMKKβ-AMPK-eNOS pathway to improve endothelium-dependent relaxation, thus reduce the blood pressure probably via one of its responsible ingredient DAA.

Ischemia-induced Netrin-4 promotes neovascularization through endothelial progenitor cell activation via Unc-5 Netrin receptor B

Endothelial progenitor cells (EPCs) promote neovascularization and tissue repair by migrating to vascular injury sites; therefore, factors that enhance EPC homing to damaged tissues are of interest. Here, we provide evidence of the prominent role of the Netrin-4 (NTN4)-Unc-5 Netrin receptor B (UNC5B) axis in EPC-specific promotion of ischemic neovascularization. Our results showed that NTN4 promoted the proliferation, chemotactic migration, and paracrine effects of small EPCs (SEPCs) and significantly increased the incorporation of large EPCs (LEPCs) into tubule networks. Additionally, NTN4 prominently augmented neovascularization in mice with hindlimb ischemia by increasing the homing of exogenously transplanted EPCs to the ischemic limb and incorporating EPCs into vessels. Moreover, silencing of UNC5B, an NTN4 receptor, abrogated the NTN4-induced cellular activities of SEPCs in vitro and blood-flow recovery and neovascularization in vivo in ischemic muscle by reducing EPC homing and incorporation. These findings suggest NTN4 as an EPC-based therapy for treating angiogenesis-dependent diseases.

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.

Netrin-1 plays a role in the effect of moderate exercise on myocardial fibrosis in rats

INTRODUCTION

This study aimed to investigate the effect of aerobic exercise on the expression of neitrin-1,DCC receptor and myocardial fibrosis in rats with acute myocardial infarction.

METHODS

Twenty-four rats were randomly divided into three groups: the sham group (n = 8), the acute myocardial infarction (AMI) model group (n = 8), and the aerobic exercise treatment after acute myocardial infarction group (ET) (n = 8). After 10 weeks, the serum levels of netrin-1, tumor necrosis factor alpha α (TNF-α), and interleukin 6 (IL-6) were measured. The expression of matrix metalloproteinase 2 and 9 (MMP2, 9), and their inhibitor, tissue inhibitor of metalloproteinase 2 (TIMP2), myocardial netrin-1, and the deleted in colorectal cancer (DCC) receptor were evaluated. Histopathological results were also evaluated. The collagen volume fraction of the myocardial tissues was also calculated.

RESULTS

Compared with the sham group, in the AMI and ET groups, left ventricular end diastolic pressure (LVEDP) were increased, while left ventricular systolic pressure (LVSP), and left ventricular pressure maximal rate of rise and fall (± dp/dtmax) were significantly decreased (P<0.05,). Compared with the AMI group, in the ET group, LVSP, and ±dp/dtmax were significantly increased while LVEDP was decreased (P<0.05). Compared with the sham group, the AMI group and ET groups showed increased levels of serum TNF-α, IL-6 and significantly reduced levels of netrin-1. Levels of TNF-α and IL-6 were significantly reduced in the ET group compared with the AMI group, whereas the level of netrin-1 was increased. The expression of myocardial MMP2 and MMP9 was significantly increased in the AMI group compared with the sham group, whereas that of myocardial netrin-1, TIMP2 and the DCC receptor, was significantly reduced. Compared with the AMI group, the ET group showed reduced expression of myocardial MMP2 and MMP9 proteins, whereas expression of myocardial netrin-1, TIMP2 and the DCC receptor, was significantly increased. The collagen volume fraction of the myocardial tissues was significantly increased in the AMI group and the ET group compared with the sham group, with a greater increase in the AMI group.

CONCLUSIONS

Aerobic exercise increased levels of serum netrin-1, myocardial netrin-1, and the DCC receptor and reduced the expression of myocardial MMP2 and MMP9 proteins, to improve the degree of fibrosis following myocardial infarction in rats.

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.

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-1 attenuates brain injury after middle cerebral artery occlusion via downregulation of astrocyte activation in mice

Background

Netrin-1 functions largely via combined receptors and downstream effectors. Evidence has shown that astrocytes express netrin-1 receptors, including DCC and UNC5H2. However, whether netrin-1 influences the function of astrocytes was previously unknown.

Methods

Lipopolysaccharide was used to stimulate the primary cultured astrocytes; interleukin release was used to track astrocyte activation. In vivo, shRNA and netrin-1 protein were injected in the mouse brain. Infarct volume, astrocyte activation, and interleukin release were used to observe the function of netrin-1 in neuroinflammation and brain injury after middle cerebral artery occlusion.

Results

Our results demonstrated that netrin-1 reduced lipopolysaccharide-induced interleukin-1β and interleukin-12β release in cultured astrocytes, and blockade of the UNC5H2 receptor with an antibody reversed this effect. Additionally, netrin-1 increased p-AKT and PPAR-γ expression in primary cultured astrocytes. In vivo studies showed that knockdown of netrin-1 increased astrocyte activation in the mouse brain after middle cerebral artery occlusion (p < 0.05). Moreover, injection of netrin-1 attenuated GFAP expression (netrin-1 0.27 ± 0.06 vs. BSA 0.62 ± 0.04, p < 0.001) and the release of interleukins and reduced infarct volume after brain ischemia (netrin-1 0.27 ± 0.06 vs. BSA 0.62 ± 0.04 mm³, p < 0.05).

Conclusion

Our results indicate that netrin-1 is an important molecule in regulating astrocyte activation and neuroinflammation in cerebral ischemia and provides a potential target for ischemic stroke therapy.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1291-5) contains supplementary material, which is available to authorized users.

Egr-1 increases angiogenesis in cartilage via binding Netrin-1 receptor DCC promoter

Background

Osteoarthritis (OA) is a joint disease characterized by degradation of cartilage. The etiology of OA is still unclear. Vascular endothelial growth factor (VEGF) plays a key role of angiogenesis in the pathogenesis of OA and contributes to the angiogenesis of NT-1/DCC. Whether or not NT-1/DCC and VEGF interact in regulating angiogenesis of OA cartilage is not known.

Methods

Histological studies for CD34, VEGF, and safranin-O staining were performed to determine angiogenesis and cartilage tissue injury. ELISA indicated the level of pro-inflammation cytokines. Immunoblotting, immunoprecipitation, and electrophoretic mobility shift assay (EMSA) were performed to assay the expression and function of NT-1/DCC-VEGF signaling pathway.

Results

Our data indicated that VEGF expression was increased in cartilage tissue from OA rats, while the chondrocytes were disorganized, and cartilage degeneration was increasing in OA rats. The inflammation factors in articular cavity fluid were higher in the OA rats than in the sham. The protein expression of NT-1, DCC, and VEGF were increased in osteoarthritic cartilage. DCC was involved in the positive regulation of osteoarthritic angiogenesis by VEGF. Egr-1 expression was higher in OA rats than in sham rats. Egr-1 is a regulator of DCC promoter activity, and the binding is higher in OA rats than in sham rats.

Conclusion

Our present study provides a mechanism by which Egr-1 induced angiogenesis via NT-1/DCC-VEGF pathway.

Netrin-1 promotes metastasis of gastric cancer by regulating YAP activity

Yes-associated protein (YAP) is a major downstream molecular of the Hippo pathway, which plays important role in cancer development. Netrin-1 conveys oncogenic activity in many types of malignant tumors. However, the downstream signaling of netrin-1 mediating its oncogenic effects in gastric cancer (GC) is not well defined. Here, we aim to investigate the role of netrin-1 in metastasis potential of GC by regulating YAP. In this study, we showed that netrin-1 inhibition significantly decreased migration and invasion abilities of GC cells, while netrin-1 overexpression effectively reversed this effect. We also demonstrated that netrin-1 upregulated YAP expression via its transmembrane receptor neogenin. Furthermore, our in vitro and in vivo results showed that the effect of netrin-1 on GC cells migration and invasion abilities was regulated by YAP. Collectively, our results defined netrin-1 as a positive regulator of malignant tumor metastasis in GC by activating the YAP signaling, with potential implications for new approaches to GC therapy.

Netrin-1 suppresses the MEK/ERK pathway and ITGB4 in pancreatic cancer

The axon guidance factor netrin-1 promotes tumorigenesis in multiple types of cancers, particularly at their advanced stages. Here, we investigate whether netrin-1 is involved in the in vivo growth of pancreatic adenocarcinoma. We show that netrin-1 is significantly under-expressed in stage-I/II pancreatic ductal adenocarcinoma (PDAC). Netrin-1 over-expression effectively arrests the growth of xenografted PDAC cells without decreasing cell proliferation or increasing apoptosis in two-dimensional cultures in vitro. Integrin-beta4 (ITGB4) expression is significantly reduced, and ITGB4-knockdown mimics the tumor-suppressive effect of netrin-1, implying that ITGB4 is a main target of netrin-1 in constraining PDAC. We further show that netrin-1 signals to UNC5B/FAK to stimulate nitric oxide production, which promotes PP2A-mediated inhibition of the MEK/ERK pathway and decreases phosphorylated-c-Jun recruitment to the ITGB4 promoter. Our findings suggest that netrin-1 can suppress the growth of PDAC and provide a mechanistic insight into this suppression.

Genetic association of deleted in colorectal carcinoma variants with breast cancer risk: A case-control study

Deleted in colorectal carcinoma (DCC), a netrin-1 dependence receptor, is correlated with cell progression, migration, and adhesion. Evidence indicated that DCC was frequently down-regulated in many cancers. However, the association of DCC with breast cancer remains uncertain. We conducted a case-control study to investigate the impact of three DCC gene variants (rs2229080, rs7504990, and rs4078288) on breast cancer susceptibility in Chinese women. This study included 560 breast cancer patients and 583 age-matched healthy controls from Northwest China. The three gene variants were genotyped via Sequenom MassARRAY. Odds ratios (ORs) and 95% confidence intervals (CIs) were utilized to evaluate the associations. We found that individuals with the rs2229080 C/G, C/C, and C/G-CC genotypes had a higher breast cancer risk, and the minor allele C was associated with increased breast cancer risk in an allele model. We observed a significantly decreased breast cancer risk with the rs7504990 C/T, T/T, and C/T-T/T genotypes, and the minor allele T was protective against breast cancer in an allele model. In addition, rs2229080 was associated with the axillary lymph node (LN) metastasis status. An age-stratified analysis revealed an association between rs2229080 and reduced breast cancer risk among older patients (≥ 49 years). Furthermore, the haplotype analysis showed that the Crs2229080Crs7504990Ars4078288 haplotype was associated with a decreased breast cancer risk. However, the results indicated a lack of association between rs4078288 and breast cancer risk. These findings affirmed that rs2229080 and rs7504990 polymorphisms in DCC might be related with breast cancer susceptibility in Chinese women.

Netrin-1 Ameliorates Blood-Brain Barrier Impairment Secondary to Ischemic Stroke via the Activation of PI3K Pathway

Secondary impairment of blood-brain barrier (BBB) occurs in the remote thalamus after ischemic stroke. Netrin-1, an axonal guidance molecule, presents bifunctional effects on blood vessels through receptor-dependent pathways. This study investigates whether netrin-1 protects BBB against secondary injury. Netrin-1 (600 ng/d for 7 days) was intracerebroventricularly infused 24 h after middle cerebral artery occlusion (MCAO) in hypertensive rats. Neurological function was assessed 8 and 14 days after MCAO, and the permeability of BBB in the ipsilateral thalamus was detected. The viability of brain microvascular endothelial cells was determined after being disposed with netrin-1 (50 ng/mL) before oxygen-glucose deprivation (OGD). The role of netrin-1 was further explored by examining its receptors and their function. We found that netrin-1 infusion improved neurological function, attenuated secondary impairment of BBB by up-regulating the levels of tight junction proteins and diminishing extravasation of albumin, with autophagy activation 14 days after MCAO. Netrin-1 also enhanced cell survival and autophagy activity in OGD-treated cells, inhibited by UNC5H2 siRNA transfection. Furthermore, the beneficial effects of netrin-1 were suppressed by PI3K inhibitors 3-Methyladenine and LY294002. Our results showed that netrin-1 ameliorated BBB impairment secondary to ischemic stroke by promoting tight junction function and endothelial survival. PI3K-mediated autophagy activation depending on UNC5H2 receptor could be an underlying mechanism.

Netrin-1 Promotes Inflammation Resolution to Achieve Endothelialization of Small-Diameter Tissue Engineering Blood Vessels by Improving Endothelial Progenitor Cells Function In Situ

The transplant of small-diameter tissue engineering blood vessels (small-diameter TEBVs) (<6 mm) in vascular replacement therapy often fails because of early onset thrombosis and long-standing chronic inflammation. The specific inflammation state involved in small-diameter TEBVs transplants remains unclear, and whether promoting inflammation resolution would be useful for small-diameter TEBVs therapy need study. The neural protuberant orientation factor 1 (Netrin-1) is found present in endothelial cells of natural blood vessels and has anti-inflammatory effects. This work generates netrin-1-modified small-diameter TEBVs by using layer-by-layer self-assembly to resolve the inflammation. The results show that netrin-1 reprograms macrophages (MΦ) to assume an anti-inflammatory phenotype and promotes the infiltration and subsequent efflux of MΦ from inflamed sites over time, which improves the local microenvironment and the function of early homing endothelial progenitor cells (EPCs). Small-diameter TEBVs modified by netrin-1 achieve endothelialization after 30 d and retain patency at 14 months. These findings suggest that promoting the resolution of inflammation in time is necessary to induce endothelialization of small-diameter TEBVs and prevent early thrombosis and problems associated with chronic inflammation. Furthermore, this work finds that the MΦ-derived exosomes can target and regulate EPCs, which may serve as a useful treatment for other inflammatory diseases.

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.

Activation of Inflammatory and Pro-Thrombotic Pathways in Acute Stress Cardiomyopathy

Stress cardiomyopathy (SCM) is a unique cardiac disorder that more often occurs in women. SCM presents in a similar fashion as acute myocardial infarction (AMI), with chest pain, ECG changes, and congestive heart failure. The primary distinguishing feature is the absence of thrombotic coronary occlusion in SCM. How this reduction in cardiac function occurs in the absence of coronary occlusion remains unknown. Therefore, we tested the hypothesis that a targeted proteomic comparison of patients with acute SCM and AMI might identify relevant mechanistic differences. Blood was drawn in normal controls (n = 6), women with AMI (n = 12), or women with acute SCM (n = 15). Two-week follow-up samples were available in AMI (n = 4) and SCM patients (n = 11). Relative concentrations of 1,310 serum proteins were measured in each of the 48 samples using the SOMAscan assay. Women with AMI had greater myocyte necrosis, as reflected by a higher peak troponin I concentration (AMI 32.03 ± 29.46 vs. SCM 2.68 ± 2.6 ng/ml, p < 0.05). AMI and SCM patients had equivalent reductions in left ventricular ejection fraction [LVEF (%) 39 ± 12 vs. 37 ± 12, p = 0.479]. In follow-up, women with SCM had a greater improvement in cardiac function [LVEF (%) 60 ± 7 vs. 45 ± 13, p < 0.001]. No differentially expressed proteins were detected (absolute log2-fold change >1; q < 0.05) between AMI and SCM in the acute or recovery phase. However, when we compared normal controls to patients with AMI, there was differential expression of 35 proteins. When we compared normal controls to patients with SCM, 45 proteins were differentially expressed. In comparison to normal controls, biological processes such as complement, coagulation, and inflammation were activated in both AMI and SCM. There were four proteins that showed a non-significant trend to be increased in acute SCM vs. AMI (netrin-1, follistatin-like 3, kallikrein 7, kynureninase). Despite a lesser degree of myocardial necrosis than AMI, SCM is characterized by a similar activation of inflammatory, complement, and coagulation pathways. These findings may explain reported thromboembolic complications in the short term and elevated risk of mortality in the long term of SCM.

Neuron-derived netrin-1 and netrin-4 proteins are additional effective targets in diabetic retinopathy beyond VEGF

Vascular endothelial growth factor (VEGF) is the typical representative factor of diabetic retinopathy (DR) and is considered to be a key inducer of retinal vascular permeability in DR. Anti-VEGF has been widely used in clinical treatment but every patient is effective, therefore, it is necessary to find other effective factors that participate in the pathology of DR. We provide evidence from both human and animal experiments for the considerable roles of classical neuronal guidance factors, netrin-1 and netrin-4, in indicating and amending the pathology of DR. We reveal that levels of both netrin-1 and netrin-4 are reduced while VEGF increases in DR patients and animal models. We demonstrate through different experimental methods that augmenting netrin-1 and netrin-4 can alleviate vasculopathy and neuropathy which appear in DR. Our findings offer additional effect targets besides VEGF for DR and suggest we should increase the focus on neurovascular crosstalk as DR is a neurovascular disease.

Netrin-1 in cancer: Potential biomarker and therapeutic target?

Netrin-1, a laminin-related protein, is known to be involved in the nervous system development. Recently, Netrin-1's involvement in other processes such as cell adhesion, motility, proliferation, and differentiation that are important for the development of epithelial tissues has been described. In addition, Netrin-1 and its receptors, deleted in colorectal cancer and uncoordinated-5 homolog, have been linked to apoptosis and angiogenesis. Since these properties are essential for tumor development, Netrin-1 and its receptors have been reported to promote tumorigenesis in many types of cancers. Here, we review the Netrin-1 mediated regulation of cancer, its potential use as a biomarker, and the targeting of the Netrin-1 pathway to treat cancers.