Netrin-1 overexpression improves neurobehavioral outcomes and reduces infarct size via inhibition of the notch1 pathway following experimental stroke

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.

Netrin-1 attenuates cerebral ischemia/reperfusion injury by limiting mitochondrial ROS and Ca2+ levels via activation of AKT phosphorylation and mitochondrial m-AAA protease AFG3L2

Cerebral ischemia-reperfusion (I/R) injury as the consequence of revascularization after ischemic stroke is associated with mitochondrial dysfunction, oxidative stress, and neuron loss. In this study, we used a deprivation/reoxygenation (OGD/R) model to determine whether interactions between Netrin-1, AKT, and the mitochondrial AAA protease AFG3L2 could influence mitochondrial function in neurons after I/R. We found that Netrin-1 protects primary cortical neurons from OGD/R-induced cell death and regulates mitochondrial reactive oxygen species (ROS) and Ca²⁺ levels. The accumulation of mitochondrial calcium uniporter (MCU) subunits was monitored in cells by immunoblot analysis. Although the regulatory subunits MICU1 and MICU2 were relatively unaffected, the accumulation of the essential MCU regulator (EMRE) subunit was impaired. In OGD/R-induced cells, the 7 kDa form of EMRE was significantly reduced. Netrin-1 inhibited the accumulation of EMRE and mitochondrial Ca²⁺ levels by upregulating AFG3L2 and AKT activation. Loss of AFG3L2 or inhibition of AKT increased levels of 7 kDa EMRE. Moreover, overexpression of AKT increased the expression of AFG3L2 in Netrin-1-knockdown neurons after OGD/R. Our results demonstrate that Netrin-1 enhanced AFG3L2 protein expression via activation of AKT. We also observed that overexpression of Netrin-1 significantly reduced infarction size in an I/R-induced brain injury model in rats but not when AKT was inhibited. Our data suggest that AFG3L2 is a protein substrate of AKT and indicate that Netrin-1 attenuates cerebral I/R injury by limiting mitochondrial ROS and Ca²⁺ levels through activating AKT phosphorylation and AFG3L2.

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.

The Prognostic Value of Deleted in Colorectal Cancer (DCC) Receptor and Serum Netrin-1 in Severe Traumatic Brain Injury

Traumatic brain injury (TBI) is a common neurological disease. Netrin-1 and deleted in colorectal cancer (DCC) receptor are potential biomarkers associated with nerve regeneration and immune regulation. We aimed to investigate the ability of the DCC receptor and Netrin-1 to predict a high ICP level after operation in severe traumatic brain injury and their prognostic significance. This study is a prospective observational study. We selected 23 patients with traumatic brain injury who had undergone surgical operations as subjects. Immunohistochemical staining was performed on the contusion tissue that was removed by the operation to determine the expression of DCC receptor. At the same time, enzyme-linked immunosorbent assay (ELISA) kits were used to detect the serum Netrin-1 content. Determination of intracranial pressure (ICP) value was measured by intraventricular catheter. The Glasgow Outcome Scale (GOS) score at six months after trauma was defined as the main study endpoint. The results showed that serum Netrin-1 concentrations of patients in the critical TBI group (GCS 3–5 points) was significantly lower than that in the severe TBI group (GCS 6–8 points). The ICP peak and average mannitol consumption in the high Netrin-1 group were significantly lower than those in the low Netrin-1 group. DCC receptor-positive patients had a significantly lower ICP peak. There was no significant difference in six month-GOS scores between patients in the high and low Netrin-1 groups, while DCC receptor concentrations below 3.82 ng/mL predicted poor prognosis (GOS 1–3 points). In conclusion, the expression level of the DCC receptor can better evaluate the postoperative high ICP level and prognosis than the level of serum Netrin-1 in severe traumatic brain injury.

Ginkgetin Promotes M2 Polarization of Microglia and Exert Neuroprotection in Ischemic Stroke via Modulation of PPARγ Pathway

Neuroinflammation plays an important role in the pathophysiological process of acute cerebral infarction, which may aggravate brain injury and hinder neuro-repair. Microglia are innate immune cells in the brain. Ginkgetin has anti-inflammatory and neuroprotective effects, but the mechanism remains unclear. This study aims to explore the regulatory effects of ginkgetin on microglia polarization in brain ischemia. Oxygen glucose deprivation (OGD) cellular model and middle cerebral artery occlusion (MCAO) animal model was used in this study. We first observed the dynamic process of microglia polarization in ischemic stroke, and then investigated the effect of ginkgetin treatment on microglia polarization. Finally, we studied the role of PPARγ signaling pathway and the blocking effect of PPARγ antagonist GW9662 in this process. OGD and cerebral ischemia polarized microglia mainly to M1 type. However, ginkgetin treatment converted microglia from M1 type to M2 type, inhibited neuroinflammation, and exerted neuronal protective effects. PPARγ signaling pathway was activated during this process. The above effects could be blocked by GW9662. Ginkgetin can promote M2 polarization of microglia through PPARγ signaling pathway, thereby inhibiting neuroinflammation and promoting recovery of neurological functions in ischemic stroke.

Analysis of Antiapoptosis Effect of Netrin-1 on Ischemic Stroke and Its Molecular Mechanism under Deleted in Colon Cancer/Extracellular Signal-Regulated Kinase Signaling Pathway

To analyze the regulatory effect of Netrin-1 in ischemic stroke and its influence on Deleted in Colon Cancer (DCC)/Extracellular Signal-regulated Kinase (ERK) signaling pathway, 20 male rats were selected to construct the rat model of middle cerebral artery occlusion (MCAO), 10 normal rats were selected as healthy controls (Normal Saline (NS)), and they were divided into the MCAO+Netrin-1 group, MCAO group, and NS group according to different treatment schemes. The positive expression of Netrin-1 was detected by immunostaining, magnetic resonance imaging (MRI) was adopted to detect the percentage of rat cerebral infarct volume in the cerebral hemispheres, and Modified Neurological Severity Score (mNSS) was adopted to evaluate postoperative neurological function in rats. Besides, a tunnel staining experiment was applied to detect the apoptosis rate of rat neurons, the sticker removal test was applied to evaluate the postoperative sensory function of rats, and fluorescence staining was adopted to detect the expression of DCC and ERK in rats. The results showed that the percentage of cerebral infarction volume in the cerebral hemispheres of the MCAO+Netrin-1 group was higher than that of the MCAO and NS groups (P < 0.05); in the MCAO+Netrin-1 group, the MCAO mNSS scoring and the time spent in the sticker removal test were lower than the MCAO group (P < 0.05); the apoptosis rate of rats in the MCAO+Netrin-1 group was lower than that in the MCAO group (P < 0.05); the average fluorescence intensity of DCC and p-ERK in the MCAO+Netrin-1 group was higher than that in the MCAO group (P < 0.05); the average fluorescence intensity of p-ERK in the MCAO+Netrin-1 group was higher than that in the MCAO group (P < 0.05). In short, Netrin-1 can effectively reduce the brain tissue damage in rats with ischemic stroke, improve the nerve function and sensory function of rats, and inhibit neuronal cell apoptosis. Netrin-1 can promote DCC expression and ERK phosphorylation, and the EPK signaling pathway may be involved in the antiapoptotic effect of Netrin-1.

Decreased Serum Netrin-1 as a Predictor for Post-Stroke Depression in Chinese Patients with Acute Ischemic Stroke

BACKGROUND AND AIMS

Experimental studies demonstrated that netrin-1 (NT-1) is an important factor influencing the recovery after ischemic stroke. However, whether NT-1 levels were associated with the post-stroke depression (PSD) remains unclear. We aimed to evaluate the relationship between NT-1 levels and PSD at 3 months in patients with ischemic stroke.

METHODS

From January 2018 to December 2019, consecutive Chinese patients with first-ever ischemic stroke were prospectively recruited. Serum NT-1 levels were measured at admission. Patients with a 17-item Hamilton Depression Scale score of ≥7 were given the Structured Clinical Interview of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, for diagnosis of PSD.

RESULTS

A total of 238 patients (mean age, 62.5 years; 45.4% female) were enrolled. The median NT-1 concentrations were 467.8 pg/mL (interquartile range, 351.8-581.0 pg/mL). During the 3-month follow-up period, 64 patients (26.9%) experienced PSD. Serum NT-1 levels were significantly lower in PSD patients than in patients without PSD (median, 380.3 pg/mL versus 478.5 pg/mL; P = 0.001). After adjusting for demographic characteristic, National Institutes of Health stroke score, and other potential confounders by multiple logistic regression analysis, patients with NT-1 levels in the first quartile were more likely to have 3-month PSD (as compared with the fourth quartile, odds ratio 3.83, 95% confidence intervals, 1.53-9.63, P = 0.004). Similar significant findings were observed when the NT-1 levels were added as a continuous variable.

CONCLUSIONS

Our data demonstrated that decreased serum NT-1 levels, in a Chinese population, were significantly associated with PSD at 3 months.

Increased Serum Netrin-1 Is Associated With Improved Prognosis of Ischemic Stroke

Background and Purpose- Previous experimental studies suggested that serum netrin-1 was associated with the progression of ischemic stroke. Knowledge about netrin-1 among ischemic stroke patients may provide new ideas for the prognostic assessment of ischemic stroke. The aim of this study was to investigate the association between serum netrin-1 and prognosis of ischemic stroke. Methods- Serum netrin-1 levels at baseline were measured for 3346 ischemic stroke patients from the CATIS (China Antihypertensive Trial in Acute Ischemic Stroke), and all patients were followed up at 3 months after stroke onset. The primary outcome was a combination of death and major disability (modified Rankin Scale score of ≥3) within 3 months after stroke onset. Results- Up to 3 months after stroke onset, 845 patients (25.25%) experienced death or major disability. After adjustment for baseline National Institutes of Health Stroke Scale score and other potential confounders, elevated serum netrin-1 was associated with a decreased risk of primary outcome (odds ratio, 0.65; 95% CI, 0.47-0.88; P_trend=0.002) when 2 extreme quartiles were compared. Each SD increase of log-transformed netrin-1 was associated with 17% (95% CI, 7%-26%) decreased risk of primary outcome. Multivariable-adjusted spline regression models showed a negative linear dose-response relationship between serum netrin-1 and the risk of primary outcome ( P_linearity=0.003). Adding netrin-1 quartile to a model containing conventional risk factors improved risk prediction for primary outcome (net reclassification improvement index =14.74%; P=0.002; integrated discrimination improvement =0.40%; P=0.005). Conclusions- Elevated serum netrin-1 levels were associated with improved prognosis at 3 months after ischemic stroke, suggesting that serum netrin-1 may be a potential prognostic biomarker for ischemic stroke. Further studies from other samples of ischemic stroke patients are needed to replicate our findings and to clarify the potential mechanisms. Clinical Trial Registration- URL: https://www.clinicaltrials.gov . Unique identifier: NCT01840072.

Melatonin attenuates white matter damage after focal brain ischemia in rats by regulating the TLR4/NF-κB pathway

OBJECTIVE

To assess the possible neuroprotective effects of melatonin against brain white matter damage via the Toll-like receptor 4 (TLR4)/ nuclear factor-kappa B (NF-κB) signaling pathway in focal cerebral ischemic rats.

METHODS

Fifty-four Sprague-Dawley rats were randomly divided into the Sham, middle cerebral artery occlusion (MCAO), and melatonin groups. The successful MCAO models were evaluated by Laser Doppler flowmetry, magnetic resonance imaging (MRI) with T2-weighted imaging (T2WI) examination and 2, 3, 5-triphenyltetrazolium chloride (TTC) staining. White matter damage was assessed by myelin basic protein (MBP) immunohistochemical, Luxol Fast Blue (LFB) staining, and diffusion tensor imaging (DTI) examination. The proliferation of oligodendrocyte progenitor cells (OPCs) was examined by proliferating cell nuclear antigen (PCNA)/neural glial antigen 2 (NG2)/DAPI immunofluorescent staining. And the effects of melatonin therapy on the TLR4, NF-κB, and interleukin (IL)-1β proteins were examined by immunohistochemical staining. The correlation between the proliferating OPCs and TLR4 protein, IL-1β and TLR4 protein was respectively analyzed by linear regression analysis.

RESULTS

The infarct volume was significantly reduced and white matter damage was also significantly alleviated in the melatonin group as compared with the MCAO group (P <  0.05), and there were more TLR4⁺, NF-κB⁺ and IL-1β⁺ cells in the MCAO group compared with the melatonin group (P <  0.01). Similarly, more PCNA⁺NG2⁺ cells were observed in the subventricular zone and white matter areas in the melatonin group compared with the MCAO group (P <  0.01). The number of TLR4⁺ cells was closely positively correlated with that of IL-1β⁺ cells, and negatively correlated with that of PCNA⁺NG2⁺ cells.

CONCLUSIONS

In summary, melatonin could promote the proliferation of endogenous OPCs and suppress the expression of IL-1β protein via inhibiting TLR4/NF-κB signaling, thus alleviate the white matter damage in focal cerebral ischemic rats.

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.

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.

Netrin-1 Promotes Synaptic Formation and Axonal Regeneration via JNK1/c-Jun Pathway after the Middle Cerebral Artery Occlusion

As a secreted axon guidance molecule, Netrin-1 has been documented to be a neuroprotective factor, which can reduce infarct volume, promote angiogenesis and anti-apoptosis after stroke in rodents. However, its role in axonal regeneration and synaptic formation after cerebral ischemic injury, and the related underlying mechanisms remain blurred. In this study, we used Adeno-associated vectors carrying Netrin-1 gene (AAV-NT-1) to up-regulate the expression level of Netrin-1 in rats’ brain after middle cerebral artery occlusion (MCAO). We found that the up-regulated level of Netrin-1 and its receptor DCC promoted axonal regeneration and synaptic formation; the overexpression of Netrin-1 activated the JNK1 signaling pathway; these effects were partially reduced when JNK1 signaling pathway was inhibited by SP600125 (JNK specific inhibitor). Taken together, these findings suggest that Netrin-1 can facilitate the synaptic formation and axonal regeneration via the JNK1 signaling pathway after cerebral ischemia, thus promoting the recovery of neural functions.

Effects of intra-arterial transplantation of adipose-derived stem cells on the expression of netrin-1 and its receptor DCC in the peri-infarct cortex after experimental stroke

Background

Stem cell transplantation has been documented to promote functional recovery in animal models of stroke; however, the underlying mechanisms are not yet fully understood. As netrin-1 and its receptor deleted in colorectal cancer (DCC) are important regulators in neuronal and vascular activities, the present study attempted to explore whether netrin-1 and DCC are involved in the neuroprotection of stem cell-based therapies in a rat ischemic stroke model.

Methods

Adult male Sprague–Dawley rats were subjected to a transient middle cerebral artery occlusion (MCAO) and subsequently received an intra-arterial injection of 2 × 10⁶ PKH26-labeled adipose-derived stem cells (ADSCs) or saline 24 h later. Neurological function was evaluated by behavioral tests before the rats were sacrificed at days 7 and 14 after MCAO. The migration of ADSCs and regeneration of neuronal fibers and blood vessels were determined by immunofluorescence staining. The expression of netrin-1 and DCC was analyzed by Western blot and immunofluorescence staining.

Results

ADSC transplantation significantly improved the neurological recovery at days 7 and 14, and noticeably promoted the regeneration of neuronal fibers and blood vessels in the peri-infarct cortex at day 14. PKH26-labeled ADSCs located mainly in the peri-infarct area at days 7 and 14. In ADSC-treated rats, the expression of netrin-1 and DCC significantly increased in the peri-infarct cortex at days 7 and 14. Immunofluorescence staining showed that netrin-1 was mainly expressed by neuronal perikaryal in the peri-infarct cortex, and DCC was mainly expressed by neuronal fibers and was present around the blood vessels in the peri-infarct cortex.

Conclusions

These findings suggest that ADSC transplantation facilitates the regeneration of neuronal fibers and blood vessels in the peri-infarct cortex and improves neurological functions, which may be attributed, at least in part, to the involvement of upregulated netrin-1 and DCC in the remodeling of neuronal and vascular networks in the peri-infarct cortex.