Expression of netrin-1 and its receptors, deleted in colorectal cancer and uncoordinated locomotion-5 homolog B, in rat brain following focal cerebral ischemia reperfusion injury

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.

Netrin-1 reduces lung ischemia-reperfusion injury by increasing the proportion of regulatory T cells

Objective

Inflammation is the primary mechanism of lung ischemia-reperfusion injury (LIRI) and neurologic factors can regulate inflammatory immune responses. Netrin-1 is an axonal guidance molecule, but whether Netrin-1 plays a role in LIRI remains unclear.

Methods

A mouse model of LIRI was established. Immunohistochemistry was used to detect expression of Netrin-1 and to enumerate macrophages and T cells in lung tissue. The proportion of regulatory T cells (Tregs) was assessed by flow cytometry. Levels of apoptosis were assessed by terminal deoxynucleotidyl transferase dUTP nick end staining.

Results

Numbers of macrophages and T cells in the lung tissues of mice with LIRI were elevated, while expression of netrin-1 was significantly decreased. Flow cytometry showed that the proportion of Tregs in mice with LIRI was significantly decreased. The proportion of Tregs among lymphocytes was positively correlated with netrin-1 expression. In vitro experiments showed that netrin-1 promoted an increase in Treg proportion through the A2b receptor. Animal experiments showed that netrin-1 could inhibit apoptosis and reduce T cell and macrophage infiltration by increasing the proportion of Tregs, ultimately reducing LIRI. Treg depletion using an anti-CD25 monoclonal antibody blocked the effects of netrin-1.

Conclusion

Netrin-1 reduced LIRI by increasing the proportion of Tregs.

Electroacupuncture decreases Netrin-1-induced myelinated afferent fiber sprouting and neuropathic pain through μ-opioid receptors

Purpose: We determined whether electroacupuncture (EA) reduces Netrin-1-induced myelinated primary afferent nerve fiber sprouting in the spinal cord and pain hypersensitivity associated with postherpetic neuralgia (PHN) through activation of μ-opioid receptors.

Methods: PHN was induced by systemic injection of resiniferatoxin (RTX) in rats. Thirty-six days after RTX injection, a μ-opioid receptor antagonist, beta-funaltrexamine (β-FNA) or a κ-opioid receptor antagonist, nor Binaltorphimine (nor-BNI), was injected intrathecally 30 mins before EA, once every other day for 4 times. Mechanical allodynia was tested with von Frey filaments. The protein expression level of Netrin-1 and its receptors (DCC and UNC5H2) were quantified by using western blotting. The myelinated primary afferent nerve fiber sprouting was mapped with the transganglionic tracer cholera toxin B-subunit (CTB).

Results: Treatment with 2 Hz EA at “Huantiao” (GB30) and “Yanglingquan” (GB34) decreased the mechanical allodynia at 22 days and the myelinated primary afferent nerve fiber preternatural sprouting into the lamina II of the spinal dorsal horn at 42 days after RTX injection. Also, treatment with 2 Hz EA reduced the protein levels of DCC and Netrin-1 and promoted the expression of UNC5H2 in the spinal dorsal horn 42 days after RTX injection. Furthermore, the μ-opioid receptor antagonist β-FNA, but not the κ-opioid receptor antagonist nor-BNI, reversed the effect of EA on neuropathic pain caused by RTX. In addition, morphine inhibited the Netrin-1 protein level induced by RTX in SH-SY5Y cells.

Conclusions: Through activation of μ-opioid receptors, treatment with EA reduces the expression level of DCC and Netrin-1 and changes a growth-permissive environment in spinal dorsal horn into an inhibitory environment by increasing UNC5H2, thus decreasing RTX-caused primary afferent nerve sprouting in the spinal dorsal horn and neuropathic pain.

The microRNAs let-7 and miR-9 down-regulate the axon-guidance genes Ntn1 and Dcc during peripheral nerve regeneration

Axon guidance helps growing neural axons to follow precise paths to reach their target locations. It is a critical step for both the formation and regeneration of neuronal circuitry. Netrin-1 (Ntn1) and its receptor, deleted in colorectal carcinoma (Dcc) are essential factors for axon guidance, but their regulation in this process is incompletely understood. In this study, using quantitative real-time RT-PCR (qRT-PCR) and biochemical and reporter gene assays, we found that the Ntn1 and Dcc genes are both robustly up-regulated in the sciatic nerve stump after peripheral nerve injury. Moreover, we found that the microRNA (miR) let-7 directly targets the Ntn1 transcript by binding to its 3'-untranslated region (3'-UTR), represses Ntn1 expression, and reduces the secretion of Ntn1 protein in Schwann cells. We also identified miR-9 as the regulatory miRNA that directly targets Dcc and found that miR-9 down-regulates Dcc expression and suppresses the migration ability of Schwann cells by regulating Dcc abundance. Functional examination in dorsal root ganglion neurons disclosed that let-7 and miR-9 decrease the protein levels of Ntn1 and Dcc in these neurons, respectively, and reduce axon outgrowth. Moreover, we identified a potential regulatory network comprising let-7, miR-9, Ntn1, Dcc, and related molecules, including the RNA-binding protein Lin-28 homolog A (Lin28), SRC proto-oncogene nonreceptor tyrosine kinase (Src), and the transcription factor NF-κB. In summary, our findings reveal that the miRs let-7 and miR-9 are involved in regulating neuron pathfinding and extend our understanding of the regulatory pathways active during peripheral nerve regeneration.

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.

Microarray Profiling and Co-Expression Network Analysis of LncRNAs and mRNAs in Neonatal Rats Following Hypoxic-ischemic Brain Damage

Long noncoding RNAs (lncRNAs) play critical roles in cellular homeostasis. However, little is known about their effect in developing rat brains with hypoxic-ischemic brain damage (HIBD). To explore the expression and function of lncRNA in HIBD, we analyzed the expression profiles of lncRNAs in hypoxic-ischemic (HI) brains and sham control using microarray analysis. The results showed a remarkable difference in lncRNA between HI and sham brains. A total of 322 lncRNAs were found to be differentially expressed in HI brains, compared to sham control. Among these, BC088414 was one of the most significantly urpregulated lncRNAs. In addition, 375 coding genes were differentially expressed between HI brains and sham control. Pathway and gene ontology analysis indicated that the upregulated coding genes mostly involved in wounding, inflammation and defense, whereas the downregulated transcripts were largely associated with neurogenesis and repair. Moreover, coding non-coding co-expression network analysis showed that the BC088414 lncRNA expression was correlated with apoptosis-related genes, including Casp6 and Adrb2. Silencing of lncRNA BC088414 in PC12 cells caused reduced mRNA level of Casp6 and Adrb2, decreased cell apoptosis and increased cell proliferation. These results suggested lncRNA might participate in the pathogenesis of HIBD via regulating coding genes.