Neuroprotection Exerted by Netrin-1 and Kinesin Motor KIF1A in Secondary Brain Injury following Experimental Intracerebral Hemorrhage in Rats

Mitochondrial transport in neurons and evidence for its involvement in acute neurological disorders

Ensuring mitochondrial quality is essential for maintaining neuronal homeostasis, and mitochondrial transport plays a vital role in mitochondrial quality control. In this review, we first provide an overview of neuronal mitochondrial transport, followed by a detailed description of the various motors and adaptors associated with the anterograde and retrograde transport of mitochondria. Subsequently, we review the modest evidence involving mitochondrial transport mechanisms that has surfaced in acute neurological disorders, including traumatic brain injury, spinal cord injury, spontaneous intracerebral hemorrhage, and ischemic stroke. An in-depth study of this area will help deepen our understanding of the mechanisms underlying the development of various acute neurological disorders and ultimately improve therapeutic options.

Decreased Netrin-1 in Mild Cognitive Impairment and Alzheimer’s Disease Patients

Background and Objective

Inflammatory mediators are closely associated with the pathogenesis of Alzheimer’s disease (AD) and mild cognitive impairment (MCI). Netrin-1 is an axon guidance protein and despite its capacity to function as a neuroimmune guidance signal, its role in AD or MCI is poorly understood. In addition, the association among netrin-1, cognitive impairment and serum inflammatory cytokines such as interleukin-17 (IL-17) and tumor necrosis (TNF-α) remains unclear. The aim of this study was to determine serum levels of IL-17, TNF-α and netrin-1in a cohort of AD and MCI patients, and to study the relationship between these cytokines and cognitive status, as well as to assess the possible relationships between netrin-1 levels and inflammatory molecules.

Methods

Serum concentrations of netrin-1, TNF-α and IL-17 were determined in 20 AD patients, 22 MCI patients and 22 healthy controls using an enzyme-linked immunosorbent assay (ELISA). In addition, neuropsychological evaluations and psychometric assessments were performed in all subjects.

Results

Serum netrin-1 levels were decreased in AD and MCI patients and were positively correlated with Mini Mental State Examination (MMSE) scores. In contrast, serum TNF-α and IL-17 levels were elevated in AD and MCI cohorts and negatively correlated with MMSE scores. Serum netrin-1 levels were inversely related with TNF-α and IL-17 levels in AD, but not MCI, patients.

Conclusion

Based on the findings reported here, netrin-1 may serve as a marker for the early recognition of dementia and predict cognitive impairment.

Unraveling Axon Guidance during Axotomy and Regeneration

During neuronal development and regeneration axons extend a cytoskeletal-rich structure known as the growth cone, which detects and integrates signals to reach its final destination. The guidance cues “signals” bind their receptors, activating signaling cascades that result in the regulation of the growth cone cytoskeleton, defining growth cone advance, pausing, turning, or collapse. Even though much is known about guidance cues and their isolated mechanisms during nervous system development, there is still a gap in the understanding of the crosstalk between them, and about what happens after nervous system injuries. After neuronal injuries in mammals, only axons in the peripheral nervous system are able to regenerate, while the ones from the central nervous system fail to do so. Therefore, untangling the guidance cues mechanisms, as well as their behavior and characterization after axotomy and regeneration, are of special interest for understanding and treating neuronal injuries. In this review, we present findings on growth cone guidance and canonical guidance cues mechanisms, followed by a description and comparison of growth cone pathfinding mechanisms after axotomy, in regenerative and non-regenerative animal models.

A Novel Netrin-1-Derived Peptide Enhances Protection against Neuronal Death and Mitigates of Intracerebral Hemorrhage in Mice

It has been reported that Netrin-1 is involved in neuroprotection following injury to the central nervous system. However, the minimal functional domain of Netrin-1 which can preserve the neuroprotection but avoid the major side effects of Netrin remains elusive. Here, we investigated the neuroprotective effect of a peptide E1 derived from Netrin-1′s EGF3 domain (residues 407–422). We found that it interacts with deleted colorectal carcinoma (DCC) to activate focal adhesion kinase phosphorylation exhibiting neuroprotection. The administration of the peptide E1 was able to improve functional recovery through reduced apoptosis in an experimental murine model of intracerebral hemorrhage (ICH). In summary, we reveal a functional sequence of Netrin-1 that is involved in the recovery process after ICH and identify a candidate peptide for the treatment of ICH.

Gene Transcript Alterations in the Spinal Cord, Anterior Cingulate Cortex, and Amygdala in Mice Following Peripheral Nerve Injury

Chronic neuropathic pain caused by nerve damage is a most common clinical symptom, often accompanied by anxiety- and depression-like symptoms. Current treatments are very limited at least in part due to incompletely understanding mechanisms underlying this disorder. Changes in gene expression in the dorsal root ganglion (DRG) have been acknowledged to implicate in neuropathic pain genesis, but how peripheral nerve injury alters the gene expression in other pain-associated regions remains elusive. The present study carried out strand-specific next-generation RNA sequencing with a higher sequencing depth and observed the changes in whole transcriptomes in the spinal cord (SC), anterior cingulate cortex (ACC), and amygdala (AMY) following unilateral fourth lumbar spinal nerve ligation (SNL). In addition to providing novel transcriptome profiles of long non-coding RNAs (lncRNAs) and mRNAs, we identified pain- and emotion-related differentially expressed genes (DEGs) and revealed that numbers of these DEGs displayed a high correlation to neuroinflammation and apoptosis. Consistently, functional analyses showed that the most significant enriched biological processes of the upregulated mRNAs were involved in the immune system process, apoptotic process, defense response, inflammation response, and sensory perception of pain across three regions. Moreover, the comparisons of pain-, anxiety-, and depression-related DEGs among three regions present a particular molecular map among the spinal cord and supraspinal structures and indicate the region-dependent and region-independent alterations of gene expression after nerve injury. Our study provides a resource for gene transcript expression patterns in three distinct pain-related regions after peripheral nerve injury. Our findings suggest that neuroinflammation and apoptosis are important pathogenic mechanisms underlying neuropathic pain and that some DEGs might be promising therapeutic targets.

Serum netrin-1 as a potential biomarker for functional outcome of traumatic brain injury

BACKGROUND

Decreased serum netrin-1 concentrations have been found after acute brain injury. We investigated the role of serum netrin in prognosis of traumatic brain injury (TBI).

METHODS

In this prospective and observational study, enzyme-linked immunosorbent assay was used to detect serum netrin-1 concentrations in 50 mild TBI patients (Glasgow coma scale (GCS) score, 13-15), 83 moderate TBI patients (GCS score, 9-12), 69 severe TBI patients (GCS score, 3-8) and 50 healthy controls. Glasgow outcome scale score of 1-3 at 6 months after trauma was defined as poor outcome.

RESULTS

Serum netrin-1 concentrations were significantly lower in moderate or severe TBI patients than in controls and in severe TBI patients than in moderate TBI patients, while not in mild TBI patients than in controls. GCS score and Rotterdam computed tomography classification were closely correlated with serum netrin-1 concentrations among TBI patients. Forty-two (20.8%) patients had poor outcome. Receiver operating characteristic curve analysis revealed that serum netrin-1 concentrations could distinguish patients with poor outcome from the other remainders significantly. In addition, serum netrin-1 concentrations were independently associated with poor outcome.

CONCLUSIONS

Serum netrin-1 might serve as a potential biomarker for prognosis of TBI.

Intranasal administration of dauricine loaded on graphene oxide: multi-target therapy for Alzheimer's disease

Alzheimer's disease (AD) is a degenerative disease of the central nervous system characterized by progressive cognitive and memory-related impairment. However, current therapeutic treatments have not proved sufficiently effective, mainly due to the complicated pathogenesis of the disease. In this study, a nano-formulation of graphene oxide (GO) loaded with dauricine (Dau) was investigated in terms of the combined anti-inflammatory and anti-oxidative stress effects of Dau and the inhibition of misfolding and aggregation of the amyloid-β (Aβ) protein by GO. Both in vivo and in vitro models were induced using Aβ_1-42, and the formulation was administered nasally in mice. The results showed that GO loaded with Dau greatly reduced oxidative stress through increasing superoxide dismutase levels and decreasing reactive oxygen species and malondialdehyde levels in vitro; it also alleviated the cognitive memory deficits and brain glial cell activation in mice with Aβ_1-42-induced AD. This proved that GO loaded with Dau could protect against Aβ_1-42-induced oxidative damage and apoptosis in both in vitro and in vivo AD models; therefore, GO loaded with Dau has the potential to be an effective and agent for the rapid treatment of AD.

Inhibition of TRIM8 restrains ischaemia-reperfusion-mediated cerebral injury by regulation of NF-κB activation associated inflammation and apoptosis

Stroke is a leading global cause of mortality and disability. However, the pathogenesis that contributes to stroke has not been fully understood. The tripartite motif (TRIM)-containing proteins usually exhibit essential regulatory roles during various biological processes. TRIM8 is a RING domain-containing E3 ubiquitin ligase, playing crucial roles in regulating inflammation and apoptosis. In the present study, we reported that TRIM8 expression was significantly induced in the peri-infarct cortex area of mice after stroke onset. TRIM8 siRNA in vivo transfection resulted in the attenuated cognitive impairments in mice with cerebral ischaemia-reperfusion (IR) injury. In addition, TRIM8 knockdown was neuroprotective, as evidenced by the reduced infarct area, decreased neurological deficit score and down-regulated number of TUNEL-positive cells in the peri-infarct area. Moreover, TRIM8 inhibition obviously repressed glial fibrillary acidic protein (GFAP) expression in peri-hematoma cortex and hippocampus. Furthermore, inflammation induced by cerebral IR injury was highly restrained by TRIM8 knockdown in serum, peri-infarct area and hippocampus, which were along with the remarkable decreases in the phosphorylated expression of IκB kinase alpha (IKKα), inhibitory κB α (IκBα) and nuclear factor kappa B (NF-κB). Moreover, TRIM8 knockdown significantly reduced apoptosis in hippocampus of mice with cerebral IR injury by reducing Caspase-3 cleavage. The in vitro experiment confirmed the neuroprotective role of TRIM8-knockdown in regulating cerebral IR injury. Intriguingly, we found that TRIM8 over-expression-promoted inflammatory response and apoptosis could be markedly attenuated by the inactivation of NF-κB signaling through pre-treatment of JSH-23 or QNZ in lipopolysaccharide (LPS)-incubated astrocytes (ASTs). Therefore, TRIM8 positively regulated cerebral IR injury by activating NF-κB pathway to enhance inflammation and apoptosis. Targeting TRIM8 could provide feasible therapeutic treatment for stroke.

Nrdp1 increases neuron apoptosis via downregulation of Bruce following intracerebral haemorrhage

Background

Neuregulin receptor degradation protein-1 (Nrdp1) is an E3 ubiquitin ligase that plays an important role in regulating cell growth, apoptosis and oxidative stress. However, the data regarding its expression and exact mechanism in neuronal injury following ICH has not been well identified.

Methods

In this study, primary cortical neurons from C57BL/6 mice were subjected to erythrocyte lysates. Nrdp1 expression, cell apoptosis, caspase-3 and BRUCE levels were detected. In addition, inflammatory response, brain edema, and neurological injury in ICH mice were also assessed.

Results

We found that the expression of Nrdp1 was significantly increased in neuron cells accompanied by up-regulation of active caspase-3 and decreased expression of BRUCE (an inhibitor of apoptosis protein). However, inhibiting Nrdp1 levels of neurons reduced caspase-3 activity but induced up-regulation of BRUCE. In vivo, inhibiting Nrdp1 levels increased pro-inflammatory cytokines, brain edema, and neurological injury following ICH.

Conclusions

Taken together, the data suggested that Nrdp1 might play a crucial role in neuronal apoptosis via inhibiting BRUCE following ICH.

Going Too Far Is the Same as Falling Short†: Kinesin-3 Family Members in Hereditary Spastic Paraplegia

Proper intracellular trafficking is essential for neuronal development and function, and when any aspect of this process is dysregulated, the resulting "transportopathy" causes neurological disorders. Hereditary spastic paraplegias (HSPs) are a family of such diseases attributed to over 80 spastic gait genes (SPG), specifically characterized by lower extremity spasticity and weakness. Multiple genes in the trafficking pathway such as those relating to microtubule structure and function and organelle biogenesis are representative disease loci. Microtubule motor proteins, or kinesins, are also causal in HSP, specifically mutations in Kinesin-I/KIF5A (SPG10) and two kinesin-3 family members; KIF1A (SPG30) and KIF1C (SPG58). KIF1A is a motor enriched in neurons, and involved in the anterograde transport of a variety of vesicles that contribute to pre- and post-synaptic assembly, autophagic processes, and neuron survival. KIF1C is ubiquitously expressed and, in addition to anterograde cargo transport, also functions in retrograde transport between the Golgi and the endoplasmic reticulum. Only a handful of KIF1C cargos have been identified; however, many have crucial roles such as neuronal differentiation, outgrowth, plasticity and survival. HSP-related kinesin-3 mutants are characterized mainly as loss-of-function resulting in deficits in motility, regulation, and cargo binding. Gain-of-function mutants are also seen, and are characterized by increased microtubule-on rates and hypermotility. Both sets of mutations ultimately result in misdelivery of critical cargos within the neuron. This likely leads to deleterious cell biological cascades that likely underlie or contribute to HSP clinical pathology and ultimately, symptomology. Due to the paucity of histopathological or cell biological data assessing perturbations in cargo localization, it has been difficult to positively link these mutations to the outcomes seen in HSPs. Ultimately, the goal of this review is to encourage future academic and clinical efforts to focus on "transportopathies" through a cargo-centric lens.

Decreased Netrin-1 and Correlated Th17/Tregs Balance Disorder in Aβ1-42 Induced Alzheimer's Disease Model Rats

There is increasing evidence indicating that inflammation represents a key pathological component of Alzheimer’s disease (AD). A possible factor that may contribute to this process is netrin-1, a neuronal guidance molecule. This molecule has been shown to exert an unexpected immunomodulatory function. However, the potential changes and correlations of netrin-1 with T helper 17/regulatory T cells (Th17/Tregs) as related to inflammation in AD has yet to be examined. In this study, netrin-1 and Th17/Tregs balance were investigated, and the relationship among netrin-1, Th17/Tregs and cognitive function were analyzed in a rat model of AD. In this model, a bilateral intracerebroventricular administration of Amyloid β_1-42 (Aβ_1–42) was used to produce spatial learning and memory deficits, as well as increased neuronal apoptosis, which were detected 7 days after injection for AD7d group and 14 days for AD14d group. Netrin-1 concentrations were significantly down regulated in both serum and cerebrospinal fluid (CSF) of these AD rats, effects which were strongly correlated with cognitive deficits. Increased levels of interleukin (IL)-17 and deceased IL-10 were observed in both the circulation and CSF and were also correlated with the percent of time spent in the target quadrant of AD in these rats. These changes resulted in netrin-1 concentrations being negatively correlated with IL-17 but positively correlated with IL-10 concentrations in the serum and CSF. We also found that the Th17/Tregs balance was disrupted in these AD rats. Collectively, these findings reveal that the reduction in netrin-1 and the correlated disruption of Th17/Tregs balance in AD rats may diminish the immunosuppressive effect of netrin-1 on Th17/Tregs in AD pathogenesis.

Using zebrafish larval models to study brain injury, locomotor and neuroinflammatory outcomes following intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is a devastating condition with limited treatment options, and current understanding of pathophysiology is incomplete. Spontaneous cerebral bleeding is a characteristic of the human condition that has proven difficult to recapitulate in existing pre-clinical rodent models. Zebrafish larvae are frequently used as vertebrate disease models and are associated with several advantages, including high fecundity, optical translucency and non-protected status prior to 5 days post-fertilisation. Furthermore, other groups have shown that zebrafish larvae can exhibit spontaneous ICH. The aim of this study was to investigate whether such models can be utilised to study the pathological consequences of bleeding in the brain, in the context of pre-clinical ICH research.

Here, we compared existing genetic (bubblehead) and chemically inducible (atorvastatin) zebrafish larval models of spontaneous ICH and studied the subsequent disease processes. Through live, non-invasive imaging of transgenic fluorescent reporter lines and behavioural assessment we quantified brain injury, locomotor function and neuroinflammation following ICH. We show that ICH in both zebrafish larval models is comparable in timing, frequency and location. ICH results in increased brain cell death and a persistent locomotor deficit. Additionally, in haemorrhaged larvae we observed a significant increase in macrophage recruitment to the site of injury. Live in vivo imaging allowed us to track active macrophage-based phagocytosis of dying brain cells 24 hours after haemorrhage. Morphological analyses and quantification indicated that an increase in overall macrophage activation occurs in the haemorrhaged brain.

Our study shows that in zebrafish larvae, bleeding in the brain induces quantifiable phenotypic outcomes that mimic key features of human ICH. We hope that this methodology will enable the pre-clinical ICH community to adopt the zebrafish larval model as an alternative to rodents, supporting future high throughput drug screening and as a complementary approach to elucidating crucial mechanisms associated with ICH pathophysiology.