Angiopoietin 2 mediates the differentiation and migration of neural progenitor cells in the subventricular zone after stroke

Associations of Angiopoietin 2 and Vascular Endothelial Growth Factor-A Concentrations with Clinical End Points

BACKGROUND

Angiopoietin 2 regulates endothelial function partially mediated by vascular endothelial growth factor-A (VEGF-A) and may play a role in diabetic kidney disease (DKD). We assessed the association of angiopoietin 2 and VEGF-A with cardiorenal outcomes and investigated the effect of canagliflozin on angiopoietin 2 and VEGF-A concentrations.

METHODS

Two thousand five hundred sixty-five study participants with DKD and available plasma samples treated with canagliflozin or placebo in the Canagliflozin and Kidney Events in Diabetes with Established Nephropathy Clinical Evaluation (CREDENCE) trial were included. Angiopoietin 2 and VEGF-A concentrations were measured at baseline, year 1, and year 3. The primary composite end point of the trial was a composite of kidney failure, doubling of the serum creatinine level, and kidney or cardiovascular death.

RESULTS

Patients with the highest baseline quartile of angiopoietin 2, but not VEGF-A, concentration had the highest risk clinical profile. Treatment with canagliflozin significantly lowered concentrations of angiopoietin 2 (adjusted geometric mean ratio: 0.94; 95% confidence interval, 0.92 to 0.95; P < 0.001), but not VEGF-A. In multivariable-adjusted modeling, each 50% increment in log baseline angiopoietin 2 concentrations was associated with a higher risk of primary composite outcome (hazard ratio, 1.27; 95% confidence interval, 1.13 to 1.43). Angiopoietin 2 change at year 1 compared with baseline explained 10% of the effect of canagliflozin on the primary composite outcome. VEGF-A concentrations were not associated with outcomes, alone or in combination with angiopoietin 2.

CONCLUSIONS

Higher angiopoietin 2 levels were associated with cardiorenal risk among individuals with DKD independent of VEGF-A. Canagliflozin lowered angiopoietin 2 concentrations.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Evaluation of the Effects of Canagliflozin on Renal and Cardiovascular Outcomes in Participants With Diabetic Nephropathy, NCT02065791 .

Angiopoietin-2 and the Vascular Endothelial Growth Factor Promote Migration and Invasion in Hepatocellular Carcinoma- and Intrahepatic Cholangiocarcinoma-Derived Spheroids

Aggressive hepatocellular carcinoma (HCC) overexpressing Angiopoietin-2 (ANG-2) (a protein linked with angiogenesis, proliferation, and epithelial-mesenchymal transition (EMT)), shares 95% of up-regulated genes and a similar poor prognosis with the proliferative subgroup of intrahepatic cholangiocarcinoma (iCCA). We analyzed the pro-invasive effect of ANG-2 and its regulator vascular endothelial growth factor (VEGF) on HCC and CCA spheroids to uncover posUsible common ways of response. Four cell lines were used: Hep3B and HepG2 (HCC), HuCC-T1 (iCCA), and EGI-1 (extrahepatic CCA). We treated the spheroids with recombinant human (rh) ANG-2 and/or VEGF and then observed the changes at the baseline, after 24 h, and again after 48 h. Proangiogenic stimuli increased migration and invasion capability in HCC- and iCCA-derived spheroids and were associated with a modification in EMT phenotypic markers (a decrease in E-cadherin and an increase in N-cadherin and Vimentin), especially at the migration front. Inhibitors targeting ANG-2 (Trebananib) and the VEGF (Bevacizumab) effectively blocked the migration ability of spheroids that had been stimulated with rh-ANG-2 and rh-VEGF. Overall, our findings highlight the critical role played by ANG-2 and the VEGF in enhancing the ability of HCC- and iCCA-derived spheroids to migrate and invade, which are key processes in cancer progression.

C/EBPβ Regulates TFAM Expression, Mitochondrial Function and Autophagy in Cellular Models of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that results from the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Since there are only symptomatic treatments available, new cellular and molecular targets involved in the onset and progression of this disease are needed to develop effective treatments. CCAAT/Enhancer Binding Protein β (C/EBPβ) transcription factor levels are altered in patients with a variety of neurodegenerative diseases, suggesting that it may be a good therapeutic target for the treatment of PD. A list of genes involved in PD that can be regulated by C/EBPβ was generated by the combination of genetic and in silico data, the mitochondrial transcription factor A (TFAM) being among them. In this paper, we observed that C/EBPβ overexpression increased TFAM promoter activity. However, downregulation of C/EBPβ in different PD/neuroinflammation cellular models produced an increase in TFAM levels, together with other mitochondrial markers. This led us to propose an accumulation of non-functional mitochondria possibly due to the alteration of their autophagic degradation in the absence of C/EBPβ. Then, we concluded that C/EBPβ is not only involved in harmful processes occurring in PD, such as inflammation, but is also implicated in mitochondrial function and autophagy in PD-like conditions.

Research hotspots and frotiers of stem cells in stroke: A bibliometric analysis from 2004 to 2022

Background: Stroke is one of the leading causes of mortality and permanent disability worldwide. However, the current stroke treatment has a limited effect. Therefore, a new treatment is urgently needed. Stem cell therapy is a cutting-edge treatment for stroke patients. This study aimed to gain better understanding of global stem cell trends in stroke via a bibliometric analysis. Methods: We used the Web of Science Core Collection to search pertinent articles about stem cells in stroke published between 2004 and 2022. Analysis was conducted using CiteSpace, VOSviewer, and the R package "bibliometrix" to identify publication outputs, countries/regions, institutions, authors/co-cited authors, journals/co-cited journals, co-cited references, and keywords. Results: A total of 6,703 publications were included in the bibliometric analysis. The total number of citations significantly and rapidly increased between 2004 and 2022, with the most pronounced growth pattern observed in the period of 2008-2009. In terms of authoritarian countries, the USA had the most publications among the countries. As for institutions and authors, the most prolific institution was the University of South Florida, followed by Oakland University and then Shanghai Jiao Tong University, and Chopp, M. and Borlongan, Cesario V, had the most output among the authors. Regarding the journals, Cell Transplantation had the highest publication, followed by Brain Research. As for references, "Mesenchymal stem cells as trophic mediators" was the most frequently cited (2,082), and the article entitled Neuronal replacement from endogenous precursors in the adult brain after stroke had the strongest burstiness (strength = 81.35). Emerging hot words in the past decade included "adhesion molecule," "mesenchymal stromal cell," "extracellular vesicle," "pluripotent stem cells," "signaling pathway," "plasticity," and "exosomes." Conclusion: Between 2004 and 2022, the terms "neurogenesis," "angiogenesis," "mesenchymal stem cells," "extracellular vesicle," "exosomes," "inflammation," and "oxidative stress" have emerged as the hot research areas for research on stem cells in stroke. Although stem cells exert a number of positive effects, the main mechanisms for mitigating the damage caused by stroke are still unknown. Clinical challenges may include complicating factors that can affect the efficacy of stem cell therapy, which are worth a deep exploration.

The promoting effect of modified Dioscorea pills on vascular remodeling in chronic cerebral hypoperfusion via the Ang/Tie signaling pathway

Objective

The objective of this study was to investigate the effect of modified Dioscorea pills (MDP) on microcirculatory remodeling in the hippocampus of rats with chronic cerebral hypoperfusion (CCH) through the angiopoietin (Ang)/tyrosine kinase receptor tyrosine kinase with immunoglobulin-like and EGF-like domains (Ang receptor) 2 (Tie-2) signaling pathways, which may underlie the cognitive improvement observed in CCH rats.

Methods

Forty male Sprague-Dawley rats raised under specific pathogen-free conditions were randomly divided into three groups: control group (10 rats), model group (15 rats), and MDP group (15 rats). The rats in the model group and MDP group underwent bilateral common carotid artery occlusion using the 2-vessel occlusion (2-VO) method to induce CCH. Rats in the control group underwent the same surgical procedures as those in the model group, except for ligation and occlusion of the carotid arteries. After 1 week of 2-VO, rats in the MDP group were administered MDP condensed decoction intragastrically at a dose of 1 ml/100 g body weight (prepared by the Preparation Room of Hubei Provincial Hospital of Traditional Chinese Medicine) for 45 days, while rats in the other two groups received normal saline intragastrically with the same dose and duration as the MDP group. After the intervention, all rats were euthanized, and brain perfusion was performed to obtain the hippocampal tissue for analysis. Immunohistochemical staining for CD43 was performed to assess microvessel density (MVD); western blot and the reverse transcription-polymerase chain reaction (RT-PCR) were used to analyze the expression of proteins and genes in angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie-2, and vascular endothelial growth factor (VEGF) proteins and genes in the hippocampal tissue and compute the Ang-1/Ang-2 ratio.

Results

MDP treatment reduced neuronal loss and promoted restoration of the damaged hippocampal structure in CCH rats. The model group showed significantly higher MVD (14.93 ± 1.92) compared to the control group (5.78 ± 1.65) (P < 0.01), whereas MDP treatment further increased MVD (21.19 ± 2.62). Western blot and RT-PCR analysis revealed that CCH significantly increased the expression of Ang-1, Ang-2, Tie-2, and VEGF proteins and genes, while MDP treatment further significantly upregulated the expression of these proteins and genes. In addition, MDP significantly elevated the gene and protein expression of the Ang-1/Ang-2 ratio compared to the control group (P = 0.041, P = 0.029).

Conclusion

CCH induces microvascular neogenesis in the hippocampus, and MDP promotes angiogenesis and microcirculation remodeling in CCH rats via the Ang/Tie signaling pathway, which may be an important mechanism for its restorative effects on hippocampal perfusion and improvement of cognitive function in CCH rats.

Neuroprotective Effect of Angiopoietin2 Is Associated with Angiogenesis in Mouse Brain Following Ischemic Stroke

Angiogenic factors play an important role in protecting, repairing, and reconstructing vessels after ischemic stroke. In the brains of transient focal cerebral ischemic mice, we observed a reduction in infarct volume after the administration of Angiopoietin 2 (Angpt2), but whether this process is promoted by Angpt2-induced angiogenesis has not been fully elaborated. Therefore, this study explored the angiogenic activities, in reference to CD34 which is a marker of activated ECs and blood vessels, of cultured ECs in vitro and in ischemic damaged cerebral area in mice following Angpt2 administration. Our results demonstrate that Angpt2 administration (100 ng/mL) is neuroprotective by significantly increasing the CD34 expression in in vitro-cultured ECs, reducing the infarct volume and mitigating neuronal loss, as well as enhancing CD34⁺ vascular length and area. In conclusion, these results indicate that Angpt2 promotes repair and attenuates ischemic injury, and that the mechanism of this is closely associated with angiogenesis in the brain after stroke.

Stoichiometric Post-Modification of Hydrogel Microparticles Dictates Neural Stem Cell Fate in Microporous Annealed Particle Scaffolds

Microporous annealed particle (MAP) scaffolds are generated from assembled hydrogel microparticles (microgels). It has been previously demonstrated that MAP scaffold are porous, biocompatible, and recruit neural progenitor cells (NPCs) to the stroke cavity after injection into the stroke core. Here, the goal is to study NPC fate inside MAP scaffolds in vitro. To create plain microgels that can later be converted to contain different types of bioactivities, the inverse electron-demand Diels-Alder reaction between tetrazine and norbornene is utilized, which allows the post-modification of plain microgels stoichiometrically. As a result of adhesive peptide attachment, NPC spreading leads to contractile force generation which can be recorded by tracking microgel displacement. Alternatively, non-adhesive peptide integration results in neurosphere formation that grows within the void space of MAP scaffolds. Although the formed neurospheres do not impose a contractile force on the scaffolds, they are seen to continuously transverse the scaffolds. It is concluded that MAP scaffolds  can be engineered to either promote neurogenesis or enhance stemness depending on the chosen post-modifications of the microgels, which can be key in modulating their phenotypes in various applications in vivo.

The angiopoietin-Tie2 pathway regulates Purkinje cell dendritic morphogenesis in a cell-autonomous manner

Neuro-vascular communication is essential to synchronize central nervous system development. Here, we identify angiopoietin/Tie2 as a neuro-vascular signaling axis involved in regulating dendritic morphogenesis of Purkinje cells (PCs). We show that in the developing cerebellum Tie2 expression is not restricted to blood vessels, but it is also present in PCs. Its ligands angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) are expressed in neural cells and endothelial cells (ECs), respectively. PC-specific deletion of Tie2 results in reduced dendritic arborization, which is recapitulated in neural-specific Ang1-knockout and Ang2 full-knockout mice. Mechanistically, RNA sequencing reveals that Tie2-deficient PCs present alterations in gene expression of multiple genes involved in cytoskeleton organization, dendritic formation, growth, and branching. Functionally, mice with deletion of Tie2 in PCs present alterations in PC network functionality. Altogether, our data propose Ang/Tie2 signaling as a mediator of intercellular communication between neural cells, ECs, and PCs, required for proper PC dendritic morphogenesis and function.

Decreased angiogenesis as a possible pathomechanism in cervical degenerative myelopathy

Endogenous immune mediated reactions of inflammation and angiogenesis are components of the spinal cord injury in patients with degenerative cervical myelopathy (DCM). The aim of this study was to identify alteration of certain mediators participating in angiogenetic and inflammatory reactions in patients with DCM. A consecutive series of 42 patients with DCM and indication for surgical decompression were enrolled for the study. 28 DCM patients were included, as CSF samples were taken preoperatively. We enrolled 42 patients requiring surgery for a thoracic abdominal aortic aneurysm (TAAA) as neurologically healthy controls. In 38 TAAA patients, CSF samples were taken prior to surgery and thus included. We evaluated the neurological status of patients and controls prior to surgery including NDI and mJOA. Protein-concentrations of factors with a crucial role in inflammation and angiogenesis were measured in CSF via ELISA testing (pg/ml): Angiopoietin 2, VEGF-A and C, RANTES, IL 1 beta and IL 8. Additionally, evaluated the status of the blood-spinal cord barrier (BSCB) by Reibers´diagnostic in all participants. Groups evidently differed in their neurological status (mJOA: DCM 10.1 ± 3.3, TAAA 17.3 ± 1.2, p < .001; NDI: DCM 47.4 ± 19.7, TAAA 5.3 ± 8.6, p < .001). There were no particular differences in age and gender distribution. However, we detected statistically significant differences in concentrations of mediators between the groups: Angiopoietin 2 (DCM 267.1.4 ± 81.9, TAAA 408.6 ± 177.1, p < .001) and VEGF C (DCM 152.2 ± 96.1, TAAA 222.4 ± 140.3, p = .04). DCM patients presented a mild to moderate BSCB disruption, controls had no signs of impairment. In patients with DCM, we measured decreased concentrations of angiogenic mediators. These results correspond to findings of immune mediated secondary harm in acute spinal cord injury. Reduced angiogenic activity could be a relevant part of the pathogenesis of DCM and secondary harm to the spinal cord.

HPG-Dependent Peri-Pubertal Regulation of Adult Neurogenesis in Mice

Adult neurogenesis, a striking form of neural plasticity, is involved in the modulation of social stimuli driving reproduction. Previous studies on adult neurogenesis have shown that this process is significantly modulated around puberty in female mice. Puberty is a critical developmental period triggered by increased secretion of the gonadotropin releasing hormone (GnRH), which controls the activity of the hypothalamic-pituitary-gonadal axis (HPG). Secretion of HPG-axis factors at puberty participates to the refinement of neural circuits that govern reproduction. Here, by exploiting a transgenic GnRH deficient mouse model, that progressively loses GnRH expression during postnatal development (GnRH::Cre;Dicer ^loxP/loxP mice), we found that a postnatally-acquired dysfunction in the GnRH system affects adult neurogenesis selectively in the subventricular-zone neurogenic niche in a sexually dimorphic way. Moreover, by examining adult females ovariectomized before the onset of puberty, we provide important evidence that, among the HPG-axis secreting factors, the circulating levels of gonadal hormones during pre-/peri-pubertal life contribute to set-up the proper adult subventricular zone-olfactory bulb neurogenic system.

Epigenetic Mechanisms Underlying Adult Post Stroke Neurogenesis

Stroke remains the leading cause of adult disability. Post-stroke neurogenesis contributes to functional recovery. As an intrinsic neurorestorative process, it is important to elucidate the molecular mechanism underlying stroke-induced neurogenesis and to develop therapies designed specifically to augment neurogenesis. Epigenetic mechanisms include DNA methylation, histone modification and its mediation by microRNAs and long-non-coding RNAs. In this review, we highlight how epigenetic factors including DNA methylation, histone modification, microRNAs and long-non-coding RNAs mediate stroke-induced neurogenesis including neural stem cell self-renewal and cell fate determination. We also summarize therapies targeting these mechanisms in the treatment of stroke.

N-Acetyl-Seryl-Aspartyl-Lysyl-Proline Augments Thrombolysis of tPA (Tissue-Type Plasminogen Activator) in Aged Rats After Stroke

Background and Purpose- Stroke is a leading cause of disability worldwide, mainly affecting the elderly. However, preclinical studies in aged ischemic animals are limited. N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is a naturally occurring tetrapeptide with vascular-protective properties. The present study investigated the effect of AcSDKP on tPA (tissue-type plasminogen activator)-induced thrombolysis in aged rats after ischemic stroke. Methods- Aged male rats (18 months) were subjected to embolic middle cerebral artery occlusion. Rats subjected to 4 hours of middle cerebral artery occlusion were randomized into the following groups: (1) AcSDKP; (2) tPA; (3) AcSDKP in combination with tPA; and (4) saline. Neurological deficits, cerebral microvascular patency and integrity, and infarction were examined at 1 day and 7 days after middle cerebral artery occlusion. In vitro experiments were performed to examine the effect of AcSDKP on aged cerebral endothelial cell permeability. Results- Compared with saline, AcSDKP, or tPA as monotherapy did not have any therapeutic effects, whereas AcSDKP in combination with tPA significantly reduced cerebral tissue infarction and improved neurological outcome without increasing cerebral hemorrhage. Concurrently, the combination treatment significantly augmented microvascular perfusion and reduced thrombosis and blood-brain barrier leakage. In vitro, compared with cerebral endothelial cells from ischemic adult rats, the endothelial cells from ischemic aged rats exhibited significantly increased leakage. AcSDKP suppressed tPA-induced aged endothelial cell leakage and reduced expression of ICAM-1 (intercellular adhesion molecule 1) and NF (nuclear factor)-κB. Conclusions- The present study provides evidence for the therapeutic efficacy of AcSDKP in combination tPA for the treatment of embolic stroke in aged rats at 4 hours after stroke onset. AcSDKP likely acts on cerebral endothelial cells to enhance the benefits of tPA by increasing tissue perfusion and augmenting the integrity of the blood-brain barrier. Visual Overview- An online visual overview is available for this article.

Mesenchymal stem cell exosomes as a cell-free therapy for nerve injury-induced pain in rats

Nerve injury-induced neuropathic pain is difficult to treat. In this study, we used exosomes derived from human umbilical cord mesenchymal stem cell (UCMSC) as a cell-free therapy for nerve injury-induced pain in rats. Isolated UCMSC exosomes range in size from 30 to 160 nm and contain CD63, HSP60, and CD81 exosome markers. After L5/6 spinal nerve ligation surgery, single intrathecal injection of exosomes reversed nerve ligation-induced mechanical and thermal hypersensitivities of right hindpaw of rats at initial and well-developed pain stages. Moreover, continuous intrathecal infusion of exosomes achieved excellent preventive and reversal effects for nerve ligation-induced pain. In immunofluorescent study, lots of Exo-green-labelled exosomes could be found majorly in the ipsilateral L5 spinal dorsal horn, dorsal root ganglion, and peripheral axons, suggesting the homing ability of UCMSC exosomes. They also appeared in the central terminals or cell bodies of IB4, CGRP, and NF200 sensory neurons. In addition, exosome treatment suppressed nerve ligation-induced upregulation of c-Fos, CNPase, GFAP, and Iba1. All these data suggest that the analgesic effects of exosomes may involve their actions on neuron and glial cells. Exosomes also inhibited the level of TNF-α and IL-1β, while enhanced the level of IL-10, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor in the ipsilateral L5/6 dorsal root ganglion of nerve-ligated rats, indicating anti-inflammatory and proneurotrophic abilities. Protein analysis revealed the content of vascular endothelial growth factor C, angiopoietin-2, and fibroblast growth factor-2 in the exosomes. In summary, intrathecal infusion of exosomes from UCMSCs may be considered as a novel therapeutic approach for nerve injury-induced pain.

Angiopoietin: A Novel Neuroprotective/Neurotrophic Agent

Angiopoietin (Ang) is an angiogenic factor, but its neuroprotective and neurotrophic effects have recently come to light. Ang exerts neuroprotective effects by inhibiting neuronal apoptosis, protecting the blood-brain/blood-spinal cord barrier, reducing inflammation and promoting neovascularization. In addition, Ang can also promote neural development and neurite outgrowth via activation of the PI3K/Akt signaling pathway and binding to the Tie2 receptor and/or integrin receptor. In addition, Ang and vascular endothelial growth factor (VEGF) are known to interact in blood vessels in the nervous system and the combination of Ang and VEGF can mitigate the negative effects of VEGF, such as inflammation and local edema. These data indicated that Ang is a novel neuroprotective/neurotrophic factor, which may become a new tool for the treatment of nerve injury.

Role of Angiopoietin-2 in Vascular Physiology and Pathophysiology

Angiopoietins 1–4 (Ang1–4) represent an important family of growth factors, whose activities are mediated through the tyrosine kinase receptors, Tie1 and Tie2. The best characterized are angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2). Ang1 is a potent angiogenic growth factor signaling through Tie2, whereas Ang2 was initially identified as a vascular disruptive agent with antagonistic activity through the same receptor. Recent data demonstrates that Ang2 has context-dependent agonist activities. Ang2 plays important roles in physiological processes and the deregulation of its expression is characteristic of several diseases. In this review, we summarize the activity of Ang2 on blood and lymphatic endothelial cells, its significance in human physiology and disease, and provide a current view of the molecular signaling pathways regulated by Ang2 in endothelial cells.

Angioneurins - Key regulators of blood-brain barrier integrity during hypoxic and ischemic brain injury

The loss of blood-brain barrier (BBB) integrity leading to vasogenic edema and brain swelling is a common feature of hypoxic/ischemic brain diseases such as stroke, but is also central to the etiology of other CNS disorders. In the past decades, numerous proteins, belonging to the family of angioneurins, have gained increasing attention as potential therapeutic targets for ischemic stroke, but also other CNS diseases attributed to BBB dysfunction. Angioneurins encompass mediators that affect both neuronal and vascular function. Recently, increasing evidence has been accumulated that certain angioneurins critically determine disease progression and outcome in stroke among others through multifaceted effects on the compromised BBB. Here, we will give a concise overview about the family of angioneurins. We further describe the most important cellular and molecular components that contribute to structural integrity and low permeability of the BBB under steady-state conditions. We then discuss BBB alterations in ischemic stroke, and highlight underlying cellular and molecular mechanisms. For the most prominent angioneurin family members including vascular endothelial growth factors, angiopoietins, platelet-derived growth factors and erythropoietin, we will summarize current scientific literature from experimental studies in animal models, and if available from clinical trials, on the following points: (i) spatiotemporal expression of these factors in the healthy and hypoxic/ischemic CNS, (ii) impact of loss- or gain-of-function during cerebral hypoxia/ischemia for BBB integrity and beyond, and (iii) potential underlying molecular mechanisms. Moreover, we will highlight novel therapeutic strategies based on the activation of endogenous angioneurins that might improve BBB dysfuntion during ischemic stroke.

Angiopoietin-2 induces the neuronal differentiation of mouse embryonic NSCs via phosphatidylinositol 3 kinase-Akt pathway-mediated phosphorylation of mTOR

The fate of neural stem cells (NSCs) is decided by numerous growth factors. Among these factors, the well-known angiogenic factor angiopoietin-2 (Ang-2) has been revealed to participate in neurogenesis separate from its role in angiogenesis. However, the effect of Ang-2 on the fate determination of mouse embryonic NSCs and the underlying mechanism remain unclear. This result of this study indicated that treatment of mouse embryonic NSCs with 200 ng/ml Ang-2 significantly promoted neuronal differentiation without affecting glial differentiation, and mammalian target of rapamycin (mTOR) was phosphorylated in a phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner during this process. Rapamycin, a specific mTOR inhibitor, suppressed the increase in neuronal differentiation stimulated by Ang-2, and this suppression did not result from an effect of Ang-2 or rapamycin on the apoptosis of differentiated NSCs. Collectively, our research demonstrates that PI3K/Akt pathway-mediated mTOR phosphorylation plays an important role in the Ang-2-enhanced neuronal differentiation of mouse embryonic NSCs.

Ablation of the microRNA-17-92 cluster in neural stem cells diminishes adult hippocampal neurogenesis and cognitive function

Impairment of adult neurogenesis in the hippocampus causes cognitive deficits; however, the underlying molecular mechanisms have not been fully elucidated. microRNAs (miRNAs) regulate neural stem cell (NSC) function. With the use of a transgenic mouse line with conditional ablation of the miR-17-92 cluster in nestin lineage NSCs, we tested the hypothesis that the miR-17-92 cluster regulates adult neurogenesis and cognitive function in vivo. Compared with wild-type mice, ablation of the miR-17-92 cluster significantly reduced the number of proliferating NSCs and neuroblasts and neuronal differentiation in the dentate gyrus (DG) of the hippocampus and significantly impaired hippocampal-dependent learning and memory, as assayed by social recognition memory, novel object recognition, and Morris water-maze tests. Statistical analysis showed a highly significant correlation between newly generated neuroblasts in the DG and cognition deficits in miR-17-92 knockout (KO) mice. Western blot analysis showed that conditional KO of the miR-17-92 cluster significantly increased and reduced a cytoskeleton-associated protein, Enigma homolog 1 (ENH1), and its downstream transcription factor, inhibitor of differentiation 1 (ID1), respectively, as well as increased phosphatase and tensin homolog gene. These proteins are related to neuronal differentiation. Our study demonstrates that the miR-17-92 cluster in NSCs is critical for cognitive and behavioral function and regulates neurogenesis and that the miR-17-92 cluster may target ENH1/ID1 signaling.-Pan, W. L., Chopp, M., Fan, B., Zhang, R., Wang, X., Hu, J., Zhang, X. M., Zhang, Z. G., Liu, X. S. Ablation of the microRNA-17-92 cluster in neural stem cells diminishes adult hippocampal neurogenesis and cognitive function.

A heparan sulfate-based matrix therapy reduces brain damage and enhances functional recovery following stroke

Alteration of the extracellular matrix (ECM) is one of the major events in the pathogenesis of brain lesions following ischemic stroke. Heparan sulfate mimetics (HSm) are synthetic pharmacologically active polysaccharides that promote ECM remodeling and tissue regeneration in various types of lesions. HSm bind to growth factors, protect them from enzymatic degradation and increase their bioavailability, which promotes tissue repair. As the ECM is altered during stroke and HSm have been shown to restore the ECM, we investigated the potential of HSm4131 (also named RGTA-4131®) to protect brain tissue and promote regeneration and plasticity after a stroke. Methods: Ischemic stroke was induced in rats using transient (1 h) intraluminal middle cerebral artery occlusion (MCAo). Animals were assigned to the treatment (HSm4131; 0.1, 0.5, 1.5, or 5 mg/kg) or vehicle control (saline) groups at different times (1, 2.5 or 6 h) after MCAo. Brain damage was assessed by MRI for the acute (2 days) and chronic (14 days) phases post-occlusion. Functional deficits were evaluated with a battery of sensorimotor behavioral tests. HSm4131-^99mTc biodistribution in the ischemic brain was analyzed between 5 min and 3 h following middle cerebral artery reperfusion. Heparan sulfate distribution and cellular reactions, including angiogenesis and neurogenesis, were evaluated by immunohistochemistry, and growth factor gene expression (VEGF-A, Ang-2) was quantified by RT-PCR. Results: HSm4131, administered intravenously after stroke induction, located and remained in the ischemic hemisphere. HSm4131 conferred long-lasting neuroprotection, and significantly reduced functional deficits with no alteration of physiological parameters. It also restored the ECM, and increased brain plasticity processes, i.e., angiogenesis and neurogenesis, in the affected brain hemisphere. Conclusion: HSm represent a promising ECM-based therapeutic strategy to protect and repair the brain after a stroke and favor functional recovery.

The protective effect of microRNA-21 in neurons after spinal cord injury

STUDY DESIGN

Experimental animal study.

OBJECTIVES

To validate the anti-apoptosis effect of microRNA-21 in neurons after spinal cord injury (SCI) and explore the mechanism.

SETTING

Xiangya Hospital, Central South University, Changsha, Hunan, People's Republic of China.

METHODS

In situ hybridization was used to detect the expression of miR-21 in spinal cord neurons (n = 24). In a rat contusion SCI model (n = 48), we upregulated the miR-21 level around the injured area using miR-21 lentiviral vectors and evaluated the therapeutic effect with histology and behavioural scores. In neuronal cells, oxygen-glucose deprivation (OGD) was exerted to imitate SCI, and we explored the biomechanism using molecular biology and a dual-luciferase reporter assay.

RESULTS

miR-21 was expressed in spinal cord neurons and was found to improve neuronal survival and promote functional recovery in rat SCI models. The in vitro results in PC-12 cells revealed that the augmentation of endogenous miR-21 was able to reduce neuronal cell death after OGD. In addition, overexpression of miR-21 was able to reduce cellular apoptosis via decreasing PDCD4 protein levels, and caspase-3 activity was also influenced. Transfection of miR-21 into 293T cells was able to decrease luciferase activity in a reporter assay system, including the 3' untranslated region of PDCD4.

CONCLUSIONS

miR-21 may have a protective role in neuronal apoptosis after SCI. PDCD4 may be a functional target gene involved in the miR-21-mediated anti-apoptotic effect through an miR-21/PDCD4/caspase-3 pathway.

Neonatal systemic inflammation and the risk of low scores on measures of reading and mathematics achievement at age 10 years among children born extremely preterm

BACKGROUND

Difficulties with reading and math occur more commonly among children born extremely preterm than among children born at term. Reasons for this are unclear.

METHODS

We measured the concentrations of 27 inflammatory-related and neurotrophic/angiogenic proteins (angio-neurotrophic proteins) in multiple blood specimens collected a week apart during the first postnatal month from 660 children born before the 28th week of gestation who at age 10 years had an IQ ≥ 70 and a Wechsler Individual Achievement Test 3rd edition (WIAT-III) assessment. We identified four groups of children, those who had a Z-score ≤ -1 on the Word Reading assessment only, on the Numerical Operations assessment only, on both of these assessments, and on neither, which served as the referent group. We then modeled the risk of each learning limitation associated with a top quartile concentration of each protein, and with high and lower concentrations of multiple proteins.

RESULTS

The protein profile of low reading scores was confined to the third and fourth postnatal weeks when increased risks were associated with high concentrations of IL-8 and ICAM-1 in the presence of low concentrations of angio-neurotrophic proteins. The profile of low math scores was very similar, except it did not include ICAM-1. In contrast, the profile of low scores on both assessments was present in each of the first four postnatal weeks. The increased risks associated with high concentrations of TNF-α in the first two weeks and of IL-8 and ICAM-1 in the next two weeks were modulated down by high concentrations of angio-neurotrophic proteins.

CONCLUSIONS

High concentrations of angio-neurotrophic proteins appear to reduce/moderate the risk of each learning limitation associated with systemic inflammation. The three categories of limitations have protein profiles with some similarities, and yet some differences, too.

Chronic stress induced disruption of the peri-infarct neurovascular unit following experimentally induced photothrombotic stroke

How stress influences brain repair is an issue of considerable importance, as patients recovering from stroke are known to experience high and often unremitting levels of stress post-event. In the current study, we investigated how chronic stress modified the key cellular components of the neurovascular unit. Using an experimental model of focal cortical ischemia in male C57BL/6 mice, we examined how exposure to a persistently aversive environment, induced by the application of chronic restraint stress, altered the cortical remodeling post-stroke. We focused on systematically investigating changes in the key components of the neurovascular unit (i.e. neurons, microglia, astrocytes, and blood vessels) within the peri-infarct territories using both immunohistochemistry and Western blotting. The results from our study indicated that exposure to chronic stress exerted a significant suppressive effect on each of the key cellular components involved in neurovascular remodeling. Co-incident with these cellular changes, we observed that chronic stress was associated with an exacerbation of motor impairment 42 days post-event. Collectively, these results highlight the vulnerability of the peri-infarct neurovascular unit to the negative effects of chronic stress.

Pediatric Phase I Trial and Pharmacokinetic Study of Trebananib in Relapsed Solid Tumors, Including Primary Tumors of the Central Nervous System ADVL1115: A Children's Oncology Group Phase I Consortium Report

Purpose: Trebananib is a first-in-class antiangiogenic peptibody (peptide-Fc fusion protein) that inhibits Angiopoietin 1 and 2. A pediatric phase 1 trial was performed to define trebananib dose-limiting toxicities (DLT), recommended phase 2 dose (RP2D), and pharmacokinetics (PK).Experimental Design: Trebananib was administered by weekly infusion. Three dose levels (10, 15, or 30 mg/kg/dose) were evaluated using a rolling-six design. Part 2 evaluated a cohort of subjects with primary central nervous system (CNS) tumors. Pharmacokinetic sampling and analysis of peripheral blood biomarkers was performed during the first 4 weeks. Response was evaluated after 8 weeks. Correlative studies included angiogenic protein expression and DCE-MRI.Results: Thirty-seven subjects were enrolled (31 evaluable for toxicity) with median age 12 years (range, 2 to 21). Two of 19 evaluable non-CNS subjects developed DLT at the 30 mg/kg dose level, including venous thrombosis and pleural effusion. In the CNS cohort, 3/12 subjects developed DLT, including decreased platelet count, transient ischemic attack, and cerebral edema with headache and hydrocephalus. Other grade 3 or 4 toxicities included lymphopenia (n = 4), anemia, thrombocytopenia, neutropenia, vomiting, and hypertension (n = 1 each). Response included stable disease in 7 subjects, no partial or complete responses. Two subjects continued study treatment with prolonged stable disease for 18 cycles (neuroblastoma) and 26 cycles (anaplastic astrocytoma). Pharmacokinetics appeared linear over 3 dose levels. Correlative studies demonstrated increased PlGF and sVCAM-1, but no change in endoglin or perfusion by DCE-MRI.Conclusions: Trebananib was well tolerated in pediatric patients with recurrent or refractory solid or CNS tumors. RP2D is 30 mg/kg. Clin Cancer Res; 23(20); 6062-9. ©2017 AACR.

Activity Dependent Modulation of Granule Cell Survival in the Accessory Olfactory Bulb at Puberty

The vomeronasal system (VNS) is specialized in the detection of salient chemical cues triggering social and neuroendocrine responses. Such responses are not always stereotyped, instead, they vary depending on age, sex, and reproductive state, yet the mechanisms underlying this variability are unclear. Here, by analyzing neuronal survival in the first processing nucleus of the VNS, namely the accessory olfactory bulb (AOB), through multiple bromodeoxyuridine birthdating protocols, we show that exposure of female mice to male soiled bedding material affects the integration of newborn granule interneurons mainly after puberty. This effect is induced by urine compounds produced by mature males, as bedding soiled by younger males was ineffective. The granule cell increase induced by mature male odor exposure is not prevented by pre-pubertal ovariectomy, indicating a lesser role of circulating estrogens in this plasticity. Interestingly, the intake of adult male urine-derived cues by the female vomeronasal organ increases during puberty, suggesting a direct correlation between sensory activity and AOB neuronal plasticity. Thus, as odor exposure increases the responses of newly born cells to the experienced stimuli, the addition of new GABAergic inhibitory cells to the AOB might contribute to the shaping of vomeronasal processing of male cues after puberty. Consistently, only after puberty, female mice are capable to discriminate individual male odors through the VNS.

Neural Stem Cell Plasticity: Advantages in Therapy for the Injured Central Nervous System

The physiological and pathological properties of the neural germinal stem cell niche have been well-studied in the past 30 years, mainly in animals and within given limits in humans, and knowledge is available for the cyto-architectonic structure, the cellular components, the timing of development and the energetic maintenance of the niche, as well as for the therapeutic potential and the cross talk between neural and immune cells. In recent years we have gained detailed understanding of the potentiality of neural stem cells (NSCs), although we are only beginning to understand their molecular, metabolic, and epigenetic profile in physiopathology and, further, more can be invested to measure quantitatively the activity of those cells, to model in vitro their therapeutic responses or to predict interactions in silico. Information in this direction has been put forward for other organs but is still limited in the complex and very less accessible context of the brain. A comprehensive understanding of the behavior of endogenous NSCs will help to tune or model them toward a desired response in order to treat complex neurodegenerative diseases. NSCs have the ability to modulate multiple cellular functions and exploiting their plasticity might make them into potent and versatile cellular drugs.

MicroRNA-433 Inhibits the Proliferation and Migration of HUVECs and Neurons by Targeting Hypoxia-Inducible Factor 1 Alpha

Emerging evidence has demonstrated an important role of microRNAs (miRNAs) in the pathogenesis of cerebral infarction. In the present study, a down-regulation of microRNA-433 (miR-433) is identified in hypoxia-induced human umbilical vein vascular endothelial cells (HUVECs) as well as in rat neurons, and is found to be negatively regulated cell proliferation and migration. Moreover, the expression of miR-433 is inversely correlated with the expression of hypoxia-inducible factor 1 alpha (HIF-1α), which has been shown to play critical role in responding to hypoxia conditions. Overexpression or knockdown of miR-433 responsively alters both mRNA and protein levels of HIF-1α and its downstream genes, vascular endothelial growth factor, Glut-1, and Angpt2. In a luciferase reporter system, miR-433 down-regulates the luciferase activity of HIF-1α 3'-UTR, and these effects are abolished by a mutation in the putative miR-433-binding site. Further investigation confirms that knockdown of HIF-1α blocked the stimulatory effect of anti-miR-433, while overexpression of HIF-1α reversed the inhibitory effects of pre-miR-433 on proliferation and migration of HUVEC and neurons. Taken together, our findings indicate that miR-433 plays an important role in response to hypoxia, inhibiting HUVEC and neuron proliferation and migration by down-regulating HIF-1α.

Identification of miRNomes associated with adult neurogenesis after stroke using Argonaute 2-based RNA sequencing

Neurogenesis is associated with functional recovery after stroke. However, the underlying molecular mechanisms have not been fully investigated. Using an Ago2-based RNA immunoprecipitation to immunoprecipated Ago2-RNA complexes followed by RNA sequencing (Ago2 RIP-seq) approach, we profiled the miRNomes in neural progenitor cells (NPCs) harvested from the subventricular zone (SVZ) of the lateral ventricles of young adult rats. We identified more than 7 and 15 million reads in normal and ischemic NPC libraries, respectively. We found that stroke substantially changed Ago2-associated miRNA profiles in NPCs compared to those in non-ischemic NPCs. We also discovered a new complex repertoire of isomiRs and multiple miRNA-miRNA* pairs and numerous novel miRNAs in the non-ischemic and ischemic NPCs. Among them, pc-3p-17172 significantly regulated NPC proliferation and neuronal differentiation. Collectively, the present study reveals profiles of Ago2-associated miRNomes in non-ischemic and ischemic NPCs, which provide a molecular basis to further investigate the role of miRNAs in mediating adult neurogenesis under physiological and ischemic conditions.

Class IIa histone deacetylases affect neuronal remodeling and functional outcome after stroke

We have previously demonstrated that stroke induces nuclear shuttling of class IIa histone deacetylase 4 (HDAC4). Stroke-induced nuclear shuttling of HDAC4 is positively and significantly correlated with improved indices of neuronal remodeling in the peri-infarct cortex. In this study, using a rat model for middle cerebral artery occlusion (MCAO), we tested the effects of selective inhibition of class IIa HDACs on functional recovery and neuronal remodeling when administered 24hr after stroke. Adult male Wistar rats (n = 15-17/group) were subjected to 2 h MCAO and orally gavaged with MC1568 (a selective class IIa HDAC inhibitor), SAHA (a non-selective HDAC inhibitor), or vehicle-control for 7 days starting 24 h after MCAO. A battery of behavioral tests was performed. Lesion volume measurement and immunohistochemistry were performed 28 days after MCAO. We found that stroke increased total HDAC activity in the ipsilateral hemisphere compared to the contralateral hemisphere. Stroke-increased HDAC activity was significantly decreased by the administration of SAHA as well as by MC1568. However, SAHA significantly improved functional outcome compared to vehicle control, whereas selective class IIa inhibition with MC1568 increased mortality and lesion volume and did not improve functional outcome. In addition, MC1568 decreased microtubule associated protein 2 (MAP2, dendrites), phosphorylated neurofilament heavy chain (pNFH, axons) and myelin basic protein (MBP, myelination) immunoreactivity in the peri-infarct cortex. Quantitative RT-PCR of cortical neurons isolated by laser capture microdissection revealed that MC1568, but not SAHA, downregulated CREB and c-fos expression. Additionally, MC1568 decreased the expression of phosphorylated CREB (active) in neurons. Taken together, these findings demonstrate that selective inhibition of class IIa HDACs impairs neuronal remodeling and neurological outcome. Inactivation of CREB and c-fos by MC1568 likely contributes to this detrimental effect.

Exosomes Derived from Mesenchymal Stromal Cells Promote Axonal Growth of Cortical Neurons

Treatment of brain injury with exosomes derived from mesenchymal stromal cells (MSCs) enhances neurite growth. However, the direct effect of exosomes on axonal growth and molecular mechanisms underlying exosome-enhanced neurite growth are not known. Using primary cortical neurons cultured in a microfluidic device, we found that MSC-exosomes promoted axonal growth, whereas attenuation of argonaut 2 protein, one of the primary microRNA (miRNA) machinery proteins, in MSC-exosomes abolished their effect on axonal growth. Both neuronal cell bodies and axons internalized MSC-exosomes, which was blocked by botulinum neurotoxins (BoNTs) that cleave proteins of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. Moreover, tailored MSC-exosomes carrying elevated miR-17-92 cluster further enhanced axonal growth compared to native MSC-exosomes. Quantitative RT-PCR and Western blot analysis showed that the tailored MSC-exosomes increased levels of individual members of this cluster and activated the PTEN/mTOR signaling pathway in recipient neurons, respectively. Together, our data demonstrate that native MSC-exosomes promote axonal growth while the tailored MSC-exosomes can further boost this effect and that tailored exosomes can deliver their selective cargo miRNAs into and activate their target signals in recipient neurons. Neuronal internalization of MSC-exosomes is mediated by the SNARE complex. This study reveals molecular mechanisms that contribute to MSC-exosome-promoted axonal growth, which provides a potential therapeutic strategy to enhance axonal growth.

Intravenous Injection of Clinical Grade Human MSCs After Experimental Stroke: Functional Benefit and Microvascular Effect

Stroke is the leading cause of disability in adults. Many current clinical trials use intravenous (IV) administration of human bone marrow-derived mesenchymal stem cells (BM-MSCs). This autologous graft requires a delay for ex vivo expansion of cells. We followed microvascular effects and mechanisms of action involved after an IV injection of human BM-MSCs (hBM-MSCs) at a subacute phase of stroke. Rats underwent a transient middle cerebral artery occlusion (MCAo) or a surgery without occlusion (sham) at day 0 (D0). At D8, rats received an IV injection of 3 million hBM-MSCs or PBS-glutamine. In a longitudinal behavioral follow-up, we showed delayed somatosensory and cognitive benefits 4 to 7 weeks after hBM-MSC injection. In a separate longitudinal in vivo magnetic resonance imaging (MRI) study, we observed an enhanced vascular density in the ischemic area 2 and 3 weeks after hBM-MSC injection. Histology and quantitative polymerase chain reaction (qPCR) revealed an overexpression of angiogenic factors such as Ang1 and transforming growth factor-1 (TGF-1) at D16 in hBM-MSC-treated MCAo rats compared to PBS-treated MCAo rats. Altogether, delayed IV injection of hBM-MSCs provides functional benefits and increases cerebral angiogenesis in the stroke lesion via a release of endogenous angiogenic factors enhancing the stabilization of newborn vessels. Enhanced angiogenesis could therefore be a means of improving functional recovery after stroke.

Induction of Neurorestoration From Endogenous Stem Cells

Neural stem cells (NSCs) persist in the subventricular zone lining the ventricles of the adult brain. The resident stem/progenitor cells can be stimulated in vivo by neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and/or physical exercise. In both animals and humans, the differentiation and survival of neurons arising from the subventricular zone may also be regulated by the trophic factors. Since stem/progenitor cells present in the adult brain and the production of new neurons occurs at specific sites, there is a possibility for the treatment of incurable neurological diseases. It might be feasible to induce neurogenesis, which would be particularly efficacious in the treatment of striatal neurodegenerative conditions such as Huntington's disease, as well as cerebrovascular diseases such as ischemic stroke and cerebral palsy, conditions that are widely seen in the clinics. Understanding of the molecular control of endogenous NSC activation and progenitor cell mobilization will likely provide many new opportunities as therapeutic strategies. In this review, we focus on endogenous stem/progenitor cell activation that occurs in response to exogenous factors including neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and an enriched environment. Taken together, these findings suggest the possibility that functional brain repair through induced neurorestoration from endogenous stem cells may soon be a clinical reality.

MicroRNA-146a Promotes Oligodendrogenesis in Stroke

Stroke induces new myelinating oligodendrocytes that are involved in ischemic brain repair. Molecular mechanisms that regulate oligodendrogenesis have not been fully investigated. MicroRNAs (miRNAs) are small non-coding RNA molecules that post-transcriptionally regulate gene expression. MiR-146a has been reported to regulate immune response, but the role of miR-146a in oligodendrocyte progenitor cells (OPCs) remains unknown. Adult Wistar rats were subjected to the right middle cerebral artery occlusion (MCAo). In situ hybridization analysis with LNA probes against miR-146a revealed that stroke considerably increased miR-146a density in the corpus callosum and subventricular zone (SVZ) of the lateral ventricle of the ischemic hemisphere. In vitro, overexpression of miR-146a in neural progenitor cells (NPCs) significantly increased their differentiation into O4⁺ OPCs. Overexpression of miR-146a in primary OPCs increased their expression of myelin proteins, whereas attenuation of endogenous miR-146a suppressed generation of myelin proteins. MiR-146a also inversely regulated its target gene-IRAK1 expression in OPCs. Attenuation of IRAK1 in OPCs substantially increased myelin proteins and decreased OPC apoptosis. Collectively, our data suggest that miR-146a may mediate stroke-induced oligodendrogenesis.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

MicroRNAs in the axon locally mediate the effects of chondroitin sulfate proteoglycans and cGMP on axonal growth

Axonal miRNAs locally regulate axonal growth by modulating local protein composition. Whether localized miRNAs in the axon mediate the inhibitory effect of Chondroitin sulfate proteoglycans (CSPGs) on the axon remains unknown. We showed that in cultured cortical neurons, axonal application of CSPGs inhibited axonal growth and altered axonal miRNA profiles, whereas elevation of axonal cyclic guanosine monophosphate (cGMP) levels by axonal application of sildenafil reversed the effect of CSPGs on inhibition of axonal growth and on miRNA profiles. Specifically, CSPGs elevated and reduced axonal levels of miR-29c and integrin β1 (ITGB1) proteins, respectively, while elevation of cGMP levels overcame these CSPG effects. Gain-of- and loss-of-function experiments demonstrated that miR-29c in the distal axon mediates axonal growth downstream of CSPGs and cGMP by regulating axonal protein levels of ITGB1, FAK, and RhoA. Together, our data demonstrate that axonal miRNAs play an important role in mediating the inhibitory action of CSPGs on axonal growth and that miR-29c at least partially mediates this process.

Are neural crest stem cells the missing link between hematopoietic and neurogenic niches?

Hematopoietic niches are defined as cellular and molecular microenvironments that regulate hematopoietic stem cell (HSC) function together with stem cell autonomous mechanisms. Many different cell types have been characterized as contributors to the formation of HSC niches, such as osteoblasts, endothelial cells, Schwann cells, and mesenchymal progenitors. These mesenchymal progenitors have themselves been classified as CXC chemokine ligand (CXCL) 12-abundant reticular (CAR) cells, stem cell factor expressing cells, or nestin-positive mesenchymal stem cells (MSCs), which have been recently identified as neural crest-derived cells (NCSCs). Together, these cells are spatially associated with HSCs and believed to provide appropriate microenvironments for HSC self-renewal, differentiation, mobilization and hibernation both by cell-cell contact and soluble factors. Interestingly, it appears that regulatory pathways governing the hematopoietic niche homeostasis are operating in the neurogenic niche as well. Therefore, this review paper aims to compare both the regulation of hematopoietic and neurogenic niches, in order to highlight the role of NCSCs and nervous system components in the development and the regulation of the hematopoietic system.

MiR-335 Regulates Hif-1α to Reduce Cell Death in Both Mouse Cell Line and Rat Ischemic Models

Hypoxia inducible factor-1α facilitates cellular adaptation to hypoxic conditions. Hence its tight regulation is crucial in hypoxia related diseases such as cerebral ischemia. Changes in hypoxia inducible factor-1α expression upon cerebral ischemia influence the expression of its downstream genes which eventually determines the extent of cellular damage. MicroRNAs are endogenous regulators of gene expression that have rapidly emerged as promising therapeutic targets in several diseases. In this study, we have identified miR-335 as a direct regulator of hypoxia inducible factor-1α and as a potential therapeutic target in cerebral ischemia. MiR-335 and hypoxia inducible factor-1α mRNA showed an inverse expression profile, both in vivo and in vitro ischemic conditions. Given the biphasic nature of hypoxia inducible factor-1α expression during cerebral ischemia, miR-335 mimic was found to reduce infarct volume in the early time (immediately after middle cerebral artery occlusion) of embolic stroke animal models while the miR-335 inhibitor appears to be beneficial at the late time of stroke (24 hrs after middle cerebral artery occlusion). Modulation of hypoxia inducible factor-1α expression by miR-335 also influenced the expression of crucial genes implicated in neurovascular permeability, cell death and maintenance of the blood brain barrier. These concerted effects, resulting in a reduction in infarct volume bring about a beneficial outcome in ischemic stroke.

A possible new focus for stroke treatment - migrating stem cells

INTRODUCTION

Stroke is a leading cause of mortality in the US. More so, its infliction often leaves patients with lasting morbidity and deficits. Ischemic stroke comprises nearly 90% of incidents and the majority of medical treatment aims at reestablishing perfusion and preventing recurrence.

AREAS COVERED

Long-term options for neurorestoration are limited by the infancy of their innovative approach. Accumulating evidence suggests the therapeutic potential of stem cells in neurorestoration, however, proper stem cell migration remains a challenge in translating stem cell therapy from the laboratory to the clinic. In this paper, we propose the role that exogenous stem cell transplantation may serve in facilitating the migration of endogenous stem cells to the site of injury, an idea termed 'biobridge'.

EXPERT OPINION

Recent research in the field of traumatic brain injury has provided a foundational understanding that, through the use of exogenous stem cells, native tissue architecture may be manipulated by proteinases to allow better communication between the endogenous sites of neural stem cells and the regions of injury. There is still much to be learned about these mechanisms, though it is the devastating nature of stroke that necessitates continued research into the prospective therapeutic potential of this novel approach.

Ventromedial prefrontal cortex stimulation enhances memory and hippocampal neurogenesis in the middle-aged rats

Memory dysfunction is a key symptom of age-related dementia. Although recent studies have suggested positive effects of electrical stimulation for memory enhancement, its potential targets remain largely unknown. In this study, we hypothesized that spatially targeted deep brain stimulation of ventromedial prefrontal cortex enhanced memory functions in a middle-aged rat model. Our results show that acute stimulation enhanced the short-, but not the long-term memory in the novel-object recognition task. Interestingly, after chronic high-frequency stimulation, both the short- and long-term memories were robustly improved in the novel-object recognition test and Morris water-maze spatial task compared to sham. Our results also demonstrated that chronic ventromedial prefrontal cortex high-frequency stimulation upregulated neurogenesis-associated genes along with enhanced hippocampal cell proliferation. Importantly, these memory behaviors were strongly correlated with the hippocampal neurogenesis. Overall, these findings suggest that chronic ventromedial prefrontal cortex high-frequency stimulation may serve as a novel effective therapeutic target for dementia-related disorders.

DOI:http://dx.doi.org/10.7554/eLife.04803.001

Memory loss in older people is a serious and widespread problem that affects up to 50% of those over the age of 85. It is a key symptom of dementia, but despite the growing impact of this disease on society, there are no treatments currently available that can effectively stop or delay the progression of the symptoms.

One therapy that may reduce memory loss is called deep brain stimulation. Electrodes are implanted into the brain and used to stimulate brain cells in particular areas of the brain to alter mental and emotional processes. Deep brain stimulation is already used to treat Parkinson's disease, depression and other conditions that affect how the brain works.

Liu et al. studied the effect of deep brain stimulation on memory in rats. The experiments show that middle-aged rats performed less well in short- and long-term memory tests than young rats. Next, Liu et al. investigated whether deep brain stimulation could improve memory in the middle-aged rats. The electrodes were positioned to stimulate a region near the front of the brain called the ‘ventromedial prefrontal cortex’; this region is important for the formation and recall of memories. Liu et al. then gave the rats a series of memory tasks that tested their recall after 90 minutes (to test their short-term memory), and after 24 hours (to test long-term memory).

The experiments reveal that a brief stimulation of brain cells in this region of the brain improved the rats' short-term memory, but not their long-term memory. However, more sustained stimulation of this region of the brain improved both the short-term and long-term memory of the rats. Furthermore, deep brain stimulation led to the formation of new brain cells in another region of the brain called the hippocampus, which is also involved in memory. The hippocampus had not been in direct contact with the electrodes so the increase in brain cells was due to its connections with the stimulated ventromedial prefrontal cortex.

Liu et al.'s findings suggest that deep brain stimulation of the ventromedial prefrontal cortex has the potential to be developed into a therapy to treat dementia and other conditions that lead to memory loss in humans.

DOI:http://dx.doi.org/10.7554/eLife.04803.002

Striatal astrocytes produce neuroblasts in an excitotoxic model of Huntington's disease

In the adult brain, subsets of astrocytic cells residing in well-defined neurogenic niches constitutively generate neurons throughout life. Brain lesions can stimulate neurogenesis in otherwise non-neurogenic regions, but whether local astrocytic cells generate neurons in these conditions is unresolved. Here, through genetic and viral lineage tracing in mice, we demonstrate that striatal astrocytes become neurogenic following an acute excitotoxic lesion. Similar to astrocytes of adult germinal niches, these activated parenchymal progenitors express nestin and generate neurons through the formation of transit amplifying progenitors. These results shed new light on the neurogenic potential of the adult brain parenchyma.

Neural precursor cells in the ischemic brain - integration, cellular crosstalk, and consequences for stroke recovery

After an ischemic stroke, neural precursor cells (NPCs) proliferate within major germinal niches of the brain. Endogenous NPCs subsequently migrate toward the ischemic lesion where they promote tissue remodeling and neural repair. Unfortunately, this restorative process is generally insufficient and thus unable to support a full recovery of lost neurological functions. Supported by solid experimental and preclinical data, the transplantation of exogenous NPCs has emerged as a potential tool for stroke treatment. Transplanted NPCs are thought to act mainly via trophic and immune modulatory effects, thereby complementing the restorative responses initially executed by the endogenous NPC population. Recent studies have attempted to elucidate how the therapeutic properties of transplanted NPCs vary depending on the route of transplantation. Systemic NPC delivery leads to potent immune modulatory actions, which prevent secondary neuronal degeneration, reduces glial scar formation, diminishes oxidative stress and stabilizes blood–brain barrier integrity. On the contrary, local stem cell delivery allows for the accumulation of large numbers of transplanted NPCs in the brain, thus achieving high levels of locally available tissue trophic factors, which may better induce a strong endogenous NPC proliferative response. Herein we describe the diverse capabilities of exogenous (systemically vs. locally transplanted) NPCs in enhancing the endogenous neurogenic response after stroke, and how the route of transplantation may affect migration, survival, bystander effects and integration of the cellular graft. It is the authors’ claim that understanding these aspects will be of pivotal importance in discerning how transplanted NPCs exert their therapeutic effects in stroke.

Endogenous neurogenesis following ischaemic brain injury: insights for therapeutic strategies

Ischaemic stroke is among the most common yet most intractable types of central nervous system (CNS) injury in the adult human population. In the acute stages of disease, neurons in the ischaemic lesion rapidly die and other neuronal populations in the ischaemic penumbra are vulnerable to secondary injury. Multiple parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. Accumulating evidence indicates that cerebral ischaemia initiates an endogenous regenerative response within the adult brain that potentiates adult neurogenesis from populations of neural stem and progenitor cells. A major research focus has been to understand the cellular and molecular mechanisms that underlie the potentiation of adult neurogenesis and to appreciate how interventions designed to modulate these processes could enhance neural regeneration in the post-ischaemic brain. In this review, we highlight recent advances over the last 5 years that help unravel the cellular and molecular mechanisms that potentiate endogenous neurogenesis following cerebral ischaemia and are dissecting the functional importance of this regenerative mechanism following brain injury. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.

Angiogenesis in multiple sclerosis and experimental autoimmune encephalomyelitis

Angiogenesis, the formation of new vessels, is found in Multiple Sclerosis (MS) demyelinating lesions following Vascular Endothelial Growth Factor (VEGF) release and the production of several other angiogenic molecules. The increased energy demand of inflammatory cuffs and damaged neural cells explains the strong angiogenic response in plaques and surrounding white matter. An angiogenic response has also been documented in an experimental model of MS, experimental allergic encephalomyelitis (EAE), where blood–brain barrier disruption and vascular remodelling appeared in a pre-symptomatic disease phase. In both MS and EAE, VEGF acts as a pro-inflammatory factor in the early phase but its reduced responsivity in the late phase can disrupt neuroregenerative attempts, since VEGF naturally enhances neuron resistance to injury and regulates neural progenitor proliferation, migration, differentiation and oligodendrocyte precursor cell (OPC) survival and migration to demyelinated lesions. Angiogenesis, neurogenesis and oligodendroglia maturation are closely intertwined in the neurovascular niches of the subventricular zone, one of the preferential locations of inflammatory lesions in MS, and in all the other temporary vascular niches where the mutual fostering of angiogenesis and OPC maturation occurs. Angiogenesis, induced either by CNS inflammation or by hypoxic stimuli related to neurovascular uncoupling, appears to be ineffective in chronic MS due to a counterbalancing effect of vasoconstrictive mechanisms determined by the reduced axonal activity, astrocyte dysfunction, microglia secretion of free radical species and mitochondrial abnormalities. Thus, angiogenesis, that supplies several trophic factors, should be promoted in therapeutic neuroregeneration efforts to combat the progressive, degenerative phase of MS.

Stem cell transplantation for neuroprotection in stroke

Stem cell-based therapies for stroke have expanded substantially over the last decade. The diversity of embryonic and adult tissue sources provides researchers with the ability to harvest an ample supply of stem cells. However, the optimal conditions of stem cell use are still being determined. Along this line of the need for optimization studies, we discuss studies that demonstrate effective dose, timing, and route of stem cells. We recognize that stem cell derivations also provide uniquely individual difficulties and limitations in their therapeutic applications. This review will outline the current knowledge, including benefits and challenges, of the many current sources of stem cells for stroke therapy.

Novel siRNA delivery strategy: a new "strand" in CNS translational medicine?

RNA interference has been envisaged as a powerful tool for molecular and clinical investigation with a great potential for clinical applications. In recent years, increased understanding of cancer biology and stem cell biology has dramatically accelerated the development of technology for cell and gene therapy in these areas. This paper is a review of the most recent report of innovative use of siRNA to benefit several central nervous system diseases. Furthermore, a description is made of innovative strategies of delivery into the brain by means of viral and non-viral vectors with high potential for translation into clinical use. Problems are also highlighted that might hamper the transition from bench to bed, analyzing the lack of reliable preclinical models with predictive validity and the lack of effective delivery systems, which are able to overcome biological barriers and specifically reach the brain site of action.

An Update on Translating Stem Cell Therapy for Stroke from Bench to Bedside

With a constellation of stem cell sources available, researchers hope to utilize their potential for cellular repair as a therapeutic target for disease. However, many lab-to-clinic translational considerations must be given in determining their efficacy, variables such as the host response, effects on native tissue, and potential for generating tumors. This review will discuss the current knowledge of stem cell research in neurological disease, mainly stroke, with a focus on the benefits, limitations, and clinical potential.

Inflammation induces neuro-lymphatic protein expression in multiple sclerosis brain neurovasculature

Background

Multiple sclerosis (MS) is associated with ectopic lymphoid follicle formation. Podoplanin⁺ (lymphatic marker) T helper17 (Th17) cells and B cell aggregates have been implicated in the formation of tertiary lymphoid organs (TLOs) in MS and experimental autoimmune encephalitis (EAE). Since podoplanin expressed by Th17 cells in MS brains is also expressed by lymphatic endothelium, we investigated whether the pathophysiology of MS involves inductions of lymphatic proteins in the inflamed neurovasculature.

Methods

We assessed the protein levels of lymphatic vessel endothelial hyaluronan receptor and podoplanin, which are specific to the lymphatic system and prospero-homeobox protein-1, angiopoietin-2, vascular endothelial growth factor-D, vascular endothelial growth factor receptor-3, which are expressed by both lymphatic endothelium and neurons. Levels of these proteins were measured in postmortem brains and sera from MS patients, in the myelin proteolipid protein (PLP)-induced EAE and Theiler’s murine encephalomyelitis virus (TMEV) induced demyelinating disease (TMEV-IDD) mouse models and in cell culture models of inflamed neurovasculature.

Results and conclusions

Intense staining for LYVE-1 was found in neurons of a subset of MS patients using immunohistochemical approaches. The lymphatic protein, podoplanin, was highly expressed in perivascular inflammatory lesions indicating signaling cross-talks between inflamed brain vasculature and lymphatic proteins in MS. The profiles of these proteins in MS patient sera discriminated between relapsing remitting MS from secondary progressive MS and normal patients. The in vivo findings were confirmed in the in vitro cell culture models of neuroinflammation.