Osteopontin is a mediator of the lateral migration of neuroblasts from the subventricular zone after focal cerebral ischemia

Olfactory Development and Dysfunction: Involvement of Microglia

Olfactory deficits are increasingly recognized in a variety of neurological, neurodevelopmental, psychiatric, and viral diseases. While the pathology underlying olfactory loss is likely to differ across diseases, one shared feature may be an immune response mediated by microglia. Microglia orchestrate the brain's response to environmental insults and maintain neurodevelopmental homeostasis. Here, we explore the potential involvement of microglia in olfactory development and loss in disease. The effects of microglia-mediated immune response during development may be of special relevance to the olfactory system, which is unique in both its vulnerability to environmental insults as well as its extended period of neurogenesis and neuronal migration.

High spatial resolution gene expression profiling and characterization of neuroblasts migrating in the peri-injured cortex using photo-isolation chemistry

In the ventricular-subventricular-zone (V-SVZ) of the postnatal mammalian brain, immature neurons (neuroblasts) are generated from neural stem cells throughout their lifetime. These V-SVZ-derived neuroblasts normally migrate to the olfactory bulb through the rostral migratory stream, differentiate into interneurons, and are integrated into the preexisting olfactory circuit. When the brain is injured, some neuroblasts initiate migration toward the lesion and attempt to repair the damaged neuronal circuitry, but their low regeneration efficiency prevents functional recovery. Elucidation of the molecular basis of neuroblast migration toward lesions is expected to lead to the development of new therapeutic strategies for brain regenerative medicine. Here, we show gene expression profiles of neuroblasts migrating in the peri-injured cortex compared with those migrating in the V-SVZ using photo-isolation chemistry, a method for spatial transcriptome analysis. Differentially expressed gene analysis showed that the expression levels of 215 genes (97 upregulated and 118 downregulated genes) were significantly different in neuroblasts migrating in the peri-injured cortex from those migrating in the V-SVZ. Gene Ontology analysis revealed that in neuroblasts migrating in the peri-injured cortex, expression of genes involved in regulating migration direction and preventing cell death was upregulated, while the expression of genes involved in cell proliferation and maintenance of the immature state was downregulated. Indeed, neuroblasts migrating in the peri-injured cortex had significantly lower Cyclin D2 mRNA and Ki67 protein expression levels than those in the V-SVZ. In the injured brain, amoeboid microglia/macrophages expressed transforming growth factor-β (TGF-β), and neuroblasts migrating in the peri-injured cortex expressed TGF-β receptors. Experiments using primary cultured neuroblasts showed that application of TGF-β significantly decreased proliferating cells labeled with BrdU. These data suggest that the proliferative activity of neuroblasts migrating toward lesions is suppressed by TGF-β secreted from cells surrounding the lesion. This is the first comprehensive study characterizing the gene expression profiles of neuroblasts migrating in the peri-injured cortex.

Zuogui Pill Promotes Neurite Outgrowth by Regulating OPN/ IGF-1R/PTEN and Downstream mTOR Signaling Pathway

AIMS AND OBJECTIVES

Zuogui pill (ZGP) is the traditional Chinese medicine for tonifying kidney yin. Clinical and animal studies have shown that ZGP effectively enhances neurologic impairment after ischemic stroke, which may be related to promoting neurite outgrowth. This investigation aimed to prove the pro-neurite outgrowth impact of ZGP and define the underlying molecular pathway in vitro.

MATERIALS AND METHODS

The major biochemical components in the ZGP were investigated using UPLC-QTOF-MS. All-trans retinoic acid (ATRA) was employed to stimulate SH-SY5Y cells to develop into mature neurons, followed by oxygen-glucose deprivation and reoxygenation damage (OGD/R). Then the cells were supplemented with different concentrations of ZGP, and cell viability was identified by CCK-8. The neurites' outgrowth abilities were detected by wound healing test, while immunofluorescence staining of β-III-tubulin was used to label neurites and measure their length. Western blot was employed to discover the changes in protein levels.

RESULTS

ZGP improved the cell viability of differentiated SH-SY5Y cells following OGD/R damage, according to the CCK-8 assay. Concurrently, ZGP promoted neurite outgrowth and improved neurite crossing and migration ability. Protein expression analysis showed that ZGP upregulated the expression of GAP43, OPN, p-IGF-1R, mTOR, and p-S6 proteins but downregulated the expression of PTEN protein. Blocking assay with IGF-1R specific inhibitor Linstinib suggested IGF-1R mediated mTOR signaling pathway was involved in the pro-neurite outgrowth effect of ZGP.

CONCLUSION

This work illustrated the molecular mechanism underpinning ZGP's action and offered more proof of its ability to promote neurite outgrowth and regeneration following ischemic stroke.

Neural repair function of osteopontin in stroke and stroke‑related diseases (Review)

Stroke, including hemorrhagic stroke and ischemic stroke, is a common disease of the central nervous system. It is characterized by a high mortality and disability rate and is closely associated with atherosclerosis, hypertension hyperglycemia, atrial fibrillation and unhealthy living habits. The continuous development of surgery and medications has decreased the mortality rate of patients with stroke and has greatly improved the disease prognosis. At present, the direction of clinical treatment and research has gradually shifted to the repair of nerve function after stroke. Osteopontin (OPN) is a widely distributed extracellular matrix protein. Due to its structural characteristics, OPN can be cut and modified into terminal fragments with different functions, which play different roles in various pathophysiological processes, such as formation of tumors, inflammation and autoimmune diseases. It has also become a potential diagnostic and therapeutic marker. In order to comprehensively analyze the specific role of OPN in nerve repair and its relationship with stroke and stroke-related diseases, the following key words were used: 'Osteopontin, stroke, atherosis, neuroplasticity, neural repair'. PubMed, Web of Science and Cochrane articles related to OPN were searched and summarized. The present review describes the OPN structure, isoforms, functions and its neural repair mechanism, and its association with the occurrence and development of stroke and related diseases was explored.

Osteopontin Promotes Angiogenesis in the Spinal Cord and Exerts a Protective Role Against Motor Function Impairment and Neuropathic Pain After Spinal Cord Injury

STUDY DESIGN

Basic science study using a hemisection spinal cord injury (SCI) model.

OBJECTIVE

We sought to assess the effect of blocking osteopontin (OPN) upregulation on motor function recovery and pain behavior after SCI and to further investigate the possible downstream target of OPN in the injured spinal cord.

SUMMARY OF BACKGROUND DATA

OPN is a noncollagenous extracellular matrix protein widely expressed across different tissues. Its expression substantially increases following SCI. A previous study suggested that this protein might contribute to locomotor function recovery after SCI. However, its neuroprotective potential was not fully explored, nor were the underlying mechanisms.

MATERIALS AND METHODS

We constructed a SCI mouse model and analyzed the expression of OPN at different time points and the particular cell distribution in the injured spinal cord. Then, we blocked OPN upregulation with lentivirus-delivering siRNA targeting OPN specifically and examined its effect on motor function impairment and neuropathic pain after SCI. The underlying mechanisms were explored in the OPN-knockdown mice model and cultured vascular endothelial cells.

RESULTS

The proteome study revealed that OPN was the most dramatically increased protein following SCI. OPN in the spinal cord was significantly increased three weeks after SCI. Suppressing OPN upregulation through siRNA exacerbated motor function impairment and neuropathic pain. In addition, SCI resulted in an increase in vascular endothelial growth factor (VEGF), AKT phosphorylation, and angiogenesis within the spinal cord, all of which were curbed by OPN reduction. Similarly, OPN knockdown suppressed VEGF expression, AKT phosphorylation, cell migration, invasion, and angiogenesis in cultured vascular endothelial cells.

CONCLUSION

OPN demonstrates a protective influence against motor function impairment and neuropathic pain following SCI. This phenomenon may result from the proangiogenetic effect of OPN, possibly due to activation of the VEGF and/or AKT pathways.

Migratory Response of Cells in Neurogenic Niches to Neuronal Death: The Onset of Harmonic Repair?

Harmonic mechanisms orchestrate neurogenesis in the healthy brain within specific neurogenic niches, which generate neurons from neural stem cells as a homeostatic mechanism. These newly generated neurons integrate into existing neuronal circuits to participate in different brain tasks. Despite the mechanisms that protect the mammalian brain, this organ is susceptible to many different types of damage that result in the loss of neuronal tissue and therefore in alterations in the functionality of the affected regions. Nevertheless, the mammalian brain has developed mechanisms to respond to these injuries, potentiating its capacity to generate new neurons from neural stem cells and altering the homeostatic processes that occur in neurogenic niches. These alterations may lead to the generation of new neurons within the damaged brain regions. Notwithstanding, the activation of these repair mechanisms, regeneration of neuronal tissue within brain injuries does not naturally occur. In this review, we discuss how the different neurogenic niches respond to different types of brain injuries, focusing on the capacity of the progenitors generated in these niches to migrate to the injured regions and activate repair mechanisms. We conclude that the search for pharmacological drugs that stimulate the migration of newly generated neurons to brain injuries may result in the development of therapies to repair the damaged brain tissue.

Osteopontin mediates the formation of corpora amylacea-like structures from degenerating neurons in the CA1 region of the rat hippocampus after ischemia

We previously demonstrated that osteopontin (OPN) is closely associated with calcium precipitation in response to ischemic brain insults. The present study was designed to elucidate the possible association between deposition of OPN and progressive neurodegeneration in the ischemic hippocampus. To address this, we analyzed the OPN deposits in the rat hippocampus after global cerebral ischemia in the chronic phase (4 to 12 weeks) after reperfusion using immunoelectron microscopy and correlative light and electron microscopy. We identified three different types of OPN deposits based on their morphological characteristics, numbered according to the order in which they evolved. Dark degenerative cells that retained cellular morphology were frequently observed in the pyramidal cell layer, and type I OPN deposits were degenerative mitochondria that accumulated among these cells. Type II deposits evolved into more complex amorphous structures with prominent OPN deposits within their periphery and within degenerative mitochondria-like structures. Finally, type III had large concentric laminated structures with irregularly shaped bodies in the center of the deposits. In all types, OPN expression was closely correlated with calcification, as confirmed by calcium fixation and Alizarin Red staining. Notably, type II and III deposits were highly reminiscent of corpora amylacea, glycoprotein-rich aggregates found in aged brains, or neurodegenerative disease, which was further confirmed by ubiquitin expression and periodic acid-Schiff staining. Overall, our data provide a novel link between ongoing neurodegeneration and the formation of corpora amylacea-like structures and calcium deposits in the ischemic hippocampus, suggesting that OPN may play an important role in such processes.

Endocrine Regulation of Extra-skeletal Organs by Bone-derived Secreted Protein and the effect of Mechanical Stimulation

Bone serves as the support for body and provide attachment points for the muscles. The musculoskeletal system is the basis for the human body to complete exercise. Studies believe that bone is not only the basis for constructing structures, but also participates in the regulation of organs outside bone. The realization of this function is closely related to the protein secreted by bone. Whether bone can realize their positions in the human body is also related to their secretion. Bone-derived proteins provide a medium for the targeted regulation of bones on organs, making the role of bone in human body more profound and concrete. Mechanical stimulation effects the extra-skeletal organs by causing quantitative changes in bone-derived factors. When bone receives mechanical stimulation, the nichle of bone responds, and the secretion of various factors changes. However, whether the proteins secreted by bone can interfere with disease requires more research. In this review article, we will first introduce the important reasons and significance of the in-depth study on bone-derived secretory proteins, and summarize the locations, structures and functions of these proteins. These functions will not only focus on the bone metabolism process, but also be reflected in the cross-organ regulation. We specifically explain the role of typical bone-derived secretory factors such as osteocalcin (OCN), osteopontin (OPN), sclerostin (SOST) and fibroblast growth factor 23 (FGF23) in different organs and metabolic processes, then establishing the relationship between them and diseases. Finally, we will discuss whether exercise or mechanical stimulation can have a definite effect on bone-derived secretory factors. Understanding their important role in cross-organ regulation is of great significance for the treatment of diseases, especially for the elderly people with more than one basic disease.

The Yin-Yang of osteopontin in nervous system diseases: damage versus repair

Osteopontin is a broadly expressed pleiotropic protein, and is attracting increased attention because of its role in the pathophysiology of several inflammatory, degenerative, autoimmune, and oncologic diseases. In fact, in the last decade, several studies have shown that osteopontin contributes to tissue damage not only by recruiting harmful inflammatory cells to the site of lesion, but also increasing their survival. The detrimental role of osteopontin has been indeed well documented in the context of different neurological conditions (i.e., multiple sclerosis, Parkinson's, and Alzheimer's diseases). Intriguingly, recent findings show that osteopontin is involved not only in promoting tissue damage (the Yin), but also in repair/regenerative mechanisms (the Yang), mostly triggered by the inflammatory response. These two apparently discordant roles are partly related to the presence of different functional domains in the osteopontin molecule, which are exposed after thrombin or metalloproteases cleavages. Such functional domains may in turn activate intracellular signaling pathways and mediate cell-cell and cell-matrix interactions. This review describes the current knowledge on the Yin and Yang features of osteopontin in nervous system diseases. Understanding the mechanisms behind the Yin/Yang would be relevant to develop highly specific tools targeting this multifunctional protein.

Neuroprotective Effect of Cudrania tricuspidata Fruit Extracts on Scopolamine-Induced Learning and Memory Impairment

Cudrania tricuspidata has diverse biological activities, such as antioxidant, anti-inflammatory, anticancer, and neuroprotective effects. This study investigated the protective effects of C. tricuspidata fruit extracts (CTFE) against scopolamine (SCO)-induced neuron impairment. The neuroprotective effects of CTFE on SCO-induced memory dysfunction were confirmed in mice using the Barnes maze test. The results showed that co-treatment of SCO and CTFE increased the stay time in the target zone compared with SCO treatment alone. Similarly, the results obtained by the fear conditioning test revealed that SCO-CTFE co-treatment induced the freezing action time under both the contextual fear condition and the cued fear condition compared with SCO treatment alone. Moreover, we showed that CTFE reduced the SCO-induced acetylcholinesterase (AChE) activity, thereby increasing the acetylcholine concentration in mice hippocampal tissues. Consistent with the improvement of memory and recognition function in vivo, our in vitro results showed that CTFE induced cAMP response element binding protein (CREB) and extracellular regulated kinase 1/2 (ERK1/2) activity in PC12 cells and reduced SCO-induced AChE activity. In addition, the microarray results of the hippocampal tissue support our data showing that CTFE affects gene expressions associated with neurogenesis and neuronal cell differentiation markers such as spp1 and klk6. Overall, CTFE exerts a neuroprotective effect via regulation of the CREB and ERK1/2 signaling pathways and could be a therapeutic candidate for neurodegenerative diseases.

Protective Mechanism and Treatment of Neurogenesis in Cerebral Ischemia

Stroke is the fifth leading cause of death worldwide and is a main cause of disability in adults. Neither currently marketed drugs nor commonly used treatments can promote nerve repair and neurogenesis after stroke, and the repair of neurons damaged by ischemia has become a research focus. This article reviews several possible mechanisms of stroke and neurogenesis and introduces novel neurogenic agents (fibroblast growth factors, brain-derived neurotrophic factor, purine nucleosides, resveratrol, S-nitrosoglutathione, osteopontin, etc.) as well as other treatments that have shown neuroprotective or neurogenesis-promoting effects.

Osteopontin as a candidate of therapeutic application for the acute brain injury

Acute brain injury is the leading cause of human death and disability worldwide, which includes intracerebral haemorrhage, subarachnoid haemorrhage, cerebral ischaemia, traumatic brain injury and hypoxia‐ischaemia brain injury. Currently, clinical treatments for neurological dysfunction of acute brain injury have not been satisfactory. Osteopontin (OPN) is a complex adhesion protein and cytokine that interacts with multiple receptors including integrins and CD44 variants, exhibiting mostly neuroprotective roles and showing therapeutic potential for acute brain injury. OPN‐induced tissue remodelling and functional repair mainly rely on its positive roles in the coordination of pro‐inflammatory and anti‐inflammatory responses, blood‐brain barrier maintenance and anti‐apoptotic actions, as well as other mechanisms such as affecting the chemotaxis and proliferation of nerve cells. The blood OPN strongly parallel with the OPN induced in the brain and can be used as a novel biomarker of the susceptibility, severity and outcome of acute brain injury. In the present review, we summarized the molecular signalling mechanisms of OPN as well as its overall role in different kinds of acute brain injury.

The Role of Osteopontin in Amyotrophic Lateral Sclerosis: A Systematic Review

Context: Osteopontin (OPN) is a matrix phosphoprotein expressed by a variety of tissues and cells, including the immune system and the nervous system. Previous studies have shown that OPN may have a role in neurodegenerative diseases, including multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. Objectives: The present study aimed to systematically review studies investigating the role of OPN in amyotrophic lateral sclerosis (ALS) patients or the disease animal model. Evidence Acquisition: We searched the Cochrane Library, PubMed, Web of Science, and Scopus to find relevant articles published up to January 20, 2019. Both human and animal model studies of ALS were considered. Results: A total of nine articles (four human studies and five animal model studies) were included. Two of the human studies reported that the CSF levels of OPN were higher among ALS patients compared to controls. The other two human studies found that OPN levels in cortical neurons did not differ significantly between ALS cases and the non-neurological control group. One of the studies found that the expression level of OPN in astrocytes was similar between ALS patients and the control group, but the level of microglial OPN significantly increased in ALS cases. Four of the animal model studies reported that the expression of OPN mRNA in spinal cord microglia significantly increased during the disease progression. The remaining animal model study found that OPN was selectively expressed by fast fatigue-resistant and slow motor neurons (MNs), which are resistant to ALS, and that the OPN expression was low among fast-fatigable MNs. Conclusions: Prompt microglial activation is a hallmark pathology of ALS, and OPN is among the most widely expressed proteins by these activated glial cells. Therefore, OPN might have a role in ALS pathogenesis. The existing evidence is not sufficient to justify whether OPN has a neurotoxic or neuroprotective role in ALS. We encourage researchers to investigate the role of OPN in ALS pathogenesis more extensively.

Influencing neuroplasticity in stroke treatment with advanced biomaterials-based approaches

Since the early 1990s, we have known that the adult brain is not static and has the capacity to repair itself. The delivery of various therapeutic factors and cells have resulted in some exciting pre-clinical and clinical outcomes in stroke models by targeting post-injury plasticity to enhance recovery. Developing a deeper understanding of the pathways that modulate plasticity will enable us to optimize delivery strategies for therapeutics and achieve more robust effects. Biomaterials are a key tool for the optimization of these potential treatments, owing to their biocompatibility and tunability. In this review, we identify factors and targets that impact plastic processes known to contribute to recovery, discuss the role of biomaterials in enhancing the efficacy of treatment strategies, and suggest combinatorial approaches based on the stage of injury progression.

New Neurons in the Post-ischemic and Injured Brain: Migrating or Resident?

The endogenous potential of adult neurogenesis is of particular interest for the development of new strategies for recovery after stroke and traumatic brain injury. These pathological conditions affect endogenous neurogenesis in two aspects. On the one hand, injury usually initiates the migration of neuronal precursors (NPCs) to the lesion area from the already existing, in physiological conditions, neurogenic niche - the ventricular-subventricular zone (V-SVZ) near the lateral ventricles. On the other hand, recent studies have convincingly demonstrated the local generation of new neurons near lesion areas in different brain locations. The striatum, cortex, and hippocampal CA1 region are considered to be locations of such new neurogenic zones in the damaged brain. This review focuses on the relative contribution of two types of NPCs of different origin, resident population in new neurogenic zones and cells migrating from the lateral ventricles, to post-stroke or post-traumatic enhancement of neurogenesis. The migratory pathways of NPCs have also been considered. In addition, the review highlights the advantages and limitations of different methodological approaches to the definition of NPC location and tracking of new neurons. In general, we suggest that despite the considerable number of studies, we still lack a comprehensive understanding of neurogenesis in the damaged brain. We believe that the advancement of methods for in vivo visualization and longitudinal observation of neurogenesis in the brain could fundamentally change the current situation in this field.

Osteopontin and its spatiotemporal relationship with glial cells in the striatum of rats treated with mitochondrial toxin 3-nitropropionic acid: possible involvement in phagocytosis

Background

Osteopontin (OPN, SPP1) is upregulated in response to acute brain injury, and based on its immunoreactivity, two distinct forms have been identified: intracellular OPN within brain macrophages and small granular OPN, identified as OPN-coated degenerated neurites. This study investigates the spatiotemporal relationship between punctate OPN deposition and astroglial and microglial reactions elicited by 3-nitropropionic acid (3-NP).

Methods

Male Sprague-Dawley rats were intraperitoneally injected with mitochondrial toxin 3-NP and euthanized at 3, 7, 14, and 28 days. Quantitative and qualitative light and electron microscopic techniques were used to assess the relationship between OPN and glial cells. Statistical significance was determined by Student’s t test or a one-way analysis of variance followed by Tukey’s multiple comparisons test.

Results

Punctate OPN-immunoreactive profiles were synthesized and secreted by amoeboid-like brain macrophages in the lesion core, but not by reactive astrocytes and activated microglia with a stellate shape in the peri-lesional area. Punctate OPN accumulation was detected only in the lesion core away from reactive astrocytes in the peri-lesional area at day 3, but had direct contact with, and even overlapped with astroglial processes at day 7. The distance between the OPN-positive area and the astrocytic scar significantly decreased from days 3 to 7. By days 14 and 28 post-lesion, when the glial scar was fully formed, punctate OPN distribution mostly overlapped with the astrocytic scar. Three-dimensional reconstructions and quantitative image analysis revealed numerous granular OPN puncta inside the cytoplasm of reactive astrocytes and brain macrophages. Reactive astrocytes showed prominent expression of the lysosomal marker lysosomal-associated membrane protein 1, and ultrastructural analysis confirmed OPN-coated degenerating neurites inside astrocytes, suggesting the phagocytosis of OPN puncta by reactive astrocytes after injury.

Conclusions

Punctate OPN-immunoreactive profiles corresponded to OPN-coated degenerated neurites, which were closely associated with, or completely engulfed by, the reactive astrocytes forming the astroglial scar in 3-NP lesioned striatum, suggesting that OPN may cause astrocytes to migrate towards these degenerated neurites in the lesion core to establish physical contact with, and possibly, to phagocytose them. Our results provide novel insights essential to understanding the recovery and repair of the central nervous system tissue.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1489-1) contains supplementary material, which is available to authorized users.

Microglia promote the proliferation of neural precursor cells by secreting osteopontin

Microglia are central nervous system-resident immune cells that play a crucial role in brain development by interacting with neural precursor cells (NPCs). It has been reported that microglia regulate the number of NPC by phagocytosis, inducing apoptosis, and promoting proliferation. Microglia surrounding the subventricular zone express osteopontin (OPN) during brain development. The present study investigated the role of microglia in proliferation of NPCs in vitro, and identified the OPN receptor critical for proliferation of NPCs. Microglia co-cultured with NPCs in the presence of an OPN-neutralizing antibody resulted in OPN inhibition and reduced microglia-induced proliferation of NPCs. NPCs express integrin αvβ3, which has been identified as an OPN receptor. Cilengitide, an inhibitor of integrin αvβ3, also inhibited microglia-induced proliferation of NPCs. These results suggest that microglia promote the proliferation of NPCs via OPN-integrin αvβ3 signaling.

Acute intranasal osteopontin treatment in male rats following TBI increases the number of activated microglia but does not alter lesion characteristics

Intranasal recombinant osteopontin (OPN) has been shown to be neuroprotective in different models of acquired brain injury but has never been tested after traumatic brain injury (TBI). We used a model of moderate-to-severe controlled cortical impact in male adult Sprague Dawley rats and tested our hypothesis that OPN treatment would improve neurological outcomes, lesion and brain tissue characteristics, neuroinflammation, and vascular characteristics at 1 day post-injury. Intranasal OPN administered 1 hr after the TBI did not improve neurological score, lesion volumes, blood-brain barrier, or vascular characteristics. When assessing neuroinflammation, we did not observe any effect of OPN on the astrocyte reactivity but discovered an increased number of activated microglia within the ipsilateral hemisphere. Moreover, we found a correlation between edema and heme oxygenase-1 (HO-1) expression which was decreased in OPN-treated animals, suggesting an effect of OPN on the HO-1 response to injury. Thus, OPN may increase or accelerate the microglial response after TBI, and early response of HO-1 in modulating edema formation may limit the secondary consequences of TBI at later time points. Additional experiments and at longer time points are needed to determine if intranasal OPN could potentially be used as a treatment after TBI where it might be beneficial by activating protective signaling pathways.

Bioluminescence imaging visualizes osteopontin-induced neurogenesis and neuroblast migration in the mouse brain after stroke

Background

Osteopontin (OPN), an acidic phosphoglycoprotein, is upregulated in the brain after cerebral ischemia. We previously reported that OPN supports migration, survival, and proliferation of neural stem cells (NSC) in primary cell culture, as well as their differentiation into neurons. We here analyzed the effects of OPN on neuroblasts in vivo in the context of cerebral ischemia.

Methods

Transgenic mice expressing luciferase under the control of the neuroblast-specific doublecortin (DCX)-promoter, allowing visualization of neuroblasts in vivo using bioluminescence imaging (BLI), were injected with OPN intracerebroventricularly while control mice were injected with vehicle buffer. To assess the effects of OPN after ischemia, additional mice were subjected to photothrombosis and injected with either OPN or vehicle.

Results

OPN enhanced the migration of neuroblasts both in the healthy brain and after ischemia, as quantified by BLI in vivo. Moreover, the number of neural progenitors was increased following OPN treatment, with the maximum effect on the second day after OPN injection into the healthy brain, and 14 days after OPN injection following ischemia. After ischemia, OPN quantitatively promoted the endogenous, ischemia-induced neuroblast expansion, and additionally recruited progenitors from the contralateral hemisphere.

Conclusions

Our results strongly suggest that OPN constitutes a promising substance for the targeted activation of neurogenesis in ischemic stroke.

Proangiogenic functions of an RGD-SLAY-containing osteopontin icosamer peptide in HUVECs and in the postischemic brain

Osteopontin (OPN) is a phosphorylated glycoprotein secreted into body fluids by various cell types. OPN contains arginine-glycine-aspartate (RGD) and serine-leucine-alanine-tyrosine (SLAY) motifs that bind to several integrins and mediate a wide range of cellular processes. In the present study, the proangiogenic effects of a 20-amino-acid OPN peptide (OPNpt20) containing RGD and SLAY motifs were examined in human umbilical vein endothelial cells (HUVECs) and in a rat focal cerebral ischemia model. OPNpt20 exerted robust proangiogenic effects in HUVECs by promoting proliferation, migration and tube formation. These effects were significantly reduced in OPNpt20-RAA (RGD->RAA)-treated cells, but only slightly reduced in OPNpt20-SLAA (SLAY->SLAA)-treated cells. Interestingly, a mutant peptide without both motifs failed to induce these proangiogenic processes, indicating that the RGD motif is crucial and that SLAY also has a role. In OPNpt20-treated HUVEC cultures, AKT and ERK signaling pathways were activated, but activation of these pathways and tube formation were suppressed by anti-α_vβ₃ antibody, indicating that OPNpt20 stimulates angiogenesis via the α_vβ₃-integrin/AKT and ERK pathways. The proangiogenic function of OPNpt20 was further confirmed in a rat middle cerebral artery occlusion model. Total vessel length and vessel densities were markedly greater in OPNpt20-treated ischemic brains, accompanied by induction of proangiogenic markers. Together, these results demonstrate that the 20-amino-acid OPN peptide containing RGD and SLAY motifs exerts proangiogenic effects, wherein both motifs have important roles, and these effects appear to contribute to the neuroprotective effects of this peptide in the postischemic brain.

Osteopontin Peptide Icosamer Containing RGD and SLAYGLR Motifs Enhances the Motility and Phagocytic Activity of Microglia

Osteopontin (OPN) is a secreted glycoprotein that is expressed in various tissues, including brain, and mediates a wide range of cellular activities. In a previous study, the authors observed the robust neuroprotective effects of recombinant OPN and of RGD and SLAYGLR-containing OPN-peptide icosamer (OPNpt20) in an animal model of transient focal ischemia, and demonstrated anti-inflammatory and pro-angiogenic effects of OPNpt20 in the postischemic brain. In the present study, we investigated the effects of OPNpt20 on the motility and phagocytic activity of BV2 cells (a microglia cell line). F-actin polymerization and cell motility were significantly enhanced in OPNpt20-treated BV2 cells, and numbers of filopodia-like processes increased and lamellipodia-like structures enlarged and thickened. In addition, treatment of cells with either of three mutant OPN icosamers containing mutation within RGD, SLAY, or RGDSLAY showed that the RGD and SLAY motifs of OPNpt20 play critical roles in the enhancement of cell motility, and the interaction between exogenous OPNpt20 and endogenous αv and α4 integrin and the activations of FAK, Erk, and Akt signaling pathways were found to be involved in the OPNpt20-mediated induction of cell motility. Furthermore, phagocytic activity of microglia was also significantly enhanced by OPNpt20 in a RGD and SLAY dependent manner. These results indicate OPNpt20 containing RGD and SLAY motifs triggers microglial motility and phagocytic activity and OPNpt20-integrin mediated signaling plays a critical role in these activities.

Monocyte depletion early after stroke promotes neurogenesis from endogenous neural stem cells in adult brain

Ischemic stroke, caused by middle cerebral artery occlusion, leads to long-lasting formation of new striatal neurons from neural stem/progenitor cells (NSPCs) in the subventricular zone (SVZ) of adult rodents. Concomitantly with this neurogenic response, SVZ exhibits activation of resident microglia and infiltrating monocytes. Here we show that depletion of circulating monocytes, using the anti-CCR2 antibody MC-21 during the first week after stroke, enhances striatal neurogenesis at one week post-insult, most likely by increasing short-term survival of the newly formed neuroblasts in the SVZ and adjacent striatum. Blocking monocyte recruitment did not alter the volume of the ischemic lesion but gave rise to reduced astrocyte activation in SVZ and adjacent striatum, which could contribute to the improved neuroblast survival. A similar decrease of astrocyte activation was found in and around human induced pluripotent stem cell (iPSC)-derived NSPCs transplanted into striatum at one week after stroke in monocyte-depleted mice. However, there was no effect on neurogenesis in the graft as determined 8weeks after implantation. Our findings demonstrate, for the first time, that a specific cellular component of the early inflammatory reaction in SVZ and adjacent striatum following stroke, i.e., infiltrating monocytes, compromises the short-term neurogenic response neurogenesis from endogenous NSPCs.

New neurons in adult brain: distribution, molecular mechanisms and therapies

"Are new neurons added in the adult mammalian brain?" "Do neural stem cells activate following CNS diseases?" "How can we modulate their activation to promote recovery?" Recent findings in the field provide novel insights for addressing these questions from a new perspective. In this review, we will summarize the current knowledge about adult neurogenesis and neural stem cell niches in healthy and pathological conditions. We will first overview the milestones that have led to the discovery of the classical ventricular and hippocampal neural stem cell niches. In adult brain, new neurons originate from proliferating neural precursors located in the subventricular zone of the lateral ventricles and in the subgranular zone of the hippocampus. However, recent findings suggest that new neuronal cells can be added to the adult brain by direct differentiation (e.g., without cell proliferation) from either quiescent neural precursors or non-neuronal cells undergoing conversion or reprogramming to neuronal fate. Accordingly, in this review we will also address critical aspects of the newly described mechanisms of quiescence and direct conversion as well as the more canonical activation of the neurogenic niches and neuroblast reservoirs in pathological conditions. Finally, we will outline the critical elements involved in neural progenitor proliferation, neuroblast migration and differentiation and discuss their potential as targets for the development of novel therapeutic drugs for neurodegenerative diseases.

From Blood to Lesioned Brain: An In Vitro Study on Migration Mechanisms of Human Nasal Olfactory Stem Cells

Stem cell-based therapies critically rely on selective cell migration toward pathological or injured areas. We previously demonstrated that human olfactory ectomesenchymal stem cells (OE-MSCs), derived from an adult olfactory lamina propria, migrate specifically toward an injured mouse hippocampus after transplantation in the cerebrospinal fluid and promote functional recoveries. However, the mechanisms controlling their recruitment and homing remain elusive. Using an in vitro model of blood-brain barrier (BBB) and secretome analysis, we observed that OE-MSCs produce numerous proteins allowing them to cross the endothelial wall. Then, pan-genomic DNA microarrays identified signaling molecules that lesioned mouse hippocampus overexpressed. Among the most upregulated cytokines, both recombinant SPP1/osteopontin and CCL2/MCP-1 stimulate OE-MSC migration whereas only CCL2 exerts a chemotactic effect. Additionally, OE-MSCs express SPP1 receptors but not the CCL2 cognate receptor, suggesting a CCR2-independent pathway through other CCR receptors. These results confirm that OE-MSCs can be attracted by chemotactic cytokines overexpressed in inflamed areas and demonstrate that CCL2 is an important factor that could promote OE-MSC engraftment, suggesting improvement for future clinical trials.

Spatiotemporal expression of osteopontin in the striatum of rats subjected to the mitochondrial toxin 3-nitropropionic acid correlates with microcalcification

Our aim was to elucidate whether osteopontin (OPN) is involved in the onset of mineralisation and progression of extracellular calcification in striatal lesions due to mitochondrial toxin 3-nitropropionic acid exposure. OPN expression had two different patterns when observed using light microscopy. It was either localised to the Golgi complex in brain macrophages or had a small granular pattern scattered in the affected striatum. OPN labelling tended to increase in number and size over a 2-week period following the lesion. Ultrastructural investigations revealed that OPN is initially localised to degenerating mitochondria within distal dendrites, which were then progressively surrounded by profuse OPN on days 7–14. Electron probe microanalysis of OPN-positive and calcium-fixated neurites indicated that OPN accumulates selectively on the surfaces of degenerating calcifying dendrites, possibly via interactions between OPN and calcium. In addition, 3-dimensional reconstruction of OPN-positive neurites revealed that they are in direct contact with larger OPN-negative degenerating dendrites rather than with fragmented cell debris. Our overall results indicate that OPN expression is likely to correlate with the spatiotemporal progression of calcification in the affected striatum, and raise the possibility that OPN may play an important role in the initiation and progression of microcalcification in response to brain insults.

Indomethacin treatment reduces microglia activation and increases numbers of neuroblasts in the subventricular zone and ischaemic striatum after focal ischaemia

Neuroblasts from the subventricular zone (SVZ) migrate to striatum following stroke, but most of them die in the ischaemic milieu and this can be related to exacerbated microglial activation. Here, we explored the effects of the non-steroidal anti-inflammatory indomethacin on microglial activation, neuronal preservation and neuroblast migration following experimental striatal stroke in adult rats. Animals were submitted to endothelin-1 (ET-1)-induced focal striatal ischaemia and were treated with indomethacin or sterile saline (i.p.) for 7 days, being perfused after 8 or 14 days. Immunohistochemistry was performed to assess neuronal loss (anti-NeuN), microglial activation (anti-Iba1, ED1) and migrating neuroblasts (anti-DCX) by counting NeuN, ED1 and DCX-positive cells in the ischaemic striatum or SVZ. Indomethacin treatment reduced microglia activation and the number of ED1+ cells in both 8 and 14 days post injury as compared with controls. There was an increase in the number of DCX+ cells in both SVZ and striatum at the same survival times. Moreover, there was a decrease in the number of NeuN+ cells in indomethacin-treated animals as compared with the control group at 8 days but not after 14 days post injury. Our results suggest that indomethacin treatment modulates microglia activation, contributing to increased neuroblast proliferation in the SVZ and migration to the ischaemic striatum following stroke.

Stroke alters behavior of human skin-derived neural progenitors after transplantation adjacent to neurogenic area in rat brain

Background

Intracerebral transplantation of human induced pluripotent stem cells (iPSCs) can ameliorate behavioral deficits in animal models of stroke. How the ischemic lesion affects the survival of the transplanted cells, their proliferation, migration, differentiation, and function is only partly understood.

Methods

Here we have assessed the influence of the stroke-induced injury on grafts of human skin iPSCs-derived long-term neuroepithelial-like stem cells using transplantation into the rostral migratory stream (RMS), adjacent to the neurogenic subventricular zone, in adult rats as a model system.

Results

We show that the occurrence of an ischemic lesion, induced by middle cerebral artery occlusion, in the striatum close to the transplant does not alter the survival, proliferation, or generation of neuroblasts or mature neurons or astrocytes from the grafted progenitors. In contrast, the migration and axonal projection patterns of the transplanted cells are markedly influenced. In the intact brain, the grafted cells send many fibers to the main olfactory bulb through the RMS and a few of them migrate in the same direction, reaching the first one third of this pathway. In the stroke-injured brain, on the other hand, the grafted cells only migrate toward the ischemic lesion and virtually no axonal outgrowth is observed in the RMS.

Conclusions

Our findings indicate that signals released from the stroke-injured area regulate the migration of and fiber outgrowth from grafted human skin-derived neural progenitors and overcome the influence on these cellular properties exerted by the neurogenic area/RMS in the intact brain.

Neurogenesis following Stroke Affecting the Adult Brain

A bulk of experimental evidence supports the idea that the stroke-damaged adult brain makes an attempt to repair itself by producing new neurons also in areas where neurogenesis does not normally occur (e.g., the striatum and cerebral cortex). Knowledge about mechanisms regulating the different steps of neurogenesis after stroke is rapidly increasing but still incomplete. The functional consequences of stroke-induced neurogenesis and the level of integration of the new neurons into existing neural circuitries are poorly understood. To have a substantial impact on the recovery after stroke, this potential mechanism for self-repair needs to be enhanced, primarily by increasing the survival and differentiation of the generated neuroblasts. Moreover, for efficient repair, optimization of neurogenesis most likely needs to be combined with promotion of other endogenous neuroregenerative responses (e.g., protection and sprouting of remaining mature neurons, transplantation of neural stem/progenitor cells [NSPC]-derived neurons and glia cells, and modulation of inflammation).

Intranasal Delivery of RGD Motif-Containing Osteopontin Icosamer Confers Neuroprotection in the Postischemic Brain via αvβ3 Integrin Binding

Osteopontin (OPN) is a phosphorylated glycoprotein possessing an arginine-glycine-aspartate (RGD)-motif, which binds to several cell surface integrins and mediates a wide range of cellular processes. Inductions of OPN have been reported in the postischemic brain, and the neuroprotective effects of OPN have been demonstrated in animal models of stroke. In the present study, we showed a robust neuroprotective effect of RGD-containing icosamer OPN peptide (OPNpt20) in a rat model of focal cerebral ischemia (middle cerebral artery occlusion, MCAO). Intranasally administered OPNpt20 reduced mean infarct volume by 79.7 % compared to the treatment-naïve MCAO control animals and markedly ameliorated neurological deficits. In addition, OPNpt20 significantly suppressed the inductions of iNOS and of inflammatory markers in postischemic brains and in primary microglial cultures, demonstrating anti-inflammatory effects. Administration of a mutant peptide, in which RGD was replaced by arginine-alanine-alanine (RAA), failed to suppress infarct volumes in MCAO animals and co-administration of OPNpt20 with anti-αvβ3 integrin antibody failed to suppress iNOS induction in primary microglia culture, indicating that the RGD motif in OPNpt20 and endogenous αvβ3 integrin play critical roles. Furthermore, pull-down assay revealed a direct binding between OPNpt20 and αvβ3 integrin in primary microglia culture. Together, these results indicate that RGD-containing OPN icosamer has therapeutic potential in the postischemic brain and αvβ3 integrin-mediated anti-inflammatory effect might be an underlying mechanism.

Matricellular proteins of the Cyr61/CTGF/NOV (CCN) family and the nervous system

Matricellular proteins are secreted proteins that exist at the border of cells and the extracellular matrix (ECM). However, instead of playing a role in structural integrity of the ECM, these proteins, that act as modulators of various surface receptors, have a regulatory function and instruct a multitude of cellular responses. Among matricellular proteins are members of the Cyr61/CTGF/NOV (CCN) protein family. These proteins exert their activity by binding directly to integrins and heparan sulfate proteoglycans and activating multiple intracellular signaling pathways. CCN proteins also influence the activity of growth factors and cytokines and integrate their activity with integrin signaling. At the cellular level, CCN proteins regulate gene expression and cell survival, proliferation, differentiation, senescence, adhesion, and migration. To date, CCN proteins have been extensively studied in the context of osteo- and chondrogenesis, angiogenesis, and carcinogenesis, but the expression of these proteins is also observed in a variety of tissues. The role of CCN proteins in the nervous system has not been systematically studied or described. Thus, the major aim of this review is to introduce the CCN protein family to the neuroscience community. We first discuss the structure, interactions, and cellular functions of CCN proteins and then provide a detailed review of the available data on the neuronal expression and contribution of CCN proteins to nervous system development, function, and pathology.

Osteopontin mediates survival, proliferation and migration of neural stem cells through the chemokine receptor CXCR4

Introduction

Osteopontin (OPN) is a phosphoglycoprotein with important roles in tissue homeostasis, wound healing, immune regulation, and stress responses. It is expressed constitutively in the brain and upregulated during neuroinflammatory responses; for example, after focal cerebral ischemia. To date, its effects on neural stem cells (NSC) remain to be elucidated and are, accordingly, the subject of this study.

Method

Primary fetal rat NSC were cultured as homogenous monolayers and treated with different concentrations of OPN. Fundamental properties of NSC were assessed following OPN exposure, including proliferative activity, survival under oxidative stress, migration, and differentiation potential. To elucidate a putative action of OPN via the CXC chemokine receptor type 4 (CXCR4), the latter was blocked with AMD3100. To investigate effects of OPN on endogenous NSC in vivo, recombinant OPN was injected into the brain of healthy adult rats as well as rats subjected to focal cerebral ischemia. Effects of OPN on NSC proliferation and neurogenesis in the subventricular zone were studied immunohistochemically.

Results

OPN dose-dependently increased the number of NSC in vitro. As hypothesized, this effect was mediated through CXCR4. The increase in NSC number was due to both enhanced cell proliferation and increased survival, and was confirmed in vivo. Additionally, OPN dose-dependently stimulated the migration of NSC via CXCR4. Moreover, in the presence of OPN, differentiation of NSC led to a significant increase in neurogenesis both in vitro as well as in vivo after cerebral ischemia.

Conclusion

Data show positive effects of OPN on survival, proliferation, migration, and neuronal differentiation of NSC. At least in part these effects were mediated via CXCR4. Results suggest that OPN is a promising substance for the targeted activation of NSC in future experimental therapies for neurological disorders such as stroke.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0098-x) contains supplementary material, which is available to authorized users.

Microglial and macrophage polarization—new prospects for brain repair

The traditional view of the adult brain as a static organ has changed in the past three decades, with the emergence of evidence that it remains plastic and has some regenerative capacity after injury. In the injured brain, microglia and macrophages clear cellular debris and orchestrate neuronal restorative processes. However, activation of these cells can also hinder CNS repair and expand tissue damage. Polarization of macrophage populations toward different phenotypes at different stages of injury might account for this dual role. This Perspectives article highlights the specific roles of polarized microglial and macrophage populations in CNS repair after acute injury, and argues that therapeutic approaches targeting cerebral inflammation should shift from broad suppression of microglia and macrophages towards subtle adjustment of the balance between their phenotypes. Breakthroughs in the identification of regulatory molecules that control these phenotypic shifts could ultimately accelerate research towards curing brain disorders.

Biodegradable gelatin microspheres enhance the neuroprotective potency of osteopontin via quick and sustained release in the post-ischemic brain

Gelatin microspheres (GMSs) are widely used as drug carriers owing to their excellent biocompatibilities and toxicologically safe degradation products. The drug release profile is easily tailored by controlling the cross-linking density and surface-to-volume ratio, i.e. size, of the GMS. In this study, we employed GMSs which are 25 μm in diameter and cross-linked with 0.03125% glutaraldehyde, to enable rapid initial and a subsequent sustained release. Therapeutic potency of human recombinant osteopontin (rhOPN) with or without encapsulation into GMSs was investigated after administrating them to rat stroke model (Sprague-Dawley; middle cerebral artery occlusion, MCAO). The administration of rhOPN/GMS (100 ng/100 μg) at 1h post-MCAO reduced the mean infarct volume by 81.8% of that of the untreated MCAO control and extended the therapeutic window at least to 12h post-MCAO, demonstrating a markedly enhanced therapeutic potency for the use of OPN in the post-ischemic brain. Scanning electron microscopy micrographs revealed that GMSs maintained the three-dimensional shape for more than 5 days in normal brain but were degraded rapidly in the post-ischemic brain, presumably due to high levels of gelatinase induction. After encapsulation with GMS, the duration of OPN release was markedly extended; from the period of 2 days to 5 days in normal brain, and from 2 days to 4 days in the post-ischemic brain; these encompass the critical period for recovery processes, such as vascularization, and controlling inflammation. Together, these results indicate that GMS-mediated drug delivery has huge potential when it was used in the hyperacute period in the post-ischemic brain.

Patterns of gene expression associated with Pten deficiency in the developing inner ear

In inner ear development, phosphatase and tensin homolog (PTEN) is necessary for neuronal maintenance, such as neuronal survival and accurate nerve innervations of hair cells. We previously reported that Pten conditional knockout (cKO) mice exhibited disorganized fasciculus with neuronal apoptosis in spiral ganglion neurons (SGNs). To better understand the genes and signaling networks related to auditory neuron maintenance, we compared the profiles of differentially expressed genes (DEGs) using microarray analysis of the inner ear in E14.5 Pten cKO and wild-type mice. We identified 46 statistically significant transcripts using significance analysis of microarrays, with the false-discovery rate set at 0%. Among the DEGs, expression levels of candidate genes and expression domains were validated by quantitative real-time RT-PCR and in situ hybridization, respectively. Ingenuity pathway analysis using DEGs identified significant signaling networks associated with apoptosis, cellular movement, and axon guidance (i.e., secreted phosphoprotein 1 (Spp1)-mediated cellular movement and regulator of G-protein signaling 4 (Rgs4)-mediated axon guidance). This result was consistent with the phenotypic defects of SGNs in Pten cKO mice (e.g., neuronal apoptosis, abnormal migration, and irregular nerve fiber patterns of SGNs). From this study, we suggest two key regulatory signaling networks mediated by Spp1 and Rgs4, which may play potential roles in neuronal differentiation of developing auditory neurons.

Blocked angiogenesis in Galectin-3 null mice does not alter cellular and behavioral recovery after middle cerebral artery occlusion stroke

Angiogenesis is thought to decrease stroke size and improve behavioral outcomes and therefore several clinical trials are seeking to augment it. Galectin-3 (Gal-3) expression increases after middle cerebral artery occlusion (MCAO) and has been proposed to limit damage 3days after stroke. We carried out mild MCAO that damages the striatum but spares the cerebral cortex and SVZ. Gal-3 gene deletion prevented vascular endothelial growth factor (VEGF) upregulation after MCAO. This inhibited post-MCAO increases in endothelial proliferation and angiogenesis in the striatum allowing us to uniquely address the function of angiogenesis in this model of stroke. Apoptosis and infarct size were unchanged in Gal-3(-/-) mice 7 and 14 days after MCAO, suggesting that angiogenesis does not affect lesion size. Microglial and astrocyte activation/proliferation after MCAO was similar in wild type and Gal-3(-/-) mice. In addition, openfield activity, motor hemiparesis, proprioception, reflex, tremors and grooming behaviors were essentially identical between WT and Gal-3(-/-) mice at 1, 3, 7, 10 and 14 days after MCAO, suggesting that penumbral angiogenesis has limited impact on behavioral recovery. In addition to angiogenesis, increased adult subventricular zone (SVZ) neurogenesis is thought to provide neuroprotection after stroke in animal models. SVZ neurogenesis and migration to lesion were overall unaffected by the loss of Gal-3, suggesting no compensation for the lack of angiogenesis in Gal-3(-/-) mice. Because angiogenesis and neurogenesis are usually coordinately regulated, identifying their individual effects on stroke has hitherto been difficult. These results show that Gal-3 is necessary for angiogenesis in stroke in a VEGF-dependant manner, but suggest that angiogenesis may be dispensable for post-stroke endogenous repair, therefore drawing into question the clinical utility of augmenting angiogenesis.

Expression of integrin and CD44 receptors recognising osteopontin in the normal and LPS-lesioned rat substantia nigra

The multifunctional protein osteopontin (OPN) is expressed in the substantia nigra (SN) and protects nigral dopaminergic neurones against toxic insult in animal models of Parkinson's disease, although the mechanisms involved are uncertain. In the periphery, OPN regulates inflammatory processes by interacting with integrin and CD44 receptors but the presence and distribution of these sites in SN is unknown. We investigated the expression of integrin receptor subunits and CD44 receptors in the normal SN and after induction of inflammation by lipopolysaccharide (LPS), and their interaction with OPN. In normal rat SN, integrin αv , β3 and β1 , and CD44, receptors were expressed on neurones including TH-positive cells but not on glia. LPS administration induced a loss of TH-positive neurones in SN and increased expression of glial cells as shown by GFAP, OX-6 and ED-1 immunoreactivity. In LPS-lesioned SN, there was up-regulation of the expression of integrin β3 and CD44 receptors. Co-localisation studies showed that this related to their increased expression on OX-6-, ED-1- and GFAP-positive cells. Furthermore, OPN interacted with integrin and CD44 receptors in the normal rat SN as demonstrated by co-immunoprecipitation and pull-down techniques. These data show that integrin and CD44 receptors are present on neurones in normal rat SN and that they are up-regulated on glial cells following LPS-mediated inflammation in SN, suggesting that they are functionally important in the inflammatory process. The interaction of OPN with these receptors suggests a role in the neuroprotective effect of this protein in the LPS model of Parkinson's disease.

Perlecan domain V therapy for stroke: a beacon of hope?

The sad reality is that in the year 2012, people are still dying or suffering from the extreme morbidity of ischemic stroke. This tragedy is only compounded by the graveyard full of once promising new therapies. While it is indeed true that the overall mortality from stroke has declined in the United States, perhaps due to increased awareness of stroke symptoms by both the lay public and physicians, it is clear that better therapies are needed. In this regard, progress has been tremendously slowed by the simple fact that experimental models of stroke and the animals that they typically employ, rats and mice, do not adequately represent human stroke. Furthermore, the neuroprotective therapeutic approach, in which potential treatments are administered with the hope of preventing the spread of dying neurons that accompanies a stroke, typically fail for a number of reasons such as there is simply more brain matter to protect in a human than there is in a rodent! For this reason, there has been somewhat of a shift in stroke research away from neuroprotection and toward a neurorepair approach. This too may be problematic in that agents that might foster brain repair could be acutely deleterious or neurotoxic and vice versa, making the timing of treatment administration after stroke critical. Therefore, in our efforts to discover a new stroke therapy, we decided to focus on identifying brain repair elements that were (1) endogenously and actively generated in response to stroke in both human and experimental animal brains, (2) present acutely and chronically after ischemic stroke, suggesting that they could have a role in acute neuroprotection and chronic neurorepair, and (3) able to be administered peripherally and reach the site of stroke brain injury. In this review, I will discuss the evidence that suggests that perlecan domain V may be just that substance, a potential beacon of hope for stroke patients.

JAK2 inhibition is neuroprotective and reduces astrogliosis after quinolinic acid striatal lesion in adult mice

Quinolinic acid (QA) striatal lesion in rodents induces neuronal death, astrogliosis and migration of neuroblasts from subventricular zone to damaged striatum. These phenomena occur in some human neurodegenerative illnesses, but the underlying mechanisms are unknown. We investigated the effect of AG490, a Janus-kinase 2 (JAK2) inhibitor, on astrogliosis, neuronal loss and neurogenesis in the striatum of adult mice after unilateral infusion of QA (30 nmol). Animals were given subcutaneous injections of AG490 (10 mg/kg) or vehicle immediately after lesion and then once daily for six days. Brain sections were used for neuronal stereological quantification, immunohistochemical and Western Blotting analyses for GFAP and doublecortin, markers of astrocytes and neuroblasts, respectively. The total area of doublecortin-positive cells (ADPC) and the number of neurons (NN) in the lesioned (L) and contralateral (CL) sides were evaluated. Neurogenesis index (NI=ADPC(L)/ADPC(CL)) and neuronal ratio (NR=NN(L)/NN(CL)) were calculated. After QA administration, blotting for GFAP showed an ipsilateral decrease of 19% in AG490- vs vehicle-treated animals. NR was 25% higher in mice given AG490 vs controls given vehicle. NI showed a decrease of 21% in AG490- vs vehicle-treated mice. Our results indicate that JAK2 inhibition reduces QA lesion and suggest that astrogliosis may impair neuronal survival in this model.

Role of neural precursor cells in promoting repair following stroke

Stem cell-based therapies for the treatment of stroke have received considerable attention. Two broad approaches to stem cell-based therapies have been taken: the transplantation of exogenous stem cells, and the activation of endogenous neural stem and progenitor cells (together termed neural precursors). Studies examining the transplantation of exogenous cells have demonstrated that neural stem and progenitor cells lead to the most clinically promising results. Endogenous activation of neural precursors has also been explored based on the fact that resident precursor cells have the inherent capacity to proliferate, migrate and differentiate into mature neurons in the uninjured adult brain. Studies have revealed that these neural precursor cell behaviours can be activated following stroke, whereby neural precursors will expand in number, migrate to the infarct site and differentiate into neurons. However, this innate response is insufficient to lead to functional recovery, making it necessary to enhance the activation of endogenous precursors to promote tissue repair and functional recovery. Herein we will discuss the current state of the stem cell-based approaches with a focus on endogenous repair to treat the stroke injured brain.

Osteopontin as a two-sided mediator in acute neuroinflammation in rat models

Osteopontin (OPN) plays an important role in the initiation of inflammation, affecting cell adhesion, chemotaxis, immune regulation, and protection against apoptosis, depending on its intracellular or extracellular localization. Although OPN in inflammation of the autoimmune central nervous system is proinflammatory, recent studies have shown that OPN during the induction stage of inflammation may also participate in neuroprotection and neurite growth. The present review examines the dual roles of OPN, specifically, its proinflammatory and subsequent neuroprotective roles, in acute neuroinflammation in rat models, including experimental autoimmune encephalomyelitis, brain injury, and autoimmune neuritis. All of these models are characterized by acute neuroinflammation, followed by remodeling of neural tissues.

Osteopontin is an alpha motor neuron marker in the mouse spinal cord

Motor neurons (MNs) are designated as alpha/gamma and fast/slow based on their target sites and the types of muscle fibers innervated; however, few molecular markers that distinguish between these subtypes are available. Here we report that osteopontin (OPN) is a selective marker of alpha MNs in the mouse spinal cord. OPN was detected in approximately 70% of postnatal choline acetyltransferase (ChAT)-positive MNs with relatively large somas, but not in those with smaller somas. OPN+/ChAT+ MNs were also positive for NeuN, an alpha MN marker, but were negative for Err3, a gamma MN marker. The size distribution of OPN+/ChAT+ cells was nearly identical to that of NeuN+/ChAT+ alpha MNs. Group Ia proprioceptive terminals immunoreactive for vesicular glutamate transporter-1 were selectively detected on the OPN+/ChAT+ cells. OPN staining was also detected at motor axon terminals at neuromuscular junctions, where the OPN+ terminals were positive or negative for SV2A, a marker distinguishing fast/slow motor endplates. Finally, retrograde labeling following intramuscular injection of fast blue indicated that OPN is expressed in both fast and slow MNs. Collectively, our findings show that OPN is an alpha MN marker present in both the soma and the endplates of alpha MNs in the postnatal mouse spinal cord.

Osteopontin increases the proliferation of neural progenitor cells

We examined the role of osteopontin in the proliferation of neural progenitor cells in vitro. Osteopontin increased the proliferation of neural progenitor cells in the presence of FGF2 as measured by cell proliferation assay and bromodeoxy uridine incorporation studies. In addition, immunoblot analysis demonstrated an increase in the phosphorylation of retinoblastoma protein with a concurrent increase in the content of phospho-Akt and cyclin D1. These results indicate that osteopontin can upregulate the content of phospho-Akt, cyclin D1 and phospho-Rb to subsequently enhance the proliferation of neural progenitor cells in the presence of FGF2.

Sustained expression of osteopontin is closely associated with calcium deposits in the rat hippocampus after transient forebrain ischemia

The present study was designed to evaluate the extent and topography of osteopontin (OPN) protein expression in the rat hippocampus 4 to 12 weeks following transient forebrain ischemia, and to compare OPN expression patterns with those of calcium deposits and astroglial and microglial reactions. Two patterns of OPN staining were recognized by light microscopy: 1) a diffuse pattern of tiny granular deposits throughout the CA1 region at 4 weeks after ischemia and 2) non-diffuse ovoid to round deposits, which formed conglomerates in the CA1 pyramidal cell layer over the chronic interval of 8 to 12 weeks. Immunogold-silver electron microscopy and electron probe microanalysis demonstrated that OPN deposits were indeed diverse types of calcium deposits, which were clearly delineated by profuse silver grains indicative of OPN expression. Intracellular OPN deposits were frequently observed within reactive astrocytes and neurons 4 weeks after ischemia but rarely at later times. By contrast, extracellular OPN deposits progressively increased in size and appeared to be gradually phagocytized by microglia or brain macrophages and some astrocytes over 8 to 12 weeks. These data indicate an interaction between OPN and calcium in the hippocampus in the chronic period after ischemia, suggesting that OPN binding to calcium deposits may be involved in scavenging mechanisms.

Meteorin is a chemokinetic factor in neuroblast migration and promotes stroke-induced striatal neurogenesis

Ischemic stroke affecting the adult brain causes increased progenitor proliferation in the subventricular zone (SVZ) and generation of neuroblasts, which migrate into the damaged striatum and differentiate to mature neurons. Meteorin (METRN), a newly discovered neurotrophic factor, is highly expressed in neural progenitor cells and immature neurons during development, suggesting that it may be involved in neurogenesis. Here, we show that METRN promotes migration of neuroblasts from SVZ explants of postnatal rats and stroke-subjected adult rats via a chemokinetic mechanism, and reduces N-methyl-D-asparate-induced apoptotic cell death in SVZ cells in vitro. Stroke induced by middle cerebral artery occlusion upregulates the expression of endogenous METRN in cells with neuronal phenotype in striatum. Recombinant METRN infused into the stroke-damaged brain stimulates cell proliferation in SVZ, promotes neuroblast migration, and increases the number of immature and mature neurons in the ischemic striatum. Our findings identify METRN as a new factor promoting neurogenesis both in vitro and in vivo by multiple mechanisms. Further work will be needed to translate METRN's actions on endogenous neurogenesis into improved recovery after stroke.