Fractalkine and CX3CR1 are involved in the migration of intravenously grafted human bone marrow stromal cells toward ischemic brain lesion in rats

An Overview of Optic Pathway Glioma With Neurofibromatosis Type 1: Pathogenesis, Risk Factors, and Therapeutic Strategies

Optic pathway gliomas (OPGs) are most predominant pilocytic astrocytomas, which are typically diagnosed within the first decade of life. The majority of affected children with OPGs also present with neurofibromatosis type 1 (NF1), the most common tumor predisposition syndrome. OPGs in individuals with NF1 primarily affect the optic pathway and lead to visual disturbance. However, it is challenging to assess risk in asymptomatic patients without valid biomarkers. On the other hand, for symptomatic patients, there is still no effective treatment to prevent or recover vision loss. Therefore, this review summarizes current knowledge regarding the pathogenesis of NF1-associated OPGs (NF1-OPGs) from preclinical studies to seek potential prognostic markers and therapeutic targets. First, the loss of the NF1 gene activates 3 distinct Ras effector pathways, including the PI3K/AKT/mTOR pathway, the MEK/ERK pathway, and the cAMP pathway, which mediate glioma tumorigenesis. Meanwhile, non-neoplastic cells from the tumor microenvironment (microglia, T cells, neurons, etc.) also contribute to gliomagenesis via various soluble factors. Subsequently, we investigated potential genetic risk factors, molecularly targeted therapies, and neuroprotective strategies for tumor prevention and vision recovery. Last, potential directions and promising preclinical models of NF1-OPGs are presented for further research. On the whole, NF1-OPGs develop as a result of the interaction between glioma cells and the tumor microenvironment. Developing effective treatments require a better understanding of tumor molecular characteristics, as well as multistage interventions targeting both neoplastic cells and non-neoplastic cells.

Insight in Hypoxia-Mimetic Agents as Potential Tools for Mesenchymal Stem Cell Priming in Regenerative Medicine

Hypoxia-mimetic agents are new potential tools in MSC priming instead of hypoxia incubators or chambers. Several pharmaceutical/chemical hypoxia-mimetic agents can be used to induce hypoxia in the tissues: deferoxamine (DFO), dimethyloxaloylglycine (DMOG), 2,4-dinitrophenol (DNP), cobalt chloride (CoCl2), and isoflurane (ISO). Hypoxia-mimetic agents can increase cell proliferation, preserve or enhance differentiation potential, increase migration potential, and induce neovascularization in a concentration- and stem cell source-dependent manner. Moreover, hypoxia-mimetic agents may increase HIF-1α, changing the metabolism and enhancing glycolysis like hypoxia. So, there is clear evidence that treatment with hypoxia-mimetic agents is beneficial in regenerative medicine, preserving stem cell capacities. These agents are not studied so wildly as hypoxia but, considering the low cost and ease of use, are believed to find application as pretreatment of many diseases such as ischemic heart disease and myocardial fibrosis and promote cardiac and cartilage regeneration. The knowledge of MSC priming is critical in evaluating safety procedures and use in clinics. In this review, similarities and differences between hypoxia and hypoxia-mimetic agents in terms of their therapeutic efficiency are considered in detail. The advantages, challenges, and future perspectives in MSC priming with hypoxia mimetic agents are also discussed.

Involvement of various chemokine/chemokine receptor axes in trafficking and oriented locomotion of mesenchymal stem cells in multiple sclerosis patients

Multiple sclerosis (MS) is a specific type of chronic immune-mediated disease in which the immune responses are almost run against the central nervous system (CNS). Despite intensive research, a known treatment for MS disease yet to be introduced. Thus, the development of novel and safe medications needs to be considered for the disease management. Application of mesenchymal stem cells (MSCs) as an emerging approach was recruited forthe treatment of MS. MSCs have several sources and they can be derived from the umbilical cord, adipose tissue, and bone marrow. Chemokines are low molecular weight proteins that their functional activities are achieved by binding to the cell surface G protein-coupled receptors (GPCRs). Chemokine and chemokine receptors are of the most important and effective molecules in MSC trafficking within the different tissues in hemostatic and non-hemostatic circumstances. Chemokine/chemokine receptor axes play a pivotal role in the recruitment and oriented trafficking of immune cells both towards and within the CNS and it appears that chemokine/chemokine receptor signaling may be the most important leading mechanisms in the pathogenesis of MS. In this article, we hypothesized that the chemokine/chemokine receptor axes network have crucial and efficacious impacts on behavior of the MSCs, nonetheless, the exact responsibility of these axes on the targeted tropism of MSCs to the CNS of MS patients yet remained to be fully elucidated. Therefore, we reviewed the ability of MSCs to migrate and home into the CNS of MS patients via expression of various chemokine receptors in response to chemokines expressed by cells of CNS tissue, to provide a great source of knowledge.

miR‑210 enhances mesenchymal stem cell‑modulated neural precursor cell migration

The migration of endogenous neural stem cells and neural precursor cells (NPCs) to sites of injury is essential for neuroregeneration following hypoxic‑ischemic events. Bone marrow‑derived mesenchymal stem cells (BMSCs) are a potential therapeutic source of cells following central nervous system damage; however, few studies have investigated the effects of BMSCs on cell migration. Thus, in the present study, the effects of BMSCs on NPC migration were investigated. In the present study, BMSCs and NPCs were isolated and cultured from mice. The effects of BMSCs on the migration of NPCs were analyzed using a Transwell cell migration assay. BMSCs were transfected with microRNA‑210 (miR‑210) mimics and inhibitors to examine the effects of the respective upregulation and downregulation of miR‑210 in BMSCs on the migration of NPCs. Then, miR‑210 expression in BMSCs were quantified and the expression levels of vascular endothelial growth factor‑C (VEGF‑C), brain derived neurotrophic factor (BDNF) and chemokine C‑C motif ligand 3 (CCL3) in the supernatant under hypoxic conditions were investigated via reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and ELISA. Subsequently, the expression of VEGF‑C, BDNF and CCL3 in BMSCs overexpressing miR‑210 or BMSCs suppressing miR‑210 was examined by RT‑qPCR and western blot analyses. BMSCs promoted the migration of NPC, particularly when pre‑cultured with BMSCs for 24 h and co‑cultured with NPCs for 24 h; the miR‑210 expression levels increased under hypoxic conditions. Additionally, the migration of NPCs was also increased when the BMSCs overexpressed miR‑210 compared with the BMSCs transfected with a negative control miR and BMSCs with downregulated miR‑210 levels. The expression levels of VEGF‑C increased in the BMSCs that overexpressed miR‑210 and were decreased in BMSCs transfected with a miR‑210 inhibitor. The results of the present study indicated that BMSCs promote the migration of NPCs. Overexpression of miR‑210 in BMSCs enhanced NPC migration and may be associated with increases in VEGF‑C expression levels.

Enhancer of zeste homolog 2 enhances the migration and chemotaxis of dental mesenchymal stem cells

Objective

To investigate the function of enhancer of zeste homolog 2 (EZH2) in the migration and chemotaxis of human dental tissue-derived mesenchymal stem cells.

Methods

The expression of EZH2, C-X-C motif chemokine ligand 11 (CXCL11), CXCL16, and CXCR1 in stem cells from the apical papilla (SCAPs) was determined by real-time reverse transcription PCR and western blotting. The effects of EZH2 on the homing of SCAPs and the effects of EZH2-overexpressing SCAP culture supernatant on periodontal ligament stem cells (PDLSCs) were tested by scratch migration assays and transwell chemotaxis assays.

Results

EZH2 overexpression significantly enhanced the migration and chemotaxis of SCAPs and upregulated the expression of CXCL11, CXCL16, and CXCR1 in SCAPs. EZH2 depletion had the opposite effect, impairing the migration and chemotaxis of SCAPs and downregulating the expression of CXCL11, CXCL16, and CXCR1. The culture supernatant of EZH2-overexpressing SCAPs advanced the migration and chemotaxis of PDLSCs.

Conclusions

EZH2 evidently promoted the migration and chemotaxis of SCAPs by upregulating the expression of CXCL11, CXCL16, and CXCR1. Moreover, EZH2-overexpressing SCAPs enhanced the homing, migration, and chemotaxis of PDLSCs via paracrine signaling.

Chemokines: Key Molecules that Orchestrate Communication among Neurons, Microglia and Astrocytes to Preserve Brain Function

In the CNS, chemokines and chemokine receptors are involved in pleiotropic physiological and pathological activities. Several evidences demonstrated that chemokine signaling in the CNS plays key homeostatic roles and, being expressed on neurons, glia and endothelial cells, chemokines mediate the bidirectional cross-talk among parenchymal cells. An efficient communication between neurons and glia is crucial to establish and maintain a healthy brain environment which ensures normal functionality. Glial cells behave as active sensors of environmental changes induced by neuronal activity or detrimental insults, supporting and exerting neuroprotective activities. In this review we summarize the evidence that chemokines (CXCL12, CX3CL1, CXCL16 and CCL2) modulate neuroprotective processes upon different noxious stimuli and participate to orchestrate neurons-microglia-astrocytes action to preserve and limit brain damage. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Expression changes of CX3CL1 and CX3CR1 proteins in the hippocampal CA1 field of the gerbil following transient global cerebral ischemia

Chemokine C-X3-C motif ligand 1 (CX3CL1) and its sole receptor, CX3CR1, are known to be involved in neuronal damage/death following brain ischemia. In the present study, time-dependent expression changes of CX3CL1 and CX3CR1 proteins were investigated in the hippocampal CA1 field following 5 min of transient global cerebral ischemia (tgCI) in gerbils. To induce tgCI in gerbils, bilateral common carotid arteries were occluded for 5 min using aneurysm clips. Expression changes of CX3CL1 and CX3CR1 proteins were assessed at 1, 2 and 5 days after tgCI using western blotting and immunohistochemistry. CX3CL1 immunoreactivity was strong in the CA1 pyramidal cells of animals in the sham operation group. Weak CX3CL1 immunoreactivity was detected at 6 h after tgCI, recovered at 1 day after tgCI and disappeared from 5 days after tgCI. CX3CR1 immunoreactivity was very weak in CA1 pyramidal cells of the sham animals. CX3CR1 immunoreactivity in CA1 pyramidal cells was significantly increased at 1 days after tgCI and gradually decreased thereafter. On the other hand, CX3CR1 immunoreactivity was significantly increased in microglia from 5 days after tgCI. These results showed that CX3CL1 and CX3CR1 protein expression levels in pyramidal cells and microglia in the hippocampal CA1 field following tgCI were changed, indicating that tgCI-induced expression changes of CX3CL1 and CX3CR1 proteins might be closely associated with tgCI-induced delayed neuronal death and microglial activation.

Overexpression of CX3CR1 in Adipose-Derived Stem Cells Promotes Cell Migration and Functional Recovery After Experimental Intracerebral Hemorrhage

Stem cell therapy has emerged as a new promising therapeutic strategy for intracerebral hemorrhage (ICH). However, the efficiency of stem cell therapy is partially limited by low retention and engraftment of the delivered cells. Therefore, it’s necessary to improve the migration ability of stem cells to the injured area in order to save the costs and duration of cell preparation. This study aimed to investigate whether overexpression of CX3CR1, the specific receptor of chemokine fractalkine (FKN), in adipose-derived stem cells (ADSCs) can stimulate the cell migration to the injured area in the brain, improve functional recovery and protect against cell death following experimental ICH. ADSCs were isolated from subcutaneous adipose tissues of rats. ICH was induced by means of an injection of collagenase type VII. ELISA showed that the expression levels of fractalkine/FKN were increased at early time points, with a peak at day 3 after ICH. And it was found that different passages of ADSCs could express the chemokine receptor CX3CR1. Besides, the chemotactic movements of ADSCs toward fractalkine have been verified by transwell migration assay. ADSCs overexpressing CX3CR1 were established through lentivirus transfection. We found that after overexpression of CX3CR1 receptor, the migration ability of ADSCs was increased both in vitro and in vivo. In addition, reduced cell death and improved sensory and motor functions were seen in the mice ICH model. Thus, ADSCs overexpression CX3CR1 might be taken as a promising therapeutic strategy for the treatment of ICH.

Fractalkine/CX3CR1 is involved in the cross-talk between neuron and glia in neurological diseases

Fractalkine (CX3C chemokine ligand 1, CX3CL1) is an essential chemokine, for regulating adhesion and chemotaxis through binding to CX3CR1, which plays a critical role in the crosstalk between glial cells and neurons by direct or indirect ways in the central nervous system (CNS). Fractalkine/CX3CR1 axis regulates microglial activation and function, neuronal survival and synaptic function by controlling the release of inflammatory cytokines and synaptic plasticity in the course of the neurological disease. The multiple functions of fractalkine/CX3CR1 make it exert neuroprotective or neurotoxic effects, which determines the pathogenesis. However, the role of fractalkine/CX3CR1 in the CNS remains controversial. Whether it can be used as a therapeutic target for neurological diseases needs to be further investigated. In this review, we summarize the studies highlighting fractalkine/CX3CR1-mediated effects and discuss the potential neurotoxic and neuroprotective actions of fractalkine/CX3CR1 in brain injury for providing useful insights into the potential applications of fractalkine/CX3CR1 in neurological diseases.

Using biomaterials to modulate chemotactic signaling for central nervous system repair

Chemotaxis enables cellular communication and movement within the body. This review focuses on exploiting chemotaxis as a tool for repair of the central nervous system (CNS) damaged from injury and/or degenerative diseases. Chemokines and factors alone may initiate repair following CNS injury/disease, but exogenous administration may enhance repair and promote regeneration. This review will discuss critical chemotactic molecules and factors that may promote neural regeneration. Additionally, this review highlights how biomaterials can impact the presentation and delivery of chemokines and growth factors to alter the regenerative response.

Modulators of microglial activation and polarization after intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is the most lethal subtype of stroke but currently lacks effective treatment. Microglia are among the first non-neuronal cells on the scene during the innate immune response to ICH. Microglia respond to acute brain injury by becoming activated and developing classic M1-like (proinflammatory) or alternative M2-like (anti-inflammatory) phenotypes. This polarization implies as yet unrecognized actions of microglia in ICH pathology and recovery, perhaps involving microglial production of proinflammatory or anti-inflammatory cytokines and chemokines. Furthermore, alternatively activated M2-like microglia might promote phagocytosis of red blood cells and tissue debris, a major contribution to haematoma clearance. Interactions between microglia and other cells modulate microglial activation and function, and are also important in ICH pathology. This Review summarizes key studies on modulators of microglial activation and polarization after ICH, including M1-like and M2-like microglial phenotype markers, transcription factors and key signalling pathways. Microglial phagocytosis, haematoma resolution, and the potential crosstalk between microglia and T lymphocytes, neurons, astrocytes, and oligodendrocytes in the ICH brain are described. Finally, the clinical and translational implications of microglial polarization in ICH are presented, including the evidence that therapeutic approaches aimed at modulating microglial function might mitigate ICH injury and improve brain repair.

Help-me signaling: Non-cell autonomous mechanisms of neuroprotection and neurorecovery

Self-preservation is required for life. At the cellular level, this fundamental principle is expressed in the form of molecular mechanisms for preconditioning and tolerance. When the cell is threatened, internal cascades of survival signaling become triggered to protect against cell death and defend against future insults. Recently, however, emerging findings suggest that this principle of self-preservation may involve not only intracellular signals; the release of extracellular signals may provide a way to recruit adjacent cells into an amplified protective program. In the central nervous system where multiple cell types co-exist, this mechanism would allow threatened neurons to "ask for help" from glial and vascular compartments. In this review, we describe this new concept of help-me signaling, wherein damaged or diseased neurons release signals that may shift glial and vascular cells into potentially beneficial phenotypes, and help remodel the neurovascular unit. Understanding and dissecting these non-cell autonomous mechanisms of self-preservation in the CNS may lead to novel opportunities for neuroprotection and neurorecovery.

Analysis of the Role of CX3CL1 (Fractalkine) and Its Receptor CX3CR1 in Traumatic Brain and Spinal Cord Injury: Insight into Recent Advances in Actions of Neurochemokine Agents

CX3CL1 (fractalkine) is the only member of the CX3C (delta) subfamily of chemokines which is unique and combines the properties of both chemoattractant and adhesion molecules. The two-form ligand can exist either in a soluble form, like all other chemokines, and as a membrane-anchored molecule. CX3CL1 discloses its biological properties through interaction with one dedicated CX3CR1 receptor which belongs to a family of G protein-coupled receptors (GPCR). The CX3CL1/CX3CR1 axis acts in many physiological phenomena including those occurring in the central nervous system (CNS), by regulating the interactions between neurons, microglia, and immune cells. Apart from the role under physiological conditions, the CX3CL1/CX3CR1 axis was implied to have a role in different neuropathologies such as traumatic brain injury (TBI) and spinal cord injury (SCI). CNS injuries represent a serious public health problem, despite improvements in therapeutic management. To date, no effective treatment has been determined, so they constitute a leading cause of death and severe disability. The course of TBI and SCI has two consecutive poorly demarcated phases: the initial, primary injury and secondary injury. Recent evidence has implicated the role of the CX3CL1/CX3CR1 axis in neuroinflammatory processes occurring after CNS injuries. The importance of the CX3CL1/CX3CR1 axis in the pathophysiology of TBI and SCI in the context of systemic and direct local immune response is still under investigation. This paper, based on a review of the literature, updates and summarizes the current knowledge about CX3CL1/CX3CR1 axis involvement in TBI and SCI pathogenesis, indicating possible molecular and cellular mechanisms with a potential target for therapeutic intervention.

Hypoxia Inducible Factor-1α Regulates the Migration of Bone Marrow Mesenchymal Stem Cells via Integrin α 4

Although hypoxic environments have been known to regulate the migratory ability of bone marrow-derived mesenchymal stem cells (BM-MSCs), which is a critical factor for maximizing the therapeutic effect, the underlying mechanisms remain unclear. Therefore, we aimed to confirm the effect of hypoxia-inducible factor-1α (HIF-1α) on the migration of BM-MSCs and to analyze the interaction between HIF-1α and integrin-mediated signals. Hypoxia-activated HIF-1α significantly increased BM-MSC migration. The expression of integrin α₄ was decreased in BM-MSCs by increased HIF-1α under hypoxia, whereas the expression of Rho-associated kinase 1 (ROCK1) and Rac1/2/3 was increased. After downregulation of HIF-1α by YC-1, which is an inhibitor of HIF-1α, BM-MSC migration was decreased via upregulation of integrin α₄ and downregulation of ROCK1 and Rac1/2/3. Knockdown of integrin α₄ by integrin α₄ siRNA (siITGA4) treatment increased BM-MSC migration by upregulation of ROCK1, Rac1/2/3, and matrix metalloproteinase-2 regardless of oxygen tension. Moreover, siITGA4 treatment increased HIF-1α expression and augmented the translocation of HIF-1α into the nucleus under hypoxia. Taken together, the alternative expression of HIF-1α induced by microenvironment factors, such as hypoxia and integrin α₄, may regulate the migration of BM-MSCs. These findings may provide insights to the underlying mechanisms of BM-MSC migration for successful stem cell-based therapy.

Rational modulation of the innate immune system for neuroprotection in ischemic stroke

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Fractalkine promotes chemotaxis of bone marrow-derived mesenchymal stem cells towards ischemic brain lesions through Jak2 signaling and cytoskeletal reorganization

The fractalkine (FKN)-CX3CR1 (FKN receptor) axis reportedly plays an important role in the progression of many neural pathologies. However, its role in the recruitment of bone marrow-derived progenitor cells for neurogenesis remains elusive. The chemokine-based mechanism underlying the migration of bone marrow-derived mesenchymal stem cells (BMSCs) was investigated in a double-chamber transmigration model with recombinant FKN and endogenous FKN extract, and the results confirmed the involvement of FKN in migration. This chemotactic response was CX3CR1-dependent and FKN-sensitive. Western blotting, immunoprecipitation and transmigration assays revealed that the Janus kinase (Jak)2-signal transducer and activator of transcription (Stat)5α-extracellular signal-related kinase (ERK)1/2 pathway was activated by FKN. Confocal laser scanning microscopy was used to demonstrate cytoskeletal reorganization caused by remodeling of the surface receptor integrin α5β1, intracellular phosphorylation of Fak and Pax, and upregulation of intercellular adhesion molecule-1 during BMSC migration. Moreover, significant inhibition of signaling and migration was detected after treatment of cells with Jak2-interfering RNA or the antagonist AG490. In addition, the results of a fluorescence immunohistochemical analysis of an in vivo chemotactic model, developed via transplantation of BMSCs into transient middle cerebral artery-occluded rats, were consistent with the in vitro results. These findings suggest that FKN activates Jak2-Stat5α-ERK1/2 signaling through CX3CR1, thereby triggering integrin-dependent machinery reorganization to allow chemotactic migration of BMSCs towards an ischemic cerebral lesion.

Trasmembrane chemokines CX3CL1 and CXCL16 drive interplay between neurons, microglia and astrocytes to counteract pMCAO and excitotoxic neuronal death

Upon noxious insults, cells of the brain parenchyma activate endogenous self-protective mechanisms to counteract brain damage. Interplay between microglia and astrocytes can be determinant to build a physiological response to noxious stimuli arisen from injury or stress, thus understanding the cross talk between microglia and astrocytes would be helpful to elucidate the role of glial cells in endogenous protective mechanisms and might contribute to the development of new strategy to mobilize such program and reduce brain cell death. Here we demonstrate that chemokines CX3CL1 and CXCL16 are molecular players that synergistically drive cross-talk between neurons, microglia and astrocytes to promote physiological neuroprotective mechanisms that counteract neuronal cell death due to ischemic and excitotoxic insults. In an in vivo model of permanent middle cerebral artery occlusion (pMCAO) we found that exogenous administration of soluble CXCL16 reduces ischemic volume and that, upon pMCAO, endogenous CXCL16 signaling restrains brain damage, being ischemic volume reduced in mice that lack CXCL16 receptor. We demonstrated that CX3CL1, acting on microglia, elicits CXCL16 release from glia and this is important to induce neroprotection since lack of CXCL16 signaling impairs CX3CL1 neuroprotection against both in vitro Glu-excitotoxic insult and pMCAO. Moreover the activity of adenosine receptor A3R and the astrocytic release of CCL2 play also a role in trasmembrane chemokine neuroprotective effect, since their inactivation reduces CX3CL1- and CXCL16 induced neuroprotection.

Chronic stress enhances microglia activation and exacerbates death of nigral dopaminergic neurons under conditions of inflammation

Background

Parkinson’s disease is an irreversible neurodegenerative disease linked to progressive movement disorders and is accompanied by an inflammatory reaction that is believed to contribute to its pathogenesis. Since sensitivity to inflammation is not the same in all brain structures, the aim of this work was to test whether physiological conditions as stress could enhance susceptibility to inflammation in the substantia nigra, where death of dopaminergic neurons takes place in Parkinson’s disease.

Methods

To achieve our aim, we induced an inflammatory process in nonstressed and stressed rats (subject to a chronic variate stress) by a single intranigral injection of lipopolysaccharide, a potent proinflammogen. The effect of this treatment was evaluated on inflammatory markers as well as on neuronal and glial populations.

Results

Data showed a synergistic effect between inflammation and stress, thus resulting in higher microglial activation and expression of proinflammatory markers. More important, the higher inflammatory response seen in stressed animals was associated with a higher rate of death of dopaminergic neurons in the substantia nigra, the most characteristic feature seen in Parkinson’s disease. This effect was dependent on glucocorticoids.

Conclusions

Our data demonstrate that stress sensitises midbrain microglia to further inflammatory stimulus. This suggests that stress may be an important risk factor in the degenerative processes and symptoms of Parkinson’s disease.

Chemokine contribution in stem cell engraftment into the infarcted myocardium

Modern life styles have made cardiovascular disease the leading cause of morbidity and mortality worldwide. Although current treatments substantially ameliorate patients’ prognosis after MI, they cannot restore the affected tissue or entirely re-establish organ function. Therefore, the main goal of modern cardiology should be to design strategies to reduce myocardial necrosis and optimize cardiac repair following MI. Cell-based therapy was considered a novel and potentially new strategy in regenerative medicine; however, its clinical implementation has not yielded the expected results. Chemokines seem to increase the efficiency of cell-therapy and may represent a reliable method to be exploited in the future. This review surveys current knowledge of cell therapy and highlights key insights into the role of chemokines in stem cell engraftment in infarcted myocardium and their possible clinical implications.

Engraftment of human mesenchymal stem cells in a rat photothrombotic cerebral infarction model : comparison of intra-arterial and intravenous infusion using MRI and histological analysis

Objective

This study aimed to evaluate the hypotheses that administration routes [intra-arterial (IA) vs. intravenous (IV)] affect the early stage migration of transplanted human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in acute brain infarction.

Methods

Male Sprague-Dawley rats (n=40) were subjected to photothrombotic infarction. Three days after photothrombotic infarction, rats were randomly allocated to one of four experimental groups [IA group : n=12, IV group : n=12, superparamagnetic iron oxide (SPIO) group : n=8, control group : n=8]. All groups were subdivided into 1, 6, 24, and 48 hours groups according to time point of sacrifice. Magnetic resonance imaging (MRI) consisting of T2 weighted image (T2WI), T2^* weighted image (T2^*WI), susceptibility weighted image (SWI), and diffusion weighted image of rat brain were obtained prior to and at 1, 6, 24, and 48 hours post-implantation. After final MRI, rats were sacrificed and grafted cells were analyzed in brain and lung specimen using Prussian blue and immunohistochemical staining.

Results

Grafted cells appeared as dark signal intensity regions at the peri-lesional zone. In IA group, dark signals in peri-lesional zone were more prominent compared with IV group. SWI showed largest dark signal followed by T2^*WI and T2WI in both IA and IV groups. On Prussian blue staining, IA administration showed substantially increased migration and a large number of transplanted hBM-MSCs in the target brain than IV administration. The Prussian blue-positive cells were not detected in SPIO and control groups.

Conclusion

In a rat photothrombotic model of ischemic stroke, selective IA administration of human mesenchymal stem cells is more effective than IV administration. MRI and histological analyses revealed the time course of cell migration, and the numbers and distribution of hBM-MSCs delivered into the brain.

Microglial responses after ischemic stroke and intracerebral hemorrhage

Stroke is a leading cause of death worldwide. Ischemic stroke is caused by blockage of blood vessels in the brain leading to tissue death, while intracerebral hemorrhage (ICH) occurs when a blood vessel ruptures, exposing the brain to blood components. Both are associated with glial toxicity and neuroinflammation. Microglia, as the resident immune cells of the central nervous system (CNS), continually sample the environment for signs of injury and infection. Under homeostatic conditions, they have a ramified morphology and phagocytose debris. After stroke, microglia become activated, obtain an amoeboid morphology, and release inflammatory cytokines (the M1 phenotype). However, microglia can also be alternatively activated, performing crucial roles in limiting inflammation and phagocytosing tissue debris (the M2 phenotype). In rodent models, microglial activation occurs very early after stroke and ICH; however, their specific roles in injury and repair remain unclear. This review summarizes the literature on microglial responses after ischemic stroke and ICH, highlighting the mediators of microglial activation and potential therapeutic targets for each condition.

Accumulation of micron sized iron oxide particles in endothelin-1 induced focal cortical ischemia in rats is independent of cell migration

PURPOSE

Endogenous labeling of stem/ progenitor cells via intracerebroventricular injection of micron-sized particles of iron oxide (MPIOs) has become standard methodology for MRI of adult neurogenesis. While this method is well characterized in the naïve rodent brain, it has not been fully investigated in disease models. Here, we describe methodological challenges that can confound data analysis when this technique is applied to a rat model of stroke, the endothelin-1 model of focal cortical ischemia.

METHODS

We intended to track endogenous neuroblast migration from the subventricular zone to the stroke area using previously described methods for in vivo labeling of endogenous neuroblasts with MPIOs and following migration with high resolution MRI.

RESULTS

MPIOs accumulation in stroke regions of endothelin-1-treated brains involves two dynamic steps: an initial rapid cell independent mechanism, followed by slower MPIOs accumulation. While the latter may in part be attributable to cell dependent delivery of the particles, the cell independent mechanism complicates the interpretation of the data. Strategies aimed at prelabeling the stem cell niche reduced cell independent MPIOs accumulation, but failed to abolish it.

CONCLUSION

We conclude that MRI-based neural stem/progenitor cell tracking via direct injection of MPIOs into the lateral and third ventricles, requires significant validation in models of brain disease/trauma.

How stem cells speak with host immune cells in inflammatory brain diseases

Advances in stem cell biology have raised great expectations that diseases and injuries of the central nervous system (CNS) may be ameliorated by the development of non-hematopoietic stem cell medicines. Yet, the application of adult stem cells as CNS therapeutics is challenging and the interpretation of some of the outcomes ambiguous. In fact, the initial idea that stem cell transplants work only via structural cell replacement has been challenged by the observation of consistent cellular signaling between the graft and the host. Cellular signaling is the foundation of coordinated actions and flexible responses, and arises via networks of exchanging and interacting molecules that transmit patterns of information between cells. Sustained stem cell graft-to-host communication leads to remarkable trophic effects on endogenous brain cells and beneficial modulatory actions on innate and adaptive immune responses in vivo, ultimately promoting the healing of the injured CNS. Among a number of adult stem cell types, mesenchymal stem cells (MSCs) and neural stem/precursor cells (NPCs) are being extensively investigated for their ability to signal to the immune system upon transplantation in experimental CNS diseases. Here, we focus on the main cellular signaling pathways that grafted MSCs and NPCs use to establish a therapeutically relevant cross talk with host immune cells, while examining the role of inflammation in regulating some of the bidirectionality of these communications. We propose that the identification of the players involved in stem cell signaling might contribute to the development of innovative, high clinical impact therapeutics for inflammatory CNS diseases.

Current status of chemokines in the adult CNS

Chemokines - chemotactic cytokines - are small secreted proteins that attract and activate immune and non-immune cells in vitro and in vivo. It has been suggested that chemokines and their receptors play a role in the central nervous system (CNS), in addition to their well established role in the immune system. We focus here on three chemokines-CXCL12 (C-X-C motif ligand 12), CCL2 (C-C motif ligand 2), and CX3CL1 (C-X-3C motif ligand 1) - and their principal receptors - CXCR4 (C-X-C motif receptor 4), CCR2 (C-C motif receptor 2) and CX3CR1 (C-X-3C motif receptor 1), respectively. We first introduce the classification of chemokines and their G-protein coupled receptors and the main signaling pathways triggered by receptor activation. We then discuss the cellular distribution of CXCL12/CXCR4, CCL2/CCR2 and CX3CL1/CX3CR1 in adult brain and the neurotransmission and neuromodulation effects controlled by these chemokines in the adult CNS. Changes in the expression of CXCL12, CCL2 and CX3CL1 and their respective receptors are also increasingly being implicated in the pathogenesis of CNS disorders, such as Alzheimer's disease, Parkinson's disease, HIV-associated encephalopathy, stroke and multiple sclerosis, and are therefore plausible targets for future pharmacological intervention. The final section thus discusses the role of these chemokines in these pathophysiological states. In conclusion, the role of these chemokines in cellular communication may make it possible: (i) to identify new pathways of neuron-neuron, glia-glia or neuron-glia communications relevant to both normal brain function and neuroinflammatory and neurodegenerative diseases; (ii) to develop new therapeutic approaches for currently untreatable brain diseases.

The role of chemokines in mesenchymal stem cell homing to myocardium

A growing body of preclinical evidence suggests that mesenchymal stem cells (MSCs) are effective for the structural and functional recovery of the infracted heart. Accordingly, clinical trials are underway to determine the benefit of MSC-based therapies. While systemic administration of MSCs is an attractive strategy, and is the route currently used for the administration of MSCs in clinical studies for myocardial infarction, the majority of infused cells do not appear to localize to infracted myocardium in animal studies. Recently, important progress has been made in identifying chemokine receptors critical for the migration and homing of MSCs. Here, we review recent literature regarding mechanisms of MSC homing and recruitment to the ischemic myocardium, and discuss potential influences of low engraftment rates of systemically administered MSCs to the infracted heart tissue on the effects of MSC-based therapies on myocardial infarction.

CX3CL1 is neuroprotective in permanent focal cerebral ischemia in rodents

The chemokine CX3CL1 and its receptor CX3CR1 are constitutively expressed in the nervous system. In this study, we used in vivo murine models of permanent middle cerebral artery occlusion (pMCAO) to investigate the protective potential of CX3CL1. We report that exogenous CX3CL1 reduced ischemia-induced cerebral infarct size, neurological deficits, and caspase-3 activation. CX3CL1-induced neuroprotective effects were long lasting, being observed up to 50 d after pMCAO in rats. The neuroprotective action of CX3CL1 in different models of brain injuries is mediated by its inhibitory activity on microglia and, in vitro, requires the activation of adenosine receptor 1 (A₁R). We show that, in the presence of the A₁R antagonist 1,3-dipropyl-8-cyclopentylxanthine and in A₁R⁻/⁻ mice, the neuroprotective effect of CX3CL1 on pMCAO was abolished, indicating the critical importance of the adenosine system in CX3CL1 protection also in vivo. In apparent contrast with the above reported data but in agreement with previous findings, cx3cl1⁻/⁻ and cx3cr1(GFP/GFP) mice, respectively, deficient in CX3CL1 or CX3CR1, had less severe brain injury on pMCAO, and the administration of exogenous CX3CL1 increased brain damage in cx3cl1⁻/⁻ ischemic mice. We also report that CX3CL1 induced a different phagocytic activity in wild type and cx3cl1⁻/⁻ microglia in vitro during cotreatment with the medium conditioned by neurons damaged by oxygen-glucose deprivation. Together, these data suggest that acute administration of CX3CL1 reduces ischemic damage via an adenosine-dependent mechanism and that the absence of constitutive CX3CL1-CX3CR1 signaling changes the outcome of microglia-mediated effects during CX3CL1 administration to ischemic brain.

Achieving stable human stem cell engraftment and survival in the CNS: is the future of regenerative medicine immunodeficient?

There is potential for a variety of stem cell populations to mediate repair in the diseased or injured CNS; in some cases, this theoretical possibility has already transitioned to clinical safety testing. However, careful consideration of preclinical animal models is essential to provide an appropriate assessment of stem cell safety and efficacy, as well as the basic biological mechanisms of stem cell action. This article examines the lessons learned from early tissue, organ and hematopoietic grafting, the early assumptions of the stem cell and CNS fields with regard to immunoprivilege, and the history of success in stem cell transplantation into the CNS. Finally, we discuss strategies in the selection of animal models to maximize the predictive validity of preclinical safety and efficacy studies.

Neurofibromatosis-1 heterozygosity increases microglia in a spatially and temporally restricted pattern relevant to mouse optic glioma formation and growth

Whereas carcinogenesis requires the acquisition of driver mutations in progenitor cells, tumor growth and progression are heavily influenced by the local microenvironment. Previous studies from our laboratory have used Neurofibromatosis-1 (NF1) genetically engineered mice to characterize the role of stromal cells and signals to optic glioma formation and growth. Previously, we have shown that Nf1+/- microglia in the tumor microenvironment are critical cellular determinants of optic glioma proliferation. To define the role of microglia in tumor formation and maintenance further, we used CD11b-TK mice, in which resident brain microglia (CD11b+, CD68+, Iba1+, CD45low cells) can be ablated at specific times after ganciclovir administration. Ganciclovir-mediated microglia reduction reduced Nf1 optic glioma proliferation during both tumor maintenance and tumor development. We identified the developmental window during which microglia are increased in the Nf1+/- optic nerve and demonstrated that this accumulation reflected delayed microglia dispersion. The increase in microglia in the Nf1+/- optic nerve was associated with reduced expression of the chemokine receptor, CX3CR1, such that reduced Cx3cr1 expression in Cx3cr1-GFP heterozygous knockout mice led to a similar increase in optic nerve microglia. These results establish a critical role for microglia in the development and maintenance of Nf1 optic glioma.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Intrahepatic levels of Fractalkine in healthy individuals and patients with hepatic fibrosis and cirrhosis

AIM: To investigate the intrahepatic levels of chemokine Fractalkine in healthy individuals and patients with hepatic fibrosis and cirrhosis.

METHODS: Hepatic tissues were obtained in surgery from 9 normal persons, 10 patients with fibrotic liver, 11 patients with cirrhosis. The content of Fractalkine in hepatic tissue was assayed by ELISA.

RESULTS: The intrahepatic levels of Fractalkine in patients with hepatic fibrosis and cirrhosis were remarkably higher than that in healthy individuals (13.72 ± 5.59 ng/g and 14.70 ± 3.52 ng/g vs 4.84 ± 3.72 ng/g, respectively; both P < 0.05). No significant difference was noted in intrahepatic level of Fractalkine between patients with hepatic fibrosis and cirrhosis.

CONCLUSION: Intrahepatic level of Fractalkine increases with the aggravation of hepatic fibrosis and remains high in liver cirrhosis.