Neurorestorative therapies for stroke: underlying mechanisms and translation to the clinic

Animal models of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity both in civilian life and on the battlefield worldwide. Survivors of TBI frequently experience long-term disabling changes in cognition, sensorimotor function and personality. Over the past three decades, animal models have been developed to replicate the various aspects of human TBI, to better understand the underlying pathophysiology and to explore potential treatments. Nevertheless, promising neuroprotective drugs that were identified as being effective in animal TBI models have all failed in Phase II or Phase III clinical trials. This failure in clinical translation of preclinical studies highlights a compelling need to revisit the current status of animal models of TBI and therapeutic strategies.

Intra-arterial cell transplantation provides timing-dependent cell distribution and functional recovery after stroke

BACKGROUND AND PURPOSE

Intra-arterial cell transplantation offers a novel therapeutic strategy for stroke; however, it remains unclear how the timing of cell administration affects cell distribution, brain repair processes, and functional recovery. Here, we investigate the hypothesis that the timing of cell transplantation changes the behavior of the cell graft and the host environment in a way that affects functional recovery.

METHODS

Rats received human mesenchymal stem cells via the internal carotid artery at 1, 4, or 7 days (D1, D4, or D7) after middle cerebral artery occlusion and reperfusion. Animals were euthanized at various time points to assess cell distribution, infiltration of activated microglia, expression of brain-derived neurotrophic factor, reactive astrocytes, angiogenesis, and functional recovery.

RESULTS

Human mesenchymal stem cells were widely distributed both in the peri-infarct and core in D1, and dominantly in the peri-infarct in D4. Very few cells were observed on D7. At day 7 poststroke, microglia activation was significantly suppressed in both the peri-infarct and core in D1, and predominantly in the peri-infarct in D4. At day 21 poststroke, brain-derived neurotrophic factor was widely distributed throughout the peri-infarct in D1 and D4, along with many reactive astrocytes and considerable angiogenesis. Motor function improved earlier in D1 and later in D4, but no recovery was obtained in D7.

CONCLUSIONS

Our results indicate that intra-arterial cell transplantation provides timing-dependent cell distribution and poststroke functional recovery via a combination of neuroprotection, reactive astrocyte enhancement, and angiogenesis.

Animal models of post-ischemic forced use rehabilitation: methods, considerations, and limitations

Many survivors of stroke experience arm impairments, which can severely impact their quality of life. Forcing use of the impaired arm appears to improve functional recovery in post-stroke hemiplegic patients, however the mechanisms underlying improved recovery remain unclear. Animal models of post-stroke rehabilitation could prove critical to investigating such mechanisms, however modeling forced use in animals has proven challenging. Potential problems associated with reported experimental models include variability between stroke methods, rehabilitation paradigms, and reported outcome measures. Herein, we provide an overview of commonly used stroke models, including advantages and disadvantages of each with respect to studying rehabilitation. We then review various forced use rehabilitation paradigms, and highlight potential difficulties and translational problems. Lastly, we discuss the variety of functional outcome measures described by experimental researchers. To conclude, we outline ongoing challenges faced by researchers, and the importance of translational communication. Many stroke patients rely critically on rehabilitation of post-stroke impairments, and continued effort toward progression of rehabilitative techniques is warranted to ensure best possible treatment of the devastating effects of stroke.

Intracerebral neural stem cell transplantation improved the auditory of mice with presbycusis

Stem cell-based regenerative therapy is a potential cellular therapeutic strategy for patients with incurable brain diseases. Embryonic neural stem cells (NSCs) represent an attractive cell source in regenerative medicine strategies in the treatment of diseased brains. Here, we assess the capability of intracerebral embryonic NSCs transplantation for C57BL/6J mice with presbycusis in vivo. Morphology analyses revealed that the neuronal rate of apoptosis was lower in the aged group (10 months of age) but not in the young group (2 months of age) after NSCs transplantation, while the electrophysiological data suggest that the Auditory Brain Stem Response (ABR) threshold was significantly decreased in the aged group at 2 weeks and 3 weeks after transplantation. By contrast, there was no difference in the aged group at 4 weeks post-transplantation or in the young group at any time post-transplantation. Furthermore, immunofluorescence experiments showed that NSCs differentiated into neurons that engrafted and migrated to the brain, even to sites of lesions. Together, our results demonstrate that NSCs transplantation improve the auditory of C57BL/6J mice with presbycusis.

Efficacy of single and multiple injections of human umbilical tissue-derived cells following experimental stroke in rats

Introduction

Human umbilical tissue-derived cells (hUTC) are a promising source of cells for regenerative treatment of stroke. In this study, we tested the efficacy of hUTC in experimental stroke and whether multiple injections of hUTC provide additional therapeutic benefits as compared to a single injection.

Methods

Adult male Wistar rats were subjected to 2 hours of middle cerebral artery occlusion (MCAo), and randomly selected animals were injected (i.v) with 3×10⁶ hUTC or with vehicle control (at day: 1, 1&3 or 1&7 after MCAo, n = 8–9/group). A battery of functional outcome tests was performed at days 1, 7, 14, 21, 28, 35, 42, 49, 56 and 63 after MCAo. Rats were sacrificed at 63 days after MCAo and lesion volumes were measured. To investigate the underlying mechanism of hUTC treatment of stroke, Von Willebrand Factor (vWF), and Synaptophysin immunostaining were performed.

Results

All hUTC treated groups, single or multiple injections, had better functional recovery compared to control (p<0.01). There was no statistically significant difference between a single and multiple injections of hUTC (p = 0.23) or between different multiple injections groups (p>0.07) in functional outcome. All hUTC treatment groups showed significant increases in Synaptophysin, vascular density and perimeter compared to the control group (p<0.05). There was no statistically significant difference between a single and multiple injections of hUTC or between the two groups of multiple injections in all immunohistochemical measurements (p>0.1).

Conclusion

hUTC treatment significantly improves long term functional outcome after stroke and promotes vascular density and synaptic plasticity. At the proscribed doses, multiple injections of hUTC were not superior to single injection therapy in both functional outcome and histological assessments.

Emerging molecular targets for brain repair after stroke

The field of neuroprotection generated consistent preclinical findings of mechanisms of cell death but these failed to be translated into clinics. The approaches that combine the modulation of the inhibitory environment together with the promotion of intrinsic axonal outgrowth needs further work before combined therapeutic strategies will be transferable to clinic trials. It is likely that only when some answers have been found to these issues will our therapeutic efforts meet our expectations. Stroke is a clinically heterogeneous disease and combinatorial treatments require much greater work in pharmacological and toxicological testing. Advances in genetics and results of the Whole Human Genome Project (HGP) provided new unknown information in relation to stroke. Genetic factors are not the only determinants of responses to some diseases. It was recognized early on that "epigenetic" factors were major players in the aetiology and progression of many diseases like stroke. The major players are microRNAs that represent the best-characterized subclass of noncoding RNAs. Epigenetic mechanisms convert environmental conditions and physiological stresses into long-term changes in gene expression and translation. Epigenetics in stroke are in their infancy but offer great promise for better understanding of stroke pathology and the potential viability of new strategies for its treatment.

Neuroprotective and neurorestorative effects of thymosin β4 treatment following experimental traumatic brain injury

Traumatic brain injury (TBI) remains a leading cause of mortality and morbidity worldwide. No effective pharmacological treatments are available for TBI because all phase II/III TBI clinical trials have failed. This highlights a compelling need to develop effective treatments for TBI. Endogenous neurorestoration occurs in the brain after TBI, including angiogenesis, neurogenesis, synaptogenesis, oligodendrogenesis, and axonal remodeling, which may be associated with spontaneous functional recovery after TBI. However, the endogenous neurorestoration following TBI is limited. Treatments amplifying these neurorestorative processes may promote functional recovery after TBI. Thymosin beta 4 (Tβ4) is the major G-actin-sequestering molecule in eukaryotic cells. In addition, Tβ4 has other properties including antiapoptosis and anti-inflammation, promotion of angiogenesis, wound healing, stem/progenitor cell differentiation, and cell migration and survival, which provide the scientific foundation for the corneal, dermal, and cardiac wound repair multicenter clinical trials. Here, we describe Tβ4 as a neuroprotective and neurorestorative candidate for treatment of TBI.

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.

High-mobility group box 1 from reactive astrocytes enhances the accumulation of endothelial progenitor cells in damaged white matter

High-mobility group box 1 (HMGB1) was initially described as a damage-associated-molecular-pattern (DAMP) mediator that worsens acute brain injury after stroke. But, recent findings suggest that HMGB1 can play a surprisingly beneficial role during stroke recovery by promoting endothelial progenitor cell (EPC) function and vascular remodeling in cortical gray matter. Here, we ask whether HMGB1 may also influence EPC responses in white matter injury. The standard lysophosphatidylcholine (LPC) injection model was used to induce focal demyelination in the corpus callosum of mice. Immunostaining showed that within the focal white matter lesions, HMGB1 was up-regulated in GFAP-positive reactive astrocytes, along with the accumulation of Flk1/CD34-double-positive EPCs that expressed pro-recovery mediators such as brain-derived neurotrophic factor and basic fibroblast growth factor. Astrocyte-EPC signaling required the HMGB1 receptor RAGE as treatment with RAGE-neutralizing antibody significantly decreased EPC accumulation. Moreover, suppression of HMGB1 with siRNA in vivo significantly decreased EPC numbers in damaged white matter as well as proliferated endothelial cell numbers. Finally, in vitro cell culture systems confirmed that HMGB1 directly affected EPC function such as migration and tube formation. Taken together, our findings suggest that HMGB1 from reactive astrocytes may attract EPCs to promote recovery after white matter injury.

[Cell therapy for stroke: from myth to reality]

INTRODUCTION

Stroke is one of the leading causes of death and disability worldwide. Intravenous recombinant tissue plasminogen activator is the only available therapy for acute ischemic stroke, but its use is limited by a narrow therapeutic window and cannot stimulate endogenous repair and regeneration of damaged brain tissue. Stem cell-based approaches hold much promise as potential novel treatments to restore neurological function after stroke.

STATE OF THE ART

In this review, we summarize data from preclinical and clinical studies to investigate the potential application of stem cell therapies for treatment of stroke. Stem cells have been proposed as a potential source of new cells to replace those lost due to central nervous system injury, as well as a source of trophic molecules to minimize damage and promote recovery. Various stem cells from multiple sources can generate neural cells that survive and form synaptic connections after transplantation in the stroke-injured brain. Stem cells also exhibit neurorevitalizing properties that may ameliorate neurological deficits through stimulation of neurogenesis, angiogenesis and inhibition of inflammation.

PERSPECTIVES/CONCLUSION

Performed in stroke, cell therapy would decrease brain damage and reduce functional deficits. After the damage has been done, it would still improve neurological functions by activating endogenous repair. Nevertheless, many questions raised by experimental studies particularly related to long-term safety and technical details of cell preparation and administration must be resolved before wider clinical use.

Endothelial progenitor cells: therapeutic perspective for ischemic stroke

Endothelial progenitor cells (EPCs), which can be cultured in vitro from mononuclear cells in peripheral blood or bone marrow, express both hematopoietic stem cell and endothelial cell markers on their surface. They are believed to participate in endothelial repair and postnatal angiogenesis due to their abilities of differentiating into endothelial cells and secreting protective cytokines and growth factors. Mounting evidence suggests that circulating EPCs are reduced and dysfunctional in various diseases including hypertension, diabetes, coronary heart disease, and ischemic stroke. Therefore, EPCs have been documented to be a potential biomarker for vascular diseases and a hopeful candidate for regenerative medicine. Ischemic stroke, as the major cause of disability and death, still has limited therapeutics based on the approaches of vascular recanalization or neuronal protection. Emerging evidence indicates that transplantation of EPCs is beneficial for the recovery of ischemic cerebral injury. EPC-based therapy could open a new avenue for ischemic cerebrovascular disease. Currently, clinical trials for evaluating EPC transfusion in treating ischemic stroke are underway. In this review, we summarize the general conceptions and the characteristics of EPCs, and highlight the recent research developments on EPCs. More importantly, the rationale, perspectives, and strategies for using them to treat ischemic stroke will be discussed.

Transduction of neural precursor cells with TAT-heat shock protein 70 chaperone: therapeutic potential against ischemic stroke after intrastriatal and systemic transplantation

Novel therapeutic concepts against cerebral ischemia focus on cell-based therapies in order to overcome some of the side effects of thrombolytic therapy. However, cell-based therapies are hampered because of restricted understanding regarding optimal cell transplantation routes and due to low survival rates of grafted cells. We therefore transplanted adult green fluorescence protein positive neural precursor cells (NPCs) either intravenously (systemic) or intrastriatally (intracerebrally) 6 hours after stroke in mice. To enhance survival of NPCs, cells were in vitro protein-transduced with TAT-heat shock protein 70 (Hsp70) before transplantation followed by a systematic analysis of brain injury and underlying mechanisms depending on cell delivery routes. Transduction of NPCs with TAT-Hsp70 resulted in increased intracerebral numbers of grafted NPCs after intracerebral but not after systemic transplantation. Whereas systemic delivery of either native or transduced NPCs yielded sustained neuroprotection and induced neurological recovery, only TAT-Hsp70-transduced NPCs prevented secondary neuronal degeneration after intracerebral delivery that was associated with enhanced functional outcome. Furthermore, intracerebral transplantation of TAT-Hsp70-transduced NPCs enhanced postischemic neurogenesis and induced sustained high levels of brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, and vascular endothelial growth factor in vivo. Neuroprotection after intracerebral cell delivery correlated with the amount of surviving NPCs. On the contrary, systemic delivery of NPCs mediated acute neuroprotection via stabilization of the blood-brain-barrier, concomitant with reduced activation of matrix metalloprotease 9 and decreased formation of reactive oxygen species. Our findings imply two different mechanisms of action of intracerebrally and systemically transplanted NPCs, indicating that systemic NPC delivery might be more feasible for translational stroke concepts, lacking a need of in vitro manipulation of NPCs to induce long-term neuroprotection.

Neural stem cells and stroke

Acute ischemic stroke causes a disturbance of neuronal circuitry and disruption of the blood-brain barrier that can lead to functional disabilities. At present, thrombolytic therapy inducing recanalization of the occluded vessels in the cerebral infarcted area is a commonly used therapeutic strategy. However, only a minority of patients have timely access to this kind of therapy. Recently, neural stem cells (NSCs) as therapy for stroke have been developed in preclinical studies. NSCs are harbored in the subventricular zone (SVZ) as well as the subgranular zone of the brain. The microenvironment in the SVZ, including intercellular interactions, extracellular matrix proteins, and soluble factors, can promote NSC proliferation, self-renewal, and multipotency. Endogenous neurogenesis responds to insults of ischemic stroke supporting the existence of remarkable plasticity in the mammalian brain. Homing and integration of NSCs to the sites of damaged brain tissue are complex morphological and physiological processes. This review provides an update on current preclinical cell therapies for stroke, focusing on neurogenesis in the SVZ and dentate gyrus and on recruitment cues that promote NSC homing and integration to the site of the damaged brain.

Sildenafil enhances neurogenesis and oligodendrogenesis in ischemic brain of middle-aged mouse

Adult neural stem cells give rise to neurons, oligodendrocytes and astrocytes. Aging reduces neural stem cells. Using an inducible nestin-CreER^T2/R26R-yellow fluorescent protein (YFP) mouse, we investigated the effect of Sildenafil, a phosphodiesterase type 5 (PDE5) inhibitor, on nestin lineage neural stem cells and their progeny in the ischemic brain of the middle-aged mouse. We showed that focal cerebral ischemia induced nestin lineage neural stem cells in the subventricular zone (SVZ) of the lateral ventricles and nestin expressing NeuN positive neurons and adenomatous polyposis coli (APC) positive mature oligodendrocytes in the ischemic striatum and corpus callosum in the aged mouse. Treatment of the ischemic middle-aged mouse with Sildenafil increased nestin expressing neural stem cells, mature neurons, and oligodendrocytes by 33, 75, and 30%, respectively, in the ischemic brain. These data indicate that Sildenafil amplifies nestin expressing neural stem cells and their neuronal and oligodendrocyte progeny in the ischemic brain of the middle-aged mouse.

Proximity of brain infarcts to regions of endogenous neurogenesis and involvement of striatum in ischaemic stroke

BACKGROUND AND PURPOSE

Clinical stroke trials with stem cell-based approaches aiming for trophic actions, modulation of inflammation and neuroprotection are ongoing. However, experimental studies also suggest that neuronal replacement by grafted neural stem cells (NSCs) and possibly by endogenous NSCs from the subventricular zone (SVZ) may restore function in the stroke-damaged striatum. To evaluate the potential clinical impact of these findings, we analyzed the spatial relationship of infarcts to the SVZ and the proportion of individuals with striatal lesions in a consecutive series of ischaemic stroke patients.

METHODS

Patients aged 20-75 years with first-ever ischaemic stroke underwent DW-MRI of the brain within 4 days after stroke onset. We analyzed location, size, number of acute focal ischaemic abnormalities and their spatial relationship to the SVZ. Stroke severity was assessed using NIH Stroke Scale (NIHSS).

RESULTS

Of 108 included patients, the distance from the nearest margin of the infarct(s) to the SVZ was ≤2 mm in 51/102 patients with visible ischaemic lesions on DW-MRI. Twenty-four patients had involvement of striatum. Eight of these had predominantly striatal lesions, that is >50% of the total ischaemic lesion volume was located in caudate nucleus and/or putamen. These 8 patients had a median NIHSS of 3.

CONCLUSIONS

Many stroke patients have infarcts located close to the SVZ, providing some supportive evidence that optimized endogenous neurogenesis may have therapeutic potential. However, predominantly striatal infarcts are rare and tend to give mild neurological deficits, indicating that striatum should not be the primary target for neuronal replacement efforts in humans.

Therapeutic potential of human induced pluripotent stem cells in experimental stroke

Ischemic stroke mainly caused by middle cerebral artery occlusion (MCAo) is a major type of stroke, but there are currently very limited therapeutic options for its cure. Neural stem cells (NSCs) or neural precursor cells (NPCs) derived from various sources are known to survive and improve neurological functions when they are engrafted in animal models of stroke. Induced pluripotent stem cells (iPSCs) generated from somatic cells of patients are novel cells that promise the autologous cell therapy for stroke. In this study, we successfully differentiated iPSCs derived from human fibroblasts into NPCs and found their robust therapeutic potential in a rodent MCAo stroke model. We observed the significant graft-induced behavioral recovery, as well as extensive neural tissue formation. Animal MRI results indicated that the majority of contralaterally transplanted iPSC-derived NPCs migrated to the peri-infarct area, showing a pathotropism critical for tissue recovery. The transplanted animals exhibited the significant reduction of stroke-induced inflammatory response, gliosis and apoptosis, and the contribution to the endogenous neurogenesis. Our results demonstrate that iPSC-derived NPCs are effective cells for the treatment of stroke.

Therapeutic effect of BDNF-overexpressing human neural stem cells (HB1.F3.BDNF) in a rodent model of middle cerebral artery occlusion

Ischemic stroke mainly caused by middle cerebral artery occlusion (MCAo) represents the major type of stroke; however, there are still very limited therapeutic options for the stroke-damaged patients. In this study, we evaluated the neurogenic and therapeutic potentials of human neural stem cells (NSCs) overexpressing brain-derived neurotrophic factor (HB1.F3.BDNF) following transplantation into a rodent model of MCAo. F3.BDNF human NSCs (F3.BDNF) were transplanted into the contralateral side of striatum at 7 days after MCAo, and the transplanted animals were monitored up to 8 weeks using animal MRI and various behavioral tests before they were sacrificed for immunohistochemical analysis. Interestingly, animal MRI results indicate that the majority of contralaterally transplanted neural stem cells were migrated to the peri-infarct area, showing a pathotropism. Transplanted animals exhibited significant behavioral improvements in stepping, rotarod, and modified neurological severity score (mNSS) tests. We also found that the transplanted human cells were colocalized with nestin, DCX, MAP2, DARPP-32, TH, GAD65/67-positive cells, of which results can be correlated with neural regeneration and behavioral recovery in the transplanted animals. More importantly, we were able to detect high levels of human BDNF protein expression, presumably derived from the transplanted F3.BDNF. Taken together, these results provide strong evidence that human neural stem cells (F3.BDNF) are effective in treating stroke animal models.

Treatment of neurological injury with thymosin β4

Neurorestorative therapy targets multiple types of parenchymal cells in the intact tissue of injured brain tissue to increase neurogenesis, angiogenesis, oligodendrogenesis, and axonal remodeling during recovery from neurological injury. In our laboratory, we tested thymosin β4 (Tβ4) as a neurorestorative agent to treat models of neurological injury. This review discusses our results demonstrating that Tβ4 improves neurological functional outcome in a rat model of embolic stroke, a mouse model of multiple sclerosis, and a rat model of traumatic brain injury. Tβ4 is a pleiotropic peptide exhibiting many actions in several different types of tissues. One mechanism associated with improvement of neurological improvement from Tβ4 treatment is oligodendrogenesis involving the differentiation of oligodendrocyte progenitor cells to mature myelin-secreting oligodendrocytes. Moreover, our preclinical data provide a basis for movement of Tβ4 into clinical trials for treatment of these devastating neurological diseases and injuries.

Therapeutic effects of hMAPC and hMSC transplantation after stroke in mice

Stroke represents an attractive target for stem cell therapy. Although different types of cells have been employed in animal models, a direct comparison between cell sources has not been performed. The aim of our study was to assess the effect of human multipotent adult progenitor cells (hMAPCs) and human mesenchymal stem cells (hMSCs) on endogenous neurogenesis, angiogenesis and inflammation following stroke. BALB/Ca-RAG 2(-/-) γC(-/-) mice subjected to FeCl(3) thrombosis mediated stroke were intracranially injected with 2 × 10(5) hMAPCs or hMSCs 2 days after stroke and followed for up to 28 days. We could not detect long-term engraftment of either cell population. However, in comparison with PBS-treated animals, hMSC and hMAPC grafted animals demonstrated significantly decreased loss of brain tissue. This was associated with increased angiogenesis, diminished inflammation and a glial-scar inhibitory effect. Moreover, enhanced proliferation of cells in the subventricular zone (SVZ) and survival of newly generated neuroblasts was observed. Interestingly, these neuroprotective effects were more pronounced in the group of animals treated with hMAPCs in comparison with hMSCs. Our results establish cell therapy with hMAPCs and hMSCs as a promising strategy for the treatment of stroke.

Endogenous CNTF mediates stroke-induced adult CNS neurogenesis in mice

Focal brain ischemia in adult rats rapidly and robustly induces neurogenesis in the subventricular zone (SVZ) but there are few and inconsistent reports in mice, presenting a hurdle to genetically investigate the endogenous neurogenic regulators such as ciliary neurotrophic factor (CNTF). Here, we first provide a platform for further studies by showing that middle cerebral artery occlusion in adult male C57BL/6 mice robustly enhances neurogenesis in the SVZ only under very specific conditions, i.e., 14days after a 30min occlusion. CNTF expression paralleled changes in the number of proliferated, BrdU-positive, SVZ cells. Stroke-induced proliferation was absent in CNTF-/- mice, suggesting that it is mediated by CNTF. MCAO-increased CNTF appears to act on C cell proliferation and by inducing FGF2 expression but not via EGF expression or Notch1 signaling of neural stem cells in the SVZ. CNTF is unique, as expression of other gp130 ligands, IL-6 and LIF, did not predict SVZ proliferation or showed no or only small compensatory increases in CNTF-/- mice. Expression of tumor necrosis factor-α, which can inhibit neurogenesis, and the presence of leukocytes in the SVZ were inversely correlated with neurogenesis, but pro-inflammatory cytokines did not affect CNTF expression in cultured astrocytes. These results suggest that slowly up-regulated CNTF in the SVZ mediates stroke-induced neurogenesis and is counteracted by inflammation. Further pharmacological stimulation of endogenous CNTF might be a good therapeutic strategy for cell replacement after stroke as CNTF regulates normal patterns of neurogenesis and is expressed almost exclusively in the nervous system.

Human induced pluripotent stem cells improve stroke outcome and reduce secondary degeneration in the recipient brain

Human induced pluripotent stem cells (hiPSCs) are a most appealing source for cell replacement therapy in acute brain lesions. We evaluated the potential of hiPSC therapy in stroke by transplanting hiPSC-derived neural progenitor cells (NPCs) into the postischemic striatum. Grafts received host tyrosine hydroxylase-positive afferents and contained developing interneurons and homotopic GABAergic medium spiny neurons that, with time, sent axons to the host substantia nigra. Grafting reversed stroke-induced somatosensory and motor deficits. Grafting also protected the host substantia nigra from the atrophy that follows disruption of reciprocal striatonigral connections. Graft innervation by tyrosine hydoxylase fibers, substantia nigra protection, and somatosensory functional recovery were early events, temporally dissociated from the slow maturation of GABAergic neurons in the grafts and innervation of substantia nigra. This suggests that grafted hiPSC-NPCs initially exert trophic effects on host brain structures, which precede integration and potential pathway reconstruction. We believe that transplantation of NPCs derived from hiPSCs can provide useful interventions to limit the functional consequences of stroke through both neuroprotective effects and reconstruction of impaired pathways.

MRI detects brain reorganization after human umbilical tissue-derived cells (hUTC) treatment of stroke in rat

Human umbilical tissue-derived cells (hUTC) represent an attractive cell source and a potential technology for neurorestoration and improvement of functional outcomes following stroke. Male Wistar rats were subjected to a transient middle cerebral artery occlusion (tMCAo) and were intravenously administered hUTC (N = 11) or vehicle (N = 10) 48 hrs after stroke. White matter and vascular reorganization was monitored over a 12-week period using MRI and histopathology. MRI results were correlated with neurological functional and histology outcomes to demonstrate that MRI can be a useful tool to measure structural recovery after stroke. MRI revealed a significant reduction in the ventricular volume expansion and improvement in cerebral blood flow (CBF) in the hUTC treated group compared to vehicle treated group. Treatment with hUTC resulted in histological and functional improvements as evidenced by enhanced expression of vWF and synaptophysin, and improved outcomes on behavioral tests. Significant correlations were detected between MRI ventricular volumes and histological lesion volume as well as number of apoptotic cells. A positive correlation was also observed between MRI CBF or cerebral blood volume (CBV) and histological synaptic density. Neurological functional tests were also significantly correlated with MRI ventricular volume and CBV. Our data demonstrated that MRI measurements can detect the effect of hUTC therapy on the brain reorganization and exhibited positive correlation with histological measurements of brain structural changes and functional behavioral tests after stroke. MRI ventricular volumes provided the most sensitive index in monitoring brain remodeling and treatment effects and highly correlated with histological and functional measurements.

Thymosin β 4 mediates oligodendrocyte differentiation by upregulating p38 MAPK

Thymosin beta 4 (Tβ4), a G-actin sequestering peptide, increases oligodendrogenesis and improves functional outcome in models of neurological injury. The molecular mechanisms of Tβ4 mediated oligodendrogenesis are unclear. The p38 mitogen-activated protein kinase (p38MAPK) regulates oligodendrocyte (OL) differentiation and myelin gene expression in other models. Therefore, we investigated p38MAPK signaling pathways. We used primary rat neural progenitor cells (NPCs) and a mouse oligodendrocyte progenitor cell (OPC) line (N20.1 cells) to investigate the molecular mechanisms of Tβ4-enhanced oligodendrogenesis. NPCs were isolated from rat subventricular zone (SVZ) of the lateral ventricles (n = 12). Primary NPCs and N20.1 cells were grown in the presence of 0, 25, and 50 ng/mL of Tβ4 (RegeneRx Biopharmaceuticals Inc, Rockville, MD) for 14 days. Quantitative real-time PCR and Western blot data showed significant induction of both expression and phosphorylation of p38MAPK with simultaneous inhibition of phosphorylation of extracellular signal regulated kinase (ERK1), c-Jun N-terminal kinase 1 (JNK1), leading to reduction of phosphorylation of c-Jun, a potent negative regulator of transcription of myelin genes. These effects were reversed with transfection of Tβ4siRNA. Our data indicate that Tβ4 treatment induces OL differentiation by inducing p38MAPK with parallel inactivation of ERK1 and JNK1, thus preventing the accumulation of phosphorylated c-Jun.

Microarray-based gene expression analysis of an animal model for closed head injury

OBJECTIVE

Traumatic brain injury (TBI) is a major cause of death and disability in both children and the elderly. Mortality from TBI is said account for 1-2% of all deaths. One-third to one-half of all traumatic deaths is due to head injury. Of those who survive, the majority is left with significant disabilities, including 3% who remain in a vegetative state and only approximately 30% who make a good recovery. Microarray studies and other genomic techniques facilitate the discovery of new targets for the treatment of diseases, which aids in drug development, immunotherapeutics and gene therapy. Gene expression profiling or microarray analysis enables the measurement of thousands of genes in a single RNA sample.

METHODS

In this study, adult Wistar-albino rats underwent TBI using a trauma device. Brain tissues and blood samples were taken for gene expression at 1, 12 and 48 h post-trauma and were then analysed via microarray. Total RNA was isolated using an RNeasy Mini Kit (QIAGEN-Sample & Assay Technologies, Hilden, Germany) and tested using a 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA). Overall changes in gene expression were evaluated using Agilent Whole Rat Genome 4 × 44 K oligonucleotide arrays and analysed with GeneSpring (GeneSpring 6.1, Silicon Genetics, Redwood City, CA) software. Only genes with a signal-to-noise ratio of above 2 in the experiments were included in the statistical analysis.

RESULTS

ANOVA (p<0.05) was performed to identify differentially expressed probe sets. Additional filtering (minimum 2-fold change) was applied to extract the most differentially expressed genes based on the study groups (Control vs. 1st hour, Control vs. 12th hour, Control vs. 48th hour). Differentially expressed genes were detected via microarray analysis. A gene interaction-based network investigation of the genes that were identified via traditional microarray data analysis describes a significantly relevant gene network that includes the C1ql2, Cbnl, Sdc1, Bdnf, MMP9, and Cd47 genes, which were differentially expressed compared with the controls.

CONCLUSIONS

In this study, we will review the current understanding of the genetic susceptibility of TBI with microarrays. Our results highlight the importance of genes that control the response of the brain to injury as well as the suitability of microarrays for identifying specific targets for further study.

Cortical electrical stimulation with varied low frequencies promotes functional recovery and brain remodeling in a rat model of ischemia

In this study, we investigated whether fully implantable CES with low current density and varying low-frequency burst impulse train enhances functional recovery and promotes brain remodeling in both the ipsilesional and contralesional cortex. Adult rats received occlusion of the right middle cerebral artery for 120min. One week after ischemia, electrodes were implanted to rats with CES lasting 2 weeks followed by 4-week observation period. After 2-week stimulation and 4-week observation period, body weight (BW) of the rats in CES group was higher than that in no stimulation (NS) group. Limb placement test, foot-fault test and beam walking test demonstrate that CES significantly enhanced functional recovery. Immunohistochemical study has shown that CES enhanced angiogenesis and dendritic sprouting, and suppressed inflammatory response in the ischemic cortex. CES also promoted dendritic sprouting and suppressed inflammatory response in the contralesional cortex. These results suggest the stimulation protocol is safe, and greatly improves functional recovery and brain remodeling in the 4 weeks following 2 weeks stimulation.

Effect of angiotensin II type 2 receptor on stroke, cognitive impairment and neurodegenerative diseases

Here, we briefly review the role of the renin-angiotensin system (RAS) in cognitive impairment and neurodegenerative disease, mainly discussing our experimental studies on the angiotensin II type 2 (AT(2)) receptor. Ischemic brain damage is enhanced in mice with overexpression of angiotensin II, with reduced cerebral blood flow in the penumbra and an increase in oxidative stress in the ischemic area. Angiotensin II binds two types of receptors, type 1 (AT(1)) and type 2 (AT(2)). Our previous experiments showed that AT(1) receptor signaling has a harmful effect, and AT(2) receptor signaling has a protective effect on the brain after stroke. AT(2) receptor signaling in bone marrow stromal cells or hematopoietic cells was shown to prevent ischemic brain damage after middle cerebral artery occlusion. In contrast, AT(2) receptor signaling also affects cognitive function. We showed that direct stimulation of the AT(2) receptor by a newly generated direct AT(2) receptor agonist, Compound 21 (C21), enhanced cognitive function in wild-type (C57BL6) mice and an Alzheimer's disease mouse model with intracerebroventricular injection of amyloid β (1-40). Finally, we carried out clinical research by investigating the levels of RAS components in patients with neurodegenerative diseases. We observed a reduction of angiotensin II and angiotensin converting enzyme (ACE) 2 levels, and an increase in ACE level in cerebrospinal fluid from patients with multiple sclerosis. These results suggest that RAS is also involved in neurodegenerative disease. Therefore, regulation of RAS might be a new therapeutic target to protect neurons from neural diseases.

Diabetes impairs cortical plasticity and functional recovery following ischemic stroke

Diabetics are at greater risk of having a stroke and are less likely to recover from it. To understand this clinically relevant problem, we induced an ischemic stroke in the primary forelimb somatosensory (FLS1) cortex of diabetic mice and then examined sensory-evoked changes in cortical membrane potentials and behavioral recovery of forelimb sensory-motor function. Consistent with previous studies, focal stroke in non-diabetic mice was associated with acute deficits in forelimb sensorimotor function and a loss of forelimb evoked cortical depolarizations in peri-infarct cortex that gradually recovered over several weeks time. In addition, we discovered that damage to FLS1 cortex led to an enhancement of forelimb evoked depolarizations in secondary forelimb somatosensory (FLS2) cortex. Enhanced FLS2 cortical responses appeared to play a role in stroke recovery given that silencing this region was sufficient to reinstate forelimb impairments. By contrast, the functional reorganization of FLS1 and FLS2 cortex was largely absent in diabetic mice and could not be explained by more severe cortical infarctions. Diabetic mice also showed persistent behavioral deficits in sensorimotor function of the forepaw, which could not be rescued by chronic insulin therapy after stroke. Collectively these results indicate that diabetes has a profound effect on brain plasticity, especially when challenged, as is often the case, by an ischemic event. Further, our data suggest that secondary cortical regions play an important role in the restoration of sensorimotor function when primary cortical regions are damaged.

Vascular endothelial cell-specific microRNA-15a inhibits angiogenesis in hindlimb ischemia

The effects and potential mechanisms of the vascular endothelial cell (EC)-enriched microRNA-15a (miR-15a) on angiogenesis remain unclear. Here, we show a novel finding that EC-selective miR-15a transgenic overexpression leads to reduced blood vessel formation and local blood flow perfusion in mouse hindlimbs at 1-3 weeks after hindlimb ischemia. Mechanistically, gain- or loss-of-miR-15a function by lentiviral infection in ECs significantly reduces or increases tube formation, cell migration, and cell differentiation, respectively. By FGF2 and VEGF 3'-UTR luciferase reporter assays, Real-time PCR, and immunoassays, we further identified that the miR-15a directly targets FGF2 and VEGF to facilitate its anti-angiogenic effects. Our data suggest that the miR-15a in ECs can significantly suppress cell-autonomous angiogenesis through direct inhibition of endogenous endothelial FGF2 and VEGF activities. Pharmacological modulation of miR-15a function may provide a new therapeutic strategy to intervene against angiogenesis in a variety of pathological conditions.

Partial motor restoration upon administration of sildenafil: a case study

OBJECTIVE

Extensive research in the past decade has confirmed that the adult brain maintains some plasticity, including neural cell birth, migration and integration. Pre-clinical data strongly suggest that phosphodiesterase type 5 (PDE5) inhibitors promote cerebral neovascularization and neurogenesis. Animal studies of cerebral stroke suggest potential regenerative benefits following treatment with sildenafil citrate, a PDE5 inhibitor. This study reports a case in which compassionate use of sildenafil was investigated as a treatment to improve physical functioning, more than 4 decades after development of spastic quadriplegia during the 1st-2nd year of life.

METHODS

Sildenafil 100 mg was administered every 24 hours for 7 months.

RESULTS

Sildenafil treatment was associated with clinical (functional) improvement.

CONCLUSIONS

The activity of sildenafil on cerebral neovascularization and neurogenesis may be the mechanism for the observed functional benefits.

Astrocytic high-mobility group box 1 promotes endothelial progenitor cell-mediated neurovascular remodeling during stroke recovery

Crosstalk between the brain and systemic responses in blood is increasingly suspected of playing critical roles in stroke. However, how this communication takes place remains to be fully understood. Here, we show that reactive astrocytes can release a damage-associated molecular-pattern molecule called high-mobility-group-box-1 (HMGB1) that promotes endothelial progenitor cell (EPC)-mediated neurovascular remodeling during stroke recovery. Conditioned media from reactive astrocytes increase EPC proliferation in vitro. siRNA suppression of HMGB1 in astrocytes or blockade of the HMGB1 receptor for advanced glycation endproducts in EPCs prevents this effect. In a mouse model of focal cerebral ischemia, reactive astrocytes in the peri-infarct cortex up-regulate HMGB1 at 14 d poststroke, along with an accumulation of endogenous EPCs. In vivo siRNA suppression of HMGB1 blocks this EPC response, reduces peri-infact angiogenesis, and worsens neurological deficits. Taken together, these molecular and in vivo findings support a previously undescribed mechanism of crosstalk between reactive astrocytes and EPCs wherein HMGB1 promotes neurovascular remodeling and functional recovery after stroke and brain injury.

Dendritic structural plasticity

Dendrites represent the compartment of neurons primarily devoted to collecting and computating input. Far from being static structures, dendrites are highly dynamic during development and appear to be capable of plastic changes during the adult life of animals. During development, it is a combination of intrinsic programs and external signals that shapes dendrite morphology; input activity is a conserved extrinsic factor involved in this process. In adult life, dendrites respond with more modest modifications of their structure to various types of extrinsic information, including alterations of input activity. Here, the author reviews classical and recent evidence of dendrite plasticity in invertebrates and vertebrates and current progress in the understanding of the molecular mechanisms that underlie this plasticity. Importantly, some fundamental questions such as the functional role of dendrite remodeling and the causal link between structural modifications of neurons and plastic processes, including learning, are still open.

Stem cells and stroke: are we further away than anyone is willing to admit?

Harnessing the potential of stem cells or other types of cell therapies to regenerate brain tissue lost from a stroke is a long way off, and a far more complicated process than is understood. There are critical safety issues regarding stem cells in stroke and many clinical trials have only just begun. We are at least 5-10 years away from knowing if cell therapies will improve clinical outcome in stroke patients. The use of stem cells in stroke therapy remains investigational only.

Chronic in vivo imaging shows no evidence of dendritic plasticity or functional remapping in the contralesional cortex after stroke

Most stroke survivors exhibit a partial recovery from their deficits. This presumably occurs because of remapping of lost capabilities to functionally related brain areas. Functional brain imaging studies suggest that remapping in the contralateral uninjured cortex might represent a transient stage of compensatory plasticity. Some postmortem studies have also shown that cortical lesions, including stroke, can trigger dendritic plasticity in the contralateral hemisphere, but the data are controversial. We used longitudinal in vivo two-photon microscopy in the contralateral homotopic cortex to record changes in dendritic spines of layer 5 pyramidal neurons in green fluorescent protein mice. We could not detect de novo growth of dendrites or changes in the density or turnover of spines for up to 4 weeks after stroke. We also used intrinsic optical signal imaging to investigate whether the forepaw (FP) sensory representation is remapped to the spared homotopic cortex after stroke. Stimulation of the contralateral FP reliably produced strong intrinsic signals in the spared hemisphere, but we could never detect a signal with ipsilateral FP stimulation after stroke. This lack of contralateral plasticity at the level of apical dendrites of layer 5 pyramidal neurons and FP sensory maps suggests that the contralesional cortex may not contribute to functional recovery after stroke and that, at least in mice, the peri-infarct cortex plays the dominant role in postischemic plasticity.

Mesenchymal stem cells as a treatment for neonatal ischemic brain damage

Mesenchymal stem cell (MSC)-based therapies have been proven effective in experimental models of numerous disorders. Treatment of ischemic brain injury by transplantation of MSCs in neonatal animal models has been shown to be effective in reducing lesion volume and improving functional outcome. The beneficial effect of MSC transplantation to treat neonatal brain injury might be explained by the great plasticity of the neonatal brain. The neonatal brain is still in a developmentally active phase, leading to a better efficiency of MSC transplantation than that observed in experiments using adult models of stroke. Enhanced neurogenesis and axonal remodeling likely underlie the improved functional outcome following MSC treatment after neonatal hypoxic-ischemic (HI) brain injury. With respect to the mechanism of repair by MSCs, MSCs do not survive long term and replace damaged tissue themselves. We propose that MSCs react to the needs of the ischemic cerebral environment by secretion of several growth factors, cytokines, and other bioactive molecules to regulate damage and repair processes. Parenchymal cells react to the secretome of the MSCs and contribute to stimulate repair processes. These intrinsic adaptive properties of MSCs make them excellent candidates for a novel therapy to treat the devastating effects of HI encephalopathy in the human neonate.

Melanocortins as potential therapeutic agents in severe hypoxic conditions

Melanocortin peptides with the adrenocorticotropin/melanocyte-stimulating hormone (ACTH/MSH) sequences and synthetic analogs have protective and life-saving effects in experimental conditions of circulatory shock, myocardial ischemia, ischemic stroke, traumatic brain injury, respiratory arrest, renal ischemia, intestinal ischemia and testicular ischemia, as well as in experimental heart transplantation. Moreover, melanocortins improve functional recovery and stimulate neurogenesis in experimental models of cerebral ischemia. These beneficial effects of ACTH/MSH-like peptides are mostly mediated by brain melanocortin MC(3)/MC(4) receptors, whose activation triggers protective pathways that counteract the main ischemia/reperfusion-related mechanisms of damage. Induction of signaling pathways and other molecular regulators of neural stem/progenitor cell proliferation, differentiation and integration seems to be the key mechanism of neurogenesis stimulation. Synthesis of stable and highly selective agonists at MC(3) and MC(4) receptors could provide the potential for development of a new class of drugs for a novel approach to management of severe ischemic diseases.

Modulation of microglial activation enhances neuroprotection and functional recovery derived from bone marrow mononuclear cell transplantation after cortical ischemia

Activated microglia may exacerbate damage in neural disorders; however, it is unknown how they affect stem cells transplanted after stroke. Focal ischemia was induced by microinjections of 40 pmol of endothelin-1 into the motor cortex of adult rats. Ischemic animals were treated with sterile saline (n = 5), bone marrow mononuclear cells (BMMCs, n = 8), minocycline (n = 5) or concomitantly with minocycline and BMMCs (n = 5). BMMC-treated animals received 5 × 10(6)BMMCs through the caudal vein 24h post-ischemia. Behavioral tests were performed to evaluate functional recovery. Morphometric and histological analyses were performed to assess infarct area, neuronal loss and microglia/macrophage activation up to 21 days post-ischemia. Treatments with minocycline, BMMCs or minocycline-BMMCs reduced infarct area, increased neuronal survival and decreased the number of caspase-3+ and ED-1+ cells, but these effects were more prominent in the minocycline-BMMC group. Behavioral analyses using the modified sticky-tape and open-field tests showed that ischemic rats concomitantly treated with BMMCs and minocycline showed better motor performance than rats treated with BMMCs or minocycline only. The results suggest that proper modulation of the inflammatory response through the blockage of microglia activation enhances neuroprotection and functional recovery induced by intravenous transplantation of BMMCs after motor cortex ischemia.

Promoting brain remodelling and plasticity for stroke recovery: therapeutic promise and potential pitfalls of clinical translation

Recent laboratory findings suggest that it might be possible to promote cerebral plasticity and neurological recovery after stroke by use of exogenous pharmacological or cell-based treatments. Brain microvasculature and glial cells respond in concert to ischaemic stressors and treatment, creating an environment in which successful recovery can ensue. Neurons remote from and adjacent to the ischaemic lesion are enabled to sprout, and neural precursor cells that accumulate with cerebral microvessels in the perilesional tissue further stimulate brain plasticity and neurological recovery. These factors interact in a highly dynamic way, facilitating temporally and spatially orchestrated responses of brain networks. In view of the complexity of the systems involved, stroke treatments that stimulate and amplify these endogenous restorative mechanisms might also provoke unwanted side-effects. In experimental studies, adverse effects have been identified when neurorestorative treatments were administered to animals with severe associated illnesses, after thrombolysis with alteplase, and when therapies were initiated outside appropriate time windows. Balancing the opportunities and possible risks, we provide suggestions for the translation of restorative therapies from the laboratory to the clinic.

Therapeutic benefit of treatment of stroke with simvastatin and human umbilical cord blood cells: neurogenesis, synaptic plasticity, and axon growth

The therapeutic efficacy of cell-based therapy after stroke can be enhanced by making the host brain tissue more receptive to the administered cells, which thereby facilitates brain plasticity. We hypothesized that simvastatin increases human umbilical cord blood cell (HUCBC) migration into the ischemic brain and promotes brain plasticity and neurological functional outcome after stroke. Rats were subjected to 2-h middle cerebral artery occlusion (MCAo) and administered subtherapeutic doses of simvastatin (0.5 mg/kg, gavaged daily for 7 days), HUCBCs (1 × 10(6), one time injection via tail vein), or combination simvastatin with HUCBCs starting at 24 h after stroke. Combination treatment of stroke showed an interactive effect in improvement of neurological outcome compared with simvastatin or HUCBC monotherapy groups. In addition, combination treatment significantly increased brain-derived neurotrophic factor/TrkB expression and the number of engrafted HUCBCs in the ischemic brain compared with HUCBC monotherapy. The number of engrafted HUCBCs was significantly correlated with functional outcome (modified neurological severity score). Combination treatment significantly increased neurogenesis and synaptic plasticity in the ischemic brain, and promoted neuroblast migration in cultured subventricular zone explants. Using primary cultured neurons (PCNs), we found that combination treatment enhanced neurite outgrowth compared with nontreatment control, simvastatin or HUCBC supernatant monotherapy. Inhibition of TrkB significantly attenuated combination treatment-induced neurite outgrowth. Our data indicate that combination simvastatin and HUCBC treatment of stroke increases BDNF/TrkB expression, enhances HUCBC migration into the ischemic brain, amplifies endogenous neurogenesis, synaptic plasticity and axonal growth, and thereby improves functional outcome after stroke.

Nitric oxide facilitates delivery and mediates improved outcome of autologous bone marrow mononuclear cells in a rodent stroke model

Background

Bone marrow mononuclear cells (MNC) represent an investigational treatment for stroke. The objective of this study was to determine the relevance of vasoactive mediators, generated in response to MNC injection, as factors regulating cerebral perfusion (CP), the biodistribution of MNC, and outcome in stroke.

Methods

Long Evans rats underwent transient middle cerebral artery occlusion. MNC were extracted from the bone marrow at 22 hrs and injected via the internal carotid artery or the femoral vein 2 hours later. CP was measured with MRI or continuous laser Doppler flowmetry. Serum samples were collected to measure vasoactive mediators. Animals were treated with the Nitric Oxide (NO) inhibitor, L-NAME, to establish the relevance of NO-signaling to the effect of MNC. Lesion size, MNC biodistribution, and neurological deficits were assessed.

Results

CP transiently increased in the peri-infarct region within 30 min after injecting MNC compared to saline or fibroblast control. This CP increase corresponded temporarily to serum NO elevation and was abolished by L-NAME. Pre-treatment with L-NAME reduced brain penetration of MNC and prevented MNC from reducing infarct lesion size and neurological deficits.

Conclusions

NO generation in response to MNC may represent a mechanism underlying how MNC enter the brain, reduce lesion size, and improve outcome in ischemic stroke.

Crosstalk between oligodendrocytes and cerebral endothelium contributes to vascular remodeling after white matter injury

After stroke and brain injury, cortical gray matter recovery involves mechanisms of neurovascular matrix remodeling. In white matter, however, the mechanisms of recovery remain unclear. In this study, we demonstrate that oligodendrocytes secrete matrix metalloproteinase-9 (MMP-9), which accelerates the angiogenic response after white matter injury. In primary oligodendrocyte cultures, treatment with the proinflammatory cytokine interleukin-1β (IL-1β) induced an upregulation and secretion of MMP-9. Conditioned media from IL-1β-stimulated oligodendrocytes significantly amplified matrigel tube formation in brain endothelial cells, indicating that MMP-9 from oligodendrocytes can promote angiogenesis in vitro. Next, we asked whether similar signals and substrates operate after white matter injury in vivo. Focal white matter injury and demyelination was induced in mice via stereotactic injection of lysophosphatidylcholine into corpus callosum. Western blot analysis showed that IL-1β expression was increased in damaged white matter. Immunostaining demonstrated MMP-9 signals in myelin-associated oligodendrocytic basic protein-positive oligodendrocytes. Treatment with an IL-1β-neutralizing antibody suppressed the MMP-9 response in oligodendrocytes. Finally, we confirmed that the broad spectrum MMP inhibitor GM6001 inhibited angiogenesis around the injury area in this white matter injury model. In gray matter, a neurovascular niche promotes cortical recovery after brain injury. Our study suggests that an analogous oligovascular niche may mediate recovery in white matter.

Perisynaptic GABA Receptors The Overzealous Protector

An attempt to find pharmacological therapies to treat stroke patients and minimize the extent of cell death has seen the failure of dozens of clinical trials. As a result, stroke/cerebral ischemia is the leading cause of lasting adult disability. Stroke-induced cell death occurs due to an excess release of glutamate. As a consequence to this, a compensatory increased release of GABA occurs that results in the subsequent internalization of synaptic GABA(A) receptors and spillover onto perisynaptic GABA(A) receptors, resulting in increased tonic inhibition. Recent studies show that the brain can engage in a limited process of neural repair after stroke. Changes in cortical sensory and motor maps and alterations in axonal structure are dependent on patterned neuronal activity. It has been assumed that changes in neuronal excitability underlie processes of neural repair and remapping of cortical sensory and motor representations. Indeed, recent evidence suggests that local inhibitory and excitatory currents are altered after stroke and modulation of these networks to enhance excitability during the repair phase can facilitate functional recovery after stroke. More specifically, dampening tonic GABA inhibition can afford an early and robust improvement in functional recovery after stroke.

Human adult dental pulp stem cells enhance poststroke functional recovery through non-neural replacement mechanisms

Human adult dental pulp stem cells (DPSCs), derived from third molar teeth, are multipotent and have the capacity to differentiate into neurons under inductive conditions both in vitro and following transplantation into the avian embryo. In this study, we demonstrate that the intracerebral transplantation of human DPSCs 24 hours following focal cerebral ischemia in a rodent model resulted in significant improvement in forelimb sensorimotor function at 4 weeks post-treatment. At this time, 2.3 ± 0.7% of engrafted cells had survived in the poststroke brain and demonstrated targeted migration toward the stroke lesion. In the peri-infarct striatum, transplanted DPSCs differentiated into astrocytes in preference to neurons. Our data suggest that the dominant mechanism of action underlying DPSC treatment that resulted in enhanced functional recovery is unlikely to be due to neural replacement. Functional improvement is more likely to be mediated through DPSC-dependent paracrine effects. This study provides preclinical evidence for the future use of human DPSCs in cell therapy to improve outcome in stroke patients.

Vascular endothelial growth factor induces contralesional corticobulbar plasticity and functional neurological recovery in the ischemic brain

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor, which also has neuroprotective activity. In view of these dual actions on vessels and neurons, we were interested whether VEGF promotes long distance axonal plasticity in the ischemic brain. Herein, we show that VEGF promotes neurological stroke recovery in mice when delivered in a delayed way starting 3 days after middle cerebral artery occlusion. Using anterograde tract-tracing experiments that we combined with histochemical and molecular biological studies, we demonstrate that although VEGF promoted angiogenesis predominantly in the ischemic hemisphere, pronounced axonal sprouting was induced by VEGF in the contralesional, but not the ipsilesional corticobulbar system. Corticobulbar plasticity was accompanied by the deactivation of the matrix metalloproteinase MMP9 in the lesioned hemisphere and the transient downregulation of the axonal growth inhibitors NG2 proteoglycan and brevican and the guidance molecules ephrin B1/2 in the contralesional hemisphere. The regulation of matrix proteinases, growth inhibitors, and guidance molecules offers insights how brain plasticity is controlled in the ischemic brain.

Therapeutic effect of human umbilical tissue-derived cell treatment in rats with experimental intracerebral hemorrhage

BACKGROUND AND PURPOSE

The present study examines whether human umbilical tissue-derived cells (hUTC) have a neuro-restorative effect and improve functional recovery after intracerebral hemorrhage (ICH) in rats.

METHODS

Primary ICH was induced in male Wistar rats by stereotactic injection of 100μL of autologous blood into the striatal region adjacent to the subventricular zone. Briefly, the rats were randomly divided into six groups, each group was intravenously injected either with 2mL phosphate-buffered saline (PBS) or 3million hUTC in PBS at 1, 3 or 7days after ICH (n=8/group). To evaluate neurological functional outcome, each animal was subjected to the modified neurological severity score (mNSS) and corner turn tests at different time points after ICH. At four weeks post treatment, each group was anesthetized intraperitoneally, sacrificed, and brain tissues were processed histologically. Immunohistochemistry was employed to measure vascularity (vWF), neurogenesis (BrdU TUJ1, DCX and NeuN), synaptogenesis (synaptophysin) and apoptosis (TUNEL).

RESULTS

The hUTC-treated animals showed significantly improved neurological functional outcomes as assessed by mNSS and corner turn tests at 14, 21 and 28days post-injection in each treatment group (P<0.05) as compared to the PBS controls. Animals treated with hUTC were seen to have significantly increased cell proliferation, vascularity and synaptogenesis, as well as reduced apoptosis in the hematoma rim compared to the corresponding control group (P<0.05).

CONCLUSIONS

Intravenously infused hUTC have a beneficial effect after experimental ICH by functional and histochemical measurements of neural cell proliferation and synaptogenesis in the ICH border zone. This brain region also shows correlative evidence of neuronal recovery with increased vascularity.

Progesterone increases circulating endothelial progenitor cells and induces neural regeneration after traumatic brain injury in aged rats

Vascular remodeling plays a key role in neural regeneration in the injured brain. Circulating endothelial progenitor cells (EPCs) are a mediator of the vascular remodeling process. Previous studies have found that progesterone treatment of traumatic brain injury (TBI) decreases cerebral edema and cellular apoptosis and inhibits inflammation, which in concert promote neuroprotective effects in young adult rats. However, whether progesterone treatment regulates circulating EPC level and fosters vascular remodeling after TBI have not been investigated. In this study, we hypothesize that progesterone treatment following TBI increases circulating EPC levels and promotes vascular remodeling in the injured brain in aged rats. Male Wistar 20-month-old rats were subjected to a moderate unilateral parietal cortical contusion injury and were treated with or without progesterone (n=54/group). Progesterone was administered intraperitoneally at a dose of 16mg/kg at 1 h post-TBI and was subsequently injected subcutaneously daily for 14 days. Neurological functional tests and immnunostaining were performed. Circulating EPCs were measured by flow cytometry. Progesterone treatment significantly improved neurological outcome after TBI measured by the modified neurological severity score, Morris Water Maze and the long term potentiation in the hippocampus as well as increased the circulating EPC levels compared to TBI controls (p<0.05). Progesterone treatment also significantly increased CD34 and CD31 positive cell number and vessel density in the injured brain compared to TBI controls (p<0.05). These data indicate that progesterone treatment of TBI improves multiple neurological functional outcomes, increases the circulating EPC level, and facilitates vascular remodeling in the injured brain after TBI in aged rats.