Subventricular zone neuroblasts emigrate toward cortical lesions

Stroke and Neurogenesis: Bridging Clinical Observations to New Mechanistic Insights from Animal Models

Stroke was the 2nd leading cause of death and a major cause of morbidity. Unfortunately, there are limited means to promote neurological recovery post-stroke, but research has unearthed potential targets for therapies to encourage post-stroke neurogenesis and neuroplasticity. The occurrence of neurogenesis in adult mammalian brains, including humans, was not widely accepted until the 1990s. Now, adult neurogenesis has been extensively studied in human and mouse neurogenic brain niches, of which the subventricular zone of the lateral ventricles and subgranular zone of the dentate gyrus are best studied. Numerous other niches are under investigation for neurogenic potential. This review offers a basic overview to stroke in the clinical setting, a focused summary of recent and foundational research literature on cortical neurogenesis and post-stroke brain plasticity, and insights regarding how the meninges and choroid plexus have emerged as key players in neurogenesis and neuroplasticity in the context of focal cerebral ischemia disrupting the anterior circulation. The choroid plexus and meninges are vital as they are integral sites for neuroimmune interactions, glymphatic perfusion, and niche signaling pertinent to neural stem cells and neurogenesis. Modulating neuroimmune interactions with a focus on astrocyte activity, potentially through manipulation of the choroid plexus and meningeal niches, may reduce the exacerbation of stroke by inflammatory mediators and create an environment conducive to neurorecovery. Furthermore, addressing impaired glymphatic perfusion after ischemic stroke likely supports a neurogenic environment by clearing out inflammatory mediators, neurotoxic metabolites, and other accumulated waste. The meninges and choroid plexus also contribute more directly to promoting neurogenesis: the meninges are thought to harbor neural stem cells and are a niche amenable to neural stem/progenitor cell migration. Additionally, the choroid plexus has secretory functions that directly influences stem cells through signaling mechanisms and growth factor actions. More research to better understand the functions of the meninges and choroid plexus may lead to novel approaches for stimulating neuronal recovery after ischemic stroke.

Targeting epidermal growth factor receptor to recruit newly generated neuroblasts in cortical brain injuries

BACKGROUND

Neurogenesis is stimulated in the subventricular zone (SVZ) of mice with cortical brain injuries. In most of these injuries, newly generated neuroblasts attempt to migrate toward the injury, accumulating within the corpus callosum not reaching the perilesional area.

METHODS

We use a murine model of mechanical cortical brain injury, in which we perform unilateral cortical injuries in the primary motor cortex of adult male mice. We study neurogenesis in the SVZ and perilesional area at 7 and 14 dpi as well as the expression and concentration of the signaling molecule transforming growth factor alpha (TGF-α) and its receptor the epidermal growth factor (EGFR). We use the EGFR inhibitor Afatinib to promote neurogenesis in brain injuries.

RESULTS

We show that microglial cells that emerge within the injured area and the SVZ in response to the injury express high levels of TGF-α leading to elevated concentrations of TGF-α in the cerebrospinal fluid. Thus, the number of neuroblasts in the SVZ increases in response to the injury, a large number of these neuroblasts remain immature and proliferate expressing the epidermal growth factor receptor (EGFR) and the proliferation marker Ki67. Restraining TGF-α release with a classical protein kinase C inhibitor reduces the number of these proliferative EGFR+ immature neuroblasts in the SVZ. In accordance, the inhibition of the TGF-α receptor, EGFR promotes migration of neuroblasts toward the injury leading to an elevated number of neuroblasts within the perilesional area.

CONCLUSIONS

Our results indicate that in response to an injury, microglial cells activated within the injury and the SVZ release TGF-α, activating the EGFR present in the neuroblasts membrane inducing their proliferation, delaying maturation and negatively regulating migration. The inactivation of this signaling pathway stimulates neuroblast migration toward the injury and enhances the quantity of neuroblasts within the injured area. These results suggest that these proteins may be used as target molecules to regenerate brain injuries.

Bilateral transcranial direct-current stimulation promotes migration of subventricular zone-derived neuroblasts toward ischemic brain

Ischemic insult stimulates proliferation of neural stem cells (NSCs) in the subventricular zone (SVZ) after stroke. However, only a fraction of NSC-derived neuroblasts from SVZ migrate toward poststroke brain region. We have previously reported that direct-current stimulation guides NSC migration toward the cathode in vitro. Accordingly, we set up a new method of transcranial direct-current stimulation (tDCS), in which the cathodal electrode is placed on the ischemic hemisphere and anodal electrode on the contralateral hemisphere of rats subjected to ischemia-reperfusion injury. We show that the application of this bilateral tDCS (BtDCS) promotes the migration of NSC-derived neuroblasts from SVZ toward the cathode direction into poststroke striatum. Reversing the position of the electrodes blocks the effect of BtDCS on the migration of neuroblasts from SVZ. BtDCS protects against neuronal death and improves the functional recovery of stroke animals. Thus, the migration of NSC-derived neuroblasts from SVZ toward poststroke brain region contributes to the effect of BtDCS against ischemia-induced neuronal death, supporting a potential development of noninvasive BtDCS as an endogenous neurogenesis-based stroke therapy.

Leukemia Inhibitory Factor Is Required for Subventricular Zone Astrocyte Progenitor Proliferation and for Prokineticin-2 Production after a Closed Head Injury in Mice

Astrogliosis is one of the hallmarks of brain injury, and after a mild injury activated astrocytes subserve neuroprotective and pro-regenerative functions. We previously found that the astroglial response to closed head injury (CHI) was blunted in mice that were haplodeficient in leukemia inhibitory factor (LIF); therefore, the goal of these studies was to determine if the delayed astrogliosis was due to decreased recruitment of subventricular zone (SVZ) progenitors. CHI's were performed on post-natal day 20 on LIF heterozygous (Het) and wild-type (WT) mice. At 48 h post-CHI, astrocyte progenitor proliferation within the SVZ increased ∼250% in WT mice but was reduced by ∼200% in LIF Het mice compared with sham controls. Using neurospheres to model the SVZ, LIF increased the percentage of proliferating astrocyte progenitors by 2-fold compared with controls but had no effect on neural stem cell proliferation. To rule out the involvement of other cytokines, 105 cytokines were analyzed using a multi-plex array and with targeted validation on injured LIF Het versus WT neocortex. Of the cytokines analyzed, only prokineticin-2 (ProK2) required LIF signaling. Correspondingly, LIF-treated neurospheres expressed higher levels of ProK2, the ProK1 and ProK2 receptors (ProKR1 and ProKR2). Using in situ hybridization, ProK2 messenger RNA (mRNA) was most abundant in neocortical neurons and highly expressed within the SVZ. However, in contrast to LIF, ProK2 decreased astrocyte progenitor proliferation 2-fold. Altogether, these data demonstrate that LIF is necessary for astrocyte progenitor proliferation after injury and reveal a new role for LIF as an essential regulator of the neurotrophic factor ProK2.

Sonic Hedgehog Signaling Promotes Peri-Lesion Cell Proliferation and Functional Improvement after Cortical Contusion Injury

Traumatic brain injury (TBI) is a leading cause of death and disability globally. No drug treatments are available, so interest has turned to endogenous neural stem cells (NSCs) as alternative strategies for treatment. We hypothesized that regulation of cell proliferation through modulation of the sonic hedgehog pathway, a key NSC regulatory pathway, could lead to functional improvement. We assessed sonic hedgehog (Shh) protein levels in the cerebrospinal fluid (CSF) of patients with TBI. Using the cortical contusion injury (CCI) model in rodents, we used pharmacological modulators of Shh signaling to assess cell proliferation within the injured cortex using the marker 5-Ethynyl-2’-deoxyuridine (EdU); 50mg/mL. The phenotype of proliferating cells was determined and quantified. Motor function was assessed using the rotarod test. In patients with TBI there is a reduction of Shh protein in CSF compared with control patients. In rodents, following a severe CCI, quiescent cells become activated. Pharmacologically modulating the Shh signaling pathway leads to changes in the number of newly proliferating injury-induced cells. Upregulation of Shh signaling with Smoothened agonist (SAG) results in an increase of newly proliferating cells expressing glial fibrillary acidic protein (GFAP), whereas the Shh signaling inhibitor cyclopamine leads to a reduction. Some cells expressed doublecortin (DCX) but did not mature into neurons. The SAG-induced increase in proliferation is associated with improved recovery of motor function. Localized restoration of Shh in the injured rodent brain, via increased Shh signaling, has the potential to sustain endogenous cell proliferation and the mitigation of TBI-induced motor deficits albeit without the neuronal differentiation.

Cellular mechanisms and treatments for chemobrain: insight from aging and neurodegenerative diseases

Chemotherapy is a life-saving treatment for cancer patients, but also causes long-term cognitive impairment, or "chemobrain", in survivors. However, several challenges, including imprecise diagnosis criteria, multiple confounding factors, and unclear and heterogeneous molecular mechanisms, impede effective investigation of preventions and treatments for chemobrain. With the rapid increase in the number of cancer survivors, chemobrain is an urgent but unmet clinical need. Here, we leverage the extensive knowledge in various fields of neuroscience to gain insights into the mechanisms for chemobrain. We start by outlining why the post-mitotic adult brain is particularly vulnerable to chemotherapy. Next, through drawing comparisons with normal aging, Alzheimer's disease, and traumatic brain injury, we identify universal cellular mechanisms that may underlie the cognitive deficits in chemobrain. We further identify existing neurological drugs targeting these cellular mechanisms that can be repurposed as treatments for chemobrain, some of which were already shown to be effective in animal models. Finally, we briefly describe future steps to further advance our understanding of chemobrain and facilitate the development of effective preventions and treatments.

Tissue Engineering and Biomaterial Strategies to Elicit Endogenous Neuronal Replacement in the Brain

Neurogenesis in the postnatal mammalian brain is known to occur in the dentate gyrus of the hippocampus and the subventricular zone. These neurogenic niches serve as endogenous sources of neural precursor cells that could potentially replace neurons that have been lost or damaged throughout the brain. As an example, manipulation of the subventricular zone to augment neurogenesis has become a popular strategy for attempting to replace neurons that have been lost due to acute brain injury or neurodegenerative disease. In this review article, we describe current experimental strategies to enhance the regenerative potential of endogenous neural precursor cell sources by enhancing cell proliferation in neurogenic regions and/or redirecting migration, including pharmacological, biomaterial, and tissue engineering strategies. In particular, we discuss a novel replacement strategy based on exogenously biofabricated "living scaffolds" that could enhance and redirect endogenous neuroblast migration from the subventricular zone to specified regions throughout the brain. This approach utilizes the first implantable, biomimetic tissue-engineered rostral migratory stream, thereby leveraging the brain's natural mechanism for sustained neuronal replacement by replicating the structure and function of the native rostral migratory stream. Across all these strategies, we discuss several challenges that need to be overcome to successfully harness endogenous neural precursor cells to promote nervous system repair and functional restoration. With further development, the diverse and innovative tissue engineering and biomaterial strategies explored in this review have the potential to facilitate functional neuronal replacement to mitigate neurological and psychiatric symptoms caused by injury, developmental disorders, or neurodegenerative disease.

Impaired differentiation of human induced neural stem cells by TOR1A overexpression

DYT-TOR1A is the most common inherited dystonia caused by a three nucleotide (GAG) deletion (dE) in the TOR1A gene. Death early after birth and cortical anomalies of the full knockout in rodents underscore its developmental importance. We therefore explored the timed effects of TOR1A-wt and TOR1A-dE during differentiation in a human neural in vitro model. We used lentiviral tet-ON expression of TOR1A-wt and -dE in induced neural stem cells derived from healthy donors. Overexpression was induced during proliferation of neural precursors, during differentiation and after differentiation into mature neurons. Overexpression of both wildtype and mutated protein had no effect on the viability and cell number of neural precursors as well as mature neurons when initiated before or after differentiation. However, if induced during differentiation, overexpression of TOR1A-wt and -dE led to a pronounced reduction of mature neurons in a dose dependent manner. Our data underscores the importance of physiological expression levels of TOR1A as crucial for proper neuronal differentiation. We did not find evidence for a specific impact of the mutated TOR1A on neuronal maturation.

Static Magnetic Field Exposure In Vivo Enhances the Generation of New Doublecortin-expressing Cells in the Sub-ventricular Zone and Neocortex of Adult Rats

Static magnetic field (SMF) is gaining interest as a potential technique for modulating CNS neuronal activity. Previous studies have shown a pro-neurogenic effect of short periods of extremely low frequency pulsatile magnetic fields (PMF) in vivo and pro-survival effect of low intensity SMF in cultured neurons in vitro, but little is known about the in vivo effects of low to moderate intensity SMF on brain functions. We investigated the effect of continuously-applied SMF on subventricular zone (SVZ) neurogenesis and immature doublecortin (DCX)-expressing cells in the neocortex of young adult rats and in primary cultures of cortical neurons in vitro. A small (3 mm diameter) magnetic disc was implanted on the skull of rats at bregma, producing an average field strength of 4.3 mT at SVZ and 12.9 mT at inner neocortex. Levels of proliferation of SVZ stem cells were determined by 5-ethynyl-2'-deoxyuridine (EdU) labelling, and early neuronal phenotype development was determined by expression of doublecortin (DCX). To determine the effect of SMF on neurogenesis in vitro, permanent magnets were placed beneath the culture dishes. We found that low intensity SMF exposure enhances cell proliferation in SVZ and new DCX-expressing cells in neocortical regions of young adult rats. In primary cortical neuronal cultures, SMF exposure increased the expression of newly generated cells co-labelled with EdU and DCX or the mature neuronal marker NeuN, while activating a set of pro neuronal bHLH genes. SMF exposure has potential for treatment of neurodegenerative disease and conditions such as CNS trauma and affective disorders in which increased neurogenesis is desirable.

Polycomb Protein Eed is Required for Neurogenesis and Cortical Injury Activation in the Subventricular Zone

The postnatal subventricular zone (SVZ) harbors neural stem cells (NSCs) that exhibit robust neurogenesis. However, the epigenetic mechanisms that maintain NSCs and regulate neurogenesis remain unclear. We report that label-retaining SVZ NSCs express Eed, the core component of Polycomb repressive complex 2. In vivo and in vitro conditional knockout and knockdown show Eed is necessary for maintaining NSC proliferation, neurogenesis and neurosphere formation. We discovered that Eed functions to maintain p21 protein levels in NSCs by repressing Gata6 transcription. Both Gata6 overexpression and p21 knockdown reduced neurogenesis, while Gata6 knockdown or p21 overexpression partially rescued neurogenesis after Eed loss. Furthermore, genetic deletion of Eed impaired injury induced SVZ proliferation and emigration. These data reveal a novel epigenetic regulated pathway and suggest an essential role for Eed in SVZ homeostasis and injury.

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

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

The role of inflammation in subventricular zone cancer

The adult subventricular zone (SVZ) stem cell niche has proven vital for discovering neurodevelopmental mechanisms and holds great potential in medicine for neurodegenerative diseases. Yet the SVZ holds a dark side - it can become tumorigenic. Glioblastomas can arise from the SVZ via cancer stem cells (CSCs). Glioblastoma and other brain cancers often have dismal prognoses since they are resistant to treatment. In this review we argue that the SVZ is susceptible to cancer because it contains stem cells, migratory progenitors and unusual inflammation. Theoretically, SVZ stem cells can convert to CSCs more readily than can postmitotic neural cells. Additionally, the robust long-distance migration of SVZ progenitors can be subverted upon tumorigenesis to an infiltrative phenotype. There is evidence that the SVZ, even in health, exhibits chronic low-grade cellular and molecular inflammation. Its inflammatory response to brain injuries and disease differs from that of other brain regions. We hypothesize that the SVZ inflammatory environment can predispose cells to novel mutations and exacerbate cancer phenotypes. This can be studied in animal models in which human mutations related to cancer are knocked into the SVZ to induce tumorigenesis and the CSC immune interactions that precede full-blown cancer. Importantly inflammation can be pharmacologically modulated providing an avenue to brain cancer management and treatment. The SVZ is accessible by virtue of its location surrounding the lateral ventricles and CSCs in the SVZ can be targeted with a variety of pharmacotherapies. Thus, the SVZ can yield aggressive tumors but can be targeted via several strategies.

Inflammation and neural repair after ischemic brain injury

Stroke causes neuronal cell death and destruction of neuronal circuits in the brain and spinal cord. Injury to the brain tissue induces sterile inflammation triggered by the extracellular release of endogenous molecules, but cerebral inflammation after stroke is gradually resolved within several days. In this pro-resolving process, inflammatory cells adopt a pro-resolving or repairing phenotype in the injured brain, activating endogenous repairing programs. Although the mechanisms involved in the transition from inflammation to neural repair after stroke remain largely unknown to date, some of the mechanisms for inflammation and neural repair have been clarified in detail. This review focuses on the molecular or cellular mechanisms involved in sterile inflammation and neural repair after stroke. This accumulation of evidence may be helpful for speculating about the endogenous repairing mechanisms in the brain and identifying therapeutic targets for improving the functional prognoses of stroke patients.

Neural stem cell heterogeneity in the mammalian forebrain

The brain was long considered an organ that underwent very little change after development. It is now well established that the mammalian central nervous system contains neural stem cells that generate progeny that are capable of making new neurons, astrocytes, and oligodendrocytes throughout life. The field has advanced rapidly as it strives to understand the basic biology of these precursor cells, and explore their potential to promote brain repair. The purpose of this review is to present current knowledge about the diversity of neural stem cells in vitro and in vivo, and highlight distinctions between neural stem cell populations, throughout development, and within the niche. A comprehensive understanding of neural stem cell heterogeneity will provide insights into the cellular and molecular regulation of neural development and lifelong neurogenesis, and will guide the development of novel strategies to promote regeneration and neural repair.

Differential Response in Novel Stem Cell Niches of the Brain after Cervical Spinal Cord Injury and Traumatic Brain Injury

Populations of neural stem cells (NSCs) reside in a number of defined niches in the adult central nervous system (CNS) where they continually give rise to mature cell types throughout life, including newly born neurons. In addition to the prototypical niches of the subventricular zone (SVZ) and subgranular zone (SGZ) of the hippocampal dentate gyrus, novel stem cell niches that are also neurogenic have recently been identified in multiple midline structures, including circumventricular organs (CVOs) of the brain. These resident NSCs serve as a homeostatic source of new neurons and glial cells under intact physiological conditions. Importantly, they may also have the potential for reparative processes in pathological states such as traumatic spinal cord injury (SCI) and traumatic brain injury (TBI). As the response in these novel CVO stem cell niches has been characterized after stroke but not following SCI or TBI, we quantitatively assessed cell proliferation and the neuronal and glial lineage fate of resident NSCs in three CVO nuclei-area postrema (AP), median eminence (ME), and subfornical organ (SFO) -in rat models of cervical contusion-type SCI and controlled cortical impact (CCI)-induced TBI. Using bromodeoxyuridine (BrdU) labeling of proliferating cells, we find that TBI significantly enhanced proliferation in AP, ME, and SFO, whereas cervical SCI had no effects at early or chronic time-points post-injury. In addition, SCI did not alter NSC differentiation profile into doublecortin-positive neuroblasts, GFAP-expressing astrocytes, or Olig2-labeled cells of the oligodendrocyte lineage within AP, ME, or SFO at both time-points. In contrast, CCI induced a pronounced increase in Sox2- and doublecortin-labeled cells in the AP and Iba1-labeled microglia in the SFO. Lastly, plasma derived from CCI animals significantly increased NSC expansion in an in vitro neurosphere assay, whereas plasma from SCI animals did not exert such an effect, suggesting that signaling factors present in blood may be relevant to stimulating CVO niches after CNS injury and may explain the differential in vivo effects of SCI and TBI on the novel stem cell niches.

Mild Fluid Percussion Injury Induces Diffuse Axonal Damage and Reactive Synaptic Plasticity in the Mouse Olfactory Bulb

Despite the regenerative capacity of the olfactory bulb (OB), head trauma causes olfactory disturbances in up to 30% of patients. While models of olfactory nerve transection, olfactory receptor neuron (ORN) ablation, or direct OB impact have been used to examine OB recovery, these models are severe and not ideal for study of OB synaptic repair. We posited that a mild fluid percussion brain injury (mFPI), delivered over mid-dorsal cortex, would produce diffuse OB deafferentation without confounding pathology. Wild type FVB/NJ mice were subjected to mFPI and OB probed for ORN axon degeneration and onset of reactive synaptogenesis. OB extracts revealed 3 d postinjury elevation of calpain-cleaved 150-kDa αII-spectrin, an indicator of axon damage, in tandem with reduced olfactory marker protein (OMP), a protein specific to intact ORN axons. Moreover, mFPI also produced a 3-d peak in GFAP+ astrocyte and IBA1+ microglial reactivity, consistent with postinjury inflammation. OB glomeruli showed disorganized ORN axons, presynaptic degeneration, and glial phagocytosis at 3 and 7 d postinjury, all indicative of deafferentation. At 21 d after mFPI, normal synaptic structure re-emerged along with OMP recovery, supporting ORN afferent reinnervation. Robust 21 d postinjury upregulation of GAP-43 was consistent with the time course of ORN axon sprouting and synapse regeneration reported after more severe olfactory insult. Together, these findings define a cycle of synaptic degeneration and recovery at a site remote to non-contusive brain injury. We show that mFPI models diffuse ORN axon damage, useful for the study of time-dependent reactive synaptogenesis in the deafferented OB.

Abnormal increase of neuronal precursor cells and exacerbated neuroinflammation in the corpus callosum in murine model of systemic lupus erythematosus

Purpose: Systemic Lupus Erythematosus (SLE) is an autoimmune disease which is characterised by elevated levels of autoantibodies and cytokines in the body. Via alteration of the regulation of inflammation, damage to different organ systems, including the central nervous system (CNS), was found in SLE patients. Patients diagnosed with SLE were reported to suffer from different kinds of psychiatric signs and symptoms. As neurogenesis has been suggested to be a potential key player of psychiatric symptoms and emotional behavior disturbances, this study aims to investigate whether neurogenesis is altered in an animal model of SLE. Also, neuroinflammation was studied.

Methods: Female NZB/W F1 mice were used as an animal model of SLE. Animals were divided into two groups: 1. pre-diseased mice (lupus-prone NZB/W F1 female mice, age 10–15 weeks, negative for proteinuria and with basal levels of serum anti-dsDNA autoantibodies) and 2. diseased mice (NZB/W F1 female mice, > 25 weeks of age, with elevated serum levels of anti-dsDNA autoantibodies and with persistent proteinuria of > 3 mg/ml for more than 2 weeks). Comparisons of the levels of neurogenesis and neuroinflammtion between two groups of mice were studied by the immunohistochemistry.

Results: After the onset of SLE symptoms, a reduction of neurogenesis in the hippocampus was found, while there was a dramatic increase of doublecortin (DCX+) neuronal precursor cells in the corpus callosum (CC) and in the subventricular zone (SVZ). Meanwhile, exacerbated inflammation was present in the corpus callosum of the diseased mice, which was suggested by the increased number of GFAP+ cells and IBA-1+ cells.

Conclusions: To the best of our knowledge, this is the first study showing an increase of neuronal precursor cells in the corpus callosum of the female NZB/W F1 mice. The present study suggests a coincidence but not a causal relationship between neurogenesis and neuroinflammation. The present results have also provided new insight showing that the altered neurogenesis and neuroinflammation may be a potential neurological mechanism for the cognitive and mood disturbance found in the SLE patients.

Intranasal Nerve Growth Factor administration improves cerebral functions in a child with severe traumatic brain injury: A case report

BACKGROUND

Nerve growth factor (NGF) promotes neural recovery after experimental traumatic brain injury (TBI) supporting neuronal growth, differentiation and survival of brain cells and up-regulating the neurogenesis-associated protein Doublecortin (DCX). Only a few studies reported NGF administration in paediatric patients with severe TBI.

METHODS

A four-year-old boy in a persistent unresponsive wakefulness syndrome (UWS) was treated with intranasal murine NGF administration 6 months after severe TBI. The patient received four cycles of intranasal NGF (0.1 mg/kg, twice a day for 10 consecutive days).

RESULTS

NGF administration improved functional [Positron Emission Tomography/Computed Tomography (PET/CT); Single photon emission/Computed Tomography (SPECT/CT) and Magnetic Resonance Imaging (MRI)] assessment, electrophysiological [Electroencephalogram (EEG) and Visual Evoked Potential (VEP)] studies and clinical conditions. He showed improvements in voluntary movements, facial mimicry, phonation, attention and verbal comprehension, ability to cry, cough reflex, oral motility, feeding capacity, and bowel and urinary functions. After NGF administration, raised levels of both NGF and DCX were found in the cerebrospinal fluid of the patient. No side effects were reported.

CONCLUSIONS

Although further studies are needed for better understanding the neuroprotective role of this neurotrophin, intranasal NGF administration appears to be a promising and safe rescuing strategy treatment in children with neurological impairment after TBI.

Traumatic Brain Injury and Stem Cell: Pathophysiology and Update on Recent Treatment Modalities

Traumatic brain injury (TBI) is a complex condition that presents with a wide spectrum of clinical symptoms caused by an initial insult to the brain through an external mechanical force to the skull. In the United States alone, TBI accounts for more than 50,000 deaths per year and is one of the leading causes of mortality among young adults in the developed world. Pathophysiology of TBI is complex and consists of acute and delayed injury. In the acute phase, brain tissue destroyed upon impact includes neurons, glia, and endothelial cells, the latter of which makes up the blood-brain barrier. In the delayed phase, “toxins” released from damaged cells set off cascades in neighboring cells eventually leading to exacerbation of primary injury. As researches further explore pathophysiology and molecular mechanisms underlying this debilitating condition, numerous potential therapeutic strategies, especially those involving stem cells, are emerging to improve recovery and possibly reverse damage. In addition to elucidating the most recent advances in the understanding of TBI pathophysiology, this review explores two primary pathways currently under investigation and are thought to yield the most viable therapeutic approach for treatment of TBI: manipulation of endogenous neural cell response and administration of exogenous stem cell therapy.

Neuroblast Distribution after Cortical Impact Is Influenced by White Matter Injury in the Immature Gyrencephalic Brain

Cortical contusions are a common type of traumatic brain injury (TBI) in children. Current knowledge of neuroblast response to cortical injury arises primarily from studies utilizing aspiration or cryoinjury in rodents. In infants and children, cortical impact affects both gray and white matter and any neurogenic response may be complicated by the large expanse of white matter between the subventricular zone (SVZ) and the cortex, and the large number of neuroblasts in transit along the major white matter tracts to populate brain regions. Previously, we described an age-dependent increase of neuroblasts in the SVZ in response to cortical impact in the immature gyrencephalic brain. Here, we investigate if neuroblasts target the injury, if white matter injury influences repair efforts, and if postnatal population of brain regions are disrupted. Piglets received a cortical impact to the rostral gyrus cortex or sham surgery at postnatal day (PND) 7, BrdU 2 days prior to (PND 5 and 6) or after injury (PND 7 and 8), and brains were collected at PND 14. Injury did not alter the number of neuroblasts in the white matter between the SVZ and the rostral gyrus. In the gray matter of the injury site, neuroblast density was increased in cavitated lesions, and the number of BrdU(+) neuroblasts was increased, but comprised less than 1% of all neuroblasts. In the white matter of the injury site, neuroblasts with differentiating morphology were densely arranged along the cavity edge. In a ventral migratory stream, neuroblast density was greater in subjects with a cavitated lesion, indicating that TBI may alter postnatal development of regions supplied by that stream. Cortical impact in the immature gyrencephalic brain produced complicated and variable lesions, increased neuroblast density in cavitated gray matter, resulted in potentially differentiating neuroblasts in the white matter, and may alter the postnatal population of brain regions utilizing a population of neuroblasts that were born prior to PND 5. This platform may be useful to continue to study potential complications of white matter injury and alterations of postnatal population of brain regions, which may contribute to the chronic effects of TBI in children.

Systemic administration of cell-free exosomes generated by human bone marrow derived mesenchymal stem cells cultured under 2D and 3D conditions improves functional recovery in rats after traumatic brain injury

Multipotent human bone marrow derived mesenchymal stem cells (hMSCs) improve functional outcome after experimental traumatic brain injury (TBI). The present study was designed to investigate whether systemic administration of cell-free exosomes generated from hMSCs cultured in 2-dimensional (2D) conventional conditions or in 3-dimensional (3D) collagen scaffolds promote functional recovery and neurovascular remodeling in rats after TBI. Wistar rats were subjected to TBI induced by controlled cortical impact; 24 h later tail vein injection of exosomes derived from hMSCs cultured under 2D or 3D conditions or an equal number of liposomes as a treatment control were performed. The modified Morris water maze, neurological severity score and footfault tests were employed to evaluate cognitive and sensorimotor functional recovery. Animals were sacrificed at 35 days after TBI. Histological and immunohistochemical analyses were performed for measurements of lesion volume, neurovascular remodeling (angiogenesis and neurogenesis), and neuroinflammation. Compared with liposome-treated control, exosome-treatments did not reduce lesion size but significantly improved spatial learning at 33-35 days measured by the Morris water maze test, and sensorimotor functional recovery, i.e., reduced neurological deficits and footfault frequency, observed at 14-35 days post injury (p < 0.05). Exosome treatments significantly increased the number of newborn endothelial cells in the lesion boundary zone and dentate gyrus, and significantly increased the number of newborn mature neurons in the dentate gyrus as well as reduced neuroinflammation. Exosomes derived from hMSCs cultured in 3D scaffolds provided better outcome in spatial learning than exosomes from hMSCs cultured in the 2D condition. In conclusion, hMSC-generated exosomes significantly improve functional recovery in rats after TBI, at least in part, by promoting endogenous angiogenesis and neurogenesis and reducing neuroinflammation. Thus, exosomes derived from hMSCs may be a novel cell-free therapy for TBI, and hMSC-scaffold generated exosomes may selectively enhance spatial learning.

Traumatic Brain Injury Activation of the Adult Subventricular Zone Neurogenic Niche

Traumatic brain injury (TBI) is common in both civilian and military life, placing a large burden on survivors and society. However, with the recognition of neural stem cells in adult mammals, including humans, came the possibility to harness these cells for repair of damaged brain, whereas previously this was thought to be impossible. In this review, we focus on the rodent adult subventricular zone (SVZ), an important neurogenic niche within the mature brain in which neural stem cells continue to reside. We review how the SVZ is perturbed following various animal TBI models with regards to cell proliferation, emigration, survival, and differentiation, and we review specific molecules involved in these processes. Together, this information suggests next steps in attempting to translate knowledge from TBI animal models into human therapies for TBI.

The balance of Id3 and E47 determines neural stem/precursor cell differentiation into astrocytes

Adult neural stem/precursor cells (NSPCs) of the subventricular zone (SVZ) are an endogenous source for neuronal replacement in CNS disease. However, adult neurogenesis is compromised after brain injury in favor of a glial cell fate, which is mainly attributed to changes in the NSPC environment. Yet, it is unknown how this unfavorable extracellular environment translates into a transcriptional program altering NSPC differentiation. Here, we show that genetic depletion of the transcriptional regulator Id3 decreased the number of astrocytes generated from SVZ-derived adult NSPCs in the cortical lesion area after traumatic brain injury. Cortical brain injury resulted in rapid BMP-2 and Id3 up-regulation in the SVZ stem cell niche. Id3(-/-) adult NSPCs failed to differentiate into BMP-2-induced astrocytes, while NSPCs deficient for the Id3-controlled transcription factor E47 readily differentiated into astrocytes in the absence of BMP-2. Mechanistically, E47 repressed the expression of several astrocyte-specific genes in adult NSPCs. These results identify Id3 as the BMP-2-induced transcriptional regulator, promoting adult NSPC differentiation into astrocytes upon CNS injury and reveal a molecular link between environmental changes and NSPC differentiation in the CNS after injury.

Regeneration, Plasticity, and Induced Molecular Programs in Adult Zebrafish Brain

Regenerative capacity of the brain is a variable trait within animals. Aquatic vertebrates such as zebrafish have widespread ability to renew their brains upon damage, while mammals have—if not none—very limited overall regenerative competence. Underlying cause of such a disparity is not fully evident; however, one of the reasons could be activation of peculiar molecular programs, which might have specific roles after injury or damage, by the organisms that regenerate. If this hypothesis is correct, then there must be genes and pathways that (a) are expressed only after injury or damage in tissues, (b) are biologically and functionally relevant to restoration of neural tissue, and (c) are not detected in regenerating organisms. Presence of such programs might circumvent the initial detrimental effects of the damage and subsequently set up the stage for tissue redevelopment to take place by modulating the plasticity of the neural stem/progenitor cells. Additionally, if transferable, those “molecular mechanisms of regeneration” could open up new avenues for regenerative therapies of humans in clinical settings. This review focuses on the recent studies addressing injury/damage-induced molecular programs in zebrafish brain, underscoring the possibility of the presence of genes that could be used as biomarkers of neural plasticity and regeneration.

Tunable Controlled Release of Bioactive SDF-1α via Protein Specific Interactions within Fibrin/Nanoparticle Composites

The chemokine, stromal cell-derived factor 1α (SDF-1α), is a key regulator of the endogenous neural progenitor/stem cell-mediated regenerative response after neural injury. Increased and sustained bioavailability of SDF-1α in the peri-injury region is hypothesized to modulate this endogenous repair response. Here, we describe poly(lactic-co-glycolic) acid (PLGA) nanoparticles capable of releasing bioactive SDF-1α in a sustained manner over 60days after a burst of 23%. Moreover, we report a biphasic cellular response to SDF-1α concentrations thus the large initial burst release in an in vivo setting may result in supratherapeutic concentrations of SDF-1α. Specific protein-protein interactions between SDF-1α and fibrin (as well as its monomer, fibrinogen) were exploited to control the magnitude of the burst release. Nanoparticles embedded in fibrin significantly reduced the amount of SDF-1α released after 72 hrs as a function of fibrin density. Therefore, the nanoparticle/fibrin composites represented a means to independently tune the magnitude of the burst phase release from the nanoparticles while perserving a bioactive depot of SDF-1α for release over 60days.

Effect of exosomes derived from multipluripotent mesenchymal stromal cells on functional recovery and neurovascular plasticity in rats after traumatic brain injury

OBJECT

Transplanted multipotent mesenchymal stromal cells (MSCs) improve functional recovery in rats after traumatic brain injury (TBI). In this study the authors tested a novel hypothesis that systemic administration of cell-free exosomes generated from MSCs promotes functional recovery and neurovascular remodeling in rats after TBI.

METHODS

Two groups of 8 Wistar rats were subjected to TBI, followed 24 hours later by tail vein injection of 100 μg protein of exosomes derived from MSCs or an equal volume of vehicle (phosphate-buffered saline). A third group of 8 rats was used as sham-injured, sham-treated controls. To evaluate cognitive and sensorimotor functional recovery, the modified Morris water maze, modified Neurological Severity Score, and foot-fault tests were performed. Animals were killed at 35 days after TBI. Histopathological and immunohistochemical analyses were performed for measurements of lesion volume, neurovascular remodeling (angiogenesis and neurogenesis), and neuroinflammation.

RESULTS

Compared with the saline-treated group, exosome-treated rats with TBI showed significant improvement in spatial learning at 34-35 days as measured by the modified Morris water maze test (p < 0.05), and sensorimotor functional recovery (i.e., reduced neurological deficits and foot-fault frequency) was observed at 14-35 days postinjury (p < 0.05). Exosome treatment significantly increased the number of newly generated endothelial cells in the lesion boundary zone and dentate gyrus and significantly increased the number of newly formed immature and mature neurons in the dentate gyrus as well as reducing neuroinflammation.

CONCLUSIONS

The authors demonstrate for the first time that MSC-generated exosomes effectively improve functional recovery, at least in part, by promoting endogenous angiogenesis and neurogenesis and by reducing inflammation in rats after TBI. Thus, MSC-generated exosomes may provide a novel cell-free therapy for TBI and possibly for other neurological diseases.

Detection of mouse endogenous type B astrocytes migrating towards brain lesions

Neuroblasts represent the predominant migrating cell type in the adult mouse brain. There are, however, increasing evidences of migration of other neural precursors. This work aims at identifying in vivo endogenous early neural precursors, different from neuroblasts, able to migrate in response to brain injuries. The monoclonal antibody Nilo1, which unequivocally identifies type B astrocytes and embryonic radial glia, was coupled to magnetic glyconanoparticles (mGNPs). Here we show that Nilo1-mGNPs in combination with magnetic resonance imaging in living mice allowed the in vivo identification of endogenous type B astrocytes at their niche, as well as their migration to the lesion site in response to glioblastoma, demyelination, cryolesion or mechanical injuries. In addition, Nilo1(+) adult radial glia-like structures were identified at the lesion site a few hours after damage. For all damage models used, type B astrocyte migration was fast and orderly. Identification of Nilo1(+) cells surrounding an induced glioblastoma was also possible after intraperitoneal injection of the antibody. This opens up the possibility of an early identification of the initial damage site(s) after brain insults, by the migration of type B astrocytes.

Toll-like receptor 4: innate immune regulator of neuroimmune and neuroendocrine interactions in stress and major depressive disorder

Major depressive disorder (MDD) poses one of the highest disease burdens worldwide. Yet, current treatments targeting serotonergic and noradrenaline reuptake systems are insufficient to provide long-term relief from depressive symptoms in most patients, indicating the need for new treatment targets. Having the ability to influence behavior similar to depressive symptoms, as well as communicate with neuronal and neuroendocrine systems, the innate immune system is a strong candidate for MDD treatments. Given the complex nature of immune signaling, the main question becomes: What is the role of the innate immune system in MDD? The current review presents evidence that toll-like receptor 4 (TLR4), via driving both peripheral and central immune responses, can interact with serotonergic neurotransmission and cause neuroendocrine disturbances, thus integrating with widely observed hallmarks of MDD. Additionally, through describing the multi-directional communication between immune, neural and endocrine systems in stress, TLR4—related mechanisms can mediate stress-induced adaptations, which are necessary for the development of MDD. Therefore, apart from exogenous pathogenic mechanisms, TLR4 is involved in immune changes as a result of endogenous stress signals, playing an integral part in the pathophysiology, and could be a potential target for pharmacological treatments to improve current interventions for MDD.

Early expressions of hypoxia-inducible factor 1alpha and vascular endothelial growth factor increase the neuronal plasticity of activated endogenous neural stem cells after focal cerebral ischemia

Endogenous neural stem cells become “activated” after neuronal injury, but the activation sequence and fate of endogenous neural stem cells in focal cerebral ischemia model are little known. We evaluated the relationships between neural stem cells and hypoxia-inducible factor-1α and vascular endothelial growth factor expression in a photothromobotic rat stroke model using immunohistochemistry and western blot analysis. We also evaluated the chronological changes of neural stem cells by 5-bromo-2′-deoxyuridine (BrdU) incorporation. Hypoxia-inducible factor-1α expression was initially increased from 1 hour after ischemic injury, followed by vascular endothelial growth factor expression. Hypoxia-inducible factor-1α immunoreactivity was detected in the ipsilateral cortical neurons of the infarct core and peri-infarct area. Vascular endothelial growth factor immunoreactivity was detected in bilateral cortex, but ipsilateral cortex staining intensity and numbers were greater than the contralateral cortex. Vascular endothelial growth factor immunoreactive cells were easily found along the peri-infarct area 12 hours after focal cerebral ischemia. The expression of nestin increased throughout the microvasculature in the ischemic core and the peri-infarct area in all experimental rats after 24 hours of ischemic injury. Nestin immunoreactivity increased in the subventricular zone during 12 hours to 3 days, and prominently increased in the ipsilateral cortex between 3–7 days. Nestin-labeled cells showed dual differentiation with microvessels near the infarct core and reactive astrocytes in the peri-infarct area. BrdU-labeled cells were increased gradually from day 1 in the ipsilateral subventricular zone and cortex, and numerous BrdU-labeled cells were observed in the peri-infarct area and non-lesioned cortex at 3 days. BrdU-labeled cells rather than neurons, were mainly co-labeled with nestin and GFAP. Early expressions of hypoxia-inducible factor-1α and vascular endothelial growth factor after ischemia made up the microenvironment to increase the neuronal plasticity of activated endogenous neural stem cells. Moreover, neural precursor cells after large-scale cortical injury could be recruited from the cortex nearby infarct core and subventricular zone.

Prospects for engineering neurons from local neocortical cell populations as cell-mediated therapy for neurological disorders

There is little cell replacement following neurological injury, limiting the regenerative response of the CNS. Progress in understanding the biology of neural stem cells has raised interest in using stem cells for replacing neurons lost to injury or to disease. Stem cell therapy may also have a role in rebuilding deficient neural circuitry underlying mood disorders, epilepsy, and pain modulation among other roles. In vitro expansion of stem cells with directed differentiation prior to transplantation is one approach to stem cell therapy. Emerging evidence suggests that it may be possible to convert in vivo endogenous neural cells to a neuronal fate directly, providing an alternative strategy for stem cell therapy to the CNS. This review assesses the evidence for engineering a subtype-specific neuronal fate of endogenous neural cells in the cerebral cortex as a function of initial cell lineage, reactive response to injury, conversion factors, and environmental context. We conclude with a discussion of some of the challenges that must be overcome to move this alternative in vivo engineered conversion process toward becoming a viable therapeutic option.

Improvements in biomaterial matrices for neural precursor cell transplantation

Progress is being made in developing neuroprotective strategies for traumatic brain injuries; however, there will never be a therapy that will fully preserve neurons that are injured from moderate to severe head injuries. Therefore, to restore neurological function, regenerative strategies will be required. Given the limited regenerative capacity of the resident neural precursors of the CNS, many investigators have evaluated the regenerative potential of transplanted precursors. Unfortunately, these precursors do not thrive when engrafted without a biomaterial scaffold. In this article we review the types of natural and synthetic materials that are being used in brain tissue engineering applications for traumatic brain injury and stroke. We also analyze modifications of the scaffolds including immobilizing drugs, growth factors and extracellular matrix molecules to improve CNS regeneration and functional recovery. We conclude with a discussion of some of the challenges that remain to be solved towards repairing and regenerating the brain.

Traumatic brain injury reveals novel cell lineage relationships within the subventricular zone

The acute response of the rodent subventricular zone (SVZ) to traumatic brain injury (TBI) involves a physical expansion through increased cell proliferation. However, the cellular underpinnings of these changes are not well understood. Our analyses have revealed that there are two distinct transit-amplifying cell populations that respond in opposite ways to injury. Mash1+ transit-amplifying cells are the primary SVZ cell type that is stimulated to divide following TBI. In contrast, the EGFR+ population, which has been considered to be a functionally equivalent progenitor population to Mash1+ cells in the uninjured brain, becomes significantly less proliferative after injury. Although normally quiescent GFAP+ stem cells are stimulated to divide in SVZ ablation models, we found that the GFAP+ stem cells do not divide more after TBI. We found, instead, that TBI results in increased numbers of GFAP+/EGFR+ stem cells via non-proliferative means-potentially through the dedifferentiation of progenitor cells. EGFR+ progenitors from injured brains only were competent to revert to a stem cell state following brief exposure to growth factors. Thus, our results demonstrate previously unknown changes in lineage relationships that differ from conventional models and likely reflect an adaptive response of the SVZ to maintain endogenous brain repair after TBI.

RalA promotes a direct exocyst-Par6 interaction to regulate polarity in neuronal development

Cell polarization is essential for neuronal development in both the embryonic and postnatal brain. Here, using primary cultures, in vivo postnatal electroporation and conditional genetic ablation, we show that the Ras-like small GTPase RalA and its effector, the exocyst, regulate the morphology and polarized migration of neural progenitors derived from the subventricular zone, a major neurogenic niche in the postnatal brain. Active RalA promotes the direct binding between the exocyst subunit Exo84 and the PDZ domain of Par6 through a non-canonical PDZ-binding motif. Blocking the Exo84-Par6 interaction impairs polarization in postnatal neural progenitors and cultured embryonic neurons. Our results provide the first in vivo characterization of RalA function in the mammalian brain and highlight a novel molecular mechanism for cell polarization. Given that the exocyst and the Par complex are conserved in many tissues, the functional significance of their interaction and its regulation by RalA are likely to be important in a wide range of polarization events.

Nanofibrous scaffolds releasing a small molecule BDNF-mimetic for the re-direction of endogenous neuroblast migration in the brain

Brain tissue engineering has the potential to harness existing elements of neurogenesis within the adult brain to overcome a microenvironment that is otherwise inhibitory to regeneration, especially following severe tissue damage. This study investigates the ability of electrospun poly ε-caprolactone (PCL) to re-direct the migratory pathway of endogenous neuroblasts from the disrupted subventricular zone (SVZ). A small molecule non-peptide ligand (BDNF-mimetic) that mimicked the trophic properties of brain-derived neurotrophic factor (BDNF) was incorporated into electrospun PCL scaffolds to improve neuroblast survival and promote neuroblast migration towards the implant. PCL scaffolds were able to support neuroblast infiltration and migration along the implant tract. In the presence of the BDNF-mimetic, neuroblasts were able to migrate towards the implant via the parenchyma, and their persistence within the implants was prolonged. In addition, the BDNF-mimetic improved implant integration and increased local neuronal plasticity by increasing neurite sprouting at the tissue-implant interface. SMI32+ neurites were observed inside scaffolds at 21 days but not 8 days post implantation, indicating that at least some of the infiltrated neuroblasts had differentiated into neurons.

Ionizing radiation induced long-term alterations in the adult rat rostral migratory stream

Ionizing radiation can induce significant injury to normal brain structures. To assess radiation-induced late effects, adult male Wistar rats received whole-body exposure with fractionated doses of gamma rays (a total dose of 4Gy) and were investigated thirty, sixty and ninety days later. Immunohistochemistry and confocal microscopy were used to determine the density of neuroblasts derived from the anterior subventricular zone (SVZa) and brain resident microglia distributed along and/or adjacent to subventricular zone-olfactory bulb axis (SVZ-OB axis). Cell counting was performed in four anatomical parts along the well defined pathway, known as the rostral migratory stream (RMS) represented by the SVZa, vertical arm, elbow and horizontal arm of the RMS. Strong overdistribution of neuroblasts was seen in the SVZa thirty and sixty days after irradiation replaced by a steep decline in the following parts of the RMS and the highest decrease ninety days after radiation treatment along the entire SVZ-OB axis. Radiation treatment led to a decline or loss of microglia in almost all counted parts through the entire experiment. Results showed that ultimate decline of the SVZa descendants and loss of microglia suggests a contributory role of reduced neurogenesis in the development of radiation-induced late effects.

Sublethal transient global ischemia stimulates migration of neuroblasts and neurogenesis in mice

Increasing evidence has shown the potential of neuronal plasticity in adult brain after injury. Neural proliferation can be triggered by a focal sublethal ischemic preconditioning event; whether mild global ischemia could cause neurogenesis has been not clear. The present study investigated stimulating effects of sublethal transient global ischemia (TGI) on endogenous neurogenesis and neuroblast migration in the subventricular zone (SVZ), dentate gyrus, and peri-infarct areas of the adult cortex. Adult mice of 129S2/Sv strain were subjected to 8-min bilateral common carotid artery ligation followed by 5-bromo-2'-deoxyuridine (BrdU; 50 mg/kg, intraperitoneal) administration every day until being sacrificed at 1-21 days after reperfusion. The mild TGI did not induce neuronal cell death for up to 7 days after TGI, as evidenced by negative terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining among NeuN-positive cells in the hippocampus and neocortex. In TGI animals, BrdU staining revealed enhanced proliferation of neuroblasts and their migration track from the SVZ into the striatum and neocortex. In the corpus callosum, there were more BrdU-positive cells in the TGI group in the first 2 days. Increasing numbers of BrdU-positive cells were seen 7-21 days later in the striatum and cortex of TGI mice. The cortex of TGI animals showed increased expression of erythropoietin, erythropoietin receptor, fibroblast growth factor 2, vascular endothelial growth factor, and phosphorylated Jun N-terminal kinase; the expression was peaked 2 to 3 days after reperfusion. BrdU and NeuN double staining in the dentate gyrus, striatum, and cortex implied increased neurogenesis induced by the TGI preconditioning. Doublecortin (DCX)-positive cells increased in the cortex of TGI mice, localized to cortical layers II, III, and V, and many stained positive for the mature neuronal markers NeuN, neurofilament, N-methyl-d-aspartic acid receptor subunit gene NR1, or the gamma-aminobutyric-acid-synthesizing enzyme glutamic acid decarboxylase (GAD67). The atypical localization of DCX-positive cells and the colabeling with mature neuronal markers suggested that, in addition to indentifying migrating neuroblasts, DCX might also be a stress marker in the cortex. It is suggested that the sublethal TGI-induced regenerative responses may contribute to the beneficial effects of ischemic preconditioning.

In vivo postnatal electroporation and time-lapse imaging of neuroblast migration in mouse acute brain slices

The subventricular zone (SVZ) is one of the main neurogenic niches in the postnatal brain. Here, neural progenitors proliferate and give rise to neuroblasts able to move along the rostral migratory stream (RMS) towards the olfactory bulb (OB). This long-distance migration is required for the subsequent maturation of newborn neurons in the OB, but the molecular mechanisms regulating this process are still unclear. Investigating the signaling pathways controlling neuroblast motility may not only help understand a fundamental step in neurogenesis, but also have therapeutic regenerative potential, given the ability of these neuroblasts to target brain sites affected by injury, stroke, or degeneration. In this manuscript we describe a detailed protocol for in vivo postnatal electroporation and subsequent time-lapse imaging of neuroblast migration in the mouse RMS. Postnatal electroporation can efficiently transfect SVZ progenitor cells, which in turn generate neuroblasts migrating along the RMS. Using confocal spinning disk time-lapse microscopy on acute brain slice cultures, neuroblast migration can be monitored in an environment closely resembling the in vivo condition. Moreover, neuroblast motility can be tracked and quantitatively analyzed. As an example, we describe how to use in vivo postnatal electroporation of a GFP-expressing plasmid to label and visualize neuroblasts migrating along the RMS. Electroporation of shRNA or CRE recombinase-expressing plasmids in conditional knockout mice employing the LoxP system can also be used to target genes of interest. Pharmacological manipulation of acute brain slice cultures can be performed to investigate the role of different signaling molecules in neuroblast migration. By coupling in vivo electroporation with time-lapse imaging, we hope to understand the molecular mechanisms controlling neuroblast motility and contribute to the development of novel approaches to promote brain repair.

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

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

Neurogenesis is required for behavioral recovery after injury in the visual system of Xenopus laevis

Nonmammalian vertebrates have a remarkable capacity to regenerate brain tissue in response to central nervous system (CNS) injury. Nevertheless, it is not clear whether animals recover lost function after injury or whether injury-induced cell proliferation mediates recovery. We address these questions using the visual system and visually-guided behavior in Xenopus laevis tadpoles. We established a reproducible means to produce a unilateral focal injury to optic tectal neurons without damaging retinotectal axons. We then assayed a tectally-mediated visual avoidance behavior to evaluate behavioral impairment and recovery. Focal ablation of part of the optic tectum prevents the visual avoidance response to moving stimuli. Animals recover the behavior over the week following injury. Injury induces a burst of proliferation of tectal progenitor cells based on phospho-histone H3 immunolabeling and experiments showing that Musashi-immunoreactive tectal progenitors incorporate the thymidine analog chlorodeoxyuridine after injury. Pulse chase experiments indicate that the newly-generated cells differentiate into N-β-tubulin-immunoreactive neurons. Furthermore, in vivo time-lapse imaging shows that Sox2-expressing neural progenitors divide in response to injury and generate neurons with elaborate dendritic arbors. These experiments indicate that new neurons are generated in response to injury. To test if neurogenesis is necessary for recovery from injury, we blocked cell proliferation in vivo and found that recovery of the visual avoidance behavior is inhibited by drugs that block cell proliferation. Moreover, behavioral recovery is facilitated by changes in visual experience that increase tectal progenitor cell proliferation. Our data indicate that neurogenesis in the optic tectum is critical for recovery of visually-guided behavior after injury.

Neurogenesis in adult human brain after traumatic brain injury

While much work has been conducted regarding the neurogenesis response to traumatic brain injury (TBI) in rodents, it remains largely unknown whether neurogenesis in adult human brain also responds to TBI in a similar manner. Here, we performed immunocytochemistry on 11 brain specimens from patients with traumatic brain injury, who underwent surgical intervention. We found that expression of neural stem/progenitor cell (NSC) protein markers, including DCX, TUC4, PSA-NCAM, SOX2 and NeuroD, was increased in the perilesional cortex of human brain after TBI compared to that of normal brain. Confocal images showed that these NSC proteins were expressed in one single cell. We also found that proliferative markers were expressed in NSC protein-positive cells after TBI, and the number of proliferative NSCs was significantly increased after TBI. Our data suggest that TBI may also induce neurogenesis in human brain.

Regulation of endogenous neural stem/progenitor cells for neural repair-factors that promote neurogenesis and gliogenesis in the normal and damaged brain

Neural stem/precursor cells in the adult brain reside in the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus. These cells primarily generate neuroblasts that normally migrate to the olfactory bulb (OB) and the dentate granule cell layer respectively. Following brain damage, such as traumatic brain injury, ischemic stroke or in degenerative disease models, neural precursor cells from the SVZ in particular, can migrate from their normal route along the rostral migratory stream (RMS) to the site of neural damage. This neural precursor cell response to neural damage is mediated by release of endogenous factors, including cytokines and chemokines produced by the inflammatory response at the injury site, and by the production of growth and neurotrophic factors. Endogenous hippocampal neurogenesis is frequently also directly or indirectly affected by neural damage. Administration of a variety of factors that regulate different aspects of neural stem/precursor biology often leads to improved functional motor and/or behavioral outcomes. Such factors can target neural stem/precursor proliferation, survival, migration and differentiation into appropriate neuronal or glial lineages. Newborn cells also need to subsequently survive and functionally integrate into extant neural circuitry, which may be the major bottleneck to the current therapeutic potential of neural stem/precursor cells. This review will cover the effects of a range of intrinsic and extrinsic factors that regulate neural stem/precursor cell functions. In particular it focuses on factors that may be harnessed to enhance the endogenous neural stem/precursor cell response to neural damage, highlighting those that have already shown evidence of preclinical effectiveness and discussing others that warrant further preclinical investigation.