Combination of Vascular Endothelial and Fibroblast Growth Factor 2 for Induction of Neurogenesis and Angiogenesis after Traumatic Brain Injury

Cellular and molecular mechanisms in vascular repair after traumatic brain injury: a narrative review

Traumatic brain injury (TBI) disrupts normal brain function and is associated with high morbidity and fatality rates. TBI is characterized as mild, moderate or severe depending on its severity. The damage may be transient and limited to the dura matter, with only subtle changes in cerebral parenchyma, or life-threatening with obvious focal contusions, hematomas and edema. Blood vessels are often injured in TBI. Even in mild TBI, dysfunctional cerebral vascular repair may result in prolonged symptoms and poor outcomes. Various distinct types of cells participate in vascular repair after TBI. A better understanding of the cellular response and function in vascular repair can facilitate the development of new therapeutic strategies. In this review, we analyzed the mechanism of cerebrovascular impairment and the repercussions following various forms of TBI. We then discussed the role of distinct cell types in the repair of meningeal and parenchyma vasculature following TBI, including endothelial cells, endothelial progenitor cells, pericytes, glial cells (astrocytes and microglia), neurons, myeloid cells (macrophages and monocytes) and meningeal lymphatic endothelial cells. Finally, possible treatment techniques targeting these unique cell types for vascular repair after TBI are discussed.

Growth factors and their peptide mimetics for treatment of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability in adults, caused by a physical insult damaging the brain. Growth factor-based therapies have the potential to reduce the effects of secondary injury and improve outcomes by providing neuroprotection against glutamate excitotoxicity, oxidative damage, hypoxia, and ischemia, as well as promoting neurite outgrowth and the formation of new blood vessels. Despite promising evidence in preclinical studies, few neurotrophic factors have been tested in clinical trials for TBI. Translation to the clinic is not trivial and is limited by the short in vivo half-life of the protein, the inability to cross the blood-brain barrier and human delivery systems. Synthetic peptide mimetics have the potential to be used in place of recombinant growth factors, activating the same downstream signalling pathways, with a decrease in size and more favourable pharmacokinetic properties. In this review, we will discuss growth factors with the potential to modulate damage caused by secondary injury mechanisms following a traumatic brain injury that have been trialled in other indications including spinal cord injury, stroke and neurodegenerative diseases. Peptide mimetics of nerve growth factor (NGF), hepatocyte growth factor (HGF), glial cell line-derived growth factor (GDNF), brain-derived neurotrophic factor (BDNF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) will be highlighted, most of which have not yet been tested in preclinical or clinical models of TBI.

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Despite extensive research efforts, the majority of trialed monotherapies to date have failed to demonstrate significant benefit. It has been suggested that this is due to the complex pathophysiology of TBI, which may possibly be addressed by a combination of therapeutic interventions. In this article, we have reviewed combinations of different pharmacologic treatments, combinations of non-pharmacologic interventions, and combined pharmacologic and non-pharmacologic interventions for TBI. Both preclinical and clinical studies have been included. While promising results have been found in animal models, clinical trials of combination therapies have not yet shown clear benefit. This may possibly be due to their application without consideration of the evolving pathophysiology of TBI. Improvements of this paradigm may come from novel interventions guided by multimodal neuromonitoring and multimodal imaging techniques, as well as the application of multi-targeted non-pharmacologic and endogenous therapies. There also needs to be a greater representation of female subjects in preclinical and clinical studies.

Holmes T, Obenaus A, Xu X. Longitudinal dynamics of microvascular recovery after acquired cortical injury

Acquired brain injuries due to trauma damage the cortical vasculature, which in turn impairs blood flow to injured tissues. There are reports of vascular morphological recovery following traumatic brain injury, but the remodeling process has not been examined longitudinally in detail after injury in vivo. Understanding the dynamic processes that influence recovery is thus critically important. We evaluated the longitudinal and dynamic microvascular recovery and remodeling up to 2 months post injury using live brain miniscope and 2-photon microscopic imaging. The new imaging approaches captured dynamic morphological and functional recovery processes at high spatial and temporal resolution in vivo. Vessel painting documented the initial loss and subsequent temporal morphological vascular recovery at the injury site. Miniscopes were used to longitudinally image the temporal dynamics of vascular repair in vivo after brain injury in individual mice across each cohort. We observe near-immediate nascent growth of new vessels in and adjacent to the injury site that peaks between 14 and 21 days post injury. 2-photon microscopy confirms new vascular growth and further demonstrates differences between cortical layers after cortical injury: large vessels persist in deeper cortical layers (> 200 μm), while superficial layers exhibit a dense plexus of fine (and often non-perfused) vessels displaying regrowth. Functionally, blood flow increases mirror increasing vascular density. Filopodia development and endothelial sprouting is measurable within 3 days post injury that rapidly transforms regions devoid of vessels to dense vascular plexus in which new vessels become increasingly perfused. Within 7 days post injury, blood flow is observed in these nascent vessels. Behavioral analysis reveals improved vascular modulation after 9 days post injury, consistent with vascular regrowth. We conclude that morphological recovery events are closely linked to functional recovery of blood flow to the compromised tissues, which subsequently leads to improved behavioral outcomes.

Molecular and Clinical Significance of Fibroblast Growth Factor 2 in Development and Regeneration of the Auditory System

The fibroblast growth factor 2 (FGF2) is a member of the FGF family which is involved in key biological processes including development, cellular proliferation, wound healing, and angiogenesis. Although the utility of the FGF family as therapeutic agents has attracted attention, and FGF2 has been studied in several clinical contexts, there remains an incomplete understanding of the molecular and clinical function of FGF2 in the auditory system. In this review, we highlight the role of FGF2 in inner ear development and hearing protection and present relevant clinical studies for tympanic membrane (TM) repair. We conclude by discussing the future implications of FGF2 as a potential therapeutic agent.

Military traumatic brain injury: a challenge straddling neurology and psychiatry

Military psychiatry, a new subcategory of psychiatry, has become an invaluable, intangible effect of the war. In this review, we begin by examining related military research, summarizing the related epidemiological data, neuropathology, and the research achievements of diagnosis and treatment technology, and discussing its comorbidity and sequelae. To date, advances in neuroimaging and molecular biology have greatly boosted the studies on military traumatic brain injury (TBI). In particular, in terms of pathophysiological mechanisms, several preclinical studies have identified abnormal protein accumulation, blood-brain barrier damage, and brain metabolism abnormalities involved in the development of TBI. As an important concept in the field of psychiatry, TBI is based on organic injury, which is largely different from many other mental disorders. Therefore, military TBI is both neuropathic and psychopathic, and is an emerging challenge at the intersection of neurology and psychiatry.

The interplay of neurovasculature and adult hippocampal neurogenesis

The subgranular zone of the dentate gyrus provides a local microenvironment (niche) for neural stem cells. In the adult brain, it has been established that the vascular compartment of such niches has a significant role in regulating adult hippocampal neurogenesis. More recently, evidence showed that neurovascular coupling, the relationship between blood flow and neuronal activity, also regulates hippocampal neurogenesis. Here, we review the most recent articles on addressing the intricate relationship between neurovasculature and adult hippocampal neurogenesis and a novel pathway where functional hyperemia enhances hippocampal neurogenesis. In the end, we have further reviewed recent research showing that impaired neurovascular coupling may cause declined neurogenesis and contribute to brain damage in neurodegenerative diseases.

Management of Traumatic Brain Injury: From Present to Future

TBI (traumatic brain injury) is a major cause of death among youth in industrialized societies. Brain damage following traumatic injury is a result of direct and indirect mechanisms; indirect or secondary injury involves the initiation of an acute inflammatory response, including the breakdown of the blood–brain barrier (BBB), brain edema, infiltration of peripheral blood cells, and activation of resident immunocompetent cells, as well as the release of numerous immune mediators such as interleukins and chemotactic factors. TBI can cause changes in molecular signaling and cellular functions and structures, in addition to tissue damage, such as hemorrhage, diffuse axonal damages, and contusions. TBI typically disturbs brain functions such as executive actions, cognitive grade, attention, memory data processing, and language abilities. Animal models have been developed to reproduce the different features of human TBI, better understand its pathophysiology, and discover potential new treatments. For many years, the first approach to manage TBI has been treatment of the injured tissue with interventions designed to reduce the complex secondary-injury cascade. Several studies in the literature have stressed the importance of more closely examining injuries, including endothelial, microglia, astroglia, oligodendroglia, and precursor cells. Significant effort has been invested in developing neuroprotective agents. The aim of this work is to review TBI pathophysiology and existing and potential new therapeutic strategies in the management of inflammatory events and behavioral deficits associated with TBI.

EphB3 signaling induces cortical endothelial cell death and disrupts the blood-brain barrier after traumatic brain injury

Damage to the cerebrovascular network is a major contributor to dysfunction in patients suffering from traumatic brain injury (TBI). Vessels are composed of lumen-forming endothelial cells that associate closely with both glial and neuronal units to establish a functional blood–brain barrier (BBB). Under normal physiological conditions, these vascular units play important roles in central nervous system (CNS) homeostasis by delivering oxygen and nutrients while filtering out molecules and cells that could be harmful; however, after TBI this system is disrupted. Here, we describe a novel role for a class of receptors, called dependence receptors, in regulating vessel stability and BBB integrity after CCI injury in mice. Specifically, we identified that EphB3 receptors function as a pro-apoptotic dependence receptor in endothelial cells (ECs) that contributes to increased BBB damage after CCI injury. In the absence of EphB3, we observed increased endothelial cell survival, reduced BBB permeability and enhanced interactions of astrocyte-EC membranes. Interestingly, the brain’s response to CCI injury is to reduce EphB3 levels and its ligand ephrinB3; however, the degree and timing of those reductions limit the protective response of the CNS. We conclude that EphB3 is a negative regulator of cell survival and BBB integrity that undermine tissue repair, and represents a protective therapeutic target for TBI patients.

FGF2 Attenuates Neural Cell Death via Suppressing Autophagy after Rat Mild Traumatic Brain Injury

Traumatic brain injury (TBI) can lead to physical and cognitive deficits, which are caused by the secondary injury process. Effective pharmacotherapies for TBI patients are still lacking. Fibroblast growth factor-2 (FGF2) is an important neurotrophic factor that can stimulate neurogenesis and angiogenesis and has been shown to have neuroprotective effects after brain insults. Previous studies indicated that FGF2's neuroprotective effects might be related to its function of regulating autophagy. The present study investigated FGF2's beneficial effects in the early stage of rat mild TBI and the underlying mechanisms. One hundred and forty-four rats were used for creating controlled cortical impact (CCI) models to simulate the pathological damage after TBI. Our results indicated that pretreatment of FGF2 played a neuroprotective role in the early stage of rat mild TBI through alleviating brain edema, reducing neurological deficits, preventing tissue loss, and increasing the number of surviving neurons in injured cortex and the ipsilateral hippocampus. FGF2 could also protect cells from various forms of death such as apoptosis or necrosis through inhibition of autophagy. Finally, autophagy activator rapamycin could abolish the protective effects of FGF2. This study extended our understanding of FGF2's neuroprotective effects and shed lights on the pharmacological therapy after TBI.

Response of the cerebral vasculature following traumatic brain injury

The critical role of the vasculature and its repair in neurological disease states is beginning to emerge particularly for stroke, dementia, epilepsy, Parkinson's disease, tumors and others. However, little attention has been focused on how the cerebral vasculature responds following traumatic brain injury (TBI). TBI often results in significant injury to the vasculature in the brain with subsequent cerebral hypoperfusion, ischemia, hypoxia, hemorrhage, blood-brain barrier disruption and edema. The sequalae that follow TBI result in neurological dysfunction across a host of physiological and psychological domains. Given the importance of restoring vascular function after injury, emerging research has focused on understanding the vascular response after TBI and the key cellular and molecular components of vascular repair. A more complete understanding of vascular repair mechanisms are needed and could lead to development of new vasculogenic therapies, not only for TBI but potentially vascular-related brain injuries. In this review, we delineate the vascular effects of TBI, its temporal response to injury and putative biomarkers for arterial and venous repair in TBI. We highlight several molecular pathways that may play a significant role in vascular repair after brain injury.

Pathophysiology Associated with Traumatic Brain Injury: Current Treatments and Potential Novel Therapeutics

Traumatic brain injury (TBI) is one of the leading causes of death of young people in the developed world. In the United States alone, 1.7 million traumatic events occur annually accounting for 50,000 deaths. The etiology of TBI includes traffic accidents, falls, gunshot wounds, sports, and combat-related events. TBI severity ranges from mild to severe. TBI can induce subtle changes in molecular signaling, alterations in cellular structure and function, and/or primary tissue injury, such as contusion, hemorrhage, and diffuse axonal injury. TBI results in blood-brain barrier (BBB) damage and leakage, which allows for increased extravasation of immune cells (i.e., increased neuroinflammation). BBB dysfunction and impaired homeostasis contribute to secondary injury that occurs from hours to days to months after the initial trauma. This delayed nature of the secondary injury suggests a potential therapeutic window. The focus of this article is on the (1) pathophysiology of TBI and (2) potential therapies that include biologics (stem cells, gene therapy, peptides), pharmacological (anti-inflammatory, antiepileptic, progrowth), and noninvasive (exercise, transcranial magnetic stimulation). In final, the review briefly discusses membrane/lipid rafts (MLR) and the MLR-associated protein caveolin (Cav). Interventions that increase Cav-1, MLR formation, and MLR recruitment of growth-promoting signaling components may augment the efficacy of pharmacologic agents or already existing endogenous neurotransmitters and neurotrophins that converge upon progrowth signaling cascades resulting in improved neuronal function after injury.

The far-reaching scope of neuroinflammation after traumatic brain injury

The 'silent epidemic' of traumatic brain injury (TBI) has been placed in the spotlight as a result of clinical investigations and popular press coverage of athletes and veterans with single or repetitive head injuries. Neuroinflammation can cause acute secondary injury after TBI, and has been linked to chronic neurodegenerative diseases; however, anti-inflammatory agents have failed to improve TBI outcomes in clinical trials. In this Review, we therefore propose a new framework of targeted immunomodulation after TBI for future exploration. Our framework incorporates factors such as the time from injury, mechanism of injury, and secondary insults in considering potential treatment options. Structuring our discussion around the dynamics of the immune response to TBI - from initial triggers to chronic neuroinflammation - we consider the ability of soluble and cellular inflammatory mediators to promote repair and regeneration versus secondary injury and neurodegeneration. We summarize both animal model and human studies, with clinical data explicitly defined throughout this Review. Recent advances in neuroimmunology and TBI-responsive neuroinflammation are incorporated, including concepts of inflammasomes, mechanisms of microglial polarization, and glymphatic clearance. Moreover, we highlight findings that could offer novel therapeutic targets for translational and clinical research, assimilate evidence from other brain injury models, and identify outstanding questions in the field.

Neural stem cells secrete factors facilitating brain regeneration upon constitutive Raf-Erk activation

The intracellular Raf-Erk signaling pathway is activated during neural stem cell (NSC) proliferation, and neuronal and astrocytic differentiation. A key question is how this signal can evoke multiple and even opposing NSC behaviors. We show here, using a constitutively active Raf (ca-Raf), that Raf-Erk activation in NSCs induces neuronal differentiation in a cell-autonomous manner. By contrast, it causes NSC proliferation and the formation of astrocytes in an extrinsic autocrine/paracrine manner. Thus, treatment of NSCs with medium (CM) conditioned in ca-Raf-transduced NSCs (Raf-CM; RCM) became activated to form proliferating astrocytes resembling radial glial cells (RGCs) or adult-type NSCs. Infusion of Raf-CM into injured mouse brains caused expansion of the NSC population in the subventricular zone, followed by the formation of new neurons that migrated to the damaged site. Our study shows an example how molecular mechanisms dissecting NSC behaviors can be utilized to develop regenerative therapies in brain disorders.

Combination therapies for neurobehavioral and cognitive recovery after experimental traumatic brain injury: Is more better?

Traumatic brain injury (TBI) is a significant health care crisis that affects two million individuals in the United Sates alone and over ten million worldwide each year. While numerous monotherapies have been evaluated and shown to be beneficial at the bench, similar results have not translated to the clinic. One reason for the lack of successful translation may be due to the fact that TBI is a heterogeneous disease that affects multiple mechanisms, thus requiring a therapeutic approach that can act on complementary, rather than single, targets. Hence, the use of combination therapies (i.e., polytherapy) has emerged as a viable approach. Stringent criteria, such as verification of each individual treatment plus the combination, a focus on behavioral outcome, and post-injury vs. pre-injury treatments, were employed to determine which studies were appropriate for review. The selection process resulted in 37 papers that fit the specifications. The review, which is the first to comprehensively assess the effects of combination therapies on behavioral outcomes after TBI, encompasses five broad categories (inflammation, oxidative stress, neurotransmitter dysregulation, neurotrophins, and stem cells, with and without rehabilitative therapies). Overall, the findings suggest that combination therapies can be more beneficial than monotherapies as indicated by 46% of the studies exhibiting an additive or synergistic positive effect versus on 19% reporting a negative interaction. These encouraging findings serve as an impetus for continued combination studies after TBI and ultimately for the development of successful clinically relevant therapies.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

Microglia in the TBI brain: The good, the bad, and the dysregulated

As the major cellular component of the innate immune system in the central nervous system (CNS) and the first line of defense whenever injury or disease occurs, microglia play a critical role in neuroinflammation following a traumatic brain injury (TBI). In the injured brain microglia can produce neuroprotective factors, clear cellular debris and orchestrate neurorestorative processes that are beneficial for neurological recovery after TBI. However, microglia can also become dysregulated and can produce high levels of pro-inflammatory and cytotoxic mediators that hinder CNS repair and contribute to neuronal dysfunction and cell death. The dual role of microglial activation in promoting beneficial and detrimental effects on neurons may be accounted for by their polarization state and functional responses after injury. In this review article we discuss emerging research on microglial activation phenotypes in the context of acute brain injury, and the potential role of microglia in phenotype-specific neurorestorative processes such as neurogenesis, angiogenesis, oligodendrogenesis and regeneration. We also describe some of the known molecular mechanisms that regulate phenotype switching, and highlight new therapeutic approaches that alter microglial activation state balance to enhance long-term functional recovery after TBI. An improved understanding of the regulatory mechanisms that control microglial phenotypic shifts may advance our knowledge of post-injury recovery and repair, and provide opportunities for the development of novel therapeutic strategies for TBI.

What's New in Traumatic Brain Injury: Update on Tracking, Monitoring and Treatment

Traumatic brain injury (TBI), defined as an alteration in brain functions caused by an external force, is responsible for high morbidity and mortality around the world. It is important to identify and treat TBI victims as early as possible. Tracking and monitoring TBI with neuroimaging technologies, including functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and high definition fiber tracking (HDFT) show increasing sensitivity and specificity. Classical electrophysiological monitoring, together with newly established brain-on-chip, cerebral microdialysis techniques, both benefit TBI. First generation molecular biomarkers, based on genomic and proteomic changes following TBI, have proven effective and economical. It is conceivable that TBI-specific biomarkers will be developed with the combination of systems biology and bioinformation strategies. Advances in treatment of TBI include stem cell-based and nanotechnology-based therapy, physical and pharmaceutical interventions and also new use in TBI for approved drugs which all present favorable promise in preventing and reversing TBI.

Endogenous repair signaling after brain injury and complementary bioengineering approaches to enhance neural regeneration

Traumatic brain injury (TBI) affects 5.3 million Americans annually. Despite the many long-term deficits associated with TBI, there currently are no clinically available therapies that directly address the underlying pathologies contributing to these deficits. Preclinical studies have investigated various therapeutic approaches for TBI: two such approaches are stem cell transplantation and delivery of bioactive factors to mitigate the biochemical insult affiliated with TBI. However, success with either of these approaches has been limited largely due to the complexity of the injury microenvironment. As such, this review outlines the many factors of the injury microenvironment that mediate endogenous neural regeneration after TBI and the corresponding bioengineering approaches that harness these inherent signaling mechanisms to further amplify regenerative efforts.

Lipoic acid and bone marrow derived cells therapy induce angiogenesis and cell proliferation after focal brain injury

Abstract Introduction: Traumatic brain injury is a main cause of disability and death in developed countries, above all among children and adolescents. The intrinsic inability of the central nervous system to efficiently repair traumatic injuries renders transplantation of bone marrow-derived cells (BMDC) a promising approach towards repair of brain lesions. On the other hand, many studies have reported the beneficial effect of Lipoic acid (LA), a potent antioxidant promoting cell survival, angiogenesis and neuroregeneration.

METHODS

In this study, the cortex of adult mice was cryo-injured in order to mimic local traumatic brain injury. Vehicle or freshly prepared BMDC were grafted in the cerebral penumbra area 24 hours after unilateral local injury alone or combined with intra-peritoneal LA administration as a new regenerative strategy.

RESULTS

Differences were found in the process of cell proliferation, angiogenesis and glial scar formation after local injury depending of the applied treatment, either LA or BMDC alone or in combination.

CONCLUSION

The data presented here suggest that transplantation of BMDC is a good alternative and valid strategy to treat a focal brain injury when LA could not be prescribed due to its non-desired secondary effects.

A new avenue for lithium: intervention in traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability and death from trauma to central nervous system (CNS) tissues. For patients who survive the initial injury, TBI can lead to neurodegeneration as well as cognitive and motor deficits, and is even a risk factor for the future development of neurodegenerative disorders such as Alzheimer's disease. Preclinical studies of multiple neuropathological and neurodegenerative disorders have shown that lithium, which is primarily used to treat bipolar disorder, has considerable neuroprotective effects. Indeed, emerging evidence now suggests that lithium can also mitigate neurological deficits incurred from TBI. Lithium exerts neuroprotective effects and stimulates neurogenesis via multiple signaling pathways; it inhibits glycogen synthase kinase-3 (GSK-3), upregulates neurotrophins and growth factors (e.g., brain-derived neurotrophic factor (BDNF)), modulates inflammatory molecules, upregulates neuroprotective factors (e.g., B-cell lymphoma-2 (Bcl-2), heat shock protein 70 (HSP-70)), and concomitantly downregulates pro-apoptotic factors. In various experimental TBI paradigms, lithium has been shown to reduce neuronal death, microglial activation, cyclooxygenase-2 induction, amyloid-β (Aβ), and hyperphosphorylated tau levels, to preserve blood-brain barrier integrity, to mitigate neurological deficits and psychiatric disturbance, and to improve learning and memory outcome. Given that lithium exerts multiple therapeutic effects across an array of CNS disorders, including promising results in preclinical models of TBI, additional clinical research is clearly warranted to determine its therapeutic attributes for combating TBI. Here, we review lithium's exciting potential in ameliorating physiological as well as cognitive deficits induced by TBI.

TAT conjugated cationic noble metal nanoparticles for gene delivery to epidermal stem cells

Most nonviral gene delivery systems are not efficient enough to manipulate the difficult-to-transfect cell types, including non-dividing, primary, neuronal or stem cells, due to a lack of an intrinsic capacity to enter the membrane and nucleus, release its DNA payload, and activate transcription. Noble metal nanoclusters have emerged as a fascinating area of widespread interest in nanomaterials. Herein, we report the synthesis of the TAT peptide conjugated cationic noble metal nanoparticles (metal NPs@PEI-TAT) as highly efficient carriers for gene delivery to stem cells. The metal NPs@PEI-TAT integrate the advantages of metal NPs and peptides: the presence of metal NPs can effectively decrease the cytotoxicity of cationic molecules, making it possible to apply them in biological systems, while the cell penetrating peptides are essential for enhanced cellular and nucleus entry to achieve high transfection efficiency. Our studies provide strong evidence that the metal NPs@PEI-TAT can be engineered as gene delivery agents for stem cells and subsequently enhance their directed differentiation for biomedical application.

Interaction between nonviral reprogrammed fibroblast stem cells and trophic factors for brain repair

There are currently no known treatment options that actually halt or permanently reverse the pathology evident in any neurodegenerative condition. Arguably, one of the most promising avenues for creating viable neuronal treatments could involve the combined use of cell replacement and gene therapy. Given the complexity of the neurodegenerative process, it stands to reason that adequate therapy should involve not only the replacement of loss neurons/synapses but also the interruption of multiple pro-death pathways. Thus, we propose the use of stem cells that are tailored to express specific trophic factors, thereby potentially encouraging synergistic effects between the stem cell properties and those of the trophic factors. The trophic factors, brain-derived neurotropic factor (BDNF), glial cell-derived neurotropic factor (GDNF), fibroblast growth factor (FGF) 2, and insulin-like growth factor (IGF) 1, in particular, have demonstrated neuroprotective actions in a number of animal models. Importantly, we use a nonviral approach, thereby minimizing the potential risk for DNA integration and tumor formation. The present study involved the development of a nonviral reprogramming system to transform adult mature mouse fibroblasts into progressive stages of cell development. We also tailored these stem cells to individually express each of the trophic factors, including BDNF, GDNF, FGF2, and IGF1. Significantly, central infusion of BDNF-expressing stem cells prevented the in vivo loss of neurons associated with infusion of the endotoxin, lipopolysaccharide (LPS). This is particularly important in light of the role of inflammatory processes that are posited to play in virtually all neurodegenerative states. Hence, the present results support the utility of using combined gene and cell-targeting approaches for neuronal pathology.

Fibroblast growth factor-2 signaling in neurogenesis and neurodegeneration

Fibroblast growth factor-2 (FGF2), also known as basic FGF, is a multi-functional growth factor. One of the 22-member FGF family, it signals through receptor tyrosine kinases encoding FGFR1-4. FGF2 activates FGFRs in cooperation with heparin or heparin sulfate proteoglycan to induce its pleiotropic effects in different tissues and organs, which include potent angiogenic effects and important roles in the differentiation and function of the central nervous system (CNS). FGF2 is crucial to development of the CNS, which explains its importance in adult neurogenesis. During development, high levels of FGF2 are detected from neurulation onwards. Moreover, developmental expression of FGF2 and its receptors is temporally and spatially regulated, concurring with development of specific brain regions including the hippocampus and substantia nigra pars compacta. In adult neurogenesis, FGF2 has been implicated based on its expression and regulation of neural stem and progenitor cells in the neurogenic niches, the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampal dentate gyrus. FGFR1 signaling also modulates inflammatory signaling through the surface glycoprotein CD200, which regulates microglial activation. Because of its importance in adult neurogenesis and neuroinflammation, manipulation of FGF2/FGFR1 signaling has been a focus of therapeutic development for neurodegenerative disorders, such as Alzheimer's disease, multiple sclerosis, Parkinson's disease and traumatic brain injury. Novel strategies include intranasal administration of FGF2, administration of an NCAM-derived FGFR1 agonist, and chitosan-based nanoparticles for the delivery of FGF2 in pre-clinical animal models. In this review, we highlight current research towards therapeutic interventions targeting FGF2/FGFR1 in neurodegenerative disorders.

Chemokine CCL2 induces apoptosis in cortex following traumatic brain injury

The chemokine C-C motif ligand 2 (CCL2) is an important mediator of neuroinflammation. Released in response to acute injury, ischemia, and neurodegenerative disease, CCL2 binds primarily to the G-protein-coupled chemokine C-C motif receptor 2 (CCR2) to recruit inflammatory cells to sites of tissue damage. Inflammation is thought to have both beneficial and deleterious consequences following traumatic brain injury (TBI), so we investigated CCL2-CCR2 signaling during the post-TBI period to assess possible neurodegenerative and protective actions. Local TBI in adult rat cortex was induced by Feeney's weight-drop method, and the expression of CCL2 and CCR2 in the tissue around the contusion site was measured by real-time quantitative PCR. Both CCL2 and CCR2 mRNA levels were increased markedly for at least 10 days after injury, peaking on day 3. The CCL2 protein was mainly co-localized with the astroglial marker glial fibrillary acidic protein and CCR2 protein with the neuronal nuclear marker NeuN as revealed by double immunofluorescence staining. A selective CCR2 antagonist, RS504393, reduced TUNEL staining, a marker of apoptosis, and improved performance in the Morris water maze 3 days post-TBI, suggesting that CCL2-CCR2 signaling has deleterious effects on neuronal survival and learning. Targeting the CCL2-CCR2 pathway may provide a novel therapeutic approach for the treatment of TBI.

Spatial relationship between NSCs/NPCs and microvessels in rat brain along prenatal and postnatal development

Neurogenesis and angiogenesis are two parallel processes that occur in brain development and repair, and so share some molecular signals. In order to better understand the interaction between the genesis of neural cells and vessels during brain development, the density of microvessels and the number of nestin positive neural stem/neural progenitor cells (NSCs/NPCs) around microvasculature in various brain regions was quantified. Results showed that the density of microvessels remained at a relative low level during embryonic development and dramatically increased after postnatal day 3 (P3), especially in subventricular zone. The number of nestin positive NSCs/NPCs per microvessel in neurogenic brain regions continually increased with fetal brain development and then gradually dropped down during postnatal development. The highest density of NSCs/NPCs appeared at postnatal day 1 (P1) and dramatically decreased after P3. Similar pattern was observed in striatum. In the olfactory bulb, the cerebral cortex and cerebellum, the dramatic decrease of NSCs/NPCs density appeared after P7, especially in the cerebral cortex. Our results demonstrated that anatomically, the spatial relationship between NSCs/NPCs and microvessels changed during brain development. The alteration patterns in neurogenic brain regions differed from non-neurogenic brain regions.

VEGF reverts the cognitive impairment induced by a focal traumatic brain injury during the development of rats raised under environmental enrichment

The role of VEGF in the nervous system is extensive; apart from its angiogenic effect, VEGF has been described as a neuroprotective, neurotrophic and neurogenic molecule. Similar effects have been described for enriched environment (EE). Moreover, both VEGF and EE have been related to improved spatial memory. Our aim was to investigate the neurovascular and cognitive effects of intracerebrally-administered VEGF and enriched environment during the critical period of the rat visual cortex development. Results showed that VEGF infusion as well as enriched environment induced neurovascular and cognitive effects in developing rats. VEGF administration produced an enhancement during the learning process of enriched animals and acted as an angiogenic factor both in primary visual cortex (V1) and dentate gyrus (DG) in order to counteract minipump implantation-induced damage. This fact revealed that DG vascularization is critical for normal learning. In contrast to this enriched environment acted on the neuronal density of the DG and V1 cortex, and results showed learning enhancement only in non-operated rats. In conclusion, VEGF administration only has effects if damage is observed due to injury. Once control values were reached, no further effects appeared, showing a ceiling effect. Our results strongly support that in addition to neurogenesis, vascularization plays a pivotal role for learning and memory.

Molecular and cellular mechanisms underlying the role of blood vessels in spinal cord injury and repair

Spinal cord injury causes immediate damage of nervous tissue accompanied by the loss of motor and sensory function. The limited self-repair ability of damaged nervous tissue underlies the need for reparative interventions to restore function after spinal cord injury. Blood vessels play a crucial role in spinal cord injury and repair. Injury-induced loss of local blood vessels and a compromised blood-brain barrier contribute to inflammation and ischemia and thus to the overall damage to the nervous tissue of the spinal cord. Lack of vasculature and leaking blood vessels impede endogenous tissue repair and limit prospective repair approaches. A reduction of blood vessel loss and the restoration of blood vessels so that they no longer leak might support recovery from spinal cord injury. The promotion of new blood vessel formation (i.e., angio- and vasculogenesis) might aid repair but also incorporates the danger of exacerbating tissue loss and thus functional impairment. The delicate interplay between cells and molecules that govern blood vessel repair and formation determines the extent of damage and the success of reparative interventions. This review deals with the cellular and molecular mechanisms underlying the role of blood vessels in spinal cord injury and repair.