Grafting of glial cell line-derived neurotrophic factor secreting cells for hypoxic-ischemic encephalopathy in neonatal rats

Limiting exercise inhibits neuronal recovery from neurological disorders

Patients who are bedridden often suffer from muscular atrophy due to reduced daily activities and can become depressed. However, patients who undergo physical therapy sometimes demonstrate positive benefits including a reduction of stressful and depressed behavior. Regenerative medicine has seen improvements in two stem cell-based therapies for central nervous system disorders. One therapy is through the transfer of exogenous stem cells. The other therapy is a more natural method and focuses on the increasing endogenous neurogenesis and restoring the neurological impairments. This study overviews how immobilization-induced disuse atrophy affects neurogenesis in rats, specifically hypothesizing that immobilization diminishes circulating trophic factor levels, like vascular endothelial growth factors or brain-derived neurotrophic factor, which in turn limits neurogenesis. This hypothesis requires the classification of the stem cell microenvironment by probing growth factors in addition to other stress-related proteins that correlate with exercise-induced neurogenesis. There is research examining the effects of increased exercise on neurogenesis while limiting exercise, which better demonstrates the pathological states of immobile stroke patients, remains relatively unexplored. To examine the effects of immobilization on neurogenesis quantitative measurements of movements, 5-bromo-2deoxyuridine labeling of proliferative cells, biochemical assays of serum, cerebrospinal fluid and neurological levels of trophic factors, growth factors, and stress-related proteins will indicate levels of neurogenesis. In further research, studies are needed to show how in vivo stimulation, or lack thereof, affects stem cell microenvironments to advance treatment procedures for strengthening neurogenesis in bedridden patients. This paper is a review article. Referred literature in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors' experiences.

Intracerebral Transplantation of Genetically Engineered Cells for Parkinson's Disease: Toward Clinical Application

Over the last decade, molecular biology has progressively developed, leading to new technology with subsequent clinical application for various cerebral diseases including Parkinson's disease (PD), one of the most investigated neurodegenerative disorders. The therapy for PD is mainly composed of medication, including drug replacement therapy, surgical treatment, and cell transplantation. Cell therapy for PD has been explored by using fetal nigral cells as an allo- or xenograft, autologous sympathetic ganglion, adrenal medulla, and carotid body in clinical settings. In addition, neurotrophic factors, including glial cell line-derived neurotrophic factor (GDNF), have a strong potency to rescue degenerating dopaminergic cells. Protein and/or gene therapy also might be a therapeutic option for PD. In this review, genetically engineered cell transplantation for animal models of PD, including catecholamine/neurotrophic factor-secreting cell transplantation with or without encapsulation, as performed in our laboratories, and their potential future as clinical applications are described with recent clinical studies in this field.

Detrimental effects of physical inactivity on neurogenesis

Patients diagnosed with neurological disorders exhibit a variety of physical and psychiatric symptoms, including muscle atrophy, general immobility, and depression. Patients who participate in physical rehabilitation at times show unexpected clinical improvement, which includes diminished depression and other stress-related behaviors. Regenerative medicine has advanced two major stem cell-based therapies for central nervous system (CNS) disorders, transplantation of exogenous stem cells, and enhancing the endogenous neurogenesis. The latter therapy utilizes a natural method of re-innervating the injured brain, which may mend neurological impairments. In this study, we examine how inactivity-induced atrophy, using the hindlimb suspension model, alters neurogenesis in rats. The hypothesis is that inactivity inhibits neurogenesis by decreasing circulation growth or trophic factors, such as vascular endothelial growth or neurotrophic factors. The restriction modifies neurogenesis and stem cell differentiation in the CNS, the stem cell microenvironment is examined by the trophic and growth factors, including stress-related proteins. Despite growing evidence revealing the benefits of “increased” exercise on neurogenesis, the opposing theory involving “physical inactivity,” which simulates pathological states, continues to be neglected. This novel theory will allow us to explore the effects on neurogenesis by an intransigent stem cell microenvironment likely generated by inactivity. 5-bromo-2-deoxyuridine labeling of proliferative cells, biochemical assays of serum, cerebrospinal fluid, and brain levels of trophic factors, growth factors, and stress-related proteins are suggested identifiers of neurogenesis, while evaluation of spontaneous movements will give insight into the psychomotor effects of inactivity. Investigations devised to show how in vivo stimulation, or lack thereof, affects the stem cell microenvironment are necessary to establish treatment methods to boost neurogenesis in bedridden patients.

No pain, no gain: lack of exercise obstructs neurogenesis

Bedridden patients develop atrophied muscles, their daily activities greatly reduced, and some display a depressive mood. Patients who are able to receive physical rehabilitation sometimes show surprising clinical improvements, including reduced depression and attenuation of other stress-related behaviors. Regenerative medicine has advanced two major stem cell-based therapies for CNS disorders, namely, transplantation of exogenous stem cells and amplification of endogenous neurogenesis. The latter strategy embraces a natural way of reinnervating the damaged brain and correcting the neurological impairments. In this study, we discussed how immobilization-induced disuse atrophy, using the hindlimb suspension model, affects neurogenesis in rats. The overarching hypothesis is that immobilization suppresses neurogenesis by reducing the circulating growth or trophic factors, such as vascular endothelial growth factor or brain-derived neurotrophic factor. That immobilization alters neurogenesis and stem cell differentiation in the CNS requires characterization of the stem cell microenvironment by examining the trophic and growth factors, as well as stress-related proteins that have been implicated in exercise-induced neurogenesis. Although accumulating evidence has revealed the contribution of "increased" exercise on neurogenesis, the reverse paradigm involving "lack of exercise," which mimics pathological states (e.g., stroke patients are often immobile), remains underexplored. This novel paradigm will enable us to examine the effects on neurogenesis by a nonpermissive stem cell microenvironment likely produced by lack of exercise. BrdU labeling of proliferative cells, biochemical assays of serum, cerebrospinal fluid and brain levels of trophic factors, growth factors, and stress-related proteins are proposed as indices of neurogenesis, while quantitative measurements of spontaneous movements will reveal psychomotor components of immobilization. Studies designed to reveal how in vivo stimulation, or lack thereof, alters the stem cell microenvironment are needed to begin to develop treatment strategies for enhancing neurogenesis in bedridden patients.

Neuroprotective effects of GDNF-expressing human amniotic fluid cells

Brain injury continues to be one of the leading causes of disability worldwide. Despite decades of research, there is currently no pharmacologically effective treatment for preventing neuronal loss and repairing the brain. As a result, novel therapeutic approaches, such as cell-based therapies, are being actively pursued to repair tissue damage and restore neurological function after injury. In this study, we examined the neuroprotective potential of amniotic fluid (AF) single cell clones, engineered to secrete glial cell derived neurotrophic factor (AF-GDNF), both in vitro and in a surgically induced model of brain injury. Our results show that pre-treatment with GDNF significantly increases cell survival in cultures of AF cells or cortical neurons exposed to hydrogen peroxide. Since improving the efficacy of cell transplantation depends on enhanced graft cell survival, we investigated whether AF-GDNF cells seeded on polyglycolic acid (PGA) scaffolds could enhance graft survival following implantation into the lesion cavity. Encouragingly, the AF-GDNF cells survived longer than control AF cells in serum-free conditions and continued to secrete GDNF both in vitro and following implantation into the injured motor cortex. AF-GDNF implantation in the acute period following injury was sufficient to activate the MAPK/ERK signaling pathway in host neural cells in the peri-lesion area, potentially boosting endogenous neuroprotective pathways. These results were complemented with promising trends in beam walk tasks in AF-GDNF/PGA animals during the 7 day timeframe. Further investigation is required to determine whether significant behavioural improvement can be achieved at a longer timeframe.

Carriers in cell-based therapies for neurological disorders

There is a pressing need for long-term neuroprotective and neuroregenerative therapies to promote full function recovery of injuries in the human nervous system resulting from trauma, stroke or degenerative diseases. Although cell-based therapies are promising in supporting repair and regeneration, direct introduction to the injury site is plagued by problems such as low transplanted cell survival rate, limited graft integration, immunorejection, and tumor formation. Neural tissue engineering offers an integrative and multifaceted approach to tackle these complex neurological disorders. Synergistic therapeutic effects can be obtained from combining customized biomaterial scaffolds with cell-based therapies. Current scaffold-facilitated cell transplantation strategies aim to achieve structural and functional rescue via offering a three-dimensional permissive and instructive environment for sustainable neuroactive factor production for prolonged periods and/or cell replacement at the target site. In this review, we intend to highlight important considerations in biomaterial selection and to review major biodegradable or non-biodegradable scaffolds used for cell transplantation to the central and peripheral nervous system in preclinical and clinical trials. Expanded knowledge in biomaterial properties and their prolonged interaction with transplanted and host cells have greatly expanded the possibilities for designing suitable carrier systems and the potential of cell therapies in the nervous system.

Hypoxic-ischemic neonatal encephalopathy: animal experiments for neuroprotective therapies

Hypoxic-ischemic neonatal encephalopathy and ensuing brain damage is still an important problem in modern perinatal medicine. In this paper, we would like to share some of the results of our recent studies on neuroprotective therapies in animal experiments, as well as some literature reviews. From the basic animal studies, we have now obtained some possible candidates for therapeutic measures against hypoxic-ischemic neonatal encephalopathy. For example, they are hypothermia, rehabilitation, free radical scavenger, neurotrophic factors and growth factors, steroid, calcium channel blocker, vagal stimulation, some anti apoptotic agents, pre- and post conditioning, antioxidants, cell therapy with stem cells, modulators of K(+)-ATP channels, and so on. Whether combination of these therapies may be more beneficial than any single therapy needs to be clarified. Hypoxia-ischemia is a complicated condition, in which the cause, severity, and time-course are different in each case. Likewise, each fetus has its own inherent potentials such as adaptation, preconditioning-tolerance, and intolerance. Therefore, further extensive studies are required to establish an individualized strategy for neuroprotection against perinatal hypoxic-ischemic insult.

Rescuing the neonatal brain from hypoxic injury with autologous cord blood

Brain injury resulting from perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of acute mortality in infants and chronic neurologic disability in surviving children. Recent multicenter clinical trials demonstrated the effectiveness of hypothermia initiated within the first 6 postnatal hours to reduce the risk of death or major neurological disabilities among neonates with HIE. However, in these trials, approximately 40% of cooled infants died or survived with significant impairments. Therefore, adjunct therapies are required to improve the outcome in neonates with HIE. Cord blood (CB) is a rich source of stem cells. Administration of human CB cells in animal models of HIE has generally resulted in improved outcomes and multiple mechanisms have been suggested including anti-inflammation, release of neurotrophic factors and stimulation of endogenous neurogenesis. Investigators at Duke are conducting studies of autologous CB infusion in neonates with HIE and in children with cerebral palsy. These pilot studies indicate no added risk from the regimens used, but results of ongoing placebo-controlled trials are needed to assess efficacy. Meanwhile, further investigations are warranted to determine the best strategies, that is, timing, dosing, route of delivery, choice of stem cells and ex vivo modulations, to attain long-term benefits of CB stem cell therapy.

Neuroprotection by GDNF in the ischemic brain

The glial cell line-derived neurotrophic factor (GDNF) was first identified as a survival factor for midbrain dopaminergic neurons, but additional studies provided evidences for a role as a trophic factor for other neurons of the central and peripheral nervous systems. GDNF regulates cellular activity through interaction with glycosyl-phosphatidylinositol-anchored cell surface receptors, GDNF family receptor-α1, which might signal through the transmembrane Ret tyrosine receptors or the neural cell adhesion molecule, to promote cell survival, neurite outgrowth, and synaptogenesis. The neuroprotective effect of exogenous GDNF has been shown in different experimental models of focal and global brain ischemia, by local administration of the trophic factor, using viral vectors carrying the GDNF gene and by transplantation of GDNF-expressing cells. These different strategies and the mechanisms contributing to neuroprotection by GDNF are discussed in this review. Importantly, neuroprotection by GDNF was observed even when administered after the ischemic injury.

Ultrasound-induced release of GDNF from lipid coated microbubbles injected into striatum reduces hypoxic-ischemic injury in neonatal rats

Previous studies showed that inflammation and apoptosis were involved in the pathogenesis of hypoxic-ischemic brain injury. The immature brain is particularly vulnerable to damage. Intracerebral injection of glial cell line-derived neurotrophic factor (GDNF) has been shown to reduce the injury induced by hypoxia-ischemia (HI). In this study, the neuroprotective effect of intracerebral ultrasound-induced dissolution of lipid-coated GDNF microbubbles was investigated in a neonatal rat model of hypoxic-ischemic brain injury. Hypoxic-ischemic injury was induced in 7-day-old rats in the present study. The rats with hypoxia-ischemia received intracerebral injections of GDNF-containing microbubbles (0.5 mg/kg). They then received low frequency ultrasound stimulation (20 kHz, 2 h intervals for a total of 24 h and each time lasted for 1 min) to induce release of GDNF into the right striatum. We found that low frequency ultrasound stimulation can induce lipid-coated GDNF microbubbles to release GDNF. Ultrasound-induced dissolution of lipid-coated GDNF microbubbles treatment reduced infarction volume and improved neurological outcomes in neonatal rats. In the meanwhile, the microbubbles attenuated the production of inducible nitric oxide synthase, nitric oxide and tumor necrosis factor-alpha, as well as the activation of caspase-3 in insulted side of brain in neonatal rats. These data demonstrated that ultrasound-induced dissolution of lipid-coated GDNF microbubbles treatment can provide a neuroprotective effect against hypoxia-ischemia in neonatal rats.

Induction of striatal neurogenesis enhances functional recovery in an adult animal model of neonatal hypoxic-ischemic brain injury

While intraventricular administration of epidermal growth factor (EGF) expands the proliferation of neural stem/progenitor cells in the subventricular zone (SVZ), overexpression of brain-derived neurotrophic factor (BDNF) is particularly effective in enhancing striatal neurogenesis. We assessed the induction of striatal neurogenesis and consequent functional recovery after chronic infusion of BDNF and EGF in an adult animal model of neonatal hypoxic-ischemic (HI) brain injury. Permanent brain damage was induced in CD-1 (ICR) mice (P7) by applying the ligation of unilateral carotid artery and hypoxic condition. At 6 weeks of age, the mice were randomly assigned to groups receiving a continuous 2-week infusion of one of the following treatments into the ventricle: BDNF, EGF, BDNF/EGF, or phosphate buffered saline (PBS). Two weeks after treatment, immunohistochemical analysis revealed an increase in the number of BrdU(+) cells in the SVZ and striata of BDNF/EGF-treated mice. The number of new neurons co-stained with BrdU and betaIII-tubulin was also significantly increased in the neostriata of BDNF/EGF-treated mice, compared with PBS group. In addition, the newly generated cells were expressed as migrating neuroblasts labeled with PSA-NCAM or doublecortin in the SVZ and the ventricular side of neostriata. The new striatal neurons were also differentiated as mature neurons co-labeled with BrdU(+)/NeuN(+). When evaluated post-surgical 8 weeks, BDNF/EGF-treated mice exhibited significantly longer rotarod latencies at constant speed (48 rpm) and under accelerating condition (4-80 rpm), relative to PBS and untreated controls. In the forelimb-use asymmetry test, BDNF/EGF-treated mice showed significant improvement in the use of the contralateral forelimb. In contrast, this BDNF/EGF-associated functional recovery was abolished in mice receiving a co-infusion of 2% cytosine-b-d-arabinofuranoside (Ara-C), a mitotic inhibitor. Induction of striatal neurogenesis by the intraventricular administration of BDNF and EGF promoted functional recovery in an adult animal model of neonatal HI brain injury. The effect of Ara-C to completely block functional recovery indicates that the effect may be the result of newly generated neurons. Therefore, this treatment may offer a promising strategy for the restoration of motor function for adults with cerebral palsy (CP).

Glial cell line-derived neurotrophic growth factor increases motility and survival of cultured mesenchymal stem cells and ameliorates acute kidney injury

Glial cell line-derived neurotrophic growth factor (GDNF), a member of the transforming growth factor family, is necessary for renal organogenesis and exhibits changes in expression in models of renal disease. Nestin is an intermediate filament protein originally believed to be a marker of neuroepithelial stem cells and recently proposed as a marker of mesenchymal stem cells (MSC). Having demonstrated the participation of nestin-expressing cells in renoprotection during acute renal ischemia, we hypothesized that growth factors and transcription factors similar to those operating in the nervous system should be also operant in the kidney and may be induced after noxious stimuli, such as an ischemic episode. Using cultured kidney-derived MSC, which abundantly express nestin, we confirmed expression of GDNF by these cells and demonstrated the GDNF-induced expression of GDNF. The cellular expression of nestin paralleled that of GDNF: serum starvation decreased the expression, whereas application of GDNF resulted in a dose-dependent increase in nestin expression. Immunohistochemical and Western blot analyses of kidneys obtained from control and postischemic mice showed that expression of GDNF was much enhanced in the renal cortex, a pattern similar to the previously reported expression of nestin. Based on the observed GDNF-induced GDNF expression, we next explored the effect of supplemental GDNF administered early after ischemia on renal function postischemia. GDNF-treated mice were protected against acute ischemia. To address potential mechanisms of the observed renoprotection, in vitro studies showed that GDNF accelerated MSC migration in a wound-healing assay. Hypoxia did not accelerate, but rather slightly reduced, the motility of MSC and reduced the expression of GDNF in MSC by approximately twofold. Furthermore, GDNF was cytoprotective against oxidative stress-induced apoptotic death of MSC. Collectively, these data establish 1) an autoregulatory circuit of GDNF-induced GDNF expression in renal MSC; 2) induction of GDNF expression in postischemic kidneys; 3) the ability of exogenous GDNF to ameliorate ischemic renal injury; and 4) a possible contribution of GDNF-induced motility and improved survival of MSC to renoprotection.

Apoptosis in perinatal hypoxic-ischemic brain injury: how important is it and should it be inhibited?

The discovery of safe and effective therapies for perinatal hypoxia-ischemia (HI) and stroke remains an unmet goal of perinatal medicine. Hypothermia and antioxidants such as allopurinol are currently under investigation as treatments for neonatal HI. Drugs targeting apoptotic mechanisms are currently being studied in adult diseases such as cancer, stroke, and trauma and have been proposed as potential therapies for perinatal HI and stroke. Before developing antiapoptosis therapies for perinatal brain injury, we must determine whether this form of cell death plays an important role in these injuries and if the inhibition of these pathways promotes more benefit than harm. This review summarizes current evidence for apoptotic mechanisms in perinatal brain injury and addresses issues pertinent to the development of antiapoptosis therapies for perinatal HI and stroke.