Inducible Expression of GDNF in Transplanted iPSC-Derived Neural Progenitor Cells

Trophic factor delivery to the brain using stem cell-derived neural progenitors is a powerful way to bypass the blood-brain barrier. Protection of diseased neurons using this technology is a promising therapy for neurodegenerative diseases. Glial cell line-derived neurotrophic factor (GDNF) has provided benefits to Parkinsonian patients and is being used in a clinical trial for amyotrophic lateral sclerosis. However, chronic trophic factor delivery prohibits dose adjustment or cessation if side effects develop. To address this, we engineered a doxycycline-regulated vector, allowing inducible and reversible expression of a therapeutic molecule. Human induced pluripotent stem cell (iPSC)-derived neural progenitors were stably transfected with the vector and transplanted into the adult mouse brain. Doxycycline can penetrate the graft, with addition and withdrawal providing inducible and reversible GDNF expression in vivo, over multiple cycles. Our findings provide proof of concept for combining gene and stem cell therapy for effective modulation of ectopic protein expression in transplanted cells.

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Created plasmid with tetracycline transactivator along with dual reporters and GDNF

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Efficient, stable transduction of human iPSC-derived neural progenitor cells

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Inducible and reversible in vivo expression of GDNF, reporter protein, and luciferase

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Promising stem cell and gene therapy strategy for neurodegenerative diseases

Systemic injection of AAV9-GDNF provides modest functional improvements in the SOD1G93A ALS rat but has adverse side effects

Injecting proteins into the central nervous system that stimulate neuronal growth can lead to beneficial effects in animal models of disease. In particular, glial cell line-derived neurotrophic factor (GDNF) has shown promise in animal and cell models of Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis (ALS). Here, systemic AAV9-GDNF was delivered via tail vein injections to young rats to determine whether this could be a safe and functional strategy to treat the SOD1^G93A rat model of ALS and, therefore, translated to a therapy for ALS patients. We found that GDNF administration in this manner resulted in modest functional improvement, whereby grip strength was maintained for longer and the onset of forelimb paralysis was delayed compared to non-treated rats. This did not, however, translate into an extension in survival. In addition, ALS rats receiving GDNF exhibited slower weight gain, reduced activity levels and decreased working memory. Collectively, these results confirm that caution should be applied when applying growth factors such as GDNF systemically to multiple tissues.

Ex vivo gene therapy for the treatment of neurological disorders

Ex vivo gene therapy involves the genetic modification of cells outside of the body to produce therapeutic factors and their subsequent transplantation back into patients. Various cell types can be genetically engineered. However, with the explosion in stem cell technologies, neural stem/progenitor cells and mesenchymal stem cells are most often used. The synergy between the effect of the new cell and the additional engineered properties can often provide significant benefits to neurodegenerative changes in the brain. In this review, we cover both preclinical animal studies and clinical human trials that have used ex vivo gene therapy to treat neurological disorders with a focus on Parkinson's disease, Huntington's disease, Alzheimer's disease, ALS, and stroke. We highlight some of the major advances in this field including new autologous sources of pluripotent stem cells, safer ways to introduce therapeutic transgenes, and various methods of gene regulation. We also address some of the remaining hurdles including tunable gene regulation, in vivo cell tracking, and rigorous experimental design. Overall, given the current outcomes from researchers and clinical trials, along with exciting new developments in ex vivo gene and cell therapy, we anticipate that successful treatments for neurological diseases will arise in the near future.

Human neural progenitors differentiate into astrocytes and protect motor neurons in aging rats

Age-associated health decline presents a significant challenge to healthcare, although there are few animal models that can be used to test potential treatments. Here, we show that there is a significant reduction in both spinal cord motor neurons and motor function over time in the aging rat. One explanation for this motor neuron loss could be reduced support from surrounding aging astrocytes. Indeed, we have previously shown using in vitro models that aging rat astrocytes are less supportive to rat motor neuron function and survival over time. Here, we test whether rejuvenating the astrocyte niche can improve the survival of motor neurons in an aging spinal cord. We transplanted fetal-derived human neural progenitor cells (hNPCs) into the aging rat spinal cord and found that the cells survive and differentiate into astrocytes with a much higher efficiency than when transplanted into younger animals, suggesting that the aging environment stimulates astrocyte maturation. Importantly, the engrafted astrocytes were able to protect against motor neuron loss associated with aging, although this did not result in an increase in motor function based on behavioral assays. We also transplanted hNPCs genetically modified to secrete glial cell line-derived neurotrophic factor (GDNF) into the aging rat spinal cord, as this combination of cell and protein delivery can protect motor neurons in animal models of ALS. During aging, GDNF-expressing hNPCs protected motor neurons, though to the same extent as hNPCs alone, and again had no effect on motor function. We conclude that hNPCs can survive well in the aging spinal cord, protect motor neurons and mature faster into astrocytes when compared to transplantation into the young spinal cord. While there was no functional improvement, there were no functional deficits either, further supporting a good safety profile of hNPC transplantation even into the older patient population.

Mifepristone-inducible transgene expression in neural progenitor cells in vitro and in vivo

Numerous gene and cell therapy strategies are being developed for the treatment of neurodegenerative disorders. Many of these strategies use constitutive expression of therapeutic transgenic proteins, and although functional in animal models of disease, this method is less likely to provide adequate flexibility for delivering therapy to humans. Ligand-inducible gene expression systems may be more appropriate for these conditions, especially within the central nervous system (CNS). Mifepristone's ability to cross the blood-brain barrier makes it an especially attractive ligand for this purpose. We describe the production of a mifepristone-inducible vector system for regulated expression of transgenes within the CNS. Our inducible system used a lentivirus-based vector platform for the ex vivo production of mifepristone-inducible murine neural progenitor cells that express our transgenes of interest. These cells were processed through a series of selection steps to ensure that the cells exhibited appropriate transgene expression in a dose-dependent and temporally controlled manner with minimal background activity. Inducible cells were then transplanted into the brains of rodents, where they exhibited appropriate mifepristone-inducible expression. These studies detail a strategy for regulated expression in the CNS for use in the development of safe and efficient gene therapy for neurological disorders.

The past, present and future of stem cell clinical trials for ALS

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder that is characterized by progressive degeneration of motor neurons in the cortex, brainstem and spinal cord. This leads to paralysis, respiratory insufficiency and death within an average of 3 to 5 years from disease onset. While the genetics of ALS are becoming more understood in familial cases, the mechanisms underlying disease pathology remain unclear and there are no effective treatment options. Without understanding what causes ALS it is difficult to design treatments. However, in recent years stem cell transplantation has emerged as a potential new therapy for ALS patients. While motor neuron replacement remains a focus of some studies trying to treat ALS with stem cells, there is more rationale for using stem cells as support cells for dying motor neurons as they are already connected to the muscle. This could be through reducing inflammation, releasing growth factors, and other potential less understood mechanisms. Prior to moving into patients, stringent pre-clinical studies are required that have at least some rationale and efficacy in animal models and good safety profiles. However, given our poor understanding of what causes ALS and whether stem cells may ameliorate symptoms, there should be a push to determine cell safety in pre-clinical models and then a quick translation to the clinic where patient trials will show if there is any efficacy. Here, we provide a critical review of current clinical trials using either mesenchymal or neural stem cells to treat ALS patients. Pre-clinical data leading to these trials, as well as those in development are also evaluated in terms of mechanisms of action, validity of conclusions and rationale for advancing stem cell treatment strategies for this devastating disorder.

Intermittent hypoxia and stem cell implants preserve breathing capacity in a rodent model of amyotrophic lateral sclerosis

RATIONALE

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease causing paralysis and death from respiratory failure. Strategies to preserve and/or restore respiratory function are critical for successful treatment. Although breathing capacity is maintained until late in disease progression in rodent models of familial ALS (SOD1(G93A) rats and mice), reduced numbers of phrenic motor neurons and decreased phrenic nerve activity are observed. Decreased phrenic motor output suggests imminent respiratory failure.

OBJECTIVES

To preserve or restore phrenic nerve activity in SOD1(G93A) rats at disease end stage.

METHODS

SOD1(G93A) rats were injected with human neural progenitor cells (hNPCs) bracketing the phrenic motor nucleus before disease onset, or exposed to acute intermittent hypoxia (AIH) at disease end stage.

MEASUREMENTS AND MAIN RESULTS

The capacity to generate phrenic motor output in anesthetized rats at disease end stage was: (1) transiently restored by a single presentation of AIH; and (2) preserved ipsilateral to hNPC transplants made before disease onset. hNPC transplants improved ipsilateral phrenic motor neuron survival.

CONCLUSIONS

AIH-induced respiratory plasticity and stem cell therapy have complementary translational potential to treat breathing deficits in patients with ALS.

Stem cell transplantation for motor neuron disease: current approaches and future perspectives

Motor neuron degeneration leading to muscle atrophy and death is a pathological hallmark of disorders, such as amyotrophic lateral sclerosis or spinal muscular atrophy. No effective treatment is available for these devastating diseases. At present, cell-based therapies targeting motor neuron replacement, support, or as a vehicle for the delivery of neuroprotective molecules are being investigated. Although many challenges and questions remain, the beneficial effects observed following transplantation therapy in animal models of motor neuron disease has sparked hope and a number of clinical trials. Here, we provide a comprehensive review of cell-based therapeutics for motor neuron disorders, with a particular emphasis on amyotrophic lateral sclerosis.

How to get from here to there: macrophage recruitment in Alzheimer's disease

Alzheimer's disease (AD) is pathologically defined by presence of intracellular neurofibrillary tangles and extracellular amyloid plaques comprised of amyoid-β (Aβ) peptides. Despite local recruitment of brain microglia to sites of amyloid deposition, these mononuclear phagocytes ultimately fail at restricting β-amyloid plaque formation. On the other hand, it is becoming increasingly clear that professional phagocytes from the periphery possess Aβ clearance aptitude. Yet, in order to harness this beneficial innate immune response, effective strategies must be developed to coax monocytes/macrophages from the periphery into the brain. It has previously been suggested that Aβ 'immunotherapy' clears cerebral Aβ deposits via mononuclear phagocytes, and recent evidence suggests that targeting transforming growth factor-β-Smad 2/3 signaling and chemokine pathways such as Ccr2 impacts blood-to-brain trafficking of these cells in transgenic mouse models of AD. It has also been shown that the fractalkine receptor (Cx3cr1) pathway plays a critical role in chemotaxis of mononuclear phagocytes toward neurons destined for death in AD model mice. In order to translate these basic science findings into AD treatments, a key challenge will be to develop a new generation of pharmacotherapeutics that safely and effectively promote recruitment of peripheral amyloid phagocytes into the AD brain.

Conference Scene: ALS in California: a report from the First Annual California ALS Research Summit

In June 2010, the first California Amyotrophic Lateral Sclerosis (ALS) Research Summit gathered major California neuroscientists in San Francisco to outline the state of ALS research and discussion a strategic roadmap for innovative ALS research in California. The Summit was developed as part of the greater vision of the California ALS Network, whose goal is to delineate a road map for important ALS research and to increase state support for ALS research, patient care and treatment. During the 2-day summit, clinical, industry and basic researchers from the fields of stem cells, protein aggregation and molecular therapies provided updates on the current status of ALS research. Summarized here are the presentations and discussions from the meeting.

Altered immune response to CNS viral infection in mice with a conditional knock-down of macrophage-lineage cells

Neuroadapted Sindbis Virus (NSV) is a neuronotropic virus that causes hindlimb paralysis in susceptible mice and rats. The authors and others have demonstrated that though death of infected motor neurons occurs, bystander death of uninfected neurons also occurs and both contribute to the paralysis that ensues following infection. The authors have previously shown that the treatment of NSV-infected mice with minocycline, an inhibitor that has many functions within the central nervous system (CNS), including inhibiting microglial activation, protects mice from paralysis and death. The authors, therefore, proposed that microglial activation may contribute to bystander death of motor neurons following NSV infection. Here, the authors tested the hypothesis using a conditional knock-out of activated macrophage-lineage cells, including endogenous CNS macrophage cells. Surprisingly, ablation of these cells resulted in more rapid death and similar weakness in the hind limbs of NSV-infected animals compared with that of control animals. Several key chemokines including IL-12 and monocyte chemoattractant protein-1 (MCP-1) did not become elevated in these animals, resulting in decreased infiltration of T lymphocytes into the CNS of the knock-down animals. Either because of the decreased macrophage activation directly or because of the reduced immune cell influx, viral replication persisted longer within the nervous system in knock-down mice than in wild type mice. The authors, therefore, conclude that although macrophage-lineage cells in the CNS may contribute to neurodegeneration in certain situations, they also serve a protective role, such as control of viral replication.

Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer's disease

Microglia are the immune cells of the brain. Here we show a massive infiltration of highly ramified and elongated microglia within the core of amyloid plaques in transgenic mouse models of Alzheimer's disease (AD). Many of these cells originate from the bone marrow, and the beta-amyloid-40 and -42 isoforms are able to trigger this chemoattraction. These newly recruited cells also exhibit a specific immune reaction to both exogenous and endogenous beta-amyloid in the brain. Creation of a new AD transgenic mouse that expresses the thymidine kinase protein under the control of the CD11b promoter allowed us to show that blood-derived microglia and not their resident counterparts have the ability to eliminate amyloid deposits by a cell-specific phagocytic mechanism. These bone marrow-derived microglia are thus very efficient in restricting amyloid deposits. Therapeutic strategies aiming to improve their recruitment could potentially lead to a new powerful tool for the elimination of toxic senile plaques.

Activation of the p38MAPK cascade is associated with upregulation of TNF alpha receptors in the spinal motor neurons of mouse models of familial ALS

Phosphorylated p38 mitogen-activated protein kinase (p38MAPK), but not activated c-jun-N-terminal kinase (JNK), increases in the motor neurons of transgenic mice overexpressing ALS-linked SOD1 mutants at different stages of the disease. This effect is associated with a selective increase of phosphorylated MKK3-6, MKK4 and ASK1 and a concomitant upregulation of the TNFalpha receptors (TNFR1 and TNFR2), but not IL1beta and Fas receptors. Activation of both p38 MAPK and JNK occurs in the activated microglial cells of SOD1 mutant mice at the advanced stage of the disease; however, this effect is not accompanied by the concomitant activation of the upstream kinases ASK1 and MKK3,4,6, while both the TNFRs are overexpressed in these cells. No changes of the upstream p38MAPK cascade kinases or TNFRs occur in reactive astrocytes. These findings highlight the activation of a selective intracellular signaling pathway in the motor neurons of SOD1 mutant mice, which is likely implicated in their death.

An inexpensive photographic technique for identifying nest predators at active nests of birds

Change in rate of nest predation due to environmental modification is considered a major cause of population decline of many bird species. Our ability to adequately understand and effectively manage this effect is limited by our ability to identify the relative roles of individual nest predators. This is because nest predation is seldom witnessed despite its high frequency. We describe and evaluate an inexpensive photographic technique for identifying nest predators at active nests. Each camera unit (A$220) was triggered by circuitry (A$30), using a magnetic reed switch attached to a supplementary egg. A total of 51 nests of New Holland honeyeaters (Phylidonyris novaehollandiae) was monitored with the equipment. Of these, 39 were preyed upon. Predation was never witnessed, but predators were captured on film for 72% of nests at which predation occurred.

Causes and Frequencey of Deaths among Birds Mist-Netted for Banding Studies at Two Localities

During studies of forest and heathland birds undertaken by the authors in south-eastem Australia, 53 (1.3%) of 4184 birds caught in mist nets died in the nets or when handled for banding. Mortality was higher in the study offorest birds, where 2.8% of individuals died, than in that of heathland birds, where 0.5% died. There was no relation between the size or kinds of birds handled and mortality. Instead, the difference between the two studies was probably the result of better procedures for handling birds in the heathland study. Causes of mortality, and ways to avoid or minimize injury to or death of birds during use of mist-nets, are discussed.