AAV9-mediated erythropoietin gene delivery into the brain protects nigral dopaminergic neurons in a rat model of Parkinson's disease

Pharmacokinetics of AAV9 Mediated Trastuzumab Expression in Rat Brain Following Systemic and Local Administration

INTRODUCTION

Recombinant adeno-associated viruses(rAAVs) are an attractive tool to ensure long-term expression monoclonal antibody(mAb) in the central nervous system(CNS). It is still unclear whether systemic injection or local CNS administration of AAV9 is more beneficial for the exposure of the expressed mAb in the brain. Hence, we compared the biodistribution and transgene expression following AAV9-Trastuzumab administration through different routes.

METHODS AND RESULT

In-house generated AAV9-Trastuzumab vectors were administered at 5E+11 Vgs/rat through intravenous(IV), intracerebroventricular(ICV), intra-cisterna magna(ICM) and intrastriatal(IST) routes. Vector and trastuzumab blood/plasma concentrations were assessed at different time points up to the terminal time point of 21 days. Different brain regions in addition to the spinal cord, cerebrospinal fluid(CSF) and interstitial fluid(ISF), were also analyzed at the terminal time point. Our results show that vector biodistribution and Trastuzumab expression in the brain could the ranked as follows: IST>ICM>ICV>IV. Rapid clearance of vector was observed after administration via the ICM and ICV routes. The ICV route produced similar expression levels across different brain regions, while the ICM route had better expression in the hindbrain and spinal cord region. The IST route had higher expression in the forebrain region compared to the hindbrain region. A sharp decline in trastuzumab plasma concentration was observed across all routes of administration due to anti-trastuzumab antibody response.

CONCLUSION

In this study we have characterized vector biodistribution and transgene mAb expression after AAV9 vector administration through different routes in rats. IST and ICM represent the best administration routes to deliver antibody genes to the brain.

Fibroblast growth factor 10 ameliorates neurodegeneration in mouse and cellular models of Alzheimer's disease via reducing tau hyperphosphorylation and neuronal apoptosis

Alzheimer's disease (AD) is characterized with senile plaques formed by Aβ deposition, and neurofibrillary tangles composed of hyperphosphorylated tau protein, which ultimately lead to cognitive impairment. Despite the heavy economic and life burdens faced by the patients with AD, effective treatments are still lacking. Previous studies have reported the neuroprotective effects of FGF10 in CNS diseases, but its role in AD remains unclear. In this study, we demonstrated that FGF10 levels were reduced in the serum of AD patients, as well as in the brains of 3xTg-AD mice and APPswe-transfected HT22 cells, suggesting a close relationship between FGF10 and AD. Further investigations revealed that intranasal delivery of FGF10 improved cognitive functions in 3xTg-AD mice. Additionally, FGF10 treatment reduced tau hyperphosphorylation and neuronal apoptosis, thereby mitigating neuronal cell damage and synaptic deficits in the cortex and hippocampus of 3xTg-AD mice, as well as APPswe-transfected HT22 cells. Furthermore, we evaluated the therapeutic potential of FGF10 gene delivery for treating AD symptoms and pathologies. Tail vein delivery of the FGF10 gene using AAV9 improved cognitive and neuronal functions in 3xTg-AD mice. Similarly, endogenous FGF10 overexpression ameliorated tau hyperphosphorylation and neuronal apoptosis in the cortex and hippocampus of 3xTg-AD mice. Importantly, we confirmed that the FGFR2/PI3K/AKT signaling pathway was activated following intranasal FGF10 delivery and AAV9-mediated FGF10 gene delivery in 3xTg-AD mice and APPswe-transfected HT22 cells. Knockdown of FGFR2 attenuated the protective effect of FGF10. Collectively, these findings suggest that intranasal delivery of FGF10 and AAV9-mediated FGF10 gene delivery could be a promising disease-modifying therapy for AD.

Neurotrophic Factors as Regenerative Therapy for Neurodegenerative Diseases: Current Status, Challenges and Future Perspectives

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS), spinal cord injury (SCI), and amyotrophic lateral sclerosis (ALS), are characterized by acute or chronic progressive loss of one or several neuronal subtypes. However, despite their increasing prevalence, little progress has been made in successfully treating these diseases. Research has recently focused on neurotrophic factors (NTFs) as potential regenerative therapy for neurodegenerative diseases. Here, we discuss the current state of knowledge, challenges, and future perspectives of NTFs with a direct regenerative effect in chronic inflammatory and degenerative disorders. Various systems for delivery of NTFs, such as stem and immune cells, viral vectors, and biomaterials, have been applied to deliver exogenous NTFs to the central nervous system, with promising results. The challenges that currently need to be overcome include the amount of NTFs delivered, the invasiveness of the delivery route, the blood-brain barrier permeability, and the occurrence of side effects. Nevertheless, it is important to continue research and develop standards for clinical applications. In addition to the use of single NTFs, the complexity of chronic inflammatory and degenerative diseases may require combination therapies targeting multiple pathways or other possibilities using smaller molecules, such as NTF mimetics, for effective treatment.

Erythropoietin in Glaucoma: From Mechanism to Therapy

Glaucoma can cause irreversible vision loss and is the second leading cause of blindness worldwide. The disease mechanism is complex and various factors have been implicated in its pathogenesis, including ischemia, excessive oxidative stress, neurotropic factor deprivation, and neuron excitotoxicity. Erythropoietin (EPO) is a hormone that induces erythropoiesis in response to hypoxia. However, studies have shown that EPO also has neuroprotective effects and may be useful for rescuing apoptotic retinal ganglion cells in glaucoma. This article explores the relationship between EPO and glaucoma and summarizes preclinical experiments that have used EPO to treat glaucoma, with an aim to provide a different perspective from the current view that glaucoma is incurable.

PEG-mediated transduction of rAAV as a platform for spatially confined and efficient gene delivery

BACKGROUND

Recombinant adeno-associated viruses (rAAV) are commonly used vectors for gene delivery in both basic neuroscience and clinical applications due to their nonpathogenic, minimally immunogenic, and sustained expression properties. However, several challenges remain for the wide-scale rAAV applications, including poor infection of many clinically important cell lines, insufficient expression at low titers, and diffusive transduction in vivo.

METHODS

In this work, PEG, which is a safe and non-toxic polymer of ethylene oxide monomer, was applied as an auxiliary transduction agent to improve the expression of rAAV. In detail, a small dose of PEG was added into the rAAV solution for the transgene expression in cell lines in vitro, and in the central nervous system (CNS) in vivo. The biocompatibility of PEG enhancer was assessed by characterizing the immune responses, cell morphology, cell tropism of rAAV, neuronal apoptosis, as well as motor function of animals.

RESULTS

The results show that small dose of PEG additive can effectively improve the gene expression characteristics of rAAV both in vitro and in vivo. Specifically, the PEG additive allows efficient transgene expression in cell lines that are difficult to be transfected with rAAV alone. In vivo studies show that the PEG additive can promote a spatially confined and efficient transgene expression of low-titer rAAV in the brain over long terms. In addition, no obvious side effects of PEG were observed on CNS in the biocompatibility studies.

CONCLUSIONS

This spatially confined and efficient transduction method can facilitate the applications of rAAV in fundamental research, especially in the precise dissection of neural circuits, and also improve the capabilities of rAAV in the treatment of neurological diseases which originate from the disorders of small nuclei in the brain.

The Effect of Neuroepo on Cognition in Parkinson's Disease Patients Is Mediated by Electroencephalogram Source Activity

We report on the quantitative electroencephalogram (qEEG) and cognitive effects of Neuroepo in Parkinson's disease (PD) from a double-blind safety trial (https://clinicaltrials.gov/, number NCT04110678). Neuroepo is a new erythropoietin (EPO) formulation with a low sialic acid content with satisfactory results in animal models and tolerance in healthy participants and PD patients. In this study, 26 PD patients were assigned randomly to Neuroepo (n = 15) or placebo (n = 11) groups to test the tolerance of the drug. Outcome variables were neuropsychological tests and resting-state source qEEG at baseline and 6 months after administering the drug. Probabilistic Canonical Correlation Analysis was used to extract latent variables for the cognitive and for qEEG variables that shared a common source of variance. We obtained canonical variates for Cognition and qEEG with a correlation of 0.97. Linear Mixed Model analysis showed significant positive dependence of the canonical variate cognition on the dose and the confounder educational level (p = 0.003 and p = 0.02, respectively). Additionally, in the mediation equation, we found a positive dependence of Cognition with qEEG for (p = < 0.0001) and with dose (p = 0.006). Despite the small sample, both tests were powered over 89%. A combined mediation model showed that 66% of the total effect of the cognitive improvement was mediated by qEEG (p = 0.0001), with the remaining direct effect between dose and Cognition (p = 0.002), due to other causes. These results suggest that Neuroepo has a positive influence on Cognition in PD patients and that a large portion of this effect is mediated by brain mechanisms reflected in qEEG.

Current knowledge and challenges associated with targeted delivery of neurotrophic factors into the central nervous system: focus on available approaches

During the last decades, numerous basic and clinical studies have been conducted to assess the delivery efficiency of therapeutic agents into the brain and spinal cord parenchyma using several administration routes. Among conventional and in-progress administrative routes, the eligibility of stem cells, viral vectors, and biomaterial systems have been shown in the delivery of NTFs. Despite these manifold advances, the close association between the delivery system and regeneration outcome remains unclear. Herein, we aimed to discuss recent progress in the delivery of these factors and the pros and cons related to each modality.

Adeno-Associated Viral Vectors as Versatile Tools for Parkinson's Research, Both for Disease Modeling Purposes and for Therapeutic Uses

It is without any doubt that precision medicine therapeutic strategies targeting neurodegenerative disorders are currently witnessing the spectacular rise of newly designed approaches based on the use of viral vectors as Trojan horses for the controlled release of a given genetic payload. Among the different types of viral vectors, adeno-associated viruses (AAVs) rank as the ones most commonly used for the purposes of either disease modeling or for therapeutic strategies. Here, we reviewed the current literature dealing with the use of AAVs within the field of Parkinson’s disease with the aim to provide neuroscientists with the advice and background required when facing a choice on which AAV might be best suited for addressing a given experimental challenge. Accordingly, here we will be summarizing some insights on different AAV serotypes, and which would be the most appropriate AAV delivery route. Next, the use of AAVs for modeling synucleinopathies is highlighted, providing potential readers with a landscape view of ongoing pre-clinical and clinical initiatives pushing forward AAV-based therapeutic approaches for Parkinson’s disease and related synucleinopathies.

Riboswitches for Controlled Expression of Therapeutic Transgenes Delivered by Adeno-Associated Viral Vectors

Vectors developed from adeno-associated virus (AAV) are powerful tools for in vivo transgene delivery in both humans and animal models, and several AAV-delivered gene therapies are currently approved for clinical use. However, AAV-mediated gene therapy still faces several challenges, including limited vector packaging capacity and the need for a safe, effective method for controlling transgene expression during and after delivery. Riboswitches, RNA elements which control gene expression in response to ligand binding, are attractive candidates for regulating expression of AAV-delivered transgene therapeutics because of their small genomic footprints and non-immunogenicity compared to protein-based expression control systems. In addition, the ligand-sensing aptamer domains of many riboswitches can be exchanged in a modular fashion to allow regulation by a variety of small molecules, proteins, and oligonucleotides. Riboswitches have been used to regulate AAV-delivered transgene therapeutics in animal models, and recently developed screening and selection methods allow rapid isolation of riboswitches with novel ligands and improved performance in mammalian cells. This review discusses the advantages of riboswitches in the context of AAV-delivered gene therapy, the subsets of riboswitch mechanisms which have been shown to function in human cells and animal models, recent progress in riboswitch isolation and optimization, and several examples of AAV-delivered therapeutic systems which might be improved by riboswitch regulation.

Next Step in Gene Delivery: Modern Approaches and Further Perspectives of AAV Tropism Modification

Today, adeno-associated virus (AAV) is an extremely popular choice for gene therapy delivery. The safety profile and simplicity of the genome organization are the decisive advantages which allow us to claim that AAV is currently among the most promising vectors. Several drugs based on AAV have been approved in the USA and Europe, but AAV serotypes’ unspecific tissue tropism is still a serious limitation. In recent decades, several techniques have been developed to overcome this barrier, such as the rational design, directed evolution and chemical conjugation of targeting molecules with a capsid. Today, all of the abovementioned approaches confer the possibility to produce AAV capsids with tailored tropism, but recent data indicate that a better understanding of AAV biology and the growth of structural data may theoretically constitute a rational approach to most effectively produce highly selective and targeted AAV capsids. However, while we are still far from this goal, other approaches are still in play, despite their drawbacks and limitations.

Long-term treatment with transcranial pulsed electromagnetic fields improves movement speed and elevates cerebrospinal erythropoietin in Parkinson's disease

Background

Parkinson’s disease is characterized by motor dysfunctions including bradykinesia. In a recent study, eight weeks of daily transcranial stimulation with bipolar pulsed electromagnetic fields improved functional rate of force development and decreased inter-hand tremor coherence in patients with mild Parkinson’s disease.

Objective

To investigate the effect of long-term treatment with transcranial bipolar pulsed electromagnetic fields on motor performance in terms of movement speed and on neurotrophic and angiogenic factors.

Methods

Patients diagnosed with idiopathic Parkinson’s disease had either daily 30-min treatment with bipolar (±50 V) transcranial pulsed electromagnetic stimulation (squared pulses, 3ms duration) for three eight-week periods separated by one-week pauses (T-PEMF group) (n = 16) or were included in a PD-control group (n = 8). Movement speed was assessed in a six-cycle sit-to-stand task performed on a force plate. Cerebrospinal fluid and venous blood were collected and analyzed for erythropoietin and vascular endothelial growth factor.

Results

Major significant improvement of movement speed compared to the natural development of the disease was found (p = 0.001). Thus, task completion time decreased gradually during the treatment period from 10.10s to 8.23s (p<0.001). The untreated PD-control group did not change (p = 0.458). The treated group did not differ statistically from that of a healthy age matched reference group at completion of treatment. Erythropoietin concentration in the cerebrospinal fluid also increased significantly in the treated group (p = 0.012).

Conclusion

Long-term treatment with transcranial bipolar pulsed electromagnetic fields increased movement speed markedly and elevated erythropoietin levels. We hypothesize that treatment with transcranial bipolar pulsed electromagnetic fields improved functional performance by increasing dopamine levels in the brain, possibly through erythropoietin induced neural repair and/or protection of dopaminergic neurons.

Emerging Technologies for Delivery of Biotherapeutics and Gene Therapy Across the Blood-Brain Barrier

Antibody, immuno- and gene therapies developed for neurological indications face a delivery challenge posed by various anatomical and physiological barriers within the central nervous system (CNS); most notably, the blood–brain barrier (BBB). Emerging delivery technologies for biotherapeutics have focused on trans-cellular pathways across the BBB utilizing receptor-mediated transcytosis (RMT). ‘Traditionally’ targeted RMT receptors, transferrin receptor (TfR) and insulin receptor (IR), are ubiquitously expressed and pose numerous translational challenges during development, including species differences and safety risks. Recent advances in antibody engineering technologies and discoveries of RMT targets and BBB-crossing antibodies that are more BBB-selective have combined to create a new preclinical pipeline of BBB-crossing biotherapeutics with improved efficacy and safety. Novel BBB-selective RMT targets and carrier antibodies have exposed additional opportunities for re-targeting gene delivery vectors or nanocarriers for more efficient brain delivery. Emergence and refinement of core technologies of genetic engineering and editing as well as biomanufacturing of viral vectors and cell-derived products have de-risked the path to the development of systemic gene therapy approaches for the CNS. In particular, brain-tropic viral vectors and extracellular vesicles have recently expanded the repertoire of brain delivery strategies for biotherapeutics. Whereas protein biotherapeutics and bispecific antibodies enabled for BBB transcytosis are rapidly heading towards clinical trials, systemic gene therapy approaches for CNS will likely remain in research phase for the foreseeable future. The promise and limitations of these emerging cross-BBB delivery technologies are further discussed in this article.

Overcoming the Blood–Brain Barrier. Challenges and Tricks for CNS Drug Delivery

Treatment of certain central nervous system disorders, including different types of cerebral malignancies, is limited by traditional oral or systemic administrations of therapeutic drugs due to possible serious side effects and/or lack of the brain penetration and, therefore, the efficacy of the drugs is diminished. During the last decade, several new technologies were developed to overcome barrier properties of cerebral capillaries. This review gives a short overview of the structural elements and anatomical features of the blood–brain barrier. The various in vitro (static and dynamic), in vivo (microdialysis), and in situ (brain perfusion) blood–brain barrier models are also presented. The drug formulations and administration options to deliver molecules effectively to the central nervous system (CNS) are presented. Nanocarriers, nanoparticles (lipid, polymeric, magnetic, gold, and carbon based nanoparticles, dendrimers, etc.), viral and peptid vectors and shuttles, sonoporation and microbubbles are briefly shown. The modulation of receptors and efflux transporters in the cell membrane can also be an effective approach to enhance brain exposure to therapeutic compounds. Intranasal administration is a noninvasive delivery route to bypass the blood–brain barrier, while direct brain administration is an invasive mode to target the brain region with therapeutic drug concentrations locally. Nowadays, both technological and mechanistic tools are available to assist in overcoming the blood–brain barrier. With these techniques more effective and even safer drugs can be developed for the treatment of devastating brain disorders.

Delivery of Glucosylceramidase Beta Gene Using AAV9 Vector Therapy as a Treatment Strategy in Mouse Models of Gaucher Disease

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the GBA gene. Enzyme replacement treatment is the most effective therapy available for type 1 GD patients, but it is very expensive and does not improve neurologic outcomes in type 2 and 3 GD patients. This study evaluated the effectiveness of an adeno-associated virus 9 (AAV9) vector expressing the Gba gene delivered systemically in GD mouse models. To detect the therapeutic effects of the AAV9-mediated Gba transfer on the systemic symptoms of GD, an inducible whole-body Gba knockout mouse was developed in which tamoxifen effectively induced whole-body Gba gene deletion, and the mice displayed systemic symptoms of GD. The AAV9-CMV-Gba vector, with the expression of Gba driven by the universal CMV promoter, restored GCase activity in multiple organs and prolonged the lifespan in tamoxifen-induced GD mice after intravenous injection. Mice with brain-specific Gba deletion were also included in this study as a model of neuropathic GD (nGD) and injected intraperitoneally on postnatal day 5 with the AAV9-SYN-Gba vector; this improved the GCase activity, ameliorated the neuropathological changes and extended the mean lifespan two-fold. This study demonstrates that AAV9-mediated gene transfer is a potentially effective treatment for GD.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

Transfection of primary brain capillary endothelial cells for protein synthesis and secretion of recombinant erythropoietin: a strategy to enable protein delivery to the brain

Treatment of chronic disorders affecting the central nervous system (CNS) is complicated by the inability of drugs to cross the blood-brain barrier (BBB). Non-viral gene therapy applied to brain capillary endothelial cells (BCECs) denotes a novel approach to overcome the restraints in this passage, as turning BCECs into recombinant protein factories by transfection could result in protein secretion further into the brain. The present study aims to investigate the possibility of transfecting primary rat brain endothelial cells (RBECs) for recombinant protein synthesis and secretion of the neuroprotective protein erythropoietin (EPO). We previously showed that 4% of RBECs with BBB properties can be transfected without disrupting the BBB integrity in vitro, but it can be questioned whether this is sufficient to enable protein secretion at therapeutic levels. The present study examined various transfection vectors, with regard to increasing the transfection efficiency without disrupting the BBB integrity. Lipofectamine 3000™ was the most potent vector compared to polyethylenimine (PEI) and Turbofect. When co-cultured with astrocytes, the genetically modified RBECs secreted recombinant EPO into the cell culture medium both luminally and abluminally, and despite lower levels of EPO reaching the abluminal chamber, the amount of recombinant EPO was sufficient to evolve a biological effect on astrocytes cultured at the abluminal side in terms of upregulated gene expression of brain-derived neurotropic factor (BDNF). In conclusion, non-viral gene therapy to RBECs leads to protein secretion and signifies a method for therapeutic proteins to target cells inside the CNS otherwise omitted due to the BBB.

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.

Non-invasive approaches for drug delivery to the brain based on the receptor mediated transport

The blood brain barrier (BBB) is a physical and biochemical barrier that prevents entry of toxic compounds into brain for preserving homeostasis. However, the BBB also strictly limits influx of most therapeutic agents into the brain. One promising method for overcoming this problem to deliver drugs is receptor mediated transport (RMT) system, which employs the vesicular trafficking machinery to transport substrates across the BBB endothelium in a noninvasive manner. The conjugates of drug or drug-loaded vector linked with appropriate ligands specifically binds to the endogenous targeting receptor on the surface of the endothelial cells. Then drugs could enter the cell body by means of transcytosis and eventual releasing into the brain parenchyma. Over the past 20years, there have been significant developments of RMT targeting strategies. Here, we will review the recent advance of various promising RMT systems and discuss the capability of these approaches for drug delivery to the brain.

Long-term protective effects of AAV9-mesencephalic astrocyte-derived neurotrophic factor gene transfer in parkinsonian rats

Intrastriatal injection of mesencephalic astrocyte-derived neurotrophic factor (MANF) protein has been shown to provide neuroprotective and neurorestorative effects in a 6-hydroxydopamine (6-OHDA) - lesioned rat model of Parkinson's disease. Here, we used an adeno-associated virus serotype 9 (AAV9) vector to deliver the human MANF (hMANF) gene into the rat striatum 10days after a 6-OHDA lesion to examine long-term effects of hMANF on nigral dopaminergic neurons and mechanisms underlying MANF neuroprotection. Intrastriatal injection of AAV9-hMANF vectors led to a robust and widespread expression of the hMANF gene in the injected striatum up to 24weeks. Increased levels of hMANF protein were also detected in the ipsilateral substantia nigra. The hMANF gene transfer promoted the survival of nigral dopaminergic neurons, regeneration of striatal dopaminergic fibers and an upregulation of striatal dopamine levels, resulting in a long-term improvement of rotational behavior up to 16weeks after viral injections. By using SH-SY5Y cells, we found that intra- and extracellular application of MANF protected cells against 6-OHDA-induced toxicity via inhibiting the endoplasmic reticulum stress and activating the PI3K/Akt/mTOR pathway. Our results suggest that AAV9-mediated hMANF gene delivery into the striatum exerts long-term neuroprotective and neuroregenerative effects on the nigrostriatal dopaminergic system in parkinsonian rats, and provide insights into mechanisms responsible for MANF neuroprotection.

Isoforms of the Erythropoietin receptor in dopaminergic neurons of the Substantia Nigra

Erythropoietin receptor (EpoR) regulates erythrocytes differentiation in blood. In the brain, EpoR has been shown to protect several neuronal cell types from cell death, including the A9 dopaminergic neurons (DA) of the Substantia Nigra (SN). These cells form the nigrostriatal pathway and are devoted to the control of postural reflexes and voluntary movements. Selective degeneration of A9 DA neurons leads to Parkinson's disease. By the use of nanoCAGE, a technology that allows the identification of Transcription Start Sites (TSSs) at a genome-wide level, we have described the promoter-level expression atlas of mouse A9 DA neurons purified with Laser Capture Microdissection (LCM). Here, we identify mRNA variants of the Erythropoietin Receptor (DA-EpoR) transcribed from alternative TSSs. Experimental validation and full-length cDNA cloning is integrated with gene expression analysis in the FANTOM5 database. In DA neurons, the EpoR gene encodes for a N-terminal truncated receptor. Based on STAT5 phosphorylation assays, we show that the new variant of N-terminally truncated EpoR acts as decoy when co-expressed with the full-length form. A similar isoform is also found in human. This work highlights new complexities in the regulation of Erythropoietin (EPO) signaling in the brain.

Gene therapy for the CNS using AAVs: The impact of systemic delivery by AAV9

Several attempts have been made to discover the ideal vector for gene therapy in central nervous system (CNS). Adeno-associated viruses (AAVs) are currently the preferred vehicle since they exhibit stable transgene expression in post-mitotic cells, neuronal tropism, low risk of insertional mutagenesis and diminished immune responses. Additionally, the discovery that a particular serotype, AAV9, bypasses the blood-brain barrier has raised the possibility of intravascular administration as a non-invasive delivery route to achieve widespread CNS gene expression. AAV9 intravenous delivery has already shown promising results for several diseases in animal models, including lysosomal storage disorders and motor neuron diseases, opening the way to the first clinical trial in the field. This review presents an overview of clinical trials for CNS disorders using AAVs and will focus on preclinical studies based on the systemic gene delivery using AAV9.

Erythropoietin reduces apoptosis of brain tissue cells in rats after cerebral ischemia/reperfusion injury: a characteristic analysis using magnetic resonance imaging

Some in vitro experiments have shown that erythropoietin (EPO) increases resistance to apoptosis and facilitates neuronal survival following cerebral ischemia. However, results from in vivo studies are rarely reported. Perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) have been applied successfully to distinguish acute cerebral ischemic necrosis and penumbra in living animals; therefore, we hypothesized that PWI and DWI could be used to provide imaging evidence in vivo for the conclusion that EPO could reduce apoptosis in brain areas injured by cerebral ischemia/reperfusion. To validate this hypothesis, we established a rat model of focal cerebral ischemia/reperfusion injury, and treated with intra-cerebroventricular injection of EPO (5,000 U/kg) 20 minutes before injury. Brain tissue in the ischemic injury zone was sampled using MRI-guided localization. The relative area of abnormal tissue, changes in PWI and DWI in the ischemic injury zone, and the number of apoptotic cells based on TdT-mediated dUTP-biotin nick end-labeling (TUNEL) were assessed. Our findings demonstrate that EPO reduces the relative area of abnormally high signal in PWI and DWI, increases cerebral blood volume, and decreases the number of apoptotic cells positive for TUNEL in the area injured by cerebral ischemia/reperfusion. The experiment provides imaging evidence in vivo for EPO treating cerebral ischemia/reperfusion injury.

Generation and characterization of anti-Adeno-associated virus serotype 8 (AAV8) and anti-AAV9 monoclonal antibodies

Adeno-associated viruses (AAVs) are promising viral vectors for therapeutic gene delivery, and the approval of an AAV1 vector for the treatment of lipoprotein lipase deficiency has heralded a new and exciting era for this system. However, preclinical and clinical studies show that neutralization from pre-existing antibodies is detrimental for medical application and this hurdle must be overcome before full clinical realization can be achieved. Thus the binding sites for capsid antibodies must be identified and eliminated through capsid engineering. Towards this goal and to recapitulate patient polyclonal responses, a panel of six new mouse monoclonal antibodies (MAbs) has been generated against AAV8 and AAV9 capsids, two vectors being developed for therapeutic application. Native (capsid) dot blot assays confirmed the specificity of these antibodies for their parental serotypes, with the exception of one MAb, HL2372, selected to cross-react against both capsids. Furthermore, in vitro assays showed that these MAbs are capable of neutralizing virus infection. These MAbs will be utilized for structural mapping of antigenic footprints on their respective capsids to inform development of the next generation of rAAV vectors capable of evading antibody neutralization while retaining parental tropism.

Sequential Adeno-Associated Viral Vector Serotype 9-Green Fluorescent Protein Gene Transfer Causes Massive Inflammation and Intense Immune Response in Rat Striatum

Green fluorescent protein (GFP) is a broadly used live cell reporter for gene transduction although side effects associated with GFP in gene transfer are reported. The present study was designed to systematically examine host responses, including inflammatory and immune responses, induced by persistent overexpression of the GFP gene mediated by adeno-associated viral vector serotype 9 (AAV9), and their effects on GFP gene transduction in rat striatum. Our results show that host responses against AAV9-GFP transduction, and GFP transgene expression in the striatum exhibited a temporal and dose-dependent pattern. Both muscular and striatal delivery of AAV9-GFP increased levels of inflammation and immune reactions against sequential AAV9-GFP transduction in the striatum, leading to reduced levels of GFP expression. We also observed that rat sera from sequential administrations of AAV9-GFP group had significantly higher levels of neutralizing antibody against AAV9 vectors when compared with the age-matched rats. As excessive GFP can trigger vigorous inflammation and intense immune response after GFP gene transduction, the use of GFP as a live cell marker protein should be deliberated, especially in repeated administration studies.

Intranasal gene delivery for treating Parkinson's disease: overcoming the blood-brain barrier

INTRODUCTION

Developing a disease-modifying gene therapy for Parkinson's disease (PD) has been a high priority for over a decade. However, due to the inability of large biomolecules to cross the blood-brain barrier (BBB), the only means of delivery to the brain has been intracerebral infusion. Intranasal administration offers a non-surgical means of bypassing the BBB to deliver neurotrophic factors, and the genes encoding them, directly to the brain.

AREAS COVERED

This review summarizes: i) evidence demonstrating intranasal delivery to the brain of a number of biomolecules having therapeutic potential for various CNS disorders; and ii) evidence demonstrating neuroprotective efficacy of a subset of biomolecules specifically for PD. The intersection of these two spheres represents the area of opportunity for development of new intranasal gene therapies for PD. To that end, our laboratory showed that intranasal administration of glial cell line-derived neurotrophic factor (GDNF), or plasmid DNA nanoparticles encoding GDNF, provides neuroprotection in a rat model of PD, and that the cells transfected by the nanoparticle vector are likely to be pericytes.

EXPERT OPINION

A number of genes encoding neurotrophic factors have therapeutic potential for PD, but few have been tested by the intranasal route and shown to be neuroprotective in a model of PD. Intranasal delivery provides a largely unexplored, promising approach for development of a non-invasive gene therapy for PD.

Neuroprotection by Orexin-A via HIF-1α induction in a cellular model of Parkinson's disease

Orexin-A, a neuropeptide secreted by hypothalamic neurons, may be neuroprotective in many neurological conditions such as cerebral ischaemia. One mechanism postulated to be involved in the neuroprotection by Orexin-A is the induction of hypoxia inducible factor 1 alpha (HIF-1α). Parkinson's disease (PD) is a progressive neurodegenerative disorder and mitochondrial dysfunction has been demonstrated to play a role in its pathogenesis. Mitochondrial dysfunction may cause reduction of O2 consumption and subsequently activate prolyl hydroxylase, which leads to decreased level of HIF-1α. In this study, we used MPP(+)-treated SH-SY5Y cells as an in vitro cellular model of PD to test the role of Orexin-A as an inducer of HIF-1α. Our results showed that Orexin-A not only induced HIF-1α but also activated downstream targets of HIF-1α, such as vascular endothelial growth factor and erythropoietin. Thus, Orexin-A treatment attenuated MPP(+)-induced cell injury and this effect was blocked when HIF-1α was suppressed. Hence, we conclude that induction of HIF-1α is one of the mechanisms involved in the neuroprotection by Orexin-A.

Erythropoietin improves neurobehavior by reducing dopaminergic neuron loss in a 6‑hydroxydopamine‑induced rat model

The purpose of this study was to determine the effectiveness of the systemic administration of high dose erythropoietin (EPO) in a 6-hydroxydopamine (6-OHDA)- induced rat model. Rats were divided into 7 groups. Groups 1–4 were administered daily EPO doses of 0; 2,500; 5,000 and 10,000 U/kg via intraperitoneal injection (i.p.) for 5 days. The EPO concentration in cerebrospinal fluid (CSF) was determined by enzyme-linked immunosorbent assay (ELISA) and western blot analysis. The dose of 10,000 U/kg was then selected for subsequent experiments. In group 5, rats received saline via medial forebrain bundle (MFB). In group 6, rats received 6-OHDA via MFB. In group 7, an EPO concentration of 10,000 U/kg was constantly administered i.p. for 5 days to rats prior to 6-OHDA injection via MFB. Behavioral analysis was performed for groups 5–7 by rat rotation tests. The number of tyrosine hydroxylase (TH)-immunopositive cells in the substantia nigra (SN) was measured by immunocytochemistry. The activation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinases (MAPKs) and caspase-3 signaling in rats were analyzed using western blotting. The results showed that there was a significant increase in EPO levels in the CSF in 10,000 U/kg group compared with the 2,500 and 5,000 U/kg groups (P<0.01). Significantly fewer rotational counts were obtained in rats that were pretreated with EPO compared with saline-pretreated 6-OHDA-lesioned rats (P<0.001). The dopaminergic neurons in the 6-OHDA-lesioned SN were also increased in the EPO-pretreated rats when compared with control rats (P<0.01). Western blot analysis revealed that EPO inhibited the 6-OHDA-induced activation of JNK, ERK, p38 MAPK and caspase-3 signaling in the rat model. In conclusion, systemic administration of a high dose of EPO exerted neuroprotective effects in reversing behavioral deficits associated with Parkinson’s disease and prevented loss of the dopaminergic neurons through the MAPK pathway.

Gene therapy for Parkinson's disease: state-of-the-art treatments for neurodegenerative disease

Pharmacological and surgical treatments offer symptomatic benefits to patients with Parkinson's disease; however, as the condition progresses, patients experience gradual worsening in symptom control, with the development of a range of disabling complications. In addition, none of the currently available therapies have convincingly shown disease-modifying effects - either in slowing or reversing the disease. These problems have led to extensive research into the possible use of gene therapy as a treatment for Parkinson's disease. Several treatments have reached human clinical trial stages, providing important information on the risks and benefits of this novel therapeutic approach, and the tantalizing promise of improved control of this currently incurable neurodegenerative disorder.

Intranasal Delivery of Bone Marrow-Derived Mesenchymal Stem Cells, Macrophages, and Microglia to the Brain in Mouse Models of Alzheimer's and Parkinson's Disease

In view of the rapid preclinical development of cell-based therapies for neurodegenerative disorders, traumatic brain injury, and tumors, the safe and efficient delivery and targeting of therapeutic cells to the central nervous system is critical for maintaining therapeutic efficacy and safety in the respective disease models. Our previous data demonstrated therapeutically efficacious and targeted delivery of mesenchymal stem cells (MSCs) to the brain in the rat 6-hydroxydopamine model of Parkinson's disease (PD). The present study examined delivery of bone marrow-derived MSCs, macrophages, and microglia to the brain in a transgenic model of PD [(Thy1)-h[A30P] aS] and an APP/PS1 model of Alzheimer's disease (AD) via intranasal application (INA). INA of microglia in naive BL/6 mice led to targeted and effective delivery of cells to the brain. Quantitative PCR analysis of eGFP DNA showed that the brain contained the highest amount of eGFP-microglia (up to 2.1 × 104) after INA of 1 × 106 cells, while the total amount of cells detected in peripheral organs did not exceed 3.4 × 103. Seven days after INA, MSCs expressing eGFP were detected in the olfactory bulb (OB), cortex, amygdala, striatum, hippocampus, cerebellum, and brainstem of (Thy1)-h[A30P] aS transgenic mice, showing predominant distribution within the OB and brainstem. INA of eGFP-expressing macrophages in 13-month-old APP/PS1 mice led to delivery of cells to the OB, hippocampus, cortex, and cerebellum. Both MSCs and macrophages contained Iba-1-positive population of small microglia-like cells and Iba-1-negative large rounded cells showing either intracellular amyloid β (macrophages in APP/PS1 model) or α-synuclein [MSCs in (Thy1)-h[A30P] aS model] immunoreactivity. Here, we show, for the first time, intranasal delivery of cells to the brain of transgenic PD and AD mouse models. Additional work is needed to determine the optimal dosage (single treatment regimen or repeated administrations) to achieve functional improvement in these mouse models with intranasal microglia/macrophages and MSCs. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.

Synthetic nucleic acids delivered by exosomes: a potential therapeutic for generelated metabolic brain diseases

Many brain diseases, including Alzheimer's disease, are associated with genetic abnormalities. The search for more effective therapeutic approaches involving nucleic acids like interfering RNA, antisense oligonucleotides and mRNA has drawn much attention in the development of alternatives to virus-based gene therapy. Potentially, nucleic acids could not only specifically down-regulate and degrade misfolded proteins, but also relieve protein deficiencies by directing the translation of functional proteins. However, clinical applications have been stalled by the lack of proper delivery systems. Exosomes are nano-scale extracellular vesicles secreted by nearly all somatic cells. Recent work has revealed that exosomes play special roles in intercellular communication via the horizontal transfer of various RNAs among cells. Recently, the use of exosomes for the delivery of therapeutic nucleic acids to targeted cells has been demonstrated to be a practical approach. Here, we briefly review the general properties of exosomes and introduce three therapeutic nucleic acids. Based upon comparison with other delivery methods, exosomes are proposed as an ideal nucleic acid delivery system for metabolic brain disease therapy.

A next step in adeno-associated virus-mediated gene therapy for neurological diseases: regulation and targeting

Recombinant adeno-associated virus (rAAV) vectors mediating long term transgene expression are excellent gene therapy tools for chronic neurological diseases. While rAAV2 was the first serotype tested in the clinics, more efficient vectors derived from the rh10 serotype are currently being evaluated and other serotypes are likely to be tested in the near future. In addition, aside from the currently used stereotaxy-guided intraparenchymal delivery, new techniques for global brain transduction (by intravenous or intra-cerebrospinal injections) are very promising. Various strategies for therapeutic gene delivery to the central nervous system have been explored in human clinical trials in the past decade. Canavan disease, a genetic disease caused by an enzymatic deficiency, was the first to be approved. Three gene transfer paradigms for Parkinson's disease have been explored: converting L-dopa into dopamine through AADC gene delivery in the putamen; synthesizing GABA through GAD gene delivery in the overactive subthalamic nucleus and providing neurotrophic support through neurturin gene delivery in the nigro-striatal pathway. These pioneer clinical trials demonstrated the safety and tolerability of rAAV delivery in the human brain at moderate doses. Therapeutic effects however, were modest, emphasizing the need for higher doses of the therapeutic transgene product which could be achieved using more efficient vectors or expression cassettes. This will require re-addressing pharmacological aspects, with attention to which cases require either localized and cell-type specific expression or efficient brain-wide transgene expression, and when it is necessary to modulate or terminate the administration of transgene product. The ongoing development of targeted and regulated rAAV vectors is described.

Pre-immunization with an intramuscular injection of AAV9-human erythropoietin vectors reduces the vector-mediated transduction following re-administration in rat brain

We have recently demonstrated that adeno-associated virus serotype 9 (AAV9)-mediated human erythropoietin (hEPO) gene delivery into the brain protects dopaminergic (DA) neurons in the substantia nigra in a rat model of Parkinson's disease. In the present study, we examined whether pre-exposure to AAV9-hEPO vectors with an intramuscular or intrastriatal injection would reduce AAV9-mediated hEPO transduction in rat brain. We first characterized transgene expression and immune responses against AAV9-hEPO vectors in rat striatum at 4 days, 3 weeks and 6 months, and with doses ranging from 10¹¹ to 10¹³ viral genomes. To sensitize immune system, rats received an injection of AAV9-hEPO into either the muscle or the left striatum, and then sequentially an injection of AAV9-hEPO into the right striatum 3 weeks later. We observed that transgene expression exhibited in a time course and dose dependent manner, and inflammatory and immune responses displayed in a time course manner. Intramuscular, but not intrastriatal injections of AAV9-hEPO resulted in reduced levels of hEPO transduction and increased levels of the major histocompatibility complex (MHC) class I and class II antigen expression in the striatum following AAV9-hEPO re-administration. There were infiltration of the cluster of differentiation 4 (CD4)-and CD8-lymphacytes, and accumulation of activated microglial cells and astrocytes in the virally injected striatum. In addition, the sera from the rats with intramuscular injections of AAV9-hEPO contained greater levels of antibodies against both AAV9 capsid protein and hEPO protein than the other treatment groups. hEPO gene expression was negatively correlated with the levels of circulating antibodies against AAV9 capsid protein. Intramuscular and intrastriatal re-administration of AAV9-hEPO led to increased numbers of red blood cells in peripheral blood. Our results suggest that pre-immunization with an intramuscular injection can lead to the reduction of transgene expression in the striatal re-administration.

Targeting erythropoietin for chronic neurodegenerative diseases

INTRODUCTION

Since erythropoietin (EPO) and EPO receptor (EPOR) are expressed in the central nervous system (CNS) beyond hematopoietic system, EPO illustrates a robust biological function in maintaining neuronal survival and regulating neurogenesis and may play a crucial role in neurodegenerative diseases.

AREAS COVERED

EPO is capable of modulating multiple cellular signal transduction pathways to promote neuronal survival and enhance the proliferation and differentiation of neuronal progenitor cells. Initially, EPO binds to EPOR to activate the Janus-tyrosine kinase 2 (Jak2) protein followed by modulation of protein kinase B (Akt), mammalian target of rapamycin, signal transducer and activators of transcription 5, mitogen-activated protein kinases, protein tyrosine phosphatases, Wnt1 and nuclear factor κB. As a result, EPO may actively prevent the progression of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, epilepsy, multiple sclerosis and motor neuron diseases.

EXPERT OPINION

Novel knowledge of the cell signaling pathways regulated by EPO in the CNS will allow us to establish the foundation for the development of therapeutic strategies against neurodegenerative diseases. Further investigation of the role of EPO in neurodegenerative diseases can not only formulate EPO as a therapeutic candidate, but also further identify novel therapeutic targets for these disorders.

Vascular growth factors in neuropsychiatry

Recent advances in understanding the cellular and molecular basis of psychiatric illnesses have shed light on the important role played by trophic factors in modulating functional parameters associated with disease causality and drug action. Disease mechanisms are now thought to involve multiple cell types, including neurons and endothelial cells. These functionally distinct but interactively coupled cell types engage in cellular cross talk via shared and common signaling molecules. Dysregulation in their cellular signaling pathways influences brain function and alters behavioral performance. Multifunctional trophic factors such as VEGF and EPO that possess both neurotrophic and angiogenic actions are of particular interest due to their ability to rescue structural and plasticity deficits in neurons and vasculature. Obtaining insight into the behavioral, cellular and molecular actions of multi-functional trophic factors has the potential to open new and transformative therapeutic approaches.

Immunologic privilege in the central nervous system and the blood-brain barrier

The brain is in many ways an immunologically and pharmacologically privileged site. The blood-brain barrier (BBB) of the cerebrovascular endothelium and its participation in the complex structure of the neurovascular unit (NVU) restrict access of immune cells and immune mediators to the central nervous system (CNS). In pathologic conditions, very well-organized immunologic responses can develop within the CNS, raising important questions about the real nature and the intrinsic and extrinsic regulation of this immune privilege. We assess the interactions of immune cells and immune mediators with the BBB and NVU in neurologic disease, cerebrovascular disease, and intracerebral tumors. The goals of this review are to outline key scientific advances and the status of the science central to both the neuroinflammation and CNS barriers fields, and highlight the opportunities and priorities in advancing brain barriers research in the context of the larger immunology and neuroscience disciplines. This review article was developed from reports presented at the 2011 Annual Blood-Brain Barrier Consortium Meeting.

Alleviation of lung inflammatory responses by adeno-associated virus 2/9 vector carrying CC10 in OVA-sensitized mice

Asthma is a chronic airway inflammatory disease characterized by eosinophilic infiltration and airway hyperresponsiveness. The over-activated Th2 and lung epithelium cells express many different cytokines, and chemokines mainly contribute to the severity of lung inflammation. Clara cell 10 kD protein (CC10) is highly expressed in airway epithelium cells and exhibits anti-inflammatory and immunomodulatory effects. Adeno-associated virus (AAV) 2/9 vector, composed of AAV2 rep and AAV9 cap genes, can efficiently and specifically target lung epithelium cells. Thus, AAV2/9 vector might carry therapeutic potential gene sequences for the treatment of asthma. This study tested whether AAV2/9 vector carrying CC10 could reduce inflammatory and asthmatic responses in OVA-induced asthmatic mouse model. The results showed that AAV2/9-CC10 vector virus significantly reduced airway hyperresponsiveness, CCL11, interleukin (IL)-4, IL-5, IL-6, IL-13, and eosinophilia in the lungs of sensitized mice. CC10 level in OVA-sensitized mice was rescued with the administration of AAV2/9-CC10 vector virus. Lung tissue remodeling, including collagen deposition and goblet cell hyperplasia, was also alleviated. However, serum levels of OVA-specific IgG1 and IgE as well as Th2 cytokine levels in OVA-stimulated splenocyte culture supernatants were at the comparable levels to the sensitized control group. The results demonstrate that AAV2/9-CC10 vector virus relieved local inflammatory and asthmatic responses in lung. Therefore, we propose that AAV2/9-CC10 vector virus guaranteed sufficient CC10 expression and had an anti-inflammatory effect in asthmatic mice. It might be applied as a novel therapeutic approach for asthma.

Pseudotyped adeno-associated virus 2/9-delivered CCL11 shRNA alleviates lung inflammation in an allergen-sensitized mouse model

Airway infiltration by eosinophils is a major characteristic of chronic asthma. CCL11 (eotaxin-1) is secreted by lung epithelial cells and functions as the major chemokine for eosinophil recruitment. Pseudotyped adeno-associated virus (AAV) 2/9, composed by the AAV2 rep and AAV9 cap genes, can efficiently target lung epithelial cells and might carry gene sequences with therapeutic potential for asthma. This study aimed to determine whether pseudotyped AAV2/9 virus carrying the small hairpin RNA targeting CCL11 and expressed by CMV/U6 promoter could reduce eosinophilia and asthmatic responses in mite allergen-sensitized mice. Mice were sensitized by intraperitoneal and challenged by intratracheal injection with recombinant Dermatophagoides pteronyssinus group 2 allergen (rDp2). AAV2/9 viral vectors were intratracheally injected three days before the first challenge. AAV2/9 sh47 virus significantly reduced airway hyperresponsiveness, airway resistance, CCL11 levels, and eosinophilia in the lungs of sensitized mice. Th2 cytokines, including interleukins (IL)-4, IL-5, and IL-10, were also significantly reduced in the bronchoalveolar lavage fluid of AAV2/9 sh47 virus-treated mice. Th2 cytokine levels were also reduced in rDp2-stimulated mediastinal lymphocytes in treated mice. However, serum levels of rDp2-specific IgG1 and IgE, as well as Th2 cytokine levels in rDp2-stimulated splenocyte culture supernatants, were comparable to the sensitized control group. The results suggest that AAV2/9 sh47 virus relieved local instead of systemic inflammatory responses. Therefore, the CMV/U6 promoter with AAV2/9 viral vector, which is preferable to target lung epithelia cells, might be applied as a novel therapeutic approach for asthma.

Structural insight into the unique properties of adeno-associated virus serotype 9

Adeno-associated virus serotype 9 (AAV9) has enhanced capsid-associated tropism for cardiac muscle and the ability to cross the blood-brain barrier compared to other AAV serotypes. To help identify the structural features facilitating these properties, we have used cryo-electron microscopy (cryo-EM) and three-dimensional image reconstruction (cryo-reconstruction) and X-ray crystallography to determine the structure of the AAV9 capsid at 9.7- and 2.8-Å resolutions, respectively. The AAV9 capsid exhibits the surface topology conserved in all AAVs: depressions at each icosahedral two-fold symmetry axis and surrounding each five-fold axis, three separate protrusions surrounding each three-fold axis, and a channel at each five-fold axis. The AAV9 viral protein (VP) has a conserved core structure, consisting of an eight-stranded, β-barrel motif and the αA helix, which are present in all parvovirus structures. The AAV9 VP differs in nine variable surface regions (VR-I to -IX) compared to AAV4, but at only three (VR-I, VR-II, and VR-IV) compared to AAV2 and AAV8. VR-I differences modify the raised region of the capsid surface between the two-fold and five-fold depressions. The VR-IV difference produces smaller three-fold protrusions in AAV9 that are less "pointed" than AAV2 and AAV8. Significantly, residues in the AAV9 VRs have been identified as important determinants of cellular tropism and transduction and dictate its antigenic diversity from AAV2. Hence, the AAV9 VRs likely confer the unique infection phenotypes of this serotype.

The advent of AAV9 expands applications for brain and spinal cord gene delivery

INTRODUCTION

Straightforward studies compared adeno-associated virus (AAV) serotypes to determine the most appropriate one for robust expression in the CNS. AAV9 was efficient when directly injected into the brain, but more surprisingly, AAV9 produced global expression in the brain and spinal cord after a peripheral, systemic route of administration to neonatal mice.

AREAS COVERED

Topics include AAV9 gene delivery from intraparenchymal, intravenous, intrathecal and intrauterine routes of administration, and related preclinical studies and disease models. Systemic AAV9 gene transfer yields remarkably consistent neuronal expression, though only in early development. AAV9 is versatile to study neuropathological proteins: microtubule-associated protein tau and transactive response DNA-binding protein 43 kDa (TDP-43).

EXPERT OPINION

AAV9 will be more widely used based on current data, although other natural serotypes and recombineered vectors may also support or improve upon wide-scale expression. A peripheral-to-central gene delivery that can affect the entire CNS without having to inject the CNS is promising for basic functional experiments, and potentially for gene therapy. Systemic or intra-cerebrospinal fluid routes of AAV9 administration should be considered for spinal muscular atrophy, lysosomal storage diseases and amyotrophic lateral sclerosis, if more neuronal expression can be achieved in adults, or if glial expression can be exploited.

Gene therapy for Parkinson's disease

Current pharmacological and surgical treatments for Parkinson's disease offer symptomatic improvements to those suffering from this incurable degenerative neurological disorder, but none of these has convincingly shown effects on disease progression. Novel approaches based on gene therapy have several potential advantages over conventional treatment modalities. These could be used to provide more consistent dopamine supplementation, potentially providing superior symptomatic relief with fewer side effects. More radically, gene therapy could be used to correct the imbalances in basal ganglia circuitry associated with the symptoms of Parkinson's disease, or to preserve or restore dopaminergic neurons lost during the disease process itself. The latter neuroprotective approach is the most exciting, as it could theoretically be disease modifying rather than simply symptom alleviating. Gene therapy agents using these approaches are currently making the transition from the laboratory to the bedside. This paper summarises the theoretical approaches to gene therapy for Parkinson's disease and the findings of clinical trials in this rapidly changing field.

Axonal degeneration as a therapeutic target in the CNS

Degeneration of the axon is an important step in the pathomechanism of traumatic, inflammatory and degenerative neurological diseases. Increasing evidence suggests that axonal degeneration occurs early in the course of these diseases and therefore represents a promising target for future therapeutic strategies. We review the evidence for axonal destruction from pathological findings and animal models with particular emphasis on neurodegenerative and neurotraumatic disorders. We discuss the basic morphological and temporal modalities of axonal degeneration (acute, chronic and focal axonal degeneration and Wallerian degeneration). Based on the mechanistic concepts, we then delineate in detail the major molecular mechanisms that underlie the degenerative cascade, such as calcium influx, axonal transport, protein aggregation and autophagy. We finally concentrate on putative therapeutic targets based on the mechanistic prerequisites.

Exploiting natural diversity of AAV for the design of vectors with novel properties

Twelve AAV serotypes have been described so far in human and nonhuman primate (NHP) populations while surprisingly high diversity of AAV sequences is detected in tissue biopsies. The analysis of these novel AAV sequences has indicated a rapid evolution of the viral genome both by accumulation of mutations and recombination. This chapter describes how this rich resource of naturally evolved sequences is used to derive gene transfer vectors with a wide array of activities depending on the nature of the cap gene used in the packaging system. AAV2-based recombinant genomes have been packaged in dozens of different capsid types, resulting in a wide array of "pseudotyped vectors" that constitute a rich resource for the development of gene therapy clinical trials. We describe a polymerase chain reaction-based molecular rescue method for novel AAV isolation that uses primers designed to recognize the highly conserved regions in known AAV isolates and generate amplicons across the hypervariable regions of novel AAV genomes present in the analyzed sample.

Neuroprotective cytokines repress PUMA induction in the 1-methyl-4-phenylpyridinium (MPP(+)) model of Parkinson's disease

The hematopoietic cytokines erythropoietin (Epo) and granulocyte-colony stimulating factor (G-CSF) provide neuroprotection in several in vitro and in vivo models of Parkinson's disease (PD). The molecular mechanism by which Epo and G-CSF signals reduce the neuronal death in PD is not clear. Here, we show that in rat pheochromocytoma PC12 cells, Epo and G-CSF efficiently repressed the 1-methyl-4-phenylpyridinium (MPP(+))-induced expression of the proapoptotic protein PUMA (p53 up-regulated modulator of apoptosis). Accordingly, Epo and G-CSF treatment reduced the PC12 cell fraction that underwent apoptosis by MPP(+) treatment and thus improved cell viability. Downregulation of PUMA expression by Epo and G-CSF in MPP(+)-treated PC12 cells seems to be mediated by repression of p53, as the expression of p53 was increased by MPP(+)-treatment and reduced by Epo and G-CSF. Together, these results suggest that the neuroprotective activities of Epo and G-CSF in an experimental model of PD involve the repression of the apoptosis-inducing action of PUMA.

PEG-modulated column chromatography for purification of recombinant adeno-associated virus serotype 9

Column chromatography has been described for purification of recombinant adeno-associated viral vectors (rAAV) serotypes 1, 2, 5, 6 and 8. Some of these purification processes have been used in manufacturing pre-clinical grade and clinical grade rAAV vectors. Recently, recombinant AAV9 has been reported to be highly efficient in transducing cardiac muscle in animal models. Systemic or cardiac gene delivery and other applications may require large quantities of rAAV9 vectors, thus a scalable method supporting large scale purification of rAAV9 is needed for clinical development. However, column chromatography-based purification has not been reported to date for rAAV9. This study reports a polyethylene glycol (PEG) modulated chromatography process for purification of AAV9 vectors. Inclusion of PEG in chromatography buffers modulated rAAV9 elution profiles in a manner that resulted in significantly improved resin binding capacity, vector purity and yield. PEG-modulated methods were developed and optimized for hydroxyapatite and ion exchange chromatography, and shown to result in vectors of high purity and functional activity.